A Comparison of Methanol and Ethanol Effects on the Activity and Distribution of Lysosomal Proteases

The activity of lysosomal proteolytic enzymes (cathepsin A, B, C, D and E) in cytosol, in the liver homogenate, and in the blood plasma of rats intoxicated with methanol and ethanol was measured 6, 12 and 24 h; and 2, 5, and 7 days after intoxication. The activity of all proteases was increased in the cytosol from 12h to 5 days of alcohol intoxication, whereas the activity of these enzymes was decreased in the liver homogenate during the same time. Ethanol caused a higher increase in cytosol proteases activity than methanol. The magnitude of the decrease in proteolytic activity in the liver homogenate depends on the amino acid active center of the enzyme and on the kind of alcohol. The greatest decrease was observed for sulfhydryl and hydroxyl proteases and a smaller one for carboxyl proteases. Moreover, methanol caused a greater decrease than ethanol. It was shown that the lysosomal protease activity in the plasma was increased from 12 h to 5 days after alcohol intoxication and ethanol caused fewer changes than methanol. The increase in the liver lipid peroxidation products examined as tiobarbituric acid reactive substances was also observed at the same time. These results indicate that during methanol and ethanol intoxication the cellular and lysosomal membranes are impaired and proteases are translocated into the blood. However, changes in proteases activities and proteases distribution within the hepatocytes may lead to disturbances in the catabolism of cell proteins and to the destruction of liver cells.