Evaluation of Biomarkers of Inflammation in Response to Benzalkonium Chloride on Corneal and Conjunctival Epithelial Cells

Purpose: Most eye drops contain preservatives; benzalkonium chloride (BAK) is most common. Recent data demonstrated BAK adding to toxicity. BAK is degraded into hydrogen peroxide (H2O2), which in even small amounts is known to be an irritant. Increased toxicity should cause localized inflammation with increased elaboration of inflammatory biomarkers. To evaluate the inflammation BAK causes to the ocular surface, enzyme linked immunosorbant assays (ELISAs) were utilized to quantify the levels of inflammatory biomarkers in response to BAK and/or H2O2. Methods: Immortalized human conjunctival and corneal epithelial cells were exposed to: BAK (0.001%-0.1%), hydrogen peroxide (H2O2) (0.01%-0.1%), and cell media for 1 h. Cytokine quantification was performed via enzyme-linked immunosorbent assays [ELISAs]). Additional experimentation was performed in which testing solutions were replaced with media after 1 h and the resulting supernatants quantified after 24 h. Results: BAK induced significant amounts of interleukin (IL-)1 and tumor necrosis factor (TNF), but only moderate amounts of C-reactive protein (CRP), IL-10 and 12, and H2O2. Lower concentrations of BAK induced proportionally less elaboration. Replacing the test solutions with media and providing 23 h for cytokine elaboration significantly increased TNF, but not IL-1. Lipopolysaccharide (LPS) positive controls induced substantial elaboration/release of both IL-1 and TNF as did in increasing the exposure to the full 24 h. Conclusions: After 1 h of exposure, BAK increased quantities of all biomarkers. The biomarkers in decreasing order of induction/upregulation were: TNF >= IL-1 >= IL-12 >= IL-10 >= CRP. Even low concentrations caused some degree of inflammation. Replacing the testing solution with media and providing 23 h for cytokine elaboration, significantly increased the elaboration/release of TNF, but not IL-1, as compared to the 1-h BAK exposure. Whereas increasing the exposure to the full 24 h by not removing the testing solution at the 1-h time point significantly increased the elaboration/release of both IL-1 and TNF.