Studies on rat liver cytochrome P-450s involved in the metabolism of antipyrine: phenobarbital- and 3-methylcholanthrene-inducible isozymes possessing 4-hydroxylase activity

Determination of antipyrine sulphoconjugates in isolated cultured rat hepatocytes

“…These authors found selective changes in metabolic profiles as a consequence of induction or inhibition, indicating that several isoforms of cytochrome P450 are involved in the metabolism of antipyrine. Several groups have investigated the effects of induction or inhibition upon the pattern of antipyrine metabolites in rat urine (Teunissen et al 1984b), human urine (Danhof et al 1982b, Onhaus et al 1987, Shaw et al 1985, Teunissen et al 1984a, on hepatic microsomal preparations (McManus andIlett 1979, Kahn et al 1982), or in isolated and cultured rat hepatocytes (Buppodom et al 1986, Chenery et al 1987, Loft and Poulsen 1989, 1990, Loft 1990). The last method raised problems in earlier years because of losses in cytochrome P450 levels within the first days of culture (Marceau et al 1986).…”

“…T o evaluate the pattern of conjugates of a given xenobiotic is not simple, and the lack of conjugate standards often complicates the problem. Hydrolysis of conjugates, either enzymically (Boettcher et al 1982c, Danhof et al 1979, Eichelbaum et al 1981, Nakagawa and Nakamura 1982, Teunissen et al 1983 or chemically (Baessman et al 1985, Boettcher et al 1984, Buppodom et al 1986), remains the standard approach, but the known instability of phase I metabolites of antipyrine makes the results questionable. This instability must be taken into account in the analytical measurements of phase I metabolites released from their conjugates by hydrolysis, especially with 4-OH-antipyrine and nor-antipyrine which are very labile (Baess-///I- , Teunissen et al 1983).…”

“…T o overcome all these difficulties, we developed an assay procedure for the direct and simultaneous quantitative determination of 4-hydroxyantipyrine sulphate (4-OH-S), Nor sulphate (Nor-S), and non-labile 3-CH20H metabolites in rat. Selective effects on the formation of the antipyrine metabolites have been shown with inducers such as phenobarbital (Buppodom et al 1986, Chenery et al 1987, Kahn et al 1982, 3-methylcholanthrene (MC) (Buppodom et al 1986, Kahn et al 1982 and with enzyme inhibitors such as S K F 525A or cimetidine (Loft 1990). These authors found selective changes in metabolic profiles as a consequence of induction or inhibition, indicating that several isoforms of cytochrome P450 are involved in the metabolism of antipyrine.…”

Effect of tacrine hydrochloride on hepatic drug metabolism

“…Antipyrine (AP) is completely metabolised by cytochrome P-450 enzymes and has been widely used as a model drug to investigate factors which influence the activity of the hepatic drug-oxidising capacity (4)(5)(6). Different isoenzymes are involved in the metabolism of AP to its three major metabolites: 3-hydroxymethyl antipyrine (HMA), 4-hydroxy antipyrine (aHA) and norantipyrine (NORA) (3,7,8). In vitro studies to identify these isoenzymes have implicated cytochrome P-450s IA2, 3A and 2A6 in the formation of aHA; HMA production was predominantly due to IA2, although 2C9 and 2EI participated to a lesser extent; IA2, 2A6, 2C9, 2C19, 2D6, 2El and 3A were involved in the formation of NORA (9).…”