Sex differences in insulin regulation of skeletal muscle glycogen synthase and changes during weight loss and exercise in adults.

OBJECTIVE: The authors sought to understand sex differences in muscle metabolism in 73 older men and women. METHODS: Body composition, VO2max, and insulin sensitivity (M) by 3-hour hyperinsulinemic-euglycemic clamp with vastus lateralis muscle biopsies were measured. RESULTS: Women had lower body weight, VO2max, and fat-free mass than men. Men had lower M, lower change (insulin minus basal) in muscle glycogen synthase (GS) activity, and lower change in AKT protein expression than women. M was associated with the change (insulin-basal) in GS activity and the change in AKT protein expression. Sex differences (n = 60) were tested with 6-month weight loss or 3×/week aerobic exercise training. The postintervention minus preintervention change (insulin-basal) (∆∆) in GS activity (fractional, independent, total) was higher in men than women in the weight loss group and ∆∆ in GS fractional activity was higher in women than men in the aerobic exercise group. In all participants, ∆∆ in GS fractional and independent activities was related to ∆∆ in AKT expression and glycogen content. CONCLUSIONS: Sex differences in insulin sensitivity may be explained at the cellular muscle level, and to improve skeletal muscle insulin action in older adults, it may be necessary to recommend different behavioral strategies depending on the individual's sex.

Hyperglycemic Clamp and Hypoglycemic Clamp in Conscious Mice.

Diabetes mellitus (DM) is caused by insufficient insulin release from the pancreatic ß-cells (Type1 DM) and insulin sensitivity in muscles, liver, and adipose tissues (Type2 DM). Insulin injection treats DM patients but leads to hypoglycemia as a side effect. Cortisol and catecholamines are released to activate glucose production from the liver to recover hypoglycemia, called counter-regulatory responses (CRR). In DM research using rodent models, glucose tolerance tests and 2-deoxy-glucose injection are used to measure insulin release and CRR, respectively. However, blood glucose concentrations change persistently during experiments, causing difficulties in assessing net insulin release and CRR. This article describes a method in which blood glucose is kept at 250 mg/dL or 50 mg/dL in conscious mice to compare the release of insulin and CRR hormones, respectively. Polyethylene tubing is implanted in the mice's carotid artery and jugular vein, and the mice are allowed to recover from the surgery. The jugular vein tubing is connected to a Hamilton syringe with a syringe pump to enable insulin or glucose infusion at a constant and variable rate. The carotid artery tubing is for blood collection. For the hyperglycemic clamp, 30% glucose is infused into the vein, and blood glucose levels are measured from the arterial blood every 5 min or 10 min. The infusion rate of 30% glucose is increased until the blood glucose level becomes 250 mg/dL. Blood is collected to measure insulin concentrations. For hypoglycemic clamp, 10 mU/kg/min insulin is infused together with 30% glucose, whose infusion rate is variable to maintain 50 mg/dL of blood glucose level. Blood is collected to measure counter-regulatory hormones when both glucose infusion and blood glucose reach a steady state. Both hyperglycemic and hypoglycemic clamps have the same surgical procedure and experimental setups. Thus, this method is useful for researchers of systemic glucose metabolism.

The Effect of High-Fat Diet on Intramyocellular Lipid Content in Healthy Adults: A Systematic Review, Meta-Analysis, and Meta-Regression.

Fatty acids are stored within the muscle as intramyocellular lipids (IMCL). Some, but not all, studies indicate that following a high-fat diet (HFD), IMCL may accumulate and affect insulin sensitivity. This systematic review and meta-analysis aimed to quantify the effects of an HFD on IMCL. It also explored the potential modifying effects of HFD fat content and duration, IMCL measurement technique, physical activity status, and the associations of IMCL with insulin sensitivity. Five databases were systematically searched for studies that examined the effect of ≥3 d of HFD (>35% daily energy intake from fat) on IMCL content in healthy individuals. Meta-regressions were used to investigate associations of the HFD total fat content, duration, physical activity status, IMCL measurement technique, and insulin sensitivity with IMCL responses. Changes in IMCL content and insulin sensitivity (assessed by hyperinsulinemic-euglycemic clamp) are presented as standardized mean difference (SMD) using a random effects model with 95% confidence intervals (95% CIs). Nineteen studies were included in the systematic review and 16 in the meta-analysis. IMCL content increased following HFD (SMD = 0.63; 95% CI: 0.31, 0.94, P = 0.001). IMCL accumulation was not influenced by total fat content (P = 0.832) or duration (P = 0.844) of HFD, physical activity status (P = 0.192), or by the IMCL measurement technique (P > 0.05). Insulin sensitivity decreased following HFD (SMD = -0.34; 95% CI: -0.52, -0.16; P = 0.003), but this was not related to the increase in IMCL content following HFD (P = 0.233). Consumption of an HFD (>35% daily energy intake from fat) for ≥3 d significantly increases IMCL content in healthy individuals regardless of HFD total fat content and duration of physical activity status. All IMCL measurement techniques detected the increased IMCL content following HFD. The dissociation between changes in IMCL and insulin sensitivity suggests that other factors may drive HFD-induced impairments in insulin sensitivity in healthy individuals. This trial was registered at PROSPERO as CRD42021257984.

Effects of exogenous lactate on lipid, protein, and glucose metabolism-a randomized crossover trial in healthy males.

Lactate may inhibit lipolysis and thus enhance insulin sensitivity, but there is a lack of metabolic human studies. This study aimed to determine how hyperlactatemia affects lipolysis, glucose- and protein metabolism, and insulin sensitivity in healthy men. In a single-blind, randomized, crossover design, eight healthy men were studied after an overnight fast on two occasions: 1) during a sodium-lactate infusion (LAC) and 2) during a sodium-matched NaCl infusion (CTR). Both days consisted of a 3-h postabsorptive period followed by a 3-h hyperinsulinemic-euglycemic clamp (HEC). Lipolysis rate, endogenous glucose production (EGP), and delta glucose rate of disappearance (ΔRdglu) were evaluated using [9,10-3H]palmitate and [3-3H]glucose tracers. In addition, whole body- and forearm protein metabolism was assessed using [15N]phenylalanine, [2H4]tyrosine, [15N]tyrosine, and [13C]urea tracers. In the postabsorptive period, plasma lactate increased to 2.7 ± 0.5 mmol/L during LAC vs. 0.6 ± 0.3 mmol/L during CTR (P < 0.001). In the postabsorptive period, palmitate flux was 30% lower during LAC compared with CTR (84 ± 32 µmol/min vs. 120 ± 35 µmol/min, P = 0.003). During the HEC, palmitate flux was suppressed similarly during both interventions (P = 0.7). EGP, ΔRdglu, and M value were similar during LAC and CTR. During HEC, LAC increased whole body phenylalanine flux (P = 0.02) and protein synthesis (P = 0.03) compared with CTR; LAC did not affect forearm protein metabolism compared with CTR. Lactate infusion inhibited lipolysis by 30% under postabsorptive conditions but did not affect glucose metabolism or improve insulin sensitivity. In addition, whole body phenylalanine flux was increased. Clinical trial registrations: NCT04710875.NEW & NOTEWORTHY Lactate is a decisive intermediary metabolite, serving as an energy substrate and a signaling molecule. The present study examines the effects of lactate on substrate metabolism and insulin sensitivity in healthy males. Hyperlactatemia reduces lipolysis by 30% without affecting insulin sensitivity and glucose metabolism. In addition, hyperlactatemia increases whole body amino acid turnover rate.

In vivo techniques for assessment of insulin sensitivity and glucose metabolism.

Metabolic tests are vital to determine in vivo insulin sensitivity and glucose metabolism in preclinical models, usually rodents. Such tests include glucose tolerance tests, insulin tolerance tests, and glucose clamps. Although these tests are not standardized, there are general guidelines for their completion and analysis that are constantly being refined. In this review, we describe metabolic tests in rodents as well as factors to consider when designing and performing these tests.

Suppression of Endogenous Insulin Secretion by Euglycemic Hyperinsulinemia.

CONTEXT: The impact of insulin, particularly exogenous hyperinsulinemia, on insulin secretion in humans is debated. OBJECTIVE: We assessed the effects of exogenous hyperinsulinemia on insulin secretion and whether the response is altered in insulin resistance associated with obesity. METHODS: Insulin secretion rates (ISRs) during euglycemic hyperinsulinemic clamp studies (52 volunteers) were calculated using a model that employs plasma C-peptide concentrations. One study involved a 2-step insulin clamp and the other study was a single step insulin clamp. For both studies the goal was to achieve plasma glucose concentrations of 95 mg/dL during the clamp irrespective of fasting glucose concentrations. The percent change in ISR from fasting to the end of the insulin clamp interval was the main outcome. Linear regression and analysis of covariance were used to test for the effects of insulin on ISR and to test for group differences. RESULTS: ISR was greater in obese volunteers (P < .001) under fasting and hyperinsulinemic clamp conditions. The change in plasma glucose from baseline to the end of the insulin clamp interval was highly correlated with the change in ISR (r = 0.61, P < .001). From baseline to the end of the clamp we observed a 27% (SD 20) suppression of ISR. The participants who underwent a 2-step insulin clamp had greater suppression of ISR during the second step than the first step (P < .001). The proportional suppression of ISR during euglycemic hyperinsulinemia was not different between nonobese and obese groups (P = .19). CONCLUSION: Hyperinsulinemia suppresses endogenous insulin secretion and the relative change in insulin secretion produced by exogenous insulin did not differ between nonobese and obese people.

Understanding the predictive accuracy of the InsuTAG index over other surrogate indices in normoglycaemic, non-obese males from Southern India.

We aimed to evaluate the predictive accuracy of InsuTAG index against M value of the hyperinsulinaemic-Euglycaemic clamp (HEC) procedure and fasting surrogate indices of insulin sensitivity/resistance in young, normoglycaemic, Asian Indian males. HEC studies were done in young (mean age 19.7 ± 1 years), non-obese (mean BMI 19.2 ± 2.6 kg/m2), normoglycemic Asian Indian males (n = 110) and the M value was calculated. Surrogate indices namely InsuTAG index, HOMA-IR, FG-IR, QUICKI and McAuley index were calculated. Pearson's correlation and ROC-AUC at 95% CI were applied. Significant negative correlation was observed for InsuTAG index with the M value (r - 0.23, p = 0.01), McAuley index (r - 0.65, p < 0.01), QUICKI (r - 0.34, p < 0.01) and FGIR (r - 0.35, p < 0.01). Significant positive correlations of InsuTAG index were observed for BMI and waist circumference. The ROC-AUC was higher for InsuTAG index (0.75) than FGIR (0.30), QUICKI (0.31), and McAuley index (0.20). The InsuTAG cut-off value ≥ 19.13 showed 66.7% sensitivity and 69.2% specificity in this study group.

Ketogenic propensity is differentially related to lipid-induced hepatic and peripheral insulin resistance.

AIM: Determine the ketogenic response (ß-hydroxybutyrate, a surrogate of hepatic ketogenesis) to a controlled lipid overload in humans. METHODS: In total, nineteen young, healthy adults (age: 28.4 ± 1.7 years; BMI: 22.7 ± 0.3 kg/m2 ) received either a 12 h overnight lipid infusion or saline in a randomized, crossover design. Plasma ketones and inflammatory markers were quantified by colorimetric and multiplex assays. Hepatic and peripheral insulin sensitivity was assessed by the hyperinsulinemic-euglycemic clamp. Skeletal muscle biopsies were obtained to quantify gene expression related to ketone body metabolism and inflammation. RESULTS: By design, the lipid overload-induced hepatic (50%, p < 0.001) and peripheral insulin resistance (73%, p < 0.01) in healthy adults. Ketones increased with hyperlipidemia and were subsequently reduced with hyperinsulinemia during the clamp procedure (Saline: Basal = 0.22 mM, Insulin = 0.07 mM; Lipid: Basal = 0.78 mM, Insulin = 0.51 mM; 2-way ANOVA: Lipid p < 0.001, Insulin p < 0.001, Interaction p = 0.07). In the saline control condition, ketones did not correlate with hepatic or peripheral insulin sensitivity. Conversely, in the lipid condition, ketones were positively correlated with hepatic insulin sensitivity (r = 0.59, p < 0.01), but inversely related to peripheral insulin sensitivity (r = -0.64, p < 0.01). Hyperlipidemia increased plasma inflammatory markers, but did not impact skeletal muscle inflammatory gene expression. Gene expression related to ketone and fatty acid metabolism in skeletal muscle increased in response to hyperlipidemia. CONCLUSION: This work provides important insight into the role of ketones in human health and suggests that ketone body metabolism is altered at the onset of lipid-induced insulin resistance.

A phase-I randomized euglycemic clamp study to demonstrate the pharmacokinetic and pharmacodynamic equivalence of an insulin degludec biosimilar (B01411) with the reference product in healthy Chinese volunteers.

BACKGROUND: B01411 is a biosimilar candidate manufactured by Jilin Huisheng Biopharmaceutical Co. Ltd for the reference insulin degludec (Tresiba) (IDeg). This study aimed to evaluate the pharmacokinetics (PK), pharmacodynamics (PD), and safety of the two IDeg products and to assess the PK/PD similarity of B01411 compared with the reference IDeg product. RESEARCH DESIGN & METHODS: A single-center, single-dose, randomized, crossover, open-labeled, phase I, euglycemic clamp study in healthy Chinese subjects to examine the bioequivalence of B01411 (0.4 U/kg) compared with the reference IDeg product. Blood samples were collected at a predefined time for the analysis of blood glucose (BG), IDeg, and C-peptide concentrations. The glucose infusion rate (GIR) was adjusted to maintain the BG at approximately 0.28 mmol/L below baseline throughout the clamp. RESULTS: Thirty-two subjects (20 males and 12 females) were enrolled, 31 of whom received both treatments. The 90% confidence intervals for the ratio of the least-squares geometric means for AUCIDeg,0-24 h, AUCGIR,0-24 h, IDegmax, and GIRmax were all in the range of 0.80-1.25. Only one adverse event of puncture site bruising occurred once in a subject in the B01411 group. CONCLUSION: B01411 exhibited a pharmacokinetic and pharmacodynamic similarity to the reference product. Both IDeg products were well tolerated. CLINICAL TRIAL REGISTRATION: http://www.chinadrugtrials.org.cn/index.html#. Identifier is CTR20192122.

Effect of hypoglycemia on baroreflex sensitivity in individuals with type 2 diabetes: implications for autonomic control of cardiovascular function in diabetes.

PURPOSE: Hypoglycemia is associated with increased mortality, though the mechanisms underlying this association are not established. Hypoglycemia impairs the counterregulatory hormonal and autonomic responses to subsequent hypoglycemia. It is unknown whether hypoglycemia elicits a generalized impairment in autonomic control of cardiovascular function in individuals with type 2 diabetes. We tested the hypothesis that in individuals with type 2 diabetes, hypoglycemia impairs a key measure of cardiovascular autonomic homeostasis, baroreflex sensitivity. METHODS: Sixteen individuals with well-controlled type 2 diabetes and without known cardiovascular disease were exposed to two 90-min episodes of experimental hypoglycemia (2.8 mmol/L, 50 mg/dL) on the same day. All individuals experienced a hypoglycemic-hyperinsulinemic clamp in the morning (AM clamp) and again in the afternoon (PM clamp). Baroreflex sensitivity was assessed using the modified Oxford method before the initiation of each hypoglycemic-hyperinsulinemic clamp, during the last 30 min of hypoglycemia, and the following morning. A mixed effects model adjusting for sex, age, BMI, and insulin level, demonstrated a significant effect of hypoglycemia on baroreflex sensitivity. The study is registered at ClinicalTrials.gov (NCT03422471). RESULTS: Baroreflex sensitivity during PM hypoglycemia was reduced compared to baseline, during AM hypoglycemia, and the next day. Insulin levels positively correlated with baroreflex sensitivity at baseline and during AM hypoglycemia. CONCLUSION: Exposure to hypoglycemia impairs a key measure of autonomic control of cardiovascular function and, thus, may increase the risk of cardiac arrhythmias and blood pressure lability in individuals with type 2 diabetes. This effect is attenuated in part by increased insulin levels.

Asian females without diabetes are protected from obesity-related dysregulation of glucose metabolism compared with males.

OBJECTIVE: The impact of obesity on the risk for type 2 diabetes differs between males and females; however, the underlying reasons are unclear. This study aimed to investigate the effect of sex on obesity-driven changes in the mechanisms regulating glucose metabolism (insulin sensitivity and secretion) among Asian individuals without diabetes in Singapore. METHODS: The study assessed glucose tolerance using oral glucose tolerance test, insulin-mediated glucose uptake using hyperinsulinemic-euglycemic clamp, acute insulin response using an intravenous glucose challenge, and insulin secretion rates in the fasting state and in response to glucose ingestion using mathematical modeling in 727 males and 952 females who had normal body weight (n = 602, BMI < 23 kg/m2 ), overweight (n = 662, 23 ≤ BMI < 27.5), or obesity (n = 415, BMI ≥ 27.5). RESULTS: There were no sex differences among lean individuals. Obesity gradually worsened metabolic function, and the progressive adverse effects of obesity on insulin action and secretion were more pronounced in males than females, such that among participants with obesity, females had greater insulin sensitivity, lower insulin secretion, and lower fasting insulin concentration than males. The increase in waist to hip ratio with increasing BMI was more pronounced in males than females. CONCLUSIONS: The female sex exerts a protective effect on obesity-driven dysregulation of glucose metabolism in Asian individuals without diabetes.

Pharmacokinetics, pharmacodynamics, and safety of prandial oral insulin (N11005) in healthy subjects.

Aims: To verify whether the oral insulin N11005 is administered as a prandial insulin by assessing the pharmacokinetics (PK), pharmacodynamics (PD), and safety profiles of N11005 with a short-acting biosynthetic human insulin (Novolin R) as reference. Methods: This was a randomized, open-label, single-dose, crossover hyperinsulinemic-euglycemic clamp study in healthy Chinese male subjects. A total of 12 subjects were enrolled in the test (T) group (N11005, 300 IU, p.o.) and the reference (R) group (Novolin R, 0.1 IU/Kg, i.h.) with a washout period of 14 days. All subjects were administered on the same day of the clamp study. Glucose Infusion Rates (GIR), serum insulin, and C-peptide concentration were determined during every 8-hour clamp cycle. Trial registration: Clinicaltrials.gov identifier NCT04975022. Results: After administration, the ratios of mean serum C-peptide concentration to baseline concentration in both T and R groups were lower than 50%, which confirmed the stability of the clamp platform. T group (N11005) showed a more rapid onset of action (tGIR10%max≈11 min) and a comparable duration of action to the R group, which was basically in line with the characteristics of prandial insulins. No adverse events (AEs) occurred throughout the study, which demonstrated that N11005 and Novolin R are safe and well-tolerated. Conclusions: The PD profiles of the single-dose N11005 in the human body are similar to those of prandial insulins, with an excellent safety profile. Clinical trial registration: Clinicaltrials.gov, identifier NCT04975022.

Skeletal muscle integrin expression in non-obese men with varying degrees of insulin sensitivity.

The remodeling of skeletal muscle extracellular matrix (ECM) components is related to the degree of insulin resistance (IR). Membrane receptors such as integrins provide two-way signaling ("inside-out" and "outside-in" signaling) between ECM components of skeletal muscle (e.g., collagen, laminin, fibronectin) and intracellular signaling pathways. The aim of the study was to analyze the relationship between the expression of integrins in skeletal muscle and insulin sensitivity (IS) in young, healthy, non-obese volunteers. We studied 36 healthy non-obese male participants. Subjects were divided into three subgroups on the basis of the hyperinsulinemic-euglycemic clamp: upper IS tertile, medium IS tertile, and lower IS tertile. Vastus lateralis muscle biopsies were performed before each clamp. Next, analysis of integrin mRNA expression was performed. Waist circumference, percent body fat, fasting serum insulin, total cholesterol, triglycerides and LDL-cholesterol were higher in the lower IS tertile subgroup compared to the other two subgroups (p < 0.05). The lower IS tertile showed increased expression of ITGA5, ITGA6, ITGA7, SPARC (p < 0.05) in comparison with the upper IS tertile and ITGA6 (p < 0.05) compared to the medium IS tertile. ITGA2, ITGA3, ITGA5, ITGA6, ITGA7, SPARC correlated inversely with IS (p < 0.05). Skeletal muscle integrin are associated with low IS in healthy nonobese men. Our data suggest that factors associated with ECM in muscle may be involved in modulation of insulin action even at the early stages of the development of IR.

Current Status of Weekly Insulin Analogs and Their Pharmacokinetic/Pharmacodynamic Evaluation by the Euglycemic Clamp Technique.

Diabetes mellitus represents a significant global health threat characterized by hyperglycemia caused by inadequate insulin secretion and/or insulin resistance. Exogenous insulin supplements had been recognized as a crucial treatment for achieving successful glycemic control in patients with Type 1 and most patients with Type 2 diabetes. Over the past century, substantial progress has been made in the development of novel insulin formulations, including the super-fast-acting and long-acting basal insulin analogs, of which the latter is indispensable for the management of nocturnal fasting and intraprandial blood glucose within the normal physiological range. Recently, combining chemical and genetic engineering with drug optimization have resulted in a formidable evolution in ultra-long-acting weekly insulin. Here, the current state of once-weekly insulin analogs and the euglycemic clamp technique used in the early clinical development to elucidate the pharmacokinetics and pharmacodynamics of this type of novel weekly insulin analogs were systematically overviewed.

Glucose-dependent inflammatory responses in obese compared to lean individuals.

PURPOSE: Obesity is characterized by chronic inflammation that may contribute to insulin resistance and promote type 2 diabetes. We have investigated whether inflammatory responses to glycemic and insulinemic variations are altered in obese individuals. METHODS: Eight obese and eight lean individuals without diabetes had undergone hyperinsulinemic-euglycemic-hypoglycemic and hyperglycemic clamps in a previous study. Using Proximity Extension Assay, 92 inflammatory markers were analyzed from plasma samples at fasting, hyperinsulinemia-euglycemia, hypoglycemia and hyperglycemia. RESULTS: In all participants, hyperinsulinemia, hypoglycemia and hyperglycemia led to reductions of 11, 19 and 62 out of the 70 fully evaluable biomarkers, respectively. FGF-21 increased during both hypoglycemia and hyperglycemia while IL-6 and IL-10 increased during hypoglycemia. In obese vs lean participants, Oncostatin-M, Caspase-8 and 4E-BP1 were more markedly suppressed during hypoglycemia, whereas VEGF-A was more markedly suppressed during hyperglycemia. BMI correlated inversely with changes of PD-L1 and CD40 during hyperinsulinemia, Oncostatin-M, TNFSF14, FGF-21 and 4EBP-1 during hypoglycemia and CCL23, VEGF-A and CDCP1 during hyperglycemia (Rho ≤ -0.50). HbA1c correlated positively with changes of MCP-2 and IL-15-RA during hyperinsulinemia (Rho ≥ 0.51) and inversely with changes of CXCL1, MMP-1 and Axin-1 during hypoglycemia (Rho ≤ -0.55). M-value correlated positively with changes of IL-12B and VEGF-A during hyperglycemia (Rho ≥ 0.51). Results above were significant (p < 0.05). CONCLUSION: Overall, hyperinsulinemia, hypo- and hyperglycemia led to suppression of several inflammatory markers and this tended to be more marked in individuals with obesity, insulin resistance and dysglycemia. Thus, acute glycemic or insulinemic variations do not seem to potentiate possible inflammatory pathways in the development of insulin resistance and disturbed glucose metabolism.

Serum HMGB1 levels are independently associated with glucose clamp-derived measures of insulin resistance in women with PCOS.

PURPOSE: PCOS is associated with low grade inflammation which could play a role in insulin resistance and ovarian dysfunction. Preliminary findings suggested that serum levels of HMGB1, a cytokine involved in inflammation, might be altered in women with PCOS. Primary aim of this study was to assess whether HMGB1 serum concentrations are associated with PCOS and with the state of insulin resistance of these women. METHODS: Sixty women with PCOS, selected to have a similar proportion of subjects with altered or normal insulin sensitivity, and 29 healthy controls were studied. Serum HMGB1 levels were compared in subgroups of PCOS women and controls. In PCOS women, insulin sensitivity was assessed by the glucose clamp technique and HMGB1 was measured at baseline and after acute hyperinsulinemia. RESULTS: HMGB1 levels were similar in women with PCOS and controls and no elements used for diagnosing PCOS were associated with serum HMGB1. However, HMGB1 concentrations were higher in insulin-resistant vs insulin-sensitive PCOS women (p = 0.017), and inversely associated with insulin-induced total and non-oxidative glucose metabolism. In both subgroups of PCOS women, serum HMBG1 levels significantly increased after acute hyperinsulinemia. CONCLUSIONS: These data suggest that HMGB1 levels are not associated with PCOS per se, but with insulin resistance. Further research should establish the underlying nature of this relationship, and whether this protein might play a role in the metabolic complications of PCOS.

Metabolic dysfunction in obesity is related to impaired suppression of fatty acid release from adipose tissue by insulin.

OBJECTIVE: The aims of this study were: 1) to assess relationships among insulin-mediated glucose uptake with standard clinical outcomes and deep-phenotyping measures (including fatty acid [FA] rate of appearance [FA Ra] into the systemic circulation); and 2) to examine the contribution of adipocyte size, fibrosis, and proteomic profile to FA Ra regulation. METHODS: A total of 66 adults with obesity (BMI = 34 [SD 3] kg/m2 ) were assessed for insulin sensitivity (hyperinsulinemic-euglycemic clamp), and stable isotope dilution methods quantified glucose, FA, and glycerol kinetics in vivo. Abdominal subcutaneous adipose tissue (aSAT) and skeletal muscle biopsies were collected, and magnetic resonance imaging quantified liver and visceral fat content. RESULTS: Insulin-mediated FA Ra suppression associated with insulin-mediated glucose uptake (r = 0.51; p < 0.01) and negatively correlated with liver (r = -0.36; p < 0.01) and visceral fat (r = -0.42; p < 0.01). aSAT proteomics from subcohorts of participants with low FA Ra suppression (n = 8) versus high FA Ra suppression (n = 8) demonstrated greater extracellular matrix collagen protein in low versus high FA Ra suppression. Skeletal muscle lipidomics (n = 18) revealed inverse correlations of FA Ra suppression with acyl-chain length of acylcarnitine (r = -0.42; p = 0.02) and triacylglycerol (r = -0.51; p < 0.01), in addition to insulin-mediated glucose uptake (acylcarnitine: r = -0.49; p < 0.01, triacylglycerol: r = -0.40; p < 0.01). CONCLUSIONS: Insulin's ability to suppress FA release from aSAT in obesity is related to enhanced insulin-mediated glucose uptake and metabolic health in peripheral tissues.

Chronic physiologic hyperglycemia impairs insulin-mediated suppression of plasma glucagon concentration in healthy humans.

BACKGROUND AND AIMS: Hyperglucagonemia is a characteristic feature of type 2 diabetes mellitus (T2DM). We examined the effect of chronic (48-72 h) physiologic increase (+50 mg/dl) in plasma glucose concentration on suppression of plasma glucagon concentration by insulin and by hyperglycemia in normal glucose tolerance (NGT) individuals. MATERIALS AND METHODS: Study One: 16 NGT subjects received OGTT and 3-step hyperinsulinemic (10, 20, 40 mU/m2·min) euglycemic clamp before and after 48 hour glucose infusion to increase plasma glucose by ~50 mg/dl. Study Two: 20 NGT subjects received OGTT and 2-step hyperglycemic (+125 and + 300 mg/dl) clamp before and after 72 hour glucose infusion. Plasma insulin, C-peptide and glucagon concentrations were measured during OGTT, euglycemic hyperinsulinemic and hyperglycemic clamps. Ratio of plasma glucagon/insulin was used as an index of insulin-mediated suppression of glucagon secretion. RESULTS: During all 3 insulin clamp steps (Study 1), plasma glucagon concentration was increased compared to baseline study, and plasma glucagon/insulin ratio was significantly reduced by 24 % (p < 0.05). The rate of insulin-stimulated glucose disposal was inversely correlated with plasma glucagon/insulin ratio (r = -0.44, p < 0.05) and with glucagon AUC (r = -0.48, p < 0.05). During the 2-step hyperglycemic clamp (Study 2) plasma glucagon was similar before and after 72 h of glucose infusion; however, glucagon/insulin ratio was significantly reduced (p < 0.05). Incremental area under plasma insulin curve during the first (r = -0.74, p < 0.001) and second (r = -0.85, p < 0.001) hyperglycemic clamp steps was strongly and inversely correlated with plasma glucagon/insulin ratio. CONCLUSION: Sustained (48-72 h) physiologic hyperglycemia (+50 mg/dl) caused whole body insulin resistance and impaired insulin-mediated suppression of glucagon secretion, suggesting a role for glucotoxicity in development of hyperglucagonemia in T2DM.

The Effect of BMI on Pharmacokinetic and Pharmacodynamic Parameters of Insulin Degludec: Results from an Euglycemic Glucose Clamp Study.

PURPOSE: This study evaluated the effect of body mass index (BMI) on pharmacokinetic (PK) and pharmacodynamic (PD) parameters of insulin degludec in healthy Chinese males, depending on an euglycemic glucose clamp study. METHODS: Sixty-five healthy male subjects were divided into four groups according to quartile of BMI value. Group A: BMI ≤ 20.7 kg/m2; group B: 20.7 < BMI ≤ 22.5 kg/m2; group C: 22.5 < BMI ≤ 23.6 kg/m2; group D: BMI > 23.6 kg/m2. Each volunteer received a single subcutaneous dose (0.4 U/kg) of insulin degludec and accepted a 24-h euglycemic glucose clamp study. The primary PK parameters were maximum observed drug concentration (Cmax) and the area under the curve (AUCINS) for the specified time intervals. The primary PD parameters were the time to the start of glucose infusion (Tonset), maximal glucose infusion rate (GIRmax) and area under the curve (AUCGIR) for the specified time intervals. The differences of these PK/PD parameters were compared among groups. RESULTS: Cmax and the AUC of insulin (0-6 h, 6-12 h and 0-24 h) were more than onefold higher in group A than those in groups B, C, D, and the concentration-time curve of group A was significantly shifted to the left compared with the other three groups. The GIRmax, total AUCGIR, and AUCGIR for each time interval were significantly higher in group A than those in other three groups. The proportion of AUCGIR in group A was the lowest proportion among four groups seen in the late stage. Multiple linear regression analysis showed that BMI was negatively correlated with AUCGIR,0-24 h. CONCLUSIONS: Insulin degludec in healthy Chinese male subjects with BMI ≤ 20.7 kg/m2 had a faster absorption, clearance, and a stronger glucose-lowering effect, but a steeper decrease of insulin action in the late stage after dosing.

Ketone Body Infusion Abrogates Growth Hormone-Induced Lipolysis and Insulin Resistance.

CONTEXT: Exogenous ketone body administration lowers circulating glucose levels but the underlying mechanisms are uncertain. OBJECTIVE: We tested the hypothesis that administration of the ketone body ß-hydroxybutyrate (ßOHB) acutely increases insulin sensitivity via feedback suppression of circulating free fatty acid (FFA) levels. METHODS: In a randomized, single-blinded crossover design, 8 healthy men were studied twice with a growth hormone (GH) infusion to induce lipolysis in combination with infusion of either ßOHB or saline. Each study day comprised a basal period and a hyperinsulinemic-euglycemic clamp combined with a glucose tracer and adipose tissue and skeletal muscle biopsies. RESULTS: ßOHB administration profoundly suppressed FFA levels concomitantly with a significant increase in glucose disposal and energy expenditure. This was accompanied by a many-fold increase in skeletal muscle content of both ßOHB and its derivative acetoacetate. CONCLUSION: Our data unravel an insulin-sensitizing effect of ßOHB, which we suggest is mediated by concomitant suppression of lipolysis.