In vitro and in vivo comparative toxicological study of a new preservative-free latanoprost formulation

Purpose: To compare in vitro, on the human reconstituted corneal epithelial SkinEthics model, and in vivo, using an acute rabbit toxicological model, the effects of a benzalkonium chloride (Bak)-preserved solution of latanoprost and a preservative-free (PF) latanoprost solution.

Methods: In vitro, the three-dimensional (3D) reconstituted human corneal epithelia (HCE) were treated with PBS, BAK-latanoprost, PF-latanoprost, or 0.02% Bak for 24 hours followed or not followed by a 24 hour post incubation recovery period. Cellular viability was evaluated using the 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test at 24 hours and the apoptotic cells were counted using TUNEL labeling on frozen sections at 24 hours and 24 hours plus 24 hours. In vivo, rabbits received 50 μL of the same solutions, which were applied at 5 minute intervals a total of 15 times. Ocular surface toxicity was investigated using slit lamp biomicroscopy examination, conjunctival impression cytology (CIC), and corneal in vivo confocal microscopy (IVCM). Standard immunohistology also assessed inflammatory CD45-positive cells.

Results: In vitro, BAK-latanoprost and 0.02% Bak induced significant Apoptosis in the apical layers that correlated with the significant decrease of cell viability as assessed by the MTT test. PF-latanoprost slightly decreased cell viability and few apoptotic cells were found in the superficial layers, without reaching statistical significance compared with PBS. In vivo, clinical observation and IVCM images showed the lowest ocular surface toxicity with PBS and PF-latanoprost, while BAK-latanoprost and Bak induced abnormal corneoconjunctival aspects. PF-latanoprost showed the lowest CIC score, close to the PBS score and induced fewer CD45-positive cells in both the limbus and the conjunctiva compared with Bak and latanoprost, as assessed by immunohistology.

Conclusions: We confirm that rabbit corneoconjunctival surfaces presented better tolerance when treated with PF-latanoprost compared with the standard BAK-latanoprost preparation or the Bak solution.