Vitamin k, D-chiro Inositol and α-lactalbumin in Bone Homeostasis

Plain-language summary

In women with breast cancer undergoing adjuvant hormone therapy, the marked tissue hypoestrogenism induced by therapy with aromatase inhibitors and/or tamoxifen ± GnRH analogues causes a significant acceleration in bone mass loss, with a consequent increased risk of fracture from the first year of therapy. It is therefore essential to start treatment with antiresorptive drugs and calcium and vitamin D supplementation. It has been hypothesized that vitamin K and α-lactalbumin have an effect in improving the absorption of calcium and vitamin D. In addition, vitamin K promotes gamma-carboxylation of osteocalcin, causing its activation and leading to increased incorporation of hydroxyapatite into the bone, resulting in increased calcium uptake from the blood and other tissues. Studies have reported that a combination of alendronate and vitamin K2 can lead to a decrease in the ratio of uncarboxylated osteocalcin to carboxylated osteocalcin, contributing to an increase in BMD, especially in the femoral neck. α-lactalbumin is able to increase the bioaccessibility of calcium due to its ability to prevent its precipitation at the neutral pH present in the absorptive tracts of the small intestine. Furthermore, α- lactalbumin has a binding site for vitamin D3, and the complexes formed by monomers of this protein and vitamin D have shown good stability in the presence of high vitamin concentrations. Inositol is a carbohydrate structurally similar to glucose which, in its isomeric form D-chiro-inositol, acts on bone remodeling by blocking the activation of osteoclasts through inhibition of the binding of RANK-L to its receptor present on pre-osteoclasts. Our hypothesis is that the use of the combination of vitamin K, α- lactalbumin, and D-chiro-inositol should improve the intestinal absorption of calcium and vitamin D, increasing the percentage of patients able to normalize serum levels of vitamin D and urinary calcium excretion (as a parameter of adequate calcium intake). This aspect, together with the direct effect of these components on bone remodeling, could enhance the anti-resorptive effect of standard therapy with bisphosphonates, improving the quantitative and qualitative parameters of bone. Therefore, we design a prospective randomized pilot study to assess efficacy of the combination of vitamin K, α-lactalbumin, and D-chiro-inositol, comparing patients with standard therapy and patients treated with Synostea®

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