Purpose: Lipoxins exert potent anti-inflammatory and pro-resolving actions by reducing polymorphonuclear neutrophil (PMN) infiltration. This study describes the effect of lipoxin A4 and a stable analog on the resolution of ocular inflammation induced by intravitreal injection of lipopolysaccharides (LPS) in rats.
Methods: Six- to eight-week-old male Sprague Dawley (SD) rats were injected intravitreally with 2.5 microL physiologically balanced solution (LPS) containing 5 ng LPS, or 5 ng LPS + 50 ng LXA4 or 5 ng LPS + 50 ng 15-epi-LXA4 analog. Rats were anesthetized with intraperitoneal injection of a ketamine and xylazine cocktail. At 24 h, the animals were again anesthetized and the eyes examined for clinical signs of inflammation. The animals were then euthanized by CO2 inhalation and aqueous humor was collected in heparinized saline. Aqueous humor PMNs were counted using an Improved Neubauer Hemocytometer, and the protein concentration was determined by standard procedure. After enucleation, the eyes were dissected to remove the lens and the ocular tissues were frozen in liquid nitrogen and stored at -80 degrees C. Myeloperoxidase assay was done by a standard procedure.
Results: Compared to untreated LPS-injected controls, rats treated with either LXA4 or its stable analog had lower clinical inflammation score, significantly reduced aqueous humor PMN cell counts, aqueous humor protein levels, and the MPO values. The difference between the mean values of aqueous humor protein and MPO in the LXA4 and the analog injected eyes was not statistically significant, but PMN cell counts were significantly different.
Conclusions: The ocular inflammatory response to intravitreally injected LPS in rats is significantly reduced by simultaneous injection of LXA4 or its analog. This finding supports an earlier independent observation of the ocular anti-inflammatory effect of LXA4. Further investigation of lipoxins in the eye might offer a novel therapeutic approach to treating ocular inflammation in man.