Potentiating effects of chlorinated hydrocarbons on carbon tetrachloride toxicity in isolated rat hepatocytes and plasma membranes

Effects of Tetrachloroethylene on Hepatic and Splenic Lymphocytotoxic Activities in Rodents

The industrial solvent tetrachloroethylene (TCE) is a liver carcinogen in experimental animals but is without significant genotoxicity. Presumably some nongenotoxic mechanism accounts for its cancer-causing effects. We have therefore investigated the effects of TCE on splenic and hepatic lymphocytotoxic activities in Sprague-Dawley rats and B6C3F1 mice, following in vivo and in vitro exposure to TCE. Natural killer (NK), natural cytotoxic, and “natural P815 killer” activities were measured in liver- and spleen-derived immune cells. Humoral and T-cell mitogenesis were assayed in lipopolysaccharide and Con-A-stimulated splenic cells, respectively. TCE administration in vivo did not significantly alter the various immunological parameters assessed, while in vitro exposure to TCE inhibited natural cytotoxic activity from liver and spleen in mice and rats. NK and “natural P815 killer” activity in rat cells exposed in vitro to TCE were also inhibited. Thus, TCE is capable of directly inhibiting natural lymphocytotoxic activity, which is indicated by these in vitro effects. While an inhibitory effect was not observed when immune cells were isolated from in vivo treated animals, the in vitro data do support the possibility that a direct inhibition of natural immune function may play some role in the carcinogenic effects of TCE in experimental mice.

Potentiation of oxidative damage to rat red blood cells by the concurrent presence of t-butyl hydroperoxide and bromotrichloromethane

Recently potentiation of oxidative damage in rat red blood cells (rRBC) incubated with t-butylhydroperoxide (BHP) in combination with bromotrichloromethane (BrCCI3) was demonstrated. The mechanism by which this combination (BrCCI3/BHP) potentiates the oxidative damage to rRBC was investigated in this study. When rRBC were incubated with 0.1 mM BHP, 0.5 mM BrCCI3, or the two combined, BrCCI3/BHP-potentiated lipid peroxidation and hemolysis were further enhanced under anaerobic conditions. However, the potentiation of lipid peroxidation was abolished by heating or trypsin digestion of rRBC. Electron spin resonance (ESR) studies demonstrated an increase of alkoyl radical induced by BrCCI3/BHP in rRBC, and this increase was abolished by heating or predigestion of hemolysates with trypsin. The inhibition of lipid peroxidation by diphenylamine (which reacts with alkoxyl radicals but not peroxyl radicals) suggests an important role of alkoxyl radicals. Overall, the present findings demonstrate that the increase in radical-related oxidative damage, possibly mediated by proteinlike materials, may be at least partially responsible for the potentiation of damage to rRBC induced by BrCCI3/BHP, and perhaps by BrCCI3. Although the in vivo significance of these results remains to be investigated, it seems likely that halocarbon toxicity may be amplified by elevated levels of lipid peroxide in blood.

Hepatotoxic interaction between carbon tetrachloride and chloroform in ethanol treated rats

The effect of coadministration of CHCl3 on CCl4-induced hepatic damage was investigated at low dose inhalation. Coexposure of CHCl3 did not influence CCl4-induced changes in any index of hepatic damage in control rats. Coadministration of CHCl3, however, enhanced CCl4 (10 ppm)-induced hepatic damage of ethanol treated rats in a dose- and duration-dependent manner: simultaneous exposure of 50 ppm CHCl3 potentiated CCl4-induced increase in plasma GPT activity and number of necrotic hepatocytes; the enhancement of CCl4-induced hepatic damage by 50 ppm CHCl3 was found over the 4 h exposure; simultaneous exposure of 10 and 25 ppm CHCl3 potentiated the CCl4-induced increase in liver malondialdehyde (MDA) content. In contrast, coadministration of 50 ppm trichloroethylene and 200 ppm 1,1,1-trichloroethane decreased CCl4-induced increase in plasma GPT activity, though these exposures did not influence the liver MDA content. These results suggest that the concentration of 10 ppm CCl4 may be significant for CHCl3 to potentiate the hepatic damage caused by CCl4 in ethanol-treated rats. Heavy drinkers may have a higher hepatotoxic risk for a mixture of CCl4 and CHCl3 than for a single exposure to CCl4 or CHCl3, and a particular attention should be therefore given to the joint exposure to CCl4 and CHCl3.