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

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. 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. 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. 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.