Protein adducts in type I and type II fibre predominant muscles of the ethanol-fed rat: preferential localisation in the sarcolemmal and subsarcolemmal region

Abstract

Background: Chronic alcoholic myopathy is characterised by reduced muscle strength and structural changes including a decrease in the diameter of Type II (glycolytic, fast-twitch, anaerobic) fibres. In contrast, the Type I fibres (oxidative, slow-twitch, aerobic) are relatively protected. It is possible that adduct formation with reactive metabolites of ethanol may be a contributory process.

Materials and methods: We analysed skeletal muscles from rats fed nutritional-complete liquid diets containing ethanol as 35% of total dietary energy; control rats were fed the same diet in which ethanol was replaced by isocaloric glucose. Reduced-acetaldehyde, unreduced-acetaldehyde, malondialdehyde, malondialdehyde-acetaldehyde and alpha-hydroxyethyl protein-adducts in both soleus and plantaris were analysed by ELISA or immunohistochemistry with comparative studies in liver.

Results: After 6 weeks, the weights of the plantaris, but not the soleus, were decreased. ELISA analyses for protein adducts showed increased amounts of unreduced-acetaldehyde adducts in soleus (P < 0.025) and plantaris (P < 0.025). Reduced-acetaldehyde, malondialdehyde, malondialdehyde-acetaldehyde and alpha-hydroxyethyl protein-adducts in both soleus and plantaris muscles from ethanol-fed rats were not significantly different from their pair-fed controls (P > 0.05). In contrast, liver from ethanol-fed rats showed significantly higher levels of unreduced-acetaldehyde (P < 0.025), reduced-acetaldehyde (P < 0.01), malondialdehyde (P < 0.01), malondialdehyde-acetaldehyde (P < 0.025) and alpha-hydroxyethyl radical (P < 0.01) protein adducts compared to pair-fed controls. Immuno-histochemical analysis using an antiserum reacting with both reduced- and unreduced-acetaldehyde adducts showed adducts were increased in soleus (P < 0.05) and plantaris (P < 0.025), confirming ELISA analysis. Adducts were located within the sarcolemmal (i.e. muscle membrane) and subsarcolemmal regions.

Conclusion: This is the first report of adduct formation in myopathic skeletal muscle due to chronic alcohol ingestion and suggests a role for acetaldehyde in the aetiology of alcoholic myopathy.