Nitric oxide and muscle repair: multiple actions converging on therapeutic efficacy

Association between serum uric acid, hyperuricemia and low muscle mass in middle-aged and elderly adults: A national health and nutrition examination study

BACKGROUNDS

Recent research suggests that uric acid, as a metabolite with antioxidant properties, may affect muscle function and health. However, the association between serum uric acid (SUA) and low muscle mass remains relatively obscure. This study focuses on the association between SUA and low muscle mass in a middle-aged and elderly population in the United States.

METHODS

Utilizing data from the National Health and Nutrition Examination Survey (NHANES), a total of 12,106 patients aged ≥45 years, possessing complete analytical data, were incorporated. Low muscle mass in our study is defined as indices below 0.789 for males and 0.512 for females, according to the FNIH Biomarkers Consortium. Gender stratified analyses were conducted employing a multivariate weighted logistic regression model. When examining serum uric acid (SUA) levels, the SUA dataset was stratified into deciles, and odds ratios (ORs) were calculated across distinct subgroups of males and females. A restricted cubic spline (RCS) method was employed to investigate the potential nonlinear association between SUA levels and low muscle mass. A series of subgroup analyses stratified by demographic variables and clinical experience were conducted.

RESULTS

A total of 2,185 participants (18.05%) were identified with low muscle mass, comprising 1,121 males and 1,064 females. Females with low muscle mass had higher SUA levels and an increased incidence of hyperuricemia compared to those without low muscle mass. In females, a fully adjusted multivariable weighted regression model revealed a positive association between hyperuricemia and low muscle mass (OR, 1.43; 95% CI, 1.06 to 1.92; P = 0.021). No significant association was observed in males. Additionally, RCS curves indicated a J-shaped relationship between increasing SUA levels and the risk of low muscle mass in females, and an inverse J-shaped relationship in males.

CONCLUSIONS

This study reveals a significant positive correlation between hyperuricemia and the risk of low muscle mass in middle-aged and older women in the United States, whereas the relationship between SUA levels and low muscle mass did not attain statistical significance. In the male cohort, neither SUA levels nor hyperuricemia demonstrated a significant association with low muscle mass.

Early administration of L-arginine in mdx neonatal mice delays the onset of muscular dystrophy in tibialis anterior (TA) muscle

Duchenne muscular dystrophy (DMD) is a genetic disorder that results in the absence of dystrophin, a cytoskeletal protein. Individuals with this disease experience progressive muscle destruction, which leads to muscle weakness. Studies have been conducted to find solutions for the relief of individuals with this disease, several of which have shown that utrophin, a protein closely related to dystrophin, when overexpressed in mdx neonatal mice (the murine model of DMD), is able to prevent the progressive muscle destruction observed in the absence of dystrophin. Furthermore, recent studies have shown that L‐arginine induces utrophin upregulation in adult mdx mice. We hypothesized that L‐arginine treatment also induces utrophin upregulation to prevent the development of muscle weakness in neonatal mdx mice. Hence, L‐arginine should also prevent progressive muscle destruction via utrophin upregulation in mdx neonatal mice. Mdx neonatal mice were injected intraperitoneally daily with 800 mg/kg of L‐arginine for 6 weeks, whereas control mice were injected with a physiological saline. The following experiments were performed on the tibialis anterior (TA) muscle: muscle contractility and resistance to mechanical stress; central nucleation and peripheral nucleation, utrophin, and creatine kinase quantification as well as a nitric oxide (NO) assay. Our findings show that early administration of L‐arginine in mdx neonatal mice prevents the destruction of the tibialis anterior (TA) muscle. However, this improvement was related to nitric oxide (NO) production rather than the expected utrophin upregulation.

Mutual inter-regulation between iNOS and TGF-β1: Possible molecular and cellular mechanisms of iNOS in wound healing

Abnormal wound healing with excessive scarring is a major health problem with socioeconomic and psychological impacts. In human, chronic wounds and scarring are associated with upregulation of the inducible nitric oxide synthase (iNOS). Recently, we have shown physiological regulation of iNOS in wound healing. Here, we sought to investigate the possible mechanistic role of iNOS in wound healing using biochemical and immunohistochemical assays. We found: (a) iNOS is the main source of wound nitric oxide (NO), (b) NOS inhibition in the wound, downregulated iNOS protein, mRNA and enzymatic activity, and reduced wound NO, and (c) iNOS inhibition resulted in delayed healing at early time points, and excessive scarring at late time points. Furthermore, molecular and cellular analysis of the wound showed that iNOS inhibition significantly (P < 0.05) increased TGF-β1 mRNA and protein levels, fibroblasts and collagen deposition. These latter findings suggest that iNOS might be exerting its action in the wound by signaling through TGF-β1 that activates wound fibroblasts to produce excessive collagen. Our current findings provide further support that iNOS is crucial for physiological wound healing, and suggest that dysregulation of iNOS during the inflammatory phase impairs healing, and results in disfiguring post-healing scarring. Thus, the mutual feedback regulation between iNOS and TGF-β1 at the gene, protein and functional levels might be the mechanism through which iNOS regulates the healing. Monitoring and maintenance of wound NO levels might be important for healing and avoiding long-term complications in susceptible people including patients with diabetic wounds, venous ulcers or keloid prone.

Effect of Gastric Acid Suppressants on Response to a Physical Activity Intervention and Major Mobility Disability in Older Adults: Results from the Lifestyle Interventions for Elders (LIFE) Study

OBJECTIVES

Proton pump inhibitors (PPIs) and histamine2 receptor antagonists (H2 RAs) are associated with pharmacologic effects that may be detrimental to mobility and response to physical activity. Mobility disability and injurious fall outcomes in PPI and H2 RA users were compared with nonusers in this secondary analysis of data from the Lifestyle Interventions for Elders (LIFE) study.

METHODS

Participants ages 70-89 years were randomized to a physical activity (PA) or successful aging intervention and evaluated by medication use. Confounders included baseline demographic characteristics, physical function, cognitive function, sleep quality, and acid reflux symptoms that were adjusted via propensity score weighting. Outcomes were incident and persistent major mobility disability (MMD and pMMD) and injurious falls. Weighted proportional hazard models evaluated independent and interaction effects of PPIs and H2 RAs.

RESULTS

No interaction was found between PPIs and H2 RAs and the PA intervention. Drug use associations were significant for H2 RAs (hazard ratio [HR] 1.74 [95% confidence interval [CI] 1.12-2.68]) and PPIs (HR 1.32 [95% CI 1.02-1.70]) compared with nonusers for pMMD. PPIs were associated with increased injurious falls compared with nonusers (HR 1.44 [95% CI 1.06-1.96]). Pooling of data from the H2 RA and PPI exposure groups showed a 26% increase in MMD (HR 1.26 [95% CI 1.07-1.48]), a 44% increase in pMMD (HR 1.44 [95% CI 1.16-1.77]), and a 48% increase in injurious falls (HR 1.48 [95% CI 1.15-1.91]) compared with nonusers. All direct comparisons between PPIs and H2 RAs were nonsignificant.

CONCLUSIONS

Compared with nonusers, participants using either PPIs or H2 RAs had an increased risk of MMD, pMMD, and injurious falls. It is not known if these effects are related to the individual pharmacology of each medication, reduced acid secretion, or the underlying disease state. Further study is required to determine causality.

Effects of PDE5 inhibition on dystrophic muscle following an acute bout of downhill running and endurance training

Lack of sarcolemma-localized neuronal nitric oxide synthase mu (nNOSμ) contributes to muscle damage and fatigue in dystrophic muscle. In this study, we examined the effects of compensating for lack of nNOSμ with a phosphodiesterase type 5 (PDE5) inhibitor in mdx mice following downhill running and endurance training. Dystrophic mice (mdx) were treated with sildenafil citrate and compared with untreated mdx and wild-type mice after an acute bout of downhill running and during a progressive low-intensity treadmill running program (5 days/wk, 4 wk). Magnetic resonance imaging (MRI) and spectroscopy (MRS) transverse relaxation time constant (T₂) of hindlimb and forelimb muscles were measured as a marker of muscle damage after downhill running and throughout training. The MRI blood oxygenation level dependence (BOLD) response and ³¹phosphorus MRS (³¹P-MRS) data were acquired after stimulated muscle contractions. After downhill running, the increase in T₂ was attenuated (P < 0.05) in treated mdx and wild-type mice compared with untreated mdx. During training, resting T₂ values did not change in wild-type and mdx mice from baseline values; however, the running distance completed during training was greater (P < 0.05) in treated mdx (>90% of target distance) and wild-type (100%) than untreated mdx (60%). The post-contractile BOLD response was greater (P < 0.05) in treated mdx that trained than untreated mdx, with no differences in muscle oxidative capacity, as measured by ³¹P-MRS. Our findings indicate that PDE5 inhibition reduces muscle damage after a single bout of downhill running and improves performance during endurance training in dystrophic mice, possibly because of enhanced microvascular function. NEW & NOTEWORTHY This study examined the combined effects of PDE5 inhibition and exercise in dystrophic muscle using high-resolution magnetic resonance imaging and spectroscopy. Our findings demonstrated that sildenafil citrate reduces muscle damage after a single bout of downhill running, improves endurance-training performance, and enhances microvascular function in dystrophic muscle. Collectively, the results support the combination of exercise and PDE5 inhibition as a therapeutic approach in muscular dystrophies lacking nNOSμ.

Association of Serum Asymmetric Dimethylarginine With Muscle Strength and Gait Speed: A Cross-Sectional Study of the HEIJO-KYO Cohort

Muscle strength and gait speed are related with functional limitations and disabilities and also predict cardiovascular and all-cause mortality. Nitric oxide (NO) plays an important role in regulating physiological process in skeletal muscles; however, the association between serum asymmetric dimethylarginine (ADMA) level, an endogenous competitive inhibitor of NO synthesis, and physical performance has not yet been studied. We investigated the associations of serum ADMA level with muscle strength and usual gait speed in a cross-sectional study of 550 elderly individuals (mean age, 71.2 ± 6.6 years). Mean ADMA level was 0.45 ± 0.06 µmol/L; mean grip and quadriceps strengths were 27.7 ± 8.4 kg and 165.1 ± 81.6 Nm, respectively; and mean gait speed was 1.37 ± 0.30 m/s. In multivariate linear regression analysis adjusted for potential confounding factors (age, gender, body weight, smoking and drinking status, household income, hypertension, diabetes, renal function, and physical activity), higher serum ADMA level was significantly associated with lower grip and quadriceps strengths and slower gait speed (grip strength: β, -1.257; 95% confidence interval [CI], -1.990 to -0.525; p = 0.001; quadriceps strength: β, -11.730; 95% CI, -20.924 to -2.536; p = 0.012; gait speed: β, -0.065; 95% CI, -0.108 to -0.022; p = 0.003). Our findings indicate the significant association between serum ADMA level and physical performance among elderly individuals, which was independent of the important potential confounders. © 2015 American Society for Bone and Mineral Research.

Integrated analysis of the involvement of nitric oxide synthesis in mitochondrial proliferation, mitochondrial deficiency and apoptosis in skeletal muscle fibres

Nitric oxide (NO) is an important signaling messenger involved in different mitochondrial processes but only few studies explored the participation of NO in mitochondrial abnormalities found in patients with genetic mitochondrial deficiencies. In this study we verified whether NO synthase (NOS) activity was altered in different types of mitochondrial abnormalities and whether changes in mitochondrial function and NOS activity could be associated with the induction of apoptosis. We performed a quantitative and integrated analysis of NOS activity in individual muscle fibres of patients with mitochondrial diseases, considering mitochondrial function (cytochrome-c-oxidase activity), mitochondrial content, mitochondrial DNA mutation and presence of apoptotic nuclei. Our results indicated that sarcolemmal NOS activity was increased in muscle fibres with mitochondrial proliferation, supporting the relevance of neuronal NOS in the mitochondrial biogenesis process. Sarcoplasmic NOS activity was reduced in cytochrome-c-oxidase deficient fibres, probably as a consequence of the involvement of NO in the regulation of the respiratory chain. Alterations in NOS activity or mitochondrial abnormalities were not predisposing factors to apoptotic nuclei. Taken together, our results show that NO can be considered a potential molecular target for strategies to increase mitochondrial content and indicate that this approach may not be associated with increased apoptotic events.

Pathways Implicated in Tadalafil Amelioration of Duchenne Muscular Dystrophy

Numerous therapeutic approaches for Duchenne and Becker Muscular Dystrophy (DMD and BMD), the most common X-linked muscle degenerative disease, have been proposed. So far, the only one showing a clear beneficial effect is the use of corticosteroids. Recent evidence indicates an improvement of dystrophic cardiac and skeletal muscles in the presence of sustained cGMP levels secondary to a blocking of their degradation by phosphodiesterase five (PDE5). Due to these data, we performed a study to investigate the effect of the specific PDE5 inhibitor, tadalafil, on dystrophic skeletal muscle function. Chronic pharmacological treatment with tadalafil has been carried out in mdx mice. Behavioral and physiological tests, as well as histological and biochemical analyses, confirmed the efficacy of the therapy. We then performed a microarray-based genomic analysis to assess the pattern of gene expression in muscle samples obtained from the different cohorts of animals treated with tadalafil. This scrutiny allowed us to identify several classes of modulated genes. Our results show that PDE5 inhibition can ameliorate dystrophy by acting at different levels. Tadalafil can lead to (1) increased lipid metabolism; (2) a switch towards slow oxidative fibers driven by the up-regulation of PGC-1α; (3) an increased protein synthesis efficiency; (4) a better actin network organization at Z-disk.

Coaxing stem cells for skeletal muscle repair

Skeletal muscle has a tremendous ability to regenerate, attributed to a well-defined population of muscle stem cells called satellite cells. However, this ability to regenerate diminishes with age and can also be dramatically affected by multiple types of muscle diseases, or injury. Extrinsic and/or intrinsic defects in the regulation of satellite cells are considered to be major determinants for the diminished regenerative capacity. Maintenance and replenishment of the satellite cell pool is one focus for muscle regenerative medicine, which will be discussed. There are other sources of progenitor cells with myogenic capacity, which may also support skeletal muscle repair. However, all of these myogenic cell populations have inherent difficulties and challenges in maintaining or coaxing their derivation for therapeutic purpose. This review will highlight recent reported attributes of these cells and new bioengineering approaches to creating a supply of myogenic stem cells or implants applicable for acute and/or chronic muscle disorders.

Effects of nitric oxide on notexin-induced muscle inflammatory responses

Excessive inflammatory response may delay the regeneration and damage the normal muscle fibers upon myoinjury. It would be important to be able to attenuate the inflammatory response and decrease inflammatory cells infiltration in order to improve muscle regeneration formation, resulting in better muscle functional recovery after myoinjury. This study was undertaken to explore the role of Nitric oxide (NO) during skeletal muscle inflammatory process, using a mouse model of Notexin induced myoinjury. Intramuscular injection (tibialis anterior, TA) of Notexin was performed for preparing mice myoinjury. NO synthase inhibitor (L-NAME) or NO donor (SNP) was intraperitoneally injected into model mice. On day 4 and 7 post-injury, expression of muscle-autoantigens and toll-like receptors (TLRs) was evaluated from muscle tissue by qRT-PCR and Western Blot; the intramuscular infiltration of monocytes/macrophage (CD11b⁺ or F4/80⁺ cells), CD8⁺ T cell (CD3ε⁺CD8α⁺), apoptotic cell (CD11b⁺caspase3⁺), and MHC-I molecule H-2K^b-expressing myofibers in damaged muscle were assessed by imunoflourecence analysis; the mRNAs expression of cytokines and chemokines associated with the preferential biological role during the muscle damage-induced inflammation response, were assessed by qRT-PCR. We detected the reduced monocytes/macrophages infiltration, and increased apoptotic cells in the damaged muscle treated with SNP comparing to untreatment. As well, SNP treatment down-regulated mRNA and protein levels of muscle autoantigens, TLR3, and mRNA levels of TNF-α, IL-6, MCP-1, MCP-3, and MIP-1α in damaged muscle. On the contrary, L-NAME induced more severe intramuscular infiltration of inflammatory cells, and mRNA level elevation of the above inflammatory mediators. Notably, we observed an increased number of MHC-I (H2-K^b) positive new myofibers, and of the infiltrated CD8⁺ T cells in damaged muscle at the day 7 after L-NAME treatment. The result herein shows that, NO can act as an endogenous anti-inflammatory molecule during the ongoing muscle inflammation. Our finding may provide new insight to optimize NO-based therapies for improving muscle regeneration after myoinjury.

Loss of nNOS inhibits compensatory muscle hypertrophy and exacerbates inflammation and eccentric contraction-induced damage in mdx mice

Approaches targeting nitric oxide (NO) signaling show promise as therapies for Duchenne and Becker muscular dystrophies. However, the mechanisms by which NO benefits dystrophin-deficient muscle remain unclear, but may involve nNOSβ, a newly discovered enzymatic source of NO in skeletal muscle. Here we investigate the impact of dystrophin deficiency on nNOSβ and use mdx mice engineered to lack nNOSμ and nNOSβ to discern how the loss of nNOS impacts dystrophic skeletal muscle pathology. In mdx muscle, nNOSβ was mislocalized and its association with the Golgi complex was reduced. nNOS depletion from mdx mice prevented compensatory skeletal muscle cell hypertrophy, decreased myofiber central nucleation and increased focal macrophage cell infiltration, indicating exacerbated dystrophic muscle damage. Reductions in muscle integrity in nNOS-null mdx mice were accompanied by decreases in specific force and increased susceptibility to eccentric contraction-induced muscle damage compared with mdx controls. Unexpectedly, muscle fatigue was unaffected by nNOS depletion, revealing a novel latent compensatory mechanism for the loss of nNOS in mdx mice. Together with previous studies, these data suggest that localization of both nNOSμ and nNOSβ is disrupted by dystrophin deficiency. They also indicate that nNOS has a more complex role as a modifier of dystrophic pathology and broader therapeutic potential than previously recognized. Importantly, these findings also suggest nNOSβ as a new drug target and provide a new conceptual framework for understanding nNOS signaling and the benefits of NO therapies in dystrophinopathies.

Macrophage plasticity in skeletal muscle repair

Macrophages are one of the first barriers of host defence against pathogens. Beyond their role in innate immunity, macrophages play increasingly defined roles in orchestrating the healing of various injured tissues. Perturbations of macrophage function and/or activation may result in impaired regeneration and fibrosis deposition as described in several chronic pathological diseases. Heterogeneity and plasticity have been demonstrated to be hallmarks of macrophages. In response to environmental cues they display a proinflammatory (M1) or an alternative anti-inflammatory (M2) phenotype. A lot of evidence demonstrated that after acute injury M1 macrophages infiltrate early to promote the clearance of necrotic debris, whereas M2 macrophages appear later to sustain tissue healing. Whether the sequential presence of two different macrophage populations results from a dynamic shift in macrophage polarization or from the recruitment of new circulating monocytes is a subject of ongoing debate. In this paper, we discuss the current available information about the role that different phenotypes of macrophages plays after injury and during the remodelling phase in different tissue types, with particular attention to the skeletal muscle.