title: R- and S-Warfarin inhibition of vitamin K and vitamin K 2,3-epoxide reductase activities in the rat.
abstract: Reduction of vitamin K 2,3-epoxide and vitamin K catalyzed by hepatic microsomal enzymes is required for normal, postribosomal, gamma-carboxyglutamate formation in the prothrombin complex Factors II, VII, IX, and X. The R- and S-warfarin enantiomers differentially inhibit (S-warfarin is 2 to 5 times more active) vitamin K function by mechanisms which have not been unambiguously determined. As a step toward determining the physiologically relevant site(s) of warfarin-antivitamin K activity we investigated in Wistar rats the effects of R- and S-warfarin on vitamin K 2,3-epoxide and vitamin K reductase activities and correlated them with effects on plasma concentrations of the Factors II, VII, and X. Based on the results of these studies we conclude that: 1) warfarin inhibition of the vitamin K 2,3-epoxide and vitamin K reductases is essentially irreversible; 2) S-warfarin stereoselectively inhibits both reductases in vivo but not in vitro; 3) the vitamin K reductase which utilizes dithiothreitol as cofactor in vitro is primarily responsible for vitamin K reduction to vitamin K hydroquinone under physiological conditions; 4) warfarin initially inhibits gamma-carboxyglutamate formation by inhibiting simultaneously the vitamin K 2,3-epoxide and vitamin K reductases; and 5) following enantiomer administration there is an apparent lack of correlation between the restoration of the reductase activities and the reinitiation of coagulation factor synthesis.
mesh_terms: D000818:Animals; D001779:Blood Coagulation Factors / Q000378:metabolism; D007536:Isomerism; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism*; D011808:Quinone Reductases / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D064417:Vitamin K Epoxide Reductases; D014859:Warfarin / Q000097:blood / Q000494:pharmacology*
chemical_list: D001779:Blood Coagulation Factors; D014859:Warfarin; D006899:Mixed Function Oxygenases; D064417:Vitamin K Epoxide Reductases; D009247:NADH, NADPH Oxidoreductases; D011808:Quinone Reductases