Frederico G.S. Toledo

Increased levels of plasma acylcarnitines in obesity and type 2 diabetes and identification of a marker of glucolipotoxicity.

Dysregulation of fatty acid oxidation (FAO) is recognized as important in the pathophysiology of obesity and insulin resistance (IR). However, demonstrating FAO defects in vivo in humans has entailed complex and invasive methodologies. Recently, the identification of genetic blocks in FAO has been vastly simplified by using tandem mass spectrometry (MS/MS) of dried bloodspots to specify acylcarnitine (AcylCN) alterations characteristic for each disorder. This technology has recently been applied to examine FAO alterations in human and animal models of obesity and type 2 diabetes mellitus (T2DM). This study focused on characterizing AcylCN profiles in human plasma from individuals with obesity and T2DM during fasting and insulin‐stimulated conditions. Following an overnight fast, plasma was obtained from lean (n = 12), obese nondiabetic (n = 14), and T2DM (n = 10) participants and analyzed for AcylCN using MS/MS. Plasma samples were also obtained at the end of a 4‐h insulin‐stimulated euglycemic clamp. In obesity and T2DM, long‐chain AcylCNs were similarly significantly increased in the fasted state; free‐CN levels were also elevated. Additionally, T2DM subjects of comparable BMI had increased short‐ and medium‐chain AcylCNs, both saturated and hydroxy, as well as increased C4‐dicarboxylcarnitine (C4DC–CN) that correlated with an index of poor glycemic control (HbA1c; r = 0.74; P < 0.0001). Insulin infusion reduced all species of plasma AcylCN but this reduction was blunted in T2DM. Plasma long‐chain AcylCN species are increased in obesity and T2DM, suggesting that more fatty acids can enter mitochondria. In T2DM, many shorter species accumulate, suggesting that they have a generalized complex oxidation defect.

Skeletal Muscle Triglycerides, Diacylglycerols, and Ceramides in Insulin Resistance: Another Paradox in Endurance-Trained Athletes?

OBJECTIVE Chronic exercise and obesity both increase intramyocellular triglycerides (IMTGs) despite having opposing effects on insulin sensitivity. We hypothesized that chronically exercise-trained muscle would be characterized by lower skeletal muscle diacylglycerols (DAGs) and ceramides despite higher IMTGs and would account for its higher insulin sensitivity. We also hypothesized that the expression of key skeletal muscle proteins involved in lipid droplet hydrolysis, DAG formation, and fatty-acid partitioning and oxidation would be associated with the lipotoxic phenotype. RESEARCH DESIGN AND METHODS A total of 14 normal-weight, endurance-trained athletes (NWA group) and 7 normal-weight sedentary (NWS group) and 21 obese sedentary (OBS group) volunteers were studied. Insulin sensitivity was assessed by glucose clamps. IMTGs, DAGs, ceramides, and protein expression were measured in muscle biopsies. RESULTS DAG content in the NWA group was approximately twofold higher than in the OBS group and ~50% higher than in the NWS group, corresponding to higher insulin sensitivity. While certain DAG moieties clearly were associated with better insulin sensitivity, other species were not. Ceramide content was higher in insulin-resistant obese muscle. The expression of OXPAT/perilipin-5, adipose triglyceride lipase, and stearoyl-CoA desaturase protein was higher in the NWA group, corresponding to a higher mitochondrial content, proportion of type 1 myocytes, IMTGs, DAGs, and insulin sensitivity. CONCLUSIONS Total myocellular DAGs were markedly higher in highly trained athletes, corresponding with higher insulin sensitivity, and suggest a more complex role for DAGs in insulin action. Our data also provide additional evidence in humans linking ceramides to insulin resistance. Finally, this study provides novel evidence supporting a role for specific skeletal muscle proteins involved in intramyocellular lipids, mitochondrial oxidative capacity, and insulin resistance.

Effects of Physical Activity and Weight Loss on Skeletal Muscle Mitochondria and Relationship With Glucose Control in Type 2 Diabetes

OBJECTIVE— Reduced mitochondrial capacity in skeletal muscle occurs in type 2 diabetic patients and in those at increased risk for this disorder, but the extent to which mitochondrial dysfunction in type 2 diabetic patients is remediable by physical activity and weight loss intervention is uncertain. We sought to address whether an intervention of daily moderate-intensity exercise combined with moderate weight loss can increase skeletal muscle mitochondrial content in type 2 diabetic patients and to address the relationship with amelioration of insulin resistance and hyperglycemia. RESEARCH DESIGN AND METHODS— Muscle biopsies were obtained before and after a 4-month intervention to assess mitochondrial morphology, mitochondrial DNA content, and mitochondrial enzyme activities. Glucose control, body composition, aerobic fitness, and insulin sensitivity were measured. RESULTS— In response to a weight loss of 7.1 ± 0.8% and a 12 ± 1.6% improvement in Vo2max (P < 0.05), insulin sensitivity improved by 59 ± 21% (P < 0.05). There were significant increases in skeletal muscle mitochondrial density (by 67 ± 17%, P < 0.01), cardiolipin content (55 ± 17%, P < 0.01), and mitochondrial oxidation enzymes. Energy expenditure during physical activity correlated with the degree of improvement in insulin sensitivity (r = 0.84, P < 0.01), and, in turn, improvement in mitochondrial content was a strong correlate of intervention-induced improvement in A1C and fasting plasma glucose. CONCLUSIONS— Intensive short-term lifestyle modifications can restore mitochondrial content and functional capacity in skeletal muscle in type 2 diabetic patients. The improvement in the oxidative capacity of skeletal muscle may be a key component mediating salutary effects of lifestyle interventions on hyperglycemia and insulin resistance.

Deficiency of electron transport chain in human skeletal muscle mitochondria in type 2 diabetes mellitus and obesity

Insulin resistance in skeletal muscle in obesity and T2DM is associated with reduced muscle oxidative capacity, reduced expression in nuclear genes responsible for oxidative metabolism, and reduced activity of mitochondrial electron transport chain. The presented study was undertaken to analyze mitochondrial content and mitochondrial enzyme profile in skeletal muscle of sedentary lean individuals and to compare that with our previous data on obese or obese T2DM group. Frozen skeletal muscle biopsies obtained from lean volunteers were used to estimate cardiolipin content, mtDNA (markers of mitochondrial mass), NADH oxidase activity of mitochondrial electron transport chain (ETC), and activity of citrate synthase and beta-hydroxyacyl-CoA dehydrogenase (beta-HAD), key enzymes of TCA cycle and beta-oxidation pathway, respectively. Frozen biopsies collected from obese or T2DM individuals in our previous studies were used to estimate activity of beta-HAD. The obtained data were complemented by data from our previous studies and statistically analyzed to compare mitochondrial content and mitochondrial enzyme profile in lean, obese, or T2DM cohort. The total activity of NADH oxidase was reduced significantly in obese or T2DM subjects. The cardiolipin content for lean or obese group was similar, and although for T2DM group cardiolipin showed a tendency to decline, it was statistically insignificant. The total activity of citrate synthase for lean and T2DM group was similar; however, it was increased significantly in the obese group. Activity of beta-HAD and mtDNA content was similar for all three groups. We conclude that the total activity of NADH oxidase in biopsy for lean group is significantly higher than corresponding activity for obese or T2DM cohort. The specific activity of NADH oxidase (per mg cardiolipin) and NADH oxidase/citrate synthase and NADH oxidase/beta-HAD ratios are reduced two- to threefold in both T2DM and obesity.

Mitochondrial capacity in skeletal muscle is not stimulated by weight loss despite increases in insulin action and decreases in intramyocellular lipid content

OBJECTIVE— In obesity and type 2 diabetes, exercise combined with weight loss increases skeletal muscle mitochondrial capacity. It remains unclear whether mitochondrial capacity increases because of weight loss, improvements in insulin resistance, or physical training. In this study, we examined the effects of an intervention of weight loss induced by diet and compared these with those of a similar intervention of weight loss by diet with exercise. Both are known to improve insulin resistance, and we tested the hypothesis that physical activity, rather than improved insulin resistance, is required to increase mitochondrial capacity of muscle. RESEARCH DESIGN AND METHODS— Sixteen sedentary overweight/obese volunteers were randomized to a 16-week intervention of diet (n = 7) or diet plus exercise (n = 9). Insulin sensitivity was measured using euglycemic clamps. Mitochondria were examined in muscle biopsies before and after intervention. We measured mitochondrial content and size by electron microscopy, electron transport chain (ETC) activity, cardiolipin content, and mitochondrial DNA content. Intramyocellular content of lipid (IMCL) and fiber-type distribution were determined by histology. RESULTS— The diet-only and diet plus exercise groups achieved similar weight loss (10.8 and 9.2%, respectively); only the diet plus exercise group improved aerobic capacity. Insulin sensitivity improved similarly in both groups. Mitochondrial content and ETC activity increased following the diet plus exercise intervention but remained unchanged following the diet-only intervention, and mitochondrial size decreased with weight loss despite improvement in insulin resistance. IMCL decreased in the diet-only but not in the diet plus exercise intervention. CONCLUSIONS— Despite similar effects to improve insulin resistance, these interventions had differential effects on mitochondria. Clinically significant weight loss in the absence of increased physical activity ameliorates insulin resistance and IMCL but does not increase muscle mitochondrial capacity in obesity.

Insulin Resistance is Associated with Higher Intramyocellular Triglycerides in Type I but not Type II Myocytes Concomitant with Higher Ceramide Content

OBJECTIVE We tested the primary hypotheses that sphingolipid and diacylglycerol (DAG) content is higher within insulin-resistant muscle and that the association between intramyocellular triglycerides (IMTG) and insulin resistance is muscle fiber type specific. RESEARCH DESIGN AND METHODS A nested case-control analysis was conducted in 22 obese (BMI >30 kg/m2) women who were classified as insulin-resistant (IR; n = 12) or insulin-sensitive (IS; n = 10), determined by hyperinsulinemic-euglycemic clamp (>30% greater in IS compared with IR, P < 0.01). Sphingolipid and DAG content was determined by high-performance liquid chromatography–tandem mass spectrometry. Fiber type–specific IMTG content was histologically determined. Gene expression was determined by quantitative PCR. RESULTS Total (555 ± 53 vs. 293 ± 54 pmol/mg protein, P = 0.004), saturated (361 ± 29 vs. 179 ± 34 pmol/mg protein, P = 0.001), and unsaturated (198 ± 29 vs. 114 ± 21 pmol/mg protein, P = 0.034) ceramides were higher in IR compared with IS. DAG concentrations, however, were similar. IMTG content within type I myocytes, but not type II myocytes, was higher in IR compared with IS subjects (P = 0.005). Insulin sensitivity was negatively correlated with IMTG within type I myocytes (R = −0.51, P = 0.026), but not with IMTG within type II myocytes. The proportion of type I myocytes was lower (41 vs. 59%, P < 0.01) in IR subjects. Several genes involved in lipid droplet and fatty acid metabolism were differentially expressed in IR compared with IS subjects. CONCLUSIONS Human skeletal muscle insulin resistance is related to greater IMTG content in type I but not type II myocytes, to greater ceramide content, and to alterations in gene expression associated with lipid metabolism.

Physical Inactivity and Obesity Underlie the Insulin Resistance of Aging

OBJECTIVE Age-associated insulin resistance may underlie the higher prevalence of type 2 diabetes in older adults. We examined a corollary hypothesis that obesity and level of chronic physical inactivity are the true causes for this ostensible effect of aging on insulin resistance. RESEARCH DESIGN AND METHODS We compared insulin sensitivity in 7 younger endurance-trained athletes, 12 older athletes, 11 younger normal-weight subjects, 10 older normal-weight subjects, 15 younger obese subjects, and 15 older obese subjects using a glucose clamp. The nonathletes were sedentary. RESULTS Insulin sensitivity was not different in younger endurance-trained athletes versus older athletes, in younger normal-weight subjects versus older normal-weight subjects, or in younger obese subjects versus older obese subjects. Regardless of age, athletes were more insulin sensitive than normal-weight sedentary subjects, who in turn were more insulin sensitive than obese subjects. CONCLUSIONS Insulin resistance may not be characteristic of aging but rather associated with obesity and physical inactivity.

Surgical vs medical treatments for type 2 diabetes mellitus: a randomized clinical trial.

IMPORTANCE Many questions remain unanswered about the role of bariatric surgery for people with type 2 diabetes mellitus (T2DM). OBJECTIVE To determine feasibility of a randomized clinical trial (RCT) and compare initial outcomes of bariatric surgery and a structured weight loss program for treating T2DM in participants with grades I and II obesity. DESIGN, SETTING, AND PARTICIPANTS A 12-month, 3-arm RCT at a single center including 69 participants aged 25 to 55 years with a body mass index (calculated as weight in kilograms divided by height in meters squared) of 30 to 40 and T2DM. INTERVENTIONS Roux-en-Y gastric bypass (RYGB), laparoscopic adjustable gastric banding (LAGB), and an intensive lifestyle weight loss intervention (LWLI). MAIN OUTCOMES AND MEASURES Primary outcomes in the intention-to-treat cohort were feasibility and effectiveness measured by weight loss and improvements in glycemic control. RESULTS Of 667 potential participants who underwent screening, 69 (10.3%) were randomized. Among the randomized participants, 30 (43%) had grade I obesity, and 56 (81%) were women. Mean (SD) age was 47.3 (6.4) years and hemoglobin A1c level, 7.9% (2.0%). After randomization, 7 participants (10%) refused to undergo their allocated intervention (3 RYGB, 1 LAGB, and 3 LWLI), and 1 RYGB participant was excluded for current smoking. Twenty participants underwent RYGB; 21, LAGB; and 20, LWLI, with 12-month retention rates of 90%, 86%, and 70%, respectively. In the intention-to-treat cohort with multiple imputation for missing data, RYGB participants had the greatest mean weight loss from baseline (27.0%; 95% CI, 30.8-23.3) compared with LAGB (17.3%; 95% CI, 21.1-13.5) and LWLI (10.2%; 95% CI, 14.8-5.61) (P < .001). Partial and complete remission of T2DM were 50% and 17%, respectively, in the RYGB group and 27% and 23%, respectively, in the LAGB group (P < .001 and P = .047 between groups for partial and complete remission), with no remission in the LWLI group. Significant reductions in use of antidiabetics occurred in both surgical groups. No deaths were noted. The 3 serious adverse events included 1 ulcer treated medically in the RYGB group and 2 rehospitalizations for dehydration in the LAGB group. CONCLUSIONS AND RELEVANCE This study highlights several potential challenges to successful completion of a larger RCT for treatment of T2DM and obesity in patients with a body mass index of 30 to 40, including the difficulties associated with recruiting and randomizing patients to surgical vs nonsurgical interventions. Preliminary results show that RYGB was the most effective treatment, followed by LAGB for weight loss and T2DM outcomes at 1 year. TRIAL REGISTRATION clinicaltrials.gov Identifier: NCT01047735.

Skeletal Muscle Mitochondrial Energetics Are Associated With Maximal Aerobic Capacity and Walking Speed in Older Adults

BACKGROUND Lower ambulatory performance with aging may be related to a reduced oxidative capacity within skeletal muscle. This study examined the associations between skeletal muscle mitochondrial capacity and efficiency with walking performance in a group of older adults. METHODS Thirty-seven older adults (mean age 78 years; 21 men and 16 women) completed an aerobic capacity (VO2 peak) test and measurement of preferred walking speed over 400 m. Maximal coupled (State 3; St3) mitochondrial respiration was determined by high-resolution respirometry in saponin-permeabilized myofibers obtained from percutanous biopsies of vastus lateralis (n = 22). Maximal phosphorylation capacity (ATPmax) of vastus lateralis was determined in vivo by (31)P magnetic resonance spectroscopy (n = 30). Quadriceps contractile volume was determined by magnetic resonance imaging. Mitochondrial efficiency (max ATP production/max O2 consumption) was characterized using ATPmax per St3 respiration (ATPmax/St3). RESULTS In vitro St3 respiration was significantly correlated with in vivo ATPmax (r (2) = .47, p = .004). Total oxidative capacity of the quadriceps (St3*quadriceps contractile volume) was a determinant of VO2 peak (r (2) = .33, p = .006). ATPmax (r (2) = .158, p = .03) and VO2 peak (r (2) = .475, p < .0001) were correlated with preferred walking speed. Inclusion of both ATPmax/St3 and VO2 peak in a multiple linear regression model improved the prediction of preferred walking speed (r (2) = .647, p < .0001), suggesting that mitochondrial efficiency is an important determinant for preferred walking speed. CONCLUSIONS Lower mitochondrial capacity and efficiency were both associated with slower walking speed within a group of older participants with a wide range of function. In addition to aerobic capacity, lower mitochondrial capacity and efficiency likely play roles in slowing gait speed with age.

Insulin Therapy and Glycemic Control in Hospitalized Patients With Diabetes During Enteral Nutrition Therapy A randomized controlled clinical trial

OBJECTIVE To compare two subcutaneous insulin strategies for glycemic management of hyperglycemia in non–critically ill hospitalized patients with diabetes during enteral nutrition therapy (ENT). RESEARCH DESIGN AND METHODS Fifty inpatients were prospectively randomized to receive sliding-scale regular insulin (SSRI) alone (n = 25) or in combination with insulin glargine (n = 25). NPH insulin was added for persistent hyperglycemia in the SSRI group (glucose >10 mmol/l). RESULTS Glycemic control was similar in the SSRI and glargine groups (mean ± SD study glucose 8.9 ± 1.6 vs. 9.2 ± 1.6 mmol/l, respectively; P = 0.71). NPH insulin was added in 48% of the SSRI group subjects. There were no group differences in frequency of hypoglycemia (1.3 ± 4.1 vs. 1.1 ± 1.8%; P = 0.35), total adverse events, or length of stay. CONCLUSIONS Both insulin strategies (SSRI with the addition of NPH for persistent hyperglycemia and glargine) demonstrated similar efficacy and safety in non–critically ill hospitalized patients with type 2 diabetes during ENT.