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Elevation of Human -Defensins and S100 Calcium-Binding Proteins A8 and A9 in Tear Fluid of Patients with Pterygium

¹From the Singapore Eye Research Institute, Singapore; the Departments of ²Ophthalmology, Yong Loo Lin School of Medicine, ⁴Chemistry, and ⁵Biological Science, National University of Singapore, Singapore; and the ³Singapore National Eye Centre, Singapore.

PURPOSE. The pathogenesis of pterygia is still not well understood. Recent studies suggest that it may be associated with inflammation and progressive proliferation triggered by ultraviolet radiation. In this study the authors determined that the inflammatory nature of pterygium is reflected in the protein components of tears.

METHODS. Consent for this study was obtained from 12 patients (average age, 57 years; eight men, four women) with unilateral pterygium. Tears were collected from diseased eyes and contralateral healthy control eyes with the use of fire-polished 10-µL calibrated glass pipettes before pterygium surgery. Tear protein profiles obtained from diseased and control eyes (seven patient samples) were compared using surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF-MS) technology. Tears from another five patients with pterygium were used for subsequent protein identification experiments with nano-LC coupled with nano-electrospray tandem mass spectrometry (nano-ESI-MS/MS).

RESULTS. SELDI mass spectra showed that one peptide cluster with a molecular weight of 3.4 kDa and two proteins with molecular weights of 10.8 kDa and 12.7 kDa were elevated in tears of eyes with pterygium. Proteins of interest were identified by nano-LC-ESI-MS/MS as human -defensins (human neutrophil peptide [HNP]-1, HNP-2, HNP-3) and S100 calcium-binding proteins A8 and A9. Mean concentrations (n = 7) of -defensins were 1.33 ± 0.47 µg/mL (HNP-1, P < 0.015) and 0.61 ± 0.23 µg/mL (HNP-2, P < 0.012) for pterygium eyes and 0.17 ± 0.12 µg/mL (HNP-1) and 0.02 ± 0.02 µg/mL (HNP-2) for fellow control eyes. Compared with tears from eyes without pterygium or other abnormalities, the level of S100 A8 increased 1.4- to 13.4-fold (average fold change, 4.5) and S100 A9 increased 1.5- to 4.0-fold (average fold change, 2.3) in 4 of 7 patients.

CONCLUSIONS. The upregulated expression of human -defensins and S100 A8 and A9 in tear fluids of patients with pterygium indicates that they may be part of the response of the ocular surface to the formation of this fibrovascular tissue or the accompanying inflammation. They may also serve as a useful indicator for predicting recurrent pterygium.