Endurance Exercise Mimetics in Skeletal Muscle

Identification and characterization of GSK-9089 metabolites through high resolution-mass spectrometry based in vitro and in vivo rat biological sample analysis

Estrogen related receptors (ERRs) agonist GSK-9089 (DY-131) reported to pose a potential in increasing exercise endurance. High resolution mass spectrometry (HRMS) based analysis has utmost importance in the detection, identification, or characterization of a molecule including its metabolites in human body. In this study, in vitro metabolism profile of GSK-9089 was investigated after incubation with liver microsomes and S9 fractions. Additionally, in vivo metabolites of the molecule were identified in plasma, urine, and faeces samples of rats. Structures of all the potential metabolites were revealed by employing an in silico tool and HRMS based analysis through data-dependent and data-independent mining strategies. Nine unknown metabolites of GSK-9089 have been identified which were found to be present in a trace amount in in vivo matrices. Most of the in vitro and in vivo phase I metabolites of the molecule were formed after imine bond hydrolysis followed by deamidation, oxidation, and N-oxidation. The molecule underwent phase II metabolism to generate more polar metabolites mainly through glucuronide, sulfate conjugation biotransformation reactions. The in vitro and in vivo metabolites of GSK-9089 could be useful to identify the abuse of this ERRs agonist in the future.

An AMP Kinase-pathway dependent integrated stress response regulates ageing and longevity

The purpose of this article is to investigate the role of the AMP-kinase pathway (AMPK pathway) in the induction of a concomitant set of health benefits by exercise, numerous drugs, and health ingredients, all of which are adversely affected by ageing. Despite the AMPK pathway being frequently mentioned in relation to both these health effects and ageing, it appears challenging to understand how the activation of a single biochemical pathway by various treatments can produce such a diverse range of concurrent health benefits, involving so many organs. We discovered that the AMPK pathway functions as an integrated stress response system because of the presence of a feedback loop in it. This evolutionary conserved stress response system detects changes in AMP/ATP and NAD/NADH ratios, as well as the presence of potential toxins, and responds by activating a common protective transcriptional response that protects against aging and promotes longevity. The inactivation of the AMPK pathway with age most likely explains why ageing has a negative impact on the above-mentioned set of health benefits. We conclude that the presence of a feedback loop in the AMP-kinase pathway positions this pathway as an AMPK-ISR (AMP Kinase-dependent integrated stress response) system that responds to almost any type of (moderate) environmental stress by inducing various age-related health benefits and longevity.

The Effect of 13 Weeks Long-Distance Bicycle Riding on Inflammatory Response Indicators Related to Joint Cartilage and Muscle Damage

This study was to investigate the effects of 13 weeks of long-distance cycling on biomarkers of joint cartilage, muscle damage and inflammation. All subjects in this study were seven participants of the “One Korea New-Eurasia Peace Cycle Expedition”, in which they rode cycles from Berlin, Germany to Seoul, Korea for thirteen weeks. The total course of the expedition was divided into three sub-courses: course 1 (from Berlin to Moscow), course 2 (from Moscow to Ulaanbaatar) and course 3 (from Ulaanbaatar to Seoul). All the selected participants rode 87.4 km/day (course 1), 70.4 km/day (course 2) and 57.6 km/day (course 3) on average, respectively. We collected their blood samples before the expedition in Seoul (S1), after course 1 in Moscow (M), after course 2 in Ulaanbaatar (U) and after the expedition in Seoul (S2), to analyze biomarkers of joint cartilage damage (Cartilage Oligomeric Matrix Protein; COMP), muscle damage (Creatine Phosphokinase; CPK, Lactate Dehydrogenase; LDH, Myoglobin), inflammation (Interleukin-6; IL-6, Interleukin-1β; IL-1β, Tumor Necrosis Factor-α; TNF-α, C-Reactive Protein; CRP) and stress hormone (Cortisol). According to this result, COMP (S1; 188.37 ± 46.68 ng/mL) showed a significant increase after the expedition course 1 (M; 246.69 ± 51.69 ng/mL, p = 0.012) and course 2 (U; 237.09 ± 62.57 ng/mL, p = 0.047), and recovered to the stable state after expedition course 3 (S2; 218.46 ± 34.78. p = 0.047). Biomarkers of muscle damage (CPK, LDH and Myoglobin) and inflammation (IL-6, IL-1β, TNF-α and CRP) were not significantly changed in all courses, but CRP (S1; 1.07 ± 0.76 ng/mL) showed a tendency to decrease after the expedition course 1 (M; 0.3 ± 0.1 mg/mL, p = 0.044). Lastly, the Cortisol level significantly increased in all courses (per p < 0.05), but the Cortisol level after expedition course 3 (S2; 21.00 ± 3.65 mg/mL) was lower than that of after the expedition course 1 (M; 24.23 ± 2.47 mg/mL, p = 0.028). In summary, it seems that repetitive and continuous 50−90 km/day of cycling can increase joint cartilage damage risk and stress hormone temporarily. However, this result suggests that the appropriate intensity of cycling for thirteen weeks does not increase physical damage, and rather enhances the human body to adapt to exercise training.

Systematic training in master swimmer athletes increases serum insulin growth factor-1 and decreases myostatin and irisin levels

During ageing, anabolic status is essential to prevent the decrease in quantity and quality of skeletal muscle mass (SMM). Exercise modulates endocrine markers of muscle status. We studied the differences of endocrine markers for muscle status in 62 non-sarcopenic Mexican swimmer adults aged 30-70 y/o, allocated into two groups: the systematic training (ST) group including master athletes with a physical activity level (PAL) >1.6, and the non-systematic training group (NST) composed by subjects with a PAL <1.5. Body composition, diet, biochemical and endocrine markers were analyzed. The ST group showed lower myostatin (MSTN) and irisin (IRI) levels, two strong regulators of SMM. The insulin growth factor-1 (IGF-1) was higher in the ST. This is consistent with most of the evidence in young athletes and resistance training programs, where IGF-1 and IRI seem to play a crucial role in maintaining anabolic status in master athletes.

Anti-fatigue effects of fermented soybean protein peptides in mice

BACKGROUND

Bioactive protein hydrolysates and peptides are believed to help counteract and ameliorate physical fatigue. Fermented soybean protein peptides (FSPPs) were prepared by protease hydrolysis and microbial fermentation. The present study aimed to evaluate the anti-fatigue properties of FSPPs.

RESULTS

The forced swimming time in the FSPP group was 35.78% longer than the control group, the oxygen-resistant survival time of the FSPP group was significantly prolonged and the prolongation rate was 31.00%. In addition, FSPPs decreased the lactic acid (LD), blood urea nitrogen (BUN) and creatine kinase (CK) concentration by 27.47%, 25.93% and 21.70%, respectively, after treatment, while increasing the levels of liver glycogen and muscle glycogen by 93.35% and 67.31%, respectively. FSPPs can significantly increase gut microbiota diversity and regulate the species richness of gut microbiota. The results of real-time polymerase chain reaction (RT-PCR) and western blotting showed that FSPPs activate p-AMPK/PGC1-α and PI3K/Akt/mTOR signaling pathways.

CONCLUSION

These results indicate that treatment with FSPPs induces anti-fatigue effects, which may be due to the mediating muscle protein synthesis and participation in skeletal muscle hypertrophy, providing energy for muscle cells. FSPPs may have potential applications in the food industry as functional material additives. © 2021 Society of Chemical Industry.

Estrogen-related receptor α is involved in angiogenesis and skeletal muscle revascularization in hindlimb ischemia

Skeletal muscle ischemia is a major consequence of peripheral arterial disease (PAD) or critical limb ischemia (CLI). Although therapeutic options for resolving muscle ischemia in PAD/CLI are limited, the issue is compounded by poor understanding of the mechanisms driving muscle vascularization. We found that nuclear receptor estrogen-related receptor alpha (ERRα) expression is induced in murine skeletal muscle by hindlimb ischemia (HLI), and in cultured myotubes by hypoxia, suggesting a potential role for ERRα in ischemic response. To test this, we generated skeletal muscle-specific ERRα transgenic (TG) mice. In these mice, ERRα drives myofiber type switch from glycolytic type IIB to oxidative type IIA/IIX myofibers, which are typically associated with more vascular supply in muscle. Indeed, RNA sequencing and functional enrichment analysis of TG muscle revealed that "paracrine angiogenesis" is the top-ranked transcriptional program activated by ERRα in the skeletal muscle. Immunohistochemistry and angiography showed that ERRα overexpression increases baseline capillarity, arterioles and non-leaky blood vessel formation in the skeletal muscles. Moreover, ERRα overexpression facilitates ischemic neo-angiogenesis and perfusion recovery in hindlimb musculature of mice subjected to HLI. Therefore, ERRα is a hypoxia inducible nuclear receptor that is involved in skeletal muscle angiogenesis and could be potentially targeted for treating PAD/CLI.

Effect of Interleukin-15 Receptor Alpha Ablation on the Metabolic Responses to Moderate Exercise Simulated by in vivo Isometric Muscle Contractions

Lack of interleukin 15 receptor alpha (IL15RA) increases spontaneous activity, exercise capacity and protects from diet-induced obesity by enhancing muscle energy metabolism, suggesting a role as exercise mimetic for IL15RA antagonists. Using controlled in vivo muscle stimulation mimicking moderate exercise in normal and Il15ra^-/- mice, we mapped and contrasted the metabolic pathways activated upon stimulation or deletion of IL15RA. Stimulation caused the differential regulation of 123 out of the 321 detected metabolites (FDR ≤ 0.05 and fold change ≥ ±1.5). The main energy pathways activated were fatty acid oxidation, nucleotide metabolism, and anaplerotic reactions. Notably, resting Il15ra^-/- muscles were primed in a semi-exercised state, characterized by higher pool sizes of fatty acids oxidized to support muscle activity. These studies identify the role of IL15RA in the system-wide metabolic response to exercise and should enable translational studies to harness the potential of IL15RA blockade as a novel exercise mimetic strategy.

Screening for adiponectin receptor agonists and their metabolites in urine and dried blood spots

AdipoRon and 112254 represent two known synthetic adiponectin receptor (adipoR) agonists. Although AdipoRon is the more potent compound, both have physiological properties that are similar to adiponectin - an adipokine with antidiabetic and antiatherogenic effects. Several transcriptional regulators are activated by adipoR-agonists leading to increased mitochondrial DNA content in vitro, an effect that can be abused by athletes for performance enhancing purposes. In the context of preventive anti-doping research, detection of AdipoRon and 112254 in routine doping control specimens would be valuable. Here, we describe our process for incorporating AdipoRon and 112254 into routine doping control methods involving urine and dried blood spot (DBS) analysis. Method validation including evaluation of specificity, limit of detection, identification capability, carryover, matrix interference, recovery, interday and intraday precision and linearity to standards provided by WADA. For identification in human urine, a liquid chromatography-tandem mass spectrometry-based testing approach was implemented for both adipoR agonists and two respective phase-I metabolites. Recovery of 85-104%, satisfactory limits of detection (i.e., 0.5-1 ng/mL), and imprecision values over three days at three concentration levels of <19% demonstrated the assay's fitness-for-purpose. For identification from DBS a liquid chromatography-high-resolution/high-accuracy tandem mass spectrometry with online solid-phase extraction was implemented for AdipoRon and 112254. Here also, acceptable recoveries (i.e., 22-33%), limits of detection of 5-10 ng/mL, and imprecision values over three days at three concentration levels of <23%, were demonstrated. Hence, two methods for doping control screening from urine and DBS were established and shown to be fit-for-purpose for routine use.

Chronic 5-Aminoimidazole-4-Carboxamide-1-β-d-Ribofuranoside Treatment Induces Phenotypic Changes in Skeletal Muscle, but Does Not Improve Disease Outcomes in the R6/2 Mouse Model of Huntington's Disease

Huntington’s disease (HD) is an autosomal dominant neurodegenerative genetic disorder characterized by motor, cognitive, and psychiatric symptoms. It is well established that regular physical activity supports brain health, benefiting cognitive function, mental health as well as brain structure and plasticity. Exercise mimetics (EMs) are a group of drugs and small molecules that target signaling pathways in skeletal muscle known to be activated by endurance exercise. The EM 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) has been shown to induce cognitive benefits in healthy mice. Since AICAR does not readily cross the blood–brain barrier, its beneficial effect on the brain has been ascribed to its impact on skeletal muscle. Our objective, therefore, was to examine the effect of chronic AICAR treatment on the muscular and neurological pathology in a mouse model of HD. To this end, R6/2 mice were treated with AICAR for 8 weeks and underwent regular neurobehavioral testing. Under our conditions, AICAR increased expression of PGC-1α, a powerful phenotypic modifier of muscle, and induced the expected shift toward a more oxidative muscle phenotype in R6/2 mice. However, this treatment failed to induce benefits on HD progression. Indeed, neurobehavioral deficits, striatal, and muscle mutant huntingtin aggregate density, as well as muscle atrophy were not mitigated by the chronic administration of AICAR. Although the muscle adaptations seen in HD mice following AICAR treatment may still provide therapeutically relevant benefits to patients with limited mobility, our findings indicate that under our experimental conditions, AICAR had no effect on several hallmarks of HD.

Comparative Proteomic and Transcriptomic Analysis of Follistatin-Induced Skeletal Muscle Hypertrophy

Skeletal muscle, the most abundant body tissue, plays vital roles in locomotion and metabolism. Myostatin is a negative regulator of skeletal muscle mass. In addition to increasing muscle mass, Myostatin inhibition impacts muscle contractility and energy metabolism. To decipher the mechanisms of action of the Myostatin inhibitors, we used proteomic and transcriptomic approaches to investigate the changes induced in skeletal muscles of transgenic mice overexpressing Follistatin, a physiological Myostatin inhibitor. Our proteomic workflow included a fractionation step to identify weakly expressed proteins and a comparison of fast versus slow muscles. Functional annotation of altered proteins supports the phenotypic changes induced by Myostatin inhibition, including modifications in energy metabolism, fiber type, insulin and calcium signaling, as well as membrane repair and regeneration. Less than 10% of the differentially expressed proteins were found to be also regulated at the mRNA level but the Biological Process annotation, and the KEGG pathways analysis of transcriptomic results shows a great concordance with the proteomic data. Thus this study describes the most extensive omics analysis of muscle overexpressing Follistatin, providing molecular-level insights to explain the observed muscle phenotypic changes.

Exercise in a Pill: The Latest on Exercise-Mimetics

There is increasing evidence that an active lifestyle benefits both body and brain. However, not everyone may be able to exercise due to disease, injury or aging-related frailty. Identification of cellular targets activated by physical activity may lead to the development of new compounds that can, to some extent, mimic systemic and central effects of exercise. This review will focus on factors relevant to energy metabolism in muscle, such as the 5’ adenosine monophosphate-activated protein kinase (AMPK) - sirtuin (SIRT1) - Peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) pathway, and the molecules affecting it. In particular, putative exercise-mimetics such as AICAR, metformin, and GW501516 will be discussed. Moreover, plant-derived polyphenols such as resveratrol and (-)epicatechin, with exercise-like effects on the body and brain will be evaluated.

Anti-sarcopenic effects of diamino-diphenyl sulfone observed in elderly female leprosy survivors: a cross-sectional study

BACKGROUND

It has been reported that 4,4'-diamino-diphenyl sulfone (DDS), the longtime treatment of choice for leprosy, prolongs the lifespan and increases mobility in animal models by reducing the levels of reactive oxygen species and inhibiting muscle pyruvate kinase activity. This study aimed to investigate whether sarcopenic status in leprosy survivors was influenced by recent history of DDS medication.

METHODS

Forty-one elderly female leprosy survivors were recruited. The DDS group was defined as survivors who had been taking the drug for the past year or more. Body composition measured by dual energy X-ray absorptiometry, limb muscle strength, short physical performance battery, and International Physical Activity Questionnaire in Korean were compared.

RESULTS

The DDS group tended to have higher skeletal muscle mass index (24.4 ± 2.7 vs. 22.6 ± 2.2%, P = 0.066) and regional skeletal muscle mass index in non-dominant leg (8.9 ± 1.0 vs. 7.9 ± 0.9%, P = 0.018) than those of the control group although they had significantly worse leprosy disability than the control group (P = 0.027). The DDS group had greater strength than the control group in non-dominant shoulder abductor, elbow flexor, hip flexor, and knee extensor (P = 0.005, P = 0.029, P = 0.021, and P = 0.002, respectively). Weekly walking amount was significantly longer (P = 0.020) in the DDS group than the control group. The total lifetime DDS exposure significantly correlated with skeletal muscle mass of the lower extremity in non-dominant leg (r = 0.379, P = 0.015).

CONCLUSIONS

DDS-taking leprosy survivors had larger skeletal muscle mass and greater muscle strength over non-taking survivors. There was a dose-response relationship between total lifetime DDS exposure and skeletal muscle mass of lower extremity. These findings might suggest potential anti-sarcopenic effects of DDS.

The impact of endurance exercise on global and AMPK gene-specific DNA methylation

Alterations in gene expression as a consequence of physical exercise are frequently described. The mechanism of these regulations might depend on epigenetic changes in global or gene-specific DNA methylation levels. The AMP-activated protein kinase (AMPK) plays a key role in maintenance of energy homeostasis and is activated by increases in the AMP/ATP ratio as occurring in skeletal muscles after sporting activity. To analyze whether exercise has an impact on the methylation status of the AMPK promoter, we determined the AMPK methylation status in human blood samples from patients before and after sporting activity in the context of rehabilitation as well as in skeletal muscles of trained and untrained mice. Further, we examined long interspersed nuclear element 1 (LINE-1) as indicator of global DNA methylation changes. Our results revealed that light sporting activity in mice and humans does not alter global DNA methylation but has an effect on methylation of specific CpG sites in the AMPKα2 gene. These regulations were associated with a reduced AMPKα2 mRNA and protein expression in muscle tissue, pointing at a contribution of the methylation status to AMPK expression. Taken together, these results suggest that exercise influences AMPKα2 gene methylation in human blood and eminently in the skeletal muscle of mice and therefore might repress AMPKα2 gene expression.

Emerging drugs affecting skeletal muscle function and mitochondrial biogenesis - Potential implications for sports drug testing programs

RATIONALE

A plethora of compounds potentially leading to drug candidates that affect skeletal muscle function and, more specifically, mitochondrial biogenesis, has been under (pre)clinical investigation for rare as well as more common diseases. Some of these compounds could be the object of misuse by athletes aiming at artificial and/or illicit and drug-facilitated performance enhancement, necessitating preventive and proactive anti-doping measures.

METHODS

Early warnings and the continuous retrieval and dissemination of information are crucial for sports drug testing laboratories as well as anti-doping authorities, as they assist in preparation of efficient doping control analytical strategies for potential future threats arising from new therapeutic developments. Scientific literature represents the main source of information, which yielded the herein discussed substances and therapeutic targets, which might become relevant for doping controls in the future. Where available, mass spectrometric data are presented, supporting the development of analytical strategies and characterization of compounds possibly identified in human sports drug testing samples.

RESULTS & CONCLUSIONS

Focusing on skeletal muscle and mitochondrial biogenesis, numerous substances exhibiting agonistic or antagonistic actions on different cellular 'control centers' resulting in increased skeletal muscle mass, enhanced performance (as determined with laboratory animal models), and/or elevated amounts of mitochondria have been described. Substances of interest include agonists for REV-ERBα (e.g. SR9009, SR9011, SR10067, GSK4112), sirtuin 1 (e.g. SRT1720, SRT2104), adenosine monophosphate-activated protein kinase (AMPK, e.g. AICAR), peroxisome proliferator-activated receptor (PPAR)δ (e.g. GW1516, GW0742, L165041), and inhibitory/antagonistic agents targeting the methionine-folate cycle (MOTS-c), the general control non-derepressible 5 (GCN5) acetyl transferase (e.g. CPTH2, MB-3), myostatin (e.g. MYO-029), the myostatin receptor (bimagrumab), and myostatin receptor ligands (e.g. sotatercept, ACE-031). In addition, potentially relevant drug targets were identified, e.g. with the sarcoplasmic transmembrane peptide myoregulin and the nuclear receptor corepressor 1 (NCOR-1). The antagonism of these has shown to result in substantially enhanced physical performance in animals, necessitating the monitoring of strategies such as RNA interference regarding these substances. Most drug candidates are of lower molecular mass and comprise non-natural compositions, facts which suggest approaches for their qualitative identification in doping control samples by mass spectrometry. Electrospray ionization/collision-induced dissociation mass spectra of representatives of the aforementioned substances and selected in vitro derived phase-I metabolites support this assumption, and test methods for a subset of these have been recently established. Expanding the knowledge on analytical data will further facilitate the identification of such analytes and related compounds in confiscated material as well as sports drug testing specimens.

Identification and characterization of in vitro and in vivo generated metabolites of the adiponectin receptor agonists AdipoRon and 112254

Peroxisome proliferator-activated receptors (PPARs), peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), sirtuin 1 (SIRT1) and adenosine monophosphate-activated protein kinase (AMPK) are regulators of transcriptional processes and effects of exercise and pseudo-exercise situations. Compounds occasionally referred to as endurance exercise mimetics such as AdipoRon and 112254, both adiponectin receptor agonists, can be used to simulate the physiology of endurance exercise via pathways including these transcriptional regulators. Adiponectin supports fatty acid utilization and triglyceride-content reduction in cells and increases both the mitochondrial biogenesis and the oxidative metabolism in muscle cells. In routine doping control analysis, knowledge about phase-I and -II metabolic products of target analytes is essential. Hence, in vitro- and in vivo-metabolism experiments are frequently employed tools in preventive doping research to determine potential urinary metabolites for sports drug testing purposes, especially concerning new, (yet) unapproved compounds. In the present study, in vitro assays were conducted using human liver microsomal and S9 fractions, and rat in vivo experiments were performed using both AdipoRon and 112254. For AdipoRon, obtained samples were analyzed using liquid chromatography-high resolution/high accuracy (tandem) mass spectrometry with both electrospray ionization or atmospheric-pressure chemical ionization techniques. Overall, more than five phase I-metabolites were found in vitro and in vivo, including particularly monohydroxylated and hydrogenated species. No phase II-metabolites were found in vitro; conversely, signals suggesting the presence of glucuronic acid or other conjugates in samples collected from in vivo experiment were observed, the structures of which were however not conclusively identified. Also for 112254, several phase-I metabolites were found in vitro, e.g. monohydroxylated and demethylated species. Here, no phase II-metabolites were observed neither using in vitro nor in vivo samples. Based on the generated data, the implementation of metabolites and unmodified drug candidates into routine doping control protocols is deemed warranted for comprehensive sports drug testing programs until human elimination study data are available.

Circulating irisin levels and muscle FNDC5 mRNA expression are independent of IL-15 levels in mice

Interleukin-15 (IL-15) and irisin are exercise-induced myokines that exert favorable effects on energy expenditure and metabolism. IL-15 can induce PGC-1α expression, which in turn induces expression of irisin and its precursor, FNDC5. Therefore, the present study tested the hypothesis that increases in circulating irisin levels and muscle FNDC5 mRNA expression are dependent on IL-15. Circulating irisin levels and gastrocnemius muscle FNDC5 mRNA expression were examined following acute exercise in control and IL-15-deleted (IL-15 KO) mice, following injection of IL-15 into IL-15 KO mice, and in transgenic mice with elevated circulating IL-15 levels (IL-15 Tg mice). Circulating IL-15 levels and muscle PGC-1α and PPARδ mRNA expressions were determined as positive controls. No effect of IL-15 deletion on post-exercise serum irisin levels or muscle FNDC5 mRNA expression was detected. While serum IL-15 levels and muscle PGC-1α expression were elevated post-exercise in control mice, both serum irisin levels and muscle FNDC5 expression decreased shortly after exercise in both control and IL-15 KO mice. A single injection of recombinant IL-15 into IL-15 KO mice that significantly increased muscle PPARδ and PGC-1α mRNA expressions had no effect on circulating irisin release, but modestly induced muscle FNDC5 expression. Additionally, serum irisin and gastrocnemius muscle FNDC5 expression in IL-15 Tg mice were similar to those of control mice. Muscle FNDC5 mRNA expression and irisin release are not IL-15-dependent in mice.

Utilizing small nutrient compounds as enhancers of exercise-induced mitochondrial biogenesis

Endurance exercise, when performed regularly as part of a training program, leads to increases in whole-body and skeletal muscle-specific oxidative capacity. At the cellular level, this adaptive response is manifested by an increased number of oxidative fibers (Type I and IIA myosin heavy chain), an increase in capillarity and an increase in mitochondrial biogenesis. The increase in mitochondrial biogenesis (increased volume and functional capacity) is fundamentally important as it leads to greater rates of oxidative phosphorylation and an improved capacity to utilize fatty acids during sub-maximal exercise. Given the importance of mitochondrial biogenesis for skeletal muscle performance, considerable attention has been given to understanding the molecular cues stimulated by endurance exercise that culminate in this adaptive response. In turn, this research has led to the identification of pharmaceutical compounds and small nutritional bioactive ingredients that appear able to amplify exercise-responsive signaling pathways in skeletal muscle. The aim of this review is to discuss these purported exercise mimetics and bioactive ingredients in the context of mitochondrial biogenesis in skeletal muscle. We will examine proposed modes of action, discuss evidence of application in skeletal muscle in vivo and finally comment on the feasibility of such approaches to support endurance-training applications in humans.

Acetic acid enhances endurance capacity of exercise-trained mice by increasing skeletal muscle oxidative properties

Acetic acid has been shown to promote glycogen replenishment in skeletal muscle during exercise training. In this study, we investigated the effects of acetic acid on endurance capacity and muscle oxidative metabolism in the exercise training using in vivo mice model. In exercised mice, acetic acid induced a significant increase in endurance capacity accompanying a reduction in visceral adipose depots. Serum levels of non-esterified fatty acid and urea nitrogen were significantly lower in acetic acid-fed mice in the exercised mice. Importantly, in the mice, acetic acid significantly increased the muscle expression of key enzymes involved in fatty acid oxidation and glycolytic-to-oxidative fiber-type transformation. Taken together, these findings suggest that acetic acid improves endurance exercise capacity by promoting muscle oxidative properties, in part through the AMPK-mediated fatty acid oxidation and provide an important basis for the application of acetic acid as a major component of novel ergogenic aids.

Effects of postweaning administration of conjugated linoleic acid on development of obesity in nescient basic helix-loop-helix 2 knockout mice

Conjugated linoleic acid (CLA) has been reported to prevent body weight gain and fat accumulation in part by improving physical activity in mice. However, the effects of postweaning administration of CLA on the development of obesity later in life have not yet been demonstrated. The current study investigated the role of postweaning CLA treatment on skeletal muscle energy metabolism in genetically induced inactive adult-onset obese model, nescient basic helix-loop-helix 2 knockout (N2KO) mice. Four-week-old male N2KO and wild type mice were fed either control or a CLA-containing diet (0.5%) for 4 weeks, and then CLA was withdrawn and control diet provided to all mice for the following 8 weeks. Postweaning CLA supplementation in wild type animals, but not N2KO mice, may activate AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor-δ (PPARδ) as well as promote desensitization of phosphatase and tensin homologue (PTEN) and sensitization of protein kinase B (AKT) at threonine 308 in gastrocnemius skeletal muscle, improving voluntary activity and glucose homeostasis. We suggest that postweaning administration of CLA may in part stimulate the underlying molecular targets involved in muscle energy metabolism to reduce weight gain in normal animals, but not in the genetically induced inactive adult-onset animal model.

Moderate exercise training is more effective than resveratrol supplementation for ameliorating lipid metabolic complication in skeletal muscle of high fat diet-induced obese mice

PURPOSE

The aim of this study was to compare the effectiveness of moderate exercise training or resveratrol supplementation with a low fat diet on lipid metabolism in the skeletal muscle of high fat diet-induced obese mice.

METHODS

C57BL/6J mice (5 weeks old, n = 30) were fed a high fat diet (45% fat) for 8 weeks first to make them obese. Afterward, all the mice were fed a low fat diet during 8 weeks of intervention with moderate exercise training and resveratrol supplementation. Before the intervention, the mice were separated into 3 groups: low-fat diet control (HLC; n = 10), low fat diet with resveratrol (HLR; n = 10) or low fat diet with exercise (HLE n = 10). The exercise group (HLE) performed treadmill running for 30-60 min/day at 10-22 m/min, 0% grade, 5 times/week for 8 weeks, while the resveratrol group (HLR) received a daily dose of resveratrol (10 mg/kg of body weight), 5 days/week for 8 weeks.

RESULTS

Body weight was significantly reduced in HLE. Further, the lipogenesis marker SREBP and the inflammatory cytokine TNF-α were significant reduced in HLE. However, there was no significant effect from resveratrol supplementation with a low fat diet. Taken together, exercise training with a low fat diet has the positive effect of ameliorating lipid disturbance in the skeletal muscle of high fat diet-induced obese mice.

CONCLUSION

These findings suggest that exercise training with a low fat diet is most effective to improve lipid metabolism by reducing lipogenesis and inflammation in the skeletal muscle of high fat diet-induced obese mice.

IL-15 is required for postexercise induction of the pro-oxidative mediators PPARδ and SIRT1 in male mice

Physical exercise induces transient upregulation of the pro-oxidative mediators peroxisome proliferator-activated receptor-δ (PPARδ), silent information regulator of transcription (sirtuin)-1 (SIRT1), PPARγ coactivator 1α (PGC-1α), and PGC-1β in skeletal muscle. To determine the role of the cytokine IL-15 in acute postexercise induction of these molecules, expression of these factors after a bout of exhaustive treadmill running was examined in the gastrocnemius muscle of untrained control and IL-15-knockout (KO) mice. Circulating IL-15 levels increased transiently in control mice after exercise. Control mice, but not IL-15-KO mice, upregulated muscle PPARδ and SIRT1 protein after exercise, accompanied by a complex pattern of mRNA expression for these factors. However, in exhaustive exercise, control mice ran significantly longer than IL-15-KO mice. Therefore, in a second experiment, mice were limited to a 20-minute run, after which a similar pattern of induction of muscle PPARδ and SIRT1 protein by control mice only was observed. In a separate experiment, IL-15-KO mice injected systemically with recombinant IL-15 upregulated muscle PPARδ and SIRT1 mRNA within 30 minutes and also exhibited increased muscle PPARδ protein levels by 3 hours. After exercise, both control and IL-15-KO mice downregulated IL-15 receptor-α (IL-15Rα) mRNA, whereas IL-15Rα-deficient mice exhibited constitutively elevated circulating IL-15 levels. These observations indicate IL-15 release after exercise is necessary for induction of PPARδ and SIRT1 at the protein level in muscle tissue and suggest that exercise releases IL-15 normally sequestered by the IL-15Rα in the resting state. These findings could be used to develop an IL-15-based strategy to induce many of the metabolic benefits of physical exercise.

Enhanced skeletal muscle for effective glucose homeostasis

As the single largest organ in the body, the skeletal muscle is the major site of insulin-stimulated glucose uptake in the postprandial state. Skeletal muscles provide the physiological foundation for physical activities and fitness. Reduced muscle mass and strength is commonly associated with many chronic diseases, including obesity and insulin resistance. The complications of diabetes on skeletal muscle mass and physiology, resulting from either insulin deprivation or insulin resistance, may not be life-threatening, but accelerate the lost physiological functions of glucose homeostasis. The formation of skeletal muscle commences in the embryonic developmental stages at the time of mesoderm generation, where somites are the developmental milestone in musculoskeletal formation. Dramatic skeletal muscle growth occurs during adolescence as a result of muscle fiber hypertrophy since muscle fiber formation is mostly completed before birth. The rate of growth rapidly decelerates in the late stages of adulthood as adipose tissue gradually accumulates more fat when energy intake exceeds expenditure. Physiologically, the key to effective glucose homeostasis is the hormone insulin and insulin sensitivity of target tissues. Enhanced skeletal muscle, by either intrinsic mechanism or physical activity, offers great advantages and benefits in facilitating glucose regulation. One key protein factor named myostatin is a dominant inhibitor of muscle mass. Depression of myostatin by its propeptide or mutated receptor enhances muscle mass effectively. The muscle tissue utilizes a large portion of metabolic energy for its growth and maintenance. We demonstrated that transgenic overexpression of myostatin propeptide in mice fed with a high-fat diet enhanced muscle mass and circulating adiponectin, while the wild-type mice developed obesity and insulin resistance. Enhanced muscle growth has positive effects on fat metabolism through increasing adiponectin expression and its regulations. Molecular studies of the exercise-induced glucose uptake in skeletal muscle also provide insights on auxiliary substances that mimic the plastic adaptations of muscle to exercise so that the body may amplify the effects of exercise in contending physical activity limitations or inactivity. The recent results from the peroxisome proliferator-activated receptor γ coactivator 1α provide a promising therapeutic approach for future metabolic drug development. In summary, enhanced skeletal muscle and fundamental understanding of the biological process are critical for effective glucose homeostasis in metabolic disorders.

Exercise acts as a drug; the pharmacological benefits of exercise

The beneficial effects of regular exercise for the promotion of health and cure of diseases have been clearly shown. In this review, we would like to postulate the idea that exercise can be considered as a drug. Exercise causes a myriad of beneficial effects for health, including the promotion of health and lifespan, and these are reviewed in the first section of this paper. Then we deal with the dosing of exercise. As with many drugs, dosing is extremely important to get the beneficial effects of exercise. To this end, the organism adapts to exercise. We review the molecular signalling pathways involved in these adaptations because understanding them is of great importance to be able to prescribe exercise in an appropriate manner. Special attention must be paid to the psychological effects of exercise. These are so powerful that we would like to propose that exercise may be considered as a psychoactive drug. In moderate doses, it causes very pronounced relaxing effects on the majority of the population, but some persons may even become addicted to exercise. Finally, there may be some contraindications to exercise that arise when people are severely ill, and these are described in the final section of the review. Our general conclusion is that exercise is so effective that it should be considered as a drug, but that more attention should be paid to the dosing and to individual variations between patients.

IL-15 overexpression promotes endurance, oxidative energy metabolism, and muscle PPARδ, SIRT1, PGC-1α, and PGC-1β expression in male mice

Endurance exercise initiates a pattern of gene expression that promotes fat oxidation, which in turn improves endurance, body composition, and insulin sensitivity. The signals from exercise that initiate these pathways have not been completely characterized. IL-15 is a cytokine that is up-regulated in skeletal muscle after exercise and correlates with leanness and insulin sensitivity. To determine whether IL-15 can induce any of the metabolic adaptations associated with exercise, substrate metabolism, endurance, and molecular expression patterns were examined in male transgenic mice with constitutively elevated muscle and circulating IL-15 levels. IL-15 transgenic mice ran twice as long as littermate control mice in a run-to-exhaustion trial and preferentially used fat for energy metabolism. Fast muscles in IL-15 transgenic mice exhibited high expression of intracellular mediators of oxidative metabolism that are induced by exercise, including sirtuin 1, peroxisome proliferator-activated receptor (PPAR)-δ, PPAR-γ coactivator-1α, and PPAR-γ coactivator-1β. Muscle tissue in IL-15 transgenic mice exhibited myosin heavy chain and troponin I mRNA isoform expression patterns indicative of a more oxidative phenotype than controls. These findings support a role for IL-15 in induction of exercise endurance, oxidative metabolism, and skeletal muscle molecular adaptations induced by physical training.

PGC-1α improves glucose homeostasis in skeletal muscle in an activity-dependent manner

Metabolic disorders are a major burden for public health systems globally. Regular exercise improves metabolic health. Pharmacological targeting of exercise mediators might facilitate physical activity or amplify the effects of exercise. The peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) largely mediates musculoskeletal adaptations to exercise, including lipid refueling, and thus constitutes such a putative target. Paradoxically, forced expression of PGC-1α in muscle promotes diet-induced insulin resistance in sedentary animals. We show that elevated PGC-1α in combination with exercise preferentially improves glucose homeostasis, increases Krebs cycle activity, and reduces the levels of acylcarnitines and sphingosine. Moreover, patterns of lipid partitioning are altered in favor of enhanced insulin sensitivity in response to combined PGC-1α and exercise. Our findings reveal how physical activity improves glucose homeostasis. Furthermore, our data suggest that the combination of elevated muscle PGC-1α and exercise constitutes a promising approach for the treatment of metabolic disorders.

Reawakening atlas: chemical approaches to repair or replace dysfunctional musculature

Muscle diseases are major health concerns. For example, ischemic heart disease is the third most common cause of death. Cell therapy is an attractive approach for treating muscle diseases, although this is hampered by the need to generate large numbers of functional muscle cells. Small molecules have become established as attractive tools for modulating cell behavior and, in this review, we discuss the recent, rapid research advances made in the development of small molecule methods to facilitate the production of functional cardiac, skeletal, and smooth muscle cells. We also describe how new developments in small molecule strategies for muscle disease aim to induce repair and remodelling of the damaged tissues in situ. Recent progress has been made in developing small molecule cocktails that induce skeletal muscle regeneration, and these are discussed in a broader context, because a similar phenomenon occurs in the early stages of salamander appendage regeneration. Although formidable technical hurdles still remain, these new advances in small molecule-based methodologies should provide hope that cell therapies for patients suffering from muscle disease can be developed in the near future.

trans-10,cis-12 conjugated linoleic acid enhances endurance capacity by increasing fatty acid oxidation and reducing glycogen utilization in mice

The supplementation of conjugated linoleic acid (CLA) has been shown to improve endurance by enhancing fat oxidation during exercise in rodents and humans. This study was designed to investigate the isomer-specific effects of CLA on endurance capacity and energy metabolism in mice during exercise. Male 129Sv/J mice were divided into three dietary groups and fed treatment diet for 6 weeks; control, 0.5 % cis-9,trans-11 (c9,t11) CLA, or 0.5 % trans-10,cis-12 (t10,c12) CLA. Dietary t10,c12 CLA induced a significant increase in maximum running time and distance until exhaustion with a dramatic reduction of total adipose depots compared to a control group, but there were no significant changes in endurance with the c9,t11 CLA treatment. Serum triacylglycerol and non-esterified fatty acid concentrations were significantly lower in the t10,c12 fed mice after exercise compared to control and the c9,t11 CLA fed-animals. Glycogen contents in livers of the t10,c12 fed-mice were higher than those in control mice, concomitant with reduction of serum L-lactate level. There were no differences in non-exercise physical activity among all treatment groups. In addition, the mRNA expression levels of carnitine palmitoyl transferase 1β, uncoupling protein 2 and peroxisome proliferator-activated receptor δ (PPARδ) in skeletal muscle during exercise were significantly up-regulated by the t10,c12 CLA but not the c9,t11 CLA. These results suggest that the t10,c12 CLA is responsible for improving endurance exercise capacity by promoting fat oxidation with a reduction of the consumption of stored liver glycogen, potentially mediated via PPARδ dependent mechanisms.

PGC-1α and exercise in the control of body weight

The increasing prevalence of obesity and its comorbidities represents a major threat to human health globally. Pharmacological treatments exist to achieve weight loss, but the subsequent weight maintenance is prone to fail in the long run. Accordingly, efficient new strategies to persistently control body weight need to be elaborated. Exercise and dietary interventions constitute classical approaches to reduce and maintain body weight, yet people suffering from metabolic diseases are often unwilling or unable to move adequately. The administration of drugs that partially mimic exercise adaptation might circumvent this problem by easing and supporting physical activity. The thermogenic peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) largely mediates the adaptive response of skeletal muscle to endurance exercise and is a potential target for such interventions. Here, we review the role of PGC-1α in mediating exercise adaptation, coordinating metabolic circuits and enhancing thermogenic capacity in skeletal muscle. We suggest a combination of elevated muscle PGC-1α and exercise as a modified approach for the efficient long-term control of body weight and the treatment of the metabolic syndrome.

Non-invasive physiological monitoring of exercise and fitness

OBJECTIVE

To review the current research of new emerging diagnostic technology for non-invasive physiological monitoring of exercise and fitness. As a personal trainer, I believe that exercise can improve the conditions of several diseases and/or events such as stroke, post-traumatic head injury, spinal cord injury, and a multitude of other diseases. This compilation of information will allow health care providers tools of a non-invasive manner to promote healing and health that go beyond the initial event. Allowing patients continued managed care beyond what is believed to be their plateau.

MATERIAL AND METHOD

Review science-based research involving non-invasive technology, including cardiovascular evaluations: heart rate monitors, near-infrared spectroscopy, blood pressure, and electrocardiography; motor capabilities: surface electromyography and manual testers, i.e. dynamometer, and digital and video photography; radiological monitoring: magnetic resonance imaging, three-dimensional computer tomography, and laser Doppler.

RESULTS

This investigation has found that a new approach should be implemented for non-invasive physiological monitoring of exercise and fitness through development and utilization across a wide variety of equipment, and monitoring technology. This non-invasive methodology will not only motivate but encourage individuals to begin and remain compliant with an exercise program allowing a variety of health care providers to assist in patient care.

DISCUSSION

We need to shift the paradigm from taking care of the sick to maintaining the health of our patients. This can be accomplished with non-invasive evaluation, tracking, and monitoring tools. Many of the suggestions for monitoring are used in a clinical setting rather than a general fitness environment. These monitoring tests need to be economical as well as available for continual re-evaluation.