Bioactivation of monocrotaline by P-450 3A in rat liver.
Monocrotaline (MCT) is bioactivated in liver cytochrome P-450s to MCT pyrrole (MCTP), which primarily injures the lung endothelium to result in the development of pulmonary hypertension (PH) in rats. However, whether there is a relation between the degree of PH and the activity of liver cytochrome P-450 to convert MCT to MCTP remains unclear. To examine the relation between these physiological and biochemical changes, we first measured the severity of MCT-induced (20 mg/kg) PH in male, female, castrated male, and phenobarbital (PB, liver P-450s inducer)-pretreated male rats. The degree of right ventricular hypertrophy was more severe in PB-pretreated male than in control male rats. It was also more severe in male than in either female or castrated male rats, suggesting that sex-specific P-450s could be involved in the metabolic pathways of MCT in the liver. Further to explore which of the isozymes (2A2, 2C11, and 3A) of P-450s in the liver is responsible for the bioactivation of MCT, we measured the rate of MCTP production in hepatic microsomes by a modified Mattock's method. Treatment of male rats with PB and pregnenolone 16alpha-carbonitrile (PCN), which is the specific inducer of P-450 3A, increased the rate of MCTP production, suggesting that P-450 3A may contribute to the conversion to pyrrole. Therefore we measured the amount of P-450 3A protein by immunoblotting and attempted to inhibit MCT metabolism by using antibodies to P-450 3A. P-450 3A was significantly induced by PCN (6.5-fold) and PB (4.6-fold) treatment and reduced by castration (0.38-fold). The amount of P-450 3A was closely correlated with the production of MCTP, and the conversion of MCT to MCTP was strongly inhibited by antibodies against P-450 3A. These results indicated that P-450 3A was predominantly responsible for the metabolism of MCT to MCTP in rat liver and suggested a tight linkage between the degree of PH and the activity of liver P-450 3A.
Kasahara
Y
Y
Department of Chest Medicine, School of Medicine, Chiba University, Japan.
Kiyatake
K
K
Tatsumi
K
K
Sugito
K
K
Kakusaka
I
I
Yamagata
S
S
Ohmori
S
S
Kitada
M
M
Kuriyama
T
T
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D001711:Biotransformation; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000276:immunology / Q000378:metabolism*; D005260:Female; D006321:Heart / Q000187:drug effects; D006352:Heart Ventricles / Q000473:pathology; D006976:Hypertension, Pulmonary / Q000139:chemically induced / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D006984:Hypertrophy; D007074:Immunoglobulin G / Q000276:immunology; D008099:Liver / Q000201:enzymology* / Q000276:immunology; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology / Q000276:immunology; D016686:Monocrotaline / Q000031:analogs & derivatives / Q000378:metabolism* / Q000633:toxicity; D009919:Orchiectomy; D009929:Organ Size; D010089:Oxidoreductases, N-Demethylating / Q000276:immunology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012737:Sex Factors; D017725:Ventricular Pressure / Q000187:drug effects
D007074:Immunoglobulin G; C014114:monocrotaline pyrrole; D016686:Monocrotaline; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; D051544:Cytochrome P-450 CYP3A; D010089:Oxidoreductases, N-Demethylating