Manganese porphyrin reduces retinal injury induced by ocular hypertension in rats

This study aimed to clarify the possible therapeutic benefit of preferential nitric oxide synthase (NOS) inhibition and catalytic antioxidant Mn (III) meso-tetrakis (N-n-hexylpyridinium-2-yl) porphyrin (MnTnHex-2-PyP5+) treatment in a rat model of elevated intraocular pressure (EIOP). Rats were randomly divided into different experimental groups which received either intraperitoneal MnTnHex-2-PyP5+ (0.1 mg/kg/day), intragastric NOS inhibitor (S-methylthiourea: SMT; 5 mg/kg/day) or both agents for a period of 6 weeks. Ocular hypertension was induced by unilaterally cauterizing three episcleral vessels and the unoperated eye served as control. Neuroprotective effects of given treatments were determined via electrophysiological measurements of visual evoked potentials (VEP) while retina and vitreous levels of MnTnHex-2-PyP5+ were measured via LC-MS/MS. Latencies of all VEP components (P1, N1, P2, N2, P3) were significantly prolonged (p < 0.05) in EIOP and returned to control levels following all three treatment protocols. Ocular hypertension significantly increased retinal protein nitration (p < 0.001) which returned to baseline levels in all treated groups. NOS-2 expression and nitrate/nitrite levels were significantly greater in non-treated rats with EIOP. Retinal TUNEL staining showed apoptosis in all ocular hypertensive rats. The presented data confirm the role of oxidative injury in EIOP and highlight the protective effect of MnTnHex-2-PyP5+ treatment and NOS inhibition in ocular hypertension.

► First report on MnTnHex-2-PyP5+ treatment in elevated intraocular pressure.
► MnTnHex-2-PyP5+ can be detected in both the vitreous and retina via LC ESI-MS/MS.
► Beneficial effects of MnTnHex-2-PyP5+ is observed in elevated intraocular pressure.