Effects of Meloxicam on COX-2 Expression, PGE2 Release, and Cytokine Expression in an Experimental Model of Rabbit Acute Ocular Inflammation

Abstract

Purpose:: The aim of this study was to investigate the effects of an ophthalmic formulation of meloxicam on COX-2 activity and expression, on inflammation-related cytokines expression (IL-1ß, IL-6, IL-10, IFNγ and TNFα), and on inflammation in an experimental animal model of acute ocular inflammation and to compare the efficacy of the meloxicam ophthalmic formulation to the effects of a typical commercial diclofenac ophthalmic formulation.

Methods:: Ocular inflammation was induced in New Zealand rabbit with topical application of croton oil at 3% for 3 h. Every 4 h after inflammation induction, two drops of ophthalmic solutions of meloxicam at 0.03%, sodium diclofenac at 0.1%, or placebo (only the vehicle of the ophthalmic solutions) were administered. At different end point times, animals were sacrificed by CO₂ inhalation and conjunctiva, cornea, aqueous and vitreum humor were obtained. Expression of COX-2 and cytokines mRNA in cornea and conjunctiva were measured by semi-quantitative RT-PCR using 18s expression as a control. PGE₂ levels in ocular tissues were measured by EIA as a measure of proinflammatory activity of COX-2.

Results:: Basal expression of COX-2 mRNA was 2.7 times higher in cornea than in conjunctiva, and croton oil treatment after 3 h up-regulated COX 2-mRNA in cornea and conjunctiva (2 fold and 3 fold increase, respectively). PGE₂ levels in aqueous humor changed in the same manner as COX-2 expression varied. In inflammated eyes, meloxicam treatment down-regulated COX-2 expression and activity (mRNA and PGE₂ levels, respectively) in a time dependent manner, and reduced inflammation at 72 h of treatment. Diclofenac could not down-regulate COX-2 mRNA or PGE₂ to basal levels after 7 days of treatment. Regarding the regulation of the immunologic profile, croton oil up-regulated IL-1ß, IL-6, IFNγ and TNFα in conjunctiva while IL-10 was not modified. In cornea, croton oil up-regulated TNFα and IL-1b, while IL-10 was not modified and IFNγ and IL-6 were not detected. Meloxicam treatment in inflammated eyes down-regulated IL-6 and IFNγ in conjunctiva , and IL-1ß and TNF-α in both cornea and conjunctiva.

Conclusions:: Expression of COX-2 mRNA in cornea and conjunctiva parallels with the levels of PGE₂ present in aqueous humor and correlate with the corneal and conjunctival inflammation. Also, meloxicam treatment was more efficient than diclofenac in down-regulating the expression and activity of COX-2, thus reducing inflammation in a shorter time than diclofenac.

Keywords: conjunctiva • cornea: basic science • inflammation