Transforming growth factor beta 1 preferentially induces apoptotic cell death in rat hepatocytes cultured under pericentral-equivalent conditions.

Abstract

The cytotoxicity of transforming growth factor beta 1 (TGF beta 1) was assessed in rat hepatocytes cultured under periportal (PP)-or pericentral (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 mitochondrial activity (rhodamine-123 uptake) were selectively reduced in PP cultures, whereas the incidence of apoptotic cells in PC cultures was about 10-fold higher than that in PP cultures. The time profiles of TGF beta 1-induced apoptotic and necrotic events and the concentration-response relationship differed in PC and PP cultures. In PC cultures the early appearance of cells with apoptotic nuclei was not associated with DNA fragmentation nor with an increase in LDH release or impaired 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 mitochondrial activity all increased in an exposure-time dependent manner in both PP and PC cultures. At this exposure level 48 and 72% of the apoptotic cells detected in PC cultures after continuous exposure for 24 hr were induced within an exposure of 1 and 4 hr, respectively. Aurintricarboxylic acid (50 microM), an inhibitor of endonucleases, significantly inhibited the appearance of apoptotic cells and the progression in apoptosis. Clearly, TGF beta 1 preferentially induced apoptotic cell death in hepatocytes with PC-equivalent metabolism at low exposure levels. High exposure levels or prolonged exposure periods produced both apoptosis and necrosis.