Betaxolol, a beta(1)-adrenoceptor antagonist, reduces Na(+) influx into cortical synaptosomes by direct interaction with Na(+) channels: comparison with other beta-adrenoceptor antagonists

Beta-blocker carteolol and oxprenolol produce cutaneous analgesia in response to needle pinpricks in the rat

BACKGROUND

This present study was undertaken to determine whether beta-blockers produce the cutaneous analgesic effect, comparing them with the long-acting local anesthetic bupivacaine.

METHODS

Using a rat model of infiltrative cutaneous analgesia, the effect of 5 beta-blockers (oxprenolol, carteolol, butaxamine, metoprolol, and acebutolol) and bupivacaine was compared and eventually combined with epinephrine.

RESULTS

Among 5 beta-blockers, oxprenolol exhibited the most potent and the longest duration of cutaneous analgesia. In dose-response studies, the rank order of efficacy (ED₅₀ [50% effective dose]) was bupivacaine (0.40 [0.35-0.47] μmol) > oxprenolol (2.33 [2.06-2.64] μmol) > carteolol (4.86 [4.27-5.53] μmol) (p< 0.01). Carteolol provoked a longer duration of analgesia (p< 0.01) than oxprenolol or bupivacaine on an equipotent basis (ED₂₅, ED₅₀, and ED₇₅). Adding epinephrine 1:200,000 to drug preparations (carteolol, oxprenolol, and bupivacaine) at ED₉₅ had a peripheral action in prolonging the duration of action.

CONCLUSIONS

Oxprenolol and carteolol had greater potencies and longer durations of cutaneous analgesia than butaxamine, metoprolol, and acebutolol. Oxprenolol produced a similar duration of action when compared to bupivacaine, while carteolol had a greater duration of action than bupivacaine. Cutaneous analgesia of oxprenolol (or carteolol) plus adrenaline was greater than that of bupivacaine plus adrenaline.

Use of β‑blockers and risk of age‑related macular degeneration among hypertensive patients: An insight from The National Health and Nutrition Examination Survey

Although age-related macular degeneration (AMD) is the leading cause of legal blindness, the treatment methods for AMD are limited. The aim of the present study was to examine the association between oral β-blockers (BBs) and the risk of developing AMD among hypertensive patients. For this purpose, a total of 3,311 hypertensive patients from the National Health and Nutrition Examination Survey were included in the study. The use of BBs and treatment duration data were collected using a self-reported questionnaire. AMD was diagnosed by gradable retinal images. Multivariate-adjusted survey-weighted univariate logistic regression was used to confirm the association between the use of BBs and the risk of developing AMD. The results revealed that the use of BBs exerted a beneficial effect (odds ratio (OR), 0.34; 95% confidence interval (95% CI, 0.13-0.92; P=0.04) in late-stage AMD in the multivariate adjusted model. When the BBs were classified into non-selective BBs and selective BBs, the protective effect in late-stage AMD was still observed in the non-selective BBs (OR, 0.20; 95% CI, 0.07-0.61; P<0.001). After accounting for treatment duration, long-term treatment with BBs (>6 years) was also found to reduce the risk of late-stage AMD (OR, 0.13; 95% CI, 0.03-0.63; P=0.01). In late-stage AMD, the long-term use of BBs was beneficial for geographic atrophy (OR, 0.07; 95% CI, 0.02-0.28; P<0.001). On the whole, the present study demonstrates that the use of non-selective BBs exerted a beneficial effect against the risk of late-stage AMD among hypertensive patients. Long-term treatment with BBs was also associated with lower risk of developing AMD. These findings may provide novel strategies for the management and treatment of AMD.

Wettability and contact angle affect precorneal retention and pharmacodynamic behavior of microspheres

In the present study, we describe the development of betaxolol hydrochloride and montmorillonite with ion exchange in a single formulation to create a novel micro-interactive dual-functioning sustained-release delivery system (MIDFDS) for the treatment of glaucoma. Betaxolol hydrochloride molecule was loaded onto the montmorillonite by ion exchange and MIDFDS formation was confirmed by XPS data. MIDFDS showed similar physicochemical properties to those of Betoptic, such as particle size, pH, osmotic pressure, and rheological properties. Nevertheless, the microdialysis and intraocular pressure test revealed better in vivo performance of MIDFDS, such as pharmacokinetics and pharmacodynamics. With regards to wettability, MIDFDS had a larger contact angle (54.66 ± 5.35°) than Betoptic (36.68 ± 1.77°), enabling the MIDFDS (2.93 s) to spread slower on the cornea than Betoptic (2.50 s). Moderate spreading behavior and oppositely charged electrostatic micro-interactions had a comprehensive influence on micro-interactions with the tear film residue, resulting in a longer precorneal retention time. Furthermore, MIDFDS had a significant sustained-release effect, with complete release near the cornea. The dual-functioning sustained-release carrier together with prolonged pre-corneal retention time (80 min) provided sufficiently high drug concentrations in the aqueous humor to achieve a more stable and long-term IOP reduction for 10 h. In addition, cytotoxicity and hemolysis tests showed that MIDFDS had better biocompatibility than Betoptic. The dual-functioning microspheres presented in this study provide the possibility for improved compliance due to low cytotoxicity and hemolysis, which suggests promising clinical implications.

Nitric Oxide Photoreleasers with Fluorescent Reporting

Nitric oxide (NO) plays a multifaceted role in human physiology and pathophysiology, and its controlled delivery has great prospects in therapeutic applications. The light-activated uncaging of NO from NO caging compounds allows this free radical to be released with accurate control of site and dosage, which strictly determine its biological effects. Molecular constructs able to activate fluorescence concomitantly to NO release offer the important advantage of easy and real-time tracking of the amount of NO uncaged in a non-invasive fashion even in the cell environment. This contribution provides an overview of the advances in photoactivatable NO releasers bearing fluorescent reporting functionalities achieved in our and other laboratories, highlighting the rationale design and their potential therapeutic applications.

Visible light-activatable cyclodextrin-conjugates for the efficient delivery of nitric oxide with fluorescent reporter and their inclusion complexes with betaxolol

Water-soluble β-CD conjugates release NO with high performances with blue and green light, liberate a fluorescent co-products useful for the real-time monitoring of the NO concentration and encapsulate additional guests within the hydrophobic cavity.

Micro-interaction of mucin tear film interface with particles: The inconsistency of pharmacodynamics and precorneal retention of ion-exchange, functionalized, Mt-embedded nano- and microparticles

Physiological reflexes and anatomical barriers render traditional eye drop delivery inefficient. We previously reported that drug-loaded nanoparticles and microspheres prepared from montmorillonite and Eudragit polymers exhibited good sustained-release and lowered intraocular pressure. Here, we compared the performance of optimized formulations to select the most suitable formulation for glaucoma therapy. We found that the microspheres had much higher encapsulation efficiency and drug loading than nanoparticles. Moreover, cytocompatibility experiments demonstrated that nanoparticles showed more severe cytotoxicity than microspheres, probably due to their smaller particles, enhanced cell uptake, and intracellular solubility. Interestingly, the pre-corneal retention time of nanoparticles reflected a clear advantage over microspheres, while the duration of the pharmacological effect of nanoparticles was not as good as that of microspheres: compared with the nanoparticle depressurization duration of only 8 h, the microspheres continuously depressurized for 12 h. The slower release of the microspheres and its micro-interaction mechanism with the discontinuous mucin layer of the tear film led to the inconsistency between duration of pharmacodynamics and fluorescence ocular retention time. In summary, the lower cytotoxicity and longer pharmacological effect of microspheres indicate their potential advantages for glaucoma applications.

Clonidine as an adjuvant for propranolol enhances its effect on infiltrative cutaneous analgesia in rats

Clonidine prolongs duration of analgesia when used as an adjunct to local anesthetics for infiltrative cutaneous analgesia, and propranolol produces local anesthesia. The purpose of the experiment was to evaluate clonidine as an adjuvant for propranolol on the quality and duration of cutaneous analgesia. A rat model of cutaneous trunci muscle reflex (CTMR) in response to local skin pinprick was employed to evaluate the cutaneous analgesic effect of propranolol combined with clonidine. The long-lasting local anesthetic bupivacaine was used as control. Cutaneous analgesia elicited by propranolol and bupivacaine was dose-dependent, and both propranolol (9.0μmol) and bupivacaine (1.8μmol) produced 100% nociceptive blockade. On an 50% effective dose (ED50) basis, the relative potency was bupivacaine [0.48 (0.42-0.55) μmol] greater than propranolol [2.27 (1.98-2.54) μmol] (p<0.01). Subcutaneous saline and clonidine (0.12μmol) did not produce cutaneous analgesia. The mixture of an ineffective-dose clonidine (0.12μmol) and a drug (propranolol or bupivacaine) at ED50 or ED95 increased the potency and extended the duration at producing cutaneous analgesia. The resulting data demonstrated that propranolol is less potent than bupivacaine as an infiltrative anesthetic. Clonidine as an adjuvant for propranolol or bupivacaine has a significant peripheral action in increasing the depth and duration of action on infiltrative cutaneous analgesia.

Selectivity of pharmacological tools: implications for use in cell physiology. A review in the theme: Cell signaling: proteins, pathways and mechanisms

Pharmacological inhibitors are frequently used to identify the receptors, receptor subtypes, and associated signaling pathways involved in physiological cell responses. Based on the effects of such inhibitors conclusions are drawn about the involvement of their assumed target or lack thereof. While such inhibitors can be useful tools for a better physiological understanding, their uncritical use can lead to incorrect conclusions. This article reviews the concept of inhibitor selectivity and its implication for cell physiology. Specifically, we discuss the implications of using inhibitor vs. activator approaches, issues of direct vs. indirect pathway modulation, implications of inverse agonism and biased signaling, and those of orthosteric vs. allosteric, competitive vs. noncompetitive, and reversible vs. irreversible inhibition. Additional problems can result from inconsistent estimates of inhibitor potency and differences in potency between cell-free systems and intact cells. These concepts are illustrated by several examples of inhibitors displaying affinity for related but distinct targets or even unrelated targets. Of note, many of the issues being addressed are also applicable to genetic inhibition strategies. The main practical conclusion following from these concepts is that investigators should be critical in the choice of inhibitor, its concentrations, and its mode of application. When this advice is adhered to, small-molecule pharmacological inhibitors can be important experimental tools in the hand of physiologists.

Corticolimbic catecholamines in stress: a computational model of the appraisal of controllability

Appraisal of a stressful situation and the possibility to control or avoid it is thought to involve frontal-cortical mechanisms. The precise mechanism underlying this appraisal and its translation into effective stress coping (the regulation of physiological and behavioural responses) are poorly understood. Here, we propose a computational model which involves tuning motivational arousal to the appraised stressing condition. The model provides a causal explanation of the shift from active to passive coping strategies, i.e. from a condition characterised by high motivational arousal, required to deal with a situation appraised as stressful, to a condition characterised by emotional and motivational withdrawal, required when the stressful situation is appraised as uncontrollable/unavoidable. The model is motivated by results acquired via microdialysis recordings in rats and highlights the presence of two competing circuits dominated by different areas of the ventromedial prefrontal cortex: these are shown having opposite effects on several subcortical areas, affecting dopamine outflow in the striatum, and therefore controlling motivation. We start by reviewing published data supporting structure and functioning of the neural model and present the computational model itself with its essential neural mechanisms. Finally, we show the results of a new experiment, involving the condition of repeated inescapable stress, which validate most of the model's predictions.

Use of the harmonic mean to the determination of dissociation constants of stereoisomeric mixtures of biologically active compounds

Herein we introduce the derivation of a mathematical expression to evaluate the dissociation constant of a mixture of stereoisomers in equal amounts (KdMIX), when the corresponding dissociation constants (Kd) or medium response (MR50) of the pure stereoisomers are known; the final equation takes the form of the harmonic mean. In order to validate the equation, we carried out a bibliographic search of experimental data of enantiomeric molecules with biological activity, considering the Kd's or MR50's of the isolated enantiomers as well as that of the racemate. The comparisons between the experimental dissociation constants of the mixtures (KdEXP or MR50EXP) and the calculated values (KdMIX or MR50MIX) were consistent; the similarity between these values is supported through statistical analyses of group comparison and simple linear correlation. The equation we obtained, which corresponds to the harmonic mean, was used to predict the values of KdMIX (or MR50MIX) or Kd (or MR50) in systems when only two of the experimental values are known: either the dissociation constants of both enantiomers or the Kd (or MR50) of one of the enantiomers and dissociation constant of the racemate.

Crystallins are regulated biomarkers for monitoring topical therapy of glaucomatous optic neuropathy

Optic nerve atrophy caused by abnormal intraocular pressure (IOP) remains the most common cause of irreversible loss of vision worldwide. The aim of this study was to determine whether topically applied IOP-lowering eye drugs affect retinal ganglion cells (RGCs) and retinal metabolism in a rat model of optic neuropathy. IOP was elevated through cauterization of episcleral veins, and then lowered either by the daily topical application of timolol, timolol/travoprost, timolol/dorzolamide, or timolol/brimonidine, or surgically with sectorial iridectomy. RGCs were retrogradely labeled 4 days prior to enucleation, and counted. Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), matrix-assisted laser desorption ionization mass spectrometry, Western blotting, and immunohistochemistry allowed the identification of IOP-dependent proteomic changes. Genomic changes were scrutinized using microarrays and qRT-PCR. The significant increase in IOP induced by episcleral vein cauterization that persisted until 8 weeks of follow-up in control animals (p<0.05) was effectively lowered by the eye drops (p<0.05). As anticipated, the number of RGCs decreased significantly following 8 weeks of elevated IOP (p<0.05), while treatment with combination compounds markedly improved RGC survival (p<0.05). 2D-PAGE and Western blot analyses revealed an IOP-dependent expression of crystallin cry-βb2. Microarray and qRT-PCR analyses verified the results at the mRNA level. IHC demonstrated that crystallins were expressed mainly in the ganglion cell layer. The data suggest that IOP and either topically applied antiglaucomatous drugs influence crystallin expression within the retina. Neuronal crystallins are thus suitable biomarkers for monitoring the progression of neuropathy and evaluating any neuroprotective effects.

Neuroprotection in glaucoma

Glaucoma is a neurodegenerative disease characterized by loss of retinal ganglion cells and their axons. Recent evidence suggests that intraocular pressure (IOP) is only one of the many risk factors for this disease. Current treatment options for this disease have been limited to the reduction of IOP; however, it is clear now that the disease progression continues in many patients despite effective lowering of IOP. In the search for newer modalities in treating this disease, much data have emerged from experimental research the world over, suggesting various pathological processes involved in this disease and newer possible strategies to treat it. This review article looks into the current understanding of the pathophysiology of glaucoma, the importance of neuroprotection, the various possible pharmacological approaches for neuroprotection and evidence of current available medications.

Effect of angiotensin II type 1 receptor blocker, candesartan, and beta 1 adrenoceptor blocker, atenolol, on brain damage in ischemic stroke

This work aims at studying the possible alteration of renal renin secretion after human ischemic stroke and correlating it to the post stroke neurological and renal function alterations using angiotensin II type 1(AT1) receptor blocker (ARB), candesartan, and beta 1 adrenoreceptor blocker atenolol, which inhibits renin secretion, in Wistar rats subjected to middle cerebral artery occlusion. Methods . This study comprised 21 patients with cerebral ischemic stroke. Seventeen normal persons were used for comparison. Recumbent and standing plasma renin activity (PRA), reflex plasma renin sensitivity, plasminogen activator inhibitor and creatinine clearance (Ccr) were estimated at admission and two weeks later. Moreover, 60 male Wistar rats were divided into two groups SHAM and ischemic. Each of the two groups was further subdivided into three subgroups, non-treated, atenolol treated, and candesartan treated. In all rats, mean arterial blood pressure (MAP), systolic blood pressure (SBP), diastolic blood pressure (DBP), pulse pressure (PP), heart rate (HR), neurobehavioral evaluation, Ccr, PRA, and infarct size were measured. Results . Together with the significant deterioration of the neurological score, focal cerebral ischemia in rats resulted in increased PRA and decreased glomerular filtration rate (GFR). In ischemic stroke patients, GFR was significantly decreased at admission and two weeks later, PRA increased at admission and two weeks later while plasma renin reflex secretion sensitivity had decreased significantly at admission relative to controls, but it increased significantly 2 weeks later. Atenolol caused significant improvement of the neurobehavioral score and renal function and decrease infarct size of rats subjected to focal cerebral ischemia whereas candesartan caused significant improvement of the neurobehavioral score and decreased infarct size with no significant change in GFR. Neither atenolol nor candesartan caused significant change in MAP, SBP, DBP, PP and HR Conclusion . (1) Ischemic stroke seems to be associated with a postischemic increase of the plasma renin secretion, which may increase the infarct size in the brain and may induce acute renal insufficiency. (2) This study confirms that Atenolol and ARBs could benefit ischemic stroke patients without altering blood pressure.

Effect of catechol-O-methyltransferase polymorphism on response to propranolol therapy in chronic musculoskeletal pain: a randomized, double-blind, placebo-controlled, crossover pilot study

INTRODUCTION

Three common haplotypes in the gene encoding catechol-O-methyltransferase (COMT) have been associated with pain modulation and the risk of developing chronic musculoskeletal pain, namely temporomandibular disorder (TMD). Haplotypes coding for higher enzymatic activity were correlated with lower pain perception. Rodent studies showed that COMT inhibition increases pain sensitivity through beta2/3-adrenergic receptors. We hypothesized that the nonselective beta-adrenergic antagonist propranolol will reduce clinical and experimental pain in TMD patients in a manner dependent on the individuals' COMT diplotype.

METHODS

Forty Caucasian female participants meeting the Research Diagnostic Criteria for TMD were genotyped for COMT polymorphisms and completed a randomized, double-blind, placebo-controlled, two-period crossover pilot study. Each period consisted of a baseline assessment week followed by an intervention week (propranolol or placebo). Changes in clinical pain ratings, psychological status, and responses to heat and pressure stimuli between baseline and intervention weeks were compared across periods.

RESULTS

The number of patients reporting a reduction in pain intensity rating was greater during propranolol treatment (P=0.014) compared with placebo. Propranolol significantly reduced a composite pain index (P=0.02) but did not decrease other clinical and experimental pain ratings. When stratified by the COMT high activity haplotype, a beneficial effect of propranolol on pain perception was noted in patients not carrying this haplotype, a diminished benefit was observed in the heterozygotes, and no benefit was noted in the homozygotes.

CONCLUSION

COMT haplotypes may serve as genetic predictors of propranolol treatment outcome, identifying a subgroup of TMD patients who will benefit from propranolol therapy.

Adrenergic dysregulation and pain with and without acute beta-blockade in women with fibromyalgia and temporomandibular disorder

In patients with fibromyalgia syndrome (FMS) and temporomandibular disorder (TMD), stress and pain may chronically enhance sympathetic activity, altering cardiovascular responses and worsening pain. This study examined cardiovascular, epinephrine (EPI), norepinephrine (NE), cortisol and clinical pain responses in 54 female patients with these disorders and 34 controls. In a subsample of 10 FMS, 10 TMD patients and 16 controls, using a counterbalanced, double-blind, crossover design, the same responses were assessed after intravenous administration of low dose propranolol vs placebo. Testing included baseline, postural, speech and ischemic pain stressors. FMS patients showed lesser heart rate (HR) increases to posture challenge but greater blood pressure (BP) increases to postural and speech tasks than controls, as well as higher overall BP and greater total vascular resistance (TVR) than TMDs or controls. TMDs showed higher overall cardiac output and lower TVR than controls. Both FMS and TMD groups showed lower baseline NE than controls, and TMDs showed lower overall EPI and NE levels. Group differences in HR, EPI and NE were abolished after propranolol although BP, CO and TVR differences persisted. In both FMS and TMD, the number of painful body sites and ratings of total clinical pain obtained 4 times during each session were significantly lower after beta-blockade vs placebo.

PERSPECTIVE

These findings support the hypothesis that both FMS and TMD may frequently involve dysregulation of beta-adrenergic activity that contributes to altered cardiovascular and catecholamine responses and to severity of clinical pain. Acute treatment with low-dose propranolol led to short-term improvement in all these domains.

Levobetaxolol hydrochloride: a review of its pharmacology and use in the treatment of chronic open-angle glaucoma and ocular hypertension

Levobetaxolol is a cardioselective beta-blocker that has been demonstrated to reduce intraocular pressure in patients affected with primary open-angle glaucoma and ocular hypertension. Levobetaxolol may be an effective neuroprotectant because of its great capacity to block sodium and calcium influx, which might confer a neuroprotective activity. Experimental and clinical studies have demonstrated the effects of levobetaxolol on ocular hemodynamics and visual field, and the pharmacologic differences between beta-blockers currently used for the treatment of elevated IOP have become of more than academic interest since a number of studies have shown improvements to various extents. Unlike the initially manufactured 0.5% ophthalmic solution, levobetaxolol is suspended in a different delivery vehicle in levobetaxolol ophthalmic suspension, to increase the ocular tolerance and allow a similarity of effect with a 2-fold reduced concentration (0.25%).

Hypoxia-induced retinal ganglion cell death and the neuroprotective effects of beta-adrenergic antagonists

Hypoxia-induced retinal ganglion cell (RGC) death has been implicated in glaucomatous optic neuropathy. However, the precise mechanism of death signaling and how neuroprotective agents affect it are still unclear. The aim of this study is to characterize the mechanisms of hypoxia-induced apoptosis of cultured purified RGCs and to study the neuroprotective effects of beta-adrenergic antagonists. Rat RGCs were purified utilizing a modified two-step immuno-panning procedure. First, the extent of apoptosis in RGCs under hypoxia was quantified. Next, the effects of glutamate-channel antagonists (MK801 or DNQX), Bax inhibiting peptide (BIP), and beta-adrenergic antagonists (betaxolol, nipradilol, timolol or carteolol) on hypoxia-induced RGC death were investigated by the cell viability assay. Third, the effects of beta-adrenergic antagonists on hypoxia-induced increase of intracellular calcium concentrations ([Ca(2+)](i)) and the additional effect of NO scavenger to nipradilol were evaluated. Apoptotic RGC percentages under hypoxia were significantly increased compared to the control. The viability of RGCs under hypoxia was not affected by MK801 or DNQX, whereas it was increased in a dose-dependent manner with exposure to BIP, and to betaxolol, nipradilol, timolol, but not to carteolol. These effective beta-adrenergic antagonists showed no significant change in hypoxia-induced [Ca(2+)](i) levels. The NO scavenger alleviated neuroprotective effect by nipradilol. In conclusion, purified RGC damage induced by hypoxia involves Bax-dependent apoptotic pathway, but mostly independent of glutamate receptor-mediated excitotoxicity. Betaxolol, timolol and nipradilol showed a protective effect against hypoxia-induced RGC death, which was thought to be irrelevant either to calcium channel or beta-adrenoceptor blocking effects.

Beta-adrenoreceptor antagonists attenuate brain injury after transient focal ischemia in rats

Beta-adrenoreceptor antagonists experimentally reduce cardiac and renal injury after ischemia and are also clinically useful for myocardial infarction and severe burns. In addition, beta-adrenoreceptor antagonists provide neuroprotective effects after focal cerebral ischemia in experimental settings. We conducted the present study to compare the neuroprotective effects of several beta-adrenoreceptor antagonists in rat transient focal cerebral ischemia. Halothane-anesthetized normothermic adult male Sprague-Dawley rats were subjected to 2 h of middle cerebral artery occlusion using the intraluminal suture technique confirmed by laser Doppler flowmetry. Rats received an IV infusion of saline 0.5 mL/h, propranolol 100 microg x kg(-1) x min(-1), carvedilol 4 microg x kg(-1) x min(-1), esmolol 200 microg x kg(-1) x min(-1), or landiolol 50 microg x kg(-1) x min(-1) (n = 6 in each group). Infusion was initiated 30 min before middle cerebral artery occlusion and continued for 24 h. Additional rats received esmolol 50 microg x kg(-1) x min(-1) or landiolol 10 microg x kg(-1) x min(-1) intrathecally (IT) via the cisterna magna (n = 5 in each group), according to the same experimental protocol. The neurological deficit score was evaluated at 22 h after reperfusion, and the brains were removed and stained with triphenyltetrazolium chloride for evaluation of infarct volume. Additional rats that received saline, esmolol, and landiolol IV (n = 6 in each group) were allowed to survive for 7 days followed by measurement of infarct size. Neurological deficit scores were smaller in rats treated with propranolol-IV, carvedilol-IV, esmolol-IV, landiolol-IV, esmolol-IT, and landiolol-IT compared with saline-treated rats (P < 0.05). Cortical and striatum infarct volumes were less in the rats receiving beta-adrenoreceptor antagonists via either IV or IT than in saline-treated rats (P < 0.05). We conclude that beta-adrenoreceptor antagonists improve neurological and histological outcomes after transient focal cerebral ischemia in rats independent of administration route.

Nitric oxide synthase in retina and optic nerve head of rat with increased intraocular pressure and effect of timolol

We investigated the expression of nitric oxide synthase (NOS) isoforms -1, -2 and -3 in the retina and optic nerve head (ONH) in an experimental rat model of elevated intraocular pressure (IOP) before and after treatment with timolol, to assess whether its neuroprotective action is associated with the activity of these enzymes. Episcleral vein cauterization in unilateral eyes of Wistar rats was performed to produce elevated IOP. Histological sections of retina and ONH from animals with normal IOP, with elevated IOP, and elevated IOP treated with timolol, were studied by immunohistochemistry with antibodies to NOS-1, NOS-2, and NOS-3. In the control rats, NOS-1 was localized to photoreceptor inner segments, amacrine cells and bipolar cells in the retina, and in astrocytes, pericytes and vascular nitrergic terminals in the ONH. NOS-3 immunostaining localized to the endothelial cells. The rats with elevated IOP showed increased expression of NOS-1 in the plexiform layers of the retina and reactive astrocytes in the ONH. These cells also showed NOS-2 positivity. The rats treated with timolol showed reduced expression of NOS-1 in the retina and ONH. NOS-2 was only detected in a few groups of astrocytes in the ONH. NOS-3 was unchanged in both elevated IOP and timolol-treated groups. These results show that excessive levels of NO synthesized by the NOS-1 and -2 isoforms, considered neurotoxic, might contribute to the progressive lesions of retinal ganglion cell axons. Their reduction after treatment suggests a possible neuroprotective effect of timolol in neurons exposed to excessive amounts of NO.

Protective effects of betaxolol in eyes with kainic acid-induced neuronal death

In the present study, we investigated whether betaxolol, a selective beta1-adrenoceptor antagonist, has neuroprotective effect on kainic acid (KA)-induced retinal damage. Neurotoxicities were induced in adult male rats by intravitreal injection of KA (total amount, 6 nmol). To examine the neuroprotective effects of betaxolol, rats were pretreated with betaxolol topically 60 min before KA injection to the rat eyes and twice daily for 1, 3, and 7 days after KA injection. The neuroprotective effects of betaxolol were estimated by measuring the thickness of the various retinal layers, and by counting the number of choline acetyltransferase (ChAT)- and tyrosine hydroxylase (TH)-positive cells in each retinal layer. The retina is highly vulnerable to KA-induced neuronal damage. Morphometric analysis of retinal damage in KA injected eyes, the thickness of the retinal layers decreased markedly after KA injection period of both 3 and 7 days. Furthermore, the numbers of ChAT- and TH-positive cells were significantly reduced by intravitreal injection of KA. However, when two drops of betaxolol, once before KA injection and twice daily for 7 days after KA injection, were continuously administered, the reductions in the retinal thickness and the retinal ChAT- and TH-positive cells were significantly attenuated. The present study suggests that topically applied betaxolol has neuroprotective effect on the retinal cell damage due to KA-induced neurotoxicity.

Effects of β-adrenoceptor antagonists in the neural nitric oxide release induced by electrical field stimulation and sodium channel activators in the rabbit corpus cavernosum

Beta-Adrenoceptor antagonists may present receptor-independent mechanisms, such as blockade of voltage-gated sodium channels. This study aimed to investigate the effects of non-selective (propranolol), and selective beta1- (atenolol, metoprolol and betaxolol) and beta2-adrenoceptor (ICI 118,551) antagonists in the nitric oxide (NO)-mediated rabbit corpus cavernosum relaxations induced by either electrical field stimulation (EFS) or activators of voltage-gated sodium channels. The sodium channel blockers tetrodotoxin and saxitoxin abolished the relaxations induced by EFS or sodium channel activators of binding site-2 (aconitine and veratridine), site-3 (Ts3 toxin), site-4 (Ts1 toxin) and site-5 (brevetoxin-3). The beta-adrenoceptor antagonists failed to affect the relaxations induced by EFS, aconitine and veratridine. Relaxations induced by Ts3 and Ts1 toxins, as well as brevetoxin-3, were markedly reduced by prior addition of propranolol, betaxolol and ICI 118,551. During the established relaxation induced by Ts3 toxin, propranolol failed to restore the basal tone. In conclusion, beta-adrenoceptor antagonists may cause an allosteric inhibition at the binding site-3, -4 and -5 of voltage-gated sodium channels, leading to blockade of neural NO release.

Migraine prophylactic drugs work via ion channels

In recent decades, the concept of a vascular origin of migraine has been replaced by theories based on a neuronal pathophysiology. These theories all involve rapid changes in the functioning of the brain, particularly the brain stem, and the trigeminal nerves. While such paroxysmal changes in function could be the result of altered synaptic transmission, or other physiological changes, they could also be due to changes in the function of voltage-regulated sodium and calcium ion channels. Support for this view of migraine as a channelopathy comes from an examination of the likely mechanism of action of migraine prophylactic drugs. It is the present hypothesis that most of the widely used drugs for migraine prevention work by inhibiting the function of one or both of these ion channels. A review of the laboratory research done on most of the commonly used migraine prophylactic drugs, divided into five classes, reveals that they all may work on sodium channels, calcium channels, or both. If this is the common mechanism of action of migraine prophylactics, it should lead toward the development of more effective prophylactic drugs.

Invited Review: Neuroprotective Properties of Certain β-Adrenoceptor Antagonists Used for the Treatment of Glaucoma

Although it is known that ganglion cell death causes loss of vision in glaucoma, the pathogenesis of the disease is complex, probably involving an initial ischemic insult to the ganglion cell axons and glial cells with the ganglion cell bodies eventually being affected. It may therefore be necessary to blunt many stages in the pathogenesis of the disease to obtain a clinically effective neuroprotective strategy. In animal experiments, one cause of ganglion cell death in ischemia is an overactivation of glutamate receptors and a subsequent rise in intracellular levels of sodium and calcium ions as well as a generation of reactive oxygen species. In contrast, optic nerve death in ischemia is mainly caused by an influx of sodium and reversal of the sodium/calcium exchanger, which leads to a rise in intracellular calcium. Thus, a substance that reduces the influx of sodium will protect the ganglion cell axon, and if it also reduces calcium influx and/or acts as an antioxidant it will protect the ganglion cell body in addition. Of all antiglaucoma drugs, only beta-blockers have both calcium and sodium channel blocking activity, with betaxolol being the most efficacious of those analyzed. In addition, of the tested ophthalmic beta-blockers only metipranolol has powerful antioxidant properties. Moreover, laboratory studies on rats have shown that topically applied beta-blockers attenuate ischemic injury to ganglion cells by mechanisms that do not appear to involve an action on beta-receptors. Thus, of the substances used to lower intraocular pressure in glaucoma, beta-blockers have unique additional characteristics that also give them the capacity to act as neuroprotectants.

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.

Control of programmed cell death by neurotransmitters and neuropeptides in the developing mammalian retina

It has long been known that a barrage of signals from neighboring and connecting cells, as well as components of the extracellular matrix, control cell survival. Given the extensive repertoire of retinal neurotransmitters, neuromodulators and neurotrophic factors, and the exhuberant interconnectivity of retinal interneurons, it is likely that various classes of released neuroactive substances may be involved in the control of sensitivity to retinal cell death. The aim of this article is to review evidence that neurotransmitters and neuropeptides control the sensitivity to programmed cell death in the developing retina. Whereas the best understood mechanism of execution of cell death is that of caspase-mediated apoptosis, current evidence shows that not only there are many parallel pathways to apoptotic cell death, but non-apoptotic programs of execution of cell death are also available, and may be triggered either in isolation or combined with apoptosis. The experimental data show that many upstream signaling pathways can modulate cell death, including those dependent on the second messengers cAMP-PKA, calcium and nitric oxide. Evidence for anterograde neurotrophic control is provided by a variety of models of the central nervous system, and the data reviewed here indicate that an early function of certain neurotransmitters, such as glutamate and dopamine, as well as neuropeptides such as pituitary adenylyl cyclase-activating polypeptide and vasoactive intestinal peptide is the trophic support of cell populations in the developing retina. This may have implications both regarding the mechanisms of retinal organogenesis, as well as pathological conditions leading to retinal dystrophies and to dysfunctional cellular behavior.

Treatment of ischemic optic neuropathy

Ischemic damage of the optic nerve has no proven effective treatment. While ischemia related to vasculitis (arteritic) is treated with systemic corticosteroids, the primary goal is to prevent further damage, either in the affected or fellow eye. Thrombolytic or anticoagulation supplementive therapy may be considerations for the future. In the more common idiopathic (nonarteritic) form (NAION), multiple attempts at therapy, including systemic corticosteroids, anticoagulants and antiplatelet agents, diphenylhydantoin, hyperbaric oxygen, and optic nerve sheath decompression have been unsuccessful. The use of levodopa has been proposed but is unproven. Megadose intravenous corticosteroid therapy has not been studied in a systematic way. Neuroprotective strategies are under intense investigation for optic neuropathies including NAION, and clinical trials in humans are in progress. Optic nerve regeneration studies are ongoing in animals. Prophylaxis in NAION is unproven.

Binding affinities of ocular hypotensive beta-blockers levobetaxolol, levobunolol, and timolol at endogenous guinea pig beta-adrenoceptors

The current study determined the relative affinities and selectivities of numerous beta-adrenoceptor antagonists at the endogenous beta(1)- and beta(2)-adrenoceptors in guinea pig heart and lung, respectively, using [(3)H]-CGP12177. Specific binding of [(3)H]-CGP12177 comprised 80 +/- 0.2% (n = 11) and 94 +/- 0.2% (n = 16) of the total binding in washed heart and lung homogenates, respectively. Concentration-dependent displacement of [(3)H]-CGP12177 binding from beta-adrenoceptors in both preparations was observed with nine different beta-adrenoceptor antagonists. Levobetaxolol, betaxolol, CGP-20712A, levobunolol, and timolol yielded bi-phasic (two-site-fit) competition curves in the heart, while CGP-20712A, ICI-118551 and levobunolol produced bi-phasic curves in the lung preparation. The high-affinity component of [(3)H]-CGP12177 binding in the heart and lung reflected binding to beta(1)-receptors and beta(2)-receptors, respectively. The binding inhibition parameters (IC(50)s) for displacement of [(3)H]-CGP12177 from these predominantly high-affinity sites were: levobetaxolol (24.9 +/- 1.6 nM heart, 4810 +/- 367 nM lung), racemic betaxolol (37.9 +/- 8.7 mM heart; 8840 +/- 424 mM lung), CGP-20712A (4.6 +/- 0.9 nM heart; 171,000 +/- 109,000 nM lung), ICI-118551 (9230 +/- 3240 nM heart; 2.9 +/- 0.6 nM lung), levobunolol (42 +/- 15 nM heart, 0.3 +/- 0.2 nM lung), (l)-timolol (3.1 nM heart, 2.9 +/- 1.5 nM lung), ICI-215001 (5840 +/- 114 nM heart; 26100 +/- 3200 nM lung), BRL-37344 (83,300 +/- 2660 nM heart; 13,200 +/- 1250 lung). These data indicated that while levobetaxolol and betaxolol possessed a 193-233-fold selectivity for beta(1)-receptors, levobunolol exhibited a 140-fold beta(2)-receptor selectivity and (l)-timolol was essentially nonselective.

Are there any benefits of Betoptic S (betaxolol HCl ophthalmic suspension) over other beta-blockers in the treatment of glaucoma?

The cardioselective beta-blocker, betaxolol, is an effective ocular antihypertensive agent. Its mode of action in lowering intraocular pressure is similar to that of the nonselective blockers, by suppressing the flow of aqueous humor. The most frequent adverse reaction to betaxolol is stinging upon administration, which is minimised by an ocular suspension with a similarly effective twofold reduced concentration (Betoptic S, 0.25%). The extent of beta 1-adrenoceptor occupancy of topically applied betaxolol in the systemic circulation is less than that of the nonselective blockers and beta 2-receptor occupancy is negligible, providing a better safety profile in patients with cardiopulmonary disease. Experimental studies have revealed that the drug reaches the retina after topical administration and displays a voltage-dependent L-type calcium channel blocking activity, which probably allows betaxolol to improve retinal perfusion and to serve as a neuroprotective agent recommendable in various forms of glaucoma.

Effectiveness of levobetaxolol and timolol at blunting retinal ischaemia is related to their calcium and sodium blocking activities: relevance to glaucoma

Glaucoma is a chronic optic neuropathy in which retinal ganglion cells die over a number of years. The initiation of the disease and its progression may involve an ischaemic-like insult to the ganglion cell axons caused by an alteration in the quality of blood flow. Thus, to effectively treat glaucoma it may be necessary to counteract the ischaemic-like insult to the region of the optic nerve head. Studies on the isolated optic nerve suggest that substances that reduce the influx of sodium would be particularly effective neuroprotectants. Significantly, of the presently used antiglaucoma substances, only beta-blockers can reduce sodium influx into cells. Moreover, they also reduce the influx of calcium and this would be expected to benefit the survival of insulted neurones. Betaxolol is the most effective antiglaucoma drug at reducing sodium/calcium influx. Our electroretinographic data indicated that topical application of levobetaxolol to rats attenuated the effects of ischaemia/reperfusion injury. Timolol was also effective but to a lesser extent. Based on these data we conclude that beta-blockers may be able to blunt ganglion cell death in glaucoma, and that levobetaxolol may be a more effective neuroprotectant than timolol because of its greater capacity to block sodium and calcium influx.

Vasodilating beta-adrenoceptor blockers as cardiovascular therapeutics

beta-Adrenoceptor blocking agents (beta-blockers) have been established as therapeutics for treatment of patients with hypertension, ischemic heart diseases, chronic heart failure, arrhythmias, and glaucoma. However, their clinical use is limited because some patients are adversely affected by their side effects. The discovery of cardioselective (beta(1)-selective) blockers has overcome some of the problems. Current retrospective studies have revealed that vasodilating beta-blockers (so-called beta-blockers of the third generation) have advantages over the conventional type of beta-blockers in terms of minimizing the adverse effects and improving the disease-derived dysfunction, thus enhancing the quality of life variables. Some of the possible advantages include improvement of insulin resistance, decrease in low-density lipoprotein cholesterol in association with increase in high-density lipoprotein cholesterol, attenuation of bronchial asthma attack and respiratory dysfunction, alleviation of coronary vasospasm provocation, peripheral circulatory disturbances, and erectile dysfunction, and better patient compliance. Release of nitric oxide, antioxidant action, beta(2)-adrenoceptor activation, Ca(2+) entry blockade, and other mechanisms underlying the vasodilating action may be responsible for the beneficial therapeutic effects of these agents.

Bunazosin hydrochloride reduces glutamate-induced neurotoxicity in rat primary retinal cultures

To study neuroprotective effects of bunazosin hydrochloride which is an alpha(1)-adrenoceptor antagonist used as an ocular hypotensive drug compared to other alpha(1)-adrenoceptor antagonists, and its mechanism of action. We evaluated the neuroprotective effects of bunazosin hydrochloride or seven other alpha(1)-adrenoceptor antagonists against glutamate-induced cell death in rat primary retinal cultures. We also evaluated the binding inhibition of bunazosin hydrochloride for 24 different receptors/channels and its effects on the Na(+) influx into cells induced by veratridine or glutamate. Bunazosin hydrochloride significantly inhibited glutamate-induced cell death at concentrations of 1 and 10 microM. Cells were also protected when treated with some alpha(1)-adrenoceptor antagonists, but not by the others. Bunazosin hydrochloride showed a high inhibition for Na(+) channels and inhibited the Na(+) influx induced by veratridine or glutamate. These findings indicate that in retinal cultures bunazosin hydrochloride has a neuroprotective effect against glutamate-induced cell death and that the inhibition of Na(+) channels by bunazosin hydrochloride may be partly responsible for this effect.

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.

Zinc and energy requirements in induction of oxidative stress to retinal pigmented epithelial cells

In age-related macular degeneration (AMD), retinal pigmented epithelium (RPE) cells are believed to be detrimentally affected. It is thought that zinc may play a part in this process. In the past, therefore, zinc supplementation has been suggested as a treatment for AMD. Experimental data shown here confound this view by indicating that whereas low amounts of zinc do protect RPE cells in culture from stress-induced effects, greater amounts of zinc have the opposite influence. These effects are partly dependent upon the "health status" of the cells. Experimental data presented herein also show that zinc-induced death of RPE cells can, however, be attenuated by compounds such as antioxidants (alpha-tocopherol, trolox, and metipranolol), or cellular energy substrates (pyruvate and oxaloacetate). It is therefore concluded that a combination of zinc and antioxidants or energy substrates rather that zinc alone should provide a safer and more effective way to treat a disease such as AMD.

Metipranolol attenuates lipid peroxidation in rat brain: a comparative study with other antiglaucoma drugs

BACKGROUND

Free radical production seems to be involved in the pathogenesis of a number of ocular diseases. Certain beta-adrenoceptor antagonists display antioxidant properties, but these have not been ascribed to any of the presently used ophthalmic beta-adrenoceptor antagonists. Therefore, we examined the influence of ophthalmic beta-adrenoceptor antagonists and other antiglaucoma drugs on stimulated lipid peroxidation in rat brain homogenates.

METHODS

Lipid peroxidation in rat brain homogenates was stimulated by iron/ascorbate or sodium nitroprusside. Lipid peroxidation was assessed by the formation of thiobarbituric acid reactive species (TBARS).

RESULTS

Of the antiglaucoma drugs tested (brimonidine, carteolol, dorzolamide, latanoprost, levobetaxolol, levobunolol, metipranolol, pilocarpine, timolol, travoprost and unoprostone), only metipranolol and its active metabolite, desacetylmetipranolol, were found to significantly reduce iron/ascorbate-induced lipid peroxidation in rat brain homogenates with IC50 values of 6.9 and 1.1 microM, respectively. Metipranolol and desacetylmetipranolol also concentration-dependently inhibited sodium nitroprusside-stimulated lipid peroxidation in rat brain homogenates, displaying IC50 values of 25.1 and 2.6 microM, respectively.

CONCLUSION

These data indicate that metipranolol and desacetylmetipranolol exhibit remarkable antioxidant properties, with an effect not dissimilar from the reference antioxidant trolox.

Beta-adrenergic receptor agonists and antagonists counteract LPS-induced neuronal death in retinal cultures by different mechanisms

Treatment with lipopolysaccharide (LPS) for 72 h was shown to dose-dependently increase nitric oxide production from 6-day-old retinal cultures. Cell death, as determined by lactate dehydrogenase (LDH) release and an increase in neuronal labelling for TUNEL, was elevated concurrently. During treatment there was an increase of both inducible nitric oxide synthase and glial fibrillary acidic protein labelling in glial cells and a reduction in the number of gamma-aminobutyric acid-positive neurones. The NOS inhibitors, N-nitro-L-arginine methyl ester, dexamethasone and indomethacin potently inhibited both nitric oxide stimulation and cell death caused by LPS. In this study, the beta(2)- (ICI-18551), beta(1)- (betaxolol) and mixed beta(1)/beta(2)- (timolol, metipranolol) adrenergic receptor antagonists were all shown to attenuate LPS-induced LDH release from these cultures, but to have no effect on LPS-stimulated nitric oxide production. This effect was mimicked by the calcium channel blocker, nifedipine. Interestingly, the beta-adrenergic receptor agonists, salbutamol, arterenol and isoproterenol were also able to attenuate cell death caused by LPS. Moreover, these compounds also inhibited LPS-stimulated nitric oxide release. These studies suggest that LPS stimulates nitric oxide release from cultured retinal glial cells and that this process leads to neurone death. beta-adrenergic receptor agonists prevent the effects of LPS by inhibiting the stimulation of nitric oxide production. The data also suggest that beta-adrenergic receptor antagonists can attenuate LPS-induced death of neurones, but that these compounds act in a manner that is neurone-dependent, is mimicked by blockade of calcium channels and is independent of the stimulation of nitric oxide release.

Randomized clinical trial of topical betaxolol for persistent macular edema after vitrectomy and epiretinal membrane removal

PURPOSE

To report the efficacy and safety of topical betaxolol for treatment of persistent macular edema.

DESIGN

Randomized clinical trial.

METHODS

Thirty-seven eyes (37 patients) with best-corrected visual acuity between 20/200 and 20/50 and macular edema that remained for 3 months after vitrectomy and removal of epiretinal membrane were prospectively, randomly assigned to receive betaxolol or placebo. Nineteen eyes of 19 patients received betaxolol twice daily, and 18 eyes of 18 patients received placebo as a randomized comparison group. The patients were followed up for 6 months. This study evaluated the effect of betaxolol on best-corrected visual acuity and area of macular edema, which was digitally measured on serial fluorescein angiogram. Calculations of mean best-corrected visual acuity were based on logarithm of the minimal angle of resolution (logMAR). To assess changes in area of edema, the initial (pretreatment) size of the edema was set to 100%, and all posttreatment measurements were normalized relative to the initial size.

RESULTS

Mean best-corrected visual acuity at baseline was 0.216 (20 of 92.6) and 0.244 (20 of 82.0) in the treatment and control group, respectively. Mean area of macular edema was 2.271 +/- 1.629 mm(2) and 2.273 +/- 1.209 mm(2) in the treatment and control group; there was no significant difference. The visual acuity at 6 months after the start of the follow-up was 0.471 (20 of 42.5) in the treatment group and 0.236 (20 of 84.7) in the control group. Mean changes in logMAR of visual acuity for 3- and 6-month follow-up were -0.282 +/- 0.191 and -0.337 +/- 0.197 in the treatment group, and -0.016 +/- 0.186 and +0.015 +/- 0.267 in the control group; a significant difference was found (P <.0001; P <.0001). Areas of macular edema at 6 months after the start of the follow-up were 1.492 +/- 1.357 mm(2) in the treatment group and 2.125 +/- 1.434 mm(2)in the control group. Mean change in area of the edema for 6 months were 76.5% +/- 24.1% and 63.4% +/- 28.3% in the treatment group and 92.9% +/- 15.4% and 87.4% +/- 25.6% in the control group; treated patients showed a significantly larger reduction than untreated patients at each examination (P =.0193; P =.0102). No complication associated with treatment or placebo was found.

CONCLUSIONS

Topical betaxolol appeared to have a favorable treatment effect in eyes with macular edema that remained after vitrectomy and removal of epiretinal membrane. Further investigation of more cases and longer follow-up are needed.

The beta-adrenoceptor antagonists metipranolol and timolol are retinal neuroprotectants: comparison with betaxolol

beta-adrenoceptor antagonists are used clinically to reduce elevated intraocular pressure in glaucoma which is characterised by a loss of retinal ganglion cells. Previous studies have shown that the beta(1)-selective adrenoceptor antagonist, betaxolol, is additionally able to protect retinal neurones in vitro and ganglion cells in vivo from the detrimental effects of either ischemia-reperfusion or from excitotoxicity, after topical application. The neuroprotective effect of betaxolol is thought not to be elicited through an interaction with beta-adrenoceptors, but by its ability to reduce influx of sodium and calcium through voltage-sensitive calcium and sodium channels. In the present study it is shown that the non-selective beta-adrenoceptor antagonists, metipranolol and timolol behave like betaxolol. When topically applied they all attenuate the detrimental effect of ischemia-reperfusion. Protection of the retina was determined by evaluating changes in the electroretinogram and by assessing the loss of mRNA for Thy-1, which is expressed in retinal ganglion cells. In addition, studies conducted on neurones in mixed retinal cultures demonstrated that metipranolol, betaxolol and timolol were all able to partially counteract anoxia-induced cell loss and viability reduction. The influence of timolol was, however, not significant. Within the confines of these investigations, an order of neuroprotective efficacy was delineated for the three beta-adrenoceptor antagonists: betaxolol>metipranolol>timolol. The ability of the beta-adrenoceptor antagonists to attenuate ligand-induced stimulation of calcium and sodium entry into neuronal preparations showed a similar order of effectiveness. In conclusion, the ability to confer neuroprotection to retinal neurones is a common feature of three ophthalmic beta-adrenoceptor antagonists (betaxolol, metipranolol and timolol). A comparison of the effectiveness of the individual compounds in protecting retinal cells in vivo was not possible in these studies. However, in vitro studies show that the capacity of the individual beta-adrenoceptor antagonists to act as neuroprotectants appears to relate to their capacity to attenuate neuronal calcium and sodium influx.

Some current ideas on the pathogenesis and the role of neuroprotection in glaucomatous optic neuropathy

The primary features of glaucomatous optic neuropathy are characteristic changes in the optic nerve head, a decrease in number of surviving ganglion cells and a reduction in vision. It is now generally accepted that a number of factors, including elevated intraocular pressure, could lead to the changes seen in the optic nerve head and to obtain a pharmacological means to treat the causes will vary from patient to patient. In contrast, a cascade of events have been proposed to explain how the changes in the optic nerve head may lead to the slow and differential death of ganglion cells in the disease. It is also proposed that drugs (neuroprotectants) influencing this cascade of events can attenuate ganglion cell death and lead to the treatment of all glaucoma patients.

Different ability of clenbuterol and salbutamol to block sodium channels predicts their therapeutic use in muscle excitability disorders

Activation of muscle beta(2)-adrenergic receptors successfully counteracted sarcolemma inexcitability in patients suffering from hyperkalemic periodic paralysis (HPP), a hereditary disease caused by mutations in the gene encoding the skeletal muscle sodium channel. Looking for potential modulation of these channels by beta(2)-adrenergic pathway using patch-clamp technique, we found that clenbuterol blocked sodium currents (I(Na)) in rat skeletal muscle fibers and in tsA201 cells transfected with the human channel isoform, whereas salbutamol did not. The effects of clenbuterol were independent of beta-adrenoceptor stimulation. Instead, clenbuterol structure and physicochemical characteristics as well as I(Na) blocking properties resembled those of local anesthetics, suggesting direct binding to the channels. Similar experiments with the chemically similar beta-antagonists propranolol and nadolol, suggested the presence of two hydroxyl groups on the aromatic moiety of the drugs as a molecular requisite for impeding sodium channel block. Importantly, clenbuterol use-dependently inhibited action potential firing in rat skeletal muscle fibers, owing to beta-adrenoceptor-independent I(Na) block. From a clinical point of view, our study defines the rationale for the safe use of salbutamol in HPP patients, whereas clenbuterol may be more indicated in patients suffering from myotonic syndromes, a condition characterized by sarcolemmal overexcitability, because use-dependent I(Na) block can inhibit abnormal runs of action potentials.

Betaxolol, a beta1-adrenoceptor antagonist, protects a transient ischemic injury of the retina

In the present study, we investigated the protective effects of the topical beta-adrenoceptor antagonist Betoptic((R)) (0.25% betaxolol) in the rat retina following the ischemic injury induced by a transient increase of intraocular pressure (IOP). Like other areas of the central nervous system, the retina is highly vulnerable to ischemic-induced injury. Ischemia was induced in the rat retina by raising the IOP above the systolic blood pressure for 60min. After an ischemia/reperfusion, the thickness of the retinal layers and the immunoreactivities of choline acetyltransferase (ChAT), gamma-amino butyric acid (GABA) and tyrosine hydroxylase (TH) were examined. After a reperfusion period of 7 days, the thickness of both the inner plexiform layer and inner nuclear layer was much decreased. After a reperfusion period of 14-28 days, the thickness of the outer nuclear layer decreased markedly. Moreover, the ChAT and TH immunoreactivity had almost completely disappeared in the retinas after 7 days, while GABA immunoreactivity remained for 28 days. These results suggest that the inner retinal layers are more susceptible to ischemic-induced injury than the outer retinal layer.Histological examination demonstrated protective effects of betaxolol on ischemic-induced retinal damage, which was more substantial in the inner retinal layer. When two drops of betaxolol, once before ischemic injury and twice daily for 28 days after ischemia, were continuously administered, the reductions in the retinal ChAT, GABA and TH immunoreactivities were significantly attenuated. The present study suggests that topically applied betaxolol is an efficient neuroprotective agent and prevents the retinal cell damage induced by ischemic injury in rats.