Effects of sodium–glucose cotransporter-2 inhibitors on cardiac structural and electrical remodeling: from myocardial cytology to cardiodiabetology

Sodium-glucose cotransporter 2 inhibitors (SGLT2i) have changed the clinical landscape of diabetes mellitus (DM) therapy through their favourable effects on cardiovascular outcomes. Notably, the use of SGLT2i has been linked to cardiovascular benefits regardless of DM status, while their pleiotropic actions remain to be fully elucidated. What we do know is that SGLT2i exert beneficial effects even at the level of the myocardial cell, and that these are linked to an improvement in the energy substrate, resulting in less inflammation and fibrosis. SGLT2i ameliorate myocardial extracellular matrix remodeling, cardiomyocyte stiffness and concentric hypertrophy, achieving beneficial remodeling of the left ventricle with significant implications for the pathogenesis and outcome of heart failure. Most studies show a significant improvement in markers of diastolic dysfunction along with a reduction in left ventricular hypertrophy. In addition to these effects there is electrophysiological remodeling, which explains initial data suggesting that SGLT2i have an antiarrhythmic action against both atrial and ventricular arrhythmias. However, future studies need to clarify not only the exact mechanisms of this beneficial functional, structural, and electrophysiological cardiac remodeling, but also its magnitude, and to determine whether this is a class or a drug effect.

Suppression of ventricular arrhythmias by targeting late L-type Ca2+ current

Ventricular arrhythmias, a leading cause of sudden cardiac death, can be triggered by cardiomyocyte early afterdepolarizations (EADs). EADs can result from an abnormal late activation of L-type Ca2+ channels (LTCCs). Current LTCC blockers (class IV antiarrhythmics), while effective at suppressing EADs, block both early and late components of ICa,L, compromising inotropy. However, computational studies have recently demonstrated that selective reduction of late ICa,L (Ca2+ influx during late phases of the action potential) is sufficient to potently suppress EADs, suggesting that effective antiarrhythmic action can be achieved without blocking the early peak ICa,L, which is essential for proper excitation–contraction coupling. We tested this new strategy using a purine analogue, roscovitine, which reduces late ICa,L with minimal effect on peak current. Scaling our investigation from a human CaV1.2 channel clone to rabbit ventricular myocytes and rat and rabbit perfused hearts, we demonstrate that (1) roscovitine selectively reduces ICa,L noninactivating component in a human CaV1.2 channel clone and in ventricular myocytes native current, (2) the pharmacological reduction of late ICa,L suppresses EADs and EATs (early after Ca2+ transients) induced by oxidative stress and hypokalemia in isolated myocytes, largely preserving cell shortening and normal Ca2+ transient, and (3) late ICa,L reduction prevents/suppresses ventricular tachycardia/fibrillation in ex vivo rabbit and rat hearts subjected to hypokalemia and/or oxidative stress. These results support the value of an antiarrhythmic strategy based on the selective reduction of late ICa,L to suppress EAD-mediated arrhythmias. Antiarrhythmic therapies based on this idea would modify the gating properties of CaV1.2 channels rather than blocking their pore, largely preserving contractility.

On the mechanism of the antiarrhythmic action of fabomotizole hydrochloride in alcoholic cardiomyopathy

It is known that the alcoholic cardiomyopathy (ACMP) is the main reason for lethality from chronic alcoholism. For ACMP the risk of development of malignant violations of a heart rhythm which result approximately at 40% of such patients is sudden heart death is extremely high. Materials and methods. Experiments were made on the ACMP translational model developed by us which is formed at rats by the end of the 24th week of compulsory reception of 10 % of ethanol solution. For studying the mechanisms which are the responsible of antiarrhythmic action of a fabomotizole dihydrochloride used a complex of morphohistological, electrophysiological and molecular researches. Results. It is shown that against the background of systematic therapy fabomotizole dihydrochloride (15 mg/kg, i.p.) daily within 28 days after 24 weeks of alcoholization, in comparison with alcoholized control the fat dystrophy of a myocardium significantly decreases and the threshold of electric fibrillation of heart ventricles is restored. According to results of molecular researches, a fabomotizole dihydrochloride significantly suppresses revealed in control alkoholized animals the abnormal mRNA expression of key receptor genes and proteins responsible for maintenance in cardiomyocytes of a homeostasis of ions of Ca++ and regulation of their rhythmic activity: regulatory proteins Epac1 (p = 0.021), Epac2 (p = 0.018), CaM (p = 0.00001) and also RyR2 (p = 0.031), IP3R2 (p = 0.006) receptors. Conclusion. The obtained results suggest that antiarrhythmic action of a fabomotizole dihydrochloride in the conditions of ACMP is connected with its ability to suppress abnormal activity of regulatory proteins Epac2 and RyR2, IP3R2 receptors.

Is selective late sodium current inhibition different from class I/B antiarrhythmic action? Comparison of the effects of GS967 to mexiletine in canine ventricular myocardium

Funding Acknowledgements Type of funding sources: Public grant(s) – EU funding. Main funding source(s): National Research, Development and Innovation Office New National Excellence Programme Enhancement of the late Na+ current (INa,late) increases arrhythmia propensity in the heart, while suppression of the current is antiarrhythmic. GS-458967 (GS) is an agent considered to be a selective blocker of INa,late. In the present study, effects of GS967 on INa,late, on L-type calcium current (ICaL), and on action potential (AP) morphology were studied in canine ventricular myocytes by using conventional voltage clamp, action potential voltage clamp and sharp microelectrode techniques. These effects of GS were compared to tetrodotoxin (TTX) and to the class I/B antiarrhythmic compound mexiletine. GS (1 μM), mexiletine (40 μM) and TTX (10 μM) dissected largely similarly shaped inward currents under action potential voltage clamp conditions. In case of GS and mexiletine, the amplitude and integral of this inward current was significantly smaller when measured in the presence of 1 μM nisoldipine, while no difference was observed in case of TTX. Under conventional voltage clamp conditions, INa,late was significantly reduced by 1 μM GS and 40 μM mexiletine (about 79% and 63% reduction of current integrals, respectively). The integral of ICa,L was moderately but significantly decreased by both drugs (reduction of 9% and 14%, respectively). These changes were associated with a faster inactivation of ICa,L. Drug effects on early Na+ current (INa,early) were assessed by analyzing the maximal rate of depolarization (V + max) in multicellular preparations. Both GS and mexiletine showed fast onset and offset kinetics: 110 ms and 289 ms offset time constants, respectively, as determined from V + max measurements in right ventricular papillary muscles, while the onset kinetics was characterized by 5.3 AP and 2.6 AP lengths, respectively, at 2.5 Hz. Effects on beat-to-beat variability of AP duration (APD) was studied in isolated myocytes. Short-term variability was significantly decreased by both GS and mexiletine (average reduction of 42% and 24%, respectively) while they caused similar shortening of the APD. The electrophysiological effects of GS are similar to those of mexiletine, but with a somewhat faster offset kinetics of V + max block. However, since GS reduced V+ max and INa,late in the same concentration, the currently accepted view that GS that selectively blocks INa,late has to be questioned and it is suggested that GS should be classified as a class I/B (or I/B + IV) antiarrhythmic agent.

IATROGENIC CHANGES IN THYROID GLAND OF PATIENTS WITH ATRIAL FIBRILLATION AFTER THERAPY WITH AMIODARON

Objective of the study: to analyze the frequency of structural and functional changes in the thyroid gland of the patients with atrial fibrillation who took amiodarone for 12 months on regular basis. The study was based on findings obtained by examining 80 patients (28 women and 52 men) with cardiosclerosis (diffuse and postinfarction), atrial fibrillation and heart failure IIA at the age of 63.5 ± 1.3 years and 15 healthy individuals of the relevant age (62,4 ± 2,4 years) and relevant sex proportions. The main inclusion criterion was the euthyroid state of the thyroid gland before the beginning of antiarrhythmic therapy. To assess the functional state of the thyroid gland, we studied the content of free thyroxine, triiodothyronine, and antibodies to thyroid peroxidase. The examination was carried out before the therapy, and in 3, 6, 9 and 12 months after the beginning of the study during the course of antiarrhythmic therapy. To detect structural changes in the thyroid gland, we used ultrasound scanning. Depending on the prescribed treatment, the participants were divided into the following groups: group I included the patients who received amiodarone in a dosage of 200 mg per day and basic therapy (n = 60); control group involved the patients who received the basic therapy with antiarrhythmic drugs, digoxin and bisoprolol (n = 20). Results. The therapy with amiodarone for a year resulted in thyroid dysfunction in 33.3% of the patients. Hypothyroidism (20.0%) is leading in the structure of amiodarone-associated thyroid dysfunctions; this condition is subclinically manifested in 11.7% of the patients. The development of amiodarone-induced thyrotoxicosis was observed in 13.3% of the patients, and the first cases of hyperthyroidism were detected not earlier than six months. Under the effect of amiodarone in the first months of the therapy, serum levels of free thyroxine may increase, while free triiodothyronine may decrease, therefore there may be a tendency to slightly increased levels of thyroid-stimulating hormone in the first weeks of the therapy. The above changes in laboratory parameters are transient and are not accompanied by the deterioration of the antiarrhythmic action of amiodarone.

Is Selective Late Na+ Current Inhibition Different From Class I/B Antiarrhythmic Action? Comparison of The Effects of GS967 to Mexiletine in Canine Ventricular Myocardium

Enhancement of the late Na+ current (INaL) increases arrhythmia propensity in the heart, while suppression of the current is antiarrhythmic. GS967 is an agent considered as a selective blocker of INaL. In the present study, effects of GS967 on INaL, on L-type calcium current (ICa), and on action potential (AP) morphology were studied in canine ventricular myocytes by using conventional voltage clamp, action potential voltage clamp and sharp microelectrode techniques. These effects of GS967 were compared to tetrodotoxin (TTX) and to the class I/B antiarrhythmic compound mexiletine. 1 µM GS967, 40 µM mexiletine, and 10 µM TTX dissected largely similarly shaped inward currents under action potential voltage clamp conditions. In case of GS967 and mexiletine, the amplitude and integral of this current was significantly smaller when measured in the presence of 1 µM nisoldipine, while no difference was observed in case of TTX. Under conventional voltage clamp conditions, INaL was significantly decreased by 1 µM GS967 and 40 µM mexiletine (79.0±3.0% and 63.3±2.7% reduction of current integrals, respectively). The integral of ICa was moderately but significantly diminished by both drugs (reduction of 9.3±3.3% and 14.1±1.5%, respectively). These changes were associated with acceleration of inactivation of ICa. Drug effects on peak Na+ current (INaP) were also assessed by recording AP upstroke in multicellular preparations. Both GS967 and mexiletine showed fast onset and offset kinetics: 110 ms and 289 ms offset time constants, respectively, as determined from V+max measurements in right ventricular papillary muscles, while the onset kinetics was characterized by 5.3 AP and 2.6 AP, respectively, at 2.5 Hz. Effects on beat-to-beat variability of AP duration (APD) was studied in isolated myocytes. Beat-to-beat variability was significantly decreased by both GS967 and mexiletine (reduction of 42.1±6.5% and 24.6±12.8%, respectively) while their shortening effect on APD was comparable. It is concluded that the electrophysiological effects of GS967 are similar to those of mexiletine, but with somewhat faster offset kinetics of V+max block. However, since GS967 depressed V+max and INaL at the same concentration, the current view that GS967 represents a new class of drugs that selectively block INaL has to be questiond and it is suggested that GS967 should be classified as a class I/B (or I/B + IV) antiarrhythmic agent.

RYR2 Channel Inhibition Is the Principal Mechanism 0f Flecainide Action in CPVT

Rationale: The class Ic antiarrhythmic drug flecainide prevents ventricular tachyarrhythmia in patients with catecholaminergic polymorphic ventricular tachycardia (CPVT), a disease caused by hyperactive cardiac ryanodine receptor (RyR2) calcium (Ca) release. Although flecainide inhibits single RyR2 channels in vitro, reports have claimed that RyR2 inhibition by flecainide is not relevant for its mechanism of antiarrhythmic action and concluded that sodium channel block alone is responsible for flecainide's efficacy in CPVT. Objective: To determine whether RyR2 block independently contributes to flecainide's efficacy for suppressing spontaneous sarcoplasmic reticulum (SR) Ca release and for preventing ventricular tachycardia in vivo. Methods and Results: We synthesized N-methylated flecainide analogues (QX-FL and NM-FL) and showed that N-methylation reduces flecainide's inhibitory potency on RyR2 channels incorporated into artificial lipid bilayers. N-Methylation did not alter flecainide's inhibitory activity on human cardiac sodium channels expressed in HEK293T cells. Antiarrhythmic efficacy was tested utilizing a calsequestrin knockout (Casq2-/-) CPVT mouse model. In membrane-permeabilized Casq2-/- cardiomyocytes — lacking intact sarcolemma and devoid of sodium channel contribution — flecainide, but not its analogues, suppressed RyR2-mediated Ca release at clinically relevant concentrations. In voltage-clamped, intact Casq2-/- cardiomyocytes pretreated with tetrodotoxin (TTX) to inhibit sodium channels and isolate the effect of flecainide on RyR2, flecainide significantly reduced the frequency of spontaneous SR Ca release, while QX-FL and NM-FL did not. In vivo, flecainide effectively suppressed catecholamine-induced ventricular tachyarrhythmias in Casq2-/- mice, whereas NM-FL had no significant effect on arrhythmia burden, despite comparable sodium channel block. Conclusions: Flecainide remains an effective inhibitor of RyR2-mediated arrhythmogenic Ca release even when cardiac sodium channels are blocked. In mice with CPVT, sodium channel block alone did not prevent ventricular tachycardia. Hence, RyR2 channel inhibition likely constitutes the principal mechanism of antiarrhythmic action of flecainide in CPVT.

Abstract 15420: Resolving a Controversy: Inhibition of Cardiac Ryanodine Receptors is the Principal Mechanism of Antiarrhythmic Action of Flecainide in Catecholaminergic Polymorphic Ventricular Tachycardia

Rationale: The class Ic antiarrhythmic drug flecainide prevents ventricular tachyarrhythmia in patients with catecholaminergic polymorphic ventricular tachycardia (CPVT), a disease caused by hyperactive cardiac ryanodine receptor (RyR2) calcium (Ca) release. Although flecainide inhibits single RyR2 channels in vitro , reports have claimed that RyR2 inhibition by flecainide is not relevant for its mechanism of antiarrhythmic action and concluded that sodium channel block alone is responsible for flecainide’s efficacy in CPVT. Objective: To determine whether RyR2 block independently contributes to flecainide’s efficacy for suppressing spontaneous sarcoplasmic reticulum (SR) Ca release and for preventing ventricular tachycardia in vivo . Methods and Results: We synthesized N -methyl flecainide analogues (QX-FL and NM-FL) and showed that N -methylation reduces flecainide’s inhibitory potency on RyR2 channels but not on cardiac sodium channels. Antiarrhythmic efficacy was tested utilizing a calsequestrin knockout (Casq2-/-) CPVT mouse model. In membrane-permeabilized Casq2-/- cardiomyocytes — lacking intact sarcolemma and devoid of sodium channel contribution — flecainide, but not its analogues, suppressed RyR2-mediated Ca release at clinically relevant concentrations. In voltage-clamped, intact Casq2-/- cardiomyocytes pretreated with tetrodotoxin (TTX) to inhibit sodium channels and isolate the effect of flecainide on RyR2, flecainide significantly reduced the frequency of spontaneous SR Ca release, while QX-FL and NM-FL did not. In vivo , flecainide effectively suppressed catecholamine-induced ventricular tachyarrhythmias in Casq2-/- mice, whereas NM-FL did not, despite comparable sodium channel block. Conclusions: Flecainide remains an effective inhibitor of RyR2-mediated arrhythmogenic Ca release even when cardiac sodium channels are blocked. In mice with CPVT, sodium channel block alone was not enough to prevent arrhythmias. Hence, RyR2 inhibition by flecainide is critical for its mechanism of antiarrhythmic action.

The journey of omega-3 fatty acids in cardiovascular medicine

In subjects with cardiovascular risk factors or in patients in need of secondary prevention, hypertriglyceridemia is a well-defined risk factor for adverse cardiac events. Drugs containing n-3 polyunsaturated fatty acids (n-3 PUFAs) are approved for treatment of hypertriglyceridemia. In 1999, a cardioprotective effect in post infarct patients was suggested by a large multicentre study, the GISSI prevention trial. The hypothesized mechanism of action was an antiarrhythmic action leading to reduction of the sudden death. However, such a cardioprotective effect of n-3 PUFAs has not been straightforward like for other cardiovascular drugs such as aspirin, statins or ACE inhibitors. On the contrary, it has been a long journey with several ups and downs. Recently, the European Medicines Agency (EMA) has not confirmed the risk benefit of low dose of n-3 PUFA in preventing outcomes after a myocardial infarction. Since the EMA decision, the use of a high dose (4g daily) of pure and stable EPA in a multicentre, international trial, the REDUCE-IT study showed a clear cardiovascular event reduction which was not confirmed in another trial, the STRENGTH study, which utilized 4g daily of an EPA+DHA mixture. It follows that the OMEGA-3 fatty acid story seems to be endless and the last word on cardiovascular benefits cannot be pronounced. We report a brief narrative of an entire journey from the beginning to nowadays.