CYTOTOXICITY OF PARACETAMOL AND 3,5-DIHALOGENATED ANALOGS - ROLE OF CYTOCHROME-P-450 AND FORMATION OF GSH CONJUGATES AND PROTEIN ADDUCTS

The effect of 3,5-dihalogenation of paracetamol (PAR) on the cytotoxic ity in rat hepatocytes isolated from P-naphthoflavone pretreated, non- fasted rats, and the role of cytochrome P-450 in this regard, were stu died. On incubation, 3,5-difluoro-PAR, 3,5-dichloro-PAR and 3,5-dibrom o-PAR, as well as PAR, caused severe leakage of lactate dehydrogenase (LDH) which was preceded by a rapid concentration- and time-dependent depletion of intracellular glutathione (GSH). IC50 values, representin g the concentration of compound that caused 50% GSH depletion after 30 min of incubation, varied from 0.1 to 0.5 mM. This LDH leakage and GS H depletion could be inhibited by 1-ethynylpyrene. In hepatocytes from uninduced rats, GSH depletion was much less prominent and the concomi tant LDH leakage almost completely absent. HPLC analysis of soluble me tabolites and gas chromatography-mass spectrometry analysis, after alk aline peralkylation of the protein fraction, revealed (a) that 3,5-dih alogenated PAR analogues were liable to structure-related detoxificati on by glucuronidation, and (b) analogous to PAR, a substantial amount of each 3,5-dihalogenated PAR analogue was bioactivated by cytochrome P-450, ultimately leading to GSH-conjugates as well as (for 3,5-dichlo ro-PAR and 3,5-dibromo-PAR), protein adducts at regio-specific aromati c positions. (C) 1997 Elsevier Science Ltd.