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Titolo:
alpha-naphthoflavone acts as activator and reversible or irreversible inhibitor of rabbit microsomal CYP3A6
Autore:
Boek-Dohalska, L; Hodek, P; Sulc, M; Stiborova, M;
Indirizzi:
Charles Univ, Fac Nat Sci, Dept Biochem, Prague 12840 2, Czech Republic Charles Univ Prague Czech Republic 12840 2 rague 12840 2, Czech Republic
Titolo Testata:
CHEMICO-BIOLOGICAL INTERACTIONS
fascicolo: 1, volume: 138, anno: 2001,
pagine: 85 - 106
SICI:
0009-2797(20011025)138:1<85:AAAAAR>2.0.ZU;2-R
Fonte:
ISI
Lingua:
ENG
Soggetto:
HUMAN CYTOCHROME-P450 3A4; HUMAN-LIVER-MICROSOMES; HUMAN CYTOCHROMES-P450; BETA-NAPHTHOFLAVONE; SUDAN-I; METABOLISM; SUBSTRATE; FLAVONOIDS; KINETICS; SITE;
Keywords:
alpha-naphthoflavone; cytochrome P450; CYP3A6; CYP3A4; modulation of enzyme activities; metabolism; mechanism-based inhibition;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Life Sciences
Citazioni:
55
Recensione:
Indirizzi per estratti:
Indirizzo: Stiborova, M Charles Univ, Fac Nat Sci, Dept Biochem, Albertov 2030, Prague 12840 2, Czech Republic Charles Univ Albertov 2030 Prague Czech Republic12840 2 lic
Citazione:
L. Boek-Dohalska et al., "alpha-naphthoflavone acts as activator and reversible or irreversible inhibitor of rabbit microsomal CYP3A6", CHEM-BIO IN, 138(1), 2001, pp. 85-106

Abstract

This report describes the effect of alpha -naphthoflavone (alpha -NF), a known substrate, inhibitor and activator of several cytochromes P450 (CYP), on rabbit CYP3A6. Hepatic microsomes of rabbit pretreated with rifampicine (RIF), enriched with CYP3A6, as well as purified CYP3A6 reconstituted with isolated NADPH:CYP reductase were used as enzymatic systems in this study. The data from difference spectroscopy experiments showed that alpha -NF does yield a type I binding spectrum. This compound is oxidized by microsomal CYP3A6 into two metabolites (5,6-epoxide and trans-7,8-dihydrodiol). While alpha -NF is a substrate of CYP3A6, it also acts as an enzyme modulator. Under the conditions used, stimulation of 17 beta -estradiol 2-hydroxylation by alpha -NF was observed. In contrast, this compound reversibly inhibited N-demethylation of erythromycin and tamoxifen, competitively with respect to these substrates, having the K-i values of 51.5 and 18.0 muM, respectively. Moreover, alpha -NF was found to be an effective inactivator of progesterone and testosterone 6 beta -hydroxylation catalyzed by CYP3A6 in RIF-microsomes. In addition, time- and concentration-dependent inactivation of human CYP3A4-mediated 6 beta -hydroxylation of testosterone by alpha -NF, was determined. The inactivation of CYP3A6 followed pseudo-first-order kinetics and was dependent on both NADPH and alpha -NF. The concentrations required for half-maximal inactivation (K-i) were 80.1 and 108.5 muM and the times required for half of the enzyme to be inactivated were 10.0 and 11.9 min for6 beta -hydroxylation of progesterone and testosterone, respectively. The loss of the enzyme activity was not recovered following dialysis, while 90%of the ability to form a reduced CO complex remained. This indicates the binding of alpha -NF to a CYP apoprotein molecule rather than to a heme. moiety. Protection from inactivation was seen in the presence of all tested CYP3A substrates. Progesterone and testosterone protected CYP3A6 against inactivation competitively with respect to inactivator, erythromycin non-competitively and 17 beta -estradiol showed a mixed type of protection. Here, we described for the first time that alpha -NF is capable of irreversible inhibition of microsomal rabbit CYP3A6 and human CYP3A4. The obtained results strongly suggest that the CYP3A active center contains at least two and probably three distinct binding sites for substrates. (C) 2001 Elsevier ScienceIreland Ltd. All rights reserved.

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Documento generato il 25/01/20 alle ore 03:26:26