The activation of poly (ADP-ribose) polymerase (PARP) plays a pivotal role in mediating N-methyl-N-nitrosourea (MNU)-induced photoreceptor cell apoptosis. We examined the retinoprotective effects of the PARP inhibitor 3-aminobenzamide (3-AB) against MNU-induced retinal damage in relation to dose and timing of prescription, and the involvement of the transcription factor nuclear factor (NF)-κB. Female Sprague-Dawley rats were intraperitoneally injected with 60 mg/kg MNU at 50 days of age, and were then immediately given a subcutaneous injection of 0, 1, 5, 10, 30 or 50 mg/kg of 3-AB, or were injected with 50 mg/kg 3-AB 12 h before, concurrently, or 4, 6 or 12 h after MNU. Rats were killed 3 and 7 days after MNU, and MNU-treated and 3-AB-injected retinas were compared with MNU-untreated control retinas or MNU-treated/3-AB-uninjected retinas. Apoptosis in photoreceptor cells was detected by performing formamide-induced DNA denaturation and staining with anti-single-stranded DNA antibody. Retinal morphologies were compared and evaluated morphometrically using the photoreceptor cell ratio and retinal damage ratio as indices to evaluate the efficacy of 3-AB. We examined expression of the phosphorylated form of NF-κB and IκBα (p-NF-κB and p-IκBα, respectively) in retinas of MNU-treated rats concurrently treated with or without 50 mg/kg 3-AB, compared with MNU-untreated control retinas. 3-AB dose-dependently suppressed photoreceptor cell apoptosis: 50 mg/kg 3-AB injected concurrently with MNU completely rescued photoreceptor cell damage; 30 mg/kg 3-AB significantly reduced photoreceptor cell damage; 10 mg/kg 3-AB tended to suppress photoreceptor cell damage; ≦5 mg/kg 3-AB was ineffective. When 50 mg/kg 3-AB was injected 12 h before or ≧4 h after MNU, it did not exert a retinoprotective effect. p-NF-κB levels of MNU-treated rat retinas were significantly lower than those of MNU-untreated control retinas, while 50 mg/kg 3-AB injected concurrently with MNU preserved the p-NF-κB levels; p-IκBα levels tended to decrease after MNU injection, compared with untreated control retinas, but the difference was not significant. Thus, 3-AB dose-dependently suppressed MNU-induced retinal damage, and 50 mg/kg 3-AB injected concurrently with MNU completely rescued photoreceptor cell apoptosis via preservation of NF-κB activity.
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