Cytoprotective effects of hyaluronic acid and carbomer 934P in ocular surface epithelial cells

PURPOSE. To investigate in vitro the cell toxicity and antioxidant effects of two major tear substitutes, hyaluronic acid and a widely used carbomer, with and without preservative. METHODS. Chang conjunctival cells were treated with different concentrations of unpreserved or preserved carbomer 934P (0.03% and 0.3%), unpreserved or preserved hyaluronic acid (0.018% and 0.18%), and berizalkonium chloride (BAC 0.0005% and 0.005%) for 15 minutes or for 15 minutes with 24 hours of cell recovery, according to previously validated methods. Microplate cold light cytofluorometry was performed to evaluate cell viability (neutral red test), chromatin condensation (Hoechst 33342 test), and reactive oxygen species (ROS) production (dichlorofluorescein diacetate and hydroethidine tests). Confocal microscopy was used to explore morphologic changes. RESULTS. No alterations were found with unpreserved and preserved hyaluronic acid at all concentrations and times tested. A decrease in cell viability with chromatin condensation appeared with 0.3% preserved carbomer 934P at the two times tested. This cytotoxicity, however, was significantly less than that observed with BAC alone, although the same concentrations of preservative were used. Unpreserved carbomer 934P induced no modification of cell viability after 15 minutes but a significant decrease in chromatin condensation, reversible after 24 hours of cell recovery, when a delayed decrease in cell viability was observed. Production of reactive oxygen species (ROS) decreased with the four formulations of tear substitutes tested at their usual concentrations, whereas a significant production of ROS occurred with BAC. CONCLUSIONS. These two ophthalmic hydrogels have no cytotoxicity but possess antioxidant properties and tend to reduce the toxic effects of preservatives. These results may allow use of hydrogels, not only in dry eye but also in ocular surface disorders involving oxidative stress and in ophthalmic drug therapy to improve ocular tolerance.