Metabolism and Cytotoxicity of Chlorpropham (CIPC) and Its Essential Metabolites in Isolated Rat Hepatocytes During a Partial Inhibition of Sulphation and Glucuronidation Reactions: A Comparative Study

Abstract.

The changes in metabolism and cytotoxicity of chlorpropham (CIPC) and its major metabolites, 4-hydroxychlorpropham (4-OH CIPC), 3-chloroaniline, and 3-chloroacetanilide were investigated in isolated rat hepatocyte suspensions after a partial inhibition of sulphation and glucuronidation and the two reactions combined in an attempt to assess the part of each of them in the enhanced CIPC toxicity observed in vivo after D-galactosamine treatment. With sulphation and glucuronidation effective, CIPC has a cytolytic effect and reduces intracellular ATP and K⁺ level while 4-OH CIPC has a weak cytolytic effect but modifies ATP and K⁺ level in a greater extent than CIPC. Inhibition of sulphation does not affect the cytotoxicity of CIPC or 4-OH CIPC because there is a compensatory increase in the amount of 4-OH CIPC glucuronide formed and the level of free 4-OH CIPC always remain low. In contrast, when incubations are carried out with either CIPC or 4-OH CIPC, the presence of D-galactosamine leads to a decrease of glucuronide and sulphate conjugates accompanied, respectively, by a 3.6-fold and 6.9-fold increase of the free 4-OH CIPC level in the culture medium. This alteration of the metabolism is followed by a marked reduction of ATP synthesis with a concomitant modification of cell permeability. The cytolytic effect is due to CIPC itself, whereas the effect on energy supply was attributed to free 4-OH CIPC. The results demonstrate a combined effect of free 4-OH CIPC and D-galactosamine on intracellular ATP level that could account for the partial inhibition of sulphation. This change in the CIPC metabolism could explain the increased CIPC toxicity observed in vivo after D-galactosamine pretreatment.