Andrea Aghi

Differential Effects of Dabigatran and Warfarin on Bone Volume and Structure in Rats with Normal Renal Function

Background Warfarin, a widely used anticoagulant, is a vitamin K antagonist impairing the activity of vitamin K-dependent Bone Gla Protein (BGP or Osteocalcin) and Matrix Gla Protein (MGP). Because dabigatran, a new anticoagulant, has no effect on vitamin K metabolism, the aim of this study was to compare the impact of warfarin and dabigatran administration on bone structure and vascular calcification. Methods Rats with normal renal function received for 6 weeks warfarin, dabigatran or placebo. Bone was evaluated immuno-histochemically and hystomorphometrically after double labelling with declomycin and calcein. Aorta and iliac arteries were examined histologically. Results Histomorphometric analysis of femur and vertebrae showed significantly decreased bone volume and increased trabecular separation in rats treated with warfarin. Vertebra analysis showed that the trabecular number was higher in dabigatran treated rats. Osteoblast activity and resorption parameters were similar among groups, except for maximum erosion depth, which was higher in warfarin treated rats, suggesting a higher osteoclastic activity. Therefore, warfarin treatment was also associated with higher bone formation rate/bone surface and activation frequency. Warfarin treatment may cause an increased bone turnover characterized by increased remodelling cycles, with stronger osteoclast activity compared to the other groups. There were no differences among experimental groups in calcium deposition either in aortic or iliac arteries. Conclusions These findings suggest for the first time that dabigatran has a better bone safety profile than warfarin, as warfarin treatment affects bone by reducing trabecular size and structure, increasing turnover and reducing mineralization. These differences could potentially result in a lower incidence of fractures in dabigatran treated patients.

Vitamin K plasma levels determination in human health.

Abstract Vitamin K (phylloquinone or vitamin K1 and menaquinones or vitamin K2) plays an important role as a cofactor in the synthesis of hepatic blood coagulation proteins, but recently has also aroused an increasing interest for its action in extra-hepatic tissues, in particular in the regulation of bone and vascular metabolism. The accurate measurement of vitamin K status in humans is still a critical issue. Along with indirect assays, such as the undercarboxylated fractions of vitamin K-dependent proteins [prothrombin, osteocalcin (OC), and matrix gla protein], the direct analysis of blood levels of phylloquinone and menaquinones forms might be considered a more informative and direct method for assessing vitamin K status. Different methods for direct quantification of vitamin K serum levels are available. High-performance liquid chromatography (HPLC) methods coupled with post-column reduction procedures and fluorimetric or electrochemical detection are commonly used for food and blood analysis of phylloquinone, but they show some limitations when applied to the analysis of serum menaquinones because of interferences from triglycerides. Recent advancements include liquid chromatography tandem mass spectrometry (LCMS/MS) detection, which assures higher specificity. The optimization and standardization of these methods requires specialized laboratories. The variability of results observed in the available studies suggests the need for further investigations to obtain more accurate analytical results.

Low vitamin K1 intake in haemodialysis patients

BACKGROUND & AIMS Vitamin K acts as a coenzyme in the γ-carboxylation of vitamin K-dependent proteins, including coagulation factors, osteocalcin, matrix Gla protein (MGP), and the growth arrest-specific 6 (GAS6) protein. Osteocalcin is a key factor for bone matrix formation. MGP is a local inhibitor of soft tissue calcification. GAS6 activity prevents the apoptosis of vascular smooth muscle cells. Few data on vitamin K intake in chronic kidney disease patients and no data in patients on a Mediterranean diet are available. In the present study, we evaluate the dietary intake of vitamin K1 in a cohort of patients undergoing haemodialysis. METHODS In this multi-centre controlled observational study, data were collected from 91 patients aged >18 years on dialysis treatment for at least 12 months and from 85 age-matched control subjects with normal renal function. Participants completed a food journal of seven consecutive days for the estimation of dietary intakes of macro- and micro-nutrients (minerals and vitamins). RESULTS Compared to controls, dialysis patients had a significant lower total energy intake, along with a lower dietary intake of proteins, fats, carbohydrates, fibres, and of all the examined minerals (Ca, P, Fe, Na, K, Zn, Cu, and Mg). With the exception of vitamin B12, vitamins intake followed a similar pattern, with a lower intake in vitamin A, B1, B2, C, D, E, folates, K1 and PP. These finding were confirmed also when normalized for total energy intake or for body weight. In respect to the adequate intakes recommended in the literature, the prevalence of a deficient vitamin K intake was very high (70-90%) and roughly double than in controls. Multivariate logistic model identified vitamin A and iron intake as predictors of vitamin K deficiency. CONCLUSIONS Haemodialysis patients had a significantly low intake in vitamin K1, which could contribute to increase the risk of bone fractures and vascular calcifications. Since the deficiency of vitamin K intake seems to be remarkable, dietary counselling to HD patients should also address the adequacy of vitamin K dietary intake and bioavailability. Whether diets with higher amounts of vitamin K1 or vitamin K supplementation can improve clinical outcomes in dialysis patients remains to be demonstrated.

Vitamin K and bone

Vitamin K is mainly known as an agent involved in blood coagulation, maintaining the activity of coagulation factors in the liver. In addition, epidemiological studies suggested that a lack of vitamin K is associated with several diseases, including osteoporosis and vascular calcification. There are two main kinds of vitamin K: Phylloquinone (or PK) and Menaquinones (MKn), both act as co-enzyme of y-glutamyl carboxylase (GGCX) transforming under-carboxylated in carboxylated vitamin K dependent proteins, such as Bone Gla Protein (or Osteocalcin) and Matrix Gla Protein. Recently, Vitamin K was also identified as a ligand of the nuclear steroid and xenobiotic receptor (SXR) (in murine species Pregnane X Receptor: PXR), expressed in osteoblasts. The purpose of this literature review is to evaluate the protective role of Vitamin K in bone and vascular health.