Influence of beta-blockers on mortality in chronic heart failure

Exploring the kinetic selectivity of drugs targeting the β1 -adrenoceptor

In this study, we report the β1 -adrenoceptor binding kinetics of several clinically relevant β1/2 -adrenoceptor (β1/2 AR) agonists and antagonists. [3 H]-DHA was used to label CHO-β1 AR for binding studies. The kinetics of ligand binding was assessed using a competition association binding method. Ligand physicochemical properties, including logD7.4 and the immobilized artificial membrane partition coefficient (KIAM ), were assessed using column-based methods. Protein Data Bank (PDB) structures and hydrophobic and electrostatic surface maps were constructed in PyMOL. We demonstrate that the hydrophobic properties of a molecule directly affect its kinetic association rate (kon ) and affinity for the β1 AR. In contrast to our findings at the β2 -adrenoceptor, KIAM , reflecting both hydrophobic and electrostatic interactions of the drug with the charged surface of biological membranes, was no better predictor than simple hydrophobicity measurements such as clogP or logD7.4 , at predicting association rate. Bisoprolol proved kinetically selective for the β1 AR subtype, dissociating 50 times slower and partly explaining its higher measured affinity for the β1 AR. We speculate that the association of positively charged ligands at the β1 AR is curtailed somewhat by its predominantly neutral/positive charged extracellular surface. Consequently, hydrophobic interactions in the ligand-binding pocket dominate the kinetics of ligand binding. In comparison at the β2 AR, a combination of hydrophobicity and negative charge attracts basic, positively charged ligands to the receptor's surface promoting the kinetics of ligand binding. Additionally, we reveal the potential role kinetics plays in the on-target and off-target pharmacology of clinically used β-blockers.

Death and hospitalization in heart failure patients receiving carvedilol vs. metoprolol tartrate

BACKGROUND

The Carvedilol or Metoprolol European Trial (COMET) demonstrated improved survival with carvedilol vs. metoprolol tartrate in patients with heart failure. The benefits of carvedilol in typical clinical practice in the United States are unknown.

METHODS

Using data from a large United States health-insurance claims database, we conducted a retrospective study to compare the risks of death and hospitalization and the cost of inpatient care in heart failure patients receiving carvedilol vs. metoprolol tartrate. The sample consisted of all patients with a prescription for carvedilol or metoprolol tartrate between September 1997 and August 2000 who also had a prior medical encounter with a primary diagnosis of heart failure, prior prescriptions for a loop diuretic and an angiotensin-converting enzyme inhibitor, and no prior prescriptions for a beta-blocker.

RESULTS

We identified 887 carvedilol patients and an equal number that received metoprolol tartrate. Mean duration of follow-up was 11 months (maximum, 36 months). Controlling for baseline characteristics using a Cox proportional hazards model, carvedilol was independently associated with a reduced risk of all-cause mortality (hazard ratio 0.78; 95% confidence interval 0.61 to 0.99) and all-cause hospitalization (hazard ratio 0.77; 95% confidence interval 0.67 to 0.90). In a propensity-matched sample of carvedilol and metoprolol tartrate patients (n = 564 each), expected costs of inpatient care at 36 months were 10,509 US dollars lower with carvedilol (95% confidence interval 2934-18,085 US dollars).

CONCLUSIONS

Use of carvedilol rather than metoprolol tartrate may improve survival and reduce costs of care in heart failure patients in typical clinical practice in the United States.

Efficacy of Beta Blockers in Severe Heart Failure

This continuing feature will update readers on recent developments in cardiovascular pharmacotherapy. Cardiovascular disease remains the number one killer in the US, and more clinical outcome trials have been conducted in cardiology than in any other field of medicine. Given this rapidly expanding knowledge base, pharmacists can have a significant impact on the prevention and treatment of cardiovascular disease—if they keep current with developments in drug therapy.

Cardiac beta ARK1 inhibition prolongs survival and augments beta blocker therapy in a mouse model of severe heart failure

Chronic human heart failure is characterized by abnormalities in beta-adrenergic receptor (betaAR) signaling, including increased levels of betaAR kinase 1 (betaARK1), which seems critical to the pathogenesis of the disease. To determine whether inhibition of betaARK1 is sufficient to rescue a model of severe heart failure, we mated transgenic mice overexpressing a peptide inhibitor of betaARK1 (betaARKct) with transgenic mice overexpressing the sarcoplasmic reticulum Ca(2+)-binding protein, calsequestrin (CSQ). CSQ mice have a severe cardiomyopathy and markedly shortened survival (9 +/- 1 weeks). In contrast, CSQ/betaARKct mice exhibited a significant increase in mean survival age (15 +/- 1 weeks; P < 0.0001) and showed less cardiac dilation, and cardiac function was significantly improved (CSQ vs. CSQ/betaARKct, left ventricular end diastolic dimension 5.60 +/- 0.17 mm vs. 4.19 +/- 0.09 mm, P < 0.005; % fractional shortening, 15 +/- 2 vs. 36 +/- 2, P < 0.005). The enhancement of the survival rate in CSQ/betaARKct mice was substantially potentiated by chronic treatment with the betaAR antagonist metoprolol (CSQ/betaARKct nontreated vs. CSQ/betaARKct metoprolol treated, 15 +/- 1 weeks vs. 25 +/- 2 weeks, P < 0.0001). Thus, overexpression of the betaARKct resulted in a marked prolongation in survival and improved cardiac function in a mouse model of severe cardiomyopathy that can be potentiated with beta-blocker therapy. These data demonstrate a significant synergy between an established heart-failure treatment and the strategy of betaARK1 inhibition.

Electrotherapeutic management of patients with heart failure

Heart failure is associated with poor long term survival due to progressive refractory heart dysfunction and sudden cardiac death. Cardiac resynchronization through atrio-biventricular pacing has been introduced to treat patients affected by drug-refractory heart failure with desynchronized ventricular activation, as for complete left bundle branch block. The technique is aimed to overcome interventricular and intraventricular conduction delays leading to ventricular dysynchrony, paradoxical septal wall motion, presystolic mitral regurgitation and reduced diastolic filling times. Short term studies demonstrated that biventricular pacing (and perhaps left ventricular pacing alone) may improve both systolic and diastolic function. Initial studies in patients receiving long term pacing consistently showed significant QRS shortening associated with improvement in symptoms, left ventricular ejection fraction, exercise tolerance, quality of life and New York Heart Association functional class. As far as sudden cardiac death prevention in heart failure is concerned, implantable cardioverter defibrillator (ICD) implantation has been demonstrated to be the most effective therapy in patients with prior cardiac arrest due to ventricular fibrillation or poorly tolerated ventricular tachycardia. Low left ventricular ejection fraction, unsustained ventricular tachycardia and inducibility at electrophysiological study also may identify high risk patients requiring ICD implantation. Further studies are needed to evaluate the effect of cardiac resynchronization on hard end-points, such as survival and long term clinical outcome, and to upgrade risk stratification criteria to be used in selection of candidates for ICD implantation.