Effect of Chronic Alcohol Abuse on Anabolic and Catabolic Signaling Pathways in Human Skeletal Muscle

Regular exercise attenuates alcoholic myopathy in zebrafish by modulating mitochondrial homeostasis

Alcoholic myopathy is caused by chronic consumption of alcohol (ethanol) and is characterized by weakness and atrophy of skeletal muscle. Regular exercise is one of the important ways to prevent or alleviate skeletal muscle myopathy. However, the beneficial effects and the exact mechanisms underlying regular exercise on alcohol myopathy remain unclear. In this study, a model of alcoholic myopathy was established using zebrafish soaked in 0.5% ethanol. Additionally, these zebrafish were intervened to swim for 8 weeks at an exercise intensity of 30% of the absolute critical swimming speed (Ucrit), aiming to explore the beneficial effects and underlying mechanisms of regular exercise on alcoholic myopathy. This study found that regular exercise inhibited protein degradation, improved locomotion ability, and increased muscle fiber cross-sectional area (CSA) in ethanol-treated zebrafish. In addition, regular exercise increases the functional activity of mitochondrial respiratory chain (MRC) complexes and upregulates the expression levels of MRC complexes. Regular exercise can also improve oxidative stress and mitochondrial dynamics in zebrafish skeletal muscle induced by ethanol. Additionally, regular exercise can activate mitochondrial biogenesis and inhibit mitochondrial unfolded protein response (UPRmt). Together, our results suggest regular exercise is an effective intervention strategy to improve mitochondrial homeostasis to attenuate alcoholic myopathy.

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.

Longitudinal assessment of strength and body composition in a mouse model of chronic alcohol-related myopathy

BACKGROUND

Excessive, chronic alcohol consumption can result in muscle atrophy and weakness (i.e., alcoholic myopathy) that impairs the quality of life. However, the precise mechanisms responsible for ethanol's detrimental impact on skeletal muscle have not been fully elucidated, in part due because the time course of disease development and progression are not well established. Therefore, we examined muscle strength and body composition longitudinally using an established preclinical mouse model of chronic alcoholic myopathy.

METHODS

To establish a time course of chronic alcoholic myopathy, we fed High Drinking in the Dark (HDID) female mice (n = 7) 20% ethanol for ~32 weeks (following a 2-week ethanol ramping period). We assessed in vivo isometric contractility of the left ankle dorsiflexor and lean mass via NMR every 4 weeks. Outcomes were compared with age-matched control HDID mice that did not consume ethanol (n = 8).

RESULTS

At study completion, mice who consumed ethanol were 12% weaker than control mice (p = 0.015). Compared to baseline, consuming ethanol resulted in an acute transient reduction in dorsiflexion torque at Week 4 (p = 0.032) that was followed by a second, more sustained reduction at Week 20 (p < 0.001). Changes in lean mass paralleled those of dorsiflexor torque, with ~40% of the variance in dorsiflexor torque being explained by the variance in lean mass of the ethanol group (p < 0.001). Dorsiflexor torque normalized to lean mass (mN·m/g lean mass) did not differ between the ethanol and control groups from Weeks 4 to 32 (p ≥ 0.498).

CONCLUSIONS

These results indicate that reductions in muscle mass and strength due to chronic, excessive ethanol intake are dynamic, not necessarily linear, processes. Moreover, the findings confirm that ethanol-induced weakness is primarily driven by muscle atrophy (i.e., loss of muscle quantity). Future studies should consider how chronic alcoholic myopathy develops and progresses rather than identifying changes after it has been diagnosed.

Role of nutrition in patients with coexisting chronic obstructive pulmonary disease and sarcopenia

Chronic obstructive pulmonary disease (COPD) is one of the most common chronic diseases in the elderly population and is characterized by persistent respiratory symptoms and airflow obstruction. During COPD progression, a variety of pulmonary and extrapulmonary complications develop, with sarcopenia being one of the most common extrapulmonary complications. Factors that contribute to the pathogenesis of coexisting COPD and sarcopenia include systemic inflammation, hypoxia, hypercapnia, oxidative stress, protein metabolic imbalance, and myocyte mitochondrial dysfunction. These factors, individually or in concert, affect muscle function, resulting in decreased muscle mass and strength. The occurrence of sarcopenia severely affects the quality of life of patients with COPD, resulting in increased readmission rates, longer hospital admission, and higher mortality. In recent years, studies have found that oral supplementation with protein, micronutrients, fat, or a combination of nutritional supplements can improve the muscle strength and physical performance of these patients; some studies have also elucidated the possible underlying mechanisms. This review aimed to elucidate the role of nutrition among patients with coexisting COPD and sarcopenia.

Excessive Ethanol Intake in Mice Does Not Impair Recovery of Torque after Repeated Bouts of Eccentric Contractions

PURPOSE

Alcoholics develop muscle atrophy and weakness from excessive ethanol (EtOH) intake. To date, most research has examined outcomes of alcohol-induced atrophy and weakness under basal or unstressed conditions despite physical stress being a normal occurrence in a physiological setting. Therefore, this study set out to determine if recovery of torque is impaired after repetitive bouts of physical stress in skeletal muscle during excessive short-term (experiment 1) and long-term (experiment 2) EtOH consumption.

METHODS

Twenty male and female mice were assigned to receive either 20% EtOH in their drinking water or 100% water. Short- and long-term consumption was predetermined to be EtOH intake starting at 4 and 26 wk, respectively. Anterior crural muscles performed repeated bouts of physical stress using in vivo eccentric contractions, with tetanic isometric torque being measured immediately pre- and postinjury. A total of 10 bouts were completed with 14 d between each bout within bouts 1-5 (experiment 1) and bouts 6-10 (experiment 2), and 12 wk between bouts 5 and 6.

RESULTS

Mice consuming EtOH had blood alcohol concentrations up to 270 mg·dL -1 . In experiment 1, five bouts of eccentric contractions did not reduce recovery of torque, regardless of sex or EtOH treatment ( P ≥ 0.173). Similarly, in experiment 2, preinjury torques did not differ from day 14 values regardless of sex or treatment ( P ≥ 0.322). However, there was a group effect in female mice for bouts 6 and 10 during experiment 2, with female EtOH mice being weaker than controls ( P ≤ 0.002).

CONCLUSIONS

Excessive short- or long-term EtOH misuse in a mouse model did not affect the muscle's ability to regain strength after repeated bouts of eccentric contractions, suggesting that EtOH may not be as detrimental to recovery as once predicted.

The effects of voluntary binge-patterned ethanol ingestion and daily wheel running on signaling of muscle protein synthesis and degradation in female mice

Excessive ethanol ingestion can reduce skeletal muscle protein synthesis (MPS) through the disruption of signaling along the Akt-mTOR pathway and increase muscle protein degradation (MPD) through the Ubiquitin Proteasome Pathway (UPP) and autophagy. Identification of interventions that curb the disrupting effects of alcohol misuse on MPS and MPD are of central importance for the prevention of chronic health complications that arise from muscle loss. Physical activity is one potential strategy to combat the deleterious effects of alcohol on skeletal muscle. Therefore, the purpose of this study was to investigate the interaction between daily wheel running and binge-patterned ethanol consumption, through episodes of voluntary binge-patterned ethanol drinking, on signaling factors along the Akt-mTOR, Ubiquitin-Proteasome, and autophagy pathways. Adult female C57BL/6J mice received daily access to cages with or without running wheels for 2.5 h/day for five weeks. During the final five days of the study, mice received 2-4 h of daily access to sipper tubes containing water (n = 14 sedentary; n = 15 running) or 20% ethanol (n = 14 sedentary; n = 16 running) 30 min after running wheel access, using the "Drinking in the Dark" (DID) model of binge-patterned ethanol consumption. Immediately after the final episode of DID, gastrocnemius muscle was extracted. Western blotting was performed to measure proteins along Akt-mTOR, Ubiquitin-Proteasome, and autophagy pathways, and PCR was used to assess mRNA expression of atrogenes. Ethanol access increased expression of MAFbx by 82% (p = 0.048), but did not robustly influence Akt-mTOR or UPP signaling. Daily wheel access did not prevent alcohol-induced MAFbx expression; however, ethanol access decreased the phosphorylation of p70S6K by 45% in running mice (p = 0.020). These results suggest that physical activity may be insufficient to prevent alcohol-induced changes to signaling factors along pathways involved in muscle loss. Instead, binge-patterned ethanol ingestion may impair the benefits of physical activity on factors involved in MPS.

Alcohol Induces Zebrafish Skeletal Muscle Atrophy through HMGB1/TLR4/NF-κB Signaling

Excessive alcohol consumption can cause alcoholic myopathy, but the molecular mechanism is still unclear. In this study, zebrafish were exposed to 0.5% alcohol for eight weeks to investigate the effect of alcohol on skeletal muscle and its molecular mechanism. The results showed that the body length, body weight, cross-sectional area of the skeletal muscle fibers, Ucrit, and MO₂max of the zebrafish were significantly decreased after alcohol exposure. The expression of markers of skeletal muscle atrophy and autophagy was increased, and the expression of P62 was significantly reduced. The content of ROS, the mRNA expression of sod1 and sod2, and the protein expression of Nox2 were significantly increased. In addition, we found that the inflammatory factors Il1β and Tnfα were significantly enriched in skeletal muscle, and the expression of the HMGB1/TLR4/NF-κB signaling axis was also significantly increased. In summary, in this study, we established a zebrafish model of alcohol-induced skeletal muscle atrophy and further elucidated its pathogenesis.

The functional and molecular effects of problematic alcohol consumption on skeletal muscle: a focus on athletic performance

Background: Chronic alcohol misuse is associated with alcoholic myopathy, characterized by skeletal muscle weakness and atrophy. Moreover, there is evidence that sports-related people seem to exhibit a greater prevalence of problematic alcohol consumption, especially binge drinking (BD), which might not cause alcoholic myopathy but can negatively impact muscle function and amateur and professional athletic performance.Objective: To review the literature concerning the effects of alcohol consumption on skeletal muscle function and structure that can affect muscle performance.Methodology: We examined the currently available literature (PubMed, Google Scholars) to develop a narrative review summarizing the knowledge about the effects of alcohol on skeletal muscle function and exercise performance, obtained from studies in human beings and animal models for problematic alcohol consumption.Results: Exercise- and sport-based studies indicate that alcohol consumption can negatively affect muscle recovery after vigorous exercise, especially in men, while women seem less affected. Clinical studies and pre-clinical laboratory research have led to the knowledge of some of the mechanisms involved in alcohol-related muscle dysfunction, including an imbalance between anabolic and catabolic pathways, reduced regeneration, increased inflammation and fibrosis, and deficiencies in energetic balance and mitochondrial function. These pathological features can appear not only under chronic alcohol misuse but also in other alcohol consumption patterns.Conclusions: Most laboratory-based studies use chronic or acute alcohol exposure, while episodic BD, the most common drinking pattern in amateur and professional athletes, is underrepresented. Nevertheless, alcohol consumption negatively affects skeletal muscle health through different mechanisms, which collectively might contribute to reduced sports performance.

The Prophylactic Effects of Glutamine on Muscle Protein Synthesis and Degradation in Rats with Ethanol-Induced Liver Damage

The purpose of this research was to investigate the prophylactic effects of glutamine on muscle protein synthesis and degradation in rats with ethanol-induced liver injury. For the first 2 weeks, Wistar rats were divided into two groups and fed a control (n = 16) or glutamine-containing diet (n = 24). For the following 6 weeks, rats fed the control diet were further divided into two groups (n = 8 per group) according to whether their diet contained no ethanol (CC) or did contain ethanol (CE). Rats fed the glutamine-containing diet were also further divided into three groups (n = 8 per group), including a GG group (glutamine-containing diet without ethanol), GE group (control diet with ethanol), and GEG group (glutamine-containing diet with ethanol). After 6 weeks, results showed that hepatic fatty change, inflammation, altered liver function, and hyperammonemia had occurred in the CE group, but these were attenuated in the GE and GEG groups. Elevated intestinal permeability and a higher plasma endotoxin level were observed in the CE group, but both were lower in the GE and GEG groups. The level of a protein synthesis marker (p70S6K) was reduced in the CE group but was higher in both the GE and GEG groups. In conclusion, glutamine supplementation might elevate muscle protein synthesis by improving intestinal health and ameliorating liver damage in rats with chronic ethanol intake.

Cellular and molecular signatures of alcohol-induced myopathy in women

Alcoholic myopathy is characterized by the reduction in cross-sectional area (CSA) of muscle fibers and impaired anabolic signaling. The goal of the current study was to investigate the causes and compare the changes in CSA and fiber type composition with the modifications of anabolic and catabolic signaling pathways at the early stages of chronic alcohol consumption in women. Skeletal muscle samples from 5 female patients with alcohol abuse (AL; 43 ± 5 yr old; alcohol abuse duration 5,6 ± 0,6 yr) were compared with the muscle from the control group of 8 healthy women (C; 35 ± 4 yr old). The average daily dose of alcohol consumption was 110 ± 10 ml of pure ethanol. In women patients, a significant decrease in CSA of type I and II muscle fibers, titin and nebulin content, plasma IGF-1 level and total IRS-1, p-Akt and p-4E-BP1 in vastus lateralis was found in comparison with the control group. The p-AMPK level was found to be increased versus the control group. In women patients with chronic alcoholic myopathy 1) both fast and slow muscle fibers are subjected to atrophy; 2) impairments in IGF-I-dependent signaling and pathways controlling translation initiation (AMPK/mTOR/4E-BP1), but not translation elongation, are observed; 3) the level of calpain-1 and ubiquitinated proteins increases, unlike E3 ligases content.