NO message from muscle

Sarcopenia as a comorbidity of cardiovascular disease

Sarcopenia, the lowered skeletal muscle mass, weakened skeletal muscle strength, and reduced physical performance with aging, is a component of frailty and high-risk factor for falls, resulting in an increase in mortality. In cardiovascular disease (CVD) patients, systemic inflammation, oxidative stress, overactivation of ubiquitin-proteasome system, endothelial dysfunction, lowering muscle blood flow, impaired glucose tolerance, hormonal changes, and physical inactivity possibly contribute to CVD-related sarcopenia. Prevalence of sarcopenia and osteosarcopenia, which is osteopenia and sarcopenia coexisting together, seems to be higher in CVD patients than in community-dwelling adults, suggesting the necessity of early diagnosis and prevention of CVD-related sarcopenia. Atrial stiffness, coronary artery calcification score, and serum vitamin D levels may be of help as the biomarkers to suspect sarcopenia, and renin-angiotensin-aldosterone system inhibitors may play a role in the medical prevention and treatment of CVD-related sarcopenia. There are few reports to convince the efficacies of dietary and antioxidant supplementation on sarcopenia at present, whereas aerobic and resistance training exercises have been recognized as an effective strategy to prevent and treat sarcopenia.

Molecular hydrogen (H2 ) as a potential treatment for acute and chronic fatigue

Many diseases as well as acute conditions can lead to fatigue, which can be either temporary or chronic in nature. Acute fatigue develops frequently after physical exercise or after alcohol hangover, whereas microbial infections such as influenza or COVID-19 and chronic diseases like Parkinson's disease or multiple sclerosis are often associated with chronic fatigue. Oxidative stress and a resulting disturbance of mitochondrial function are likely to be common denominators for many forms of fatigue, and antioxidant treatments have been shown to be effective in alleviating the symptoms of fatigue. In this study, we review the role of reactive oxygen and nitrogen species in fatigue and the antioxidant effects of the intake of molecular hydrogen. We propose that molecular hydrogen is well suited for the treatment of temporary and chronic forms of oxidative stress-associated fatigue.

Nicorandil Affects Mitochondrial Respiratory Chain Function by Increasing Complex III Activity and ROS Production in Skeletal Muscle Mitochondria

Adenosine triphosphate (ATP)-dependent potassium channels openers (K_ATP) protect skeletal muscle against function impairment through the activation of the mitochondrial K_ATP channels (mitoK_ATP). Previous reports suggest that modulators of the mitochondrial K_ATP channels have additional effects on isolated mitochondria. To determine whether the K_ATP channel opener nicorandil has non-specific effects that explain its protective effect through the mitochondrial function, chicken muscle mitochondria were isolated, and respiration rate was determined pollarographically. The activity of the electron transport chain (ETC) complexes (I-IV) was measured using a spectrophotometric method. Reactive oxygen species (ROS) levels and lipid peroxidation were assessed using flow cytometry and thiobarbituric acid assay, respectively. Both K_ATP channel opener nicorandil and K_ATP channel blocker 5-hydroxydecanoate (5-HD) decreased mitochondrial respiration; nicorandil increased complex III activity and decreased complex IV activity. The effects of nicorandil on complex III were antagonized by 5-HD. Nicorandil increased ROS levels, effect reverted by either 5-HD or the antioxidant N-2-mercaptopropionyl glycine (MPG). None of these drugs affected lipid peroxidation levels. These findings suggest that K_ATP channel opener nicorandil increases mitochondrial ROS production from complex III. This results by partially blocking electron flow in the complex IV, setting electron carriers in a more reduced state, which is favored by the increase in complex III activity by nicorandil. Overall, our study showed that nicorandil like other mitochondrial K_ATP channel openers might not act through mitoK_ATP channel activation.

Glutathione and Nitric Oxide: Key Team Players in Use and Disuse of Skeletal Muscle

Glutathione (GSH) is the main non-enzymatic antioxidant playing an important role in detoxification, signal transduction by modulation of protein thiols redox status and direct scavenging of radicals. The latter function is not only performed against reactive oxygen species (ROS) but GSH also has a fundamental role in buffering nitric oxide (NO), a physiologically-produced molecule having-multifaceted functions. The efficient rate of GSH synthesis and high levels of GSH-dependent enzymes are characteristic features of healthy skeletal muscle where, besides the canonical functions, it is also involved in muscle contraction regulation. Moreover, NO production in skeletal muscle is a direct consequence of contractile activity and influences several metabolic myocyte pathways under both physiological and pathological conditions. In this review, we will consider the homeostasis and intersection of GSH with NO and then we will restrict the discussion on their role in processes related to skeletal muscle function and degeneration.

nNOS/GSNOR interaction contributes to skeletal muscle differentiation and homeostasis

Neuronal nitric oxide synthase (nNOS) plays a crucial role in the maintenance of correct skeletal muscle function due, at least in part, to S-nitrosylation of specific protein targets. Similarly, we recently provided evidence for a muscular phenotype in mice lacking the denitrosylase S-nitrosoglutathione reductase (GSNOR). Here, we demonstrate that nNOS and GSNOR are concomitantly expressed during differentiation of C2C12. They colocalizes at the sarcolemma and co-immunoprecipitate in cells and in myofibers. We also provide evidence that GSNOR expression decreases in mouse models of muscular dystrophies and of muscle atrophy and wasting, i.e., aging and amyotrophic lateral sclerosis, suggesting a more general regulatory role of GSNOR in skeletal muscle homeostasis.

Nitric oxide signalling and neuronal nitric oxide synthase in the heart under stress

Nitric oxide (NO) is an imperative regulator of the cardiovascular system and is a critical mechanism in preventing the pathogenesis and progression of the diseased heart. The scenario of bioavailable NO in the myocardium is complex: 1) NO is derived from both endogenous NO synthases (endothelial, neuronal, and/or inducible NOSs [eNOS, nNOS, and/or iNOS]) and exogenous sources (entero-salivary NO pathway) and the amount of NO from exogenous sources varies significantly; 2) NOSs are located at discrete compartments of cardiac myocytes and are regulated by distinctive mechanisms under stress; 3) NO regulates diverse target proteins through different modes of post-transcriptional modification (soluble guanylate cyclase [sGC]/cyclic guanosine monophosphate [cGMP]/protein kinase G [PKG]-dependent phosphorylation, S-nitrosylation, and transnitrosylation); 4) the downstream effectors of NO are multidimensional and vary from ion channels in the plasma membrane to signalling proteins and enzymes in the mitochondria, cytosol, nucleus, and myofilament; 5) NOS produces several radicals in addition to NO (e.g. superoxide, hydrogen peroxide, peroxynitrite, and different NO-related derivatives) and triggers redox-dependent responses. However, nNOS inhibits cardiac oxidases to reduce the sources of oxidative stress in diseased hearts. Recent consensus indicates the importance of nNOS protein in cardiac protection under pathological stress. In addition, a dietary regime with high nitrate intake from fruit and vegetables together with unsaturated fatty acids is strongly associated with reduced cardiovascular events. Collectively, NO-dependent mechanisms in healthy and diseased hearts are better understood and shed light on the therapeutic prospects for NO and NOSs in clinical applications for fatal human heart diseases.

Reversible oxidation of vicinal-thiols motif in sarcoplasmic reticulum calcium regulatory proteins is involved in muscle fatigue mechanism

The mechanism underlying fatigue in skeletal muscle (SM) related to the redox-potential hypothesis, ranges from a direct effect of oxygen reactive species, to a number of other free radical intermediates targeting specific amino acids in the Ca(2+)-regulatory proteins of the sarcoplasmic reticulum (SR). In the present study, we investigate the selective oxidation/reduction of the protein motif Cys-(Xn=2-6)-Cys, known as a vicinal thiol group (VTG), present in the SR Ca(2+)-ATPase (SERCA) and in the Ca(2+)-channel ryanodine receptor (RyR) which are modified during muscle fatigue in SM. Selective oxidation of VTG with phenyl arsine oxide (PAO) increases fatigue in rat isolated SM and fatigue is prevented when muscle is previously incubated with a VTG selective reducing agent, 2,3-dimercaptopropanol (British anti-Lewisite (BAL)). In isolated SR membranes, PAO [<0.1mM] modifies SERCA conformation and inhibits ATPase activity but does not affect Ca(2+)-release. However, PAO at [>0.1mM] inhibits SERCA and RyR activities in a reversible manner by selectively reducing them. Interestingly, as observed by differential scanning calorimetry, the conformation of SERCA from fatigued muscle changed in a similar manner as when SERCA VTG where oxidized. The addition of BAL to fatigued muscle restored the structural conformation and activity of SERCA with full recovery of muscle force production after fatigue. We conclude that VTG reversible oxidation of SR Ca(2+) regulatory proteins are involved in muscle contraction/relaxation and are a molecular mechanism to be considered for muscle fatigue.

Expression of nNOS in the human larynx

Although intrinsic laryngeal neurons and ganglia have been studied in various species, they have been overlooked in humans. We aimed to investigate the presence of intrinsic laryngeal neurons in humans and, if present, to analyze their neuronal nitric oxide synthase (nNOS) expression. An immunohistochemical study using anti-nNOS antibodies was performed on samples obtained from four cadavers. Intrinsic laryngeal nNOS+ neurons were assessed in the submucosal layer, but nNOS+ nerves were found in all histological layers of the larynx. nNOS expression was also found in striated muscle fibers of larynx. This might reveal the anatomical basis of an upwards extension of the nonadrenergic noncholinergic system in human airways, but further experiments are needed to assess an exact role of NO influence on neural transmission and muscular functions of human larynx.

The production of nitric oxide, IL-6, and TNF-alpha in palmitate-stimulated PBMNCs is enhanced through hyperglycemia in diabetes

We examined nitric oxide (NO), IL-6, and TNF-α secretion from cultured palmitate-stimulated PBMNCs or in the plasma from type 2 diabetes mellitus (T2MD) patients or nondiabetic (ND) controls. Free fatty acids (FFA) have been suggested to induce chronic low-grade inflammation, activate the innate immune system, and cause deleterious effects on vascular cells and other tissues through inflammatory processes. The levels of NO, IL-6, TNF-α, and MDA were higher in supernatant of palmitate stimulated blood cells (PBMNC) or from plasma from patients. The results obtained in the present study demonstrated that hyperglycemia in diabetes exacerbates in vitro inflammatory responses in PBMNCs stimulated with high levels of SFA (palmitate). These results suggest that hyperglycemia primes PBMNCs for NO, IL-6, and TNF-alpha secretion under in vitro FFA stimulation are associated with the secretion of inflammatory biomarkers in diabetes. A combined therapy targeting signaling pathways activated by hyperglycemia in conjunction with simultaneous control of hyperglycemia and hypertriglyceridemia would be suggested for controlling the progress of diabetic complications.

Endothelial nitric oxide synthase g894t (rs1799983) gene polymorphism in polish athletes

The NOS3 gene has been associated with athletic endurance performance and elite power athletic status. With respect to NOS3 G894T and its relation to athletic performance or status, results across various studies have not been consistent. Therefore, the lack of consistency among previous studies prompted us to design a case-control study in a Polish Caucasian population to examine the relationship between the NOS3 G894T polymorphism and athletes' status, i.e. type and intensity of exercise performed (poweroriented, “mixed” power/endurance activity, endurance-oriented) and the possible association between the G894T variant and athletic performance. The case-control study was performed in a group of 360 Polish athletes (cases) of the highest nationally competitive standard (male n=156 and female n=67) and 191 unrelated, sedentary control subjects. The G894T genotype and allele distributions differed significantly between power-oriented (P=0.009, P=0.003), “mixed” (P=0.021, P=0.009), endurance (P=0.043, P=0.014) athletes when compared to control subjects (P values for genotypes and alleles, respectively). There were no significant differences between elite and sub-elite athletes in any group. The over-representation of the GG genotype and G allele in all athletes suggests that the G894 allele may favour all types of sports, however, the strongest predisposition was seen among power-oriented athletes.

S-nitrosation and ubiquitin-proteasome system interplay in neuromuscular disorders

Protein S-nitrosation is deemed as a prototype of posttranslational modifications governing cell signaling. It takes place on specific cysteine residues that covalently incorporate a nitric oxide (NO) moiety to form S-nitrosothiol derivatives and depends on the ratio between NO produced by NO synthases and nitrosothiol removal catalyzed by denitrosating enzymes. A large number of cysteine-containing proteins are found to undergo S-nitrosation and, among them, the enzymes catalyzing ubiquitination, mainly the class of ubiquitin E3 ligases and the 20S component of the proteasome, have been reported to be redox modulated in their activity. In this review we will outline the processes regulating S-nitrosation and try to debate whether and how it affects protein ubiquitination and degradation via the proteasome. In particular, since muscle and neuronal health largely depends on the balance between protein synthesis and breakdown, here we will discuss the impact of S-nitrosation in the efficiency of protein quality control system, providing lines of evidence and speculating about its involvement in the onset and maintenance of neuromuscular dysfunctions.

The role of nNOS and PGC-1α in skeletal muscle cells

Neuronal nitric oxide synthase (nNOS) and peroxisome proliferator activated receptor γ co-activator 1α (PGC-1α) are two fundamental factors involved in the regulation of skeletal muscle cell metabolism. nNOS exists as several alternatively spliced variants, each having a specific pattern of subcellular localisation. Nitric oxide (NO) functions as a second messenger in signal transduction pathways that lead to the expression of metabolic genes involved in oxidative metabolism, vasodilatation and skeletal muscle contraction. PGC-1α is a transcriptional coactivator and represents a master regulator of mitochondrial biogenesis by promoting the transcription of mitochondrial genes. PGC-1α can be induced during physical exercise, and it plays a key role in coordinating the oxidation of intracellular fatty acids with mitochondrial remodelling. Several lines of evidence demonstrate that NO could act as a key regulator of PGC-1α expression; however, the link between nNOS and PGC-1α in skeletal muscle remains only poorly understood. In this Commentary, we review important metabolic pathways that are governed by nNOS and PGC-1α, and aim to highlight how they might intersect and cooperatively regulate skeletal muscle mitochondrial and lipid energetic metabolism and contraction.

Cardiac and respiratory dysfunction in Duchenne muscular dystrophy and the role of second messengers

Duchenne muscular dystrophy (DMD) affects young boys and is characterized by the absence of dystrophin, a large cytoskeletal protein present in skeletal and cardiac muscle cells and neurons. The heart and diaphragm become necrotic in DMD patients and animal models of DMD, resulting in cardiorespiratory failure as the leading cause of death. The major consequences of the absence of dystrophin are high levels of intracellular Ca(2+) and the unbalanced production of NO that can finally trigger protein degradation and cell death. Cytoplasmic increase in Ca(2+) concentration directly and indirectly triggers different processes such as necrosis, fibrosis, and activation of macrophages. The absence of the neuronal isoform of nitric oxide synthase (nNOS) and the overproduction of NO by the inducible isoform (iNOS) further increase the intracellular Ca(2+) via a hypernitrosylation of the ryanodine receptor. NO overproduction, which further induces the expression of iNOS but decreases the expression of the endothelial isoform (eNOS), deregulates the muscle tissue blood flow creating an ischemic situation. The high levels of Ca(2+) in dystrophic muscles and the ischemic state of the muscle tissue would culminate in a positive feedback loop. While efforts continue toward optimizing cardiac and respiratory care of DMD patients, both Ca(2+) and NO in cardiac and respiratory muscle pathways have been shown to be important to the etiology of the disease. Understanding the mechanisms behind the fine regulation of Ca(2+) -NO may be important for a noninterventional and noninvasive supportive approach to treat DMD patients, improving the quality of life and natural history of DMD patients.

Nitric oxide in skeletal muscle: role on mitochondrial biogenesis and function

Nitric oxide (NO) has been implicated in several cellular processes as a signaling molecule and also as a source of reactive nitrogen species (RNS). NO is produced by three isoenzymes called nitric oxide synthases (NOS), all present in skeletal muscle. While neuronal NOS (nNOS) and endothelial NOS (eNOS) are isoforms constitutively expressed, inducible NOS (iNOS) is mainly expressed during inflammatory responses. Recent studies have demonstrated that NO is also involved in the mitochondrial biogenesis pathway, having PGC-1α as the main signaling molecule. Increased NO synthesis has been demonstrated in the sarcolemma of skeletal muscle fiber and NO can also reversibly inhibit cytochrome c oxidase (Complex IV of the respiratory chain). Investigation on cultured skeletal myotubes treated with NO donors, NO precursors or NOS inhibitors have also showed a bimodal effect of NO that depends on the concentration used. The present review will discuss the new insights on NO roles on mitochondrial biogenesis and function in skeletal muscle. We will also focus on potential therapeutic strategies based on NO precursors or analogs to treat patients with myopathies and mitochondrial deficiency.

Effects of moderate electrical stimulation on reactive species production by primary rat skeletal muscle cells: cross talk between superoxide and nitric oxide production

The effects of a moderate electrical stimulation on superoxide and nitric oxide production by primary cultured skeletal muscle cells were evaluated. The involvement of the main sites of these reactive species production and the relationship between superoxide and nitric oxide production were also examined. Production of superoxide was evaluated by cytochrome c reduction and dihydroethidium oxidation assays. Electrical stimulation increased superoxide production after 1 h incubation. A xanthine oxidase inhibitor caused a partial decrease of superoxide generation and a significant amount of mitochondria-derived superoxide was also observed. Nitric oxide production was assessed by nitrite measurement and by using 4,5-diaminofluorescein diacetate (DAF-2-DA) assay. Using both methods an increased production of nitric oxide was obtained after electrical stimulation, which was also able to induce an increase of iNOS content and NF-κB activation. The participation of superoxide in nitric oxide production was investigated by incubating cells with DAF-2-DA in the presence or absence of electrical stimulation, a superoxide generator system (xanthine-xanthine oxidase), a mixture of NOS inhibitors and SOD-PEG. Our data show that the induction of muscle contraction by a moderate electrical stimulation protocol led to an increased nitric oxide production that can be controlled by superoxide generation. The cross talk between these reactive species likely plays a role in exercise-induced maintenance and adaptation by regulating muscular glucose metabolism, force of contraction, fatigue, and antioxidant systems activities.

Mineralocorticoid antagonism: a novel way to treat sarcopenia and physical impairment in older people?

Dysregulation of the renin-angiotensin-aldosterone system has been associated with a number of age-related pathologies including hypertension, heart failure and chronic kidney disease. More recently, it has been suggested that alterations within the RAAS may contribute to the development of sarcopenia and subsequent decline in physical function. There is growing interest in developing interventions to prevent age-associated decline in muscle function. We postulate that inhibition of the RAAS with the mineralocorticoid antagonist spironolactone may have a role in countering the effects of physical impairment in older people by improving skeletal muscle function. Spironolactone may prevent skeletal myocyte apoptosis, improve vascular endothelial function and enhance muscle contractility by increasing muscle magnesium and sodium-potassium pumps. This article will review the literature underpinning the hypothesis that spironolactone may have a role in maintaining muscle function in older people.

Inhibition of nNOS prevents and inhibition of iNOS reverses α,β-meATP-induced facilitation of neck muscle nociception in mice

Infusion of α,β-methylene ATP (α,β-meATP) into murine neck muscle facilitates brainstem nociception. Unspecific nitric oxide synthase (NOS) inhibition prevents and reverses this sensitization. It is unclear whether neuronal (nNOS), inducible (iNOS) or endothelial NOS isoenzymes are involved in this α,β-meATP effect. Hypothesized involvement of nNOS isoenzyme was addressed by preceding (0.5, 1, and 2 mg/kg) and subsequent (2 mg/kg) intraperitoneal injection of the nNOS-inhibitor NPLA. iNOS involvement was addressed by subsequent, intraperitoneal administration of the iNOS-inhibitor 1400 W (2 mg/kg). Brainstem nociception was monitored by the jaw-opening reflex elicited via electrical tongue stimulation in 45 anesthetized mice. Preceding NPLA dose-dependently prevented α,β-meATP-induced reflex facilitation. Whereas subsequent inhibition of nNOS showed no effect, iNOS inhibition by 1400 W significantly reversed reflex facilitation. Data provide evidence that nNOS plays a major role in induction and iNOS in maintenance of facilitation in neck muscle nociception. Divergent roles of NOS isoenzymes may promote research on target specific treatment for headache and neck muscle pain.

Sarcolemmal neuronal nitric oxide synthase defect in limb-girdle muscular dystrophy: an adverse modulating factor in the disease course?

Reduction of neuronal nitric oxide synthase (nNOS) has been associated with the pathogenesis and clinical expression of inherited myopathies. To determine whether a defect in nNOS might be an adverse modulating factor in the course of limb-girdle muscular dystrophy, we investigated cytosolic and sarcolemmal nNOS expression in muscle biopsies from 32 patients with 7 forms of limb-girdle muscular dystrophy. Primary calpainopathy, dysferlinopathy, and caveolinopathy biopsies showed normal levels of cytosolic nNOS and preserved sarcolemmal nNOS immunoreactivity. By contrast, the cytosolic nNOS levels in sarcoglycanopathy muscles were variably reduced. Sarcolemmal nNOS immunoreactivity varied from absent to reduced, depending on the integrity of the sarcoglycan complex. In muscles with loss of the entire sarcoglycan complex, sarcolemmal nNOS was absent; it otherwise depended on the specific sarcoglycan gene and type of mutation. The integrity of the entire sarcoglycan complex is, therefore, essential for the stabilization of nNOS to the sarcolemma. Absence of sarcolemmal nNOS in sarcoglycanopathy muscle was always associated with severe muscular dystrophy and sometimes with dilated cardiomyopathy, supporting the hypothesis that nNOS defect might contribute to skeletal and cardiac muscle disease progression. These results emphasize the value of nNOS immunohistochemical analysis in limb-girdle muscular dystrophy and provide additional insights for future therapeutic interventions in these disorders.

Systemic and mitochondrial adaptive responses to moderate exercise in rodents

The systemic and nonmuscular adaptive response to moderate exercise is reviewed and compared with muscle responses to moderate and exhaustive exercise. Rats participating in voluntary wheel running and mice subjected to treadmill exercise on a lifelong basis showed 10-19% increased median life span. Mice also showed improved neurological functions, such as better (35-216%) neuromuscular coordination (tightrope test) and better (11-27%) exploratory activity (T maze). These effects are consistent with the systemic effects of moderate exercise lowering hyperglycemia, hypercholesterolemia, and hypertension. Mitochondria isolated from brain, liver, heart, and kidney of exercised mice show a 12-32% selectively increased complex IV activity, with a significant correlation between complex IV activity and performance in the tightrope test. Chronic exercise decreases (10-20%) the mitochondrial content of TBARS and protein carbonyls in the four organs after 24 weeks of training. Protein carbonyls were linearly and negatively related to complex IV activity. Exercise increased the levels of nNOSmu in human muscle and of nNOS in mouse brain. It is concluded that chronic moderate exercise exerts a whole-body beneficial effect that exceeds muscle adaptation, likely through mechanosensitive afferent nerves and beta-endorphin release to brain and plasma that promote mitochondrial biogenesis in distant organs.

Sarco(endo)plasmic reticulum and plasmalemmal Ca(2+)-ATPase activities in cremaster muscles and sacs differ according to the associated inguinal pathology

Sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) and plasmalemmal Ca(2+)-ATPase (PMCA) activities in cremaster muscles and sacs, which have been subjected to different autonomic tonuses, were determined and compared. Samples of cremaster muscles and sacs associated with male or female inguinal hernia, hydrocele or undescended testis were obtained from children during operations and activities of SERCA and PMCA were determined. While highest SERCA and PMCA activities were encountered among cremaster muscles and sacs associated with undescended testis, least activities were encountered among structures associated with hydrocele. The alterations in SERCA and PMCA activities in cremaster muscles associated with undescended testis appear to reflect the attempts at maintaining the levels of cytosolic calcium. Despite similar total calcium contents, lower SERCA and PMCA activities were found in sacs associated with hydrocele compared to those associated with undescended testis suggest a difference among the levels of cytosolic calcium.

Aspects of nitric oxide in health and disease: a focus on hypertension and cardiovascular disease

Nitric oxide (nitrogen monoxide) (NO) plays an important role in a wide range of physiologic processes. A major mediator of endothelial function, NO regulates vasodilatory and antithrombotic actions in the vasculature and plays a role in reproductive functions, bronchodilation, bone formation, memory, insulin sensitivity, and gastrointestinal relaxation. NO is formed from NO synthase. Impaired NO bioactivity is strongly associated with endothelial dysfunction and cardiovascular disease, but is also implicated in a broad range of other disorders, including pulmonary hypertension, insulin resistance, erectile dysfunction, and preeclampsia. Numerous therapies designed to target NO are being investigated and developed, including NO donors and stimulants. The recent African-American Heart Failure Trial (A-HeFT) showed that the NO donor isosorbide dinitrate, combined with the vasodilator hydralazine, significantly reduced morbidity and mortality in black patients with moderate-to-severe heart failure. Antihypertensive drugs, including angiotensin-converting enzyme inhibitors, calcium channel blockers, and third-generation beta-blockers, are NO stimulants that have demonstrated significant improvement of endothelial function and NO bioactivity. Other cardiovascular therapies that may improve NO bioactivity include statins, l-arginine, and nonpharmacologic approaches such as exercise and dietary changes.

Real-time measurement of nitric oxide in single mature mouse skeletal muscle fibres during contractions

Nitric oxide (NO) is thought to play multiple roles in skeletal muscle including regulation of some adaptations to contractile activity, but appropriate methods for the analysis of intracellular NO activity are lacking. In this study we have examined the intracellular generation of NO in isolated single mature mouse skeletal muscle fibres at rest and following a period of contractile activity. Muscle fibres were isolated from the flexor digitorum brevis muscle of mice and intracellular NO production was visualized in real-time using the fluorescent NO probe 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate (DAF-FM DA). Some leakage of DAF-FM was apparent from fibres loaded with the probe, but they retained sufficient probe to respond to changes in intracellular NO following addition of the NO donor 3-(2-hydroxy-1-methyl-2-nitrosohydrazino)-N-methyl-1-propanamine (NOC-7) up to 30 min after loading. Electrically stimulated contractions in isolated fibres increased the rate of change in DAF-FM fluorescence by approximately 48% compared to non-stimulated fibres (P < 0.05) and the rate of change in DAF-FM fluorescence in the stimulated fibres returned to control values by 5 min after contractions. Treatment of isolated fibres with the NO synthase inhibitors NG-nitro-L-arginine methyl ester hydrochloride (L-NAME) or NG-monomethyl-L-arginine (L-NMMA) reduced the increase in DAF-FM fluorescence observed in response to contractions of untreated fibres. Treatment of fibres with the cell-permeable superoxide scavenger 4,5-dihydroxy-1,3-benzenedisulphonic acid (Tiron) also reduced the increase in fluorescence observed during contractions suggesting that superoxide, or more probably peroxynitrite, contributes to the fluorescence observed. Thus this technique can be used to examine NO generation in quiescent and contracting skeletal muscle fibres in real time, although peroxynitrite and other reactive nitrogen species may potentially contribute to the fluorescence values observed.

Early vulnerability to ischemia/reperfusion injury in motor terminals innervating fast muscles of SOD1-G93A mice

In mouse models of familial amyotrophic lateral sclerosis (fALS), motor neurons are especially vulnerable to oxidative stresses in vitro. To determine whether this increased vulnerability also extends to motor nerve terminals in vivo, we assayed the effect of tourniquet-induced ischemia/reperfusion (I/R) injury on motor terminals innervating fast and slow hindlimb muscles in male G93A-SOD1 mice and their wild-type littermates. These mice also expressed yellow fluorescent protein (YFP) in motor neurons. We report that in SOD1-G93A/YFP mice the motor terminals innervating two predominantly fast muscles, extensor digitorum longus (EDL) and plantaris, were more vulnerable to I/R injury than motor terminals innervating the predominantly slow soleus muscle. The mean duration of EDL ischemia required to produce a 50% reduction in endplate innervation in SOD1-G93A/YFP mice was 26 min, compared to 45 min in YFP-only mice. The post-I/R destruction of EDL terminals in SOD1-G93A mice was rapid (<2 h) and was not duplicated by cutting the sciatic nerve at the tourniquet site. The increased sensitivity to I/R injury was evident in EDL muscles of SOD1-G93A/YFP mice as young as 31 days, well before the onset of motor neuron death at approximately 90 days. This early vulnerability to I/R injury may correlate with the finding (confirmed here) that in fALS mice motor nerve terminals innervating fast hindlimb muscles degenerate before those innervating slow muscles, at ages that precede motor neuron death. Early vulnerability of fast motor terminals to I/R injury thus may signal, and possibly contribute to, early events involved in motor neuron death.

Reactive oxygen species and redox-regulation of skeletal muscle adaptations to exercise

Skeletal muscle has been shown to generate a complex set of reactive oxygen and nitrogen species (ROS) both at rest and during contractile activity. The primary ROS generated are superoxide and nitric oxide and the pattern and magnitude of their generation is influenced by the nature of the contractile activity. It is increasingly clear that the ROS generated by skeletal muscle play an important role in influencing redox-regulated processes that control, at least some of, the adaptive responses to contractile activity. These processes are also recognized to be modified during ageing and in some disease states, providing the potential that interventions affecting ROS activity may influence muscle function or viability in these situations.

A transverse tubule NADPH oxidase activity stimulates calcium release from isolated triads via ryanodine receptor type 1 S -glutathionylation

We report here the presence of an NADPH oxidase (NOX) activity both in intact and in isolated transverse tubules and in triads isolated from mammalian skeletal muscle, as established by immunochemical, enzymatic, and pharmacological criteria. Immunohistochemical determinations with NOX antibodies showed that the gp91(phox) membrane subunit and the cytoplasmic regulatory p47(phox) subunit co-localized in transverse tubules of adult mice fibers with the alpha1s subunit of dihydropyridine receptors. Western blot analysis revealed that isolated triads contained the integral membrane subunits gp91(phox) and p22(phox), which were markedly enriched in isolated transverse tubules but absent from junctional sarcoplasmic reticulum vesicles. Isolated triads and transverse tubules, but not junctional sarcoplasmic reticulum, also contained varying amounts of the cytoplasmic NOX regulatory subunits p47(phox) and p67(phox). NADPH or NADH elicited superoxide anion and hydrogen peroxide generation by isolated triads; both activities were inhibited by NOX inhibitors but not by rotenone. NADH diminished the total thiol content of triads by one-third; catalase or apocynin, a NOX inhibitor, prevented this effect. NADPH enhanced the activity of ryanodine receptor type 1 (RyR1) in triads, measured through [3H]ryanodine binding and calcium release kinetics, and increased significantly RyR1 S-glutathionylation over basal levels. Preincubation with reducing agents or NOX inhibitors abolished the enhancement of RyR1 activity produced by NADPH and prevented NADPH-induced RyR1 S-glutathionylation. We propose that reactive oxygen species generated by the transverse tubule NOX activate via redox modification the neighboring RyR1 Ca2+ release channels. Possible implications of this putative mechanism for skeletal muscle function are discussed.

Systemic administration of L-arginine benefits mdx skeletal muscle function

A major consequence of muscular dystrophy is that increased membrane fragility leads to high calcium influx and results in muscle degeneration and myonecrosis. Prior reports have demonstrated that increased nitric oxide production via L-arginine treatment of normal and mdx mice resulted in increased expression of utrophin and increased activation of muscle satellite cells, which could ameliorate the dystrophic pathology. We delivered L-arginine to normal and mdx mice, and examined muscles for any functional changes associated with its administration. Treated mdx muscles were less susceptible to contraction-induced damage and exhibited a rightward shift of the force-frequency relationship. Immunoblotting revealed increases in utrophin and gamma-sarcoglycan in the treated muscles. There was also a decrease in Evans blue dye uptake, indicating a reduction in myonecrosis. However, there was no decrease in serum creatine kinase or the proportion of central nuclei, nor any improvement in specific force. Together, these results show that L-arginine treatment can be beneficial to mdx muscle function, perhaps through a combination of enhanced calcium handling and increased utrophin, thereby decreasing muscle degeneration.

Impaired exercise capacity, but unaltered mitochondrial respiration in skeletal or cardiac muscle of mice lacking cellular prion protein

The studies of physiological roles for cellular prion protein (PrP(c)) have focused on possible functions of this protein in the CNS, where it is largely expressed. However, the observation that PrP(c) is expressed also in muscle tissue suggests that the physiological role of PrP(c) might not be limited to the central nervous system. In the present study, we investigated possible functions of PrP(c) in muscle using PrP(c) gene (Prnp) null mice (Prnp(0/0)). For this purpose, we submitted Prnp(0/0) animals to different protocols of exercise, and compared their performance to that of their respective wild-type controls. Prnp(0/0) mice showed an exercise-dependent impairment of locomotor activity. In searching for possible mechanisms associated with the impairment observed, we evaluated mitochondrial respiration (MR) in skeletal or cardiac muscle from these mice during resting or after different intensities of exercise. Baseline MR (states 3 and 4), respiratory control ratio (RCR) and mitochondrial membrane potential (DeltaPsi) were evaluated and were not different in skeletal or cardiac muscle tissue of Prnp(0/0) mice when compared with wild-type animals. We concluded that Prnp(0/0) mice show impairment of swimming capacity, perhaps reflecting impairment of muscular activity under more extreme exercise conditions. In spite of the mitochondrial abnormalities reported in Prnp(0/0) mice, our observation seems not to be related to MR. Our results indicate that further investigations should be conducted in order to improve our knowledge about the function of PrP(c) in muscle physiology and its possible role in several different neuromuscular pathologies.

Altered behavioural response to acute stress in mice lacking cellular prion protein

Although many studies have investigated the function of cellular prion protein (PrPc), its physiologic role remains elusive. PrPc null mice have been reported to develop normally and to show normal performance in most behavioural tests. In the present study we investigated whether this also holds true after episodes of acute stress. PrPc gene ablated (Prnp0/0) and wild-type mice were subjected to restraint stress, electric foot shock, or swimming and compared with non-stressed animals. Immediately after the stressful situation, the anxiety levels and locomotion of the animals were measured using plus-maze and open-field tests. Among non-stressed animals, there was no significant difference in performance between Prnp0/0 and wild type animals in either test. However, after acute stress provoked by a foot shock or a swimming trial, Prnp0/0 animals showed a significant decrease in anxiety levels when compared with control animals. Moreover, after the swimming test, knockout mice presented decreased locomotion when compared to wild-type mice. Because of this observation, we also assessed both types of mice in a forced swimming test with the objective of better evaluating muscle function and found that Prnp0/0 animals presented reduced forced swimming capacity when compared to controls. As far as we know, this is the first report suggesting that cellular prion protein is involved in modulation of anxiety or muscular activity after acute psychic or physical stress.

CAPON expression in skeletal muscle is regulated by position, repair, NOS activity, and dystrophy

In skeletal muscle, the localization of nNOS is destabilized in the absence of dystrophin, which impacts muscle function and satellite cell activation. In neurons, the adaptor protein, carboxy-terminal PDZ ligand of nNOS (CAPON), regulates the distribution of neuronal nitric oxide synthase (nNOS), which produces the key signaling molecule nitric oxide (NO). While a CAPON-like gene is known to compensate functionally for a dystrophic phenotype in muscle of Caenorhabditis elegans, CAPON expression has not been reported for mammalian muscle. Here, CAPON expression was identified in mouse muscle using Northern and Western blotting and in situ hybridization in combination with immunostaining for laminin. CAPON RNA was expressed in developing normal and dystrophic muscles near fiber junctions with tendons, and levels increased from 1 to 3 weeks. In regenerating normal muscle and also in dystrophic muscles in the mdx mouse, CAPON transcripts were prominent in satellite cells and new myotubes. Expression of CAPON RNA increased in diaphragm muscle of normal and mdx mice after treatment with L-arginine, the NOS substrate. Both CAPON and utrophin protein levels increased in dystrophic quadriceps muscle after treatment with the steroid deflazacort plus L-arginine, known to reduce the dystrophic phenotype. The identification of CAPON transcripts and protein in mammalian muscle and responses to L-arginine suggest CAPON may have a functional role in stabilizing neuronal NOS in skeletal muscle in the cytoskeletal complex associated with dystrophin/utrophin, with possible applications to therapy for human muscular dystrophy.

The effects of N(omega)-propyl-L-arginine on reperfusion injury of skeletal muscle

N(omega)-Propyl-L-arginine (NPA) is reported to be a highly selective inhibitor of neuronal nitric oxide synthase (nNOS). This in vivo study observed its role in ischemia/reperfusion (I/R) injury in rat skeletal muscle. Our results showed that NPA infusion significantly increased vessel diameters and blood flow in reperfused cremaster muscle, and slightly increased contractile function in reperfused extensor digitorum longus (EDL) muscle. In addition, NPA treatment slightly increased I/R-mediated downregulation of nNOS and eNOS mRNA and protein levels. Although NPA showed a beneficial role in I/R injury, our in vivo data do not support NPA as a selective nNOS inhibitor. Also, our data do not provide any insight into the mechanism of NPA. Thus, the in vivo mechanism of action of NPA needs to be further identified, and the role of nNOS in skeletal muscle I/R still remains to be determined.

Heme proteins and nitric oxide (NO): the neglected, eloquent chemistry in NO redox signaling and regulation

The role of nitric oxide (NO) in cellular physiology and signaling has been an important aspect in biomedical science over the last decade. As NO is a small uncharged radical, the chemistry of NO within the redox environment of the cell dictates the majority of its biological effects. The mechanisms that have received the most attention from a biological perspective involve reactions with oxygen and superoxide, despite the rich literature of metal-NO chemistry. However, NO and its related species participate in important chemistry with metalloproteins. In addition to the well known direct interactions of NO with heme proteins such as soluble guanylate cyclase and oxyhemoglobin, there is much important, but often underappreciated, chemistry between other nitrogen oxides and heme/metal proteins. Here the basic chemistry of nitrosylation and the interactions of NO and other nitrogen oxides with metal-oxo species such as found in peroxidases and monoxygenases are discussed.

Early postdenervation depolarization is controlled by acetylcholine and glutamate via nitric oxide regulation of the chloride transporter

Resting non-quantal acetylcholine (ACh) and probably glutamate (Glu) release from nerve endings activates M1- and NMDA receptor-mediated Ca2+ entry into the sarcoplasm with following activation of NOS and production of NO. This is a trophic message from motoneurons, which keeps the Cl- transport inactive in the innervated sarcolemma. After denervation, the secretion of ACh and Glu at the neuromuscular junction is eliminated within 3-4 h and the production of NO in the sarcoplasm is lowered. As a result, the Cl- influx is probably activated by dephosphorylation of the Cl- transporter with subsequent elevation of intracellular Cl- concentration. The equilibrium Cl- potential becomes more positive and the muscle membrane becomes depolarized.

Effects of nitrogen monoxide and carbon monoxide on molecular and cellular iron metabolism: mirror-image effector molecules that target iron

Many effector functions of nitrogen monoxide (NO) and carbon monoxide (CO) are mediated through their high-affinity for iron (Fe). In this review, the roles of NO and CO are examined in terms of their effects on the molecular and cellular mechanisms involved in Fe metabolism. Both NO and CO avidly form complexes with a plethora of Fe-containing molecules. The generation of NO and CO is mediated by the nitric oxide synthase and haem oxygenase (HO) families of enzymes respectively. The effects of NO on Fe metabolism have been well characterized, whereas knowledge of the effects of CO remains within its infancy. In terms of the role of NO in Fe metabolism, one of the best characterized interactions includes its effect on the iron regulatory proteins. These molecules are mRNA-binding proteins that control the expression of the transferrin receptor 1 and ferritin, molecules that are involved in Fe uptake and storage respectively. Apart from this, activated macrophages impart their cytotoxic activity by generating NO, which results in marked Fe mobilization from tumour-cell targets. This deprives the cell of the Fe that is required for DNA synthesis and energy production. Considering that HO degrades haem, resulting in the release of CO, Fe(II) and biliverdin, it is suggested that a CO-Fe complex will form. This may account for the rapid Fe mobilization observed from macrophages after haemoglobin catabolism. Intriguingly, overexpression of HO results in cellular Fe mobilization, suggesting that CO has a similar effect to NO on Fe trafficking. Preliminary evidence suggests that, like NO, CO plays important roles in Fe metabolism.

Demystified. Nitric oxide

The discovery of nitric oxide (NO) demonstrated that cells could communicate via the manufacture and local diffusion of an unstable lipid soluble molecule. Since the original demonstration of the vascular relaxant properties of endothelium derived NO, this fascinating molecule has been shown to have multiple, complex roles within many biological systems. This review cannot hope to cover all of the recent advances in NO biology, but seeks to place the discovery of NO in its historical context, and show how far our understanding has come in the past 20 years. The role of NO in mitochondrial respiration, and consequently in oxidative stress, is described in detail because these processes probably underline the importance of NO in the development of disease.