Vitamin D and vitamin D receptor in patients with ophthalmic pterygium

Pterygium, an ultraviolet radiation (UV)-related disease, is a relatively benign process, but since it displays tumor-like features, it has been proposed to be a neoplastic-like growth disorder. Vitamin D performs a number of functions in addition to calcium homeostasis, as inhibition of cell proliferation, activation of apoptotic pathways, and inhibition of angiogenesis. Since the antitumor actions of vitamin D are mediated primarily through the nuclear vitamin D receptor (VDR), the aim of the present study was to investigate vitamin D status in patients with pterygium and in control subjects, and VDR immunohistochemical expression in samples of pterygium and normal conjunctiva in order to evaluate a possible role of vitamin D pathway in the pathogenesis of the disease. Serum vitamin D concentration was measured among 41 patients with pterygium and 47 volunteers by an automated chemiluminescence immunoassay. Moreover, 23 formalin-fixed and paraffin-embedded pterygium biopsy samples and 24 conjunctiva specimens were treated for the immunohistochemical demonstration of VDR using the streptavidin-biotin alkaline phosphatase method. No differences were observed about vitamin D level between patients with pterygium and control group, but significant differences between VDR immunolocalization in pterygium and normal conjunctiva were observed (P=0.00001). In conjunctiva, the immunoreactivity, localized mainly in cytoplasm of epithelial cells, may probably demonstrate VDR regulation of cell growth, differentiation, and apoptosis, while in pterygium VDR co-localization in the nucleus and cytoplasm of epithelial cells may indicate alternative nuclear pathways by which vitamin D might exert its antiinflammatory and anti-proliferative effects by the regulation of gene expression.