THE MECHANISM OF THIOACETAMIDE-INDUCED APOPTOSIS IN THE L37 ALBUMIN-SV40 T-ANTIGEN TRANSGENIC RAT HEPATOCYTE-DERIVED CELL-LINE OCCURS WITHOUT DNA FRAGMENTATION

The hepatotoxicant thioacetamide (TH) has classically been used as a m odel to study hepatic necrosis; however, recent studies have shown tha t TH can also induce apoptosis. In this report we demonstrate that 2.6 8 +/- 0.54% of the albumin-SV40 T-antigen transgenic rat hepatocytes u ndergo TH-induced apoptosis, a level comparable to other in vivo model s of liver apoptosis. In addition, TH could induce apoptosis and necro sis in the L37 albumin-SV40 T-antigen transgenic rat liver-derived cel l line. Examination of dying L37 cells treated with 100 mM TH by elect ron microscopy revealed distinct morphological characteristics that co uld he attributed to apoptosis. Quantitation of apoptosis by FACS anal ysis 24 h after treatment with 100 mM TH revealed that 81.3 +/- 1.6% o f the cells were undergoing apoptosis. in contrast, when L37 cells wer e treated with 250 mM TH, cells exhibited characteristics consistent w ith necrotic cell death. DIVA fragmentation ladders were produced by g rowth factor withdrawal-induced apoptosis; however, in 100 mM TH-induc ed apoptosis, DNA fragmentation ladders were not observed. Analysis of endonuclease activity in L37 cells revealed that the enzymes were not inactivated in the presence of 100 mM TH. The data presented in this report indicate that the L37 cell line could Lr used to study the mech anism of TH-induced apoptosis that was not mediated through a mechanis m requiring DNA fragrnentation.