Ocular safety of cationic emulsion of cyclosporine in an in vitro corneal wound-healing model and an acute in vivo rabbit model

PURPOSE Topical preparations of cyclosporine (CsA) are common therapeutics for the treatment of dry eye. However, they are not devoid of side effects, such as allergy and irritation. The present study aimed at evaluating the safety profile of a new CsA formulation in cationic emulsion (CEm) in vitro with a dynamic corneal wound healing assay using human corneal epithelial (HCE) cells, and in vivo in a rabbit acute toxicity model. METHODS Three different csa formulations were tested: 1) 0.05%CsA-CEm, 2) commercial 0.05%CsA-Anionic emulsion (CsA-AEm, Restasis®), and 3) 0.05%CsA-Oil solution. Phosphate buffered saline (PBS) was used as negative control and 0.02% benzalkonium chloride (BAK) as the toxic control. In vitro, a wound was created by scratching through a confluent HCE cell layer and exposed 30 min to 1/10 dilutions of the different formulations. Cytotoxicity, cell migration, and proliferation were performed to analyze the recovery at days 1, 2, and 3. In vivo, the eye drops were applied to rabbit eyes 15 times at 5-min intervals. The ocular surface structures were examined with a slit-lamp and by corneal in vivo confocal microscopy (IVCM) for detailed examination of corneal epithelium, stroma, limbus, and conjunctiva-associated lymphoid tissue (CALT) structures. RESULTS The in vitro study confirmed that a 0.02% BAK solution delayed the corneal healing process (-57%) by severely damaging the remaining HCE cells. The other formulations maintained a normal healing rate with a similar behavior for CsA-CEm, CsA-AEm, and PBS with no significant differences (at D3, 66%-74% closure). In the rabbit, 0.02%BAK showed the highest toxicity, inducing redness, chemosis with damaged corneal epithelium, and inflammatory cell infiltrations. CsA-AEm and CsA-Oil induced moderate infiltrations of inflammatory cells around the CALT. CsA-CEm presented the lowest toxicity with patterns similar to PBS. CONCLUSIONS The combination of these in vitro and in vivo models evaluated the tolerance/cytotoxicity and the dynamic wound healing potential of CsA in different formulations. While CsA-AEm, CsA-CEm, and CsA-Oil are generally well tolerated, only CsA-CEm appeared to maintain the HCE cells' normal healing rate in vitro and low levels of inflammation in vivo.