Adipose tissue and skeletal muscle insulin-mediated glucose uptake in insulin resistance: role of blood flow and diabetes

Resveratrol as a potential therapeutic agent for sarcopenic obesity: Insights from in vivoperiments

Sarcopenic obesity (SO) is a metabolic disorder with increasing prevalence. It is characterized by a reduction in skeletal muscle mass and strength. Resveratrol (RSV) is one of the most frequently used herbs in the treatment of skeletal muscle atrophy. However, the precise mechanism of the action of RSV in SO remains unclear. The objective of this study was to examine the pharmacological mechanism of RSV in the context of SO through the lens of network pharmacology, to validate these findings through in vivo experimentation. A list of potential RSV targets was compiled by retrieving the data from multiple databases. This list was then cross-referenced with a list of potential targets related to SO. The intersections of RSV- and SO-related targets were analyzed using Venn diagrams. To identify the core genes, a protein-protein interaction (PPI) network of the intersection targets was constructed and subsequently analyzed. Molecular docking was used to predict RSV binding to its core targets. A high-fat diet was used to induce SO in mice. These findings indicated that RSV may prevent SO by acting on 11 targets. Among these, interleukin-6 (IL-6), C-reactive protein (CRP), and tumor necrosis factor (TNF) are considered core targets. The Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment results indicated that the anti-SO effect of RSV was predominantly linked to metabolic disease-related pathways, including those associated with nonalcoholic fatty liver disease. The anti-inflammatory effects of RSV were confirmed in vivo in an SO mouse model. This study contributes to a more comprehensive understanding of the key mechanisms of the action of RSV against SO and provides new possibilities for drug development in the pathological process of SO.

Dapagliflozin treatment is associated with a reduction of epicardial adipose tissue thickness and epicardial glucose uptake in human type 2 diabetes

OBJECTIVE

We recently demonstrated that treatment with sodium-glucose cotransporter-2 inhibitors (SGLT-2i) leads to an increase in myocardial flow reserve in patients with type 2 diabetes (T2D) with stable coronary artery disease (CAD). The mechanism by which this occurs is, however, unclear. One of the risk factors for cardiovascular disease is inflammation of epicardial adipose tissue (EAT). Since the latter is often increased in type 2 diabetes patients, it could play a role in coronary microvascular dysfunction. It is also well known that SGLT-2i modify adipose tissue metabolism. We aimed to investigate the effects of the SGLT-2i dapagliflozin on metabolism and visceral and subcutaneous adipose tissue thickness in T2D patients with stable coronary artery disease and to verify whether these changes could explain observed changes in myocardial flow.

METHODS

We performed a single-center, prospective, randomized, double-blind, controlled clinical trial with 14 T2D patients randomized 1:1 to SGLT-2i dapagliflozin (10 mg daily) or placebo. The thickness of visceral (epicardial, mediastinal, perirenal) and subcutaneous adipose tissue and glucose uptake were assessed at baseline and 4 weeks after treatment initiation by 2-deoxy-2-[18F]fluoro-D-glucose Positron Emission Tomography/Computed Tomography during hyperinsulinemic euglycemic clamp.

RESULTS

The two groups were well-matched for baseline characteristics (age, diabetes duration, HbA1c, BMI, renal and heart function). Dapagliflozin treatment significantly reduced EAT thickness by 19% (p = 0.03). There was a significant 21.6% reduction in EAT glucose uptake during euglycemic hyperinsulinemic clamp in the dapagliflozin group compared with the placebo group (p = 0.014). There were no significant effects on adipose tissue thickness/metabolism in the other depots explored.

CONCLUSIONS

SGLT-2 inhibition selectively reduces EAT thickness and EAT glucose uptake in T2D patients, suggesting a reduction of EAT inflammation. This could explain the observed increase in myocardial flow reserve, providing new insights into SGLT-2i cardiovascular benefits.

Aerobic exercise and metformin on intermuscular adipose tissue (IMAT): insights from multimodal MRI and histological changes in prediabetic rats

BACKGROUND

Physical exercise is the first-line intervention for prediabetes, and metformin is the most widely used oral insulin-sensitizing agent. Moreover, intermuscular adipose tissue (IMAT) directly affects insulin resistance by helping maintain glucose homeostasis. Here, we evaluated the effects of moderate aerobic exercise and/or metformin on histological IMAT parameters in non-streptozotocin-induced prediabetes.

METHODS

Male Wistar rats with prediabetes fed a high-fat diet and high-sugar drinks were randomly assigned to high-fat diet (PRE), metformin (MET), moderate aerobic exercise (EXE), combined therapy (EMC), or EMC + compound-c (EMA) groups for 4 weeks. Multimodal magnetic resonance imaging (MRI) was then performed, and tissue-specific inflammation and energy and lipid metabolism were evaluated in IMAT.

RESULTS

The EXE group had lower inflammatory factor levels, lipid metabolism, and mitochondrial oxidative stress, and shorter IMAT adipocyte diameters than the MET group. The MET group exhibited lower IL-1β and Plin5 expression than the PRE group. Furthermore, the IMAT of the EMC group had lower TNF-α and phosphorylated NF-κB levels and higher GLUT1 and GLUT4 expression than the PRE group. Multimodal MRI revealed significant changes in transverse-relaxation time 2, apparent diffusion coefficient, and fractional anisotropy values in the IMAT and muscles, as well as lower IMAT% values in the EXE and EMC groups than in the MET and PRE groups.

CONCLUSION

Moderate aerobic exercise training can effectively improve IMAT function and structure via the AMP-activated protein kinase pathway in prediabetes. Combining metformin with moderate aerobic exercise might elicit modest synergy, and metformin does not counterbalance the beneficial effects of exercise.

GABA Prevents Age-Related Sarcopenic Obesity in Mice with High-Fat-Diet-Induced Obesity

Sarcopenic obesity is characterized by concurrent obesity and muscle wasting (sarcopenia) and is common in the elderly. Sarcopenic obesity has steadily increased as the aging population has grown and is an increasing public health burden. Both obesity and sarcopenia independently increase health risks of the elderly, but sarcopenic obesity has a greater effect on metabolic disease than either obesity or sarcopenia alone. The metabolic mechanisms of obesity and sarcopenia are strongly interconnected, and obesity and sarcopenia form a vicious cycle, with each pathology exacerbating the other. The pathogenesis of sarcopenic obesity is more complex than either disease alone and remains incompletely understood, underscoring the significant unmet clinical need for effective sarcopenic obesity treatments. We aimed to determine the efficacy and underlying regulatory mechanisms of Gamma-aminobutyric acid (GABA) in sarcopenic obesity in high-fat-diet-fed obese aged mice and alterations in related mechanisms to determine the potential of GABA as a therapeutic modality for sarcopenic obesity. In this study, we used young (3 months) and aged (20 months) mice to evaluate age-related sarcopenic obesity. The daily administration of GABA for 8 weeks resulted in decreased fat mass and increased muscle mass and strength in aged mice. GABA also enhanced energy expenditure in both adipose tissue and skeletal muscle. In addition, GABA promoted muscle synthesis and decreased muscle degradation by activating the phosphatidylinositol-3-kinase (PI3K)/Akt pathway. These findings demonstrate that GABA has potential uses in preventing age-related sarcopenic obesity and related metabolic diseases.

Association of physical activity with increased PI3K and Akt mRNA levels in adipose tissues of obese and non-obese adults

Phosphatidylinositol-3-kinase (PI3K)/Akt signaling pathway regulates glucose and lipid metabolism. We examined the association of PI3K and Akt expression in visceral (VAT) and subcutaneous adipose tissue (SAT) with daily physical activity (PA) in non-diabetic obese and non-obese adults. In this cross-sectional study, we included 105 obese (BMI ≥ 30 kg/m²) and 71 non-obese (BMI < 30 kg/m²) subjects (aged/ ≥ 18 years). PA was measured using a valid and reliable International Physical Activity Questionnaire(IPAQ)-long-form, and the metabolic equivalent of task(MET) was calculated. Real-time PCR was performed to analyze the mRNA relative expression. VAT PI3K expression had a lower level in obese compared to non-obese (P = 0.015), while its expression was higher in active individuals than inactive ones (P = 0.029). SAT PI3K expression was increased in active individuals compared to inactive ones (P = 0.031). There was a rise in VAT Akt expression in the actives compared to the inactive participants (P = 0.037) and in non-obese/active compared to non-obese/inactive individuals (P = 0.026). Obese individuals had a decreased expression level of SAT Akt compared to non-obsesses (P = 0.005). VAT PI3K was directly and significantly associated with PA in obsesses (β = 1.457, P = 0.015). Positive association between PI3K and PA suggests beneficial effects of PA for obese individuals that can be partly described by PI3K/Akt pathway acceleration in adipose tissue.

Autocrine FGF1 signaling promotes glucose uptake in adipocytes

Fibroblast growth factor 1 (FGF1) is an autocrine growth factor released from adipose tissue during over-nutrition or fasting to feeding transition. While local actions underlie the majority of FGF1's anti-diabetic functions, the molecular mechanisms downstream of adipose FGF receptor signaling are unclear. We investigated the effects of FGF1 on glucose uptake and its underlying mechanism in murine 3T3-L1 adipocytes and in ex vivo adipose explants from mice. FGF1 increased glucose uptake in 3T3-L1 adipocytes and epididymal WAT (eWAT) and inguinal WAT (iWAT). Conversely, glucose uptake was reduced in eWAT and iWAT of FGF1 knockout mice. We show that FGF1 acutely increased adipocyte glucose uptake via activation of the insulin-sensitive glucose transporter GLUT4, involving dynamic crosstalk between the MEK1/2 and Akt signaling proteins. Prolonged exposure to FGF1 stimulated adipocyte glucose uptake by MEK1/2-dependent transcription of the basal glucose transporter GLUT1. We have thus identified an alternative pathway to stimulate glucose uptake in adipocytes, independent from insulin, which could open new avenues for treating patients with type 2 diabetes.

11β-HSD as a New Target in Pharmacotherapy of Metabolic Diseases

Glucocorticoids (GCs), which are secreted by the adrenal cortex, are important regulators in the metabolism of carbohydrates, lipids, and proteins. For the proper functioning of the body, strict control of their release is necessary, as increased GCs levels may contribute to the development of obesity, type 2 diabetes mellitus, hypertension, cardiovascular diseases, and other pathological conditions contributing to the development of metabolic syndrome. 11β-hydroxysteroid dehydrogenase type I (11β-HSD1) locally controls the availability of the active glucocorticoid, namely cortisol and corticosterone, for the glucocorticoid receptor. Therefore, the participation of 11β-HSD1 in the development of metabolic diseases makes both this enzyme and its inhibitors attractive targets in the pharmacotherapy of the above-mentioned diseases.

GDF11 inhibits adipogenesis and improves mature adipocytes metabolic function via WNT/β-catenin and ALK5/SMAD2/3 pathways

Objective

GDF11 is a member of the TGF‐β superfamily that was recently implicated as potential “rejuvenating” factor, which can ameliorate metabolic disorders. The main objective of the presented study was to closely characterize the role of GDF11 signaling in the glucose homeostasis and in the differentiation of white adipose tissue.

Methods

We performed microscopy imaging, biochemical and transcriptomic analyses of adipose tissues of 9 weeks old ob/ob mice and murine and human pre‐adipocyte cell lines.

Results

Our in vivo experiments employing GDF11 treatment in ob/ob mice showed improved glucose/insulin homeostasis, decreased weight gain and white adipocyte size. Furthermore, GDF11 treatment inhibited adipogenesis in pre‐adipocytes by ALK5‐SMAD2/3 activation in cooperation with the WNT/β‐catenin pathway, whose inhibition resulted in adipogenic differentiation. Lastly, we observed significantly elevated levels of the adipokine hormone adiponectin and increased glucose uptake by mature adipocytes upon GDF11 exposure.

Conclusion

We show evidence that link GDF11 to adipogenic differentiation, glucose, and insulin homeostasis, which are pointing towards potential beneficial effects of GDF11‐based “anti‐obesity” therapy.

Early introduction of exercise prevents insulin resistance in postnatal overfed rats

Early childhood obesity increases the risk of developing metabolic diseases. We examined the early introduction of exercise in small-litter obese-induced rats (SL) on glucose metabolism in the epididymal adipose tissue (AT) and soleus muscle (SM). On day 3 post-birth, pups were divided into groups of ten or three (SL). On day 22, rats were split into sedentary (S and SLS) and exercise (E and SLE) groups. The rats swam three times/week carrying a load for 30 min. In the first week, they swam without a load; in the 2nd week, they carried a load equivalent to 2% of their body weight; from the 3rd week to the final week, they carried a 5% body load. At 85 days of age, an insulin tolerance test was performed in some rats. At 90 days of age, rats were killed, and blood was harvested for plasma glucose, cholesterol, and triacylglycerol measurements. Mesenteric, epididymal, retroperitoneal, and brown adipose tissues were removed and weighed. SM and AT were incubated in the Krebs-Ringer bicarbonate buffer, 5.5 mM glucose for 1 h with or without 10 mU/mL insulin. Comparison between the groups was performed by 3-way ANOVA followed by the Tukey post-hoc test. Sedentary, overfed rats had greater body mass, more visceral fat, lower lactate production, and insulin resistance. Early introduction of exercise reduced plasma cholesterol and contained the deposition of white adipose tissue and insulin resistance. In conclusion, the early introduction of exercise prevents the effects of obesity on glucose metabolism in adulthood in this rat model.

Role of anatomical location, cellular phenotype and perfusion of adipose tissue in intermediary metabolism: A narrative review

It is well-established that adipose tissue accumulation is associated with insulin resistance through multiple mechanisms. One major metabolic link is the classical Randle cycle: enhanced release of free fatty acids (FFA) from hydrolysis of adipose tissue triglycerides impedes insulin-mediated glucose uptake in muscle tissues. Less well studied are the different routes of this communication. First, white adipose tissue depots may be regionally distant from muscle (i.e., gluteal fat and diaphragm muscle) or contiguous to muscle but separated by a fascia (Scarpa's fascia in the abdomen, fascia lata in the thigh). In this case, released FFA outflow through the venous drainage and merge into arterial plasma to be transported to muscle tissues. Next, cytosolic triglycerides can directly, i.e., within the cell, provide FFA to myocytes (but also pancreatic ß-cells, renal tubular cells, etc.). Finally, adipocyte layers or lumps may be adjacent to, but not anatomically segregated, from muscle, as is typically the case for epicardial fat and cardiomyocytes. As regulation of these three main delivery paths is different, their separate contribution to substrate competition at the whole-body level is uncertain. Another important link between fat and muscle is vascular. In the resting state, blood flow is generally higher in adipose tissue than in muscle. In the insulinized state, fat blood flow is directly related to whole-body insulin resistance whereas muscle blood flow is not; consequently, fractional (i.e., flow-adjusted) glucose uptake is stimulated in muscle but not fat. Thus, reduced blood supply is a major factor for the impairment of in vivo insulin-mediated glucose uptake in both subcutaneous and visceral fat. In contrast, the insulin resistance of glucose uptake in resting skeletal muscle is predominantly a cellular defect.

Skeletal muscle loss is associated with diabetes in middle-aged and older Chinese men without non-alcoholic fatty liver disease

BACKGROUND

Skeletal muscle, a key insulin target organ, has been reported to be associated with diabetes mellitus (DM). Compared to non-diabetic patients, diabetic patients have decreased muscle mass and a higher prevalence of sarcopenia, and patients with sarcopenia may be at increased risk of developing diabetes. In individuals with nonalcoholic fatty liver disease (NAFLD), sarcopenia is associated with the severity of fibrosis and steatosis. Previous studies have demonstrated that NAFLD is strongly associated with DM and sarcopenia.

AIM

To determine the relationship between skeletal muscle mass and DM in Chinese middle-aged and elderly men, and whether the association is affected by NAFLD.

METHODS

Skeletal muscle mass was calculated as appendicular skeletal muscle mass (ASM) in kg/body weight × 100%. Liver fat content (LFC) was measured using a quantitative ultrasound method.

RESULTS

As the ASM decreased, fasting blood glucose (FBG), 2-h postprandial blood glucose (2hBG), and LFC increased in both genders, as did the prevalence of DM and NAFLD. Spearman analysis showed that the ASM was negatively correlated with the FBG, 2hBG, and LFC. Stepwise logistic regression analysis showed that after adjustments, the ASM quartile was negatively associated with the presence of DM in males, but not in females. Subgroup analysis showed that the ASM quartiles remained negatively correlated with the presence of DM in the non-NAFLD population (including males and females), but no correlation was found between ASM quartiles and the presence of DM in the NAFLD population. When stratified by LFC quartiles, ASM was negatively correlated with the presence of DM in the first and second LFC quartiles in males.

CONCLUSION

Skeletal muscle mass loss was shown to be associated with the presence of DM in males, but not in females; NAFLD weakens this association. The results suggested that the stratified management of diabetes mellitus should be considered according to skeletal muscle mass and NAFLD.

Physical Exercise Potentially Targets Epicardial Adipose Tissue to Reduce Cardiovascular Disease Risk in Patients with Metabolic Diseases: Oxidative Stress and Inflammation Emerge as Major Therapeutic Targets

Excess epicardial adiposity, within a state of obesity and metabolic syndrome, is emerging as an important risk factor for the development of cardiovascular diseases (CVDs). Accordingly, increased epicardial fat thickness (EFT) implicates the exacerbation of pathological mechanisms involving oxidative stress and inflammation within the heart, which may accelerate the development of CVDs. This explains increased interest in targeting EFT reduction to attenuate the detrimental effects of oxidative stress and inflammation within the setting of metabolic syndrome. Here, we critically discuss clinical and preclinical evidence on the impact of physical exercise on EFT in correlation with reduced CVD risk within a setting of metabolic disease. This review also brings a unique perspective on the implications of oxidative stress and inflammation as major pathological consequences that link increased EFT to accelerated CVD risk in conditions of metabolic disease.

Subcutaneous Adipose Tissue Metabolic Function and Insulin Sensitivity in People With Obesity

We used stable isotope-labeled glucose and palmitate tracer infusions, a hyperinsulinemic-euglycemic clamp, positron emission tomography of muscles and adipose tissue after [18F]fluorodeoxyglucose and [15O]water injections, and subcutaneous adipose tissue (SAT) biopsy to test the hypotheses that 1) increased glucose uptake in SAT is responsible for high insulin-stimulated whole-body glucose uptake in people with obesity who are insulin sensitive and 2) putative SAT factors thought to cause insulin resistance are present in people with obesity who are insulin resistant but not in those who are insulin sensitive. We found that high insulin-stimulated whole-body glucose uptake in insulin-sensitive participants with obesity was not due to channeling of glucose into SAT but, rather, was due to high insulin-stimulated muscle glucose uptake. Furthermore, insulin-stimulated muscle glucose uptake was not different between insulin-sensitive obese and lean participants even though adipocytes were larger, SAT perfusion and oxygenation were lower, and markers of SAT inflammation, fatty acid appearance in plasma in relation to fat-free mass, and plasma fatty acid concentration were higher in the insulin-sensitive obese than in lean participants. In addition, we observed only marginal or no differences in adipocyte size, SAT perfusion and oxygenation, and markers of SAT inflammation between insulin-resistant and insulin-sensitive obese participants. Plasma fatty acid concentration was also not different between insulin-sensitive and insulin-resistant obese participants, even though SAT was resistant to the inhibitory effect of insulin on lipolysis in the insulin-resistant obese group. These data suggest that several putative SAT factors commonly implicated in causing insulin resistance are normal consequences of SAT expansion unrelated to insulin resistance.

α1-Antitrypsin A treatment attenuates neutrophil elastase accumulation and enhances insulin sensitivity in adipose tissue of mice fed a high-fat diet

Neutrophils accumulate in insulin-sensitive tissues during obesity and may play a role in impairing insulin sensitivity. The major serine protease expressed by neutrophils is neutrophil elastase (NE), which is inhibited endogenously by α1-antitrypsin A (A1AT). We investigated the effect of exogenous (A1AT) treatment on diet-induced metabolic dysfunction. Male C57Bl/6j mice fed a chow or a high-fat diet (HFD) were randomized to receive intraperitoneal injections three times weekly of either Prolastin (human A1AT; 2 mg) or vehicle (PBS) for 10 wk. Prolastin treatment did not affect plasma NE concentration, body weight, glucose tolerance, or insulin sensitivity in chow-fed mice. In contrast, Prolastin treatment attenuated HFD-induced increases in plasma and white adipose tissue (WAT) NE without affecting circulatory neutrophil levels or increases in body weight. Prolastin-treated mice fed a HFD had improved insulin sensitivity, as assessed by insulin tolerance test, and this was associated with higher insulin-dependent IRS-1 (insulin receptor substrate) and Akt^Ser473 phosphorylation, and reduced inflammation markers in WAT but not liver or muscle. In 3T3-L1 adipocytes, Prolastin reversed recombinant NE-induced impairment of insulin-stimulated glucose uptake and IRS-1 phosphorylation. Furthermore, PDGF mediated p-Akt^Ser473 activation and glucose uptake (which is independent of IRS-1) was not affected by recombinant NE treatment. Collectively, our findings suggest that NE infiltration of WAT during metabolic overload contributes to insulin resistance by impairing insulin-induced IRS-1 signaling.NEW & NOTEWORTHY Neutrophils accumulate in peripheral tissues during obesity and are critical coordinators of tissue inflammatory responses. Here, we provide evidence that inhibition of the primary neutrophil protease, neutrophil elastase, with α1-antitrypsin A (A1AT) can improve insulin sensitivity and glucose homeostasis of mice fed a high-fat diet. This was attributed to improved insulin-induced IRS-1 phosphorylation in white adipose tissue and provides further support for a role of neutrophils in mediating diet-induced peripheral tissue insulin resistance.

Impact of Cutaneous Blood Flow on NIR-DCS Measures of Skeletal Muscle Blood Flow Index

Near-infrared diffuse correlation spectroscopy (NIR-DCS) is an optical technique for estimating relative changes in skeletal muscle perfusion during exercise, but may be affected by changes in cutaneous blood flow, as photons emitted by the laser must first pass through the skin. Accordingly, the purpose of this investigation was to examine how increased cutaneous blood flow affects NIR-DCS blood flow index (BFI) at rest and during exercise using a passive whole-body heating protocol that increases cutaneous, but not skeletal muscle, perfusion in the uncovered limb. BFI and cutaneous perfusion (laser Doppler flowmetry) were assessed in 15 healthy young subjects before (e.g., rest) and during 5-minutes of moderate-intensity hand-grip exercise in normothermic conditions and after cutaneous blood flow was elevated via whole-body heating. Hyperthermia significantly increased both cutaneous perfusion (~7.3-fold; p≤0.001) and NIR-DCS BFI (~4.5-fold; p≤0.001). Although relative BFI (i.e., fold-change above baseline) exhibited a typical exponential increase in muscle perfusion during normothermic exercise (2.81±0.95), there was almost no change in BFI during hyperthermic exercise (1.43±0.44). A subset of 8 subjects were subsequently treated with intradermal injection of botulinum toxin-A (Botox) to block heating-induced elevations in cutaneous blood flow, which 1) nearly abolished the hyperthermia-induced increase in BFI, and 2) restored BFI kinetics during hyperthermic exercise to values that were not different from normothermic exercise (p=0.091). Collectively, our results demonstrate that cutaneous blood flow can have a substantial, detrimental impact on NIR-DCS estimates of skeletal muscle perfusion and highlight the need for technical and/or pharmacological advancements to overcome this issue moving forward.

Computed Tomography-Derived Myosteatosis and Metabolic Disorders

The role of ectopic adipose tissue infiltration into skeletal muscle (i.e., myosteatosis) for metabolic disorders has received considerable and increasing attention in the last 10 years. The purpose of this review was to evaluate and summarize existing studies focusing on computed tomography (CT)-derived measures of myosteatosis and metabolic disorders. There is consistent evidence that CT-derived myosteatosis contributes to dysglycemia, insulin resistance, type 2 diabetes mellitus, and inflammation, and, to some extent, dyslipidemia, independent of general obesity, visceral fat, and other relevant risk factors, suggesting that it may serve as a tool for metabolic risk prediction. Identification of which muscles should be examined, and the standardized CT protocols to be employed, are necessary to enhance the applicability of findings from epidemiologic studies of myosteatosis. Additional and longer longitudinal studies are necessary to confirm a role of myosteatosis in the development of type 2 diabetes mellitus, and examine these associations in a variety of muscles across multiple race/ethnic populations. Given the emerging role of myosteatosis in metabolic health, well-designed intervention studies are needed to investigate relevant lifestyle and pharmaceutical approaches.

Mechanisms linking endoplasmic reticulum (ER) stress and microRNAs to adipose tissue dysfunction in obesity

Over accumulation of lipids in adipose tissue disrupts metabolic homeostasis by affecting cellular processes. Endoplasmic reticulum (ER) stress is one such process affected by obesity. Biochemical and physiological alterations in adipose tissue due to obesity interfere with adipose ER functions causing ER stress. This is in line with increased irregularities in other cellular processes such as inflammation and autophagy, affecting overall metabolic integrity within adipocytes. Additionally, microRNAs (miRNAs), which can post-transcriptionally regulate genes, are differentially modulated in obesity. A better understanding and identification of such miRNAs could be used as novel therapeutic targets to fight against diseases. In this review, we discuss ways in which ER stress participates as a common molecular process in the pathogenesis of obesity-associated metabolic disorders. Moreover, our review discusses detailed underlying mechanisms through which ER stress and miRNAs contribute to metabolic alteration in adipose tissue in obesity. Hence, identifying mechanistic involvement of miRNAs-ER stress cross-talk in regulating adipose function during obesity could be used as a potential therapeutic approach to combat chronic diseases, including obesity.

Heterogeneity in insulin-stimulated glucose uptake among different muscle groups in healthy lean people and people with obesity

AIMS/HYPOTHESIS

It has been proposed that muscle fibre type composition and perfusion are key determinants of insulin-stimulated muscle glucose uptake, and alterations in muscle fibre type composition and perfusion contribute to muscle, and consequently whole-body, insulin resistance in people with obesity. The goal of the study was to evaluate the relationships among muscle fibre type composition, perfusion and insulin-stimulated glucose uptake rates in healthy, lean people and people with obesity.

METHODS

We measured insulin-stimulated whole-body glucose disposal and glucose uptake and perfusion rates in five major muscle groups (erector spinae, obliques, rectus abdominis, hamstrings, quadriceps) in 15 healthy lean people and 37 people with obesity by using the hyperinsulinaemic-euglycaemic clamp procedure in conjunction with [²H]glucose tracer infusion (to assess whole-body glucose disposal) and positron emission tomography after injections of [¹⁵O]H₂O (to assess muscle perfusion) and [¹⁸F]fluorodeoxyglucose (to assess muscle glucose uptake). A biopsy from the vastus lateralis was obtained to assess fibre type composition.

RESULTS

We found: (1) a twofold difference in glucose uptake rates among muscles in both the lean and obese groups (rectus abdominis: 67 [51, 78] and 32 [21, 55] μmol kg^-1 min^-1 in the lean and obese groups, respectively; erector spinae: 134 [103, 160] and 66 [24, 129] μmol kg^-1 min^-1, respectively; median [IQR]) that was unrelated to perfusion or fibre type composition (assessed in the vastus only); (2) the impairment in insulin action in the obese compared with the lean group was not different among muscle groups; and (3) insulin-stimulated whole-body glucose disposal expressed per kg fat-free mass was linearly related with muscle glucose uptake rate (r² = 0.65, p < 0.05).

CONCLUSIONS/INTERPRETATION

Obesity-associated insulin resistance is generalised across all major muscles, and is not caused by alterations in muscle fibre type composition or perfusion. In addition, insulin-stimulated whole-body glucose disposal relative to fat-free mass provides a reliable index of muscle glucose uptake rate.

Dysmetabolic adipose tissue in obesity: morphological and functional characteristics of adipose stem cells and mature adipocytes in healthy and unhealthy obese subjects

The way by which subcutaneous adipose tissue (SAT) expands and undergoes remodeling by storing excess lipids through expansion of adipocytes (hypertrophy) or recruitment of new precursor cells (hyperplasia) impacts the risk of developing cardiometabolic and respiratory diseases. In unhealthy obese subjects, insulin resistance, type 2 diabetes, hypertension, and obstructive sleep apnoea are typically associated with pathologic SAT remodeling characterized by adipocyte hypertrophy, as well as chronic inflammation, hypoxia, increased visceral adipose tissue (VAT), and fatty liver. In contrast, metabolically healthy obese individuals are generally associated with SAT development characterized by the presence of smaller and numerous mature adipocytes, and a lower degree of VAT inflammation and ectopic fat accumulation. The remodeling of SAT and VAT is under genetic regulation and influenced by inherent depot-specific differences of adipose tissue-derived stem cells (ASCs). ASCs have multiple functions such as cell renewal, adipogenic capacity, and angiogenic properties, and secrete a variety of bioactive molecules involved in vascular and extracellular matrix remodeling. Understanding the mechanisms regulating the proliferative and adipogenic capacity of ASCs from SAT and VAT in response to excess calorie intake has become a focus of interest over recent decades. Here, we summarize current knowledge about the biological mechanisms able to foster or impair the recruitment and adipogenic differentiation of ASCs during SAT and VAT development, which regulate body fat distribution and favorable or unfavorable metabolic responses.

Evaluation of Plasma AA/DHA+EPA Ratio in Obese Romanian Children

The aim of the study was to evaluate the plasma profile of arachidonic acid (AA), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA), as well to analyze the relationship of Omega 6/Omega 3 ratio with anthropo-metric parameters and insulin resistance markers.

Material and methods: Plasma levels of free fatty acids (FFAs) were measured using a high-throughput LC-MS AB Sciex4600 in 202 children (127 obese and 75 non-obese), age and sex-matched. Lipid and glucose profiles were assessed with current laboratory methods, while insulin resistance and beta-cell function were evaluated using HOMA-IR and HOMA-β respectively.

Results: In obese children, AA and AA/(DHA+EPA) ratio were significantly higher regardless of age and gender. In the lowest quartile of DHA, there was a clear trend for insulin resistance, with plasma insulin level, HOMA-IR, and HOMA-β significantly higher compared to the highest quartile of DHA. After adjustment for age and gender DHA remains a negative predictive factor for insulin resistance. Waist-to-height ratio (WHtR), a marker of visceral obesity was higher in children with a higher AA/(DHA+EPA) ratio.

Conclusions: In obese children, the AA is higher in concordance with insulin resistance. Additionally, children with a higher AA/(DHA+EPA) ratio have greater BMI, fat mass, waist circumference, and WHtR, important indicators of central adiposity, and cardio-metabolic disorders. LC/MS is a versatile tool for Omega ratio assessment, especially in children where the sample size is a limiting factor for metabolic and nutrition evaluation.

Insulin-Stimulated Muscle Glucose Uptake and Insulin Signaling in Lean and Obese Humans

PURPOSE

Skeletal muscle is the primary site for insulin-stimulated glucose disposal, and muscle insulin resistance is central to abnormal glucose metabolism in obesity. Whether muscle insulin signaling to the level of Akt/AS160 is intact in insulin-resistant obese humans is controversial.

METHODS

We defined a linear range of insulin-stimulated systemic and leg glucose uptake in 14 obese and 14 nonobese volunteers using a 2-step insulin clamp (Protocol 1) and then examined the obesity-related defects in muscle insulin action in 16 nonobese and 25 obese male and female volunteers matched for fitness using a 1-step, hyperinsulinemic, euglycemic clamp coupled with muscle biopsies (Protocol 2).

RESULTS

Insulin-stimulated glucose disposal (Si) was reduced by > 60% (P < 0.0001) in the obese group in Protocol 2; however, the phosphorylation of Akt and its downstream effector AS160 were not different between nonobese and obese groups. The increase in phosphorylation of Akt2 in response to insulin was positively correlated with Si for both the nonobese (r = 0.53, P = 0.03) and the obese (r = 0.55, P = 0.01) groups. Total muscle GLUT4 protein was 17% less (P < 0.05) in obese subjects.

CONCLUSIONS

We suggest that reduced muscle glucose uptake in obesity is not due to defects in the insulin signaling pathway at the level of Akt/AS160, which suggests there remain significant gaps in our knowledge of muscle insulin resistance in obesity. Our data imply that models of acute lipotoxicity do not replicate the pathophysiology of obesity.

Transient systemic inflammation in adult male mice results in underweight progeny

PROBLEM

While the testes represent an immune-privileged organ, there is evidence that systemic inflammation is accompanied by local inflammatory responses. We therefore examined whether transient systemic inflammation caused any inflammatory and functional consequences in murine testes.

METHOD OF STUDY

Using a single systemic administration of Toll-like receptor (TLR) agonists [lipopolysaccharide (LPS) or peptidoglycan (PG) or polyinosinic-polycytidylic acid (polyIC)] in young adult male mice, we assessed testicular immune-inflammatory landscape and reproductive functionality.

RESULTS

Our findings demonstrated a significant induction of testicular TNF-α, IL-1β and IL-6 transcripts within 24 h of TLR agonist injection. By day 6, these cytokine levels returned to baseline. While there was no change in caudal sperm counts at early time points, eight weeks later, twofold decrease in sperm count and reduced testicular testosterone levels were evident. When these mice were subjected to mating studies, no differences in mating efficiencies or litter sizes were observed compared with controls. Nonetheless, the neonatal weights of progeny from LPS/PG/polyIC-treated sires were significantly lower than controls. Postnatal weight gain up to three weeks was also slower in the progeny of LPS/polyIC-treated sires. Placental weights at 17.5 days post-coitum were significantly lower in females mated to LPS- and polyIC-treated males. Given this likelihood of an epigenetic effect, we found lower testicular levels of histone methyltransferase enzyme, mixed-lineage leukaemia-1, in mice given LPS/PG/polyIC 8 weeks earlier.

CONCLUSION

Exposure to transient systemic inflammation leads to transient local inflammation in the testes, with persistent sperm-mediated consequences for foetal development.

A Journey in Diabetes: From Clinical Physiology to Novel Therapeutics: The 2020 Banting Medal for Scientific Achievement Lecture

Insulin resistance and β-cell dysfunction are the core pathophysiological mechanisms of all hyperglycemic syndromes. Advances in in vivo investigative techniques have made it possible to quantify insulin resistance in multiple sites (skeletal and myocardial muscle, subcutaneous and visceral fat depots, liver, kidney, vascular tissues, brain and intestine), to clarify its consequences for tissue substrate selection, and to establish its relation to tissue perfusion. Physiological modeling of β-cell function has provided a uniform tool to measure β-cell glucose sensitivity and potentiation in response to a variety of secretory stimuli, thereby allowing us to establish feedbacks with insulin resistance, to delineate the biphasic time course of conversion to diabetes, to gauge incretin effects, and to identify primary insulin hypersecretion. As insulin resistance also characterizes several of the comorbidities of diabetes (e.g., obesity, hypertension, dyslipidemia), with shared genetic and acquired influences, the concept is put forward that diabetes is a systemic disease from the outset, actually from the prediabetic stage. In fact, early multifactorial therapy, particularly with newer antihyperglycemic agents, has shown that the burden of micro- and macrovascular complications can be favorably modified despite the rising pressure imposed by protracted obesity.

miR-223-3p as a potential biomarker and player for adipose tissue dysfunction preceding type 2 diabetes onset

Circulating microRNAs (miRNAs) have been proposed as biomarkers for type 2 diabetes (T2D). Adipose tissue (AT), for which dysfunction is widely associated with T2D development, has been reported as a major source of circulating miRNAs. However, the role of dysfunctional AT in the altered pattern of circulating miRNAs associated with T2D onset remains unexplored. Herein, we investigated the relationship between T2D-associated circulating miRNAs and AT function, as well as the role of preadipocytes and adipocytes as secreting cells of candidate circulating miRNAs. Among the plasma miRNAs related to T2D onset in the CORonary Diet Intervention with Olive oil and cardiovascular PREVention (CORDIOPREV) cohort, baseline miR-223-3p levels (diminished in patients who next developed T2D [incident-T2D]) were significantly related to AT insulin resistance (IR). Baseline serum from incident-T2D participants induced inflammation and IR in 3T3-L1 adipocytes. We demonstrated that tumor necrosis factor (TNF)-α inhibited miR-223-3p secretion while enhancing miR-223-3p intracellular accumulation in 3T3-L1 (pre)adipocytes. Overexpression studies showed that an intracellular increase of miR-223-3p impaired glucose and lipid metabolism in these cells. Our findings provide mechanistic insights into the alteration of circulating miRNAs preceding T2D, unveiling both preadipocytes and adipocytes as miR-223-3p-secreting cells and suggesting that inflammation promotes miR-223-3p intracellular accumulation, which might contribute to (pre)adipocyte dysfunction and body metabolic dysregulation.

Intermuscular Fat Content in Young Chinese Men With Newly Diagnosed Type 2 Diabetes: Based on MR mDIXON-Quant Quantitative Technique

OBJECTIVE

Skeletal muscle fat content is one of the important contributors to insulin resistance (IR), but its diagnostic value remains unknown, especially in the Chinese population. Therefore, we aimed to analyze differences in skeletal muscle fat content and various functional MRI parameters between diabetic patients and control subjects to evaluate the early indicators of diabetes. In addition, we aimed to investigate the associations among skeletal muscle fat content, magnetic resonance parameters of skeletal muscle function and IR in type 2 diabetic patients and control subjects.

METHODS

We enrolled 12 patients (age:29-38 years, BMI: 25-28 kg/m²) who were newly diagnosed with type 2 diabetes (intravenous plasma glucose concentration≥11.1mmol/l or fasting blood glucose concentration≥7.0mmol/l) together with 12 control subjects as the control group (age: 26-33 years, BMI: 21-28 kg/m²). Fasting blood samples were collected for the measurement of glucose, insulin, 2-hour postprandial blood glucose (PBG2h), and glycated hemoglobin (HbAlc). The magnetic resonance scan of the lower extremity and abdomen was performed, which can evaluate visceral fat content as well as skeletal muscle metabolism and function through transverse relaxation times (T2), fraction anisotropy (FA) and apparent diffusion coefficient (ADC) values.

RESULTS

We found a significant difference in intermuscular fat (IMAT) between the diabetes group and the control group (p<0.05), the ratio of IMAT in thigh muscles of diabetes group was higher than that of control group. In the entire cohort, IMAT was positively correlated with HOMA-IR, HbAlc, T2, and FA, and the T2 value was correlated with HOMA-IR, PBG2h and HbAlc (p<0.05). There were also significant differences in T2 and FA values between the diabetes group and the control group (p<0.05). According to the ROC, assuming 8.85% of IMAT as the cutoff value, the sensitivity and specificity of IMAT were 100% and 83.3%, respectively. Assuming 39.25ms as the cutoff value, the sensitivity and specificity of T2 value were 66.7% and 91.7%, respectively. All the statistical analyses were adjusted for age, BMI and visceral fat content.

CONCLUSION

Deposition of IMAT in skeletal muscles seems to be an important determinant for IR in type 2 diabetes. The skeletal muscle IMAT value greater than 8.85% and the T2 value greater than 39.25ms are suggestive of IR.

Effects of High-Intensity Exercise Training on Adipose Tissue Mass, Glucose Uptake and Protein Content in Pre- and Post-menopausal Women

The menopausal transition is accompanied by changes in adipose tissue storage, leading to an android body composition associated with increased risk of type 2 diabetes and cardiovascular disease in post-menopausal women. Estrogens probably affect local adipose tissue depots differently. We investigated how menopausal status and exercise training influence adipose tissue mass, adipose tissue insulin sensitivity and adipose tissue proteins associated with lipogenesis/lipolysis and mitochondrial function. Healthy, normal-weight pre- (n = 21) and post-menopausal (n = 20) women participated in high-intensity exercise training three times per week for 12 weeks. Adipose tissue distribution was determined by dual-energy x-ray absorptiometry and magnetic resonance imaging. Adipose tissue glucose uptake was assessed by positron emission tomography/computed tomography (PET/CT) by the glucose analog [18F]fluorodeoxyglucose ([18F]FDG) during continuous insulin infusion (40 mU·m⁻²·min⁻¹). Protein content associated with insulin signaling, lipogenesis/lipolysis, and mitochondrial function were determined by western blotting in abdominal and femoral white adipose tissue biopsies. The mean age difference between the pre- and the post-menopausal women was 4.5 years. Exercise training reduced subcutaneous (~4%) and visceral (~6%) adipose tissue masses similarly in pre- and post-menopausal women. Insulin-stimulated glucose uptake, assessed by [18F]FDG-uptake during PET/CT, was similar in pre- and post-menopausal women in abdominal, gluteal, and femoral adipose tissue depots, despite skeletal muscle insulin resistance in post- compared to pre-menopausal women in the same cohort. Insulin-stimulated glucose uptake in adipose tissue depots was not changed after 3 months of high-intensity exercise training, but insulin sensitivity was higher in visceral compared to subcutaneous adipose tissue depots (~139%). Post-menopausal women exhibited increased hexokinase and adipose triglyceride lipase content in subcutaneous abdominal adipose tissue. Physical activity in the early post-menopausal years reduces abdominal obesity, but insulin sensitivity of adipose tissue seems unaffected by both menopausal status and physical activity.

Oral L-glutamine rescues fructose-induced poor fetal outcome by preventing placental triglyceride and uric acid accumulation in Wistar rats

BACKGROUND

Metabolic adaptation of pregnant mothers is crucial for placental development and fetal growth/survival. However, evidence exists that indiscriminate consumption of fructose-enriched drink (FED) during pregnancy disrupts maternal-fetal metabolic tolerance with attendant adverse fetal outcomes. Glutamine supplementation (GLN) has been shown to exert a modulatory effect in metabolic disorders. Nevertheless, the effects of GLN on FED-induced poor fetal outcome, and in particular the impacts on placental uric acid/lipid accumulation are unknown. The present study was conducted to test the hypothesis that oral GLN improves fetal outcome by attenuating placental lipid accumulation and uric acid synthesis in pregnant rats exposed to FED.

MATERIALS AND METHODS

Pregnant Wistar rats (160-180 g) were randomly allotted to control, GLN, FED and FED + GLN groups (6 rats/group). The groups received vehicle by oral gavage, glutamine (1 g/kg) by oral gavage, fructose (10%; w/v) and fructose + glutamine, respectively, through gestation.

RESULTS

Data showed that FED during pregnancy caused placental inefficiency, reduced fetal growth, and caused insulin resistance with correspondent increase in fasting blood glucose and plasma insulin. FED also resulted in an increased placental triglyceride, total cholesterol and de novo uric acid synthesis by activating adenosine deaminase and xanthine oxidase activities. Moreover, FED during pregnancy led to increased lipid peroxidation, lactate production with correspondent decreased adenosine and glucose-6-phosphate dehydrogenase-dependent antioxidant defense. These alterations were abrogated by GLN supplementation.

CONCLUSION

These findings implicate that high FED intake during pregnancy causes poor fetal outcome via defective placental uric acid/triglyceride-dependent mechanism. The findings also suggest that oral GLN improves fetal outcome by ameliorating placental defects through suppression of uric acid/triglyceride accumulation.

Total-body PET Imaging: A New Frontier for the Assessment of Metabolic Disease and Obesity

Obesity and associated metabolic syndrome are a global public health issue. Understanding the pathophysiology of this systemic disease is of critical importance for the development of future therapeutic interventions to improve clinical outcomes. The multiorgan nature of the pathophysiology of obesity presents a unique challenge. Total-body PET imaging, either static or dynamic, provides a vital set of tools to study organ crosstalk. The visualization and quantification of tissue metabolic kinetics with total-body PET in health and disease provides essential information to better understand disease physiology and potentially develop diagnostic and therapeutic modalities.

[18F]FDG Uptake in Adipose Tissue Is Not Related to Inflammation in Type 2 Diabetes Mellitus

Purpose

2-deoxy-2-[¹⁸F]fluoro-d-glucose ([¹⁸F]FDG) uptake is a marker of metabolic activity and is therefore used to measure the inflammatory state of several tissues. This radionuclide marker is transported through the cell membrane via glucose transport proteins (GLUTs). The aim of this study is to investigate whether insulin resistance (IR) or inflammation plays a role in [¹⁸F]FDG uptake in adipose tissue (AT).

Procedures

This study consisted of an in vivo clinical part and an ex vivo mechanistic part. In the clinical part, [¹⁸F]FDG uptake in abdominal visceral AT (VAT) and subcutaneous AT (SAT) was determined using PET/CT imaging in 44 patients with early type 2 diabetes mellitus (T2DM) (age 63 [54–66] years, HbA1c [6.3 ± 0.4 %], HOMA-IR 5.1[3.1–8.5]). Plasma levels were measured with ELISA. In the mechanistic part, AT biopsies obtained from 8 patients were ex vivo incubated with [¹⁸F]FDG followed by autoradiography. Next, a qRT-PCR analysis was performed to determine GLUT and cytokine mRNA expression levels. Immunohistochemistry was performed to determine CD68⁺ macrophage infiltration and GLUT4 protein expression in AT.

Results

In vivo VAT [¹⁸F]FDG uptake in patients with T2DM was inversely correlated with HOMA-IR (r = − 0.32, p = 0.034), and positively related to adiponectin plasma levels (r = 0.43, p = 0.003). Ex vivo [¹⁸F]FDG uptake in VAT was not related to CD68⁺ macrophage infiltration, and IL-1ß and IL-6 mRNA expression levels. Ex vivo VAT [¹⁸F]FDG uptake was positively related to GLUT4 (r = 0.83, p = 0.042), inversely to GLUT3 (r = − 0.83, p = 0.042) and not related to GLUT1 mRNA expression levels.

Conclusions

In vivo [¹⁸F]FDG uptake in VAT from patients with T2DM is positively correlated with adiponectin levels and inversely with IR. Ex vivo [¹⁸F]FDG uptake in AT is associated with GLUT4 expression but not with pro-inflammatory markers. The effect of IR should be taken into account when interpreting data of [¹⁸F]FDG uptake as a marker for AT inflammation.

Electronic supplementary material

The online version of this article (10.1007/s11307-020-01538-0) contains supplementary material, which is available to authorized users.

Oral L-glutamine restores adenosine and glutathione content in the skeletal muscle and adipose tissue of insulin-resistant pregnant rats

OBJECTIVES

Mishandling of lipid and glycogen has been documented as a feature of metabolic tissues in insulin resistance-related disorders. However, reports exist detailing that L-glutamine (GLN) protects non-adipose tissue against the deleterious effects of metabolic disorders. Therefore, we hypothesized that GLN would protect skeletal muscle and adipose tissue against the deleterious effects of lipid and glycogen mishandlings by increasing adenosine and glutathione levels in pregnant rats exposed to fructose (FRU)-enriched drinks.

METHODS

Pregnant Wistar rats weighing 150 to 180 g were randomly assigned to control, GLN, FRU, and FRU + GLN groups (six rats/group). The groups received vehicle (P.o.), glutamine (1 g/kg), FRU (10%; w/v), and FRU + GLN, respectively, for 19 d.

RESULTS

Data show that FRU caused insulin resistance with corresponding increased blood glucose, circulating and pancreatic insulin levels, and lipid accumulation and glycogen depletion in skeletal muscle, but glycogen accumulation and a decreased lipid profile in adipose tissue. Adenosine and glutathione content decreased, whereas adenosine deaminase, xanthine oxidase, uric acid, and malondialdehyde concentrations increased in both tissues. In addition, glucose-6-phosphate dehydrogenase activity decreased in skeletal muscle but remained unaltered in adipose tissue. However, supplementation with GLN improved perturbed lipid and glycogen with a corresponding increase in adenosine and glutathione.

CONCLUSIONS

The present results collectively indicate that lipid and glycogen mishandlings caused by high gestational FRU intake result in the depletion of adenosine and glutathione in skeletal muscle and adipose tissue. These findings also suggest that L-glutamine protects against skeletal muscle and adipose tissue dysmetabolism by enhancing adenosine and glutathione.

Effects of a Hypercaloric and Hypocaloric Diet on Insulin-Induced Microvascular Recruitment, Glucose Uptake, and Lipolysis in Healthy Lean Men

OBJECTIVE

In mice fed a high-fat diet, impairment of insulin signaling in endothelium is an early phenomenon that precedes decreased insulin sensitivity of skeletal muscle, adipose tissue, and liver. We assessed in humans whether short-term overfeeding affects insulin-induced microvascular recruitment in skeletal muscle and adipose tissue before changes occur in glucose uptake and lipolysis. Approach and Results: Fifteen healthy males underwent a hypercaloric and subsequent hypocaloric diet intervention. Before, during, and after the hypercaloric diet, and upon return to baseline weight, all participants underwent (1) a hyperinsulinemic-euglycemic clamp to determine insulin-induced glucose uptake and suppression of lipolysis (2) contrast-enhanced ultrasonography to measure insulin-induced microvascular recruitment in skeletal muscle and adipose tissue. In addition, we assessed insulin-induced vasodilation of isolated skeletal muscle resistance arteries by pressure myography after the hypercaloric diet in study participants and controls (n=5). The hypercaloric diet increased body weight (3.5 kg; P<0.001) and fat percentage (3.5%; P<0.001) but did not affect glucose uptake nor lipolysis. The hypercaloric diet increased adipose tissue microvascular recruitment (P=0.041) and decreased the ratio between skeletal muscle and adipose tissue microvascular blood volume during hyperinsulinemia (P=0.019). Insulin-induced vasodilation of isolated skeletal muscle arterioles was significantly lower in participants compared with controls (P<0.001). The hypocaloric diet reversed all of these changes, except the increase in adipose tissue microvascular recruitment.

CONCLUSIONS

In lean men, short-term overfeeding reduces insulin-induced vasodilation of skeletal muscle resistance arteries and shifts the distribution of tissue perfusion during hyperinsulinemia from skeletal muscle to adipose tissue without affecting glucose uptake and lipolysis. Registration: URL: https://www.clinicaltrials.gov. Unique identifier: NCT02628301.

Usefulness of surrogate markers to determine insulin action in fat cells

BACKGROUND

Obesity is a major factor behind insulin resistance. The validity of simple biochemical surrogate measures to estimate insulin resistance at the fat cell level is unclear.

OBJECTIVE

To investigate if the surrogate measures HOMA-IR (glucose/insulin product) and Adipo-IR (fatty acids/insulin product) reflect insulin action on glucose/lipid metabolism in fat cells.

DESIGN

Insulin-induced lipogenesis and lipolysis inhibition (antilipolysis) in subcutaneous fat cells were investigated for sensitivity (reflecting receptor-near events) and responsiveness (i.e., maximum action reflecting distal post-receptor events) in 363 subjects. Results were compared with log₁₀ transformed values for HOMA-IR and Adipo-IR.

RESULTS

Individually, the four measures of in vitro insulin action on fat cells correlated significantly (p < 0.0001) but weakly with each other (adjusted r² 0.05-0.23). HOMA-IR and Adipo-IR correlated strongly with each other (adjusted r² = 0.81). Using Spearman or simple linear regression all in vitro measures except antilipolytic responsiveness expressed per lipid weight, correlated significantly with Adipo-IR or HOMA-IR (p values <0.0001). Similar relationships remained after combined correction for age, body mass index and sex. Together, the four in vitro measures explained 50% of the variability in HOMA-IR and ADIPO-IR (p < 0.0001). Receiver-operating characteristic analysis showed good sensitivity and specificity for Adipo-IR and HOMA-IR to detect combined insulin resistance of antilipolysis and lipogenesis in fat cells (area under the curve = 0.8).

CONCLUSIONS

Insulin action at the receptor and post-receptor levels on lipolysis and lipogenesis in fat cells correlates significantly with Adipo-IR and HOMA-IR. Both surrogate measures give similar information about insulin resistance of glucose and lipid metabolism in fat cells.

Glucose metabolism among obese and non-obese children of mothers with gestational diabetes

OBJECTIVES

Abdominal obesity is more closely associated with diabetes than general obesity in adults, however, it is unknown which kind of obesity is more closely associated with abnormal glucose metabolism in children.

RESEARCH DESIGN AND METHODS

We recruited 973 children (aged 3.08±1.06) of mothers with prior gestational diabetes mellitus (GDM). Children's height, weight, waist circumstance, fasting glucose and insulin were measured using standardized methods. Logistic regression models were used to assess the single and joint associations of general and abdominal obesity with the risks of hyperglycemia (the upper quartile of fasting glucose), insulin resistance (the upper quartile of homeostatic model assessment of insulin resistance (HOMA-IR)), and β-cell dysfunction (the lower quartile of HOMA-%β).

RESULTS

Compared with normal weight children, children with general overweight/obesity had higher levels of HOMA-IR and HOMA-%β, higher ORs for hyperglycemia (1.56, 95% CI 1.06 to 2.30) and insulin resistance (3.44, 95% CI 2.32 to 5.09), but a lower OR for β-cell dysfunction (0.65, 95% CI 0.41 to 1.04). Children with abdominal obesity had an increased risk of insulin resistance (2.54, 95% CI 1.71 to 3.76) but not hyperglycemia and β-cell dysfunction compared with children with normal waist circumstance. In the joint analyses, general overweight children with and without abdominal obesity had an increased risk of hyperglycemia and insulin resistance compared with normal weight children.

CONCLUSIONS

General obesity was more closely associated with abnormal glucose metabolism than abdominal obesity in children of mothers with GDM.

Effect of Rice Processing towards Lower Rapidly Available Glucose (RAG) Favors Idli, a South Indian Fermented Food Suitable for Diabetic Patients

The Asian food pattern primarily embraces rice and rice-based products, which mainly comprise 90% starch. Among these various food products, Idli is mostly prepared through fermentation. It has high palatability, and the rapid and highly digestible nature of the food product results in a higher post-glucose level in diabetic patients. A heat-treated Idli rice sample was prepared by roasting parboiled rice at the temperature range of 155 to 165 °C for 65 to 75 s. Idli/rice-based Dokala made from heat-treated rice is better when compared to untreated rice in terms of its microbiological profile and physiochemical properties. The proximate composition of heat-treated parboiled rice Idli/Rice Dokala showed slightly higher values than the untreated parboiled rice Idli/Rice Dokala, which reveals that it has marginally higher nutritive value. Determination of the Rapidly Available Glucose (RAG) and Slowly Available Glucose (SAG) values, SEM analysis, resistant starch analysis, microbial assay, and in vivo studies were performed to determine the glycemic index (GI) and glycemic load in normal and diabetic persons. Sensory analysis also proved that heat-treated Idli/Rice Dokala is superior to untreated based on the color, flavor, appearance, taste, and texture.

Insulin and Insulin Receptors in Adipose Tissue Development

Insulin is a major endocrine hormone also involved in the regulation of energy and lipid metabolism via the activation of an intracellular signaling cascade involving the insulin receptor (INSR), insulin receptor substrate (IRS) proteins, phosphoinositol 3-kinase (PI3K) and protein kinase B (AKT). Specifically, insulin regulates several aspects of the development and function of adipose tissue and stimulates the differentiation program of adipose cells. Insulin can activate its responses in adipose tissue through two INSR splicing variants: INSR-A, which is predominantly expressed in mesenchymal and less-differentiated cells and mainly linked to cell proliferation, and INSR-B, which is more expressed in terminally differentiated cells and coupled to metabolic effects. Recent findings have revealed that different distributions of INSR and an altered INSR-A:INSR-B ratio may contribute to metabolic abnormalities during the onset of insulin resistance and the progression to type 2 diabetes. In this review, we discuss the role of insulin and the INSR in the development and endocrine activity of adipose tissue and the pharmacological implications for the management of obesity and type 2 diabetes.