Normal and warfarin-resistant rat hepatocyte metabolism of vitamin K 2,3-epoxide: evidence for multiple pathways of hydroxyvitamin K formation.
Vitamin K and 3- (and/or 2)-hydroxy-2,3-dihydro-2-methyl-3-phytyl-1,4-naphthoquinone (hydroxyvitamin K) have been identified as metabolites of vitamin K 2,3-epoxide incubated with hepatocytes isolated from normal and warfarin-resistant rats. Dithiothreitol added to the extracellular medium differentially enhanced the formation of both metabolites: hydroxyvitamin K formation, almost undetectable in the absence of dithiothreitol, was particularly affected. Addition of the vitamin K 2,3-epoxide reductase inhibitors warfarin (5 to 100 microM) and brodifacoum (1 to 5 microM) to normal rat hepatocyte cultures produced a slight increase in hydroxyvitamin K formation and a marked inhibition of vitamin K formation. Brodifacoum was a weak inhibitor of hydroxyvitamin K formation at higher concentrations. Hepatocytes from warfarin-resistant rats catalyzed hydroxyvitamin K formation 1.5 to 2 times faster and vitamin K formation 1.5 to 2 times slower than did normal rat hepatocytes. The addition of warfarin to these cultures had no effect on epoxide metabolism to hydroxyvitamin K and only partially diminished metabolism to vitamin K. In contrast, brodifacoum (1 microM) addition produced 50% inhibition of hydroxyvitamin K formation and almost complete inhibition of vitamin K formation. These data suggest that in resistant, but not in normal rat hepatocytes, the vitamin K 2,3-epoxide reductase makes a significant contribution to hydroxyvitamin K formation. A second sulfhydryl-dependent pathway, present in both strains, is also involved in the formation of this metabolite. They also suggest that in resistant rats, warfarin inhibition of the vitamin K 2,3-epoxide reductase, and presumably the sulfhydryl-dependent vitamin K reductase, is incomplete and independent of concentration.
Trivedi
L S
LS
Wadsworth Center for Laboratories and Research, New York State Department of Health, Albany 12201.
Rhee
M
M
Galivan
J H
JH
Fasco
M J
MJ
D000818:Animals; D002478:Cells, Cultured; D004229:Dithiothreitol / Q000494:pharmacology; D004351:Drug Resistance; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D014812:Vitamin K / Q000031:analogs & derivatives* / Q000096:biosynthesis; D010837:Vitamin K 1 / Q000031:analogs & derivatives* / Q000378:metabolism; D014859:Warfarin / Q000494:pharmacology*
C017420:gamma-hydroxyvitamin K; D014812:Vitamin K; C016186:vitamin K1 oxide; D014859:Warfarin; D010837:Vitamin K 1; D004229:Dithiothreitol