Cardio-selective beta-blocker: pharmacological evidence and their influence on exercise capacity

Neurotransmitter Switching Coupled to β-Adrenergic Signaling in Sympathetic Neurons in Prehypertensive States

Single or combinatorial administration of β-blockers is a mainstay treatment strategy for conditions caused by sympathetic overactivity. Conventional wisdom suggests that the main beneficial effect of β-blockers includes resensitization and restoration of β1-adrenergic signaling pathways in the myocardium, improvements in cardiomyocyte contractility, and reversal of ventricular sensitization. However, emerging evidence indicates that another beneficial effect of β-blockers in disease may reside in sympathetic neurons. We investigated whether β-adrenoceptors are present on postganglionic sympathetic neurons and facilitate neurotransmission in a feed-forward manner. Using a combination of immunocytochemistry, RNA sequencing, Förster resonance energy transfer, and intracellular Ca2+ imaging, we demonstrate the presence of β-adrenoceptors on presynaptic sympathetic neurons in both human and rat stellate ganglia. In diseased neurons from the prehypertensive rat, there was enhanced β-adrenoceptor-mediated signaling predominantly via β2-adrenoceptor activation. Moreover, in human and rat neurons, we identified the presence of the epinephrine-synthesizing enzyme PNMT (phenylethanolamine-N-methyltransferase). Using high-pressure liquid chromatography with electrochemical detection, we measured greater epinephrine content and evoked release from the prehypertensive rat cardiac-stellate ganglia. We conclude that neurotransmitter switching resulting in enhanced epinephrine release, may provide presynaptic positive feedback on β-adrenoceptors to promote further release, that leads to greater postsynaptic excitability in disease, before increases in arterial blood pressure. Targeting neuronal β-adrenoceptor downstream signaling could provide therapeutic opportunity to minimize end-organ damage caused by sympathetic overactivity.

Genome-Wide Association Approach Identified Novel Genetic Predictors of Heart Rate Response to β-Blockers

Background

For many indications, the negative chronotropic effect of β‐blockers is important to their efficacy, yet the heart rate (HR) response to β‐blockers varies. Herein, we sought to use a genome‐wide association approach to identify novel single nucleotide polymorphisms (SNPs) associated with HR response to β‐blockers.

Methods and Results

We first performed 4 genome‐wide association analyses for HR response to atenolol (a β1‐adrenergic receptor blocker) as: (1) monotherapy or (2) add‐on therapy, in 426 whites and 273 blacks separately from the PEAR (Pharmacogenomic Evaluation of Antihypertensive Responses) study. A meta‐analysis was then performed between the genome‐wide association analysis performed in PEAR atenolol monotherapy and add‐on therapy, in each race separately, using the inverse variance method assuming fixed effects. From this analysis, SNPs associated with HR response to atenolol at a P<1E‐05 were tested for replication in whites (n=200) and blacks (n=168) treated with metoprolol (a β1‐adrenergic receptor blocker). From the genome‐wide association meta‐analyses, SNP rs17117817 near olfactory receptor family10 subfamily‐p‐member1 (OR10P1), and SNP rs2364349 in sorting nexin‐9 (SNX9) replicated in blacks. The combined studies meta‐analysis P values for the rs17117817 and rs2364349 reached genome‐wide significance (rs17117817G‐allele; Meta‐β=5.53 beats per minute, Meta‐P=2E‐09 and rs2364349 A‐allele; Meta‐β=3.5 beats per minute, Meta‐P=1E‐08). Additionally, SNPs in the OR10P1 and SNX9 gene regions were also associated with HR response in whites.

Conclusions

This study highlights OR10P1 and SNX9 as novel genes associated with changes in HR in response to β‐blockers.

Clinical Trial Registration

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00246519.

Sympathetically mediated cardiac responses to isolated muscle metaboreflex activation following exercise are modulated by body position in humans

Isolated muscle metaboreflex activation with posthandgrip exercise ischemia (PEI) increases sympathetic nerve activity and partially maintains the exercise-induced increase in blood pressure, but a smaller heart rate (HR) response occurs. The cardiopulmonary baroreceptors, mechanically sensitive receptors that respond to changes in central blood volume and pressure, are strongly associated with changes in body position and upon activation elicit reflex sympathoinhibition. Here, we tested the hypothesis that postural changes modulate the sympathetically mediated cardiac response to PEI in humans. Beat-to-beat HR (electrocardiography) and blood pressure (finger photoplethysmography) were continuously measured, and cardiac function was assessed by echocardiography in 13 healthy men (21 ± 3 yr). After a 15-min rest period, 90-s static handgrip at 40% maximum voluntary contraction was performed followed by 3 min of PEI. Four trials were randomly conducted during either seated or supine position with and without β₁-adrenergic blockade (25 mg atenolol). During PEI under control conditions, HR remained elevated from baseline in the seated [change (Δ): 4 ± 1 beats/min] but not in the supine (change: -1 ± 1 beats/min) position. Similarly, stroke volume and cardiac output were increased from baseline in the seated (∆13.0 ± 2.4 ml and ∆1.1 ± 0.2 l/min, respectively) but not in the supine (∆2.5 ± 2.9 ml and ∆0.13 ± 0.20 l/min, respectively) position. During β₁-adrenergic blockade, HR, stroke volume, and cardiac output remained unchanged in both conditions. We conclude that sympathetically mediated cardiac responses to PEI are influenced by changes in body position. These findings indicated that muscle metaboreflex and cardiopulmonary baroreflex have an interactive influence on the neural control of cardiovascular function in humans. NEW & NOTEWORTHY In the present study, we demonstrated that muscle metaboreflex activation increases heart rate, stroke volume, and cardiac output in the seated position but not in the supine position and not after β₁-adrenergic blockade. These findings indicate that sympathetically mediated cardiac responses to isolated muscle metaboreflex activation after exercise are modulated by central blood volume mobilization.

Management of Supraventricular Tachycardia in Infants

Supraventricular tachycardia is the most common tachyarrhythmia encountered in infants. In older children and adults, definitive treatment of the supraventricular tachycardia substrate with catheter ablation is a common approach to management. However, in infants, the risks of catheter ablation are significantly higher, and the patients often outgrow the potential to experience episodes. Therefore, antiarrhythmic medications are often utilized to minimize the likelihood of experiencing episodes. This article reviews the common arrhythmia mechanisms encountered in infants and the medications used to treat these patients.

Synthesis and activity of newly designed aroxyalkyl or aroxyethoxyethyl derivatives of piperazine on the cardiovascular and the central nervous systems

In the search for new hypotensive agents some new aroxyalkyl or aroxyethoxyethyl derivatives of piperazine have been synthesized and evaluated for their pharmacological properties. Pharmacological tests included receptor binding assays toward adrenergic receptors α₁, α₂ and β₁, additionally 5-HT_1A, functional bioassay and in vivo evaluation of hypotensive activity as well as antidepressant-like potential. All the tested compounds exhibited α₁-antagonistic properties, three of them possessed also hypotensive activity in rats. The most promising compound 3 1-[4-(2,6-dimethylphenoxy)butyl]-4-(2-methoxyphenyl)piperazine hydrochloride was a selective α₁ receptor antagonist (K_i=23.5±1.3, α₁/α₂=15.77, pK_B=8.538±0.109). It was active in all tested doses in vivo (1, 0.5, and 0.1mg/kg) and it reduced blood pressure by 10-13% at the dose of 1mg/kg (rats, i.v.). Compound 5 1-[2-(2,3-dimethylphenoxy)ethoxyethyl]-4-(2-methoxyphenyl)piperazine dihydrochloride exhibited the lowest dose for antidepressant-like activity 5mg/kgb.w. (mice, i.p.) without influence on spontaneous activity (mice, i.p.).

C-Type Natriuretic Peptide Improves Left Ventricular Functional Performance at Rest and Restores Normal Exercise Responses after Heart Failure

In heart failure (HF), the impaired left ventricular (LV) arterial coupling and diastolic dysfunction present at rest are exacerbated during exercise. C-type natriuretic peptide (CNP) is elevated in HF; however, its functional effects are unclear. We tested the hypotheses that CNP with vasodilating, natriuretic, and positive inotropic and lusitropic actions may prevent this abnormal exercise response after HF. We determined the effects of CNP (2 μg/kg plus 0.4 μg/kg per minute, i.v., 20 minutes) on plasma levels of cGMP before and after HF and assessed LV dynamics during exercise in 10 chronically instrumented dogs with pacing-induced HF. Compared with the levels before HF, CNP infusion caused significantly greater increases in cGMP levels after HF. After HF, at rest, CNP administration significantly reduced LV end-systolic pressure (PES), arterial elastance (EA), and end-diastolic pressure. The peak mitral flow (dV/dtmax) was also increased owing to decreased minimum LVP (LVPmin) and the time constant of LV relaxation (τ) (P < 0.05). In addition, LV contractility (EES) was increased. The LV-arterial coupling (EES/EA) was improved. The beneficial effects persisted during exercise. Compared with exercise in HF preparation, treatment with CNP caused significantly less important increases in PES but significantly decreased τ (34.2 vs. 42.6 ms) and minimum left ventricular pressure with further augmented dV/dtmax Both EES, EES/EA (0.87 vs. 0.32) were increased. LV mechanical efficiency improved from 0.38 to 0.57 (P < 0.05). After HF, exogenous CNP produces arterial vasodilatation and augments LV contraction, relaxation, diastolic filling, and LV arterial coupling, thus improving LV performance at rest and restoring normal exercise responses after HF.

Analysis of Skeletal Muscle Torque Capacity and Circulating Ceramides in Patients with Advanced Heart Failure

BACKGROUND

Heart failure (HF)-related exercise intolerance is thought to be perpetuated by peripheral skeletal muscle functional, structural, and metabolic abnormalities. We analyzed specific dynamics of muscle contraction in patients with HF compared with healthy, sedentary controls.

METHODS

Isometric and isokinetic muscle parameters were measured in the dominant upper and lower limbs of 45 HF patients and 15 healthy age-matched controls. Measurements included peak torque normalized to body weight, work normalized to body weight, power, time to peak torque, and acceleration and deceleration to maximum strength times. Body morphometry (dual energy X-ray absorptiometry scan) and circulating fatty acids and ceramides (lipodomics) were analyzed in a subset of subjects (18 HF and 9 controls).

RESULTS

Extension and flexion time-to-peak torque was longer in the lower limbs of HF patients. Furthermore, acceleration and deceleration times in the lower limbs were also prolonged in HF subjects. HF subjects had increased adiposity and decreased lean muscle mass compared with controls. Decreased circulating unsaturated fatty acids and increased ceramides were found in subjects with HF.

CONCLUSIONS

Delayed torque development suggests skeletal muscle impairments that may reflect abnormal neuromuscular functional coupling. These impairments may be further compounded by increased adiposity and inflammation associated with increased ceramides.

Aerobic Exercise and Pharmacological Therapies for Skeletal Myopathy in Heart Failure: Similarities and Differences

Skeletal myopathy has been identified as a major comorbidity of heart failure (HF) affecting up to 20% of ambulatory patients leading to shortness of breath, early fatigue, and exercise intolerance. Neurohumoral blockade, through the inhibition of renin angiotensin aldosterone system (RAS) and β-adrenergic receptor blockade (β-blockers), is a mandatory pharmacological therapy of HF since it reduces symptoms, mortality, and sudden death. However, the effect of these drugs on skeletal myopathy needs to be clarified, since exercise intolerance remains in HF patients optimized with β-blockers and inhibitors of RAS. Aerobic exercise training (AET) is efficient in counteracting skeletal myopathy and in improving functional capacity and quality of life. Indeed, AET has beneficial effects on failing heart itself despite being of less magnitude compared with neurohumoral blockade. In this way, AET should be implemented in the care standards, together with pharmacological therapies. Since both neurohumoral inhibition and AET have a direct and/or indirect impact on skeletal muscle, this review aims to provide an overview of the isolated effects of these therapeutic approaches in counteracting skeletal myopathy in HF. The similarities and dissimilarities of neurohumoral inhibition and AET therapies are also discussed to identify potential advantageous effects of these combined therapies for treating HF.

Orthostatic plasma norepinephrine level as a predictor for therapeutic response to metoprolol in children with postural tachycardia syndrome

Background

Postural tachycardia syndrome (POTS) is a heterogeneous disorder that creates challenges for treatment. Beta-blocker was one of the most commonly used drugs, but it is inconsistently effective. The purpose of this study is to explore whether orthostatic plasma norepinephrine level could be an indicator of therapeutic effectiveness of metoprolol for POTS in children.

Methods

Twenty-seven children with POTS were enrolled in our study. They received metoprolol treatment, and their orthostatic plasma norepinephrine levels were measured by high-performance liquid chromatography method. Three months after rmetoprolol treatment, 25 patients were followed up. A receiver-operating characteristic (ROC) curve was used to explore the predictive value of orthostatic plasma norepinephrine level.

Results

The symptom severity and increment of heat rate from supine position to upright of patients positively correlated with their orthostatic plasma norepinephrine level (r = 0.599, P < 0.001; r = 0.633, P <0.001, respectively). Orthostatic plasma norepinephrine level in responders to metoprolol was significantly higher than that of nonresponders (P = 0.028). A ROC curve on the predictive value of orthostatic plasma norepinephrine level showed that the area under the curve was 0.785. Using a cutoff value for orthostatic plasma norepinephrine level of 3.59 pg/ml yielded both sensitivity (76.9%) and specificity (91.7%) in predicting the efficacy of metoprolol therapy for POTS.

Conclusion

Orthostatic plasma norepinephrine level of > 3.59 pg/ml was an indicator of the effectiveness of metoprolol therapy for POTS in children and adolescents.

β3-Adrenergic receptor antagonist improves exercise performance in pacing-induced heart failure

In heart failure (HF), the impaired left ventricular (LV) arterial coupling and diastolic dysfunction present at rest are exacerbated during exercise. We have previously shown that in HF at rest stimulation of β3-adrenergic receptors by endogenous catecholamine depresses LV contraction and relaxation. β3-Adrenergic receptors are activated at higher concentrations of catecholamine. Thus exercise may cause increased stimulation of cardiac β3-adrenergic receptors and contribute to this abnormal response. We assessed the effect of L-748,337 (50 μg/kg iv), a selective β3-adrenergic receptor antagonist (β3-ANT), on LV dynamics during exercise in 12 chronically instrumented dogs with pacing-induced HF. Compared with HF at rest, exercise increased LV end-systolic pressure (PES), minimum LV pressure (LVPmin), and the time constant of LV relaxation (τ) with an upward shift of early diastolic portion of LV pressure-volume loop. LV contractility decreased and arterial elastance (EA) increased. LV arterial coupling (EES/EA) (0.40 vs. 0.51) was impaired. Compared with exercise in HF preparation, exercise after β3-ANT caused similar increases in heart rate and PES but significantly decreased τ (34.9 vs. 38.3 ms) and LVPmin with a downward shift of the early diastolic portion of LV pressure-volume loop and further augmented dV/dtmax. Both EES and EES/EA (0.68 vs. 0.40) were increased. LV mechanical efficiency improved from 0.39 to 0.53. In conclusion, after HF, β3-ANT improves LV diastolic filling; increases LV contractility, LV arterial coupling, and mechanical efficiency; and improves exercise performance.

Low-dose propranolol and exercise capacity in postural tachycardia syndrome: a randomized study

OBJECTIVE

To determine the effect of low-dose propranolol on maximal exercise capacity in patients with postural tachycardia syndrome (POTS).

METHODS

We compared the effect of placebo vs a single low dose of propranolol (20 mg) on peak oxygen consumption (VO2max), an established measure of exercise capacity, in 11 patients with POTS and 7 healthy subjects in a randomized, double-blind study. Subjects exercised on a semirecumbent bicycle, with increasing intervals of resistance to maximal effort.

RESULTS

Maximal exercise capacity was similar between groups following placebo. Low-dose propranolol improved VO2max in patients with POTS (24.5 ± 0.7 placebo vs 27.6 ± 1.0 mL/min/kg propranolol; p = 0.024), but not healthy subjects. The increase in VO2max in POTS was associated with attenuated peak heart rate responses (142 ± 8 propranolol vs 165 ± 4 bpm placebo; p = 0.005) and improved stroke volume (81 ± 4 propranolol vs 67 ± 3 mL placebo; p = 0.013). In a separate cohort of POTS patients, neither high-dose propranolol (80 mg) nor metoprolol (100 mg) improved VO2max, despite similar lowering of heart rate.

CONCLUSIONS

These findings suggest that nonselective β-blockade with propranolol, when used at the low doses frequently used for treatment of POTS, may provide a modest beneficial effect to improve heart rate control and exercise capacity.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that a single low dose of propranolol (20 mg) as compared with placebo is useful in increasing maximum exercise capacity measured 1 hour after medication.

Insulin resistance and heart failure: molecular mechanisms

This article addresses the issue of insulin resistance and associated reductions in cardiac insulin metabolic signaling, which is emerging as a major factor in the development of heart failure, and assumes more importance because of an epidemic increase in obesity and the cardiorenal metabolic syndrome in our aging population. The effects of cardiac insulin resistance are exacerbated by metabolic, endocrine, and cytokine alterations associated with systemic insulin resistance. Understanding the molecular mechanisms linking insulin resistance and heart failure may help to design new and more effective mechanism-based drugs to improve myocardial and systemic insulin resistance.