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Establishing a Severe Corneal Inflammation Model in Rats Based on Corneal Epithelium Curettage Combined with Corneal Sutures
Published on: November 22, 2024
Involvement of cyclooxygenase-2 in rat models of conjunctivitis
Takayuki Oka1, Thomas Shearer, Mitsuyoshi Azuma
1Research Laboratories, Senju Pharmaceutical Co. Ltd., 1-5-4 Murotani, Nishiku, Kobe 651-2241, Japan.
Purpose:
Using two animal models to determine which isoform of cyclooxygenase (COX), constitutive COX-1 or inducible COX-2, is involved in the progression of anterior ocular inflammation.
Methods:
Lambda-carrageenan (500 mg/eye) or bacterial lipopolysaccharide (LPS; 3 mg/eye) was injected into rat conjunctiva to induce conjunctivitis. Vascular permeability in inflamed conjunctiva was measured by uptake of systemic Evans blue. Changes in mRNA for COX-1 and COX-2 in conjunctiva were detected by RT-PCR. Changes in COX-2 protein were detected by immunoblotting after immunoprecipitation. To assess involvement of COX-2 in carrageenan and LPS-induced conjunctivitis, NS-398 (a selective COX-2 inhibitor) or indomethacin (non-selective COX inhibitor) was topically administrated at 15 and 30 minutes before inflammatory stimulator-injection.
Results:
In the carrageenan-injected model, the dye content of conjunctiva (12.4 +/- 2.8 mg/eye) was significantly increased 4 hours after injection compared to saline-injected control rats (3.7 +/-1.1 mg/eye). mRNA for COX-2 was significantly increased by 2 hours and gradually increased until 24 hours; COX-1 mRNA did not show major changes until 24 hours after injection. COX-2 protein was markedly elevated 4 hours after injection of carrageenan. COX-2 protein levels were well correlated with increased mRNA levels. In the LPS-injected model, the dye content of conjunctiva (5.8 +/- 1.2 mg/eye) was significantly increased 4 hours after injection compared to saline-injected control rats (3.1 +/- 0.6 mg/eye). Expression of COX-2 mRNA was increased 1 hour after injection, peaked at 2 hours, and decreased at 4 hours. mRNA for COX-1 did not change by 24 hours. COX- 2 protein increased 2 hours after injection of LPS. COX-2 protein levels were well correlated with increased mRNA. Topical administration of 1% NS-398 exhibited strong inhibition of dye-leakage into conjunctiva 4 hours after injection of carrageenan or LPS, since 59% or 83% of dye-uptake were inhibited, respectively. 1% of indomethacin eye drops showed only a minimal effect.
Conclusions:
These results suggest that the mechanism for anterior ocular inflammation may be due to up-regulation of COX-2.
