Activity of lysosomal proteases in the liver and in the plasma from rats intoxicated with methanol

The activity of lysosomal proteolytic enzymes (cathepsin A, B, C, D and E) in cytosol and in the whole homogenate of the liver and in the blood plasma from rats intoxicated with 1.5, 3.0 and 6.0 g methanol/kg b.w. was measured 6, 12 and 24 h and 2, 5 and 7 days after the intoxication. The activity of all proteases was increased in the cytosol from 12 h to 5 days of intoxication, whereas the activity of these enzymes was decreased in the whole liver homogenate during the same time. The magnitude of the decrease in proteolytic activity in the whole homogenate of the liver depended on the amino acid active center of the enzyme. The greatest decrease was observed for sulfhydryl and hydroxyl proteases and smaller one for carboxyl proteases. The proteases activity in the plasma was increased from 12 h to 5 days after methanol intoxication. These results suggest that during methanol 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 destruction of liver cells.