Research article
Circulating matrix Gla protein is associated with coronary artery calcification and vitamin K status in healthy women

https://doi.org/10.1016/j.jnutbio.2012.02.012Get rights and content

Abstract

Matrix Gla protein (MGP) is a vitamin K-dependent protein and an inhibitor of vascular calcification. Vitamin K is required for the carboxylation of MGP and can thereby reduce calcification. Circulating MGP species with different conformations have been investigated as markers for coronary artery calcification (CAC). In high-risk populations, high total uncarboxylated MGP (t-ucMGP) was associated with decreased CAC, while high non-phosphorylated uncarboxylated MGP (dp-ucMGP) was associated with a poor vitamin K status. This cross-sectional study investigated the association of MGP species with CAC, vitamin K status among 200 healthy women. Circulating dp-ucMGP, t-ucMGP and, non-phosphorylated carboxylated MGP (dp-cMGP) levels were measured by ELISA techniques and Agatston score by multi-detector computed tomography. The ratio of uncarboxylated to carboxylated osteocalcin was used as proxy of vitamin K status. A borderline significant (P=.06) association between higher circulating dp-ucMGP levels and high CAC was observed (β=0.091, 95% CI−0.01; 0.19). In the entire study population, high t-ucMGP levels tended to be associated (P=.09) with lower CAC (β=−0.36, 95% CI:−0.78; 0.06). This association strengthened amongst women with CAC to a significant relation between high t-ucMGP levels and lower CAC (β=−0.55, 95% CI−1.01;−0.10). Dp-cMGP was not associated with CAC. Low vitamin K-status was associated with high dp-ucMGP concentrations (β=0.138, 95% CI 0.09; 0.19) but not with other MGP species. These results show that dp-ucMGP may serve as a biomarker of vitamin K status. Circulating dp-ucMGP and t-ucMGP may serve as markers for the extent of CAC, but these findings need to be confirmed.

Introduction

Coronary artery calcification (CAC) is an important predictor for cardiovascular disease (CVD) [1]. Matrix-Gla protein (MGP) is a vitamin K-dependent protein and a potent inhibitor of vascular calcification [2]. The importance of MGP for vascular health was demonstrated in MGP-deficient animals, who all died of massive arterial calcification within 6–8 weeks after birth [3]. Vitamin K is required for the function of MGP through its role as a cofactor for the enzyme gamma-glutamyl carboxylase, catalyzing the carboxylation of certain glutamic acid residues (Gla) in proteins [4]. Previous studies have shown that high vitamin K intake is associated with reduced CAC and risk of CVD [5], [6]. These effects are thought to be mediated by increased activation of MGP [7].

MGP exists as various species, which differ in their state of phosphorylation and/or carboxylation: phosphorylated (pMGP), non-phosphorylated (dephospho-MGP, dpMGP), carboxylated (cMGP), or uncarboxylated (ucMGP) (Fig. 1). Studies showed that low dp-ucMGP levels were associated with a high vitamin K status [8]. dp-ucMGP has very low affinity for vascular calcification and, therefore, high vitamin K status or intake is leading to lower dp-ucMGP circulating levels. Such low dp-ucMGP concentrations are thought to be associated with reduced CAC, but studies, mainly in high-risk populations, have thus far shown inconsistent results ranging from no to a positive association [9], [10], [11], [12].

Low circulating total uncarboxylated MGP (t-ucMGP) has been associated with high vascular burden [13], increased CAC in hemodialysis patients [14] and increased risk of mortality and cardiovascular disease among outpatients with stable coronary artery diseases [15]. The phosphorylated fraction of t-ucMGP is thought to bind to arterial calcification thereby causing a decrease in the plasma circulation levels of t-ucMGP, leading to lower t-ucMGP at higher CAC [14]. This relation is, however, not investigated in a healthy population. Finally, the association of dp-cMGP with vitamin K status or CAC has not been investigated in healthy populations.

This study will therefore investigate the determinants of different MGP species and the association of different MGP species with CAC, vitamin K status and intake among 200 healthy post-menopausal women.

Section snippets

Study population

The present study was designed as cross-sectional study among 200 postmenopausal healthy women. These 200 women were selected from a study among 1000 postmenopausal healthy women as previously described, conducted in 2002–2004 [16]. Of these 1000 women, a random selection of 573 underwent a multislice computed tomography (CT) examination at a second visit between January and December 2004. Of these women we randomly selected 100 women without coronary calcification (CAC score less than 1), 25

Results

Table 1 shows the baseline characteristics of our study population. For five and 18 women, no blood samples were available for MGP and OCR measurement and they were therefore excluded from the analyses. The baseline characteristics of these women did not differ from the total study population. The mean age of the study population was 67 years. The median of the Agatston score was 0.2 with a range of 0–2264. The median of the circulating MGP levels of the different species were 579 pmol/l for

Discussion

To our knowledge, this is the first study investigating the association of concentrations of different MGP species with CAC and vitamin K status in healthy women. We observed that high circulating dp-ucMGP levels were associated with low vitamin K status. High dp-ucMGP and low t-ucMGP concentrations tended to be associated with higher CAC. Among women with CAC, circulating t-ucMGP levels were significantly, inversely associated with the extent of CAC.

We hypothesized that dp-cMGP and t-ucMGP may

Acknowledgments

This research was supported by a personal Dr. Dekker postdoctoral grant (2008T062) from the Netherlands Heart Foundation (JW Beulens). The data collection of this study was financial supported by grant 2100.0078 from the Netherlands Organization of Health research and Development. The authors declare to have no conflict of interest. Cees Vermeer is CEO of VitaK B.V., The Netherlands. There were no commercial funding involved.

References (31)

  • N. Wajih et al.

    Processing and transport of matrix gamma-carboxyglutamic acid protein and bone morphogenetic protein-2 in cultured human vascular smooth muscle cells: evidence for an uptake mechanism for serum fetuin

    J Biol Chem

    (2004)
  • C.M. Shanahan et al.

    The role of Gla proteins in vascular calcification

    Crit Rev Eukaryot Gene Expr

    (1998)
  • G. Luo et al.

    Spontaneous calcification of arteries and cartilage in mice lacking matrix GLA protein

    Nature

    (1997)
  • L.J. Schurgers et al.

    Matrix Gla-protein: the calcification inhibitor in need of vitamin K

    Thromb Haemost

    (2008)
  • R.J. Rennenberg et al.

    Calcium scores and matrix Gla protein levels: association with vitamin K status

    Eur J Clin Invest

    (2010)
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    Grants: J.W.J. Beulens was supported by a personal Dr. Dekker postdoctoral grant (2008T062) from The Netherlands Heart Foundation.

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