Expression of Vascular Endothelial Growth Factor and Inducible Nitric Oxide Synthase in Pterygia

Purpose: To evaluate the expression of vascular endothelial growth factor (VEGF) in pterygium and investigate the interrelationships between VEGF and nitric oxide (NO) in the development of pterygia.

Methods: Specimens of normal conjunctiva acquired incidentally to conjunctival transplantation during pterygium and strabismus surgery and the excised pterygium were used in this study. Cryopreserved tissue specimens consisting of normal conjunctiva and pterygium were used to study the expression of VEGF and inducible NO synthetase (iNOS), using immunohistochemistry. For confirmation of NOS activity, reduced nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase staining was done. Enzyme-linked immunosorbent assay (ELISA) for detection and quantification of VEGF was performed.

Results: Expression of VEGF and iNOS was strongly revealed mainly in the epithelium of the head portions of pterygial specimens, although not in the epithelium of conjunctival ones. Pterygial epithelium was stained with NADPH diaphorase, confirming NOS activity. ELISA showed a greater amount of VEGF in pterygium (11.7 +/- 2.1 pg/mg) compared with normal conjunctiva (4 +/- 0.47 pg/mg) ( p < 0.05).

Conclusion: These data are the first to demonstrate that VEGF and NO may play an important role in the development of pterygium and to identify VEGF and NO in the epithelium of pterygium. We hypothesize that environmental stress, such as ultraviolet irradiation and local inflammation stimulate the elaboration of NO and VEGF, resulting in the conjunctival fibrovascular ingrowth characteristic of pterygium.