title: CYP4 isozyme specificity and the relationship between omega-hydroxylation and terminal desaturation of valproic acid.
abstract: The cytochrome P450-dependent terminal desaturation of valproic acid (VPA) is of both toxicological and mechanistic interest because the product, 4-ene-VPA, is a more potent hepatotoxin than the parent compound and its generation represents a rather novel metabolic reaction for the cytochrome P450 system. In the present study, lung microsomes from rabbits were identified as a rich source of VPA desaturase activity. Monospecific polyclonal antibodies directed against CYP4B1 (anti-4B) inhibited 82% of 4-ene-VPA formation, whereas monospecific polyclonal antibodies directed against CYP2B4 (anti-2B) inhibited only 15% of 4-ene-VPA formation. Anti-4B also inhibited 95% of the 5-hydroxy-VPA formation, but only 42% of 4-hydroxy-VPA formation. These data suggest that CYP4B1 accounts for more than 80% of the 4-ene- and 5-hydroxy-VPA metabolites generated by rabbit lung microsomes. CYP4B1 expressed in HepG2 cells metabolized VPA with a turnover number of 35 min-1 and formed the 5-hydroxy-, 4-hydroxy-, and 4-ene-VPA metabolites in a ratio of 110:2:1, respectively. In contrast, the lauric acid omega-hydroxylases, CYP4A1 and CYP4A3, did not give rise to detectable levels of any of these VPA metabolites. Therefore, these studies demonstrate a new functional role for CYP4B1 in the terminal desaturation and omega-hydroxylation of this short, branched-chain fatty acid.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Medicinal Chemistry, University of Washington, Seattle 98195, USA.
authors.forename: A E
authors.initials: AE
authors.lastname: Rettie
authors.forename: P R
authors.initials: PR
authors.lastname: Sheffels
authors.forename: K R
authors.initials: KR
authors.lastname: Korzekwa
authors.forename: F J
authors.initials: FJ
authors.lastname: Gonzalez
authors.forename: R M
authors.initials: RM
authors.lastname: Philpot
authors.forename: T A
authors.initials: TA
authors.lastname: Baillie
mesh_terms: D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D003903:Deuterium; D005229:Fatty Acids, Monounsaturated / Q000378:metabolism*; D005260:Female; D006900:Hydroxylation; D007527:Isoenzymes / Q000378:metabolism*; D008168:Lung / Q000201:enzymology*; D008297:Male; D008861:Microsomes / Q000201:enzymology; D010088:Oxidoreductases / Q000378:metabolism; D011817:Rabbits; D013379:Substrate Specificity; D014635:Valproic Acid / Q000378:metabolism*
chemical_list: D005229:Fatty Acids, Monounsaturated; D007527:Isoenzymes; C045022:2-propyl-4-pentenoic acid; D014635:Valproic Acid; D003577:Cytochrome P-450 Enzyme System; D003903:Deuterium; D010088:Oxidoreductases