Effect of glutathione depletion and oxidative stress on the in vitro cytotoxicity of velnacrine maleate.

Velnacrine maleate (Mentane) is an aminoacridine drug developed for the treatment of Alzheimer's disease. Although velnacrine maleate has not been observed to cause prominent cytotoxicity in in vitro hepatocyte cultures, this drug was associated with elevated serum levels of hepatic enzymes in clinical trials. The purpose of the present study was to manipulate cultures of rat hepatocytes in an attempt to elicit a cytotoxic response from this drug and to better understand the in vitro mechanisms of action. Cytotoxicity was evaluated by measuring lactate dehydrogenase (LDH) leakage, neutral red (NR) uptake, and 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyl tetrazolium bromide (MTT) reduction. Preliminary studies with fluorescent probes did not indicate a role for calcium influx or the formation of reactive oxygen species in the cytotoxicity of velnacrine maleate. However, depletion of cellular glutathione (GSH) by diamide (DA) pretreatment resulted in a cytotoxic response at concentrations of velnacrine maleate (1 and 10 micrograms/ml) which were approximately 25-fold lower than those in the absence of DA. Similarly, pretreatment with velnacrine maleate enhanced the cytotoxicity of DA. Pre-exposure of cells to a mixture of DA and t-butyl hydroperoxide (t-BHP) at non-toxic concentrations resulted in significant cytotoxicity of the hepatocyte cultures by velnacrine maleate. Results from these studies indicate that oxidative stress and GSH depletion may enhance Alzheimer patients' susceptibility to the hepatotoxic potential of aminoacridine drugs.