Insulin Sensitivity In Obesity Research Articles

1502-P: Adipose Tissue Protein Response and Insulin Sensitivity in Obesity

Dysregulation of adipose tissue (AT) lipolysis, a hallmark of obesity and type 2 diabetes, results in elevated postabsorptive and postprandial plasma free fatty acid (FFA) concentrations. This is thought to be due to adipose insulin resistance with regards to anti-lipolysis effects. Alterations in intracellular adipocyte pathways and/or proteins that mediate this phenomenon in humans are poorly understood. To test the hypothesis that impaired insulin signaling is associated with adipose insulin resistance measured whole body insulin sensitivity (the insulin concentration that suppresses palmitate flux by 50% (IC50 FFA)) in 12 lean, 7 lower body obese and 15 upper body obese (n=15) volunteers using a single step hyperinsulinemic-euglycemic clamp. We also measured adipose pAkt/Akt (a measure of insulin signaling) and hormone sensitive lipase (pHSL/HSL) (a measure of lipolysis protein regulation) in biopsies of abdominal and thigh adipose obtained before and during the insulin clamp were measured. Contrary to our hypothesis, there was a positive relationship between IC50 FFA and insulin clamp fold change of pAkt/Akt in thigh samples (ρ = 0.38, p <0.05) and no relationship for abdominal adipose samples. There was good correlation between abdominal and thigh adipose samples in the fractional change in pAkt/Akt in response to insulin clamp (ρ= 0.49, p < 0.01). IC50 FFA was correlated to fractional decrease in HSL phosphorylation in both abdominal (r = 0.36, p< 0.05) and thigh (r = 0.41, p <0.05) Surprisingly, fold changes of pAKT/AKT in response to insulin clamp were positively correlated to fold change of pHSL/HSL in abdominal adipose tissue (ρ= 0.41, p < 0.05) but not thigh samples. In conclusion we found that insulin resistance in adipose is not related to canonical insulin signaling responses but is related to lipase responses. Disclosure K.Lytle: None. M.D.Jensen: Other Relationship; Novo Nordisk, Elsevier. Funding National Institute of Diabetes and Digestive and Kidney Diseases (DK40484)

Comparison of Metabolic Response to Colonic Fermentation in Lean Youth vs Youth With Obesity

Pediatric obesity is a growing health care burden. Understanding how the metabolic phenotype of youth with obesity may modify the effect of intestinal fermentation on human metabolism is key to designing early intervention. To assess whether adiposity and insulin resistance in youth may be associated with colonic fermentation of dietary fibers and its production of acetate, gut-derived hormone secretion, and adipose tissue lipolysis. Cross-sectional study of youths aged 15 to 22 years with body mass index in the 25th to 75th percentile or higher than the 85th percentile for age and sex throughout the New Haven County community in Connecticut. Recruitment, studies, and data collection occurred from June 2018 to September 2021. Youths were assigned to a lean, obese insulin sensitive (OIS), or obese insulin resistant (OIR) group. Data were analyzed from April 2022 to September 2022. Participants consumed 20 g of lactulose during a continuous 10-hour sodium d3-acetate intravenous infusion to measure the rate of appearance of acetate in plasma. Plasma was obtained hourly to measure acetate turnover, peptide tyrosine tyrosine (PYY), ghrelin, active glucagon-like peptide 1 (GLP-1), and free fatty acids (FFA). A total of 44 youths participated in the study (median [IQR] age, 17.5 [16.0-19.3] years; 25 [56.8%] were female; 23 [52.3%] were White). Consequent to lactulose ingestion, there was a reduction of plasma FFA, an improvement of adipose tissue insulin sensitivity index, an increase in colonic acetate synthesis, and an anorexigenic response characterized by an increased plasma concentration of PYY and active GLP-1 and a reduction of ghrelin in the subgroups. Compared with the lean and OIS groups, the OIR group showed a less marked median (IQR) rate of acetate appearance (OIR: 2.00 [-0.86 to 2.69] μmol × kg-1 × min-1; lean: 5.69 [3.04 to 9.77] μmol × kg-1 × min-1; lean vs OIR P = .004; OIS: 2.63 [1.22 to 4.52] μmol × kg-1 × min-1; OIS vs OIR P = .09), a blunted median (IQR) improvement of adipose insulin sensitivity index (OIR: 0.043 [ 0.006 to 0.155]; lean: 0.277 [0.220 to 0.446]; lean vs OIR P = .002; OIS: 0.340 [0.048 to 0.491]; OIS vs OIR P = .08), and a reduced median (IQR) PYY response (OIR: 25.4 [14.8 to 36.4] pg/mL; lean: 51.3 [31.6 to 83.3] pg/mL; lean vs OIR P = .002; OIS: 54.3 [39.3 to 77.2] pg/mL; OIS vs OIR P = .011). In this cross-sectional study, lean, OIS, and OIR youth demonstrated different associations between colonic fermentation of indigestible dietary carbohydrates and the metabolic response, with OIR youth showing minimal metabolic modifications as compared with the other 2 groups. ClinicalTrials.gov Identifier: NCT03454828.

Adipose-specific deletion of the cation channel TRPM7 inhibits TAK1 kinase-dependent inflammation and obesity in male mice

Chronic inflammation of white adipose tissue is a key link between obesity and the associated metabolic syndrome. Transient receptor potential melastatin-like 7 (TRPM7) is known to be related to inflammation; however, the role of TRPM7 in adipocyte phenotype and function in obesity remains unclear. Here, we observe that the activation of adipocyte TRPM7 plays an essential role in pro-inflammatory responses. Adult male mice are used in our experiments. Adipocyte-specific deficiency in TRPM7 attenuates the pro-inflammatory phenotype, improves glucose homeostasis, and suppresses weight gain in mice fed a high-fat diet. Mechanistically, the pro-inflammatory effect of TRPM7 is dependent on Ca2+ signaling. Ca2+ influx initiated by TRPM7 enhances transforming growth factor-β activated kinase 1 activation via the co-regulation of calcium/calmodulin-dependent protein kinase II and tumor necrosis factor receptor-associated factor 6, leading to exacerbated nuclear factor kappa B signaling. Additionally, obese mice treated with TRPM7 inhibitor are protected against obesity and insulin resistance. Our results demonstrate TRPM7 as a factor in the development of adipose inflammation that regulates insulin sensitivity in obesity.

Fibroblast Growth Factor 6 Promotes Adipocyte Progenitor Cell Proliferation for Adipose Tissue Homeostasis.

The de novo differentiation of hyperplastic adipocytes from adipocyte progenitor cells (APCs) is accompanied by the reduction of adipose tissue fibrosis and inflammation and improvement in insulin sensitivity in obesity and aging. However, the regulators of APC proliferation are poorly understood. Here, we show that fibroblast growth factor 6 (FGF6) secreted by adipocytes controls PDGFRa+ APC proliferation via extracellular signal-regulated kinase (ERK) signaling. Specific FGF6 overexpression in inguinal white adipose tissue (iWAT) improved the signs of high-fat diet- or aging-induced adipose hypertrophy and insulin resistance. Conversely, chronic FGF6 expression blockade in iWAT, mediated by a neutralizing antibody or Fgf6 expression deficiency, impaired adipose tissue expansion and glucose tolerance. Overall, our data suggest that FGF6 acts as a proliferative factor for APCs to maintain fat homeostasis and insulin sensitivity.

아이스플랜트 추출물의 3T3-L1 지방세포 내 TNF-α 유도 염증 및 인슐린 저항성 개선 효과

Obesity is classified as a low-grade chronic inflammatory disease. Obesity-induced inflammation is associated with the development of insulin resistance (IR). In this study, we investigated the effects of Mesembryanthemum crystallinum extract (MCE) on tumor necrosis factor-alpha (TNF-α)-induced inflammation and IR in 3T3-L1 adipocytes, as well as underlying mechanisms. Lipolysis was monitored by oil red O staining. Glucose uptake was measured by 2-deoxyglucose (2-DG). The production of cytokines and adiponectin was evaluated using enzyme-linked immunosorbent assay (ELISA). Protein expression was measured using western blotting. IR was induced in differentiated 3T3-L1 adipocytes by treatment with TNF-α. MCE treatment decreased lipolysis while increasing adiponectin production. MCE inhibited the production of pro-inflammatory cytokines such as interleukn (IL)-6 and monocyte chemoattractant protein (MCP)-1, as well as the Nuclear factor-κB (NF-κB) translocation. Additionally, MCE increased glucose uptake, prevented the protein expression of phosphorylated insulin receptor supstrate (IRS) and increased the protein expression of Glucose Transporter Type 4 (GLUT4) in a dose-dependent manner. These results demonstrate the potential of MCE in improving chronic inflammation and insulin sensitivity in obesity. Therefore, MCE can be used as a novel candidate for developing functional foods.

197-LB: Adipocyte ZAG Improves Obesity-Triggered Insulin Resistance by Reshaping Macrophages Populations in Adipose Tissue

Adipose tissues macrophages (ATMs) serve as critical effectors in the mediating occurrence of metabolic inflammation to impact whole-body insulin sensitivity in obesity. Discovering the key adipokines mediating crosstalk of adipocyte-macrophage and understanding the molecular mechanism of ATMs polarization and function have become hot topic issues in the immunometabolism fields. Zinc-α2-glycoprotein (ZAG) as an anti-inflammatory adipokines plays important roles in obesity-related metabolic diseases. We attempt to explore the precise role of adipose ZAG in metabolic inflammation and obesity-associated insulin resistance. Here we showed that Omental ZAG was positively associated with insulin sensitivity and M2 macrophages markers. ZAG-specific ablation in adipocyte aggravated insulin resistance and adipose tissues inflammation as evidenced by enhanced M1 macrophages proportion and inhibited AKT signaling pathway in mice fed with a high-fat diet. ZAG overexpression attenuated insulin resistance and accumulation of pro-inflammatory macrophages. Exogenous ZAG inhibits PA-induced M1 macrophage polarization via β3-AR/PKA/STAT3 signaling in RAW264.7 macrophages. These findings suggest that adipocyte ZAG maintains insulin sensitivity via the cross talk with adipose-resident macrophages. Keywords: ZAG; inflammation; insulin resistance; obesity; adipose tissue macrophages Disclosure X. Xiao: None. Z. Liao: None. Y. Wang: None. X. Qi: None. Funding National Natural Science Foundation of China (82070873, 82000813) , Natural Science Foundation of Hunan province (2020JJ8097, 2021JJ40496) and Major special projects of Hunan provincial health and family planning commission (A2017011)

Macrophage activation marker sCD163 is associated with liver injury and hepatic insulin resistance in obese patients before and after Roux-en-Y gastric bypass.

BackgroundMacrophages are associated with metabolic complications to obesity including fatty liver disease and impaired hepatic and muscle insulin sensitivity (IS). Bariatric surgery induces weight loss and improves IS. We investigated associations between the macrophage activation marker soluble (s)CD163, alanine‐aminotransferase (ALT), and IS before and after Roux‐en‐Y Gastric Bypass (RYGB).MethodsWe analyzed sCD163 from 10 type 2 diabetes (T2D) and 10 obese patients with normal glucose tolerance (NGT) undergoing RYGB for associations with hepatic, adipose tissue, and muscle IS and ALT after 1‐week, 3, and 12 months postoperatively. IS was evaluated by hyperinsulinemic‐euglycemic clamp in combination with glucose tracer technique.ResultsPreoperative sCD163 correlated with ALT (r = 0.58, p = 0.007) and tended to associate inversely with hepatic (r = −0.39, p = 0.1) and adipose tissue (r = −0.39, p = 0.09), but not muscle IS. Following RYGB, sCD163 decreased significantly in all patients. The decrease in sCD163 during the first 3 months correlated inversely with the improvement of hepatic IS (r = −0.65, p = 0.01) and tended to be associated with changes in muscle IS (r = −0.45, p = 0.09). After 3 months sCD163 remained associated with ALT (r = 0.75, p < 0.001) and inversely with hepatic IS (r = −0.39, p = 0.1), but not muscle or adipose tissue IS. One year after RYGB, sCD163 correlated with ALT (r = 0.61, p = 0.007), but not with hepatic, adipose tissue, or muscle IS.ConclusionMacrophage activation is associated with liver injury and hepatic IS in obese patients. Improvements in these measures correlate during the first 3 months following RYGB, supporting a link between macrophages and hepatic IS in severe obesity and diabetes.

Effects of Weight Loss on Adipose and Muscular Neuropilin 1 mRNA Expression in Obesity: Potential Implication in SARS-CoV-2 Infections?

Introduction: Neuropilin 1 (NRP-1) is a novel co-receptor promoting SARS-CoV-2 infectivity. Animal data indicate a role in trans-endothelial lipid transport and storage. As human data are sparse, we aimed to assess the role of NRP-1 in 2 metabolic active tissues in human obesity and in the context of weight loss-induced short- and long-term metabolic changes. Methods: After a standardized 12-week weight reduction program, 143 subjects (age >18; body mass index ≥27 kg/m², 78% female) were randomized to a 12-month lifestyle intervention or a control group using a stratified randomization scheme. This was followed by 6-month follow-up without any intervention. Phenotyping was performed before and after weight loss, after 12-month intervention and after subsequent 6 months of follow-up. Tissue-specific insulin sensitivity was estimated by HOMA-IR (whole body and mostly driven by liver), insulin sensitivity index (ISI)_Clamp (predominantly skeletal muscle), and free fatty acid (FFA) suppression during hyperinsulinemic-euglycemic clamp (FFA_Supp) (predominantly adipose tissue). NRP-1 mRNA expression was measured in subcutaneous adipose tissue (NRP-1_AT) and skeletal muscle (NRP-1_SM) before and after weight loss. Results: NRP-1 was highly expressed in adipose tissue (7,893 [7,303–8,536] counts), but neither NRP-1_AT nor NRP-1_SM were related to estimates of obesity. Higher NRP-1_AT was associated with stronger FFA_Supp (r = −0.343, p = 0.003) and a tendency to higher ISI_Clamp (r = 0.202, p = 0.085). Weight loss induced a decline of NRP-1_AT but not NRP-1_SM. This was more pronounced in subjects with stronger reduction of adipose ACE-2 mRNA expression (r = 0.250; p = 0.032) but was not associated with short- and long-term improvement of FFA_Supp and ISI_Clamp. Conclusion: NRP-1_AT is related to adipose insulin sensitivity in obesity. Weight loss-induced decline of NRP-1_AT seems not to be involved in metabolic short- and long-term improvements after weight loss. However, weight loss-induced reduction of both NRP-1_AT and ACE-2_AT indicates a lower susceptibility of adipose tissue for SARS-CoV-2 after body weight reduction.

Orexin receptors 1 and 2 in serotonergic neurons differentially regulate peripheral glucose metabolism in obesity

The wake-active orexin system plays a central role in the dynamic regulation of glucose homeostasis. Here we show orexin receptor type 1 and 2 are predominantly expressed in dorsal raphe nucleus-dorsal and -ventral, respectively. Serotonergic neurons in ventral median raphe nucleus and raphe pallidus selectively express orexin receptor type 1. Inactivation of orexin receptor type 1 in serotonin transporter-expressing cells of mice reduced insulin sensitivity in diet-induced obesity, mainly by decreasing glucose utilization in brown adipose tissue and skeletal muscle. Selective inactivation of orexin receptor type 2 improved glucose tolerance and insulin sensitivity in obese mice, mainly through a decrease in hepatic gluconeogenesis. Optogenetic activation of orexin neurons in lateral hypothalamus or orexinergic fibers innervating raphe pallidus impaired or improved glucose tolerance, respectively. Collectively, the present study assigns orexin signaling in serotonergic neurons critical, yet differential orexin receptor type 1- and 2-dependent functions in the regulation of systemic glucose homeostasis.

Relationship between insulin-sensitive obesity and retinal microvascular abnormalities.

Obesity and insulin resistance (IR) are risk factors for microvascular disease (MVD). Whether insulin-sensitive obese individuals are at higher risk for MVD is still debated. We aimed to investigate whether insulin-sensitive obesity is associated with retinal microvascular abnormalities. This cross-sectional study recruited a total of 8,313 participants (3,604 males and 4,709 females) aged 21 years or older from 13 villages in rural area and 8 communities in urban area in Fujian province in China between 2011 to 2012. Participants were categorized by insulin-sensitive/-resistant and general/ abdominal obese status. IR was defined as homeostasis model assessment of IR >1.99 (75% percentile). Direct ophthalmoscopic examination was used to diagnose MVD, which was defined as the presence of retinal microvascular abnormalities. Among the older subjects (aged 65-79 years), those who were obese had a markedly higher risk for MVD, both in insulin-sensitive [odds ratio (OR): 2.259, 95% confidence interval (CI): 1.041-4.904, P=0.039] and insulin-resistant (OR: 2.356, 95% CI: 1.064-5.218, P=0.035) individuals. Additionally, insulinsensitive/-resistant abdominal obesity in middle-aged people showed an increased risk for prevalent MVD in women (OR: 2.061, 3.322; 95% CI: 1.004-4.233, 1.645-6.709; P values: 0.049, <0.001). In this study, obesity was closely related to an elevated higher risk of MVD, regardless of IR, especially in older people and abdominally obese middle-aged women. Obesity may be similar to diabetes mellitus, with chronic complications that not only cause cardiovascular diseases but also MVD. Direct ophthalmoscopy may be a noninvasive and meaningful method of early screening for obesity-related MVD. Insulin-sensitive obesity, like impaired glucose tolerance, is a pre-existing state of insulin resistant obesity.

Obesity-related changes in the vascular actions of insulin

Over the past 2 to 3 decades, research has focused on the changes in the vascular effects of insulin occurring in insulin resistant states like obesity. Consistent evidence indicates that obesity results in reduced endothelial release of nitric oxide in response to insulin, associated with concomitant enhancement in the production of endothelin-1. More recent work has pointed toward reduced vascular permeability and changes in the physical-chemical characteristics of the perivascular extracellular matrix as additional mechanisms of impaired insulin sensitivity in obesity. All these perturbations are important, because they contribute to impaired delivery of insulin itself and metabolic substrates to the target tissues and may play a role in the development of both diabetes and vascular damage. This review will describe the physiological vascular actions of insulin and their changes in obesity, focusing on some established pathophysiological determinants of the derangement of vascular insulin signaling, such as the lipid overflow from expanded fat depots and signals originating from inflamed obese adipose tissue (both distant and perivascular). Also, it will outline novel evidence underscoring the contribution of dysregulated adipokine secretion and changes in intestinal permeability and gut microbiome. Finally, it will touch upon some unresolved issues, such as the potential role of vascular insulin resistance in obesity-driven adipose tissue remodeling, and will discuss perspectives for future studies, regarding in particular possible therapeutic strategies with translational implications for the patients care.

MiR-30a targets gene networks that promote browning of human and mouse adipocytes.

MicroRNA-30a (miR-30a) impacts adipocyte function, and its expression in white adipose tissue (WAT) correlates with insulin sensitivity in obesity. Bioinformatic analysis demonstrates that miR-30a expression contributes to 2% of all miRNA expression in human tissues. However, molecular mechanisms of miR-30a function in fat cells remain unclear. Here, we expanded our understanding of how miR-30a expression contributes to antidiabetic peroxisome proliferator-activated receptor-γ (PPARγ) agonist activity and metabolic functions in adipocytes. We found that WAT isolated from diabetic patients shows reduced miR-30a levels and diminished expression of the canonical PPARγ target genes ADIPOQ and FABP4 relative to lean counterparts. In human adipocytes, miR-30a required PPARγ for maximal expression, and the PPARγ agonist rosiglitazone robustly induced miR-30a but not other miR-30 family members. Transcriptional activity studies in human adipocytes also revealed that ectopic expression of miR-30a enhanced the activity of rosiglitazone coupled with higher expression of fatty acid and glucose metabolism markers. Diabetic mice that overexpress ectopic miR-30a in subcutaneous WAT display durable reductions in serum glucose and insulin levels for more than 30 days. In agreement with our in vitro findings, RNA-seq coupled with Gene Set Enrichment Analysis (GSEA) suggested that miR-30a enabled activation of the beige fat program in vivo, as evidenced by enhanced mitochondrial biogenesis and induction of UCP1 expression. Metabolomic and gene expression profiling established that the long-term effects of ectopic miR-30a expression enable accelerated glucose metabolism coupled with subcutaneous WAT hyperplasia. Together, we establish a putative role of miR-30a in mediating PPARγ activity and advancing metabolic programs of white to beige fat conversion.

SUN-LB103 The Relationship Between Alcohol Consumption Patterns and Insulin Sensitivity in Obesity

BACKGROUNDThe effects of alcohol intake on insulin sensitivity have produced conflicting results with both beneficial and adverse effects observed. This study aimed to compare the relationship between patterns of alcohol consumption and insulin sensitivity in obese Veterans. METHODSWe performed a cross-sectional study of obese (BMI 30.0-45.0 kg/m2), nondiabetic U.S. Military Veterans without active mental health diagnoses, including no report of dependent alcohol use within the last 12 months. Alcohol exposure over the previous 12 months (mos) was assessed using a study-developed questionnaire and Michigan Alcoholism Screening Test (MAST). Fasting insulin, glucose, and a 75gm OGTT were completed to determine Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) and prediabetes (preDM) score of 0, 1, or 2 based on fulfilling 0, 1, or at least 2 of the ADA criteria for preDM, respectively. Linear regression was used to assess for associations between measures of insulin resistance and alcohol consumption; unstandardized β and p-value are reported for variable of interest. RESULTS104 Veterans participated (66% males; 44±8years (range: 25-60); BMI 36±4kg/m2 (range: 29-45); 53% White, 46% African American, 2% Alaskan/Native American, 1% Other). 83 participants reported any alcohol intake in the previous 12 mos and neither preDM score (p=0.57) nor HOMA-IR (p=0.14) were predicted by this question. PreDM score groups were similar in gender, BMI, and weight, but age predicted both preDM score (r2=0.09, β=0.025, p=0.006) and HOMA-IR (r2=0.05, β=-0.09, p=0.034); therefore, all regressions were adjusted for age. There was a negative association between the number of days of alcohol intake with HOMA-IR (β=-0.271, p=0.037) but no association occurred with preDM score (p=0.15). Fewer days of binge drinking was associated with higher HOMA-IR (β= -0.342, p=0.058) and preDM score (β=-0.075, p=0.05). There was no significant association between total quantity of alcohol intake and HOMA-IR (p=0.13) nor preDM score (p=0.15). There was no association between MAST score and HOMA-IR (p=0.7) or preDM score (p=0.3). CONCLUSIONIn our cohort of obese, non-alcohol dependent Veterans, the reported number of days of alcohol intake and days of binge drinking in the previous 12 mos were lower in those with markers of insulin resistance. These results suggest that drinking patterns among obese patients may have unique effects on insulin sensitivity that warrant further investigation.

Hypoxia and exercise interactions on skeletal muscle insulin sensitivity in obese subjects with metabolic syndrome: results of a randomized controlled trial.

Physical activity improves insulin sensitivity in obesity. Hypoxia training is claimed to augment this effect. We tested the hypothesis that normobaric hypoxia training would improve insulin sensitivity in obese patients with metabolic syndrome. In a randomized controlled trial, 23 obese men with metabolic syndrome who were not informed of the FiO2 conditions underwent a 6-week physical exercise intervention under ambient (n = 11; FiO2 21%) conditions or hypoxia (n = 12; FiO2 15%) using a normobaric hypoxic chamber. Three 60-min sessions of interval training were performed each week at 60% of individual V̇O2max. Assessment of myocellular insulin sensitivity by euglycemic hyperinsulinemic clamp was performed in 21 of these subjects before and after 6 weeks of training. Comprehensive phenotyping also included biopsies of subcutaneous adipose tissues. The intermittent moderate physical exercise protocol did not substantially change the myocellular insulin sensitivity within 6 weeks under normoxic conditions (ISIClamp: 0.035 (IQR 0.016-0.075) vs. 0.037 (IQR 0.026-0.056) mg* kg-1 *min-1/(mU* l-1); p = 0.767). In contrast, ISIClamp improved during hypoxia training (0.028 (IQR 0.018-0.035) vs. 0.038 (IQR 0.024-0.060) mg * kg-1 *min-1/(mU *l-1); p < 0.05). Between group comparison of ISIClamp change revealed a small difference between groups (Cohen's d = 0.26). Within the hypoxic group, improvement of ISIClamp during training was associated with individual increase of circulating vascular endothelial growth factor (VEGF) levels (r = 0.678, p = 0.015), even if mean VEGF levels were not modified by any training condition. Atrial natriuretic peptide (ANP) system components were not associated with increased ISIClamp during hypoxic training. Physical training under hypoxic conditions could partially augment the favorable effects of exercise alone on myocellular insulin sensitivity in obese men with metabolic syndrome. Concomitant changes in VEGF might represent an underlying pathophysiological mechanism.

Metabolic signature of obesity-associated insulin resistance and type 2 diabetes

BackgroundObesity is associated with an increased risk of insulin resistance and type 2 diabetes mellitus (T2DM). However, some obese individuals maintain their insulin sensitivity and exhibit a lower risk of associated comorbidities. The underlying metabolic pathways differentiating obese insulin sensitive (OIS) and obese insulin resistant (OIR) individuals remain unclear.MethodsIn this study, 107 subjects underwent untargeted metabolomics of serum samples using the Metabolon platform. Thirty-two subjects were lean controls whilst 75 subjects were obese including 20 OIS, 41 OIR, and 14 T2DM individuals.ResultsOur results showed that phospholipid metabolites including choline, glycerophosphoethanolamine and glycerophosphorylcholine were significantly altered from OIS when compared with OIR and T2DM individuals. Furthermore, our data confirmed changes in metabolic markers of liver disease, vascular disease and T2DM, such as 3-hydroxymyristate, dimethylarginine and 1,5-anhydroglucitol, respectively.ConclusionThis pilot data has identified phospholipid metabolites as potential novel biomarkers of obesity-associated insulin sensitivity and confirmed the association of known metabolites with increased risk of obesity-associated insulin resistance, with possible diagnostic and therapeutic applications. Further studies are warranted to confirm these associations in prospective cohorts and to investigate their functionality.

Mitochondrial Activity and Skeletal Muscle Insulin Resistance in Kidney Disease

Insulin resistance is a key feature of the metabolic syndrome, a cluster of medical disorders that together increase the chance of developing type 2 diabetes and cardiovascular disease. In turn, type 2 diabetes may cause complications such as diabetic kidney disease (DKD). Obesity is a major risk factor for developing systemic insulin resistance, and skeletal muscle is the first tissue in susceptible individuals to lose its insulin responsiveness. Interestingly, lean individuals are not immune to insulin resistance either. Non-obese, non-diabetic subjects with chronic kidney disease (CKD), for example, exhibit insulin resistance at the very onset of CKD, even before clinical symptoms of renal failure are clear. This uraemic insulin resistance contributes to the muscle weakness and muscle wasting that many CKD patients face, especially during the later stages of the disease. Bioenergetic failure has been associated with the loss of skeletal muscle insulin sensitivity in obesity and uraemia, as well as in the development of kidney disease and its sarcopenic complications. In this mini review, we evaluate how mitochondrial activity of different renal cell types changes during DKD progression, and discuss the controversial role of oxidative stress and mitochondrial reactive oxygen species in DKD. We also compare the involvement of skeletal muscle mitochondria in uraemic and obesity-related muscle insulin resistance.

Identification of biomarkers, pathways and potential therapeutic agents for white adipocyte insulin resistance using bioinformatics analysis

ABSTRACTFor the better understanding of insulin resistance (IR), the molecular biomarkers in IR white adipocytes and its potential mechanism, we downloaded two mRNA expression profiles from Gene Expression Omnibus (GEO). The white adipocyte samples in two databases were collected from the human omental adipose tissue of IR obese (IRO) subjects and insulin-sensitive obese (ISO) subjects, respectively. We identified 86 differentially expressed genes (DEGs) between the IRO and ISO subjects using limma package in R software. Gene Set Enrichment Analysis (GSEA) provided evidence that the most gene sets enriched in kidney mesenchyme development in the ISO subjects, as compared with the IRO subjects. The Gene Ontology (GO) analysis indicated that the most significantly enriched in cellular response to interferon-gamma. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that the DEGs were most significantly enriched in cytokine-cytokine receptor interaction. Protein–Protein Interaction (PPI) network was performed with the STRING, and the top 10 hub genes were identified with the Cytohubba. CMap analysis found several small molecular compounds to reverse the altered DEGs, including dropropizine, aceclofenac, melatonin, and so on. Our outputs could empower the novel potential targets to treat omental white adipocyte insulin resistance, diabetes, and diabetes-related diseases.

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-/β-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-/β-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-/β-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.

Adipose tissue oxygenation is associated with insulin sensitivity independently of adiposity in obese men and women.

Adipose tissue (AT) dysfunction contributes to the pathophysiology of insulin resistance and type 2 diabetes. Previous studies have shown that altered AT oxygenation affects adipocyte functionality, but it remains to be elucidated whether altered AT oxygenation is more strongly related to obesity or insulin sensitivity. In the present study, we tested the hypothesis that AT oxygenation is associated with insulin sensitivity rather than adiposity in humans. Thirty-five lean and obese individuals (21 men and 14 women, aged 40-65 years) with either normal or impaired glucose metabolism participated in a cross-sectional single-centre study. We measured abdominal subcutaneous AT oxygenation, body composition and insulin sensitivity. AT oxygenation was higher in obese insulin resistant as compared to obese insulin sensitive (IS) individuals with similar age, body mass index and body fat percentage, both in men and women. No significant differences in AT oxygenation were found between obese IS and lean IS men. Moreover, AT oxygenation was positively associated with insulin resistance (r = 0.465; P = .005), even after adjustment for age, sex and body fat percentage (standardized β = 0.479; P = .005). In conclusion, abdominal subcutaneous AT oxygenation is associated with insulin sensitivity both in men and women, independently of adiposity. AT oxygenation may therefore be a promising target to improve insulin sensitivity.

MiR-221 negatively regulates inflammation and insulin sensitivity in white adipose tissue by repression of sirtuin-1 (SIRT1).

It is well known that obesity-induced white adipose tissue inflammation is an important reason for insulin-resistance and type 2 diabetes mellitus. Sirtuin-1 (SIRT1) is an important regulator of inflammtion response pathways in white adipose tissue. Here, we found that miR-221 negatively regulated SIRT1 in white adipose tissue during inflammation and HFD-induced obesity. MiR-221 is a putative oncogene which has been found overexpressed in a number of human tumors. Recently, it has also found that miR-221 was increased in obese adipose tissue and may be involved in inflammation and insulin-resistance. However the specific mechanism remains to be elucidated. In our present study, we found that overexpression of miR-221 decreased the protein abundance of SIRT1 and caused inflammation and insulin-resistance in differentiated 3T3-L1 cells. Conversely, miR-221 inhibition increased the protein levels, ameliorated inflammation, and improved insulin sensitivity. Moreover, inhibition of SIRT1 by EX527 significantly diminished the downregulation of the inflammation and insulin-resistance levels induced by the miR-221 inhibitor. In conclusion, our data suggest that miR-221 promotes white adipose tissue inflammation and decreases insulin sensitivity in obesity, at least in part, through suppressing SIRT1.