Abstract
Purpose: :
Retinitis pigmentosa (RP) is a group of diseases caused by many different mutations. The mutations cause rod photoreceptor cells to die and then gradually cone photoreceptors die due to progressive oxidative damage. Along with oxidative damage, there is also staining for nitrotyrosine, a sign of peroxynitrite-induced nitrosative damage. In this study, we tested the hypothesis that after death of rods, cones die from oxidative and nitrosative damage.
Methods: :
rd1 mice were treated with twice daily intraperitoneal injections of a mixture of nitric oxide synthase (NOS) inhibitors including NG-nitro-L-arginine (L-NNA, 400mg/kg), N(omega)-nitro-L-arginine methyl ester (L-NAME,400mg/kg), N-monomethyl-L-arginine (L-NMMA, 200mg/kg), and aminoguanidine bicarbonate (400mg/kg) from P18. Mice were sacrificed for recording of photopic ERGs at P25, and for cone density measurement by confocal microscopy and real time RT-PCR for m-cone opsin and s-cone opsin at P35. In separate experiments, rd1 mice were given twice daily intraperitoneal injections of relatively selective inducible NOS inhibitor, aminoguanidine bicarbonate (1250mg/kg) or the neuronal NOS specific inhibitor 7-nitroindazole (30mg/kg) between P18 and P35, when cone density was measured.
Results: :
Cone density was significantly higher in NOS inhibitor-treated mice in all 4 quadrants of the retina compared vehicle treated mice. The amount of m-cone opsin mRNA, but not s-cone opsin mRNA, was significantly greater in NOS inhibitor-treated mice compared to vehicle-treated mice. ERGs done on rd1 mice treated with NOS inhibitors at P25 showed greater b-wave amplitudes than those seen in vehicle-treated mice. There was no significant difference in cone density in any quadrant of the retina in mice treated with aminoguanidine, but cone density was significantly higher in 2 of 4 quadrants of the retina in mice treated with 7-nitroindazole compared to vehicle treated mice.
Conclusions: :
In this study, we have demonstrated that nitric oxide amplifies and exacerbates damage from oxidative stress that occurs from loss of rods and that by blocking nNOS cone cell death is reduced even without reducing the underlying oxidative stress.
Keywords: retinal degenerations: hereditary • nitric oxide • oxidation/oxidative or free radical damage