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We aimed to investigate the effect of acute glucose shift on the activation of the NLRP3 inflammasome, IL-1β secretion, and underlying signaling pathways in THP-1 cells. THP-1 cells were divided into four groups and exposed to the following glucose concentrations for 24 h: constant normal glucose (NG, 5.5 mM), constant high glucose (HG, 25 mM), normal to high glucose shift (NG-to-HG, 5.5 to 25 mM), and high to normal glucose shift (HG-to-NG, 25 to 5.5 mM). Cell viability, oxidative stress, and the levels of NLRP3 inflammasome components were assessed. Both directions of the acute glucose shift increased the activation of the NLRP3 inflammasome, generation of reactive oxygen species (ROS), and expression of phosphorylated p38 MAPK, JNK, and NF-κB compared with either constant NG or HG. Treatment with N-acetylcysteine, a pharmacological antioxidant, inhibited the acute glucose shift-induced generation of ROS, activation of NLRP3 inflammasome, and upregulation of MAPK-NF-κB. Further analysis using inhibitors of p38 MAPK, JNK, and NF-κB indicated that acute glucose shifts promoted IL-1β secretion by activating the signaling pathway in a ROS-MAPK-NF-κB-NLRP3 inflammasome in THP-1 cells. These findings suggested that acute changes in glucose concentration might cause monocyte inflammation, which is associated with diabetic complications.

This work was initiated to determine whether toxicity generated through inhibition of mitochondrial fuel metabolism is similar to high glucose/palmitate (HG/PA)-induced glucolipotoxicity. Influx of glucose and free fatty acids into the tricarboxylic acid (TCA) cycle was inhibited by treatment with the pyruvate carboxylase (PC) inhibitor phenylacetic acid (PAA) and carnitine palmitoyl transferase-1 (CPT-1) inhibitor etomoxir (Eto), or knockdown of PC and CPT-1. Treatment of PAA/Eto or knockdown of PC/CPT-1 induced apoptotic death in INS-1 beta cells. Similar to HG/PA treatment, PAA/Eto increased endoplasmic reticulum stress responses but decreased the Akt signal. JNK inhibitor or chemical chaperone was protective against both PAA/Eto- and HG/PA-induced cell death. All attempts to reduce [Ca²⁺](i), stimulate lipid metabolism, and increase the TCA cycle intermediate pool protected PAA/Eto-induced death as well as HG/PA-induced death. These data suggest that signals induced from impaired mitochondrial fuel metabolism play a critical role in HG/PA-induced glucolipotoxicity., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)

Reactive oxygen species (ROS), driven by excessive levels of glucose and free fatty acids, appears to induce cell apoptosis. However, the underlying molecular mechanism of this process remains unclear in cardiac myocytes. We investigated the glucolipotoxicity effects of high glucose and palmitic acid (C16:0) on the rat cardiomyoblast cell line (H9c2) focusing on tumor suppressor p53. Cultured H9c2 rat cardiomyoblasts were exposed to palmitate and /or to an elevated glucose concentration for 18 hours. Only the glucolipotoxic condition of 30 mM glucose in combination with 250 μM palmitate resulted in significant generation of ROS and upregulation of p53 which caused to an increased cleavage of caspase-3. On the other hand, the expression of NF-E2-related factor 2 (Nrf2) showed increased tendency while the expression of NAD(P)H: quinone oxidoreductase-1 (NQO1) was decreased. N-acetyl L cysteins and pifithrin-α, an inhibitor of p53 abrogated glucolipotoxicity-induced ROS generation and p53 expression. Chromatin immunoprecipitation analysis revealed that p53 interacted antioxidant responsive elements (ARE)-containing promoter of NQO1. Upregulated p53 counteracted the Nrf2-induced transcription of ARE-containing promoter of NQO1 gene and leaded to decrease in NQO1 expression. We demonstrated that the elevated p53 mediated glucolipotoxicity-induced apoptosis of rat cardiomyoblast cell through dual pathways: stimulating pro-apoptosis signaling as well as suppressing anti-apoptosis pathway of Nrf2-NQO1 signaling., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Elevated fatty acid levels have been thought to contribute to insulin resistance. Repression of the glucose transporter 4 (GLUT4) gene as well as impaired GLUT4 translocation may be a mediator for fatty acid-induced insulin resistance. This study was initiated to determine whether palmitate treatment repressed GLUT4 expression, whether glucose/fatty acid metabolism influenced palmitate-induced GLUT4 gene repression (PIGR), and whether attempts to prevent PIGR restored palmitate-induced impairment of glucose uptake (PIIGU) in C2 myotubes. Not only stimulators of fatty acid oxidation, such as bezafibrate, AICAR, and TOFA, but also TCA cycle substrates, such as pyruvate, leucine/glutamine, and α-ketoisocaproate/monomethyl succinate, significantly prevented PIGR. In particular, supplementing with pyruvate through methyl pyruvate resulted in nearly complete prevention of PIIGU, whereas palmitate treatment reduced the intracellular pyruvate level. These results suggest that pyruvate depletion plays a critical role in PIGR and PIIGU; thus, pyruvate supplementation may help prevent obesity-induced insulin resistance in muscle cells., (Crown Copyright © 2011. Published by Elsevier Ireland Ltd. All rights reserved.)

The aim of this study is to investigate the effect of mitochondrial metabolism on high glucose/palmitate (HG/PA)-induced INS-1 beta cell death. Long-term treatment of INS-1 cells with HG/PA impaired energy-producing metabolism accompanying with depletion of TCA cycle intermediates. Whereas an inhibitor of carnitine palmitoyl transferase 1 augmented HG/PA-induced INS-1 cell death, stimulators of fatty acid oxidation protected the cells against the HG/PA-induced death. Furthermore, whereas mitochondrial pyruvate carboxylase inhibitor phenylacetic acid augmented HG/PA-induced INS-1 cell death, supplementation of TCA cycle metabolites including leucine/glutamine, methyl succinate/α-ketoisocaproic acid, dimethyl malate, and valeric acid or treatment with a glutamate dehydrogenase activator, aminobicyclo-heptane-2-carboxylic acid (BCH), significantly protected the cells against the HG/PA-induced death. In particular, the mitochondrial tricarboxylate carrier inhibitor, benzene tricarboxylate (BTA), also showed a strong protective effect on the HG/PA-induced INS-1 cell death. Knockdown of glutamate dehydrogenase or tricarboxylate carrier augmented or reduced the HG/PA-induced INS-1 cell death, respectively. Both BCH and BTA restored HG/PA-induced reduction of energy metabolism as well as depletion of TCA intermediates. These data suggest that depletion of the TCA cycle intermediate pool and impaired energy-producing metabolism may play a role in HG/PA-induced cytotoxicity to beta cells and thus, HG/PA-induced beta cell glucolipotoxicity can be protected by nutritional or pharmacological maneuver enhancing anaplerosis or reducing cataplerosis., (Copyright © 2010 Elsevier Inc. All rights reserved.)

Aim: To evaluate the efficacy and safety of dapagliflozin versus placebo as an add‐on in patients with type 2 diabetes who did not achieve adequate glycaemic control with evogliptin and metformin combination. Patients and Methods: In this multicentre, randomized, double‐blind, placebo‐controlled Phase 3 trial, patients with glycated haemoglobin (HbA1c) levels ≥7.0% (≥53 mmol/mol) and ≤10.5% (≤91 mmol/mol) who had received stable‐dose metformin (≥1000 mg) and evogliptin (5 mg) for at least 8 weeks were randomized to receive dapagliflozin 10 mg or placebo once daily for 24 weeks. Participants continued treatment with metformin and evogliptin. The primary endpoint was change in HbA1c level after 24 weeks of treatment from baseline level. Results: In total, 198 patients were randomized, and 195 patients were included in the efficacy analyses (dapagliflozin: 96, placebo: 99). At Week 24, dapagliflozin significantly reduced HbA1c levels. The least squares mean difference in HbA1c level change from baseline after 24 weeks of treatment was −0.70% (−7.7 mmol/mol) (p < 0.0001). The proportion of participants achieving HbA1c <7.0% (≥53 mmol/mol) was higher in the dapagliflozin group than in the placebo group. Compared to placebo, dapagliflozin significantly reduced fasting plasma glucose, mean daily glucose, 2‐h postprandial plasma glucose, fasting insulin, uric acid and gamma‐glutamyl transferase levels, homeostatic model assessment for insulin resistance index, body weight, hepatic steatosis index, and albuminuria. Adiponectin level significantly increased from baseline level after 24 weeks of dapagliflozin treatment. Adverse event rates were similar in the two groups. Conclusion: Dapagliflozin add‐on to evogliptin plus metformin improved glycaemic control and was well tolerated by the target patients. [ABSTRACT FROM AUTHOR]

Aim: We investigated whether rosiglitazone protects β-cells from glucolipotoxicity directly. Methods: INS-1 cells were incubated with 25 mM glucose and 0.5 mM palmitate in the absence or presence of 2.5 μM rosiglitazone. We evaluated caspase-3 expression and nuclear DAPI staining. An in vivo study was performed, in which 18-week-old Otsuka Long-Evans Tokushima Fatty (OLETF) rats were treated with rosiglitazone (4 mg/kg/day, n = 6) and with placebo (n = 6) for 10 weeks. At 28 weeks of age, an oral glucose tolerance test, insulin sensitivity test, TUNEL assay and histologic examination were performed. Results: Rosiglitazone attenuated glucolipotoxicity-induced nuclear change and caspase-3 expression for 8 h after treatment, but this effect was not observed at 12 h in INS-1 cells. Rosiglitazone treatment decreased β-cell apoptosis, preserved β-cell mass and improved glucose tolerance in OLETF rats. Conclusion: The present in vitro findings suggest that rosiglitazone can inhibit the early stage of glucolipotoxicity-induced β-cell apoptosis. Our results suggest that the antidiabetic action of rosiglitazone is, at least in part, related to a direct effect on β-cells rather than simply an indirect effect of improving insulin sensitivity. Copyright © 2008 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]