The effect of K201 on isolated working rabbit heart mechanical function during pharmacologically induced Ca2+ overload

A novel ryanodine receptor 2 inhibitor, M201-A, enhances natriuresis, renal function and lusi-inotropic actions: Preclinical and phase I study

BACKGROUND AND PURPOSE

The ryanodine receptor 2 (RyR2) is present in both the heart and kidneys, and plays a crucial role in maintaining intracellular Ca2+ homeostasis in cells in these organs. This study aimed to investigate the impact of M201-A on RyR2, as well as studying its effects on cardiac and renal functions in preclinical and clinical studies.

EXPERIMENTAL APPROACH

Following the administration of M201-A (1,4-benzothiazepine-1-oxide derivative), we monitored diastolic Ca2+ leak via RyR2 and intracellular Ca2+ concentration in isolated rat cardiomyocytes and in cardiac and renal function in animals. In a clinical study, M201-A was administered intravenously at doses of 0.2 and 0.4 mg·kg-1 once daily for 20 min for four consecutive days in healthy males, with the assessment of haemodynamic responses.

KEY RESULTS

In rat heart cells, M201-A effectively inhibited spontaneous diastolic Ca2+ leakage through RyR2 and exhibited positive lusi-inotropic effects on the rat heart. Additionally, it enhanced natriuresis and improved renal function in dogs. In human clinical studies, when administered intravenously, M201-A demonstrated an increase in natriuresis, glomerular filtration rate and creatinine clearance, while maintaining acceptable levels of drug safety and tolerability.

CONCLUSIONS AND IMPLICATIONS

The novel drug M201-A inhibited diastolic Ca2+ leak via RyR2, improved cardiac lusi-inotropic effects in rats, and enhanced natriuresis and renal function in humans. These findings suggest that this drug may offer a potential new treatment option for chronic kidney disease and heart failure.

Novelties in the pharmacological approaches for chronic heart failure: new drugs and cardiovascular targets

Despite recent advances in chronic heart failure (HF) management, the prognosis of HF patients is poor. This highlights the need for researching new drugs targeting, beyond neurohumoral and hemodynamic modulation approach, such as cardiomyocyte metabolism, myocardial interstitium, intracellular regulation and NO-sGC pathway. In this review we report main novelties on new possible pharmacological targets for HF therapy, mainly on new drugs acting on cardiac metabolism, GCs-cGMP pathway, mitochondrial function and intracellular calcium dysregulation.

Pathophysiology-based novel pharmacotherapy for heart failure with preserved ejection fraction

Heart failure has become increasingly prevalent and poses a significant socioeconomic burden in the developed world. Approximately half of heart failure patients have preserved ejection fraction (HFpEF) and experience an increased morbidity and mortality attributed to the lack of effective therapies and to the presence of comorbidities. Suppression of neurohormonal activation by beta-blockers and renin-angiotensin-aldosterone system inhibitors is the cornerstone in the pharmacotherapy of heart failure with reduced ejection fraction (HFrEF). However, these medications are not associated with significant clinical benefit in HFpEF. In this review, we provide an in-depth pathophysiology-based update on novel pharmacotherapies of HFpEF. A deeper insight into the pathophysiologic mechanisms of HFpEF may create opportunities for novel pharmacological interventions.

Specific nephrotoxicity and cardiotoxicity of BT-CAL®, Sigma Anti-bonding Molecule Calcium Carbonate, in mice

According to a high anti-osteoporotic efficacy of Sigma Anti-bonding Molecule Calcium Carbonate (SAC), repeated-dose toxicities of SAC were investigated to assess its feasibility as drug or functional food ingredient. Male ICR mice were given drinking water containing 0.006, 0.02 or 0.06% SAC for 4 weeks. SAC feeding decreased the body weights and feed and water consumptions of mice in a dose-dependent manner, especially, leading to severe emaciation and 70% death in 3 weeks in the high-dose (0.06%) group. Not only kidney and heart weights, but also the levels of blood urea nitrogen, creatinine, aspartate transaminase, and creatine phospokinase significantly increased after SAC administration, indicative of nephrotoxicity and cardiotoxicity. Such renal and cardiac toxicities were also confirmed by microscopic findings, exhibiting renal crystals and cardiac fibrosis, which may be due to the insoluble crystal formation and calcium overload, respectively. In conclusion, it is suggested that no observed adverse effect level of SAC is lower than 0.006% in mice, and that a long-term intake may cause serious adverse effects on renal and cardiac functions.

Cardiac ion channels and mechanisms for protection against atrial fibrillation

Atrial fibrillation (AF) is recognised as the most common sustained cardiac arrhythmia in clinical practice. Ongoing drug development is aiming at obtaining atrial specific effects in order to prevent pro-arrhythmic, devastating ventricular effects. In principle, this is possible due to a different ion channel composition in the atria and ventricles. The present text will review the aetiology of arrhythmias with focus on AF and include a description of cardiac ion channels. Channels that constitute potentially atria-selective targets will be described in details. Specific focus is addressed to the recent discovery that Ca(2+)-activated small conductance K(+) channels (SK channels) are important for the repolarisation of atrial action potentials. Finally, an overview of current pharmacological treatment of AF is included.

Isolated rabbit working heart function during progressive inhibition of myocardial SERCA activity

RATIONALE

The extent to which sarcoplasmic reticulum Ca(2+)ATPase (SERCA) activity alone determines left ventricular (LV) pump function is unknown.

OBJECTIVE

To correlate SERCA activity with hemodynamic function of rabbit LV during thapsigargin perfusion.

METHODS AND RESULTS

Isolated rabbit hearts were perfused in working heart configuration, and LV pump function was assessed using a pressure-volume catheter. Rapid and complete (>95%) inhibition of SERCA was associated with a moderate decrease in cardiac function (to 70%-85% of control). Further decrease in cardiac function to 50%-75% of control occurred over the next ≈ 30 minutes despite no detectable further inhibition of SERCA activity. Analysis of the 20 seconds prior to pump failure revealed a rapid decrease in end diastolic volume. Intermediate levels of SERCA function (≈ 50% of control) had only minor hemodynamic effects. Parallel experiments in field-stimulated isolated ventricular cardiomyocytes monitored intracellular Ca(2+) and cell shortening. On perfusion with thapsigargin, Ca(2+) transient amplitude and cell shortening fell to ≈ 70% of control followed by increased diastolic Ca(2+) concentration and diastolic cell shortening to achieve a new steady state.

CONCLUSIONS

The relationship between SERCA activity and LV function in the rabbit is highly nonlinear. In the short term, only moderate effects on LV pump function were observed despite almost complete (>95%) reduction in SERCA activity. The terminal decline of function was associated with sudden sustained increase in diastolic tone comparable to the sustained contraction observed in isolated cardiomyocytes. Secondary increases of intracellular Ca(2+) and Na(+) following complete SERCA inhibition eventually limit contractile function and precipitate LV pump failure.