Free radicals: a potential pathogenic mechanism in inherited muscular dystrophy

Redox Control of Skeletal Muscle Regeneration

Skeletal muscle shows high plasticity in response to external demand. Moreover, adult skeletal muscle is capable of complete regeneration after injury, due to the properties of muscle stem cells (MuSCs), the satellite cells, which follow a tightly regulated myogenic program to generate both new myofibers and new MuSCs for further needs. Although reactive oxygen species (ROS) and reactive nitrogen species (RNS) have long been associated with skeletal muscle physiology, their implication in the cell and molecular processes at work during muscle regeneration is more recent. This review focuses on redox regulation during skeletal muscle regeneration. An overview of the basics of ROS/RNS and antioxidant chemistry and biology occurring in skeletal muscle is first provided. Then, the comprehensive knowledge on redox regulation of MuSCs and their surrounding cell partners (macrophages, endothelial cells) during skeletal muscle regeneration is presented in normal muscle and in specific physiological (exercise-induced muscle damage, aging) and pathological (muscular dystrophies) contexts. Recent advances in the comprehension of these processes has led to the development of therapeutic assays using antioxidant supplementation, which result in inconsistent efficiency, underlying the need for new tools that are aimed at precisely deciphering and targeting ROS networks. This review should provide an overall insight of the redox regulation of skeletal muscle regeneration while highlighting the limits of the use of nonspecific antioxidants to improve muscle function. Antioxid. Redox Signal. 27, 276-310.

Increased constitutive nitric oxide production by whole body periodic acceleration ameliorates alterations in cardiomyocytes associated with utrophin/dystrophin deficiency

Duchenne Muscular Dystrophy (DMD) cardiomyopathy is a progressive lethal disease caused by the lack of the dystrophin protein in the heart. The most widely used animal model of DMD is the dystrophin-deficient mdx mouse; however, these mice exhibit a mild dystrophic phenotype with heart failure only late in life. In contrast, mice deficient for both dystrophin and utrophin (mdx/utrn^-/-, or dKO) can be used to model severe DMD cardiomyopathy where pathophysiological indicators of heart failure are detectable by 8-10weeks of age. Nitric oxide (NO) is an important signaling molecule involved in vital functions of regulating rhythm, contractility, and microcirculation of the heart, and constitutive NO production affects the function of proteins involved in excitation-contraction coupling. In this study, we explored the efficacy of enhancing NO production as a therapeutic strategy for treating DMD cardiomyopathy using the dKO mouse model of DMD. Specifically, NO production was induced via whole body periodic acceleration (pGz), a novel non-pharmacologic intervention which enhances NO synthase (NOS) activity through sinusoidal motion of the body in a headward-footward direction, introducing pulsatile shear stress to the vascular endothelium and cardiomyocyte plasma membrane. Male dKO mice were randomized at 8weeks of age to receive daily pGz (480cpm, Gz±3.0m/s², 1h/d) for 4weeks or no treatment, and a separate age-matched group of WT animals (pGz-treated and untreated) served as non-diseased controls. At the conclusion of the protocol, cardiomyocytes from untreated dKO animals had, respectively, 4.3-fold and 3.5-fold higher diastolic resting concentration of Ca²⁺ ([Ca²⁺]_d) and Na⁺ ([Na⁺]_d) compared to WT, while pGz treatment significantly reduced these levels. For dKO cardiomyocytes, pGz treatment also improved the depressed contractile function, decreased oxidative stress, blunted the elevation in calpain activity, and mitigated the abnormal increase in [Ca²⁺]_d upon mechanical stress. These improvements culminated in a significant reduction in circulating cardiac troponin T (cTnT) and an extension of the median lifespan of dKO mice from 16 to 31weeks. Treatment with L-NAME (NOS inhibitor) significantly decreased overall lifespan and abolished the cardioprotective properties elicited by pGz. Our results provide evidence that enhancement of NO synthesis by pGz can ameliorate cellular dysfunction in dKO cardiomyocytes and may represent a novel therapeutic intervention in DMD cardiomyopathy patients.

Cytoprotective propensity of green tea polyphenols against citrinin-induced skeletal-myotube damage in C2C12 cells

The mycotoxin citrinin, is produced by several species of Penicillium, Aspergillus and Monascus, and is capable of inducing cytotoxicity, oxidative stress and apoptosis. The aim of the present study was to investigate the effect of citrinin in mouse skeletal muscle cells (C2C12) and to overcome the cellular adverse effects by supplementing green tea extract (GTE) rich in polyphenols. C2C12 myoblasts were differentiated to myotubes and were exposed to citrinin in a dose dependent manner (0-100 µM) for 24 h and IC₅₀ value was found to be 100 µM that resulted in decreased cell viability, increased LDH leakage and compromised membrane integrity. Mitochondrial membrane potential loss, increased accumulation of intracellular ROS and sub G1 phase of cell cycle was observed. To ameliorate the cytotoxic effects of CTN, C2C12 cells were pretreated with GTE (20, 40, 80 µg/ml) for 2 h followed by citrinin (100 µM) treatment for 24 h. GTE pretreatment combated citrinin-induced cytotoxicity and oxidative stress. GTE at 40 and 80 µg/ml significantly promoted cell survival and upregulated antioxidant enzyme activities (CAT, SOD, GPx) and endogenous antioxidant GSH, while the gene and protein expression levels were significantly restored through its effective antioxidant mechanism. Present study results suggested the antioxidant properties of GTE as a herbal source in ameliorating the citrinin-induced oxidative stress.

Nutrition strategies to improve physical capabilities in Duchenne muscular dystrophy

There is no current cure for Duchenne muscular dystrophy (DMD), and palliative and prophylactic interventions to improve the quality of life of patients remain limited, with the exception of corticosteroids. This article describes 2 potential nutritional interventions for the treatment of DMD, green tea extract (GTE) and the branched-chain amino acid leucine, and their positive effects on physical activity. Both GTE and leucine are suitable for human consumption, are easily tolerated with no side effects, and, with appropriate preclinical data, could be brought forward to clinical trials rapidly.

Increased catalase expression improves muscle function in mdx mice

It has been well established that oxidative stress contributes to pathology associated with Duchenne muscular dystrophy (DMD). I hypothesized that overexpression of the antioxidant enzyme catalase would improve muscle function in the mdx mouse, the mouse model of DMD. To test this hypothesis, neonatal mdx mice were injected with a recombinant adeno-associated virus driving the catalase transgene. Animals were killed 4 or 6 weeks or 6 months following injection. Muscle function was generally improved by catalase overexpression. Four weeks following injection, extensor digitorum longus specific tension was improved twofold, while soleus was similar between groups. Resistance to contraction-induced injury was similar between groups; however, resistance to fatigue was increased 25% in catalase-treated soleus compared with control muscle. Six weeks following injection, extensor digitorum longus specific tension was increased 15%, while soleus specific tension was similar between treated and untreated limbs. Catalase overexpression reduced contraction-induced injury by 30-45% and fatigue by 20% compared with control limbs. Six months following injection, diaphragm specific tension was similar between groups, but resistance to contraction-induced injury was improved by 35% and fatigue by 25%. Taken together, these data indicate that catalase can improve a subset of parameters of muscle function in dystrophin-deficient skeletal muscle.

Protection of dystrophic muscle cells with polyphenols from green tea correlates with improved glutathione balance and increased expression of 67LR, a receptor for (-)-epigallocatechin gallate

Duchenne muscular dystrophy (DMD) is a fatal muscle wasting disease caused by the absence of the protein dystrophin. Because oxidative stress contributes to the pathogenesis of DMD, we investigated if a green tea polyphenol blend (GTP) and its major polyphenol (-)-epigallocatechin gallate (EGCg), could protect muscle cell primary cultures from oxidative damage induced by hydrogen peroxide (H(2)O(2)) in the widely used mdx mouse model. On-line fluorimetric measurements using an H(2)O(2)-sensitive probe indicated that GTP and EGCg scavenged peroxide in a concentration-dependent manner. A 48 h exposure to EGCg increased glutathione content but did not alter the expression of proteins involved in membrane stabilization and repair. Pretreatment of dystrophic cultures with GTP or EGCg 48 h before exposure to H(2)O(2) improved cell survival. Normal cultures were protected by GTP but not by EGCg. 67LR, a receptor for EGCg, was seven times more abundant in dystrophic compared with normal cultures. Altogether our results demonstrate that GTP and EGCg protect muscle cells by scavenging H(2)O(2) and by improving the glutathione balance. In addition, the higher levels of 67LR in dystrophic muscle cells compared with normal ones likely contribute to EGCg-mediated survival.

Lipid peroxidation inhibition blunts nuclear factor-kappaB activation, reduces skeletal muscle degeneration, and enhances muscle function in mdx mice

Duchenne muscular dystrophy (DMD) is a progressive muscle-wasting disease resulting from lack of the sarcolemmal protein dystrophin. However, the mechanism leading to the final disease status is not fully understood. Several lines of evidence suggest a role for nuclear factor (NF)-kappaB in muscle degeneration as well as regeneration in DMD patients and mdx mice. We investigated the effects of blocking NF-kappaB by inhibition of oxidative stress/lipid peroxidation on the dystrophic process in mdx mice. Five-week-old mdx mice received three times a week for 5 weeks either IRFI-042 (20 mg/kg), a strong antioxidant and lipid peroxidation inhibitor, or its vehicle. IRFI-042 treatment increased forelimb strength (+22%, P < 0.05) and strength normalized to weight (+23%, P < 0.05) and decreased fatigue (-45%, P < 0.05). It also reduced serum creatine kinase levels (P < 0.01) and reduced muscle-conjugated diene content and augmented muscle-reduced glutathione (P < 0.01). IRFI-042 blunted NF-kappaB DNA-binding activity and tumor necrosis factor-alpha expression in the dystrophic muscles (P < 0.01), reducing muscle necrosis (P < 0.01) and enhancing regeneration (P < 0.05). Our data suggest that oxidative stress/lipid peroxidation represents one of the mechanisms activating NF-kappaB and the consequent pathogenetic cascade in mdx muscles. Most importantly, these new findings may have clinical implications for the pharmacological treatment of patients with DMD.

Nuclear factor kappa-B blockade reduces skeletal muscle degeneration and enhances muscle function in Mdx mice

Duchenne muscular dystrophy (DMD) is a progressive muscle-wasting disease due to a mutation in the dystrophin gene and the consequential protein deficiency in muscle. How the lack of the sarcolemmal protein dystrophin gives rise to the final disease status is still not clear. Several evidences suggest a role of nuclear factor kappa-B (NF-kappaB), a pleiotropic transcription factor, in muscle degeneration and regeneration in DMD patients and mdx mice. We investigated the effects of NF-kappaB blocking by pyrrolidine dithiocarbamate (PDTC), a well-known NF-kappaB inhibitor, on dystrophic process in mdx mice. Five-week-old mdx and wild-type mice received three times a week for 5 weeks either PDTC (50 mg/kg) or its vehicle. PDTC treatment: (i) increased forelimb strength (+20%; P < 0.05) and strength normalized to weight (+24%; P < 0.05) and a decreased fatigue percentage (-61%; P < 0.05) in mdx mice, (ii) blunted the augmented NF-kappaB nuclear binding activity and the enhanced TNF-alpha expression in dystrophic muscles (P < 0.01), (iii) at a quantitative morphological evaluation of extensor digitorum longus (EDL) and biceps muscles, increased area with normal fibers (P < 0.05, in EDL), reduced muscle necrosis (P < 0.05 in biceps; P < 0.01 in EDL), and enhanced muscle regeneration (P < 0.01, in biceps). Our data support the hypothesis that NF-kappaB contributes to the perpetuation of the dystrophic damage and show that its blockade produces beneficial effects on functional, biochemical, and morphological parameters in mdx mice. Most importantly, these new findings may have clinical implications for the pharmacological treatment of patients with DMD.

Is midazolam effective as an antioxidant in preventing reperfusion injury in rat kidney?

This experimental study was designed to investigate whether midazolam has antioxidant effects in reperfused rat kidneys following ischemia. Twenty Wistar Albino rats were included in the study. Rats were anesthetized with the mixture of ketamine 90 mg/kg and xylazine 10 mg/kg administered intraperitoneally. Following anesthesia, the rats were divided into two groups. The first group was considered as the control group, whereas the second group received additional midazolam 3.5 mg/kg intraperitoneally. The left kidney was approached via a transabdominal incision and the left renal artery was dissected. Left renal ischemia was created by clamping the left renal artery for 45 minutes. Following the ischemia period, the kidney was reperfused for one hour. Both kidneys were then removed. Half of the left kidneys were immediately immersed in liquid nitrogen for transportation and then frozen at -70 C until measurements of tissue malondialdehyde (MDA) and glutathione (GSH) levels. The remaining halves of the left kidneys and right kidneys were fixed in 10% formalin. The changes which developed during the ischemia-reperfusion period in the left kidney were investigated by histopathological examination and compared with those of the normal contralateral kidney. When compared with the control group, tissue MDA and GSH levels were similar in the midazolam group (p > 0.05). Tubular damage with tubulitis and focal interstitial inflammatory infiltration were observed in histopathological examinations of reperfused left kidneys of the control group. There was PMNL infiltration only in perirenal fat tissue of the midazolam group. Right kidneys were histopathologically normal in both groups. We concluded that within this dosage midazolam does not have any antioxidant effect in reperfused rat kidneys following ischemia.

Oxidative stress and the pathogenesis of muscular dystrophies

The muscular dystrophies represent a diverse group of diseases differing in underlying genetic basis, age of onset, mode of inheritance, and severity of progression, but they share certain common pathologic features. Most prominent among these features is the necrotic degeneration of muscle fibers. Although the genetic basis of many of the dystrophies has been known for over a decade and new disease genes continue to be discovered, the pathogenetic mechanisms leading to muscle cell death in the dystrophies remain a mystery. This review focuses on the oxidative stress theory, which states that the final common pathway of muscle cell death in these diseases involves oxidative damage.

Green tea extract decreases muscle necrosis in mdx mice and protects against reactive oxygen species

BACKGROUND

Duchenne muscular dystrophy is a severe X-linked congenital disorder characterized by lethal muscle wasting caused by the absence of the structural protein dystrophin.

OBJECTIVE

Because generation of reactive oxygen species appears to play an important role in the pathogenesis of this disease, we tested whether antioxidant green tea extract could diminish muscle necrosis in the mdx mouse dystrophy model.

DESIGN

A diet supplemented with 0.01% or 0.05% green tea extract was fed to dams and neonates for 4 wk beginning on the day of birth. Muscle necrosis and regeneration were determined in stained cryosections of soleus and elongator digitorum longus muscles. Radical scavenging by green tea extract was determined in differentiated cultured C2C12 cells treated with tert-butylhydroperoxide, with the use of 2',7'-dichlorofluorescin diacetate as a radical detector.

RESULTS

This feeding regimen significantly and dose-dependently reduced necrosis in the fast-twitch muscle elongator digitorum longus but at the doses tested had no effect on the slow-twitch soleus muscle. Green tea extract concentration-dependently decreased oxidative stress induced by tert-butylhydroperoxide treatment of cultured mouse C2C12 myotubes. The lower effective dose tested in mdx mice corresponds to approximately equal to 1.4 L (7 cups) green tea/d in humans.

CONCLUSION

Green tea extract may improve muscle health by reducing or delaying necrosis in mdx mice by an antioxidant mechanism.

Effect of vitamin E and selenium on resistance to oxidative stress in chicken superficial pectoralis muscle

One-day-old chicks were reared using diets that differed in their vitamin E and/or selenium content. In chicks depleted of both selenium and vitamin E, signs of exudative diathesis on the superficial pectoralis muscle were observed. The purpose of this research was to determine the defective points of the antioxidant defense system, which made this tissue highly susceptible to nutritionally-induced oxidative stress. Vitamin E, and selenium in lower magnitude, were the factors that strikingly affected the course of mitochondrial lipid peroxidation. Animals fed diets deficient in vitamin E and selenium displayed the lowest reduced glutathione level and glutathione peroxidase activity. The decreased levels of reduced glutathione were not due to a defective activity of glutathione reductase, which was increased in both mitochondria and cytosol. The absence of vitamin E was linked to lowering of mitochondrial thiol levels. The Glutathione peroxidase/Cu,Zn-superoxide dismutase ratio was 2.8 in animals fed selenium and vitamin E, and decreased to 0.13 in animals deficient in both nutrients. This change was indicative of oxidant-induced damage mediated by hydrogen peroxide. Catalase activity increased in an attempt to counteract the decrease in glutathione peroxidase activity. The results obtained showed that alpha-tocopherol and Se deficiencies caused multiple alterations in the antioxidant system and adversely affected the redox state of chicken superficial pectoralis muscle.

Effects of iron deprivation on the pathology and stress protein expression in murine X-linked muscular dystrophy

Duchenne muscular dystrophy (DMD) is caused by dystrophin deficiency, which results in muscle necrosis and the upregulation of heat shock/stress proteins (HSP). We hypothesized that reactive oxygen species, and in particular hydroxyl radicals (.OH), participate in muscle necrosis and HSP expression. It was assumed that iron deprivation decreases .OH generation, restraining the disease process and reducing the oxidant-induced expression of HSP. The role of iron-catalyzed free radical reactions in the pathology of dystrophin-deficient muscle was evaluated in the murine model for Duchenne muscular dystrophy (mdx), by examining the effects of dietary deficiency and supplementation of iron on serum creatine kinase (CK), muscle morphology, lipid peroxidation and HSP levels in mice maintained on diets deficient in or supplemented with iron for 6 weeks. Iron-deprived mdx mice showed a significant decrease in the number of macrophage-invaded necrotic fibers and the expression of the 70-kDa heat shock protein (Hsp70). This suggests that the iron-dependent generation of .OH relates to muscle necrosis in the mdx mouse and modulates the expression of Hsp70 in vivo. In contrast, iron deprivation had no influence on other HSP or on lipid peroxidation in mdx mice, while maintenance on either diet caused a significant decrease in serum creatine kinase activity. The potential therapeutic effects of iron deprivation in mdx should be considered.

Oxidative damage to muscle protein in Duchenne muscular dystrophy

The hypothesis that reactive free radical species (ROS) may contribute to the pathogenesis of Duchenne muscular dystrophy (DMD) has been suggested previously, but experimental data obtained in support of the above have to date proved inconclusive. The recent discovery that nitric oxide synthase (required for muscle relaxation) is associated with the sarcolemmal protein dystrophin normally and that both proteins are absent in DMD has heightened interest in the potential role of ROS in this disorder. We therefore investigated oxidative damage to proteins in the quadriceps femoris muscle by quantifying protein carbonyl levels in six patients with DMD and six normal controls. In DMD, the mean protein carbonyl level in the quadriceps femoris muscle was increased by 211% (p < 0.005) compared with the normal control subjects. The data thus support the hypothesis for the role of ROS induced protein oxidation of muscle cell damage in DMD.

The role of free radicals in toxicity and disease

Free radicals are defined as atoms or molecules that contain one or more unpaired electrons. The toxicity of many xenobiotics is associated with the metabolic activation of foreign compounds to form free radicals or with the production of reactive oxygen species as superoxide anion, hydroxyl radicals or hydrogen peroxide which are responsible for the tissue damaging effects as lipid peroxidation, and DNA and protein damage. Oxidative stress associated with production of reactive oxygen species is believed to be involved not only in the toxicity of xenobiotics but also in the pathophysiology of aging, and various age-related diseases, including cataracts, atherosclerosis, neoplastic diseases, diabetes, diabetic retinopathy, chronic inflammatory diseases of the gastrointestinal tract, aging of skin, diseases associated with cartilage, Alzheimer's disease, and other neurologic disorders. The cellular sources of free radicals and reactive oxygen species, the biological targets of free radicals, and clinical conditions which are associated with free radical production and tissue damage are reviewed. In addition, potential therapeutic approaches to the prevention of free radical damage are considered. Free radical-induced injury can explain many clinical conditions.

Lazaroids enhance skeletal myogenesis in primary cultures of dystrophin-deficient mdx mice

Growing evidence suggests a role for free radicals in the degeneration of dystrophin-deficient muscle (as observed in Duchenne muscular dystrophy). We therefore decided to test the action of the lazaroid antioxidant compounds on primary skeletal muscle cell cultures derived from an animal model of Duchenne muscular dystrophy, the mdx mouse. Both vitamin E-derived U-83836E and glucocorticoid-derived U-74389F enhanced myogenesis of dystrophin-deficient cultures as determined by the number of myotubes, the amount of nicotinic acetylcholine receptor, skeletal muscle alpha-actin levels and myosin light chain. U-83836E enhanced myogenesis of control congenic C57BL/10 mouse-derived muscle cultures whereas U-74389F had no detectable effect. This enhanced myogenesis was in most respects similar to the one triggered by alpha-methylprednisolone which is the only drug known to be beneficial in Duchenne muscular dystrophy.

Potential oxyradical damage and energy status in individual muscle fibres from degenerating muscle diseases

Inherited degenerating muscle diseases result in disintegration of muscle fibres, which is initiated by a lack of or alteration to a muscle protein. In Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) the protein is known to be dystrophin. The cellular function of dystrophin is not known in any detail but its absence appears to lead to a weakening of the sarcolemma. It has been proposed by Murphy and Kehrer that this leads ultimately to increased oxyradical production which may accelerate the degeneration. Studies have been carried out on individual muscle fibres derived from biopsy samples from patients with a number of degenerative muscle diseases. The glutathione cycling components, in particular glutathione and glutathione peroxidase, are significantly elevated in DMD, BMD and other diseases. Glutathione reductase is also elevated in some of these diseases. Energy producing systems are also affected particularly in intact fibres of muscle derived from muscle at an advanced stage of the disease. These results suggest that oxyradical damage may occur as a secondary consequence of muscle degenerating disease, leading to a breakdown in the glycogenolytic energy producing system.

The pentose phosphate pathway in skeletal muscle under patho-physiological conditions. A combined histochemical and biochemical study

Over the last 30 years, research into the neuromuscular apparatus, has expanded greatly. Multidisciplinary investigations have rapidly advanced our understanding both of diseases and of the basic neuromuscular mechanisms. The mode of pathological reaction of the neuromuscular apparatus is now quite well understood. The most notable aspect of the reaction of the injured neuromuscular apparatus is the remarkably stereotyped character of the resulting pathological changes as demonstrated by a wide variety of harmful causes, producing surprisingly similar effects. The findings of our combined histochemical and biochemical investigations presented in this monograph, are in complete harmony with the stereotyped character of the pathological changes. For example, it is particularly striking that many affected muscle fibres of patients with muscular dystrophies, congenital myopathies, inflammatory myopathies, metabolic myopathies, endocrine myopathies, or with diseases of the lower motor neuron, display an enhanced activity of both oxidative enzymes of the pentose phosphate pathway. Likewise, we found that experimental animals with disordered skeletal muscles, provoked by different types of agents or treatments, reveal the same marked rise in activity of GPDH and PGDH in the muscle fibres, with a positive correlation between the activity of both enzymes. Other findings of our investigations point to a positive correlation between the activity of GPDH and PGDH on the one hand and that of the non-oxidative enzymes of the pentose phosphate pathway, the enzymes TA, TK, RPI and RPE on the other hand. The rise in activity of PGDH and, in particular, of GPDH is regulated by two different mechanisms. The first represents a rapid control mechanism based on the stimulation of both oxidative enzymes of the pentose phosphate pathway by NADP+ and on their inhibition by NADPH. The other mechanism represents a long-term effect directed at the synthesis of the enzymes. It is this type of mechanism which is responsible for the rise in activity of GPDH and PGDH we observed. The findings obtained with the applied enzyme histochemical techniques clearly demonstrated that the rise in activity of both enzymes is not homogeneously distributed in the disordered skeletal muscles of man and experimental animals. For that reason, in order to obtain reliable quantitative information about enzyme activities in the muscle fibres themselves, the application of biochemical assays on a micro-scale was indispensable. The biochemical assay of enzyme activities was performed on histologically and histochemically selected dissected muscle specimens.(ABSTRACT TRUNCATED AT 400 WORDS)

The pathological damage in Duchenne muscular dystrophy may be due to increased intracellular OXY-radical generation caused by the absence of dystrophin and subsequent alterations in Ca2+ metabolism

Recent advances in the genetic and molecular pathogenesis of Duchenne muscular dystrophy and the evidence suggesting a role for oxygen free radicals (oxy-radicals) in the development of this disease are reviewed. In addition, we outline a working of hypothesis as to how disruptions in intracellular Ca2+ homeostasis within the dystrophic cell may initiate cycles of increased oxy-radical fluxes within these cells, leading to intracellular oxidative damage.

Elevated activity of several antioxidant enzymes in neuromuscular diseases. A histochemical and biochemical study

In the present study the activity of glucose-6-phosphate dehydrogenase, phosphogluconate dehydrogenase, glutathione peroxidase, glutathione reductase, superoxide dismutase and catalase was measured in dissected specimens from muscle biopsies of patients with various neuromuscular diseases and from controls. The biopsy specimens investigated were selected by means of histological and enzyme histochemical staining methods. Specimens were used which contained muscle fibres with a high or low activity of glucose-6-phosphate dehydrogenase and phosphogluconate dehydrogenase and which were free from inflammatory infiltrates. A rise in activity of glucose-6-phosphate dehydrogenase in pathologically changed muscle fibres was always found to be coupled with a significant rise in activity of phosphogluconate dehydrogenase, glutathione peroxidase and glutathione reductase. In these muscle fibres the activity of superoxide dismutase and catalase was not significantly changed. On the basis of the histochemical and biochemical findings it is concluded that the application of the histochemical method for the demonstration of glucose-6-phosphate dehydrogenase activity can be highly recommended for the study of antioxidant enzymes in skeletal muscles with neuromuscular diseases.

Monocyte function in chickens with hereditary muscular dystrophy

Monocyte functions of Storrs strain muscular dystrophic (MD) chickens and Storrs control strain were compared. After short-term in vitro culture of monocytes, cells taken from Storrs MD chickens had a significantly lower incidence of cells capable of phagocytizing sheep red blood cells than did cells cultured from the control strain. In contrast, no difference was found in the ability of MD vs. control strain blood mononuclear cells to undergo in vitro chemotaxis in response to a bacterial culture supernatant. The study also revealed a distinct peripheral blood leukocyte profile of young MD chickens: elevated percentages and absolute numbers of granulocytes. The total leukocyte count in MD chickens was not significantly different from that of normal chickens. These findings extend previous observations concerning altered reticuloendothelial system function in MD strain chickens.

Oxidative stress and muscular dystrophy

Oxidative stress may be the fundamental basis of many of the structural, functional and biochemical changes characteristic of the inherited muscular dystrophies in animals and humans. The presence of by-products of oxidative damage, and the compensatory increases in cellular antioxidants, both indicate oxidative stress may be occurring in dystrophic muscle. Changes in the proportions and metabolism of cellular lipids, abnormal functions of cellular membranes, altered activity of membrane-bound enzymes such as the SR Ca2+-ATPase, disturbances in cellular protein turnover and energy production and a variety of other changes all indicate that these inherited muscular dystrophies appear more like the results of oxidative stress to muscle than any other type of underlying muscle disturbance. Particular details of these altered characteristics of dystrophic muscle, in combination with current knowledge on the processes of oxidative damage to cells, may provide some insight into the underlying biochemical defect responsible for the disease, as well as direct research towards the ultimate goal of an effective treatment.

Active oxygen in neuromuscular disorders

Although muscle and nerve are reasonably well protected against active oxygen and related free radicals, environmental or inherited malfunctions can overpower their defences. Active oxygen is involved in many neuropathies and myopathies. In every case the damage is caused by agents which exert effects disproportionately greater than the quantities encountered, through a variety of amplification mechanisms. We can categorize these amplification mechanisms as follows: (a) non-replacement of targets (e.g. loss of genetic information, ataxia telangectasia being an hereditary ataxia in which an oxygen mediated chromosomal instability is apparent), (b) non-removal of unwanted materials (e.g. lipofuscin accumulation in brain and heart), (c) redox cycling, usually involving catalysis by trace-metal ions (e.g. some forms of Parkinsonism), (d) non-redox catalysis (e.g. toxicity in cardiac muscle or brain due to vanadium or aluminium respectively), (e) modification of ion transport (e.g. calcium ionophore or acrylamide induce histopathological changes in muscle, similar in some respects to those seen in Duchenne muscular dystrophy), (f) compromised defences (e.g. muscle and nerve become particularly susceptible to free radical damage after loss of the protective actions of vitamin E), and (g) amplification by inflammatory and immune responses (e.g. multiple sclerosis, reperfusion injury to brain and heart, and traumatic injury to nervous tissue). Unfortunately, a variety of therapeutic agents which might be expected to protect against almost every conceivable form of oxygen mediated damage have proved clinically ineffective in most of these disorders. The reasons for this will be explored with an emphasis on common features, differences, mechanisms, and potential therapeutic approaches.

Oxygen-derived free radicals in cerulein-induced acute pancreatitis

Conscious rats were treated with a supramaximal dose of 5.10(-6)g.kg-1.h-1 of cerulein for periods of 3 and 12 h. In both groups of animals typical features of acute oedematous pancreatitis were proved by biochemical and histologic examinations. The most important finding of our study was the decrease of superoxide dismutase (SOD) activity in pancreatic tissue, accompanied by a slight increase of this scavenger enzyme in serum of rats stimulated with cerulein during 3 h. Parallelly, evident elevation of malondialdehyde (MDA) concentration in pancreatic tissue was noted. After the 12-h infusion of cerulein we were not able to detect any SOD activity in pancreatic tissue, whereas this activity appeared in ascitic fluid of tested animals. Further increase of MDA concentration in pancreatic tissue, in comparison with 3-h pancreatitis, was found. These data suggest that in 3-h and 12-h cerulein-induced pancreatitis the oxygen-derived free radicals mediate the increased lipid peroxidation in pancreatic tissue. We think that the depletion of the scavenger enzyme SOD may be responsible for such a disturbance of lipid metabolism.

Micromethods in single muscle fibers. 2. Determination of glutathione reductase and glutathione peroxidase

This paper extends the previous study for systems which control intracellular oxidative events in muscle and describes procedures suitable to assay glutathione peroxidase (GSHPx), glutathione reductase (GR), and total glutathione (GSH + GSSG) after fiber typing of individual muscle fibers. In human skeletal muscle, both GR and GSHPx activities were relatively low when compared to those of other tissue. No difference was found among fiber types (I, IIA, and IIB) with regard to GR activity, but in contrast GSHPx activity was significantly lower in type IIB fibers than in the other types. These results suggest that type IIB fibers may have a reduced ability to cope with hydroperoxides generated during oxidative stress, which, in turn, could lead to increased damage to membrane structures by lipid peroxidation or oxidation of sensitive intracellular thiol (-SH) enzymes by hydrogen peroxide. The Km of skeletal muscle GR for GSSG was 27 microM and for NADPH was 22 microM. If one assumes approximately 95% of total glutathione is present in the reduced state, then GSSG concentration would be of the order of 0.3 mmol/kg and under these conditions skeletal muscle GR would be efficient in all muscle fiber types.

Micromethods in single muscle fibers. 1. Determination of catalase and superoxide dismutase

Methods have been developed for the measurements of catalase and superoxide dismutase (SOD) in single, isolated muscle fibers. These fibers are also classified according to fiber type. Catalase is determined using a fluorescent method for the measurement of hydrogen peroxide consumed. SOD measurements are carried out using a modification of established techniques whereby the inhibition of oxidation of epinephrine by SOD is assayed fluorometrically. Both enzymes may be determined in submicrogram samples of dried muscle. This approach avoids the complication of the inclusion of nonmuscle tissue with varying enzymatic activities which is frequently experienced when using homogenates of muscle, particularly diseased muscle. In addition, these techniques can be used to determine the inherent variation in SOD and catalase activities within individual fibers of the same fiber type. The Km and Vmax for catalase, determined using homogenates of human muscle, were found to be 12 mM and 1.45 mumol/min/mg dry wt, respectively. Catalase of muscle was inhibited 50% by 2 microM sodium azide. Mn-SOD contributes less than one-fifth of the total SOD activity. Therefore the activity is largely due to the Cu-Zn form of SOD. These methods are applicable to a wide variety of tissues.

Free radical mechanisms in the central nervous system: an overview

Free radicals are highly toxic compounds which can react with a number of molecules such as glycoproteins or amino acids. These reactions can lead to the denaturation of proteins, destabilization of cellular membrane and eventually, cell death. Free radicals have been recently implicated in the pathogenesis and clinical course of a number of neuropsychiatric disorders including aging of the central nervous system (CNS), schizophrenia, and the development of tardive dyskinesia during chronic use of neuroleptics. This paper provides an overview of the nature of free radicals and discusses briefly their participation in the toxicity associated with catecholamines in the CNS.