Vitamin K supplementation increases vitamin K tissue levels but fails to counteract ectopic calcification in a mouse model for pseudoxanthoma elasticum.

Pseudoxanthoma elasticum (PXE) is an autosomal recessive disorder in which calcification of connective tissue leads to pathology in skin, eye and blood vessels. PXE is caused by mutations in ABCC6. High expression of this transporter in the basolateral hepatocyte membrane suggests that it secretes an as-yet elusive factor into the circulation which prevents ectopic calcification. Utilizing our Abcc6 (-/-) mouse model for PXE, we tested the hypothesis that this factor is vitamin K (precursor) (Borst et al. 2008, Cell Cycle). For 3 months, Abcc6 (-/-) and wild-type mice were put on diets containing either the minimum dose of vitamin K required for normal blood coagulation or a dose that was 100 times higher. Vitamin K was supplied as menaquinone-7 (MK-7). Ectopic calcification was monitored in vivo by monthly micro-CT scans of the snout, as the PXE mouse model develops a characteristic connective tissue mineralization at the base of the whiskers. In addition, calcification of kidney arteries was measured by histology. Results show that supplemental MK-7 had no effect on ectopic calcification in Abcc6 ( -/- ) mice. MK-7 supplementation increased vitamin K levels (in skin, heart and brain) in wild-type and in Abcc6 (-/-) mice. Vitamin K tissue levels did not depend on Abcc6 genotype. In conclusion, dietary MK-7 supplementation increased vitamin K tissue levels in the PXE mouse model but failed to counteract ectopic calcification. Hence, we obtained no support for the hypothesis that Abcc6 transports vitamin K and that PXE can be cured by increasing tissue levels of vitamin K.

Vascular endothelial growth factor a in eyes with uveal melanoma.

OBJECTIVES: To determine the presence of vascular endothelial growth factor A (VEGF-A) in the aqueous humor of eyes with uveal melanoma and to identify its source. METHODS: The VEGF-A concentrations were determined in aqueous humor samples obtained after enucleation from 74 eyes with untreated uveal melanoma and from 8 eyes with treated uveal melanoma. Patient survival and clinical and histopathological tumor variables were compared. In situ hybridization, Western blot analysis, and enzyme-linked immunosorbent assay were used to determine expression of VEGF-A in tumor tissue and in overlying retina. RESULTS: Aqueous VEGF-A concentrations ranged from 18 to 826 pg/mL in 74 untreated eyes, while concentrations in 30 control eyes were significantly lower (median, 50.1 pg/mL) (P<.001). Concentrations in 8 treated eyes were much higher (median, 364 pg/mL). In situ hybridization on tissue sections and Western blot analysis and enzyme-linked immunosorbent assay on tissue extracts revealed VEGF-A in uveal melanoma tissue and in retinal tissue. CONCLUSIONS: Uveal melanoma is associated with increased concentrations of VEGF-A in aqueous humor. Aqueous VEGF-A concentration correlates with largest basal tumor diameter and with the tumor height. In eyes with uveal melanoma, tumor and retinal tissues are sources of VEGF-A.