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Nutrients
  • Editorial
  • Open Access

Published: 23 June 2022

Editorial for the Special Issue “Vitamin K in Chronic Disease and Human Health”

and
1
Department of Nephrology, Faculty of Medicine, School of Health Sciences, University of Ioannina, 45110 Ioannina, Greece
2
Section of Nephrology and Hypertension, First Department of Medicine, AHEPA Hospital, Medical School, Aristotle University of Thessaloniki, 54636 Thessaloniki, Greece
*
Author to whom correspondence should be addressed.
This article belongs to the Special Issue Vitamin K in Chronic Disease and Human Health

1. Introduction

Vitamin K and its derivatives represent a complex of fat-soluble vitamins, playing a major role in the regulation of a large number of physiologic processes required for optimal homeostasis []. Vitamin K was first described as a key factor implicated in blood coagulation nearly a century ago; however, accumulating evidence indicates pleiotropic actions of vitamin K extending well beyond the coagulation cascade [,]. Two main natural forms of vitamin K have been described, which differ in terms of not only structure but also kinetics of absorption and tissue distribution, bioavailability, and functional properties []. Vitamin K1 is mainly found in green vegetables (phylloquinone) and is also produced as a synthetic form (Phytonadione), whereas vitamin K2 (menaquinone) includes several forms characterized by an isoprenoid side chain of various lengths [,]. Meat and dairy products contain Vitamin K2 compounds, and they may also be generated from phylloquinone in the body or synthesized by the gut microbiota [,]. Despite the wide availability of vitamin K, a number of challenges remain in determining vitamin K status or body stores, especially with regard to vitamin K2.
The pivotal function of both vitamin K1 and K2 involves the hydroquinone form, serving as a cofactor for the enzyme gamma-glutamylcarboxylase, which catalyzes the generation of gamma-carboxyglutamic acid (Gla) residues in vitamin K-dependent proteins. During this process, hydroquinone is oxidized to vitamin K-epoxide, which is subsequently converted to hydroquinone by the vitamin K-oxidoreductase (VKOR), thus maintaining and perpetuating the vitamin K cycle [,].
Among the already identified vitamin K-dependent proteins, the coagulation cascade proteins, including factors VII, IX, X, and prothrombin, together with the regulatory proteins C and S, are the most well-acknowledged [,]. In addition, the spectrum of vitamin K-dependent proteins encompasses several proteins involved in the regulation of bone metabolism and vascular remodeling, such as matrix Gla protein (MGP), osteocalcin, and Gla-rich protein (GRP). Their main properties include the regulation of bone mineral deposition, the transition of osteoblasts to osteocytes, the inhibition of osteoclastogenesis, and the prevention of the development of ectopic calcifications in vascular smooth muscle cells and the extracellular matrix of blood vessels. Remarkably, recent research has brought to the forefront additional beneficial properties of vitamin K and specifically vitamin K2, including antioxidative and immunoregulatory effects, associated with the protection of the cellular membrane lipids from peroxidation and suppressed T-cell activation and proliferation. The beneficial physiological roles of vitamin K appear to translate into improved clinical outcomes in various organ systems, including the brain, the liver, the kidneys, and the cardiovascular system, among others [].
However, despite the growing body of evidence on molecular mechanisms underlying the emerging new roles for vitamin K, there are several pending issues remaining to be elucidated by ongoing clinical research.

3. Conclusions

Ongoing research regarding Vitamin K and its derivatives is continuously trying to shed light on its molecular pathways of action, including a wide range of effects not related to coagulation. Although available evidence indicates promising beneficial effects with clinical implications especially with regard to cardiovascular disease and CKD specifically, pending questions remain regarding differences between different forms of Vitamin K and their therapeutic clinical utilization.

Funding

This research received no external funding.

Conflicts of Interest

The authors declare no conflict of interest.

References

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