Reassessment of Cox-2 Expression in the Normal Human Eye

Abstract

Purpose: : Cyclooxygenase-2 (COX-2) is traditionally recognized as an inducible COX isoform during inflammatory or pathologic states. Previous studies have identified COX-2 expression as being limited to the ciliary body and outer plexiform layer of the retina in normal human eyes. The current study aimed to challenge previous reports about this limited expression of COX-2 in normal human eyes.

Materials and Methods: : Eight paraffin-embedded eyes from 5 adult human donors (Eye Bank of Canada) were used in this study. Additionally, one fetal eye (approximately 10 weeks gestation) was obtained for analysis. All specimens were immunostained for COX-2 expression using a monoclonal mouse anti-human antibody (COX229, Zymed Laboratory Inc). All ocular structures were evaluated for immunoreactivity. Sections of colon cancer were used as positive controls and for negative controls the primary antibody was omitted.

Results: : Positive staining for COX-2 was observed in the following structures: non-pigmented epithelium of ciliary body in 3 of 8 adult eyes; ciliary muscle fibers in 5 of 8 eyes; iris smooth muscle or iris sphincter in 3 of 8 eyes; RPE (focally) in 2 of 8 eyes; ganglion cells in the macular region in 6 of 8 eyes; inner segments of photoreceptors, outer plexiform layer of the retina and nerve fiber layer showed variable positivity. Other structures were consistently negative in the adult eyes evaluated. Positive staining was observed in the human fetal eye in the anterior part of the optic vesicle only.

Conclusions: : The current study demonstrates more extensive expression of COX-2 in donor adult eyes than was previously reported, suggesting a normal physiological role for this COX isoform in the eye. Consideration should be given to this observation when planning and implementing ocular anti-COX-2 therapies.

Keywords: enzymes/enzyme inhibitors • immunohistochemistry • development