Abstract
Two areas of current interest in toxicology have been studied using in vitro models. 1. Carcinogen-induced nuclear enlargement has been reported both in vitro and in vivo, but the mechanism, and whether it is causally related to carcinogenesis, has not yet been established. In order to obtain some insight into potential mechanisms, several cell culture systems were used to investigate the role of increased DNA content in induction of nuclear enlargement. N-methyl-N-nitrosourea and adriamycin were shown to induce nuclear enlargement in vitro following ‘pulse’ treatment. This was accompanied by an increase in the proportions of cells in the G2+M phase of the cell cycle, possibly due to G2 block. There was some evidence of polyploidy induction following adriamycin treatment, but not following N-methyl-N-nitrosourea treatment. In contrast, diethylstilboestrol increased the range of nuclear areas and DNA content, to both less than and greater than that of control cells, but only after a prolonged exposure period of 48h. These data were consistent with diethylstilboestrol inducing spindle damage. 2. In vitro models were also used to investigate steatogen-induced hepatotoxicity and hepatotoxicity induced by fibrinogen receptor antagonists. The need to include toxicity markers in in vitro hepatotoxicity tests which are relevant to the type of in vivo hepatotoxicity was investigated. In both cases, simple cytotoxicity markers were used in combination with more sensitive biochemical or morphological markers. In the case of steatogen-induced hepatotoxicity it was found that measurement of intracellular triglyceride levels provided more information on the in vitro toxicity of ethanol and valproic acid than measurement of simple cytotoxicity. However, the inclusion of triglyceride measurement did not provide additional information on the in vitro toxicity of ethionine. It was also found that in vitro examination of mitochondrial changes following treatment of hepatocytes with fibrinogen receptor antagonists was a more sensitive marker than simple cytotoxicity markers.