Surface chemistry study of the interactions of hyaluronic acid and benzalkonium chloride with meibomian and corneal cell lipids

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 (M-w 1 x 10(6) 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 M-w 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 M-w 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.