Vitamin K for Vascular Calcification in Kidney Patients: Still Alive and Kicking, but Still a Lot to Learn

Patients with chronic kidney disease (CKD) suffer disproportionately from a high burden of cardiovascular disease, which, despite recent scientific advances, remains partly understood. Vascular calcification (VC) is the result of an ongoing process of misplaced calcium in the inner and medial layers of the arteries, which has emerged as a critical contributor to cardiovascular events in CKD. Beyond its established role in blood clotting and bone health, vitamin K appears crucial in regulating VC via vitamin K-dependent proteins (VKDPs). Among these, the matrix Gla protein (MGP) serves as both a potent inhibitor of VC and a valuable biomarker (in its inactive form) for reflecting circulating vitamin K levels. CKD patients, especially in advanced stages, often present with vitamin K deficiency due to dietary restrictions, medications, and impaired intestinal absorption in the uremic environment. Epidemiological studies confirm a strong association between vitamin K levels, inactive MGP, and increased CVD risk across CKD stages. Based on the promising results of pre-clinical data, an increasing number of clinical trials have investigated the potential benefits of vitamin K supplementation to prevent, delay, or even reverse VC, but the results have remained inconsistent.

Vitamin K-Dependent Carboxylation of Osteocalcin in Bone-Ally or Adversary of Bone Mineral Status in Rats with Experimental Chronic Kidney Disease?

Chronic kidney disease (CKD) commonly occurs with vitamin K (VK) deficiency and impaired bone mineralization. However, there are no data explaining the metabolism of endogenous VK and its role in bone mineralization in CKD. In this study, we measured serum levels of phylloquinone (VK1), menaquinone 4 and 7 (MK4, MK7), and VK-dependent proteins: osteocalcin, undercarboxylated osteocalcin (Glu-OC), and undercarboxylated matrix Gla protein (ucMGP). The carboxylated osteocalcin (Gla-OC), Glu-OC, and the expression of genes involved in VK cycle were determined in bone. The obtained results were juxtaposed with the bone mineral status of rats with CKD. The obtained results suggest that the reduced VK1 level observed in CKD rats may be caused by the accelerated conversion of VK1 to the form of menaquinones. The bone tissue possesses all enzymes, enabling the conversion of VK1 to menaquinones and VK recycling. However, in the course of CKD with hyperparathyroidism, the intensified osteoblastogenesis causes the generation of immature osteoblasts with impaired mineralization. The particular clinical significance seems to have a finding that serum osteocalcin and Glu-OC, commonly used biomarkers of VK deficiency, could be inappropriate in CKD conditions, whereas Gla-OC synthesized in bone appears to have an adverse impact on bone mineral status in this model.

Vitamin K and D Supplementation and Bone Health in Chronic Kidney Disease-Apart or Together?

Vitamin K (VK) and vitamin D (VD) deficiency/insufficiency is a common feature of chronic kidney disease (CKD), leading to impaired bone quality and a higher risk of fractures. CKD patients, with disturbances in VK and VD metabolism, do not have sufficient levels of these vitamins for maintaining normal bone formation and mineralization. So far, there has been no consensus on what serum VK and VD levels can be considered sufficient in this particular population. Moreover, there are no clear guidelines how supplementation of these vitamins should be carried out in the course of CKD. Based on the existing results of preclinical studies and clinical evidence, this review intends to discuss the effect of VK and VD on bone remodeling in CKD. Although the mechanisms of action and the effects of these vitamins on bone are distinct, we try to find evidence for synergy between them in relation to bone metabolism, to answer the question of whether combined supplementation of VK and VD will be more beneficial for bone health in the CKD population than administering each of these vitamins separately.

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.

Evaluation of vitamin K status and rationale for vitamin K supplementation in dialysis patients

The cardinal biological role of vitamin K is to act as cofactor for the carboxylation of a number of vitamin K-dependent proteins, some of which are essential for coagulation, bone formation and prevention of vascular calcification. Functional vitamin K deficiency is common and severe among dialysis patients and has garnered attention as a modifiable risk factor in this population. However, no single biochemical parameter can adequately assess vitamin K status. For each biological function of vitamin K, the degree of carboxylation of the relevant vitamin K-dependent protein most accurately reflects vitamin K status. Dephosphorylated uncarboxylated matrix Gla protein (dp-ucMGP) is the best biomarker for vascular vitamin K status when cardiovascular endpoints are studied. Dp-ucMGP levels are severely elevated in haemodialysis patients and correlate with markers of vascular calcification and mortality in some but not all studies. The aetiology of vitamin K deficiency in haemodialysis is multifactorial, including deficient intake, uraemic inhibition of the vitamin K cycle and possibly interference of vitamin K absorption by phosphate binders. The optimal vitamin K species, dose and duration of supplementation to correct vitamin K status in dialysis patients are unknown. Dp-ucMGP levels dose-proportionally decrease with supraphysiological vitamin K2 supplementation, but do not normalize even with the highest doses. In the general population, long-term vitamin K1 or K2 supplementation has beneficial effects on cardiovascular disease, bone density and fracture risk, and insulin resistance, although some studies reported negative results. In haemodialysis patients, several trials on the effects of vitamin K on surrogate markers of vascular calcification are currently ongoing.

Vitamin K Status in Adherent and Non-Adherent Patients with Phenylketonuria: A Cross-Sectional Study

This is the first study to evaluate vitamin K status in relation to dietary intake and phenylalanine dietary compliance in patients with phenylketonuria (PKU). The dietary and PKU formula intake of vitamin K was calculated in 34 PKU patients, with vitamin K status determined by the measurement of prothrombin induced by vitamin K absence (PIVKA-II). Blood phenylalanine concentrations in the preceding 12 months were considered. There were significantly more phenylalanine results exceeding 6 mg/dL in patients with normal PIVKA-II concentrations than in those with abnormal PIVKA-II levels (p = 0.035). Similarly, a higher total intake of vitamin K and dietary vitamin intake expressed as μg/day (p = 0.033 for both) and %RDA (p = 0.0002 and p = 0.003, respectively) was observed in patients with normal PIVKA-II levels. Abnormal PIVKA-II concentrations were associated with a lower OR (0.1607; 95%CI: 0.0273-0.9445, p = 0.043) of having a median phenylalanine concentration higher than 6 mg/dL. In conclusion, vitamin K deficiency is not uncommon in phenylketonuria and may also occur in patients with adequate vitamin K intake. PKU patients with better dietary compliance have a higher risk of vitamin K deficiency. The present findings highlight the need for further studies to re-evaluate dietary recommendations regarding vitamin K intake, both concerning formula-based and dietary consumption of natural products.

Prevalence and correlates of vitamin K deficiency in children with inflammatory bowel disease

Although vitamin K deficiency has been implicated in adult inflammatory bowel disease (IBD), its prevalence in pediatric IBD remains unknown. We carried out a cross-sectional study in 63 children with Crohn's disease (CD) and 48 with ulcerative colitis (UC) to assess the prevalence of vitamin K deficiency and to search for potential correlation between vitamin K status and pediatric IBD activity. Vitamin K status was assessed using protein induced by vitamin K absence-II (PIVKA-II; ELISA). Prevalence of vitamin K deficiency was 54.0% in CD and 43.7% in UC. Vitamin K deficiency was more common in patients with higher CD activity, in CD patients with higher mass Z-scores, and less common among children with CD treated with infliximab. Relation of vitamin K deficiency to pediatric IBD clinical course and treatment demand further research.

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.

Vitamin K status in chronic kidney disease: a report of a study and a mini-review

Hepatic vitamin K-dependent proteins (e.g., Factors II, VII, IX and X) form part of the clotting cascade. Factor II (FII)/Prothrombin incorporates 10 Glu residues on the N-terminal region that are γ-carboxylated to Gla residues by the action of γ-glutamyl carboxylase to confer biological activity. Vitamin K is also required for the normal function of Matrix Gla Protein (MGP)--one of several non-clotting-related extra-hepatic vitamin K-dependent proteins. MGP is known to have protective action against vascular calcification--indeed it is a powerful tissue-bound inhibitory mechanism and can be found in blood vessel walls. The mature protein is also dependent on activation by γ-glutamyl carboxylase enzyme to convert Glu residues in its amino acid sequence to Gla. This reaction can only take place when the enzyme is activated in the presence of vitamin K. It is of great potential interest to investigate whether subtle deficiencies of vitamin K may, through its effect on the action of MGP, be a contributing factor to vascular calcification in CKD patients, in whom CV disease is greatly accelerated and in whom vascular calcification is not only common, but progresses aggressively, and is something for which as yet there is no clinically applicable remedy.