Mechanisms of benzalkonium chloride toxicity in a human trabecular meshwork cell line and the protective role of preservative-free tafluprost.

Abstract

Benzalkonium chloride (BAK) is a controversial ophthalmic preservative because of its prominent side-effect profile. In this study, we examined the mechanism of BAK toxicity in human trabecular meshwork cells (HTMC) and compared the effects of BAK with tafluprost free acid, which is an active form of tafluprost commercially available in a preservative-free formulation. Primary HTMC were treated with different BAK concentrations over various exposure times. Cell viability was quantified using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenol tetrazolium bromide assay, and apoptosis was measured by enzyme-linked immunosorbent assay. The cell viability of primary HTMC exposed to various concentrations and times of tafluprost free acid was also determined. Cells were treated with BAK and tafluprost free acid for 30 min at 37°C, and cell viability was again assessed. The effect of BAK on the gap junction protein Connexin-43 (Cx43) expression was subsequently examined. BAK treatment resulted in a dose- and time-dependent decline in cell viability. Apoptosis increased following BAK treatment. Tafluprost-free acid treatment did not significantly affect cell viability. Tafluprost co-treatment with BAK resulted in an increase in cell viability as compared with BAK treatment alone. BAK treatment upregulated Cx43 expression in HTMC. These results demonstrate that BAK is harmful to the health of cultured HTMC. Tafluprost is both safe and cytoprotective against BAK for these HTMC. The effect of tafluprost on the gap junctions of the HTM should be further investigated.