β-Adrenergic Blockers

Controversial therapeutics: the β-adrenergic antagonist and cocaine-associated cardiovascular complications dilemma

Cocaine abuse is associated with cardiovascular complications that include chest pain and myocardial infarction. Traditional therapy for these conditions includes a β-adrenergic antagonist. However, guidelines released in 2008 recommended against this treatment option because of the prevailing theory that cocaine will potentiate vasospasm secondary to unopposed α-adrenergic effects. Subsequently, further evidence and updated guidelines have become available, debunking this claim. Current literature is limited but suggests that β-adrenergic antagonists are harmful. Although case reports support a detrimental effect of β-adrenergic antagonists, the anecdotal data are inconsistent, and the conclusions from case studies are overruled by larger studies. The pharmacology, pathophysiology, and literature on the use of β-adrenergic antagonists in association with cocaine are reviewed. Future studies that focus on outcomes and different pharmacologic profiles of β-adrenergic antagonists are needed.

β-Blockers

Objective: To review the pharmacology, pharmacokinetics, and pharmacodynamic properties of commonly used β-blockers (atenolol, carvedilol, metoprolol succinate, metoprolol tartrate, and nebivolol). Data Sources: A MEDLINE literature search (1966-May 2013) was performed using the following key terms: hypertension, β-blockers, atenolol, carvedilol, metoprolol tartrate, metoprolol succinate, nebivolol, pharmacology, pharmacodynamics, pharmacokinetics, blood pressure, metabolic, lipid, central aortic pressure, diabetes, and insulin resistance. References from publications reviewed were included. Study Selection and Data Extraction: English-language articles identified were reviewed. Animal studies and studies in patients for a primary diagnosis of coronary artery disease were excluded. Data Synthesis: β-Blockers are no longer recommended first-line therapy for primary hypertension, based on data showing that β-blockers are inferior to other antihypertensives and no better than placebo, in spite of provision of blood pressure reduction. Because atenolol is the β-blocker used in 75% of these studies, uncertainty about widespread application to all β-blockers exists. Different pharmacological and physiological properties, both within β-blockers and compared with other antihypertensives, may explain divergent effects. Evidence shows that β-blockers have a truncated effect on central aortic pressure, an independent predictor of cardiovascular events, compared with other antihypertensive classes; differences within the class may exist, but the evidence is inconclusive. Metabolic effects differ within the β-blocker class, with evidence that carvedilol causes less metabolic dysregulation. Conclusion: Emerging evidence reveals physiological differences within the β-blocker class and in comparison to other antihypertensives. These differences provide insight into the diverse clinical effects β-blockers provide in cardiovascular disease.

Landiolol: a review of its use in intraoperative and postoperative tachyarrhythmias

Landiolol (Onoact(®)) is an intravenously administered, ultra short-acting β1-blocker with an elimination half-life of 3-4 min and ≈8-fold greater cardioselectivity than esmolol in vitro. It is approved in Japan for the treatment of intraoperative and postoperative tachyarrhythmias, but in clinical practice is also used to prevent postoperative tachyarrhythmias, such as atrial fibrillation after coronary artery bypass grafting. Randomized controlled trials in patients undergoing open-heart surgery demonstrated that various dosages of landiolol (0.0005-0.04 mg/kg/min) [0.5-40 μg/kg/min] were more effective than diltiazem in converting postoperative atrial fibrillation to normal sinus rhythm during the first 8 h after surgery, and were more effective than placebo (or no landiolol) in preventing the development of atrial fibrillation during the first week after surgery (primary efficacy endpoints). In patients undergoing surgical procedures, landiolol 0.125 mg/kg/min for 1 min followed by 0.04 mg/kg/min for 10 min was superior to placebo in improving intraoperative tachycardia in randomized double-blind trials. The beneficial effects of landiolol in attenuating adverse haemodynamic or other changes that can occur during surgery or invasive procedures (e.g. percutaneous coronary intervention) have been demonstrated in a large number of randomized controlled trials. For example, several studies showed that landiolol attenuated the increase in heart rate associated with tracheal intubation, without adversely affecting blood pressure or other haemodynamic parameters. Landiolol was generally well tolerated in clinical trials, with a relatively low risk of hypotension and bradycardia, although routine monitoring of cardiac function during landiolol administration is important. In general, adverse events such as reduced blood pressure resolve quickly after discontinuation of landiolol. Thus, as an ultra short-acting β1-blocker with a rapid onset of action and readily titratable and rapidly reversible effects, landiolol represents an important agent for the management of intraoperative and postoperative tachyarrhythmias.

Broad-scale phosphoprotein profiling of beta adrenergic receptor (β-AR) signaling reveals novel phosphorylation and dephosphorylation events

β-adrenergic receptors (β-ARs) are model G-protein coupled receptors that mediate signal transduction in the sympathetic nervous system. Despite the widespread clinical use of agents that target β-ARs, the signaling pathways that operate downstream of β-AR stimulation have not yet been completely elucidated. Here, we utilized a lysate microarray approach to obtain a broad-scale perspective of phosphoprotein signaling downstream of β-AR. We monitored the time course of phosphorylation states of 54 proteins after β-AR activation mouse embryonic fibroblast (MEF) cells. In response to stimulation with the non-selective β-AR agonist isoproterenol, we observed previously described phosphorylation events such as ERK1/2(T202/Y204) and CREB(S133), but also novel phosphorylation events such as Cdc2(Y15) and Pyk2(Y402). All of these events were mediated through cAMP and PKA as they were reproduced by stimulation with the adenylyl cyclase activator forskolin and were blocked by treatment with H89, a PKA inhibitor. In addition, we also observed a number of novel isoproterenol-induced protein dephosphorylation events in target substrates of the PI3K/AKT pathway: GSK3β(S9), 4E-BP1(S65), and p70s6k(T389). These dephosphorylations were dependent on cAMP, but were independent of PKA and correlated with reduced PI3K/AKT activity. Isoproterenol stimulation also led to a cAMP-dependent dephosphorylation of PP1α(T320), a modification known to correlate with enhanced activity of this phosphatase. Dephosphorylation of PP1α coincided with the secondary decline in phosphorylation of some PKA-phosphorylated substrates, suggesting that PP1α may act in a feedback loop to return these phosphorylations to baseline. In summary, lysate microarrays are a powerful tool to profile phosphoprotein signaling and have provided a broad-scale perspective of how β-AR signaling can regulate key pathways involved in cell growth and metabolism.

The decline effect in cardiovascular medicine: is the effect of cardiovascular medicine and stent on cardiovascular events decline over the years?

The term decline effect is referred to a diminution of scientifically discovered effects over time. Reasons for the decline effect are multifaceted and include publication bias, selective reporting, outcomes reporting bias, regression to the mean, scientific paradigm shift, overshadowing and habituation, among others. Such effects can be found in cardiovascular medicines through medications (e.g., aspirin, antithrombotics, proton pump inhibitor, beta-blockers, statins, estrogen/progestin, angiotensin converting enzyme inhibitor etc.), as well as with interventional devices (e.g., angioplasty, percutaneous coronary intervention, stents). The scientific community should understand the various dimensions of the decline effects, and effective steps should be undertaken to prevent or recognize such decline effects in cardiovascular medicines.

β-Adrenergic blockade in cardiovascular disease

The development and subsequent clinical application of the β-adrenergic receptor blocking drugs represent one of the major advances in human pharmacotherapeutics. No other class of synthetic drugs has demonstrated such widespread therapeutic utility for the treatment and prevention of so many cardiovascular diseases. In addition, these drugs have proven to be molecular probes that have contributed to our understanding of the disease, and on the molecular level, both the structure and function of the 7 transmembrane G protein receptors that mediate the actions of many different hormones, neurotransmitters, and drugs. The evolution of β-blocker drug development has led to refinements in their pharmacodynamic actions that include agents with relative β1-selectivity, partial agonist activity, concomitant α-adrenergic blockers activity, and direct vasodilator activity. In addition, long-acting and ultra-short-acting formulations of β-blockers have also demonstrated a remarkable record of clinical safety in patients of all ages.

Beta-adrenergic stimulation maintains cardiac function in Serca2 knockout mice

Previous studies on Serca2 knockout (KO) mice showed that cardiac function is sustained in vivo for several weeks after knockout, whereas SERCA protein levels decrease and calcium dynamics are significantly impaired. In this study, we reconcile observed cellular and organ level contractile function using a cardiac multiscale model. We identified and quantified the changes in cellular function that are both consistent with observations and able to compensate for the decrease in SERCA. Calcium transients were used as input for multiscale computational simulations to predict whole-organ response. Although this response matched experimental pressure-volume (PV) measurements in healthy mice, the reduced magnitude calcium transients observed in KO cells were insufficient to trigger ventricular ejection. To replicate the effects of elevated catecholamine levels observed in vivo, cells were treated with isoproterenol. Incorporation of the resulting measured β-adrenergically stimulated calcium transients into the model resulted in a close match with experimental PV loops. Changes in myofilament properties, when considered in isolation, were not able to increase tension development to levels consistent with measurements, further confirming the necessity of a high β-adrenergic state. Modeling additionally indicated that increased venous return observed in the KO mice helps maintain a high ejection fraction via the Frank-Starling effect. Our study shows that increased β-adrenergic stimulation is a potentially highly significant compensatory mechanism by which cardiac function is maintained in Serca2 KO mice, producing the increases in both systolic and diastolic calcium, consistent with the observed contractile function observed in experimental PV measurements.

CYP2C19 genotype has a major influence on labetalol pharmacokinetics in healthy male Chinese subjects

PURPOSE

The pharmacokinetics (PK) of labetalol show wide inter-subject variability, but the genetic causes for this are largely undetermined. This study was performed to examine whether common polymorphisms in UGT1A1, UGT2B7, CYP2C19 and ABCB1 affect the PK of labetalol.

METHODS

The PK of labetalol were determined in 37 Chinese healthy male subjects who took a single oral dose of 200 mg labetalol. Plasma concentrations of labetalol were determined by a high-performance liquid chromatographic method. Subjects were genotyped for the CYP2C19 2 and 3, UGT1A1 6, 28 and 60, UGT2B7 2 and ABCB1 1236C>T, 2677G>T/A and 3435C>T polymorphisms.

RESULTS

Subjects with the CYP2C19 2/ 2 genotype had a higher peak concentration (255.5 ± 80.1 vs. 156.0  ±  66.3 ng/mL; P < 0.05) and area under the concentration-time curve (AUC0-∞; 1,473.7 ± 493.6 vs. 502.8 ± 176.1 ng[Symbol: see text]h/mL; P < 0.001) than subjects with 60 or 28, and UGT2B7 2 did not result in a significant effect. Subjects with ABCB1 2677TA or TT or ABCB1 3435TT genotypes had higher AUC0-∞ and lower total clearance than the wild-types (P < 0.05), but this appeared to be related to the distribution of CYP2C19 genotypes. The CYP2C19 genotype appeared to be the only predictor of labetalol concentrations, accounting for approximately 60 % of the total variance in the AUC0-∞.

CONCLUSION

Our results suggest that the PK of labetalol are significantly affected by the common CYP2C19 polymorphisms in individuals of Chinese ethnicity. Future larger studies are needed to evaluate the effect of CYP2C19 and UGT1A1 polymorphisms on the PK of labetalol stereoisomers and the pharmacodynamic effects.

Cardioselective beta-blocker treatment of hypertension in patients with asthma: when do benefits outweigh risks?

BACKGROUND

Benefits outweigh risks of cardioselective beta-blocker therapy in patients with nonsevere asthma and a history of heart failure or myocardial infarction (MI). This review summarizes the risks versus benefits of using cardioselective beta-blockers in the treatment of hypertension in patients with asthma.

METHODS

We searched the English literature from 1976 to 2011 via PubMed, EMBASE, and SCOPUS using the following search terms: "beta-blocker treatment of hypertension" AND "asthma"; "cardioselective beta-blockers" AND "asthma." When pertinent articles were found, we assessed relevant articles cited in those papers. All studies related to cardioselective beta-blocker use in patients with asthma and hypertension were included.

RESULTS

Seven studies with patient populations ranging from 10 to 17 patients evaluated cardioselective beta-blockers in patients with asthma and hypertension. Atenolol and/or immediate-release metoprolol were evaluated in these studies. The duration of beta-blocker therapy in four studies was 1-8 weeks; two studies were single dose and one investigation lasted 8 months. Metoprolol and atenolol were generally well tolerated except at higher doses such as metoprolol >100 mg daily.

CONCLUSION

In the absence of concomitant cardiovascular disease, routine use of beta-blockers for the treatment of hypertension in patients with asthma should be avoided.

The evolving role of β-adrenergic receptor blockers in managing hypertension

β-Adrenergic blocking agents (or β-blockers) have been widely used for the treatment of hypertension for the past 50 years, and continue to be recommended as a mainstay of therapy in many national guidelines. They have also been used in a variety of cardiovascular conditions commonly complicating hypertension, including angina pectoris, myocardial infarction (MI), acute and chronic heart failure, as well as conditions like essential tremor and migraine. Moreover, they have played a primary role in controlling blood pressure in patients with these specific comorbidities and in reducing cardiovascular risk with regard to the composite outcome of death, stroke, and MI among patients younger than 60 years of age. However, in patients 60 years of age or older, β-blockers were not associated with significantly lower rates of MI, heart failure or death, and demonstrated higher rates of stroke compared with other first-line therapies. Consequently, the Canadian Hypertension Education Program recommends the use of β-blockers as first-line therapy in hypertensive patients younger than 60 years of age but not for those age 60 and older, with the exception of patients with concomitant β-blocker-requiring cardiac diseases. Several reports suggest that the lack of consistent outcome data may relate to the use of traditional β-blockers such as atenolol and their ability only to reduce cardiac output, without beneficial effect on peripheral vascular resistance. The present report will describe the clinically relevant mechanisms of action of β-blockers, their pharmacological differences, their metabolic effects, and their usefulness in patients with hypertension.

Pharmacology of myocardial calcium-handling

Disturbed myocardial calcium (Ca(+)) handling is one of the pathophysiologic hallmarks of cardiovascular diseases such as congestive heart failure, cardiac hypertrophy, and certain types of tachyarrhythmias. Pharmacologic treatment of these diseases thus focuses on restoring myocardial Ca(2+) homeostasis by interacting with Ca(2+)-dependent signaling pathways. In this article, we review the currently used pharmacologic agents that are able to restore or maintain myocardial Ca(2+) homeostasis and their mechanism of action as well as emerging new substances.

Therapeutic potential of functional selectivity in the treatment of heart failure

Adrenergic and angiotensin receptors are prominent targets in pharmacological alleviation of cardiac remodeling and heart failure, but their use is associated with cardiodepressant side effects. Recent advances in our understanding of seven transmembrane receptor signaling show that it is possible to design ligands with "functional selectivity," acting as agonists on certain signaling pathways while antagonizing others. This represents a major pharmaceutical opportunity to separate desired from adverse effects governed by the same receptor. Accordingly, functionally selective ligands are currently pursued as next-generation drugs for superior treatment of heart failure.