Mitochondrial Bioenergetics and Turnover during Chronic Muscle Disuse.

Periods of muscle disuse promote marked mitochondrial alterations that contribute to the impaired metabolic health and degree of atrophy in the muscle. Thus, understanding the molecular underpinnings of muscle mitochondrial decline with prolonged inactivity is of considerable interest. There are translational applications to patients subjected to limb immobilization following injury, illness-induced bed rest, neuropathies, and even microgravity. Studies in these patients, as well as on various pre-clinical rodent models have elucidated the pathways involved in mitochondrial quality control, such as mitochondrial biogenesis, mitophagy, fission and fusion, and the corresponding mitochondrial derangements that underlie the muscle atrophy that ensues from inactivity. Defective organelles display altered respiratory function concurrent with increased accumulation of reactive oxygen species, which exacerbate myofiber atrophy via degradative pathways. The preservation of muscle quality and function is critical for maintaining mobility throughout the lifespan, and for the prevention of inactivity-related diseases. Exercise training is effective in preserving muscle mass by promoting favourable mitochondrial adaptations that offset the mitochondrial dysfunction, which contributes to the declines in muscle and whole-body metabolic health. This highlights the need for further investigation of the mechanisms in which mitochondria contribute to disuse-induced atrophy, as well as the specific molecular targets that can be exploited therapeutically.

Lipids activate skeletal muscle mitochondrial fission and quality control networks to induce insulin resistance in humans.

BACKGROUND AND AIMS: A diminution in skeletal muscle mitochondrial function due to ectopic lipid accumulation and excess nutrient intake is thought to contribute to insulin resistance and the development of type 2 diabetes. However, the functional integrity of mitochondria in insulin-resistant skeletal muscle remains highly controversial. METHODS: 19 healthy adults (age:28.4 ±â€¯1.7 years; BMI:22.7 ±â€¯0.3 kg/m2) received an overnight intravenous infusion of lipid (20% Intralipid) or saline followed by a hyperinsulinemic-euglycemic clamp to assess insulin sensitivity using a randomized crossover design. Skeletal muscle biopsies were obtained after the overnight lipid infusion to evaluate activation of mitochondrial dynamics proteins, ex-vivo mitochondrial membrane potential, ex-vivo oxidative phosphorylation and electron transfer capacity, and mitochondrial ultrastructure. RESULTS: Overnight lipid infusion increased dynamin related protein 1 (DRP1) phosphorylation at serine 616 and PTEN-induced kinase 1 (PINK1) expression (P = 0.003 and P = 0.008, respectively) in skeletal muscle while reducing mitochondrial membrane potential (P = 0.042). The lipid infusion also increased mitochondrial-associated lipid droplet formation (P = 0.011), the number of dilated cristae, and the presence of autophagic vesicles without altering mitochondrial number or respiratory capacity. Additionally, lipid infusion suppressed peripheral glucose disposal (P = 0.004) and hepatic insulin sensitivity (P = 0.014). CONCLUSIONS: These findings indicate that activation of mitochondrial fission and quality control occur early in the onset of insulin resistance in human skeletal muscle. Targeting mitochondrial dynamics and quality control represents a promising new pharmacological approach for treating insulin resistance and type 2 diabetes. CLINICAL TRIAL REGISTRATION: NCT02697201, ClinicalTrials.gov.

Citrus hassaku Extract Powder Increases Mitochondrial Content and Oxidative Muscle Fibers by Upregulation of PGC-1α in Skeletal Muscle.

Peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) is expressed in skeletal muscles and regulates systemic metabolism. Thus, nutraceuticals targeting skeletal muscle PGC-1α have attracted attention to modulate systemic metabolism. As auraptene contained in citrus fruits promotes lipid metabolism and improves mitochondrial respiration, it could increase mitochondrial function through PGC-1α. Therefore, we hypothesized that PGC-1α is activated by auraptene and investigated its effect using Citrus hassaku extract powder (CHEP) containing >80% of auraptene. C2C12 myotubes were incubated with vehicle or CHEP for 24 h; C57BL/6J mice were fed a control diet or a 0.25% (w/w) CHEP-containing diet for 5 weeks. PGC-1α protein level and mitochondrial content increased following CHEP treatment in cultured myotubes and skeletal muscles. In addition, the number of oxidative fibers increased in CHEP-fed mice. These findings suggest that CHEP-mediated PGC-1α upregulation induced mitochondrial biogenesis and fiber transformation to oxidative fibers. Furthermore, as CHEP increased the expression of the protein sirtuin 3 and of phosphorylated AMP-activated protein kinase (AMPK) and the transcriptional activity of PGC-1α, these molecules might be involved in CHEP-induced effects in skeletal muscles. Collectively, our findings indicate that CHEP mediates PGC-1α expression in skeletal muscles and may serve as a dietary supplement to prevent metabolic disorders.

Supplement with whey protein hydrolysate in contrast to carbohydrate supports mitochondrial adaptations in trained runners.

BACKGROUND: Protein supplementation has been suggested to augment endurance training adaptations by increasing mixed muscle and myofibrillar protein synthesis and lean body mass. However, a potential beneficial effect on mitochondrial adaptations is yet to be clarified. The aim of the present study was to investigate the effect of consuming whey protein hydrolysate before and whey protein hydrolysate plus carbohydrate (PRO-CHO) after each exercise session during a six-week training period compared to similarly timed intake of isocaloric CHO supplements on biomarkers of mitochondrial biogenesis, VO2max and performance in trained runners. METHODS: Twenty-four trained runners (VO2max 60.7 ± 3.7 ml O2 kg- 1 min1) completed a six-week block randomized controlled intervention period, consisting of progressive running training. Subjects were randomly assigned to either PRO-CHO or CHO and matched in pairs for gender, age, VO2max, training and performance status. The PRO-CHO group ingested a protein beverage (0.3 g kg- 1) before and protein-carbohydrate beverage (0.3 g protein kg- 1 and 1 g carbohydrate kg- 1) after each exercise session. The CHO group ingested an energy matched carbohydrate beverage. Resting muscle biopsies obtained pre and post intervention were analyzed for mitochondrial specific enzyme activity and mitochondrial protein content. Subjects completed a 6 K time trial (6 K TT) and a VO2max test pre, midway (only 6 K TT) and post intervention. RESULTS: Following six weeks of endurance training Cytochrome C (Cyt C) protein content was significantly higher in the PRO-CHO group compared to the CHO group (p < 0.05), with several other mitochondrial proteins (Succinate dehydrogenase (SDHA), Cytochrome C oxidase (COX-IV), Voltage-dependent anion channel (VDAC), Heat shock protein 60 (HSP60), and Prohibitin (PHB1)) following a similar, but non-significant pattern (p = 0.07-0.14). ß-hydroxyacyl-CoA dehydrogenase (HAD) activity was significantly lower after training in the CHO group (p < 0.01), but not in the PRO-CHO group (p = 0.24). VO2max and 6 K TT was significantly improved after training with no significant difference between groups. CONCLUSION: Intake of whey PRO hydrolysate before and whey PRO hydrolysate plus CHO after each exercise session during a six-week endurance training period may augment training effects on specific mitochondrial proteins compared to intake of iso-caloric CHO but does not alter VO2max or 6 K TT performance. TRIAL REGISTRATION: clinicaltrials.gov , NCT03561337 . Registered 6 June 2018 - Retrospectively registered.

Local Heat Therapy to Accelerate Recovery After Exercise-Induced Muscle Damage.

The prolonged impairment in muscle strength, power, and fatigue resistance after eccentric exercise has been ascribed to a plethora of mechanisms, including delayed muscle refueling and microvascular and mitochondrial dysfunction. This review explores the hypothesis that local heat therapy hastens functional recovery after strenuous eccentric exercise by facilitating glycogen resynthesis, reversing vascular derangements, augmenting mitochondrial function, and stimulating muscle protein synthesis.

Prophylaxis of mitochondrial dysfunction caused by cellular decompression from hyperbaric exposure.

Mitochondrial dysfunction occurring in response to cellular perturbations can include altered mitochondrial motility and bioenergetic function having intracellular heterogeneity. Exogenous mitochondrial directed therapy may correct these dysfunctions. Using in vitro approaches, we find that cell perturbations induced by rapid decompression from hyperbaric conditions with specific gas exposures has differential effects on mitochondrial motility, inner membrane potential, cellular respiration, reactive oxygen species production, impaired maintenance of cell shape and altered intracellular distribution of bioenergetic capacity in perinuclear and cell peripheral domains. Addition of a first-generation cell-permeable succinate prodrug to support mitochondrial function has positive overall effects in blunting the resultant bioenergy responses. Our results with this model of perturbed cell function induced by rapid decompression indicate that alterations in bioenergetic state are partitioned within the cell, as directly assessed by a combination of mitochondrial respiration and dynamics measurements. Reductions in the observed level of dysfunction produced can be achieved with application of the cell-permeable succinate prodrug.

Polyphenols and their potential role in preventing skeletal muscle atrophy.

Skeletal muscle atrophy is the consequence of various conditions, such as disuse, denervation, fasting, aging, and disease. Even if the underlying molecular mechanisms are still not fully understood, an elevated oxidative stress related to mitochondrial dysfunction has been proposed as one of the major contributors to skeletal muscle atrophy. Researchers have described various forms of nutritional supplementation to prevent oxidative stress-induced muscle wasting. Among a variety of nutrients, attention has also focused on polyphenols, a wide range of plant-based compounds with antioxidant and inflammatory properties, many of which have beneficial effects on human health and might retard skeletal muscle loss and function impairment. The purpose of this review is to describe polyphenol actions in skeletal muscle atrophy prevention. Published articles from the last 10 years were searched on PubMed and other databases. Polyphenols are important molecules that should be considered when discussing possible strategies against muscle atrophy. In particular, the collected studies describe, for each polyphenol subclass, the beneficial effect on muscle mass preservation in various skeletal muscle disorders. In these examples, the polyphenol compounds appear to mainly act by reversing mitochondrial dysfunction. Given that the current information on polyphenols is mostly restricted to basic studies, more comprehensive research and additional studies should be performed to clarify their mechanisms of action in improving skeletal muscle functions during atrophy.

Nicotinamide riboside does not alter mitochondrial respiration, content or morphology in skeletal muscle from obese and insulin-resistant men.

KEY POINTS: This is the first long-term human clinical trial to report on effects of nicotinamide riboside (NR) on skeletal muscle mitochondrial function, content and morphology. NR supplementation decreases nicotinamide phosphoribosyltransferase (NAMPT) protein abundance in skeletal muscle. NR supplementation does not affect NAD metabolite concentrations in skeletal muscle. Respiration, distribution and quantity of muscle mitochondria are unaffected by NR. NAMPT in skeletal muscle correlates positively with oxidative phosphorylation Complex I, sirtuin 3 and succinate dehydrogenase. ABSTRACT: Preclinical evidence suggests that the nicotinamide adenine dinucleotide (NAD+ ) precursor nicotinamide riboside (NR) boosts NAD+ levels and improves diseases associated with mitochondrial dysfunction. We aimed to determine if dietary NR supplementation in middle-aged, obese, insulin-resistant men affects mitochondrial respiration, content and morphology in skeletal muscle. In a randomized, placebo-controlled clinical trial, 40 participants received 1000 mg NR or placebo twice daily for 12 weeks. Skeletal muscle biopsies were collected before and after the intervention. Mitochondrial respiratory capacity was determined by high-resolution respirometry on single muscle fibres. Protein abundance and mRNA expression were measured by Western blot and quantitative PCR analyses, respectively, and in a subset of the participants (placebo n = 8; NR n = 8) we quantified mitochondrial fractional area and mitochondrial morphology by laser scanning confocal microscopy. Protein levels of nicotinamide phosphoribosyltransferase (NAMPT), an essential NAD+ biosynthetic enzyme in skeletal muscle, decreased by 14% with NR. However, steady-state NAD+ levels as well as gene expression and protein abundance of other NAD+ biosynthetic enzymes remained unchanged. Neither respiratory capacity of skeletal muscle mitochondria nor abundance of mitochondrial associated proteins were affected by NR. Moreover, no changes in mitochondrial fractional area or network morphology were observed. Our data do not support the hypothesis that dietary NR supplementation has significant impact on skeletal muscle mitochondria in obese and insulin-resistant men. Future studies on the effects of NR on human skeletal muscle may include both sexes and potentially provide comparisons between young and older people.

Ginsenoside Rg3 upregulates myotube formation and mitochondrial function, thereby protecting myotube atrophy induced by tumor necrosis factor-alpha.

ETHNOPHARMACOLOGICAL RELEVANCE: Ginsenoside Rg3 from Panax ginseng has reported to have multiple pharmacological activities including anti-diabetics, anti-inflammation and anti-cancer. However, the effect of ginsenoside Rg3 on myogenic differentiation and muscle atrophy is unknown. AIM TO THE STUDY: In this study, we investigated the myogenic effect and underlying molecular mechanisms of ginsenoside Rg3 on myotube atrophy induced by tumor necrosis factor-α (TNF-α). MATERIALS AND METHODS: C2C12 myoblasts were induced to differentiate for one day followed by the treatment of TNF-α along with vehicle or ginsenoside Rg3 for additional 2 days and subjected to immunoblotting, immunocytochemistry, quantitative RT-PCR and biochemical analysis for mitochondrial function. RESULTS: Ginsenoside Rg3 promotes myogenic differentiation and multinucleated myotube formation through Akt activation in a dose-dependent manner, without any cytotoxicity. Ginsenoside Rg3 treatment restores myotube formation and increases myotube diameters under TNF-α-treated conditions. Ginsenoside Rg3 enhances Akt/mTOR (mammalian target of rapamycin) signaling that in turn stimulates muscle-specific gene expression such as myosin heavy chain (MHC) and Myogenin, and suppresses the expression of muscle-specific ubiquitin ligases. In addition, ginsenoside Rg3 in TNF-α-treated myotubes significantly inhibits the production of mitochondrial ROS and restores mitochondrial membrane potential (MMP) and ATP contents. Furthermore, ginsenoside Rg3 upregulates the activities and expression of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1α) and the mitochondrial biogenetic transcription factors, nuclear respiratory factor-1 (NRF1) and mitochondrial transcription factor A (Tfam) in TNF-α-induced myotube atrophy. CONCLUSIONS: This study provides a mechanistic insight into the effect of ginsenoside Rg3 on myogenic differentiation and myotube atrophy, suggesting that ginsenoside Rg3 has a promising potential as a therapeutic or neutraceutical remedy to intervene muscle weakness and atrophy.

Daily heat treatment maintains mitochondrial function and attenuates atrophy in human skeletal muscle subjected to immobilization.

Skeletal muscle immobilization leads to atrophy, decreased metabolic health, and substantial losses in function. Animal models suggest that heat stress can provide protection against atrophy in skeletal muscle. This study investigated the effects of daily heat therapy on human skeletal muscle subjected to 10 days of immobilization. Muscle biopsies were collected, and MRIs were analyzed from the vastus lateralis of 23 healthy volunteers (11 women, 12 men) before and after either 10 days of immobilization with a daily sham treatment (Imm) or with a targeted, daily 2-h heat treatment using pulsed shortwave diathermy (Imm + H). Diathermy increased intramuscular temperature 4.2 ± 0.29°C (P < 0.0001), with no change during sham treatment. As a result, heat shock protein (HSP)70 and HSP90 increased (P < 0.05) following Imm + H (25 ± 6.6 and 20 ± 7.4%, respectively) but were unaltered with Imm only. Heat treatment prevented the immobilization-induced loss of coupled (-27 ± 5.2% vs. -8 ± 6.0%, P = 0.0041) and uncoupled (-25 ± 7.0% vs. -10 ± 3.9%, P = 0.0302) myofiber respiratory capacity. Likewise, heat treatment prevented the immobilization-induced loss of proteins associated with all five mitochondrial respiratory complexes (P < 0.05). Furthermore, decreases in muscle cross-sectional area following Imm were greater than Imm + H at both the level of the whole muscle (-7.6 ± 0.96% vs. -4.5 ± 1.09%, P = 0.0374) and myofiber (-10.8 ± 1.52% vs. -5.8 ± 1.49%, P = 0.0322). Our findings demonstrate that daily heat treatments, applied during 10 days of immobilization, prevent the loss of mitochondrial function and attenuate atrophy in human skeletal muscle. NEW & NOTEWORTHY Limb immobilization results in substantial decreases in skeletal muscle size, function, and metabolic capacity. To date, there are few, if any, interventions to prevent the deleterious effects of limb immobilization on skeletal muscle health. Heat stress has been shown to elicit a stress response, resulting in increased heat shock protein expression and improved mitochondrial function. We show that during 10 days of lower-limb immobilization in humans, daily exposure to heat stress maintains mitochondrial respiratory capacity and attenuates atrophy in skeletal muscle. Our findings suggest that heat stress may serve as an effective therapeutic strategy to attenuate the decreases of muscle mass and metabolic function that accompany periods of disuse.

Dietary supplementation with ketoacids protects against CKD-induced oxidative damage and mitochondrial dysfunction in skeletal muscle of 5/6 nephrectomised rats.

BACKGROUND: A low-protein diet supplemented with ketoacids (LPD + KA) maintains the nutritional status of patients with chronic kidney disease (CKD). Oxidative damage and mitochondrial dysfunction associated with the upregulation of p66SHC and FoxO3a have been shown to contribute to muscle atrophy. This study aimed to determine whether LPD + KA improves muscle atrophy and attenuates the oxidative stress and mitochondrial damage observed in CKD rats. METHODS: 5/6 nephrectomy rats were randomly divided into three groups and fed with either 22% protein (normal-protein diet; NPD), 6% protein (low-protein diets; LPD) or 5% protein plus 1% ketoacids (LPD + KA) for 24 weeks. Sham-operated rats with NPD intake were used as the control. RESULTS: KA supplementation improved muscle atrophy and function in CKD + LPD rats. It also reduced the upregulation of genes related to the ubiquitin-proteasome system and 26S proteasome activity, as well as protein and mitochondrial oxidative damage in the muscles of CKD + LPD rats. Moreover, KA supplementation prevented the drastic decrease in activities of mitochondrial electron transport chain complexes, mitochondrial respiration, and content in the muscles of CKD + LPD rats. Furthermore, KA supplementation reversed the elevation in p66Shc and FoxO3a expression in the muscles of CKD + LPD rats. CONCLUSIONS: Our results showed that KA supplementation to be beneficial to muscle atrophy in CKD + LPD, which might be associated with improvement of oxidative damage and mitochondrial dysfunction through suppression of p66Shc and FoxO3a.

Attenuation of obesity and insulin resistance by fish oil supplementation is associated with improved skeletal muscle mitochondrial function in mice fed a high-fat diet.

Omega-3 polyunsaturated fatty acids (n-3 PUFAs) have been reported to improve insulin sensitivity and glucose homeostasis in animal models of insulin resistance, but the involved mechanisms still remain unresolved. In this study, we evaluated the effects of fish oil (FO), a source of n-3 PUFAs, on obesity, insulin resistance and muscle mitochondrial function in mice fed a high-fat diet (HFD). C57Bl/6 male mice, 8 weeks old, were divided into four groups: control diet (C), high-fat diet (H), C+FO (CFO) and H+FO (HFO). FO was administered by oral gavage (2 g/kg b.w.), three times a week, starting 4 weeks before diet administration until the end of the experimental protocol. HFD-induced obesity and insulin resistance associated with impaired skeletal muscle mitochondrial function, as indicated by decreased oxygen consumption, tricarboxylic acid cycle intermediate (TCAi) contents (citrate, α-ketoglutarate, malate and oxaloacetate), oxidative phosphorylation protein content and mitochondrial biogenesis. These effects were associated with elevated reactive oxygen species production, decreased PGC1-a transcription and reduced Akt phosphorylation. The changes induced by the HFD were partially attenuated by FO, which decreased obesity and insulin resistance and increased mitochondrial function. In the H group, FO supplementation also improved oxygen consumption; increased TCAi content, and Akt and AMPK phosphorylation; and up-regulated mRNA expression of Gpat1, Pepck, catalase and mitochondrial proteins (Pgc1α, Pparα, Cpt1 and Ucp3). These results suggest that dietary FO attenuates the deleterious effects of the HFD (obesity and insulin resistance) by improving skeletal muscle mitochondrial function.

The influence of hyperbaric environment on the skeletal muscle mitochondrial energetic of rats after induced muscle contusion.

OBJECTIVE: Analyze the influence of the hyperbaric environment on skeletal muscle mitochondrial bioenergetic end-points of rats submitted to muscle contusion. METHODS: Twelve female Wistar rats were randomly assigned to three groups. All rats were submitted to muscle contusion in the right gastrocnemius through a standard protocol. The control group (C) remained under normobaric conditions without any treatment. The hyperbaric air (HB) and the hyperbaric oxygen (HBO2) groups had four sessions of HBO2 therapy 60 minutes, six, 12, 24 and 48 hours after the injury at 253.25 kPa (2.5 atmospheres absolute/ATA) with air or 100% oxygen, respectively. The animals were sacrificed 48 hours after muscle injury, and both muscles (injured and non-injured) were analyzed. Muscle mitochondrial bioenergetics and mitochondrial permeability transition pore (MPTP) susceptibility were evaluated. RESULTS: Significant differences were found in all parameters between the injured and the non-injured gastrocnemius in the C group. In the HB group, significantly better results concerning bioenergetics-related end points with complex I and II substrates where found in the right gastrocnemius, whereas in the HBO2 group the time to Vmax (time that elapsed until the faster swelling kinetics starts) was significantly higher and the swelling amplitude was significantly smaller than in other groups, which suggest a lower susceptibility to MPTP opening. CONCLUSION: The present data suggest that hyperbaric exposure, particularly with oxygen, positively modulates the efficiency of skeletal muscle mitochondria after muscle contusion.

Curcumin treatment enhances the effect of exercise on mitochondrial biogenesis in skeletal muscle by increasing cAMP levels.

BACKGROUND: In response to physiologic stressors, skeletal muscle has the potential to elicit wide variety of adaptive responses, such as biogenesis of mitochondria and clearance of damaged mitochondria to promote healthy muscle. The polyphenol curcumin, derived from the rhizome Curcuma longa L., is a natural antioxidant that exhibits various pharmacological activities and therapeutic properties. However, the effect of curcumin on the regulation of mitochondrial biogenesis in skeletal muscle remains unknown. The present study aimed to examine the effects of combination of endurance training (eTR) and curcumin treatment on the expression of AMPK, SIRT1, PGC-1α, and OXPHOS subunits, mitochondrial DNA copy number, and CS activity in rat skeletal muscle. Furthermore, the present study also examined the effect of exercise and curcumin treatment on the levels of cAMP and downstream targets of PKA including phosphorylated CREB and LKB-1. METHODS: Ten-week-old male Wistar rats were randomly divided into non-eTR and eTR groups. Low doses (50 mg/kg-BW/day) or high doses (100 mg/kg-BW/day) of curcumin dissolved in dimethyl sulfoxide (DMSO) were injected intraperitoneally in all animals for 28 days to investigate the effect of curcumin alone and the combined effect of curcumin with eTR. Western blotting (WB) and immunoprecipitation (IP) were performed to detect the presence of proteins. RESULTS: Our results demonstrated that combination of curcumin treatment and eTR increased the expression of COX-IV, OXPHOS subunits, mitochondrial DNA copy number and CS activity in the gastrocnemius (Gas) and soleus (Sol) muscles. In addition, this combination increased AMPK phosphorylation, NAD(+)/NADH ratio, SIRT1 expression, and PGC-1α deacetylation. Furthermore, curcumin treatment as well as exercise also increased levels of cAMP and downstream target of PKA including phosphorylation CREB and LKB-1 which are involved in the regulation of mitochondrial biogenesis. CONCLUSION: Taken together, these results suggest that the combination of curcumin treatment and eTR has the potential to accelerate mitochondrial biogenesis in skeletal muscle by increasing cAMP levels.

Redox modulation of mitochondriogenesis in exercise. Does antioxidant supplementation blunt the benefits of exercise training?

Physical exercise increases the cellular production of reactive oxygen species (ROS) in muscle, liver, and other organs. This is unlikely due to increased mitochondrial production but rather to extramitochondrial sources such as NADPH oxidase or xanthine oxidase. We have reported a xanthine oxidase-mediated increase in ROS production in many experimental models from isolated cells to humans. Originally, ROS were considered as detrimental and thus as a likely cause of cell damage associated with exhaustion. In the past decade, evidence showing that ROS act as signals has been gathered and thus the idea that antioxidant supplementation in exercise is always recommendable has proved incorrect. In fact, we proposed that exercise itself can be considered as an antioxidant because training increases the expression of classical antioxidant enzymes such as superoxide dismutase and glutathione peroxidase and, in general, lowering the endogenous antioxidant enzymes by administration of antioxidant supplements may not be a good strategy when training. Antioxidant enzymes are not the only ones to be activated by training. Mitochondriogenesis is an important process activated in exercise. Many redox-sensitive enzymes are involved in this process. Important signaling molecules like MAP kinases, NF-κB, PGC-1α, p53, heat shock factor, and others modulate muscle adaptation to exercise. Interventions aimed at modifying the production of ROS in exercise must be performed with care as they may be detrimental in that they may lower useful adaptations to exercise.

Effects of acute lipid overload on skeletal muscle insulin resistance, metabolic flexibility, and mitochondrial performance.

We hypothesized that acute lipid-induced insulin resistance would be attenuated in high-oxidative muscle of lean trained (LT) endurance athletes due to their enhanced metabolic flexibility and mitochondrial capacity. Lean sedentary (LS), obese sedentary (OS), and LT participants completed two hyperinsulinemic euglycemic clamp studies with and without (glycerol control) the coinfusion of Intralipid. Metabolic flexibility was measured by indirect calorimetry as the oxidation of fatty acids and glucose during fasted and insulin-stimulated conditions, the latter with and without lipid oversupply. Muscle biopsies were obtained for mitochondrial and insulin-signaling studies. During hyperinsulinemia without lipid, glucose infusion rate (GIR) was lowest in OS due to lower rates of nonoxidative glucose disposal (NOGD), whereas state 4 respiration was increased in all groups. Lipid infusion reduced GIR similarly in all subjects and reduced state 4 respiration. However, in LT subjects, fat oxidation was higher with lipid oversupply, and although glucose oxidation was reduced, NOGD was better preserved compared with LS and OS subjects. Mitochondrial performance was positively associated with better NOGD and insulin sensitivity in both conditions. We conclude that enhanced mitochondrial performance with exercise is related to better metabolic flexibility and insulin sensitivity in response to lipid overload.

Mitochondria-targeted antioxidant promotes recovery of skeletal muscle mitochondrial function after burn trauma assessed by in vivo 31P nuclear magnetic resonance and electron paramagnetic resonance spectroscopy.

Burn injury causes a major systemic catabolic response that is associated with mitochondrial dysfunction in skeletal muscle. We investigated the effects of the mitochondria-targeted peptide antioxidant Szeto-Schiller 31 (SS-31) on skeletal muscle in a mouse burn model using in vivo phosphorus-31 nuclear magnetic resonance ((31)P NMR) spectroscopy to noninvasively measure high-energy phosphate levels; mitochondrial aconitase activity measurements that directly correlate with TCA cycle flux, as measured by gas chromatography mass spectrometry (GC-MS); and electron paramagnetic resonance (EPR) to assess oxidative stress. At 6 h postburn, the oxidative ATP synthesis rate was increased 5-fold in burned mice given a single dose of SS-31 relative to untreated burned mice (P=0.002). Furthermore, SS-31 administration in burned animals decreased mitochondrial aconitase activity back to control levels. EPR revealed a recovery in redox status of the SS-31-treated burn group compared to the untreated burn group (P<0.05). Our multidisciplinary convergent results suggest that SS-31 promotes recovery of mitochondrial function after burn injury by increasing ATP synthesis rate, improving mitochondrial redox status, and restoring mitochondrial coupling. These findings suggest use of noninvasive in vivo NMR and complementary EPR offers an approach to monitor the effectiveness of mitochondrial protective agents in alleviating burn injury symptoms.

Transcranial magnetic stimulation and amyotrophic lateral sclerosis: pathophysiological insights.

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegenerative disorder of the motor neurons in the motor cortex, brainstem and spinal cord. A combination of upper and lower motor neuron dysfunction comprises the clinical ALS phenotype. Although the ALS phenotype was first observed by Charcot over 100 years ago, the site of ALS onset and the pathophysiological mechanisms underlying the development of motor neuron degeneration remain to be elucidated. Transcranial magnetic stimulation (TMS) enables non-invasive assessment of the functional integrity of the motor cortex and its corticomotoneuronal projections. To date, TMS studies have established motor cortical and corticospinal dysfunction in ALS, with cortical hyperexcitability being an early feature in sporadic forms of ALS and preceding the clinical onset of familial ALS. Taken together, a central origin of ALS is supported by TMS studies, with an anterograde transsynaptic mechanism implicated in ALS pathogenesis. Of further relevance, TMS techniques reliably distinguish ALS from mimic disorders, despite a compatible peripheral disease burden, thereby suggesting a potential diagnostic utility of TMS in ALS. This review will focus on the mechanisms underlying the generation of TMS measures used in assessment of cortical excitability, the contribution of TMS in enhancing the understanding of ALS pathophysiology and the potential diagnostic utility of TMS techniques in ALS.

Korean mistletoe (Viscum album coloratum) extract improves endurance capacity in mice by stimulating mitochondrial activity.

The beneficial effects of exercise on overall health make it desirable to identify the orally active agents that enhance the effects of exercise in an effort to cure metabolic diseases. Natural compounds such as resveratrol (RSV) are known to increase endurance by potentiating mitochondrial function. Korean mistletoe (Viscum album coloratum) extract (KME) has characteristics similar to those of RSV. In the present study, we determined whether KME could increase mitochondrial activity and exert an anti-fatigue effect. We found that KME treatment significantly increased the mitochondrial oxygen consumption rate (OCR) in L6 cells and increased the expression of peroxisome proliferator-activated receptor γ coactivator (PGC)-1α and silent mating type information regulation 2 homolog 1 (SIRT1), two major regulators of mitochondria function, in C2C12 cells. In the treadmill test, KME-treated mice could run 2.5-times longer than chow-fed control mice. Additionally, plasma lactate levels of exhausted mice were significantly lower in the KME-treated group. In addition, the swimming time to exhaustion of mice treated with KME was prolonged by as much as 212% in the forced-swim test. Liver and kidney histology was similar between the KME-treated and phosphate-buffered saline-treated animals, indicating that KME was nontoxic. Taken together, our data show that KME induces mitochondrial activity, possibly by activating PGC-1α and SIRT1, and improves the endurance of mice, strongly suggesting that KME has great potential as a novel mitochondria-activating agent.