0 zyxwvutsrqponm 145-6008/93/1706-1309$3.00/0 zyxwvutsrqponm ALCOHOLISM. CLINICAL AND EXPERIMENTAL RESEARCH zyxwvutsrqpo Vol. 17, No. 6 Novernber/Decernber zy I993 Chronic Ethanol Administration Impairs Degradation of Formaldehyde-Treated Albumin by the Perfused Rat Liver Georgia M. Rees, Jacqueline A. Miller, Carol A. Casey, and Dean J. Turna Nonparenchymal cells of the liver appear to be important in the pathogenesis of various liver diseases, including that caused by ethanol. It is known that chronic ethanol administration impairs the process of receptor-mediated endocytosis in hepatocytes. Liver endothelial cells are also actively endocytic cells, playing a promi- nent role in the clearance from the circulation of a variety of macro- molecules. In this study, we assessed the effect of ethanol admin- istration on this “scavenger” function of liver endothelial cells by measuring the degradation of formaldehyde-treated albumin in iso- lated, perfused livers of ethanol-ted rats. Rats were pair-fed for 1 or 4 weeks with a liquid diet containing either ethanol as 36% of total calories or an isocaloric amount of carbohydrate. Chronic ethanol administrationin this manner for 1 or 4 weeks significantly impaired the degradation of this endothelial cell ligand (by 60 f 9% and 37 zyxwvu 2 9%, respectively).Liver perfusionswere also performed on rats that had been administered ethanol acutely or in which ethanol was added to the perfusate. No acute effect of ethanol on the degradation of this ligand was seen. These results demonstrate that chronic ethanol ingestion impairs receptor-mediated endocytosis of formal- dehyde-treatedalbumin by liver endothelial cells, indicating that the adverse effects of ethanol on protein trafficking within the liver are not limited to the hepatocytes. Key Words: Ethanol, Endothelium, Receptor-Mediated Endocyto- sis, Formaldehyde-Treated Albumin. ONPARENCHYMAL CELLS of the liver appear to N play a key role in the development of liver injury due to chronic ethanol ingestion.’ For example, current research would indicate that early in the fibrogenic process, the Ito cell becomes activated, developing the myofibroblast morphology, whereupon it becomes the predominant source of collagen during fibrogenesis. The immediate cause of this transformation is not yet known. Direct effects of either ethanol or acetaldehyde do not appear to explain sufficientlythis transition or the increase in collagen synthe~is.’.~ The possible involvement of cy- tokines and other soluble factors, particularly Kupffer cell- derived, has also been in~estigated.~ Little is known, how- ever, about the potential role of the liver endothelial cell (LEC) in modulating ethanol-induced liver injury. zyxwvut From the Liver Study Unit, Omaha VeteransAdministration Medical Center (G.M.R., D.J.T.); and the Departments of Internal Medicine (G.M.R.. J.A.M., C.A.C.. D.J.T.) and Biochemistry (C.A.C.. D.J.T.), University zyxwvutsrqponm of Nebraska Medical Center, Omaha, Nebraska. Received for publication March zyxwvutsrqp 1, 1993; accepted June 10, 1993 This research was supported by the Department of Veterans Aflairs and by Grant AA04961 from the National Institute on Alcohol Abuse and Alcoholism. Reprint requests: Dean J. Tuma, Ph.D., Liver Study Unit, Veterans Administration Medical Center, 4101 Woolworth Avenue, Omaha. NE 68105. Copyright 0 1993 by The Research Society on Alcoholism. Alcohol CIin €xp Res. Vol 17, No 6, 1993: pp 1309-1312 Endothelial cells are known to play an active role in the immune response in several ways, including the increased expression of leukocyte adhesion molecules and local elab- oration of vasodilators.’ As one feature of their role in the reticuloendothelial system, hepatic endothelial cells have also been normally found to take up and degrade a variety of modified proteins and other macromolecules via the process of receptor-mediated endocytosis (RMEp RME is a multistep process whereby soluble molecules are spe- cifically bound to cell surface receptors, internalized into the cell, and then sorted into 1 of 4 pathways for delivery to lysosomes, return to the cell surface or transport across the The specialized “scavenger” function of liver endothelial cells has been studied for a number of ligands including formaldehyde-treated albumin (f-Alb), acety- lated low-density lipoproteins, hyaluronic acid, and de- natured collagen (reviewed in ref. 6). Endocytosis of these ligands by the endothelial cells may function to modulate, either positively or negatively, the development of certain disease processes, including atherosclerosis and diabetic complications. The RME of f-Alb has been used by many investigators as a model system to study the scavenger function of LECS.~,~-I ’ The f-Alb receptor is present on both macrophages and Intravenously injected “’I-f-Alb is cleared from the circulation almost exclusively by LECs, with <5% being recovered in Kupffer cells.’o There is some recent evidence that Kupffer cells become more involved in the uptake of this modified protein if it has become poly- merized.” This may occur with prolonged storage of the modified protein.” There are - 1 zyxw O5 receptors/cell on LECs.12 The receptor was purified from sinusoidal cell membranes by Horiuchi et al.,I3 who found that it is a 125 kDa membrane glycoprotein composed of two non- covalently linked subunits of M, 53,000 and 30,000. Eskild et a1.I2 found the receptor to have a high affinity for f-Alb (Kd M). They also found the rate of internalization to be quite rapid, with a tllZ of 24 sec. The rate-limiting step in metabolism of f-Alb by LECs was found to be degra- dation within the lysosomes. Binding was found to be calci~m-independent,~~ however, binding could be re- versed by lowering the pH to 56.0.’’ The rate of uptake of f-Alb in vivo is comparable with that in vitro.” Chronic ethanol ingestion is known to have a deleterious effect on RME of a variety of ligands by hepatocytes (reviewed in ref. 16). Ethanol-induced defects in hepato- cyte RME via the asialoglycoproteinreceptor, for example, include a decrease in both the number of cell-surface as 1309