Multiorgan insulin sensitivity in lean and obese subjects

Muscle and adipose tissue insulin resistance: malady without mechanism?

Insulin resistance is a major risk factor for numerous diseases, including type 2 diabetes and cardiovascular disease. These disorders have dramatically increased in incidence with modern life, suggesting that excess nutrients and obesity are major causes of "common" insulin resistance. Despite considerable effort, the mechanisms that contribute to common insulin resistance are not resolved. There is universal agreement that extracellular perturbations, such as nutrient excess, hyperinsulinemia, glucocorticoids, or inflammation, trigger intracellular stress in key metabolic target tissues, such as muscle and adipose tissue, and this impairs the ability of insulin to initiate its normal metabolic actions in these cells. Here, we present evidence that the impairment in insulin action is independent of proximal elements of the insulin signaling pathway and is likely specific to the glucoregulatory branch of insulin signaling. We propose that many intracellular stress pathways act in concert to increase mitochondrial reactive oxygen species to trigger insulin resistance. We speculate that this may be a physiological pathway to conserve glucose during specific states, such as fasting, and that, in the presence of chronic nutrient excess, this pathway ultimately leads to disease. This review highlights key points in this pathway that require further research effort.

Insulin-stimulated glucose uptake in skeletal muscle, adipose tissue and liver: a positron emission tomography study

OBJECTIVE

Insulin resistance is reflected by the rates of reduced glucose uptake (GU) into the key insulin-sensitive tissues, skeletal muscle, liver and adipose tissue. It is unclear whether insulin resistance occurs simultaneously in all these tissues or whether insulin resistance is tissue specific.

DESIGN AND METHODS

We measured GU in skeletal muscle, adipose tissue and liver and endogenous glucose production (EGP), in a single session using ¹⁸F-fluorodeoxyglucose with positron emission tomography (PET) and euglycemic-hyperinsulinemic clamp. The study population consisted of 326 subjects without diabetes from the CMgene study cohort.

RESULTS

Skeletal muscle GU less than 33 µmol/kg tissue/min and subcutaneous adipose tissue GU less than 11.5 µmol/kg tissue/min characterized insulin-resistant individuals. Men had considerably worse insulin suppression of EGP compared to women. By using principal component analysis (PCA), BMI inversely and skeletal muscle, adipose tissue and liver GU positively loaded on same principal component explaining one-third of the variation in these measures. The results were largely similar when liver GU was replaced by EGP in PCA. Liver GU and EGP were positively associated with aging.

CONCLUSIONS

We have provided threshold values, which can be used to identify tissue-specific insulin resistance. In addition, we found that insulin resistance measured by GU was only partially similar across all insulin-sensitive tissues studied, skeletal muscle, adipose tissue and liver and was affected by obesity, aging and gender.

Effect of Progressive Weight Loss on Lactate Metabolism: A Randomized Controlled Trial

OBJECTIVE

Lactate is an intermediate of glucose metabolism that has been implicated in the pathogenesis of insulin resistance. This study evaluated the relationship between glucose kinetics and plasma lactate concentration ([LAC]) before and after manipulating insulin sensitivity by progressive weight loss.

METHODS

Forty people with obesity (BMI = 37.9 ± 4.3 kg/m2 ) were randomized to weight maintenance (n = 14) or weight loss (n = 19). Subjects were studied before and after 6 months of weight maintenance and before and after 5%, 11%, and 16% weight loss. A hyperinsulinemic-euglycemic clamp procedure in conjunction with [6,6-2 H2 ]glucose tracer infusion was used to assess glucose kinetics.

RESULTS

At baseline, fasting [LAC] correlated positively with endogenous glucose production rate (r = 0.532; P = 0.001) and negatively with insulin sensitivity, assessed as the insulin-stimulated glucose disposal (r = -0.361; P = 0.04). Progressive (5% through 16%) weight loss caused a progressive decrease in fasting [LAC], and the decrease in fasting [LAC] after 5% weight loss was correlated with the decrease in endogenous glucose production (r = 0.654; P = 0.002) and the increase in insulin sensitivity (r = -0.595; P = 0.007).

CONCLUSIONS

This study demonstrates the interrelationships among weight loss, hepatic and muscle glucose kinetics, insulin sensitivity, and [LAC], and it suggests that [LAC] can serve as an additional biomarker of glucose-related insulin resistance.

The possible role of stress induced hormonal disbalance in the patophysiology of insulin resistane in lean individuals

Insulin resistance (IR) is a common denominator of metabolic and hemodynamic disorders simultaneously present in one person and responsible for elevated risk of developing type 2 diabetes (T2DM) and cardiovascular incidents. According to the latest research, IR is present in 25-45% of the general population. Therefore, the mechanism of its development is in the center of scientific and professional interest. Established or acquired factors, or combinations thereof, which disturb any step of the physiological insulin action mechanism: its binding to the cellular receptor, through the complex cascade of intracellular signaling pathways might cause IR. Although the adiposity and its underlying risk factors are considered to be the primary cause of IR, it is present in a great porportion in lean individuals as well. There are insights of the possible role of psychological factors: exposure to stress and deprssion to IR development, although the mechanism of this relationship has not been comperhensively studied. Data driven from cell cultures and experimental animal models suggest that there is an elevated level of counter-regulatory insulin hormones: growth hormone, prolactin and cortisol due to acute stress exposure. However, the relationship between these psychological disorders with the hyperreactivity of the axis of the hypothalamic-pituitaryadrenal axis as the underlying mechanism in the patophysiology of IR in lean individuals has not been systematically investigated. Based on the aforementioned, we hypothesise that this mechanism would be responsible for the formation of IR, and consequently, T2DM in lean individuals. The possible effect of the amount of stress in conjunction with the serum concentration of growth hormone, cortisol, prolactin and dehydroepiandrostendone to the abnormal 5-h oral glucose tollerance test results could contribute to the primary prevention of diabetes and its complications.

Alterations in 3-Hydroxyisobutyrate and FGF21 Metabolism Are Associated With Protein Ingestion-Induced Insulin Resistance

Systemic hyperaminoacidemia, induced by either intravenous amino acid infusion or protein ingestion, reduces insulin-stimulated glucose disposal. Studies of mice suggest that the valine metabolite 3-hydroxyisobutyrate (3-HIB), fibroblast growth factor 21 (FGF21), adiponectin, and nonesterified fatty acids (NEFAs) may be involved in amino acid-mediated insulin resistance. We therefore measured in 30 women the rate of glucose disposal, and plasma 3-HIB, FGF21, adiponectin, and NEFA concentrations, under basal conditions and during a hyperinsulinemic-euglycemic clamp procedure (HECP), with and without concomitant ingestion of protein (n = 15) or an amount of leucine that matched the amount of protein (n = 15). We found that during the HECP without protein or leucine ingestion, the grand mean ± SEM plasma 3-HIB concentration decreased (from 35 ± 2 to 14 ± 1 µmol/L) and the grand median [quartiles] FGF21 concentration increased (from 178 [116, 217] to 509 [340, 648] pg/mL). Ingestion of protein, but not leucine, decreased insulin-stimulated glucose disposal (P < 0.05) and prevented both the HECP-mediated decrease in 3-HIB and increase in FGF21 concentration in plasma. Neither protein nor leucine ingestion altered plasma adiponectin or NEFA concentrations. These findings suggest that 3-HIB and FGF21 might be involved in protein-mediated insulin resistance in humans.

HIV infection does not prevent the metabolic benefits of diet-induced weight loss in women with obesity

OBJECTIVE

To test the hypothesis that HIV infection impairs the beneficial effects of weight loss on insulin sensitivity, adipose tissue inflammation, and endoplasmic reticulum (ER) stress.

METHODS

A prospective clinical trial evaluated the effects of moderate diet-induced weight loss on body composition, metabolic function, and adipose tissue biology in women with obesity who were HIV-seronegative (HIV-) or HIV-positive (HIV+). Body composition, multiorgan insulin sensitivity (assessed by using a two-stage hyperinsulinemic-euglycemic clamp procedure with stable isotopically labeled tracer infusions), and adipose tissue expression of markers of inflammation, autophagy, and ER stress were evaluated in 8 HIV- and 20 HIV+ women with obesity before and after diet-induced weight loss of 6% to 8%.

RESULTS

Although weight loss was not different between groups (∼7.5%), the decrease in fat-free mass was greater in HIV+ than HIV- subjects (-4.4 ± 0.7% vs. -1.7 ± 1.0%, P < 0.05). Weight loss improved insulin sensitivity in adipose tissue (suppression of palmitate rate of appearance [Ra]), liver (suppression of glucose Ra), and muscle (glucose disposal) similarly in both groups. Weight loss did not affect adipose tissue expression of markers of inflammation or ER stress in either group.

CONCLUSIONS

Moderate diet-induced weight loss improves multiorgan insulin sensitivity in HIV+ women to the same extent as women who are HIV-. However, weight loss causes a greater decline in fat-free mass in HIV+ than HIV- women.

Insulin Resistance in Adipose Tissue but Not in Liver Is Associated with Aortic Valve Calcification

Background. Insulin resistance is involved in the pathogenesis of cardiovascular disease, but its relationship with cardiovascular calcification has yielded conflicting results. The purpose of the present study was to investigate the role of hepatic and adipose tissue insulin resistance on the presence of coronary artery (CAC > 0) and aortic valve calcification (AVC > 0). Methods. In 1201 subjects (52% women, 53.6 ± 9.3 years old) without familiar and personal history of coronary heart disease, CAC and AVC were assessed by multidetector-computed tomography. Cardiovascular risk factors were documented and lipid profile, inflammation markers, glucose, insulin, and free fatty acids were measured. Hepatic insulin resistance (HOMA-IR) and adipose tissue insulin resistance (Adipo-IR) indices were calculated. Results. There was a significant relationship between HOMA-IR and Adipo-IR indices (r = 0.758, p < 0.001). Participants in the highest quartiles of HOMA-IR and Adipo-IR indices had a more adverse cardiovascular profile and higher prevalence of CAC > 0 and AVC > 0. After full adjustment, subjects in the highest quartile of Adipo-IR index had higher odds of AVC > 0 (OR: 2.40; 95% CI: 1.30-4.43), as compared to those in the lowest quartile. Conclusions. Adipo-IR was independently associated with AVC > 0. This suggests that abnormal adipose tissue function favors insulin resistance that may promote the development and progression of AVC.

High-Protein Intake during Weight Loss Therapy Eliminates the Weight-Loss-Induced Improvement in Insulin Action in Obese Postmenopausal Women

High-protein (HP) intake during weight loss (WL) therapy is often recommended because it reduces the loss of lean tissue mass. However, HP intake could have adverse effects on metabolic function, because protein ingestion reduces postprandial insulin sensitivity. In this study, we compared the effects of ∼10% WL with a hypocaloric diet containing 0.8 g protein/kg/day and a hypocaloric diet containing 1.2 g protein/kg/day on muscle insulin action in postmenopausal women with obesity. We found that HP intake reduced the WL-induced decline in lean tissue mass by ∼45%. However, HP intake also prevented the WL-induced improvements in muscle insulin signaling and insulin-stimulated glucose uptake, as well as the WL-induced adaptations in oxidative stress and cell structural biology pathways. Our data demonstrate that the protein content of a WL diet can have profound effects on metabolic function and underscore the importance of considering dietary macronutrient composition during WL therapy for people with obesity.

One Week of Bed Rest Leads to Substantial Muscle Atrophy and Induces Whole-Body Insulin Resistance in the Absence of Skeletal Muscle Lipid Accumulation

Short (<10 days) periods of muscle disuse, often necessary for recovery from illness or injury, lead to various negative health consequences. The current study investigated mechanisms underlying disuse-induced insulin resistance, taking into account muscle atrophy. Ten healthy, young males (age: 23 ± 1 years; BMI: 23.0 ± 0.9 kg · m(-2)) were subjected to 1 week of strict bed rest. Prior to and after bed rest, lean body mass (dual-energy X-ray absorptiometry) and quadriceps cross-sectional area (CSA; computed tomography) were assessed, and peak oxygen uptake (VO2peak) and leg strength were determined. Whole-body insulin sensitivity was measured using a hyperinsulinemic-euglycemic clamp. Additionally, muscle biopsies were collected to assess muscle lipid (fraction) content and various markers of mitochondrial and vascular content. Bed rest resulted in 1.4 ± 0.2 kg lean tissue loss and a 3.2 ± 0.9% decline in quadriceps CSA (both P < 0.01). VO2peak and one-repetition maximum declined by 6.4 ± 2.3 (P < 0.05) and 6.9 ± 1.4% (P < 0.01), respectively. Bed rest induced a 29 ± 5% decrease in whole-body insulin sensitivity (P < 0.01). This was accompanied by a decline in muscle oxidative capacity, without alterations in skeletal muscle lipid content or saturation level, markers of oxidative stress, or capillary density. In conclusion, 1 week of bed rest substantially reduces skeletal muscle mass and lowers whole-body insulin sensitivity, without affecting mechanisms implicated in high-fat diet-induced insulin resistance.

Brown Adipose Tissue Activation Is Linked to Distinct Systemic Effects on Lipid Metabolism in Humans

Recent studies suggest that brown adipose tissue (BAT) plays a role in energy and glucose metabolism in humans. However, the physiological significance of human BAT in lipid metabolism remains unknown. We studied 16 overweight/obese men during prolonged, non-shivering cold and thermoneutral conditions using stable isotopic tracer methodologies in conjunction with hyperinsulinemic-euglycemic clamps and BAT and white adipose tissue (WAT) biopsies. BAT volume was significantly associated with increased whole-body lipolysis, triglyceride-free fatty acid (FFA) cycling, FFA oxidation, and adipose tissue insulin sensitivity. Functional analysis of BAT and WAT demonstrated the greater thermogenic capacity of BAT compared to WAT, while molecular analysis revealed a cold-induced upregulation of genes involved in lipid metabolism only in BAT. The accelerated mobilization and oxidation of lipids upon BAT activation supports a putative role for BAT in the regulation of lipid metabolism in humans.

Metabolic Effects of Obesity and Its Interaction with Endocrine Diseases

Obesity in pet dogs and cats is a significant problem in developed countries, and seems to be increasing in prevalence. Excess body fat has adverse metabolic consequences, including insulin resistance, altered adipokine secretion, changes in metabolic rate, abnormal lipid metabolism, and fat accumulation in visceral organs. Obese cats are predisposed to endocrine and metabolic disorders such as diabetes and hepatic lipidosis. A connection likely also exists between obesity and diabetes mellitus in dogs. No system has been developed to identify obese pets at greatest risk for development of obesity-associated metabolic diseases, and further study in this area is needed.

Protein Ingestion Induces Muscle Insulin Resistance Independent of Leucine-Mediated mTOR Activation

Increased plasma branched-chain amino acid concentrations are associated with insulin resistance, and intravenous amino acid infusion blunts insulin-mediated glucose disposal. We tested the hypothesis that protein ingestion impairs insulin-mediated glucose disposal by leucine-mediated mTOR signaling, which can inhibit AKT. We measured glucose disposal and muscle p-mTOR(Ser2448), p-AKT(Ser473), and p-AKT(Thr308) in 22 women during a hyperinsulinemic-euglycemic clamp procedure with and without concomitant ingestion of whey protein (0.6 g/kg fat-free mass; n = 11) or leucine that matched the amount given with whey protein (n = 11). Both whey protein and leucine ingestion raised plasma leucine concentration by approximately twofold and muscle p-mTOR(Ser2448) by ∼30% above the values observed in the control (no amino acid ingestion) studies; p-AKT(Ser473) and p-AKT(Thr308) were not affected by whey protein or leucine ingestion. Whey protein ingestion decreased insulin-mediated glucose disposal (median 38.8 [quartiles 30.8, 61.8] vs. 51.9 [41.0, 77.3] µmol glucose/µU insulin · mL(-1) · min(-1); P < 0.01), whereas ingestion of leucine did not (52.3 [43.3, 65.4] vs. 52.3 [43.9, 73.2]). These results indicate that 1) protein ingestion causes insulin resistance and could be an important regulator of postprandial glucose homeostasis and 2) the insulin-desensitizing effect of protein ingestion is not due to inhibition of AKT by leucine-mediated mTOR signaling.

Pathway-selective insulin resistance and metabolic disease: the importance of nutrient flux

Hepatic glucose and lipid metabolism are altered in metabolic disease (e.g. obesity, metabolic syndrome, and Type 2 diabetes). Insulin-dependent regulation of glucose metabolism is impaired. In contrast, lipogenesis, hypertriglyceridemia, and hepatic steatosis are increased. Because insulin promotes lipogenesis and liver fat accumulation, to explain the elevation in plasma and tissue lipids, investigators have suggested the presence of pathway-selective insulin resistance. In this model, insulin signaling to glucose metabolism is impaired, but insulin signaling to lipid metabolism is intact. We discuss the evidence for the differential regulation of hepatic lipid and glucose metabolism. We suggest that the primary phenotypic driver is altered substrate delivery to the liver, as well as the repartitioning of hepatic nutrient handling. Specific alterations in insulin signaling serve to amplify the alterations in hepatic substrate metabolism. Thus, hyperinsulinemia and its resultant increased signaling may facilitate lipogenesis, but are not the major drivers of the phenotype of pathway-selective insulin resistance.

Metabolically normal obese people are protected from adverse effects following weight gain

BACKGROUND. Obesity is associated with insulin resistance and increased intrahepatic triglyceride (IHTG) content, both of which are key risk factors for diabetes and cardiovascular disease. However, a subset of obese people does not develop these metabolic complications. Here, we tested the hypothesis that people defined by IHTG content and insulin sensitivity as "metabolically normal obese" (MNO), but not those defined as "metabolically abnormal obese" (MAO), are protected from the adverse metabolic effects of weight gain. METHODS. Body composition, multiorgan insulin sensitivity, VLDL apolipoprotein B100 (apoB100) kinetics, and global transcriptional profile in adipose tissue were evaluated before and after moderate (~6%) weight gain in MNO (n = 12) and MAO (n = 8) subjects with a mean BMI of 36 ± 4 kg/m2 who were matched for BMI and fat mass. RESULTS. Although the increase in body weight and fat mass was the same in both groups, hepatic, skeletal muscle, and adipose tissue insulin sensitivity deteriorated, and VLDL apoB100 concentrations and secretion rates increased in MAO, but not MNO, subjects. Moreover, biological pathways and genes associated with adipose tissue lipogenesis increased in MNO, but not MAO, subjects. CONCLUSIONS. These data demonstrate that MNO people are resistant, whereas MAO people are predisposed, to the adverse metabolic effects of moderate weight gain and that increased adipose tissue capacity for lipogenesis might help protect MNO people from weight gain-induced metabolic dysfunction. TRIAL REGISTRATION. ClinicalTrials.gov NCT01184170. FUNDING. This work was supported by NIH grants UL1 RR024992 (Clinical Translational Science Award), DK 56341 (Nutrition and Obesity Research Center), DK 37948 and DK 20579 (Diabetes Center Grant), and UL1 TR000450 (KL2 Award); a Central Society for Clinical and Translational Research Early Career Development Award; and by grants from the Longer Life Foundation and the Kilo Foundation.

Brown adipose tissue improves whole-body glucose homeostasis and insulin sensitivity in humans

Brown adipose tissue (BAT) has attracted scientific interest as an antidiabetic tissue owing to its ability to dissipate energy as heat. Despite a plethora of data concerning the role of BAT in glucose metabolism in rodents, the role of BAT (if any) in glucose metabolism in humans remains unclear. To investigate whether BAT activation alters whole-body glucose homeostasis and insulin sensitivity in humans, we studied seven BAT-positive (BAT(+)) men and five BAT-negative (BAT(-)) men under thermoneutral conditions and after prolonged (5-8 h) cold exposure (CE). The two groups were similar in age, BMI, and adiposity. CE significantly increased resting energy expenditure, whole-body glucose disposal, plasma glucose oxidation, and insulin sensitivity in the BAT(+) group only. These results demonstrate a physiologically significant role of BAT in whole-body energy expenditure, glucose homeostasis, and insulin sensitivity in humans, and support the notion that BAT may function as an antidiabetic tissue in humans.

Matched weight loss induced by sleeve gastrectomy or gastric bypass similarly improves metabolic function in obese subjects

OBJECTIVE

The effects of marked weight loss, induced by Roux-en-Y gastric bypass (RYGB) or sleeve gastrectomy (SG) surgeries, on insulin sensitivity, β-cell function and the metabolic response to a mixed meal were evaluated.

METHODS

Fourteen nondiabetic insulin-resistant patients who were scheduled to undergo SG (n = 7) or RYGB (n = 7) procedures completed a hyperinsulinemic-euglycemic clamp procedure and a mixed-meal tolerance test before surgery and after losing ∼20% of their initial body weight.

RESULTS

Insulin sensitivity (insulin-stimulated glucose disposal during a clamp procedure), oral glucose tolerance (postprandial plasma glucose area under the curve), and β-cell function (insulin secretion in relationship to insulin sensitivity) improved after weight loss, and were not different between surgical groups. The metabolic response to meal ingestion was similar after RYGB or SG, manifested by rapid delivery of ingested glucose into the systemic circulation and a large early postprandial increase in plasma glucose, insulin, and C-peptide concentrations in both groups.

CONCLUSIONS

When matched on weight loss, RYGB and SG surgeries result in similar improvements in the two major factors involved in regulating plasma glucose homeostasis, insulin sensitivity and β-cell function in obese people without diabetes.

One day of overfeeding impairs nocturnal glucose but not fatty acid homeostasis in overweight men

OBJECTIVE

Overfeeding is associated with insulin resistance. Studies on animals suggest this is likely due to disruption of fatty acid metabolism and increased plasma free fatty acid (FFA) availability during the night. We tested the hypothesis that overfeeding induces insulin resistance and increases nocturnal but not daytime plasma FFA availability in human subjects.

DESIGN AND METHODS

We measured plasma glucose, insulin, and FFA concentrations hourly for 24 h during a day of isocaloric feeding and a day of hypercaloric feeding (30% calorie excess) in 8 overweight and obese, nondiabetic men (age: 38±3 years; body mass index: 34±2 kg/m²).

RESULTS

Overfeeding had no effect on daytime plasma glucose, insulin, and FFA concentrations compared to isocaloric feeding, but increased nocturnal glucose (P = 0.007) and insulin (P = 0.003) concentrations and decreased nocturnal FFA concentration (P = 0.006). The homeostasis model assessment of insulin resistance score was ∼30% greater the morning after hypercaloric than isocaloric feeding (P = 0.040).

CONCLUSIONS

One day of overfeeding has no effect on daytime plasma glucose and FFA concentrations but increases nocturnal plasma glucose and insulin concentrations, whereas nocturnal plasma FFA availability is reduced. The acute overfeeding-induced development of insulin resistant glucose metabolism therefore does not appear to be directly mediated by plasma FFA availability.

One day of mixed meal overfeeding reduces hepatic insulin sensitivity and increases VLDL particle but not VLDL-triglyceride secretion in overweight and obese men

CONTEXT

The exact mechanisms responsible for increased plasma triglyceride (TG) concentration in obese people are unclear, and it is not known whether excess energy intake per se is involved in the pathophysiology of this abnormality.

OBJECTIVE

The purpose of our study was to examine how excess energy intake from a balanced diet for 1 day affects very-low-density lipoprotein (VLDL)-TG kinetics and its putative regulators hepatic insulin sensitivity and plasma free fatty acid availability.

SUBJECTS AND DESIGN

We used stable isotope-labeled tracer methods to evaluate glucose and lipid kinetics in 8 overweight and obese men (age, 38 ± 3 years; body mass index, 33.7 ± 1.7 kg/m(2); means ± SEM) on 2 occasions (randomized crossover design): once, the day after they consumed a balanced diet that provided an amount of energy that matched their energy expenditure, and another time, the day after they consumed a balanced diet that provided 30% excess calories. Eight healthy, lean men (34 ± 1 years; 22.5 ± 0.6 kg/m(2)) were studied under isocaloric conditions only to provide a reference for normal lipid kinetics.

RESULTS

VLDL-TG and VLDL-apolipoprotein B-100 (apoB-100) concentrations and secretion rates were significantly greater (P < .01) in overweight/obese compared with lean men. Hypercaloric, compared with isocaloric, feeding in overweight/obese men increased glucose rate of appearance in plasma (904 ± 21 vs 873 ± 26 μmol/min), the hepatic insulin resistance index (10.9 ± 2.2 vs 8.3 ± 1.8), and VLDL-apoB-100 concentration and secretion rate (1.91 ± 0.24 vs. 1.53 ± 0.13 nmol/min), whereas VLDL-apoB-100 plasma clearance rate, VLDL-TG secretion and plasma clearance rates, and free fatty acid rate of appearance in plasma were not affected by overfeeding.

CONCLUSION

One day of moderate overfeeding (30% excess energy intake) stimulates hepatic glucose and VLDL-apo B-100 secretion rates but has no effect on hepatic and adipose tissue fatty acid metabolism in overweight/obese men.

A ~60-min brisk walk increases insulin-stimulated glucose disposal but has no effect on hepatic and adipose tissue insulin sensitivity in older women

The purpose of this study was to determine whether brisk walking improves multiorgan (liver, muscle, adipose tissue) insulin sensitivity in older women. Ten nonobese older women (age: 66.7 ± 1.5 yr, mean ± SE) completed two 2-stage hyperinsulinemic-euglycemic clamp procedures [insulin infusion rate stage 1: 10 mU/m(2) body surface area (BSA) per min; stage 2: 50 mU/m(2) BSA per min] in conjunction with stable isotope-labeled glucose and palmitate tracer infusions: one in the morning after a single, ∼1-h bout of brisk treadmill walking, the other after an equivalent period of rest in the late afternoon of the preceding day. We found that basal glucose rate of appearance (Ra) into plasma was not different after rest and after exercise (17.3 ± 0.8 and 17.1 ± 0.4 μmol/kg fat-free mass per min, respectively). The insulin-mediated decrease in glucose Ra during stage 1 of the clamp was also not different after rest and exercise (82.2% ± 3.4% and 77.7% ± 2.1%, respectively), but glucose rate of disappearance (Rd) during stage 2 of the clamp was significantly greater (P < 0.05) after exercise than rest (88.0 ± 5.9 and 78.4 ± 6.5 μmol/kg fat-free mass per min, respectively). There were no differences in palmitate Ra during basal conditions or insulin infusion after exercise and after rest. Therefore, we conclude that a single bout of brisk walking for ∼1 h improves muscle insulin sensitivity but has no effect on liver and adipose tissue insulin sensitivity in older women.

Metabolic inflexibility is a feature of women with polycystic ovary syndrome and is associated with both insulin resistance and hyperandrogenism

CONTEXT

Metabolic inflexibility, ie, the impaired ability of the body to switch from fat to carbohydrate oxidation under insulin-stimulated conditions, is associated with insulin resistance. This alteration in metabolic plasticity can lead to organ dysfunction and is considered a key issue among the abnormalities of the metabolic syndrome. It is still unknown whether this phenomenon occurs in women with polycystic ovary syndrome (PCOS).

OBJECTIVE

Our objective was to examine whether metabolic inflexibility is a feature of PCOS women and whether hyperandrogenism may contribute to this phenomenon.

DESIGN AND PATIENTS

Eighty-nine Caucasian women with PCOS were submitted to hyperinsulinemic-euglycemic clamp. Respiratory exchange ratios were evaluated at baseline and during hyperinsulinemia by indirect calorimetry to quantify substrate oxidative metabolism. Total testosterone was measured by liquid chromatography mass spectrometry and free testosterone by equilibrium dialysis.

SETTING

Outpatients were seen in a tertiary care academic center.

MAIN OUTCOME MEASURE

Metabolic flexibility was assessed by the change in respiratory quotient upon insulin stimulation.

RESULTS

Sixty-five of the 89 PCOS women (73%) had increased serum free testosterone, 68 (76%) were insulin resistant, and 62 (70%) had an impaired metabolic flexibility. Comparison of hyperandrogenemic and normoandrogenemic women showed that the 2 subgroups were of similar age but differed in terms of several anthropometric and metabolic features. In particular, hyperandrogenemic women had greater body mass index (32.9 ± 1.0 vs 24.7 ± 0.9 kg/m(2), P < .001) and lower glucose utilization during the clamp (9.2 ± 0.4 vs 10.9 ± 0.7 mg/kg fat-free mass · min, P = .023) and metabolic flexibility (0.09 ± 0.06 vs 0.12 ± 0.01, P = .014). In univariate analysis, metabolic flexibility was associated with several anthropometric, endocrine, and metabolic features. In multivariate analysis, this feature was directly associated with baseline respiratory quotient and insulin sensitivity and inversely with free testosterone and free fatty acids concentrations under insulin suppression (R(2) = 0.634, P < .001).

CONCLUSIONS

Metabolic inflexibility is a feature of PCOS women. Both insulin resistance and androgen excess might contribute to this abnormality.

Measurement of insulin-mediated glucose uptake: direct comparison of the modified insulin suppression test and the euglycemic, hyperinsulinemic clamp

BACKGROUND

Two direct measurements of peripheral insulin sensitivity are the M value derived from the euglycemic, hyperinsulinemic clamp (EC) and the steady-state plasma glucose (SSPG) concentration derived from the insulin suppression test (IST). Prior work suggests that these measures are highly correlated, but the agreement between them is unknown. To determine the agreement between SSPG and M and to develop transformation equations to convert SSPG to M and vice versa, we directly compared these two measurements in the same individuals.

METHODS

A total of 15 nondiabetic subjects (9 women and 6 men) underwent both an EC and a modified version of the IST within a median interval of 5days. We performed standard correlation metrics of the two measures and developed transformation regression equations for the two measures.

RESULTS

The mean±SD age of the subjects was 57±7years and body mass index, 27.7±3.9kg/m(2). The median (interquartile range) SSPG concentration was 6.7 (5.1, 9.8) mmol/L and M value, 49.6 (28.9, 64.2) μmol/min/kg-LBM. There was a highly significant correlation between SSPG and M (r=-0.87, P <0.001). The relationship was best fit by regression models with exponential/logarithmic functions (R(2)=0.85). Bland-Altman plots demonstrated an excellent agreement between these measures of insulin action.

CONCLUSION

The SSPG and M are highly related measures of insulin sensitivity and the results provide the means to directly compare the two measurements.

Decrease of Plasma Glucose byHibiscus taiwanensisin Type-1-Like Diabetic Rats

Hibiscus taiwanensis (Malvaceae) is widely used as an alternative herb to treat disorders in Taiwan. In the present study, it is used to screen the effect on diabetic hyperglycemia in streptozotocin-induced diabetic rats (STZ-diabetic rats). The extract of Hibiscus taiwanensis showed a significant plasma glucose-lowering action in STZ-diabetic rats. Stems of Hibiscus taiwanensis are more effective than other parts to decrease the plasma glucose in a dose-dependent manner. Oral administration of Hibiscus taiwanensis three times daily for 3 days into STZ-diabetic rats increased the sensitivity to exogenous insulin showing an increase in insulin sensitivity. Moreover, similar repeated administration of Hibiscus taiwanensis for 3 days in STZ-diabetic rats produced a marked reduction of phosphoenolpyruvate carboxykinase (PEPCK) expression in liver and an increased expression of glucose transporter subtype 4 (GLUT 4) in skeletal muscle. Taken together, our results suggest that Hibiscus taiwanensis has the ability to lower plasma glucose through an increase in glucose utilization via elevation of skeletal GLUT 4 and decrease of hepatic PEPCK in STZ-diabetic rats.

Gastric bypass and banding equally improve insulin sensitivity and β cell function

Bariatric surgery in obese patients is a highly effective method of preventing or resolving type 2 diabetes mellitus (T2DM); however, the remission rate is not the same among different surgical procedures. We compared the effects of 20% weight loss induced by laparoscopic adjustable gastric banding (LAGB) or Roux-en-Y gastric bypass (RYGB) surgery on the metabolic response to a mixed meal, insulin sensitivity, and β cell function in nondiabetic obese adults. The metabolic response to meal ingestion was markedly different after RYGB than after LAGB surgery, manifested by rapid delivery of ingested glucose into the systemic circulation, by an increase in the dynamic insulin secretion rate, and by large, early postprandial increases in plasma glucose, insulin, and glucagon-like peptide-1 concentrations in the RYGB group. However, the improvement in oral glucose tolerance, insulin sensitivity, and overall β cell function after weight loss were not different between surgical groups. Additionally, both surgical procedures resulted in a similar decrease in adipose tissue markers of inflammation. We conclude that marked weight loss itself is primarily responsible for the therapeutic effects of RYGB and LAGB on insulin sensitivity, β cell function, and oral glucose tolerance in nondiabetic obese adults.

Antihyperglycemic effect of syringaldehyde in streptozotocin-induced diabetic rats

The antihyperglycemic effect of syringaldehyde (1), purified from the stems of Hibiscus taiwanensis, was investigated in streptozotocin-induced diabetic rats (STZ-diabetic rats) showing type-1 like diabetes mellitus. Bolus intravenous injection of 1 showed antihyperglycemic activity in a dose-dependent manner in STZ-diabetic rats. An effective dose of 7.2 mg/kg of 1 attenuated significantly the increase of plasma glucose induced by an intravenous glucose challenge test in normal rats. A glucose uptake test showed that 1 exhibits an increase of glucose uptake activity in a concentration-related manner. Moreover, an effect by 1 was shown for insulin sensitivity in STZ-diabetic rats. The compound was found to increase insulin sensitivity in STZ-diabetic rats. These results suggest that syringaldehyde (1) can increase glucose utilization and insulin sensitivity to lower plasma glucose in diabetic rats.