Vitamin K does not prevent soft tissue mineralization in a mouse model of pseudoxanthoma elasticum

Abstract

Pseudoxanthoma elasticum (PXE) is a heritable disease characterized by calcified elastic fibers in cutaneous, ocular and vascular tissues. PXE is caused by mutations in ABCC6, which encodes a protein of the ATP-driven organic anion transporter family. The inability of this transporter to secrete its substrate into the circulation is the likely cause of PXE. Vitamin K plays a role in the regulation of mineralization processes as a co-factor in the carboxylation of calcification inhibitors such as Matrix Gla Protein (MGP). Vitamin K precursor or a conjugated form has been proposed as potential substrate(s) for ABCC6. We investigated whether an enriched diet of vitamin K1 or vitamin K2 (MK4) could stop or slow the disease progression in Abcc6(-/-) mice. Abcc6(-/-) mice were placed on a diet of either vitamin K1 or MK4 at 5 or 100 mg/kg at prenatal, 3 weeks or 3 months of age. Disease progression was quantified by measuring the calcium content of one side of the mouse muzzle skin and histological staining for calcium of the opposing side. Raising the vitamin K1 or MK4 content of the diet increased the concentration of circulating MK4 in the serum. However, this increase did not significantly affect the MGP carboxylation status or reduce its abnormal abundance, the total calcium content or the pathologic calcification in the whiskers of the 3 treatment groups compared to controls. Our findings showed that raising the dietary intake of vitamin K1 or MK4 was not beneficial in the treatment of PXE and suggested that the availability of vitamin K may not be a limiting factor in this pathology

Vitamin K reduces hypermineralisation in zebrafish models of PXE and GACI

“…Similar results were obtained in Abcc6 −/− mice (Li et al, 2013). However, ectopic mineralisation in Abcc6 −/− mice was not reduced by dietary administration of vitamin K 1 or K 2 (Brampton et al, 2011;Gorgels et al, 2011;Jiang et al, 2011) despite successfully raising the vitamin K concentration in tissues and serum; interestingly, this increase was significantly subdued in knockout mice and was accompanied by hepatic lesions, suggesting that Abcc6 −/− mice have an impaired ability to absorb, metabolise or distribute vitamin K (Brampton et al, 2011).…”

“…We propose that the reduced serum level of vitamin K seen in PXE patients is a consequence of its utilisation by GGCX in an attempt to restrict mineralisation, and not a consequence of the loss of ABCC6; subsequent administration of vitamin K could increase MGP carboxylation by GGCX, thus preventing hypermineralisation. This could also explain why Abcc6 −/− mice were more resistant to increases in serum levels caused by a vitamin K-rich diet (Brampton et al, 2011). One prediction of this model is that serum vitamin K would also be depleted in GACI patients (ENPP1…”

Matrix Gla Protein and Alkaline Phosphatase Are Differently Modulated in Human Dermal Fibroblasts from PXE Patients and Controls

“…Vit K is a group of fat-soluble vitamins, which, in their reduced form, are needed for the posttranslational g-carboxylation of glutamic acid residues in proteins involved in blood coagulation and in the mineralization process (Booth, 2009). Interestingly, the low vit K concentrations measured in the circulation of PXE patients (Vanakker et al, 2010) were not associated by an impairment of their blood coagulation system, indicating that the vitamin can reach the liver to be metabolized and used for the activation of coagulation factors, whereas it seems to be extruded or transported less efficiently from hepatocytes to the periphery (Borst et al, 2008;Brampton et al, 2011), thus affecting connective tissues. In this scenario, it has been suggested that vit K supplementation might be capable of restoring MGP carboxylation and to inhibit ectopic calcifications (Borst et al, 2008).…”

“…In this scenario, it has been suggested that vit K supplementation might be capable of restoring MGP carboxylation and to inhibit ectopic calcifications (Borst et al, 2008). However, recent studies in the PXE animal model (ABCC6 À / À mice) demonstrated that vit K supplementation does not counteract the mineralization of soft connective tissues (Brampton et al, 2011;Gorgels et al, 2011;Jiang et al, 2011). Key question is whether PXE fibroblasts are able to utilize vit K and restore an adequate MGP carboxylation.…”

Is classical pseudoxanthoma elasticum a consequence of hepatic ‘intoxication’ due to ABCC6 substrate accumulation in the liver?

“…In three separate animal studies, oral administration of high doses of vitamin K yielded elevated vitamin serum levels, but this elevation was insufficient to counteract ectopic mineralization in kidney arteries [51] and connective tissue surrounding the vibrissae of the Abcc6-deficient mouse [51][52][53]. These observations were affirmed by intravenous vitamin K administration in which vitamin K supply to peripheral tissue via the liver was bypassed, thus assuring that potentially defective hepatic Abcc6 protein did not affect vitamin K levels in peripheral tissues of Abcc6 −/− mice [52].…”