Glucocorticoid hepatopathy: effect on receptor-mediated endocytosis of asialoglycoproteins.
Histologic and electron microscopic examination of liver tissue from glucocorticoid-treated dogs (GT dogs) showed a markedly abnormal hepatocellular morphology which consisted of severe hepatocellular swelling, vacuolation, and peripheral displacement of subcellular organelles. The abnormal cell morphology was typical of that seen in clinical cases of canine Cushing's Syndrome. The hepatocyte isolation procedure used here works equally well for the preparation of viable hepatocytes from both normal and GT dogs even though GT dogs displayed a pronounced hepatopathy. Cell yields (10(9) cells from a 30-cm3 section of liver) are similar to those reported for rat hepatocytes using whole liver in situ perfusion and cell viability is routinely greater than 85%. The isolation procedure preserved the "abnormal" state or swollen morphology of the hepatocytes from GT dogs and thus can be used in pathophysiological studies of glucocorticoid-induced hepatopathy. The isolated hepatocytes were 3.2 times greater in cell volume than normal hepatocytes. We also observed over a 12.3-fold increase in alkaline phosphatase activity and the appearance in both the liver and the serum of GT dogs of the unique, corticosteroid alkaline phosphatase isozyme (CALP). In spite of the obvious abnormal liver morphology and elevated serum and liver alkaline phosphatase activities, the function of the hepatic cell surface carbohydrate binding protein, the Gal/GalNAc or asialoglycoprotein receptor, was not impaired. We found a trend of about a 1.5-fold increase in the initial rate of ligand uptake as well as 1.6-fold more receptors on GT dog hepatocytes compared to normal hepatocytes. The ligand binding affinity of these receptors, as well as the rate of ligand degradation, was identical in hepatocytes isolated from normal and diseased dogs. When intestinal alkaline phosphatase (IALP) is used as the ligand, approximately 25% was exocytosed intact following endocytosis. These results demonstrate that dogs with glucocorticoid hepatopathy possess a normally functioning Gal/GalNAc receptor. Furthermore, these data are consistent with the hypothesis that structurally related IALP and CALP isozymes may also be metabolically related through the Gal/GalNAc receptor endocytosis pathway. That is, a portion of the IALP normally endocytosed through the Gal/GalNAc receptor pathway in glucocorticoid-treated dogs may be recycled and converted (hyperglycosylated) to the abnormal serum CALP isozyme rather than being degraded.
Kuhlenschmidt
M S
MS
Department of Pathobiology, College of Veterinary Medicine, University of Illinois, Urbana 61801.
Hoffmann
W E
WE
Rippy
M K
MK
D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D037263:Asialoglycoprotein Receptor; D001212:Asialoglycoproteins / Q000378:metabolism*; D056486:Chemical and Drug Induced Liver Injury / Q000209:etiology* / Q000473:pathology; D004247:DNA / Q000032:analysis; D004285:Dogs; D004705:Endocytosis / Q000187:drug effects*; D005089:Exocytosis / Q000502:physiology; D005938:Glucocorticoids / Q000633:toxicity*; D006023:Glycoproteins / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism; D008657:Metabolic Clearance Rate / Q000502:physiology; D008854:Microscopy, Electron; D011971:Receptors, Immunologic / Q000378:metabolism*
D037263:Asialoglycoprotein Receptor; D001212:Asialoglycoproteins; D005938:Glucocorticoids; D006023:Glycoproteins; D007527:Isoenzymes; D011971:Receptors, Immunologic; D004247:DNA; D000469:Alkaline Phosphatase