Vitamin K Metabolism in a Rat Model of Chronic Kidney Disease.

<bold>Background: </bold>Patients with chronic kidney disease (CKD) have very high levels of uncarboxylated, inactive, extra-hepatic vitamin K-dependent proteins measured in circulation, putting them at risk for complications of vitamin K deficiency. The major form of vitamin K found in the liver is phylloquinone (K1). Menaquinone-4 (MK-4) is the form of vitamin K that is preferentially found in extra-hepatic tissues.<bold>Methods: </bold>In the present study, we assessed tissue concentrations of K1 and MK-4 and the expression of vitamin K-related genes in a rat model of adenine-induced CKD.<bold>Results: </bold>It was found that rats with both mild and severe CKD had significantly lower amounts of K1 measured in liver, spleen and heart and higher levels of MK-4 measured in kidney cortex and medulla. All animals treated with high dietary K1 had an increase in tissue levels of both K1 and MK-4; however, the relative increase in K1 differed suggesting that the conversion of K1 to MK-4 may be a regulated/limiting process in some tissues. There was a decrease in the thoracic aorta expression of vitamin K recycling (Vkor) and utilization (Ggcx) enzymes, and a decrease in the kidney level of vitamin K1 to MK-4 bioconversion enzyme Ubiad1 in CKD.<bold>Conclusion: </bold>Taken together, these findings suggest that CKD impacts vitamin K metabolism, and this occurs early in the disease course. Our findings that vitamin K metabolism is altered in the presence of CKD provides further support that sub-clinical vitamin K deficiency may represent a modifiable risk factor for vascular and bone health in this population. [ABSTRACT FROM AUTHOR]