PT  - JOURNAL ARTICLE
AU  - D E Williams
AU  - R L Reed
AU  - B Kedzierski
AU  - G A Dannan
AU  - F P Guengerich
AU  - D R Buhler
TI  - Bioactivation and detoxication of the pyrrolizidine alkaloid senecionine by cytochrome P-450 enzymes in rat liver.
DP  - 1989 Jul 01
TA  - Drug Metabolism and Disposition
PG  - 387--392
VI  - 17
IP  - 4
4099  - http://dmd.aspetjournals.org/content/17/4/387.short
4100  - http://dmd.aspetjournals.org/content/17/4/387.full
SO  - Drug Metab Dispos1989 Jul 01; 17
AB  - Rats display a marked sex difference in the oxidation of the pyrrolizidine alkaloid senecionine, especially with respect to N-oxidation. This sex difference was largely eliminated following treatment with dexamethasone. These observations suggested the potential involvement of the male-specific cytochrome P-450 UT-A and the P-450 PCN-E in the metabolism of this pyrrolizidine alkaloid. Reconstituted rat P-450 UT-A exhibited a high rate of N-oxidation (15 nmol min-1 nmol P-450-1) which is almost 3-fold higher than the turnover number observed with male rat liver microsomes. In contrast, rat P-450 UT-A displayed a much lower activity toward necine pyrrole [+/-)-6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine, DHP) formation (1.0 nmol min-1 nmol P-450-1). The N-oxygenation and pyrrole formation activities displayed by rat cytochromes P-450 PB-B and P-450 BNF-B toward senecionine were low, with rates less than 1 nmol min-1 nmol P-450-1. Rabbit antibody to rat P-450 UT-A inhibited the senecionine-N-oxidation activity of untreated male rat liver microsomes by 60%, with lesser inhibition of DHP production. Rabbit antibody to human P-450NF (the human homologue to rat P-450 PCN-E) was a potent inhibitor of DHP production by untreated male rat liver microsomes. With microsomes from dexamethasone-pretreated rats, anti-P-450NF inhibited DHP and N-oxide production in parallel. We conclude that the large sex difference in senecionine N-oxidation probably is the result of the specificity of P-450 isozymes UT-A and PCN-E.(ABSTRACT TRUNCATED AT 250 WORDS)