Nitric oxide-mediated effect of nipradilol, an alpha- and beta-adrenergic blocker, on glutamate neurotoxicity in rat cortical cultures

Nitric oxide donating anti-glaucoma drugs: advances and prospects

Glaucoma is a disease that causes irreversible blindness. Reducing intraocular pressure (IOP) is the main treatment at present. Nitric oxide (NO), an endogenous gas signaling molecule, can increase aqueous humor outflow facility, inhibit aqueous humor production thereby reducing IOP, as well as regulate eye blood flow and protect the optic nerve. Therefore, NO donating anti-glaucoma drugs have broad research prospects. In this review, we summarize NO-mediated therapy for glaucoma, and the state of the art of some NO donating molecules, including latanoprostene bunod in market and some other candidate compounds, for the intervention of glaucoma, as well as prospects and challenges ahead in this field.

Evaluation of nicotine and cotinine analogs as potential neuroprotective agents for Alzheimer's disease

The currently available therapies for Alzheimer's disease (AD) and related forms of dementia are limited by modest efficacy, adverse side effects, and the fact that they do not prevent the relentless progression of the illness. The purpose of the studies described here was to investigate the neuroprotective effects of the nicotine metabolite cotinine as well as a small series of cotinine and nicotine analogs (including stereoisomers) and to compare their effects to the four clinically prescribed AD therapies.

Protective action of nipradilol mediated through S-nitrosylation of Keap1 and HO-1 induction in retinal ganglion cells

Nipradilol (Nip), which has α1- and β-adrenoceptor antagonist and nitric oxide (NO)-donating properties, has clinically been used as an anti-glaucomatous agent in Japan. NO mediates cellular signaling pathways that regulate physiological functions. The major signaling mechanisms mediated by NO are cGMP-dependent signaling and protein S-nitrosylation-dependent signalings. Nip has been described as having neuroprotective effects through cGMP-dependent pathway in retinal ganglion cells (RGCs). However, the effect seems to be partial. On the other hand, whether Nip can prevent cell death through S-nitrosylation is not yet clarified. In this study, we therefore focused on the neuroprotective mechanism of Nip through S-nitrosylation. Nip showed a dramatic neuroprotective effect against oxidative stress-induced death of RGC-5 cells. However, denitro-nipradilol, which does not have NO-donating properties, was not protective against oxidative stress. Furthermore, an NO scavenger significantly reversed the protective action of Nip against oxidative stress. In addition, we demonstrated that α1- or β-adrenoceptor antagonists (prazosin or timolol) did not show any neuroprotective effect against oxidative stress in RGC-5 cells. We also demonstrated that Nip induced the expression of the NO-dependent antioxidant enzyme, heme oxygenase-1 (HO-1). S-nitrosylation of Kelch-like ECH-associated protein by Nip was shown to contribute to the translocation of NF-E2-related factor 2 to the nucleus, and triggered transcriptional activation of HO-1. Furthermore, RGC death and levels of 4-hydroxy-2-nonenal (4HNE) were increased after optic nerve injury in vivo. Pretreatment with Nip significantly suppressed RGC death and accumulation of 4HNE after injury through an HO-1 activity-dependent mechanism. These data demonstrate a novel neuroprotective action of Nip against oxidative stress-induced RGC death in vitro and in vivo.

Oestrogen and progestins differently prevent glutamate toxicity in cortical neurons depending on prior hormonal exposure via the induction of neural nitric oxide synthase

Sex steroids are important for brain function and protection. However, growing evidence suggests that these actions might depend on the timing of exposure to steroids. We have studied the effects of steroid administration on the survival of neural cells and we have partially characterized the possible mechanisms. The effect of a 24h pre-treatment with 17beta-estradiol or 17beta-estradiol plus progesterone or medroxyprogesterone acetate on the toxic action of l-glutamate was used to test the experimental hypothesis. Pre-exposure to either steroid combinations turned in enhanced cell survival. Instead, addition of sex steroids together with l-glutamate, in the absence of a pre-exposure had no protective effect. Pre-treatment with the steroid combinations resulted in increased neural NOS expression and activity and blockade of NOS abolished the cytoprotective effects of steroids. These results suggest that NOS induction might be involved in sex steroid-induced neuroprotection. Furthermore, these data supports the hypothesis that prolonged and continued exposure to oestrogen and progesterone, leading to changes in gene expression, is necessary to obtain neuroprotection induced by sex steroids.

Nipradilol protects rat retinal ganglion cells from apoptosis induced by serum deprivation in vitro and by diabetes in vivo

PURPOSE

To investigate if nipradilol has an anti-apoptotic effect in serum-deprived RGC-5 cells and in the streptozotocin-induced diabetic rat retina.

METHODS

Apoptosis was quantified by activated caspase-3 immunohistochemistry or terminal dUTP nick end-labeling assay.

RESULTS

Nipradilol dose-dependently suppressed apoptosis in a protein kinase A- and G-dependent manner and counteracted glutamate-induced calcium entry in the RGC-5 cells and reduced apoptotic cells in the retinal ganglion cell layer of 4- and 12-week diabetic retinas compared to controls when instilled for 5 days. Removal of the nitric oxide moiety from nipradilol blocked these effects.

CONCLUSIONS

Nipradilol protects RGCs from apoptosis induced by serum-deprivation in vitro and by diabetes in vivo. The NO-related signaling pathway mediates the anti-apoptotic ability of nipradilol.

Neuroprotective effect of nipradilol, an NO donor, on hypoxic-ischemic brain injury of neonatal rats

Hypoxia-ischemia is a common cause of neonatal brain injuries. Nitric oxide (NO) is upregulated in the brain after hypoxia-ischemia and generally believed to exert a paradoxical effect on neurons, neurodestruction and neuroprotection, but it has not been demonstrated that NO is actually neuroprotective in neonatal hypoxic-ischemic encephalopathy. We evaluated the effect of intracerebroventricular administration of nipradilol (3,4-dihydro-8-(2-hydroxy-3-isopropylamino)-propoxy-3-nitroxy-2H-1-benzopyran), a potent NO donor, at various concentrations (0.1 muM to 1 mM in 5 mul PBS/brain) to neonatal rats with hypoxic-ischemic treatment. The extent of the infarct area in the brain was significantly reduced by injection of the 1 muM nipradilol solution. However, denitro-nipradilol (3,4-dihydro-8-(2-hydroxy-3-isopropylamino)-propoxy-3-hydroxy-2H-1-benzopyran), that does not release NO, did not show the neuroprotective effect, suggesting that NO released from nipradilol exerts a neuroprotective effect on neonatal neurons.

Cerebral microvascular dilation during hypotension and decreased oxygen tension: a role for nNOS

Endothelial (eNOS) and neuronal nitric oxide synthase (nNOS) are implicated as important contributors to cerebral vascular regulation through nitric oxide (NO). However, direct in vivo measurements of NO in the brain have not been used to dissect their relative roles, particularly as related to oxygenation of brain tissue. We found that, in vivo, rat cerebral arterioles had increased NO concentration ([NO]) and diameter at reduced periarteriolar oxygen tension (Po(2)) when either bath oxygen tension or arterial pressure was decreased. Using these protocols with highly selective blockade of nNOS, we tested the hypothesis that brain tissue nNOS could donate NO to the arterioles at rest and during periods of reduced perivascular oxygen tension, such as during hypotension or reduced local availability of oxygen. The decline in periarteriolar Po(2) by bath manipulation increased [NO] and vessel diameter comparable with responses at similarly decreased Po(2) during hypotension. To determine whether the nNOS provided much of the vascular wall NO, nNOS was locally suppressed with the highly selective inhibitor N-(4S)-(4-amino-5-[aminoethyl]aminopentyl)-N'-nitroguanidine. After blockade, resting [NO], Po(2), and diameters decreased, and the increase in [NO] during reduced Po(2) or hypotension was completely absent. However, flow-mediated dilation during occlusion of a collateral arteriole did remain intact after nNOS blockade and the vessel wall [NO] increased to approximately 80% of normal. Therefore, nNOS predominantly increased NO during decreased periarteriolar oxygen tension, such as that during hypotension, but eNOS was the dominant source of NO for flow shear mechanisms.

FeTPPS protects against global cerebral ischemic-reperfusion injury in gerbils

Neuronal damage following cerebral ischemia is mediated by various mechanisms, among which nitrosative stress plays an important role. Peroxynitrite, a powerful oxidant, contributes heavily to the neuronal damage in cerebral ischemic-reperfusion (IR) injury. In the present study, we have investigated the neuroprotective effects of a peroxynitrite decomposition catalyst, 5,10,15,20-tetrakis(4-sulfonatophenyl) porphyrinato iron(III) [FeTPPS] in global cerebral IR injury in gerbils. Neurological damage was significantly attenuated by FeTPPS treatment (1 and 3mgkg(-1), i.p.) as evident from reduction in neurological symptoms, hyperlocomotion, memory impairment and CA1 hippocampal neuronal damage in IR challenged gerbils. FeTPPS treatment also attenuated the increased malondialdehyde (MDA) levels and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) positive cells after cerebral IR injury. Results of this study demonstrates the neuroprotective activity of FeTPPS in global cerebral IR injury and its neuroprotective effects may be attributed to reduction in oxidative stress and DNA fragmentation.

cAMP-responsive element binding protein mediates a cGMP/protein kinase G-dependent anti-apoptotic signal induced by nitric oxide in retinal neuro-glial progenitor cells

Nitric oxide (NO) is cytoprotective to certain types of neuronal cells. The neuroprotective ability of NO in the retina was reportedly mediated by the cyclic GMP (cGMP) to protein kinase G (PKG) pathway. Cyclic AMP-responsive element binding protein (CREB) plays an essential role in the NO/cGMP/PKG-mediated survival of rat cerebellar granule cells. We tested whether CREB transduces the NO/cGMP/PKG anti-apoptotic cascade in R28 neuro-glial progenitor cells. Apoptosis was induced in R28 cells by serum deprivation for 24 h. Varying concentrations of two NO donors, sodium nitroprusside (SNP) and nipradilol, were added to medium with or without an NO scavenger, a soluble guanylyl cyclase inhibitor, or a PKG inhibitor. The cells were immunostained against activated caspase-3 and counterstained with Hoechst 33258. Apoptosis was quantified by counting activated caspase-3 positive or pyknotic cells. SNP and nipradilol rescued R28 cells from apoptosis in a dose-dependent manner, at an optimal concentration of 1.0 microM and 10 microM, respectively. Higher concentrations were cytotoxic. The NO scavenger and the inhibitors decreased the anti-apoptotic effect of the NO donors. Intracellular cGMP levels were increased after exposure to SNP and nipradilol. Western blotting showed that both NO donors increased CREB phosphorylation, which was blocked when pre-exposed to the inhibitors. Transfection with a dominant negative CREB construct defective of phosphorylation at Ser-133 interfered with the anti-apoptotic activity of SNP. These results indicate that CREB at least in part mediates the cGMP/PKG-dependent anti-apoptotic signal induced by NO in R28 cells.