Evaluation of the Dose-Dependent Inflammatory Response and No-Observable Adverse Effect Level of Intravitreal Endotoxin in the African Green Monkey

PURPOSE: To evaluate the inflammatory effects and no-observed adverse effect level (NOAEL) of intravitreal endotoxin in an African green monkey model of uveitis. METHODS: Fifteen green monkeys were administered intravitreal endotoxin ranging from 0.005 to 0.08 endotoxin unit (EU)/eye. Inflammation was evaluated by slit-lamp biomicroscopy, indirect fundoscopy, tonometry, color fundus photography, ocular coherence tomography, laser flare photometry, and histopathology, with analysis of cytokine levels in aqueous and vitreous humor. The inter-rater reliability of a refined nonhuman primate ophthalmic scoring system was evaluated. RESULTS: A dose-dependent inflammatory response was observed beginning at 0.02 EU/eye; no inflammatory response exceeding the vehicle was observed at 0.005 EU/eye. Retinal pathology was minimal, and posterior visualization degraded with increasing inflammation. Inflammation was observed by histopathology at 0.04 EU/eye. Inter-rater reliability of the scoring system was high, with 99.2% of individual scores differing by 1 scale unit or less and 87.2% of summary scores differing by 2 scale units or less. CONCLUSIONS: The NOAEL for intravitreal endotoxin in the green monkey is 0.005 EU/eye, with inflammation increasing with increasing dose beginning at 0.02 EU/eye. This updated nonhuman primate ophthalmic scoring system allows for high inter-rater reliability for the quantification of mild to severe inflammation in the green monkey eye. TRANSLATIONAL RELEVANCE: Validation of the ophthalmic inflammation scoring system enables application of the green monkey as a valuable translational model. Candidate therapeutics should be confirmed to have endotoxin levels below this threshold before safety testing in this species to enable interpretation of inflammation and minimize impact on animal welfare.