Vitamin K status in healthy volunteers.

Vitamin K's recommended dietary allowance (RDA) is based on the hepatic requirement for clotting factor synthesis, but substantial concentrations of undercarboxylated extra-hepatic Gla-proteins are found in the circulation of non-supplemented individuals. This suggests that vitamin K intake above the RDA is required for an optimal extra-hepatic vitamin K status. Circulating uncarboxylated osteocalcin (ucOC) and desphospho-uncarboxylated matrix Gla-protein (dp-ucMGP) are considered markers of the vitamin K status in bone and the vasculature, respectively. We measured these markers in 896 samples of healthy volunteers and defined target groups for vitamin K supplementation based on increased levels indicative of tissue-specific vitamin K deficiency. We studied the response to vitamin K supplements at different states of vitamin K deficiency by measuring the circulating dp-ucMGP level in samples from two short-term trials on menaquinone-7 (MK-7, vitamin K2) supplementation in 42 children and 68 adults. Children had high ucOC levels (3.4-96.9 ng ml(-1)); other age groups had values in the range of 1.5-5.0 ng ml(-1). From the age of 40 years, dp-ucMGP levels gradually increased. Children and adults with more pronounced vitamin K deficiency gave the highest responses to MK-7 supplementation. Children and adults above 40 years showed the largest tissue-specific vitamin deficiency and accordingly may benefit from MK-7 supplementation to improve their extra-hepatic vitamin K status.

Extremes in vitamin K status of bone are related to bone ultrasound properties in children with juvenile idiopathic arthritis.

OBJECTIVE: Osteopenia is a common complication of juvenile idiopathic arthritis (JIA). In adults, low bone density and increased fracture risk are associated with low vitamin K status of bone. The vitamin K-dependent protein osteocalcin plays an important role in bone metabolism. Its activity depends upon post-translational carboxylation in which vitamin K is an essential co-factor. Hence, vitamin K deficiency leads to under-carboxylated (i.e., inactive) osteocalcin (ucOC). Little is known about the vitamin K status and bone health in children with juvenile idiopathic arthritis (JIA). We studied the vitamin K status of bone and its association with bone mass properties in children with JIA compared to healthy children. METHODS: We performed a cross sectional study in 55 children with JIA and 54 healthy controls between 6-18 years of age. Bone markers, ultrasound bone mass properties and vitamin K status of bone were determined. RESULTS: Overall, no differences in vitamin K status of bone were found between the study groups. Among children with JIA, a high ratio of ucOC/cOC indicating low vitamin K status was associated with low bone ultrasound parameters, whereas children with a high vitamin K status had markedly higher bone properties. This association was independent of physical activity, age, gender and BMI. CONCLUSION: These results suggest that vitamin K may be one of multiple risk factors for low bone mass in children with JIA, in addition to other recognized determinants of bone mass. The question remains whether JIA patients would benefit from increased dietary vitamin K intake.

Calcinosis in juvenile dermatomyositis: a possible role for the vitamin K-dependent protein matrix Gla protein.

OBJECTIVES: The aims of the present study were to investigate whether the calcification inhibitor matrix Gla protein (MGP) is expressed in muscle biopsies of patients with juvenile dermatomyositis (JDM), and whether different forms of MGP are differentially expressed in JDM patients with and without subcutaneous calcifications. METHODS: Muscle tissue from six JDM patients (three without calcinosis, two with calcinosis and one recently diagnosed patient), four patients with muscular dystrophy, three patients with IBM and five normal histological control subjects was used for immunohistochemistry staining using novel antibodies to different conformations of MGP. RESULTS: In the JDM patients, all forms of MGP [non-carboxylated MGP (ucMGP), carboxylated MGP (cMGP), non-phosphorylated MGP (serMGP) and phosphorylated MGP (pserMGP)] were more intensely stained in the perifascicular compared with the central muscle fibres. In addition, these MGP species were demonstrated in the pathological muscle fibres of IBM and dystrophy patients, but hardly in normal histological muscle tissue. In JDM patients with calcifications, only pserMGP was increased compared with those without calcifications. All forms of MGP were also found in various staining intensities in the microvasculature and macrophages of normal histological and disease biopsies. CONCLUSIONS: MGP was expressed at the site of muscle damage in JDM patients as well as in patients with muscular dystrophy and IBM. The difference in staining intensity of pserMGP appeared to distinguish between JDM patients with and without calcifications, whereas cMGP, the other functional form, was equally expressed.