Resolution of liver fibrosis in chronic CCl4 administration in the rat after discontinuation of treatment: effect of silymarin, silibinin, colchicine and trimethylcolchicinic acid.

The aim of the present study was to investigate the hypothesis that liver tissue repair induced by exposure to chloroform (CHCl(3))+trichloroethylene binary mixture (BM) is dose-dependent similar to that elicited by exposure to these compounds individually. Male Sprague-Dawley rats (250-300 g) received three dose combinations of binary mixture (74+250, 185+500 and 370+1250 mg CHCl(3)+trichloroethylene/kg, intraperitoneally) in corn oil (maximum of 0.5 ml/kg). Liver injury was assessed by plasma alanine amino transaminase (ALT) activity and histopathology by haematoxylin & eosin. Liver tissue repair was measured by (3)H-thymidine incorporation into hepatonuclear DNA. Blood and liver levels of both the parent compounds and two major metabolites of trichloroethylene (trichloroacetic acid and trichloroethanol) were quantified by gas chromatography. The blood and liver CHCl(3) levels after the administration of binary mixture were similar compared to the administration of CHCl(3) alone. The blood and liver trichloroethylene levels after the binary mixture were significantly lower compared to trichloroethylene alone due to higher elimination in presence of CHCl(3), resulting in decreased production of metabolites. The antagonistic toxicokinetics resulted in lower liver injury than the summation of injury caused by the individual components at all three dose levels. On the other hand, tissue repair elicited by the binary mixture was dose-dependent. The interactive toxicity of this binary mixture of CHCl(3) and trichloroethylene led to subadditive initial liver injury because of a combined effect of higher elimination of TCE and mitigated progression of liver injury was prevented by timely dose-dependent stimulation of compensatory tissue repair. Even though the doses of the toxicants employed in this study are much higher than found in the environment, the results suggest that a mixture of these two compounds at environmental levels is unlikely to cause any exaggerated interactive acute liver toxicity of any biological significance.