ETHANOL-CONSUMPTION REDUCES THE PROTEOLYTIC CAPACITY AND PROTEASE ACTIVITIES OF HEPATIC LYSOSOMES

Chronic ethanol consumption causes decreased hepatic protein degradati on, resulting in protein accumulation within hepatocytes. In this inve stigation, we sought to determine whether chronic ethanol feeding alte rs the degradative capacity and protease activities of isolated hepati c lysosomes, Male Sprague-Dawley-dervived rats were fed a liquid diet containing either ethanol (36% of calories) or isocaloric maltose-dext rin for 1-5 wk. Hepatic lysosomes were isolated by differential centri fugation and purified through Percoll gradients. Lysosomes obtained fr om livers of ethanol-fed rats degraded both endogenous protein substra tes and the exogenously added radioactive substrate, I-125-RNase A, 26 -42% more slowly than lysosomes from pair fed controls. The ethanol-el icited reduction in proteolytic capacity appeared to result in part, f rom a deficiency of the lysosomal cathepsins B, L, and H. Compared wit h controls, the specific activities of these enzymes were 31-45% lower in lysosomes from ethanol-fed rats, Immunoblot analyses also revealed that the intralysosomal as well as the intracellular content of cathe psin B was significantly lower in ethanol-fed rats. In contrast, ethan ol consumption did not affect the cellular quantity of cathepsin L but lowered its amount in isolated lysosomes. Our findings suggest that c hronic ethanol consumption causes a deficiency in lysosomal cathepsins by altering their biosynthesis and/or their trafficking into lysosome s.