Biophysical interaction of oleic acid with tear lipids at an air-tear interface

![CDATA[Purpose : Topical ophthalmic preparations may contain compounds that can interfere with the functioning of the tear film. Eye drops for treating dry eye often contain oils that have oleic acid which acts as a lubricant and emollient, can serve as carrier for drugs, and can also improve ocular drug delivery and bioavailability by increasing corneal permeability. However, topically added oleic acid might interact with the lipid layer of the tear film and alter its stability. This study aimed at investigating interactions of oleic acid with tear lipids and model non-polar and polar lipids of tears using Langmuir film technology. Methods : Human meibomian lipids, Oleic acid (OA), cholesterol oleate (CO) and dipalmitoyl phosphatidylcholine (DPPC) were spread separately on an artificial tear solution at 35°C in a Langmuir trough. The lipid films at the air-liquid interface were compressed and expanded to record pressure-area profiles. OA was mixed with meibomian lipids in various mole fraction ratios and pressure-area profiles of mixed films were recorded. OA was mixed with CO and DPPC in equal mole fraction ratios and pressure-area profiles of mixed films were recorded. Results : Meibomian lipids had a Πmax of ~14mN/m which increased by double by addition of OA. Increasing amount of OA added as mole fraction 0.2, 0.4, 0.6 and 0.8 increased the lift-off area of meibomian lipids from 30 Å2 to 36, 39, 42 and 45 Å2, respectively. Equimolar fraction of OA added to CO decreased its molecular area by ~19Å2 and Πmax by ~14mN/m. Equimolar fraction of OA added to DPPC decreased its molecular area by ~15Å2 but did not much affect Πmax. The plateau at ~45mN/m in the pure films of CO and DPPC and their mixed films with OA represented a highly compressible bilayer. Conclusions : Oleic acid interacts with meibomian lipids by expanding and increasing the surface pressure. It condenses non-polar and polar lipids of the tear film. Its effects are concentration dependent and can alter tear stability. Use of oleic acid in topical ophthalmic preparations should be tested using Langmuir film technology to determine suitable concentration for desirable benefits without affecting tear stability.]]