Excessive mineralization with growth plate closure in rats on chronic warfarin treatment.

Abstract

Rats maintained for 8 months on a level of warfarin sufficient to decrease the vitamin K-dependent protein of bone (bone Gla protein) to 2% ofnormal have an excessive mineralization disorder characterized by complete fusion of the proximal tibial growth plate and cessation of longitudinal growth. The general features of this abnormality resemble the fetal warfarin syndrome in humans, a disorder also characterized by excessive mineralization of the growth plate. These excessive mineralization disorders may be caused by the decreased levels of bone Gla protein, a protein that potently inhibits mineralization in vitro.The metabolism of vitamin K presents several intriguing problems in vertebrate physiology and biochemistry. One of the most interesting ofthese is the role ofvitamin K in systems other than blood coagulation. The classical approach to the analysis ofvitamin K physiology has been the study ofdefects in vitamin K-deficient animals. Such studies have established that the first consequence of acute vitamin K deficiency is bleeding and death due to the synthesis of abnormal forms of blood coagulation factors such as prothrombin and factors VII, IX, and X. It is now known that the abnormality in these factors is the absence of 'y-carboxyglutamate (Gla), a Ca2" binding amino acid whose post-translational synthesis from glutamate requires vitamin K (1, 2).Our primary interest over the past several years has been the function of bone Gla protein (BGP), a 49-residue protein of known structure (3, 4) which is numerically one of the 10 most abundant proteins in a typical vertebrate (5,6). To analyze the function ofthis protein in bone metabolism we developed a simple protocol by which rats can be maintained on the vitamin K antagonist warfarin without problems due to bleeding (7). In previous studies we found that animals maintained from birth to 2 months of age on this protocol grow normally and have normal bone structure and mineralization in spite of bone levels of BGP which are only 2% of normal (7).We report here the discovery of excessive mineralization with growth plate closure in the proximal tibia ofrats maintained on warfarin from birth to 8 months of age. MATERIALS AND METHODSMaintenance of Animals on Warfarin. Simonsen albino rats (Sprague-Dawley-derived, Simonsen Laboratories, Gilroy, CA) were maintained from birth to 8 months of age on daily dosages ofwarfarin and vitamin K1 as described (7). To facilitate comparisons, the 10 control rats were selected from litters born at the same time as experimental animals and received daily doses of saline and vitamin K1 (7). Both experimental and control groups had seven male and three female rats. None of the 10 experimental rats chosen at birth for this study showed signs of bleeding or ill health over the 8 months of the experiment. As reported (7), the weight gain ofexperimental and control rats was identical up to 90 days ofage. At8 months ofage the average weights were 402 g for the male and 237 g for the female experimental rats and 455 g for t...

VKORC1L1, an Enzyme Rescuing the Vitamin K 2,3-Epoxide Reductase Activity in Some Extrahepatic Tissues during Anticoagulation Therapy

“…In laboratory animals, ectopic calcifications were observed in mice ApoE Ϫ/Ϫ treated by warfarin (20). Similarly, OC depletion in bone was observed consecutively to the use of warfarin (22,23). Nevertheless, the dose of warfarin used in both studies was completely disproportionate compared with the therapeutic dose used in human medicine.…”

“…In other soft tissues known to also express MGP at a high rate, no calcification was observed in the different studies. When rats were treated with a warfarin dose given once every 24 h, a complete absence of artery calcification was noted (22,23,34,35). Some of these studies described a depletion of OC in bone consecutively to the inhibition of ␥-carboxylation of this VKDP (22,23,35,36).…”

“…When rats were treated with a warfarin dose given once every 24 h, a complete absence of artery calcification was noted (22,23,34,35). Some of these studies described a depletion of OC in bone consecutively to the inhibition of ␥-carboxylation of this VKDP (22,23,35,36). Nevertheless, these various experiments were performed in rats receiving a vitamin K-depleted diet, and undercarboxylated OC in plasma and OC in bone are considered as very good markers of the deficiency in vit K. It is thus very difficult to interpret these experiences.…”

Low vitamin K status is associated with osteoarthritis in the hand and knee

“…Hence, vitamin K is an important regulator of bone and cartilage mineralization. Vitamin K also regulates growth plate cartilage calcification, as revealed by effects of vitamin K antagonism by warfarin (6)(7)(8)(9)(10). Genetic deficiencies of MGP in humans and mice have been linked to skeletal abnormalities, including premature epiphyseal calcification and shortening of long limb bones, reflecting endochondral bone formation (11)(12)(13)(14).…”

New Perspectives for the Nutritional Value of Vitamin K in Human Health

“…Since then, many in vitro and in vivo experiments have shown that VKAs induce vitamin K deficiency, which has been unequivocally related to increased mineralization of several tissues, particularly in the vascular tree and skeletal elements. Rats treated with warfarin presented extensive vascular calcification which could be inhibited by simultaneous treatments with vitamin K [28][29][30]. Furthermore, vitamin K was shown to induce a regression of preformed warfarin-induced vascular calcifications, with restoration of arterial distensibility [31].…”