Insulin Resistance In Human Obesity Research Articles

How does bariatric surgery remodel adipose tissue?

This lecture delves into the pivotal role of adipose tissue in obesity and its response to weight loss, particularly via bariatric surgery. Adipose tissue, responsible for storing excess energy, undergoes significant changes during obesity, marked by inflammation and fibrosis. Bariatric surgery, serving as a model, allow the exploration of adipose tissue remodeling post-weight loss, inducing metabolic and fibro-inflammatory shifts. Despite successful weight loss, inflammation and fibrosis persist, as evidenced by changes in immune cells, altered cytokine profiles and the accumulation of extracellular matrix (ECM). Unfortunately, these lingering effects impair the normal adipose tissue function. In this context, adipose progenitors, an heterogenous resident population of mesenchymal stromal cells, display functions important to fibrosis development, capable of differentiating into myofibroblasts and contributing to ECM deposition. Particularly, a distinct subpopulation of adipose progenitors with high CD9 expression (CD9high) is associated with fibrosis and insulin resistance in human obesity. The persistence of fibrosis post-weight loss poses challenges, correlating with metabolic dysfunction despite improved glucose tolerance. A comprehensive understanding of the mechanisms driving adipose tissue remodeling and fibrosis post-weight loss is imperative for the development of effective treatments for obesity. The intricate interplay between adipose tissue, inflammation, and fibrosis underscores the necessity for further in-depth research to elucidate these mechanisms and formulate targeted therapies for obesity-related complications.

Augmented CCL5/CCR5 signaling in brown adipose tissue inhibits adaptive thermogenesis and worsens insulin resistance in obesity.

Chemokine (C-C motif) ligand 5 (CCL5) and CCR5, one of its receptors have been reported to be highly expressed in white adipose tissue (WAT) and are associated with the progression of inflammation and the development of insulin resistance in obese humans and mice. However, the role of CCL5/CCR5 signaling in obesity-associated dysregulation of energy metabolism remains unclear. Here, we demonstrate that global CCL5/CCR5 double knockout (DKO) mice have higher cold stress-induced energy expenditure and thermogenic function in brown adipose tissue (BAT) than wildtype (WT) mice. DKO mice have higher cold stress-induced energy expenditure and thermogenic function in BAT than WT mice. KEGG pathway analysis indicated that deletion of CCL5/CCR5 further facilitated the cold-induced expression of genes related to oxidative phosphorylation (OxPhos) and lipid metabolic pathways. In primary brown adipocytes of DKO mice, the augmentation of CL-316243-stimulated thermogenic and lipolysis responses was reversed by co-treatment with AMPKα1 and α2 short interfering RNA (siRNA). Overexpression of BAT CCL5/CCR5 genes by local lentivirus injection in WT mice suppressed cold stress-induced lipolytic processes and thermogenic activities. In contrast, knockdown of BAT CCL5/CCR5 signaling further up-regulated AMPK phosphorylation as well as thermogenic and lipolysis responses to chronic adrenergic stimuli and subsequently decreased level of body weight gain. Chronic knockdown of BAT CCL5/CCR5 signaling improved high-fat diet (HFD)-induced insulin resistance in WT mice. It is suggested that obesity-induced augmentation of adipose tissue (AT) CCL5/CCR5 signaling could, at least in part, suppress energy expenditure and adaptive thermogenesis by inhibiting AMPK-mediated lipolysis and oxidative metabolism in thermogenic AT to exacerbate the development of obesity and insulin resistance.

The nuclear retinoid-related orphan receptor RORα controls adipose tissue inflammation in patients with morbid obesity and diabetes.

Inflammation governs adipose tissue (AT) dysfunction in obesity. Retinoic acid receptor-related orphan receptor alpha (RORα) is associated with inflammation and insulin resistance in animal studies, but its role in human obesity remains elusive. We investigated the expression and function of RORα on AT inflammation in patients with morbid obesity with/without diabetes. We assessed RORα expression in paired biopsies of subcutaneous and omental AT from 41 patients (body mass index (BMI) 43.3 ± 0.8 kg/m2) during Roux-en-Y-gastric surgery and explored the functional consequences of pharmacological RORα blockade in AT ex vivo. RORα expression was significantly higher in omental AT than in subcutaneous AT (p = 0.03) and was positively associated with BMI (r = 0.344, p = 0.027) and homeostasis model assessment of insulin resistance (r = 0.319, p = 0.041). In ex vivo assays, IL-8/CXCL8 and MCP-1/CCL2 chemokine release was significantly higher in omental fat explants from diabetic patients than from non-diabetics and was significantly diminished by RORα blockade (p < 0.05). Inhibition of RORα improved protein kinase B signaling and decreased NF-κB activity in omental AT from patients with diabetes (p < 0.05). Under dynamic flow conditions, RORα blockade prevented mononuclear cell attachment to human dysfunctional endothelial cells. RORα blockade represents a potential therapy to prevent AT dysfunction and inflammation associated with insulin resistance in human obesity.

The association between vitamin D receptor polymorphisms and tissue-specific insulin resistance in human obesity.

To investigate (1) the association of four VDR polymorphisms (TaqI/rs731236, ApaI/rs7975232, FokI/rs10735810, and Bsml/rs1544410) with markers of adiposity and tissue-specific insulin resistance at baseline, after weight loss and weight maintenance; (2) the effect of the VDR polymorphisms in the SAT transcriptome in overweight/obese Caucasians of the DiOGenes cohort. We included 553 adult obese individuals (mean BMI 34.8 kg/m2), men (n = 197) and women (n = 356) at baseline, following an 8-week weight loss intervention and 26 weeks weight maintenance. Genotyping was performed using an Illumina 660W-Quad SNP chip on the Illumina iScan Genotyping System. Tissue-specific IR was determined using Hepatic Insulin Resistance Index (HIRI), Muscle Insulin Sensitivity Index (MISI), and Adipose Tissue Insulin Resistance Index (Adipo-IR). Expression quantitative trait loci (eQTL) analysis was performed to determine the effect of SNPs on SAT gene expression. None of the VDR polymorphisms were associated with HIRI or MISI. Interestingly, carriers of the G allele of VDR FokI showed higher Adipo-IR (GG + GA 7.8 ± 0.4 vs. AA 5.6 ± 0.5, P = 0.010) and higher systemic FFA (GG + GA: 637.8 ± 13.4 vs. AA: 547.9 ± 24.7 µmol/L, P = 0.011), even after adjustment with age, sex, center, and FM. However, eQTL analysis showed minor to no effect of these genotypes on the transcriptional level in SAT. Also, VDR polymorphisms were not related to changes in body weight and IR as result of dietary intervention (P > 0.05 for all parameters). The VDR Fokl variant is associated with elevated circulating FFA and Adipo-IR at baseline. Nevertheless, minor to no effect of VDR SNPs on the transcriptional level in SAT, indicating that putative mechanisms of action remain to be determined. Finally, VDR SNPs did not affect dietary intervention outcome in the present cohort.

Cholesterol 25-hydroxylase (CH25H) as a promoter of adipose tissue inflammation in obesity and diabetes

ObjectiveExpansion of visceral adipose tissue (VAT) and metabolic inflammation are consequences of obesity and associated with type 2 diabetes (T2DM). Metabolically activated adipose tissue macrophages (ATMs) undergo qualitative and quantitative changes that influence their inflammatory responses. How these cells contribute to insulin resistance (IR) in humans is not well understood. Cholesterol 25-Hydroxylase (CH25H) converts cholesterol into 25-Hydroxycholesterol (25-HC), an oxysterol that modulates immune responses. Using human and murine models, we investigated the role of CH25H in metabolic inflammation. MethodsWe performed transcriptomic (RNASeq) analysis on the human whole AT biopsies and sorted ATMs from obese non-diabetic (NDM) and obese diabetic (DM) subjects to inquire if CH25H was increased in DM. We challenged mice lacking Ch25h with a high-fat diet (HFD) to characterize their metabolic and immunologic profiling. Ch25h KO mice and human adipose tissue biopsies from NDM and DM subjects were analyzed. LC-MS was conducted to measure 25-HC level in AT. In vitro analysis permitted us to investigate the effect of 25-HC on cytokine expression. ResultsIn our RNASeq analysis of human visceral and subcutaneous biopsies, gene pathways related to inflammation were increased in obese DM vs. non-DM subjects that included CH25H. CH25H was enriched in the stromal vascular fraction of human adipose tissue and highly expressed in CD206+ human ATMs by flow cytometry analysis. We measured the levels of the oxysterols, 25-HC and 7α25diHC, in human visceral adipose tissue samples and showed a correlation between BMI and 25-HC. Using mouse models of diet-induced obesity (DIO), we found that HFD-induced Ch25h expression in eWAT and increased levels of 25-HC in AT. On HFD, Ch25h KO mice became obese but exhibited reduced plasma insulin levels, improved insulin action, and decreased ectopic lipid deposit. Improved insulin sensitivity in Ch25h KO mice was due to attenuation of CD11c+ adipose tissue macrophage infiltration in eWAT. Finally, by testing AT explants, bone marrow-derived macrophages (BMDMs) and SVF cells from Ch25h deficient mice, we observed that 25-HC is required for the expression of pro-inflammatory genes. 25-HC was also able to induce inflammatory genes in preadipocytes. ConclusionsOur data suggest a critical role for CH25H/25-HC in the progression of meta-inflammation and insulin resistance in obese humans and mouse models of obesity. In response to obesogenic stimuli, CH25H/25-HC could exert a pro-inflammatory role.

Metabolic profiling of tissue-specific insulin resistance in human obesity: results from the Diogenes study and the Maastricht Study.

Recent evidence indicates that insulin resistance (IR) in obesity may develop independently in different organs, representing different etiologies toward type 2 diabetes and other cardiometabolic diseases. The aim of this study was to investigate whether IR in the liver and IR in skeletal muscle are associated with distinct metabolic profiles. This study includes baseline data from 634 adults with overweight or obesity (BMI ≥ 27 kg/m2) (≤65 years; 63% women) without diabetes of the European Diogenes Study. Hepatic insulin resistance index (HIRI) and muscle insulin sensitivity index (MISI), were derived from a five-point OGTT. At baseline 17 serum metabolites were identified and quantified by nuclear-magnetic-resonance spectroscopy. Linear mixed model analyses (adjusting for center, sex, body mass index (BMI), waist-to-hip ratio) were used to associate HIRI and MISI with these metabolites. In an independent sample of 540 participants without diabetes (BMI ≥ 27 kg/m2; 40-65 years; 46% women) of the Maastricht Study, an observational prospective population-based cohort study, 11 plasma metabolites and a seven-point OGTT were available for validation. Both HIRI and MISI were associated with higher levels of valine, isoleucine, oxo-isovaleric acid, alanine, lactate, and triglycerides, and lower levels of glycine (all p < 0.05). HIRI was also associated with higher levels of leucine, hydroxyisobutyrate, tyrosine, proline, creatine, and n-acetyl and lower levels of acetoacetate and 3-OH-butyrate (all p < 0.05). Except for valine, these results were replicated for all available metabolites in the Maastricht Study. In persons with obesity without diabetes, both liver and muscle IR show a circulating metabolic profile of elevated (branched-chain) amino acids, lactate, and triglycerides, and lower glycine levels, but only liver IR associates with lower ketone body levels and elevated ketogenic amino acids in circulation, suggestive of decreased ketogenesis. This knowledge might enhance developments of more targeted tissue-specific interventions to prevent progression to more severe disease stages.

Human Obesity: A Noxious Sequel of Inverse Intents of Ligands and Receptors

Diabetes and cardiovascular disease are the two most common deleterious side effects in the first line complications of chronic human obesity. Hyperleptinemia, hyperinsulinemia and hypercholesterolemia are the reported proximal outbreaks in progressive human obesity. Leptin, insulin and LDL remain interacted through their cognate receptors. A phase matched comparison has been conducted in present study between expressions of cognate receptors and plasma profile of their respective ligands in three human male groups viz. normal (18.5&lt; BMI &lt; 25), obese (25&lt; BMI &lt;40) and morbid obese (BMI &gt; 40). Our study shows a declined leptin receptor concentration on peripheral blood mononuclear cells (PBMC) with a meagre change in its soluble counterpart (sOR/ OB-Re) in blood circulation, averring the outbreak of hyperleptinemia with obesity. Simultaneously, a cumulative decline of concentrations of LDL receptor (LDLR) and insulin receptor (IR) in PBMC are the reasons behind hypercholesterolemia and hyperinsulinemia cum insulin resistance in human obesity.

Plasma lipid profiling of tissue-specific insulin resistance in human obesity.

Obesity-associated insulin resistance (IR) may develop in multiple organs, representing different aetiologies towards cardiometabolic diseases. This study aimed to identify distinct plasma lipid profiles in overweight/obese individuals who show muscle-IR and/or liver-IR. Baseline data of the European multicenter DiOGenes project were used (n = 640; 401 women, nondiabetic BMI: 27-45 kg/m2). Muscle insulin sensitivity index (MISI) and hepatic insulin resistance index (HIRI) were derived from a 5-point oral glucose tolerance test. The 140 plasma lipids were quantified by liquid chromatography-mass spectrometry. Linear mixed models were used to evaluate associations between MISI, HIRI and plasma lipids. MISI was comparable between sexes while HIRI and triacylglycerol (TAG) levels were lower in women than in men. MISI was associated with higher lysophosphatidylcholine (LPC) levels (standardized (std)β = 0.126; FDR-p = 0.032). Sex interactions were observed for associations between HIRI, TAG and diacylglycerol (DAG) lipid classes. In women, but not in men, HIRI was associated with higher levels of TAG (44 out of 55 species) and both DAGspecies (stdβ: 0.139-0.313; FDR-p < 0.05), a lower odd-chain/even-chain TAG ratio (stdβ = -0.182; FDR-p = 0.005) and a lower very-long-chain/long-chain TAG ratio (stdβ = -0.156; FDR-p = 0.037). In overweight/obese individuals, muscle insulin sensitivity is associated with higher plasma LPC concentrations. Women have less hepatic IR and lower TAG than men. Nevertheless, hepatic IR is associated with higher plasma TAG and DAG concentrations and a lower abundance of odd-chain and very-long-chain TAG in women, but not in men. This suggests a more pronounced worsening of plasma lipid profile in women with the progression of hepatic IR.

Insulin Resistance and In Vivo Lipolytic Rate Are Positively Associated with Body Iron Stores in Obese Women

High body iron stores are positively related to insulin resistance in humans, but the underlying mechanisms remain unresolved. Iron stimulates lipolysis in murine adipocytes in vitro, but the influence of iron stores on lipolytic rate in vivo is unknown. Our aim was to determine if body iron stores are associated with lipolytic rate and whole-body insulin sensitivity in obese, pre-menopausal women. We studied 20 subjects with clinically-normal (20-200 ng/mL) plasma [ferritin], an index of body iron stores. Fatty acid rate of appearance into systemic circulation (FA Ra) was assessed by 13C-palmitate isotope dilution, insulin resistance was assessed by hyperinsulinemic-euglycemic clamp, and abdominal subcutaneous adipose tissue protein expression was assessed via immunoblot. [Ferritin] was significantly (p &amp;lt; 0.01), positively correlated with FA Ra (r2 = 0.42), adipose hormone sensitive lipaseser660 phosphorylation (p-HSLser660, a marker of lipolytic activation in adipose tissue; r2 = 0.41), and whole-body insulin resistance (r2 = 0.33). Importantly, [ferritin] remained a significant, independent predictor for these parameters in multiple regression models including body mass index, plasma [adiponectin], and plasma [CRP] as covariates. We stratified subjects into tertiles based on [ferritin] to compare high-normal and low-normal [ferritin] groups (138 ± 30 vs. 40 ± 15 ng/mL). Compared with the low-normal [ferritin] group, the high-normal [ferritin] group had significantly (p &amp;lt; 0.02) higher FA Ra (15.6 ± 5.5 vs. 8.8 ± 2.4 µmol/kg fat mass/min), adipose p-HSLser660 (1.3 ± 0.4 vs. 0.6 ± 0.2 AU) and whole-body insulin resistance (glucose infusion rate 9.2 ± 2.3 vs. 14.3 ± 3.5 mg/kg fat free mass/min). There were no between-group differences in anthropometric characteristics, plasma [adiponectin], or plasma [CRP]. Our findings suggest that iron-mediated activation of adipose lipolysis may be a mechanism linking body iron stores and insulin resistance in obese humans. Disclosure B.J. Ryan: None. D.W. Van Pelt: None. L.M. Guth: None. A. Ludzki: None. R.A. Gioscia-Ryan: None. C. Ahn: None. J.F. Horowitz: None.

Upregulation of angiostatic chemokines IP-10/CXCL10 and I-TAC/CXCL11 in human obesity and their implication for adipose tissue angiogenesis.

Impaired angiogenesis is linked to adipose tissue (AT) dysfunction, inflammation, and insulin resistance in human obesity. Chemokine (C-X-C motif) receptor. (CXCR3) ligands are important regulators of angiogenesis in different disease contexts such as cancer; however, their role in human morbid obesity is unknown. We investigated the role of the CXCR3 axis in AT angiogenesis in morbidly obese patients. The study group comprised 50 morbidly obese patients (mean age 44 ± 1 years, body mass index 44 ± 1 kg/m2) who had undergone laparoscopic Roux-Y-gastric bypass surgery, and 25 age-matched non-obese control subjects. We measured the circulating levels of the CXCR3 ligands monokine induced by interferon-γ (MIG/CXCL9), interferon-γ inducible protein 10 (IP-10/CXCL10), and interferon-γ-inducible T-cell alpha chemoattractant (I-TAC/CXCL11) in all studied subjects. Additionally, the expression of CXCR3 ligands was analyzed in paired biopsies of subcutaneous and visceral AT obtained during the laparoscopic procedure in morbidly obese patients. Additionally, we explored the functional role of CXCR3 ligands on angiogenesis in AT from morbidly obese patients using an ex vivo assay. Plasma levels of CXCL10 and CXCL11 were significantly higher in morbidly obese patients than in controls (p < 0.01). In ex vivo assays, angiogenic growth was markedly lower in visceral AT than in subcutaneous AT (p < 0.05), which was related to significant tissue upregulation of CXCL10, CXCL11 and CXCR3 (p < 0.05). CXCL10 or CXCL11 inhibited AT angiogenesis (p < 0.05), and blockade of CXCR3 function significantly increased capillary sprouting in visceral fat deposits (p < 0.05). Western blot analysis showed that the p38 mitogen-activated protein kinase signaling pathway was implicated in the angiostatic effects of CXCR3 in AT. CXCL10 and CXCL11 may play. deleterious role in obesity as potential inhibitors of AT angiogenesis. Accordingly, pharmacological blockade of CXCR3 could represent. therapy to prevent AT dysfunction in obesity.

Myocardin-Related Transcription Factor A Promotes Recruitment of ITGA5+ Profibrotic Progenitors during Obesity-Induced Adipose Tissue Fibrosis

Adipose tissue fibrosis is associated with inflammation and insulin resistance in human obesity. In particular, visceral fat fibrosis is correlated with hyperlipidemia and ectopic fat accumulation. Myocardin-related transcription factor A (MRTFA) is an important coactivator that mediates the transcription of extracellular matrix and other fibrogenic genes. Here, we examine the role of MRTFA in the development of adipose tissue fibrosis and identify a signaling pathway that regulates the fate of vascular progenitors. We demonstrate that obesity induces the formation of Sca1-, Sma+, ITGA5+ fibrogenic progenitor cells (FPCs) in adipose tissue. MRTFA deficiency in mice shifts the fate of perivascular progenitors from FPCs to adipocyte precursor cells and protects against chronic obesity-induced fibrosis and accompanying metabolic dysfunction, without a shift in energy expenditure. Our findings highlight the ITGA5-MRTFA pathway as a potential target to ameliorate obesity-associated metabolic disease.

Duodenal L cell density correlates with features of metabolic syndrome and plasma metabolites.

BackgroundEnteroendocrine cells are essential for the regulation of glucose metabolism, but it is unknown whether they are associated with clinical features of metabolic syndrome (MetS) and fasting plasma metabolites.ObjectiveWe aimed to identify fasting plasma metabolites that associate with duodenal L cell, K cell and delta cell densities in subjects with MetS with ranging levels of insulin resistance.Research design and methodsIn this cross-sectional study, we evaluated L, K and delta cell density in duodenal biopsies from treatment-naïve males with MetS using machine-learning methodology.ResultsWe identified specific clinical biomarkers and plasma metabolites associated with L cell and delta cell density. L cell density was associated with increased plasma metabolite levels including symmetrical dimethylarginine, 3-aminoisobutyric acid, kynurenine and glycine. In turn, these L cell-linked fasting plasma metabolites correlated with clinical features of MetS.ConclusionsOur results indicate a link between duodenal L cells, plasma metabolites and clinical characteristics of MetS. We conclude that duodenal L cells associate with plasma metabolites that have been implicated in human glucose metabolism homeostasis. Disentangling the causal relation between L cells and these metabolites might help to improve the (small intestinal-driven) pathophysiology behind insulin resistance in human obesity.

Myocardin-Related Transcription Factor A Promotes Recruitment of ITGA5&amp;#43; Profibrotic Progenitors During Obesity-Induced Adipose Tissue Fibrosis

Adipose tissue fibrosis is associated with inflammation and insulin resistance in human obesity. In particular, visceral fat fibrosis is correlated with hyperlipidemia and ectopic fat accumulation. Myocardin-related transcription factor A (MRTFA) is an important coactivator that mediates the transcription of extracellular matrix and other fibrogenic genes. Here, we examine the role of MTRFA in the development of adipose tissue fibrosis and identify a novel signaling pathway that regulates myofibroblast differentiation. We demonstrate that obesity induces the formation of Sca1-, PDGFRa+, Sma+, ITGA5+ fibrogenic progenitors in adipose tissue. MRTFA deficiency in mice shifts the fate of perivascular progenitors from fibrogenic to adipocyte precursor cells and protects against diet-induced fibrosis and accompanying metabolic dysfunction. Our findings highlight the MRTFA-ITGA5 pathway as a potential target to ameliorate obesity associated metabolic disease.

Red wine polyphenols do not improve obesity-associated insulin resistance: A randomized controlled trial.

Preclinical studies have suggested that polyphenols extracted from red wine (RWPs) favourably affect insulin sensitivity, but there is controversy over whether RWPs exert similar effects in humans. The aim of the present study was to determine whether RWPs improve insulin sensitivity in obese volunteers. Obese (body mass index >30 kg/m2 ) volunteers were randomly allocated to RWPs 600 mg/d (n = 14) or matched placebo (n = 15) in a double-blind parallel-arm study for 8 weeks. The participants were investigated at baseline and at the end of the study. Insulin sensitivity was determined using a hyperinsulinaemic-euglycaemic clamp (M-value), a mixed-meal test (Matsuda index), and homeostatic model assessment of insulin resistance (HOMA-IR). RWPs elicited no significant changes in M-value (RWP group: median [interquartile range; IQR] baseline 3.0 [2.4; 3.6]; end of study 3.3 [2.4; 4.8] vs placebo group: median [IQR] baseline 3.4 [2.8; 4.4]; end of study 2.9 [2.8; 5.9] mg/kg/min; P = .65), in Matsuda index (RWP group: median [IQR] baseline 3.3 [2.2; 4.8]; end of study 3.6 [2.4; 4.8] vs placebo group: median [IQR] baseline 4.0 [3.0; 6.0]; end of study 4.0 [3.0; 5.2]; P = .88), or in HOMA-IR. This study showed that 8 weeks of RWP supplementation did not improve insulin sensitivity in 29 obese volunteers. Our findings were not consistent with the hypothesis that RWPs ameliorate insulin resistance in human obesity.

Perturbed adipose tissue hydrogen peroxide metabolism in centrally obese men: Association with insulin resistance.

ObjectiveAlthough adipose tissue hydrogen peroxide (H2O2) and its metabolizing enzymes have been linked to obesity and insulin resistance in animal studies, this relation remains to be evaluated in humans.MethodsNon-diabetic men (N = 43, median age, 49 (37, 54 y)) undergoing abdominal surgeries were studied. Participants were classified by body mass index (BMI) into normal-weight (N = 19), or overweight/obese (Ow/Ob; BMI ≥25; N = 24). Centrally obese men were identified by waist-height ratio ≥0.5. H2O2 and activities of superoxide dismutase, catalase and glutathione peroxidase enzymes were assayed in subcutaneous fat samples, and visceral fat (available from N = 33), and their associations with anthropometric parameters, fasting serum lipids, and the homeostasis model of insulin resistance (HOMA-IR) were tested using correlations and multivariate linear regression.ResultsH2O2 concentrations and catalase activity were increased in visceral fat from Ow/Ob men, compared to normal-weight subjects (+32%, P = 0.038 and +51%, P = 0.043 respectively). Centrally obese subjects had >2-fold higher superoxide dismutase activity (P = 0.005), 46% higher H2O2 (P = 0.028), and 89% higher catalase activity (P = 0.009) in visceral fat, compared to lean subjects. Central obesity did not alter these markers in subcutaneous fat, apart from a 50% increase in catalase, and did not affect glutathione peroxidase in either fat depot. H2O2 in visceral fat positively correlated with insulin resistance (r = 0.40, P = 0.032). Catalase activity in visceral fat was an independent determinant of HOMA-IR, explaining ~18% of the variance (ß = 0.42, P = 0.016), after adjustment for age and BMI.ConclusionThese findings suggest that adipose tissue catalase shows compensatory up-regulation in response to obesity-induced H2O2 accumulation, and that perturbed H2O2 metabolism in visceral fat is linked to insulin resistance in obese humans.

Caloric restriction ameliorates cardiomyopathy in animal model of diabetes

BackgroundThe db/db mouse is an animal model of diabetes in which leptin receptor activity is deficient resulting accelerated cardiomyopathy when exposed to angiotensin (AT). Toll-like receptors 4 and 2 (TLR4, TLR2) are pattern recognition receptors, that recognize pathogen-associated molecular patterns and exacerbate and release inflammatory cytokines. Fetuin A (Fet A) is a fatty acid carrier which affects inflammation and insulin resistance in obese humans and animals through TLRs.The aim of this study was to investigate the effect of caloric restriction (CR) on free fatty acids (FFA) level and the inflammatory response in diabetic cardiomyopathy. Methods and resultsLeft ventricular hypertrophy, increased fibrosis and leukocytes infiltration were observed in db/db AT treated hearts. Serum glucose, FFA, and cholesterol levels were elevated in db/db AT treated mice. Cardiac expression of PPARα increased while AKT phosphorylation was decreased. ConclusionsCumulatively, CR elevated cardiac PPARα improved the utilization of fatty acids, and reduced myocardial inflammation as seen by reduced levels of Fet A. Thus CR negated cardiomyopathy associated with AT in an animal model of diabetes suggesting that CR is an effective therapeutic approach in the treatment of diabetes and associated cardiomyopathy.

Evolution of subcutaneous adipose tissue fibrosis after bariatric surgery

AimObesity is associated with the development of metabolic complications such as insulin resistance (IR). The mechanisms leading to IR remain unclear. This study aimed to investigate the relationship between adipose tissue fibrosis and IR in obese patients before and after bariatric surgery. MethodsThirty-five obese patients awaiting bariatric surgery (12 with type 2 diabetes) were included in the study. Non-diabetic patients were classified as either insulin-sensitive (n=11) or insulin-resistant (n=12), based on the Matsuda insulin sensitivity index (ISIMatsuda). Homoeostasis model assessment (HOMA-IR) was used for longitudinal evaluation of insulin resistance. Fibrosis was quantified by Masson's trichrome staining on microscopy, and mRNA levels of fibrosis-related genes were examined in subcutaneous (SAT) and visceral adipose tissue (VAT) biopsies collected during and 6 months after bariatric surgery (SAT only). ResultsDespite their similar age, body mass index and fat mass, SAT fibrosis was significantly higher in diabetic vs insulin-sensitive patients (P<0.05), and associated with IR as assessed by both ISIMatsuda (r=−0.417, P=0.038) and HOMA-IR (r=0.464, P=0.007) at baseline, whereas VAT fibrosis was not. Six months after surgery and significant weight loss, fibrosis levels remained unchanged in SAT, although IR was significantly reduced in all groups (P<0.0001). No correlation was found between SAT fibrosis and IR after surgery. ConclusionOverall, these results show a significant but, most likely, transient association between SAT fibrosis and IR in obese humans.

WNT5A-JNK regulation of vascular insulin resistance in human obesity.

Obesity is associated with the development of vascular insulin resistance; however, pathophysiological mechanisms are poorly understood. We sought to investigate the role of WNT5A-JNK in the regulation of insulin-mediated vasodilator responses in human adipose tissue arterioles prone to endothelial dysfunction. In 43 severely obese (BMI 44±11 kg/m2) and five metabolically normal non-obese (BMI 26±2 kg/m2) subjects, we isolated arterioles from subcutaneous and visceral fat during planned surgeries. Using videomicroscopy, we examined insulin-mediated, endothelium-dependent vasodilator responses and characterized adipose tissue gene and protein expression using real-time polymerase chain reaction and Western blot analyses. Immunofluorescence was used to quantify endothelial nitric oxide synthase (eNOS) phosphorylation. Insulin-mediated vasodilation was markedly impaired in visceral compared to subcutaneous vessels from obese subjects (p<0.001), but preserved in non-obese individuals. Visceral adiposity was associated with increased JNK activation and elevated expression of WNT5A and its non-canonical receptors, which correlated negatively with insulin signaling. Pharmacological JNK antagonism with SP600125 markedly improved insulin-mediated vasodilation by sixfold (p<0.001), while endothelial cells exposed to recombinant WNT5A developed insulin resistance and impaired eNOS phosphorylation (p<0.05). We observed profound vascular insulin resistance in the visceral adipose tissue arterioles of obese subjects that was associated with up-regulated WNT5A-JNK signaling and impaired endothelial eNOS activation. Pharmacological JNK antagonism markedly improved vascular endothelial function, and may represent a potential therapeutic target in obesity-related vascular disease.

Asymmetric dimethylarginine (ADMA) elevation and arginase up-regulation contribute to endothelial dysfunction related to insulin resistance in rats and morbidly obese humans.

The presence of insulin resistance (IR) is determinant for endothelial dysfunction associated with obesity. Although recent studies have implicated the involvement of mitochondrial superoxide and inflammation in the defective nitric oxide (NO)-mediated responses and subsequent endothelial dysfunction in IR, other mechanisms could compromise this pathway. In the present study, we assessed the role of asymmetric dimethylarginine (ADMA) and arginase with respect to IR-induced impairment of endothelium-dependent vasodilatation in human morbid obesity and in a non-obese rat model of IR. We show that both increased ADMA and up-regulated arginase are determinant factors in the alteration of the l-arginine/NO pathway associated with IR in both models and also that acute treatment of arteries with arginase inhibitor or with l-arginine significantly alleviate endothelial dysfunction. These results help to expand our knowledge regarding the mechanisms of endothelial dysfunction that are related to obesity and IR and establish potential therapeutic targets for intervention. Insulin resistance (IR) is determinant for endothelial dysfunction in human obesity. Although we have previously reported the involvement of mitochondrial superoxide and inflammation, other mechanisms could compromise NO-mediated responses in IR. We evaluated the role of the endogenous NOS inhibitor asymmetric dimethylarginine (ADMA) and arginase with respect to IR-induced impairment of l-arginine/NO-mediated vasodilatation in human morbid obesity and in a non-obese rat model of IR. Bradykinin-induced vasodilatation was evaluated in microarteries derived from insulin-resistant morbidly obese (IR-MO) and non-insulin-resistant MO (NIR-MO) subjects. Defective endothelial vasodilatation in IR-MO was improved by l-arginine supplementation. Increased levels of ADMA were detected in serum and adipose tissue from IR-MO. Serum ADMA positively correlated with IR score and negatively with pD2 for bradykinin. Gene expression determination by RT-PCR revealed not only the decreased expression of ADMA degrading enzyme dimethylarginine dimethylaminohydrolase (DDAH)1/2 in IR-MO microarteries, but also increased expression of arginase-2. Arginase inhibition improved endothelial vasodilatation in IR-MO. Analysis of endothelial vasodilatation in a non-obese IR model (fructose-fed rat) confirmed an elevation of circulating and aortic ADMA concentrations, as well as reduced DDAH aortic content and increased aortic arginase activity in IR. Improvement of endothelial vasodilatation in IR rats by l-arginine supplementation and arginase inhibition provided functional corroboration. These results demonstrate that increased ADMA and up-regulated arginase contribute to endothelial dysfunction as determined by the presence of IR in human obesity, most probably by compromising arginine availability. The results provide novel insights regarding the mechanisms of endothelial dysfunction related to obesity and IR and establish potential therapeutic targets for intervention.

The effect of the accessory proteins, soluble CD14 and lipopolysaccharide-binding protein on Toll-like receptor 4 activity in human monocytes and adipocytes.

There is a growinge body of evidence pointing towards an important role for Toll-like receptors (TLR) especially TLR4 in obesity and metabolic syndrome. Owing to the paucity of data on the effect of the accessory proteins, lipopolysaccharide (LPS)-binding protein (LBP) and soluble CD14 (sCD14) on TLR4 activation, the present study was undertaken to examine the effect of sCD14 and LBP on TLR4 activation in pivotal cells of meta-inflammation, monocytes and adipocytes. The dose-response effects of sCD14 and LBP on TLR4 protein abundance in monocytes obtained from normal human volunteers was determined by flow cytometry and in human-differentiated adipocytes by western blotting. Additionally, the nuclear factor-kappaB (NF-κB) p65 and downstream biomediators interleukin (IL)-1β, IL-8, IL-6 and tumor necrosis factor (TNF)-α were measured in the cell culture supernatants by ELISA (enzyme-linked immunosorbent assay). In LPS-primed monocytes, sCD14 but not LBP, augments both TLR4 abundance and inflammatory biomediators (IL-1β, IL-8, IL-6 and TNF-α).sCD14 also showed a similar effect in LPS-primed human adipocytes by augmenting TLR4 protein expression and activity in terms of NF-κB p65 and downstream biomediators (IL-1β, IL-8, IL-6 and TNF-α). LBP at the highest concentration only promoted secretion of IL-8 and TNF-α. However in both monocytes and adipocytes, the effect of sCD14 was superior to LBP. In the present report, we make the novel observation that sCD14 compared with LBP, offers a preferred target to ameliorate TLR especially TLR4-induced inflammation and insulin resistance in human obesity and metabolic syndrome.