Background: Vascular calcification is highly prevalent in persons with chronic kidney disease (CKD) and predicts cardiovascular disease (CVD) events. Matrix Gla protein (MGP) is a potent inhibitor of vascular calcification, and lower levels of its precursor-uncarboxylated MGP (ucMGP)--are associated with vascular calcification and atherosclerosis. Whether mild to moderate decrements in kidney function are associated with lower serum ucMGP is unknown.
Methods: In a cross-sectional study among 842 outpatients with stable CVD, estimated glomerular filtration rate (eGFR), serum cystatin-C and urine albumin-to-creatinine ratio (ACR) were measured and serum ucMGP levels were determined by ELISA. Multivariate linear regression evaluated the association of each kidney function measure with serum ucMGP levels.
Results: The mean eGFR was 76 +/- 23 mL/min/1.73 m(2), and 186 subjects (22%) had moderate CKD (eGFR <60 mL/min/1.73 m(2)). The mean +/- SD ucMGP level was 3289 +/- 1177 nM. In unadjusted analysis, each 10 mL/ min/1.73 m(2) lower eGFR was associated with 101 nM lower ucMGP level. This association was only minimally attenuated in final multivariate models wherein each 10 mL/ min/1.73 m(2) lower eGFR was associated with 79 nM lower ucMGP (95% confidence interval [CI]; 44 to 115; P < 0.001) after adjustment for age, sex, race, body mass index, blood pressure, smoking, hypertension, diabetes; and serum albumin, calcium, phosphorus, and fetuin-A levels. Similarly, in models adjusted for identical covariates, each 0.1 mg/L higher cystatin-C was associated with 39 nM lower ucMGP (95% CI 23 to 55; P < 0.001). In contrast, no significant association was observed between ACR and ucMGP in either unadjusted or adjusted analyses (adjusted P = 0.17). All associations were similar among subjects with or without diabetes (P-values for interaction > 0.50).
Conclusions: Among outpatients with stable CVD, a reduced glomerular filtration rate is associated with a decreased serum ucMGP level. In contrast, ACR is not associated with ucMGP levels. Whether ucMGP is a useful marker of vascular calcification and CVD event risk in persons with CKD deserves future study.