20 May 2005: Tear proteins altered by eye disease

A proteomics study of tears of patients afflicted with the chronic eye disease blepharitis has shed light on the pathogenesis of the disease.

Blepharitis is one of the most common eye diseases, affecting the outer eyelid where the eyelashes are attached, as well as the inner eyelid. It is commonly associated with bacterial infections and skin conditions such as dandruff and acne. The disease is difficult to manage and often recurs. No specific diagnostic tests exist.

A clearer understanding of the molecular basis of blepharitis could identify symptomatic biomarker compounds and lead to a better understanding of the disease process. Chan-Wha Kim and colleagues from Korea University and Chung-Ang University in Korea compared the protein content of tears from patients and healthy individuals by two-dimensional gel electrophoresis, using just 2-3 microlitres of tears. Comparison of the gel spot intensities between the two groups of subjects revealed nine proteins that were downregulated by about 50 per cent compared with controls.

These proteins were identified following in-gel digestion with trypsin and mass spectrometric analysis by searching a protein sequence database. The balance between protease and protease inhibitors (PIs) plays a key role in maintaining normal ocular function but the team found that the PIs cystatin SA-III and alpha-1-antitrypsin are both much less abundant in the patient group. This implies a greater degree of protein degradation in blepharitis.

A third downregulated protein, prolactin inducible protein, is associated with the inhibition of bacterial growth, and a fourth, human lacritin, is known to stimulate cell secretion and signalling in the cornea and tear gland. Their reduced abundances would promote blepharitis conditions, according to Kim.

All the reduced proteins appear to affect the function of the tear film and are candidate biomarkers, although further research is required to establish their exclusivity for blepharitis. 

Steve Down