Surface chemistry study of the interactions of hyaluronic acid and benzalkonium chloride with meibomian and corneal cell lipids†
Abstract
Hyaluronic acid (HA) is a non-surface active water soluble anionic polyelectrolyte found in sub-nanomolar levels in human tears and implemented in substitutes of human tears' aqueous layer. In the current work we studied the interactions of high molecular weight (Mw 1 × 106 Da) HA with films of ocular surface lipids and investigated the potential of HA to modify the interactions of the lipid films with the low Mw cationic surfactant dodecyldimethylbenzylammonium chloride (C12-BAC) known for its adverse effects on tear film compounds. The interactions of HA and/or C12-BAC with meibomian and corneal lipid films were examined using a Langmuir surface balance. The film morphology was monitored by Brewster Angle Microscopy. The HA/C12-BAC interactions at the air/water interface and in the solution bulk were also examined. HA interacted with meibomian lipids and enhanced the structure and the rheological properties of the meibum films. HA bound C12-BAC in bulky polymer/surfactant complexes and at ≥0.1% HA neutralized the capability of C12-BAC to penetrate the lipid layers and to disrupt their integrity and viscoelasticity. The results were correlated with the capability of HA to maintain the viability of C12-BAC treated corneal cells. Our study suggests a possible novel implementation of high Mw anionic polyelectrolytes like HA: the polymers can be instilled on the ocular surface together with cationic surfactant containing drugs, and increase the biocompatibility of the ophthalmic formulations. A molecular scale mechanism is proposed for the interactions of HA with tear lipids and cationic surfactants.