Investigation of Unscheduled DNA Synthesis in Rabbit Corneas Following Instillation of Genotoxic Agents

Purpose: An unscheduled DNA synthesis (UDS) test is used for or genotoxicity evaluation. The UDS test with hepatocytes is well established; however, drug exposure levels at the application site for topically administered drugs (e.g. ophthalmic drugs) often exceed the exposure levels for systemic administration. To establish genotoxicity on the ocular surface, we performed the UDS test using rabbit corneas from eyes subjected to instillation of genotoxic agents.

Materials And Methods: Five genotoxic agents - 1,1'-dimethyl-4,4'-bipyridinium dichloride (paraquat); acridine orange; ethidium bromide; acrylamide; and 4-nitroquinoline 1-oxide (4-NQO) - were instilled once onto both eyes of male Japanese white rabbits. Physiological saline or a general vehicle for ophthalmic solution were instilled as the negative controls. Dimethyl sulfoxide was instilled as the vehicle control. Isolated corneas were incubated with tritium-labelled thymidine and the number of sparsely labelled cells (SLCs, cells undergoing UDS) was counted by autoradiography.

Results: Statistically significant increases in the mean appearance rates of SLCs in the corneal epithelium were noted in paraquat-, acridine orange-, ethidium bromide-, and 4-NQO-treated eyes compared with those of the controls. These increases generally appeared in a dose-dependent manner. Acrylamide did not induce an increase in the mean appearance rates of SLCs, presumably because it caused the generation of fewer metabolites in the cornea.

Conclusions: UDS tests revealed DNA damage in the cornea epitheliums treated with well-known genotoxic agents. These results suggest that the UDS test is one of the useful tools for the assessment of genotoxicity on the ocular surface in the development of ophthalmic drugs.