Impairment of the asialoglycoprotein receptor by ethanol oxidation

It is well established that ethanol exposure impairs the process of receptor-mediated endocytosis in hepatic cells, although the molecular mechanism(s) and the physiological consequence(s) of this impairment are unclear. Because addressing these mechanistic questions is difficult in vivo, we have developed a recombinant cell line of hepatic origin capable of metabolizing ethanol. In this study, we have used these recombinant cells, designated HAD cells, to investigate the ethanol-induced impairment to the receptor-mediated endocytosis of the hepatic asialoglycoprotein receptor. Comparing the binding of the ligand asialoorosomucoid in both the parental Hep G2 cells and the recombinant HAD cells, maintained in the presence and absence of ethanol, revealed decreased ligand binding in the HAD cells. This impairment was accentuated by prolonging the ethanol exposure, reaching approximately 40% in both surface and total receptor populations by 7 days. Addition of the alcohol dehydrogenase inhibitor pyrazole to the ethanol-containing medium abolished this impairment, indicating that the decreased binding was a result of the alcohol dehydrogenase-mediated oxidation of ethanol. Furthermore, using antibody specific to the asialoglycoprotein receptor, it was demonstrated that the ethanol-induced impairment in ligand binding was a consequence of decreased ligand binding and not a result of diminished receptor numbers. These results indicated that ethanol oxidation was required for the ethanol-induced impairment in ligand binding, and that the reduced ligand binding was a result of a decrease in the ability of the ligand to bind to the receptor.