Determination of a No Observable Effect Level for Endotoxin Following a Single Intravitreal Administration to Cynomolgus Monkeys.

ABSTRACT

Purpose: To characterize the inflammatory response and determine the no-observable-effect level (NOEL) in cynomolgus monkey eyes after intravitreal (ITV) injection of endotoxin. Methods: The inflammatory response to endotoxin was assessed in a single-dose study in monkeys at doses of 0.01 to 0.51 endotoxin units (EU)/eye. Tolerability was assessed by clinical ophthalmic examinations, intraocular pressure measurements, fundus color photography, optical coherence tomography, and anatomic pathology. Results: ITV injection of endotoxin at ≥0.04 EU/eye resulted in a dose-related anterior segment inflammatory response. No aqueous flare or cell was noted in the 0.01 EU/eye dose group. A more delayed posterior segment response characterized by vitreous cell was observed beginning on day 5, peaking on day 15, and decreasing in some groups. Microscopic findings of mononuclear cell infiltrates in the vitreous were observed in eyes given ≥0.21 EU/eye. Conclusion: The NOEL for ITV endotoxin in cynomolgus monkeys was 0.01 EU/eye, suggesting that this species is as sensitive as rabbits to the effects of endotoxin. The vitreous cavity also appears more sensitive to endotoxin than the anterior segment/aqueous chamber. Overall, the magnitude of the inflammatory response at ≥0.04 EU/eye suggests that dose-response curve in monkeys is steeper than in rabbits. These data highlight the importance of assessing endotoxin level in ITV formulations, as levels as low as 0.04 EU/eye may confound the safety evaluations of ITV therapeutics in cynomolgus monkeys.