Purpose: To test the hypothesis that nitric oxide, synthesized by inducible nitric oxide synthase, causes degeneration of retinal ganglion cells in an animal model of glaucoma.
Methods: Rats with unilateral, chronic, moderately elevated intraocular pressure were treated orally with L-N(6)-(1-iminoethyl)lysine 5-tetrazole amide, a prodrug of an inhibitor of inducible nitric oxide synthase. The loss of retinal ganglion cells was quantitated as an indicator of glaucomatous damage.
Results: At the end of seven months, rat eyes with chronic, moderately elevated intraocular pressure lost approximately 20,000 retinal ganglion cells. Treatment with L-N(6)-(1-iminoethyl)lysine 5-tetrazole amide for seven months completely prevented the loss of retinal ganglion cells in eyes with chronic, moderately elevated intraocular pressure. When treatment with L-N(6)-(1-iminoethyl)lysine 5-tetrazole amide was delayed and started after three months of chronic, moderately elevated intraocular pressure, further loss of retinal ganglion cells was prevented.
Conclusion: Pharmacological neuroprotection with a selective inhibitor of inducible nitric oxide synthase may be useful for the treatment of glaucoma.