Deposition of secretory phospholipase A2 on soft hydrophilic contact lenses.

Abstract

Abstract: : Purpose: Phospholipids are the most important class of lipids in maintaining the tear film stability. We have recently shown that phospholipids level in tears of contact lens wearers was lower than normal controls. The concentration of secretory phospholipase A2 (sPLA2), the enzyme that hydrolyzes phospholipids, in tears is known to exceed the levels found in serum by four orders of magnitude. This study was performed to determine the level of sPLA2 from the deposition on two different frequent replacement contact lens materials. Methods: FDA Group I (low water/non–ionic) and Group IV (high water/ionic) contact lenses worn for 2 weeks by normal subjects were used for the analysis. Following lipid extraction by Folchs method, total lipids were determined by and sulfo–phospho–vanillin reaction. Phospholipids in lipid extracts are estimated by phosphorus determination with ammmonium molybdate through enzamatic digestion. A solvent consisting of a 50:50 mix of 0.2% trifluoroacetic acid and acetonitrile was used to extract protein. Total protein was determined by BCA analysis, and sPLA2 activity in was measured by the use of 1, 2–diheptanoyl thio–phosphatidylcholine as a substrate. Results: Total lipid was found to be greater in group I contact lenses (16.8±3.6 µg/lens) in comparison to group IV lenses. Group IV lenses had greater deposition of protein (2.44±0.27 mg/lens) than group I lenses. Phospholipids was not found in either group. The activity of sPLA2 in group IV lenses was 27.1±11.8 µmol/min/mg protein, which was significantly higher (approximately 40 x ) than found in tears. Conclusions: There was a significant difference in the lipid and protein deposition profiles between the two groups. The Group I lenses deposited more lipid and the Group IV lenses deposited more protein. A significant amount of sPLA2 in the deposition on group IV lenses may play a role in the tear film instability in contact lens wearers.

Keywords: contact lens • lipids • enzymes/enzyme inhibitors