Prolyl Carboxypeptidase Activity Is Present in Human Adipose Tissue and Is Elevated in Serum of Obese Men with Type 2 Diabetes.

Prolyl carboxypeptidase (PRCP) is involved in metabolic disorders by hydrolyzing anorexigenic peptides. A link between serum PRCP activity and obesity has been reported, but its origin/source is still unclear. Previously proven correlations between human serum PRCP activity and the amount of adipose tissue may suggest that adipose tissue is an important source of circulating PRCP. We investigated PRCP activity in visceral, subcutaneous adipose tissue (VAT and SCAT), skeletal muscle tissue and serum of lean and obese men with or without type 2 diabetes (T2D). Correlations between PRCP activity, metabolic and biochemical parameters and immune cell populations were assessed. PRCP activity was the highest in VAT, compared to SCAT, and was very low in skeletal muscle tissue in the overall group. Serum PRCP activity was significantly higher in T2-diabetic obese men, compared to lean and obese non-diabetic men, and was positively correlated with glycemic control. A positive correlation was observed between serum PRCP activity and VAT immune cell populations, which might indicate that circulating PRCP activity is deriving rather from the immune fraction than from adipocytes. In conclusion, PRCP activity was observed in human adipose tissue for the first time and serum PRCP activity is correlated with T2D in obese men.

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

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

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

BACKGROUND/OBJECTIVES: 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. SUBJECTS/METHODS: 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. RESULTS: 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)ß = 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 DAG species (stdß: 0.139-0.313; FDR-p < 0.05), a lower odd-chain/even-chain TAG ratio (stdß = -0.182; FDR-p = 0.005) and a lower very-long-chain/long-chain TAG ratio (stdß = -0.156; FDR-p = 0.037). CONCLUSIONS: 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.

Vitamin D deficiency in the aetiology of obesity-related insulin resistance.

The obese insulin-resistant state is often associated with low circulating concentration of vitamin D 25-hydroxyvitamin D3 [25(OH)D3 ]. Fat sequestration of vitamin D in the expanded obese adipose tissue mass has been pointed out as a plausible explanation for this circulating vitamin D deficiency. However, the putative mechanisms behind this hypovitaminosis D remain to be elucidated. The presence of vitamin D receptor and vitamin D-metabolizing enzymes in insulin-sensitive organs suggests that vitamin D may be involved in glucose and lipid metabolism and may be related to insulin sensitivity. Indeed, mainly in vitro studies support a role of vitamin D in regulating glucose and lipid metabolism in several insulin-sensitive tissues including adipose tissue, skeletal muscle, liver, as well as pancreatic insulin secretion. A potential role of vitamin D in gut barrier function and metabolism has also been suggested. This review summarizes recent knowledge on vitamin D deficiency in the aetiology of obesity-related insulin resistance and discusses potential underlying mechanisms. Finally, the role of vitamin D supplementation on insulin sensitivity and glycaemic control is discussed.

Supplementation of Diet With Galacto-oligosaccharides Increases Bifidobacteria, but Not Insulin Sensitivity, in Obese Prediabetic Individuals.

BACKGROUND & AIMS: The gut microbiota affects host lipid and glucose metabolism, satiety, and chronic low-grade inflammation to contribute to obesity and type 2 diabetes. Fermentation end products, in particular the short-chain fatty acid (SCFA) acetate, are believed to be involved in these processes. We investigated the long-term effects of supplementation with galacto-oligosaccharides (GOS), an acetogenic fiber, on the composition of the human gut microbiota and human metabolism. METHODS: We performed a double-blinded, placebo-controlled, parallel intervention study of 44 overweight or obese (body mass index, 28-40 kg/m2) prediabetic men and women (ages, 45-70 y) from October 2014 through October 2015 in Maastricht, The Netherlands. The participants were assigned randomly to groups who ingested 15 g GOS or isocaloric placebo (maltodextrin) daily with their regular meals for 12 weeks. Before and after this period, we collected data on peripheral and adipose tissue insulin sensitivity, fecal microbiota composition, plasma and fecal SCFA, energy expenditure and substrate oxidation, body composition, and hormonal and inflammatory responses. The primary outcome was the effect of GOS on peripheral insulin sensitivity, measured by the hyperinsulinemic-euglycemic clamp method. RESULTS: Supplementation of diets with GOS, but not placebo, increased the abundance of Bifidobacterium species in feces by 5-fold (P = .009; q = 0.144). Microbial richness or diversity in fecal samples were not affected. We did not observe any differences in fecal or fasting plasma SCFA concentrations or in systemic concentrations of gut-derived hormones, incretins, lipopolysaccharide-binding protein, or other markers of inflammation. In addition, no significant alterations in peripheral and adipose tissue insulin sensitivity, body composition, and energy and substrate metabolism were found. CONCLUSIONS: Twelve-week supplementation of GOS selectively increased fecal Bifidobacterium species abundance, but this did not produce significant changes in insulin sensitivity or related substrate and energy metabolism in overweight or obese prediabetic men and women. ClincialTrials.gov number, NCT02271776.

Adrenergically and non-adrenergically mediated human adipose tissue lipolysis during acute exercise and exercise training.

Obesity-related adipose tissue (AT) dysfunction, in particular subcutaneous AT (SCAT) lipolysis, is characterized by catecholamine resistance and impaired atrial natriuretic peptide (ANP) responsiveness. It remains unknown whether exercise training improves (non-)adrenergically mediated lipolysis in metabolically compromised conditions. We investigated the effects of local combined α-/ß-adrenoceptor blockade on abdominal SCAT lipolysis in lean insulin sensitive (IS) (n=10), obese IS (n=10), and obese insulin resistant (IR) (n=10) men. Obese men participated in a 12-week exercise training intervention to determine the effects on SCAT lipolysis. Abdominal SCAT extracellular glycerol concentration and blood flow (ATBF) were investigated using microdialysis, with/without locally combined α-/ß-adrenoceptor blockade at rest, during low-intensity endurance-type exercise and post-exercise recovery. In obese IR men, microdialysis was repeated after exercise intervention. The exercise-induced increase in SCAT extracellular glycerol was more pronounced in obese IS compared with lean IS men, possibly resulting from lower ATBF in obese IS men. The exercise-induced increase in extracellular glycerol was blunted in obese IR compared with obese IS men, despite comparable local ATBF. Abdominal SCAT extracellular glycerol was markedly reduced (remaining ~60% of exercise-induced SCAT extracellular glycerol) following the local α-/ß-adrenoceptor blockade in obese IS but not in IR men, suggesting reduced catecholamine-mediated lipolysis during exercise in obese IR men. Exercise training did not affect (non-)adrenergically mediated lipolysis in obese IR men. Our findings showed a major contribution of non-adrenergically-mediated lipolysis during exercise in male abdominal SCAT. Furthermore, catecholamine-mediated lipolysis may be blunted during exercise in obese IR men but could not be improved by exercise intervention, despite an improved metabolic profile and body composition.

Altered skeletal muscle fatty acid handling is associated with the degree of insulin resistance in overweight and obese humans.

INTRODUCTION/HYPOTHESIS: Disturbances in skeletal muscle fatty acid (FA) handling may contribute to the development and progression of whole-body insulin resistance (IR). In this study, we compared fasting and postprandial skeletal muscle FA handling in individuals with varying degrees of IR. METHODS: Seventy-four overweight/obese participants (62 men) were divided into two groups based on the HOMA-IR median (3.35). Fasting and postprandial skeletal muscle FA handling were determined by combining the forearm muscle balance technique with stable isotopes. [2H2]palmitate was infused i.v. to label VLDL-triacylglycerol (VLDL-TAG) and NEFA in the circulation, whereas [U-13C]palmitate was incorporated in a high-saturated FA mixed-meal labelling chylomicron-TAG. Skeletal muscle biopsies were taken to assess intramuscular lipid content, fractional synthetic rate (FSR) and the transcriptional regulation of FA metabolism. RESULTS: Postprandial forearm muscle VLDL-TAG extraction was elevated in the high-IR vs the mild-IR group (AUC0-4h: 0.57 ± 0.32 vs -0.43 ± 0.38 nmol [100 ml tissue]-1 min-1, respectively, p = 0.045). Although no differences in skeletal muscle TAG, diacylglycerol, NEFA content and FSR were present between groups, the high-IR group showed increased saturation of the intramuscular NEFA pool (p = 0.039). This was accompanied by lower muscle GPAT1 (also known as GPAM) expression (p = 0.050). CONCLUSIONS/INTERPRETATION: Participants with high-IR demonstrated increased postprandial skeletal muscle VLDL-TAG extraction and higher saturation of the intramuscular NEFA pool vs individuals with mild-IR. These data support the involvement of disturbances in skeletal muscle FA handling in the progression of whole-body IR.

Attenuated atrial natriuretic peptide-mediated lipolysis in subcutaneous adipocytes of obese type 2 diabetic men.

Catecholamines and atrial natriuretic peptide (ANP) are major regulators of adipocyte lipolysis. Although obesity is characterized by catecholamine resistance in subcutaneous adipose tissue (SCAT), data on ANP lipolytic response and sensitivity in different adipose tissue (AT) depots of metabolically distinct humans are scarce. Ex vivo catecholamine- and ANP-induced lipolysis was investigated in adipocytes derived from SCAT and visceral AT (VAT) depot of lean (n=13) and obese men, with (n=11) or without (n=18) type 2 diabetes (HbA1c < or ≥ 6.5%). Underlying molecular mechanisms were examined by looking at functional receptors in the NP signalling pathway at the mRNA and protein level. Maximal ANP- and catecholamine-induced lipolysis in SCAT was blunted in obese type 2 diabetics compared with age-matched lean men whereas non-diabetic obese subjects showed intermediate responses. This blunted ANP-mediated lipolytic response was accompanied by lower mRNA and protein expression of the type-A natriuretic peptide (NP) receptor and higher mRNA but reduced protein expression of the scavenging type-C receptor. Maximal ANP-induced lipolysis was lower in VAT compared with SCAT but not different between groups. Collectively, our data show that both ANP- and catecholamine-mediated lipolysis is attenuated in SCAT of obese men with type 2 diabetes, and might be partially explained by NP receptor defects. Therefore, improving maximal ANP responsiveness in adipose tissue might be a potential novel strategy to improve obesity-associated metabolic complications.

Impaired mitochondrial respiration in upper compared to lower body differentiated human adipocytes and adipose tissue.

CONTEXT: Abdominal obesity is associated with increased cardiometabolic disease risk, while lower body fat seems to confer protection against obesity-related complications. The functional differences between upper and lower body adipose tissue (AT) remain poorly understood. OBJECTIVE: We aimed to examine whether mitochondrial respiration is impaired in abdominal as compared to femoral differentiated human multipotent adipose-derived stem cells (hMADS; primary outcome) and AT in postmenopausal women. DESIGN: In this cross-sectional study, 23 postmenopausal women with normal weight or obesity were recruited at the University of Birmingham/Queen Elizabeth Hospital Birmingham (Birmingham, UK). We collected abdominal and femoral subcutaneous AT biopsies to determine mitochondrial oxygen consumption rates in differentiated abdominal and femoral hMADS. Furthermore, we assessed OXPHOS protein expression and mtDNA content in abdominal and femoral AT as well as hMADS. Finally, we explored in vivo fractional oxygen extraction and carbon dioxide release across abdominal and femoral subcutaneous AT in a subgroup of the same individuals with normal weight or obesity. RESULTS: We found lower basal and maximal uncoupled mitochondrial oxygen consumption rates in abdominal compared to femoral hMADS. In line, in vivo fractional oxygen extraction and carbon dioxide release were lower across abdominal than femoral AT. OXPHOS protein expression and mtDNA content did not significantly differ between abdominal and femoral differentiated hMADS and AT. CONCLUSION: The present findings demonstrate that in vitro mitochondrial respiration and in vivo oxygen fractional extraction are lower in upper compared to lower body differentiated hMADS and AT, respectively, in postmenopausal women.

Insulin-mediated suppression of lipolysis in adipose tissue and skeletal muscle of obese type 2 diabetic men and men with normal glucose tolerance.

AIMS/HYPOTHESIS: Impaired regulation of lipolysis and accumulation of lipid intermediates may contribute to obesity-related insulin resistance and type 2 diabetes mellitus. We investigated insulin-mediated suppression of lipolysis in abdominal subcutaneous adipose tissue (AT) and skeletal muscle (SM) of obese men with normal glucose tolerance (NGT) and obese type 2 diabetic men. METHODS: Eleven NGT men and nine long-term diagnosed type 2 diabetic men (7 ± 1 years), matched for age (58 ± 2 vs 62 ± 2 years), BMI (31.4 ± 0.6 vs 30.5 ± 0.6 kg/m(2)) and [Formula: see text] (28.9 ± 1.5 vs 29.5 ± 2.4 ml kg(-1) min(-1)) participated in this study. Interstitial glycerol concentrations in AT and SM were assessed using microdialysis during a 1 h basal period and a 6 h stepwise hyperinsulinaemic-euglycaemic clamp (8, 20 and 40 mU m(-2) min(-1)). AT and SM biopsies were collected to investigate underlying mechanisms. RESULTS: Hyperinsulinaemia suppressed interstitial SM glycerol concentrations less in men with type 2 diabetes (-7 ± 6%, -13 ± 9% and -27 ± 9%) compared with men with NGT (-21 ± 7%, -38 ± 8% and -53 ± 8%) (p = 0.014). This was accompanied by increased circulating fatty acid and glycerol concentrations, a lower glucose infusion rate (21.8 ± 3.1 vs 30.5 ± 2.0 µmol kg body weight(-1) min(-1); p < 0.05), higher hormone-sensitive lipase (HSL) serine 660 phosphorylation, increased saturated diacylglycerol (DAG) lipid species in the muscle membrane and increased protein kinase C (PKC) activation in type 2 diabetic men vs men with NGT. No significant differences in insulin-mediated reduction in AT interstitial glycerol were observed between groups. CONCLUSIONS/INTERPRETATION: Our results suggest that a blunted insulin-mediated suppression of SM lipolysis may promote the accumulation of membrane saturated DAG, aggravating insulin resistance, at least partly mediated by PKC. This may represent an important mechanism involved in the progression of insulin resistance towards type 2 diabetes. TRIAL REGISTRATION: ClinicalTrials.gov NCT01680133.

Distinct inflammatory signatures of upper and lower body adipose tissue and adipocytes in women with normal weight or obesity.

Introduction: Upper and lower body fat accumulation poses an opposing obesity-related cardiometabolic disease risk. Depot-differences in subcutaneous adipose tissue (SAT) function may underlie these associations. We aimed to investigate the inflammatory signatures of abdominal (ABD) and femoral (FEM) SAT in postmenopausal women with normal weight or obesity. Methods: We included 23 postmenopausal women with normal weight (n = 13) or obesity (n = 10). In vivo secretion of adipokines from ABD and FEM SAT was measured using the arterio-venous balance technique. Adipokine gene expression and adipocyte morphology were examined in ABD and FEM SAT. Furthermore, adipokine expression and secretion were investigated in vitro using differentiated human primary ABD and FEM subcutaneous adipocytes derived from the study participants. Results: Plasma leptin and plasminogen activator inhibitor (PAI)-1 concentrations were higher, and ABD and FEM adipocytes were larger in women with obesity than normal weight. No differences in adipocyte size and blood flow were apparent between ABD and FEM SAT. We found significant release of leptin and monocyte chemoattractant protein (MCP)-1 from ABD and FEM SAT, with higher fractional release of MCP-1 from ABD than FEM SAT. Gene expression of leptin, PAI-1, and tumor necrosis factor-α was lower in ABD than FEM SAT and higher in women with obesity than normal weight. In ABD adipocytes, interleukin-6, PAI-1, and leptin gene expression were higher, while adiponectin and dipeptidyl-peptidase-4 gene expression were lower than in FEM adipocytes. Finally, ABD adipocytes secreted less MCP-1 compared to FEM adipocytes. Discussion: These findings demonstrate that upper and lower body SAT and adipocytes are characterized by distinct inflammatory signatures in postmenopausal women, which seem independent of adipocyte size.

Circulating and adipose tissue immune cells in tissue-specific insulin resistance in humans with overweight and obesity.

OBJECTIVE: A proinflammatory adipose tissue (AT) microenvironment and systemic low-grade inflammation may differentially affect tissue-specific insulin sensitivity. This study investigated the relationships of abdominal subcutaneous AT (aSAT) and circulating immune cells, aSAT gene expression, and circulating inflammatory markers with liver and skeletal muscle insulin sensitivity in people with overweight and obesity. METHODS: Individuals with overweight and obesity from the PERSonalized Glucose Optimization Through Nutritional Intervention (PERSON) Study (n = 219) and the Maastricht Study (replication cohort; n = 1256) underwent a seven-point oral glucose tolerance test to assess liver and muscle insulin sensitivity, and circulating inflammatory markers were determined. In subgroups, flow cytometry was performed to identify circulating and aSAT immune cells, and aSAT gene expression was evaluated. RESULTS: The relative abundances of circulating T cells, nonclassical monocytes, and CD56dim CD16+ natural killer cells were inversely associated with liver, but not muscle, insulin sensitivity in the PERSON Study. The inverse association between circulating (classical) monocytes and liver insulin sensitivity was confirmed in the Maastricht Study. In aSAT, immune cell populations were not related to insulin sensitivity. Furthermore, aSAT gene expression of interleukin 6 and CD14 was positively associated with muscle, but not liver, insulin sensitivity. CONCLUSIONS: The present findings demonstrate that circulating immune cell populations and inflammatory gene expression in aSAT show distinct associations with liver and muscle insulin sensitivity.

Liver X receptor (LXR) regulates human adipocyte lipolysis.

The Liver X receptor (LXR) is an important regulator of carbohydrate and lipid metabolism in humans and mice. We have recently shown that activation of LXR regulates cellular fuel utilization in adipocytes. In contrast, the role of LXR in human adipocyte lipolysis, the major function of human white fat cells, is not clear. In the present study, we stimulated in vitro differentiated human and murine adipocytes with the LXR agonist GW3965 and observed an increase in basal lipolysis. Microarray analysis of human adipocyte mRNA following LXR activation revealed an altered gene expression of several lipolysis-regulating proteins, which was also confirmed by quantitative real-time PCR. We show that expression and intracellular localization of perilipin1 (PLIN1) and hormone-sensitive lipase (HSL) are affected by GW3965. Although LXR activation does not influence phosphorylation status of HSL, HSL activity is required for the lipolytic effect of GW3965. This effect is abolished by PLIN1 knockdown. In addition, we demonstrate that upon activation, LXR binds to the proximal regions of the PLIN1 and HSL promoters. By selective knock-down of either LXR isoform, we show that LXRα is the major isoform mediating the lipolysis-related effects of LXR. In conclusion, the present study demonstrates that activation of LXRα up-regulates basal human adipocyte lipolysis. This is at least partially mediated through LXR binding to the PLIN1 promoter and down-regulation of PLIN1 expression.

Increased adipose tissue oxygen tension in obese compared with lean men is accompanied by insulin resistance, impaired adipose tissue capillarization, and inflammation.

BACKGROUND: Adipose tissue (AT) dysfunction in obesity contributes to chronic, low-grade inflammation that predisposes to type 2 diabetes mellitus and cardiovascular disease. Recent in vitro studies suggest that AT hypoxia may induce inflammation. We hypothesized that adipose tissue blood flow (ATBF) regulates AT oxygen partial pressure (AT P(O2)), thereby affecting AT inflammation and insulin sensitivity. METHODS AND RESULTS: We developed an optochemical measurement system for continuous monitoring of AT P(O2) using microdialysis. The effect of alterations in ATBF on AT P(O2) was investigated in lean and obese subjects with both pharmacological and physiological approaches to manipulate ATBF. Local administration of angiotensin II (vasoconstrictor) in abdominal subcutaneous AT decreased ATBF and AT P(O2), whereas infusion of isoprenaline (vasodilator) evoked opposite effects. Ingestion of a glucose drink increased ATBF and AT P(O2) in lean subjects, but these responses were blunted in obese individuals. However, AT P(O2) was higher (hyperoxia) in obese subjects despite lower ATBF, which appears to be explained by lower AT oxygen consumption. This was accompanied by insulin resistance, lower AT capillarization, lower AT expression of genes encoding proteins involved in mitochondrial biogenesis and function, and higher AT gene expression of macrophage infiltration and inflammatory markers. CONCLUSIONS: Our findings establish ATBF as an important regulator of AT P(O2). Nevertheless, obese individuals exhibit AT hyperoxia despite lower ATBF, which seems to be explained by lower AT oxygen consumption. This is accompanied by insulin resistance, impaired AT capillarization, and higher AT gene expression of inflammatory cell markers. CLINICAL TRIAL REGISTRATION- URL: http://www.trialregister.nl. Unique identifier: NTR2451.

Physiological Oxygen Levels Differentially Regulate Adipokine Production in Abdominal and Femoral Adipocytes from Individuals with Obesity Versus Normal Weight.

Adipose tissue (AT) inflammation may increase obesity-related cardiometabolic complications. Altered AT oxygen partial pressure (pO2) may impact the adipocyte inflammatory phenotype. Here, we investigated the effects of physiological pO2 levels on the inflammatory phenotype of abdominal (ABD) and femoral (FEM) adipocytes derived from postmenopausal women with normal weight (NW) or obesity (OB). Biopsies were collected from ABD and FEM subcutaneous AT in eighteen postmenopausal women (aged 50-65 years) with NW (BMI 18-25 kg/m2, n = 9) or OB (BMI 30-40 kg/m2, n = 9). We compared the effects of prolonged exposure to different physiological pO2 levels on adipokine expression and secretion in differentiated human multipotent adipose-derived stem cells. Low physiological pO2 (5% O2) significantly increased leptin gene expression/secretion in ABD and FEM adipocytes derived from individuals with NW and OB compared with high physiological pO2 (10% O2) and standard laboratory conditions (21% O2). Gene expression/secretion of IL-6, DPP-4, and MCP-1 was reduced in differentiated ABD and FEM adipocytes from individuals with OB but not NW following exposure to low compared with high physiological pO2 levels. Low physiological pO2 decreases gene expression and secretion of several proinflammatory factors in ABD and FEM adipocytes derived from individuals with OB but not NW.

Sexual dimorphism in cardiometabolic health: the role of adipose tissue, muscle and liver.

Obesity is associated with many adverse health effects, such as an increased cardiometabolic risk. Despite higher adiposity for a given BMI, premenopausal women are at lower risk of cardiometabolic disease than men of the same age. This cardiometabolic advantage in women seems to disappear after the menopause or when type 2 diabetes mellitus develops. Sexual dimorphism in substrate supply and utilization, deposition of excess lipids and mobilization of stored lipids in various key metabolic organs (such as adipose tissue, skeletal muscle and the liver) are associated with differences in tissue-specific insulin sensitivity and cardiometabolic risk profiles between men and women. Moreover, lifestyle-related factors and epigenetic and genetic mechanisms seem to affect metabolic complications and disease risk in a sex-specific manner. This Review provides insight into sexual dimorphism in adipose tissue distribution, adipose tissue, skeletal muscle and liver substrate metabolism and tissue-specific insulin sensitivity in humans, as well as the underlying mechanisms, and addresses the effect of these sex differences on cardiometabolic health. Additionally, this Review highlights the implications of sexual dimorphism in the pathophysiology of obesity-related cardiometabolic risk for the development of sex-specific prevention and treatment strategies.

Acetate Does Not Affect Palmitate Oxidation and AMPK Phosphorylation in Human Primary Skeletal Muscle Cells.

Our recent in vivo human studies showed that colonic administration of sodium acetate (SA) resulted in increased circulating acetate levels, which was accompanied by increments in whole-body fat oxidation in overweight-obese men. Since skeletal muscle has a major role in whole-body fat oxidation, we aimed to investigate effects of SA on fat oxidation and underlying mechanisms in human primary skeletal muscle cells (HSkMC). We investigated the dose (0-5 mmol/L) and time (1, 4, 20, and 24 h) effect of SA on complete and incomplete endogenous and exogenous oxidation of 14C-labeled palmitate in HSkMC derived from a lean insulin sensitive male donor. Both physiological (0.1 and 0.25 mmol/L) and supraphysiological (0.5, 1 and 5 mmol/L) concentrations of SA neither increased endogenous nor exogenous fat oxidation over time in HSkMC. In addition, no effect of SA was observed on Thr172-AMPKα phosphorylation. In conclusion, our previously observed in vivo effects of SA on whole-body fat oxidation in men may not be explained via direct effects on HSkMC fat oxidation. Nevertheless, SA-mediated effects on whole-body fat oxidation may be triggered by other mechanisms including gut-derived hormones or may occur in other metabolically active tissues.

The angiotensin II type 1 receptor blocker valsartan in the battle against COVID-19.

OBJECTIVE: Severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) uses the host's angiotensin-converting enzyme 2 (ACE2) as a cellular entry point. Therefore, modulating ACE2 might impact SARS-CoV-2 viral replication, shedding, and coronavirus disease 2019 (COVID-19) severity. Here, it was investigated whether the angiotensin II type 1 receptor blocker valsartan alters the expression of renin-angiotensin system (RAS) components, including ACE2, in human adipose tissue (AT) and skeletal muscle. METHODS: A randomized, double-blind, placebo-controlled clinical trial was performed, in which 36 participants (BMI 31.0 ± 0.8 kg/m2 ) with impaired glucose metabolism received either valsartan or placebo for 26 weeks. Before and after 26 weeks' treatment, abdominal subcutaneous AT and skeletal muscle biopsies were obtained, and gene expression of RAS components was measured by quantitative reverse transcription polymerase chain reaction. RESULTS: Valsartan treatment did not significantly impact the expression of RAS components, including ACE2, in AT and skeletal muscle. CONCLUSIONS: Given the pivotal role of ACE2 in SARS-CoV-2 spread and the clinical outcomes in COVID-19 patients, the data suggest that the putative beneficial effects of angiotensin II type 1 receptor blockers on the clinical outcomes of patients with COVID-19 may not be mediated through altered ACE2 expression in abdominal subcutaneous AT.

Mild intermittent hypoxia exposure induces metabolic and molecular adaptations in men with obesity.

OBJECTIVE: Recent studies suggest that hypoxia exposure may improve glucose homeostasis, but well-controlled human studies are lacking. We hypothesized that mild intermittent hypoxia (MIH) exposure decreases tissue oxygen partial pressure (pO2) and induces metabolic improvements in people who are overweight/obese. METHODS: In a randomized, controlled, single-blind crossover study, 12 men who were overweight/obese were exposed to MIH (15 % O2, 3 × 2 h/day) or normoxia (21 % O2) for 7 consecutive days. Adipose tissue (AT) and skeletal muscle (SM) pO2, fasting/postprandial substrate metabolism, tissue-specific insulin sensitivity, SM oxidative capacity, and AT and SM gene/protein expression were determined. Furthermore, primary human myotubes and adipocytes were exposed to oxygen levels mimicking the hypoxic and normoxic AT and SM microenvironments. RESULTS: MIH decreased systemic oxygen saturation (92.0 ± 0.5 % vs 97.1 ± 0.3, p < 0.001, respectively), AT pO2 (21.0 ± 2.3 vs 36.5 ± 1.5 mmHg, p < 0.001, respectively), and SM pO2 (9.5 ± 2.2 vs 15.4 ± 2.4 mmHg, p = 0.002, respectively) compared to normoxia. In addition, MIH increased glycolytic metabolism compared to normoxia, reflected by enhanced fasting and postprandial carbohydrate oxidation (pAUC = 0.002) and elevated plasma lactate concentrations (pAUC = 0.005). Mechanistically, hypoxia exposure increased insulin-independent glucose uptake compared to standard laboratory conditions (~50 %, p < 0.001) and physiological normoxia (~25 %, p = 0.019) through AMP-activated protein kinase in primary human myotubes but not in primary human adipocytes. MIH upregulated inflammatory/metabolic pathways and downregulated extracellular matrix-related pathways in AT but did not alter systemic inflammatory markers and SM oxidative capacity. MIH exposure did not induce significant alterations in AT (p = 0.120), hepatic (p = 0.132) and SM (p = 0.722) insulin sensitivity. CONCLUSIONS: Our findings demonstrate for the first time that 7-day MIH reduces AT and SM pO2, evokes a shift toward glycolytic metabolism, and induces adaptations in AT and SM but does not induce alterations in tissue-specific insulin sensitivity in men who are overweight/obese. Future studies are needed to investigate further whether oxygen signaling is a promising target to mitigate metabolic complications in obesity. CLINICAL TRIAL REGISTRATION: This study is registered at the Netherlands Trial Register (NL7120/NTR7325).

The Effect of Vitamin D Supplementation on Insulin Sensitivity: A Systematic Review and Meta-analysis.

BACKGROUND: Vitamin D has been suggested to affect peripheral insulin sensitivity. Evidence regarding the effect of vitamin D supplementation on insulin sensitivity is still conflicting. PURPOSE: This meta-analysis aimed to assess the effect of vitamin D supplementation on insulin sensitivity in humans with or at risk for insulin resistance. DATA SOURCES AND STUDY SELECTION: PubMed, Web of Science, Embase, CINAHL, and Cochrane Library were systematically searched for randomized controlled trials (RCTs) from 1980 until 31 December 2018 reporting treatment effects of vitamin D supplementation on insulin sensitivity. DATA EXTRACTION: The main outcome of interest was the change in insulin sensitivity, derived from the gold standard hyperinsulinemic-euglycemic clamp or the Matsuda index derived from the oral glucose tolerance test and insulin sensitivity index from intravenous glucose tolerance test. We extracted data on the standardized mean difference between the vitamin D treatment and placebo groups in change from baseline insulin sensitivity. DATA SYNTHESIS: Eighteen RCTs were included in this meta-analysis comparing vitamin D supplementation (n = 612) with placebo (n = 608). Vitamin D supplementation had no effect on insulin sensitivity (standardized mean difference -0.01, 95% CI -0.12, 0.10; P = 0.87, I 2 = 0%). Visual inspection of funnel plot symmetry did not suggest potential publication bias. LIMITATIONS: The number of individuals who participated in the included studies was relatively small, possibly due to the invasive character of the measurement (e.g., clamp). CONCLUSIONS: This meta-analysis provides no evidence that vitamin D supplementation has a beneficial effect on peripheral insulin sensitivity in people with or at risk for insulin resistance.