Regression of warfarin-induced medial elastocalcinosis by high intake of vitamin K in rats

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.

Prevention of vasculopathy by vitamin K supplementation: can we turn fiction into fact?

With the discovery that vitamin K-dependent matrix Gla-protein (MGP) is a strong and modifiable factor in the prevention of arterial calcification, vitamin K was put forward as novel treatment option in cardiovascular disease. The vasculoprotective properties of vitamin K are in part based on the ability to improve gamma-glutamylcarboxylation of MGP, which is a prerequisite for MGP as a calcification inhibitor. Data from experimental animal models reveal that high intake of vitamin K can prevent and even reverse vascular calcifications. In addition, clinical data demonstrate that prescription of vitamin K antagonists for long-term oral anticoagulant therapy accelerates vascular calcification. However, controlled data from randomized prospective vitamin K interventional trials are lacking, thereby weakening a general recommendation for supplementation. The present article summarizes our current knowledge on the association between vitamin K and cardiovascular health. Additionally, we focus on an outlook on important ongoing prospective vitamin K intervention studies. These studies address the issues whether vitamin K substitution helps modifying relevant cardiovascular surrogates such as vascular calcification and whether non-vitamin K oral anticoagulants provide an alternative to support cardiovascular health benefits. So research about cardiovascular protection by vitamin K is an evolving field in which we expect a boost of novel and relevant evidence shortly.

Vascular calcification: from pathophysiology to biomarkers

The link between vascular calcification (VC) and increased mortality is now well established. Over time, as clinical importance of this phenomenon has begun to be fully considered, scientists have highlighted more and more physiopathological mechanisms and signaling pathways that underlie VC. Several conditions such as diabetes, dyslipidemia and renal diseases are undoubtedly identified as predisposing factors. But even if the process is better understood, many questions still remain unanswered. This review briefly develops the various theories that attempt to explain mineralization genesis. Nonetheless, the main purpose of the article is to provide a profile of the various existing biomarkers of VC. Indeed, in the past years, a lot of inhibitors and promoters, which form a dense and interconnected network, were identified. Given importance to assess and control mineralization process, a focusing on accumulated knowledge of each marker seemed to be necessary. Therefore, we tried to define their respective role in the physiopathology and how they can contribute to calcification risk assessment. Among these, Klotho/fibroblast growth factor-23, fetuin-A, Matrix Gla protein, Bone morphogenetic protein-2, osteoprotegerin, osteopontin, osteonectin, osteocalcin, pyrophosphate and sclerostin are specifically discussed.

Vitamin K antagonists: beyond bleeding

Warfarin is the most widely used oral anticoagulant in clinical use today. Indications range from prosthetic valve replacement to recurrent thromboembolic events due to antiphospholipid syndrome. In hemodialysis (HD) patients, warfarin use is even more frequent than in the nonrenal population due to increased cardiovascular comorbidities. The use of warfarin in dialysis patients with atrial fibrillation requires particular caution because side effects may outweigh the assumed benefit of reduced stroke rates. Besides increased bleeding risk, coumarins exert side effects which are not in the focus of clinical routine, yet they deserve special consideration in dialysis patients and should influence the decision of whether or not to prescribe vitamin K antagonists in cases lacking clear guidelines. Issues to be taken into consideration in HD patients are the induction or acceleration of cardiovascular calcifications, a 10-fold increased risk of calciphylaxis and problems related to maintaining a target INR range. New anticoagulants like direct thrombin inhibitors are promising but have not yet been approved for ESRD patients. Here, we summarize the nontraditional side effects of coumarins and give recommendations about the use of vitamin K antagonists in ESRD patients.

Vitamin K1 to slow vascular calcification in haemodialysis patients (VitaVasK trial): a rationale and study protocol

BACKGROUND

Patients on haemodialysis (HD) exhibit increased cardiovascular mortality associated with accelerated vascular calcification (VC). VC is influenced by inhibitors such as matrix Gla protein (MGP), a protein activated in the presence of vitamin K. HD patients exhibit marked vitamin K deficiency, and supplementation with vitamin K reduces inactive MGP levels in these patients. The VitaVasK trial analyses whether vitamin K1 supplementation affects the progression of coronary and aortic calcification in HD patients.

METHODS

VitaVasK is a prospective, randomized, parallel group, multicentre trial (EudraCT No.: 2010-021264-14) that will include 348 HD patients in an open-label, two-arm design. After baseline multi-slice computed tomography (MSCT) of the heart and thoracic aorta, patients with a coronary calcification volume score of at least 100 will be randomized to continue on standard care or to receive additional supplementation with 5 mg vitamin K1 orally thrice weekly. Treatment duration will be 18 months, and MSCT scans will be repeated after 12 and 18 months. Primary end points are the progression of thoracic aortic and coronary artery calcification (calculated as absolute changes in the volume scores at the 18-month MSCT versus the baseline MSCT). Secondary end points comprise changes in Agatston score, mitral and aortic valve calcification as well as major adverse cardiovascular events (MACE) and all-cause mortality. VitaVask also aims to record MACE and all-cause mortality in the follow-up period at 3 and 5 years after treatment initiation. This trial may lead to the identification of an inexpensive and safe treatment or prophylaxis of VC in HD patients.

Impaired vitamin K recycling in uremia is rescued by vitamin K supplementation

In chronic kidney disease, vitamin K-dependent proteins, including the calcification inhibitor matrix Gla protein, are largely uncarboxylated indicating that functional vitamin K deficiency may contribute to uremic vascular calcification. Since the effects of uremia on the vitamin K cycle are unknown, we investigated the influence of uremia and vitamin K supplementation on the activity of the vitamin K cycle and extraosseous calcification. Uremia was induced in rats by an adenine-supplemented diet and vitamin K1 or K2 was administered over 4 and 7 weeks. After 4 weeks of adenine diet, the activity of the vitamin K cycle enzyme γ-carboxylase but not the activities of DT-diaphorase or vitamin K epoxide reductase were reduced. Serum levels of undercarboxylated matrix Gla protein increased, indicating functional vitamin K deficiency. There was no light microscopy-detectable calcification at this stage but chemically determined aortic and renal calcium content was increased. Vitamin K treatment reduced aortic and renal calcium content after 4 weeks. Seven weeks of uremia induced overt calcification in the aorta, heart, and kidneys; however, addition of vitamin K restored intrarenal γ-carboxylase activity and overstimulated it in the liver along with reducing heart and kidney calcification. Thus, uremic vitamin K deficiency may partially result from a reduction of the γ-carboxylase activity which possibly contributes to calcification. Pharmacological vitamin K supplementation restored the vitamin K cycle and slowed development of soft tissue calcification in experimental uremia.

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

BACKGROUND

High vitamin K intake is associated with a reduced risk of coronary heart disease (CHD). This is thought to be mediated by increased activation of the vitamin K-dependent matrix γ-carboxyglutamate protein (MGP). Desphospho-uncarboxylated MGP (dp-ucMGP) is associated with both vitamin K status and vascular calcification. However, the association of dp-ucMGP with CHD and stroke in the general population has not been investigated to date.

OBJECTIVE

To investigate the association of dp-ucMGP with incident CHD or stroke.

METHODS

A prospective case-cohort study with a representative baseline sample of 1406 participants and 1154 and 380 incident cases of CHD and stroke, respectively, was nested within the EPIC-NL study. Circulating dp-ucMGP levels were measured with ELISA in baseline plasma samples. The incidence rates of fatal and non-fatal CHD and stroke were obtained by linkage to national registers. Cox proportional hazard models were used to calculate hazard ratios (HRs) per standard deviation (SD) and per quartile of circulating dp-ucMGP levels.

RESULTS AND CONCLUSION

The average follow-up was 11.5 years. Levels of dp-ucMGP were not associated with CHD risk, with an HR per SD of 1.00 (95% confidence interval [CI] 0.93-1.07) and an HRQ4 vs. Q1 of 0.94 (95% CI 0.79-1.13) after adjustment for cardiovascular risk factors. There was no association of dp-ucMGP stroke risk (HRSD  0.98, 95% CI 0.90-1.08; and HRQ4 vs. Q1  1.09, 95% CI 0.78-1.51). This study could not confirm that high dp-ucMGP levels, reflecting poor vitamin K status, are associated with increased CHD or stroke risk in the general population.

Gla-rich protein is a potential new vitamin K target in cancer: evidences for a direct GRP-mineral interaction

Gla-rich protein (GRP) was described in sturgeon as a new vitamin-K-dependent protein (VKDP) with a high density of Gla residues and associated with ectopic calcifications in humans. Although VKDPs function has been related with γ-carboxylation, the Gla status of GRP in humans is still unknown. Here, we investigated the expression of recently identified GRP spliced transcripts, the γ-carboxylation status, and its association with ectopic calcifications, in skin basal cell and breast carcinomas. GRP-F1 was identified as the predominant splice variant expressed in healthy and cancer tissues. Patterns of γ-carboxylated GRP (cGRP)/undercarboxylated GRP (ucGRP) accumulation in healthy and cancer tissues were determined by immunohistochemistry, using newly developed conformation-specific antibodies. Both GRP protein forms were found colocalized in healthy tissues, while ucGRP was the predominant form associated with tumor cells. Both cGRP and ucGRP found at sites of microcalcifications were shown to have in vitro calcium mineral-binding capacity. The decreased levels of cGRP and predominance of ucGRP in tumor cells suggest that GRP may represent a new target for the anticancer potential of vitamin K. Also, the direct interaction of cGRP and ucGRP with BCP crystals provides a possible mechanism explaining GRP association with pathological mineralization.

Vascular calcification in patients with type 2 diabetes: the involvement of matrix Gla protein

BACKGROUND

Matrix Gla protein (MGP) is an important inhibitor of calcification. The objective of the present study of patients with type 2 diabetes and normal or slightly altered kidney function was to evaluate levels of inactive, dephospho-uncarboxylated MGP(dp-ucMGP) and total uncarboxylated MGP(t-ucMGP) and assess their links with biological and clinical parameters (including peripheral vascular calcification).

METHODS

The DIACART study is a cross-sectional cohort study of 198 patients with type 2 diabetes and normal or slightly altered kidney function. Matrix Gla protein levels were measured with an ELISA and all patients underwent multislice spiral computed tomography scans to score below-knee arterial calcification.

RESULTS

In the study population as a whole, the mean dp-ucMGP and t-ucMGP levels were 627 ± 451 pM and 4868 ± 1613 nM, respectively. Glomerular filtration rate, age and current vitamin K antagonist use were independently associated with dp-ucMGP levels. When the study population was divided according to the median peripheral arterial calcification score, patients with the higher score displayed significantly lower t-ucMGP and significantly higher dp-ucMGP levels. Furthermore, plasma dp-ucMGP was positively associated with the peripheral arterial calcification score (independently of age, gender, previous cardiovascular disease and t-ucMGP levels).

CONCLUSIONS

High dp-ucMGP levels were independently associated with below-knee arterial calcification score in patients with type 2 diabetes and normal or slightly altered kidney function. The reversibility of the elevation of dp-ucMGP levels and the latter's relationship with clinical events merit further investigation.

Phosphate: an old bone molecule but new cardiovascular risk factor

Phosphate handling in the body is complex and involves hormones produced by the bone, the parathyroid gland and the kidneys. Phosphate is mostly found in hydroxyapatite. however recent evidence suggests that phosphate is also a signalling molecule associated with bone formation. Phosphate balance requires careful regulation of gut and kidney phosphate transporters, SLC34 transporter family, but phosphate signalling in osteoblasts and vascular smooth muscle cells is likely mediated by the SLC20 transporter family (PiT1 and PiT2). If not properly regulated, phosphate imblanace could lead to mineral disorders as well as vascular calcification. In chronic kidney disease-mineral bone disorder, hyperphosphataemia has been consistently associated with extra-osseous calcification and cardiovascular disease. This review focuses on the physiological mechanisms involved in phosphate balance and cell signalling (i.e. osteoblasts and vascular smooth muscle cells) as well as pathological consequences of hyperphosphataemia. Finally, conventional as well as new and experimental therapeutics in the treatment of hyperphosphataemia are explored.

Oral anticoagulant therapy in patients receiving haemodialysis: is it time to abandon it?

Oral anticoagulant (OAC) therapy in haemodialysis patients causes a great deal of controversy. This is because a number of pro- and anticoagulant factors play an important role in end-stage renal failure due to the nature of the disease itself. In these conditions, the pharmacokinetic and pharmacodynamic properties of the OACs used change as well. In the case of the treatment of venous thromboembolism, the only remaining option is OAC treatment according to regimens used for the general population. Prevention of HD vascular access thrombosis with the use of OACs is not very effective and can be dangerous. However, OAC treatment in patients with atrial fibrillation in dialysis population may be associated with an increase in the incidence of stroke and mortality. Doubts should be dispelled by prospective, randomised studies; at the moment, there is no justification for routine use of OACs in the above-mentioned indications. In selected cases of OAC therapy in this group of patients, it is absolutely necessary to control and monitor the applied treatment thoroughly. Indications for the use of OACs in patients with end-stage renal disease, including haemodialysis patients, should be currently limited.

Vitamin K status in chronic kidney disease

The purpose of this review is to summarize the research to date on vitamin K status in chronic kidney disease (CKD). This review includes a summary of the data available on vitamin K status in patients across the spectrum of CKD as well as the link between vitamin K deficiency in CKD and bone dynamics, including mineralization and demineralization, as well as ectopic mineralization. It also describes two current clinical trials that are underway evaluating vitamin K treatment in CKD patients. These data may inform future clinical practice in this population.

Warfarin induces cardiovascular damage in mice

OBJECTIVE

Vascular calcification is an independent risk factor for cardiovascular disease. Once thought to be a passive process, vascular calcification is now known to be actively prevented by proteins acting systemically (fetuin-A) or locally (matrix Gla protein). Warfarin is a vitamin K antagonist, widely prescribed to reduce coagulation by inhibiting vitamin K-dependent coagulation factors. Recently, it became clear that vitamin K antagonists also affect vascular calcification by inactivation of matrix Gla protein. Here, we investigated functional cardiovascular characteristics in a mouse model with warfarin-induced media calcification.

APPROACH AND RESULTS

DBA/2 mice received diets with variable concentrations of warfarin (0.03, 0.3, and 3 mg/g) with vitamin K1 at variable time intervals (1, 4, and 7 weeks). Von Kossa staining revealed that warfarin treatment induced calcified areas in both medial layer of aorta and heart in a dose- and time-dependent fashion, which could be inhibited by simultaneous vitamin K2 treatment. With ongoing calcification, matrix Gla protein mRNA expression decreased, and inactive matrix Gla protein expression increased. TdT-mediated dUTP-biotin nick end labeling-positive apoptosis increased, and vascular smooth muscle cell number was concomitantly reduced by warfarin treatment. On a functional level, warfarin treatment augmented aortic peak velocity, aortic valve-peak gradient, and carotid pulse-wave velocity.

CONCLUSION

Warfarin induced significant calcification with resulting functional cardiovascular damage in DBA/2 wild-type mice. The model would enable future researchers to decipher mechanisms of vascular calcification and may guide them in the development of new therapeutic strategies.

VKORC1L1, an enzyme rescuing the vitamin K 2,3-epoxide reductase activity in some extrahepatic tissues during anticoagulation therapy

Vitamin K is involved in the γ-carboxylation of the vitamin K-dependent proteins, and vitamin K epoxide is a by-product of this reaction. Due to the limited intake of vitamin K, its regeneration is necessary and involves vitamin K 2,3-epoxide reductase (VKOR) activity. This activity is known to be supported by VKORC1 protein, but recently a second gene, VKORC1L1, appears to be able to support this activity when the encoded protein is expressed in HEK293T cells. Nevertheless, this protein was described as being responsible for driving the vitamin K-mediated antioxidation pathways. In this paper we precisely analyzed the catalytic properties of VKORC1L1 when expressed in Pichia pastoris and more particularly its susceptibility to vitamin K antagonists. Vitamin K antagonists are also inhibitors of VKORC1L1, but this enzyme appears to be 50-fold more resistant to vitamin K antagonists than VKORC1. The expression of Vkorc1l1 mRNA was observed in all tissues assayed, i.e. in C57BL/6 wild type and VKORC1-deficient mouse liver, lung, and testis and rat liver, lung, brain, kidney, testis, and osteoblastic cells. The characterization of VKOR activity in extrahepatic tissues demonstrated that a part of the VKOR activity, more or less important according to the tissue, may be supported by VKORC1L1 enzyme especially in testis, lung, and osteoblasts. Therefore, the involvement of VKORC1L1 in VKOR activity partly explains the low susceptibility of some extrahepatic tissues to vitamin K antagonists and the lack of effects of vitamin K antagonists on the functionality of the vitamin K-dependent protein produced by extrahepatic tissues such as matrix Gla protein or osteocalcin.

Association between circulating vitamin K1 and coronary calcium progression in community-dwelling adults: the Multi-Ethnic Study of Atherosclerosis

BACKGROUND

Animal studies have shown that vitamin K treatment reduced vascular calcification, but human data are limited.

OBJECTIVE

We determined the association between vitamin K status and coronary artery calcium (CAC) progression in the Multi-Ethnic Study of Atherosclerosis by using a case-cohort design.

DESIGN

Serum phylloquinone (vitamin K1) was measured in 296 participants with extreme CAC progression and 561 randomly selected participants without extreme CAC progression; all subjects had baseline and follow-up CAC measures (mean follow-up: 2.5 y). A serum vitamin K1 concentration was considered low at <1.0 nmol/L (the distribution median). Outcomes were replicated by using post hoc per-protocol analyses of a vitamin K1 supplementation trial.

RESULTS

The OR (95% CI) for extreme CAC progression for subjects with low serum vitamin K1 compared with subjects without extreme CAC progression was 1.34 (0.94, 1.90; NS) when adjusted for demographics and confounders. A significant interaction between low vitamin K1 and antihypertension medication use was detected (P = 0.016). Hypertension medication users with low serum vitamin K1 were more likely to have extreme CAC progression than were medication users without extreme CAC progression [OR (95% CI): 2.37 (1.38, 4.09)]. In replication, baseline antihypertensive medication users in the supplementation group had less CAC progression than did those in the control group [adjusted mean ± SEM of the 3-y CAC change was +5 ± 20 Agatston units (AU) in the vitamin K1 group (n = 40) and +44 ± 13 AU in the placebo group (n = 49); P < 0.01].

CONCLUSIONS

Although the point estimate of our primary analysis suggests low serum vitamin K1 is associated with greater CAC progression, the difference was NS. Low serum vitamin K1 was significantly associated with CAC progression in antihypertension medication users, which, to our knowledge, is a novel finding conditionally replicated by using an independent sample. Intervention trials are needed to determine whether improving serum vitamin K1 reduces CAC progression, especially in hypertensive individuals. This trial was registered at clinicaltrials.gov as NCT00183001.

Warfarin accelerates ectopic mineralization in Abcc6(-/-) mice: clinical relevance to pseudoxanthoma elasticum

Pseudoxanthoma elasticum (PXE) is a multisystem ectopic mineralization disorder caused by mutations in the ABCC6 gene. Warfarin, a commonly used anticoagulant, is associated with increased mineralization of the arterial blood vessels and cardiac valves. We hypothesized that warfarin may accelerate ectopic tissue mineralization in PXE, with clinical consequences. To test this hypothesis, we developed a model in which Abcc6(-/-) mice, which recapitulate features of PXE, were fed a diet supplemented with warfarin and vitamin K1. Warfarin action was confirmed by significantly increased serum levels of oxidized vitamin K. For mice placed on a warfarin-containing diet, quantitative chemical and morphometric analyses revealed massive accumulation of mineral deposits in a number of tissues. Mice fed a warfarin-containing diet were also shown to have abundant uncarboxylated form of matrix Gla protein, which allowed progressive tissue mineralization to ensue. To explore the clinical relevance of these findings, 1747 patients with PXE from the approximately 4000 patients in the PXE International database were surveyed about the use of warfarin. Of the 539 respondents, 2.6% reported past or present use of warfarin. Based on the prevalence of PXE (approximately 1:50,000), thousands of patients with PXE worldwide may be at risk for worsening of PXE as a result of warfarin therapy.

Vitamin K-dependent carboxylation of matrix Gla-protein: a crucial switch to control ectopic mineralization

Vascular mineralization has recently emerged as a risk factor for cardiovascular morbidity and mortality. Previously regarded as a passive end-stage process, vascular mineralization is currently recognized as an actively regulated process with cellular and humoral contributions. The discovery that the vitamin K-dependent matrix Gla-protein (MGP) is a strong inhibitor of vascular calcification has propelled our mechanistic understanding of this process and opened novel avenues for diagnosis and treatment. This review focuses on molecular mechanisms of vascular mineralization involving MGP and discusses the potential for treatments and biomarkers to monitor patients at risk for vascular mineralization.

Quercetin attenuates warfarin-induced vascular calcification in vitro independently from matrix Gla protein

Warfarin can stimulate vascular calcification in vitro via activation of β-catenin signaling and/or inhibition of matrix Gla protein (MGP) carboxylation. Calcification was induced in vascular smooth muscle cells (VSMCs) with therapeutic levels of warfarin in normal calcium and clinically acceptable phosphate levels. Although TGF/BMP and PKA pathways are activated in calcifying VSMCs, pharmacologic analysis reveals that their activation is not contributory. However, β-catenin activity is important because inhibition of β-catenin with shRNA or bioflavonoid quercetin prevents calcification in primary human VSMCs, rodent aortic rings, and rat A10 VSMC line. In the presence of quercetin, reactivation of β-catenin using the glycogen synthase kinase-3β (GSK-3β) inhibitor LiCl restores calcium accumulation, confirming that quercetin mechanism of action hinges on inhibition of the β-catenin pathway. Calcification in VSMCs induced by 10 μm warfarin does not associate with reduced levels of carboxylated MGP, and inhibitory effects of quercetin do not involve induction of MGP carboxylation. Further, down-regulation of MGP by shRNA does not alter the effect of quercetin. These results suggest a new β-catenin-targeting strategy to prevent vascular calcification induced by warfarin and identify quercetin as a potential therapeutic in this pathology.

Dietary vitamin K and therapeutic warfarin alter the susceptibility to vascular calcification in experimental chronic kidney disease

The leading cause of death in patients with chronic kidney disease (CKD) is cardiovascular disease, with vascular calcification being a key modifier of disease progression. A local regulator of vascular calcification is vitamin K. This γ-glutamyl carboxylase substrate is an essential cofactor in the activation of several extracellular matrix proteins that inhibit calcification. Warfarin, a common therapy in dialysis patients, inhibits the recycling of vitamin K and thereby decreases the inhibitory activity of these proteins. In this study, we sought to determine whether modifying vitamin K status, either by increasing dietary vitamin K intake or by antagonism with therapeutic doses of warfarin, could alter the development of vascular calcification in male Sprague-Dawley rats with adenine-induced CKD. Treatment of CKD rats with warfarin markedly increased pulse pressure and pulse wave velocity, as well as significantly increased calcium concentrations in the thoracic aorta (3-fold), abdominal aorta (8-fold), renal artery (4-fold), and carotid artery (20-fold). In contrast, treatment with high dietary vitamin K1 increased vitamin K tissue concentrations (10-300-fold) and blunted the development of vascular calcification. Thus, vitamin K has an important role in modifying mechanisms linked to the susceptibility of arteries to calcify in an experimental model of CKD.

Mechanisms of arterial remodeling: lessons from genetic diseases

Vascular disease is still the leading cause of morbidity and mortality in the Western world, and the primary cause of myocardial infarction, stroke, and ischemia. The biology of vascular disease is complex and still poorly understood in terms of causes and consequences. Vascular function is determined by structural and functional properties of the arterial vascular wall. Arterial stiffness, that is a pathological alteration of the vascular wall, ultimately results in target-organ damage and increased mortality. Arterial remodeling is accelerated under conditions that adversely affect the balance between arterial function and structure such as hypertension, atherosclerosis, diabetes mellitus, chronic kidney disease, inflammatory disease, lifestyle aspects (smoking), drugs (vitamin K antagonists), and genetic abnormalities [e.g., pseudoxanthoma elasticum (PXE), Marfan's disease]. The aim of this review is to provide an overview of the complex mechanisms and different factors that underlie arterial remodeling, learning from single gene defect diseases like PXE, and PXE-like, Marfan's disease and Keutel syndrome in vascular remodeling.

Sailing between Scylla and Charybdis: oral long-term anticoagulation in dialysis patients

End-stage renal disease (ESRD) patients exhibit an increased risk of bleeding compared with non-chronic kidney disease (CKD) patients due to uraemic platelet dysfunction, altered vessel architecture and other factors. This renders any long-term oral anticoagulation potentially difficult. While there is little doubt that ESRD patients with recurrent thromboembolism or a mechanical cardiac valve should receive vitamin K antagonists (coumarins), the use of coumarins in ESRD patients with atrial fibrillation is a matter of debate. In non-CKD patients, current guidelines strongly recommend the use of oral anticoagulants for stroke prophylaxis in atrial fibrillation if certain risk factors are present (CHA2DS2-VASc score). This recommendation is often extrapolated to patients with advanced CKD or ESRD but data supporting this practice are weak to absent. Besides an increased bleeding risk in ESRD patients, coumarins will also accelerate cardiovascular calcification and are potent risk factors for the development of calcific uraemic arteriolopathy (calciphylaxis). Novel coumarin alternatives such as direct thrombin inhibitors are promising but none is currently approved for use in ESRD patients. Whether interventional treatment strategies such as atrial appendage occlusion are safe and effective options in advanced CKD is also as yet unresolved. This review attempts to balance the potential risks and benefits of coumarin usage in ESRD patients and to give the best possible recommendations for everyday patient care.

Transglutaminase inhibitors attenuate vascular calcification in a preclinical model

OBJECTIVE

In vitro, transglutaminase-2 (TG2)-mediated activation of the β-catenin signaling pathway is central in warfarin-induced calcification, warranting inquiry into the importance of this signaling axis as a target for preventive therapy of vascular calcification in vivo.

METHODS AND RESULTS

The adverse effects of warfarin-induced elastocalcinosis in a rat model include calcification of the aortic media, loss of the cellular component in the vessel wall, and isolated systolic hypertension, associated with accumulation and activation of TG2 and activation of β-catenin signaling. These effects of warfarin can be completely reversed by intraperitoneal administration of the TG2-specific inhibitor KCC-009 or dietary supplementation with the bioflavonoid quercetin, known to inhibit β-catenin signaling. Our study also uncovers a previously uncharacterized ability of quercetin to inhibit TG2. Quercetin reversed the warfarin-induced increase in systolic pressure, underlying the functional consequence of this treatment. Molecular analysis shows that quercetin diet stabilizes the phenotype of smooth muscle and prevents its transformation into osteoblastic cells.

CONCLUSIONS

Inhibition of the TG2/β-catenin signaling axis seems to prevent warfarin-induced elastocalcinosis and to control isolated systolic hypertension.

Vitamin K-antagonists accelerate atherosclerotic calcification and induce a vulnerable plaque phenotype

BACKGROUND

Vitamin K-antagonists (VKA) are treatment of choice and standard care for patients with venous thrombosis and thromboembolic risk. In experimental animal models as well as humans, VKA have been shown to promote medial elastocalcinosis. As vascular calcification is considered an independent risk factor for plaque instability, we here investigated the effect of VKA on coronary calcification in patients and on calcification of atherosclerotic plaques in the ApoE(-/-) model of atherosclerosis.

METHODOLOGY/PRINCIPAL FINDINGS

A total of 266 patients (133 VKA users and 133 gender and Framingham Risk Score matched non-VKA users) underwent 64-slice MDCT to assess the degree of coronary artery disease (CAD). VKA-users developed significantly more calcified coronary plaques as compared to non-VKA users. ApoE(-/-) mice (10 weeks) received a Western type diet (WTD) for 12 weeks, after which mice were fed a WTD supplemented with vitamin K(1) (VK(1), 1.5 mg/g) or vitamin K(1) and warfarin (VK(1)&W; 1.5 mg/g & 3.0 mg/g) for 1 or 4 weeks, after which mice were sacrificed. Warfarin significantly increased frequency and extent of vascular calcification. Also, plaque calcification comprised microcalcification of the intimal layer. Furthermore, warfarin treatment decreased plaque expression of calcification regulatory protein carboxylated matrix Gla-protein, increased apoptosis and, surprisingly outward plaque remodeling, without affecting overall plaque burden.

CONCLUSIONS/SIGNIFICANCE

VKA use is associated with coronary artery plaque calcification in patients with suspected CAD and causes changes in plaque morphology with features of plaque vulnerability in ApoE(-/-) mice. Our findings underscore the need for alternative anticoagulants that do not interfere with the vitamin K cycle.

Phylloquinone and vitamin D status: associations with incident chronic kidney disease in the Framingham Offspring cohort

BACKGROUND

Cardiovascular risk factors are associated with the development of chronic kidney disease (CKD), and CKD and vascular disease are etiologically linked. Evidence suggests deficiencies of vitamins D and K may adversely affect the cardiovascular system, but data from longitudinal studies are lacking. We hypothesized that deficiencies of vitamins D and K may be associated with incident CKD and/or incident albuminuria amongst members of the general population.

METHODS

We analyzed 1,442 Framingham Heart Study participants (mean age 58 years; 50.5% women), free of CKD (eGFR <60 ml/min/1.73 m(2)), with a mean follow-up of 7.8 years in 2005-2008. Incident albuminuria was defined using sex-specific cut-offs of urine albumin-to-creatinine ratio (≥17 mg/g men and ≥25 mg/g women). Baseline log plasma phylloquinone (vitamin K(1)) and 25(OH)D levels, analyzed as continuous variables and by quartile, were related to risk of incident CKD (n = 108) and incident albuminuria (n = 106) using logistic regression models adjusted for standard risk factors.

RESULTS

Participants in the highest phylloquinone quartile (≥1.78 nmol/l) had an increased risk of CKD (multivariable-adjusted OR Q(4) vs. Q(1) 2.39; p = 0.006) and albuminuria at follow-up (multivariable-adjusted OR Q(4) vs. Q(1) 1.95; p = 0.05), whereas no association was observed with continuous phylloquinone levels for either endpoint. Deficiency of 25(OH)D was not associated with incident CKD or albuminuria in either analysis.

CONCLUSIONS

Contrary to our hypothesis, higher plasma phylloquinone levels are associated with an increased risk of incident CKD. Whether plasma phylloquinone is a marker for another unmeasured risk factor requires further study. External validation is necessary given the unexpected nature of these results.

Elastin in large artery stiffness and hypertension

Large artery stiffness, as measured by pulse wave velocity, is correlated with high blood pressure and may be a causative factor in essential hypertension. The extracellular matrix components, specifically the mix of elastin and collagen in the vessel wall, determine the passive mechanical properties of the large arteries. Elastin is organized into elastic fibers in the wall during arterial development in a complex process that requires spatial and temporal coordination of numerous proteins. The elastic fibers last the lifetime of the organism but are subject to proteolytic degradation and chemical alterations that change their mechanical properties. This review discusses how alterations in the amount, assembly, organization, or chemical properties of the elastic fibers affect arterial stiffness and blood pressure. Strategies for encouraging or reversing alterations to the elastic fibers are addressed. Methods for determining the efficacy of these strategies, by measuring elastin amounts and arterial stiffness, are summarized. Therapies that have a direct effect on arterial stiffness through alterations to the elastic fibers in the wall may be an effective treatment for essential hypertension.

Vascular calcification: the price to pay for anticoagulation therapy with vitamin K-antagonists

Vitamin K-antagonists (VKA) are the most widely used anti-thrombotic drugs with substantial efficacy in reducing risk of arterial and venous thrombosis. Several lines of evidence indicate, however, that VKA inhibit not only post-translational activation of vitamin K-dependent coagulation factors but also synthesis of functional extra-hepatic vitamin K-dependent proteins thereby eliciting undesired side-effects. Vascular calcification is one of the recently revealed side-effects of VKA. Vascular calcification is an actively regulated process involving vascular cells and a number of vitamin K-dependent proteins. Mechanistic understanding of vascular calcification is essential to improve VKA-based treatments of both thrombotic disorders and atherosclerosis. This review addresses vitamin K-cycle and vitamin K-dependent processes of vascular calcification that are affected by VKA. We conclude that there is a growing need for better understanding of the effects of anticoagulants on vascular calcification and atherosclerosis.

Vitamin K status and vascular calcification: evidence from observational and clinical studies

Vascular calcification occurs when calcium accumulates in the intima (associated with atherosclerosis) and/or media layers of the vessel wall. Coronary artery calcification (CAC) reflects the calcium burden within the intima and media of the coronary arteries. In population-based studies, CAC independently predicts cardiovascular disease (CVD) and mortality. A preventive role for vitamin K in vascular calcification has been proposed based on its role in activating matrix Gla protein (MGP), a calcification inhibitor that is expressed in vascular tissue. Although animal and in vitro data support this role of vitamin K, overall data from human studies are inconsistent. The majority of population-based studies have relied on vitamin K intake to measure status. Phylloquinone is the primary dietary form of vitamin K and available supplementation trials, albeit limited, suggest phylloquinone supplementation is relevant to CAC. Yet observational studies have found higher dietary menaquinone, but not phylloquinone, to be associated with less calcification. Vascular calcification is highly prevalent in certain patient populations, especially in those with chronic kidney disease (CKD), and it is plausible vitamin K may contribute to reducing vascular calcification in patients at higher risk. Subclinical vitamin K deficiency has been reported in CKD patients, but studies linking vitamin K status to calcification outcomes in CKD are needed to clarify whether or not improving vitamin K status is associated with improved vascular health in CKD. This review summarizes the available evidence of vitamin K and vascular calcification in population-based studies and clinic-based studies, with a specific focus on CKD patients.

Calciphylaxis in CKD and beyond

Calciphylaxis is still an incompletely understood rare disease, which most often affects people on haemodialysis. For the majority of patients, calciphylaxis means a massive reduction in quality of life and is associated with high morbidity and mortality. We still know little about the concert of local and systemic risk factors and underlying causes that finally lead to the development of calciphylaxis. Recent work from Asia points towards persistent uncertainties in the diagnosis and management of the disease which the nephrology community has to address by establishing standards in both diagnosis as well as treatment strategies. Hayashi et al. have published results from a Japanese survey in which the authors collected data from calciphylaxis patients and compared clinical and laboratory data with those of control subjects. This innovative approach allowed the authors to calculate relative risks for various parameters in terms of calciphylaxis development. While uncontrolled hyperparathyroidism seemingly plays a secondary role, vitamin K antagonist usage proved to be of particular importance. Survey as well as registry data may help to close the gap in our knowledge about calciphylaxis which may ultimately result in improved prevention, patient care and outcome.

Warfarin-induced calciphylaxis successfully treated with sodium thiosulphate

Calciphylaxis is a rare life-threatening form of skin necrosis. Although traditionally observed in patients with end-stage renal disease and/or hyperparathyroidism, calciphylaxis has also been reported to occur in 'non-traditional' patients with normal renal and parathyroid function. We report a case of warfarin-induced calciphylaxis treated successfully with sodium thiosulphate and discuss the role of Vitamin K2 as a potential therapeutic option in the management of warfarin-induced calciphylaxis.

Effect of vitamin K2 supplementation on functional vitamin K deficiency in hemodialysis patients: a randomized trial

BACKGROUND

Vascular calcification is a predictor of cardiovascular morbidity and mortality. Hemodialysis patients experience severe vascular calcifications. Matrix Gla protein (MGP) is a central calcification inhibitor of the arterial wall; its activity depends on vitamin K-dependent γ-glutamate carboxylation. Uncarboxylated MGP, formed as a result of vitamin K deficiency, is associated with cardiovascular disease. Recent studies suggest poor vitamin K status in hemodialysis patients. We therefore aimed to investigate whether daily vitamin K supplementation improves the bioactivity of vitamin K-dependent proteins in hemodialysis patients, assessed by circulating dephosphorylated-uncarboxylated MGP, uncarboxylated osteocalcin, and uncarboxylated prothrombin (PIVKA-II [protein induced by vitamin K absence II]).

STUDY DESIGN

Interventional randomized non-placebo-controlled trial with 3 parallel groups.

SETTING & PARTICIPANTS

53 long-term hemodialysis patients in stable conditions, 18 years or older. 50 healthy age-matched individuals served as controls.

INTERVENTIONS

Menaquinone-7 (vitamin K(2)) treatment at 45, 135, or 360 μg/d for 6 weeks.

OUTCOMES

Plasma levels of dephosphorylated-uncarboxylated MGP, uncarboxylated osteocalcin, and PIVKA-II.

MEASUREMENTS

Plasma levels were assessed using enzyme-linked immunosorbent assays.

RESULTS

At baseline, hemodialysis patients had 4.5-fold higher dephosphorylated-uncarboxylated MGP and 8.4-fold higher uncarboxylated osteocalcin levels compared with controls. PIVKA-II levels were elevated in 49 hemodialysis patients. Vitamin K(2) supplementation induced a dose- and time-dependent decrease in circulating dephosphorylated-uncarboxylated MGP, uncarboxylated osteocalcin, and PIVKA-II levels. Response rates in the reduction in dephosphorylated-uncarboxylated MGP levels were 77% and 93% in the groups receiving 135 μg and 360 μg of menaquinone-7, respectively.

LIMITATIONS

Small sample size.

CONCLUSIONS

This study confirms that most hemodialysis patients have a functional vitamin K deficiency. More importantly, it is the first study showing that inactive MGP levels can be decreased markedly by daily vitamin K(2) supplementation. Our study provides the rationale for intervention trials aimed at decreasing vascular calcification in hemodialysis patients by vitamin K supplementation.

Vitamin K: fracture prevention and beyond

Morbidity and decreased function related to osteoporosis, fracture, cardiovascular disease, stroke, and peripheral vascular disease are encountered by clinicians daily. Although we have seen vast advancement in treatment and management of these conditions, preventative practice has unfortunately served a lesser role in patient care. Increasing the dietary intake of vitamin K may have substantial utility in the prevention of these disease states. Since the discovery of vitamin K in 1935, its primary role was thought to be involved in the synthesis of clotting factors II, VII, IX, and X. Recently, its function in other metabolic pathways has emerged, leading to exploration of its significance beyond coagulation. Vitamin K is essential to bone physiology and prevention of atherosclerosis. It is involved in bone remodeling, cell signaling, apoptosis, arterial calcification, and chemotaxis, and it has anti-inflammatory effects. Conversely, warfarin, a potent vitamin K inhibitor, has demonstrated adverse effects on bone remodeling and atherosclerosis. Natural forms of vitamin K are available in multiple dietary sources, and some structural forms are more readily available for use in metabolic pathways than are others. With regard to supplementation, the specific form of vitamin K is often not disclosed, and the recommended daily value is potentially less than what is physiologically required. On the basis of a review of the literature, it appears advantageous to encourage patients to eat a diet rich in vitamin K; however, the benefit of vitamin K supplementation alone is yet to be thoroughly conveyed.

The association of matrix Gla protein isomers with calcification in capsules surrounding silicone breast implants

Implanted silicone medical prostheses induce a dynamic sequence of histologic events in adjacent tissue resulting in the formation of a fibrotic peri-prosthetic capsule. In some cases, capsular calcification occurs, requiring surgical intervention. In this study we investigated capsules from silicone gel-filled breast prostheses to test the hypothesis that this calcification might be regulated by the small vitamin K-dependent protein, matrix Gla protein (MGP), a potent inhibitor of arterial calcification, or by Fetuin-A, a hepatocyte-derived glycoprotein also implicated as a regulator of pathologic calcification. Immunolocalization studies of explanted capsular tissue, using conformation-specific antibodies, identified the mineralization-protective γ-carboxylated MGP isomer (cMGP) within cells of uncalcified capsules, whereas the non-functional undercarboxylated isomer (uMGP) was typically absent. Both were upregulated in calcific capsules and co-localized with mineral plaque and adjacent fibers. Synovial-like metaplasia was present in one uncalcified capsule in which MGP species were differentially localized within the pseudosynovium. Fetuin-A was localized to cells within uncalcified capsules and to mineral deposits within calcific capsules. The osteoinductive cytokine bone morphogenic protein-2 localized to collagen fibers in uncalcified capsules. These findings demonstrate that MGP, in its vitamin K-activated conformer, may represent a pharmacological target to sustain the health of the peri-prosthetic tissue which encapsulates silicone breast implants as well as other implanted silicone medical devices.

Matrix Gla protein metabolism in vascular smooth muscle and role in uremic vascular calcification

Matrix Gla protein (MGP) is an inhibitor of vascular calcification but its mechanism of action and pathogenic role are unclear. This was examined in cultured rat aortas and in a model of vascular calcification in rats with renal failure. Both carboxylated (GlaMGP) and uncarboxylated (GluMGP) forms were present in aorta and disappeared during culture with warfarin. MGP was also released into the medium and removed by ultracentrifugation, and similarly affected by warfarin. In a high-phosphate medium, warfarin increased aortic calcification but only in the absence of pyrophosphate, another endogenous inhibitor of vascular calcification. Although GlaMGP binds and inactivates bone morphogenic protein (BMP)-2, a proposed mediator of vascular calcification through up-regulation of the osteogenic transcription factor runx2, neither warfarin, BMP-2, nor the BMP-2 antagonist noggin altered runx2 mRNA content in aortas, and noggin did not prevent warfarin-induced calcification. Aortic content of MGP mRNA was increased 5-fold in renal failure but did not differ between calcified and noncalcified aortas. Immunoblots showed increased GlaMGP in noncalcified (5-fold) and calcified (20-fold) aortas from rats with renal failure, with similar increases in GluMGP. We conclude that rat aortic smooth muscle produces both GlaMGP and GluMGP in tissue-bound and soluble, presumably vesicular, forms. MGP inhibits calcification independent of BMP-2-driven osteogenesis and only in the absence of pyrophosphate, consistent with direct inhibition of hydroxyapatite formation. Synthesis of MGP is increased in renal failure and deficiency of GlaMGP is not a primary cause of medial calcification in this condition.

Circulating uncarboxylated matrix gla protein is associated with vitamin K nutritional status, but not coronary artery calcium, in older adults

Matrix Gla protein (MGP) is a calcification inhibitor in vascular tissue that must be carboxylated by vitamin K to function. Evidence suggests circulating uncarboxylated MGP (ucMGP) is elevated in persons with disease characterized by vascular calcification. The primary purpose of this study was to determine cross-sectional and longitudinal associations between plasma ucMGP, vitamin K status, and coronary artery calcium (CAC) in older adults without coronary heart disease. Genetic determinants of ucMGP were also explored. Cross-sectional associations among baseline plasma ucMGP, vitamin K status biomarkers [plasma phylloquinone, uncarboxylated prothrombin (PIVKA-II), serum uncarboxylated osteocalcin (%ucOC)], CAC, and plausible genetic polymorphisms were examined in 438 community-dwelling adults (60-80 y, 59% women). The effect of phylloquinone supplementation (500 μg/d) for 3 y on plasma ucMGP was determined among 374 participants. At baseline, plasma phylloquinone was lower and %ucOC and PIVKA-II were greater across higher plasma ucMGP quartiles (all P < 0.001, age-adjusted). Major allele homozygotes for MGP rs1800801 and rs4236 had higher plasma ucMGP than heterozygotes or minor allele homozygotes. (P ≤ 0.004). The decrease in plasma ucMGP was greater in the 190 participants who received phylloquinone (mean ± SD) (-345 ± 251 pmol/L) than in the 184 who did not (-40 ± 196 pmol/L) (P < 0.0001). CAC did not differ according to ucMGP quartile (P = 0.35, age-adjusted). In the phylloquinone-supplemented group, the 3-y change in ucMGP was not associated with the 3-y change in CAC [unstandard β (SE) = -0.02 (0.02); P = 0.44]. Plasma ucMGP was associated with vitamin K status biomarkers and was reduced following phylloquinone supplementation, suggesting it may be a useful marker of vitamin K status in vascular tissue. Plasma ucMGP did not reflect CAC in healthy older adults.

Vitamin K supplementation increases vitamin K tissue levels but fails to counteract ectopic calcification in a mouse model for pseudoxanthoma elasticum

Pseudoxanthoma elasticum (PXE) is an autosomal recessive disorder in which calcification of connective tissue leads to pathology in skin, eye and blood vessels. PXE is caused by mutations in ABCC6. High expression of this transporter in the basolateral hepatocyte membrane suggests that it secretes an as-yet elusive factor into the circulation which prevents ectopic calcification. Utilizing our Abcc6 (-/-) mouse model for PXE, we tested the hypothesis that this factor is vitamin K (precursor) (Borst et al. 2008, Cell Cycle). For 3 months, Abcc6 (-/-) and wild-type mice were put on diets containing either the minimum dose of vitamin K required for normal blood coagulation or a dose that was 100 times higher. Vitamin K was supplied as menaquinone-7 (MK-7). Ectopic calcification was monitored in vivo by monthly micro-CT scans of the snout, as the PXE mouse model develops a characteristic connective tissue mineralization at the base of the whiskers. In addition, calcification of kidney arteries was measured by histology. Results show that supplemental MK-7 had no effect on ectopic calcification in Abcc6 ( -/- ) mice. MK-7 supplementation increased vitamin K levels (in skin, heart and brain) in wild-type and in Abcc6 (-/-) mice. Vitamin K tissue levels did not depend on Abcc6 genotype. In conclusion, dietary MK-7 supplementation increased vitamin K tissue levels in the PXE mouse model but failed to counteract ectopic calcification. Hence, we obtained no support for the hypothesis that Abcc6 transports vitamin K and that PXE can be cured by increasing tissue levels of vitamin K.

Vitamin K does not prevent soft tissue mineralization in a mouse model of pseudoxanthoma elasticum

Pseudoxanthoma elasticum (PXE) is a heritable disease characterized by calcified elastic fibers in cutaneous, ocular, and vascular tissues. PXE is caused by mutations in ABCC6, which encodes a protein of the ATP-driven organic anion transporter family. The inability of this transporter to secrete its substrate into the circulation is the likely cause of PXE. Vitamin K plays a role in the regulation of mineralization processes as a co-factor in the carboxylation of calcification inhibitors such as Matrix Gla Protein (MGP). Vitamin K precursor or a conjugated form has been proposed as potential substrate(s) for ABCC6. We investigated whether an enriched diet of vitamin K1 or vitamin K2 (MK4) could stop or slow the disease progression in Abcc6 (-/-) mice. Abcc6 (-/-) mice were placed on a diet of either vitamin K1 or MK4 at 5 or 100 mg/kg at prenatal, 3 weeks or 3 months of age. Disease progression was quantified by measuring the calcium content of one side of the mouse muzzle skin and histological staining for calcium of the opposing side. Raising the vitamin K1 or MK4 content of the diet increased the concentration of circulating MK4 in the serum. However, this increase did not significantly affect the MGP carboxylation status or reduce its abnormal abundance, the total calcium content or the pathologic calcification in the whiskers of the 3 treatment groups compared to controls. Our findings showed that raising the dietary intake of vitamin K1 or MK4 was not beneficial in the treatment of PXE and suggested that the availability of vitamin K may not be a limiting factor in this pathology.

Emerging Issues in Vitamin K Research

Vitamin K is traditionally recognized for its role in blood clotting. More recently, new roles for vitamin K have emerged. The current evidence for the role of vitamin K in bone, cardiovascular, and reproductive health will be discussed. There will be a particular focus on populations who could be at risk for vitamin K deficiency.

Association of warfarin use with valvular and vascular calcification: a review

Vitamin K is required for the activity of various biologically active proteins in our body. Apart from clotting factors, vitamin K-dependent proteins include regulatory proteins like protein C, protein S, protein Z, osteocalcin, growth arrest-specific gene 6 protein, and matrix Gla protein. Glutamic acid residues in matrix Gla protein are γ-carboxylated by vitamin K-dependent γ-carboxylase, which enables it to inhibit calcification. Warfarin, being a vitamin K antagonist, inhibits this process, and has been associated with calcification in various animal and human studies. Though no specific guidelines are currently available to prevent or treat this less-recognized side effect, discontinuing warfarin and using an alternative anticoagulant seems to be a reasonable option. Newer anticoagulants such as dabigatran and rivaroxaban offer promise as future therapeutic options in such cases. Drugs including statins, alendronate, osteoprotegerin, and vitamin K are currently under study as therapies to prevent or treat warfarin-associated calcification. Copyright © 2011 Wiley Periodicals, Inc. The authors have no funding, financial relationships, or conflicts of interest to disclose.

Vascular Calcification in Chronic Renal Failure

Accelerated atherosclerotic plaque calcification and extensive medial calcifications are common and highly detrimental complications of chronic kidney disease. Valid murine models have been developed to investigate both pathologically distinguishable complications, which allow for better insight into the cellular mechanisms underlying these vascular pathologies and evaluation of compounds that might prevent or retard the onset or progression of vascular calcification. This review describes various experimental models that have been used for the study of arterial intimal and/or medial calcification and discusses the extent to which this experimental research has contributed to our current understanding of vascular calcification, particularly in the setting of chronic renal failure.

Recent progress in the treatment of vascular calcification

Vascular calcification is common in patients with advanced chronic kidney disease and is associated with poorer outcomes. Although the pathophysiology is not completely understood, it is clear that it is a multifactorial process involving altered mineral metabolism, as well as changes in systemic and local factors that can promote or inhibit vascular calcification, and all of these are potential therapeutic targets. Current therapy is closely linked to strategies for preventing disordered bone and mineral metabolism in advanced kidney disease and involves lowering the circulating levels of both phosphate and calcium. The efficacy of compounds that specifically target calcification, such as bisphosphonates and thiosulfate, has been shown in animals but only in small numbers of humans, and safety remains an issue. Additional therapies, such as pyrophosphate, vitamin K, and lowering of pH, are supported by animal studies, but are yet to be investigated clinically. As the mineral composition of vascular calcifications is the same as in bone, potential effects on bone must be addressed with any therapy for vascular calcification.

Undercarboxylated matrix Gla protein is associated with indices of heart failure and mortality in symptomatic aortic stenosis

OBJECTIVE

Matrix Gla protein (MGP) is a calcification inhibitor and alterations in circulating MGP have been observed in different populations characterized by vascular calcification. We hypothesized that patients with calcific valvular aortic stenosis (AS) would have dysregulated circulating MGP levels.

DESIGN AND SUBJECTS

We examined plasma levels of nonphosphorylated carboxylated and undercarboxylated MGP (dp-cMGP and dp-ucMGP, respectively) in 147 patients with symptomatic severe AS and in matched healthy controls.

MAIN OUTCOME MEASURES

We further investigated the relationship between MGP levels and aortic pressure gradients and valve area by echocardiography and measures of heart failure. Finally, we assessed the prognostic value of elevated plasma dp-ucMGP level in relation to all-cause mortality in patients with AS.

RESULTS

We found markedly enhanced plasma levels of dp-cMGP and in particular of dp-ucMGP in patients with symptomatic AS. Although only weak correlations were found with the degree of AS, circulating dp-ucMGP was associated with cardiac function and long-term mortality in multivariate analysis.

CONCLUSIONS

A dysregulated MGP system may have a role in the development of left ventricular dysfunction in patients with symptomatic AS.