UNDERCARBOXYLATED OSTEOCALCIN AND DEVELOPMENT OF A METHOD TO DETERMINE VITAMIN-K STATUS

We developed a RIA involving a polyclonal antibody against bovine oste ocalcin, which has a carboxy-terminal epitope. Although the antibody r ecognizes both native and descarboxy osteocalcin, the two forms of ost eocalcin were differentiated by adsorption to barium sulfate, taking a dvantage of the calcium-binding properties of the vitamin K-dependent gla domain. To test the clinical application of undercarboxylated oste ocalcin, we examined the effect of minidose warfarin on this measure i n nine healthy subjects, ages 60 to 80 years. The percentage of underc arboxylated osteocalcin increased by 170% +/- 36% (mean +/- SE) after 7 days of treatment with warfarin, 1 mg/day. The effectiveness of unde rcarboxylated osteocalcin as a sensitive measure of vitamin K nutritio nal status was further established when concentrations dropped to 17% +/- 14% below baseline with 2 days of repletion with vitamin K-1, 5 mg /day, during which prothrombin times did not leave the normal range.