Carboxylation of osteocalcin may be related to bone quality: a possible mechanism of bone fracture prevention by vitamin K |
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Authors: | Toshihiro Sugiyama Shinya Kawai |
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Institution: | (1) Department of Orthopedic Surgery, Yamaguchi University School of Medicine, Ube 755-8505, Japan, JP |
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Abstract: | Vitamin K is essential for the carboxylation of glutamic acid residues, such as osteocalcin. Recent studies have reported
that vitamin K reduces vertebral and hip fractures without increasing bone mass in patients with osteoporosis, suggesting
that vitamin K could affect bone quality. However, the mechanism is unknown. To investigate the involvement of the carboxylation
of osteocalcin in bone quality, the present preliminary study examined serum bone markers and ultrasound velocity, a possible
indicator of bone quality, in 14 healthy prepubertal children (eight boys and six girls) aged between 7 and 12 years. Venous
blood was collected between 0800 and 0900 h after an overnight fast, and serum levels of intact, carboxylated and undercarboxylated
osteocalcin, bone-specific alkaline phosphatase and type I procollagen carboxyl extension peptide were measured. Speed of
sound in the right tibia was measured using a SoundScan 2000 Compact (Myriad Ultrasound System, Rehovot, Israel). As a result,
there was no significant correlation between the serum bone markers and the Z score for the speed of sound. In contrast, the ratio of serum carboxylated osteocalcin to serum intact osteocalcin was positively
correlated with the Z score for the speed of sound (r = 0.621, P = 0.016). These findings suggest, for the first time, that carboxylation of osteocalcin is related to bone quality. Further
studies are needed to clarify the role of carboxylation of osteocalcin in bone, and this will provide a new insight into the
mechanism of vitamin K treatment in osteoporosis.
Received: September 9, 2000 / Accepted: November 30, 2000 |
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Keywords: | vitamin K osteocalcin carboxylation bone quality ultrasound |
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