Dissociation of cytochrome P-450 inactivation and induction

Montellano, Paul R. Ortiz de; Costa, Anita K.

doi:10.1016/0003-9861(86)90359-0

Cited by 25 publications

(10 citation statements)

References 42 publications

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“…Our data from the AD hydroxylation assay (Tables 3 and 4) provide direct evidence that ABT is an effective mechanismbased inactivator of rat hepatic CYP2A, CYP2B, CYP2C11, and CYP3A forms. Consistent with previous reports (Ortiz de Montellano and Costa 1986;Mugford et al 1992), we have found that a near-maximally effective concentration of ABT (1 mM) can only destroy approximately 60% of the total CYP in microsomes from untreated rats (Table 3) and 80% in microsomes from PB-treated rats (Table 4). Thus, there are at least some constitutive hepatic CYPs that do not recognize ABT as a substrate and (or) cannot activate ABT to a heme-destructive species.…”

Section: Figsupporting

confidence: 93%

Lack of mechanism-based inactivation of rat hepatic microsomal cytochromes P450 by doxorubicin

Re¹,

Lee²,

Riddick³

1999

Can. J. Physiol. Pharmacol.

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Administration of the antineoplastic doxorubicin to rodents causes depression of hepatic cytochrome P450 (CYP) dependent biotransformation, an effect that has been partially attributed to the ability of doxorubicin to stimulate microsomal lipid peroxidation. Since doxorubicin can be bioactivated by the CYP/NADPH-CYP reductase system to products that bind covalently to microsomal protein, we hypothesized that doxorubicin functions as a mechanism-based inactivator of hepatic microsomal CYPs and (or) NADPH-CYP reductase under conditions in which doxorubicin-stimulated NADPH-dependent lipid peroxidation is minimized. In vitro studies were conducted with hepatic microsomes isolated from untreated and phenobarbital-treated male rats. Unlike the positive control carbon tetrachloride, doxorubicin (10 microM) did not stimulate NADPH-dependent lipid peroxidation in microsomal incubations containing EDTA (1.5 mM). Doxorubicin did not cause NADPH-dependent loss of microsomal CYP, heme, or steroid hydroxylation activities selective for CYP2A, CYP2B, CYP2C11, and CYP3A. The positive control 1-aminobenzotriazole caused marked NADPH-dependent decreases in all of these parameters. Neither doxorubicin nor 1-aminobenzotriazole caused NADPH-dependent loss of NADPH-CYP reductase activity, and neither compound altered the immunoreactive protein levels of CYP2B, CYP2C11, CYP3A, and NADPH-CYP reductase. These results indicate that a pharmacologically relevant concentration of doxorubicin does not cause direct mechanism-based inactivation of hepatic microsomal CYPs or NADPH-CYP reductase, suggesting that the ability of doxorubicin to depress hepatic CYP-mediated biotransformation in vivo is due to lipid peroxidation mediated heme destruction, altered heme metabolism, and (or) decreased expression of selected CYP enzymes.

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Section: Figsupporting

confidence: 93%

Lack of mechanism-based inactivation of rat hepatic microsomal cytochromes P450 by doxorubicin

Re¹,

Lee²,

Riddick³

1999

Can. J. Physiol. Pharmacol.

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“…First, prolonged suppression of the catalytic activities of P-450s 2B1 and 2B2 by treatment with the mechanism-based, irreversible P-450 inactivator 1-aminobenzotriazole neither induces P-450s 2B1 and 2B2, nor blocks their induction by PB (Ortiz de Montellano & Costa, 1986). By contrast, this same inactivator effectively blocks clofibrate induction of both peroxisomal fatty acid fl-oxidation and the P-450 4A1-catalysed formation of fatty acid metabolites that is postulated to lead to this peroxisome proliferative response (Chan et al, 1991).…”

Section: Mechanisms Of Pb Inductionmentioning

confidence: 99%

Phenobarbital induction of cytochrome P-450 gene expression

Waxman

Azaroff

1992

Biochemical Journal

496

265

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“…The inactivation of P450 by 1-ABT involves the catalytic formation of benzyne, which either adds across two of the prosthetic heme nitrogen atoms to give an N,N-bridged porphyrin adduct (34,35) or covalently modifies the protein (36). Previous studies have demonstrated that 1-ABT inactivates the P450-dependent fatty acid -hydroxylation activity in rat microsomal preparations (36) and in vivo (37)(38)(39)(40). This inactivation was unexpected, because 1-ABT is a bulky aromatic compound with little resemblance to the normal CYP4A fatty acid substrates.…”

Section: Expression and Spectroscopic Characterization Of Cyp4a11mentioning

confidence: 99%

The Catalytic Site of Cytochrome P4504A11 (CYP4A11) and Its L131F Mutant

Dierks¹,

Zhang²,

Johnson³

et al. 1998

Journal of Biological Chemistry

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CYP4A11, the principal known human fatty acid -hydroxylase, has been expressed as a polyhistidine-tagged protein and purified to homogeneity. Based on an alignment with P450 BM-3 , the CYP4A11 L131F mutant has been constructed and similarly expressed. The two proteins are spectroscopically indistinguishable, but wildtype CYP4A11 primarily catalyzes -hydroxylation, and the L131F mutant only -1 hydroxylation, of lauric acid. The L131F mutant is highly uncoupled in that it slowly ( -1)-hydroxylates lauric acid yet consumes NADPH at approximately the same rate as the wild-type enzyme. Wild-type CYP4A11 is inactivated by 1-aminobenzotriazole under turnover conditions but the L131F mutant is not. This observation, in conjunction with the binding affinities of substituted imidazoles for the two proteins, indicates that the L131F mutation decreases access of exogenous substrates to the heme site. Leu-131 thus plays a key role in controlling the regioselectivity of substrate hydroxylation and the extent of coupled versus uncoupled enzyme turnover. A further important finding is that the substituted imidazoles bind more weakly to CYP4A11 and its L131F mutant when these proteins are reduced by NADPH-cytochrome P450 reductase than by dithionite. This finding suggests that the ferric enzyme undergoes a conformational change that depends on both reduction of the iron and the presence of cytochrome P450 reductase and NADPH.CYP4A11, one of the three known members of the human CYP4 family (1-4), is the only established fatty acid -hydroxylase in human liver and kidney (5, 6). Little is actually known about the structure and function of CYP4A11 other than its fatty acid hydroxylation activity and its requirement for both cytochrome P450 reductase and cytochrome b 5 for optimal activity (2). In the presence of these electron transfer partners, CYP4A11 catalyzes the -hydroxylation of lauric, palmitic, and arachidonic acids with turnover numbers of 9.8, 2.2, and 0.6 min Ϫ1 , but it does not hydroxylate prostaglandins (2). The paucity of information on this enzyme is unfortunate, because current evidence suggests that it may play an important role in human physiology and may be a potential drug target. These conclusions derive from studies with rats which show that (a) 20-hydroxyeicosatetraenoic acid, the -hydroxylation product of arachidonic acid, is a potent vasoconstrictor (7, 8), (b) 20-hydroxyeicosatetraenoic acid is a major arachidonic acid metabolite in the spontaneously hypertensive rat (9), and (c) inhibition of arachidonic acid -hydroxylation by 17-octadecynoic acid alters renal function (10).Most of our understanding of CYP4A11 derives from an extrapolation of the available information on rat CYP4A1, with which it exhibits 76% sequence identity (1). A defining feature of the CYP4A enzymes is their ability to favor -over ( -1)-hydroxylation, a preference that requires the thermodynamically disfavored breaking of a strong primary terminal methyl C-H bond rather than a weaker secondary C-H bond of the -1 (or -n, n Ͼ 0) methyl...

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Dissociation of cytochrome P-450 inactivation and induction

Cited by 25 publications

References 42 publications

Lack of mechanism-based inactivation of rat hepatic microsomal cytochromes P450 by doxorubicin

Lack of mechanism-based inactivation of rat hepatic microsomal cytochromes P450 by doxorubicin

Phenobarbital induction of cytochrome P-450 gene expression

The Catalytic Site of Cytochrome P4504A11 (CYP4A11) and Its L131F Mutant

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