Cardioprotective effects of simvastatin on reversing electrical remodeling induced by myocardial ischemia-reperfusion in normocholesterolemic rabbits:

Inhibitory Perturbations of Fluvastatin on Afterhyperpolarization Current, Erg-mediated K+ Current, and Hyperpolarization-activated Cation Current in Both Pituitary GH3 Cells and Primary Embryonic Mouse Cortical Neurons

Fluvastatin (FLV), the first synthetically derived 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, is a potent inhibitor of cholesterol biosynthesis. While its primary mechanism of action is to reduce cholesterol levels, there is some evidence suggesting that it may also have effects on K+ channels. However, the overall effects of fluvastatin on ionic currents are not yet well understood. The whole-cell clamp recordings were applied to evaluate the ionic currents and action potentials of cells. Here, we have demonstrated that FLV can effectively inhibit the amplitude of erg-mediated K+ current (IK(erg)) in pituitary tumor (GH3) cells, with an IC50 of approximately 3.2 µM. In the presence of FLV, the midpoint in the activation curve of IK(erg) was distinctly shifted to a less negative potential by 10 mV, with minimal modification of the gating charge. However, the magnitude of hyperpolarization-activated cation current (Ih) elicited by long-lasting membrane hyperpolarization was progressively decreased, with an IC50 value of 8.7 µM, upon exposure to FLV. More interestingly, we also found that FLV (5 µM) could regulate the action potential and afterhyperpolarization properties in primary embryonic mouse cortical neurons. Our study presents compelling evidence indicating that FLV has the potential to impact both the amplitude and gating of the ion channels IK(erg) and Ih. We also provide credible evidence suggesting that this drug has the potential to modify the properties of action potentials and the afterhyperpolarization current in electrically excitable cells. However, the assumption that these findings translate to similar in-vivo results remains unclear.

Mechanisms Underlying Antiarrhythmic Properties of Cardioprotective Agents Impacting Inflammation and Oxidative Stress

The prevention of cardiac life-threatening ventricular fibrillation and stroke-provoking atrial fibrillation remains a serious global clinical issue, with ongoing need for novel approaches. Numerous experimental and clinical studies suggest that oxidative stress and inflammation are deleterious to cardiovascular health, and can increase heart susceptibility to arrhythmias. It is quite interesting, however, that various cardio-protective compounds with antiarrhythmic properties are potent anti-oxidative and anti-inflammatory agents. These most likely target the pro-arrhythmia primary mechanisms. This review and literature-based analysis presents a realistic view of antiarrhythmic efficacy and the molecular mechanisms of current pharmaceuticals in clinical use. These include the sodium-glucose cotransporter-2 inhibitors used in diabetes treatment, statins in dyslipidemia and naturally protective omega-3 fatty acids. This approach supports the hypothesis that prevention or attenuation of oxidative and inflammatory stress can abolish pro-arrhythmic factors and the development of an arrhythmia substrate. This could prove a powerful tool of reducing cardiac arrhythmia burden.

Effects of atorvastatin on sevoflurane postconditioning in in vivo rabbit hearts

OBJECTIVES

Myocardial ischemia-reperfusion injury is a phenomenon that promotes myocardial damage when the blood supply returns to the tissue after a period of ischemia. Anesthetic postconditioning involves myocardial protection against myocardial I/R injury. The effects of atorvastatin (ATV) on sevoflurane postconditioning against myocardial ischemia-reperfusion injury have not been thoroughly studied. The present study aimed to investigate if ATV interacts synergistically with sevoflurane postconditioning against myocardial infarction in rabbit hearts in vivo.

METHODS

Twenty-eight male rabbits underwent 30 min of left anterior descending coronary artery occlusion that was followed by reperfusion for 180 min under ketamine/xylazine (K/X) anesthesia. Rabbits were randomly assigned to four groups that included Group K/X (under K/X anesthesia only), Group POST (sevoflurane exposure at initial reperfusion), Group ATV (ATV 5 mg/kg/day administered before ischemia), and Group ATV + POST (POST intervention with atorvastatin administered once daily for 3 days). At the end of reperfusion, the myocardial infarct size and the area at risk were both measured.

RESULTS

The mean infarct sizes in the POST, ATV, and ATV + POST groups were significantly smaller compared to those in the K/X group. Furthermore, the mean infarct size in Group ATV + POST was significantly smaller than was that in Group POST and significantly smaller compared to that in Group ATV.

CONCLUSION

The combination of sevoflurane postconditioning and pre-administration of ATV further reduced the myocardial infarction size compared to that observed with sevoflurane postconditioning alone or ATV alone. Our data suggest that sevoflurane postconditioning and ATV may function additively to enhance cardioprotection.

Single Bolus Rosuvastatin Accelerates Calcium Uptake and Attenuates Conduction Inhomogeneity in Failing Rabbit Hearts With Regional Ischemia-Reperfusion Injury

Acute statin therapy reduces myocardial ischemia/reperfusion (IR) injury-induced ventricular fibrillation (VF), but the underlying electrophysiological mechanisms remain unclear. This study sought to investigate the antiarrhythmic effects of a single bolus rosuvastatin injection in failing rabbit hearts with IR injury and to unveil the underlying molecular mechanisms. Rabbits were divided into rosuvastatin, rosuvastatin + L-NAME, control, and L-NAME groups. Intravenous bolus rosuvastatin (0.5 mg/kg) and/or L-NAME (10 mg/kg) injections were administered 1 hour and 15 minutes before surgery, respectively. Heart failure was induced using rapid ventricular pacing. Under general anesthesia with isoflurane, an IR model was created by coronary artery ligation for 30 minutes, followed by reperfusion for 15 minutes. Plasma NO end product levels were measured during IR. Then, hearts were excised and Langendorff-perfused for optical mapping studies. Cardiac tissues were sampled for Western blot analysis. Rosuvastatin increased plasma NO levels during IR, which was abrogated by L-NAME. Spontaneous VF during IR was suppressed by rosuvastatin (P < 0.001). Intracellular calcium (Cai) decay and conduction velocity were significantly slower in the IR zone. Rosuvastatin accelerated Cai decay, ameliorated conduction inhomogeneity, and reduced the inducibility of spatially discordant alternans and VF significantly. Western blots revealed significantly higher expression of enhancing endothelial NO-synthase and phosphorylated enhancing endothelial NO-synthase proteins in the Rosuvastatin group. Furthermore, SERCA2a, phosphorylated connexin43, and phosphorylated phospholamban were downregulated in the IR zone, which was attenuated or reversed by rosuvastatin. Acute rosuvastatin therapy before ischemia reduced IR-induced VF by improving SERCA2a function and ameliorating conduction disturbance in the IR zone.

Atorvastatin blocks increased l-type Ca2+ current and cell injury elicited by angiotensin II via inhibiting oxide stress

Thel-type Ca(2+)current (ICa,l) plays a crucial role in shaping action potential and is involved in cardiac arrhythmia. Statins have been demonstrated to contribute to anti-apoptotic and anti-arrhythmic effects in the heart. Here, we examined whether atorvastatin regulates theICa,land cell injury induced by angiotensin II (AngII) as well as the putative intracellular cascade responsible for the effects. Cultured neonatal rat ventricular myocytes were incubated with AngII for 24 h, and then cell injury and expression levels of Nox2/gp91(phox), p47(phox) ,and Cav1.2 were analyzed. In addition,ICa,lwas recorded using the whole-cell patch-clamp technique, and mechanisms of atorvastatin actions were also investigated. It was found that the number of apoptotic cardiomyocytes was increased and cell viability was significantly decreased after AngII administration. AngII also augmented the expressions of Nox2/gp91(phox)and p47(phox)compared with control cardiomyocytes. Exposure to AngII evokedICa,lin a voltage-dependent manner without affecting theI-Vrelationship. In addition, AngII enhanced membrane Cav1.2 expression. These effects were abolished in the presence of the reactive oxygen species (ROS) scavenger, manganese (III)-tetrakis 4-benzoic acid porphyrin [Mn(III)TBAP], or the 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor, atorvastatin. These results suggested that atorvastatin mediates cardioprotection against arrhythmias and cell injury by controlling the AngII-ROS cascade.

Effects of dantrolene on arrhythmogenicity in isolated regional ischemia-reperfusion rabbit hearts with or without pacing-induced heart failure

Dantrolene was reported to suppress ventricular fibrillation (VF) in failing hearts with acute myocardial infarction, but its antiarrhythmic efficacy in regional ischemia-reperfusion (IR) hearts remains debatable. Heart failure (HF) was induced by right ventricular pacing. The IR rabbit model was created by coronary artery ligation for 30 min, followed by reperfusion for 15 min in vivo in both HF and non-HF groups (n = 9 in each group). Simultaneous voltage and intracellular Ca²⁺ (Ca_i) optical mapping was then performed in isolated Langendorff-perfused hearts. Electrophysiological studies were conducted and VF inducibility was evaluated by dynamic pacing. Dantrolene (10 μM) was administered after baseline studies. The HF group had a higher VF inducibility than the control group. Dantrolene had both antiarrhythmic (prolonged action potential duration (APD) and effective refractory period) and proarrhythmic effects (slowed conduction velocity, steepened APD restitution slope, and enhanced arrhythmogenic alternans induction) but had no significant effects on ventricular premature beat (VPB) suppression and VF inducibility in both groups. A higher VF conversion rate in the non-HF group was likely due to greater APD prolonging effects in smaller hearts compared to the HF group. The lack of significant effects on VPB suppression by dantrolene suggests that triggered activity might not be the dominant mechanism responsible for VPB induction in the IR model.

Simvastatin attenuates sympathetic hyperinnervation to prevent atrial fibrillation during the postmyocardial infarction remodeling process

Statin, as a 3-hydroxy-3-methyl-glutaryl-CoA reductase inhibitor, has been shown to prevent atrial fibrillation (AF) due to its anti-inflammatory and antioxidant effects. However, it is still not known whether statin can improve autonomic remodeling to prevent AF. In the present study, using an in vivo rat myocardial infarction (MI) model, we aimed to test whether simvastatin can attenuate nerve sprouting and sympathetic hyperinnervation to prevent AF during the post-MI remodeling process. Our data demonstrate that simvastatin, delivered 3 days after MI for 4 wk, can result in significant decreases in plasma levels of both TNF-α (239 ± 23 pg/ml) and IL-1β (123 ± 11 pg/ml) compared with MI rats without therapy (TNF-α, 728 ± 57 pg/ml; IL-1β, 213 ± 21 pg/ml; P < 0.05), which, however, were still higher than sham-operated rats (TNF-α, 194 ± 20 pg/ml; IL-1β, 75 ± 8 pg/ml; P < 0.05). The similar pattern of changes in inflammation responses was also observed in TNF-α and IL-1β protein expression in the left atrium free wall. The suppressed inflammation responses were associated with reduced superoxide and malondialdehyde generation in the atrium. These changes account for decreases in neural growth factor expression at levels of both mRNA (1.2 ± 0.09 AU vs. MI group, 1.78 ± 0.16 AU) and protein (1.57 ± 0.17 AU vs. MI group, 2.24 ± 0.19 AU; P < 0.05), thus resulting in reduced nerve sprouting and sympathetic hyperinnervation. Accordingly, the rate adaptation of the atrial effective refractory period also recovered, leading to the decreased inducibility of AF. These data suggest that simvastatin administration after MI can prevent AF through reduced sympathetic hyperinnervation.

Growth hormone secretagogues preserve the electrophysiological properties of mouse cardiomyocytes isolated from in vitro ischemia/reperfusion heart

Ischemic heart diseases often induce cardiac arrhythmia with irregular cardiac action potential (AP). This study aims to demonstrate that GH secretagogues (GHS) ghrelin and its synthetic analog hexarelin can preserve the electrophysiological properties of cardiomyocytes experiencing ischemia/reperfusion (I/R). Isolated hearts from adult male mice underwent 20 min global ischemia followed by 30 min reperfusion using a Langendorff apparatus. Ghrelin (10 nM) or hexarelin (1 nM) was administered in the perfusion solution either 10 min before or after ischemia, termed pre- or posttreatments. Cardiomyocytes isolated from these hearts were used for whole-cell patch clamping to measure AP, voltage-gated L-type calcium current (I(CaL)), transient outward potassium current (I(to)), and sodium current (I(Na)). AP amplitude and duration were significantly decreased by I/R, but GHS treatments maintained their normality. GHS treatments prevented the decrease in I(CaL) and I(Na) after I/R, thereby maintaining AP amplitude. Although the significant increase in I(to) after I/R partially explained the shortened AP duration, the normalization of it by GHS treatments might contribute to the preservation of AP duration. Phosphorylated p38 and c-Jun NH(2)-terminal kinase and the downstream active caspase-9 in the cellular apoptosis pathway were significantly increased after I/R but not when GHS treatments were included, whereas phosphorylation of ERK1/2 associated with cell survival showed increase after I/R and a further increase after GHS treatments by binding to its receptor GHS receptor type 1a. These results suggest GHS can not only preserve the electrophysiological properties of cardiomyocytes after I/R but also inhibit cardiomyocyte apoptosis and promote cell survival by modification of MAPK pathways through activating GHS receptor type 1a.

Statins and the reduction of sudden cardiac death: antiarrhythmic or anti-ischemic effect?

Sudden cardiac death is an important cause of cardiovascular mortality with the majority of cases occurring in low-risk groups. HMG-CoA reductase inhibitors (statins) have recently been shown to reduce the incidence of ventricular tachycardia (VT)/fibrillation (VF) and sudden cardiac death, and this has been attributed to their pleiotropic effects. However, it is unclear whether this occurs through an 'indirect' anti-ischemic or 'direct' antiarrhythmic effect. We systematically reviewed articles published on MEDLINE between January 1996 and December 2009 focusing on the reduction of VT/VF and sudden cardiac death by statins and the potential mechanisms. Studies reporting sudden cardiac death or VT/VF outcomes with statin use (n = 23) or the pathophysiology of sudden cardiac death reduction by statins (n = 19) were included. We found that statins have been shown to reduce VT/VF and sudden cardiac death only in subjects with underlying coronary artery disease or ischemic cardiomyopathy. No definite benefits were seen with statins in sudden cardiac death and VT/VF in patients with non-ischemic cardiomyopathy. There is insufficient evidence to point toward a benefit in populations at low risk for VT/VF. In conclusion, an anti-ischemic rather than a primary antiarrhythmic effect emerges as the likely mechanism of sudden cardiac death reduction with statins.