Significance of type II fiber atrophy in chronic alcoholic myopathy

Alcohol Alters Skeletal Muscle Bioenergetic Function: A Scoping Review

Bioenergetic pathways uniquely support sarcomere function which, in turn, helps to maintain functional skeletal muscle (SKM) mass. Emerging evidence supports alcohol (EtOH)-induced bioenergetic impairments in SKM and muscle precursor cells. We performed a scoping review to synthesize existing evidence regarding the effects of EtOH on SKM bioenergetics. Eligible articles from six databases were identified, and titles, abstracts, and full texts for potentially relevant articles were screened against inclusion criteria. Through the search, we identified 555 unique articles, and 21 met inclusion criteria. Three studies investigated EtOH effects on the adenosine triphosphate (ATP)-phosphocreatine (PCr) system, twelve investigated EtOH effects on glycolytic metabolism, and seventeen investigated EtOH effects on mitochondrial metabolism. Despite increased ATP-PCr system reliance, EtOH led to an overall decrease in bioenergetic function through decreased expression and activity of glycolytic and mitochondrial pathway components. However, effects varied depending on the EtOH dose and duration, model system, and sample type. The results detail the EtOH-induced shifts in energy metabolism, which may adversely affect sarcomere function and contribute to myopathy. These findings should be used to develop targeted interventions that improve SKM bioenergetic function, and thus sarcomere function, in people with Alcohol Use Disorder (AUD). Key areas in need of further investigation are also identified.

Alcohol and Skeletal Muscle in Health and Disease

PURPOSE

Alcohol-related myopathy is one of the earliest alcohol-associated pathological tissue changes that is progressively exacerbated by cumulative long-term alcohol misuse. Acute and chronic alcohol use leads to changes in skeletal muscle mass and function. As discussed in this evidence-based review, alcohol-mediated mechanisms are multifactorial with effects on anabolic and catabolic signaling, mitochondrial bioenergetics, extracellular matrix remodeling, and epigenomic alterations. However, systematic studies are limited, especially regarding the acute effects of alcohol on skeletal muscle.

SEARCH METHODS

This review focuses on peer-reviewed manuscripts published between January 2012 and November 2022 using the search terms "alcohol" or "ethanol" and "skeletal muscle" in MEDLINE, PubMed, and Web of Science using EndNote reference management software.

SEARCH RESULTS

Eligible manuscripts included full-length research papers that discussed acute and chronic effects of alcohol on skeletal muscle mass and function in both clinical and preclinical studies. The review also includes alcohol-mediated skeletal muscle effects in the context of comorbidities. The three databases together yielded 708 manuscripts. Of these, the authors excluded from this review 548 papers that did not have "alcohol" or "muscle" in the title and 64 papers that were duplicates or did not discuss skeletal muscle. Thus, of all the manuscripts considered for this review, 96 are included and 612 are excluded. Additionally, relevant papers published earlier than 2012 are included to provide context to the review.

DISCUSSION AND CONCLUSIONS

Both acute and chronic alcohol use decrease protein synthesis and increase protein degradation. Alcohol also impairs mitochondrial function and extracellular matrix remodeling. However, there is a gap in the literature on the known alcohol-mediated mechanisms, including senescence, role of immune activation, and interorgan communication, on the development of alcohol-related myopathy. With increased life expectancy, changing alcohol use patterns, and increasing frequency of alcohol use among females, current observational studies are needed on the prevalence of alcohol-related myopathy. Additionally, the compounding effects of acute and chronic alcohol use on skeletal muscle with aging or exercise, in response to injury or disuse, and in the context of comorbidities including diabetes and human immunodeficiency virus (HIV), call for further investigation. Though evidence suggests that abstinence or reducing alcohol use can improve muscle mass and function, they are not restored to normal levels. Hence, understanding the pathophysiological mechanisms can help in the design of therapeutic strategies to improve skeletal muscle health.

Skeletal Muscle Fibre Type Changes in an Avian Model of Hepatic Fibrosis

We investigated the susceptibility of type I and type II skeletal myofibres to atrophy in hens with hepatic fibrosis induced by bile duct ligation (BDL). Seven hens, approximately 2 years old, were randomly assigned to BDL (n = 4) and sham surgery (SHAM) (n = 3) groups. Mean body weight and mean liver weight as a percentage of mean body weight were significantly lower in the BDL group than in the SHAM group at 4 weeks post surgery (P = 0.002, P = 0.005, respectively). Mean plasma aspartate aminotransferase activity was slightly higher, while total cholesterol (P <0.001), total bilirubin (P = 0.022) and NH₃ (P = 0.048) concentrations were significantly higher in the BDL group than in the SHAM group. Liver lesions were induced in all hens in the BDL group. The weights of the pectoralis (PCT) (P = 0.049) and flexor perforans et perforatus digiti III (FPPD III) muscles (P = 0.006) as a percentage of body weight were significantly decreased in the BDL group. A significantly reduced mean myofibre cross-sectional area in the PCT of BDL hens (P = 0.005) was indicative of atrophy. No significant differences were observed in the fibre type composition of the PCT, supracoracoideus or FPPD III muscles between the SHAM and BDL groups. However, there was an approximate 43% increase in the number of type I fibres in the femorotibialis lateralis of the BDL group and small angular type II fibres and large round type I fibres in this muscle were characteristic of peripheral neuropathy. The results suggest that type II fibres are more susceptible to atrophy than type I fibres in this model of hepatic fibrosis.

Mechanisms Underlying Muscle Protein Imbalance Induced by Alcohol

Both acute intoxication and longer-term cumulative ingestion of alcohol negatively impact the metabolic phenotype of both skeletal and cardiac muscle, independent of overt protein calorie malnutrition, resulting in loss of skeletal muscle strength and cardiac contractility. In large part, these alcohol-induced changes are mediated by a decrease in protein synthesis that in turn is governed by impaired activity of a protein kinase, the mechanistic target of rapamycin (mTOR). Herein, we summarize recent advances in understanding mTOR signal transduction, similarities and differences between the effects of alcohol on this central metabolic controller in skeletal muscle and in the heart, and the effects of acute versus chronic alcohol intake. While alcohol-induced alterations in global proteolysis via activation of the ubiquitin-proteasome pathway are equivocal, emerging data suggest alcohol increases autophagy in muscle. Further studies are necessary to define the relative contributions of these bidirectional changes in protein synthesis and autophagy in the etiology of alcoholic myopathy in skeletal muscle and the heart.

A pattern-based approach to the interpretation of skeletal muscle biopsies

The interpretation of muscle biopsies is complex and provides the most useful information when integrated with the clinical presentation of the patient. These biopsies are performed for workup of a wide range of diseases including dystrophies, metabolic diseases, and inflammatory processes. Recent insights have led to changes in the classification of inflammatory myopathies and have changed the role that muscle biopsies have in the workup of inherited diseases. These changes will be reviewed. This review follows a morphology-driven approach by discussing diseases of skeletal muscle based on a few basic patterns that include cases with (1) active myopathic damage and inflammation, (2) active myopathic damage without associated inflammation, (3) chronic myopathic changes, (4) myopathies with distinctive inclusions or vacuoles, (5) biopsies mainly showing atrophic changes, and (6) biopsies that appear normal on routine preparations. Each of these categories goes along with certain diagnostic considerations and pitfalls. Individual biopsy features are only rarely pathognomonic. Establishing a firm diagnosis therefore typically requires integration of all of the biopsy findings and relevant clinical information. With this approach, a muscle biopsy can often provide helpful information in the diagnostic workup of patients presenting with neuromuscular problems.

Human alcohol-related neuropathology

Alcohol-related diseases of the nervous system are caused by excessive exposures to alcohol, with or without co-existing nutritional or vitamin deficiencies. Toxic and metabolic effects of alcohol (ethanol) vary with brain region, age/developmental stage, dose, and duration of exposures. In the mature brain, heavy chronic or binge alcohol exposures can cause severe debilitating diseases of the central and peripheral nervous systems, and skeletal muscle. Most commonly, long-standing heavy alcohol abuse leads to disproportionate loss of cerebral white matter and impairments in executive function. The cerebellum (especially the vermis), cortical-limbic circuits, skeletal muscle, and peripheral nerves are also important targets of chronic alcohol-related metabolic injury and degeneration. Although all cell types within the nervous system are vulnerable to the toxic, metabolic, and degenerative effects of alcohol, astrocytes, oligodendrocytes, and synaptic terminals are major targets, accounting for the white matter atrophy, neural inflammation and toxicity, and impairments in synaptogenesis. Besides chronic degenerative neuropathology, alcoholics are predisposed to develop severe potentially life-threatening acute or subacute symmetrical hemorrhagic injury in the diencephalon and brainstem due to thiamine deficiency, which exerts toxic/metabolic effects on glia, myelin, and the microvasculature. Alcohol also has devastating neurotoxic and teratogenic effects on the developing brain in association with fetal alcohol spectrum disorder/fetal alcohol syndrome. Alcohol impairs function of neurons and glia, disrupting a broad array of functions including neuronal survival, cell migration, and glial cell (astrocytes and oligodendrocytes) differentiation. Further progress is needed to better understand the pathophysiology of this exposure-related constellation of nervous system diseases and better correlate the underlying pathology with in vivo imaging and biochemical lesions.

Human alcohol-related neuropathology

Alcohol-related diseases of the nervous system are caused by excessive exposures to alcohol, with or without co-existing nutritional or vitamin deficiencies. Toxic and metabolic effects of alcohol (ethanol) vary with brain region, age/developmental stage, dose, and duration of exposures. In the mature brain, heavy chronic or binge alcohol exposures can cause severe debilitating diseases of the central and peripheral nervous systems, and skeletal muscle. Most commonly, long-standing heavy alcohol abuse leads to disproportionate loss of cerebral white matter and impairments in executive function. The cerebellum (especially the vermis), cortical-limbic circuits, skeletal muscle, and peripheral nerves are also important targets of chronic alcohol-related metabolic injury and degeneration. Although all cell types within the nervous system are vulnerable to the toxic, metabolic, and degenerative effects of alcohol, astrocytes, oligodendrocytes, and synaptic terminals are major targets, accounting for the white matter atrophy, neural inflammation and toxicity, and impairments in synaptogenesis. Besides chronic degenerative neuropathology, alcoholics are predisposed to develop severe potentially life-threatening acute or subacute symmetrical hemorrhagic injury in the diencephalon and brainstem due to thiamine deficiency, which exerts toxic/metabolic effects on glia, myelin, and the microvasculature. Alcohol also has devastating neurotoxic and teratogenic effects on the developing brain in association with fetal alcohol spectrum disorder/fetal alcohol syndrome. Alcohol impairs function of neurons and glia, disrupting a broad array of functions including neuronal survival, cell migration, and glial cell (astrocytes and oligodendrocytes) differentiation. Further progress is needed to better understand the pathophysiology of this exposure-related constellation of nervous system diseases and better correlate the underlying pathology with in vivo imaging and biochemical lesions.

Aging accentuates alcohol-induced decrease in protein synthesis in gastrocnemius

The present study sought to determine whether the protein catabolic response in skeletal muscle produced by chronic alcohol feeding was exaggerated in aged rats. Adult (3 mo) and aged (18 mo) female F344 rats were fed a nutritionally complete liquid diet containing alcohol (36% of total calories) or an isocaloric isonitrogenous control diet for 20 wk. Muscle (gastrocnemius) protein synthesis, as well as mTOR and proteasome activity did not differ between control-fed adult and aged rats, despite the increased TNF-α and IL-6 mRNA and decreased IGF-I mRNA in muscle of aged rats. Compared with alcohol-fed adult rats, aged rats demonstrated an exaggerated alcohol-induced reduction in lean body mass and protein synthesis (both sarcoplasmic and myofibrillar) in gastrocnemius. Alcohol-fed aged rats had enhanced dephosphorylation of 4E-BP1, as well as enhanced binding of raptor with both mTOR and Deptor, and a decreased binding of raptor with 4E-BP1. Alcohol feeding of both adult and aged rats reduced RagA binding to raptor. The LKB1-AMPK-REDD1 pathway was upregulated in gastrocnemius from alcohol-fed aged rats. These exaggerated alcohol-induced effects in aged rats were associated with a greater decrease in muscle but not circulating IGF-I, but no further increase in inflammatory mediators. In contrast, alcohol did not exaggerate the age-induced increase in atrogin-1 and MuRF1 mRNA or the increased proteasome activity. Our results demonstrate that, compared with adult rats, the gastrocnemius from aged rats is more sensitive to the catabolic effects of alcohol on protein synthesis, but not protein degradation, and this exaggerated response may be AMPK-dependent.

25 hydroxyvitamin D serum levels influence adequate response to bisphosphonate treatment in postmenopausal osteoporosis

It remains unclear whether vitamin D sufficiency optimizes response to bisphosphonate (BP) treatment in postmenopausal osteoporosis. We evaluated the role and possible mechanisms of vitamin D in adequate response to standard BP treatment for postmenopausal osteoporosis.

METHODS

We included 120 postmenopausal osteoporotic women (aged 68 ± 8 years) receiving BP (alendronate or risedronate) at their annual follow-up, performing complete anamnesis, including treatment adherence, use of vitamin D supplements, and previous falls and fractures during the last year. We analyzed the evolution of bone mineral density (BMD) during this period and serum PTH and 25 hydroxyvitamin D (25(OH)D) and urinary NTx levels. Patients were classified as inadequate responders to antiosteoporotic treatment based on BMD loss>2% and/or the presence of fragility fractures during the last year.

RESULTS

Thirty percent of patients showed inadequate response to BP treatment, with significantly lower levels of 25(OH)D (22.4 ± 1.3 vs. 26.6 ± 0.3 ng/ml, p=0.01), a higher frequency of 25(OH)D levels<30 ng/ml (91% vs. 69%, p=0.019) and higher urinary NTx values (42.2 ± 3.9 vs. 30.9 ± 2.3 nM/mM, p=0.01). Patients with 25(OH)D>30 ng/ml had a greater significant increase in lumbar BMD than women with values <30 ng/ml (3.6% vs. 0.8%, p<0.05). The probability of inadequate response was 4-fold higher in patients with 25(OH)D<30 (OR, 4.42; 95% CI, 1.22-15.97, p=0.02).

CONCLUSIONS

Inadequate response to BP treatment is frequent in postmenopausal women with osteoporosis as is vitamin D insufficiency, despite vitamin D supplementation. Maintenance of 25(OH)D levels >30 ng/ml is especially indicated for adequate response to BP treatment.

Induction of muscle weakness by local inflammation: an experimental animal model

OBJECTIVE AND DESIGN

The objective of this study was to characterize the response of skeletal muscle to a localized inflammation induced by the inflammatory agent casein.

METHODS

An inflammatory agent, casein, was injected into the right hindlimb and saline was injected into the left hindlimb of normal adult mice, once daily for six consecutive days. Inflammatory response was monitored by immunohistochemical labeling of leukocytes. Muscle protein levels were determined by electrophoresis and muscle function was determined by isometric force measurements.

RESULTS

Local inflammation was induced by casein in association with the accumulation of extensive neutrophils and macrophages in the soleus muscle. This local inflammation resulted in a shift in myosin heavy chain (MHC) isoform expression and a significant reduction in total MHC concentration in the soleus. Maximal twitch and tetanic forces were significantly reduced in the inflamed soleus. Contractile function in soleus was fully restored after two weeks of recovery, along with the restoration of protein concentration and the disappearance of inflammatory cells.

CONCLUSION

This study establishes a unique and robust model in which mechanisms of local inflammation induced muscle protein degradation, reduction of contractile force, and subsequent recovery from this condition can be further studied.

Oxidative phenotype protects myofibers from pathological insults induced by chronic heart failure in mice

The fiber specificity of skeletal muscle abnormalities in chronic heart failure (CHF) has not been defined. We show here that transgenic mice (8 weeks old) with cardiac-specific overexpression of calsequestrin developed CHF (50.9% decrease in fractional shortening and 56.4% increase in lung weight, P<0.001), cachexia (37.8% decrease in body weight, P<0.001), and exercise intolerance (69.3% decrease in running distance to exhaustion, P<0.001) without a significant change in muscle fiber-type composition. Slow oxidative soleus muscle maintained muscle mass, whereas fast glycolytic tibialis anterior and plantaris muscles underwent atrophy (11.6 and 13.3%, respectively; P<0.05). In plantaris muscle, glycolytic type IId/x and IIb, but not oxidative type I and IIa, fibers displayed significant decreases in cross-sectional area (20.3%, P<0.05). Fast glycolytic white vastus lateralis muscle showed sarcomere degeneration and decreased cytochrome c oxidase IV (39.5%, P<0.01) and peroxisome proliferator-activated receptor gamma co-activator 1alpha protein expression (30.3%, P<0.01) along with a dramatic induction of the MAFbx/Atrogin-1 mRNA. These findings suggest that exercise intolerance can occur in CHF without fiber type switching in skeletal muscle and that oxidative phenotype renders myofibers resistant to pathological insults induced by CHF.

Protein adduct species in muscle and liver of rats following acute ethanol administration

AIMS

Previous immunohistochemical studies have shown that the post-translational formation of aldehyde-protein adducts may be an important process in the aetiology of alcohol-induced muscle disease. However, other studies have shown that in a variety of tissues, alcohol induces the formation of various other adduct species, including hybrid acetaldehyde-malondialdehyde-protein adducts and adducts with free radicals themselves, e.g. hydroxyethyl radical (HER)-protein adducts. Furthermore, acetaldehyde-protein adducts may be formed in reducing or non-reducing environments resulting in distinct molecular entities, each with unique features of stability and immunogenicity. Some in vitro studies have also suggested that unreduced adducts may be converted to reduced adducts in situ. Our objective was to test the hypothesis that in muscle a variety of different adduct species are formed after acute alcohol exposure and that unreduced adducts predominate.

METHODS

Rabbit polyclonal antibodies were raised against unreduced and reduced aldehydes and the HER-protein adducts. These were used to assay different adduct species in soleus (type I fibre-predominant) and plantaris (type II fibre-predominant) muscles and liver in four groups of rats administered acutely with either [A] saline (control); [B] cyanamide (an aldehyde dehydrogenase inhibitor); [C] ethanol; [D] cyanamide+ethanol.

RESULTS

Amounts of unreduced acetaldehyde and malondialdehyde adducts were increased in both muscles of alcohol-dosed rats. However there was no increase in the amounts of reduced acetaldehyde adducts, as detected by both the rabbit polyclonal antibody and the RT1.1 mouse monoclonal antibody. Furthermore, there was no detectable increase in malondialdehyde-acetaldehyde and HER-protein adducts. Similar results were obtained in the liver.

CONCLUSIONS

Adducts formed in skeletal muscle and liver of rats exposed acutely to ethanol are mainly unreduced acetaldehyde and malondialdehyde species.

Effect of Zinc supplementation on ethanol-mediated bone alterations

Ethanol consumption leads to bone alterations, mainly osteoporosis. Ethanol itself may directly alter bone synthesis, but other factors, such as accompanying protein malnutrition--frequently observed in alcoholics, chronic alcoholic myopathy with muscle atrophy, alcohol induced hypogonadism or hypercortisolism, or liver damage, may all contribute to altered bone metabolism. Some data suggest that zinc may exert beneficial effects on bone growth. Based on these facts, we analyzed the relative and combined effects of ethanol, protein malnutrition and treatment with zinc, 227 mg/l in the form of zinc sulphate, on bone histology, biochemical markers of bone formation (osteocalcin) and resorption (urinary hydroxyproline excretion), and hormones involved in bone homeostasis (insulin growth factor 1 (IGF-1), vitamin D, parathormone (PTH), free testosterone and corticosterone), as well as the association between these parameters and muscle fiber area and liver fibrosis, in eight groups of adult Sprague Dawley rats fed following the Lieber de Carli model during 5 weeks. Ethanol showed an independent effect on TBV (F=14.5, p<0.001), causing it to decrease, whereas a low protein diet caused a reduction in osteoid area (F=8.9, p<0.001). Treatment with zinc increased osteoid area (F=11.2, p<0.001) and serum vitamin D levels (F=3.74, p=0.057). Both ethanol (F=45, p<0.001) and low protein diet (F=46.8, p<0.01) decreased serum osteocalcin levels. Ethanol was the only factor independently related with serum IGF-1 (F=130.24, p<0.001), and also showed a synergistic interaction with protein deficiency (p=0.027). In contrast, no change was observed in hydroxyproline excretion and serum PTH levels. No correlation was found between TBM and muscle atrophy, liver fibrosis, corticosterone, or free testosterone levels, but a significant relationship was observed between type II-b muscle fiber area and osteoid area (rho=0.34, p<0.01). Osteoporosis is, therefore, present in alcohol treated rats. Both alcohol and protein deficiency lead to reduced bone formation. Muscle atrophy is related to osteoid area, suggesting a role for chronic alcoholic myopathy in decreased bone mass. Treatment with zinc increases osteoid area, but has no effect on TBV.

Is there morphological difference between branchiomeric and somitic muscles submitted to alcohol consumption? An experimental study in rats (Rattus norvegicus)

Alcoholism is considered a physical dependence disorder. More than 18 million people are alcoholics in the USA and England and between 1/3 to ½ of them present some kind of physical disorder. In general the literature is focused on alcoholic trunk muscle disorders. These muscles have different embryological origins if compared to the masticatory muscles. The aim of this research was to evaluate the effects of alcohol on the masticatory muscles in order to compare them with the somitic muscles. For this purpose, 15 male Wistar rats weighing around 250g were used. The rats were divided into three groups: Normal control (N), Alcoholic (A) and Isocaloric (I). Slices of the masseter muscle, temporalis muscle and rectus abdominal muscle were harvested and submitted to histochemical reactions (m-ATPase: acid and alkaline pre incubation and NADH-TR). The myofibers were classified in SO, FOG and FG. The results showed atrophy of the fast fibers (FG and FOG) in the masticatory muscles but this atrophy was not statistically significant in this study (p< 0.05). On the other hand, significant atrophy occurred in the rectus abdominal muscle (p<0.05). Based on these data it can concluded that the effect of alcohol on the branchiomeric jaw elevator muscles (masseter and temporalis muscles) is different compared to the effect on somitic muscle (rectus abdominal muscle).

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.

Evidence of apoptosis in chronic alcoholic skeletal myopathy

Apoptosis is a common mechanism of programmed cell death that has been implicated in the pathogenesis of alcohol-induced organ damage. Experimental studies have suggested alcohol-mediated apoptosis in cardiac muscle. The relationship between skeletal and cardiac muscle damage in alcoholism led us to consider the possible role of apoptosis in the pathogenesis of skeletal myopathy. We prospectively evaluated apoptosis in skeletal muscle biopsies of 30 consecutively selected male high-dose well-nourished chronic alcohol consumers and 12 nonalcoholic controls. Alcohol consumption, evaluation of muscle strength by myometry, and deltoid muscle biopsy with immunohistochemical and morphometric analysis were performed. Apoptosis was assessed by TUNEL, BAX, and BCL-2 immunohistochemical assays. Chronic alcoholics compared with controls showed a significantly higher apoptotic index in TUNEL (2.35% +/- 0.25% versus 0.18% +/- 0.03%, P < 0.001), BAX (9.16% +/- 2.00% versus 0.66% +/- 0.22%, P < 0.001), and BCL-2 muscle assays (8.08% +/- 0.20% versus 0.83% +/- 0.20%, P = 0.001), respectively. In addition, these apoptotic indexes were higher in alcoholics with skeletal myopathy compared with in those without skeletal myopathy (3.04% +/- 0.36% versus 1.65% +/- 0.26%, P = 0.004 for TUNEL; 17.00% +/- 2.78% versus 1.33% +/- 0.22%, P < 0.001 for BAX; and 15.13% +/- 3.2% versus 1.03% +/- 0.33%, P < 0.001 for BCL-2 assays, respectively). We conclude that apoptosis is present in the skeletal muscle of high-dose alcohol consumers, mainly in those affected by myopathy. However, the specific pathogenic mechanism of apoptosis in chronic skeletal myopathy in alcoholics remains to be elucidated.

Acute and chronic effects of alcohol exposure on skeletal muscle c-myc, p53, and Bcl-2 mRNA expression

Skeletal muscle atrophy is a common feature in alcoholism that affects up to two-thirds of alcohol misusers, and women appear to be particularly susceptible. There is also some evidence to suggest that malnutrition exacerbates the effects of alcohol on muscle. However, the mechanisms responsible for the myopathy remain elusive, and some studies suggest that acetaldehyde, rather than alcohol, is the principal pathogenic perturbant. Previous reports on rats dosed acutely with ethanol (<24 h) have suggested that increased proto-oncogene expression (i.e., c-myc) may be a causative process, possibly via activating preapoptotic or transcriptional pathways. We hypothesized that 1) increases in c-myc mRNA levels also occur in muscle exposed chronically to alcohol, 2) muscle of female rats is more sensitive than that from male rats, 3) raising acetaldehyde will also increase c-myc, 4) prior starvation will cause further increases in c-myc mRNA expression in response to ethanol, and 5) other genes involved in apoptosis (i.e., p53 and Bcl-2) would also be affected by alcohol. To test this, we measured c-myc mRNA levels in skeletal muscle of rats dosed either chronically (6-7 wk; ethanol as 35% of total dietary energy) or acutely (2.5 h; ethanol as 75 mmol/kg body wt ip) with ethanol. All experiments were carried out in male Wistar rats (approximately 0.1-0.15 kg body wt) except the study that examined gender susceptibility in male and female rats. At the end of the studies, rats were killed, and c-myc, p53, and Bcl-2 mRNA was analyzed in skeletal muscle by RT-PCR with an endogenous internal standard, GAPDH. The results showed that 1) in male rats fed ethanol chronically, there were no increases in c-myc mRNA; 2) increases, however, occurred in c-myc mRNA in muscle from female rats fed ethanol chronically; 3) raising endogenous acetaldehyde with cyanamide increased c-myc mRNA in acute studies; 4) starvation per se increased c-myc mRNA levels and at 1 day potentiated the acute effects of ethanol, indicative of a sensitization response; 5) the only effect seen with p53 mRNA levels was a decrease in muscle of rats starved for 1 day compared with fed rats, and there was no statistically significant effect on Bcl-2 mRNA in any of the experimental conditions. The increases in c-myc may well represent a preapoptotic effect, or even a nonspecific cellular stress response to alcohol and/or acetaldehyde. These data are important in our understanding of a common muscle pathology induced by alcohol.

Influence of nutritional status on alcoholic myopathy

BACKGROUND

Muscle weakness and structural changes in striated skeletal muscle are common in persons with chronic alcoholism.

OBJECTIVE

The objective of the study was to assess the role of malnutrition in the development of chronic alcoholic myopathy.

DESIGN

We prospectively evaluated 146 men who reported an intake >/=100 g ethanol/d for the previous 5 y and 73 well-nourished control subjects. Alcohol consumption, energy and protein nutritional status, and deltoid muscle strength were determined. Deltoid muscle tissue specimens were taken from alcoholics and from 14 control subjects for histochemical studies and morphometric measurements of the fibers.

RESULTS

Deltoid muscle strength was less in alcoholics than in control subjects (P < 0.001). Muscle strength correlated with lifetime consumption of ethanol (r = -0.56, P < 0.001), and a decrease in muscle strength was significantly greater in the presence of energy malnutrition. Using logistic regression analysis, we observed that alcoholics with muscle strength < 18 kg had the independent risk factors of an arm muscle area < 50 cm(2) (odds ratio: 5.4; 95% CI: 2.3, 12.3), consumption of > 1600 kg ethanol throughout their lives (odds ratio: 4.5; 95% CI: 2.0, 10.1), and protein malnutrition (odds ratio: 4.2; 95% CI: 1.4, 12.7). Protein malnutrition was also associated with muscle inefficiency (P < 0.001). Histologic myopathy was present in 58% of alcoholics, was related to lifetime ethanol consumption (P = 0.001), and was more severe in the presence of protein malnutrition (P = 0.01).

CONCLUSION

Malnutrition is an additional developmental factor in the functional and structural muscle damage induced by chronic ethanol consumption.

[Rhabdomyolysis and myoglobinuria]

Rhabdomyolysis is a disorder characterized by acute damage of the sarcolemma of the skeletal muscle leading to release of potentially toxic muscle cell components into the circulation, most notably creatine phosphokinase (CK) and myoglobin, and is frequently accompanied by myoglobinuria. Therefore, the term myoglobinuria is often used interchangeably with the term rhabdomyolysis. This disorder may result in potential life-threatening complications such as acute myoglobinuric renal failure, hyperkalemia and cardiac arrest, disseminated intravascular coagulation, and compartment syndrome. The condition is etiologically heterogeneous and may result from a large variety of diseases affecting muscle membranes, membrane ion channels, and muscle energy supply including acquired causes (e.g., exertion, crush injury and trauma, alcoholism, drugs, and toxins) and hereditary causes (e.g., disorders of carbohydrate metabolism, disorders of lipid metabolism, or diseases of the muscle associated with malignant hyperthermia). In many patients with idiopathic recurrent rhabdomyolysis, specific inherited metabolic defects have not been recognized up to now.

Iatrogenic and toxic myopathies

There has been increasing awareness of the adverse effects of therapeutic agents and exogenous toxins on the structure and function of muscle. The resulting clinical syndrome varies from one characterized by muscle pain to profound myalgia, paralysis, and myoglobinuria. Because toxic myopathies are potentially reversible, their prompt recognition may reduce their damaging effects or prevent a fatal outcome. Interest in the toxic myopathies, however, derives not only from their clinical importance but also from the fact that they serve as useful experimental models in muscle research. Morphological and biochemical studies have increased our understanding of the basic cellular mechanisms of myotoxicity. Toxins may produce, for instance, necrotizing, lysosomal-related, inflammatory, anti-microtubular, mitochondrial, hypokalemia-related, or protein synthesis-related muscle damage.

Free radicals in alcoholic myopathy: indices of damage and preventive studies

Chronic alcoholic myopathy affects up to two-thirds of all alcohol misusers and is characterized by selective atrophy of Type II (glycolytic, fast-twitch, anaerobic) fibers. In contrast, the Type I fibers (oxidative, slow-twitch, aerobic) are relatively protected. Alcohol increases the concentration of cholesterol hydroperoxides and malondialdehyde-protein adducts, though protein-carbonyl concentration levels do not appear to be overtly increased and may actually decrease in some studies. In alcoholics, plasma concentrations of alpha-tocopherol may be reduced in myopathic patients. However, alpha-tocopherol supplementation has failed to prevent either the loss of skeletal muscle protein or the reductions in protein synthesis in alcohol-dosed animals. The evidence for increased oxidative stress in alcohol-exposed skeletal muscle is thus inconsistent. Further work into the role of ROS in alcoholic myopathy is clearly warranted.

Malnutrition-induced myopathy following Roux-en-Y gastric bypass

A 42-year-old man developed a myopathy in the setting of malnutrition following Roux-en-Y gastric bypass for the treatment of morbid obesity. No specific vitamin or electrolyte deficiency was identified. Muscle biopsy revealed type II fiber atrophy. He recovered after the initiation of continuous enteral feeding. We suggest that malnutrition was the underlying cause of his myopathy.

Alcoholic skeletal muscle myopathy: definitions, features, contribution of neuropathy, impact and diagnosis

Alcohol misusers frequently have difficulties in gait, and various muscle symptoms such as cramps, local pain and reduced muscle mass. These symptoms are common in alcoholic patients and have previously been ascribed as neuropathological in origin. However, biochemical lesions and/or the presence of a defined myopathy occur in alcoholics as a direct consequence of alcohol misuse. The myopathy occurs independently of peripheral neuropathy, malnutrition and overt liver disease. Chronic alcoholic myopathy is characterized by selective atrophy of Type II fibres and the entire muscle mass may be reduced by up to 30%. This myopathy is arguably the most prevalent skeletal muscle disorder in the Western Hemisphere and occurs in approximately 50% of alcohol misusers. Alcohol and acetaldehyde are potent inhibitors of muscle protein synthesis, and both contractile and non-contractile proteins are affected by acute and chronic alcohol dosage. Muscle RNA is also reduced by mechanisms involving increased RNase activities. In general, muscle protease activities are either reduced or unaltered, although markers of muscle membrane damage are increased which may be related to injury by reactive oxygen species. This supposition is supported by the observation that in the UK, alpha-tocopherol status is poor in myopathic alcoholics. Reduced alpha-tocopherol may pre-dispose the muscle to metabolic injury. However, experimental alpha-tocopherol supplementation is ineffective in preventing ethanol-induced lesions in muscle as defined by reduced rates of protein synthesis and in Spanish alcoholics with myopathy, there is no evidence of impaired alpha-tocopherol status. In conclusion, by a complex series of mechanisms, alcohol adversely affects skeletal muscle. In addition to the mechanical changes to muscle, there are important metabolic consequences, by virtue of the fact that skeletal muscle is 40% of body mass and an important contributor to whole-body protein turnover.

Alcoholic myopathy: biochemical mechanisms

Between one- and two-thirds of all alcohol abusers have impairment of muscle function that may be accompanied by biochemical lesions and/or the presence of a defined myopathy characterised by selective atrophy of Type II fibres. Perturbations in protein metabolism are central to the effects on muscle and account for the reductions in muscle mass and fibre diameter. Ethanol abuse is also associated with abnormalities in carbohydrate (as well as lipid) metabolism in skeletal muscle. Ethanol-mediated insulin resistance is allied with the inhibitory effects of ethanol on insulin-stimulated carbohydrate metabolism. It acutely impairs insulin-stimulated glucose and lipid metabolism, although it is not known whether it has an analogous effect on insulin-stimulated protein synthesis. In alcoholic cirrhosis, insulin resistance occurs with respect to carbohydrate metabolism, although the actions of insulin to suppress protein degradation and stimulate amino acid uptake are unimpaired. In acute alcohol-dosing studies defective rates of protein synthesis occur, particularly in Type II fibre-predominant muscles. The relative amounts of mRNA-encoding contractile proteins do not appear to be adversely affected by chronic alcohol feeding, although subtle changes in muscle protein isoforms may occur. There are also rapid and sustained reductions in total (largely ribosomal) RNA in chronic studies. Loss of RNA appears to be related to increases in the activities of specific muscle RNases in these long-term studies. However, in acute dosing studies (less than 1 day), the reductions in muscle protein synthesis are not due to overt loss of total RNA. These data implicate a role for translational modifications in the initial stages of the myopathy, although changes in transcription and/or protein degradation may also be superimposed. These events have important implications for whole-body metabolism.

Nutritional assessment in alcoholic patients. Its relationship with alcoholic intake, feeding habits, organic complications and social problems

To establish their ability to predict malnutrition, irregular feeding, alcoholic intake, derangement of social and familial links and organic complications (liver cirrhosis) were assessed in 181 hospitalized male alcoholic. BMI was under 18.5 kg/m(2) in 8.9%, between 18.5-20 kg/m(2) in 8.9%, 20-25 kg/m(2) in 42%, 25-30 kg/m(2) in 32.2% and over 30 kg/m(2) in 8.2% of patients. Malnutrition was related to the intensity of ethanol intake, development of social or familial problems, irregularity of feeding habits and cirrhosis with ascites. Irregularity of feeding habits was also related to heavy drinking and to social or familial derangement. By logistic regression analysis, the only variables which independently predict malnutrition were irregular feeding habits and liver cirrhosis with ascites. In a second step, irregular feeding was dependent on social or familial troubles and daily intake of ethanol. So, malnutrition related to alcoholism seems multifactorial in its pathogenesis.