Effects of the Inhibition of Nitric Oxide Synthase and Lipoxygenase on the Development of Endotoxin-Induced Uveitis

The anti-inflammatory effect of the inhibition of nitric oxide synthase (NOS) or 5lipoxygenase (5-LO), and a concomitant inhibition of both pathways were investigated on the endotoxin-induced uveitis (EIU) model in the rabbit. EIU was induced in albino rabbits by intravitreal injection of 100 ng lipopolisaccharide (LPS) in both eyes. Four groups of rabbits were treated intraperitoneally with phosphate buffered saline (PBS) and 50% DMSO (control group), 10 mg/kg nordihydroguayaretic acid (NDGA) in 50% DMSO, 50 mg/kg NG-nitro-L-arginine methyl ester (L-NAME) in PBS, or with the combination NDGA+L-NAME. The severity of uveitis was graded under slit lamp examination. Six hours after the induction of EIU, animals were sacrificed, and protein (Bio-Rad assay), PGE2and LTB4(RIA), and nitrites were determined in aqueous humor. Leukocyte infiltration in iris/ciliary body was estimated by myeloperoxidase (MPO) activity. NDGA or L-NAME alone did not reduce the severity of EIU when compared to the control group. NDGA reduced MPO in iris/ciliary body correlating with a reduction in LTB4levels, but did not change protein, nitrite and PGE2levels. L-NAME produced a slight decrease in MPO activity and LTB4levels, and reduced protein, nitrite, and PGE2levels. The combination NDGA+L-NAME significantly reduced the severity of uveitis as well as all inflammatory parameters and mediators. We conclude that an additive effect between NO and LO-metabolites plays a role in the development of EIU, and we speculate that interactions between NO and oxygen free radicals could modulate the inflammatory response.