These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


PUBMED FOR HANDHELDS

Search MEDLINE/PubMed


  • Title: The potent antioxidant activity of the vitamin K cycle in microsomal lipid peroxidation.
    Author: Vervoort LM, Ronden JE, Thijssen HH.
    Journal: Biochem Pharmacol; 1997 Oct 15; 54(8):871-6. PubMed ID: 9354587.
    Abstract:
    In the vitamin K cycle, vitamin K-hydroquinone, the active cofactor for gamma-glutamylcarboxylase, is continuously regenerated. The successive pathways contain oxidation of the hydroquinone to the epoxide, followed by reduction to the quinone and reduction to the hydroquinone. Vitamin K-hydroquinone is a potent radical scavenging species (Mukai et al., J Biol Chem 267: 22277-22281, 1992). We tested the potential antioxidant activity of the vitamin K cycle in lipid peroxidation reactions (thiobarbituric acid reactive substances, TBARS) in rat liver microsomes. As prooxidant we used Fe2+/ascorbate, NADPH-Fe3+/ATP, and NADPH/CCl4. Vitamin K (< or = 50 microM) on its own did not influence the formation of TBARS. In combination with 1 mM dithiothreitol (DTT), the reductive cofactor for the microsomal enzyme vitamin K epoxide reductase, vitamin K suppressed lipid peroxidation with a concentration that blocked the maximal response by 50% (IC50) of ca. 0.2 microM. Vitamin K1 (phylloquinone) and vitamin K2 (menaquinone-4) were equally active. Warfarin (5 microM) and chloro-vitamin K (50 microM), inhibitors of vitamin K epoxide reductase and gamma-glutamylcarboxylase, respectively, were able to completely abolish the antioxidant effect. Lipid peroxidation was inversely related to the amount of vitamin K hydroquinone in the reaction. Vitamin K epoxide reductase seemed sensitive to lipid peroxidation, with half of the activity being lost within 10 min during oxidation with NADPH/CCl4. The inactivation could be attenuated by antioxidants such as vitamin E, reduced glutathione, and menadione and also by a K vitamin in combination with DTT, but not by superoxide dismutase and catalase. The results show that the vitamin K cycle could act as a potent antioxidant, that the active species in all probability is vitamin K-hydroquinone, and that the primary reaction product is the semiquinone. The results also show that the reaction product is processed in the vitamin K cycle to regenerate vitamin K-hydroquinone.
    [Abstract] [Full Text] [Related] [New Search]