Bucindolol, a nonselective beta 1- and beta 2-adrenergic receptor antagonist, decreases beta-adrenergic receptor density in cultured embryonic chick cardiac myocyte membranes

Sepsis With Preexisting Heart Failure: Management of Confounding Clinical Features

Preexisting heart failure (HF) in patients with sepsis is associated with worse clinical outcomes. Core sepsis management includes aggressive volume resuscitation followed by vasopressors (and potentially inotropes) if fluid is inadequate to restore perfusion; however, large fluid boluses and vasoactive agents are concerning amid the cardiac dysfunction of HF. This review summarizes evidence regarding the influence of HF on sepsis clinical outcomes, pathophysiologic concerns, resuscitation targets, hemodynamic interventions, and adjunct management (ie, antiarrhythmics, positive pressure ventilatory support, and renal replacement therapy) in patients with sepsis and preexisting HF. Patients with sepsis and preexisting HF receive less fluid during resuscitation; however, evidence suggests traditional fluid resuscitation targets do not increase the risk of adverse events in HF patients with sepsis and likely improve outcomes. Norepinephrine remains the most well-supported vasopressor for patients with sepsis with preexisting HF, while dopamine may induce more cardiac adverse events. Dobutamine should be used cautiously given its generally detrimental effects but may have an application when combined with norepinephrine in patients with low cardiac output. Management of chronic HF medications warrants careful consideration for continuation or discontinuation upon development of sepsis, and β-blockers may be appropriate to continue in the absence of acute hemodynamic decompensation. Optimal management of atrial fibrillation may include β-blockers after acute hemodynamic stabilization as they have also shown independent benefits in sepsis. Positive pressure ventilatory support and renal replacement must be carefully monitored for effects on cardiac function when HF is present.

β-blockers Reverse Agonist-Induced β2-AR Downregulation Regardless of Their Signaling Profile

Altered β-adrenergic receptor (β-AR) density has been reported in cells, animals, and humans receiving β-blocker treatment. In some cases, β-AR density is upregulated, but in others, it is unaffected or even reduced. Collectively, these results would imply that changes in β-AR density and β-blockade are not related. However, it has still not been clarified whether the effects of β-blockers on receptor density are related to their ability to activate different β-AR signaling pathways. To this aim, five clinically relevant β-blockers endowed with inverse, partial or biased agonism at the β₂-AR were evaluated for their effects on β₂-AR density in both human embryonic kidney 293 (HEK293) cells expressing exogenous FLAG-tagged human β₂-ARs and human lymphocytes expressing endogenous β₂-ARs. Cell surface β₂-AR density was measured by enzyme-linked immunosorbent assay (ELISA) and flow cytometry. Treatment with propranolol, carvedilol, pindolol, sotalol, or timolol did not induce any significant change in surface β₂-AR density in both HEK293 cells and human lymphocytes. On the contrary, treatment with the β-AR agonist isoproterenol reduced the number of cell surface β₂-ARs in the tested cell types without affecting β₂-AR-mRNA levels. Isoproterenol-induced effects on receptor density were completely antagonized by β-blocker treatment. In conclusion, the agonistic activity of β-blockers does not exert an important effect on short-term regulation of β₂-AR density.

The deubiquitinase ubiquitin-specific protease 20 is a positive modulator of myocardial β1-adrenergic receptor expression and signaling

Reversible ubiquitination of G protein-coupled receptors regulates their trafficking and signaling; whether deubiquitinases regulate myocardial β₁-adrenergic receptors (β₁ARs) is unknown. We report that ubiquitin-specific protease 20 (USP20) deubiquitinates and attenuates lysosomal trafficking of the β₁AR. β₁AR-induced phosphorylation of USP20 Ser-333 by protein kinase A-α (PKAα) was required for optimal USP20-mediated regulation of β₁AR lysosomal trafficking. Both phosphomimetic (S333D) and phosphorylation-impaired (S333A) USP20 possess intrinsic deubiquitinase activity equivalent to WT activity. However, unlike USP20 WT and S333D, the S333A mutant associated poorly with the β₁AR and failed to deubiquitinate the β₁AR. USP20-KO mice showed normal baseline systolic function but impaired β₁AR-induced contractility and relaxation. Dobutamine stimulation did not increase cAMP in USP20-KO left ventricles (LVs), whereas NKH477-induced adenylyl cyclase activity was equivalent to WT. The USP20 homolog USP33, which shares redundant roles with USP20, had no effect on β₁AR ubiquitination, but USP33 was up-regulated in USP20-KO hearts suggesting compensatory regulation. Myocardial β₁AR expression in USP20-KO was drastically reduced, whereas β₂AR expression was maintained as determined by radioligand binding in LV sarcolemmal membranes. Phospho-USP20 was significantly increased in LVs of wildtype (WT) mice after a 1-week catecholamine infusion and a 2-week chronic pressure overload induced by transverse aortic constriction (TAC). Phospho-USP20 was undetectable in β₁AR KO mice subjected to TAC, suggesting a role for USP20 phosphorylation in cardiac response to pressure overload. We conclude that USP20 regulates β₁AR signaling in vitro and in vivo Additionally, β₁AR-induced USP20 phosphorylation may serve as a feed-forward mechanism to stabilize β₁AR expression and signaling during pathological insults to the myocardium.

Responses of PKCε to cardiac overloads on myocardial sympathetic innervation and NET expression

Protein kinase C (PKC) is a key mediator of many diverse physiological and pathological responses. PKC activation play an important regulatory role of cardiac function. The present study was performed to investigate whether there were differential activations of the PKCε and how the activation coupled with norepinephrine transporter (NET) surface expression, sympathetic innervation pattern and extracellular matrix remodeling in different cardiac hemodynamic overloads induced by abdominal aortic constriction or aortocaval fistula. At 8weeks after the operations, heart failure were induced, accompanied with myocardial hypertrophy, which was more pronounced in pressure overload (POL) than that of volume overload (VOL) rats, left ventricular dysfunction and increased plasma norepinephrine (NE). In POL rats there was an increase in myocardial collagen deposition, in contrast, the amount decreased in VOL as compared with the sham rats. POL remarkably upregulated PKCε membrane-cytosol ratio and downregulated NET membrane fraction, whereas, in VOL induced opposite changes. Accompanied with the PKCε activation, nerve sprouting, evidenced by myocardial GAP43 protein increased, and different nerve phenotypes were found, in POL tyrosine hydroxylase (TH) positive nerve density increased with NET and choline acetyltransferase (ChAT) immunoreactivity density decreased, in contrast, in VOL NET and ChAT increased, TH did not change. The overloads did not induce alteration of NET mRNA expression, but resulted in different myocardial β₁-AR mRNA expression, in POL β₁-AR mRNAwas significantly downregulated, while in VOL rats unaltered. Conclusion, the present results suggested that the different cardiac hemodynamic overload could differentially activate a common signaling, PKCε intermediate and thereby generate biological diversity.

Beta-blockers in heart failure: are pharmacological differences clinically important?

Beta-blockers are not an homogeneous group of agents. Only three beta-blockers, carvedilol, bisoprolol and metoprolol succinate, have had favorable effects on prognosis in controlled clinical trials in the patients with chronic heart failure. However, pharmacological differences exist between them. Metoprolol and bisoprolol are selective for beta(1)-adrenergic receptors while carvedilol blocks also beta(2)-, and alpha(1)- adrenergic receptors, and has associated antioxidant, anti-endothelin and antiproliferative properties. In COMET carvedilol was associated with a significant reduction in mortality compared to metoprolol tartrate further showing that different beta-blockers may have different effects on the outcome. These differences may be related to the ancillary properties of carvedilol or to its broader antiadrenergic profile. However, also more effective and prolonged blockade of beta1 adrenergic receptors may occur with carvedilol compared to metoprolol.

Carvedilol Exerts More Potent Antiadrenergic Effect than Metoprolol in Heart Failure

BACKGROUND

It is still uncertain whether or not there is a difference between metoprolol and carvedilol for the treatment of congestive heart failure. We attempted to determine the difference between the two beta-blockers in terms of their antiadrenergic effect during exercise in patients with heart failure and their efficacy based on the baseline plasma brain natriuretic peptide concentration.

METHODS

Fifty-three patients with mild to moderate heart failure with a radionuclide left ventricular ejection fraction <40% received open label metoprolol or carvedilol in a randomized fashion. The increase in the heart rate normalized to the increase in the plasma norepinephrine concentration during exercise, was calculated as an index of adrenergic responsiveness during exercise.

RESULTS

The increase in heart rate normalized by the increase in plasma norepinephrine concentration, decreased after the initiation of beta-blockers in the carvedilol group, but not in the metoprolol group. The change in cardiac function was more favorable for carvedilol than metoprolol in patients who exhibited a higher baseline brain natriuretic peptide concentration.

CONCLUSIONS

Carvedilol exerts a more potent antiadrenergic effect than metoprolol during stress in patients with mild to moderate heart failure. Carvedilol appears to be more efficacious than metoprolol in patients who exhibit higher baseline brain natriuretic peptide concentrations. These differences should be kept in mind when selecting appropriate pharmacologic agents in the treatment of heart failure.

Influence of heart rate, blood pressure, and beta-blocker dose on outcome and the differences in outcome between carvedilol and metoprolol tartrate in patients with chronic heart failure: results from the COMET trial

AIMS

We studied the influence of heart rate (HR), systolic blood pressure (SBP), and beta-blocker dose on outcome in the 2599 out of 3029 patients in Carvedilol Or Metoprolol European Trial (COMET) who were alive and on study drug at 4 months after randomization (time of first visit on maintenance therapy).

METHODS AND RESULTS

By multivariable analysis, baseline HR, baseline SBP, and their change after 4 months were not independently related to subsequent outcome. In a multivariable analysis including clinical variables, HR above and SBP below the median value achieved at 4 months predicted subsequent increased mortality [relative risk (RR) for HR>68 b.p.m. 1.333; 95% confidence intervals (CI) 1.152-1.542; P<0.0001 and RR for SBP>120 mmHg 0.78; 95% CI 0.671-0.907; P<0.0013]. Achieving target beta-blocker dose was associated with a better outcome (RR 0.779; 95% CI 0.662-0.916; P<0.0025). The superiority of carvedilol as compared to metoprolol tartrate was maintained in a multivariable model (RR 0.767; 95% CI 0.663-0.887; P=0.0004) and there was no interaction with HR, SBP, or beta-blocker dose.

CONCLUSION

Beta-blocker dose, HR, and SBP achieved during beta-blocker therapy have independent prognostic value in heart failure. None of these factors influenced the beneficial effects of carvedilol when compared with metoprolol tartrate at the pre-defined target doses used in COMET.

Carvedilol but not metoprolol reduces beta-adrenergic responsiveness after complete elimination from plasma in vivo

BACKGROUND

Carvedilol but not metoprolol exhibits persistent binding to beta-adrenergic receptors (beta-ARs) even after washout in cell culture experiments. Here, we determined the significance of this phenomenon on human beta-ARs in vitro and in vivo.

METHODS AND RESULTS

Experiments were conducted on human atrial trabeculae (n=8 to 10 per group). In the presence of metoprolol, isoproterenol potency was reduced compared with controls (P<0.001). In the presence of carvedilol, isoproterenol identified 2 distinct binding sites of high (36+/-6%; -8.8+/-0.4 log mol/L) and low affinity (-6.5+/-0.2 log mol/L). After beta-blocker washout, isoproterenol potency returned to control values in metoprolol-treated muscles, whereas in carvedilol-treated preparations, isoproterenol potency remained decreased (P<0.001 versus control). In vivo studies were performed in 9 individuals receiving metoprolol succinate (190 mg/d) or carvedilol (50 mg/d) for 11 days in a randomized crossover design. Dobutamine stress echocardiography (5 to 40 microg x kg(-1) x min(-1)) was performed before, during, and 44 hours after application of study medication. Beta-blocker medication reduced heart rate, heart rate-corrected velocity of circumferential fiber shortening, and cardiac output compared with baseline (P<0.02 to 0.0001). After withdrawal of metoprolol, all parameters returned to baseline values, whereas after carvedilol, all parameters remained reduced (P<0.05 to 0.001) despite complete plasma elimination of carvedilol.

CONCLUSIONS

Carvedilol but not metoprolol inhibits the catecholamine response of the human heart beyond its plasma elimination. The persistent beta-blockade by carvedilol may be explained by binding of carvedilol to an allosteric site of beta-ARs.

Selective versus nonselective beta-blockade for heart failure therapy: are there lessons to be learned from the COMET trial?

The recently reported COMET trial found that the beta1/beta2/alpha1 receptor blocking agent carvedilol given in a relatively high beta1-receptor blocking dose regimen was superior in mortality reduction to immediate release metoprolol given in a relatively low beta1-receptor blocking dose schedule. We analyze the problems with the trial design of COMET from the standpoint of comparing 2 therapeutic agents at different positions on a common dose-response curve, and discuss the theoretical reasons why postjunctional adrenergic receptor blockade that is in addition to beta1-receptor antagonism will likely produce only minimal or no incremental benefit in chronic heart failure.

Partial agonist activity of bucindolol is dependent on the activation state of the human beta1-adrenergic receptor

BACKGROUND

In contrast to other beta-blockers, bucindolol has failed to reduce mortality in patients with chronic heart failure. It is currently debated whether this is due to partial agonist activity of this agent. We investigated whether conflicting results previously reported concerning the intrinsic activity of bucindolol can be explained by species differences or by different activation states of beta-adrenergic receptors (beta-ARs) in the respective tissues.

METHODS AND RESULTS

On isolated right atria from transgenic mice with cardiac overexpression of human beta1-ARs, bucindolol led to a greater increase in beating frequency (P<0.05) compared with wild-type mice. The increase amounted to 47% of the effect of xamoterol and was blocked by propranolol. On isolated, electrically stimulated, left ventricular muscle-strip preparations from failing human myocardium, bucindolol did not change the force of contraction under control conditions. In myocardial preparations pretreated with metoprolol (30 micromol/L, 90 minutes, subsequent washout), bucindolol significantly increased the force of contraction (P<0.001 vs control). In nonfailing atrial myocardium, isoproterenol pretreatment (1 micromol/L, 60 minutes) abolished the positive inotropic effect of xamoterol that was present under control conditions (P<0.05 vs control). The inotropic effects of bucindolol or xamoterol were inversely correlated to the inotropic response to forskolin in the respective specimens (r=-0.75 and -0.74, respectively; P<0.005).

CONCLUSIONS

We conclude that bucindolol is a partial agonist at the human beta1-AR. In human failing myocardium, its partial agonist activity is masked by increased activation states of beta-ARs and is unmasked after in vitro pretreatment with metoprolol. Thus, the partial agonist activity of bucindolol is dependent on the activation state of the human beta1-AR.

Beta-blocker therapy influences the hemodynamic response to inotropic agents in patients with heart failure: a randomized comparison of dobutamine and enoximone before and after chronic treatment with metoprolol or carvedilol

OBJECTIVE

We compared the hemodynamic effects of dobutamine and enoximone administration before and after long-term beta-blocker therapy with metoprolol or carvedilol in patients with chronic heart failure (HF).

BACKGROUND

Patients with HF on beta-blocker therapy may need hemodynamic support with inotropic agents, and the hemodynamic response may be influenced by both the inotropic agent and the beta-blocker used.

METHODS

The hemodynamic effects of dobutamine (5 to 20 microg/kg/min intravenously) and enoximone (0.5 to 2 mg/kg intravenously) were assessed by pulmonary artery catheterization in 29 patients with chronic HF before and after 9 to 12 months of treatment with metoprolol or carvedilol at standard target maintenance oral doses. Hemodynamic studies were performed after >/=12 h of wash-out from all cardiovascular medications, except the beta-blockers that were administered 3 h before the second study.

RESULTS

Compared with before beta-blocker therapy, metoprolol treatment decreased the magnitude of mean pulmonary artery pressure (PAP) and pulmonary wedge pressure (PWP) decline during dobutamine infusion and increased the cardiac index (CI) and stroke volume index (SVI) response to enoximone administration, without any effect on other hemodynamic parameters. Carvedilol treatment abolished the increase in heart rate, SVI, and CI and caused a rise, rather than a decline, in PAP, PWP, systemic vascular resistance, and pulmonary vascular resistance during dobutamine infusion. The hemodynamic response to enoximone, however, was maintained or enhanced in the presence of carvedilol.

CONCLUSIONS

In contrast with its effects on enoximone, carvedilol and, to a lesser extent, metoprolol treatment may significantly inhibit the favorable hemodynamic response to dobutamine. No such beta-blocker-related attenuation of hemodynamic effects occurs with enoximone.