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A role for fat overfeeding in metabolic dysfunction in humans is commonly implied in the literature. Comparatively less is known about acute carbohydrate overfeeding (COF). We tested the hypothesis that COF predisposes to oxidative stress by channeling electrons away from antioxidants to support energy storage. In a study of 24 healthy human subjects with and without obesity, COF was simulated by oral administration of excess carbohydrates; a two-step hyperinsulinemic clamp was used to evaluate insulin action. The distribution of electrons between oxidative and reductive pathways was evaluated by the changes in the reduction potentials (Eh) of cytoplasmic (lactate, pyruvate) and mitochondrial (b-hydroxybutyrate, acetoacetate) redox couples. Antioxidant redox was measured by the ratio of reduced to oxidized glutathione. We used cross-correlation analysis to evaluate the relationships between the trajectories of Eh, insulin, glucose, and respiratory exchange during COF. DDIT3 and XBP1s/u mRNA were measured as markers of endoplasmic reticulum stress (ER stress) in adipose tissue before and after COF. Here, we show that acute COF is characterized by net transfer of electrons from mitochondria to cytoplasm. Circulating glutathione is oxidized in a manner that significantly cross-correlates with increasing insulin levels and precedes the decrease in cytoplasmic Eh. This effect is more pronounced in overweight individuals (OW). Markers of ER stress in subcutaneous fat are detectable in OW within 4 h. We conclude that acute COF contributes to metabolic dysfunction through insulin-dependent pathways that promote electron transfer to the cytoplasm and decrease antioxidant capacity. Characterization of redox during overfeeding is important for understanding the pathophysiology of obesity and type 2 diabetes. [ABSTRACT FROM AUTHOR]

Triggers of the autoimmune response that leads to type 1 diabetes (T1D) remain poorly understood. A possibility is that parallel changes in both T cells and target cells provoke autoimmune attack. We previously documented greater Ca2+ transients in fibroblasts from T1D subjects than non-T1D after exposure to fatty acids (FA) and tumor necrosis factor α (TNFα). These data indicate that metabolic and signal transduction defects present in T1D can be elicited ex vivo in isolated cells. Changes that precede T1D, including inflammation, may activate atypical responses in people that are genetically predisposed to T1D. To identify such cellular differences in T1D, we quantified a panel of metabolic responses in fibroblasts and peripheral blood cells (PBMCs) from age-matched T1D and non-T1D subjects, as models for non-immune and immune cells, respectively. Fibroblasts from T1D subjects accumulated more lipid, had higher LC-CoA levels and converted more FA to CO2, with less mitochondrial proton leak in response to oleate alone or with TNFα, using the latter as a model of inflammation. T1D-PBMCs contained and also accumulated more lipid following FA exposure. In addition, they formed more peroxidized lipid than controls following FA exposure. We conclude that both immune and non-immune cells in T1D subjects differ from controls in terms of responses to FA and TNFα. Our results suggest a differential sensitivity to inflammatory insults and FA that may precede and contribute to T1D by priming both immune cells and their targets for autoimmune reactions. [ABSTRACT FROM AUTHOR]

Glucose metabolism promotes insulin secretion in β-cells via metabolic coupling factors that are incompletely defined. Moreover, chronically elevated glucose causes β-cell dysfunction, but little is known about how cells handle excess fuels to avoid toxicity. Here we sought to determine which among the candidate pathways and coupling factors best correlates with glucosestimulated insulin secretion (GSIS), define the fate of glucose in the β-cell, and identify pathways possibly involved in excessfuel detoxification. We exposed isolated rat islets for 1 h to increasing glucose concentrations and measured various pathways and metabolites. Glucose oxidation, oxygen consumption, and ATP production correlated well with GSIS and saturated at 16 mM glucose. However, glucose utilization, glycerol release, triglyceride and glycogen contents, free fatty acid (FFA) content and release, and cholesterol and cholesterol esters increased linearly up to 25 mM glucose. Besides being oxidized, glucose was mainly metabolized via glycerol production and release and lipid synthesis (particularly FFA, triglycerides, and cholesterol), whereas glycogen production was comparatively low. Using targeted metabolomics in INS-1(832/13) cells, we found that several metabolites correlated well with GSIS, in particular some Krebs cycle intermediates, malonyl-CoA, and lower ADP levels. Glucose dose-dependently increased the dihydroxyacetone phosphate/glycerol 3-phosphate ratio in INS-1(832/13) cells, indicating a more oxidized state of NAD in the cytosol upon glucose stimulation. Overall, the data support a role for accelerated oxidative mitochondrial metabolism, anaplerosis, and malonyl-CoA/lipid signaling in β-cell metabolic signaling and suggest that a decrease in ADP levels is important in GSIS. The results also suggest that excess-fuel detoxification pathways in β-cells possibly comprise glycerol and FFA formation and release extracellularly and the diversion of glucose carbons to triglycerides and cholesterol esters. [ABSTRACT FROM AUTHOR]

Background: Many tissues play an important role in metabolic homeostasis and the development of diabetes and obesity. We hypothesized that the circulating redox metabolome is a master metabolic regulatory system that impacts all organs and modulates reactive oxygen species (ROS) production, lipid peroxidation, energy production and changes in lipid turnover in many cells including adipocytes. Methods: Differentiated human preadipocytes were exposed to the redox couples, lactate (L) and pyruvate (P), β–hydroxybutyrate (βOHB) and acetoacetate (Acoc), and the thiol-disulfides cysteine/ cystine (Cys/CySS) and GSH/GSSG for 1.5–4 hours. ROS measurements were done with CM-H2DCFDA. Lipid peroxidation (LPO) was assessed by a modification of the thiobarbituric acid method. Lipolysis was measured as glycerol release. Lipid synthesis was measured as 14C-glucose incorporated into lipid. Respiration was assessed using the SeaHorse XF24 analyzer and the proton leak was determined from the difference in respiration with oligomycin and antimycin A. Results: Metabolites with increasing oxidation potentials (GSSG, CySS, Acoc) increased adipocyte ROS. In contrast, P caused a decrease in ROS compared with L. Acoc also induced a significant increase in both LPO and lipid synthesis. L and Acoc increased lipolysis. βOHB increased respiration, mainly due to an increased proton leak. GSSG, when present throughout 14 days of differentiation significantly increased fat accumulation, but not when added later. Conclusions: We demonstrated that in human adipocytes changes in the external redox state impacted ROS production, LPO, energy efficiency, lipid handling, and differentiation. A more oxidized state generally led to increased ROS, LPO and lipid turnover and more reduction led to increased respiration and a proton leak. However, not all of the redox couples were the same suggesting compartmentalization. These data are consistent with the concept of the circulating redox metabolome as a master metabolic regulatory system. [ABSTRACT FROM AUTHOR]

Displacement of romodomain and xtra-erminal (BET) proteins from chromatin has promise for cancer and inflammatory disease treatments, but roles of BET proteins in metabolic disease remain unexplored. Small molecule BET inhibitors, such as JQ1, block BET protein binding to acetylated lysines, but lack selectivity within the BET family (Brd2, Brd3, Brd4, Brdt), making it difficult to disentangle contributions of each family member to transcriptional and cellular outcomes. Here, we demonstrate multiple improvements in pancreatic β-cells upon BET inhibition with JQ1 or BET-specific siRNAs. JQ1 (50–400 nM) increases insulin secretion from INS-1 cells in a concentration dependent manner. JQ1 increases insulin content in INS-1 cells, accounting for increased secretion, in both rat and human islets. Higher concentrations of JQ1 decrease intracellular triglyceride stores in INS-1 cells, a result of increased fatty acid oxidation. Specific inhibition of both Brd2 and Brd4 enhances insulin transcription, leading to increased insulin content. Inhibition of Brd2 alone increases fatty acid oxidation. Overlapping yet discrete roles for individual BET proteins in metabolic regulation suggest new isoform-selective BET inhibitors may be useful to treat insulin resistant/diabetic patients. Results imply that cancer and diseases of chronic inflammation or disordered metabolism are related through shared chromatin regulatory mechanisms. [ABSTRACT FROM AUTHOR]

Lipid signals derived from lipolysis and membrane phospholipids play an important role in glucose-stimulated insulin secretion (GSIS), though the exact secondary signals remain unclear. Previous reports have documented a stimulatory role of exogenously added mono-acyl-glycerol (MAG) on insulin secretion from cultured β-cells and islets. In this report we have determined effects of increasing intracellular MAG in the β-cell by inhibiting mono-acyl-glycerol lipase (MGL) activity, which catalyzes the final step in triacylglycerol breakdown, namely the hydrolysis of MAG to glycerol and free fatty acid (FA). To determine the role of MGL in GSIS, we used three different pharmacological agents (JZL184, MJN110 and URB602). All three inhibited GSIS and depolarization-induced insulin secretion in INS-1 (832/13). JZL184 significantly inhibited both GSIS and depolarization-induced insulin secretion in rat islets. JZL184 significantly decreased lipolysis and increased both mono- and diacyglycerol species in INS-1 cells. Analysis of the kinetics of GSIS showed that inhibition was greater during the sustained phase of secretion. A similar pattern was observed in the response of Ca2+ to glucose and depolarization but to a lesser degree suggesting that altered Ca2+ handling alone could not explain the reduction in insulin secretion. In addition, a significant reduction in long chain-CoA (LC-CoA) was observed in INS-1 cells at both basal and stimulatory glucose following inhibition of MGL. Our data implicate an important role for MGL in insulin secretion. [ABSTRACT FROM AUTHOR]

Our previous work has demonstrated that islet depolarization with KCl opens connexin36 hemichannels in β-cells of mouse pancreatic islets allowing the exchange of small metabolites with the extracellular medium. In this study, the opening of these hemichannels has been further characterized in rat islets and INS–1 cells. Taking advantage of hemicannels’opening, the uptake of extracellular ATP and its effect on insulin release were investigated. 70 mM KCl stimulated light emission by luciferin in dispersed rat islets cells transduced with the fire-fly luciferase gene: it was suppressed by 20 mM glucose and 50 μM mefloquine, a specific connexin36 inhibitor. Extracellular ATP was taken up or released by islets depolarized with 70 mM KCl at 5 mM glucose, depending on the external ATP concentration. 1 mM ATP restored the loss of ATP induced by the depolarization itself. ATP concentrations above 5 mM increased islet ATP content and the ATP/ADP ratio. No ATP uptake occurred in non-depolarized or KCl-depolarized islets simultaneously incubated with 50 μM mefloquine or 20 mM glucose. Extracellular ATP potentiated the secretory response induced by 70 mM KCl at 5 mM glucose in perifused rat islets: 5 mM ATP triggered a second phase of insulin release after the initial peak triggered by KCl-depolarization itself; at 10 mM, it increased both the initial, KCl-dependent, peak and stimulated a greater second phase of secretion than at 5 mM. These stimulatory effects of extracellular ATP were almost completely suppressed by 50 μM mefloquine. The magnitude of the second phase of insulin release due to 5 mM extracellular ATP was decreased by addition of 5 mM ADP (extracellular ATP/ADP ratio = 1). ATP acts independently of KATP channels closure and its intracellular concentration and its ATP/ADP ratio seems to regulate the magnitude of both the first (triggering) and second (amplifying) phases of glucose-induced insulin secretion. [ABSTRACT FROM AUTHOR]

Hyperinsulinemia (HI) is elevated plasma insulin at basal glucose. Impaired glucose tolerance is associated with HI, although the exact cause and effect relationship remains poorly defined. We tested the hypothesis that HI can result from an intrinsic response of the β-cell to chronic exposure to excess nutrients, involving a shift in the concentration dependence of glucose-stimulated insulin secretion. INS-1 (832/13) cells were cultured in either a physiological (4mM) or high (11mM) glucose concentration with or without concomitant exposure to oleate. Isolated rat islets were also cultured with or without oleate. A clear hypersensitivity to submaximal glucose concentrations was evident in INS-1 cells cultured in excess nutrients such that the 25% of maximal (S0.25) glucose-stimulated insulin secretion was significantly reduced in cells cultured in 11mM glucose (S0.25 = 3.5 mM) and 4 mM glucose with oleate (S0.25=4.5 mM) compared with 4mM glucose alone (S0.25= 5.7 mM). The magnitude of the left shift was linearly correlated with intracellular lipid stores in INS-1 cells (r² = 0.97). We observed no significant differences in the dose responses for glucose stimulation of respiration, NAD(P)H autofluorescence, or Ca2+ responses between left and right-shifted β-cells. However, a left shift in the sensitivity of exocytosis to Ca2+ was documented in permeabilized INS-1 cells cultured in 11 versus 4 mM glucose (S0.25 = 1.1 and 1.7 = M, respectively). Our results suggest that the sensitivity of exocytosis to triggering is modulated by a lipid component, the levels of which are influenced by the culture nutrient environment. [ABSTRACT FROM AUTHOR]

Circulating redox state changes, determined by the ratio of reduced/oxidized pairs of different metabolites, have been associated with metabolic diseases. However, the pathogenic contribution of these changes and whether they modulate normal tissue function is unclear. As alterations in hepatic gluconeogenesis and glycogen metabolism are hallmarks that characterize insulin resistance and type 2 diabetes, we tested whether imposed changes in the extracellular redox state could modulate these processes. Thus, primary hepatocytes were treated with different ratios of the following physiological extracellular redox couples: β-hydroxybutyrate (βOHB)/acetoacetate (Acoc), reduced glutathione (GSH)/oxidized glutathione (GSSG), and cysteine/cystine. Exposure to a more oxidized ratio via extracellular βOHB/Acoc, GSH/GSSG, and cysteine/cystine in hepatocytes from fed mice increased intracellular hydrogen peroxide without causing oxidative damage. On the other hand, addition of more reduced ratios of extracellular βOHB/Acoc led to increased NAD(P)H and maximal mitochondrial respiratory capacity in hepatocytes. Greater βOHB/Acoc ratios were also associated with decreased β-oxidation, as expected with enhanced lipogenesis. In hepatocytes from fasted mice, a more extracellular reduced state of βOHB/Acoc led to increased alanine-stimulated gluconeogenesis and enhanced glycogen synthesis capacity from added glucose. Thus, we demonstrated for the first time that the extracellular redox state regulates the major metabolic functions of the liver and involves changes in intracellular NADH, hydrogen peroxide, and mitochondrial respiration. Because redox state in the blood can be communicated to all metabolically sensitive tissues, this work confirms the hypothesis that circulating redox state may be an important regulator of whole body metabolism and contribute to alterations associated with metabolic diseases. [ABSTRACT FROM AUTHOR]

Abstract: Aims: Obesity and insulin resistance are associated with increased oxidant stress. However, treatments of obese subjects with different types of antioxidants often give mixed outcomes. In this work, we sought to determine if long-term supplementation of a thiol antioxidant, ?-mercaptoethanol, to diet-induced obese mice may improve their health conditions. Main methods: Middle-age mice with pre-existing diet-induced obesity were provided with low concentration ?-mercaptoethanol (BME) in drinking water for six months. Animals were assessed for body composition, gripping strength, spontaneous physical and metabolic activities, as well as insulin and pyruvate tolerance tests. Markers of inflammation were assessed in plasma, fat tissue, and liver. Key findings: BME-treated mice gained less fat mass and more lean mass than the control animals. They also showed increased nocturnal locomotion and respiration, as well as greater gripping strength. BME reduced plasma lipid peroxidation, decreased abdominal fat tissue inflammation, reduced fat infiltration into muscle and liver, and reduced liver and plasma C-reactive protein. However, BME was found to desensitize insulin signaling in vivo, an effect also confirmed by in vitro experiments. Significance: Long-term supplementation of low dose thiol antioxidant BME improved functional outcomes in animals with pre-existing obesity. Additional studies are needed to address the treatment impact on insulin sensitivity if a therapeutic value is to be explored. [Copyright &y& Elsevier]

Adrenergic stimulation of brown adipocytes ( BA) induces mitochondrial uncoupling, thereby increasing energy expenditure by shifting nutrient oxidation towards thermogenesis. Here we describe that mitochondrial dynamics is a physiological regulator of adrenergically-induced changes in energy expenditure. The sympathetic neurotransmitter Norepinephrine ( NE) induced complete and rapid mitochondrial fragmentation in BA, characterized by Drp1 phosphorylation and Opa1 cleavage. Mechanistically, NE-mediated Drp1 phosphorylation was dependent on Protein Kinase-A ( PKA) activity, whereas Opa1 cleavage required mitochondrial depolarization mediated by FFAs released as a result of lipolysis. This change in mitochondrial architecture was observed both in primary cultures and brown adipose tissue from cold-exposed mice. Mitochondrial uncoupling induced by NE in brown adipocytes was reduced by inhibition of mitochondrial fission through transient Drp1 DN overexpression. Furthermore, forced mitochondrial fragmentation in BA through Mfn2 knock down increased the capacity of exogenous FFAs to increase energy expenditure. These results suggest that, in addition to its ability to stimulate lipolysis, NE induces energy expenditure in BA by promoting mitochondrial fragmentation. Together these data reveal that adrenergically-induced changes to mitochondrial dynamics are required for BA thermogenic activation and for the control of energy expenditure. [ABSTRACT FROM AUTHOR]

Abstract: Inherited glucose-6-phosphate isomerase (GPI) deficiency is the second most frequent glycolytic erythroenzymopathy in humans. Patients present with non-spherocytic anemia of variable severity and with neuromuscular dysfunction. We previously described Chinese hamster (CHO) cell lines with mutations in GPI and loss of GPI activity. This resulted in a temperature sensitivity and severe reduction in the synthesis of glycerolipids due to a reduction in phosphatidate phosphatase (PAP). In the current article we attempt to describe the nature of this pleiotropic effect. We cloned and sequenced the CHO lipin 1 cDNA, a gene that codes for PAP activity. Overexpression of lipin 1 in the GPI-deficient cell line, GroD1 resulted in increased PAP activity, however it failed to restore glycerolipid biosynthesis. Fluorescence microscopy showed a failure of GPI-deficient cells to localize lipin 1α to the nucleus. We also found that glucose-6-phosphate levels in GroD1 cells were 10-fold over normal. Lowering glucose levels in the growth medium partially restored glycerolipid biosynthesis and nuclear localization of lipin 1α. Western blot analysis of the elements within the mTOR pathway, which influences lipin 1 activity, was consistent with an abnormal activation of this system. Combined, these data suggest that GPI deficiency results in an accumulation of glucose-6-phosphate, and possibly other glucose-derived metabolites, leading to activation of mTOR and sequestration of lipin 1 to the cytosol, preventing its proper functioning. These results shed light on the mechanism underlying the pathologies associated with inherited GPI deficiency and the variability in the severity of the symptoms observed in these patients. [Copyright &y& Elsevier]

Abstract: This review focuses on the emerging evidence that reactive oxygen species (ROS) derived from glucose metabolism, such as H2O2, act as metabolic signaling molecules for glucose-stimulated insulin secretion (GSIS) in pancreatic beta-cells. Particular emphasis is placed on the potential inhibitory role of endogenous antioxidants, which rise in response to oxidative stress, in glucose-triggered ROS and GSIS. We propose that cellular adaptive response to oxidative stress challenge, such as nuclear factor E2-related factor 2 (Nrf2)-mediated antioxidant induction, plays paradoxical roles in pancreatic beta-cell function. On the one hand, induction of antioxidant enzymes protects beta-cells from oxidative damage and possible cell death, thus minimizing oxidative damage-related impairment of insulin secretion. On the other hand, the induction of antioxidant enzymes by Nrf2 activation blunts glucose-triggered ROS signaling, thus resulting in reduced GSIS. These two premises are potentially relevant to impairment of beta-cells occurring in the late and early stage of Type 2 diabetes, respectively. In addition, we summarized our recent findings that persistent oxidative stress due to absence of uncoupling protein 2 activates cellular adaptive response which is associated with impaired pancreatic beta-cell function. [Copyright &y& Elsevier]

OBJECTIVE--Previous studies have reported that β-cell mitochondria exist as discrete organelles that exhibit heterogeneous bioenergetic capacity. To date, networking activity, and its role in mediating β-cell mitochondrial morphology and function, remains unclear. In this article, we investigate β-cell mitochondrial fusion and fission in detail and report alterations in response to various combinations of nutrients. RESEARCH DESIGN AND METHODS--Using matrix-targeted photoactivatable green fluorescent protein, mitochondria were tagged and tracked in β-cell within intact islets, as isolated cells and as cell lines, revealing frequent fusion and fission events. Manipulations of key mitochondrial dynamics proteins OPAl, DRP1, and Fis1 were tested for their role in 13-cell mitochondrial morphology. The combined effects of free fatty acid and glucose on B-cell survival, function, and mitochondrial morphology were explored with relation to alterations in fusion and fission capacity. RESULTS--β-Cell mitochondria are constantly involved in fusion and fission activity that underlies the overall morphology of the organelle. We find that networking activity among mitochondria is capable of distributing a localized green fluorescent protein signal throughout an isolated β-cell, a β-cell within an islet, and an INS1 cell. Under noxious conditions, we find that β-cell mitochondria become fragmented and lose their ability to undergo fusion. Interestingly, manipulations that shift the dynamic balance to favor fusion are able to prevent mitochondrial fragmentation, maintain mitochondrial dynamics, and prevent apoptosis. CONCLUSIONS--These data suggest that alterations in mitochondrial fusion and fission play a critical role in nutrient-induced β-cell apoptosis and may be involved in the pathophysiology of type 2 diabetes. Diabetes 58:2303-2315, 2009 [ABSTRACT FROM AUTHOR]

The proapoptotic BCL-2 family member BAD resides in a glucokinase-containing complex that regulates glucose-driven mitochondrial respiration. Here, we present genetic evidence of a physiologic role for BAD in glucose-stimulated insulin secretion by beta cells. This novel function of BAD is specifically dependent upon the phosphorylation of its BH3 sequence, previously defined as an essential death domain. We highlight the pharmacologic relevance of phosphorylated BAD BH3 by using cell-permeable, hydrocarbon-stapled BAD BH3 helices that target glucokinase, restore glucose-driven mitochondrial respiration and correct the insulin secretory response in Bad-deficient islets. Our studies uncover an alternative target and function for the BAD BH3 domain and emphasize the therapeutic potential of phosphorylated BAD BH3 mimetics in selectively restoring beta cell function. Furthermore, we show that BAD regulates the physiologic adaptation of beta cell mass during high-fat feeding. Our findings provide genetic proof of the bifunctional activities of BAD in both beta cell survival and insulin secretion. [ABSTRACT FROM AUTHOR]

Accumulation of depolarized mitochondria within β-cells has been associated with oxidative damage and development of diabetes. To determine the source and fate of depolarized mitochondria, individual mitochondria were photolabeled and tracked through fusion and fission. Mitochondria were found to go through frequent cycles of fusion and fission in a ‘kiss and run’ pattern. Fission events often generated uneven daughter units: one daughter exhibited increased membrane potential (Δψm) and a high probability of subsequent fusion, while the other had decreased membrane potential and a reduced probability for a fusion event. Together, this pattern generated a subpopulation of non-fusing mitochondria that were found to have reduced Δψm and decreased levels of the fusion protein OPA1. Inhibition of the fission machinery through DRP1K38A or FIS1 RNAi decreased mitochondrial autophagy and resulted in the accumulation of oxidized mitochondrial proteins, reduced respiration and impaired insulin secretion. Pulse chase and arrest of autophagy at the pre-proteolysis stage reveal that before autophagy mitochondria lose Δψm and OPA1, and that overexpression of OPA1 decreases mitochondrial autophagy. Together, these findings suggest that fission followed by selective fusion segregates dysfunctional mitochondria and permits their removal by autophagy. [ABSTRACT FROM AUTHOR]

One of the unique features of β-cells is their relatively low expression of many antioxidant enzymes. This could render β-cells susceptible to oxidative damage but may also provide a system that is sensitive to reactive oxygen species as signals. In isolated mouse islets and INS-1(832/13) cells, glucose increases intracellular accumulation of H2O2. In both models, insulin secretion could be stimulated by provision of either exogenous H2O2 or diethyl maleate, which raises intracellular H2O2 levels. Provision of exogenous H2O2 scavengers, including cell permeable catalase and N-acetyl-L-cysteine, inhibited glucose-stimulated H2O2 accumulation and insulin secretion (GSIS). In contrast, cell permeable superoxide dismutase, which metabolizes superoxide into H2O2, had no effect on GSIS. Because oxidative stress is an important risk factor for β-cell dysfunction in diabetes, the relationship between glucose-induced H2O2 generation and GSIS was investigated under various oxidative stress conditions. Acute exposure of isolated mouse islets or INS-1(832/ 13) cells to oxidative stressors, including arsenite, 4-hydroxynonenal, and methylglyoxal, led to decreased GSIS. This impaired GSIS was associated with increases in a battery of endogenous antioxidant enzymes. Taken together, these findings suggest that H2O2 derived from glucose metabolism is one of the metabolic signals for insulin secretion, whereas oxidative stress may disturb its signaling function. Diabetes 56:1783-1791, 2007 [ABSTRACT FROM AUTHOR]

We examined the effects of different physiological concentrations of glucose on cytoplasmic Ca2+ handling and mitochondrial membrane potential (ΔΨm) and insulin secretion in single mouse islet cells. The threshold for both glucose-induced changes in Ca2+ and ΔΨm ranged from 6 to 8 mM. Glucose step-jumps resulted in sinusoidal oscillations of cytoplasmic Ca2+, whereas AΨm reached sustained plateaus with oscillations interposed on the top of these plateaus. The amplitude of the Ca2+ rise (height of the peak) did not vary with glucose concentration, suggesting a ‘digital’ rather than ‘analog’ character of this aspect of the oscillatory Ca2+ response. The average glucose-dependent elevation of cytoplasmic Ca2+ concentration during glucose stimulation reached saturation at 8 mM stimulatory glucose, whereas ΔΨm showed a linear glucose dose-response relationship over the range of stimulatory glucose concentrations (4–16 mM). Glucose-dependent increases in insulin secretion correlated well with ΔΨm but not with average Ca2+ concentration. These data show that an ATP-dependent K+ channel-independent pathway is operative at the single cell level and suggest mitochondrial metabolism may be a determining factor in explaining graded, glucose concentration-dependent increases in insulin secretion. [ABSTRACT FROM AUTHOR]

We previously reported decreased glucose-stimulated insulin secretion (GSIS) in hormone-sensitive lipase-null mice (HSL-/-), both in vivo and in vitro. The focus of the current study was to gain further insight into the signaling role and regulation of lipolysis in islet tissue. The effect of glucagon-like peptide 1 (GLP-1) on GSIS was also studied, as GLP-1 could augment GSIS via protein kinase A activation of HSL and lipolysis. Freshly isolated islets from fasted and fed male HSL-/- and wild-type (HSL+/+) mice were studied at ages 4 and 7 months. Neutral cholesterol ester hydrolase activity was markedly reduced in islets from both 4and 7-month-old male HSL-/- mice, whereas a marked deficiency in triglyceride lipase activity became evident only in the older mice. The deficiencies in lipase activities were associated with higher islet triglyceride content and reduced lipolysis at basal glucose levels. Lipolysis was stimulated by high glucose in islets of both wild-type and HSL-null mice. Severe deficiencies in GSIS were found, but only in islets from 7-month-old, fasted, male HSL-/- mice. GSIS was less affected in 4-month-old fasted male HSL-/- mice and not reduced in female mice. Exogenous delivery of free fatty acids (FFAs) rescued GSIS, supporting the view that the lack of endogenous FFA supply for lipid-signaling processes in HSL-/- mice was responsible for the loss of GSIS. GLP-1 also rescued GSIS in HSL-/- mice, indicating that signaling via HSL is not a major pathway for its incretin effect. Thus, the secretory phenotype of HSL-null mice is gender dependent, increases with age, and is influenced by the nutritional state. Under most circumstances, the major determinant of lipolytic flux in the β-cell involves an enzyme(s) other than HSL that is acutely activated by glucose. Our results support the view that the availability of endogenous FFA through HSL and an additional enzyme(s) is involved in providing lipid moieties for β-cell signaling for secretion in response to glucose. [ABSTRACT FROM AUTHOR]

Skeletal muscle insulin resistance may be aggravated by intramyocellular accumulation of fatty acid-derived metabolites that inhibit insulin signaling. We tested the hypothesis that enhanced fatty acid oxidation in myocytes should protect against fatty acid-induced insulin resistance by limiting lipid accumulation. L6 myotubes were transduced with adenoviruses encoding carnitine palmitoyltransferase I (CPT I) isoforms or β-galactosidase (control). Two to 3-fold overexpression of L-CPT I, the endogenous isoform in L6 cells, proportionally increased oxidation of the long-chain fatty acids palmitate and oleate and increased insulin stimulation of [14C]glucose incorporation into glycogen by 60% while enhancing insulin-stimulated phosphorylation of p38MAPK. Incubation of control cells with 0.2 mM palmitate for 18 h caused accumulation of triacylglycerol, diacylglycerol, and ceramide (but not long-chain acyl-CoA) and decreased insulin-stimulated [14C]glucose incorporation into glycogen (60%), [3H]deoxyglucose uptake (60%), and protein kinase B phosphorylation (20%). In the context of L-CPT I over- expression, palmitate preincubation produced a relative decrease in insulin-stimulated incorporation of [14C]glucose into glycogen (60%) and [3H]deoxyglucose uptake (40%) but did not inhibit phosphorylation of protein kinase B. Due to the enhancement of insulin-stimulated glucose metabolism induced by L-CPT I overexpression itself, net insulin-stimulated incorporation of [14C]glucose into glycogen and [3H]deoxyglucose uptake in L-CPT I-transduced, palmitate-treated cells were significantly greater than in palmitate-treated control cells (71 and 75% greater, respectively). However, L-CPT I overexpression failed to decrease intracellular triacylglycerol, diacyl- glycerol, ceramide, or long-chain acyl-CoA. We propose that accelerated E-oxidation in muscle cells exerts an in- sulin-sensitizing effect independently of changes in intra- cellular lipid content. [ABSTRACT FROM AUTHOR]

Studies the rapid flip-flop of oleic acid across the plasma membrane. Binding of oleic acid to the plasma membrane by measuring the fluorescent fatty acid-binding protein; Measurement of changes in internal hydrogen-ion concentration caused by flip-flop and metabolism; Evaluation of the metabolic end products of oleic acid.

The secondary signals emanating from increased glucose metabolism, which lead to specific increases in proinsulin biosynthesis translation, remain elusive. It is known that signals for glucose-stimulated insulin secretion and proinsulin biosynthesis diverge downstream of glycolysis. Consequently, the mitochondrial products ATP, Krebs cycle intermediates, glutamate, and acetoacetate were investigated as candidate stimulus-coupling signals specific for glucose-induced proinsulin biosynthesis in rat islets. Decreasing ATP levels by oxidative phosphorylation inhibitors showed comparable effects on proinsulin biosynthesis and total protein synthesis. Although it is a cofactor, ATP is unlikely to be a metabolic stimulus-coupling signal specific for glucose-induced proinsulin biosynthesis. Neither glutamic acid methyl ester nor acetoacetic acid methyl ester showed a specific effect on glucose-stimulated proinsulin biosynthesis. Interestingly, among Krebs cycle intermediates, only succinic acid monomethyl ester specifically stimulated proinsulin biosynthesis. Malonic acid methyl ester, an inhibitor of succinate dehydrogenase, also specifically increased glucose-induced proinsulin biosynthesis without affecting islet ATP levels or insulin secretion. Glucose caused a 40% increase in islet intracellular succinate levels, but malonic acid methyl ester showed no further effect, probably due to efficient conversion of succinate to succinyl-CoA. In this regard, a GTP-dependent succinyl-CoA synthetase activity was found in cytosolic fractions of pancreatic islets. Thus, succinate and/or succinyl-CoA appear to be preferential metabolic stimulus-coupling factors for glucose-induced proinsulin biosynthesis translation. [ABSTRACT FROM AUTHOR]

Chronic exposure of pancreatic beta-cells to high glucose has pleiotropic action on beta-cell function. In particular, it induces key glycolytic genes, promotes glycogen deposition, and causes beta-cell proliferation and altered insulin secretion characterized by sensitization to low glucose. Postglycolytic events, in particular, anaplerosis and lipid signaling, are thought to be implicated in beta-cell activation by glucose. To understand the biochemical nature of the beta-cell adaptive process to hyperglycemia, we studied the regulation by glucose of lipogenic genes in the beta-cell line INS-1. A 3-day exposure of cells to elevated glucose (5-25 mmol/l) increased the enzymatic activities of fatty acid synthase 3-fold, acetyl-CoA carboxylase 30-fold, and malic enzyme 1.3-fold. Pyruvate carboxylase and citrate lyase expression remained constant. Similar observations were made at the protein and mRNA levels except for malic enzyme mRNA, which did not vary. Metabolic gene expression changes were associated with chronically elevated levels of citrate, malate, malonyl-CoA, and conversion of glucose carbon into lipids, even in cells that were subsequently exposed to low glucose. Similarly, fatty acid oxidation was suppressed and phospholipid and triglyceride synthesis was enhanced independently of the external glucose concentration in cells preexposed to high glucose. The results suggest that a coordinated induction of glycolytic and lipogenic genes in conjunction with glycogen and triglyceride deposition, as well as increased anaplerosis and altered lipid partitioning, contribute to the adaptive process to hyperglycemia and glucose sensitization of the beta-cell. [ABSTRACT FROM AUTHOR]

Competing Interests: Declaration of interests FR declares research grants from Ethicon (Johnson & Johnson), Novo Nordisk, and Medtronic; consulting fees from Morphic Medical; speaking honoraria from Medtronic, Ethicon, Novo Nordisk, Eli Lilly, and Amgen; has served (unpaid) as a member of the scientific advisory board for Keyron, and a member of data safety and monitoring board for GI Metabolic Solutions; is president of the Metabolic Health Institute (non-profit); and is sole director of Metabolic Health International and London Metabolic and Bariatric Surgery (private practice). JRLF declares personal consulting or speaker fees from Novo Nordisk, IFA Celtics, Eli Lilly, and Merck. PS declares research grants (paid to institution) from the National Health and Medical Research Council; coauthorship of manuscripts with medical writing assistance from Novo Nordisk and Eli Lilly; and an unpaid position in the leadership group of the Obesity Collective. WAB declares research grants from Johnson & Johnson, Medtronic, Gore, Applied Medical, Novo Nordisk, National Health and Medical Research Council, Myerton, and the Australian Commonwealth Government; and personal consulting fees for lectures and advisory boards from Johnson & Johnson, Gore, Novo Nordisk, Pfizer, Medtronic, Eli Lily, and Merck Sharp & Dohme. GM declares consulting fees from Novo Nordisk, Boehringer Ingelheim, Eli Lilly, Medtronic, Fractyl, and Recor; and is a scientific advisor for Keyron, Metadeq, GHP Scientific, and Jemyll. MB declares personal honoraria as a consultant and speaker from Amgen, AstraZeneca, Bayer, Boehringer Ingelheim, Daiichi Sankyo, Eli Lilly, Novo Nordisk, Novartis, Pfizer, and Sanofi. ML declares personal consulting fees from, and has served on scientific boards for, Novo Nordisk, Pfizer, and Eli Lilly. LMSC declares consultancy fees from Antaros Medical. MTvdM declares past consulting fees from Netcare PTY and Novo Nordisk. RVC declares research grants from Johnson & Johnson and Medtronic; honoraria for lectures and presentations from Johnson & Johnson, Medtronic, and Novo Nordisk; and serving on scientific advisory boards for Morphic Medical, Johnson & Johnson, and Medtronic. AM declares research grants from USV (India) and AstraZeneca; honoraria for lectures from USV (India), Eli Lilly, Lupin, Boehringer Ingelheim, Janssen, Cipla, AstraZeneca, Glenmark, Zydus, Novo Nordisk, Sanofi, Danone, Abbott, and the Almond Board of California; support for attending meetings or travel from USV (India), Eli Lilly, Boehringer Ingelheim, AstraZeneca, Lupin, and the Almond Board of California. KC is a primary investigator for Rhythm Pharmaceuticals, Bioprojects, and Integrative Phenomic (SME) trials; declares support for attending meetings or travel from Rhythm Pharmaceuticals and Novo Nordisk; and received research grants or support from Rhythm Pharmaceuticals to conduct research or deliver lectures via Institutions (Assistance Publique-Hôpitaux de Paris, Sorbonne Université). RFK declares consulting fees from Novo Nordisk, Weight Watchers, Eli Lilly, Boehringer Ingelheim, Altimmune, Structure, and Regeneron. JN has no personal relationships with industry; is an employee of the Obesity Action Coalition, which receives unrestricted support from a wide variety of companies and organisations interested in obesity care including, from the pharmaceutical industry (NovoNordisk, Eli Lilly, Boehringer Ingelheim, Pfizer, Amgen, Genentech, Regeneron, Wave Life Sciences, Zealand Pharma, KVKTech, Madrigal Pharmaceuticals, Structure Therapeutics, Biohaen Pharmaceuticals, and Currax), surgical industry (Intuitive, Ethicon, Medtronic, and Boston Scientific), behavioural care (WW International and WondrHealth), and not-for-profit medical societies (American Society for Metabolic and Bariatric Surgery, the Obesity Society, and the Obesity Medicine Association); and is president and chief executive officer for the Obesity Action Coalition. NS declares consulting or speaker honoraria from Abbott, Amgen, AstraZeneca, Boehringer Ingelheim, Eli Lilly, Hanmi Pharmaceuticals, Janssen, Merck Sharp & Dohme, Novartis, Novo Nordisk, Pfizer, Roche Diagnostics, and Sanofi; and grants (paid to institution) from AstraZeneca, Boehringer Ingelheim, Novartis, and Roche Diagnostics. WTG declares consulting fees as a member of advisory boards for Boehringer Ingelheim, Eli Lilly, Novo Nordisk, Pfizer, Fractyl Health, Alnylam Pharmaceuticals, Inogen, Zealand Pharma, Allurion, Carmot Therapeutics (Roche), Regeneron, and Merck; research grants as a site principal investigator for multicentre clinical trials sponsored by his university and funded by Novo Nordisk, Eli Lilly, Epitomee, Neurovalens, and Pfizer; has served as a consultant on an advisory board for the non-profit Milken Foundation; and is a member of the data monitoring committee for phase 3 clinical trials conducted by Boehringer Ingelheim and Eli Lilly. BL declares research grants from US National Institutes of Health (not related to this Commission); and personal consulting fees from UpToDate. RHE declares consulting fees from Novo Nordisk, The Healthy Aging Co, and WW International. AK declares research grants from Novo Nordisk, ELPEN Pharma, and Pharmaserve–Lilly; serving on scientific advisory boards for Novo Nordisk, Pharmaserve–Lilly, Sanofi, and Boehringher Ingelheim; and honoraria for lectures by Novo Nordisk, Pharmaserve–Lilly, AstraZeneca, MSD, Sanofi, Bausch Health, Ethicon, Galenica Pharma, Epsilon Health, and Winmedica. J-PD declares grants from the Canadian Institutes of Health Research; and personal consulting fees from INVERSAGO Pharma as a member of the advisory board. KWT declares speaker honoraria or consulting fees from Novo Nordisk, Eurodrug Laboratories, iNova Pharmaceuticals, and DKSH; travel support from Novo Nordisk; and serving on advisory boards of Novo Nordisk, DKSH (representing Eli Lilly), Abbott Nutrition, and Boehringer Ingelheim. ER declares research grants from Eli Lilly and Novo Nordisk; and consulting fees from Energesis Pharmaceuticals, Eli Lilly, Amway, Kintai Therapeutics, YSOPIA Bioscience (previously LNC Therapeutics), CINFINA Pharmaceuticals, and Boehringer Ingelheim. JBD declares personal consulting fees from Reshape Lifescience, and Nestle Health Science Australia; serving on advisory boards and speaker panels for Reshape Lifescience, Nestle Health Science Australia, Novo Nordisk, Eli Lilly, and I-nova; and speaker fees from HealthED and Eurodrug Laboratories. FP declares personal consulting fees from Medtronic, Ethicon, Novo Nordisk, and Eli Lilly. DEC declares serving on scientific advisory boards for GI Dynamics, Gila Therapeutics, and Endogenex. TK declares research grants from Nippon Boehringer Ingelheim and Sumitomo Pharma; consulting fees from Taisho Pharmaceutical, Eli Lilly Japan, and Novo Nordisk; and honoraria for lectures from Nippon Boehringer Ingelheim, Sumitomo Pharma, Teijin Pharma, MSD, Eli Lilly Japan, Mitsubishi Tanabe Pharma Corporation, Taisho Pharmaceutical, and Novo Nordisk. NBAB declares research grants from NovoNordisk and AstraZeneca; and honoraria for lectures and presentations from Novo Nordisk, Boehringer Ingelheim, AstraZeneca, Merck, MSD, Sanofi, and Servier. JV was national clinical director for diabetes and obesity at NHS England from April, 2013, to September, 2023; declares funding support from the North West London National Institute for Health and Care Research Applied Research Collaboration, CW+ (the official charity of Chelsea and Westminster Hospital NHS Foundation Trust), European Commission Horizon Europe 2022, and UK Research and Innovation Horizon Europe. CWlR declares grants from the Irish Research Council, Science Foundation Ireland, Anabio, and the Health Research Board; serving on advisory boards and speakers panels for Novo Nordisk, Herbalife, GI Dynamics, Eli Lilly, Johnson & Johnson, Glia, Irish Life Health, Boehringer Ingelheim, Currax, Zealand Pharma, Keyron, and Rhythm Pharmaceuticals; was the chief medical officer and director (unpaid) of the Medical Device Division of Keyron in 2021; was a previous investor in Keyron, which develops endoscopically implantable medical devices intended to mimic the surgical procedures of sleeve gastrectomy and gastric bypass (no patients have been included in any of Keyron's studies and they are not listed on the stock market); was gifted stock holdings in September, 2021, and divested all stock holdings in Keyron in September, 2021; continues to provide scientific advice (unpaid) to Keyron; and provides (unpaid) obesity clinical care in the Beyond BMI clinic (Dublin, Ireland), and is a shareholder in the clinic. NJF-L declares personal consulting fees from WHO and the European Commission (Best Re-MaP joint action [a project aimed to develop and implement policy proposals in nutrition for children]). NFA declares personal consulting fees from Ethicon and Eli Lilly; and serving on scientific advisory boards for Novo Nordisk and Eli Lilly. ISF declares personal consulting fees from Rhythm Pharmaceuticals, Eli Lilly, Novo Nordisk, SV Health, Nodthera Therapeutics, and Goldman Sachs. VMM declares personal consulting fees from Boehringer Ingelheim and Novo Nordisk. JPK declares research grants from the US National Institutes of Health (grants U54, U01, and U54 GM104940 that could be indirectly linked to the work of this Commission); and honoraria for serving on scientific advisory boards of Novo Nordisk and the Annual Reviews of Nutrition. KMM reports serving on scientific advisory boards for Novo Nordisk and Rhythm Pharmaceuticals; and is a member of a drug safety and monitoring board for Novartis. PRS declares research grants from Ethicon and Medtronic; personal consulting fees or honoraria from GI Dynamics, Keyron, Persona, Mediflix, Metabolic Health International, Eli Lilly, Heron, Novo Nordisk, and Klens; serving on scientific advisory boards for SE Healthcare Board of Directors, GI Dynamics, Keyron, Persona, and Mediflix; and has ownership interest in SE Healthcare, Mediflix, and Metabolic Health International. HT declares research grants from Amgen, Boehringer Ingelheim, Daiichi Sankyo, Novartis, and Novo Nordisk; serving on advisory boards for Novo Nordisk, Daiichi Sankyo, and Novartis; and speakers fees from Daiichi Sankyo, Novartis, and Novo Nordisk. MHT declares participation in a scientific advisory board meeting of ERX Pharmaceuticals (Cambridge, MA, USA) in 2019; was a member of the Research Cluster Advisory Panel of the Novo Nordisk Foundation between 2017 and 2019; funding for research projects from Novo Nordisk (2016–20) and Sanofi-Aventis (2012–19); consulted twice for Boehringer Ingelheim (2020 and 2021); delivered scientific lectures for Sanofi-Aventis (2020), Boehringer Ingelheim (2024), and AstraZeneca (2024); is cofounder of the biotech startups Ghrelco and Bluewater Biotech (2024); is chief executive officer and chief scientific officer of Helmholtz Munich, and is co-responsible for countless collaborations of the employees with a multitude of companies and institutions worldwide (in this capacity, discusses potential projects with and signs contracts for the centres institutes related to research collaborations worldwide, including, but not limited to, pharmaceutical corporations such as Boehringer Ingelheim, Novo Nordisk, Roche Diagnostics, Arbormed, Eli Lilly, and SCG Cell Therapy, and as chief scientific officer is responsible for commercial technology transfer activities); and is a former member of the scientific advisory board of ERX, which is developing the drug celastrol, but has no current competing interests. JPHW declares consultancy or advisory board work for the pharmaceutical industry contracted via the University of Liverpool (no personal payment) for Altimmune, Amgen, AstraZeneca, Boehringer Ingelheim, Eli Lilly, Napp, Novo Nordisk, Menarini, Pfizer, Regeneron, Rhythm Pharmaceuticals, Sanofi, Saniona, Tern, Shionogi, and YSOPIA Bioscience; research grants for clinical trials from AstraZeneca and Novo Nordisk; personal honoraria or lecture fees from AstraZeneca, Boehringer Ingelheim, Medscape, Napp, Novo Nordisk, and Rhythm Pharmaceuticals; is past president of the World Obesity Federation; and was national lead for the Metabolic and Endocrine Speciality Group of the National Institute of Health and Reasearch Clinical Research Network from 2010–24; and is a member of the Rank Prize Funds Nutrition Committee and a past member of the RCP committee on nutrition, weight, and health. FCS declares personal consulting fees from Eli Lilly, Novo Nordisk, Boehringer Ingelheim, Pfizer, Gelesis, Currax, and Rhythm Pharmaceuticals; and has served on scientific advisory boards for Eli Lilly and Novo Nordisk. LAB declares serving on scientific advisory board for Novo Nordisk (for the ACTION Teens study) and Eli Lilly; and speaker fees (paid to institution) from Novo Nordisk. LMK declares participation on advisory boards for Boehringer Ingelheim and Eli Lilly; and consulting fees from Altimmune, Amgen, AstraZeneca, Boehringer Ingelheim, Cytoki, Ethicon, Glyscend, Kallyope, Eli Lilly, Neurogastrx, Novo Nordisk, Optum Health, Perspectum, Pfizer, Sidekick Health, Xeno Biosciences, and Zealand Pharma. RLB declares research grants from the Sir Jules Thorn Trust, National Institutes for Health and Care Research, Rosetrees Trust, and Novo Nordisk; personal consulting fees from Eli Lilly, Novo Nordisk, Gila Therapeutics, Epitomee Medical, Medscape, ViiV, and International Medical Press; serving on scientific advisory boards for Eli Lilly, Novo Nordisk, Pfizer, ViiV, and International Medical Press; leadership or fiduciary roles (unpaid) in other board, society, committee, or advocacy groups for the Royal College of Physicians; is a committee member of the British Obesity and Metabolic Surgery Society and the National Bariatric Surgery Registry; is scientific chair of the International Federation for the Surgery of Obesity, European Chapter; is a trustee for the Association for the Study of Obesity and the Obesity Empowerment Network UK; is a member of the Obesity Guideline Update Committee for the National Institutes for Health and Care Excellence; and, since May 15, 2023, is senior vice president for Eli Lilly and holds shares in Eli Lilly, and as a result has had no active involvement in this Commission since May 1, 2023 (however, to comply with authorship requirements, RLB read and approved the final draft [see Acknowledgements for details]). RV declares research grants from Pfizer; fees for educational purposes from Novo Nordisk, AstraZeneca, and Eli Lilly; and serving on scientific advisory boards for Eli Lilly and Novo Nordisk. MO-G declares research grants from Adamed Poland; personal consulting fees from Baush Health, Novo Nordisk, and Promed Poland; and serving on scientific advisory boards for Baush Health, Novo Nordisk, and Boehringer Ingelheim. HJG declares consulting fees from Gila Pharmaceuticals and Pfizer. SL declares research grants from Merck Sharp & Dohme, Novo Nordisk, and LG Chem; and honoraria as a consultant or speaker for AstraZeneca, Boehringer Ingelheim, Abbott, LG Chem, Daewoong Pharmaceutical, Chong Kun Dang Pharmaceutical, and Novo Nordisk. All other authors have no competing interests.

This review seeks to address major gaps and delays between our rapidly evolving body of knowledge on type 2 diabetes and its translation into real-world practice. Through updated and improved best practices informed by recent evidence and described herein, we stand to better attain A1c targets, help preserve beta cell integrity and moderate glycemic variability, minimize treatment-emergent hypoglycemia, circumvent prescribing to "treatment failure," and prevent long-term complications. The first topic addressed in this review concerns updates in the 2023 and 2024 diabetes treatment guidelines for which further elaboration can help facilitate integration into routine care. The second concerns advances in diabetes research that have not yet found their way into guidelines, though they are endorsed by strong evidence and are ready for real-world use in appropriate patients. The final theme addresses lingering misconceptions about the underpinnings of type 2 diabetes-fundamental fallacies that continue to be asserted in the textbooks and continuing medical education upon which physicians build their approaches. A corrected and up-to-date understanding of the disease state is essential for practitioners to both conceptually and translationally manage initial onset through late-stage type 2 diabetes., (© 2024. The Author(s).)

Despite varied treatment, mitigation, and prevention efforts, the global prevalence and severity of obesity continue to worsen. Here we propose a combined model of obesity, a unifying paradigm that links four general models: the energy balance model (EBM), based on calories as the driver of weight gain; the carbohydrate-insulin model (CIM), based on insulin as a driver of energy storage; the oxidation-reduction model (REDOX), based on reactive oxygen species (ROS) as a driver of altered metabolic signaling; and the obesogens model (OBS), which proposes that environmental chemicals interfere with hormonal signaling leading to adiposity. We propose a combined OBS/REDOX model in which environmental chemicals (in air, food, food packaging, and household products) generate false autocrine and endocrine metabolic signals, including ROS, that subvert standard regulatory energy mechanisms, increase basal and stimulated insulin secretion, disrupt energy efficiency, and influence appetite and energy expenditure leading to weight gain. This combined model incorporates the data supporting the EBM and CIM models, thus creating one integrated model that covers significant aspects of all the mechanisms potentially contributing to the obesity pandemic. Importantly, the OBS/REDOX model provides a rationale and approach for future preventative efforts based on environmental chemical exposure reduction., (© 2024. The Author(s).)

Changes correlating with increasing obesity include insulin resistance, hyperlipidaemia, hyperinsulinaemia, highly processed food and environmental toxins including plastics and air pollution. The relationship between the appearance of each of these potential causes and the onset of obesity is unknown. The cause(s) must precede obesity, the consequence, and temporally relate to its rising incidence. Macronutrients such as carbohydrates or fats are unlikely to cause obesity since these have long been constituents of human diets. Furthermore, food consumption and body weight have been well-regulated in most humans and other species until recent times. Thus, attention must focus on changes that have occurred in the last half-century and the relationship between such changes and specific populations that are impacted. The hypothesis presented here is that substances that have entered our bodies recently cause obesity by generating false and misleading information about energy status. We propose that this misinformation is caused by changes in the oxidation-reduction (redox) potential of metabolites that circulate and communicate to organs throughout the body. Examples are provided of food additives that generate reactive oxygen species and impact redox state, thereby, eliciting inappropriate tissue-specific functional changes, including insulin secretion. Reversal requires identification, neutralization, or removal of these compounds. This article is part of a discussion meeting issue 'Causes of obesity: theories, conjectures and evidence (Part I)'.

On September 7 and 8, 2022, Healthy Environment and Endocrine Disruptors Strategies, an Environmental Health Sciences program, convened a scientific workshop of relevant stakeholders involved in obesity, toxicology, or obesogen research to review the state of the science regarding the role of obesogenic chemicals that might be contributing to the obesity pandemic. The workshop's objectives were to examine the evidence supporting the hypothesis that obesogens contribute to the etiology of human obesity; to discuss opportunities for improved understanding, acceptance, and dissemination of obesogens as contributors to the obesity pandemic; and to consider the need for future research and potential mitigation strategies. This report details the discussions, key areas of agreement, and future opportunities to prevent obesity. The attendees agreed that environmental obesogens are real, significant, and a contributor at some degree to weight gain at the individual level and to the global obesity and metabolic disease pandemic at a societal level; moreover, it is at least, in theory, remediable., (Copyright © 2023 American Society for Nutrition. All rights reserved.)

Several unrelated findings led us to hypothesize that induction of autoimmunity is a consequence of a prior major inflammatory event in individuals with susceptible HLA phenotypes and elevated sensitivity to cytokines and free fatty acids (FFA). We observed provocative enhanced responsiveness of cultured human fibroblasts from individuals with type 1 diabetes (T1D), but not control subjects, to FFA and the inflammatory cytokines TNFα and IL1-β. Major infections increase inflammatory cytokines as well as circulating FFA. Endotoxin-treated animal models of sepsis also exhibit elevated inflammatory cytokines that inhibit FFA oxidation and elevate FFA. The pancreatic β-cell possesses low reactive oxygen species (ROS) scavenging capacity and responds to both elevated FFA and cytokines with increased ROS production, a combination that increases exocytosis and trafficking of secretory vesicles to the plasma membrane. Increased trafficking is accompanied by increased cycling of secretory granule proteins and may be linked with increased surface presentation of granule proteins to the immune system. We propose that this ultimately targets β-cell granular proteins at the cell surface and is consistent with the preponderance of autoantibodies to granule proteins. Our hypothesis encourages testing of potential early therapeutic interventions to prevent progression of β-cell destruction., (© 2022 by the American Diabetes Association.)

In this review, we focus on recent developments in our understanding of nutrient-induced insulin secretion that challenge a key aspect of the "canonical" model, in which an oxidative phosphorylation-driven rise in ATP production closes K ATP channels. We discuss the importance of intrinsic β cell metabolic oscillations; the phasic alignment of relevant metabolic cycles, shuttles, and shunts; and how their temporal and compartmental relationships align with the triggering phase or the secretory phase of pulsatile insulin secretion. Metabolic signaling components are assigned regulatory, effectory, and/or homeostatic roles vis-à-vis their contribution to glucose sensing, signal transmission, and resetting the system. Taken together, these functions provide a framework for understanding how allostery, anaplerosis, and oxidative metabolism are integrated into the oscillatory behavior of the secretory pathway. By incorporating these temporal as well as newly discovered spatial aspects of β cell metabolism, we propose a much-refined Mito Cat -Mito Ox model of the signaling process for the field to evaluate., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 Elsevier Inc. All rights reserved.)

We hypothesize that basal hyperinsulinemia is synergistically mediated by an interplay between increased oxidative stress and excess lipid in the form of reactive oxygen species (ROS) and long-chain acyl-CoA esters (LC-CoA). In addition, ROS production may increase in response to inflammatory cytokines and certain exogenous environmental toxins that mislead β-cells into perceiving nutrient excess when none exists. Thus, basal hyperinsulinemia is envisioned as an adaptation to sustained real or perceived nutrient excess that only manifests as a disease when the excess demand can no longer be met by an overworked β-cell. In this article we will present a testable hypothetical mechanism to explain the role of lipids and ROS in basal hyperinsulinemia and how they differ from glucose-stimulated insulin secretion (GSIS). The model centers on redox regulation, via ROS, and S -acylation-mediated trafficking via LC-CoA. These pathways are well established in neural systems but not β-cells. During GSIS, these signals rise and fall in an oscillatory pattern, together with the other well-established signals derived from glucose metabolism; however, their precise roles have not been defined. We propose that failure to either increase or decrease ROS or LC-CoA appropriately will disturb β-cell function., (© 2021 by the American Diabetes Association.)

Combined fatty acid esterification and lipolysis, termed lipid cycling, is an ATP-consuming process that contributes to energy expenditure. Therefore, interventions that stimulate energy expenditure through lipid cycling are of great interest. Here we find that pharmacological and genetic inhibition of the mitochondrial pyruvate carrier (MPC) in brown adipocytes activates lipid cycling and energy expenditure, even in the absence of adrenergic stimulation. We show that the resulting increase in ATP demand elevates mitochondrial respiration coupled to ATP synthesis and fueled by lipid oxidation. We identify that glutamine consumption and the Malate-Aspartate Shuttle are required for the increase in Energy Expenditure induced by MPC inhibition in Brown Adipocytes (MAShEEBA). We thus demonstrate that energy expenditure through enhanced lipid cycling can be activated in brown adipocytes by decreasing mitochondrial pyruvate availability. We present a new mechanism to increase energy expenditure and fat oxidation in brown adipocytes, which does not require adrenergic stimulation of mitochondrial uncoupling., (© 2020 The Authors. Published under the terms of the CC BY 4.0 license.)

The consensus model of glucose-stimulated insulin secretion (GSIS) holds that ATP generation by oxidative phosphorylation directly regulates K ATP channel activity and thus insulin granule release, a concept inconsistent with bioenergetic principles. Here, Lewandowski et al. (2020) and Abulizi et al. (2020) report that regulation of GSIS is much more complex as different sources of ATP generation are essential to control this process, which can be targeted in vivo and additionally modulate hepatic glucose production. These findings establish an important new conceptual framework of GSIS and in vivo glucose homeostasis., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Key tissues are dysfunctional in obesity, diabetes, cardiovascular disease, fatty liver and other metabolic diseases. Focus has centered on individual organs as though each was isolated. Attention has been paid to insulin resistance as the key relevant pathosis, particularly insulin receptor signaling. However, many tissues play important roles in synergistically regulating metabolic homeostasis and should be considered part of a network. Our approach identifies redox as an acute regulator of the greater metabolic network. Redox reactions involve the transfer of electrons between two molecules and in this work refer to commonly shared molecules, reflective of energy state, that can readily lose electrons to increase or gain electrons to decrease the oxidation state of molecules including NAD(P), NAD(P)H, and thiols. Metabolism alters such redox molecules to impact metabolic function in many tissues, thus, responding to anabolic and catabolic stimuli appropriately and synergistically. It is also important to consider environmental factors that have arisen or increased in recent decades as putative modifiers of redox and reactive oxygen species (ROS) and thus metabolic state. ROS are highly reactive, controlled by the thiol redox state and influence the function of thousands of proteins. Lactate (L) and pyruvate (P) in cells are present in a ratio of about 10 reflective of the cytosolic NADH to NAD ratio. Equilibrium is maintained in cells because lactate dehydrogenase is highly expressed and near equilibrium. The major source of circulating lactate and pyruvate is muscle, although other tissues also contribute. Acetoacetate (A) is produced primarily by liver mitochondria where β-hydroxybutyrate dehydrogenase is highly expressed, and maintains a ratio of β-hydroxybutyrate (β) to A of about 2, reflective of the mitochondrial NADH to NAD ratio. All four metabolites as well as the thiols, cysteine and glutathione, are transported into and out of cells, due to high expression of relevant transporters. Our model supports regulation of all collaborating metabolic organs through changes in circulating redox metabolites, regardless of whether change was initiated exogenously or by a single organ. Validation of these predictions suggests novel ways to understand function by monitoring and impacting redox state., (Copyright © 2020 Corkey and Deeney.)

Chronic exposure of pancreatic β-cells to excess glucose can lead to metabolic acceleration and loss of stimulus-secretion coupling. Here, we examined how exposure to excess glucose (defined here as concentrations above 5 mM) affects mTORC1 signaling and the metabolism of β-cells. Acute exposure to excess glucose stimulated glycolysis-dependent mTORC1 signaling, without changes in the PI3K or AMPK pathways. Prolonged exposure to excess glucose led to hyperactivation of mTORC1 and metabolic acceleration, characterized by higher basal respiration and maximal respiratory capacity, increased energy demand, and enhanced flux through mitochondrial pyruvate metabolism. Inhibition of pyruvate transport to the mitochondria decelerated the metabolism of β-cells chronically exposed to excess glucose and re-established glucose-dependent mTORC1 signaling, disrupting a positive feedback loop for mTORC1 hyperactivation. mTOR inhibition had positive and negative impacts on various metabolic pathways and insulin secretion, demonstrating a role for mTOR signaling in the long-term metabolic adaptation of β-cells to excess glucose., Competing Interests: Declaration of Interests The Authors declare no competing interests., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

Significant advances have been made in deciphering the mechanisms underlying fuel-stimulated insulin secretion by pancreatic beta cells. The contribution of the triggering/ATP-sensitive potassium (K ATP )-dependent Ca 2+ signalling and K ATP -independent amplification pathways, that include anaplerosis and lipid signalling of glucose-stimulated insulin secretion (GSIS), are well established. A proposed model included a key role for a metabolic partitioning 'switch', the acetyl-CoA carboxylase (ACC)/malonyl-CoA/carnitine palmitoyltransferase-1 (CPT-1) axis, in beta cell glucose and fatty acid signalling for insulin secretion. This model has gained overwhelming support from a number of studies in recent years and is now refined through its link to the glycerolipid/NEFA cycle that provides lipid signals through its lipolysis arm. Furthermore, acetyl-CoA carboxylase may also control beta cell growth. Here we review the evidence supporting a role for the ACC/malonyl-CoA/CPT-1 axis in the control of GSIS and its particular importance under conditions of elevated fatty acids (e.g. fasting, excess nutrients, hyperlipidaemia and diabetes). We also document how it is linked to a more global lipid signalling system that includes the glycerolipid/NEFA cycle.

Hyperinsulinemia is strongly associated with type 2 diabetes. Racial and ethnic minority populations are disproportionately affected by diabetes and obesity-related complications. This mini-review provides an overview of the genetic and environmental factors associated with hyperinsulinemia with a focus on racial and ethnic differences and its metabolic consequences. The data used in this narrative review were collected through research in PubMed and reference review of relevant retrieved articles. Insulin secretion and clearance are regulated processes that influence the development and progression of hyperinsulinemia. Environmental, genetic, and dietary factors are associated with hyperinsulinemia. Certain pharmacotherapies for obesity and bariatric surgery are effective at mitigating hyperinsulinemia and are associated with improved metabolic health. Hyperinsulinemia is associated with many environmental and genetic factors that interact with a wide network of hormones. Recent studies have advanced our understanding of the factors affecting insulin secretion and clearance. Further basic and translational work on hyperinsulinemia may allow for earlier and more personalized treatments for obesity and metabolic diseases., Competing Interests: Disclosure Summary: C.M.A. reports grants from Aspire Bariatrics, the Vela Foundation, Coherence Laboratory, Energesis, NIH, and PCORI; grants and personal fees from GI Dynamics, Takeda, Novo Nordisk, and Gelesis; and personal fees from Orexigen, EnteroMedics, Nutrisystem, Zafgen, Sanofi-Aventis, Scientific Intake, Xeno Biosciences, Rhythm Pharmaceuticals, Eisai, and Bariatrix Nutrition and other fees from Science-Smart LLC, outside the submitted work. The remaining authors have nothing to disclose.Data sharing is not applicable to this article as no data sets were generated or analyzed during the current study.

This review is motivated by the need to question dogma that has not yielded significant improvements in outcomes of Type 2 Diabetes treatment: that insulin resistance is the driver of ß-Cell failure and resulting hyperglycemia. We highlight the fact that hyperlipidemia, insulin resistance, and hyperinsulinemia all precede overt diabetes diagnosis and can each induce the other when tested experimentally. New research highlights the importance of high levels of circulating insulin as both a driver of weight gain and insulin resistance. Data from our lab and others document that several nutrients and environmental toxins can stimulate insulin secretion at non-stimulatory glucose in the absence of insulin resistance. This occurs either by direct action on the ß-Cell or by shifting its sensitivity to known secretagogues. We raise the next logical question of whether ß-Cell dysfunction in Type 2 Diabetes is due to impaired function, defined as failure, or if chronic overstimulation of the ß-Cell that exceeds its capacity to synthesize and secrete insulin, defined as abuse, is the main abnormality in Type 2 Diabetes. These questions are important as they have direct implications for how to best prevent and treat Type 2 Diabetes.

Purpose: Globally, the age-standardised prevalence of type 2 diabetes mellitus (T2DM) has nearly doubled from 1980 to 2014, rising from 4.7% to 8.5% with an estimated 422 million adults living with the chronic disease. The MULTI sTUdy Diabetes rEsearch (MULTITUDE) consortium was recently established to harmonise data from 17 independent cohort studies and clinical trials and to facilitate a better understanding of the determinants, risk factors and outcomes associated with T2DM., Participants: Participants range in age from 3 to 88 years at baseline, including both individuals with and without T2DM. MULTITUDE is an individual-level pooled database of demographics, comorbidities, relevant medications, clinical laboratory values, cardiac health measures, and T2DM-associated events and outcomes across 45 US states and the District of Columbia., Findings to Date: Among the 135 156 ongoing participants included in the consortium, almost 25% (33 421) were diagnosed with T2DM at baseline. The average age of the participants was 54.3, while the average age of participants with diabetes was 64.2. Men (55.3%) and women (44.6%) were almost equally represented across the consortium. Non-whites accounted for 31.6% of the total participants and 40% of those diagnosed with T2DM. Fewer individuals with diabetes reported being regular smokers than their non-diabetic counterparts (40.3% vs 47.4%). Over 85% of those with diabetes were reported as either overweight or obese at baseline, compared with 60.7% of those without T2DM. We observed differences in all-cause mortality, overall and by T2DM status, between cohorts., Future Plans: Given the wide variation in demographics and all-cause mortality in the cohorts, MULTITUDE consortium will be a unique resource for conducting research to determine: differences in the incidence and progression of T2DM; sequence of events or biomarkers prior to T2DM diagnosis; disease progression from T2DM to disease-related outcomes, complications and premature mortality; and to assess race/ethnicity differences in the above associations., Competing Interests: Competing interests: None declared., (© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2018. All rights reserved. No commercial use is permitted unless otherwise expressly granted.)

Mitochondria associate with lipid droplets (LDs) in fat-oxidizing tissues, but the functional role of these peridroplet mitochondria (PDM) is unknown. Microscopic observation of interscapular brown adipose tissue reveals that PDM have unique protein composition and cristae structure and remain adherent to the LD in the tissue homogenate. We developed an approach to isolate PDM based on their adherence to LDs. Comparison of purified PDM to cytoplasmic mitochondria reveals that (1) PDM have increased pyruvate oxidation, electron transport, and ATP synthesis capacities; (2) PDM have reduced β-oxidation capacity and depart from LDs upon activation of brown adipose tissue thermogenesis and β-oxidation; (3) PDM support LD expansion as Perilipin5-induced recruitment of mitochondria to LDs increases ATP synthase-dependent triacylglyceride synthesis; and (4) PDM maintain a distinct protein composition due to uniquely low fusion-fission dynamics. We conclude that PDM represent a segregated mitochondrial population with unique structure and function that supports triacylglyceride synthesis., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Metabolic deceleration in pancreatic β-cells is associated with inhibition of glucose-induced insulin secretion (GIIS), but only in the presence of intermediate/submaximal glucose concentrations. Here, we used acute metformin treatment as a tool to induce metabolic deceleration in INS1 (832/13) β-cells, with the goal of identifying key pathways and metabolites involved in GIIS. Metabolites and pathways previously implicated as signals for GIIS were measured in the cells at 2-25 mm glucose, with or without 5 mm metformin. We defined three criteria to identify candidate signals: 1) glucose-responsiveness, 2) sensitivity to metformin-induced inhibition of the glucose effect at intermediate glucose concentrations, and 3) alleviation of metformin inhibition by elevated glucose concentrations. Despite the lack of recovery from metformin-induced impairment of mitochondrial energy metabolism (glucose oxidation, O 2 consumption, and ATP production), insulin secretion was almost completely restored at elevated glucose concentrations. Meeting the criteria for candidates involved in promoting GIIS were the following metabolic indicators and metabolites: cytosolic NAD + /NADH ratio (inferred from the dihydroxyacetone phosphate:glycerol-3-phosphate ratio), mitochondrial membrane potential, ADP, Ca 2+ , 1-monoacylglycerol, diacylglycerol, malonyl-CoA, and HMG-CoA. On the contrary, most of the purine and nicotinamide nucleotides, acetoacetyl-CoA, H 2 O 2 , reduced glutathione, and 2-monoacylglycerol were not glucose-responsive. Overall these results underscore the significance of mitochondrial energy metabolism-independent signals in GIIS regulation; in particular, the candidate lipid signaling molecules 1-monoacylglycerol, diacylglycerol, and malonyl-CoA; the predominance of K ATP /Ca 2+ signaling control by low ADP·Mg 2+ rather than by high ATP levels; and a role for a more oxidized state (NAD + /NADH) in the cytosol during GIIS that favors high glycolysis rates., (© 2017 by The American Society for Biochemistry and Molecular Biology, Inc.)

BAT-controlled thermogenic activity is thought to be required for its capacity to prevent the development of insulin resistance. This hypothesis predicts that mediators of thermogenesis may help prevent diet-induced insulin resistance. We report that the mitochondrial fusion protein Mitofusin 2 (Mfn2) in BAT is essential for cold-stimulated thermogenesis, but promotes insulin resistance in obese mice. Mfn2 deletion in mice through Ucp1-cre (BAT-Mfn2-KO) causes BAT lipohypertrophy and cold intolerance. Surprisingly however, deletion of Mfn2 in mice fed a high fat diet (HFD) results in improved insulin sensitivity and resistance to obesity, while impaired cold-stimulated thermogenesis is maintained. Improvement in insulin sensitivity is associated with a gender-specific remodeling of BAT mitochondrial function. In females, BAT mitochondria increase their efficiency for ATP-synthesizing fat oxidation, whereas in BAT from males, complex I-driven respiration is decreased and glycolytic capacity is increased. Thus, BAT adaptation to obesity is regulated by Mfn2 and with BAT-Mfn2 absent, BAT contribution to prevention of insulin resistance is independent and inversely correlated to whole-body cold-stimulated thermogenesis., (© 2017 The Authors. Published under the terms of the CC BY 4.0 license.)

Purpose of Review: This perspective is motivated by the need to question dogma that does not work: that the problem is insulin resistance (IR). We highlight the need to investigate potential environmental obesogens and toxins., Recent Findings: The prequel to severe metabolic disease includes three interacting components that are abnormal: (a) IR, (b) elevated lipids and (c) elevated basal insulin (HI). HI is more common than IR and is a significant independent predictor of diabetes. We hypothesize that (1) the initiating defect is HI that increases nutrient consumption and hyperlipidemia (HL); (2) the cause of HI may include food additives, environmental obesogens or toxins that have entered our food supply since 1980; and (3) HI is sustained by HL derived from increased adipose mass and leads to IR. We suggest that HI and HL are early indicators of metabolic dysfunction and treating and reversing these abnormalities may prevent the development of more serious metabolic disease.

Objective: To review the metabolomic studies carried out so far to identify metabolic markers associated with surgical and dietary treatments for weight loss in subjects with obesity., Methods: The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed., Results: Thirty-two studies successfully met the eligibility criteria. The metabolic adaptations shared by surgical and dietary interventions mirrored a state of starvation ketoacidosis (increase of circulating ketone bodies), an increase of acylcarnitines and fatty acid β-oxidation, a decrease of specific amino acids including branched-chain amino acids (BCAA) and (lyso)glycerophospholipids previously associated with obesity, and adipose tissue expansion. The metabolic footprint of bariatric procedures was specifically characterized by an increase of bile acid circulating pools and a decrease of ceramide levels, a greater perioperative decline in BCAA, and the rise of circulating serine and glycine, mirroring glycemic control and inflammation improvement. In one study, 3-hydroxybutyrate was particularly identified as an early metabolic marker of long-term prognosis after surgery and proposed to increase current prognostic modalities and contribute to personalized treatment., Conclusions: Metabolomics helped in deciphering the metabolic response to weight loss treatments. Moving from association to causation is the next challenge to move to a further level of clinical application., (© 2016 The Obesity Society.)

The "chemical obesogen" hypothesis conjectures that synthetic, environmental contaminants are contributing to the global epidemic of obesity. In fact, intentional food additives (e.g., artificial sweeteners and colors, emulsifiers) and unintentional compounds (e.g., bisphenol A, pesticides) are largely unstudied in regard to their effects on overall metabolic homeostasis. With that said, many of these contaminants have been found to dysregulate endocrine function, insulin signaling, and/or adipocyte function. Although momentum for the chemical obesogen hypothesis is growing, supportive, evidence-based research is lacking. In order to identify noxious synthetic compounds in the environment out of the thousands of chemicals that are currently in use, tools and models from toxicology should be adopted (e.g., functional high throughput screening methods, zebrafish-based assays). Finally, mechanistic insight into obesogen-induced effects will be helpful in elucidating their role in the obesity epidemic as well as preventing and reversing their effects.

Obesity and diabetes are caused by defects in metabolically sensitive tissues. Attention has been paid to insulin resistance as the key relevant pathosis, with a detailed focus on signal transduction pathways in metabolic tissues. Evidence exists to support an important role for each tissue in metabolic homeostasis and a potential causative role in both diabetes and obesity. The redox metabolome, that coordinates tissue responses and reflects shared control and regulation, is our focus. Consideration is given to the possibility that pathosis results from contributions of all relevant tissues, by virtue of a circulating communication system. Validation of this model would support simultaneous regulation of all collaborating metabolic organs through changes in the circulation, regardless of whether change was initiated exogenously or by a single organ., (Copyright © 2012 Elsevier Ltd. All rights reserved.)