TRANSFORMING GROWTH-FACTOR-BETA-1 PREFERENTIALLY INDUCES APOPTOTIC CELL-DEATH IN RAT HEPATOCYTES CULTURED UNDER PERICENTRAL-EQUIVALENT CONDITIONS

The cytotoxicity of transforming growth factor beta 1 (TGF beta 1) was assessed in rat hepatocytes cultured under periportal (PP)- or perice ntral (PC)-equivalent conditions. TGF beta 1 induced a 5-fold greater DNA fragmentation and LDH release in PC cultures than in PP cultures. At low exposure level (1 ng/ml TGF beta 1), albumin secretion and mito chondrial activity (rhodamine-123 uptake) were selectively reduced in PP cultures, whereas the incidence of apoptotic cells in PC cultures w as about 10-fold higher than that in PP cultures. The time profiles of TGF beta 1-induced apoptotic and necrotic events and the concentratio n-response relationship differed in PC and PP cultures. In PC cultures the early appearance of cells with apoptotic nuclei was not associate d with DNA fragmentation nor with an increase in LDH release or impair ed mitochondrial function. At a high exposure level (5 ng/ml TGF beta 1), again cells with apoptotic nuclei were much more strongly induced in PC cultures but DNA fragmentation, LDH release, and impairment of m itochondrial activity all increased in an exposure-time dependent mann er in both PP and PC cultures. At this exposure level 48 and 72% of th e apoptotic cells detected in PC cultures after continuous exposure fo r 24 hr were induced within an exposure of 1 and 4 hr, respectively. A urintricarboxylic acid (50 mu M), an inhibitor of endonucleases, signi ficantly inhibited the appearance of apoptotic cells and the progressi on in apoptosis. Clearly, TGF beta 1 preferentially induced apoptotic cell death in hepatocytes with PC-equivalent metabolism at low exposur e levels. High exposure levels or prolonged exposure periods produced both apoptosis and necrosis. (C) 1995 Academic Press, Inc.