Degradation of rat hepatic cytochrome P-450 heme by 3,5-dicarbethoxy-2,6-dimethyl-4-ethyl-1,4-dihydropyridine to irreversibly bound protein adducts.
Administration of 3,5-dicarbethoxy-2,6-dimethyl-4-ethyl-1,4-dihydropyridine (DDEP) (a structural analog of the dihydropyridine Ca2+ antagonists) to untreated, phenobarbital-, or dexamethasone-pretreated rats results in time-dependent losses of hepatic cytochrome P-450 content. Functional markers for various cytochrome P-450 isozymes have permitted the identification of P-450h, P-450 PB-1/k, and P-450p as the isozymes inactivated preferentially by the drug. DDEP-mediated cytochrome P-450 destruction may be reproduced in vitro, is most prominent after pretreatment of rats with dexamethasone, pregnenolone 16 alpha-carbonitrile or phenobarbital, and is blocked by triacetyloleandomycin. These findings together with the observation that DDEP markedly inactivates hepatic 2 beta- and 6 beta-testosterone hydroxylase and erythromycin N-demethylase tend to indict the steroid-inducible P-450p isozyme as a key protagonist in this event. The precise mechanism of such DDEP-mediated P-450p heme destruction is unclear, but involves prosthetic heme alkylation of the apocytochrome at its active site in what appears to be a novel mechanism-based "suicide" inactivation. Such inactivation appears to involve fragmentation of the heme to reactive metabolites that irreversibly bind to the protein, but the chemical structure of the heme-protein adducts is yet to be established. Intriguingly, such DDEP-mediated P-450p destruction in vivo also results in accelerated loss of immunochemically detectable apocytochrome P-450p. It remains to be determined whether or not this loss is due to enhanced proteolysis triggered by the structural modification of the apocytochrome.
Correia
M A
MA
Department of Pharmacology, University of California, San Francisco 94143.
Decker
C
C
Sugiyama
K
K
Caldera
P
P
Bornheim
L
L
Wrighton
S A
SA
Rettie
A E
AE
Trager
W F
WF
D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology; D003997:Dicarbethoxydihydrocollidine / Q000031:analogs & derivatives / Q000494:pharmacology*; D004095:Dihydropyridines / Q000494:pharmacology*; D006418:Heme / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*; D010634:Phenobarbital / Q000494:pharmacology; D011485:Protein Binding; D051381:Rats; D011919:Rats, Inbred Strains
D004095:Dihydropyridines; C030826:3,5-dicarbethoxy-2,6-dimethyl-4-ethyl-1,4-dihydropyridine; D006418:Heme; D003997:Dicarbethoxydihydrocollidine; D003907:Dexamethasone; D003577:Cytochrome P-450 Enzyme System; D010634:Phenobarbital