INVESTIGATION OF LIVER BINDING OF PENTACHLOROPHENOL BASED UPON MEASUREMENT OF PROTEIN ADDUCTS

Covalent binding of reactive metabolites of pentachlorophenol (PCP) wa s investigated both in vitro and in vivo in the livers of mate Sprague -Dawley rats via measurement of protein adducts. Cysteinyl adducts of quinones and semiquinones in liver cytosolic (Cp) and nuclear (Np) pro teins were assayed after catalytic cleavage by Raney nickel. Results f rom in vitro experiments confirmed that PCP metabolism produced tetrac hlorobenzoquinones and the corresponding tetrachlorobenzosemiquinones which subsequently bound to sulphydryl groups in liver proteins. In vi vo, the production of cysteinyl adducts increased with the administere d dosage (0-40 mg PCP per kg body weight) and presented evidence of sa turable metabolism. Results suggest two metabolic pathways for PCP, in cluding a high-affinity low-capacity pathway and a low-affinity high-c apacity pathway. Time-course experiments in vivo and in vitro suggeste d that quinone adducts participated in multiple substitution reactions with protein and/or non-protein thiols, and pointed to possible forma tion of protein-protein cross-links in vivo. The elimination rate cons tants of quinone adducts in vitro were about 0.35 h(-1) in liver Cp. T he elimination of quinone adducts in vivo appeared to follow biphasic kinetics with rate constants for the terminal phase being 0.014 and 0. 008 h(-1) in liver Cp and Np, respectively.