Abstract
Abstract: :
Purpose: Nipradilol is a recently developed anti–glaucoma agent, which reduces intraocular pressure by α1–and ß–adrenoceptor–blocking properties. In addition, nipradilol is thought to be a vasodilator and a neuroprotectant due to a nitric oxide (NO) donation action. NO’s neuroprotective ability in PC12 cells and C6 cells is known to be mediated by a cyclic GMP (cGMP) / protein kinase G (PKG) pathway. The purpose of this study is to test whether nipradilol protects retinal neurons from apoptosis by the NO/cGMP/PKG pathway. Methods: R28 cells, a model of retinal neurons in culture, were induced to undergo apoptosis by 24h serum deprivation as previously reported (Nakamura et al. J Biol Chem 276,43748,2001). Varying concentrations of nipradilol, sodium nitroprusside (SNP), a well known NO donor, or vehicles were added to medium with or without carboxy–PTIO, a NO scavenger, or KT5823, a PKG inhibitor. The cells were stained with Hoechst 33258 and immunostained with an anti–activated caspase–3 antibody. The percentages of pycnotic or activated caspase–3 positive cells relative to total cells in five, randomly selected microscopic fields were compared among the different treatment conditions. Results: Nipradilol and SNP inhibited apoptosis in a dose–dependent fashion with an optimal concentration of 10µM and 1.0µM, respectively, whereas vehicles did not. They showed cytotoxicity at higher concentrations and less neuroprotection at lesser concentrations. Carboxy–PTIO (1.0µM) and KT5823 (0.2µM) decreased the antiapoptotic effect of 10µM Nipradilol as well as of 1.0µM SNP. Conclusions: Nipradilol exerts the antiapoptotic effect in R28 cells via the NO/cGMP/PKG pathway.
Keywords: neuroprotection • nitric oxide • retinal culture