It has been demonstrated that the oral administration of ethanol (Lieber-DeCarli liquid diet) to rats results in a decreased expression and content of the asialoglycoprotein receptor (ASGP-R) in the resultant fatty liver. In the present study, we wanted to determine whether the extent of impaired receptor content was correlated with the severity of liver pathology by using the intragastric feeding model. When ASGP-R protein and mRNA levels were measured in animals infused with ethanol or dextrose in the presence of fish oil (FO) or medium-chain triglyceride as the source of fat, more significant impairments to the ASGP-R were observed in the FO-ethanol group compared with the medium-chain triglyceride-ethanol group. Furthermore, only the FO-ethanol group showed pathological liver changes. These results demonstrate that a correlation exists between the progression of alcohol-associated liver injury, as defined by the severity of liver pathology, and an ethanol-induced decline in ASGP-R content.

During receptor-mediated endocytosis (RME), extracellular molecules are internalized after being recognized and bound to specific cell surface receptors. In previous studies of the asialoglycoprotein receptor (ASGPR) in rats, we showed that ethanol impairs RME at multiple ASGPR sites. Ethanol administration has been shown to increase apoptosis, and we demonstrated increased sensitization to apoptotic induction in hepatocytes from ethanol-fed rats. Although a physiological role for the ASGPR has not been identified, investigators have shown its involvement in the uptakelclearance of apoptotic cells in vitvo. This suggests apotential role for the ASGPR in the removal of apoptotic cells, and the recent availability of an ASGPR-deficient mouse strain provides an excellent opportunity to examine the role of the ASGPR during ethanol impairment. In this study, we examined ethanol-impaired RME in mice and began the characterization of ASGPR-deficient mice for use in ethanol studies. Similar to our findings with rats, ligand binding, internalization, and degradation were decreased 45-50% in hepatocytes from ethanol-fed wild-type mice. In ASGPR-deficient mice, these parameters did not vary among the chow-fed, pair-fed control, or ethanol groups and were negligible compared with those of wild-type mice. TUNEL analysis of liver sections showed an ethanol-induced increase in apoptotic bodies in all mouse strains with a significant difference in the receptor-deficient mice. Further, the livers of ASGPR-deficient mice had three times more apoptotic bodies, in all feeding groups, compared with wild-type mice. These results support the use of the ASGPR-deficient mouse model for studying ethanol-induced liver injury, specifically ethanol-induced apoptosis.

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Chronic ethanol consumption is associated with multiple impairments in receptor-mediated endocytosis (RME) in hepatocytes. RME mediated by the asialoglycoprotein receptor seems to be especially impaired by ethanol. In the present study, we determined susceptibility of RME to alterations in ethanol-fed and pair-fed control animals by the addition of a carboxylic ionophore, monensin. Monensin inhibits acidification of prelysosomal vesicular compartments, which results in a decrease in the rate of receptor-ligand dissociation within the cell. Low levels (25 microM) of monensin have been shown to preferentially affect receptor-ligand dissociation of one subset (state 2) of asialoglycoprotein receptor, whereas dissociation in a second subset (state 1 receptors) seems to be relatively unaffected. We examined whether ethanol treatment preferentially affected one or another of these receptor subpopulations. Male Wistar rats were fed a standard ethanol-containing (36% of calories) or control diet for 10 to 14 weeks, and hepatocytes were prepared from the animals. Similar to previous results from our laboratory, surface and total ligand and antibody binding were decreased by 30 to 45% (p < 0.01) in ethanol animals, compared with controls. An ethanol-induced impairment of receptor-ligand dissociation was also apparent in these cells, as shown by increased ratios of bound-to-free ligand during continuous endocytosis. After monensin treatment, surface receptors on both ethanol and control cells showed a similar pattern of redistribution to the cell interior and intracellular inactivation. When kinetics of intracellular receptor-ligand dissociation were examined upon addition of monensin, the bound-to-free ligand ratios in both control and ethanol cells increased dramatically and to an equal extent. These results indicate that, in the ethanol animals, the pattern of sensitivity to monensin is unchanged relative to controls. Thus, the relative proportion of state 1 and state 2 receptor populations do not seem to be affected after long-term feeding, and ethanol may be a perturbant that affects both state 1 and state 2 receptor function.

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