Enzyme Activity In Skeletal Muscle Research Articles

Effects of endurance training under calorie restriction on the metabolic enzyme activity and transporter levels in mouse skeletal muscle and liver

Although endurance training (ET) and calorie restriction (CR) induce metabolic adaptations in skeletal muscle, the interaction of them have yet to be clarified. This study investigated the effects of endurance training with calorie restriction on the metabolic enzyme activity and transporter levels in mouse skeletal muscle and liver. Ten-week-old male ICR mice were fed ad libitum or subjected to 30% CR. The animals were subdivided into sedentary and ET groups. The animals in the ET group performed treadmill running (20 m/min, 30 min) five days a week for five weeks. Respiratory gas analysis during 24 h of rest showed that CR, but not ET, reduced carbohydrate consumption. While ET enhanced hexokinase (HK) activity in the plantaris and soleus muscles, CR decreased HK, phosphofructokinase, and lactate dehydrogenase activities and monocarboxylate transporter (MCT) 4 protein content. Although ET and CR alone increased citrate synthase (CS) activity and MCT1 protein content in the plantaris muscle, no additive or synergistic effects were observed. In the soleus muscle, ET increased CS, β-hydroxyacyl-CoA dehydrogenase (β-HAD), and total carnitine palmitoyltransferase (CPT) activities; however, CR significantly decreased CS and β-HAD activities but enhanced total CPT activity. Additionally, CR enhanced the glucose transporter 4 protein content in the plantaris and soleus muscles. In the liver, CR enhanced the protein levels of glucose 6-phosphatase, fructose 1,6-bisphosphatase, and mitochondrial phosphoenolpyruvate carboxykinase. Moreover, ET partially normalized the CR-induced increase in fatty acid synthase and acetyl-CoA carboxylase. These observations suggest that CR enhances the capacity for glucose and fatty acid synthesis in the liver as well as the glucose and lactate uptake capacity in skeletal muscle while reducing carbohydrate consumption in skeletal muscle. It is suggested that CR partially interferes with skeletal muscle adaptations to ET. This study was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI (Grant numbers 20H04071, 21K21249, and 23K16718). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Locally applied heat stress during exercise training may promote adaptations to mitochondrial enzyme activities in skeletal muscle

There is some evidence for temperature-dependent stimulation of mitochondrial biogenesis; however, the role of elevated muscle temperature during exercise in mitochondrial adaptation to training has not been studied in humans in vivo. The purpose of this study was to determine the role of elevating muscle temperature during exercise in temperate conditions through the application of mild, local heat stress on mitochondrial adaptations to endurance training. Eight endurance-trained males undertook 3 weeks of supervised cycling training, during which mild (~ 40 °C) heat stress was applied locally to the upper-leg musculature of one leg during all training sessions (HEAT), with the contralateral leg serving as the non-heated, exercising control (CON). Vastus lateralis microbiopsies were obtained from both legs before and after the training period. Training-induced increases in complex I (fold-change, 1.24 ± 0.33 vs. 1.01 ± 0.49, P = 0.029) and II (fold-change, 1.24 ± 0.33 vs. 1.01 ± 0.49, P = 0.029) activities were significantly larger in HEAT than CON. No significant effects of training, or interactions between local heat stress application and training, were observed for complex I–V or HSP70 protein expressions. Our data provides partial evidence to support the hypothesis that elevating local muscle temperature during exercise augments training-induced adaptations to mitochondrial enzyme activity.

Effect of Yamadazyma triangularis derived peptide XHY69AP on muscle fatigue via regulation of AMPK/PGC-1α and Nrf2/Keap1 pathways

The peptide XHY69AP was derived from Yamadazyma triangularis with a molecular weight of less than 3 kDa from our lab. The objective of this study was to explore the effect of XHY69AP on muscle fatigue in vivo. Exercising mice were given 100, 200, and 400 mg/kg∙d XHY69AP by gavage daily during four weeks of treadmill training. XHY69AP was found to increase treadmill exhaustion time and energy reserve (glycogen, adenosine triphosphate, and sodium-potassium pump), decrease the metabolite accumulations (lactic acid, urea nitrogen, lactate dehydrogenase, and creatine kinase) in serum, and attenuate morphological injury of gastrocnemius muscle. Meantime, XHY69AP reduced the malondialdehyde content and improved antioxidant enzyme activities (superoxide dismutase and glutathione peroxidase) in skeletal muscles and liver to decrease oxidative damage caused by excessive exercise. Moreover, RT-qPCR and western blotting results further verified that XHY69AP activated AMPK/PGCC-1α and Nrf2/Keap1 signal pathways to relieve muscle fatigue of mice.

Naringenin promotes the expression of oxidized myofibers via the PKA signaling pathway in C57BL/6J mice and C2C12 cells

Naringenin, a citrus-derived flavonoid, has been reported to positively exert skeletal muscle function. The study designed to explore the potential role and mechanisms of naringenin on regulating the expression of oxidized myofibrils in mice and C2C12 myotubes. In this study, we found that naringenin supplementation significantly improved exercise endurance and oxygen consumption of mice, and also increased aerobic enzyme activity and oxidative myofibers expression in skeletal muscle and C2C12 cells. Meanwhile, naringenin activated the expression of p-PKA/PKA, p-LKB1/LKB1, p-AMPK/AMPK and PGC-1α in skeletal muscle. Furthermore, in vitro studies shown that inhibition of PKA, LKB1 and AMPK could attenuate naringenin-regulated increase in slow muscle fiber proteins. This study suggests that naringenin supplementation can enhance slow myofiber expression by activating the PKA signaling pathway in C57BL/6J mice and C2C12 myotubes. These findings provide a new application of naringenin as a natural candidate to regulate oxidized fiber types and endurance of skeletal muscle.

Dietary apple polyphenols enhance mitochondrial turnover and respiratory chain enzymes.

Previous studies have demonstrated the beneficial effects of apple polyphenol (AP) intake on muscle endurance. Since mitochondria are critical for muscle endurance, we investigated mitochondrial enzyme activity, biogenesis, degradation and protein quality control. Twenty-four Wistar rats were randomly fed a 5% AP diet (5% AP group, n=8), a 0.5% AP diet (0.5% AP group, n=8), or a control diet (control group, n=8). After a 4-week feeding period, the expression level of peroxisome proliferator-activated receptor γ coactivator-1α, a mitochondrial biosynthetic factor, did not increase, whereas that of transcription factor EB, another regulator of mitochondrial synthesis, significantly increased. Moreover, the mitochondrial count did not differ significantly between the groups. In contrast, mitophagy-related protein levels were significantly increased. The enzymatic activities of mitochondrial respiratory chain complexes II, III and IV were significantly higher in the AP intake group than in the control group. We conclude that AP feeding increases the activity of respiratory chain complex enzymes in rat skeletal muscles. Moreover, mitochondrial biosynthesis and degradation may have increased in AP-treated rats. NEW FINDINGS: What is the central question of this study? Does the administration of apple polyphenols (AP) affect mitochondrial respiratory chain complex enzyme activity, biogenesis, degradation and protein quality control in rat skeletal muscles? What is the main finding and its importance? AP feeding increases respiratory chain complex enzyme activity in rat skeletal muscle. Moreover, AP administration increases transcription factor EB activation, and mitophagy may be enhanced to promote degradation of dysfunctional mitochondria, but mitochondrial protein quality control was not affected.

Potential Biomarkers of Mitochondrial Dysfunction Associated with COVID-19 Infection.

Mitochondria play crucial roles in modulating immune responses, and viruses can in turn moderate mitochondrial functioning. Therefore, it is not judicious to assume that clinical outcome experienced in patients with COVID-19 or long COVID may be influenced by mitochondrial dysfunction in this infection. Also, patients who are predisposed to mitochondrial respiratory chain (MRC) disorders may be more susceptible to worsened clinical outcome associated with COVID-19 infection and long COVID. MRC disorders and dysfunction require a multidisciplinary approach for their diagnosis of which blood and urinary metabolite analysis may be utilized, including the measurement of lactate, organic acid and amino acid levels. More recently, hormone-like cytokines including fibroblast growth factor-21 (FGF-21) have also been used to assess possible evidence of MRC dysfunction. In view of their association with MRC dysfunction, assessing evidence of oxidative stress parameters including GSH and coenzyme Q10 (CoQ10) status may also provide useful biomarkers for diagnosis of MRC dysfunction. To date, the most reliable biomarker available for assessing MRC dysfunction is the spectrophotometric determination of MRC enzyme activities in skeletal muscle or tissue from the disease-presenting organ. Moreover, the combined use of these biomarkers in a multiplexed targeted metabolic profiling strategy may further improve the diagnostic yield of the individual tests for assessing evidence of mitochondrial dysfunction in patients pre- and post-COVID-19 infection.

Aberrant DNA and RNA Methylation Occur in Spinal Cord and Skeletal Muscle of Human SOD1 Mouse Models of ALS and in Human ALS: Targeting DNA Methylation Is Therapeutic.

Amyotrophic lateral sclerosis (ALS) is a fatal disease. Skeletal muscles and motor neurons (MNs) degenerate. ALS is a complex disease involving many genes in multiple tissues, the environment, cellular metabolism, and lifestyles. We hypothesized that epigenetic anomalies in DNA and RNA occur in ALS and examined this idea in: (1) mouse models of ALS, (2) human ALS, and (3) mouse ALS with therapeutic targeting of DNA methylation. Human superoxide dismutase-1 (hSOD1) transgenic (tg) mice were used. They expressed nonconditionally wildtype (WT) and the G93A and G37R mutant variants or skeletal muscle-restricted WT and G93A and G37R mutated forms. Age-matched non-tg mice were controls. hSOD1 mutant mice had increased DNA methyltransferase enzyme activity in spinal cord and skeletal muscle and increased 5-methylcytosine (5mC) levels. Genome-wide promoter CpG DNA methylation profiling in skeletal muscle of ALS mice identified hypermethylation notably in cytoskeletal genes. 5mC accumulated in spinal cord MNs and skeletal muscle satellite cells in mice. Significant increases in DNA methyltransferase-1 (DNMT1) and DNA methyltransferase-3A (DNMT3A) levels occurred in spinal cord nuclear and chromatin bound extracts of the different hSOD1 mouse lines. Mutant hSOD1 interacted with DNMT3A in skeletal muscle. 6-methyladenosine (6mA) RNA methylation was markedly increased or decreased in mouse spinal cord depending on hSOD1-G93A model, while fat mass and obesity associated protein was depleted and methyltransferase-like protein 3 was increased in spinal cord and skeletal muscle. Human ALS spinal cord had increased numbers of MNs and interneurons with nuclear 5mC, motor cortex had increased 5mC-positive neurons, while 6mA was severely depleted. Treatment of hSOD1-G93A mice with DNMT inhibitor improved motor function and extended lifespan by 25%. We conclude that DNA and RNA epigenetic anomalies are prominent in mouse and human ALS and are potentially targetable for disease-modifying therapeutics.

Effects of Endurance Training on Metabolic Enzyme Activity and Transporter Proteins in Skeletal Muscle of Ovariectomized Mice.

Estrogen deficiency or insufficiency can occur under several conditions, leading to negative health outcomes. To establish an effective countermeasure against estrogen loss, we investigated the effects of endurance training on ovariectomy (OVX)-induced metabolic disturbances. Female Institute of Cancer Research mice underwent OVX or sham operations. On day 7 of recovery, the mice were randomized to remain either sedentary or undergo 5 wk of treadmill running (15-20 m·min -1 , 60 min, 5 d·wk -1 ). During week 5 of the training, all animals performed a treadmill running test (15 m·min -1 , 60 min). After the experimental period, OVX resulted in greater gains in body mass, fat mass, and triglyceride content in the gastrocnemius muscle. OVX enhanced phosphofructokinase activity in the plantaris muscle and decreased lactate dehydrogenase activity in the plantaris and soleus muscles. OVX decreased the protein content of NDUFB8, a mitochondrial respiratory chain subunit, but did not decrease other mitochondrial proteins or enzyme activities. Endurance training significantly enhanced mitochondrial enzyme activity and protein content in the skeletal muscles. Although OVX increased the respiratory exchange ratio during the treadmill running test, and postexercise blood lactate levels, endurance training normalized these parameters. The present findings suggest that endurance training is a viable strategy to counteract the negative metabolic consequences in hypoestrogenism.

A Comparison Of Protein And Carbohydrate-fed Sprint Interval Training On Skeletal Muscle And Performance Adaptations

Sprint interval training (SIT) has emerged as a potent metabolic stimulus inducing beneficial musculoskeletal adaptations. However, nutritional support to optimise the adaptive response to SIT remains poorly characterised. Carbohydrate (CHO) has previously been shown to blunt metabolic adaptations to training while there is increased interest in the role of protein in regulating training adaptations. PURPOSE: The aim of this study was to determine the effects of whey protein concentrate (WPC) compared with CHO feeding on the acute regulation of skeletal muscle mitochondrial gene expression, enzyme activity and performance following a 3 week SIT intervention. METHODS: This study was ethically approved and conducted in line with the Declaration of Helsinki. Healthy, recreationally active (VO2 max <50 ml.kg-1.min-1) males (n = 17) were randomised to complete SIT under CHO or WPC conditions. Participants attended the lab after an overnight fast (≥10 h) and ingested 0.33 g.kg-1 body mass (BM) of WPC, or 0.91 g.kg-1 BM maltodextrin (CHO) 45 min prior to SIT consisting of four 30 s sprints at a resistance of 7.5 % BM, interspersed with 4 min recovery. Muscle biopsies were obtained under local anaesthetic from m. vastus lateralis at rest and 3 h post-exercise. RNA extracted from skeletal muscle underwent multiplex PCR to determine mRNA expression relative to reference gene UBE2D2. Independent t-tests determined between-group differences in changes from baseline. RESULTS: Acute changes in PGC-1α, NMRK2, NNMNAT1/3 were not differentially regulated by condition (p > 0.05). Fold-change in PDK4, SIRT4, NAMPT and NNMT were differentially regulated by nutrient condition following an acute bout of SIT (WPC vs CHO: 6.6. vs 2.6; 0.62 vs 0.86; 1.73 vs 1.14; 6.0 vs 2.8, respectively, p < 0.05). Citrate synthase and β-3-Hydroxyacyl-CoA dehydrogenase (HAD) enzyme activity increased to a greater extent in response to SIT with WPC (Fold change WPC vs CHO: 1.3 vs 1.1; 1.23 vs 1.02, respectively, p < 0.05). Post-SIT Wingate performance changes were not different between conditions (% change WPC vs CHO: 6.3 vs 4.1%, p > 0.05). CONCLUSION: Pre-exercise nutrients result in divergent regulation of mitochondrial enzyme activity and some genes in response to SIT, however this is not associated with differential performance adaptations.

Mechanisms of eccentric contraction-induced muscle damage and nutritional supplementations for mitigating it.

Eccentric contraction (ECC) often results in large and long-lasting force deficits accompanied by muscle soreness, primarily due to muscle damage. In this sense, exercises that involve ECC are less desirable. Paradoxically, exercise training that includes a substantial eccentric phase leads to a more powerful activation of the genes responsible for skeletal muscle remodeling (e.g., hypertrophy) than other types of training that emphasize a concentric or isometric phase. Therefore, effective strategies that lessen ECC-induced muscle damage will be of interest and importance to many individuals. The purpose of this brief review is to highlight the published literature on the effects of ECC and/or nutritional supplementations on proteins, lipids, metabolic and ionic changes, and enzyme activities in skeletal muscles subjected to an acute bout of ECC. First, we discuss the potential mechanisms by which ECC causes muscle damage. Previous findings implicate a Ca2+ overload-oxidative modification pathway as one possible mechanism contributing to muscle damage. Thereafter, the efficacy of two nutritional supplementations, i.e., L-arginine and antioxidant, is discussed because L-arginine and antioxidant would be expected to ameliorate the adverse effects of Ca2+ overload and oxidative modification, respectively. Of these, L-arginine ingestion before ECC seems likely to be the effective strategy for mitigating ECC-related proteolysis. More studies are needed to establish the effectiveness of antioxidant ingestion. The application of effective strategies against muscle damage may contribute to improvements in health and fitness, muscle function, and sports performance.

The Biochemical Assessment of Mitochondrial Respiratory Chain Disorders.

Mitochondrial respiratory chain (MRC) disorders are a complex group of diseases whose diagnosis requires a multidisciplinary approach in which the biochemical investigations play an important role. Initial investigations include metabolite analysis in both blood and urine and the measurement of lactate, pyruvate and amino acid levels, as well as urine organic acids. Recently, hormone-like cytokines, such as fibroblast growth factor-21 (FGF-21), have also been used as a means of assessing evidence of MRC dysfunction, although work is still required to confirm their diagnostic utility and reliability. The assessment of evidence of oxidative stress may also be an important parameter to consider in the diagnosis of MRC function in view of its association with mitochondrial dysfunction. At present, due to the lack of reliable biomarkers available for assessing evidence of MRC dysfunction, the spectrophotometric determination of MRC enzyme activities in skeletal muscle or tissue from the disease-presenting organ is considered the ‘Gold Standard’ biochemical method to provide evidence of MRC dysfunction. The purpose of this review is to outline a number of biochemical methods that may provide diagnostic evidence of MRC dysfunction in patients.

Effect of the ethanolic extract of Randia aculeata’s fruit in heart and skeletal muscle oxidative stress caused by snake venom

The purpose of this investigation was to prove if Randia aculeata is able to protect against oxidative stress generated by snake’s venom. Forty-eight male CD1 mice were used divided in groups of 8. 1) control group, 2) Randia aculeata, 3) Bothrops asper venom, 4) Randia aculeata and Bothrops asper, 5) Crotalus simus venom and 6) Randia aculeata and Crotalus simus. Blood was obtained and then fibrinogen, Lactate Dehydrogenase (ldh) and Creatin kinase (ck) were quantified. Muscle and hearts from animals were obtained in order to analyse Lipid-peroxidation (lpx), and antioxidant enzymes (catalase, super oxide dismutase [sod], and glutathione peroxidase, [gpx]). Mice treated with the venom had an increase in ck and ldh enzyme activity. Fibrinogen decreased. These disturbances were prevented with the administration of extract. It also prevented increasing levels of lipoperoxidation in both organs. It was found that sod, catalase and gpx enzyme activity in skeletal muscle, were not altered. In heart tissue, sod and gpx decreased levels were found in groups that received the venom, but ethanol extract prevented this decrease. Catalase activity increased in groups treated with snake venom, and the one that received venom from C. simus and ethanol extract. The plant minimizes significantly.

Sex-specific differences in the metabolic enzyme activity and transporter levels in mouse skeletal muscle during postnatal development.

Although sex-associated differences in energy metabolism in adults are well-characterized, developmental sex-specific changes in skeletal muscle metabolism are largely unknown. This study investigated sex differences in high-energy phosphate, glycolytic, and mitochondrial enzyme activities and metabolite transporter protein levels in mouse skeletal muscles during the early postnatal period (day 10), post-weaning (day 28), sexual maturity (day 56), and adult life (day 140). No significant sex-specific differences were observed on days 10 and 28, except for glucose transporter (GLUT) 4 level. The hexokinase, phosphofructokinase, and lactate dehydrogenase activities of skeletal muscle were higher and the citrate synthase, cytochrome c oxidase, and β-hydroxyacyl-CoA dehydrogenase activities were lower in female mice than those in male mice on days 56 and 140. The GLUT4 and FAT/CD36 protein levels were higher and the monocarboxylate transporter 4 level was lower in the skeletal muscles of female mice than those of male mice, particularly on days 56 and 140. At 140 days of age, the respiratory exchange ratio during treadmill running (15m/min, 60min) was lower in females than that in males, despite no sex differences at rest. In summary, sex differences were not evident in the early postnatal and post-weaning periods but became apparent after the mice reached sexual maturity. These findings indicate that sexually mature animals are a better model for investigating sex differences, particularly in the context of studying energy metabolism in mice.

Histological and biochemical evaluation of skeletal muscle in the two salmonid species Coregonus maraena and Oncorhynchus mykiss.

The growth of fishes and their metabolism is highly variable in fish species and is an indicator for fish fitness. Therefore, somatic growth, as a main biological process, is ecologically and economically significant. The growth differences of two closely related salmonids, rainbow trout (Oncorhynchus mykiss) and maraena whitefsh (Coregonus maraena), have not been adequately studied as a comparative study and are therefore insufficiently understood. For this reason, our aim was to examine muscle growth in more detail and provide a first complex insight into the growth and muscle metabolism of these two fish species at slaughter size. In addition to skeletal muscle composition (including nuclear counting and staining of stem and progenitor cells), biochemical characteristics, and enzyme activity (creatine kinase, lactate dehydrogenase, isocitrate dehydrogenase) of rainbow trout and maraena whitefish were determined. Our results indicate that red muscle contains cells with a smaller diameter compared to white muscle and those fibres had more stem and progenitor cells as a proportion of total nuclei. Interestingly, numerous interspecies differences were identified; in rainbow trout muscle RNA content, intermediate fibres and fibre diameter and in whitefish red muscle cross-sectional area, creatine kinase activity were higher compared to the other species at slaughter weight. The proportional reduction in red muscle area, accompanied by an increase in DNA content and a lower activity of creatine kinase, exhibited a higher degree of hypertrophic growth in rainbow trout compared to maraena whitefish, which makes this species particularly successful as an aquaculture species.

Distinct glycolytic pathway regulation in liver, tumour and skeletal muscle of mice with cancer cachexia.

Energetically inefficient inter-organ substrate shuttles are proposed contributors to cachexia-related weight loss. Here, we examined glycolytic pathway metabolites, enzyme activity and transport proteins in skeletal muscle, liver and tumours of mice with cachexia-related weight loss induced by colon-26 cancer cells. Skeletal muscle of cachexic mice had increased [L-lactate]/[pyruvate], LDH activity and lactate transporter MCT1. Cachexic livers also showed increased MCT1. This is consistent with the proposal that the rate of muscle-derived lactate shuttling to liver for use in gluconeogenesis is increased, that is, an increased Cori cycle flux in weight-losing cachexic mice. A second shuttle between liver and tumour may also contribute to disrupted energy balance and weight loss. We found increased high-affinity glucose transporter GLUT1 in tumours, suggesting active glucose uptake, tumour MCT1 detection and decreased intratumour [L-lactate]/[pyruvate], implying increased lactate efflux and/or intratumour lactate oxidation. Last, high [L-lactate]/[pyruvate] and MCT1 in cachexic muscle provides a potential muscle-derived lactate supply for the tumour (a 'reverse Warburg effect'), supporting tumour growth and consequent cachexia. Our findings suggest several substrate shuttles among liver, skeletal muscle and tumour contribute to metabolic disruption and weight loss. Therapies that aim to normalize dysregulated substrate shuttling among energy-regulating tissues may alleviate unintended weight loss in cancer cachexia. SIGNIFICANCE OF THE STUDY: Cachexia is a serious complication of cancer characterized by severe weight loss, muscle atrophy and frailty. Cachexia occurs in roughly half of all cancer patients, and in up to 80% of patients with advanced disease. Cachexia independently worsens patient prognosis, lowers treatment efficacy, increases hospitalization cost and length of stay, and accounts for 20-30% of cancer-related deaths. There are no effective treatments. Our findings suggest several substrate shuttles among liver, skeletal muscle and tumour contribute to metabolic disruption and weight loss in cancer cachexia. Identifying therapies that normalize dysregulated substrate shuttling among energy-regulating tissues may protect against cachexia-related weight loss.

Six Weeks of Aerobic Exercise in Untrained Men With Overweight/Obesity Improved Training Adaptations, Performance and Body Composition Independent of Oat/Potato or Milk Based Protein-Carbohydrate Drink Supplementation.

Background: Protein availability around aerobic exercise might benefit aerobic capacity and body composition in normal weight adults. However, it is unknown if individuals with overweight/obesity elicit similar adaptations or improve other cardiometabolic/health-related markers in response to different types of protein. Thus, our aim was to study the effect of supplementation of two different protein drinks in conjunction with exercise on aerobic capacity, body composition and blood health markers in untrained subjects with overweight or obesity.Methods: The present study measured training adaptation and health parameters over a 6 week period in untrained men with overweight/obesity (n = 28; BMI 30.4 ± 2.2 kg/m2) ingesting either plant- (Oat/Potato; n = 8) or animal-based (Milk; n = 10) protein-carbohydrate drinks (10 g of protein/serving), or a control carbohydrate drink (n = 10) acutely before and after each training session (average three sessions/week @ 70% HRmax). Pre-post intervention , muscle biopsies and blood samples were collected, body composition measured (DXA) and two different exercise tests performed. Body weight was controlled with participants remaining weight stable throughout the intervention.Results: For the groups combined, the training intervention significantly increased (8%; P < 0.001), performance in a time-to-exhaustion trial (~ 100%; P < 0.001), mitochondrial protein content and enzyme activity (~20–200%). Lean body mass increased (1%; P < 0.01) and fat mass decreased (3%; P < 0.01). No significant effects on fasting blood glucose, insulin, lipids or markers of immune function were observed. There were no significant interactions between drink conditions for training adaptation or blood measurements. For body composition, the Oat/Potato and carbohydrate group decreased leg fat mass significantly more than the Milk group (interaction P < 0.05).Conclusions: Aerobic capacity and body composition were improved and a number of mitochondrial, glycolytic and oxidative skeletal muscle proteins and enzyme activities were upregulated by a 6 week training intervention. However, none of the parameters for endurance training adaptation were influenced by protein supplementation before and after each training session.

Effect of chronic AICAR treatment on muscle fiber composition and enzyme activity in skeletal muscle of rats

ABSTRACT Muscle fiber is the basic unit of skeletal muscle. Muscle fiber types play a crucial role in improving meat quality. In the current study, Wistar rats were chronic injected with 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR) for four weeks in order to define the 5′-AMP-activated protein kinase (AMPK) protein activity on muscle fiber composition, enzyme activity and the mRNA expression of muscle fiber type-related genes in gastrocnemius (GS) muscle. Food intake and body weight did not show a significant difference after AICAR treatment (P > .05). The AICAR treatment caused a significantly increased number and area proportion of type I muscle fiber and expression level MyHC I mRNA (P < .05), succinic dehydrogenase (SDH) and malate dehydrogenase (MDH) activities (P < .05), but decrease in the number proportion of type IIB muscle fiber and MyHC IIb and MyHC IIx mRNA level (P < .05). The Peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) mRNA level (P < .05) was increased and glucose transporter 4 (GLUT-4) mRNA level tended to be higher (P = .052) in the AICAR group. These results demonstrated that chronic AICRA treatment induces oxidative muscle fiber switching, enhances oxidative enzyme activity and GLUT4 mRNA level, mediated by PGC-1α.

Effect of Quercetin and Metformin on Glucose Transporter-4 Expression, Oxidative Stress, Inflammation Markers and Insulin Resistance in Type 2 Diabetes Mellitus

Background: Defects in glucose transporter-4 (GLUT-4) expression and function in the skeletal muscles and adipose tissue can be considered as the main cause of insulin resistance (IR) in type 2 diabetes mellitus (T2DM). Also, Oxidative stress and inflammation play a very important role in the development of IR and T2DM. Aim: Studying the effect of quercetin and metformin on GLUT-4 expression, oxidative stress, inflammation markers and IR in T2DM. Method: This study was carried out on 50 male Wistar rats which were divided into five groups; control, untreated diabetic rats, diabetic rats treated with metformin, diabetic rats treated with quercetin and diabetic rats treated with metformin and quercetin. Results: The use of metformin and quercetin separately produced significant decrease in plasma glucose, insulin, IL-6, TNF-α levels, HOMA-IR and TBARS level in skeletal muscle. Also, they caused significant elevation in the antioxidant enzyme activities in skeletal muscles with increased expression of GLUT-4 in the skeletal muscles and adipose tissue compared to the diabetic rats. Evidently, the quercetin effects were more significant than that of metformin on all the parameters except on HOMA-IR (similar significant improvement). Moreover, the combined use of quercetin and metformin produced highly significant improvement approaching control level in all the parameters than that observed by using either of them. Conclusion: The combined use of QC and MF improved hyperglycemia and IR by increasing the expression of GLUT-4 in skeletal muscles and adipose tissue together with the reversal of the oxidative stress and inflammatory states.

Costs of exploratory behavior: the energy trade-off hypothesis and the allocation model tested under caloric restriction

In order to maintain the energy balance, animals often exhibit several physiological adjustments when subjected to a decrease in resource availability. Specifically, some rodents show increases in behavioral activity in response to food restriction; a response regarded as a paradox because it would imply an investment in locomotor activity, despite the lack of trophic resources. Here, we aim to explore the possible existence of trade-offs between metabolic variables and behavioral responses when rodents are faced to stochastic deprivation of food and caloric restriction. Adult BALB/c mice were acclimatized for four weeks to four food treatments: two caloric regimens (ad libitum and 60% restriction) and two periodicities (continuous and stochastic). In these mice, we analyzed: exploratory behavior and home-cage behavior, basal metabolic rate, citrate synthase and cytochrome oxidase c enzyme activity (in liver and skeletal muscle), body temperature and non-shivering thermogenesis. Our results support the model of allocation, which indicates commitments between metabolic rates and exploratory behavior, in a caloric restricted environment. Specifically, we identify the role of thermogenesis as a pivotal budget item, modulating the reallocation of energy between behavior and basal metabolic rate. We conclude that brown adipose tissue and liver play a key role in the development of paradoxical responses when facing decreased dietary availability.

Effects of lactate administration on mitochondrial enzyme activity and monocarboxylate transporters in mouse skeletal muscle.

Growing evidence shows that lactate is not merely an intermediate metabolite, but also a potential signaling molecule. However, whether daily lactate administration induces physiological adaptations in skeletal muscle remains to be elucidated. In this study, we first investigated the effects of daily lactate administration (equivalent to 1 g/kg of body weight) for 3 weeks on mitochondrial adaptations in skeletal muscle. We demonstrated that 3‐week lactate administration increased mitochondrial enzyme activity (citrate synthase, 3‐hydroxyacyl CoA dehydrogenase, and cytochrome c oxidase) in the plantaris muscle, but not in the soleus muscle. MCT1 and MCT4 protein contents were not different after 3‐week lactate administration. Next, we examined whether lactate administration enhances training‐induced adaptations in skeletal muscle. Lactate administration prior to endurance exercise training (treadmill running, 20 m/min, 60 min/day), which increased blood lactate concentration during exercise, enhanced training‐induced mitochondrial enzyme activity in the skeletal muscle after 3 weeks. MCT protein content and blood lactate removal were not different after 3‐week lactate administration with exercise training compared to exercise training alone. In a single bout experiment, lactate administration did not change the phosphorylation state of AMPK, ACC, p38 MAPK, and CaMKII in skeletal muscle. Our results suggest that lactate can be a key factor for exercise‐induced mitochondrial adaptations, and that the efficacy of high‐intensity training is, at least partly, attributed to elevated blood lactate concentration.