Undercarboxylated Osteocalcin Is a Biomarker of Carotid Calcification in Patients with Essential Hypertension

The development of vascular calcification is an active, highly regulated process with similarities to bone formation. Osteocalcin (OC), a vitamin K-dependent protein expressed by osteoblasts, contains 3  -carboxyglutamic acid residues derived from the vitamin K-dependent posttranslational modification of glutamic acid residues. Circulating undercarboxylated OC (ucOC) is increased in vitamin K deficiency and serum ucOC is reported to be a clinical marker of vitamin K status. Vitamin K deficiency is associated with vascular calcification as well as osteoporosis. We evaluated the relationship between ucOC and carotid artery calcification in 92 patients with essential hypertension. Ultrasound of the common carotid artery was performed to identify vascular calcification and subjects were divided into 2 groups: a calcification (+) group and a calcification (–) group. Serum creatinine and ucOC levels were higher in the calcification (+) group than in the calcification (–) group and serum ucOC correlated with serum creatinine. To identify the independent determinant factor for carotid artery calcification, we Received: September 23, 2009 Accepted: January 19, 2010 Published online: March 2, 2010 Takafumi Okura, MD, PhD Department of Integrated Medicine and Informatics Ehime University Graduate School of Medicine Toon City 791-0295 (Japan) Tel. +81 89 960 5302, Fax +81 89 960 5306, E-Mail okura @ m.ehime-u.ac.jp © 2010 S. Karger AG, Basel 1420–4096/10/0331–0066$26.00/0 Accessible online at: www.karger.com/kbr D ow nl oa de d by : 54 .7 0. 40 .1 1 10 /6 /2 01 7 2: 49 :0 3 A M ucOC and Carotid Artery Calcification Kidney Blood Press Res 2010;33:66–71 67 undercarboxylated OC (ucOC) level has been reported to be increased in elderly women [8] , particularly those with hip fractures [9] , and to be negatively correlated with bone mineral density [10] . ucOC is also reported to be a clinical marker of vitamin K status and intake [11] , as deficiency in vitamin K leads to increased circulating ucOC. Vitamin K deficiency is associated with both vascular calcification and osteoporosis [12, 13] . Recently, Gössl et al. [14] reported that patients with coronary atherosclerosis have increased circulating endothelial progenitor cells that display an osteogenic phenotype, including OC, providing a potential mechanism for the link between OC and atherosclerosis or vascular calcification. In the present study, we investigated the relationship between carotid artery calcification and serum ucOC in patients with essential hypertension (EHT).