Background: Vascular calcifications are related to cardiovascular mortality and morbidity in dialysis patients. Limited data exist on the role of calcification inhibitors, such as matrix-carboxyglutamic acid protein (MGP) in dialysis patients. Methods: In 120 dialysis patients and 41 age-matched healthy controls, circulating undercarboxylated (uc) MGP levels were measured with a novel ELISA-based competitive assay. The association between ucMGP levels and determinants of bone mineral metabolism, including the calcification inhibitor fetuin-A, was studied. Moreover, the relation between ucMGP levels and arterial stiffness was investigated. Results: The ucMGP level was significantly lower in dialysis patients compared to controls (173 ± 70 vs. 424 ± 126 nmol/l; p < 0.0001). After adjustment for age, sex and duration of dialysis an independent negative association between time-averaged phosphate levels [regression coefficient β with 95% confidence interval = –64 (–107 to –21)] and a positive association between serum ucMGP and fetuin-A [131 (55–208)] was observed. Duration of dialysis was inversely correlated with ucMGP (r = –0.24, p = 0.007). ucMGP levels were not related to high-sensitivity C-reactive protein or time-averaged calcium levels. After adjustment for age, sex, cardiovascular disease, diabetes, height and mean arterial pressure, ucMGP level was negatively associated with the aortic augmentation index [–0.036 (–0.061 to –0.010)] but not with pulse wave velocity or pulse pressure. Conclusion: Significantly lower serum ucMGP levels were observed in dialysis patients compared to healthy controls. ucMGP levels were inversely associated with phosphate and positively associated with serum fetuin-A levels. Furthermore, ucMGP levels were inversely associated with the aortic augmentation index. These data suggest that low ucMGP levels may be a marker of active calcification.

Keywords:
Matrix GLA protein, Calcium-phosphate metabolism, Aortic augmentation index
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© 2007 S. Karger AG, Basel
2007
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