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Diet-associated alterations of the intestinal barrier and gut microbiota promote intestinal lipopolysaccharide (LPS) translocation from the lumen to the lamina propria through different pathways, leading to an increase in LPS levels in the plasma known as metabolic endotoxemia. As a pharmacological dose of grape seed proanthocyanidin extract (GSPE) can reduce metabolic endotoxemia of obese rats, in the current study, we aimed to evaluate GSPE modulation of LPS translocation and the underlying mechanisms. We performed both an in vitro experiment with Caco-2 cells and an in vivo experiment with Wistar female rats fed a cafeteria (CAF) diet. GSPE was effective in regulating intestinal permeability through the modulation of receptor-mediated endocytosis pathway, as well as the gut microbiota interaction with the endocannabinoid system through epigenetic mechanisms. Our results confirm that GSPE can ameliorate intestinal dysfunction and metabolic endotoxemia caused by an excess of dietary lipids by modulating the endotoxin-translocation pathways.

Obesity constitutes a major global public health threat. It can lead to a cluster of metabolic disorders and a higher risk of developing various types of pathological conditions and diseases. Among multiple environmental factors, high fat diets (HFD) play an important role in the development of obesity. Flavonoids are one of the most abundant categories of bioactive compounds present in the human diet. My dissertation work identified mechanisms by which the flavan-3-ol (-)-epicatechin (EC), could mitigate high fat diet-induced obesity-associated intestinal permeabilization and metabolic endotoxemia. Chapter one looked at the protective effects of EC from HFD-induced intestinal barrier permeabilization and endotoxemia and its implications for steatosis and insulin resistance in vivo. We subsequently found that the luminal content of total bile acid and select secondary bile acids, particularly deoxycholic acid, were increased by HFD consumption. The second chapter focused on investigating if EC could prevent DCA-induced intestinal permeabilization in vitro. Such effect could in turn, help prevent the paracellular transport of lipopolysaccharides (LPS) from the lumen into the bloodstream. The last chapter provided additional mechanistic insight into how flavan-3-ols and procyanidins (PCAs) can mitigate HFD-induced endotoxemia through their capacity to prevent chylomicron- dependent transcellular transport of LPS in Caco-2 monolayers and high fat-induced postprandial endotoxemia in mice. In summary, this thesis works provide evidence that EC can decrease HFD-associated endotoxemia, characterizing the underlying mechanisms. This action would be critical to the capacity of EC to mitigate HFD- and obesity-associated comorbidities.

Obesity constitutes a major global public health threat. It can lead to a cluster of metabolic disorders and a higher risk of developing various types of pathological conditions and diseases. Among multiple environmental factors, high fat diets (HFD) play an important role in the development of obesity. Flavonoids are one of the most abundant categories of bioactive compounds present in the human diet. My dissertation work identified mechanisms by which the flavan-3-ol (-)-epicatechin (EC), could mitigate high fat diet-induced obesity-associated intestinal permeabilization and metabolic endotoxemia. Chapter one looked at the protective effects of EC from HFD-induced intestinal barrier permeabilization and endotoxemia and its implications for steatosis and insulin resistance in vivo. We subsequently found that the luminal content of total bile acid and select secondary bile acids, particularly deoxycholic acid, were increased by HFD consumption. The second chapter focused on investigating if EC could prevent DCA-induced intestinal permeabilization in vitro. Such effect could in turn, help prevent the paracellular transport of lipopolysaccharides (LPS) from the lumen into the bloodstream. The last chapter provided additional mechanistic insight into how flavan-3-ols and procyanidins (PCAs) can mitigate HFD-induced endotoxemia through their capacity to prevent chylomicron- dependent transcellular transport of LPS in Caco-2 monolayers and high fat-induced postprandial endotoxemia in mice. In summary, this thesis works provide evidence that EC can decrease HFD-associated endotoxemia, characterizing the underlying mechanisms. This action would be critical to the capacity of EC to mitigate HFD- and obesity-associated comorbidities.

Lipopolysaccharides (LPSs) are bacterial surface glycolipids, produced by Gram-negative bacteria. LPS is known to determine acute inflammatory reactions, particularly in the context of sepsis. However, LPS can also trigger chronic inflammation. In this case, the source of LPS is not an external infection, but rather an increase in endogenous production, which is usually sustained by gut microbiota (GM), and LPS contained in food. The first site in which LPS can exert its inflammatory action is the gut: both GM and gut-associated lymphoid tissue (GALT) are influenced by LPS and shift towards an inflammatory pattern. The changes in GM and GALT induced by LPS are quite similar to the ones seen in IBD: GM loses diversity, while GALT T regulatory (Tregs) lymphocytes are reduced in number, with an increase in Th17 and Th1 lymphocytes. Additionally, the innate immune system is triggered, through the activation of toll-like receptor (TLR)-4, while the epithelium is directly damaged, further triggering inflammation. In this review, we will discuss the importance of the crosstalk between LPS, GM, and GALT, and discuss the possible implications.

Scope Methionine restriction (MR) is known to potently alleviate inflammation and improve gut microbiome in obese mice. The gut microbiome exhibits diurnal rhythmicity in composition and function, and this, in turn, drives oscillations in host metabolism. High-fat diet (HFD) strongly altered microbiome diurnal rhythmicity, however, the role of microbiome diurnal rhythmicity in mediating the improvement effects of MR on obesity-related metabolic disorders remains unclear. Methods and results 10-week-old male C57BL/6J mice are fed a low-fat diet or HFD for 4 weeks, followed with a full diet (0.86% methionine, w/w) or a methionine-restricted diet (0.17% methionine, w/w) for 8 weeks. Analyzing microbiome diurnal rhythmicity at six time points, the results show that HFD disrupts the cyclical fluctuations of the gut microbiome in mice. MR partially restores these cyclical fluctuations, which lead to time-specifically enhance the abundance of short-chain fatty acids producing bacteria, increases the acetate and butyric, and dampens the oscillation of inflammation-relatedDesulfovibrionalesandStaphylococcaceaeover the course of 1 day. Notably, MR, which protects against systemic inflammation, influences brain function and synaptic plasticity. Conclusion MR could serve as a potential nutritional intervention for attenuating obesity-induced cognitive impairments by balancing the circadian rhythm in microbiome-gut-brain homeostasis.

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. The intestinal barrier is constantly exposed to potentially harmful environmental factors, including food components and bacterial endotoxins. When intestinal barrier function and immune homeostasis are compromised (intestinal dysfunction), inflammatory conditions may develop and impact overall health. Evidence from experimental animal and cell culture studies suggests that exposure of intestinal mucosa to proanthocyanidin (PAC)-rich plant products, such as grape seeds, may contribute to maintaining the barrier function and to ameliorating the pathological inflammation present in diet-induced obesity and inflammatory bowel disease. In this review, we aim to update the current knowledge on the bioactivity of PACs in experimental models of intestinal dysfunction and in humans, and to provide insights into the underlying biochemical and molecular mechanisms.

Metabolic syndrome (MetS) is a consequence of obesity and defined as cluster of at least three out of five criteria covering insulin resistance/glucose intolerance, abdominal obesity, hypertension, low HDL-c and elevated TG levels. Imbalance between energy intake and expenditure is known to alter normal physiological function in many aspects, and leads to obesity, which in the long run may turn into type 2 diabetes (T2D) and ultimately cardiovascular disease (CVD). Looking at our everyday meal patterns (breakfast, lunch, dinner and snacks in between), we are constantly being challenged by foods that vary in macronutrient composition. In association with meal patterns, it is well established that the postprandial (occurring a meal) response is importantly associated with cardiovascular risk factors. Exaggerated response in the postprandial glucose and TG levels are known to provoke an atherogenic milieu. Diet and lifestyle interventions are key to alleviating obesity prior to the onset of CVD. Several strategies have been suggested to be beneficial, including the consumption of fibre-rich and whole grains foods, increasing fruit and vegetable intake, lowering fat and processed meat intake, reducing high sugar foods and salt as well as avoiding saturated and trans-fatty acids consumption, features that are also part of current Nordic Nutrition Recommendations. Plants, including spices are rich in various bioactive compounds owing pleiotropic health-associated benefits. Many studies have shown that diverse bioactives might beneficially influence several aspects of human metabolism by improving appetite regulation mediated by gut hormones or through their interaction with transient receptor potential (TRP) channels, inhibiting alpha-amylase and alpha-glucosidase leading to reduced glucose absorption, affecting lipid metabolism by influencing lipid-associated enzymes as well as modulating the transcription factors of genes associated with metabolic processes. Although in

Objective—The purpose of this investigation was to understand the metabolic adaptations to a short-term (5 days), isocaloric, high fat diet (HFD) in healthy, young males. Methods—Two studies were undertaken with 12 subjects. Study 1 investigated the effect of the HFD on skeletal muscle substrate metabolism and insulin sensitivity. Study 2 assessed the metabolic and transcriptional response in skeletal muscle to the transition from a fasted-to-fed state using a high fat meal challenge prior to and following 5 days of HFD. Results—Study 1 showed no effect of a HFD on skeletal muscle metabolism or insulin sensitivity in fasting samples. Study 2 showed that a HFD elicits significant increases in fasting serum endotoxin, and disrupts the normal postprandial excursions of serum endotoxin, and metabolic and transcriptional responses in skeletal muscle. These effects following 5 days of HFD were accompanied by an altered fasting and postprandial response in the ratio of phosphorylated to total p38 protein. These changes all occurred in the absence of alterations in insulin sensitivity. Conclusions—Our findings provide evidence for early biological adaptations to high fat feeding that proceed and possibly lead to insulin resistance.

Objective—The purpose of this investigation was to understand the metabolic adaptations to a short-term (5 days), isocaloric, high fat diet (HFD) in healthy, young males. Methods—Two studies were undertaken with 12 subjects. Study 1 investigated the effect of the HFD on skeletal muscle substrate metabolism and insulin sensitivity. Study 2 assessed the metabolic and transcriptional response in skeletal muscle to the transition from a fasted-to-fed state using a high fat meal challenge prior to and following 5 days of HFD. Results—Study 1 showed no effect of a HFD on skeletal muscle metabolism or insulin sensitivity in fasting samples. Study 2 showed that a HFD elicits significant increases in fasting serum endotoxin, and disrupts the normal postprandial excursions of serum endotoxin, and metabolic and transcriptional responses in skeletal muscle. These effects following 5 days of HFD were accompanied by an altered fasting and postprandial response in the ratio of phosphorylated to total p38 protein. These changes all occurred in the absence of alterations in insulin sensitivity. Conclusions—Our findings provide evidence for early biological adaptations to high fat feeding that proceed and possibly lead to insulin resistance.

High-fat diets and obesity have been linked to unfavorable changes in gut bacteria and increased leakage of bacterially-derived lipopolysaccharide (endotoxin) from the intestinal tract into circulation, which is associated with low-grade inflammation, metabolic dysregulation and degradation of tight-junction proteins between intestinal cells. Probiotic supplementation is the practice of ingesting live strains of bacteria that are proposed to have a beneficial effect on the host by enriching the intestine with healthy bacteria. The purpose of this project was to determine if probiotic supplementation would prevent increased inflammatory tone, decreased oxidative capacity, and decreased tight-junction protein expression associated with high-fat feeding and elevated endogenous endotoxin. Male C57BL/6J mice were fed either a control (CD, 10% fat) or high-fat (HFD, 60% fat) diet for 4 weeks while receiving a daily oral gavage of water (C-VSL#3, HF-VSL#3) or probiotics (C+VSL#3, HF+VSL#3) equivalent to 1.2 billion live cultures. Changes in body weight, body composition, respiratory exchange ratio, energy expenditure, and glucose and insulin tolerance were measured in live mice. Markers of metabolic function were measured in whole muscle homgenates and mitochondria isolated from red and white skeletal muscle. Plasma endotoxin was measured in blood collected from fasted mice at the time of euthanization. The large and small intestines were collected and mRNA levels of tight-junction proteins and markers of nutrient sensing were measured. To determine a possible protective effect against endogenous LPS, a second cohort of mice were given an intraperitoneal injection of 0.1µg/kg LPS or saline to induce endotoxemia after four weeks of the aforementioned feeding protocol. Markers of metabolic function and inflammation were measured in mitochondria, skeletal muscle and liver. VSL#3 supplementation improved glucose homeostasis and markers of inflammation while enhancing nutrient

Obesity is associated with metabolic alterations related to glucose homeostasis and cardiovascular risk factors. These metabolic alterations are associated with low-grade inflammation that contributes to the onset of these diseases. We and others have provided evidence that gut microbiota participates in whole-body metabolism by affecting energy balance, glucose metabolism, and low-grade inflammation associated with obesity and related metabolic disorders. Recently, we defined gut microbiota-derived lipopolysaccharide (LPS) (and metabolic endotoxemia) as a factor involved in the onset and progression of inflammation and metabolic diseases. In this review, we discuss mechanisms involved in the development of metabolic endotoxemia such as the gut permeability. We also discuss our latest discoveries demonstrating a link between the gut microbiota, endocannabinoid system tone, leptin resistance, gut peptides (glucagon-like peptide-1 and -2), and metabolic features. Finally, we will introduce the role of the gut microbiota in specific dietary treatments (prebiotics and probiotics) and surgical interventions (gastric bypass).

Growing evidence supports the role of gut microbiota in the development of obesity, type 2 diabetes, and low-grade inflammation. The endocrine activity of adipose tissue has been found to contribute to the regulation of glucose homeostasis and low-grade inflammation. Among the key hormones produced by this tissue, apelin has been shown to regulate glucose homeostasis. Recently, it has been proposed that gut microbiota participate in adipose tissue metabolism via the endocannabinoid system (eCB) and gut microbiota-derived compounds, namely lipopolysaccharide (LPS). We have investigated gut microbiota composition in obese and diabetic leptin-resistant mice (db/db) by combining pyrosequencing and phylogenetic microarray analysis of 16S ribosomal RNA gene sequences. We observed a significant higher abundance of Firmicutes, Proteobacteria, and Fibrobacteres phyla in db/db mice compared to lean mice. The abundance of 10 genera was significantly affected by the genotype. We identified the roles of the eCB and LPS in the regulation of apelinergic system tone (apelin and APJ mRNA expression) in genetic obese and diabetic mice. By using in vivo and in vitro models, we have demonstrated that both the eCB and low-grade inflammation differentially regulate apelin and APJ mRNA expression in adipose tissue. Finally, deep-gut microbiota profiling revealed that the gut microbial community of type 2 diabetic mice is significantly different from that of their lean counterparts. This indicates specific relationships between the gut microbiota and the regulation of the apelinergic system. However, the exact roles of specific bacteria in shaping the phenotype of db/db mice remain to be determined.

Growing evidence supports the role of gut microbiota in the development of obesity, type 2 diabetes, and low-grade inflammation. The endocrine activity of adipose tissue has been found to contribute to the regulation of glucose homeostasis and low-grade inflammation. Among the key hormones produced by this tissue, apelin has been shown to regulate glucose homeostasis. Recently, it has been proposed that gut microbiota participate in adipose tissue metabolism via the endocannabinoid system (eCB) and gut microbiota-derived compounds, namely lipopolysaccharide (LPS). We have investigated gut microbiota composition in obese and diabetic leptin-resistant mice (db/db) by combining pyrosequencing and phylogenetic microarray analysis of 16S ribosomal RNA gene sequences. We observed a significant higher abundance of Firmicutes, Proteobacteria, and Fibrobacteres phyla in db/db mice compared to lean mice. The abundance of 10 genera was significantly affected by the genotype. We identified the roles of the eCB and LPS in the regulation of apelinergic system tone (apelin and APJ mRNA expression) in genetic obese and diabetic mice. By using in vivo and in vitro models, we have demonstrated that both the eCB and low-grade inflammation differentially regulate apelin and APJ mRNA expression in adipose tissue. Finally, deep-gut microbiota profiling revealed that the gut microbial community of type 2 diabetic mice is significantly different from that of their lean counterparts. This indicates specific relationships between the gut microbiota and the regulation of the apelinergic system. However, the exact roles of specific bacteria in shaping the phenotype of db/db mice remain to be determined

Obesity over the last several has become a major health concern in our country as well as the world. Obesity is also one of the risk factors which lead to several inflammatory complications such as diabetes, artherosclerosis, etc. Two leading factors involved in the causes of inflammatory complications include leptin and low dose endotoxin lipopolysaccharide (LPS). However, the mechanism underlying the involvement of these two mediators is not clearly understood. The purpose of this study is to understand the mechanism underlying inflammatory complications caused by leptin and low dose endotoxin most recently coined metabolic endotoxemia. Interleukin-Receptor Associated Kinase 1 (IRAK-1) is an intracellular signaling component shown to activate NFκB which leads to the induction of proinflammatory mediators. Deletion of IRAK-1 in mice has beneficial effects in alleviating inflammatory complications and human variations in IRAK-1 gene are correlated with higher risks for inflammatory diseases. Therefore, we hypothesized that IRAK-1 is critically involved for the induction of proinflammatory mediators induced by leptin and low dose LPS. IL-6 mRNA levels were measured in THP-1 (human monocytic cells) and wild type and IRAK-deficient bone marrow derived macrophages (BMDM) challenged with different combinations of leptin and LPS. Data shows that leptin alone will not induce inflammatory mediators. However, increased induction of IL-6 was observed in a synergistic manner involving both LPS and leptin in an IRAK-1 dependent manner causing a robust inflammatory response. With regard to the effect of low dose LPS, we observed that human monocytic cells treated with low concentrations of LPS showed a mild yet sustained induction of proinflammatory cytokines, which is contrast to the robust and transient induction of cytokines by a high dose LPS. To further determine the molecular mechanisms, we measured several key signaling molecules that include IRAK-1, IKKepsilon, and C/EB