First-In-Man Trial of β3-Adrenoceptor Agonist Treatment in Chronic Heart Failure: Impact on Diastolic Function.

Diastolic dysfunction (DD) in heart failure is associated with increased myocardial cytosolic calcium and calcium-efflux through the sodium-calcium exchanger depends on the sodium gradient. Beta-3-adrenoceptor (β3-AR) agonists lower cytosolic sodium and have reversed organ congestion. Accordingly, β3-AR agonists might improve diastolic function, which we aimed to assess.

Hemodynamic Effects of Cyclic Guanosine Monophosphate-Dependent Signaling Through β3 Adrenoceptor Stimulation in Patients With Advanced Heart Failure: A Randomized Invasive Clinical Trial.

Background: β3-AR (β3-adrenergic receptor) stimulation improved systolic function in a sheep model of systolic heart failure (heart failure with reduced ejection fraction [HFrEF]). Exploratory findings in patients with New York Heart Association functional class II HFrEF treated with the β3-AR-agonist mirabegron supported this observation. Here, we measured the hemodynamic response to mirabegron in patients with severe HFrEF.

Targeting Cardiac Myocyte Na-K Pump Function With β3 Adrenergic Agonist in Rabbit Model of Severe Congestive Heart Failure.

Background: Abnormally high cytosolic Na concentrations in advanced heart failure impair myocardial contractility. Stimulation of the membrane Na-K pump should lower Na concentrations, and the β3 adrenoceptor (β3 AR) mediates pump stimulation in myocytes. We examined if β3 AR-selective agonists given in vivo increase myocyte Na-K pump activity and reverse organ congestion in severe heart failure (HF).

The first-in-man randomized trial of a beta3 adrenoceptor agonist in chronic heart failure: the BEAT-HF trial.

Aims: The third isotype of beta adrenergic receptors (β3 ARs) has distinctly different effects on cardiomyocytes compared with β1 and β2 ARs. Stimulation of β3 ARs may reduce cardiomyocyte Na overload and reduce oxidative stress in heart failure (HF). We examined if treatment with the β3 AR agonist mirabegron increases LVEF in patients with HF.

Glutathionylation mediates angiotensin II-induced eNOS uncoupling, amplifying NADPH oxidase-dependent endothelial dysfunction.

Background: Glutathionylation of endothelial nitric oxide synthase (eNOS) "uncouples" the enzyme, switching its function from nitric oxide (NO) to O2(•-) generation. We examined whether this reversible redox modification plays a role in angiotensin II (Ang II)-induced endothelial dysfunction.

Methods And Results: Ang II increased eNOS glutathionylation in cultured human umbilical vein endothelial cells (HUVECs), rabbit aorta, and human arteries in vitro.

Extracellular allosteric Na(+) binding to the Na(+),K(+)-ATPase in cardiac myocytes.

Whole-cell patch-clamp measurements of the current, Ip, produced by the Na(+),K(+)-ATPase across the plasma membrane of rabbit cardiac myocytes show an increase in Ip over the extracellular Na(+) concentration range 0-50 mM. This is not predicted by the classical Albers-Post scheme of the Na(+),K(+)-ATPase mechanism, where extracellular Na(+) should act as a competitive inhibitor of extracellular K(+) binding, which is necessary for the stimulation of enzyme dephosphorylation and the pumping of K(+) ions into the cytoplasm. The increase in Ip is consistent with Na(+) binding to an extracellular allosteric site, independent of the ion transport sites, and an increase in turnover via an acceleration of the rate-determining release of K(+) to the cytoplasm, E2(K(+))2 → E1 + 2K(+).

Redox-dependent regulation of the Na⁺-K⁺ pump: new twists to an old target for treatment of heart failure.

By the time it was appreciated that the positive inotropic effect of cardiac glycosides is due to inhibition of the membrane Na(+)-K(+) pump, glycosides had been used for treatment of heart failure on an empiric basis for ~200 years. The subsequent documentation of their lack of clinical efficacy and possible harmful effect largely coincided with the discovery that a raised Na(+) concentration in cardiac myocytes plays an important role in the electromechanical phenotype of heart failure syndromes. Consistent with this, efficacious pharmacological treatments for heart failure have been found to stimulate the Na(+)-K(+) pump, effectively the only export route for intracellular Na(+) in the heart failure.

Protein kinase-dependent oxidative regulation of the cardiac Na+-K+ pump: evidence from in vivo and in vitro modulation of cell signalling.

The widely reported stimulation of the cardiac Na(+)-K(+) pump by protein kinase A (PKA) should oppose other effects of PKA to increase contractility of the normal heart. It should also reduce harmful raised myocyte Na(+) levels in heart failure, yet blockade of the β1 adrenergic receptor (AR), coupled to PKA signalling, is beneficial. We treated rabbits with the β1 AR antagonist metoprolol to modulate PKA activity and studied cardiac myocytes ex vivo.

Susceptibility of β1 Na+-K+ pump subunit to glutathionylation and oxidative inhibition depends on conformational state of pump.

Glutathionylation of cysteine 46 of the β1 subunit of the Na(+)-K(+) pump causes pump inhibition. However, the crystal structure, known in a state analogous to an E2·2K(+)·P(i) configuration, indicates that the side chain of cysteine 46 is exposed to the lipid bulk phase of the membrane and not expected to be accessible to the cytosolic glutathione. We have examined whether glutathionylation depends on the conformational changes in the Na(+)-K(+) pump cycle as described by the Albers-Post scheme.