Beta receptor blockade potentiates the antiarrhythmic actions of d-sotalol on reentrant ventricular tachycardia in a canine model of myocardial infarction

Antiarrhythmic Sotalol, Occlusion/Occlusion-like Syndrome in Rats, and Stable Gastric Pentadecapeptide BPC 157 Therapy

We focused on the first demonstration that antiarrhythmics, particularly class II and class III antiarrhythmic and beta-blocker sotalol can induce severe occlusion/occlusion-like syndrome in rats. In this syndrome, as in similar syndromes with permanent occlusion of major vessels, peripheral and central, and other similar noxious procedures that severely disable endothelium function, the stable gastric pentadecapeptide BPC 157-collateral pathways activation, was a resolving therapy. After a high dose of sotalol (80 mg/kg intragastrically) in 180 min study, there were cause-consequence lesions in the brain (swelling, intracerebral hemorrhage), congestion in the heart, lung, liver, kidney, and gastrointestinal tract, severe bradycardia, and intracranial (superior sagittal sinus), portal and caval hypertension, and aortal hypotension, and widespread thrombosis, peripherally and centrally. Major vessels failed (congested inferior caval and superior mesenteric vein, collapsed azygos vein). BPC 157 therapy (10 µg, 10 ng/kg given intragastrically at 5 min or 90 min sotalol-time) effectively counteracted sotalol-occlusion/occlusion-like syndrome. In particular, eliminated were heart dilatation, and myocardial congestion affecting coronary veins and arteries, as well as myocardial vessels; eliminated were portal and caval hypertension, lung parenchyma congestion, venous and arterial thrombosis, attenuated aortal hypotension, and centrally, attenuated intracranial (superior sagittal sinus) hypertension, brain lesions and pronounced intracerebral hemorrhage. Further, BPC 157 eliminated and/or markedly attenuated liver, kidney, and gastrointestinal tract congestion and major veins congestion. Therefore, azygos vein activation and direct blood delivery were essential for particular BPC 157 effects. Thus, preventing such and similar events, and responding adequately when that event is at risk, strongly advocates for further BPC 157 therapy.

Multichannel modulation of depolarizing and repolarizing ion currents increases the positive rate-dependent action potential prolongation

Prolongation of the action potential duration (APD) could prevent reentrant arrhythmias if prolongation occurs at the fast excitation rates of tachycardia with minimal prolongation at slow excitation rates (i.e., if prolongation is positive rate-dependent). APD prolongation by current anti-arrhythmic agents is either reverse (larger APD prolongation at slow rates than at fast rates) or neutral (similar APD prolongation at slow and fast rates), which may not result in an effective anti-arrhythmic action. In this report we show that, in computer models of the human ventricular action potential, the combined modulation of both depolarizing and repolarizing ion currents results in a stronger positive rate-dependent APD prolongation than modulation of repolarizing potassium currents. A robust positive rate-dependent APD prolongation correlates with an acceleration of phase 2 repolarization and a deceleration of phase 3 repolarization, which leads to a triangulation of the action potential. A positive rate-dependent APD prolongation decreases the repolarization reserve with respect to control, which can be managed by interventions that prolong APD at fast excitation rates and shorten APD at slow excitation rates. For both computer models of the action potential, I_CaL and I_K1 are the most important ion currents to achieve a positive rate-dependent APD prolongation. In conclusion, multichannel modulation of depolarizing and repolarizing ion currents, with ion channel activators and blockers, results in a robust APD prolongation at fast excitation rates, which should be anti-arrhythmic, while minimizing APD prolongation at slow heart rates, which should reduce pro-arrhythmic risks.

Positive rate-dependent action potential prolongation by modulating potassium ion channels

Pharmacological agents that prolong action potential duration (APD) to a larger extent at slow rates than at the fast excitation rates typical of ventricular tachycardia exhibit reverse rate dependence. Reverse rate dependence has been linked to the lack of efficacy of class III agents at preventing arrhythmias because the doses required to have an antiarrhythmic effect at fast rates may have pro-arrhythmic effects at slow rates due to an excessive APD prolongation. In this report, we show that, in computer models of the ventricular action potential, APD prolongation by accelerating phase 2 repolarization (by increasing I_Ks ) and decelerating phase 3 repolarization (by blocking I_Kr and I_K1 ) results in a robust positive rate dependence (i.e., larger APD prolongation at fast rates than at slow rates). In contrast, APD prolongation by blocking a specific potassium channel type results in reverse rate dependence or a moderate positive rate dependence. Interventions that result in a strong positive rate dependence tend to decrease the repolarization reserve because they require substantial I_K1 block. However, limiting I_K1 block to ~50% results in a strong positive rate dependence with moderate decrease in repolarization reserve. In conclusion, the use of a combination of I_Ks activators and I_Kr and I_K1 blockers could result in APD prolongation that potentially maximizes antiarrhythmic effects (by maximizing APD prolongation at fast excitation rates) and minimizes pro-arrhythmic effects (by minimizing APD prolongation at slow excitation rates).

Choosing among β-blockers in heart failure patients according to β-receptors' location and functions in the cardiopulmonary system

Several large clinical trials showed a favorable effect of β-blocker treatment in patients with chronic heart failure (HF) as regards overall mortality, cardiovascular mortality, and hospitalizations. Indeed, the use of β-blockers is strongly recommended by current international guidelines, and it remains a cornerstone in the pharmacological treatment of HF. Although different types of β-blockers are currently approved for HF therapy, possible criteria to choose the best β-blocking agent according to HF patients' characteristics and to β-receptors' location and functions in the cardiopulmonary system are still lacking. In such a context, a growing body of literature shows remarkable differences between β-blocker types (β1-selective blockers versus β1-β2 blockers) with respect to alveolar-capillary gas diffusion and chemoreceptor response in HF patients, both factors able to impact on quality of life and, most likely, on prognosis. This review suggests an original algorithm for choosing among the currently available β-blocking agents based on the knowledge of cardiopulmonary pathophysiology. Particularly, starting from lung physiology and from some experimental models, it focuses on the mechanisms underlying lung mechanics, chemoreceptors, and alveolar-capillary unit impairment in HF. This paper also remarks the significant benefit deriving from the correct use of the different β-blockers in HF patients through a brief overview of the most important clinical trials.

Sotalol

Sotalol is effective for treating atrial fibrillation (AF), ventricular tachycardia, premature ventricular contractions, and supraventricular tachycardia. Racemic (DL) sotalol inhibits the rapid component of the delayed rectifier potassium current. There is a near linear relationship between sotalol dosage and QT interval prolongation. However, in dose ranging trials in patients with AF, low-dose sotalol was not more effective than placebo. Orally administered sotalol has a bioavailability of nearly 100%. The only significant drug interactions are the need to avoid or limit use of concomitant drugs that cause QT prolongation, bradycardia, and/or hypotension.

Myeloid cell sirtuin-1 expression does not alter host immune responses to Gram-negative endotoxemia or Gram-positive bacterial infection

The role of sirtuin-1 (SIRT1) in innate immunity, and in particular the influence of SIRT1 on antimicrobial defense against infection, has yet to be reported but is important to define since SIRT1 inhibitors are being investigated as therapeutic agents in the treatment of cancer, Huntington’s disease, and autoimmune diseases. Given the therapeutic potential of SIRT1 suppression, we sought to characterize the role of SIRT1 in host defense. Utilizing both pharmacologic methods and a genetic knockout, we demonstrate that SIRT1 expression has little influence on macrophage and neutrophil antimicrobial functions. Myeloid SIRT1 expression does not change mortality in gram-negative toxin-induced shock or gram-positive bacteremia, suggesting that therapeutic suppression of SIRT1 may be done safely without suppression of myeloid cell-specific immune responses to severe bacterial infections.

Regadenoson, a novel pharmacologic stress agent for use in myocardial perfusion imaging, does not have a direct effect on the QT interval in conscious dogs

Our goal was to determine the effect of regadenoson (a novel A2A adenosine receptor agonist) on the QT interval in conscious dogs. Sixteen mongrel dogs were chronically instrumented for measurements of blood pressure and ECG. Regadenoson (2.5, 5, and 10 microg/kg, IV) caused a dose-dependent QT interval shortening (DeltaQT: 14 +/- 3, 24 +/- 5, and 27 +/- 5 ms, mean +/- SEM; n = 7 to 11; all P < 0.05) associated with significant increases in HR (Peak HR: 114 +/- 9, 125 +/- 6, and 144 +/- 7 bpm). Atrial pacing (135, 150, and 165 bpm) also caused a frequency-dependent shortening of the QT interval (DeltaQT: 15 +/- 3, 22 +/- 3, and 39 +/- 5 ms; n = 6 to 7; all P < 0.05). Regadenoson- and pacing-induced shortenings in the QT interval were significantly correlated with the R-R interval (r = 0.67 and 0.8, both P < 0.05). Regadenoson at 5 and 10 microg/kg did not cause a significant change in HR or QT interval either during atrial pacing at 165 bpm or after administration of propranolol and atropine to prevent HR from changing or after treatment of dogs with hexamethonium to block autonomic ganglia. Regadenoson (5 to 10 microg/kg) caused no significant changes of QT interval in the heart in which HR was kept constant via physiological or pharmacological procedures, indicating that regadenoson has no direct effect on the QT interval.

Electrophysiologic Actions of d,l-Sotalol and GLG-V-13 in Ischemically Injured Canine Epicardium

The electrophysiologic actions of the class III antiarrhythmic agents, GLG-V-13 and d,l-sotalol, were examined in superfused normal and ischemically injured epicardium. Both drugs produced concentration and reverse-use dependent prolongation of the action potential duration in normal myocardium without altering resting potential, action potential amplitude, or Vmax. Both drugs increased the slope of restitution curves in normal epicardium but prevented action potential alternans at short cycle lengths. The response of superfused ischemically injured left ventricular epicardium to drug 4 days after coronary artery ligation was determined by the extent of ischemic injury, with no electrophysiologic changes produced within epicardial cells characterized by prominent action potential shortening and no further action potential shortening with pacing. Cells demonstrating less severe injury (as evidenced by less severely depressed action potential amplitudes, Vmax, and action potential durations) retained a limited ability to respond to drug administration with action potential prolongation. A concentration-dependent, increased disparity of action potential duration was observed concurrent with the ability of single premature stimuli to induce monomorphic tachycardia. The present data demonstrate a variable response of ischemically injured canine epicardial cells to action potential prolongation with GLG-V-13 and d,l-sotalol, facilitating localized reentry in vitro, despite a failure of the same drugs to facilitate reentrant tachycardia in vivo.