Synthesis of 2-methyl-1,4-naphthoquinones with higher gamma-glutamyl carboxylase activity than MK-4 both in vitro and in vivo.

Vitamin K is the collective term for compounds that share a 2-methyl-1,4-naphthoquinone ring, but differ in the side-chain at the 3-position. We synthesized novel 2-methyl-1,4-naphthoquinone derivatives with different side chain length at the 3-position. Derivatives with C-14 and C-16 tails showed the highest in vitro bioactivity resulting in 2.5 and 2-fold higher carboxylated osteocalcin synthesis in MG63 cells than menaquinone-4 (MK-4, form of vitamin K2). Longer side chain lengths resulted in lower bioactivity. The in vivo vitamin K activity of the C-14 tail derivative was further tested in WKY rats receiving a vitamin K-deficient diet that resulted in a 40% decrease of prothrombin activity. The C-14 tail derivative was able to counteract the effects on vitamin K deficiency induced by the diet and resulted in the complete restoration of prothrombin activity. Compared to naturally occurring forms of vitamin K, synthetic vitamin K derivatives may have higher bioactivity and different pharmacological characteristics that are more favorable for use as supplements or in clinical settings.

Menaquinone Content of Cheese.

Vitamin K2 (menaquinone) concentrations were measured in a wide range of cheeses and the effects of fat content, ripening and origin of the cheeses were investigated. Moreover, the menaquinone content of cheese was compared with that of other foods known to contain vitamin K2. It was found that cheese and curd are the most important sources of long-chain menaquinones in the Western diet and, in general, hard cheeses are richer in menaquinones than soft cheeses. However, the actual menaquinone content varies substantially and is dependent on the type of cheese, the time of ripening, the fat content and the geographic area where the cheeses are produced. Given the fact that poor vitamin K status has been mentioned as a risk factor for cardiovascular disease and mortality, while there is no clear evidence for adverse cardiovascular effects of dairy fats, cheese should be considered as a recommendable component in a heart-healthy diet.

Vitamin-K-Dependent Protection of the Renal Microvasculature: Histopathological Studies in Normal and Diseased Kidneys.

Vitamin-K-dependent carboxylation of matrix Gla protein (MGP) protects the macrocirculation against calcification. We recently reported in a multiethnic population study that the estimated glomerular filtration rate, a microvascular trait, decreased and the risk of chronic kidney disease increased with higher circulating levels of inactive dephospho-uncarboxylated MGP, a marker of vitamin K deficiency. These findings highlighted the possibility that vitamin K might have a beneficial effect on the renal microcirculation. To substantiate these epidemiological findings, we undertook a pilot study, in which we stained renal tissue samples obtained by biopsy from 2 healthy kidney donors and 4 patients with nephropathy for carboxylated and uncarboxylated MGP and calcium deposits. Three patients had renal calcifications, which were consistently associated with carboxylated and uncarboxylated MGP. Normal renal tissue was devoid of microcalcifications and staining for carboxylated and uncarboxylated MGP. Pending confirmation in a larger study covering a wider range of renal pathologies, these histopathological findings suggest that MGP might inhibit calcification not only in large arteries, as was known before, but in renal tissue as well, thereby highlighting potentially new avenues for promoting renal health, for instance by vitamin K supplementation.

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.