Skeletal Muscle Oxidative Capacity Research Articles

Effect of l-arginine on energy metabolism, skeletal muscle and brown adipose tissue in South Asian and Europid prediabetic men: a randomised double-blinded crossover study

Aims/hypothesisIndividuals of South Asian origin are at increased risk of developing type 2 diabetes mellitus and associated comorbidities compared with Europids. Disturbances in energy metabolism may contribute to this increased risk. Skeletal muscle and possibly also brown adipose tissue (BAT) are involved in human energy metabolism and nitric oxide (NO) is suggested to play a pivotal role in regulating mitochondrial biogenesis in both tissues. We aimed to investigate the effects of 6 weeks of supplementation with l-arginine, a precursor of NO, on energy metabolism by BAT and skeletal muscle, as well as glucose metabolism in South Asian men compared with men of European descent.MethodsWe included ten Dutch South Asian men (age 46.5 ± 2.8 years, BMI 30.1 ± 1.1 kg/m2) and ten Dutch men of European descent, that were similar with respect to age and BMI, with prediabetes (fasting plasma glucose level 5.6–6.9 mmol/l or plasma glucose levels 2 h after an OGTT 7.8–11.1 mmol/l). Participants took either l-arginine (9 g/day) or placebo orally for 6 weeks in a randomised double-blind crossover study. Participants were eligible to participate in the study when they were aged between 40 and 55 years, had a BMI between 25 and 35 kg/m2 and did not have type 2 diabetes. Furthermore, ethnicity was defined as having four grandparents of South Asian or white European origin, respectively. Blinding of treatment was done by the pharmacy (Hankintatukku) and an independent researcher from Leiden University Medical Center randomly assigned treatments by providing a coded list. All people involved in the study as well as participants were blinded to group assignment. After each intervention, glucose tolerance was determined by OGTT and basal metabolic rate (BMR) was determined by indirect calorimetry; BAT activity was assessed by cold-induced [18F]fluorodeoxyglucose ([18F]FDG) positron emission tomography–computed tomography scanning. In addition, a fasting skeletal muscle biopsy was taken and analysed ex vivo for respiratory capacity using a multisubstrate protocol. The primary study endpoint was the effect of l-arginine on BAT volume and activity.Resultsl-Arginine did not affect BMR, [18F]FDG uptake by BAT or skeletal muscle respiration in either ethnicity. During OGTT, l-arginine lowered plasma glucose concentrations (AUC0–2 h − 9%, p < 0.01), insulin excursion (AUC0–2 h − 26%, p < 0.05) and peak insulin concentrations (−26%, p < 0.05) in Europid but not South Asian men. This coincided with enhanced cold-induced glucose oxidation (+44%, p < 0.05) in Europids only. Of note, in skeletal muscle biopsies several respiration states were consistently lower in South Asian men compared with Europid men.Conclusions/interpretationl-Arginine supplementation does not affect BMR, [18F]FDG uptake by BAT, or skeletal muscle mitochondrial respiration in Europid and South Asian overweight and prediabetic men. However, l-arginine improves glucose tolerance in Europids but not in South Asians. Furthermore, South Asian men have lower skeletal muscle oxidative capacity than men of European descent.FundingThis study was funded by the EU FP7 project DIABAT, the Netherlands Organization for Scientific Research, the Dutch Diabetes Research Foundation and the Dutch Heart Foundation.Trial registration:ClinicalTrials.gov NCT02291458.

Iron deficiency as energetic insult to skeletal muscle in chronic diseases.

Specific skeletal myopathy constitutes a common feature of heart failure, chronic obstructive pulmonary disease, and type 2 diabetes mellitus, where it can be characterized by the loss of skeletal muscle oxidative capacity. There is evidence from in vitro and animal studies that iron deficiency affects skeletal muscle functioning mainly in the context of its energetics by limiting oxidative metabolism in favour of glycolysis and by alterations in both carbohydrate and fat catabolic processing. In this review, we depict the possible molecular pathomechanisms of skeletal muscle energetic impairment and postulate iron deficiency as an important factor causally linked to loss of muscle oxidative capacity that contributes to skeletal myopathy seen in patients with heart failure, chronic obstructive pulmonary disease, and type 2 diabetes mellitus.

In This Issue…

A wide variety of clinical and basic science articles comprise this issue of the Canadian Journal of Diabetes. Some of the topics covered in this issue are included below. Cimo and Dewa present a qualitative study aimed at exploring the perspectives of adults with type 2 diabetes and mental illness. The authors studied the challenges to engaging in self-care behaviours and accessing diabetes education services (pages 372–81). They highlight the importance of addressing these issues in this population, given the increased prevalence of type 2 diabetes among individuals with mental health illnesses and poorer self-care practices and, ultimately, the poorer outcomes observed in this population. The authors conducted focus groups with individuals who self-identified as having type 2 diabetes and major depressive disorders. Transcripts were analyzed and major themes identified. Participants identified a wide range of barriers to care, including physiological, physical and social challenges. The authors suggest that addressing these issues will be necessary to close the gaps in care that currently exist in this population. Combined aerobic and anaerobic exercise improved the oxidative capacity of skeletal muscle and improved insulin sensitivity in a rodent model of type 1 diabetes, according to the authors of this study (pages 404–11). The improvement in the oxidative capacity of muscle in the combined aerobic and anaerobic group was greater than that of the aerobic-only group. This result led the authors to suggest that combined exercise training may result in a synergistic effect on the oxidative capacity of muscle. Contrary to their original hypothesis, combined aerobic and anaerobic exercise did not reduce lipid accumulation in the skeletal muscle; this was seen in the aerobic-only exercise group. The authors hypothesize that although lipid stores were not decreased, the composition of the lipid stores may differ in the combined aerobic and anaerobic exercise group. They suggest that the fat stores in the aerobic- and anaerobic-exercised rodents are potentially composed of energy-rich neutral triacylglycerol molecules in comparison to the insulin-desensitizing diacylglycerol molecules seen in unexercised animals. Thus, the animals undergoing combined aerobic and anaerobic exercise would have access to energy stores without the effect of insulin resistance. The authors suggest that combined exercise may promote positive metabolic adaptation with increased capacity to both store and oxidize lipids, compared with aerobic activity alone. This is an intriguing hypothesis that is yet to be confirmed among those living with type 1 diabetes. Increased awareness of the criteria and contraindications for islet-cell transplantation is needed for people living with type 1 diabetes and health-care providers, according to Ling et al (pages 419–25). In this article, the authors describe the referral patterns and initial eligibility assessment for the largest clinical islet-cell transplant program in Canada. The authors undertook a retrospective chart review (2009 to 2012) to identify the most common factors resulting in an applicant's being deemed eligible or ineligible for islet-cell transplantation. Overall, only 19% of applicants were deemed acceptable for listing for transplant. The majority of applicants were self-referrals, and among the indications for no transplant, severe hypoglycemia and glucose lability were the most common causes of ineligibility. In addition, the use of a suboptimal insulin regimen was the most common exclusion criterion identified. The majority of applicants were from Alberta. Only a small number of applications came from the 2 most populous provinces (Ontario and Quebec), despite neither of these provinces having a transplant program at the time. In addition to increasing awareness of eligibility for islet-cell transplantation, the authors suggest that their findings can be used as benchmarks for future studies and ongoing program evaluation. Conflicts of interest: None.

Oxygen availability and skeletal muscle oxidative capacity in patients with peripheral artery disease: implications from in vivo and in vitro assessments.

Evidence suggests that the peak skeletal muscle mitochondrial ATP synthesis rate ( Vmax) in patients with peripheral artery disease (PAD) may be attenuated due to disease-related impairments in O2 supply. However, in vitro assessments suggest intrinsic deficits in mitochondrial respiration despite ample O2 availability. To address this conundrum, Doppler ultrasound, near-infrared spectroscopy, phosphorus magnetic resonance spectroscopy, and high-resolution respirometry were combined to assess convective O2 delivery, tissue oxygenation, Vmax, and skeletal muscle mitochondrial capacity (complex I + II, state 3 respiration), respectively, in the gastrocnemius muscle of 10 patients with early stage PAD and 11 physical activity-matched healthy control (HC) subjects. All participants were studied in free-flow control conditions (FF) and with reactive hyperemia (RH) induced by a period of brief ischemia during the last 30 s of submaximal plantar flexion exercise. Patients with PAD repeated the FF and RH trials under hyperoxic conditions (FF + 100% O2 and RH + 100% O2). Compared with HC subjects, patients with PAD exhibited attenuated O2 delivery at the same absolute work rate and attenuated tissue reoxygenation and Vmax after relative intensity-matched exercise. Compared with the FF condition, only RH + 100% O2 significantly increased convective O2 delivery (~44%), tissue reoxygenation (~54%), and Vmax (~60%) in patients with PAD ( P < 0.05), such that Vmax was now not different from HC subjects. Furthermore, there was no evidence of an intrinsic mitochondrial deficit in PAD, as assessed in vitro with adequate O2. Thus, in combination, this comprehensive in vivo and in vitro investigation implicates O2 supply as the predominant factor limiting mitochondrial oxidative capacity in early stage PAD. NEW & NOTEWORTHY Currently, there is little accord as to the role of O2 availability and mitochondrial function in the skeletal muscle dysfunction associated with peripheral artery disease. This is the first study to comprehensively use both in vivo and in vitro approaches to document that the skeletal muscle dysfunction associated with early stage peripheral artery disease is predominantly a consequence of limited O2 supply and not the impact of an intrinsic mitochondrial defect in this pathology.

Acute Resistance Exercise Improves Postprandial Lipid Metabolism in Men with Obesity and Prediabetes

Purpose: The purpose of this study was to characterize the effect of acute resistance exercise on post-prandial lipid metabolism in obese men with prediabetes using a novel dual-tracer approach. Participants: Ten men with obesity (age 47 ± 10, BMI 33 ± 2) and prediabetes (fasting glucose 110 ± 4 mg/dL, HbA1c 5.6% ± .2%, 2-hour OGTT glucose 162 ± 14 mg/dL). Methods: Randomized cross-over design. Participants completed a 1-hour bout of whole-body resistance exercise (RE: 8 exercises, 3 sets, 12 reps, 80% 1RM), or 1-hour of rest on separate visits. Participants received a constant infusion of [U-13C16] palmitate and consumed a mixed meal containing 10 mg/kg body weight of [(13C4-palmitate)3] tripalmitin to assess incorporation of endogenous and exogenous fatty acids into postprandial lipids, respectively. Plasma samples were analyzed for total triglyceride (TG), chylomicron, triglyceride rich lipoprotein (TRL), and fatty acid concentrations and isotopic enrichment of tracers. Indirect calorimtery was used to measure whole-body lipid oxidation. Skeletal muscle biopsies were used to measure muscle mitochondrial fatty acid oxidation capacity using high-resolution respirometry. Results: Compared to rest, a single bout of RE reduced post-prandial total TG, chylomicron-TG, VLDL-TG, and TRL-TG concentration area under the curve (all p&amp;lt;0.05). Enrichment analyses revealed the contribution of meal-derived TG to circulating chylomicrons and TRL was significantly reduced after RE, as was the contribution of TG in chylomicrons that came from the meal (all p&amp;lt;0.05). RE increased whole-body lipid oxidation for up to three hours after the exercise session, and significantly improved skeletal muscle oxidative capacity (p=.031). Conclusions: Resistance exercise improves post-prandial lipid clearance and oxidation, thereby reducing post-prandial triglyceride excursions in men with obesity and prediabetes. These improvements could lower the risk of CVD and progression to T2DM. Disclosure A. Bittel: None. D. Bittel: None. B.W. Patterson: None. B. Mittendorfer: None. W.T. Cade: None.

Genetic variants predicting aerobic capacity response to training are also associated with skeletal muscle oxidative capacity in moderate-to-severe COPD.

Muscle oxidative capacity is a major determinant of maximum oxygen uptake (V̇O2max). V̇O2max predicts survival in humans. Muscle oxidative capacity is low in chronic obstructive pulmonary disease (COPD) and can be assessed from the muscle oxygen consumption recovery rate constant (k) by near-infrared spectroscopy. We hypothesized that 11 SNPs, previously associated with the increase in V̇O2max following exercise training, would correlate with k in 152 non-Hispanic White and African American smokers with and without COPD. Associations were adjusted for age, weight, FEV1% predicted, steps/day, and principal components of genetic ancestry. No SNPs were significantly associated with k. rs2792022 within BTAF1 (β = 0.130, P = 0.053) and rs24575771 within SLC22A3 (β = 0.106, P = 0.058) approached nominal significance. Case-control stratification identified three SNPs nominally associated with k in moderate-to-severe COPD (rs6481619 within SVIL β = 0.152, P = 0.013; BTAF1 β = 0.196, P = 0.046; rs7386139 within DEPTOR β = 0.159, P = 0.047). These data support further study of the genomic contributions to skeletal muscle dysfunction in COPD.

Mild hyperbaric oxygen inhibits the growth-related decline in skeletal muscle oxidative capacity and prevents hyperglycemia in rats with type 2 diabetes mellitus.

Humans and animals with type 2 diabetes mellitus (T2DM) exhibit low skeletal muscle oxidative capacity and impaired glucose metabolism. The aim of the present study was to investigate the effects of exposure to mild hyperbaric oxygen on these changes in obese rats with T2DM. Five-week-old non-diabetic Long-Evans Tokushima Otsuka (LETO) and diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats were divided into normobaric (LETO-NB and OLETF-NB) and mild hyperbaric oxygen (LETO-MHO and OLETF-MHO) groups. The LETO-MHO and OLETF-MHO groups received 1266 hPa with 36% oxygen for 3 h daily for 22 weeks. Fasting and non-fasting blood glucose, HbA1c, and triglyceride levels were lower in the OLETF-MHO group than in the OLETF-NB group (P < 0.05). In the soleus muscle, peroxisome proliferator-activated receptor δ/β (Pparδ/β), Pparγ, and PPARγ coactivator-1α (Pgc-1α) mRNA levels were lower in the OLETF-NB group than in all other groups (P < 0.05), whereas myogenin (Myog) and myogenic factor 5 (Myf5) mRNA levels were higher in the OLETF-MHO group than in the LETO-NB and OLETF-NB groups (P < 0.05). The soleus muscles in the OLETF-NB group contained only low-oxidative Type I fibers, whereas those in all other groups contained high-oxidative Type IIA and Type IIC fibers in addition to Type I fibers. Exposure to mild hyperbaric oxygen inhibits the decline in skeletal muscle oxidative capacity and prevents the hyperglycemia associated with T2DM. Pgc-1α, Myog, and Myf5 mRNA levels appear to be closely associated with skeletal muscle oxidative capacity in rats with T2DM.

Enhanced Local Skeletal Muscle Oxidative Capacity and Microvascular Blood Flow Following 7-Day Ischemic Preconditioning in Healthy Humans.

Ischemic preconditioning (IPC), which involves intermittent periods of ischemia followed by reperfusion, is an effective clinical intervention that reduces the risk of myocardial injury and confers ischemic tolerance to skeletal muscle. Repeated bouts of IPC have been shown to stimulate long-term changes vascular function, however, it is unclear what metabolic adaptations may occur locally in the muscle. Therefore, we investigated 7 days of bilateral lower limb IPC (4 × 5 min) above limb occlusion pressure (220 mmHg; n = 10), or sham (20 mmHg; n = 10), on local muscle oxidative capacity and microvascular blood flow. Oxidative capacity was measured using near-infrared spectroscopy (NIRS) during repeated short duration arterial occlusions (300 mmHg). Microvascular blood flow was assessed during the recovery from submaximal isometric plantar flexion exercises at 40 and 60% of maximal voluntary contraction (MVC). Following the intervention period, beyond the late phase of protection (72 h), muscle oxidative recovery kinetics were speeded by 13% (rate constant pre 2.89 ± 0.47 min-1 vs. post 3.32 ± 0.69 min-1; P < 0.05) and resting muscle oxygen consumption (mO2) was reduced by 16.4% (pre 0.39 ± 0.16%.s-1 vs. post 0.33 ± 0.14%.s-1; P < 0.05). During exercise, changes in deoxygenated hemoglobin (HHb) from rest to steady state were reduced at 40 and 60% MVC (16 and 12%, respectively, P < 0.05) despite similar measures of total hemoglobin (tHb). At the cessation of exercise, the time constant for recovery in oxygenated hemoglobin (O2Hb) was accelerated at 40 and 60% MVC (by 33 and 43%, respectively) suggesting enhanced reoxygenation in the muscle. No changes were reported for systemic measures of resting heart rate or blood pressure. In conclusion, repeated bouts of IPC over 7 consecutive days increased skeletal muscle oxidative capacity and microvascular muscle blood flow. These findings are consistent with enhanced mitochondrial and vascular function following repeated IPC and may be of clinical or sporting interest to enhance or offset reductions in muscle oxidative capacity.

Sexual dimorphism of substrate utilization: Differences in skeletal muscle mitochondrial volume density and function.

What is the central question of this study? Females rely to a greater extent than males on fat oxidation during exercise. Whether any difference in skeletal muscle mitochondrial phenotype and oxidative capacity contributes to this sexual dimorphism remains incompletely explored. What is the main finding and its importance? Female prioritization of fat during exercise occurs in parallel to augmented mitochondrial volume density and intrinsic fatty acid and lactate oxidation in skeletal muscle fibres compared with males, independently of aerobic exercise capacity. The enlarged metabolic machinery in skeletal muscle of females is associated with lower body size and leg mass. Fat oxidation during exercise is greater in females than in males. We sought to determine whether sex differences in substrate metabolism are paralleled by distinct skeletal muscle mitochondrial volume density and oxidative capacity. Whole-body substrate (fat and carbohydrate) utilization during submaximal treadmill running was assessed, and skeletal muscle biopsies were taken to determine mitochondrial volume density and function in healthy young females (n=12) and males (n=12) matched by aerobic exercise capacity and exercise performance. Females presented a lower respiratory exchange ratio (0.87±0.04 versus 0.91±0.04, P=0.023) and whole-body carbohydrate oxidation (27.8±8.3 versus 35.8±6.5mgkg-1 min-1 , P=0.027), whereas fat oxidation was higher (8.7±2.8 versus 5.9±2.6mgkg-1 min-1 , P=0.034) during submaximal exercise compared with males. In skeletal muscle biopsies, females demonstrated augmented mitochondrial volume density (7.51±1.77 versus 5.90±1.72%, P=0.035) and oxidative capacity for fatty acid [36.6±12.8 versus 24.5±7.3pmol O2 s-1 (mg wet weight)-1 , P=0.009] and lactate [71.1±24.4 versus 53.2±14.6pmol O2 s-1 (mg wet weight)-1 , P=0.040]. No sex differences in respiratory exchange ratio, whole-body fat oxidation and skeletal muscle variables were detected when adjusted for anthropometric variables including body mass or leg mass, which were lower in females. In conclusion, female prioritization of fat over carbohydrate oxidation during exercise is underpinned by augmented body size-related mitochondrial volume density, fatty acid and lactate oxidative capacity in skeletal muscle fibres.

Distinct roles for REV-ERBα and REV-ERBβ in oxidative capacity and mitochondrial biogenesis in skeletal muscle.

The nuclear receptors REV-ERBα and REV-ERBβ have been demonstrated to be core members of the circadian clock and participate in the regulation of a diverse set of metabolic functions. Due to their overlapping tissue expression patterns and gene expression profiles, REV-ERBβ is thought to be redundant to REV-ERBα. Recent work has highlighted REV-ERBα’s role in the regulation of skeletal muscle oxidative capacity and mitochondrial biogenesis. Considering the similarity between the REV-ERBs and the hypothesized overlap in function, we sought to determine whether REV-ERBβ-deficiency presented with a similar skeletal muscle phenotype as REV-ERBα-deficiency. Ectopic overexpression in C2C12 cells demonstrated that REV-ERBβ drives mitochondrial biogenesis and the expression of genes involved in fatty acid oxidation. Intriguingly, knock down of REV-ERBβ in C2C12 cultures also resulted in mitochondrial biogenesis and increased expression of genes involved in fatty acid β-oxidation. To determine whether these effects occurred in vivo, we examined REV-ERBβ-deficient mice and observed a similar increase in expression of genes involved in mitochondrial biogenesis and fatty acid β-oxidation. Consistent with these results, REV-ERBβ-deficient mice exhibited an altered metabolic phenotype compared to wild-type littermate controls when measured by indirect calorimetry. This likely compensated for the increased food consumption that occurred, possibly aiding in the maintenance of their weight over time. Since feeding behaviors are a direct circadian output, this study suggests that REV-ERBβ may have more subtle effects on circadian behaviors than originally identified. Furthermore, these data implicate REV-ERBβ in the control of skeletal muscle metabolism and energy expenditure and suggest that development of REV-ERBα versus REV-ERBβ selective ligands may have therapeutic utility in the treatment of metabolic syndrome.

Localization Of Myoglobin In Mitochondria

PURPOSE: Mitochondria play a principal role for metabolism and have a primary role in regulating respiration and energy expenditure. Recently, we showed that the muscle- specific protein myoglobin (Mb) interacted with complex IV to augment mitochondrial respiratory capacity in skeletal muscles. However, the precise mechanism for the Mb- mediated upregulation remains under debate. The present study has focused on localizing Mb within the mitochondria. METHODS: Muscle specimen from deep portion of m. Gastrocnemius in Wistar rat was homogenized. Crude mitochondria were isolated by differential centrifugations and washed with the mitochondrial isolation buffer. The isolated mitochondria were treated with proteinase K (PK), osmotic shock (OS), and SDS (or TriX) in order to digest proteins on the outer membrane and in the intramembrane. The final samples were subjected to SDS-PAGE and immunoblotting using antibodies to localize the proteins in the mitochondria. RESULTS: Western blotting analysis revealed that the PK digests Tom20, which localized on the outer membrane of mitochondria. The Tom20 band intensity decreased with the amount of PK used. Other mitochondrial proteins such as cytochrome c (intermembrane space), COX-IV (inner membrane), and PDH (matrix), were not affected by PK treatment. PK treatment did not affect Mb. The results suggested that Mb did not localize on the outer membrane of mitochondria. The combined treatment of PK, OS and SDS (or TrX) allowed immunoblotting detection of the mitochondrial proteins in specific regions of the mitochondria. For example, cytochrome c disappeared with OS treatment. Timm22 disappeared with PK+OS treatment. However, Mb was detected with either PK or OS treatment. But it cannot be detected with a combined PK+OS treatment. The results suggest that Mb associated with the inner membrane (intramembrane side, not matrix side) of the mitochondria. CONCLUSIONS: We conclude that Mb in muscle cells localizes in the cytosol and in the mitochondrial intermembrane space. Since exercise training increases Mb expressions of skeletal muscle, the increased Mb concentration may play a direct role in modulation skeletal muscle respiration and oxidative phosphorylation capacity.

Are Improvements in Skeletal Muscle Oxidative Capacity Possible in the Elderly?

Loss of skeletal muscle function is a key factor contributing to the reduced quality of life and mobility in aging individuals. While several mechanisms have been implicated, reduced skeletal muscle oxidative capacity is thought to play a major role. Exercise training is known to improve skeletal muscle oxidative capacity in young healthy populations. Whether exercise training can improve skeletal muscle oxidative capacity in elderly individuals, with associated cardiovascular risk factors, remains unclear. To address this question, we recruited 8 elderly participants from the local Dallas‐Fort Worth community (73 ± 7 yrs; m/f: 2/6; BMI: 25.9 ± 3.1 kg). Subjects completed two baseline visits to establish our day‐to‐day reproducibility, followed by 4‐weeks of handgrip exercise training at 30% of maximal voluntary contraction (MVC, non‐dominant arm), five (5) days a week. MVC was reassessed each week, and the total number of contractions was gradually increased, for a total of 600, 900, 1200, and 1500 grips per day, respectively. Skeletal muscle oxidative capacity was assessed using a well‐established near‐infrared spectroscopy (NIRS) protocol, expressed as the post‐exercise muscle oxygen consumption recovery time constant (i.e. tau, in seconds). To date, we have completed data collection on 5 of 8 participants. All five participants increased their MVC with exercise training (pre‐training MVC: 23.1 ± 17.2 kg; post‐training MVC: 26.8 ± 16.1 kg, or 16.0% increase). Despite measurable increases in muscle strength however, skeletal muscle oxidative capacity was unchanged from baseline (pre‐training tau: 45.9 ± 16.5 s; post‐training tau: 49.6 ± 13.5 s, or 8.1% increase). These data are in contrast to at least two prior reports showing an improvement in skeletal muscle oxidative capacity in young, healthy subjects, and elderly participants at least 10 years younger than those studied here. We interpret these data to reflect an upper limit to the training adaptation previously reported.Support or Funding InformationThis work was supported by a UT Arlington Interdisciplinary Research Program grant.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Moderate Intensity Endurance Exercise Training Increases Muscle Glycogen Content but Does Not Alter Substrate Oxidation in C57BL6 Mice

INTRODUCTIONAerobic exercise training induces a range of desirable cardiovascular and metabolic adaptations but questions remain regarding the minimum thresholds of intensity, duration, and frequency of training required to elicit measurable changes in health outcomes. We examined the effects of a moderate intensity treadmill endurance training protocol in mice in order to determine whether this intensity level would induce changes in body composition and serum parameters. Furthermore, we investigated the extent to which any such changes would be accompanied by similar changes in muscle and liver substrate oxidation in an effort to better characterize the suite of metabolic adaptations that occur in response to moderate intensity exercise.METHODS20 male C57BL6 mice, approximately 12 weeks of age, were randomly assigned to either an exercise (EX) or sedentary (CON) group. All animals were maintained on low‐fat (13%) rodent chow (LabDiet 5001) and group housed. The EX group underwent a 6‐week program daily treadmill exercise at speeds no greater than 20 meters/min at an incline of 5°. Moderate‐intensity training sessions elicited a 50% increase in circulating lactate, but remained below a lactate threshold level. Body composition was measured weekly by NMR. Mice were euthanized following the cessation of the exercise training protocol. Muscle and liver tissues were collected and substrate oxidation was assessed using 14C labeled substrates. Glycogen content was assayed in liver and quadriceps muscle. Serum parameters were also assessed.RESULTSThe EX group exhibited reduction in body weight and fat mass. Glycogen storage in muscle was significantly increased (p&lt;0.05) by exercise training, whereas intramuscular triglycerides were decreased (p&lt;0.05). There were no statistically significant changes observed in pyruvate, leucine, palmitate, or lignocerate oxidation between the groups, which was supported by a relative lack of changes in gene/protein expression of relevant pathways.CONCLUSIONA moderate intensity 6‐week treadmill endurance exercise program was sufficient to induce a set of “traditional” training adaptations (reduced body weight and fat mass, increased glycogen); however, the stimulus was not sufficient to alter substrate oxidative capacity in skeletal muscle. Collectively these data suggest that in order for exercise training to induce remodeling of substrate metabolism pathways at a molecular level, protocols using higher intensities may be required.Support or Funding InformationThis work was supported by NIH R01 DK103860‐01 (R.C.N.).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Partitioning key determinants of oxygen consumption: Novel insight from Dual Wavelength Diffuse Correlation Spectroscopy

Near‐infrared diffuse correlation spectroscopy (DCS) is an emerging technique for non‐invasive measurement of local muscle blood flow at the microvascular level. We have previously shown excellent agreement between single wavelength DCS and Doppler ultrasound of the brachial artery during rhythmic handgrip exercise, supporting the role of DCS in exercise physiology. Here, we report novel DCS data from our lab, incorporating two‐different wavelengths (785 nm and 852 nm), allowing for direct assessment of microvascular perfusion, together with oxyhemoglobin and deoxyhemoglobin. To‐date, we have studied eight individuals (male/female: 3/5, mean: age 48±22 (range: 22–76 years), height 170±8 cm, and weight 75±12 kg). Subjects were instrumented with the DCS probe located over the belly of the flexor digitorum profundus. Duplex ultrasound of the brachial artery was also performed as a secondary measure of skeletal muscle blood flow. Each subject performed two bouts of rhythmic hand grip exercise at 20% of their maximum voluntary contraction (MVC). Each exercise bout was preceded by a standardized resting baseline, and each period of data collection was separated by at least 10 minutes of rest. Data from each round of data collection were averaged. As reported previously using our single wavelength DCS device, blood flow index (BFI, the primary output from DCS) increased significantly (119±37%) with exercise. We also observed a −1.9±1.1% change in oxyhemoglobin and 21.8±10.0% change in deoxyhemoglobin resulting in a −5.9±2.6% change in tissue saturation with exercise. As a result, relative muscle oxygen consumption (rmVO2) increased by 160.2±55.4%. The novelty of this new approach is best illustrated by a case‐comparison between two subjects, who performed similar absolute (11 vs 10 kg) and relative work (20%), and yet achieved disparate levels of oxygen utilization during exercise (ΔrmO2 = 307% vs. 214%, Case A vs. Case B respectively). This difference appears to be explained predominantly by muscle oxygen extraction as both brachial artery blood flow and microvascular perfusion (by DCS) were similar in both subjects. In contrast, Case A exhibited a much greater change in StO2 (−17.8%) compared to Case B, whose StO2 more closely mirrored the group average (−6.8%). To help interpret these results, we evaluated skeletal muscle oxidative capacity in both subjects using an established NIRS‐based cuff occlusion protocol (Rosenberry et al. 2018. JoVE). Remarkably, these additional data corroborated our assumptions, showing a muscle oxygen consumption recovery time of 34 seconds in Case A and 93 seconds in Case B. Taken together, these data establish strong proof‐of‐concept that dual wavelength DCS can provide important mechanistic insight into the determinants of oxygen consumption. Extending these findings to patients with exercise intolerance (e.g. heart failure with preserved or reduced ejection fraction) may provide important therapeutic insight.Support or Funding InformationThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

3,5-Diiodo-L-Thyronine Affects Structural and Metabolic Features of Skeletal Muscle Mitochondria in High-Fat-Diet Fed Rats Producing a Co-adaptation to the Glycolytic Fiber Phenotype.

Hyperlipidemic state-associated perturbations in the network of factors controlling mitochondrial functions, i. e., morphogenesis machinery and metabolic sensor proteins, produce metabolic inflexibility, insulin resistance and reduced oxidative capacity in skeletal muscle. Moreover, intramyocellular lipid (IMCL) accumulation leads to tissue damage and inflammation. The administration of the naturally occurring metabolite 3,5-diiodo-L-thyronine (T2) with thyromimetic actions to high fat diet (HFD)-fed rats exerts a systemic hypolipidemic effect, which produces a lack of IMCL accumulation, a shift toward glycolytic fibers and amelioration of insulin sensitivity in gastrocnemius muscle. In this study, an integrated approach combining large-scale expression profile and functional analyses was used to characterize the response of skeletal muscle mitochondria to T2 during a HFD regimen. Long-term T2 administration to HDF rats induced a glycolytic phenotype of gastrocnemius muscle as well as an adaptation of mitochondria to the fiber type, with a decreased representation of enzymes involved in mitochondrial oxidative metabolism. At the same time, T2 stimulated the activity of individual respiratory complex I, IV, and V. Moreover, T2 prevented the HFD-associated increase in the expression of peroxisome proliferative activated receptor γ coactivator-1α and dynamin-1-like protein as well as mitochondrial morphological aberrations, favoring the appearance of tubular and tethered organelles in the intermyofibrillar regions. Remarkably, T2 reverted the HDF-associated expression pattern of proinflammatory factors, such as p65 subunit of NF-kB, and increased the fiber-specific immunoreactivity of adipose differentiation–related protein in lipid droplets. All together, these results further support a role of T2 in counteracting in vivo some of the HFD-induced impairment in structural/metabolic features of skeletal muscle by impacting the mitochondrial phenotype.

Influence of exercise on oxidative stress in patients with heart failure

Reactive oxygen species play an important role in the pathophysiology of heart failure (HF). In contrast, regular physical exercise can promote adaptations to reactive oxygen species that are beneficial for patients with HF. We completed a systematic review of randomized controlled trials that evaluate the influence of exercise on oxidative stress in patients with HF. Articles were searched in the PubMed, Cochrane, SciELO, and LILACS databases. The search was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The quality of the included studies was assessed using the Physiotherapy Evidence Database scale. We selected 12 studies with a total of 353 participants. The included patients had a left ventricle ejection fraction of < 52% and New York Heart Association functional class II or III disease. A significant increase was observed in peak oxygen consumption (between 10 and 46%) in the group that underwent training (TG). There was an improvement in the oxidative capacity of skeletal muscles in the TG, related to the positive activity of mitochondrial cytochrome c oxidase (between 27 and 41%). An increase in the expression of the enzymes glutathione peroxidase (41%), catalase (between 14 and 42%), and superoxide dismutase (74.5%), and a decrease in lipid peroxidation (between 28.8 and 58.5%) were observed in the TG. Physical training positively influenced the cardiorespiratory capacity and enhanced the benefits of oxidant and antioxidant biomarkers in patients with HF. High-intensity training promoted a 15% increase in the plasma total antioxidant capacity, whereas moderate training had no effect.

Skeletal Muscle Neurovascular Coupling, Oxidative Capacity, and Microvascular Function with 'One Stop Shop' Near-infrared Spectroscopy

Exercise represents a major hemodynamic stress that demands a highly coordinated neurovascular response in order to match oxygen delivery to metabolic demand. Reactive hyperemia (in response to a brief period of tissue ischemia) is an independent predictor of cardiovascular events and provides important insight into vascular health and vasodilatory capacity. Skeletal muscle oxidative capacity is equally important in health and disease, as it determines the energy supply for myocellular processes. Here, we describe a simple, non-invasive approach using near-infrared spectroscopy to assess each of these major clinical endpoints (reactive hyperemia, neurovascular coupling, and muscle oxidative capacity) during a single clinic or laboratory visit. Unlike Doppler ultrasound, magnetic resonance images/spectroscopy, or invasive catheter-based flow measurements or muscle biopsies, our approach is less operator-dependent, low-cost, and completely non-invasive. Representative data from our lab taken together with summary data from previously published literature illustrate the utility of each of these end-points. Once this technique is mastered, application to clinical populations will provide important mechanistic insight into exercise intolerance and cardiovascular dysfunction.

Skeletal Muscle Neurovascular Coupling, Oxidative Capacity, and Microvascular Function with 'One Stop Shop' Near-infrared Spectroscopy.

Exercise represents a major hemodynamic stress that demands a highly coordinated neurovascular response in order to match oxygen delivery to metabolic demand. Reactive hyperemia (in response to a brief period of tissue ischemia) is an independent predictor of cardiovascular events and provides important insight into vascular health and vasodilatory capacity. Skeletal muscle oxidative capacity is equally important in health and disease, as it determines the energy supply for myocellular processes. Here, we describe a simple, non-invasive approach using near-infrared spectroscopy to assess each of these major clinical endpoints (reactive hyperemia, neurovascular coupling, and muscle oxidative capacity) during a single clinic or laboratory visit. Unlike Doppler ultrasound, magnetic resonance images/spectroscopy, or invasive catheter-based flow measurements or muscle biopsies, our approach is less operator-dependent, low-cost, and completely non-invasive. Representative data from our lab taken together with summary data from previously published literature illustrate the utility of each of these end-points. Once this technique is mastered, application to clinical populations will provide important mechanistic insight into exercise intolerance and cardiovascular dysfunction.

Adaptations in muscle oxidative capacity, fiber size, and oxygen supply capacity after repeated-sprint training in hypoxia combined with chronic hypoxic exposure.

In this study, we investigate adaptations in muscle oxidative capacity, fiber size and oxygen supply capacity in team-sport athletes after six repeated-sprint sessions in normobaric hypoxia or normoxia combined with 14 days of chronic normobaric hypoxic exposure. Lowland elite field hockey players resided at simulated altitude (≥14 h/day at 2,800-3,000 m) and performed regular training plus six repeated-sprint sessions in normobaric hypoxia (3,000 m; LHTLH; n = 6) or normoxia (0 m; LHTL; n = 6) or lived at sea level with regular training only (LLTL; n = 6). Muscle biopsies were obtained from the m. vastus lateralis before (pre), immediately after (post-1), and 3 wk after the intervention (post-2). Changes over time between groups were compared, including likelihood of the effect size (ES). Succinate dehydrogenase activity in LHTLH largely increased from pre to post-1 (~35%), likely more than LHTL and LLTL (ESs = large-very large), and remained elevated in LHTLH at post-2 (~12%) vs. LHTL (ESs = moderate-large). Fiber cross-sectional area remained fairly similar in LHTLH from pre to post-1 and post-2 but was increased at post-1 and post-2 in LHTL and LLTL (ES = moderate-large). A unique observation was that LHTLH and LHTL, but not LLTL, improved their combination of fiber size and oxidative capacity. Small-to-moderate differences in oxygen supply capacity (i.e., myoglobin and capillarization) were observed between groups. In conclusion, elite team-sport athletes substantially increased their skeletal muscle oxidative capacity, while maintaining fiber size, after only 14 days of chronic hypoxic residence combined with six repeated-sprint training sessions in hypoxia. NEW & NOTEWORTHY Our novel findings show that elite team-sport athletes were able to substantially increase the skeletal muscle oxidative capacity in type I and II fibers (+37 and +32%, respectively), while maintaining fiber size after only 14 days of chronic hypoxic residence combined with six repeated-sprint sessions in hypoxia. This increase in oxidative capacity was superior to groups performing chronic hypoxic residence with repeated sprints in normoxia and residence at sea level with regular training only.

Does Exercise Effect on Mitochondrial Dysfunction and Insulin Sensitivity?

Skeletal muscle has an important role in the pathogenesis of insulin resistance. Several studies have found that insulin action may be related to the oxidative capacity of skeletal muscle. Aerobic exercises improve both insulin sensitivity and activity of oxidative enzymes in muscle. Individuals having disorders and diseases like insulin resistance, obesity or type 2 diabetes were found to have lower muscle oxidative enzyme activity. Some hypotheses have been developed regarding the hypothesis that insulin infusion stimulates the mitochondrial protein synthesis rate in skeletal muscle. The effects of exercise on mitochondrial dysfunction and insulin sensitivity are summarized and discussed in this review.