Markers of skeletal muscle mitochondrial function and lipid accumulation are moderately associated with the homeostasis model assessment index of insulin resistance in obese men.
ABSTRACT: Lower skeletal muscle mitochondrial oxidative phosphorylation capacity (OXPHOS) and intramyocellular lipid (IMCL) accumulation have been implicated in the etiology of insulin resistance (IR) in obesity. The purpose of this study was to examine the impact of endurance exercise on biochemical and morphological measures of IMCL and mitochondrial content, and their relationship to IR in obese individuals. We examined mitochondrial content (subunit protein abundance and maximal activity of electron transport chain enzymes), IMCL/mitochondrial morphology in both subsarcolemmal (SS) and intermyofibrillar (IMF) regions by transmission electron microscopy, and intracellular lipid metabolites (diacylglycerol and ceramide) in vastus lateralis biopsies, as well as, the homeostasis model assessment index of IR (HOMA-IR) prior to and following twelve weeks of an endurance exercise regimen in healthy age- and physical activity-matched lean and obese men. Obese men did not show evidence of mitochondrial OXPHOS dysfunction, disproportionate IMCL content in sub-cellular regions, or diacylglycerol/ceramide accretion despite marked IR vs. lean controls. Endurance exercise increased OXPHOS and mitochondrial size and density, but not number of individual mitochondrial fragments, with moderate improvements in HOMA-IR. Exercise reduced SS IMCL content (size, number and density), increased IMF IMCL content, while increasing IMCL/mitochondrial juxtaposition in both regions. HOMA-IR was inversely associated with SS (r?=?-0.34; P?=?0.051) and IMF mitochondrial density (r?=?-0.29; P?=?0.096), IMF IMCL/mitochondrial juxtaposition (r?=?-0.30; P?=?0.086), and COXII (r?=?-0.32; P?=?0.095) and COXIV protein abundance (r?=?-0.35; P?=?0.052); while positively associated with SS IMCL size (r?=?0.28; P?=?0.119) and SS IMCL density (r?=?0.25; P?=?0.152). Our findings suggest that once physical activity and cardiorespiratory fitness have been controlled for, skeletal muscle mitochondrial and IMCL profile in obesity may only partially contribute to the development of IR.
Project description:Obesity is associated with poor fitness and adverse metabolic consequences in children.To investigate how exercise and lifestyle modification may improve fitness and insulin sensitivity in this population.Randomized controlled trial, 21 obese (body mass index???95% percentile) subjects, ages 10 to 17 years.Subjects were given standardized healthful lifestyle advice for 8 weeks. In addition, they were randomized to an in-home supervised exercise intervention (n?=?10) or control group (n?=?11).Fasting laboratory studies (insulin, glucose, lipid profile) and assessments of fitness, body composition, skeletal muscle oxidative phosphorylation and intramyocellular lipid content (IMCL), were performed at baseline and study completion.Subjects were 13.0?±?1.9 (standard deviation) years old, 72% female and 44% non-white. Exercise improved fitness (P?=?0.03) and power (P?=?0.01), and increased IMCL (P?=?0.02). HOMA-IR decreased among all subjects in response to lifestyle modification advice (P?=?0.01), regardless of exercise training assignment. In univariate analysis in all subjects, change in cardiovascular fitness was associated with change in HOMA-IR. In exploratory analyses, increased IMCL was associated with greater resting energy expenditure (r?=?0.78, P?=?0.005) and a decrease in fasting respiratory quotient (r?=?-0.70, P?=?0.02) (n?=?11).Change in fitness was found to be related to change in insulin resistance in response to lifestyle modification and exercise in obese children. IMCL increased with exercise in these obese children, which may reflect greater muscle lipid oxidative capacity.
Project description:Mitochondrial dysfunction plays a role in the development of muscle insulin resistance (IR) and the accumulation of intramyocellular lipid (IMCL) in skeletal muscle that can, in turn, interfere with insulin signaling. The purpose of this study was to assess mitochondrial function (MF) and IMCL in obese adolescent girls with and without IR to determine whether: (1) Girls with IR have impaired MF, and (2) impaired MF in girls with IR is related to higher IMCL.We examined 22 obese girls aged 13-21 years old for IR [defined as a homeostasis model assessment of insulin resistance (HOMA-IR) value >4. Phosphorus magnetic resonance spectroscopy (31P-MRS) and proton magnetic resonance spectroscopy (1H-MRS), respectively, were used to determine MF and IMCL of the soleus muscle along with magnetic resonance imaging (MRI) measures of visceral, subcutaneous, and total adipose tissue (VAT, SAT, and TAT) in girls with HOMA-IR >4 (insulin-resistant group) versus HOMA-IR ≤ 4 (insulin-sensitive group). Serum lipids and waist-to-hip ratio (W/H) were also measured.Girls with IR (n=8) did not differ from the insulin-sensitive group (n=14) for age, bone age, weight, VAT, SAT, TAT, or IMCL. However, the insulin-resistant group had higher W/H. Additionally the insulin-resistance group had a lower log rate of postexercise phosphocreatine (PCr) recovery (ViPCr) and a higher log PCr recovery constant (tau), indicative of impaired MF.Obese girls with increased IR have impaired mitochondrial function. This association is not mediated by alterations in IMCL or adipose tissue. Further studies are necessary to determine whether there is a causal relation between impaired mitochondrial function and IR in obesity and mediators of such a relationship.
Project description:INTRODUCTION:Current evidence indicates mitochondrial dysfunction in humans with obesity. Acute exercise appears to enhance mitochondrial function in the muscle of nonobese humans, but its effects on mitochondrial function in muscle of humans with obesity are not known. We sought to determine whether acute aerobic exercise stimulates mitochondrial function in subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondria in humans with obesity. METHODS:We assessed maximal adenosine triphosphate production rate (MAPR) and citrate synthase (CS) activity in isolated SS and IMF mitochondria from subjects with body mass index < 27 kg·m (median age, 25 yr; interquartile range, 22-39 yr) and subjects with body mass index > 32 kg·m (median age, 29 yr; interquartile range, 20-39 yr) before and 3 h after a 45-min cycling exercise at an intensity corresponding to 65% HR reserve. The SS and IMF mitochondria were isolated from muscle biopsies using differential centrifugation. Maximal adenosine triphosphate production rate and CS activities were determined using luciferase-based and spectrophotometric enzyme-based assays, respectively. RESULTS:Exercise increased MAPR in IMF mitochondria in both nonobese subjects and subjects with obesity (P < 0.05), but CS-specific activity did not change in either group (P > 0.05). Exercise increased MAPR supported by complex II in SS mitochondria, in both groups (P < 0.05), but MAPR supported by complex I or palmitate did not increase by exercise in the subjects with obesity (P > 0.05). Citrate synthase-specific activity increased in SS mitochondria in response to exercise only in nonobese subjects (P < 0.05). CONCLUSIONS:In nonobese humans, acute aerobic exercise increases MAPR in both SS and IMF mitochondria. In humans with obesity, the exercise increases MAPR in IMF mitochondria, but this response is less evident in SS mitochondria.
Project description:Insulin resistance is associated with the higher content of intermuscular adipose tissue (IMAT) and the saturation of intramyocellular lipid (IMCL), but a paucity of data exist in humans. This study examined associations among IMAT content, IMCL saturation, and fasting glucose concentration in middle-aged and older adults with overweight or obesity.Seventy-five subjects (26 males, 49 females) were recruited and thigh muscle and IMAT were assessed using magnetic resonance imaging. Vastus lateralis tissue was acquired from a subset of nine subjects and IMCL content and saturation were assessed using nonlinear dual complex microscopy.The characteristics of the 75 subjects were as follows: age 59±11 years, body mass index 30±5 kg/m², fasting glucose concentration 5.2±0.5 mmol/L, fasting insulin concentration 12.2±7.3 ?U/mL, fasting homeostatic model assessment of insulin resistance (HOMA-IR) 2.9±2.0 (mean±SD). IMAT to muscle tissue (MT) volume ratio was positively associated with the saturated fatty acid to unsaturated fatty acid ratio in IMCL. IMAT:MT was positively associated with fasting glucose concentration and HOMA-IR. IMCL saturation was positively associated with fasting glucose concentration while muscle cell area, IMCL area, and % IMCL in muscle cell were not associated with fasting glucose concentration.These results indicate that higher intermuscular fat content and IMCL saturation may impact fasting glucose concentration in middle-aged and older adults with overweight or obesity. The centralization of adipose tissue in the appendicular region of the body may promote insulin resistance.
Project description:BACKGROUND:Skeletal muscle mitochondrial content and function appear to be altered in obesity. Mitochondria in muscle are found in well-defined regions within cells, and they are arranged in a way that form distinct subpopulations of subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondria. We sought to investigate differences in the proteomes of SS and IMF mitochondria between lean subjects and subjects with obesity. METHODS:We performed comparative proteomic analyses on SS and IMF mitochondria isolated from muscle samples obtained from lean subjects and subjects with obesity. Mitochondria were isolated using differential centrifugation, and proteins were subjected to label-free quantitative tandem mass spectrometry analyses. Collected data were evaluated for abundance of mitochondrial proteins using spectral counting. The Reactome pathway database was used to determine metabolic pathways that are altered in obesity. RESULTS:Among proteins, 73 and 41 proteins showed different (mostly lower) expression in subjects with obesity in the SS and IMF mitochondria, respectively (false discovery rate-adjusted P???0.05). We specifically found an increase in proteins forming the tricarboxylic acid cycle and electron transport chain (ETC) complex II, but a decrease in proteins forming protein complexes I and III of the ETC and adenosine triphosphate (ATP) synthase in subjects with obesity in the IMF, but not SS, mitochondria. Obesity was associated with differential effects on metabolic pathways linked to protein translation in the SS mitochondria and ATP formation in the IMF mitochondria. CONCLUSIONS:Obesity alters the expression of mitochondrial proteins regulating key metabolic processes in skeletal muscle, and these effects are distinct to mitochondrial subpopulations located in different regions of the muscle fibers. TRIAL REGISTRATION:ClinicalTrials.gov (NCT01824173).
Project description:Purpose:An increasing number of studies have linked the severity of obstructive sleep apnea (OSA) with metabolic dysfunction. However, little is known about the lipid compartments (intramyocellular [IMCL] and extramyocellular [EMCL] lipids) inside the musculature in these patients. The present study was designed to investigate the IMCL and EMCL, biochemical data, and functional performance in patients with severe OSA, and to examine the correlations between intramuscular lipid contents and test variables. Participants and Methods:Twenty patients with severe OSA (apnea-hypopnea index [AHI]: ?30/h; body mass index [BMI]: 26.05±2.92) and 20 age- and BMI-matched controls (AHI <5/h) were enrolled. Proton magnetic resonance spectroscopy was used to measure the IMCL and EMCL of the right vastus lateralis muscle. Biochemical data, including levels of fasting plasma glucose, insulin, lipid profiles, and high-sensitivity C-reactive protein (hsCRP), were measured. Insulin resistance index (IR) was calculated using the homeostasis model assessment method. Performance tests included a cardiopulmonary exercise test and knee extension strength and endurance measurements. Results:Patients with severe OSA had significantly (P<0.05) lower values of IMCL (14.1±5.4 AU) and EMCL (10.3±5.8 AU) compared to the control group (25.2±17.6 AU and 14.3±11.1 AU, respectively). Patients with severe OSA had significantly higher hsCRP, IR, and dyslipidemia compared with controls (all P<0.05). Furthermore, IMCL was negatively correlated with AHI, cumulative time with nocturnal pulse oximetric saturation lower than 90% (TSpO2<90%) (?=-0.35, P<0.05), IR (?=-0.40, P<0.05), glucose (?=-0.33, P<0.05), and insulin (?=-0.36, P<0.05), and positively correlated with lowest oximetric saturation (?=0.33, P<0.01). Conclusion:Skeletal muscle dysfunction and metabolic abnormalities were observed in patients with OSA that did not have obesity. IMCL was positively correlated with aerobic capacity and muscular performance, but negatively correlated with AHI and IR. Large-scale clinical trials are required to explore the complicated mechanism among OSA, intramuscular metabolism, and insulin action. Clinical Trial Registration:ClinicalTrials.gov Identifier: NCT00813852.
Project description:Sarcopenia and exercise intolerance are major contributors to reduced quality of life in the elderly for which there are few effective treatments. We tested whether enhancing mitochondrial function and reducing mitochondrial oxidant production with SS-31 (elamipretide) could restore redox balance and improve skeletal muscle function in aged mice. Young (5 mo) and aged (26 mo) female C57BL/6Nia mice were treated for 8-weeks with 3?mg/kg/day SS-31. Mitochondrial function was assessed in vivo using 31P and optical spectroscopy. SS-31 reversed age-related decline in maximum mitochondrial ATP production (ATPmax) and coupling of oxidative phosphorylation (P/O). Despite the increased in vivo mitochondrial capacity, mitochondrial protein expression was either unchanged or reduced in the treated aged mice and respiration in permeabilized gastrocnemius (GAS) fibers was not different between the aged and aged+SS-31 mice. Treatment with SS-31 also restored redox homeostasis in the aged skeletal muscle. The glutathione redox status was more reduced and thiol redox proteomics indicated a robust reversal of cysteine S-glutathionylation post-translational modifications across the skeletal muscle proteome. The gastrocnemius in the age+SS-31 mice was more fatigue resistant with significantly greater mass compared to aged controls. This contributed to a significant increase in treadmill endurance compared to both pretreatment and untreated control values. These results demonstrate that the shift of redox homeostasis due to mitochondrial oxidant production in aged muscle is a key factor in energetic defects and exercise intolerance. Treatment with SS-31 restores redox homeostasis, improves mitochondrial quality, and increases exercise tolerance without an increase in mitochondrial content. Since elamipretide is currently in clinical trials these results indicate it may have direct translational value for improving exercise tolerance and quality of life in the elderly.
Project description:We investigated the relationship between insulin resistance markers and subsarcolemmal (SS) and intramyofibrillar (IMF) ceramide concentrations, as well as the contribution of plasma palmitate (6.5-h infusion of [U-13C]palmitate) to intramyocellular ceramides. Seventy-six postabsorptive men and women had muscle biopsies 1.5, 6.5, and 24 h after starting the tracer infusion. Concentrations and enrichment of muscle ceramides were measured by liquid chromatography-tandem mass spectrometry. We found that HOMA of insulin resistance, plasma insulin, and triglyceride concentrations were positively correlated with SS C16:0 and C18:1 ceramide, but not SS C14:0-Cer, C20:0-Cer, C24:0-Cer, and C24:1-Cer concentrations; IMF ceramide concentrations were not correlated with any metabolic parameters. The fractional contribution of plasma palmitate to 16:0 ceramide was greater in SS than IMF (SS, 18.2% vs. IMF, 8.7%; P = 0.0006). Plasma insulin concentrations correlated positively with the fractional contribution of plasma palmitate to SS 16:0 ceramide. The fractional contribution of plasma palmitate to intramyocellular SS 16:0 ceramide was positively correlated with SS C16:0 ceramide concentrations (? = 0.435; P = 0.002). We conclude that skeletal muscle SS ceramides, especially C16 to C18 chain lengths and the de novo synthesis of intramyocellular ceramide from plasma palmitate are associated with markers of insulin resistance.
Project description:BACKGROUND/OBJECTIVES:Accumulation of lipid droplets inside skeletal muscle fibers (intramyocellular lipids or IMCL) with increasing obesity has been linked to skeletal muscle insulin resistance and risk of type 2 diabetes in both adults and prepubertal children. We aimed to evaluate the associations of race, genotype, prenatal factors, and postnatal factors with IMCL in early childhood. SUBJECTS/METHODS:This study was a secondary analysis performed on the GUSTO birth cohort. Soleus muscle IMCL of 392 children at 4.5 years of age was measured by magnetic resonance spectroscopy, of which usable imaging data were obtained from 277 children (137 Chinese, 87 Malays, and 53 Indians). Metabolic assessments (fasting glucose, insulin, and HOMA-IR) were performed at age 6. RESULTS:The mean IMCL level at 4.5 years was 0.481?±?0.279% of water resonance (mean?±?sd). Corroborating with results from adults, Indian children had the highest IMCL levels compared with Malay and Chinese children. Among the prenatal factors, the rate of gestational weight gain (GWG rate) was associated with offspring IMCL (B?=?0.396 (0.069, 0.724); p?=?0.018). Both race and GWG rate continued to be associated with offspring IMCL even after accounting for current offspring BMI. Postnatally, IMCL was associated with shorter breastfeeding duration (B?=?0.065 (0.001, 0.128); p?=?0.045) and conditional relative weight gain between ages 2 and 3 (B?=?0.052 (0.012, 0.093); p?=?0.012). The associations with postnatal factors were attenuated after adjusting for current offspring BMI. IMCL was positively associated with offspring BMI (B?=?0.028 (0.012, 0.044); p?=?0.001). IMCL levels were not associated with fasting glucose, fasting insulin, and HOMA-IR at age 6. CONCLUSION:This study provides evidence that IMCL accumulation occurs in early childhood and that developmental factors and race are associated with it. We also show that early childhood IMCL accumulation is well tolerated, suggesting that the adverse associations between IMCL and insulin resistance may emerge at older ages.
Project description:Obesity is associated with mitochondrial dysfunction in skeletal muscle. Increasing the plasma amino acid (AA) concentrations stimulates mitochondrial adenosine triphosphate (ATP) production in lean individuals.To determine whether acute elevation in plasma AAs enhances muscle mitochondrial respiration and ATP production in subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondria in obese adults.Assessment of SS and IMF mitochondrial function during saline (i.e., control) and AA infusions.Eligible participants were healthy lean (body mass index, <25 kg/m2; age, 37 ± 3 years; n = 10) and obese (body mass index >30 kg/m2; age 35 ± 3 years; n = 11) subjects.Single trial of saline infusion followed by AA infusion. SS and IMF mitochondria were isolated from muscle biopsies collected at the end of the saline and AA infusions.Mitochondrial respiration and ATP production.AA infusion increased adenosine 5'-diphosphate (ADP)-stimulated respiration and ATP production rates of SS mitochondria in the lean (P < 0.05), but not obese, subjects. Furthermore, AA infusion increased the uncoupled (i.e., non-ADP-stimulated) respiration of SS mitochondria in the lean subjects only (P < 0.05). AA infusion had no effect on any of these parameters in IMF mitochondria in either lean or obese subjects (P > 0.05).Increasing the plasma AA concentrations enhances the capacity for respiration and ATP production of muscle SS, but not IMF, mitochondria in lean individuals, in parallel with increases in uncoupled respiration. However, neither of these parameters increases in muscle SS or IMF mitochondria in obese individuals.