Protective action of nipradilol against ischemia-induced retinal damage in rats

Retinal Concentration and Protective Effect against Retinal Ischemia of Nilvadipine in Rats

Purpose

Several calcium entry blockers have neuroprotective effects on cellular damage in the brain induced by ischemia. The purpose of this study was to determine whether nilvadipine (NID) crosses the blood–retinal barrier, and if so, whether it can then protect the photoreceptors against retinal ischemia-reperfusion injury.

Methods

Rats received an intramuscular injection of 1 mg/kg of NID and nifedipine (NIF), and the retinal and serum concentrations were measured. Ischemia was induced by raising the intraocular pressure for 45 minutes. Twenty-four hours after the reperfusion, the number of TUNEL positive cells and retinal ganglion cells (RGCs) were counted, and the thickness of the retina was measured.

Results

After 60 minutes, the concentration of NID, but not NIF, was higher in retina than in the serum. The number of TUNEL-positive cells was fewer and the reduction in the number of RGCs and the thickness of retina was less in the eyes that had received NID than controls.

Conclusions

The findings show that NID has high permeability to retina compared with NIF, which has less fat solubility than NID, and neuroprotective effect to retinal cells. NID might be useful for the treatment of glaucoma or other retinal diseases that have some relation to apoptosis.

Effect of five years of treatment with nipradilol eye drops in patients with normal tension glaucoma

Background

The purpose of this study was to evaluate the effects of topical nipradilol monotherapy for 5 years on intraocular pressure, visual field performance, and optic disk topography.

Methods

Thirty patients with normal tension glaucoma were monitored for intraocular pressure every 1–3 months. A Humphrey visual field test and measurement of optic disk configuration using the Heidelberg retina tomograph II was done after every year of treatment and the results compared with those before treatment. Visual field performance was also evaluated by trend and event analysis.

Results

The mean intraocular pressure ± standard deviation after 3 years of nipradilol treatment (14.1 ± 2.0 mmHg) and after 5 years of nipradilol treatment (13.7 ± 2.1 mmHg) was significantly lower than that before treatment (17.0 ± 1.8 mmHg, P < 0.0001). Heidelberg retina tomograph II parameters, such as mean cup depth and height variation contour after treatment, were significantly increased compared with those before treatment. Visual field performance worsened in eight eyes by trend analysis and eight eyes by event analysis.

Conclusion

Nipradilol monotherapy was effective in reducing intraocular pressure over at least 5 years without worsening of optic disk topography. Furthermore, mean cup depth and height variation contour were also significantly improved. However, visual field performance worsened in 16.0% of patients with normal tension glaucoma.

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.

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.

Axonal regeneration of cat retinal ganglion cells is promoted by nipradilol, an anti-glaucoma drug

Neurons in the CNS can regenerate their axons in an environment of the peripheral nervous system, but this ability is limited. Here we show that an anti-glaucoma drug, nipradilol, at low concentration led to a four-fold increase in the number of cat retinal ganglion cells regenerating their axons into a transplanted peripheral nerve 4 and 6 weeks after axotomy. Nipradilol also increased the number of three main regenerating retinal ganglion cell types (alpha, beta, not alpha/beta), and enhanced the rate of axonal regeneration of these retinal ganglion cells. Nipradilol is a donor of nitric oxide and an antagonist of alpha-1, beta-1 and -2 adrenoreceptors, and we therefore examined whether one of these pharmacological effects might be more important in promoting axon regeneration. A nitric oxide donor increased the number of regenerating retinal ganglion cells, but not the rate of axonal regeneration. Denitro-nipradilol (nitric oxide-deprived nipradilol) or a nitric oxide scavenger injected before nipradilol increased the number of regenerating retinal ganglion cells but did not promote regeneration rate. Blockade of individual alpha- and beta-adrenoreceptors did not increase the number of regenerating retinal ganglion cells or the rate of regeneration. From these results, it is suggested that nitric oxide plays a crucial role in mediating the effects of nipradilol on axon regeneration and neuroprotection, and the metabolite of nipradilol supports the effects.

Optic nerve and neuroprotection strategies

BACKGROUND

Experimental studies have yielded a wealth of information related to the mechanism of ganglion cell death following injury either to the myelinated ganglion cell axon or to the ganglion cell body. However, no suitable animal models exist where injury can be directed to the optic nerve head region, particularly the unmyelinated ganglion cell axons. The process of relating the data from the various animal models to many different types of optic neuropathies in man must, therefore, be cautious.

RESULTS

Extensive studies on the isolated optic nerve have yielded valuable information on the way white matter is affected by ischaemia and how certain types of compounds can attenuate the process. Moreover, there are now persuasive data on how ganglion cell survival is affected when the ocular blood flow is reduced in various animal models. As a consequence, the molecular mechanisms involved in ganglion cell death are fairly well understood and various pharmacological agents have been shown to blunt the process when delivered before or shortly after the insult.

CONCLUSIONS

A battery of agents now exist that can blunt animal ganglion cell death irrespective of whether the insult was to the ganglion cell body or the myelinated axon. Whether this information can be applied for use in patients remains a matter of debate, and major obstacles need to be overcome before the laboratory studies may be applied clinically. These include the delivery of the pharmacological agents to the site of ganglion cell injury and side effects to the patients. Moreover, it is necessary to establish whether effective neuroprotection is only possible when the drug is administered at a defined time after injury to the ganglion cells. This information is essential in order to pursue the idea that a neuroprotective strategy can be applied to a disease like glaucoma, where ganglion cell death appears to occur at different times during the lifetime of the patient.

Retinal ischemia: mechanisms of damage and potential therapeutic strategies

Retinal ischemia is a common cause of visual impairment and blindness. At the cellular level, ischemic retinal injury consists of a self-reinforcing destructive cascade involving neuronal depolarisation, calcium influx and oxidative stress initiated by energy failure and increased glutamatergic stimulation. There is a cell-specific sensitivity to ischemic injury which may reflect variability in the balance of excitatory and inhibitory neurotransmitter receptors on a given cell. A number of animal models and analytical techniques have been used to study retinal ischemia, and an increasing number of treatments have been shown to interrupt the "ischemic cascade" and attenuate the detrimental effects of retinal ischemia. Thus far, however, success in the laboratory has not been translated to the clinic. Difficulties with the route of administration, dosage, and adverse effects may render certain experimental treatments clinically unusable. Furthermore, neuroprotection-based treatment strategies for stroke have so far been disappointing. However, compared to the brain, the retina exhibits a remarkable natural resistance to ischemic injury, which may reflect its peculiar metabolism and unique environment. Given the increasing understanding of the events involved in ischemic neuronal injury it is hoped that clinically effective treatments for retinal ischemia will soon be available.