Nebivolol, carvedilol and metoprolol do not influence cardiac Ca(2+) sensitivity

Negative inotropic mechanisms of β-cardiotoxin in cardiomyocytes by depression of myofilament ATPase activity without activation of the classical β-adrenergic pathway

Beta-cardiotoxin (β-CTX) from the king cobra venom (Ophiophagus hannah) was previously proposed as a novel β-adrenergic blocker. However, the involvement of β-adrenergic signaling by this compound has never been elucidated. The objectives of this study were to investigate the underlying mechanisms of β-CTX as a β-blocker and its association with the β-adrenergic pathway. The effects of β-CTX on isolated cardiac myocyte functions, calcium homeostasis, the phosphorylation level of targeted proteins, and the myofibrillar ATPase activity were studied. Healthy Sprague Dawley rats were used for cardiomyocytes isolation. Like propranolol, β-CTX attenuated the cardiomyocyte inotropy and calcium transient alterations as induced by isoproterenol stimulation. In contrast, these effects were not observed in forskolin-treated cells. Interestingly, cardiomyocytes treated with β-CTX showed no changes in phosphorylation level at any PKA-targeted sites in the myofilaments as demonstrated in Western blot analysis. The skinned fibers study revealed no change in myofilament kinetics by β-CTX. However, this protein exhibited the direct inhibition of myofibrillar ATPase activity with calcium de-sensitization of the enzyme. In summary, the negative inotropic mechanism of β-CTX was discovered. β-CTX exhibits an atypical β-blocker mechanism. These properties of β-CTX may benefit in developing a novel agent aid to treat hypertrophic cardiomyopathy.

Nebivolol Desensitizes Myofilaments of a Hypertrophic Cardiomyopathy Mouse Model

Background: Hypertrophic cardiomyopathy (HCM) patients often present with diastolic dysfunction and a normal to supranormal systolic function. To counteract this hypercontractility, guideline therapies advocate treatment with beta-adrenoceptor and Ca²⁺ channel blockers. One well established pathomechanism for the hypercontractile phenotype frequently observed in HCM patients and several HCM mouse models is an increased myofilament Ca²⁺ sensitivity. Nebivolol, a commonly used beta-adrenoceptor antagonist, has been reported to lower maximal force development and myofilament Ca²⁺ sensitivity in rabbit and human heart tissues. The aim of this study was to evaluate the effect of nebivolol in cardiac muscle strips of an established HCM Mybpc3 mouse model. Furthermore, we investigated actions of nebivolol and epigallocatechin-gallate, which has been shown to desensitize myofilaments for Ca²⁺ in mouse and human HCM models, in cardiac strips of HCM patients with a mutation in the most frequently mutated HCM gene MYBPC3.

Methods and Results: Nebivolol effects were tested on contractile parameters and force-Ca²⁺ relationship of skinned ventricular muscle strips isolated from Mybpc3-targeted knock-in (KI), wild-type (WT) mice and cardiac strips of three HCM patients with MYBPC3 mutations. At baseline, KI strips showed no difference in maximal force development compared to WT mouse heart strips. Neither 1 nor 10 μM nebivolol had an effect on maximal force development in both genotypes. 10 μM nebivolol induced myofilament Ca²⁺ desensitization in WT strips and to a greater extent in KI strips. Neither 1 nor 10 μM nebivolol had an effect on Ca²⁺ sensitivity in cardiac muscle strips of three HCM patients with MYBPC3 mutations, whereas epigallocatechin-gallate induced a right shift in the force-Ca²⁺ curve.

Conclusion: Nebivolol induced a myofilament Ca²⁺ desensitization in both WT and KI strips, which was more pronounced in KI muscle strips. In human cardiac muscle strips of three HCM patients nebivolol had no effect on myofilament Ca²⁺ sensitivity.

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.

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.

Chronic treatment with carvedilol improves Ca(2+)-dependent ATP consumption in triton X-skinned fiber preparations of human myocardium

Evidence is given that beta-blocker treatment differentially influences gene expression and up-regulation of beta(1)-adrenoceptors in human myocardium. Here, we investigate whether long-term treatment with carvedilol or metoprolol may functionally alter myofibrillar function in end-stage human heart failure. Investigations were performed in Triton X (1%, 4 degrees C, 20 h)-skinned fiber preparations of explanted hearts from patients undergoing heart transplantation due to idiopathic dilative cardiomyopathy. Five patients were not on beta-adrenoceptor blocker treatment (DCM_NBB), and 5 patients received either carvedilol (DCM_CAR) or metoprolol (DCM_MET). Nonfailing (NF) donor hearts (n = 5), which could not be transplanted due to technical reasons, were investigated for comparison. Ca(2+)-dependent tension (DT) development and actomyosin-ATPase activity (MYO) were measured and tension-dependent ATP consumption was calculated by the ratio of DT and MYO ("tension cost"). In addition, we measured the phosphorylation of troponin I (TNI) by back phosphorylation. Maximal DT and TNI phosphorylation were reduced, with myofibrillar Ca(2+) sensitivity of DT and MYO as well as tension cost being increased in DCM_NBB compared with NF. Metoprolol treatment restored TNI phosphorylation, decreased Ca(2+) sensitivity of tension development and of myosin-ATPase activity, but did not alter the tension-dependent ATP consumption. Carvedilol treatment improved maximal DT and significantly decreased tension-dependent ATP consumption without altering myofibrillar Ca(2+) sensitivity. TNI dephosphorylation was increased in patients treated with carvedilol. In conclusion, chronic beta-adrenoceptor blockade functionally alters myofibrillar function. The more economic cross-bridge cycling in patients under carvedilol treatment may provide an explanation for the efficacy of carvedilol in the treatment of chronic heart failure patients.

Lack of inverse agonistic activity of nebivolol, its D- and L-enantiomers and of in vivo metabolized nebivolol in human myocardium

The pharmacological profile of nebivolol may be mediated by its enantiomers and/or its hydroxylated metabolites. Therefore, the cardiac effects of the nebivolol enantiomers as well as of serum specimens containing hydroxylated nebivolol metabolites were studied in human myocardium. For control, the beta1-adrenoceptor selective antagonist metoprolol was used. After pre-stimulation of force of contraction with forskolin (0.3 microM) or isoprenaline (0.01 microM), force developement was decreased only at high concentrations (> or =300 nM) of nebivolol or its enantiomers in isolated trabeculae. Nebivolol and its enantiomers, in contrast to metoprolol (0.4 microM: -72% basal force), produced only minor negative intropic effects in isolated trabeculae under basal conditions. Basal force of contraction was not decreased by in vivo metabolized nebivolol in pharmacological concentrations. Neither D- nor L-nebivolol (30 microM) influenced myofibrillar Ca2+ responsiveness. Nebivolol and the D-enantiomer, but not the L-enantiomer (all 0.5 microM), improved the frequency-dependent force generation. D-Nebivolol, in contrast to L-nebivolol, was a beta1-adrenoceptor selective compound in membrane preparations from non-failing donor hearts. In conclusion, nebivolol and its enantiomers as well as in vivo metabolized nebivolol produce only minor negative inotropic effects. This and the finding that nebivolol and its D-enantiomer improve the frequency-dependent force generation may be of particular advantage when treating patients with already compromised cardiac function.