Vitamin K deficiency from long-term warfarin anticoagulation does not alter skeletal status in male rhesus monkeys.

UNLABELLED: Vitamin K (K) inadequacy may cause bone loss. Thus, K deficiency induced by anticoagulants (e.g., warfarin) may be an osteoporosis risk factor. The skeletal impact of long-term warfarin anticoagulation was evaluated in male monkeys. No effect on BMD or bone markers of skeletal turnover was observed. This study suggests that warfarin-induced K deficiency does not have skeletal effects. INTRODUCTION: The skeletal role of vitamin K (K) remains unclear. It is reasonable that a potential role of vitamin K in bone health could be elucidated by study of patients receiving oral anticoagulants that act to produce vitamin K deficiency. However, some, but not all, reports find K deficiency induced by warfarin (W) anticoagulation to be associated with low bone mass. Additionally, epidemiologic studies have found W use to be associated with either increased or no change in fracture risk. Such divergent results may imply that human studies are compromised by the physical illnesses for which W was prescribed. MATERIALS AND METHODS: To remove this potential confounder, we prospectively assessed skeletal status during long-term W anticoagulation of healthy nonhuman primates. Twenty adult (age, 7.4-17.9 yr, mean, 11.7 yr) male rhesus monkeys (Macaca mulatta) were randomized to daily W treatment or control groups. Bone mass of the total body, lumbar spine, and distal and central radius was determined by DXA at baseline and after 3, 6, 9, 12, 18, 24, and 30 mo of W treatment. Serum chemistries, urinary calcium excretion, bone-specific alkaline phosphatase, and total and percent unbound osteocalcin were measured at the same time-points. Prothrombin time and international normalized ratio (INR) were monitored monthly. Serum 25-hydroxyvitamin D was measured at the time of study conclusion. RESULTS: W treatment produced skeletal K deficiency documented by elevation of circulating undercarboxylated osteocalcin (8.3% W versus 0.4% control, p<0.0001) but did not alter serum markers of skeletal turnover, urinary calcium excretion, or BMD. CONCLUSIONS: In male rhesus monkeys, long-term W anticoagulation does not alter serum markers of bone turnover or BMD. Long-term W therapy does not have adverse skeletal consequences in primates with high intakes of calcium and vitamin D.

Nutritional vitamin K-intake and urinary gamma-carboxyglutamate excretion in the rat.

Using the rat as an experimental animal model we have found that prothrombin synthesis reaches its maximal level at a relatively low dietary vitamin K intake. At still higher vitamin K intakes, however, the urinary Gla-excretion was substantially increased, showing a different vitamin K requirement for liver and extrahepatic tissues. The increased urinary Gla-excretion was found for both phylloquinone and menaquinone-4, but not for menaquinone-8, which questions the bioavailability of higher menaquinones for extrahepatic tissues. A discrepancy was found between effects of nutritional vitamin K-deficiency and treatment with a vitamin K-antagonist (brodifacoum). With both regimens plasma prothrombin rapidly decreased to well below 10% of the starting values, but in case of K-deficiency urinary Gla had hardly decreased in 7 days, whereas after 3 days of brodifacoum treatment Gla-excretion had decreased to 17% of the starting values. An explanation for this observation is that prothrombin procoagulant activity does not decrease proportional to the prothrombin Gla-content, but that a wide range of undercarboxylated prothrombins have lost nearly all activity. During vitamin K-deficiency the remaining low levels of vitamin K would mainly give rise to undercarboxylated prothrombin, whereas during brodifacoum treatment only non-carboxylated prothrombin is formed. It seems plausible that in the latter case the urinary Gla originates from proteins with long half-life times, such as the bone Gla-proteins.

Effect of vitamin K deficiency on urinary gamma-carboxyglutamic acid excretion in rats.

Since gamma-carboxyglutamic acid (Gla) in Gla-containing proteins is stoichiometrically excreted into urine as free Gla, urinary Gla excretion is believed to reflect the rate of synthesis and degradation of vitamin K-dependent proteins and the utilization of vitamin K in body. We studied the daily changes in urinary Gla excretion and plasma vitamin K-dependent clotting factor levels in rats fed vitamin K-deficient diets followed by subcutaneous injection of vitamin K1 or after the oral administration of Warfarin. Urinary Gla excretion in normal rats fed a standard diet that contained about 500 ng of vitamin K1 per gram of diet was 2.35 +/- 0.25 mumoles/day, but the level in rats fed a markedly vitamin K-deficient diet (less than 5 ng/g) decreased to 1.40 +/- 0.14 mumoles/day. When rats were fed a moderately vitamin K-deficient diet (20-50 ng/g), plasma vitamin K-dependent clotting factor levels decreased significantly, but urinary Gla excretion did not decrease. Warfarin, a vitamin K antagonist, caused a significant decrease in urinary Gla excretion and plasma clotting factor levels. When vitamin K, (200 micrograms/kg) was injected subcutaneously in rats fed a markedly vitamin K-deficient diet, the plasma vitamin K-dependent clotting factor levels recovered quickly to normal, but urinary Gla excretion showed only a partial recovery to 1.74 +/- 0.15 mumoles/day. These results indicate that urinary Gla excretion decreases in vitamin K deficiency, but changes in urinary Gla excretion do not reflect vitamin K deficiency in rats as sensitively as changes in the prothrombin time and plasma K-dependent clotting factor levels.