Mixed beta3-adrenoceptor agonist and alpha1-adrenoceptor antagonist properties of nebivolol in rat thoracic aorta

Role of β-Adrenergic Receptors in Stress-Induced Cardiac Injury

Stress-induced cardiac injury (SICI) was modeled on female Wistar rats using a 24-h immobilization. SICI was quantified by 99mTc-pyrophosphate accumulation in the myocardium. Blockade of β1- and β2-adrenergic receptors (AR) led to a decrease in SICI. β1-AR antagonists nebivolol and atenolol almost completely prevented SICI. The selective β2-AR antagonist ICI 118,551 increased SICI, while the selective β3-AR antagonist L-748337 did not affect heart damage. The selective β2-AR agonist formoterol increased cardiac tolerance to stress. These findings suggest that β1-AR play a key role in the pathogenesis of SICI. Stimulation of β2-AR enhances cardiac tolerance to stress. β3-AR are not involved in the pathogenesis of SICI.

Multitargeting in cardioprotection: An example of biaromatic compounds

A multitarget drug design approach is actively developing in modern medicinal chemistry and pharmacology, especially with regard to multifactorial diseases such as cardiovascular diseases, cancer, and neurodegenerative diseases. A detailed study of many well-known drugs developed within the single-target approach also often reveals additional mechanisms of their real pharmacological action. One of the multitarget drug design approaches can be the identification of the basic pharmacophore models corresponding to a wide range of the required target ligands. Among such models in the group of cardioprotectors is the linked biaromatic system. This review develops the concept of a "basic pharmacophore" using the biaromatic pharmacophore of cardioprotectors as an example. It presents an analysis of possible biological targets for compounds corresponding to the biaromatic pharmacophore and an analysis of the spectrum of biological targets for the five most known and most studied cardioprotective drugs corresponding to this model, and their involvement in the biological effects of these drugs.

Clinical pharmacology of β-3 adrenergic receptor agonists for cardiovascular diseases

INTRODUCTION

Few agonists of the third isotype of beta-adrenergic receptors, the β3-adrenoreceptor, are currently used clinically, and new agonists are under development for the treatment of overactive bladder disease. As the receptor is expressed in human cardiac and vascular tissues, it is important to understand their beneficial (or adverse) effect(s) on these targets.

AREAS COVERED

We discuss the most recent results of clinical trials testing the benefit and safety of β3-adrenoreceptor activation on cardiovascular outcomes in light of current knowledge on the receptor biology, genetic polymorphisms, and agonist pharmacology.

EXPERT OPINION

While evidence from small clinical trials is limited so far, the β3-agonist, mirabegron seems to be safe in patients at high cardiovascular risk but produces benefits on selected cardiovascular outcomes only at higher than standard doses. Activation of cardiovascular β3-adrenoreceptors deserves to be tested with more potent agonists, such as vibegron.

Role of endothelial dysfunction in heart failure

Coronary artery disease is a major underlying etiology for heart failure. The role of coronary microvascular disease, and endothelial dysfunction, in the pathophysiology of heart failure is poorly appreciated. Endothelial dysfunction, induced by oxidative stress, contributes to the development of heart failure. Alterations of endothelial function and nitric oxide-cyclic guanosine monophosphate (NO-cGMP) pathway are involved in the pathophysiology of heart failure with both reduced and preserved ejection fraction. Indeed, an altered endothelium dependent vasodilatation, causing repeated episodes of ischemia/reperfusion, can induce a chronic stunned myocardium with systolic dysfunction and an increased diastolic stiffness with diastolic dysfunction. Moreover, the altered NO-cGMP pathway directly affects myocardial homeostasis. Endothelial dysfunction is associated with worse prognosis and higher rate of cardiovascular events. Potential therapeutic strategies targeting the NO-cGMP pathway in patients with HF will be discussed in this review article. Although clinical data are still inconclusive, the NO-cGMP pathway represents a promising target for therapy.

Nebivolol/valsartan combination for the treatment of hypertension: a review

Nebivolol (N) is a β₁-adrenoreceptor antagonist that is approved for treatment of hypertension in the USA. Effective treatment of hypertension is becoming an increasingly difficult process that often requires multiple drug combinations to meet target guidelines. This has resulted in the increasing introduction of multidrug single-pill combinations (SPCs) to facilitate cost and compliance issues. Some of the SPCs have added valsartan (V), an angiotensin receptor blocker, which is an increasingly advocated antihypertensive class. Pharmacological profiles of N and V, alone and combined, are well characterized. In 2007, the SPC of N and V, 5 and 80 mg, respectively, was approved by the US FDA for treatment of hypertension. This paper will summarize and update key issues in pharmacology, clinical use and benefit.

α1-adrenoceptor activity of β-adrenoceptor ligands - An expected drug property with limited clinical relevance

Many β-adrenoceptor agonists and antagonists including several clinically used drugs have been reported to also exhibit binding to α₁-adrenoceptors. Such promiscuity within the adrenoceptor family appears to occur more often than off-target effects of drugs in general. It should not be considered surprising based on the amino acid homology among the nine adrenoceptor subtypes including the counter-ions for binding the endogenous catecholamines. When β-adrenoceptor ligands also bind to α₁-adrenoceptors, they almost always act as antagonists, regardless of being agonists or antagonists at the β-adrenoceptor. The α₁-adrenoceptor affinity of β-adrenoceptor ligands in most cases is at least one, and often more log units lower than at their cognate receptor. Consistent evidence from multiple investigators indicates that β-adrenoceptor ligands relatively have the highest affinity for α_1A- and lowest for α_1B-adrenoceptors. While promiscuity among adrenoceptor subtypes causes misleading interpretation of experimental in vitro data, it is proposed based on the law of mass action that α₁-adrenoceptor binding of β-adrenoceptor ligands rarely contributes to the clinical profile of such drugs, particularly if they are agonists at the β-adrenoceptor.

Nebivolol Improves Obesity-Induced Vascular Remodeling by Suppressing NLRP3 Activation

Nebivolol is a novel β-adrenergic receptor (β-AR) blocker with anti-inflammatory and antioxidant properties. The NLRP3 inflammasome plays a pivotal role in the pathogenesis of obesity-induced vascular dysfunction. Our study aimed to explore the effect of nebivolol on the NLRP3 inflammasome and vascular remodeling in diet-induced obese rats. Eight-week-old Sprague-Dawley male rats were fed with either a standard chow diet or a high-fat diet (HFD) for 8 weeks. Next, the obese rats were subdivided into 3 groups as follows: (1) HFD control group, (2) HFD with low doses of nebivolol (5 mg/kg·d), and (3) HFD with high doses of nebivolol (10 mg/kg·d). A 4-week treatment with nebivolol improved acetylcholine-induced vascular relaxation in accordance with an increased aortic endothelial nitric oxide synthase. Nebivolol attenuated NLRP3 inflammasome activation and suppressed autophagy. In parallel, nebivolol enhanced the levels of phase-II detoxifying enzymes, including superoxide dismutase and catalase. These effects were associated with an increased β3-AR level. Moreover, nebivolol treatment significantly increased Adenosine 5'-monophosphate (AMP)-activated protein kinase activity and decreased phosphorylation of the mammalian target of rapamycin. These results demonstrated that nebivolol improves obesity-induced vascular remodeling by attenuating NLRP3 inflammasome activation and restoring the antioxidant defense.

Rationale for nebivolol/valsartan combination for hypertension: review of preclinical and clinical data

To treat hypertension, combining two or more antihypertensive drugs from different classes is often necessary. β-Blockers and renin–angiotensin–aldosterone system inhibitors, when combined, have been deemed ‘less effective’ based on partially overlapping mechanisms of action and limited evidence. Recently, the single-pill combination (SPC) of nebivolol (Neb) 5 mg – a vasodilatory β1-selective antagonist/β3 agonist – and valsartan 80 mg, an angiotensin II receptor blocker, was US Food and Drug Administration-approved for hypertension. Pharmacological profiles of Neb and valsartan, alone and combined, are well characterized. In addition, a large 8-week randomized trial in stages I–II hypertensive patients (N = 4161) demonstrated greater blood pressure-reducing efficacy for Neb/valsartan SPCs than component monotherapies with comparable tolerability. In a biomarkers substudy (N = 805), Neb/valsartan SPCs prevented valsartan-induced increases in plasma renin, and a greater reduction in plasma aldosterone was observed with the highest SPC dose vs. valsartan 320 mg/day. This review summarizes preclinical and clinical evidence supporting Neb/valsartan as an efficacious and well tolerated combination treatment for hypertension.

Role of β3 adrenoceptor in rat thoracic aorta contractility

To clarify the role of β₃-AR in rat thoracic aorta contractility and underlying mechanisms. BRL 37344 (BRL) was used to detect the role of β₃-AR on rat thoracic aorta. 40 rats were randomly divided into Sham control group, Sham+SR group with SR 59230A (SR) injected, chronic heart failure (CHF) control group, and CHF+SR group. The effects of SR on thoracic aorta structure, function and NF-κB expression were estimated. BRL produced relaxant effect in both endothelium-intact and endothelium-free aorta rings, which was antagonized by SR and partially by L-NAME, but not changed by Propranolol. Similar results were obtained on thoracic aorta smooth muscle of CHF rats. β₃-AR was located in both vascular smooth muscle layer and endothelial layer. After SR injection, the aorta rings in Sham+SR group showed reduced endothelium-dependent relaxation response to Ach compared with Sham control group. The aorta rings in CHF control group showed reduced endothelium-dependent relaxation to Ach, with increased endothelium-dependent relaxation in CHF+SR group. Besides, SR injection showed increased contraction to NA. Meanwhile, NF-κB expression in Sham+SR group was higher than Sham control group, with increased expression in CHF control group but decreased in CHF+SR group. Microarray screening showed 48 and 42 differentially expressed miRNAs in Sham+SR rats and CHF+SR rats respectively with 19 of them associated with NF-κB pathways. β₃-AR is expressed in rat aorta and exerts relaxant effects through NOS-dependent pathway. β₃-AR Inhibition delayed damage of vessels in development of heart failure possibly through regulation of NF-κB signaling pathway.

Effects of long-term active immunization with the second extracellular loop of human β1- or β3-adrenoceptors in thoracic aorta and mesenteric arteries in Lewis rats

OBJECTIVE

To evaluate whether active immunization producing β₁- or β₃-antibodies (β₁-ABs and β₃-ABs) detected in sera of patients with dilated cardiomyopathies has deleterious effects on vascular reactivity in Lewis rat thoracic aorta (TA) and small mesenteric arteries (SMA).

DESIGN AND METHOD

Lewis rats were immunized for 6months with peptidic sequences corresponding to the second extracellular loop of β₁- and β₃-adrenoceptors (ARs). During the immunization, systolic blood pressure (SBP) was monitored using the tail cuff method. The vascular reactivity of immunized rats was assessed by ex vivo studies on SMA and TA using various β-AR agonists, phenylephrine and KCl.

RESULTS

The immunizations producing functional β₁-ABs and β₃-ABs did not affect the SBP. However, in TA from β₁-AR-immunized rats, the relaxations mediated by dobutamine and salbutamol were significantly impaired in comparison with adjuvant rats whereas nebivolol-induced relaxation was not modified. Moreover, phenylephrine and KCl-mediated contractions were enhanced in these rats. In contrast, immunization with β₃-AR peptide led to the increase of relaxations induced by dobutamine in TA but did not change those induced by salbutamol and nebivolol. Surprisingly, in SMA from both rats immunized with β₁- or β₃-peptides, relaxations induced by the various β-agonists were not changed whereas phenylephrine and KCl-mediated contractions were impaired.

CONCLUSIONS

Our study shows that β₁- and β₃-ABs can affect vascular reactivity. β₁-ABs would have a pathogenic action whereas β₃-ABs would have a beneficial effect on aorta reactivity.

Mirabegron relaxes urethral smooth muscle by a dual mechanism involving β3 -adrenoceptor activation and α1 -adrenoceptor blockade

LINKED ARTICLE

This article is commented on by Michel, M. C., pp. 429-430 of this issue. To view this commentary visit http://dx.doi.org/10.1111/bph.13379.

BACKGROUND AND PURPOSE

Mirabegron is the first β3 -adrenoceptor agonist approved for treatment of overactive bladder syndrome. This study aimed to investigate the effects of β3 -adrenoceptor agonist mirabegron in mouse urethra. The possibility that mirabegron also exerts α1 -adrenoceptor antagonism was also tested in rat smooth muscle preparations presenting α1A - (vas deferens and prostate), α1D - (aorta) and α1B -adrenoceptors (spleen).

EXPERIMENTAL APPROACH

Functional assays were carried out in mouse and rat isolated tissues. Competition assays for the specific binding of [(3) H]prazosin to membrane preparations of HEK-293 cells expressing each of the human α1 -adrenoceptors, as well as β-adrenoceptor mRNA expression and cyclic AMP measurements in mouse urethra, were performed.

KEY RESULTS

Mirabegron produced concentration-dependent urethral relaxations that were shifted to the right by the selective β3 -adrenoceptor antagonist L-748,337 but unaffected by β1 - and β2 -adrenoceptor antagonists (atenolol and ICI-118,551 respectively). Mirabegron-induced relaxations were enhanced by the PDE4 inhibitor rolipram, and the agonist stimulated cAMP synthesis. Mirabegron also produced rightward shifts in urethral contractions induced by the α1 -adrenoceptor agonist phenylephrine. Schild regression analysis revealed that mirabegron behaves as a competitive antagonist of α1 -adrenoceptors in urethra, vas deferens and prostate (α1A -adrenoceptor, pA2  ≅ 5.6) and aorta (α1D -adrenoceptor, pA2  ≅ 5.4) but not in spleen (α1B -adrenoceptor). The affinities estimated for mirabegron in functional assays were consistent with those estimated in radioligand binding with human recombinant α1A - and α1D -adrenoceptors (pKi  ≅ 6.0).

CONCLUSION AND IMPLICATIONS

The effects of mirabegron in urethral smooth muscle are the result of β3 -adrenoceptor agonism together with α1A and α1D -adrenoceptor antagonism.

β3 -AR and the vertebrate heart: a comparative view

Recent cardiovascular research showed that, together with β1- and β2-adrenergic receptors (ARs), β3-ARs contribute to the catecholamine (CA)-dependent control of the heart. β3-ARs structure, function and ligands were investigated in mammals because of their applicative potential in human cardiovascular diseases. Only recently, the concept of a β3-AR-dependent cardiac modulation was extended to non-mammalian vertebrates, although information is still scarce and fragmentary. β3-ARs were structurally described in fish, showing a closer relationship to mammalian β1-AR than β2-AR. Functional β3-ARs are present in the cardiac tissue of teleosts and amphibians. As in mammals, activation of these receptors elicits a negative modulation of the inotropic performance through the involvement of the endothelium endocardium (EE), Gi/0 proteins and the nitric oxide (NO) signalling. This review aims to comparatively analyse data from literature on β3-ARs in mammals, with those on teleosts and amphibians. The purpose is to highlight aspects of uniformity and diversity of β3-ARs structure, ligands activity, function and signalling cascades throughout vertebrates. This may provide new perspectives aimed to clarify the biological relevance of β3-ARs in the context of the nervous and humoral control of the heart and its functional plasticity.

Hypoglycemia, polycythemia and hyponatremia in a newborn exposed to nebivolol during pregnancy

Nebivolol is a third-generation beta blocker that exerts selective antagonistic activity on β₁ receptors. It has vasodilating properties that result from direct stimulation of endothelial nitric oxide synthase. Nebivolol is indicated for the treatment of hypertension and heart failure, and is generally well tolerated. In this article, we report a case of an infant who was admitted to the Pediatrics and Neonatology Unit of the Moscati Hospital (Aversa, Italy) about 24 hours after birth. The reason for hospitalization was persistent severe hypoglycemia (blood glucose = 30 mg/dL) and jaundice (total bilirubin = 12.5 mg/dL, indirect bilirubin 11.75 mg/dL). He was born by spontaneous delivery after a normal term pregnancy. Birth weight was 3040 g and the Apgar score was 6-9. The mother reported taking nebivolol 5 mg/day for unspecified tachycardia in the last 4 months of pregnancy. Clinical and instrumental investigations carried out during hospitalization did not reveal any congenital or perinatal abnormalities. After treatment for metabolic and electrolyte imbalance, he was discharged on the 10^th day of hospitalization, in good clinical condition and with normalization of clinical and laboratory parameters. Currently, there are no specific studies on nebivolol tolerability during pregnancy. Our data suggest that the risk profile of nebivolol during pregnancy is the same as that of other β-blockers. Therefore, further studies are required to determine the safety of β-blockers during pregnancy and the risks to the unborn child.

β1-Adrenergic receptor blockade extends the life span of Drosophila and long-lived mice

Chronic treatment with β-adrenergic receptor (βAR) agonists increases mortality and morbidity while βAR antagonists (β-blockers) decrease all-cause mortality for those at risk of cardiac disease. Levels of sympathetic nervous system βAR agonists and βAR activity increase with age, and this increase may hasten the development of age-related mortality. Here, we show that β-blockers extend the life span of healthy metazoans. The β-blockers metoprolol and nebivolol, administered in food daily beginning at 12 months of age, significantly increase the mean and median life span of isocalorically fed, male C3B6F1 mice, by 10 and 6.4%, respectively (P < 0.05). Neither drug affected the weight or food intake of the mice, indicating that induced CR is not responsible for these effects, and that energy absorption and utilization are not altered by the drugs. Both β-blockers were investigated to control for their idiosyncratic, off-target effects. Metoprolol and nebivolol extended Drosophila life span, without affecting food intake or locomotion. Thus, βAR antagonists are capable of directly extending the life span of two widely divergent metazoans, suggesting that these effects are phylogenetically highly conserved. Thus, long-term use of β-blockers, which are generally well-tolerated, may enhance the longevity of healthy humans.

New advances in beta-blocker therapy in heart failure

The use of β-blockers (BB) in heart failure (HF) has been considered a contradiction for many years. Considering HF simply as a state of inadequate systolic function, BB were contraindicated because of their negative effects on myocardial contractility. Nevertheless, evidence collected in the past years have suggested that additional mechanisms, such as compensatory neuro-humoral hyperactivation or inflammation, could participate in the pathogenesis of this complex disease. Indeed, chronic activation of the sympathetic nervous system, although initially compensating the reduced cardiac output from the failing heart, increases myocardial oxygen demand, ischemia and oxidative stress; moreover, high catecholamine levels induce peripheral vasoconstriction and increase both cardiac pre- and after-load, thus determining additional stress to the cardiac muscle (1). As a consequence of such a different view of the pathogenic mechanisms of HF, the efficacy of BB in the treatment of HF has been investigated in numerous clinical trials. Results from these trials highlighted BB as valid therapeutic tools in HF, providing rational basis for their inclusion in many HF treatment guidelines. However, controversy still exists about their use, in particular with regards to the selection of specific molecules, since BB differ in terms of adrenergic β-receptors selectivity, adjunctive effects on α-receptors, and effects on reactive oxygen species and inflammatory cytokines production. Further concerns about the heterogeneity in the response to BB, as well as the use in specific patients, are matter of debate among clinicians. In this review, we will recapitulate the pharmacological properties and the classification of BB, and the alteration of the adrenergic system occurring during HF that provide a rationale for their use; we will also focus on the possible molecular mechanisms, such as genetic polymorphisms, underlying the different efficacy of molecules belonging to this class.

The new radioligand [(3)H]-L 748,337 differentially labels human and rat β3-adrenoceptors

As no suitable radioligand exists for the detection of β3-adrenoceptors, we have explored the radioligand binding properties of a tritiated version of the selective β3-adrenoceptor antagonist L 748,337. Kinetic and equilibrium saturation and competition binding experiments were performed with [(3)H]-L 748,337 on membrane fractions of HEK and CHO cells stably transfected with human and rat β-adrenoceptor subtypes. Based on both association/dissociation kinetic and equilibrium saturation binding studies in transfected HEK cells, [(3)H]-L 748,337 exhibited an affinity of approximately 2 nM for human β3-adrenoceptors. Competition studies with agonists and subtype-selective antagonists validated its binding to β3-adrenoceptors. In CHO cells transfected with human β3-adrenoceptors similar saturable high-affinity of [(3)H]-L 748,337 was observed. While some isoprenaline-sensitive [(3)H]-L 748,337 binding was also observed in CHO cells transfected with human β1- or β2-adrenoceptors, this was not saturable in a similar concentration range and/or not sensitive to the antagonists propranolol and SR 59,230, indicating that it did not primarily involve β-adrenoceptors. In CHO cells transfected with rat β3-adrenoceptors [(3)H]-L 748,337 exhibited a considerably lower affinity than with the human subtype (12-95 nM). Low affinity for the rat β3-adrenoceptor was also found with unlabelled L 748,337 in rat bladder strip relaxation experiments. We conclude that L 748,337 apparently has lower affinity for the rat than the human β3-adrenoceptors and that [(3)H]-L 748,337 can bind to a low-affinity site distinct from the orthosteric pocket of β-adrenoceptors. Nevertheless, [(3)H]-L 748,337 appears to be the most promising radioligand for the selective labelling of human β3-adrenoceptors reported to date.

Celiprolol induces β(3)-adrenoceptors-dependent relaxation in isolated porcine coronary arteries

In porcine coronary arteries (PCAs), celiprolol, a selective β(1)-adrenoceptors antagonist, induces vasodilatation by an endothelium- and nitric oxide (NO)-dependent pathway. However, the mechanisms of that vascular effect have not been precisely established. β(3)-Adrenoceptors have been shown to be involved in the relaxation per se of various vascular beds, including coronary vessels. Thus, we evaluated (i) the presence of β(3)-adrenoceptors in the PCA and (ii) their role in celiprolol-induced vasodilatation. PCA rings were placed in organ baths and preconstricted with KCl. All experiments were performed in the presence of nadolol (a β(1)/β(2)-adrenoceptor antagonist). Cumulative concentration-response curves to SR 58611A and ICI 215001 (2 β(3)-adrenoceptor agonists) and to celiprolol were constructed. We also used semiquantitative reverse transcription - polymerase chain reaction, which clearly showed the presence of β(3)-adrenoceptor transcripts. SR 58611A, ICI 215001, and celiprolol induced concentration-dependent relaxations in PCA rings. SR 58611A-induced relaxation was almost abolished after removal of endothelium or pretreatment with L-NAME (a NO synthase inhibitor). The vasorelaxations induced by SR 58611A and celiprolol were inhibited in the presence of SR 59230A and L-748337 (2 selective β(3)-adrenoceptor antagonists). We showed (i) that PCAs possess functional β(3)-adrenoceptors mediating endothelium- and NO-dependent relaxation, and (ii) that celiprolol exerts a β(3)-adrenoceptor agonistic activity in this vascular bed.

Nebivolol prevents desensitization of β-adrenoceptor signaling and induction of cardiac hypertrophy in response to isoprenaline beyond β1-adrenoceptor blockage

The importance of chronic stimulation of β-adrenoceptors in the development of cardiac dysfunction is the rationale for the use of β-blockers in the treatment of heart failure. Nebivolol is a third-generation β-blocker, which has further properties including stimulation of endothelial nitric oxide synthase and/or β3-adrenoceptors. The aim of this study was to investigate whether nebivolol has additional effects on β-adrenoceptor-mediated functional responses along with morphologic and molecular determinants of cardiac hypertrophy compared with those of metoprolol, a selective β1-adrenoceptor blocker. Rats infused by isoprenaline (100 μg·kg−1·day−1, 14 days) were randomized into three groups according to the treatment with metoprolol (30 mg·kg−1·day−1), nebivolol (10 mg·kg−1·day−1), or placebo for 13 days starting on day 1 after implantation of minipump. Both metoprolol and nebivolol caused a similar reduction on heart rate. Nebivolol mediated a significant improvement on cardiac mass, coronary flow, mRNA expression levels of sarcoplasmic reticulum Ca2+ ATPase (SERCA2a) and atrial natriuretic peptide and phospholamban (PLN)/SERCA2a and phospho-PLN/PLN ratio compared with metoprolol and placebo. Nebivolol prevented the detrimental effects of isoprenaline infusion on isoprenaline (68% of control at 30 μM), BRL37344 (63% of control at 0.1 μM), and forskolin (64% of control at 1 μM) responses compared with metoprolol (isoprenaline, 34% of control; BRL37344, no response; forskolin, 26% of control) and placebo (isoprenaline, 33% of control; BRL37344, 28% of control; forskolin, 12% of control). Both β-blockers improved the changes in mRNA expressions of β1- and β3-adrenoceptors. Our results suggest that nebivolol partially protects the responsiveness of β-adrenoceptor signaling and the development of cardiac hypertrophy independent of its β1-adrenoceptor blocking effect.

Vasodilatory mechanisms of beta receptor blockade

Beta-blockers are widely prescribed for the treatment of a variety of cardiovascular pathologies. Compared to traditional beta-adrenergic antagonists, beta-blockers of the new generation exhibit ancillary properties such as vasodilation through different mechanisms. This translates into a more favorable hemodynamic profile. The relative affinities of beta-adrenoreceptor antagonists towards the three beta-adrenoreceptor isotypes matter for predicting their functional impact on vasomotor control. This review will focus on the mechanisms underlying beta-blocker-evoked vasorelaxation with a specific emphasis on agonist properties of beta(3)-adrenergic receptors.

Nebivolol-induced vasodilation of renal afferent arterioles involves β3-adrenergic receptor and nitric oxide synthase activation

Nebivolol is a β(1)-adrenergic blocker that also elicits renal vasodilation and increases the glomerular filtration rate (GFR). However, its direct actions on the renal microvasculature and vasodilator mechanism have not been established. We used the in vitro blood-perfused juxtamedullary nephron technique to determine the vasodilator effects of nebivolol and to test the hypothesis that nebivolol induces vasodilation of renal afferent arterioles via an nitric oxide synthase (NOS)/nitric oxide (NO)/soluble guanylate cyclase (sGC)/cGMP pathway and the afferent arteriolar vasodilation effect may be mediated through the release of NO by activation of NOS via a β(3)-adrenoceptor-dependent mechanism. Juxtamedullary nephrons were superfused with nebivolol either alone or combined with the sGC inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) or the NOS inhibitor N(ω)-nitro-l-arginine (l-NNA) or the β-blockers metoprolol (β(1)), butoxamine (β(2)), and SR59230A (β(3)). Nebivolol (100 μmol/l) markedly increased afferent and efferent arteriolar diameters by 18.9 ± 3.0 and 15.8 ± 1.8%. Pretreatment with l-NNA (1,000 μmol/l) or ODQ (10 μmol/l) decreased afferent vasodilator diameters and prevented the vasodilator effects of nebivolol (2.0 ± 0.2 and 2.4 ± 0.6%). Metoprolol did not elicit significant changes in afferent vasodilator diameters and did not prevent the effects of nebivolol to vasodilate afferent arterioles. However, treatment with SR59230A, but not butoxamine, markedly attenuated the vasodilation responses to nebivolol. Using a monoclonal antibody to β(3)-receptors revealed predominant immunostaining on vascular and glomerular endothelial cells. These data indicate that nebivolol vasodilates both afferent and efferent arterioles and that the afferent vasodilator effect is via a mechanism that is independent of β(1)-receptors but is predominantly mediated via a NOS/NO/sGC/cGMP-dependent mechanisms initiated by activation of endothelial β(3)-receptors.

Improvement of left ventricular diastolic function induced by β-blockade: a comparison between nebivolol and metoprolol

OBJECTIVES

Enhanced adrenergic drive is involved in the development of left ventricular (LV) diastolic dysfunction observed in metabolic syndrome (MS). Thus, β-blockers might improve LV dysfunction observed in MS, but whether this occurs is unknown.

METHODS

We assessed in Zucker fa/fa rats the effects of short- (5 days) and long-term (90 days) metoprolol ('pure' β-blockade; 80 mg/kg/day) or nebivolol (β-blocker with vasodilating properties; 5mg/kg/day) treatment on LV hemodynamics and remodeling, as well as the long-term effects on coronary and peripheral endothelial dysfunction.

RESULTS

At identical degree of β(1)-receptor blockade, metoprolol and nebivolol decreased heart rate to the same extent and preserved cardiac output via increased stroke volume. None of the β-blockers, either after long- or short-term administration, modified LV end-systolic pressure-volume relation. Both β-blockers reduced, after long-term administration, LV end-diastolic pressure, Tau and end-diastolic pressure-volume relation, and this was associated with reduced LV collagen density, but not heart weight. Similar hemodynamic effects were also observed after short-term nebivolol, but not short-term metoprolol. These short-term effects of nebivolol were abolished by NO synthase inhibition. At the vascular level, nebivolol, and to a lesser extend metoprolol, improved NO dependent coronary vasorelaxation, which was abolished by NO synthase inhibition.

CONCLUSIONS

In a model of MS, the β-blockers metoprolol and nebivolol improve to the same extent LV hemodynamics, remodeling and diastolic function, but nebivolol prevent more markedly endothelium dependent vasorelaxation involving a more marked enhancement of NO bio-availability.

Lack of evidence that nebivolol is a β₃-adrenoceptor agonist

Nebivolol is a selective β₁-adrenoceptor antagonist which, in addition, displays endothelium-dependent vasodilating properties in humans and other species. β₃-adrenoceptors have been proposed to be a molecular target of nebivolol-induced vasodilatation. Therefore, we have investigated possible β₃-adrenoceptor agonism by nebivolol for relaxation of the human and rat urinary bladder (prototypical β₃-adrenoceptor-mediated responses) as well as for cAMP accumulation in Chinese hamster ovary cells stably transfected with the human β-adrenoceptor subtypes. Nebivolol concentration-dependently relaxed both human and rat isolated urinary bladder strips but with low potency, similar to that reported for vasodilatation. However, nebivolol-induced bladder relaxation in either species was not inhibited by the β₃-adrenoceptor antagonist SR 59,230A (10μM), although this compound inhibited the isoprenaline-induced relaxation with the expected potency. In radioligand binding studies nebivolol had lower affinity for human β₃-adrenoceptors than the other two β-adrenoceptor subtypes, but this low affinity was in line with its potency to relax the bladder or isolated blood vessels. In functional studies nebivolol even in high concentrations did not stimulate cAMP formation via any of the three cloned human β-adrenoceptors or in rat bladder smooth muscle cells. Taken together these data demonstrate that nebivolol can relax not only vascular but also urinary bladder smooth muscle. However, they do not support the hypothesis that nebivolol is an agonist at cloned human β₃-adrenoceptors or in rat or human urinary bladder.

Clinical and economic aspects of the use of nebivolol in the treatment of elderly patients with heart failure

Heart failure is a common and disabling condition with morbidity and mortality that increase dramatically with advancing age. Large observational studies, retrospective subgroup analyses and meta-analyses of clinical trials in systolic heart failure, and recently published randomized studies have provided data supporting the use of beta-blockers as a baseline therapy in heart failure in the elderly. Despite the available evidence about beta-blockers, this therapy is still less frequently used in elderly compared to younger patients. Nebivolol is a third-generation cardioselective beta-blocker with L-arginine/nitric oxide-induced vasodilatory properties, approved in Europe and several other countries for the treatment of essential hypertension, and in Europe for the treatment of stable, mild, or moderate chronic heart failure, in addition to standard therapies in elderly patients aged 70 years old or older. The effects of nebivolol on left ventricular function in elderly patients with chronic heart failure (ENECA) and the study of effects of nebivolol intervention on outcomes and rehospitalization in seniors with heart failure (SENIORS) have been specifically aimed to assess the efficacy of beta-blockade in elderly heart failure patients. The results of these two trials demonstrate that nebivolol is well tolerated and effective in reducing mortality and morbidity in older patients, and that the beneficial clinical effect is present also in patients with mildly reduced ejection fraction. Moreover, nebivolol appears to be significantly cost-effective when prescribed in these patients. However, further targeted studies are needed to better define the efficacy as well as safety profile in frail and older patients with comorbid diseases.

[Nebivolol: the first vasodilatory beta-blocker with a beta3-adrenergic agonist activity]

Several studies suggest that the beta(3)-adrenergic stimulation could be a new therapeutic target for the treatment of cardiovascular diseases. The vascular effects induced by beta(3)-adrenergic stimulation are able to decrease the left ventricular strain allowing to reduce after-load. In addition, the increased coronary blood flow due to vasorelaxation increases the myocardial oxygene delivery. The hypothesis about the beneficial role of beta(3)-adrenoceptors is supported by recent data about a beta-blocker of third generation, nebivolol, currently used in the treatment of heart failure and hypertension. The present review presents the beta(3)-adrenoceptors characteristics as well as its involvement in the cardiovascular effects of nebivolol.

Ligand-directed signalling at beta-adrenoceptors

beta-Adrenoceptors (ARs) classically mediate responses to the endogenous ligands adrenaline and noradrenaline by coupling to Gsalpha and stimulating cAMP production; however, drugs designed as beta-AR agonists or antagonists can activate alternative cell signalling pathways, with the potential to influence clinical efficacy. Furthermore, drugs acting at beta-ARs have differential capacity for pathway activation, described as stimulus trafficking, biased agonism, functional selectivity or ligand-directed signalling. These terms refer to responses where drug A has higher efficacy than drug B for one signalling pathway, but a lower efficacy than drug B for a second pathway. The accepted explanation for such responses is that drugs A and B have the capacity to induce or stabilize distinct active conformations of the receptor that in turn display altered coupling efficiency to different effectors. This is consistent with biophysical studies showing that drugs can indeed promote distinct conformational states. Agonists acting at beta-ARs display ligand-directed signalling, but many drugs acting as cAMP antagonists are also able to activate signalling pathways central to cell survival and proliferation or cell death. The observed complexity of drug activity at beta-ARs, prototypical G protein-coupled receptors, necessitates rethinking of the approaches used for screening and characterization of novel therapeutic agents. Most studies of ligand-directed signalling employ recombinant cell systems with high receptor abundance. While such systems are valid for examining upstream signalling events, such as receptor conformational changes and G protein activation, they are less robust when comparing downstream signalling outputs as these are likely to be affected by complex pathway interactions.

Beta3-adrenergic receptors in cardiac and vascular tissues emerging concepts and therapeutic perspectives

Catecholamines released by the orthosympathetic system play a major role in the short- and long-term regulation of cardiovascular function. Beta1- and beta2-adrenoreceptors (ARs) have classically been considered as mediating most of their effects on cardiac contraction. After their initial cloning and pharmacologic characterization in the late 1980s, beta3-ARs have been mostly thought of as receptors mediating metabolic effects (e.g., lipolysis) in adipocytes. However, definitive evidence for their expression and functional coupling in cardiovascular tissues (including in humans) has recently initiated a re-examination of their implication in the pathophysiology of cardiovascular diseases. Distinctive pharmacodynamic properties of beta3-AR, e.g., their upregulation in disease and resistance to desensitization, suggest that they may be attractive targets for therapeutic intervention. They may substitute efficient vasodilating pathways when beta1/2-ARs are inoperative. In the heart, their contractile effects, which are functionally antipathetic to those of beta1/2-AR, may protect the myocardium against adverse effects of excessive catecholamine stimulation and perhaps mediate additional ancillary effects on key aspects of electrophysiology or remodeling. Longitudinal studies in animals and patients with different stages of heart failure are now needed to identify the optimal therapeutic scheme using specific combinations of agonists or antagonists at all three beta-ARs.

Evolving mechanisms of action of beta blockers: focus on nebivolol

Beta (beta) blockers are widely used for treatment of cardiovascular and noncardiovascular diseases. Nevertheless, their mechanism of action is not fully understood and differs significantly among agents in this class. Chronic increases in adrenergic activity in heart failure result in desensitization of cardiac beta-adrenergic receptor signal transduction and adverse effects on myocytes. By reducing heart rate and decreasing myocardial workload, the pathologic remodeling of the heart may be reversed with beta-blocking agents. Among beta-blockers, there are clear differences in pharmacodynamic and pharmacokinetic properties. Newer beta-blockers differ from older agents with respect to beta-adrenoceptor affinity and selectivity and partial agonist activity, which may affect their mechanism of action and be important in clinical use.The first beta-antagonist compounds were nonselective; the next generation of beta-blockers was selective for beta1-receptors. The most recent beta-blockers may be nonselective or selective, and they have the additional ancillary property of vasodilation. Nebivolol is among the newer third-generation beta-blockers. It is unique in the class, since apart from its cardioselectivity, it also produces nitric oxide-mediated vasodilation. As a result, its hemodynamic profile is clearly different from those of traditional beta-blockers. This review will evaluate this class of agents and the basis for their differences in clinical use.

Nebivolol: the somewhat-different beta-adrenergic receptor blocker

Although its clinical use in Europe dates almost 10 years, nebivolol is a beta-blocker that has been only recently introduced in the U.S. market. Like carvedilol, nebivolol belongs to the third generation of beta-blockers, which possess direct vasodilator properties in addition to their adrenergic blocking characteristics. Nebivolol has the highest beta(1)-receptor affinity among beta-blockers and, most interestingly, it substantially improves endothelial dysfunction via its strong stimulatory effects on the activity of the endothelial nitric oxide synthase and via its antioxidative properties. Because impaired endothelial activity is attributed a major causal role in the pathophysiology of hypertension, coronary artery disease, and congestive heart failure, the endothelium-agonistic properties of nebivolol suggest that this drug might provide additional benefit beyond beta-receptor blockade. Although lesser beta-blocker-related side effects have been reported in patients with chronic obstructive pulmonary disease or impotence taking nebivolol, side effects and contraindications overlap those of other beta-blockers. Clinically, this compound has been proven to have antihypertensive and anti-ischemic effects as well as beneficial effects on hemodynamics and prognosis in patients with chronic congestive heart failure. Further studies are now necessary to compare the benefit of nebivolol with that of other drugs in the same class and, most importantly, its prognostic impact in patients with hypertension.

Nebivolol, a vasodilating selective beta(1)-blocker, is a beta(3)-adrenoceptor agonist in the nonfailing transplanted human heart

OBJECTIVES

The present study was to assess whether nebivolol could activate beta(3)-adrenergic receptors (ARs) in the human heart.

BACKGROUND

Nebivolol is a third-generation beta-blocker used in the treatment of heart failure. It associates selective beta(1)-adrenergic antagonist properties with endothelial and nitric oxide (NO)-dependent vasodilation. Several studies reported that this vasodilation could result from an activation of beta(3)-ARs, but no data are available in the heart.

METHODS

The effect of nebivolol (0.1 nmol/l to 10 micromol/l) upon the developed peak tension was tested in endomyocardial biopsies from human nonrejecting transplanted hearts. Tension was recorded at steady state using a mechanoelectric force transducer.

RESULTS

Nebivolol induced a concentration-dependent decrease in peak tension (maximum effect obtained at 10 micromol/l: -55 +/- 4%, n = 6), which was similar to that obtained with a preferential beta(3)-AR agonist, BRL 37344 (maximum effect obtained at 1 micromol/l: -45 +/- 2%, n = 12). The nebivolol effect was not modified by 10 micromol/l nadolol, a beta(1,2)-AR antagonist, but was significantly reduced in the presence of 1 micromol/l L-748,337, a selective beta(3)-AR antagonist, and after pre-treatment with 100 micromol/l N(G)-monomethyl-L-arginine, an NOS inhibitor.

CONCLUSIONS

Our study demonstrated that nebivolol activated beta(3)-AR in the human ventricle. The NO-dependent negative inotropic effect of nebivolol associated with its vasodilating properties previously described in human microcoronary arteries could improve the energetic balance in heart. Those effects could explain the improvement of hemodynamic parameters obtained in patients with heart failure after nebivolol administration as previously described in clinical trials.

Nitric oxide mechanisms of nebivolol

β-blockers are among the most widely used drugs in the prevention and treatment of cardiovascular disease, although they are associated with increased peripheral resistance. Third-generation β-blockers avoid this adverse effect by inducing vasodilation through different mechanisms. In particular, nebivolol, a highly selective blocker of β1-adrenergic receptors, is the only β-blocker known to induce vascular production of nitric oxide, the main endothelial vasodilator. The specific mechanism of nebivolol is particularly relevant in hypertension, where nitric oxide dysfunction occurs. Indeed, nebivolol is able to reverse endothelial dysfunction. Nebivolol induces nitric oxide production via activation of β3-adrenergic receptors, which can explain the good metabolic profile observed after treatment with this drug. Moreover, nebivolol can also stimulate the β3-adrenergic receptor-mediated production of nitric oxide in the heart, and this stimulation can result in a greater protection against heart failure. In conclusion, nebivolol has a unique profile among antihypertensive drugs, adding to a very high selectivity against β1 adrenergic receptors, and an agonist action on β3 receptors and nitric oxide (NO), which has led to clinically significant improvements in hypertensive patients.

Investigation of the different adrenoceptor targets of nebivolol enantiomers in rat thoracic aorta

BACKGROUND AND PURPOSE

Nebivolol is a highly selective beta(1)-adrenoceptor antagonist with beta(3)-adrenoceptor agonist properties and is a racemate mixture of D- and L-enantiomers. However, the cellular mechanisms of the effects of each enantiomer are not yet clear and are a matter for debate. The aim of the present experiments was to determine the adrenoceptors involved in the vascular effects of D- and L-enantiomers of nebivolol in rat thoracic aorta.

EXPERIMENTAL APPROACH

Responses to nebivolol enantiomers were evaluated in rings of thoracic aorta from male Sprague-Dawley rats.

KEY RESULTS

D-nebivolol (0.1-10 micromol.L(-1)), but not L-nebivolol, significantly shifted to the right the concentration-response curve to phenylephrine, an alpha(1)-adrenoceptor agonist, in a concentration-dependent manner. For the following experiments, aortic rings were constricted with endothelin 1 and now both enantiomers produced an endothelium-dependent relaxation of the rings involving the nitric oxide pathway. This relaxation was not modified by 1 micromol.L(-1) CGP 20,712A (beta(1)-adrenoceptor antagonist), but significantly blunted by 7 micromol.L(-1) L-74,8337 (beta(3)-adrenoceptor antagonist). However, only the vasorelaxation induced by D-nebivolol was significantly reduced by 1 micromol.L(-1) ICI 118,551 (beta(2)-adrenoceptor antagonist).

CONCLUSIONS AND IMPLICATIONS

Our results suggest that the nebivolol enantiomers act on different targets. D-nebivolol induced vasorelaxation by activating beta(2)- and beta(3)-adrenoceptors and antagonizing alpha(1)-adrenoceptors. L-nebivolol induced vasorelaxation by activating only beta(3)-adrenoceptors in our model. Our results emphasize that nebivolol is a beta(1)-adrenoceptor antagonist with several important pharmacological differences from other beta(1)-adrenoceptor antagonists.

Genetics and pathophysiology of arterial stiffness

Arterial stiffness is a cardiovascular risk factor that is independent of arterial pressure. Clinically, carotid-femoral pulse wave velocity (PWV) is the gold-standard parameter of arterial stiffness. Recent genetic studies have revealed specific genes that contribute to arterial stiffening. Here we review the recent findings on genome-wide linkage analyses and candidate gene polymorphism association studies. We also focus on the latest advances in the identification of gene variants affecting PWV using high density array single nucleotide polymorphism technology in a recent genome-wide association (GWA) study. Linkage and polymorphism studies revealed a first group of genes affecting the renin-angiotensin-aldosterone system, elastic fibre structural components, metalloproteinases, and the NO pathway. A second group of genes, identified by polymorphism association studies and possibly involved in the pathophysiology of arterial stiffness, includes beta-adrenergic receptors, endothelin receptors, and inflammatory molecules. The last group of genes, identified by GWA studies and unrelated to currently suspected mechanisms of arterial stiffness, may target transcriptional pathways controlling gene expression, differentiation of vascular smooth muscle cells, apoptosis of endothelial cells, or the immune response within the vascular wall.

The beta3-adrenoceptor agonist 4-[[(Hexylamino)carbonyl]amino]-N-[4-[2-[[(2S)-2-hydroxy-3-(4-hydroxyphenoxy)propyl]amino]ethyl]-phenyl]-benzenesulfonamide (L755507) and antagonist (S)-N-[4-[2-[[3-[3-(acetamidomethyl)phenoxy]-2-hydroxypropyl]amino]-ethyl]phenyl]benzenesulfonamide (L748337) activate different signaling pathways in Chinese hamster ovary-K1 cells stably expressing the human beta3-adrenoceptor

This study identifies signaling pathways activated by the beta(2)-/beta(3)-adrenoceptor (AR) agonist zinterol, the selective beta(3)-AR agonist L755507, and the selective beta(3)-AR antagonist L748337 in CHO-K1 cells expressing human beta(3)-adrenoceptors. Zinterol and L755507 caused a robust concentration-dependent increase in cAMP accumulation (pEC(50) values of 8.5 and 12.3, respectively), whereas L748337 had low efficacy. Maximal cAMP accumulation with zinterol and L755507 was increased after pretreatment with pertussis toxin, indicating that the human beta(3)-AR couples to G(i) and to G(s). In contrast to cAMP, zinterol, L755507 and L748337 increased phosphorylation of extracellular signal-regulated kinase 1/2 (Erk1/2) with very high potency (pEC(50) values of 10.9, 11.7, and 11.6). These compounds also stimulated phosphorylation of p38 mitogen-activated protein kinase (MAPK) but with much lower potency than Erk1/2 (pEC(50) values of 5.9, 5.5, and 5.7, respectively). Pertussis toxin completely blocked Erk1/2 and p38 MAPK phosphorylation in response to L748337, demonstrating a requirement for G(i/o) coupling, whereas L755507-stimulated p38 MAPK phosphorylation was not inhibited by pertussis toxin, and Erk1/2 phosphorylation was inhibited by only 30%. We found that high levels of cAMP interfered with agonist-activated p38 MAPK phosphorylation. L748337 increased extracellular acidification rate (ECAR) in the cytosensor microphysiometer with efficacy similar to zinterol and L755507, albeit with lower potency (pEC(50) value of 7.2 compared with zinterol, 8.1, and L755507, 8.6). The ECAR response to L748337 was largely via activation of p38 MAPK, demonstrated by 65% inhibition with 4-[4-(4-fluorophenyl)-1-(3-phenylpropyl)-5-(4-pyridinyl)-1H-imidazol-2-yl]-3-butyn-1-ol (RWJ67657). We conclude that the beta(3)-AR agonist L755507 couples to both G(s) and G(i) to activate adenylate cyclase and MAPK signaling, whereas the beta(3)-AR antagonist L748337 couples predominantly to G(i) to activate MAPK signaling.

Nebivolol Induces Nitric Oxide Release in the Heart Through Inducible Nitric Oxide Synthase Activation

Nebivolol is a beta1-adrenergic receptor antagonist that also reduces blood pressure by evoking endothelial NO production and vasodilation. We aimed at assessing whether nebivolol induces NO production also in the heart and delineating the molecular mechanisms involved. Using the fluorescent probe diaminofluorescein, we found that nebivolol induces a dose-dependent NO production in the heart, statistically significant already at 10(-7) mol/L. It is not an effect because of the blockade of beta1-adrenergic receptor, because this effect is not shared by another drug of the same class, atenolol. Because nebivolol has been reported to act as an agonist on other beta-adrenergic receptors, we tested NO production in the presence of receptor antagonists. Nebivolol was not able to induce NO production in presence of the beta3-antagonist SR59230A, indicating a fundamental role for beta3-adrenergic receptors in cardiac NO production by nebivolol. Moreover, inducible NO synthase inhibition abolishes NO release in the heart, indicating that nebivolol induces NO production by acting on the inducible isoform of the enzyme. The action of nebivolol on inducible NO synthase was confirmed by real-time PCR experiments, showing cardiac overexpression of inducible NO synthase but not neuronal NO synthase or endothelial NO synthase, after 5 hours of treatment with nebivolol. In conclusion, our study demonstrates that nebivolol also stimulates NO production in the heart. This action of nebivolol is exerted via a signaling pathway starting from the activation of beta3-adrenergic receptors and leading to overexpression of inducible NO synthase. Cardiac NO production by nebivolol could participate in the cardiovascular effects of nebivolol treatment in patients affected by hypertension and heart failure.

Vasodilator Effects of Nebivolol in a Rat Model of Hypertension and a Rabbit Model of Congestive Heart Failure

Both hypertension and congestive heart failure are characterized by a reduced vasodilatory capacity. In both conditions, the impairment of endothelial function is mainly the result of a reduced nitric oxide availability. The highly beta1-selective third-generation adrenoceptor blocker nebivolol displays additional endothelium-dependent vasodilating actions in humans as well as in animal models. In this study, we investigated whether these vasodilating properties of nebivolol are preserved in conditions with endothelial dysfunction. The vasodilatory effects of nebivolol were compared with those of the muscarinic agonist methacholine in isolated aortic rings obtained from spontaneous hypertensive rats and rabbits with experimental heart failure. The methacholine-induced responses were attenuated in aortic rings from both spontaneous hypertensive rats and congestive heart failture rabbits (42+/-6% and 25+/-3% vs. 89+/-3% and 54+/-7% for controls, respectively; P<0.05, n=6-13), indicating an endothelial dysfunction in these preparations. In contrast, nebivolol-induced vasorelaxation remained unaffected in both preparations when compared to control preparations (40+/-12% and 43+/-6% vs. 52+/-8% and 50+/-13% for controls, respectively; P>0.05, n=6-13). These results implicate that the favorable hemodynamic profile of nebivolol may be preserved in patients with hypertension or congestive heart failure despite an impaired endothelial function.

Evidence for an estradiol-agonistic action of nebivolol in spontaneously hypertensive rats

OBJECTIVES

Unlike classical beta1-selective blockers, nebivolol (NEB) has vasodilatory properties due to the release of nitric oxide (NO) by a mechanism that is, so far, unknown. We hypothesized that NEB stimulates NO release by binding to estrogen receptors (ER) and subsequent activation of endothelial NO synthase (eNOS). The aim of this study was to elucidate the underlying mechanism of NEB action by investigating estradiol-dependent effects of NEB on the NO system in spontaneously hypertensive rats (SHR).

METHODS

The effects of NEB on the NO system were determined by measuring urinary nitrate/nitrite (NOx) as well as eNOS and caveolin-1 protein expression in aortae.

RESULTS

NEB did not influence NOx excretion in sham-operated (SO) female rats during proestrus. In male and ovariectomized female (OVX) rats, NEB increased NOx excretion significantly, whereas N(G)-nitro-L-arginine methyl ester (L-NAME) inhibited the NEB-induced increase in NOx. ER blockade with ICI182,780 prevented NEB-induced NOx excretion in OVX rats. In the aortae of SO females, NEB treatment did not alter eNOS expression. In OVX rats eNOS expression was increased two-fold after NEB application and this could be prevented by pretreatment with ICI182,780. In contrast to eNOS, NEB did not influence caveolin-1 expression in either group.

CONCLUSION

The ability of NEB to up-regulate NOx excretion in male and OVX SHR and the inhibitory effect of ICI182,780 on NEB-induced NOx excretion suggests that NEB has an estradiol-agonistic action in vivo. NEB provokes NO generation by up-regulation of eNOS protein expression, whereas the expression of the negative eNOS regulator caveolin-1 remains unaffected.

Are we misunderstanding beta-blockers

In myocardial ischaemia and heart failure, beta-blockers with intrinsic sympathomimetic activity (ISA) e.g. pindolol, xamoterol, bucindolol, nebivolol, have performed poorly in reducing morbidity and mortality. In both indications beta-1 blockade is the vital active ingredient. Beta-1 blockade (bisoprolol) is now an alternative first-line choice to Ace-inhibition in the treatment of heart failure. The therapeutic role of beta-blockers in hypertension is less well understood, particularly since the new recommendations in the UK from the NICE committee stating that: 1. beta-blockers are no longer preferred as a routine initial therapy, 2. the combination with diuretics is discouraged due to the risk of induced diabetes, and 3. in younger patients first-choice initial therapy should be an ACE-inhibitor. Recent data from the Framingham Heart Study and other epidemiological studies have indicated that the development of diastolic hypertension in younger subjects is closely linked to weight-increase and an increase in peripheral resistance; such subjects have a high adrenergic drive and cardiac output. In contrast, elderly systolic hypertension mostly arises de novo via poor vascular compliance. Thus in younger, probably overweight, hypertensives (including diabetics) first-line beta-blockade has performed well in preventing myocardial infarction (a fact hidden by meta-analyses that do not take age into account). Conversely, in elderly hypertensives first-line beta-blockade (atenolol) has performed poorly in reducing cardiovascular risk (due to partial beta-2 blockade atenolol evokes metabolic disturbance and does not improve vascular compliance, or effectively lower central aortic pressure or reverse left ventricular hypertrophy). Thus beta-blockers like atenolol are ill-equipped for first-line therapy in elderly hypertension. Some beta-blockers, e.g. bisoprolol (up to 10 mg/day is highly beta-1 selective) and nebivolol (beta-2/3 intrinsic sympathomimetic activity), do improve vascular compliance and cause no metabolic disturbance. Beta-blockers as second-line to low-dose diuretics (which, by improving vascular compliance and increasing sympathetic nerve activity, create an optimal environment for beta-blockade) in elderly hypertension (including diabetics) have performed well in reducing cardiovascular events (this combination has the added bonus of reducing the risk of bone fracture by about 30%). Meta-analyses which include studies where it is unclear whether a diuretic or beta-blocker was a first-line therapy will dilute the benefit stemming from first-line diuretic/second-line beta-blockade. Hypertensives (of all ages) with ischaemia are well suited to beta-blockade.

Effect of dl-nebivolol, its enantiomers and metabolites on the intracellular production of superoxide and nitric oxide in human endothelial cells

Nebivolol, a third generation selective beta(1)-adrenoceptor (beta(1)-AR) antagonist, has been reported to reduce intracellular oxidative stress and to induce the release of nitric oxide (NO) from the endothelium. Nebivolol is also subjected to a complex metabolic process where glucuronidation, aromatic and alicyclic hydroxylation are the major pathways leading to several metabolites. We have studied the effect of nebivolol, its enantiomers and metabolites on intracellular oxidative stress and NO availability in human umbilical vein endothelial cells (HUVECs). Furthermore, since the receptors involved in this endothelial effect of nebivolol remain controversial, we have studied this matter by the use of antagonists of beta-AR. dl-Nebivolol, d-nebivolol and l-nebivolol significantly reduced the formation of reactive oxygen species (ROS) and superoxide induced by oxidized-low density lipoprotein (ox-LDL), although the racemic and l-form were significantly more active than d-nebivolol in this activity. A marked decrease in the availability of intracellular NO was found in HUVECs exposed to ox-LDL and this parameter was normalized by the prior incubation with dl-nebivolol, d-nebivolol and l-nebivolol; the effect of racemate was mainly mimicked by its l-enantiomer. eNOS activity significantly increased by a 5-min contact of HUVECs with dl-nebivolol and l-nebivolol, but not with d-nebivolol, and a similar pattern was observed when the intracellular calcium increase was measured. The metabolites A2, A3', A12 and A14 but not A1, A3 and R 81,928, derived from different metabolic pathways, retained the antioxidant activity of the parent racemic compound dl-nebivolol, reducing the intracellular formation of ROS and superoxide. The effects of dl-nebivolol on intracellular formation of NO, eNOS activity and intracellular Ca(2+) were partially antagonized by the antagonists of beta(1-2)-AR nadolol or by the beta(3)-AR antagonist SR59230A and further antagonized by their combination or by (beta(1-2-3)-AR antagonist bupranolol. In conclusion, this study shows that the NO releasing effect of nebivolol is mainly due to its l-enantiomer; the racemate and its enantiomers possess a remarkable antioxidant activity that contributes to its effect on the cellular NO metabolism and the activation of beta(3)-AR through a calcium dependent pathway is involved in the mechanisms leading to the NO release.

New drugs for hypertension: What do they offer?

A new drug might make a positive contribution to existing therapies for hypertension by: 1) reducing blood pressure (BP) via a novel pharmacologic mechanism; 2) possessing pharmacologic or pharmacokinetic properties that make it superior to other members of its class; or 3) facilitating BP control in refractory patients. In this paper, we review four experimental agents that promise to advance therapeutics by one of these mechanisms. Aliskiren is the first in a new class of potent, orally effective renin inhibitors. Aliskiren produces dose-dependent BP reduction with few side effects and constitutes a novel pharmacologic approach to renin-angiotensin-aldosterone inhibition. Nebivolol is a third-generation, cardioselective beta-blocker that produces vasodilation and improves endothelial function via the l-arginine/nitric oxide pathway. Clevidipine is an ultra-short-acting, vascular-selective, dihydropyridine calcium antagonist that is being developed for intravenous use in acute hospitalized patients. Darusentan is an endothelin(A) selective endothelin receptor antagonist that is effective in achieving BP control in a significant percentage of patients who remain uncontrolled despite treatment with three or more antihypertensive drugs.