Inhibition of xanthine oxidase reduces oxidative stress and improves skeletal muscle function in response to electrically stimulated isometric contractions in aged mice

Reactive oxygen species promote endurance exercise-induced adaptations in skeletal muscles

The discovery that contracting skeletal muscle generates reactive oxygen species (ROS) was first reported over 40 years ago. The prevailing view in the 1980s was that exercise-induced ROS production promotes oxidation of proteins and lipids resulting in muscle damage. However, a paradigm shift occurred in the 1990s as growing research revealed that ROS are signaling molecules, capable of activating transcriptional activators/coactivators and promoting exercise-induced muscle adaptation. Growing evidence supports the notion that reduction-oxidation (redox) signaling pathways play an important role in the muscle remodeling that occurs in response to endurance exercise training. This review examines the specific role that redox signaling plays in this endurance exercise-induced skeletal muscle adaptation. We begin with a discussion of the primary sites of ROS production in contracting muscle fibers followed by a summary of the antioxidant enzymes involved in the regulation of ROS levels in the cell. We then discuss which redox-sensitive signaling pathways promote endurance exercise-induced muscle adaptation and debate the strength of the evidence supporting the notion that redox signaling plays an essential role in muscle adaptation to endurance exercise training. In hopes of stimulating future research, we highlight several important unanswered questions in this field.

The mediating role of inflammaging between mitochondrial dysfunction and sarcopenia in aging: a review

Sarcopenia, characterized by the insidious reduction of skeletal muscle mass and strength, detrimentally affects the quality of life in elderly cohorts. Present therapeutic strategies are confined to physiotherapeutic interventions, signaling a critical need for elucidation of the etiological underpinnings to facilitate the development of innovative pharmacotherapies. Recent scientific inquiries have associated mitochondrial dysfunction and inflammation with the etiology of sarcopenia. Mitochondria are integral to numerous fundamental cellular processes within muscle tissue, including but not limited to apoptosis, autophagy, signaling via reactive oxygen species, and the maintenance of protein equilibrium. Deviations in mitochondrial dynamics, coupled with compromised oxidative capabilities, autophagic processes, and protein equilibrium, result in disturbances to muscular architecture and functionality. Mitochondrial dysfunction is particularly detrimental as it diminishes oxidative phosphorylation, escalates apoptotic activity, and hinders calcium homeostasis within muscle cells. Additionally, deleterious feedback loops of deteriorated respiration, exacerbated oxidative injury, and diminished quality control mechanisms precipitate the acceleration of muscular senescence. Notably, mitochondria exhibiting deficient energetic metabolism are pivotal in precipitating the shift from normative muscle aging to a pathogenic state. This analytical review meticulously examines the complex interplay between mitochondrial dysfunction, persistent inflammation, and the pathogenesis of sarcopenia. It underscores the imperative to alleviate inflammation and amend mitochondrial anomalies within geriatric populations as a strategy to forestall and manage sarcopenia. An initial overview provides a succinct exposition of sarcopenia and its clinical repercussions. The discourse then progresses to an examination of the direct correlation between mitochondrial dysfunction and the genesis of sarcopenia. Concomitantly, it accentuates potential synergistic effects between inflammatory responses and mitochondrial insufficiencies during the aging of skeletal muscle, thereby casting light upon emergent therapeutic objectives. In culmination, this review distills the prevailing comprehension of the mitochondrial and inflammatory pathways implicated in sarcopenia and delineates extant lacunae in knowledge to orient subsequent scientific inquiry.

Mitochondria Transplantation from Stem Cells for Mitigating Sarcopenia

Sarcopenia is defined as the age-related loss of muscle mass and function that can lead to prolonged hospital stays and decreased independence. It is a significant health and financial burden for individuals, families, and society as a whole. The accumulation of damaged mitochondria in skeletal muscle contributes to the degeneration of muscles with age. Currently, the treatment of sarcopenia is limited to improving nutrition and physical activity. Studying effective methods to alleviate and treat sarcopenia to improve the quality of life and lifespan of older people is a growing area of interest in geriatric medicine. Therapies targeting mitochondria and restoring mitochondrial function are promising treatment strategies. This article provides an overview of stem cell transplantation for sarcopenia, including the mitochondrial delivery pathway and the protective role of stem cells. It also highlights recent advances in preclinical and clinical research on sarcopenia and presents a new treatment method involving stem cell-derived mitochondrial transplantation, outlining its advantages and challenges.

Cancer Cachexia and breast cancer stem cell signalling - A crosstalk of signalling molecules

Cancer Cachexia is a condition characterized by the involuntary loss of lean body mass, a negative protein and energy balance, and systemic inflammation. This syndrome profoundly impacts the patient's quality of life and is linked to poor chemotherapy response and reduced survival. Despite multiple mechanisms being implicated in its development, and various cytokines believed to contribute to the persistent catabolic state, cachexia is still not fully recognized and is often left untreated. Cachexia is caused by altered metabolic adaptation and lack of anticactic therapy due to systemic cytokines promoting and fuelling cancer growth. The exact molecular mechanisms and clinical endpoints remain poorly defined. It has an occurrence rate of 30%-80%, accounting for 20% of total cancer mortality. Tumor cells remodel the microenvironment suitable for their proliferation, wherein they communicate with fibroblast cells to modulate their expression and induce tumor progressive cytokines. Several studies have reported its strong correlation with systemic cytokines that initiate and aggravate the condition. Plenty of studies show the prominent role of cancer-induced cachexia in pancreatic cancer, colon cancer, and lung cancer. However, limited data are available for breast cancer-induced cachexia, highlighting the need for studying it. Breast cancer stem cells (BCSCs) are a prominently explored area in breast cancer research. They are characterized by CD44+/CD24-/ALDH+ expression and are a focus of cancer research. They are a source of renewal and differentiation within the tumor environment and are responsible for progression, and chemotherapeutic resistance. The tumor microenvironment and its cytokines are responsible for maintaining and inducing their differentiation. Cytokines significantly impact BCSC development and self-renewal, stimulating or inhibiting proliferation depending on cytokine and environment. Pro-inflammatory mediators like IL-6, TNF-α, and IL-8 increase proliferation, promoting tumor growth. Experimental models and clinical studies have shown a direct relationship between cytokines and BCSC proliferation. Several of them seem to be interconnected as they initiate signalling down different pathways but converge at BCSC increase and tumor proliferation. This review highlights the common pathways between cachexia and BCSC signalling, to identify potential therapeutic targets that can aid both conditions.

Microalgae Produce Antioxidant Molecules with Potential Preventive Effects on Mitochondrial Functions and Skeletal Muscular Oxidative Stress

In recent years, microalgae have become a source of molecules for a healthy life. Their composition of carbohydrates, peptides, lipids, vitamins and carotenoids makes them a promising new source of antioxidant molecules. Skeletal muscle is a tissue that requires constant remodeling via protein turnover, and its regular functioning consumes energy in the form of adenosine triphosphate (ATP), which is produced by mitochondria. Under conditions of traumatic exercise or muscular diseases, a high production of reactive oxygen species (ROS) at the origin of oxidative stress (OS) will lead to inflammation and muscle atrophy, with life-long consequences. In this review, we describe the potential antioxidant effects of microalgae and their biomolecules on mitochondrial functions and skeletal muscular oxidative stress during exercises or in musculoskeletal diseases, as in sarcopenia, chronic obstructive pulmonary disease (COPD) and Duchenne muscular dystrophy (DMD), through the increase in and regulation of antioxidant pathways and protein synthesis.

Endogenous and Exogenous Antioxidants in Skeletal Muscle Fatigue Development during Exercise

Muscle fatigue is defined as a decrease in maximal force or power generated in response to contractile activity, and it is a risk factor for the development of musculoskeletal injuries. One of the many stressors imposed on skeletal muscle through exercise is the increased production of reactive oxygen species (ROS) and reactive nitrogen species (RNS), which intensifies as a function of exercise intensity and duration. Exposure to ROS/RNS can affect Na⁺/K⁺-ATPase activity, intramyofibrillar calcium turnover and sensitivity, and actin-myosin kinetics to reduce muscle force production. On the other hand, low ROS/RNS concentrations can likely upregulate an array of cellular adaptative responses related to mitochondrial biogenesis, glucose transport and muscle hypertrophy. Consequently, growing evidence suggests that exogenous antioxidant supplementation might hamper exercise-engendering upregulation in the signaling pathways of mitogen-activated protein kinases (MAPKs), peroxisome-proliferator activated co-activator 1α (PGC-1α), or mammalian target of rapamycin (mTOR). Ultimately, both high (exercise-induced) and low (antioxidant intervention) ROS concentrations can trigger beneficial responses as long as they do not override the threshold range for redox balance. The mechanisms underlying the two faces of ROS/RNS in exercise, as well as the role of antioxidants in muscle fatigue, are presented in detail in this review.

Xanthine Oxidoreductase Inhibitor Use Associated With Reduced Risk of Sarcopenia and Severe Sarcopenia in Patients Undergoing Hemodialysis

Background

Xanthine oxidoreductase (XOR) inhibition reduces reactive oxygen species (ROS) production and enhances adenosine triphosphate (ATP) synthesis. We investigated the protective effects of XOR inhibitor treatment on sarcopenia, frequently observed in patients undergoing hemodialysis (HD), in which increased ROS and ATP shortage are known to be involved.

Methods

This retrospective cross-sectional study included 296 HD patient (203 males, 93 females). Muscle mass, physical performance, and muscle strength were assessed using dual-energy X-ray absorptiometry, five-time chair stand testing, and handgrip strength, respectively. The Asian Working Group for Sarcopenia 2019 criteria were used to define low muscle mass, low physical performance, and low muscle strength, as well as sarcopenia and severe sarcopenia.

Results

Sarcopenia and severe sarcopenia prevalence rates were 42.2 and 20.9%, respectively. XOR inhibitor users (n = 119) showed a significantly (p < 0.05) lower prevalence of sarcopenia and severe sarcopenia, as well as reduced muscle mass, physical performance, and muscle strength than non-users (n = 177). Multivariate logistic regression analyses also revealed XOR inhibitor use to be significantly associated with low muscle mass [odds ratio (OR), 0.384; 95% confidence interval (CI), 0.183–0.806; p = 0.011] and low physical performance (OR, 0.286; 95% CI, 0.142–0.578; p < 0.001), while significance with low muscle strength was borderline. Furthermore, XOR inhibitor use was significantly associated with sarcopenia (OR, 0.462; 95% CI, 0.226–0.947; p = 0.035) and severe sarcopenia (OR, 0.236; 95% CI, 0.091–0.614; p = 0.003).

Conclusions

XOR inhibitor use was significantly associated with reduced risk of sarcopenia/severe sarcopenia in HD patients, suggesting that XOR inhibitor treatment has protective effects on sarcopenia in HD patients.

Associations of circulating xanthine oxidoreductase activity with cardiometabolic risk markers in overweight and obese Japanese men: a cross-sectional pilot study

Circulating xanthine oxidoreductase (XOR) activity may contribute to the pathogenesis of obesity-related adverse cardiometabolic profiles. This pilot study aimed to examine the cross-sectional associations between plasma XOR activity and cardiometabolic risk (CMR) markers in overweight and obese men. In 64 overweight and obese Japanese men (aged 31–63 years), plasma XOR activity and several CMR markers, such as homeostasis model assessment of insulin resistance (HOMA-IR), and clustered CMR score were measured in each participant. Clustered CMR score was constructed based on waist circumference, triglyceride, blood pressure, fasting plasma glucose, and high-density lipoprotein cholesterol. Plasma XOR activity in overweight and obese men was positively associated with the body mass index, waist circumference, visceral fat area, body fat mass, hemoglobin A1c, serum 8-hydroxy-2'-deoxyguanosine, HOMA-IR, and clustered CMR score and was inversely associated with handgrip strength and high-density lipoprotein cholesterol. Multiple linear regression analysis further demonstrated that the associations of plasma XOR activity with HOMA-IR and the clustered CMR score remained significant after adjustment for covariates including uric acid. Our data demonstrate that circulating XOR activity was independently associated, albeit modestly, with HOMA-IR and the clustered CMR score. These preliminary findings suggest that circulating XOR activity can potentially be one of the preventive targets and biomarkers of cardiometabolic disorders in over­weight and obese men.

Butyrate ameliorates skeletal muscle atrophy in diabetic nephropathy by enhancing gut barrier function and FFA2-mediated PI3K/Akt/mTOR signals

BACKGROUND AND PURPOSE

Muscle protein catabolism in patients with diabetic nephropathy (DN) results in striking loss of muscle proteins, which increases morbidity and mortality risks. Evidence shows that short-chain fatty acids (SCFAs) play an important role in health maintenance and disease development. Recently, the connection between butyrate (a SCFA) and DN has been revealed, although the relationship between butyrate and muscle atrophy remains unclear.

EXPERIMENTAL APPROACH

We studied changes in serum butyrate levels in DN patients using metabolomic analyses. In db/db mice, protective effects of butyrate on DN-induced muscle atrophy. were explored. Inhibition of muscle atrophy by butyrate and the underlying mechanism(s) were studied in C2C12 cells exposed to high glucose/lipopolysaccharide (HG/LPS).

KEY RESULTS

Butyrate levels in DN patients were significantly decreased. In db/db mice, supplementing normal diet with butyrate improved intestinal barrier function. Concurrently, butyrate alleviated muscle atrophy, promoted PI3K/Akt/mTOR signalling, and suppressed oxidative stress and autophagy in skeletal muscle of db/db mice, and in HG/LPS-exposed C2C12 cells. Further, FFA2 receptors, key components of SCFA signalling, were decreased in skeletal muscle of db/db mice and in HG/LPS-exposed C2C12 cells. Overexpression of FFA2 receptors activated PI3K/Akt/mTOR signalling and inhibited oxidative stress and autophagy in HG/LPS-exposed C2C12 cells. Silencing of FFA2 blocked PI3K/Akt/mTOR signalling that was improved by butyrate, as well as the suppression of oxidative stress and reduction of autophagy.

CONCLUSION AND IMPLICATION

Butyrate exerts protective effects on muscle atrophy induced by DN by enhancing intestinal barrier function and activating the FFA2 receptor-mediated PI3K/Akt/mTOR pathway.

Effect of uric acid-lowering therapy on renal function in patients with chronic kidney disease: a systematic review and meta-analysis

Background

Whether uric acid (UA)-lowering therapy (ULT) is effective in reducing the progression of renal dysfunction in patients with chronic kidney disease (CKD) remains controversial. Since several advances have been made in therapies for hyperuricemia, including novel xanthine oxidoreductase (XOR) inhibitors, we conducted a systematic review to clarify the effectiveness of ULT in preserving renal function among CKD patients.

Methods

In this systematic review, the MEDLINE database was searched up to June 2019. We included complete randomized controlled trials comparing renal events between adult non-dialyzed CKD patients, defined as estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73 m2, with and without ULTs. Changes in eGFR were expressed as the mean difference (MD). The incidence of dichotomous outcomes was expressed as a risk ratio. This review was performed using the predefined protocol published in PROSPERO (CRD 42019140346).

Results

Eleven studies with 4277 CKD patients were included. Drugs used in the intervention groups of all studies were XOR inhibitors (allopurinol, febuxostat or topiroxostat). Although patients with ULT tended to show superior preservation of eGFR as compared to those without ULT, no significant differences were identified (MD, 2.52; 95% confidence interval, − 0.15 to 5.18). In subgroup analysis, the use of allopurinol was associated with superior preservation of eGFR, whereas the newer XOR inhibitors, febuxostat and topiroxostat, showed no significant effects on eGFR changes. Neither incidence of end-stage kidney disease nor treatment-emergent adverse events differed significantly between groups.

Conclusions

The present systematic review and meta-analysis suggested that CKD patients with ULT tend to show superior eGFR preservation as compared to patients without ULT, but further studies are needed to verify the renoprotective effects of ULT.

Age and Sport Intensity-Dependent Changes in Cytokines and Telomere Length in Elite Athletes

Exercise-associated immune response plays a crucial role in the aging process. The aim of this study is to investigate the effect of sport intensity on cytokine levels, oxidative stress markers and telomere length in aging elite athletes. In this study, 80 blood samples from consenting elite athletes were collected for anti-doping analysis at an anti-doping laboratory in Italy (FMSI). Participants were divided into three groups according to their sport intensity: low-intensity skills and power sports (LI, n = 18); moderate-intensity mixed soccer players (MI, n = 31); and high-intensity endurance sports (HI, n = 31). Participants were also divided into two age groups: less than 25 (n = 45) and above 25 years old (n = 35). Serum levels of 10 pro and anti-inflammatory cytokines and two antioxidant enzymes were compared in age and sport intensity groups and telomere lengths were measured in their respective blood samples. Tumor necrosis factor-alpha (TNF-α) was the only cytokine showing significantly higher concentration in older athletes, regardless of sport intensity. Interleukin (IL)-10 increased significantly in HI regardless of age group, whereas IL-6 concentration was higher in the older HI athletes. IL-8 showed a significant interaction with sport intensity in different age groups. Overall, significant positive correlations among levels of IL-6, IL-10, IL-8 and TNF-α were identified. The antioxidant catalase activity was positively correlated with levels of TNF-α. Telomere length increased significantly with sport intensity, especially in the younger group. HI had longer telomeres and higher levels of pro- and anti-inflammatory cytokines, suggesting less aging in HI compared to low and moderate counterparts in association with heightened immune response. Investigation of the functional significance of these associations on the health and performance of elite athletes is warranted.

Exercise-Stimulated ROS Sensitive Signaling Pathways in Skeletal Muscle

Physical exercise represents a major challenge to whole-body homeostasis, provoking acute and adaptative responses at the cellular and systemic levels. Different sources of reactive oxygen species (ROS) have been described in skeletal muscle (e.g., NADPH oxidases, xanthine oxidase, and mitochondria) and are closely related to the physiological changes induced by physical exercise through the modulation of several signaling pathways. Many signaling pathways that are regulated by exercise-induced ROS generation, such as adenosine monophosphate-activated protein kinase (AMPK), mitogen activated protein kinase (MAPK), nuclear respiratory factor2 (NRF2), and PGC-1α are involved in skeletal muscle responses to physical exercise, such as increased glucose uptake, mitochondriogenesis, and hypertrophy, among others. Most of these adaptations are blunted by antioxidants, revealing the crucial role played by ROS during and after physical exercise. When ROS generation is either insufficient or exacerbated, ROS-mediated signaling is disrupted, as well as physical exercise adaptations. Thus, an understanding the limit between "ROS that can promote beneficial effects" and "ROS that can promote harmful effects" is a challenging question in exercise biology. The identification of new mediators that cause reductive stress and thereby disrupt exercise-stimulated ROS signaling is a trending on this topic and are covered in this current review.

Effect of allopurinol on phosphocreatine recovery and muscle function in older people with impaired physical function: a randomised controlled trial

Background

Allopurinol has vascular antioxidant effects and participates in purinergic signalling within muscle. We tested whether allopurinol could improve skeletal muscle energetics and physical function in older people with impaired physical performance.

Methods

We conducted a randomised, double blind, parallel group, placebo-controlled trial, comparing 20 weeks of allopurinol 600 mg once daily versus placebo. We recruited community-dwelling participants aged 65 and over with baseline 6-min walk distance of <400 m and no contraindications to magnetic resonance imaging scanning. Outcomes were measured at baseline and 20 weeks. The primary outcome was post-exercise phosphocreatine (PCr) recovery rate measured using ³¹P magnetic resonance spectroscopy of the calf. Secondary outcomes included 6-min walk distance, short physical performance battery (SPPB), lean body mass measured by bioimpedance, endothelial function and quality of life.

Results

In total, 124 participants were randomised, mean age 80 (SD 6) years. A total of 59 (48%) were female, baseline 6-min walk distance was 293 m (SD 80 m) and baseline SPPB was 8.5 (SD 2.0). Allopurinol did not significantly improve PCr recovery rate (treatment effect 0.10 units [95% CI, −0.07 to 0.27], P = 0.25). No significant changes were seen in endothelial function, quality of life, lean body mass or SPPB. Allopurinol improved 6-min walk distance (treatment effect 25 m [95% 4–46, P = 0.02]). This was more pronounced in those with high baseline oxidative stress and urate.

Conclusion

Allopurinol improved 6-min walk distance but not PCr recovery rate in older people with impaired physical function. Antioxidant strategies to improve muscle function for older people may need to be targeted at subgroups with high baseline oxidative stress.

Harnessing hyperuricemia to atherosclerosis and understanding its mechanistic dependence

Atherosclerosis is regarded as the disease of the arterial vasculature. The main characteristics of atherosclerosis are the abnormal accumulation of lipids, increased inflammatory cells, matrix deposits, and proliferation of smooth muscle cells. Diabetes mellitus, obesity, and hyperlipidemia are the most studied risk factors of atherosclerosis. One least studied risk factor is the uric acid (UA), a high UA in circulation is interlinked with many pathological processes. Several epidemiological studies suggest elevated UA levels as an essential biomarker in the forecast of several cardiovascular diseases. Available evidence claims that UA upholds the atherosclerosis process via disturbing lipid metabolism, reducing the nitric oxide synthesis in endothelial cells, promoting the proliferation of vascular smooth muscle cells, and overwhelms inflammation. In endothelial dysfunction and coronary artery lesions, UA is considered as an independent predictor. The updated studies on the involvement of hyperuricemia in atherosclerosis prove that treatment with xanthine oxidase (XO) inhibitors not just benefits the treatment of hyperuricemia but also reduces the burden of atherosclerosis to a greater extent. In this review, we highlight how the hyperuricemia affects vascular integrity, causes atherosclerosis, and the mechanism of action of XO inhibitors on atherosclerosis.

Pro-Aging Effects of Xanthine Oxidoreductase Products

The senescence process is the result of a series of factors that start from the genetic constitution interacting with epigenetic modifications induced by endogenous and environmental causes and that lead to a progressive deterioration at the cellular and functional levels. One of the main causes of aging is oxidative stress deriving from the imbalance between the production of reactive oxygen (ROS) and nitrogen (RNS) species and their scavenging through antioxidants. Xanthine oxidoreductase (XOR) activities produce uric acid, as well as reactive oxygen and nitrogen species, which all may be relevant to such equilibrium. This review analyzes XOR activity through in vitro experiments, animal studies and clinical reports, which highlight the pro-aging effects of XOR products. However, XOR activity contributes to a regular level of ROS and RNS, which appears essential for the proper functioning of many physiological pathways. This discourages the use of therapies with XOR inhibitors, unless symptomatic hyperuricemia is present.

Sarcopenia: Current treatments and new regenerative therapeutic approaches

Sarcopenia is characterized by loss of muscle and reduction in muscle strength that contributes to higher mortality rate and increased incidence of fall and hospitalization in the elderly. Mitochondria dysfunction and age-associated inflammation in muscle are two of the main attributors to sarcopenia progression. Recent clinical trials on sarcopenia therapies such as physical exercise, nutraceutical, and pharmaceutical interventions have revealed that exercise is the only effective strategy shown to alleviate sarcopenia. Unlike nutraceutical and pharmaceutical interventions that showed controversial results in sarcopenia alleviation, exercise was found to restore mitochondria homeostasis and dampen inflammatory responses via a complex exchange of myokines and osteokines signalling between muscle and bone. However, as exercise have limited benefit to immobile patients, the use of stem cells and their secretome are being suggested to be novel therapeutics that can be catered to a larger patient population owing to their mitochondria restoration effects and immune modulatory abilities. As such, we reviewed the potential pros and cons associated with various stem cell types/secretome in sarcopenia treatment and the regulatory and production barriers that need to be overcome to translate such novel therapeutic agents into bedside application.

Translational potential: This review summarizes the causes underlying sarcopenia from the perspective of mitochondria dysfunction and age-associated inflammation, and the progress of clinical trials for the treatment of sarcopenia. We also propose therapeutic potential of stem cell therapy and bioactive secretome for sarcopenia.

Increased Adenine Nucleotide Degradation in Skeletal Muscle Atrophy

Adenine nucleotides (AdNs: ATP, ADP, AMP) are essential biological compounds that facilitate many necessary cellular processes by providing chemical energy, mediating intracellular signaling, and regulating protein metabolism and solubilization. A dramatic reduction in total AdNs is observed in atrophic skeletal muscle across numerous disease states and conditions, such as cancer, diabetes, chronic kidney disease, heart failure, COPD, sepsis, muscular dystrophy, denervation, disuse, and sarcopenia. The reduced AdNs in atrophic skeletal muscle are accompanied by increased expression/activities of AdN degrading enzymes and the accumulation of degradation products (IMP, hypoxanthine, xanthine, uric acid), suggesting that the lower AdN content is largely the result of increased nucleotide degradation. Furthermore, this characteristic decrease of AdNs suggests that increased nucleotide degradation contributes to the general pathophysiology of skeletal muscle atrophy. In view of the numerous energetic, and non-energetic, roles of AdNs in skeletal muscle, investigations into the physiological consequences of AdN degradation may provide valuable insight into the mechanisms of muscle atrophy.

Altered oxidative stress and antioxidant defence in skeletal muscle during the first year following spinal cord injury

Oxidative stress promotes protein degradation and apoptosis in skeletal muscle undergoing atrophy. We aimed to determine whether spinal cord injury leads to changes in oxidative stress, antioxidant capacity, and apoptotic signaling in human skeletal muscle during the first year after spinal cord injury. Vastus lateralis biopsies were obtained from seven individuals 1, 3, and 12 months after spinal cord injury and from seven able-bodied controls. Protein content of enzymes involved in reactive oxygen species production and detoxification, and apoptotic signaling were analyzed by western blot. Protein carbonylation and 4-hydroxynonenal protein adducts were measured as markers of oxidative damage. Glutathione content was determined fluorometrically. Protein content of NADPH oxidase 2, xanthine oxidase, and pro-caspase-3 was increased at 1 and 3 months after spinal cord injury compared to able-bodied controls. Furthermore, total and reduced glutathione content was increased at 1 and 3 months after spinal cord injury. Conversely, mitochondrial complexes and superoxide dismutase 2 protein content were decreased 12 months after spinal cord injury compared to able-bodied controls. In conclusion, we provide indirect evidence of increased reactive oxygen species production and increased apoptotic signaling at 1 and 3 months after spinal cord injury. Concomitant increases in glutathione antioxidant defences may reflect adaptations poised to maintain redox homeostasis in skeletal muscle following spinal cord injury.

The role of SIRT1 in skeletal muscle function and repair of older mice

BACKGROUND

Sirtuin 1 (SIRT1) is a NAD+ sensitive deacetylase that has been linked to longevity and has been suggested to confer beneficial effects that counter aging-associated deterioration. Muscle repair is dependent upon satellite cell function, which is reported to be reduced with aging; however, it is not known if this is linked to an aging-suppression of SIRT1. This study tested the hypothesis that Sirtuin 1 (SIRT1) overexpression would increase the extent of muscle repair and muscle function in older mice.

METHODS

We examined satellite cell dependent repair in tibialis anterior, gastrocnemius, and soleus muscles of 13 young wild-type mice (20-30 weeks) and 49 older (80+ weeks) mice that were controls (n = 13), overexpressed SIRT1 in skeletal muscle (n = 14), and had a skeletal muscle SIRT1 knockout (n = 12) or a satellite cell SIRT1 knockout (n = 10). Acute muscle injury was induced by injection of cardiotoxin (CTX), and phosphate-buffered saline was used as a vector control. Plantarflexor muscle force and fatigue were evaluated before or 21 days after CTX injection. Satellite cell proliferation and mitochondrial function were also evaluated in undamaged muscles.

RESULTS

Maximal muscle force was significantly lower in control muscles of older satellite cell knockout SIRT1 mice compared to young adult wild-type (YWT) mice (P < 0.001). Mean contraction force at 40 Hz stimulation was significantly greater after recovery from CTX injury in older mice that overexpressed muscle SIRT1 than age-matched SIRT1 knockout mice (P < 0.05). SIRT1 muscle knockout models (P < 0.05) had greater levels of p53 (P < 0.05 MKO, P < 0.001 OE) in CTX-damaged tissues as compared to YWT CTX mice. SIRT1 overexpression with co-expression of p53 was associated with increased fatigue resistance and increased force potentiation during repeated contractions as compared to wild-type or SIRT1 knockout models (P < 0.001). Muscle structure and mitochondrial function were not different between the groups, but proliferation of satellite cells was significantly greater in older mice with SIRT1 muscle knockout (P < 0.05), but not older SIRT1 satellite cell knockout models, in vitro, although this effect was attenuated in vivo after 21 days of recovery.

CONCLUSIONS

The data suggest skeletal muscle structure, function, and recovery after CTX-induced injury are not significantly influenced by gain or loss of SIRT1 abundance alone in skeletal muscle; however, muscle function is impaired by ablation of SIRT1 in satellite cells. SIRT1 appears to interact with p53 to improve muscle fatigue resistance after repair from muscle injury.

The antioxidant system in the soleus muscle of growing rats is stimulated by the administration of a low-protein/high-carbohydrate diet

The aim of this study was to evaluate the generation of reactive oxygen species (ROS) by xanthine oxidase (XO), the enzymatic antioxidant system and oxidative damage in soleus and extensor digitorum longus (EDL) muscles of growing rats fed a low-protein, high-carbohydrate (LPHC; 6% protein, 74% carbohydrate) diet for 15 days. The LPHC diet increased the total antioxidant capacity by 45% and the activities of glutathione peroxidase (GPx), glutathione reductase and catalase in the soleus muscles. There was an increase in the carbonylated proteins with no increase thiobarbituric acid reactive substances (TBARS), although the XO activity had increased 20%. In EDL muscles, the LPHC diet increased XO activity by 66% and the TBARS levels by 80%, and only GPx had its activity increased. These results suggest that the enzymatic antioxidant system of the soleus muscle has a better response to the increase of ROS production stimulated by LPHC diet.

Atractylenolide III Attenuates Muscle Wasting in Chronic Kidney Disease via the Oxidative Stress-Mediated PI3K/AKT/mTOR Pathway

Oxidative stress contributes to muscle wasting in advanced chronic kidney disease (CKD) patients. Atractylenolide III (ATL-III), the major active constituent of Atractylodes rhizome, has been previously reported to function as an antioxidant. This study is aimed at investigating whether ATL-III has protective effects against CKD-induced muscle wasting by alleviating oxidative stress. The results showed that the levels of serum creatinine (SCr), blood urea nitrogen (BUN), and urinary protein significantly decreased in the ATL-III treatment group compared with the 5/6 nephrectomy (5/6 Nx) model group but were higher than those in the sham operation group. Skeletal muscle weight was increased, while inflammation was alleviated in the ATL-III administration group compared with the 5/6 Nx model group. ATL-III-treated rats also showed reduced dilation of the mitochondria, increased CAT, GSH-Px, and SOD activity, and decreased levels of MDA both in skeletal muscles and serum compared with 5/6 Nx model rats, suggesting that ATL-III alleviated mitochondrial damage and increased the activity of antioxidant enzymes, thus reducing the production of ROS. Furthermore, accumulated autophagosomes (APs) and autolysosomes (ALs) were reduced in the gastrocnemius (Gastroc) muscles of ATL-III-treated rats under transmission electron microscopy (TEM) together with the downregulation of LC3-II and upregulation of p62 according to Western blotting. This evidence indicated that ATL-III improved skeletal muscle atrophy and alleviated oxidative stress and autophagy in CKD rats. Furthermore, ATL-III could also increase the protein levels of p-PI3K, p-AKT, and p-mTOR in skeletal muscles in CKD rats. To further reveal the relevant mechanism, the oxidative stress-mediated PI3K/AKT/mTOR pathway was assessed, which showed that a reduced expression of p-PI3K, p-AKT, and p-mTOR in C2C12 myoblast atrophy induced by TNF-α could be upregulated by ATL-III; however, after the overexpression of Nox2 to increase ROS production, the attenuated effect was reversed. Our findings indicated that ATL-III is a potentially protective drug against muscle wasting via activation of the oxidative stress-mediated PI3K/AKT/mTOR pathway.

Shortage of Cellular ATP as a Cause of Diseases and Strategies to Enhance ATP

Germline mutations in cellular-energy associated genes have been shown to lead to various monogenic disorders. Notably, mitochondrial disorders often impact skeletal muscle, brain, liver, heart, and kidneys, which are the body’s top energy-consuming organs. However, energy-related dysfunctions have not been widely seen as causes of common diseases, although evidence points to such a link for certain disorders. During acute energy consumption, like extreme exercise, cells increase the favorability of the adenylate kinase reaction 2-ADP -> ATP+AMP by AMP deaminase degrading AMP to IMP, which further degrades to inosine and then to purines hypoxanthine -> xanthine -> urate. Thus, increased blood urate levels may act as a barometer of extreme energy consumption. AMP deaminase deficient subjects experience some negative effects like decreased muscle power output, but also positive effects such as decreased diabetes and improved prognosis for chronic heart failure patients. That may reflect decreased energy consumption from maintaining the pool of IMP for salvage to AMP and then ATP, since de novo IMP synthesis requires burning seven ATPs. Similarly, beneficial effects have been seen in heart, skeletal muscle, or brain after treatment with allopurinol or febuxostat to inhibit xanthine oxidoreductase, which catalyzes hypoxanthine -> xanthine and xanthine -> urate reactions. Some disorders of those organs may reflect dysfunction in energy-consumption/production, and the observed beneficial effects related to reinforcement of ATP re-synthesis due to increased hypoxanthine levels in the blood and tissues. Recent clinical studies indicated that treatment with xanthine oxidoreductase inhibitors plus inosine had the strongest impact for increasing the pool of salvageable purines and leading to increased ATP levels in humans, thereby suggesting that this combination is more beneficial than a xanthine oxidoreductase inhibitor alone to treat disorders with ATP deficiency.

Enhancement of Exercise Performance by 48 Hours, and 15-Day Supplementation with Mangiferin and Luteolin in Men

The natural polyphenols mangiferin and luteolin have free radical-scavenging properties, induce the antioxidant gene program and down-regulate the expression of superoxide-producing enzymes. However, the effects of these two polyphenols on exercise capacity remains mostly unknown. To determine whether a combination of luteolin (peanut husk extract containing 95% luteolin, PHE) and mangiferin (mango leave extract (MLE), Zynamite^®) at low (PHE: 50 mg/day; and 140 mg/day of MLE containing 100 mg of mangiferin; L) and high doses (PHE: 100 mg/day; MLE: 420 mg/day; H) may enhance exercise performance, twelve physically active men performed incremental exercise to exhaustion, followed by sprint and endurance exercise after 48 h (acute effects) and 15 days of supplementation (prolonged effects) with polyphenols or placebo, following a double-blind crossover design. During sprint exercise, mangiferin + luteolin supplementation enhanced exercise performance, facilitated muscle oxygen extraction, and improved brain oxygenation, without increasing the VO₂. Compared to placebo, mangiferin + luteolin increased muscle O₂ extraction during post-exercise ischemia, and improved sprint performance after ischemia-reperfusion likely by increasing glycolytic energy production, as reflected by higher blood lactate concentrations after the sprints. Similar responses were elicited by the two doses tested. In conclusion, acute and prolonged supplementation with mangiferin combined with luteolin enhances performance, muscle O₂ extraction, and brain oxygenation during sprint exercise, at high and low doses.

Evaluation of Oxidative Stress Parameters and Antioxidant Status in Plasma and Erythrocytes of Elderly Diabetic Patients with Sarcopenia

OBJECTIVES

Oxidative stress may play a role in the pathogenesis of both sarcopenia and diabetes. Although the risk of sarcopenia is increased in people with type 2 diabetes, the relationship between sarcopenia oxidative stress and antioxidant status among the older diabetes population is not well studied. The aim of this present study was to evaluate the relationship between oxidative stress and antioxidant status and sarcopenia in elderly diabetic patients.

DESIGN

This was a cross-sectional designed study with a control group. A total of 60 type 2 diabetic elderly patients were enrolled in the study (30 sarcopenic and 30 controls).

MEASUREMENTS

Comprehensive geriatric assessments and anthropometric measurements were performed. Sarcopenia was diagnosed according to the European Working Group on Sarcopenia in Older People. Skeletal muscle mass was measured using bioelectrical impedance analysis. A handheld dynamometer was used for skeletal muscle strength measurements. Gait speed was measured using a 4 meter walking test. Plasma malondialdehyde (MDA), glutathione peroxidase (GSH-Px) and erythrocyte MDA, GSH-Px, superoxide dismutase (SOD), catalase and xanthine oxidase (XO) measurements were performed.

RESULTS

While plasma XO was significantly higher in sarcopenic individuals (0.406(0.225-0.775)) compared to controls (0.312(0.112-0.712)) (p=0.006), plasma GSH-Px was significantly lower in sarcopenic individuals (0.154(0.101-0.274)) compared to controls (0.204(0.12-.0312)) (p=0.003). Plasma XO (OR: 2.69 (CI 95% 0.13-52.76, p=0.041) and BMI (OR: 0.6 (CI 95% 0.41-0.89, p=0.009) were independently associated with sarcopenia of diabetes in multivariate analysis.

CONCLUSIONS

Only plasma XO was found to be independently associated with sarcopenia. XO can be important in the pathogenesis of sarcopenia in diabetes. Oxidative stress and antioxidant status might be associated with sarcopenia in diabetic older individuals but this association seems to be mediated by other factors. Further studies are needed on this subject.

Analysis of NT-proBNP and uric acid due to left ventricle hypertrophy in the patients of aortic valve disease

Objective:

To evaluate the concentration of N terminal proBNP (NT-proBNP) and partially the serum uric acid in the severe condition of aortic valve dysfunction for assessment of left ventricle hypertrophy.

Methods:

The study was conducted in the signal transduction lab department of biochemistry Quaid-I-Azam University, Islamabad from September 2013 to February 2017. NT-proBNP and serum uric acid were measured in one hundred patients of aortic valve dysfunction. The patients were divided into three main groups: 1) Aortic stenosis, 2) Aortic regurgitation, and 3) Aortic stenosis with Aortic regurgitation. The results were compared between disease and controls groups.

Results:

High level of plasma NT-proBNP was detected in all the three disease groups of aortic valve (stenosis, p<0.001), (regurgitation, p<0.001) and (stenosis with regurgitation, p<0.001). In addition, non-significantly increased level of serum uric acid was also observed in left ventricle hypertrophy in all the three respective disease groups of aortic valve.

Conclusion:

Increased secretion of NT-proBNP during cardiac remodeling can be related to the severity of left ventricle hypertrophy due to aortic valve abnormality in all the disease groups of severe stenosis, severe regurgitation, and combine disease condition of severe stenosis and severe regurgitation. However, non-significant increase in uric acid concentration is also identified which may be due to one of the factors involved in left ventricle hypertrophy in all the three disease groups of aortic valve. The interaction of uric acid with NT-proBNP during cardiac remolding due to aortic valve dysfunction is still not clear.

Mitochondria-Targeted Antioxidants and Skeletal Muscle Function

One of the main sources of reactive oxygen species (ROS) in skeletal muscle is the mitochondria. Prolonged or very high ROS exposure causes oxidative damage, which can be deleterious to muscle function, and as such, there is growing interest in targeting antioxidants to the mitochondria in an effort to prevent or treat muscle dysfunction and damage associated with disease and injury. Paradoxically, however, ROS also act as important signalling molecules in controlling cellular homeostasis, and therefore caution must be taken when supplementing with antioxidants. It is possible that mitochondria-targeted antioxidants may limit oxidative stress without suppressing ROS from non-mitochondrial sources that might be important for cell signalling. Therefore, in this review, we summarise literature relating to the effect of mitochondria-targeted antioxidants on skeletal muscle function. Overall, mitochondria-targeted antioxidants appear to exert beneficial effects on mitochondrial capacity and function, insulin sensitivity and age-related declines in muscle function. However, it seems that this is dependent on the type of mitochondrial-trageted antioxidant employed, and its specific mechanism of action, rather than simply targeting to the mitochondria.

Lipoproteins and Cardiovascular Redox Signaling: Role in Atherosclerosis and Coronary Disease

SIGNIFICANCE

Lipoproteins, such as low-density lipoprotein, play a causal role in the development of atherosclerosis and coronary disease. Recent Advances: Lipoproteins can stimulate vascular production of reactive oxygen species, which act as important signaling molecules in the cardiovascular system contributing to the pathophysiology of endothelial dysfunction, hypertension, and atherosclerosis.

CRITICAL ISSUES

Modified lipoproteins have emerged as important regulators of redox signaling, such as oxidized or carbamylated low-density lipoprotein or modified high-density lipoproteins, that contain oxidized lipids, an altered protein cargo, and associated small molecules, such as symmetric dimethylarginine.

FUTURE DIRECTIONS

In this review, we provide an overview on signaling pathways stimulated by modified lipoproteins in the cardiovascular system and their potential role in cardiovascular disease development. Moreover, we highlight novel aspects of how gut microbiome-related mechanisms-a growing research field-may contribute to lipoprotein modification with subsequent impact on cardiovascular redox signaling. Antioxid. Redox Signal. 29, 337-352.

Voluntary wheel running increases satellite cell abundance and improves recovery from disuse in gastrocnemius muscles from mice

Reloading of atrophied muscles after hindlimb suspension unloading (HSU) can induce injury and prolong recovery. Low-impact exercise, such as voluntary wheel running, has been identified as a nondamaging rehabilitation therapy in rodents, but its effects on muscle function, morphology, and satellite cell activity after HSU are unclear. This study tested the hypothesis that low-impact wheel running would increase satellite cell proliferation and improve recovery of muscle structure and function after HSU in mice. Young adult male and female C57BL/6 mice ( n = 6/group) were randomly placed into five groups. These included HSU without recovery (HSU), normal ambulatory recovery for 14 days after HSU (HSU+NoWR), and voluntary wheel running recovery for 14 days after HSU (HSU+WR). Two control groups were used: nonsuspended mouse cage controls (Control) and voluntary wheel running controls (ControlWR). Satellite cell activation was evaluated by providing mice 5-bromo-2'-deoxyuridine (BrdU) in their drinking water. As expected, HSU significantly reduced in vivo maximal force, decreased in vivo fatigability, and decreased type I and IIa myosin heavy chain (MHC) abundance in plantarflexor muscles. HSU+WR mice significantly improved plantarflexor fatigue resistance, increased type I and IIa MHC abundance, increased fiber cross-sectional area, and increased the percentage of type I and IIA muscle fibers in the gastrocnemius muscle. HSU+WR mice also had a significantly greater percentage of BrdU-positive and Pax 7-positive nuclei inside muscle fibers and a greater MyoD-to-Pax 7 protein ratio compared with HSU+NoWR mice. The mechanotransduction protein Yes-associated protein (YAP) was elevated with reloading after HSU, but HSU+WR mice had lower levels of the inactive phosphorylated YAPserine127, which may have contributed to increased satellite cell activation with reloading after HSU. These results indicate that voluntary wheel running increased YAP signaling and satellite cell activity after HSU and this was associated with improved recovery. NEW & NOTEWORTHY Although satellite cell involvement in muscle remodeling has been challenged, the data in this study suggest that voluntary wheel running increased satellite cell activity and suppressed Yes-associated protein (YAP) protein relative to no wheel running and this was associated with improved muscle recovery of force, fatigue resistance, expression of type I myosin heavy chain, and greater fiber cross-sectional area after disuse.

Association of Serum Zinc Level With Prognosis in Patients With Heart Failure

BACKGROUND

Zinc is an essential cofactor for energy transfer and physiological heart function, has antioxidant properties, and is involved in multiple signaling pathways. We aimed to investigate the associations between serum zinc levels with prognosis, as well as underlying cardiac function and exercise capacity, in patients with heart failure (HF).

METHODS AND RESULTS

We measured serum zinc levels in 968 consecutive hospitalized patients with decompensated HF, who were divided into 3 groups based on serum zinc levels (µg/dL): first (zinc ≥75, n = 323), second (62≤ zinc <75, n = 322), and third (zinc <62, n = 323) tertiles. We examined cardiac function and exercise capacity and followed up on all patients. Although cardiac function did not differ among the 3 groups, peak oxygen consumption was significantly lower in the third tertile than in the first and second tertiles (peak oxygen consumption, 14.2 vs 15.9 and 15.2 mL/kg/min, P = .010). In the Kaplan-Meier analysis (mean duration of follow-up 1103 days), cardiac and all-cause mortality was highest in the third tertile compared with the first and second tertiles. In the Cox proportional hazard analysis, serum zinc level was a predictor of cardiac and all-cause mortality. In the subgroup analysis, there were no interactions concerning associations between serum zinc levels with prognosis and other important variables, including age, gender, comorbidities, medications, other micronutrient levels, B-type natriuretic peptide, and left ventricular ejection fraction. The associations between zinc levels with mortality were consistent in all subgroups.

CONCLUSION

Decreased serum zinc levels are associated with high mortality, accompanied by impaired exercise capacity.

Maternal serum uric acid levels and blood pressure during pregnancy: A community-based cohort study

OBJECTIVE

Studies find both very low and high serum uric acid (UA) levels are related to oxidative stress and to conditions such as cardiovascular diseases and chronic kidney disease in the general population. Pregnancy studies have focused only on high maternal UA. In present study, we tested whether unusually high and low levels of maternal serum UA are associated with increases in blood pressure (BP) during pregnancy.

STUDY DESIGN

The Pregnancy Outcomes and Community Health Study enrolled 3019 pregnant women between their 16th-27th week of pregnancy from 52 clinics in 5 Michigan communities (1998-2004). UA levels were measured in maternal blood collected at enrollment from a sub-cohort of 1223 participants. BP was abstracted from prenatal medical records; these analyses used highest recorded diastolic BP (DBP) and its companion systolic BP (SBP). Mean arterial pressure (MAP) was calculated using the formula of (2 × DBP + SBP)/3. Covariates, including maternal race/ethnicity, age at enrollment, education level, medical insurance status, body mass index before pregnancy, parity, smoking during pregnancy, alcohol use during pregnancy, and gestational week at blood collection, were considered as potential confounding variables. Associations between UA levels and BP were evaluated with linear spline or multiple linear regression models. Models' robustness was examined with bootstrap estimation of variance, sensitivity analysis, and 10-fold cross-validation.

RESULTS

Both DBP and MAP had a J-shaped relationship with maternal UA; the breakpoints (nadirs) were 0.153 and 0.161 mmol/L UA, respectively. For DBP versus UA, adjusted regression coefficient (β) = -95.67 (standard error (SE) = 37.67 and p = 0.01) for the left and adjusted β = 48.95 (SE = 9.56 and p < 0.01) for the right; for MAP versus UA, adjusted β = -58.48 (SE = 31.42 and p = 0.06) for the left and adjusted β = 52.23 (SE = 11.39 and p < 0.01) for the right. Maternal SBP followed a positive linear trend with UA levels (adjusted β = 37.75, SE = 12.93, and p < 0.01). All results were robust.

CONCLUSION

Extreme high and low maternal serum UA levels may be informative in studying maternal blood pressure during pregnancy.

Role of Oxidative Stress as Key Regulator of Muscle Wasting during Cachexia

Skeletal muscle atrophy is a pathological condition mainly characterized by a loss of muscular mass and the contractile capacity of the skeletal muscle as a consequence of muscular weakness and decreased force generation. Cachexia is defined as a pathological condition secondary to illness characterized by the progressive loss of muscle mass with or without loss of fat mass and with concomitant diminution of muscle strength. The molecular mechanisms involved in cachexia include oxidative stress, protein synthesis/degradation imbalance, autophagy deregulation, increased myonuclear apoptosis, and mitochondrial dysfunction. Oxidative stress is one of the most common mechanisms of cachexia caused by different factors. It results in increased ROS levels, increased oxidation-dependent protein modification, and decreased antioxidant system functions. In this review, we will describe the importance of oxidative stress in skeletal muscles, its sources, and how it can regulate protein synthesis/degradation imbalance, autophagy deregulation, increased myonuclear apoptosis, and mitochondrial dysfunction involved in cachexia.

Reactive oxygen species enhance mitochondrial function, insulin sensitivity and glucose uptake in skeletal muscle of senescence accelerated prone mice SAMP8

Whereas reactive oxygen species (ROS) can have opposite impacts on insulin signaling, they have mainly been associated with mitochondrial dysfunction in skeletal muscle. We analyzed the relationship between these three features in skeletal muscle of senescence accelerated mice (SAM) prone (P8), which are characterized by enhanced oxidative stress compared to SAM resistant (R1). Oxidative stress, ROS production, antioxidant system, mitochondrial content and functioning, as well as in vitro and in vivo insulin signaling were investigated in gastrocnemius and quadriceps muscles. In SAMP8 compared to SAMR1, muscle content in carbonylated proteins was two-fold (p < 0.01) and ROS production by xanthine oxidase 70% (p < 0.05) higher. Furthermore, insulin-induced Akt phosphorylation measured in vivo and ex vivo as well as muscle glucose uptake measured ex vivo were significantly higher (p < 0.05). Mitochondrial respiration evidenced uncoupling and higher respiration rates with substrates of complexes II and IV, in agreement with higher maximal activity of complexes II and IV (+ 18% and 62%, respectively, p < 0.05). By contrast, maximal activity of complex I was 22% lower (p < 0.05). All strain differences were corrected after 6 months of N-acetylcysteine (NAC) treatment, thus supporting the involvement of high ROS production in these differences. In conclusion in muscle of SAMP8 compared to SAMR1, high ROS production is associated to higher insulin sensitivity and glucose uptake but to lower mitochondrial complex I activity. These conflicting adaptations, with regards to the resulting imbalance between NADH production and use, were associated with intrinsic adjustments in the mitochondrial respiration chain (mitochondrial uncoupling, enhanced complexes II and IV activity). We propose that these bioenergetics adaptations may help at preserving muscle metabolic flexibility of SAMP8.

Mitochondria Initiate and Regulate Sarcopenia

We present the hypothesis that an accumulation of dysfunctional mitochondria initiates a signaling cascade leading to motor neuron and muscle fiber death and culminating in sarcopenia. Interactions between neural and muscle cells that contain dysfunctional mitochondria exacerbate sarcopenia. Preventing sarcopenia will require identifying mitochondrial sources of dysfunction that are reversible.

The participation of oxidative stress in the pathogenesis of bronchial asthma

Reactive oxygen species are produced during oxygen reduction and are characterized by high reactivity. They participate in many important physiological processes, but if produced in high concentrations they lead to oxidative stress development and disturb pro-oxidative/anti-oxidative balance towards the oxidation reaction - leading to damage of lipids, proteins, carbohydrates or nucleic acids. Asthma is a chronic inflammatory disease of the airways of various pathogenesis and clinical symptoms, prevalence in recent years has increased significantly. Recently published literature point out the involvement of reactive oxygen species in the pathogenesis of asthma. Changes in the protein and lipid oxidation lead, among others, to pathological changes in the respiratory epithelial cells, an increase in vascular permeability, mucus overproduction, smooth muscle contraction or airway hyperresponsiveness (AHR). The aim of this study is to present the current state of knowledge on the influence of oxidative stress parameters on asthma development.

Epigallocatechin-3-gallate increases autophagy signaling in resting and unloaded plantaris muscles but selectively suppresses autophagy protein abundance in reloaded muscles of aged rats

We have previously found that Epigallocatechin-3-gallate (EGCg), an abundant catechin in green tea, reduced apoptotic signaling and improved muscle recovery in response to reloading after hindlimb suspension (HS). In this study, we investigated if EGCg altered autophagy signaling in skeletal muscle of old rats in response to HS or reloading after HS. Fischer 344×Brown Norway inbred rats (age 34months) were given 1ml/day of purified EGCg (50mg/kg body weight), or the same sample volume of the vehicle by gavage. One group of animals received HS for 14days and the second group of rats received 14days of HS, then the HS was removed and they were allowed to recover by ambulating normally around the cage for two weeks. EGCg decreased a small number of autophagy genes in control muscles, but it increased the expression of other autophagy genes (e.g., ATG16L2, SNCA, TM9SF1, Pink1, PIM-2) and HS did not attenuate these increases. HS increased Beclin1, ATG7 and LC3-II/I protein abundance in hindlimb muscles. Relative to vehicle treatment, EGCg treatment had greater ATG12 protein abundance (35.8%, P<0.05), but decreased Beclin1 protein levels (-101.1%, P<0.05) after HS. However, in reloaded muscles, EGCg suppressed Beclin1 and LC3-II/I protein abundance as compared to vehicle treated muscles. EGCg appeared to "prime" autophagy signaling before and enhance autophagy gene expression and protein levels during unloading in muscles of aged rats, perhaps to improve the clearance of damaged organelles. However, EGCg suppressed autophagy signaling after reloading, potentially to increase the recovery of hindlimb muscles mass and function after loading is restored.

MicroRNA-434-3p regulates age-related apoptosis through eIF5A1 in the skeletal muscle

Increased activation of catabolic pathways, including apoptosis causes sarcopenia. However, the precise molecular mechanism that initiates apoptosis during aging is not well understood. Here, we report that aging alters miRNA expression profile in mouse skeletal muscle as evidenced by miRNA microarray and real-time PCR. We identified miR-434-3p as a highly downregulated miRNA in the skeletal muscle of aging mice. Myocytes transfected with miR-434-3p mimic prevents apoptosis induced by various apoptotic stimuli, and co-transfection of miR-434-3p antagomir abolishes the inhibitory role of miR-434-3p. We found that miR-434-3p inhibits apoptosis by targeting the eukaryotic translation initiation factor 5A1 (eIF5A1). Overexpression of miR-434-3p in myocytes reduces the loss of mitochondrial transmembrane potential, and activation of caspases-3, -8 and -9 by suppressing eIF5A1 in response to various apoptotic stimuli whereas inhibition of miR-434-3p reversed this scenario. Skeletal muscles from aging mice exhibit low levels of miR-434-3p and high levels of eIF5A1, suggesting a possible role for miR-434-3p in the initiation of apoptosis in aging muscle. Overall, our data identified for the first time that miR-434-3p is an anti-apoptotic miRNA that may be therapeutically useful for treating muscle atrophy in various pathophysiological conditions, including sarcopenia.

Impaired mitochondrial function and reduced energy cost as a result of muscle damage

PURPOSE

Although it has been largely acknowledged that isometric neuromuscular electrostimulation (NMES) exercise induces larger muscle damage than voluntary contractions, the corresponding effects on muscle energetics remain to be determined. Voluntary exercise-induced muscle damage (EIMD) has been reported to have minor slight effects on muscle metabolic response to subsequent dynamic exercise, but the magnitude of muscle energetics alterations for NMES EIMD has never been documented.

METHODS

³¹P magnetic resonance spectroscopy measurements were performed in 13 young healthy males during a standardized rest-exercise-recovery protocol before (D0) and 2 d (D2) and 4 d (D4) after NMES EIMD on knee extensor muscles. Changes in kinetics of phosphorylated metabolite concentrations (i.e., phosphocreatine [PCr], inorganic phosphate [Pi], and adenosine triphosphate [ATP]) and pH were assessed to investigate aerobic and anaerobic rates of ATP production and energy cost of contraction (Ec).

RESULTS

Resting [Pi]/[PCr] ratio increased at D2 (+39%) and D4 (+29%), mainly owing to the increased [Pi] (+43% and +32%, respectively), whereas a significant decrease in resting pH was determined (-0.04 pH unit and -0.03 pH unit, respectively). PCr recovery rate decreased at D2 (-21%) and D4 (-23%) in conjunction with a significantly decreased total rate of ATP production at D4 (-18%) mainly owing to an altered aerobic ATP production (-19%). Paradoxically, Ec was decreased at D4 (-21%).

CONCLUSION

Overall, NMES EIMD led to intramuscular acidosis in resting muscle and mitochondrial impairment in exercising muscle. Alterations of noncontractile processes and/or adaptive mechanisms to muscle damage might account for the decreased Ec during the dynamic exercise.

Dysregulation of SIRT-1 in aging mice increases skeletal muscle fatigue by a PARP-1-dependent mechanism

Accumulation of reactive oxygen species (ROS) in skeletal muscles and the resulting decline in muscle performance are hallmarks of sarcopenia. However, the precise mechanism by which ROS results in a decline in muscle performance is unclear. We demonstrate that isometric-exercise concomitantly increases the activities of Silent information regulator 1 (SIRT-1) and Poly [ADP-ribose] polymerase (PARP-1), and that activated SIRT-1 physically binds with and inhibits PARP-1 activity by a deacetylation dependent mechanism in skeletal muscle from young mice. In contrast, skeletal muscle from aged mice displays higher PARP-1 activity and lower SIRT-1 activity due to decreased intracellular NAD⁺ content, and as a result reduced muscle performance in response to exercise. Interestingly, injection of PJ34, a PARP-1 inhibitor, in aged mice increased SIRT-1 activity by preserving intracellular NAD⁺ content, which resulted in higher skeletal muscle mitochondrial biogenesis and performance. We found that the higher activity of PARP-1 in H₂O₂-treated myotubes or in exercised-skeletal muscles from aged mice is due to an elevated level of PARP-1 acetylation by the histone acetyltransferase General control of amino acid synthesis protein 5-like 2 (GCN-5). These results suggest that activation of SIRT-1 and/or inhibition of PARP-1 may ameliorate skeletal muscle performance in pathophysiological conditions such as sarcopenia and disuse-induced atrophy in aging.

Characterization of reactive oxygen species in diaphragm

Reactive oxygen species (ROS) exist as natural mediators of metabolism to maintain cellular homeostasis. However, ROS production may significantly increase in response to environmental stressors, resulting in extensive cellular damage. Although several potential sources of increased ROS have been proposed, exact mechanisms of their generation have not been completely elucidated. This is particularly true for diaphragmatic skeletal muscle, the key muscle used for respiration. Several experimental models have focused on detection of ROS generation in rodent diaphragm tissue under stressful conditions, including hypoxia, exercise, and heat, as well as ROS formation in single myofibres. Identification methods include direct detection of ROS with confocal or fluorescent microscopy and indirect detection of ROS through end product analysis. This article explores implications of ROS generation and oxidative stress, and also evaluates potential mechanisms of cellular ROS formation in diaphragmatic skeletal muscle.

Dahuang Fuzi Decoction ameliorates tubular epithelial apoptosis and renal damage via inhibiting TGF-β1-JNK signaling pathway activation in vivo

ETHNOPHARMACOLOGICAL RELEVANCE

Dahuang Fuzi Decoction (DFD) is a traditional well-prescribed formula for the treatment of chronic kidney disease (CKD) in China. This study was carried out to examine the effects of DFD in adenine-induced tubular epithelial apoptosis and renal damage, in comparison with allopurinol (AP), then to clarify the therapeutic mechanisms in vivo.

MATERIALS AND METHODS

A rat model of renal damage was created by adenine. Rats in Normal and Vehicle groups received distilled water, while rats in DFD and AP groups received DFD and AP, respectively. Proteinuria; urinary N-acetyl-β-D-glucosaminidase (NAG) levels; the blood biochemical parameters; renal histopathology damage; transferase-mediated dUTP nick-end labeling (TUNEL)-staining; the key molecular protein expressions in mitochondrial and transforming growth factor (TGF)-β1-c-JunNH2-terminal kinase (JNK) pathways were examined, respectively.

RESULTS

Adenine administration induced severe renal damages, as indicated by the mass proteinuria, the heavy urinary NAG, and the marked histopathological injury in tubules and interstitium. This was associated with the activation of TGF-β1-JNK signaling pathway and tubular epithelial apoptosis. DFD treatment, however, significantly prevented proteinuria and urinary NAG elevation, and attenuated tubular epithelial apoptosis. It suppressed the protein expressions of Bax and cleaved caspase-3, whereas it enhanced the protein expression of Bcl-2. Furthermore, it also suppressed the protein levels of TGF-β1 as well as phosphorylated-JNK (p-JNK).

CONCLUSION

DFD alleviated adenine-induced tubular epithelial apoptosis and renal damage in vivo, presumably through the suppression of TGF-β1-JNK pathway activation.

Regulation of satellite cell function in sarcopenia

The mechanisms contributing to sarcopenia include reduced satellite cell (myogenic stem cell) function that is impacted by the environment (niche) of these cells. Satellite cell function is affected by oxidative stress, which is elevated in aged muscles, and this along with changes in largely unknown systemic factors, likely contribute to the manner in which satellite cells respond to stressors such as exercise, disuse, or rehabilitation in sarcopenic muscles. Nutritional intervention provides one therapeutic strategy to improve the satellite cell niche and systemic factors, with the goal of improving satellite cell function in aging muscles. Although many elderly persons consume various nutraceuticals with the hope of improving health, most of these compounds have not been thoroughly tested, and the impacts that they might have on sarcopenia and satellite cell function are not clear. This review discusses data pertaining to the satellite cell responses and function in aging skeletal muscle, and the impact that three compounds: resveratrol, green tea catechins, and β-Hydroxy-β-methylbutyrate have on regulating satellite cell function and therefore contributing to reducing sarcopenia or improving muscle mass after disuse in aging. The data suggest that these nutraceutical compounds improve satellite cell function during rehabilitative loading in animal models of aging after disuse (i.e., muscle regeneration). While these compounds have not been rigorously tested in humans, the data from animal models of aging provide a strong basis for conducting additional focused work to determine if these or other nutraceuticals can offset the muscle losses, or improve regeneration in sarcopenic muscles of older humans via improving satellite cell function.

Oxidative stress and vascular inflammation in aging

Vascular aging, a determinant factor for cardiovascular disease and health status in the elderly, is now viewed as a modifiable risk factor. Impaired endothelial vasodilation is a early hallmark of arterial aging that precedes the clinical manifestations of vascular dysfunction, the first step to cardiovascular disease and influencing vascular outcomes in the elderly. Accordingly, the preservation of endothelial function is thought to be an essential determinant of healthy aging. With special attention on the effects of aging on the endothelial function, this review is focused on the two main mechanisms of aging-related endothelial dysfunction: oxidative stress and inflammation. Aging vasculature generates an excess of the reactive oxygen species (ROS), superoxide and hydrogen peroxide, that compromise the vasodilatory activity of nitric oxide (NO) and facilitate the formation of the deleterious radical, peroxynitrite. Main sources of ROS are mitochondrial respiratory chain and NADPH oxidases, although NOS uncoupling could also account for ROS generation. In addition, reduced antioxidant response mediated by erythroid-2-related factor-2 (Nrf2) and downregulation of mitochondrial manganese superoxide dismutase (SOD2) contributes to the establishment of chronic oxidative stress in aged vessels. This is accompanied by a chronic low-grade inflammatory phenotype that participates in defective endothelial vasodilation. The redox-sensitive transcription factor, nuclear factor-κB (NF-κB), is upregulated in vascular cells from old subjects and drives a proinflammatory shift that feedbacks oxidative stress. This chronic NF-κB activation is contributed by increased angiotensin-II signaling and downregulated sirtuins and precludes adequate cellular response to acute ROS generation. Interventions targeted to recover endogenous antioxidant capacity and cellular stress response rather than exogenous antioxidants could reverse oxidative stress-inflammation vicious cycle in vascular aging. Lifestyle attitudes such as caloric restriction and exercise training appear as effective ways to overcome defective antioxidant response and inflammation, favoring successful vascular aging and decreasing the risk for cardiovascular disease.

Oxidative stress and Nrf2 signaling in McArdle disease

McArdle disease (MD) is a metabolic myopathy due to myophosphorylase deficiency, which leads to a severe limitation in the rate of adenosine triphosphate (ATP) resynthesis. Compensatory flux through the myoadenylate deaminase > > xanthine oxidase pathway should result in higher oxidative stress in skeletal muscle; however, oxidative stress and nuclear factor erythroid 2-related factor 2 (Nrf2) mediated antioxidant response cascade in MD patients have not yet been examined. We show that MD patients have elevated muscle protein carbonyls and 4-hydroxynonenal (4-HNE) in comparison with healthy, age and activity matched controls (P < 0.05). Nuclear abundance of Nrf2 and Nrf2-antioxidant response element (ARE) binding was also higher in MD patients compared with controls (P < 0.05). The expressions of Nrf2 target genes were also higher in MD patients vs. controls. These observations suggest that MD patients experience elevated levels of oxidative stress, and that the Nrf2-mediated antioxidant response cascade is up-regulated in skeletal muscle to compensate.

Cancer cachexia: impact, mechanisms and emerging treatments

Many forms of cancer present with a complex metabolic profile characterised by loss of lean body mass known as cancer cachexia. The physical impact of cachexia contributes to decreased patient quality of life, treatment success and survival due to gross alterations in protein metabolism, increased oxidative stress and systemic inflammation. The psychological impact also contributes to decreased quality of life for both patients and their families. Combination therapies that target multiple pathways, such as eicosapentaenoic acid administered in combination with exercise, appetite stimulants, antioxidants or anti-inflammatories, have potential in the treatment of this complex syndrome and require further development.

Long-term supplementation with a cystine-based antioxidant delays loss of muscle mass in aging

Oxidative stress increases with age and is postulated to be a major causal factor for sarcopenia in aging. Here, we examined whether the administration of a cystine-based antioxidant (F1) can alleviate/delay age-specific changes in skeletal muscles. C57BL6 male mice aged 17 months (middle aged) were fed with normal diet with or without supplementation of F1 (3 mg/kg food) for 6 months. Compared with young (5 months old) mice old mice exhibited increased markers of oxidative stress, inflammation, and muscle cell apoptosis and decreased muscle weight. These age-related changes were further associated with inactivation of adenosine-5'-monophosphate-activated protein kinase (AMPK), increased lipogenesis, activation of c-Jun NH2-terminal kinase, and decreased expression of Delta 1, phospho-Akt, and proliferating cell nuclear antigen in aged skeletal muscle. Such alterations were significantly prevented by F1. These results demonstrate the beneficial effects of F1 to attenuate loss of muscle mass associated with aging.

Inhibition of xanthine oxidase by allopurinol prevents skeletal muscle atrophy: role of p38 MAPKinase and E3 ubiquitin ligases

Alterations in muscle play an important role in common diseases and conditions. Reactive oxygen species (ROS) are generated during hindlimb unloading due, at least in part, to the activation of xanthine oxidase (XO). The major aim of this study was to determine the mechanism by which XO activation causes unloading-induced muscle atrophy in rats, and its possible prevention by allopurinol, a well-known inhibitor of this enzyme. For this purpose we studied one of the main redox sensitive signalling cascades involved in skeletal muscle atrophy i.e. p38 MAPKinase, and the expression of two well known muscle specific E3 ubiquitin ligases involved in proteolysis, the Muscle atrophy F-Box (MAFbx; also known as atrogin-1) and Muscle RING (Really Interesting New Gene) Finger-1 (MuRF-1). We found that hindlimb unloading induced a significant increase in XO activity and in the protein expression of the antioxidant enzymes CuZnSOD and Catalase in skeletal muscle. The most relevant new fact reported in this paper is that inhibition of XO with allopurinol, a drug widely used in clinical practice, prevents soleus muscle atrophy by ∼20% after hindlimb unloading. This was associated with the inhibition of the p38 MAPK-MAFbx pathway. Our data suggest that XO was involved in the loss of muscle mass via the activation of the p38MAPK-MAFbx pathway in unloaded muscle atrophy. Thus, allopurinol may have clinical benefits to combat skeletal muscle atrophy in bedridden, astronauts, sarcopenic, and cachexic patients.

Inactivity-induced oxidative stress: a central role in age-related sarcopenia?

Ageing causes a progressive decline in skeletal muscle mass that may lead to decreased strength and functionality. The term sarcopenia is especially used to characterise this geriatric syndrome. Numerous conditions and behaviours are considered to accelerate the progression of sarcopenia such as chronic diseases, malnutrition and physical inactivity. As people in modern countries are more and more sedentary, the impact of physical inactivity on the prevalence of sarcopenia might be more and more important in the future. In this review, we discuss how reactive oxygen species (ROS) could mediate the effects of lifelong inactivity in the onset and progression of age-related sarcopenia. Although the cellular mechanisms responsible for muscle ROS production are not necessarily the same, both inactivity and ageing are indeed known to increase basal ROS concentrations in skeletal muscle. New data and literature review are provided showing that chronic ROS overproduction induced by physical inactivity may exacerbate the activation of some redox-sensitive signalling pathways involved in age-related sarcopenia. We also address the scientific evidences implicating the role of ROS overproduction in the precocious failure of aged muscles to activate intracellular signalling responses to contractions.