Uroporphyrin accumulation produced by halogenated biphenyls in chick-embryo hepatocytes. Reversal of the accumulation by piperonyl butoxide

Abstract

Cultures of chick-embryo hepatocytes were used to study the mechanism by which 3,4,3',4'-tetrachlorobiphenyl and 2,4,5,3',4'-pentabromobiphenyl cause accumulation of uroporphyrin. In a previous paper, an isoenzyme of cytochrome P-450 induced by 3-methylcholanthrene had been implicated in this process [Sinclair, Bement, Bonkovsky & Sinclair (1984) Biochem. J. 222, 737-748]. Cells treated with 3,4,3',4'-tetrachlorobiphenyl and 5-aminolaevulinate accumulated uroporphyrin and heptacarboxyporphyrin, whereas similarly treated cells accumulated protoporphyrin immediately after piperonyl butoxide was added. Piperonyl butoxide also restored haem synthesis as detected by incorporation of radioactive 5-aminolaevulinate into haem, and decrease in drug-induced 5-aminolaevulinate synthase activity. The restoration of synthesis of protoporphyrin and haem by piperonyl butoxide was not affected by addition of cycloheximide, indicating recovery was probably not due to protein synthesis de novo. Piperonyl butoxide also reversed uroporphyrin accumulation caused by 3,4,5,3',4',5'-hexachlorobiphenyl, mixtures of other halogenated biphenyls, lindane, parathion, nifedipine and verapamil. The effect of piperonyl butoxide was probably not due to inhibition of metabolism of these compounds, since the hexachlorobiphenyl was scarcely metabolized. Other methylenedioxyphenyl compounds, as well as ellipticine and acetylaminofluorene, also reversed the uroporphyrin accumulation caused by 3,4,3',4'-tetrachlorobiphenyl. SKF-525A (2-dimethylaminoethyl-2,2-diphenyl valerate) did not reverse the uroporphyrin accumulation caused by the halogenated biphenyls, but did reverse that caused by phenobarbital and propylisopropylacetamide. We conclude that the mechanism of the uroporphyrin accumulation cannot be due to covalent binding of activated metabolites of halogenated compounds to uroporphyrinogen decarboxylase.

Tetrachlorobiphenyl metabolism, toxicity, and regulation of cytochrome P50 expression in a marine teleost fish

“…TCB exposure has previously been reported to inhibit heme synthesis in chick embryo hepatocytes (Sassa et al, 1986;Sinclair et al, 1986). However, in the present study CYPlA1 was the only microsomal heme protein with strongly reduced content at the high TCB dose as compared to the low dose.…”

Effects of mifepristone (RU‐486) on heme metabolism and cytochromes P ‐450 in cultured chick embryo liver cells

“…The lack of induction of cytochrome P-450 1A and 2H may account for the inability of RU-486 to increase uroporphyrin. Activities of cytochromes P-450 1A and 2H have been shown to play a role in increasing uroporphyrin accumulation in these cells after treatment with certain compounds, in the absence of a detectable inhibition of uroporphyrinogen decarboxylase [47][48][49][56][57][58]. Since cytochrome P-450 3A, but not cytochrome P-450 1A or cytochrome P-450 2H, is increased by RU-486, it appears that the 3A form is not able to catalyze the oxidation of uroporphyrinogen and, therefore, not increase uroporphyrin.…”

Involvement of Cytochrome P450 1A in the toxicity of aryl hydrocarbon receptor agonists : alteration arachidonic acid metabolism and production of reactive oxygen species

“…Previously, CYP1A from scup and rat were shown to produce ROS during their interaction with planar CB congeners (Chapter 4). Oxidation of bilirubin in chicken and rat liver microsomes was suggested to occur as a result of ROS formed during uncoupling of the CYP1A catalytic cycle by non-ortho CB congeners (Sinclair et al, 1986;DeMatteis et al, 1989). In rats, bilirubin oxidation has been shown to be catalyzed by CYP1A1 (DeMatteis et al, 1991).…”

“…That oxidation was suggested to occur as a result of ROS formed during uncoupling of the CYP1A catalytic cycle by nonortho PCBs (Sinclair et al, 1986;DeMatteis et al, 1991). Oxidative damage correlated with CYP1A induction following treatment of cells with pHAH (Toborek et al, 1995;Park et al, 1996) further suggests uncoupling of CYP1A.…”