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  • Title: The effects of warfarin and edoxaban, an oral direct factor Xa inhibitor, on gammacarboxylated (Gla-osteocalcin) and undercarboxylated osteocalcin (uc-osteocalcin) in rats.
    Author: Morishima Y, Kamisato C, Honda Y, Furugohri T, Shibano T.
    Journal: Thromb Res; 2013 Jan; 131(1):59-63. PubMed ID: 22999414.
    Abstract:
    INTRODUCTION: Osteocalcin plays a role in bone homeostasis. The vitamin K cycle is essential for the gamma-carboxylation of glutamic acid residues in osteocalcin. Some evidence suggests that long-term warfarin therapy, which inhibits the vitamin K cycle and prevents gamma-carboxylation, is associated with increased bone-fracture risk. The aim of this study was to determine the effects of warfarin and edoxaban, a direct factor Xa inhibitor, on the serum concentration of total, gamma-carboxylated (Gla-osteocalcin) and undercarboxylated osteocalcin (uc-osteocalcin) in rats. MATERIALS AND METHODS: Rats received orally administered warfarin or edoxaban, and 24h later serum and plasma were prepared. Osteocalcin level in serum was measured with ELISA. A Gla-osteocalcin was precipitated by the addition of hydroxyapatite, and the resulting supernatant was used for measuring uc-osteocalcin. Prothrombin time (PT) of plasma was also measured. RESULTS: Warfarin at 1mg/kg (a dose which prolonged PT 2.62-fold) markedly increased the serum level of uc-osteocalcin and slightly increased the total osteocalcin level compared with control in rats. Serum Gla-osteocalcin significantly decreased by warfarin. Edoxaban at 1mg/kg (an antithrombotic dose) and 54mg/kg (a dose which prolonged PT 2.25-fold) had no effects on total, uc-, and Gla-osteocalcin levels. CONCLUSIONS: This study demonstrates that warfarin impaired the carboxylation of osteocalcin in rats. In contrast, edoxaban at or higher doses than needed for an antithrombotic effect sustained the circulating Gla-osteocalcin level. These findings suggest that edoxaban has no effects on the production of Gla-osteocalcin and thus, may have a lower risk of adverse effects on bone health.
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