Physiological interindividual variability in endogenous estradiol concentration does not influence adipose tissue and hepatic lipid kinetics in women.

Objective: Increased triglyceride (TG) and apolipoprotein B-100 (apoB-100) concentrations in plasma are important risk factors for cardiovascular disease in women. Administration of some estrogen preparations raises plasma TG and apoB-100 concentrations by increasing hepatic very low-density lipoprotein (VLDL) TG and apoB-100 secretion rates. However, the influence of physiological variation in endogenous estradiol on VLDL-TG and VLDL-apoB-100 metabolism and on free fatty acid (FFA) release into plasma (the major source of fatty acids for VLDL-TG production) is not known. Design and methods: We measured basal VLDL-TG, VLDL-apoB-100, and plasma FFA kinetics by using stable isotopically labeled tracers in 36 eumenorrheic, premenopausal women (age: 33 ± 2 years, BMI: 31 ± 1 kg/m2; mean ± s.e.m.) during the follicular phase of the menstrual cycle; participants were divided into two groups based on low (n = 18) or high (n = 18) plasma estradiol concentrations (defined as below or above the median value of 140 pmol/L in the whole group). Results: Mean plasma estradiol concentration was >3-fold higher in the high-estradiol than in the low-estradiol group (299 ± 37 and 96 ± 7 pmol/L, P < 0.001); there was no difference in plasma progesterone concentrations between the two groups (P = 0.976). There were no significant differences in plasma FFA concentration, FFA rate of appearance in plasma, VLDL-TG and VLDL-apoB-100 concentrations, hepatic VLDL-TG and VLDL-apoB-100 secretion rates, VLDL-TG and VLDL-apoB-100 plasma clearance rates, and mean residence times (all P ≥ 0.45). No significant associations were found between plasma estradiol concentration and FFA, VLDL-TG, and VLDL-apoB-100 concentrations and kinetics (all P > 0.19). Conclusions: Plasma estradiol concentration is not an important correlate of basal plasma FFA, VLDL-TG, and VLDL-apoB-100 kinetics in premenopausal women.

Biliopancreatic Diversion Induces Greater Metabolic Improvement Than Roux-en-Y Gastric Bypass.

Diabetes remission is greater after biliopancreatic diversion (BPD) than Roux-en-Y gastric bypass (RYGB) surgery. We used a mixed-meal test with ingested and infused glucose tracers and the hyperinsulinemic-euglycemic clamp procedure with glucose tracer infusion to assess the effect of 20% weight loss induced by either RYGB or BPD on glucoregulation in people with obesity (ClinicalTrials.gov number: NCT03111953). The rate of appearance of ingested glucose into the circulation was much slower, and the postprandial increases in plasma glucose and insulin concentrations were markedly blunted after BPD compared to after RYGB. Insulin sensitivity, assessed as glucose disposal rate during insulin infusion, was ∼45% greater after BPD than RYGB, whereas ß cell function was not different between groups. These results demonstrate that compared with matched-percentage weight loss induced by RYGB, BPD has unique beneficial effects on glycemic control, manifested by slower postprandial glucose absorption, blunted postprandial plasma glucose and insulin excursions, and greater improvement in insulin sensitivity.

Effects of canagliflozin on amputation risk in type 2 diabetes: the CANVAS Program.

AIMS/HYPOTHESIS: The primary analysis of the Canagliflozin cardioVascular Assessment Study (CANVAS) Program showed canagliflozin to have a beneficial effect on cardiovascular and renal outcomes in people with type 2 diabetes at high cardiovascular risk, but also an unexpected increased risk of major or minor lower extremity amputation. These secondary analyses explore this finding in more detail. METHODS: The effect of canagliflozin on amputation risk in the CANVAS Program was calculated for amputations of different types and proximate aetiologies and different canagliflozin doses. Univariate and multivariate associations of baseline characteristics with amputation risk were determined and proportional and absolute effects of canagliflozin were compared across subgroups. RESULTS: There were 187 (1.8%) participants with atraumatic lower extremity amputations (minor 71%, major 29%); as previously published, rates were 6.30 vs 3.37 per 1000 participant-years with canagliflozin vs placebo (HR 1.97 [95% CI 1.41, 2.75]). Risk was similar for ischaemic and infective aetiologies and for 100 mg and 300 mg doses. Overall amputation risk was strongly associated with baseline history of prior amputation (major or minor) (HR 21.31 [95% CI 15.40, 29.49]) and other established risk factors. No interactions between randomised treatment and participant characteristics explained the effect of canagliflozin on amputation risk. For every clinical subgroup studied, numbers of amputation events projected were smaller than numbers of major adverse cardiovascular events averted. CONCLUSIONS/INTERPRETATION: The CANVAS Program demonstrated that canagliflozin increased the risk of amputation (mainly minor) in this study population. Anticipated risk factors for amputation were identified, such as prior history of amputation, peripheral vascular disease and neuropathy, but no specific aetiological mechanism or at-risk subgroup for canagliflozin was identified.

Factors influencing longitudinal changes of circulating liver enzyme concentrations in subjects randomized to placebo in four clinical trials.

Liver enzyme concentrations are measured as safety end points in clinical trials to detect drug-related hepatotoxicity, but little is known about the epidemiology of these biomarkers in subjects without hepatic dysfunction who are enrolled in drug trials. We studied alanine and aspartate aminotransferase (ALT and AST) in subjects randomized to placebo who completed assessments over 36 mo in a cardiovascular outcome trial [the Stabilisation of Atherosclerotic Plaque by Initiation of Darapladib Therapy ("STABILITY") trial; n = 4,264; mean age: 64.2 yr] or over 12 mo in three trials that enrolled only subjects with type 2 diabetes (T2D) [the DIA trials; n = 308; mean age: 62.4 yr] to investigate time-dependent relationships and the factors that might affect ALT and AST, including body mass index (BMI), T2D, and renal function. Multivariate linear mixed models examined time-dependent relationships between liver enzyme concentrations as response variables and BMI, baseline T2D status, hemoglobin A1c levels, and renal function, as explanatory variables. At baseline, ALT was higher in individuals who were men, <65 yr old, and obese and who had glomerular filtration rate (GFR) >60 ml·min-1·1.73 m-2. ALT was not significantly associated with T2D at baseline, although it was positively associated with HbA1c. GFR had a greater impact on ALT than T2D. ALT concentrations decreased over time in subjects who lost weight but remained stable in individuals with increasing BMI. Weight change did not alter AST concentrations. We provide new insights on the influence of time, GFR, and HbA1c on ALT and AST concentrations and confirm the effect of sex, age, T2D, BMI, and BMI change in subjects receiving placebo in clinical trials. NEW & NOTEWORTHY Clinical trials provide high-quality data on liver enzyme concentrations from subjects randomized to placebo that can be used to investigate the epidemiology of these biomarkers. The adjusted models show the influence of sex, age, time, renal function, type 2 diabetes, HbA1c, and body mass index on alanine aminotransferase and aspartate aminotransferase concentrations and their relative importance. These factors need to be considered when assessing potential signals of hepatotoxicity in trials of new drugs and in clinical trials investigating subjects with nonalcoholic fatty liver disease.

Canagliflozin for Primary and Secondary Prevention of Cardiovascular Events: Results From the CANVAS Program (Canagliflozin Cardiovascular Assessment Study).

BACKGROUND: Canagliflozin is a sodium glucose cotransporter 2 inhibitor that significantly reduces the composite of cardiovascular death, nonfatal myocardial infarction, or nonfatal stroke in patients with type 2 diabetes mellitus and elevated cardiovascular risk. The comparative effects among participants with and without a history of cardiovascular disease (secondary versus primary prevention) were prespecified for evaluation. METHODS: The CANVAS Program (Canagliflozin Cardiovascular Assessment Study) randomly assigned 10 142 participants with type 2 diabetes mellitus to canagliflozin or placebo. The primary prevention cohort comprised individuals ≥50 years of age with ≥2 risk factors for cardiovascular events but with no prior cardiovascular event, and the secondary prevention cohort comprised individuals ≥30 years of age with a prior cardiovascular event. The primary end point was a composite of cardiovascular death, nonfatal myocardial infarction, or nonfatal stroke. Secondary outcomes included heart failure hospitalization and a renal composite (40% reduction in estimated glomerular filtration rate, renal replacement therapy, or renal death). RESULTS: Primary prevention participants (N=3486; 34%) were younger (63 versus 64 years of age), were more often female (45% versus 31%), and had a longer duration of diabetes mellitus (14 versus 13 years) compared with secondary prevention participants (N=6656; 66%). The primary end point event rate was higher in the secondary prevention group compared with the primary prevention group (36.9 versus 15.7/1000 patient-years, P<0.001). In the total cohort, the primary end point was reduced with canagliflozin compared with placebo (26.9 versus 31.5/1000 patient-years; hazard ratio [HR], 0.86; 95% confidence interval [CI], 0.75-0.97; P<0.001 for noninferiority, P=0.02 for superiority) with no statistical evidence of heterogeneity (interaction P value=0.18) between the primary (HR, 0.98; 95% CI, 0.74-1.30) and secondary prevention (HR, 0.82; 95% CI, 0.72-0.95) cohorts. Renal outcomes (HR, 0.59; 95% CI, 0.44-0.79 versus HR, 0.63; 95% CI, 0.39-1.02; interaction P value=0.73) and heart failure hospitalization (HR, 0.68; 95% CI, 0.51-0.90 versus HR, 0.64; 95% CI, 0.35-1.15; interaction P value=0.91) were similarly reduced in the secondary and primary prevention cohorts, respectively. Lower extremity amputations were similarly increased in the secondary and primary prevention cohorts (HR, 2.07; 95% CI, 1.43-3.00 versus HR, 1.52; 95% CI, 0.70-3.29; interaction P value=0.63). CONCLUSIONS: Patients with type 2 diabetes mellitus and prior cardiovascular events had higher rates of cardiovascular outcomes compared with the primary prevention patients. Canagliflozin reduced cardiovascular and renal outcomes with no statistical evidence of heterogeneity of the treatment effect across the primary and secondary prevention groups. Additional studies will provide further insights into the effects of canagliflozin in these patient populations. CLINICAL TRIAL REGISTRATION: URL: https://www.clinicaltrials.gov. Unique identifiers: NCT01032629 and NCT01989754.

Effect of Weight Gain and Weight Loss on In Vivo Colonocyte Proliferation Rate in People with Obesity.

OBJECTIVE: To evaluate the effects of diet-induced changes in energy balance and body weight on in vivo colonocyte fractional proliferation rates (FPR) in people with obesity. METHODS: In vivo colonocyte FPR was assessed in 31 men and women with obesity (BMI: 35.4 ± 4.0 kg/m2 , age: 52.6 ± 8.9 years) before and after diet-induced weight loss, weight gain, or weight maintenance. Subjects ingested aliquots of 2 H2 O (heavy water) daily for 4 to 7 days, followed by flexible sigmoidoscopy with colon biopsies to assess the incorporation of 2 H into the DNA of dividing colonocytes. RESULTS: Colonocyte FPR averaged 12.7% ± 3.8% per day and correlated directly with intra-abdominal adipose tissue (IAAT) volume (r = 0.364, P = 0.044). Colonocyte FPR decreased in the weight loss group, did not change in the weight maintenance group, and increased in the weight gain group. The change in colonocyte FPR correlated directly with the percent change in body weight (r = 0.409, P = 0.028) and IAAT volume (r = 0.598, P = 0.001). CONCLUSIONS: A high-calorie diet and weight gain increase, whereas a low-calorie diet and weight loss decrease, in vivo colonocyte proliferation rate in people with obesity. These results suggest that changes in energy balance influence the risk of developing colon cancer in people with obesity by regulating colonic mucosal growth rates.

Physiological Mechanisms of Weight Gain-Induced Steatosis in People With Obesity.

Weight gain is associated with an increase in intrahepatic triglycerides (IHTGs), and is the primary cause of nonalcoholic fatty liver disease in obese individuals. We combined imaging and stable isotope tracer techniques to evaluate the physiologic mechanisms of weight gain-induced steatosis in 27 obese people. Weight gain appeared to increase IHTG content by generating an imbalance between hepatic fatty acid availability and disposal, and resulted in increased hepatic de novo lipogenesis, decreased intrahepatic fatty acid oxidation, and inadequate increases in IHTG export via very low-density lipoprotein secretion. ClinicalTrials.gov ID NCT01184170.

Effect of Duodenal-Jejunal Bypass Surgery on Glycemic Control in Type 2 Diabetes: A Randomized Controlled Trial.

OBJECTIVE: To determine whether upper gastrointestinal tract (UGI) bypass itself has beneficial effects on the factors involved in regulating glucose homeostasis in patients with type 2 diabetes (T2D). METHODS: A 12-month randomized controlled trial was conducted in 17 overweight/obese subjects with T2D, who received standard medical care (SC, n = 7, BMI = 31.7 ± 3.5 kg/m(2) ) or duodenal-jejunal bypass surgery with minimal gastric resection (DJBm) (n = 10; BMI = 29.7 ± 1.9 kg/m(2)). A 5-h modified oral glucose tolerance test was performed at baseline and at 1, 6, and 12 months after surgery or starting SC. RESULTS: Body weight decreased progressively after DJBm (7.9 ± 4.1%, 9.6 ± 4.2%, and 10.2 ± 4.3% at 1, 6, and 12 months, respectively) but remained stable in the SC group (P < 0.001). DJBm, but not SC, improved: (1) oral glucose tolerance (decreased 2-h glucose concentration, P = 0.039), (2) insulin sensitivity (decreased homeostasis model assessment of insulin resistance, P = 0.013), (3) early insulin response to a glucose load (increased insulinogenic index, P = 0.022), and (4) overall glycemic control (reduction in HbA1c with fewer diabetes medications). CONCLUSIONS: DJBm causes moderate weight loss and improves metabolic function in T2D. However, our study cannot separate the benefits of moderate weight loss from the potential therapeutic effect of UGI tract bypass itself on the observed metabolic improvements.

Hepatic Steatosis as a Marker of Metabolic Dysfunction.

Nonalcoholic fatty liver disease (NAFLD) is the liver manifestation of the complex metabolic derangements associated with obesity. NAFLD is characterized by excessive deposition of fat in the liver (steatosis) and develops when hepatic fatty acid availability from plasma and de novo synthesis exceeds hepatic fatty acid disposal by oxidation and triglyceride export. Hepatic steatosis is therefore the biochemical result of an imbalance between complex pathways of lipid metabolism, and is associated with an array of adverse changes in glucose, fatty acid, and lipoprotein metabolism across all tissues of the body. Intrahepatic triglyceride (IHTG) content is therefore a very good marker (and in some cases may be the cause) of the presence and the degree of multiple-organ metabolic dysfunction. These metabolic abnormalities are likely responsible for many cardiometabolic risk factors associated with NAFLD, such as insulin resistance, type 2 diabetes mellitus, and dyslipidemia. Understanding the factors involved in the pathogenesis and pathophysiology of NAFLD will lead to a better understanding of the mechanisms responsible for the metabolic complications of obesity, and hopefully to the discovery of novel effective treatments for their reversal.

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.

Adipose tissue monomethyl branched-chain fatty acids and insulin sensitivity: Effects of obesity and weight loss.

OBJECTIVES: An increase in circulating branched-chain amino acids (BCAA) is associated with insulin resistance. Adipose tissue is a potentially important site for BCAA metabolism. It was evaluated whether monomethyl branched-chain fatty acids (mmBCFA) in adipose tissue, which are likely derived from BCAA catabolism, are associated with insulin sensitivity. METHODS: Insulin-stimulated glucose disposal was determined by using the hyperinsulinemic-euglycemic clamp procedure with stable isotope glucose tracer infusion in nine lean and nine obese subjects, and in a separate group of nine obese subjects before and 1 year after Roux-en-Y gastric bypass (RYGB) surgery (38% weight loss). Adipose tissue mmBCFA content was measured in tissue biopsies taken in the basal state. RESULTS: Total adipose tissue mmBCFA content was ∼30% lower in obese than lean subjects (P=0.02) and increased by ∼65% after weight loss in the RYGB group (P=0.01). Adipose tissue mmBCFA content correlated positively with skeletal muscle insulin sensitivity (R(2) =35%, P=0.01, n=18). CONCLUSIONS: These results demonstrate a novel association between adipose tissue mmBCFA content and obesity-related insulin resistance. Additional studies are needed to determine whether the association between adipose tissue mmBCFA and muscle insulin sensitivity is causal or a simple association.

Adipose and muscle tissue profile of CD36 transcripts in obese subjects highlights the role of CD36 in fatty acid homeostasis and insulin resistance.

OBJECTIVE: Fatty acid (FA) metabolism is tightly regulated across several tissues and impacts insulin sensitivity. CD36 facilitates cellular FA uptake, and CD36 genetic variants associate with lipid abnormalities and susceptibility to metabolic syndrome. The objective of this study was to gain insight regarding the in vivo metabolic influence of muscle and adipose tissue CD36. For this, we determined the relationships between CD36 alternative transcripts, which can reflect tissue-specific CD36 regulation, and measures of FA metabolism and insulin resistance. RESEARCH DESIGN AND METHODS: The relative abundance of alternative CD36 transcripts in adipose tissue and skeletal muscle from 53 nondiabetic obese subjects was measured and related to insulin sensitivity and FA metabolism assessed by hyperinsulinemic-euglycemic clamps and isotopic tracers for glucose and FA. RESULTS: Transcript 1C, one of two major transcripts in adipose tissue, that is restricted to adipocytes predicted systemic and tissue (adipose, liver, and muscle) insulin sensitivity, suggesting adipocyte CD36 protects against insulin resistance. Transcripts 1B and 1A, the major transcripts in skeletal muscle, correlated with FA disposal rate and triglyceride clearance, supporting importance of muscle CD36 in clearance of circulating FA. Additionally, the common CD36 single nucleotide polymorphism rs1761667 selectively influenced CD36 transcripts and exacerbated insulin resistance of glucose disposal by muscle. CONCLUSIONS: Alternative CD36 transcripts differentially influence tissue CD36 and consequently FA homeostasis and insulin sensitivity. Adipocyte CD36 appears to be metabolically protective, and its selective upregulation might have therapeutic potential in insulin resistance.

Effect of plasma uric acid on antioxidant capacity, oxidative stress, and insulin sensitivity in obese subjects.

Oxidative stress is purported to be involved in the pathogenesis of obesity-associated insulin resistance. We evaluated whether alterations in levels of circulating uric acid (UA), a systemic antioxidant, affects the following: 1) systemic (plasma and saliva) nonenzymatic antioxidant capacity (NEAC); 2) markers of systemic (urinary 8-iso-prostaglandin-F2α) and muscle (carbonylated protein content) oxidative stress; and 3) whole-body insulin sensitivity (percentage increase in glucose uptake during a hyperinsulinemic-euglycemic clamp procedure). Thirty-one obese subjects (BMI 37.1 ± 0.7 kg/m(2)) with either high serum UA (HUA; 7.1 ± 0.4 mg/dL; n = 15) or normal serum UA (NUA; 4.5 ± 0.2 mg/dL; n = 16) levels were studied; 13 subjects with HUA levels were studied again after reduction of serum UA levels to 0 by infusing a recombinant urate oxidase. HUA subjects had 20-90% greater NEAC, but lower insulin sensitivity (40%) and levels of markers of oxidative stress (30%) than subjects in the NUA group (all P < 0.05). Acute UA reduction caused a 45-95% decrease in NEAC and a 25-40% increase in levels of systemic and muscle markers of oxidative stress (all P < 0.05), but did not affect insulin sensitivity (from 168 ± 25% to 156 ± 17%, P = NS). These results demonstrate that circulating UA is a major antioxidant and might help protect against free-radical oxidative damage. However, oxidative stress is not a major determinant of insulin action in vivo.

Association between specific adipose tissue CD4+ T-cell populations and insulin resistance in obese individuals.

BACKGROUND & AIMS: An increased number of macrophages in adipose tissue is associated with insulin resistance and metabolic dysfunction in obese people. However, little is known about other immune cells in adipose tissue from obese people, and whether they contribute to insulin resistance. We investigated the characteristics of T cells in adipose tissue from metabolically abnormal insulin-resistant obese (MAO) subjects, metabolically normal insulin-sensitive obese (MNO) subjects, and lean subjects. Insulin sensitivity was determined by using the hyperinsulinemic euglycemic clamp procedure. METHODS: We assessed plasma cytokine concentrations and subcutaneous adipose tissue CD4(+) T-cell populations in 9 lean, 12 MNO, and 13 MAO subjects. Skeletal muscle and liver samples were collected from 19 additional obese patients undergoing bariatric surgery to determine the presence of selected cytokine receptors. RESULTS: Adipose tissue from MAO subjects had 3- to 10-fold increases in numbers of CD4(+) T cells that produce interleukin (IL)-22 and IL-17 (a T-helper [Th] 17 and Th22 phenotype) compared with MNO and lean subjects. MAO subjects also had increased plasma concentrations of IL-22 and IL-6. Receptors for IL-17 and IL-22 were expressed in human liver and skeletal muscle samples. IL-17 and IL-22 inhibited uptake of glucose in skeletal muscle isolated from rats and reduced insulin sensitivity in cultured human hepatocytes. CONCLUSIONS: Adipose tissue from MAO individuals contains increased numbers of Th17 and Th22 cells, which produce cytokines that cause metabolic dysfunction in liver and muscle in vitro. Additional studies are needed to determine whether these alterations in adipose tissue T cells contribute to the pathogenesis of insulin resistance in obese people.

Metabolic response to high-carbohydrate and low-carbohydrate meals in a nonhuman primate model.

We established a model of chronic portal vein catheterization in an awake nonhuman primate to provide a comprehensive evaluation of the metabolic response to low-carbohydrate/high-fat (LCHF; 20% carbohydrate and 65% fat) and high-carbohydrate/low-fat (HCLF; 65% carbohydrate and 20% fat) meal ingestion. Each meal was given 1 wk apart to five young adult (7.8 ± 1.3 yr old) male baboons. A [U-¹³C]glucose tracer was added to the meal, and a [6,6-²H2]glucose tracer was infused systemically to assess glucose kinetics. Plasma areas under the curve (AUCs) of glucose, insulin, and C-peptide in the femoral artery and of glucose and insulin in the portal vein were higher (P ≤ 0.05) after ingestion of the HCLF compared with the LCHF meal. Compared with the LCHF meal, the rate of appearance of ingested glucose into the portal vein and the systemic circulation was greater after the HCLF meal (P < 0.05). Endogenous glucose production decreased by ∼40% after ingestion of the HCLF meal but was not affected by the LCHF meal (P < 0.05). Portal vein blood flow increased (P < 0.001) to a similar extent after consumption of either meal. In conclusion, a LCHF diet causes minimal changes in the rate of glucose appearance in both portal and systemic circulations, does not affect the rate of endogenous glucose production, and causes minimal stimulation of C-peptide and insulin. These observations demonstrate that LCHF diets cause minimal perturbations in glucose homeostasis and pancreatic ß-cell activity.

Gastric bypass and banding equally improve insulin sensitivity and ß 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 ß 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 ß 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, ß cell function, and oral glucose tolerance in nondiabetic obese adults.

Relationship between Changes in Plasma Adiponectin Concentration and Insulin Sensitivity after Niacin Therapy.

BACKGROUND: Niaspan® (extended-release niacin) is a nicotinic acid formulation used to treat dyslipidemia in obese subjects. Niaspan binds to the GPR109A receptor in adipose tissue and stimulates adiponectin secretion, which should improve insulin sensitivity. However, Niaspan therapy often causes insulin resistance. The purpose of this study was to evaluate whether Niaspan-induced changes in plasma adiponectin concentration are associated with a blunting of Niaspan's adverse effect on insulin action in obese subjects with non-alcoholic fatty liver disease (NAFLD). METHODS: A hyperinsulinemic-euglycemic clamp procedure was used to assess muscle insulin sensitivity before and after 16 weeks of Niaspan therapy in 9 obese subjects with NAFLD [age 43 ± 5 years; BMI 35.1 ± 1.3 (means ± SEM)]. RESULTS: Niaspan therapy did not affect body weight (99.1 ± 4.2 vs. 100 ± 4.4 kg) or percent body fat (37.8 ± 2.5 vs. 37.0 ± 2.5%). However, Niaspan therapy caused a 22% reduction in insulin-mediated glucose disposal (p < 0.05). The deterioration in glucose disposal was inversely correlated with the Niaspan-induced increase in plasma adiponectin concentration (r = 0.67, p = 0.05). CONCLUSIONS: These results demonstrate that Niaspan causes skeletal muscle insulin resistance, independent of changes in body weight or body fat, and the Niaspan-induced increase in plasma adiponectin concentration might partially ameliorate Niaspan's adverse effect on insulin action in obese subjects with NAFLD.

Multiorgan insulin sensitivity in lean and obese subjects.

OBJECTIVE: To provide a comprehensive assessment of multiorgan insulin sensitivity in lean and obese subjects with normal glucose tolerance. RESEARCH DESIGN AND METHODS: The hyperinsulinemic-euglycemic clamp procedure with stable isotopically labeled tracer infusions was performed in 40 obese (BMI 36.2 ± 0.6 kg/m(2), mean ± SEM) and 26 lean (22.5 ± 0.3 kg/m(2)) subjects with normal glucose tolerance. Insulin was infused at different rates to achieve low, medium, and high physiological plasma concentrations. RESULTS: In obese subjects, palmitate and glucose R(a) in plasma decreased with increasing plasma insulin concentrations. The decrease in endogenous glucose R(a) was greater during low-, medium-, and high-dose insulin infusions (69 ± 2, 74 ± 2, and 90 ± 2%) than the suppression of palmitate R(a) (52 ± 4, 68 ± 1, and 79 ± 1%). Insulin-mediated increase in glucose disposal ranged from 24 ± 5% at low to 253 ± 19% at high physiological insulin concentrations. The suppression of palmitate R(a) and glucose R(a) were greater in lean than obese subjects during low-dose insulin infusion but were the same in both groups during high-dose insulin infusion, whereas stimulation of glucose R(d) was greater in lean than obese subjects across the entire physiological range of plasma insulin. CONCLUSIONS: Endogenous glucose production and adipose tissue lipolytic rate are both very sensitive to small increases in circulating insulin, whereas stimulation of muscle glucose uptake is minimal until high physiological plasma insulin concentrations are reached. Hyperinsulinemia within the normal physiological range can compensate for both liver and adipose tissue insulin resistance, but not skeletal muscle insulin resistance, in obese people who have normal glucose tolerance.