The use of shotgun label‐free quantitative proteomic mass spectrometry to evaluate the inflammatory response in aqueous humor from horses with uveitis compared to ophthalmologically healthy horses

Objective The objective of this study was to use shotgun label‐free tandem mass spectrometry (LF‐MS/MS) to evaluate aqueous humor (AH) from horses with uveitis (UH) compared to ophthalmologically healthy horses (HH). Animals Studied Twelve horses diagnosed with uveitis based on ophthalmic examination and six ophthalmologically healthy horses (postmortem) purchased for teaching purposes. Procedures All horses received a complete ophthalmic examination and physical exam. Aqueous paracentesis was performed on all horses and AH total protein concentrations were measured with nanodrop (TPn) and refractometry (TPr). AH samples were analyzed with shotgun LF‐MS/MS and proteomic data were compared between groups using Wilcoxon rank‐sum test. Results A total of 147 proteins were detected, 11 proteins had higher abundance in UH, and 38 proteins had lower abundance in UH. Proteins with higher abundance included apolipoprotein E, alpha‐2‐macroglobulin (A2M), alpha‐2‐HS‐glycoprotein, prothrombin, fibrinogen, complement component 4 (C4), joining chain for IgA and IgM, afamin, and amine oxidase. There were positive correlations between TPn (p = .003) and TPr (p = .0001) compared to flare scores. Conclusion Differential abundance of A2M, prothrombin, fibrinogen, and C4 indicate upregulation of the complement and coagulation cascade in equine uveitis. Proinflammatory cytokines and the complement cascade have potential as therapeutic targets for equine uveitis.