Background  

The purpose of the study was to compare toxic effects and responses to histamine and IFNγ associated with the use of some widely used anti-allergic eye drops commercially available today.

Methods  

For dynamic studies, the Wong-Kilbourne cell line was stimulated for 24 h with histamine or IFNγ in the presence or absence of anti-allergic eye drops. Supernatants of histamine-stimulated cells were evaluated for the production of IL-6 and IL-8 by ELISA, while the expression of ICAM-1 was evaluated by flow cytometry on IFNγ-stimulated cells. Toxicological assays were performed using cold light cytofluorometry: viability and apoptosis as well as reactive oxygen species (ROS) and O2^.- production were assessed using neutral red, Hoechst/propidium iodide, H₂-DCFDA and hydroethidine tests, respectively.

Results  

Antihistamines reduced IL-6 release and presented dose-dependent inhibitory effects on IL-8 production. None of the eye drops decreased the basal or IFNγ-stimulated expression of ICAM-1. Conversely, eye drops preserved with benzalkonium chloride (BAC) induced even higher ICAM-1 expression levels on IFNγ-stimulated cells than did IFNγ alone, whereas unpreserved drugs had no effect. Toxicological assays confirmed the pivotal role of BAC in proportionally reducing cell viability while increasing apoptosis and oxidative stress.

Conclusions  

The ability of topical ocular anti-H₁ drugs to significantly reduce the production of IL-6 and IL-8 argues that they may help treat the inflammatory processes occurring in allergic ocular surface disorders. Nevertheless, preserved ophthalmic formulations may enhance epithelial conjunctival expression of ICAM-1 in the presence of a low inflammatory stimulus, such as IFNγ, and displayed toxic as well as pro-oxidative effects on these cells. Therefore, BAC used as preservative might in part interfere with the potential anti-inflammatory properties of the active compound by modulating the immuno-inflammatory response of epithelial conjunctival cells.