Circulating desphospho-uncarboxylated matrix γ-carboxyglutamate protein and the risk of coronary heart disease and stroke

Association of desphospho-uncarboxylated matrix gla protein with incident cardiovascular disease and all-cause mortality: Results from the prospective Bruneck Study

BACKGROUND AND AIMS

Matrix Gla protein (MGP), a vitamin K-dependent protein, is a potent inhibitor of vascular calcification. Desphospho-uncarboxylated MGP (dp-ucMGP), a marker of vitamin K insufficiency, has been shown to predict cardiovascular disease (CVD) and all-cause mortality in high-risk populations. Whether the increased risk associated with dp-ucMGP also applies to the general, and especially, the elderly population has not yet been fully elucidated.

METHODS AND RESULTS

Plasma dp-ucMGP was measured in 684 individuals aged 50-89 years of the prospective population-based Bruneck Study (baseline evaluation in 2000). Baseline median dp-ucMGP was 478.4 (IQR 335.0-635.2) pmol/L. Over a median follow-up of 15.5 years, 163 CVD events occurred and 235 participants died. Age-/sex-adjusted hazard ratios (HRs) per 1-SD higher level of loge transformed dp-ucMGP were 1.30 (95%CI: 1.09-1.55; p=0.004) for incident CVD and 1.36 (95%CI: 1.17-1.57; p<0.001) for all-cause mortality. After multivariable adjustment, the associations remained significant with HRs of 1.23 (95%CI: 1.02-1.47, p=0.029) for CVD and 1.40 (95%CI: 1.20-1.64; p<0.001) for all-cause mortality. The associations remained virtually unchanged after additional adjustment for dietary quality as measured with the Alternative Healthy Eating Index. We found no association of dp-ucMGP with myocardial infarction and sudden cardiac deaths, but a strong association with other vascular deaths and non-vascular/non-cancer deaths.

CONCLUSIONS

This study shows a significant association of plasma dp-ucMGP with incident CVD and a significant and even stronger association with all-cause mortality. Clinical trials are needed to investigate whether vitamin K substitution results in improved health outcomes.

Joint Association of Low Vitamin K1 and D Status With First Stroke in General Hypertensive Adults: Results From the China Stroke Primary Prevention Trial (CSPPT)

Background

Vitamin K plays a role in preventing vascular calcification and may have a synergetic influence with vitamin D on cardiovascular health. However, whether this relationship applies to stroke, especially in a high-risk population of hypertensive individuals, remains unclear. The present study aims to study the joint association of low vitamin K1 and D status with first stroke in general hypertensive adults.

Methods

This study used a nested, case–control design with data from the China Stroke Primary Prevention Trial. The analysis included 604 first total stroke patients and 604 matched controls from a Chinese population with hypertension. Odds ratios (ORs) and 95% confidence intervals were calculated using conditional logistic regression.

Results

There was a non-linear negative association between plasma vitamin K1 and the risk of first total stroke or ischemic stroke in the enalapril-only group. Compared to participants in vitamin K1 quartile 1, a significantly lower risk of total stroke (OR = 0.58, 95% CI: 0.36, 0.91, P = 0.020) or ischemic stroke (OR = 0.34, 95% CI: 0.17, 0.63, P < 0.001) was found in participants in vitamin K1 quartile 2-4 in the enalapril-only group. When further divided into four subgroups by 25(OH)D and vitamin K1, a significantly higher risk of total stroke or ischemic stroke was observed in participants with both low vitamin K1 and 25(OH)D compared to those with both high vitamin K1 and 25(OH)D in the enalapril-only group. No increased risk was observed in the groups low in one vitamin only.

Conclusion

Low concentrations of both vitamin K1 and 25(OH)D were associated with increased risk of stroke.

The Role of Vitamin K in CKD-MBD

PURPOSE OF REVIEW

We describe the mechanism of action of vitamin K, and its implication in cardiovascular disease, bone fractures, and inflammation to underline its protective role, especially in chronic kidney disease (CKD).

RECENT FINDINGS

Vitamin K acts as a coenzyme of y-glutamyl carboxylase, transforming undercarboxylated in carboxylated vitamin K-dependent proteins. Furthermore, through the binding of the nuclear steroid and xenobiotic receptor, it activates the expression of genes that encode proteins involved in the maintenance of bone quality and bone remodeling. There are three main types of K vitamers: phylloquinone, menaquinones, and menadione. CKD patients, for several conditions typical of the disease, are characterized by lower levels of vitamin K than the general populations, with a resulting higher prevalence of bone fractures, vascular calcifications, and mortality. Therefore, the definition of vitamin K dosage is an important issue, potentially leading to reduced bone fractures and improved vascular calcifications in the general population and CKD patients.

High vitamin K status is prospectively associated with decreased left ventricular mass in women: the Hoorn Study

Background

Vitamin K is associated with reduced cardiovascular disease risk such as heart failure, possibly by carboxylation of matrix-gla protein (MGP), a potent inhibitor of vascular calcification. The relationship of vitamin K intake or status with cardiac structure and function is largely unknown. Therefore this study aims to investigate the prospective association of vitamin K status and intake with echocardiographic measures.

Methods

This study included 427 participants from the Hoorn Study, a population-based cohort. Vitamin K status was assessed at baseline by plasma desphospho-uncarboxylated MGP (dp-ucMGP) with higher concentrations reflecting lower vitamin K status. Vitamin K intake was assessed at baseline with a validated food-frequency questionnaire. Echocardiography was performed at baseline and after a mean follow-up time of 7.6, SD=±0.7 years. We used linear regression for the association of vitamin K status and intake with left ventricular ejection fraction (LVEF), left atrial volume index (LAVI) and left ventricular mass index (LVMI), adjusted for potential confounders.

Results

The mean age was 66.8, SD=±6.1 years (51% were male). A high vitamin K status was prospectively associated with decreased LVMI (change from baseline to follow-up: -5.0, 95% CI: -10.5;0.4 g/m^2.7) for the highest quartile compared to the lowest in women (P-interaction sex=0.07). No association was found in men. Vitamin K status was not associated with LVEF or LAVI. Vitamin K intake was not associated with any of the echocardiographic measures.

Conclusions

This study showed a high vitamin K status being associated with decreased LVMI only in women, while intakes of vitamin K were not associated with any cardiac structure or function measures. These results extend previous findings for a role of vitamin K status to decrease heart failure risk.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12937-021-00742-0.

Role of Matrix Gla Protein in the Complex Network of Coronary Artery Disease: A Comprehensive Review

Coronary artery disease (CAD) is widely recognized as one of the most important clinical entities. In recent years, a large body of accumulated data suggest that coronary artery calcification, a process highly prevalent in patients with CAD, occurs via well-organized biologic processes, rather than passively, as previously regarded. Matrix Gla protein (MGP), a vitamin K-dependent protein, emerged as an important inhibitor of both intimal and medial vascular calcification. The functionality of MGP hinges on two post-translational modifications: phosphorylation and carboxylation. Depending on the above-noted modifications, various species of MGP may exist in circulation, each with their respective level of functionality. Emerging data suggest that dysfunctional species of MGP, markedly, dephosphorylated-uncarboxylated MGP, might find its application as biomarkers of microvascular health, and assist in clinical decision making with regard to initiation of vitamin K supplementation. Hence, in this review we summarized the current knowledge with respect to the role of MGP in the complex network of vascular calcification with concurrent inferences to CAD. In addition, we discussed the effects of warfarin use on MGP functionality, with concomitant implications to coronary plaque stability.

On the association between circulating biomarkers and atherosclerotic calcification in a cohort of arterial disease participants

BACKGROUND AND AIMS

Atherosclerotic calcification is a powerful predictor of cardiovascular disease. This study aims to determine whether circulating levels of a local/systemic calcification inhibitor or a marker of bone formation correlate with measures of coronary or extracoronary calcification.

METHODS AND RESULTS

Clinical computed tomography (CT) was performed on 64 arterial disease participants undergoing carotid and lower extremity endarterectomy. Coronary artery calcium (CAC) scores and volumes were acquired from the CT scans (n = 42). CAC scores and volumes were used to derive CAC density scores. Micro-CT was performed on excised carotid (n = 36) and lower extremity (n = 31) plaques to quantify the volume and volume fraction of extracoronary calcification. Circulating levels of dephospho-uncarboxylated Matrix Gla Protein (dp-ucMGP), fetuin-A, carboxylated and uncarboxylated osteocalcin (ucOC) were quantified using commercial immunoassays. Carotid participant CAC density scores were moderately negatively correlated with plasma dp-ucMGP (rs = -0.592, P = 0.008). A weak negative association was found between CAC scores and %ucOC for all participants (rs = -0.335, P = 0.040). Another weak negative correlation was observed between fetuin-A and the volume of calcification within excised carotid specimens (rs = -0.366, P = 0.031). Despite substantial differences in coronary and extracoronary calcium measurements, the levels of circulating biomarkers did not vary significantly between carotid and lower extremity subgroups.

CONCLUSION

Correlations identified between circulating biomarkers and measures of coronary and extracoronary calcium were not consistent among participant subgroups. Further research is required to determine the association between circulating biomarkers, coronary and extracoronary calcium.

Perspective: Evidence before Enthusiasm-A Critical Review of the Potential Cardiovascular Benefits of Vitamin K

A protective role for vitamin K in cardiovascular disease (CVD), a leading cause of morbidity and mortality, has been proposed because vitamin K-dependent proteins, such as matrix Gla (γ-carboxyglutamic acid) protein (MGP), are present in vascular tissue. MGP functions as a vascular calcification inhibitor-but only when it is carboxylated, which requires vitamin K. There is more than one naturally occurring form of vitamin K. Phylloquinone (vitamin K1) is found in plant-based foods, whereas menaquinones (vitamin K2) are a class of vitamin K compounds found in animal-based and fermented foods. Phylloquinone and menaquinones are capable of carboxylating MGP and other vitamin K-dependent proteins. In rodent models, high intakes of either phylloquinone or menaquinone reduced vascular calcification. Evidence of the relative importance of phylloquinone and menaquinone to CVD in humans is limited and controversial. In some observational studies, higher dietary menaquinone intake, but not phylloquinone intake, was associated with less coronary artery calcification (a subclinical manifestation of CVD) and a lower risk for clinical CVD events. These findings have led to claims that menaquinones have unique cardiovascular health benefits compared with phylloquinone. However, this claim is not supported by the results of the limited number of intervention trials conducted to date. The purpose of this review is to evaluate the strengths and limitations of the available evidence regarding the role of vitamin K in vascular calcification, CVD, and mortality.

Functional vitamin K insufficiency, vascular calcification and mortality in advanced chronic kidney disease: A cohort study

Patients with chronic kidney disease (CKD) suffer from vitamin K deficiency and are at high risk of vascular calcification (VC) and premature death. We investigated the association of functional vitamin K deficiency with all-cause mortality and whether this association is modified by the presence of VC in CKD stage 5 (CKD G5). Plasma dephosphorylated-uncarboxylated matrix Gla-protein (dp-ucMGP), a circulating marker of functional vitamin K deficiency, and other laboratory and clinical data were determined in 493 CKD G5 patients. VC was assessed in subgroups by Agatston scoring of coronary artery calcium (CAC) and aortic valve calcium (AVC). Backward stepwise regression did not identify dp-ucMGP as an independent determinant of VC. During a median follow-up of 42 months, 93 patients died. Each one standard deviation increment in dp-ucMGP was associated with increased risk of all-cause mortality (sub-hazard ratio (sHR) 1.17; 95% confidence interval, 1.01-1.37) adjusted for age, sex, cardiovascular disease, diabetes, body mass index, inflammation, and dialysis treatment. The association remained significant when further adjusted for CAC and AVC in sub-analyses (sHR 1.22, 1.01-1.48 and 1.27, 1.01-1.60, respectively). In conclusion, functional vitamin K deficiency associates with increased mortality risk that is independent of the presence of VC in patients with CKD G5.

Circulating Levels of Dephosphorylated-Uncarboxylated Matrix Gla Protein in Patients with Acute Coronary Syndrome

Vascular calcification contributes to the pathogenesis of coronary artery disease while matrix Gla protein (MGP) was recently identified as a potent inhibitor of vascular calcification. MGP fractions, such as dephosphorylated-uncarboxylated MGP (dp-ucMGP), lack post-translational modifications and are less efficient in vascular calcification inhibition. We sought to compare dp-ucMGP levels between patients with acute coronary syndrome (ACS), stratified by ST-elevation myocardial infarction (STEMI) and non-ST-elevation myocardial infarction (NSTEMI) status. Physical examination and clinical data, along with plasma dp-ucMGP levels, were obtained from 90 consecutive ACS patients. We observed that levels of dp-ucMGP were significantly higher in patients with NSTEMI compared to STEMI patients (1063.4 ± 518.6 vs. 742.7 ± 166.6 pmol/L, p < 0.001). NSTEMI status and positive family history of cardiovascular diseases were only independent predictors of the highest tertile of dp-ucMGP levels. Among those with NSTEMI, patients at a high risk of in-hospital mortality (adjudicated by GRACE score) had significantly higher levels of dp-ucMGP compared to non-high-risk patients (1417.8 ± 956.8 vs. 984.6 ± 335.0 pmol/L, p = 0.030). Altogether, our findings suggest that higher dp-ucMGP levels likely reflect higher calcification burden in ACS patients and might aid in the identification of NSTEMI patients at increased risk of in-hospital mortality. Furthermore, observed dp-ucMGP levels might reflect differences in atherosclerotic plaque pathobiology between patients with STEMI and NSTEMI.

Vitamin K for the Treatment of Cardiovascular Disease in End-Stage Renal Disease Patients: Is there Hope?

In Chronic Kidney Disease, vascular calcification (VC) is highly prevalent even at early stages and is gradually enhanced, along with disease progression to End-Stage Renal Disease (ESRD). The calcification pattern in uremia includes all types of mineralization and contributes to the heavy cardiovascular (CV) burden that is common in these patients. Ectopic mineralization is the result of the imbalance between inhibitors and promoters of vascular calcification, with the latter overwhelming the former. The most powerful, natural inhibitor of calcification is Matrix Gla Protein (MGP), a small vitamin K dependent protein, secreted by chondrocytes and vascular smooth muscle cells. In uremia, MGP was reported as the only molecule able to reverse VC by "sweeping" calcium and hydroxyapatite crystals away from the arterial wall. To become biologically active, this protein needs to undergo carboxylation and phosphorylation, reactions highly dependent on vitamin K status. The inactive form of MGP reflects the deficiency of vitamin K and has been associated with CV events and mortality in ESRD patients. During the past decade, vitamin K status has emerged as a novel risk factor for vascular calcification and CV disease in various populations, including dialysis patients. This review presents evidence regarding the association between vitamin K and CV disease in ESRD patients, which are prone to atherosclerosis and atheromatosis.

Uncarboxylated matrix Gla-protein: A biomarker of vitamin K status and cardiovascular risk

BACKGROUND

Dephosphorylated uncarboxylated matrix Gla-protein (dp-ucMGP) is a biomarker of functional vitamin K status. High plasma dp-ucMGP concentrations reflect a low vitamin K status and have been related to vascular calcification. Our aims were to assess plasma levels of dp-ucMGP and their association with cardiovascular risk in a general population.

METHODS

Plasma dp-ucMGP measurements were performed using the IDS-iSYS InaKtif MGP assay in 491 consecutive participants in a Danish general population study (229 males and 262 females, aged 19-71 years). Multivariable linear and logistic regressions were used to assess the association between dp-ucMGP levels and cardiovascular risk factors.

RESULTS

Mean ± standard deviation (SD) for dp-ucMGP was 465 ± 181 pmol/L, and upper 95th percentile was 690 pmol/L. In logistic regression analyses, an increase in dp-ucMGP category (<300, 300-399, 400-499, ≥500 pmol/L) was positively associated with obesity, odds ratio (OR) 2.27 (95% confidence interval (CI) 1.54-3.33), history of cardiovascular disease, OR 1.77 (CI 1.02-3.05), and above-median estimated pulse wave velocity (ePWV), OR 1.54 (CI 1.21-1.96), when adjusted for age, sex, and lifestyle factors. 1 SD increase in diastolic and systolic blood pressure (BP) corresponded to a 5.5% (CI 2.9-8.0%) and 4.7% (CI 2.1-7.4%) increase in dp-ucMGP, respectively, when adjusted for age and sex.

CONCLUSION

Plasma dp-ucMGP levels were positively associated with obesity, BP, ePWV, and history of cardiovascular disease. These findings support that dp-ucMGP is a biomarker of cardiovascular risk, and that vitamin K status could play a role in vascular calcification. The strong association with obesity deserves further attention.

Vitamin K status, cardiovascular disease, and all-cause mortality: a participant-level meta-analysis of 3 US cohorts

BACKGROUND

Vitamin K-dependent proteins in vascular tissue affect vascular stiffness and calcification, which is associated with cardiovascular disease (CVD) and all-cause mortality.

OBJECTIVE

To determine the association of circulating vitamin K concentrations with CVD and all-cause mortality by conducting a participant-level meta-analysis.

METHODS

We obtained individual participant-level data from the Health, Aging, and Body Composition Study, the Multi-Ethnic Study of Atherosclerosis, and the Framingham Offspring Study, known cohorts with available measures of fasting circulating phylloquinone (vitamin K-1) and confirmed CVD events and mortality. Circulating phylloquinone was measured in a central laboratory from fasting blood samples and categorized as ≤0.5 nmol/L, >0.5-1.0 nmol/L, and >1.0 nmol/L. Multivariable Cox proportional hazard regression with multiple imputations was used to evaluate the association of circulating phylloquinone with incident CVD and all-cause mortality risk.

RESULTS

Among 3891 participants (mean age 65 ± 11 y; 55% women; 35% nonwhite), there were 858 incident CVD events and 1209 deaths over a median of 13.0 y. The risk of CVD did not significantly differ according to circulating phylloquinone [fully adjusted HR (95% CI) relative to >1.0 nmol/L: ≤0.5 nmol/L, 1.12 (0.94, 1.33); >0.5-1.0 nmol/L, 1.02 (0.86, 1.20)]. Participants with ≤0.5 nmol/L circulating phylloquinone had an adjusted 19% higher risk of all-cause mortality compared with those with >1.0 nmol/L [fully adjusted HR (95% CI): 1.19 (1.03, 1.38)]. Mortality risk was similar in participants with >0.5-1.0 nmol/L compared with >1.0 nmol/L [fully adjusted HR (95% CI): 1.04 (0.92, 1.17)].

CONCLUSIONS

Low circulating phylloquinone concentrations were associated with an increased risk of all-cause mortality, but not of CVD. Additional studies are needed to clarify the mechanism underlying this association and evaluate the impact of increased phylloquinone intake on cardiovascular and other health outcomes in individuals with low vitamin K status.

Vascular Calcification in Chronic Kidney Disease: The Role of Vitamin K- Dependent Matrix Gla Protein

Arterial calcification is highly prevalent in chronic kidney disease (CKD) patients and is associated with cardiovascular (CV) morbidity and mortality. Patients at early CKD stages are more likely to suffer a fatal CV event than to develop end-stage renal disease and require hemodialysis treatment. The heavy CV burden of these patients cannot be solely explained by traditional calcification risk factors. Moreover, the pathophysiologic mechanisms underlying this association are complex and yet not fully understood. Although vascular calcification was regarded as a passive degenerative process for over a century, this theory changed by recent evidence that pointed toward an active process, where calcification promoters and inhibitors were involved. Matrix Gla Protein (MGP) has been established as a strong inhibitor of calcification both in vitro and in vivo. Not only it prevents mineralization of the arterial wall, but it is the only factor that can actually reverse it. To become fully active, MGP must undergo carboxylation of specific protein bound glutamate residues, a process fully dependent on the availability of vitamin K. Low vitamin K status leads to inactive, uncarboxylated forms of MGP and has been repeatedly associated with accelerated vascular calcification. Aim of this review is to present the pathophysiologic mechanisms underlying the activation and function of MGP and review the existing, accumulating data regarding the association between vitamin K, MGP and vascular calcification/CV disease in CKD patients.

The Inhibitory Roles of Vitamin K in Progression of Vascular Calcification

Vitamin K is a fat-soluble vitamin that is indispensable for the activation of vitamin K-dependent proteins (VKDPs) and may be implicated in cardiovascular disease (CVD). Vascular calcification is intimately associated with CV events and mortality and is a chronic inflammatory process in which activated macrophages promote osteoblastic differentiation of vascular smooth muscle cells (VSMCs) through the production of proinflammatory cytokines such as IL-1β, IL-6, TNF-α, and oncostatin M (OSM) in both intimal and medial layers of arterial walls. This process may be mainly mediated through NF-κB signaling pathway. Vitamin K has been demonstrated to exert anti-inflammatory effects through antagonizing NF-κB signaling in both in vitro and in vivo studies, suggesting that vitamin K may prevent vascular calcification via anti-inflammatory mechanisms. Matrix Gla protein (MGP) is a major inhibitor of soft tissue calcification and contributes to preventing both intimal and medial vascular calcification. Vitamin K may also inhibit progression of vascular calcification by enhancing the activity of MGP through facilitating its γ-carboxylation. In support of this hypothesis, the procalcific effects of warfarin, an antagonist of vitamin K, on arterial calcification have been demonstrated in several clinical studies. Among the inactive MGP forms, dephospho-uncarboxylated MGP (dp-ucMGP) may be regarded as the most useful biomarker of not only vitamin K deficiency, but also vascular calcification and CVD. There have been several studies showing the association of circulating levels of dp-ucMGP with vitamin K intake, vascular calcification, mortality, and CVD. However, additional larger prospective studies including randomized controlled trials are necessary to confirm the beneficial effects of vitamin K supplementation on CV health.

Vitamin K as a Powerful Micronutrient in Aging and Age-Related Diseases: Pros and Cons from Clinical Studies

Vitamin K is a multifunctional micronutrient implicated in age-related diseases such as cardiovascular diseases, osteoarthritis and osteoporosis. Although vitamin K-dependent proteins (VKDPs) are described to have a crucial role in the pathogenesis of these diseases, novel roles have emerged for vitamin K, independently of its role in VKDPs carboxylation. Vitamin K has been shown to act as an anti-inflammatory by suppressing nuclear factor κB (NF-κB) signal transduction and to exert a protective effect against oxidative stress by blocking the generation of reactive oxygen species. Available clinical evidences indicate that a high vitamin K status can exert a protective role in the inflammatory and mineralization processes associated with the onset and progression of age-related diseases. Also, vitamin K involvement as a protective super-micronutrient in aging and ‘inflammaging’ is arising, highlighting its future use in clinical practice. In this review we summarize current knowledge regarding clinical data on vitamin K in skeletal and cardiovascular health, and discuss the potential of vitamin K supplementation as a health benefit. We describe the clinical evidence and explore molecular aspects of vitamin K protective role in aging and age-related diseases, and its involvement as a modulator in the interplay between pathological calcification and inflammation processes.

Associations of vitamin K status with mortality and cardiovascular events in peritoneal dialysis patients

PURPOSE

Vitamin K deficiency, expressed by a high level of desphospho-uncarboxylated matrix GLA protein (dp-ucMGP), is highly prevalent in dialysis patients. However, the predictive ability of the vitamin K status remains unclear in continuous ambulatory peritoneal dialysis (CAPD) patients.

METHODS

158 prevalent CAPD patients with a median level of dp-ucMGP of 1093 (752, 1485) pmol/L were enrolled. Patient outcomes including all-cause mortality and cardiovascular events (CVEs) were recorded during follow-up. Survival curves were performed using Kaplan-Meier method, and the influences of dp-ucMGP on outcomes were analyzed by Cox regression models.

RESULTS

A total of 59 deaths and 82 new episodes of CVEs occurred during median follow-up of 31.4 ± 13.1 months (range: 3.8-48.0 months). Kaplan-Meier analysis revealed patients with higher dp-ucMGP levels (≥ 1093 pmol/L) had an increased risk for both mortality (P = 0.005) and CVEs (P < 0.001). Multivariable Cox regression confirmed that higher dp-ucMGP levels increase the mortality risk [hazard ratio (HR), 1.763; 95% CI 1.045-3.291] and CVEs (HR, 1.846; 95% CI 1.074-3.172). For every 100 pmol/L increase in serum dp-ucMGP, the adjusted HRs for mortality and CVEs were 1.054 (95% CI 1.008-1.106) and 1.034 (95% CI 1.012-1.089), respectively.

CONCLUSIONS

Vitamin K deficiency, as expressed by high dp-ucMGP levels, showed independently associations with mortality and CVEs in CAPD patients.

Association of the Inactive Circulating Matrix Gla Protein with Vitamin K Intake, Calcification, Mortality, and Cardiovascular Disease: A Review

Matrix Gla Protein (MGP), a small Gla vitamin K-dependent protein, is the most powerful natural occurring inhibitor of calcification in the human body. To become biologically active, MGP must undergo vitamin K-dependent carboxylation and phosphorylation. Vitamin K deficiency leads to the inactive uncarboxylated, dephosphorylated form of MGP (dpucMGP). We aimed to review the existing data on the association between circulating dpucMGP and vascular calcification, renal function, mortality, and cardiovascular disease in distinct populations. Moreover, the association between vitamin K supplementation and serum levels of dpucMGP was also reviewed.

Circulating osteogenic proteins are associated with coronary artery calcification and increase after myocardial infarction

BACKGROUND

Coronary artery calcification (CAC) and atherosclerotic inflammation associate with increased risk of myocardial infarction (MI). Vascular calcification is regulated by osteogenic proteins (OPs). It is unknown whether an association exists between CAC and plasma OPs and if they are affected by atherothrombotic inflammation. We tested the association of osteogenic and inflammatory proteins with CAC and assessed these biomarkers after MI.

METHODS

Circulating OPs (osteoprotegerin, RANKL, fetuin-A, Matrix Gla protein [MGP]) and inflammatory proteins (C-reactive protein, oxidized-LDL, tumoral necrosis factor-α, transforming growth factor [TGF]-β1) were compared between stable patients with CAC (CAC ≥ 100 AU, n = 100) and controls (CAC = 0 AU, n = 30). The association between biomarkers and CAC was tested by multivariate analysis. In patients with MI (n = 40), biomarkers were compared between acute phase and 1-2 months post-MI, using controls as a baseline.

RESULTS

MGP and fetuin-A levels were higher within individuals with CAC. Higher levels of MGP and RANKL were associated with CAC (OR 3.12 [95% CI 1.20-8.11], p = 0.02; and OR 1.75 [95% CI 1.04-2.94] respectively, p = 0.035). After MI, C-reactive protein, OPG and oxidized-LDL levels increased in the acute phase, whereas MGP and TGF-β1 increased 1-2 months post-MI.

CONCLUSIONS

Higher MGP and RANKL levels associate with CAC. These findings highlight the potential role of these proteins as modulators and markers of CAC. In addition, the post-MI increase in OPG and MGP, as well as of inflammatory proteins suggest that the regulation of these OPs is affected by atherothrombotic inflammation.

Vitamin K and cancer

Subclinical vitamin K deficits refer to carboxylation defects of different types of vitamin K-dependent hepatic and extrahepatic so-called Gla proteins without prolongation of the prothrombin time. This condition has been reported in different clinical situations due to insufficient supply or malabsorption of vitamin K as well as drug interactions. This review discusses the effects of different vitamin K subspecies on tumour growth and the possible anti-tumour effects of increased vitamin K intake. Blocking carboxylation of vitamin K-dependent proteins with warfarin anticoagulation - what are the risks/benefits for carcinogenesis? Previous studies on both heparin and low molecular weight heparin blocking of the vitamin K-dependent factors X and II have shown tumour suppressive effects. Vitamin K has anti-inflammatory effects that could also impact carcinogenesis, but little data exists on this subject.

The Role of Vitamin K Status in Cardiovascular Health: Evidence from Observational and Clinical Studies

PURPOSE OF REVIEW

Vitamin K is a fat-soluble vitamin required for the activation of several vitamin K-dependent proteins to confer functioning. A growing body of evidence supports that vitamin K has beneficial effects on bone and cardiovascular health. This review summarizes key evidence on vitamin K status as measured by circulating measures and cardiovascular outcomes.

RECENT FINDINGS

Overall, observational studies indicate that low vitamin K status as measured by high dephosphorylated uncarboxylated matrix gla protein concentrations plays a potential role in cardiovascular disease development, particularly in high-risk and chronic kidney disease populations. Very few vitamin K intervention trials have been conducted with cardiovascular-related outcomes. A couple of intervention trials studied the effect of the combination of vitamin D + K supplementation, which might have synergistic effects compared to vitamin K supplementation alone.

SUMMARY

Assessing vitamin K status in prospective studies and well-designed randomized trials would provide important insight whether vitamin K is causally related to vascular calcification and cardiovascular disease.

Joint Association of Low Vitamin D and Vitamin K Status With Blood Pressure and Hypertension

Low vitamin D and K status are both associated with an increased cardiovascular risk. New evidence from experimental studies on bone health suggest an interaction between vitamin D and K; however, a joint association with vascular health outcomes is largely unknown. To prospectively investigate whether the combination of low vitamin D and K status is associated with higher systolic and diastolic blood pressure in 402 participants and with incident hypertension in 231 participants free of hypertension at baseline. We used data from a subsample of the Longitudinal Aging Study Amsterdam, a population-based cohort of Dutch participants aged 55 to 65 years. Vitamin D and K status were assessed by 25-hydroxyvitamin D and dp-ucMGP (dephosphorylated uncarboxylated matrix gla protein) concentrations (high dp-ucMGP is indicative for low vitamin K status) in stored samples from 2002 to 2003. Vitamin D and K status were categorized into 25-hydroxyvitamin D <50/≥50 mmol/L and median dp-ucMGP <323/≥323 pmol/L. During a median follow-up of 6.4 years, 62% of the participants (n=143) developed hypertension. The combination of low vitamin D and K status was associated with increased systolic 4.8 mm Hg (95% confidence interval, 0.1–9.5) and diastolic 3.1 mm Hg (95% confidence interval, 0.5–5.7) blood pressure compared with high vitamin D and K status ( P for interaction =0.013 for systolic blood pressure and 0.068 for diastolic blood pressure). A similar trend was seen for incident hypertension: hazard ratio=1.62 (95% confidence interval, 0.96–2.73) for the low vitamin D and K group. The combination of low vitamin D and K status was associated with increased blood pressure and a trend for greater hypertension risk.

Circulating Vitamin K Is Inversely Associated with Incident Cardiovascular Disease Risk among Those Treated for Hypertension in the Health, Aging, and Body Composition Study (Health ABC)

Background: A role for vitamin K in coronary artery calcification (CAC), a subclinical manifestation of cardiovascular disease (CVD), has been proposed because vitamin K-dependent proteins, including the calcification inhibitor matrix Gla protein (MGP), are present in vascular tissue. Observational studies found that low circulating phylloquinone (vitamin K-1) was associated with increased CAC progression, especially in persons treated for hypertension. It is unknown whether hypertension treatment modifies this putative role of vitamin K in clinical CVD risk.Objective: We determined the association between vitamin K status and incident clinical CVD in older adults in the Health ABC (Health, Aging, and Body Composition Study) and whether the association differed by hypertension treatment status.Methods: Plasma phylloquinone was measured in 1061 participants free of CVD (70-79 y of age, 58% women, 39% black). Plasma uncarboxylated MGP [(dp)ucMGP] was measured in a subset of 635 participants. Multivariate Cox models estimated the HR for incident CVD over 12.1 follow-up years. Effect modification by hypertension was tested with the use of interaction terms.Results: Neither low plasma phylloquinone (<0.2 nmol/L) nor elevated (dp)ucMGP (≥574 pmol/L) was significantly associated with incident CVD [respective HRs (95% CIs): 1.27 (0.75, 2.13) and 1.02 (0.72, 1.45)]. In participants treated for hypertension (n = 489; 135 events), low plasma phylloquinone was associated with higher CVD risk overall (HR: 2.94; 95% CI: 1.41, 6.13). In those with untreated hypertension (n = 153; 48 events) and without hypertension (n = 418; 92 events), low plasma phylloquinone was not associated with incident CVD. The association between high (dp)ucMGP did not differ by hypertension treatment status (P-interaction = 0.72).Conclusions: Vitamin K status was not significantly associated with CVD risk overall, but low plasma phylloquinone was associated with a higher CVD risk in older adults treated for hypertension. Additional evidence from larger clinical studies is needed to clarify the importance of vitamin K to CVD in persons treated for hypertension, a segment of the population at high risk of clinical CVD events.

Subclinical atherosclerosis is linked to small intestinal bacterial overgrowth via vitamin K2-dependent mechanisms

AIM

To assess the rate of matrix Gla-protein carboxylation in patients with small intestinal bacterial overgrowth (SIBO) and to decipher its association with subclinical atherosclerosis.

METHODS

Patients with suspected SIBO who presented with a low risk for cardiovascular disease and showed no evidence of atherosclerotic plaques were included in the study. A glucose breath test was performed in order to confirm the diagnosis of SIBO and vascular assessment was carried out by ultrasound examination. Plasma levels of the inactive form of MGP (dephosphorylated-uncarboxylated matrix Gla-protein) were quantified by ELISA and vitamin K2 intake was estimated using a food frequency questionnaire.

RESULTS

Thirty-nine patients were included in the study. SIBO was confirmed in 12/39 (30.8%) patients who also presented with a higher concentration of dephosphorylated-uncarboxylated matrix Gla-protein (9.5 μg/L vs 4.2 μg/L; P = 0.004). Arterial stiffness was elevated in the SIBO group (pulse-wave velocity 10.25 m/s vs 7.68 m/s; P = 0.002) and this phenomenon was observed to correlate linearly with the levels of dephosphorylated-uncarboxylated matrix Gla-protein (β = 0.220, R2 = 0.366, P = 0.03). Carotid intima-media thickness and arterial calcifications were not observed to be significantly elevated as compared to controls.

CONCLUSION

SIBO is associated with reduced matrix Gla-protein activation as well as arterial stiffening. Both these observations are regarded as important indicators of subclinical atherosclerosis. Hence, screening for SIBO, intestinal decontamination and supplementation with vitamin K2 has the potential to be incorporated into clinical practice as additional preventive measures.

Vitamin K intake and all-cause and cause specific mortality

BACKGROUND & AIMS

Vitamin K has been associated with various health outcomes, including non-fatal cardiovascular diseases (CVD) and cancer. However, little is known about the association between vitamin K intake and all-cause and cause specific mortality. This study aims to investigate the association between vitamin K intake and all-cause and cause-specific mortality.

METHODS

This prospective cohort study included 33,289 participants from the EPIC-NL cohort, aged 20-70 years at baseline and recruited between 1993 and 1997. Dietary intake was assessed at baseline with a validated food frequency questionnaire and intakes of phylloquinone, and total, short chain and long chain menaquinones were calculated. Information on vital status and causes of death was obtained through linkage to several registries. The association between the different forms of vitamin K intake and mortality was assessed with Cox proportional hazards, adjusted for risk factors for chronic diseases and nutrient intake.

RESULTS

During a mean follow-up of 16.8 years, 2863 deaths occurred, including 625 from CVD (256 from coronary heart disease (CHD)), 1346 from cancer and 892 from other causes. After multivariable adjustment, phylloquinone and menaquinones were not associated with all-cause mortality with hazard ratios for the upper vs. the lowest quartile of intake of 1.04 (0.92;1.17) and 0.94 (0.82;1.07) respectively. Neither phylloquinone intake nor menaquinone intake was associated with risk of CVD mortality. Higher intake of long chain menaquinones was borderline significantly associated (p_trend = 0.06) with lower CHD mortality with a HR_10μg of 0.86 (0.74;1.00). None of the forms of vitamin K intake were associated with cancer mortality or mortality from other causes.

CONCLUSIONS

Vitamin K intake was not associated with all-cause mortality, cancer mortality and mortality from other causes.

The Role of Vitamin K in Chronic Aging Diseases: Inflammation, Cardiovascular Disease, and Osteoarthritis

Vitamin K is an enzyme cofactor required for the carboxylation of vitamin K dependent proteins, several of which have been implicated in diseases of aging. Inflammation is recognized as a crucial component of many chronic aging diseases and evidence suggests vitamin K has an anti-inflammatory action that is independent of its role as an enzyme co-factor. Vitamin K-dependent proteins and inflammation have been implicated in cardiovascular disease and osteoarthritis, which are leading causes of disability and mortality in older adults. The purpose of this review is to summarize observational studies and randomized trials focused on vitamin K status and inflammation, cardiovascular disease, and osteoarthritis. Although mechanistic evidence suggests a protective role for vitamin K in these age-related conditions, the benefit of vitamin K supplementation is controversial because observational data are equivocal and the number of randomized trials is few.

Concepts and Controversies in Evaluating Vitamin K Status in Population-Based Studies

A better understanding of vitamin K's role in health and disease requires the assessment of vitamin K nutritional status in population and clinical studies. This is primarily accomplished using dietary questionnaires and/or biomarkers. Because food composition databases in the US are most complete for phylloquinone (vitamin K1, the primary form in Western diets), emphasis has been on phylloquinone intakes and associations with chronic diseases. There is growing interest in menaquinone (vitamin K2) intakes for which the food composition databases need to be expanded. Phylloquinone is commonly measured in circulation, has robust quality control schemes and changes in response to phylloquinone intake. Conversely, menaquinones are generally not detected in circulation unless large quantities are consumed. The undercarboxylated fractions of three vitamin K-dependent proteins are measurable in circulation, change in response to vitamin K supplementation and are modestly correlated. Since different vitamin K dependent proteins are implicated in different diseases the appropriate vitamin K-dependent protein biomarker depends on the outcome under study. In contrast to other nutrients, there is no single biomarker that is considered a gold-standard measure of vitamin K status. Most studies have limited volume of specimens. Strategic decisions, guided by the research question, need to be made when deciding on choice of biomarkers.

Vitamin K status and mortality after kidney transplantation: a cohort study

BACKGROUND

Vitamin K modulates calcification by activating calcification inhibitors such as matrix Gla protein (MGP). In kidney transplant recipients, vitamin K insufficiency is common, but implications for long-term outcomes are unclear.

STUDY DESIGN

Single-center observational study with a longitudinal design.

SETTING & PARTICIPANTS

518 stable kidney transplant recipients; 56% men; mean age, 51±12 (SD) years; and a median of 6 (IQR, 3-12) years after kidney transplantation.

FACTOR

Plasma desphosphorylated-uncarboxylated MGP (dp-ucMGP) levels, reflecting vitamin K status.

OUTCOMES

All-cause mortality and transplant failure.

RESULTS

At inclusion, median dp-ucMGP level was 1,038 (IQR, 733-1,536) pmol/L, with 473 (91%) patients having vitamin K insufficiency (defined as dp-ucMGP>500pmol/L). During a median follow-up of 9.8 (IQR, 8.5-10.2) years, 152 (29%) patients died and 54 (10%) developed transplant failure. Patients in the highest quartile of dp-ucMGP were at considerably higher mortality risk compared with patients in the lowest quartile (HR, 3.10; 95% CI, 1.87-5.12; P for trend<0.001; P for quartile 1 [Q1] vs Q4<0.001). After adjustment for potential confounders, including kidney function and exclusion of patients treated with a vitamin K antagonist, this association remained significant. Patients in the highest quartile also were at higher risk of developing transplant failure (HR, 2.61; 95% CI, 1.22-5.57; P for trend=0.004; P for Q1 vs Q4=0.01), but this association was lost after adjustment for baseline kidney function (HR, 1.20; 95% CI, 0.52-2.75; P for trend=0.6; P for Q1 vs Q4=0.7).

LIMITATIONS

Although MGP exists as various species, only dp-ucMGP was measured. No data were available for vascular calcification as an intermediate end point.

CONCLUSIONS

Vitamin K insufficiency, that is, a high circulating level of dp-ucMGP, is highly prevalent in stable kidney transplant recipients and is associated independently with increased risk of mortality. Future studies should address whether vitamin K supplementation may lead to improved outcomes after kidney transplantation.

Inactive matrix Gla protein is causally related to adverse health outcomes: a Mendelian randomization study in a Flemish population

Matrix Gla-protein is a vitamin K-dependent protein that strongly inhibits arterial calcification. Vitamin K deficiency leads to production of inactive nonphosphorylated and uncarboxylated matrix Gla protein (dp-ucMGP). The risk associated with dp-ucMGP in the population is unknown. In a Flemish population study, we measured circulating dp-ucMGP at baseline (1996-2011), genotyped MGP, recorded adverse health outcomes until December 31, 2012, and assessed the multivariable-adjusted associations of adverse health outcomes with dp-ucMGP. We applied a Mendelian randomization analysis using MGP genotypes as instrumental variables. Among 2318 participants, baseline dp-ucMGP averaged 3.61 μg/L. Over 14.1 years (median), 197 deaths occurred, 58 from cancer and 70 from cardiovascular disease; 85 participants experienced a coronary event. The risk of death and non-cancer mortality curvilinearly increased (P≤0.008) by 15.0% (95% confidence interval, 6.9-25.3) and by 21.5% (11.1-32.9) for a doubling of the nadir (1.43 and 0.97 μg/L, respectively). With higher dp-ucMGP, cardiovascular mortality log-linearly increased (hazard ratio for dp-ucMGP doubling, 1.14 [1.01-1.28]; P=0.027), but coronary events log-linearly decreased (0.93 [0.88-0.99]; P=0.021). dp-ucMGP levels were associated (P≤0.001) with MGP variants rs2098435, rs4236, and rs2430692. For non-cancer mortality and coronary events (P≤0.022), but not for total and cardiovascular mortality (P≥0.13), the Mendelian randomization analysis suggested causality. Higher dp-ucMGP predicts total, non-cancer and cardiovascular mortality, but lower coronary risk. For non-cancer mortality and coronary events, these associations are likely causal.