Nitric oxide-generating beta-adrenergic blocker nipradilol preserves postischemic cardiac function

Does the ADMA/DDAH/NO pathway modulate early regression of left ventricular hypertrophy with esmolol?

Hypertensive left ventricular hypertrophy (LVH) is a maladaptive response to chronic pressure overload and a strong independent risk factor for cardiovascular disease. Regression of LVH is associated with improved prognosis. Regression of LVH with antihypertensive therapy (angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, beta-blockers, calcium channel blockers, and diuretics) has been reported, although only after long-term treatment. Asymmetrical dimethylarginine (ADMA), the most potent endogenous NO synthase inhibitor, is emerging as an important cardiovascular risk factor in patients with arterial hypertension and LVH, and dimethylarginine dimethylaminohydrolase (DDAH) is the mechanism that most frequently leads to accumulation of ADMA (plasma ADMA is cleared in small part by renal excretion, although the bulk of ADMA is degraded by DDAH). Left ventricular mass is strongly modulated by the NO system. As an important inhibitor of the bioavailability of NO, ADMA is an underlying mechanism of LVH. Beta-blockers can induce regression of LVH and reduced plasma ADMA levels. Oxidative stress is increased in patients with LVH, and this in turn increases generation of ADMA. In a previous preclinical study of spontaneously hypertensive rats, we found that short-term treatment (48 h) with esmolol reverses early LVH, increases the bioavailability of NO, and improves antioxidant status in plasma. Therefore, we propose that the ADMA/DDAH/NO pathway could modulate early regression of LVH with esmolol.

Short-term esmolol improves coronary artery remodeling in spontaneously hypertensive rats through increased nitric oxide bioavailability and superoxide dismutase activity

The aim of this study was to assess the effects of short-term esmolol therapy on coronary artery structure and function and plasma oxidative stress in spontaneously hypertensive rats (SHR). For this purpose, 14-month-old male SHR were treated for 48 hours with esmolol (SHR-E, 300 μg/kg/min). Age-matched untreated male SHR and Wistar Kyoto rats (WKY) were used as hypertensive and normotensive controls, respectively. At the end of intervention we performed a histological study to analyze coronary artery wall width (WW), wall-to-lumen ratio (W/L), and media cross-sectional area (MCSA). Dose-response curves for acetylcholine (ACh) and sodium nitroprusside were constructed. We also assessed several plasma oxidative stress biomarkers, namely, superoxide scavenging activity (SOSA), nitrites, and total antioxidant capacity (TAC). We observed a significant reduction in WW (P < 0.001), W/L (P < 0.05), and MCSA (P < 0.01) and improved endothelium-dependent relaxation (AUC_SHR-E = 201.2 ± 33 versus AUC_SHR = 97.5 ± 21, P < 0.05) in SHR-E compared with untreated SHR; no differences were observed for WW, MCSA, and endothelium-dependent relaxation by ACh at higher concentrations (10⁻⁶ to 10⁻⁴ mol/l) for SHR-E with respect to WKY. SOSA (P < 0.001) and nitrite (P < 0.01) values were significantly higher in SHR-E than in untreated SHR; however, TAC did not increase after treatment with esmolol. Esmolol improves early coronary artery remodeling in SHR.

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

Nipradilol (3,4-dihydro-8-(2-hydroxy-3-isopropylamino)propoxy-3-nitroxy-2H-1-benzopyran) is used clinically as an anti-glaucoma ophthalmic solution in Japan, and was recently reported to suppress N-methyl-d-aspartate-induced retinal damage in rats. Here we investigated cytotoxic and cytoprotective actions of nipradilol on primary cultures of rat cortical neurons. Treatment of cortical cultures with a high concentration (500 microM) of nipradilol significantly reduced cell viability, increased lactate dehydrogenase (LDH) release and nitrite concentration in culture medium, whereas desnitro-nipradilol (3,4-dihydro-8-(2-hydroxy-3-isopropylamino)propoxy-3-hydroxy-2H-1-benzopyran) had no significant effects. Nipradilol-induced neuronal damage was inhibited by S-hexylglutathione, a glutathione S-transferase inhibitor, and FeTPPS (5,10,15,20-tetrakis(4-sulfonatophenyl)prophyrinato iron (III) chloride), a peroxynitrite decomposition catalyst. On the other hand, relatively low concentrations (10-100 microM) of nipradilol but not desnitro-nipradilol prevented neuronal cell death induced by 24 h application of 100 microM glutamate. Importantly, neuroprotective concentration (100 microM) of nipradilol suppressed glutamate-induced elevation of intracellular Ca2+ concentrations, but had no effect on intracellular cyclic GMP levels. Hence, nipradilol can protect cultured cortical neurons against glutamate neurotoxicity via cyclic GMP-independent mechanisms, and nitric oxide (NO) released from the nitoroxy moiety of nipradilol may mediate neuroprotective effect through the modulation of NMDA receptor function.

Cardioprotection afforded by ischemic preconditioning interferes with chronic beta-blocker treatment

OBJECTIVES

The efficacy of ischemic preconditioning of the heart has remained controversial. We investigated whether chronic treatment with beta-blockers affects the ischemic preconditioning in the isolated rat heart model.

DESIGN

Wistar rats were treated with propranolol (50 mg/kg/day, p.o.) (PRL), with nipradilol (10 mg/kg/day, p.o.) (NPL), or with vehicle, for 4 weeks. Isolated rat hearts were divided into global ischemia hearts (GI, PRL and NPL, each n=6) and ischemic preconditioned hearts (IP, PRL+IP and NPL+IP, each n=6).

RESULTS

Significant differences in left ventricular pressure were observed between the PRL and PRL+IP, and between the NPL and NPL+IP groups. In the NPL group, significant amelioration and preservation of left ventricular peak pressure, coronary flow, reduction of infarct size, and NOx preservation were observed. Lipid peroxidation in the NPL group was significantly reduced before and after global ischemia compared to the GI group.

CONCLUSIONS

The effect of ischemic preconditioning was abolished in the hearts of rats following oral treatment of propranolol or nipradilol. However, the administration of nipradilol protected the ischemic and reperfused myocardium, partly due to the prevention of lipid peroxide formation.

Nipradilol inhibits atmospheric pressure-induced cell proliferation in human aortic smooth muscle cells

Hypertension is a major risk factor for atherosclerosis and the genesis of cardiovascular and cerebrovascular diseases. Therefore, the protection of atherosclerosis progression is one of the purpose of an anti-hypertensive treatment in vascular system. Nitric oxide (NO)-releasing drugs have been reported to have an inhibitory effect on shear stress-induced extracellular signal-regulated kinase (ERK) activation in endothelial cells. For further understanding of the effects of these drugs, the present study focused on the effects on intracellular signal transduction and cell proliferation in cultured human aortic smooth muscle cells (HASMC) under high atmospheric pressure. Three hours of 160-mmHg atmospheric pressure resulted in an approximately 380% increase in cell proliferation compared to non-pressurized controls. Nipradilol (3,4-dihydro-8-(2-hydroxy-3-isopropylaminoproxy)-3-nitroxy-2H-1-benzopyran) (10(-6)M) demonstrated approximately 40% reduction in cell proliferation compared to that shown by pressurized HASMC as a vehicle control. Three hours of 160-mmHg atmospheric pressure resulted in a 25% increase in the amount of activated ERKs. Nipradilol (10(-6)M) demonstrated approximately a 26% reduction in the amount of activated ERKs. NO(x) concentration under the presence of nipradilol (10microM) with HASMC resulted in a 7.2microM of NO production and was 2.4-fold more than that from no dug control (3.0microM). An administration of L-NAME (10(-4)M) supplemented with Nipradilol (10(-6)M) did not show any significant effect on cell proliferation. From these observations, we concluded that nipradilol has an anti-proliferative effect on HASMC under high atmospheric pressure. Nipradilol may act as a nitric oxide inducer from HASMC and suspected to work as a supplement to mitigate the impaired endothelial cell function caused by hypertension.

Exogenous NO triggers preconditioning via a cGMP- and mitoKATP-dependent mechanism

Exogenous nitric oxide (NO) triggers a preconditioning-like effect in heart via a pathway that is dependent on reactive oxygen species. This study examined the signaling pathway by which the NO donor S-nitroso-N-acetylpenicillamine (SNAP, 2 microM) triggers its anti-infarct effect. Isolated rabbit hearts experienced 30 min of regional ischemia and 120 min of subsequent reperfusion. Infarct size was determined by triphenyltetrazolium chloride staining. Infarct size was reduced from 30.5 +/- 3.0% of the risk zone in control hearts to 10.2 +/- 2.0% in SNAP-treated hearts. Bracketing the SNAP infusion with either the guanylyl cyclase blocker 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (2 microM) or the mitochondrial ATP-sensitive K(+) (mitoK(ATP)) channel blocker 5-hydroxydecanoate (200 microM) completely blocked the infarct-sparing effect of SNAP (34.3 +/- 3.8 and 32.2 +/- 1.6% infarction, respectively). Pretreatment of hearts with 8-(4-chlorophenylthio)-guanosine 3',5'-cyclic monophosphate (10 microM), which is a cell-permeable cGMP analog that activates protein kinase G, mimicked the preconditioning effect of SNAP by reducing infarct size to 7.5 +/- 1.1% of the risk zone. This salutary effect was abolished by either the free radical scavenger N-(2-mercaptopropionyl)glycine (1 mM) or 5-hydroxydecanoate (100 microM; 28.9 +/- 2.7 and 33.6 +/- 5.0% infarction of the risk zone, respectively). To confirm these functional data and the effect of SNAP on the guanylyl cyclase-protein kinase G signaling pathway, cGMP levels were measured. SNAP increased the level from 0.18 +/- 0.04 to 0.61 +/- 0.14 pmol/mg of protein (P < 0.05). These data suggest that exogenous NO triggers the preconditioning effect by initiating a cascade of events including stimulation of guanylyl cyclase to make cGMP, activation of protein kinase G, opening of mitoK(ATP) channels, and, finally, production of reactive oxygen species.

Anaesthetics and cardiac preconditioning. Part II. Clinical implications

There is compelling evidence that preconditioning occurs in humans. Experimental studies with potential clinical implications as well as clinical studies evaluating ischaemic, pharmacological and anaesthetic cardiac preconditioning in the perioperative setting are reviewed. These studies reveal promising results. However, there are conflicting reports on the efficacy of preconditioning in the diseased and aged myocardium. In addition, many anaesthetics and a significant number of perioperatively administered drugs affect the activity of cardiac sarcolemmal and mitochondrial K(ATP) channels, the end-effectors of cardiac preconditioning, and thereby markedly modulate preconditioning effects in myocardial tissue. Although these modulatory effects on K(ATP) channels have been investigated almost exclusively in laboratory investigations, they may have potential implications in clinical medicine. Important questions regarding the clinical utility and applicability of perioperative cardiac preconditioning remain unresolved and need more experimental work and randomized controlled clinical trials.

Potent adenylate cyclase agonist forskolin restores myoprotective effects of ischemic preconditioning in rat hearts after myocardial infarction

BACKGROUND

The purpose of this study was to determine whether ischemic preconditioning (IPC) provides myoprotective effects in post-myocardial infarction (MI) hearts, and whether beta adrenergic signaling is involved in IPC.

METHODS

Rats were subjected to either ligation of the left anterior descending coronary artery (LAD) resulting in MI, or a sham operation. Two weeks later, hearts were isolated and perfused. Six groups (n = 7 each) were studied: group 1, control (sham operation); group 2, sham operation + IPC; group 3, post-MI; group 4, post-MI + IPC; group 5, post-MI + forskolin; group 6, post-MI + forskolin + IPC. IPC consisted of two cycles of 5 minutes of global ischemia. The adenylate cyclase agonist forskolin (1.0 x 10(-5) M) was administered in post-MI hearts either alone (group 5) or for 5 minutes before IPC (group 6). All hearts were then subjected to 20 minutes of global ischemia followed by 120 minutes of reperfusion, after which infarct size was measured. Concentrations of endogenous catecholamines and myocardial mRNA expression of beta 2 adrenergic receptor were measured in the post-MI model.

RESULTS

(1) IPC reduced infarct size in shams, from 34.7 +/- 5.2% in group 1 to 21.4 +/- 3.8% in group 2, but did not affect infarct size in post-MI hearts (group 3 versus group 4). (2) Forskolin combined with IPC reduced infarct size in post-MI hearts to 29.3 +/- 3.4% (group 6), but not in group 5 where the value was 39.3 +/- 4.8%. (3) Beta 2 adrenergic receptor mRNA expression in post-MI hearts was significantly decreased as compared with sham-operated animals.

CONCLUSIONS

The results indicate that downregulation of beta adrenergic receptors in post-MI hearts may be associated with ineffectiveness of IPC, and that beta adrenergic signaling, especially in relation to adenylate cyclase activation, may be required to generate the IPC response in post-MI hearts.

Gap junction uncoupling protects the heart against ischemia

BACKGROUND

Many stimuli can successfully protect the heart against ischemia. We investigated whether gap junction uncoupling before ischemia was myoprotective. We also studied the function of the adenosine triphosphate-dependent potassium channel, which has been implicated in the mechanism of pharmacologic preconditioning, with respect to gap junction physiology.

METHODS

Twenty-eight rabbit hearts were placed on a Langendorff perfusion apparatus. Five were given a 5-minute infusion of 1 mmol/L heptanol (a gap junction uncoupler), 5 were given 10 micromol/L 2,3-butanedione monoxime (an electromechanical uncoupler), and 6 were given no drug. The left anterior descending coronary artery was then occluded for 1 hour and reperfused for 2 hours. Six hearts received 10 micromol/L glybenclamide before heptanol to evaluate the role of the adenosine triphosphate-dependent potassium channel. Six hearts underwent ischemic preconditioning with 2 cycles of 5 minutes of global ischemia and reperfusion. Action-potential duration of the ischemic zone, left ventricular developed pressure, and coronary flow were measured continuously. Infarct size was determined at the end of reperfusion.

RESULTS

Heptanol significantly reduced infarct size (from 46% +/- 2% to 22% +/- 5%, P <.01), an effect that was not prevented by glybenclamide. Butanedione monoxime decreased developed pressure but did not significantly reduce infarct size (46% +/- 5% vs 46% +/- 2%, P = not significant). There were no differences among groups with regard to developed pressure or action-potential duration.

CONCLUSION

Directly blocking gap junctions preconditions the heart. This protection is not a direct result of a decrease in developed pressure before a prolonged ischemic period nor is it achieved through a mechanism involving the adenosine triphosphate-dependent potassium channel.

Neuroprotective effect of nipradilol on axotomized rat retinal ganglion cells

PURPOSE

To determine whether nipradilol, a new anti-glaucoma drug, can protect retinal ganglion cells (RGCs) from secondary cell death caused by transection of the optic nerve (ON).

METHODS

The ON was transected 0.7 mm from its exit from the eye in Sprague Dawley rats. Nipradilol (1 x 10(-8) - 10(-3) M), timolol, prazosin, or sodium nitroprusside (SNP) (1 x 10(-6) - 10(-4) M) was injected intravitreally fifteen-minutes before the ON transection. Control eyes received the same amount of phosphate buffered (PB). The RGCs were labeled retrogradely by placing gelfoam soaked in fluoro-gold (FG) on the stump of ON. RGCs density was determined by counting the FG-labeled RGCs in flat-mounted retinas 3 to 14 days post-transection. To determine whether the neuroprotective action of nipradilol was due to its NO-donor property, carboxy-PTIO, a NO-scavenger, or KT5832, a protein kinase G inhibitor, was injected with the nipradilol.

RESULTS

After ON transection, the number of surviving RGCs after intravitreal injection of 1 x 10(-4) M nipradilol was significantly higher than that following PB injection. This protective activity was dose-dependent. Neither timolol nor prazosin had a neuroprotective effect but SNP protected RGCs in a dose-dependent manner. Carboxy-PTIO and KT5832 decreased the neuroprotective effect of nipradilol.

CONCLUSIONS

These results indicate that nipradilol has a possibility of neuroprotective effect on axotomized RGCs, and the effect depended mainly on its NO-donor property.

Long-term treatment with nipradilol, a nitric oxide-releasing beta-adrenergic blocker, enhances postischemic recovery and limits infarct size

BACKGROUND

This study examines whether the chronic administration of nipradilol, a nitric oxide-releasing beta-adrenergic blocker, decreases ischemia-reperfusion injury.

METHODS

Rats were treated with nipradilol (10 mg/kg per day orally) or a vehicle alone for 4 weeks. Isolated rat hearts were assigned to one of five groups (each n = 6): global ischemia groups treated with the vehicle or with nipradilol were subjected to 20 minutes of ischemia; ischemic preconditioning groups treated with the vehicle or with nipradilol were subjected to 3 minutes of ischemic preconditioning; and the L-arginine group treated with the vehicle received 1 mmol/L of L-arginine before global ischemia. Hemodynamic variables and coronary flow were recorded continuously. Nitrites and nitrates levels were measured 60 minutes after reperfusion, and the infarct size was determined. In another series (each n = 6), lipid peroxidation was investigated.

RESULTS

In the nipradilol group, significant preservation of the left ventricular pressure and coronary flow, as well as the level of nitrates and nitrites, was observed, compared with the global ischemia group. The infarct size was also significantly reduced in the ischemic preconditioning (23.5%+/-5.47%), L-arginine (25.6%+/-5.59%), and especially the nipradilol (10.7%+/-1.65%) groups. However, in the nipradilol plus ischemic preconditioning group, the protective effects were eliminated. Lipid peroxidation after nipradilol treatment was significantly reduced before and after global ischemia, compared with the global ischemia group.

CONCLUSIONS

The chronic administration of nipradilol improves postischemic functional recovery and infarct size, partly by preventing the formation of lipid peroxides. These cardioprotective effects were, however, abolished by ischemic preconditioning.

Modulation of beta-adrenergic receptor subtype activities in perioperative medicine: mechanisms and sites of action

This review focuses on the mechanisms and sites of action underlying beta-adrenergic antagonism in perioperative medicine. A large body of knowledge has recently emerged from basic and clinical research concerning the mechanisms of the life-saving effects of beta-adrenergic antagonists (beta-AAs) in high-risk cardiac patients. This article re-emphasizes the mechanisms underlying beta-adrenergic antagonism and also illuminates novel rationales behind the use of perioperative beta-AAs from a biological point of view. Particularly, it delineates new concepts of beta-adrenergic signal transduction emerging from transgenic animal models. The role of the different characteristics of various beta-AAs is discussed, and evidence will be presented for the selection of one specific agent over another on the basis of individual drug profiles in defined clinical situations. The salutary effects of beta-AAs on the cardiovascular system will be described at the cellular and molecular levels. Beta-AAs exhibit many effects beyond a reduction in heart rate, which are less known by perioperative physicians but equally desirable in the perioperative care of high-risk cardiac patients. These include effects on core components of an anaesthetic regimen, such as analgesia, hypnosis, and memory function. Despite overwhelming evidence of benefit, beta-AAs are currently under-utilized in the perioperative period because of concerns of potential adverse effects and toxicity. The effects of acute administration of beta-AAs on cardiac function in the compromised patient and strategies to counteract potential adverse effects will be discussed in detail. This may help to overcome barriers to the initiation of perioperative treatment with beta-AAs in a larger number of high-risk cardiac patients undergoing surgery.

Mitochondrial ATP-sensitive potassium channel plays a dominant role in ischemic preconditioning of rabbit heart

BACKGROUND

The ATP-sensitive potassium (K(ATP)) channel has been shown to be important in the ischemic preconditioning (IPC) response. Recently, the mitochondrial rather than the sarcolemmal K(ATP) channel has been focused on due to its energy-modulating property. Hence, this study was undertaken to elucidate the role of the mitochondrial K(ATP) channel in IPC by modulating the mitochondrial K(ATP) channel in isolated perfused rabbit hearts.

METHODS

Seven hearts served as a control with no interventions. Seven hearts underwent IPC consisting of two 5-min cycles of global ischemia followed by 5 min of reperfusion. Seven hearts received the selective mitochondrial K(ATP) channel blocker 5-dehydroxydecanoate (5-HD, 100 microM) for 5 min before IPC, and 7 hearts received the selective mitochondrial K(ATP) channel opener diazoxide (50 microM) for 5 min. Then, all hearts were subjected to 1 h of left anterior descending coronary artery ischemia and 1 h of reperfusion. Left ventricular pressures, monophasic action potentials and coronary flow were measured throughout the experiment and infarct size was detected at the end of experiment.

RESULTS

(1) The mitochondria-selective K(ATP) channel opener diazoxide reduced infarct size as compared to control (p < 0.05); (2) IPC reduced infarct size and preserved postischemic diastolic function as compared to control (p < 0.05), and (3) the mitochondria-selective K(ATP) channel blocker 5-HD reversed these effects.

CONCLUSION

The mitochondrial ATP-sensitive potassium channel may be a potential site of cardioprotection.

Exogenous nitric oxide can trigger a preconditioned state through a free radical mechanism, but endogenous nitric oxide is not a trigger of classical ischemic preconditioning

Nitric oxide (NO) has been reported to play an important role in the late phase of ischemic preconditioning (PC) in the rabbit heart. However, the role of NO in the early phase of ischemic PC ("classical PC") is controversial. Accordingly, the present study was designed to determine whether NO contributes to the cardioprotective effect of classical PC in rabbits. Isolated hearts experienced 30 min of regional ischemia followed by 120 min of reperfusion. Infarct size was measured with triphenyltetrazolium chloride. In control hearts infarction was 30.2+/-3.3% of the risk zone. PC with 5 min of global ischemia and 10 min of reperfusion reduced infarct size to 10.2+/-2.4% (P<0.05). Perfusion with 2 microm S-nitroso-N-acetylpenicillamine (SNAP), a NO donor, in lieu of ischemia mimicked PC (4.4+/-1.9% infarction, P<0.01 v control). To determine whether this protection was dependent on either protein kinase C (PKC) as has previously been demonstrated for classical PC or free radicals known to be produced during exogenous NO administration, chelerythrine (5 microm), a PKC inhibitor, or N-(2-mercaptopropionyl)-glycine (300 microm), a free radical scavenger, was administered with or shortly after SNAP. Neither drug had any independent effect on infarct size, and each blocked SNAP's cardioprotection (31.0+/-5.1 and 25.7+/-5.2% infarction, resp.). N(omega)-nitro- L -arginine methyl ester (L -NAME, 100 microm), a NO synthase inhibitor, failed to block the cardioprotection from the above ischemic PC protocol (9.5+/-2.8% infarction, P<0.05 v control). L -NAME alone had no effect on infarct size (30.6+/-2.7%). These results suggest that the beneficial effect of exogenous NO production during SNAP pretreatment is mediated by a protein kinase C-dependent pathway via MPG-sensitive oxidants. However, we were unable to show any contribution of endogenous NO to classical PC's protection in isolated rabbit hearts.