Evidence of apoptosis in chronic alcoholic skeletal myopathy

Alcoholism: A systemic proinflammatory condition

Excessive ethanol consumption affects virtually any organ, both by indirect and direct mechanisms. Considerable research in the last two decades has widened the knowledge about the paramount importance of proinflammatory cytokines and oxidative damage in the pathogenesis of many of the systemic manifestations of alcoholism. These cytokines derive primarily from activated Kupffer cells exposed to Gram-negative intestinal bacteria, which reach the liver in supra-physiological amounts due to ethanol-mediated increased gut permeability. Reactive oxygen species (ROS) that enhance the inflammatory response are generated both by activation of Kupffer cells and by the direct metabolic effects of ethanol. The effects of this increased cytokine secretion and ROS generation lie far beyond liver damage. In addition to the classic consequences of endotoxemia associated with liver cirrhosis that were described several decades ago, important research in the last ten years has shown that cytokines may also induce damage in remote organs such as brain, bone, muscle, heart, lung, gonads, peripheral nerve, and pancreas. These effects are even seen in alcoholics without significant liver disease. Therefore, alcoholism can be viewed as an inflammatory condition, a concept which opens the possibility of using new therapeutic weapons to treat some of the complications of this devastating and frequent disease. In this review we examine some of the most outstanding consequences of the altered cytokine regulation that occurs in alcoholics in organs other than the liver.

Autophagy in alcohol-induced multiorgan injury: mechanisms and potential therapeutic targets

Autophagy is a genetically programmed, evolutionarily conserved intracellular degradation pathway involved in the trafficking of long-lived proteins and cellular organelles to the lysosome for degradation to maintain cellular homeostasis. Alcohol consumption leads to injury in various tissues and organs including liver, pancreas, heart, brain, and muscle. Emerging evidence suggests that autophagy is involved in alcohol-induced tissue injury. Autophagy serves as a cellular protective mechanism against alcohol-induced tissue injury in most tissues but could be detrimental in heart and muscle. This review summarizes current knowledge about the role of autophagy in alcohol-induced injury in different tissues/organs and its potential molecular mechanisms as well as possible therapeutic targets based on modulation of autophagy.

Neurologic complications of alcoholism

PURPOSE OF REVIEW

This review serves as an overview of neurologic conditions associated with alcohol abuse or withdrawal, including epidemiology, clinical symptoms, diagnostic approach, and treatment.

RECENT FINDINGS

Frequent alcohol abuse and frank alcoholism are very common among adults in the United States. Although rates decline with each decade, as many as 10% of the elderly drink excessively. Given the ubiquitous nature of alcoholism in society, its complications have been clinically recognized for generations, with recent advances focusing on improved understanding of ethanol's biochemical targets and the pathophysiology of its complications.

SUMMARY

The chronic effects of alcohol abuse are myriad and include neurologic complications through both direct and indirect effects on the central and peripheral nervous systems. These disorders include several encephalopathic states related to alcohol intoxication, withdrawal, and related nutritional deficiencies; acute and chronic toxic and nutritional peripheral neuropathies; and myopathy. Although prevention of alcoholism and its neurologic complications is the optimal strategy, this article reviews the specific treatment algorithms for alcohol withdrawal and its related nutritional deficiency states.

Chronic alcohol ingestion delays skeletal muscle regeneration following injury

Background

Chronic alcohol ingestion may cause severe biochemical and pathophysiological derangements to skeletal muscle. Unfortunately, these alcohol-induced events may also prime skeletal muscle for worsened, delayed, or possibly incomplete repair following acute injury. As alcoholics may be at increased risk for skeletal muscle injury, our goals were to identify the effects of chronic alcohol ingestion on components of skeletal muscle regeneration. To accomplish this, age- and gender-matched C57Bl/6 mice were provided normal drinking water or water that contained 20% alcohol (v/v) for 18–20 wk. Subgroups of mice were injected with a 1.2% barium chloride (BaCl₂) solution into the tibialis anterior (TA) muscle to initiate degeneration and regeneration processes. Body weights and voluntary wheel running distances were recorded during the course of recovery. Muscles were harvested at 2, 7 or 14 days post-injection and assessed for markers of inflammation and oxidant stress, fiber cross-sectional areas, levels of growth and fibrotic factors, and fibrosis.

Results

Body weights of injured, alcohol-fed mice were reduced during the first week of recovery. These mice also ran significantly shorter distances over the two weeks following injury compared to uninjured, alcoholics. Injured TA muscles from alcohol-fed mice had increased TNFα and IL6 gene levels compared to controls 2 days after injury. Total protein oxidant stress and alterations to glutathione homeostasis were also evident at 7 and 14 days after injury. Ciliary neurotrophic factor (CNTF) induction was delayed in injured muscles from alcohol-fed mice which may explain, in part, why fiber cross-sectional area failed to normalize 14 days following injury. Gene levels of TGFβ₁ were induced early following injury before normalizing in muscle from alcohol-fed mice compared to controls. However, TGFβ₁ protein content was consistently elevated in injured muscle regardless of diet. Fibrosis was increased in injured, muscle from alcohol-fed mice at 7 and 14 days of recovery compared to injured controls.

Conclusions

Chronic alcohol ingestion appears to delay the normal regenerative response following significant skeletal muscle injury. This is evidenced by reduced cross-sectional areas of regenerated fibers, increased fibrosis, and altered temporal expression of well-described growth and fibrotic factors.

Notch pathway activation contributes to inhibition of C2C12 myoblast differentiation by ethanol

The loss of muscle mass in alcoholic myopathy may reflect alcohol inhibition of myogenic cell differentiation into myotubes. Here, using a high content imaging system we show that ethanol inhibits C2C12 myoblast differentiation by reducing myogenic fusion, creating smaller and less complex myotubes compared with controls. Ethanol administration during C2C12 differentiation reduced MyoD and myogenin expression, and microarray analysis identified ethanol activation of the Notch signaling pathway target genes Hes1 and Hey1. A reporter plasmid regulated by the Hes1 proximal promoter was activated by alcohol treatment in C2C12 cells. Treatment of differentiating C2C12 cells with a gamma secretase inhibitor (GSI) abrogated induction of Hes1. On a morphological level GSI treatment completely rescued myogenic fusion defects and partially restored other myotube parameters in response to alcohol. We conclude that alcohol inhibits C2C12 myoblast differentiation and the inhibition of myogenic fusion is mediated by Notch pathway activation.

Spontaneous and in vitro induced apoptosis of lymphocytes and neutrophils in patients with alcohol dependence

Spontaneous and induced apoptosis of neutrophils and lymphocytes was studied in alcoholics during the abstinent syndrome and in healthy individuals. In alcoholics, the levels of lymphocyte and neutrophil apoptosis at the receptor and cellular levels were higher than in healthy subjects. Blood cells from alcohol addicts and normal individuals similarly react to stimuli (hyperthermia and synthetic glucocorticoid prednisolone) in vitro.

The effect of ethanol intake on tendon healing: a histological and biomechanical study in a rat model

INTRODUCTION

Ethanol has a suppressive effect on inflammation and the immune system, but the effect of ethanol on tendon healing in vivo has not been studied. The purpose of this study was to investigate the histological and biomechanical effects of ethanol intake on tendon healing in a rat tendon injury model.

MATERIALS AND METHODS

Forty-seven rats were randomly assigned to either ethanol or control groups. Progressively increasing concentrations of ethanol combined with glucose were administered to these rats in their drinking water. After 1 week, the Achilles tendon of each rat was injured proximal to its insertion on the calcaneus. All rats were euthanized at 4 weeks. The tendons were evaluated both histologically and biomechanically. The histologic examination of these tendons was done using a semi-quantitative 4-point scale to rate cell morphology, the degree of ground substance staining, collagen organization, and vascular changes. Load to failure (N) strength was obtained with biomechanical testing.

RESULTS

Tendon failure loads were lower in the ethanol group (31.6 +/- 8.8 N) than in the control group (39.7 +/- 8.2 N) (P = 0.04). Histologic tenocyte scores were higher in the ethanol group (1.90 +/- 0.73) than the control group (0.9 +/- 0.73) (P = 0.01).

CONCLUSION

Ethanol ingestion resulted in abnormal tenocyte morphology, disorganized collagen bundles with a tendency toward increased tenocyte number, and neovascularization 3 weeks after the tendon injury indicating delayed and abnormal healing. The healing tendons in the alcohol treated group failed at statistically lower loads than the control group.

Procysteine stimulates expression of key anabolic factors and reduces plantaris atrophy in alcohol-fed rats

BACKGROUND

Long-term alcohol ingestion may produce severe oxidant stress and lead to skeletal muscle dysfunction. Emerging evidence has suggested that members of the interleukin-6 (IL-6) family of cytokines play diverse roles in the regulation of skeletal muscle mass. Thus, our goals were (i) to minimize the degree of oxidant stress and attenuate atrophy by supplementing the diets of alcohol-fed rats with the glutathione precursor, procysteine, and (ii) to identify the roles of IL-6 family members in alcoholic myopathy.

METHODS

Age- and gender-matched Sprague-Dawley rats were fed the Lieber-DeCarli liquid diet containing either alcohol or an isocaloric substitution (control diet) for 35 weeks. Subgroups of alcohol-fed rats received procysteine (0.35%, w/v) for the final 12 weeks. Plantaris morphology was assessed by hematoxylin and eosin staining. Major components of glutathione metabolism were determined using assay kits. Real-time PCR was used to determine expression levels of several genes.

RESULTS

Plantaris muscles from alcohol-fed rats displayed extensive atrophy, as well as decreased glutathione levels, decreased activities of glutathione reductase and glutathione peroxidase, decreased superoxide dismutase (SOD)-2 (Mn-SOD2), and increased NADPH oxidase-1 gene expression-each indicative of significant oxidant stress. Alcohol also induced gene expression of catabolic factors including IL-6, oncostatin M, atrogin-1, muscle ring finger protein-1, and IGFBP-1. Procysteine treatment attenuated plantaris atrophy, restored glutathione levels, and increased catalase, Cu/Zn-SOD1, and Mn-SOD2 mRNA expression, but did not reduce other markers of oxidant stress or levels of these catabolic factors. Instead, procysteine stimulated gene expression of anabolic factors such as insulin-like growth factor-1, ciliary neurotrophic factor, and cardiotrophin-1.

CONCLUSIONS

Procysteine significantly attenuated, but did not completely abrogate, alcohol-induced oxidant stress or catabolic factors. Rather, procysteine minimized the extent of plantaris atrophy by inducing components of several anabolic pathways. Therefore, anti-oxidant treatments such as procysteine supplementation may benefit individuals with alcoholic myopathy.

Molecular and cellular events in alcohol-induced muscle disease

Alcohol consumption induces a dose-dependent noxious effect on skeletal muscle, leading to progressive functional and structural damage of myocytes, with concomitant reductions in lean body mass. Nearly half of high-dose chronic alcohol consumers develop alcoholic skeletal myopathy. The pathogenic mechanisms that lie between alcohol intake and loss of muscle tissue involve multiple pathways, making the elucidation of the disease somewhat difficult. This review discusses the recent advances in basic and clinical research on the molecular and cellular events involved in the development of alcohol-induced muscle disease. The main areas of recent research interest on this field are as follows: (i) molecular mechanisms in alcohol exposed muscle in the rat model; (ii) gene expression changes in alcohol exposed muscle; (iii) the role of trace elements and oxidative stress in alcoholic myopathy; and (iv) the role of apoptosis and preapoptotic pathways in alcoholic myopathy. These aforementioned areas are crucial in understanding the pathogenesis of this disease. For example, there is overwhelming evidence that both chronic alcohol ingestion and acute alcohol intoxication impair the rate of protein synthesis of myofibrillar proteins, in particular, under both postabsorptive and postprandial conditions. Perturbations in gene expression are contributory factors to the development of alcoholic myopathy, as ethanol-induced alterations are detected in over 400 genes and the protein profile (i.e., the proteome) of muscle is also affected. There is supportive evidence that oxidative damage is involved in the pathogenesis of alcoholic myopathy. Increased lipid peroxidation is related to muscle fibre atrophy, and reduced serum levels of some antioxidants may be related to loss of muscle mass and muscle strength. Finally, ethanol induces skeletal muscle apoptosis and increases both pro- and antiapoptotic regulatory mechanisms.

Oxidant-induced atrogin-1 and transforming growth factor-beta1 precede alcohol-related myopathy in rats

Alcohol-related chronic myopathy is characterized by severe biochemical and structural changes to skeletal muscle. Our goals were to: (1) identify early regulatory elements that precede the overt manifestation of plantaris atrophy; and (2) circumvent these derangements by supplementing alcohol-fed rats with the glutathione precursor, procysteine. After 6 weeks of daily ingestion, before the development of overt atrophy of the plantaris muscle, alcohol increased several markers of oxidative stress and increased gene expressions of atrogin-1 and transforming growth factor-beta1 (TGF-beta1) by approximately 60- and approximately 65-fold, respectively, which were attenuated by procysteine supplementation. Interestingly, after 28 weeks of alcohol ingestion, when overt plantaris atrophy had developed, atrogin-1 and TGF-beta1 gene expression had returned to baseline levels. Together, these findings suggest that alcohol-induced, redox-sensitive alterations drive pro-atrophy signaling pathways that precede muscle atrophy. Therefore, targeted anti-oxidant treatments such as procysteine supplementation may benefit individuals with chronic alcohol abuse, particularly if given prior to the development of clinically significant myopathy.

The total body mass of fatty acid ethyl esters in skeletal muscles following ethanol exposure greatly exceeds that found in the liver and the heart

AIMS

Skeletal muscle appears to be susceptible to chronic and acute excess alcohol intake, giving rise to alcoholic myopathy, a common disease among alcoholics. Fatty acid ethyl esters (FAEE), non-oxidative metabolites of ethanol, have been shown to be toxic to cells in vitro and in vivo. We hypothesized that accumulation of FAEE in skeletal muscle could contribute to the development of alcoholic myopathy.

METHODS

Male wistar rats were treated either with 75 mmol ethanol/kg body weight or saline, in the fed state or starved for 1 or 2 days before administration. Rats were thus divided into the following groups: fed-saline (n = 8); fed-ethanol (n = 8); starved 1 day, saline (n = 8); starved 1 day, ethanol (n = 9); starved 2 days, saline (n = 7); and starved 2 days, ethanol (n = 8). At the end of the incubation, skeletal muscles (abdominal and gastrocnemius), liver, and heart were isolated and processed for FAEE isolation and analysis by gas chromatography-mass spectrometry (GC-MS).

RESULTS

Total mass of FAEE in the muscles was much greater than that found in the liver and the heart. In general, the animals that were fasted for 1 day and received ethanol had the highest FAEE levels among the three groups of animals. The major ethyl ester species in all cases were ethyl 16:0, ethyl 18:0, ethyl 18:1 n-9, and ethyl 18:2 n-6. Ethyl 20:4 n-6 and ethyl 22:6 n-3 were also present, except in the fasted 1-day group, where ethyl 22:6 disappeared, though it reappeared in the fasted 2-day group.

CONCLUSION

These findings demonstrate that skeletal muscles contain high levels of FAEE that are synthesized in the body after ethanol exposure. The concentration of FAEE in skeletal muscle in this study was very similar to FAEE concentration in the liver. This differs from previous studies suggesting a low concentration of skeletal muscle FAEE with ethanol exposure.

Activation of mitochondrial-driven apoptosis in skeletal muscle cells is not mediated by reactive oxygen species production

While the acquisition of apoptosis resistance is part of the differentiation program of skeletal muscle cells, differentiated muscle cells can undergo apoptosis in response to physiological or pathological stimuli. The generation of reactive oxygen species by mitochondria plays a major role in the control of apoptosis in many cell types. Indeed their involvement in controlling apoptosis in differentiated muscle cells, or in generating resistance to apoptosis remains unknown. Moreover, differentiated muscle cells specifically express the uncoupling protein-3, a mitochondrial protein potentially involved in controlling reactive oxygen species production. To study the role of mitochondrial reactive oxygen species in the control of apoptosis in skeletal muscle cells, L6E9 myoblasts and myotubes were exposed to staurosporine, an inducer of apoptosis via mitochondrial pathways. Staurosporine activated apoptotic pathways (i.e. caspase-3 and caspase-9) increasing reactive oxygen species in myoblasts and, to a minor extent, in myotubes. However, the increase in reactive oxygen species was not needed to induce apoptosis nor was it involved in the differential sensitization of myoblasts and myotubes to apoptosis. Moreover, expression of uncoupling protein-3 in myotubes did not affect reactive oxygen species production, although it produced a slight sensitization for staurosporine-induced apoptosis. Results indicate that apoptotic activation in skeletal muscle cells mainly involves reactive oxygen species-independent mechanisms and that mitochondrial uncoupling protein-3 is not protective either for reactive oxygen species production or for apoptotic activation in muscle cells.

Alcoholic myopathy: lack of effect of zinc supplementation

A chronic form of myopathy has been described in alcoholics, characterized by atrophy of type II fibers, due both to reduced protein synthesis and increased protein breakdown. Increased production of reactive oxygen species could probably play a role in increased protein breakdown. In addition, treatment with zinc might be beneficial, since it acts as a cofactor of several enzymes involved in the synthesis of proteins and antioxidants as copper-zinc-superoxidedismutase (SOD) and selenium dependent glutathione peroxidase (GPX). Based on these facts, we analyze the relative and combined effects of ethanol, protein malnutrition and treatment with zinc, 227 mg/l in form of zinc sulphate, on muscle changes in 8 groups of adult Sprague-Dawley rats fed following the Lieber-de Carli model during 5 weeks. We also study the association between muscle histological changes and the activity of GPX, SOD and lipid peroxidation products (MDA), with hormones such as IGF-1, and with trace elements involved in antioxidant systems and/or in lipid peroxidation, such as selenium, copper, zinc, and iron. We found type IIa and IIb fiber atrophy in the alcoholic animals, especially in the low-protein fed ones. This effect was mainly due to protein deficiency. Zinc played no role at all. Muscle iron increased in ethanol, low protein fed rats, either with or without zinc, and was directly related with muscle MDA levels, which in turn were related with muscle atrophy, as was also found for serum IGF-1 levels. Ethanol was the main responsible for all these changes, although protein undernutrition also played an independent role in MDA levels. A positive interaction between ethanol and protein deficiency on serum IGF-1 was also detected. These results suggest that both protein deficiency and ethanol contribute to muscle atrophy observed in alcoholized rats; this atrophy is associated with increased lipid peroxidation and muscle iron overload. Treatment with zinc sulphate confers no benefit.

Short communication: HIV infection, antiretrovirals, and apoptosis: studies on skeletal muscle

Increased apoptosis in CD4+ T lymphocytes plays an important role in the pathogenesis of HIV infection and it has also invoked some HIV-related as well as antiretroviral-related adverse events. We assessed whether increased apoptosis is also present in the skeletal muscle of HIV-infected patients. We included 36 consecutive individuals, 18 without (group A) and 18 with HIV infection. The latter group consisted of five asymptomatic antiretroviral-naive HIV-infected individuals (group B), six asymptomatic HIV-infected individuals on highly active antiretroviral therapy (HAART, group C), and seven HIV-infected individuals on HAART with lipodystrophy (group D). Immunohistochemical reaction using deoxyribonucleotidyltransferase-mediated- dUTP-biotin nick-end labeling (TUNEL) was performed on skeletal muscle samples. None of the uninfected patients (group A) showed data of increased apoptosis, while 16 out of 18 infected patients did (p < 0.001). All subgroups of infected subjects (groups B-D) showed a significant increase of apoptosis in TUNEL with respect to uninfected individuals, but the comparison between the different subgroups of infected patients did not reveal significant differences. We conclude that skeletal muscle of HIV-infected patients exhibits increased apoptosis compared with that of uninfected patients, but the role of HAART in inducing apoptosis remains to be established.

Effects of alcohol on skeletal and cardiac muscle

The acute and chronic toxic effects of alcohol on skeletal and cardiac muscle are clinically important. Muscle weakness and atrophy are the main manifestations of skeletal myopathy, and arrhythmias and progressive left-ventricular dysfunction are those of cardiomyopathy. Most patients remain asymptomatic from these effects for a long time. Myocyte atrophy and death are the main pathological findings. A clear dose-related effect has been established with ethanol consumption, with gender and some specific gene polymorphisms being factors of increased susceptibility to alcohol-induced muscle damage. Pathogenic mechanisms are pleiotropic, the most relevant being disturbances in carbohydrate, protein, and energy cell turnover, signal transduction, and induction of apoptosis and gene dysregulation. Ethanol abstinence is the only effective treatment, although controlled drinking is useful in patients who do not achieve abstinence. Persistent high-dose consumption results in deterioration of muscle and heart function, with a high mortality due to arrhythmias and progression of heart failure.

Muscle-fiber apoptosis in neuromuscular diseases

Muscle-fiber loss is a characteristic of many progressive neuromuscular disorders. Over the past decade, identification of a growing number of apoptosis-associated factors and events in pathological skeletal muscle provided increasing evidence that apoptotic cell-death mechanisms account significantly for muscle-fiber atrophy and loss in a wide spectrum of neuromuscular disorders. It became obvious that there is not one specific pathway for muscle fibers to undergo apoptotic degradation. In contrast, certain neuromuscular diseases seem to involve characteristic expression patterns of apoptosis-related factors and pathways. Furthermore, there are some characteristics of muscle-fiber apoptosis that rely on the muscle fiber itself as an extremely specified cell type. Multinucleated muscle fibers with successive muscle-fiber segments controlled by individual nuclei display some specifics different from apoptosis of mononucleated cells. This review focuses on the expression patterns of apoptosis-associated factors in different primary and secondary neuromuscular disorders and gives a synopsis of current knowledge.