TETRAHYDROAMINOACRIDINE-INDUCED APOPTOSIS IN RAT HEPATOCYTES

Tacrine (tetrahydroaminoacridine, THA) is currently administered to th ousands of patients for the treatment of Alzheimer's disease. Unfortun ately, THA therapy is often limited by this drugs' propensity to induc e reversible hepatotoxicity. In the present study we investigated the mechanism of THA cytotoxicity by measuring the effect of THA on cell v iability, protein synthesis activity and the induction of apoptosis in suspensions of freshly isolated rat hepatocytes. Our experimental fin dings indicate that THA-mediated apoptosis is responsible for the acut e in vitro hepatotoxicity observed with this aminoacridine derivative. We found that THA-treated hepatocytes (0.1, 0.25 and 0.5 mM) demonstr ated a significant and dose-dependent reduction in cellular protein sy nthesis activity (84, 55 and 5% of control activity, respectively) aft er 1 hr of incubation. However, in hepatocytes exposed to 0.1 and 0.25 mM THA, the inhibition of protein synthesis was short-lived. In these treated cells, protein synthesis activity returned to control levels (100%) by the fifth hr of incubation without a significant increase in cellular lactate dehydrogenase (LDH) leakage or the induction of apop tosis. In hepatocytes exposed to 0.5 mM THA, the near complete inhibit ion of protein synthesis was not reversible and a dramatic increase in LDH leakage (necrosis) was observed after 6 hr of treatment. In 0.5 m M THA-treated hepatocytes the appearance of apoptotic nuclei and cells were observed with electron microscopy following 2 hr of treatment (1 2% of total hepatocytes analysed) and steadily increased to 42% by the fifth hr (compared with 4% for control cells). We speculate that THA' s ability to inhibit hepatocyte protein synthesis (> 50%) and induce a poptosis may have an important role in the hepatotoxic episodes experi enced by Alzheimer's patients taking this drug. However, the role of a poptosis in clinical THA-induced hepatotoxicity and the relevance of u sing rat hepatocyte suspensions as an in vitro model for THA hepatotox icity in vivo require additional investigation. Copyright (C) 1996 Els evier Science Ltd.