Objective: The purpose of this study was to assess the effects of olopatadine on the release of mast cell-derived mediators after conjunctival allergen challenge(CAC) in humans.
Methods: This was a double-masked, randomized, placebo-controlled clinical trial. Subjects with a clinical history of seasonal allergic conjunctivitis (but no current symptoms or treatment at baseline) were studied. At visit 1, subjects underwent bilateral CAC with increasing doses of allergen every 15 minutes until a significant clinical reaction was obtained, then were evaluated at 15 minutes and 5 hours after CAC. At visit 2 (2 weeks later), subjects were rechallenged to confirm the allergic response. Subjects exhibiting positive reactions at both visits (at both 15 minutes and 5 hours) were randomized and instructed to treat 1 eye with olopatadine and the contralateral eye with placebo (commercially available artificial ears) in a double-masked fashion twice daily for the 5 days immediately preceding visit 3. At visit 3, bilateral CAC was performed with the same dose as at visit 2. Itching and redness were recorded. Tear cytology for inflammatory cell counts(ie, neutrophils, eosinophils, and lymphocytes) was carried out using precolored slides, and cell numbers were counted at 400x magnification. Tear histamine was assessed using radioimmunoassay histamine measurement. Intercellular adhesion molecule (ICAM)-1/CD54 monoclonal antibody was used for immunohistochemical staining of conjunctival epithelial cells obtained by impression cytology. Slides were examined by 3 masked investigators and redness was classified on a scale of 0 (absent) to 3 (very intense).
Results: Ten subjects completed the trial. Olopatadine significantly reduced postchallenge itching and redness compared with placebo (P < 0.01 and P < 0.03,respectively). Olopatadine also reduced the number of neutrophils and the total number of cells at 30 minutes (both P = 0.015), and the number of eosinophils(P < 0.001), neutrophils (P < 0.004), lymphocytes (P = 0.011), and total number of cells (P = 0.001) at 5 hours postchallenge compared with placebo. Tear histamine levels were significantly lower after challenge in the eyes pretreated with olopatadine compared with placebo (mean [SD], 7 [8] vs 22 [12] nmol/L; P = 0.04). Olopatadine significantly reduced tear histamine levels compared with those measured in the same eyes after CAC at visit 2 (P = 0.001), whereas placebo did not affect histamine levels. Olopatadine also significantly reduced ICAM-1 expression compared with placebo at 30 minutes and 5 hours postchallenge(P < 0.03 and P < 0.01, respectively).
Conclusion: In the present study, olopatadine significantly reduced the levels of histamine, cellular infiltrate, and ICAM expression compared with placebo after CAC, suggesting that it reduced the release of mast cell-derived mediators in humans. This inhibition of mediator release correlated with reduction of itching and redness.