Corneal epithelial toxicity of antiglaucoma formulations: in vitro study of repeated applications

BACKGROUND: By using a biologically relevant and sensitive three-dimensional model of human corneal epithelium and multiple endpoint analysis, assessment of the potential for eye irritation and long-term compatibility of four registered ophthalmological preparations, ie, Timolabak(®), Timoptol(®), Nyogel(®), and Timogel(®), was performed. This approach enables classification of the potential for irritation, discriminating between mildly irritant and non-irritant ocular substances. METHODS: The exposure protocol included two time periods, ie, 24 hours (acute application) and 72 hours (repeated applications twice daily). This approach allows assessment of not only the acute reaction but also possible recovery, as well as mimicking the potential cumulative effects associated with long-term application. Using benzalkonium chloride (BAK) 0.01% as a positive control, the following parameters were quantified: cellular viability by MTT test, histological analysis by hematoxylin and eosin staining, passive release of interleukin-1α by enzyme-linked immunosorbent assay, and OCLN gene expression by quantitative real-time polymerase chain reaction. RESULTS: Cell viability was reduced to under the 50% cutoff value after acute exposure (24 hours) to BAK 0.01%, and after repeated application (72 hours) of Timoptol and Nyogel. Histological analysis after acute exposure showed signs of superficial damage with all formulations, and severe changes after repeated applications of Timoptol, BAK 0.01%, and Nyogel. Timolabak and Timogel did not significantly alter the morphology of the human corneal epithelial cells after the different exposure times. Interleukin-1α release was greater than that for the negative control (>20 pg/mL) and the positive control (BAK 0.01%), Nyogel, and Timoptol treatments and not different after treatment with Timolabak and Timogel. Expression of OCLN, a sign of epithelial barrier impairment, was only significantly upregulated at 24 hours by BAK 0.01%, suggesting a toxic reaction at the ocular surface. OCLN was also overexpressed after repeated application of Nyogel and Timogel. CONCLUSION: Overall, the multiple endpoint analysis approach allows classification of these products according to decreasing order of irritation potential as follows: BAK 0.01%, Timoptol, Nyogel, Timogel, and Timolabak.