Ranolazine reduces Ca2+ overload and oxidative stress and improves mitochondrial integrity to protect against ischemia reperfusion injury in isolated hearts

Ranolazine toxicity precipitating seizure in the elderly

An 80+ year old woman with stage III chronic kidney disease presented after having an episode of sudden stiffening, shaking and confusion. This was the third such episode that the patient had in the past 4 weeks, and the patient has never had such an episo de previously. Of note, she was prescribed ranolazine for chronic angina 6 weeks prior. She initially started taking 500 mg two times per day which was subsequently increased to 1000 two times per day. Laboratory work up revealed an elevated creatinine of 2.42 compared with baseline of 1.9. Imaging studies revealed no acute findings suggestive of stroke. Electroencephalogram demonstrated seizure activity, and lacosamide 100 mg two times per day was prescribed. During her hospital stay, ranolazine was discontinued and the patient gradually returned to her mental baseline. This case demonstrates ranolazine toxicity that manifests as new-onset epilepsy which is more likely to occur in the elderly and patients with renal dysfunction.

Mitochondrial dysfunction is a key link involved in the pathogenesis of sick sinus syndrome: a review

Sick sinus syndrome (SSS) is a grave medical condition that can precipitate sudden death. The pathogenesis of SSS remains incompletely understood. Existing research postulates that the fundamental mechanism involves increased fibrosis of the sinoatrial node and its surrounding tissues, as well as disturbances in the coupled-clock system, comprising the membrane clock and the Ca2+ clock. Mitochondrial dysfunction exacerbates regional tissue fibrosis and disrupts the functioning of both the membrane and calcium clocks. This plays a crucial role in the underlying pathophysiology of SSS, including mitochondrial energy metabolism disorders, mitochondrial oxidative stress damage, calcium overload, and mitochondrial quality control disorders. Elucidating the mitochondrial mechanisms involved in the pathophysiology of SSS and further investigating the disease's mechanisms is of great significance.

Improvement of Vascular Insulin Sensitivity by Ranolazine

Ranolazine (RN) is a drug used in the treatment of chronic coronary ischemia. Different clinical trials have shown that RN behaves as an anti-diabetic drug by lowering blood glucose and glycosylated hemoglobin (HbA1c) levels. However, RN has not been shown to improve insulin (IN) sensitivity. Our study investigates the possible facilitating effects of RN on the actions of IN in the rabbit aorta. IN induced vasodilation of the abdominal aorta in a concentration-dependent manner, and this dilatory effect was due to the phosphorylation of endothelial nitric oxide synthase (eNOS) and the formation of nitric oxide (NO). On the other hand, IN facilitated the vasodilator effects of acetylcholine but not the vasodilation induced by sodium nitroprusside. RN facilitated all the vasodilatory effects of IN. In addition, IN decreased the vasoconstrictor effects of adrenergic nerve stimulation and exogenous noradrenaline. Both effects were in turn facilitated by RN. The joint effect of RN with IN induced a significant increase in the ratio of p-eNOS/eNOS and pAKT/AKT. In conclusion, RN facilitated the vasodilator effects of IN, both direct and induced, on the adrenergic system. Therefore, RN increases vascular sensitivity to IN, thus decreasing tissue resistance to the hormone, a key mechanism in the development of type II diabetes.

Administration of metformin rescues age-related vulnerability to ischemic insults through mitochondrial energy metabolism

Ischemic heart disease (IHD) is the leading cause of death on a global scale. Despite significant advances in the reperfusion treatment of acute myocardial infarction, there is still a significant early mortality rate among the elderly, as angioplasty-achieved reperfusion can exacerbate myocardial damage, leading to severe ischemia/reperfusion (I/R) injury and induce fatal arrhythmias. Mitochondria are a key mediator of ischemic insults; a transient blockade of the electron transport chain (ETC) at complex I during reperfusion can reduce myocardial infarct caused by ischemic insults. The reversible, transient modulation of complex I during early reperfusion is limited by the available of clinically tractable agents. We employed the novel use of acute, high dose metformin to modulate complex I activity during early reperfusion to decrease cardiac injury in the high-risk aged heart. Young (3-6 months) and aged (22-24 months) male and female C57BL/6 J mice were subjected to in vivo regional ischemia for 45 min, followed by metformin (2 mM, i. v.) injection 5 min prior to reperfusion for 24 h. The cardiac functions were measured with echocardiography. A Seahorse XF24 Analyzer was used to ascertain mitochondrial function. Cardiomyocyte sarcomere shortening and calcium transients were measured using the IonOptix Calcium and Contractility System. The results demonstrated that administration of acute, high dose metformin at the onset of reperfusion significantly limited cardiac damage and rescued cardiac dysfunction caused by I/R in both young and aged mice. Importantly, metformin treatment improves contractile functions of isolated cardiomyocytes and maintains mitochondrial integrity under I/R stress conditions. Thus, acute metformin administration at the onset of reperfusion has potential as a mitochondrial-based therapeutic to mitigate reperfusion injury and reduce infarct size in the elderly heart attack patient who remains at greater mortality risk despite reperfusion alone.

Mitochondrial Dysfunction in Cardiac Diseases and Therapeutic Strategies

Mitochondria are the main site of intracellular synthesis of ATP, which provides energy for various physiological activities of the cell. Cardiomyocytes have a high density of mitochondria and mitochondrial damage is present in a variety of cardiovascular diseases. In this paper, we describe mitochondrial damage in mitochondrial cardiomyopathy, congenital heart disease, coronary heart disease, myocardial ischemia-reperfusion injury, heart failure, and drug-induced cardiotoxicity, in the context of the key roles of mitochondria in cardiac development and homeostasis. Finally, we discuss the main current therapeutic strategies aimed at alleviating mitochondrial impairment-related cardiac dysfunction, including pharmacological strategies, gene therapy, mitochondrial replacement therapy, and mitochondrial transplantation. It is hoped that this will provide new ideas for the treatment of cardiovascular diseases.

Calcium and Reactive Oxygen Species Signaling Interplays in Cardiac Physiology and Pathologies

Mitochondria are key players in energy production, critical activity for the smooth functioning of energy-demanding organs such as the muscles, brain, and heart. Therefore, dysregulation or alterations in mitochondrial bioenergetics primarily perturb these organs. Within the cell, mitochondria are the major site of reactive oxygen species (ROS) production through the activity of different enzymes since it is one of the organelles with the major availability of oxygen. ROS can act as signaling molecules in a number of different pathways by modulating calcium (Ca2+) signaling. Interactions among ROS and calcium signaling can be considered bidirectional, with ROS regulating cellular Ca2+ signaling, whereas Ca2+ signaling is essential for ROS production. In particular, we will discuss how alterations in the crosstalk between ROS and Ca2+ can lead to mitochondrial bioenergetics dysfunctions and the consequent damage to tissues at high energy demand, such as the heart. Changes in Ca2+ can induce mitochondrial alterations associated with reduced ATP production and increased production of ROS. These changes in Ca2+ levels and ROS generation completely paralyze cardiac contractility. Thus, ROS can hinder the excitation-contraction coupling, inducing arrhythmias, hypertrophy, apoptosis, or necrosis of cardiac cells. These interplays in the cardiovascular system are the focus of this review.

Effects of Subnormothermic Regulated Hepatic Reperfusion on Mitochondrial and Transcriptomic Profiles in a Porcine Model

OBJECTIVE

We sought to investigate the biological effects of pre-reperfusion treatments of the liver after warm and cold ischemic injuries in a porcine donation after circulatory death model.

SUMMARY OF BACKGROUND DATA

Donation after circulatory death represents a severe form of liver ischemia and reperfusion injury that has a profound impact on graft function after liver transplantation.

METHODS

Twenty donor pig livers underwent 60 minutes of in situ warm ischemia after circulatory arrest and 120 minutes of cold static preservation prior to simulated transplantation using an ex vivo perfusion machine. Four reperfusion treatments were compared: Control-Normothermic (N), Control- Subnormothermic (S), regulated hepatic reperfusion (RHR)-N, and RHR-S (n = 5 each). The biochemical, metabolic, and transcriptomic profiles, as well as mitochondrial function were analyzed.

RESULTS

Compared to the other groups, RHR-S treated group showed significantly lower post-reperfusion aspartate aminotransferase levels in the reperfusion effluent and histologic findings of hepatocyte viability and lesser degree of congestion and necrosis. RHR-S resulted in a significantly higher mitochondrial respiratory control index and calcium retention capacity. Transcriptomic profile analysis showed that treatment with RHR-S activated cell survival and viability, cellular homeostasis as well as other biological functions involved in tissue repair such as cytoskeleton or cytoplasm organization, cell migration, transcription, and microtubule dynamics. Furthermore, RHR-S inhibited organismal death, morbidity and mortality, necrosis, and apoptosis.

CONCLUSION

Subnormothermic RHR mitigates IRI and preserves hepatic mitochondrial function after warm and cold hepatic ischemia. This organ resuscitative therapy may also trigger the activation of protective genes against IRI. Sub- normothermic RHR has potential applicability to clinical liver transplantation.

Facilitation of Insulin Effects by Ranolazine in Astrocytes in Primary Culture

Ranolazine (Rn) is a drug used to treat persistent chronic coronary ischemia. It has also been shown to have therapeutic benefits on the central nervous system and an anti-diabetic effect by lowering blood glucose levels; however, no effects of Rn on cellular sensitivity to insulin (Ins) have been demonstrated yet. The present study aimed to investigate the permissive effects of Rn on the actions of Ins in astrocytes in primary culture. Ins (10−8 M), Rn (10−6 M), and Ins + Rn (10−8 M and 10−6 M, respectively) were added to astrocytes for 24 h. In comparison to control cells, Rn and/or Ins caused modifications in cell viability and proliferation. Rn increased protein expression of Cu/Zn-SOD and the pro-inflammatory protein COX-2 was upregulated by Ins. On the contrary, no significant changes were found in the protein expression of NF-κB and IκB. The presence of Rn produced an increase in p-ERK protein and a significant decrease in COX-2 protein expression. Furthermore, Rn significantly increased the effects of Ins on the expression of p-AKT, p-eNOS, p-ERK, Mn-SOD, and PPAR-γ. In addition, Rn + Ins produced a significant decrease in COX-2 expression. In conclusion, Rn facilitated the effects of insulin on the p-AKT, p-eNOS, p-ERK, Mn-SOD, and PPAR-γ signaling pathways, as well as on the anti-inflammatory and antioxidant effects of the hormone.

Hypothermia Prevents Cardiac Dysfunction during Acute Ischemia Reperfusion by Maintaining Mitochondrial Bioenergetics and by Promoting Hexokinase II Binding to Mitochondria

Background

Hypothermia (H), cardioplegia (CP), and both combined (HCP) are known to be protective against myocardial ischemia reperfusion (IR) injury. Mitochondria have molecular signaling mechanisms that are associated with both cell survival and cell death. In this study, we investigated the dynamic changes in proapoptotic and prosurvival signaling pathways mediating H, CP, or HCP-induced protection of mitochondrial function after acute myocardial IR injury.

Methods

Rats were divided into five groups. Each group consists of 3 subgroups based on a specific reperfusion time (5, 20, or 60 min) after a 25-min global ischemia. The time control (TC) groups were not subjected to IR but were perfused with 37 °C Krebs-Ringer's (KR) buffer, containing 4.5 mM K⁺, in a specific perfusion protocol that corresponded with the duration of each IR protocol. The IR group (control) was perfused for 20 min with KR, followed by 25-min global ischemia, and then KR reperfusion for 5, 20, or 60 min. The treatment groups were exposed to 17 °C H, 37 °C CP (16 mM K⁺), or HCP (17 °C + CP) for 5 min before ischemia and for 2 min on reperfusion before switching to 37 °C KR perfusion for the remainder of each of the reperfusion times. Cardiac function and mitochondrial redox state (NADH/FAD) were monitored online in the ex vivo hearts before, during, and after ischemia. Mitochondria were isolated at the end of each specified reperfusion time, and changes in O₂ consumption, membrane potential (ΔΨ_m), and Ca²⁺ retention capacity (CRC) were assessed using complex I and complex II substrates. In another set of hearts, mitochondrial and cytosolic fractions were isolated after a specified reperfusion time to conduct western blot assays to determine hexokinase II (HKII) and Bax binding/translocation to mitochondria, cytosolic pAkt levels, and cytochrome c (Cyto-c) release into the cytosol.

Results

H and HCP were more protective of mitochondrial integrity and, concomitantly, cardiac function than CP alone; H and HCP improved post-ischemic cardiac function by (1) maintaining mitochondrial bioenergetics, (2) maintaining HKII binding to mitochondria with an increase in pAkt levels, (3) increasing CRC, and (4) decreasing Cyto-c release during reperfusion. Bax translocation/binding to mitochondria was unaffected by any treatment, regardless of cardiac functional recovery.

Conclusions

Hypothermia preserved mitochondrial function and cardiac function, in part, by maintaining mitochondrial bioenergetics, by retaining HKII binding to mitochondria via upstream pAkt, and by reducing Cyto-c release independently of Bax binding to mitochondria.

Protective mechanisms of 10-gingerol against myocardial ischemia may involve activation of JAK2/STAT3 pathway and regulation of Ca2+ homeostasis

10-Gingerol (10-Gin), an active ingredient extracted from ginger, has been reported to have beneficial effects on the cardiovascular system. However, its protective effects on myocardial ischemia (MI) and the underlying cellular mechanisms are still unclear. To investigate the protection conferred by 10-Gin against MI injury and its potential mechanisms in cardiomyocytes via patch-clamp and molecular biology techniques. A rat MI model was established using the subcutaneous injection of isoproterenol (85 mg/kg) administered on two consecutive days. 10-Gin was pre-administered to rats for seven days to assess its cardio-protection. The patch-clamp and IonOptix Myocam detection techniques were used to investigated 10-Gin's effects on L-type Ca²⁺ channels (LTCCs), Ca²⁺ transients and cell contractility in isolated rat cardiomyocytes. 10-Gin administration alleviated MI injury, improved cardiac function and myocardial histopathology, reduced myocardial infarct area, downregulated oxidative stress and Ca²⁺ levels, and decreased the expression of apoptotic factors. Importantly, 10-Gin led to an increase in phosphorylated Janus kinase 2 and signal transducer and activator of transcription 3 (JAK2 and STAT3, respectively) expressions. Furthermore, 10-Gin inhibited LTCCs in a concentration-dependent manner with a half-maximal inhibitory concentration of 75.96 μM. Moreover, 10-Gin administration inhibited Ca²⁺ transients and cell contractility. Our results suggest that 10-Gin exerts cardioprotective effects on MI in vivo and in vitro in connection with the inhibition of oxidative stress and apoptosis via activation of the JAK2/STAT3 signalling pathway, and regulation of Ca²⁺ homeostasis by LTCCs.

CD137 Signal Mediates Cardiac Ischemia-Reperfusion Injury by Regulating the Necrosis of Cardiomyocytes

The injury of cardiomyocytes after ischemia-reperfusion is the main reason of cardiac dysfunction. Necrosis is one of the methods of programmed cell death and cardiomyocyte necrosis occurs in the process of reperfusion. The activation of CD137 signal is involved in various diseases. In vivo experiments proved that CD137^-/- mice have less heart damage than wild-type mice after ischemia-reperfusion. In vitro experiments, we found that after inhibiting the CD137 signal, the degree of necrosis of HL-1 cells was reduced and it was caused by reducing the Ca2 + overload in the mitochondria, which caused the reduction of mPTP opening. Ca2 + overload in mitochondria induced by activation of CD137 signal was caused by increased Ca2 + released into mitochondria by activation of IP3R and increased MCU level. These results indicate that CD137 signaling aggravates cardiac ischemia-reperfusion injury by inducing myocardial cell necrosis.

Verapamil Alleviates Myocardial Ischemia/Reperfusion Injury by Attenuating Oxidative Stress via Activation of SIRT1

Myocardial ischemia/reperfusion (I/R) injury is a potential complication of ischemic heart disease after recanalization. One of the primary reasons for I/R injury is the excessive accumulation of reactive oxygen species (ROS) in cardiomyocytes. Verapamil, a classic calcium channel blocker, has the potential to mitigate I/R-evoked oxidative stress. However, the underlying mechanisms have not been fully elucidated. SIRT1 is an essential regulator of I/R and offers resistance to oxidative stress arising from I/R. It is still inconclusive if verapamil can reduce myocardial I/R-triggered oxidative damage through modulating SIRT1 antioxidant signaling. To verify our hypothesis, the H9c2 cardiomyocytes and the mice were treated with verapamil and then exposed to hypoxia/reoxygenation (H/R) or I/R in the presence or absence of the SIRT1 inhibitor EX527. As expected, verapamil stimulated SIRT1 antioxidant signaling evidenced by upregulation of SIRT1, FoxO1, SOD2 expressions and downregulation of Ac-FoxO1 expression in vitro and in vivo. In addition, verapamil remarkably suppressed H/R and I/R-induced oxidative stress proven by declined ROS level and MDA content. The cardioprotective actions of verapamil via SIRT1 were further confirmed in the experiments with the presence of the specific SIRT1 inhibitor EX527. We demonstrated that verapamil alleviated myocardial I/R-evoked oxidative stress partially via activation of SIRT1 antioxidant signaling. Subsequently, verapamil protected against cardiac dysfunction and myocardial infarction accompanied by oxidative stress.

Role of ranolazine in heart failure: From cellular to clinic perspective

Ranolazine was approved by the US Food and Drug Administration as an antianginal drug in 2006, and has been used since in certain groups of patients with stable angina. The therapeutic action of ranolazine was initially attributed to inhibitory effects on fatty acids metabolism. As investigations went on, however, it developed that the main beneficial effects of ranolazine arise from its action on the late sodium current in the heart. Since late sodium currents were discovered to be involved in various heart pathologies such as ischemia, arrhythmias, systolic and diastolic dysfunctions, and all these conditions are associated with heart failure, ranolazine has in some way been tested either directly or indirectly on heart failure in numerous experimental and clinical studies. As the heart continuously remodels following any sort of severe injury, the inhibition by ranolazine of the underlying mechanisms of cardiac remodeling including ion disturbances, oxidative stress, inflammation, apoptosis, fibrosis, metabolic dysregulation, and neurohormonal impairment are discussed, along with unresolved issues. A projection of pathologies targeted by ranolazine from cellular level to clinical is provided in this review.

Ranolazine: An Old Drug with Emerging Potential; Lessons from Pre-Clinical and Clinical Investigations for Possible Repositioning

Ischemic heart disease is a significant public health problem with high mortality and morbidity. Extensive scientific investigations from basic sciences to clinics revealed multilevel alterations from metabolic imbalance, altered electrophysiology, and defective Ca²⁺/Na⁺ homeostasis leading to lethal arrhythmias. Despite the recent identification of numerous molecular targets with potential therapeutic interest, a pragmatic observation on the current pharmacological R&D output confirms the lack of new therapeutic offers to patients. By contrast, from recent trials, molecules initially developed for other fields of application have shown cardiovascular benefits, as illustrated with some anti-diabetic agents, regardless of the presence or absence of diabetes, emphasizing the clear advantage of “old” drug repositioning. Ranolazine is approved as an antianginal agent and has a favorable overall safety profile. This drug, developed initially as a metabolic modulator, was also identified as an inhibitor of the cardiac late Na⁺ current, although it also blocks other ionic currents, including the hERG/Ikr K⁺ current. The latter actions have been involved in this drug’s antiarrhythmic effects, both on supraventricular and ventricular arrhythmias (VA). However, despite initial enthusiasm and promising development in the cardiovascular field, ranolazine is only authorized as a second-line treatment in patients with chronic angina pectoris, notwithstanding its antiarrhythmic properties. A plausible reason for this is the apparent difficulty in linking the clinical benefits to the multiple molecular actions of this drug. Here, we review ranolazine’s experimental and clinical knowledge on cardiac metabolism and arrhythmias. We also highlight advances in understanding novel effects on neurons, the vascular system, skeletal muscles, blood sugar control, and cancer, which may open the way to reposition this “old” drug alone or in combination with other medications.

Late sodium current and calcium homeostasis in arrhythmogenesis

The cardiac late sodium current (INa,late) is the small sustained component of the sodium current active during the plateau phase of the action potential. Several studies demonstrated that augmentation of the current can lead to cardiac arrhythmias; therefore, INa,late is considered as a promising antiarrhythmic target. Fundamentally, enlarged INa,late increases Na+ influx into the cell, which, in turn, is converted to elevated intracellular Ca2+ concentration through the Na+/Ca2+ exchanger. The excessive Ca2+ load is known to be proarrhythmic. This review describes the behavior of the voltage-gated Na+ channels generating INa,late in health and disease and aims to discuss the physiology and pathophysiology of Na+ and Ca2+ homeostasis in context with the enhanced INa,late demonstrating also the currently accessible antiarrhythmic choices.

Influence of Ca2+ on mitochondrial apoptosis activation and yak meat tenderization during postmortem aging

The objective of this study was to investigate the underlying molecular mechanisms of mitochondrial Ca2+ homeostasis disequilibrium in mitochondrial apoptosis and its impact on yak meat tenderness. Results indicated that CaCl2 treatment significantly promoted glycolysis by increasing lactic acid level and decreasing glycogen content, pH, and ATP production (P < 0.01 and P < 0.05). The activities of Na+-K+-ATPase pump and Ca2+-ATPase pump in the early aging stage were significantly influenced by CaCl2 treatment. The activities of synchronous digital hierarchy and citrate synthase were also significantly improved by CaCl2 treatment (P < 0.01 and P < 0.05). Mitochondrial reactive oxygen species (ROS) levels were significantly higher in the CaCl2 group than in the control group (P < 0.01); at 24 h, the value in the Ca2+ group was 64.27% higher than that in the control group. Furthermore, CaCl2 treatment significantly enhanced the mitochondrial apoptosis cascade reaction and meat tenderization by improving the myofibril fragmentation index and shear force (P < 0.01). These results demonstrated that the imbalance of mitochondrial Ca2+ homeostasis played a significant role in the mitochondrial apoptosis pathway by regulating energy metabolism factors, meat intracellular environment, mitochondrial functions, and ROS-mediated oxidative stress. These conditions further improved meat tenderization during postmortem aging.

Vasomotor Dysfunction in Patients with Ischemia and Non-Obstructive Coronary Artery Disease: Current Diagnostic and Therapeutic Strategies

Many patients who present with symptoms or objective evidence of ischemia have no or non-physiologically-significant disease on invasive coronary angiography. The diagnosis of ischemic heart disease is thus often dismissed, and patients receive false reassurance or other diagnoses are pursued. We now know that a significant proportion of these patients have coronary microvascular dysfunction and/or vasospastic disease as the underlying pathophysiology of their clinical presentation. Making the correct diagnosis of such abnormalities is important not only because they impact the quality of life, with recurring symptoms and unnecessary repeated testing, but also because they increase the risk for adverse cardiovascular events. The mainstay of diagnosis remains an invasive comprehensive physiologic assessment, which further allows stratifying these patients into appropriate “endotypes”. It has been shown that tailoring treatment to the patient’s assigned endotype improves symptoms and quality of life. In addition to the conventional drugs used in chronic stable angina, multiple newer agents are being investigated. Moreover, innovative non-pharmacologic and interventional therapies are emerging to provide a bail-out in refractory cases. Many of these novel therapies fail to show consistent benefits, but others show quite promising results.

10-Gingerol alleviates hypoxia/reoxygenation-induced cardiomyocyte injury through inhibition of the Wnt5a/Frizzled-2 pathway

10-Gingerol (10-Gin), an active ingredient extracted from ginger, has been reported to have beneficial effects on the cardiovascular system. However, 10-Gin has not been proved to offer protection against cardiomyocyte injury induced by hypoxia/reoxygenation (H/R). This study aimed to investigate the protective effects of 10-Gin against H/R-induced injury and its potential mechanisms in cardiomyocytes. A H/R injury model of H9c2 cardiomyocytes was established using 600 μmol/L CoCl2 to induce hypoxia in the cells for 24 hr and then reoxygenated for 3 hr. 10-Gin was pretreated with H9c2 cardiomyocytes for 24 hr to assess its cardiomyocyte protection. Our results showed that 10-Gin improved the viability of H9c2 cardiomyocytes in the H/R model and decreased the activities of creatine kinase, lactate dehydrogenase, and the generation of reactive oxygen species. By intracellular Ca2+ ([Ca2+]i) fluorescence, we found that 10-Gin could significantly reduce the [Ca2+]i concentration. 10-Gin administration increased the activities of antioxidase and reduced malondialdehyde content and inflammatory cytokine levels. 10-Gin also reduced the apoptosis levels. Importantly, 10-Gin administration decreased the gene and protein expressions of Wnt5a and Frizzled-2. In conclusion, 10-Gin alleviates H/R-induced cardiomyocyte injury, which is associated with the antioxidation, anti-inflammation, antiapoptosis action, and reduction of [Ca2+]i overload by suppressing the Wnt5a/Frizzled-2 pathway.

Ranolazine Improves Glycemic Variability and Endothelial Function in Patients with Diabetes and Chronic Coronary Syndromes: Results from an Experimental Study

BACKGROUND

Ranolazine is a second-line drug for the management of chronic coronary syndromes (CCS). Glucose-lowering and endothelial effects have also been reported with this agent. However, whether ranolazine may improve short-term glycemic variability (GV), strictly related to the prognosis of patients with type 2 diabetes (T2D), is unknown. Thus, we aimed to explore the effects of adding ranolazine to standard anti-ischemic and glucose-lowering therapy on long- and short-term GV as well as on endothelial function and oxidative stress in patients with T2D and CCS.

METHODS

Patients starting ranolazine (n = 16) were evaluated for short-term GV, haemoglobin 1Ac (Hb1Ac) levels, endothelial-dependent flow-mediated vasodilation (FMD), and oxidative stress levels at enrolment and after 3-month follow-up. The same measurements were collected from 16 patients with CCS and T2D that did not receive ranolazine, matched for age, gender, and body mass index.

RESULTS

A significant decline in Hb1Ac levels was reported after 3-month ranolazine treatment (mean change -0.60%; 2-way ANOVA p = 0.025). Moreover, among patients receiving ranolazine, short-term GV indexes were significantly improved over time compared with baseline (p = 0.001 for time in range; 2-way ANOVA p = 0.010). Conversely, no significant changes were reported in patients without ranolazine. Finally, greater FMD and lower oxidative stress levels were observed in patients on ranolazine at 3 months.

CONCLUSIONS

Ranolazine added to standard anti-ischemic and glucose-lowering therapy demonstrated benefit in improving the glycemic status of patients with T2D and CCS. How this improvement contributes to the overall myocardial benefit of ranolazine requires further studies.

Mechanisms of ranolazine pretreatment in preventing ventricular tachyarrhythmias in diabetic db/db mice with acute regional ischemia-reperfusion injury

Studies have demonstrated that diabetic (db/db) mice have increased susceptibility to myocardial ischemia-reperfusion (IR) injury and ventricular tachyarrhythmias (VA). We aimed to investigate the antiarrhythmic and molecular mechanisms of ranolazine in db/db mouse hearts with acute IR injury. Ranolazine was administered for 1 week before coronary artery ligation. Diabetic db/db and control db/+ mice were divided into ranolazine-given and -nongiven groups. IR model was created by 15-min left coronary artery ligation and 10-min reperfusion. In vivo electrophysiological studies showed that the severity of VA inducibility was higher in db/db mice than control (db/ +) mice. Ranolazine suppressed the VA inducibility and severity. Optical mapping studies in Langendorff-perfused hearts showed that ranolazine significantly shortened action potential duration, Cai transient duration, Cai decay time, ameliorated conduction inhomogeneity, and suppressed arrhythmogenic alternans induction. Western blotting studies showed that the expression of pThr17-phospholamban, calsequestrin 2 and voltage-gated sodium channel in the IR zone was significantly downregulated in db/db mice, which was ameliorated with ranolazine pretreatment and might play a role in the anti-arrhythmic actions of ranolazine in db/db mouse hearts with IR injury.

Modulation of peroxynitrite produced via mitochondrial nitric oxide synthesis during Ca2+ and succinate-induced oxidative stress in cardiac isolated mitochondria

We hypothesized that NO^• is generated in isolated cardiac mitochondria as the source for ONOO^- production during oxidative stress. We monitored generation of ONOO^- from guinea pig isolated cardiac mitochondria subjected to excess Ca²⁺ uptake before adding succinate and determined if ONOO^- production was dependent on a nitric oxide synthase (NOS) located in cardiac mitochondria (mtNOS). Mitochondria were suspended in experimental buffer at pH 7.15, and treated with CaCl₂ and then the complex II substrate Na-succinate, followed by menadione, a quinone redox cycler, to generate O₂^•-. L-tyrosine was added to the mitochondrial suspension where it is oxidized by ONOO^- to form dityrosine (diTyr) in proportion to the ONOO^- present. We found that exposing mitochondria to excess CaCl₂ before succinate resulted in an increase in diTyr and amplex red fluorescence (H₂O₂) signals, indicating that mitochondrial oxidant stress, induced by elevated mtCa²⁺ and succinate, increased mitochondrial ONOO^- production via NO^• and O₂^•-. Changes in mitochondrial ONOO^- production dependent on NOS were evidenced by using NOS inhibitors L-NAME/L-NNA, TEMPOL, a superoxide dismutase (SOD) mimetic, and PTIO, a potent global NO^• scavenger. L-NAME and L-NNA decreased succinate and menadione-mediated ONOO^- production, PTIO decreased production of ONOO^-, and TEMPOL decreased ONOO^- levels by converting more O₂^•- to H₂O₂. Electron microscopy showed immuno-gold labeled iNOS and nNOS in mitochondria isolated from cardiomyocytes and heart tissue. Western blots demonstrated iNOS and nNOS bands in total heart tissue, bands for both iNOS and nNOS in β-tubulin-free non-purified (crude) mitochondrial preparations, and a prominent iNOS band, but no nNOS band, in purified (Golgi and ER-free) mitochondria. Prior treatment of guinea pigs with lipopolysacharride (LPS) enhanced expression of iNOS in liver mitochondria but not in heart mitochondria. Our results indicate that release of ONOO^- into the buffer is dependent both on O₂^•- released from mitochondria and NO^• derived from a mtCa²⁺-inducible nNOS isoform, possibly attached to mitochondria, and a mtNOS isoform like iNOS that is non-inducible.

Mechanisms and potential interventions associated with the cardiotoxicity of ErbB2-targeted drugs: Insights from in vitro, in vivo, and clinical studies in breast cancer patients

Breast cancer is the most frequently occurring cancer among women worldwide. Human epidermal growth factor receptor 2 (HER2 or ErbB2) is overexpressed in between 20 and 25% of invasive breast cancers and is associated with poor prognosis. Trastuzumab, an anti-ErbB2 monoclonal antibody, reduces cancer recurrence and mortality in HER2-positive breast cancer patients, but unexpectedly induces cardiac dysfunction, especially when used in combination with anthracycline-based chemotherapy. Novel approved ErbB2-targeting drugs, including lapatinib, pertuzumab, and trastuzumab-emtansine, also potentially cause cardiotoxicity, although early clinical studies demonstrate their cardiac safety profile. Unfortunately, the mechanism involved in causing the cardiotoxicity is still not completely understood. In addition, the use of preventive interventions against trastuzumab-induced cardiac dysfunction, including angiotensin-converting enzyme inhibitors and beta-blockers, remain controversial. Thus, this review aims to summarize and discuss the evidence currently available from in vitro, in vivo, and clinical studies regarding the mechanism and potential interventions associated with the cardiotoxicity of ErbB2-targeted drugs.

Wenxin Keli Regulates Mitochondrial Oxidative Stress and Homeostasis and Improves Atrial Remodeling in Diabetic Rats

Mitochondrial dysfunction and oxidative stress play an important role in the pathogenesis of both atrial fibrillation (AF) and diabetes mellitus (DM). Wenxin Keli (WXKL), an antiarrhythmic traditional Chinese medicine, has been shown to prevent cardiac arrhythmias through modulation of cardiac ion channels. This study tested the hypothesis that WXKL can improve atrial remodeling in diabetic rats by restoring mitochondrial function. Primary atrial fibroblasts of neonatal SD rats were divided into four groups: control, hydrogen peroxide (H2O2), H2O2+WXKL 1 g/L, and H2O2+WXKL 3 g/L groups. Intracellular mitochondrial membrane potential (MMP), reactive oxygen species (ROS), and mitochondrial oxygen consumption were measured. SD male rats were randomly divided into three groups: control, DM, and DM+WXKL groups. Rats in the DM+WXKL group were treated with daily gavage of WXKL at 3 g/kg. After eight weeks, echocardiography, hemodynamic examination, histology, electrophysiology study, mitochondrial respiratory function, and western blots were assessed. H2O2 treatment led to increased ROS and decreased intracellular MMP and mitochondrial oxygen consumption in primary atrial fibroblasts. WXKL improved the above changes. DM rats showed increased atrial fibrosis, greater left atrial diameter, lower atrial conduction velocity, higher conduction heterogeneity, higher AF inducibility, and lower mitochondrial protein expression, and all these abnormal changes except for left atrial diameter were improved in the DM+WXKL group. WXKL improves atrial remodeling by regulating mitochondrial function and homeostasis and reducing mitochondrial ROS in diabetic rats.

Fluorescence Imaging of Mitochondrial Redox State to Assess Diabetic Wounds

Background: Diabetes is known to cause delayed wound healing, and chronic non-healing lower extremity ulcers may end with lower limb amputations and mortalities. Given the increasing prevalence of diabetes mellitus worldwide, it is critical to focus on underlying mechanisms of these debilitating wounds to find novel therapeutic strategies and thereby improve patient outcome. Methods: This study aims to design a label-free optical fluorescence imager that captures metabolic indices (NADH and FAD autofluorescence) and monitors the in vivo wound healing progress noninvasively. Furthermore, 3D optical cryo-imaging of the mitochondrial redox state was utilized to assess the volumetric redox state of the wound tissue. Results: The results from our in vivo fluorescence imager and the 3D cryo-imager quantify the differences between the redox state of wounds on diabetic mice in comparison with the control mice. These metabolic changes are associated with mitochondrial dysfunction and higher oxidative stress in diabetic wounds. A significant correlation was observed between the redox state and the area of the wounds. Conclusion: The results suggest that our developed novel optical imaging system can successfully be used as an optical indicator of the complex wound healing process noninvasively.

Optical Metabolic Imaging for Assessment of Radiation-Induced Injury to Rat Kidney and Mitigation by Lisinopril

The kidney is one of the most radiosensitive organs; it is the primary dose-limiting organ in radiotherapies for upper abdominal cancers. The role of mitochondrial redox state in the development and treatment of renal radiation injury, however, remains ill-defined. This study utilizes 3D optical cryo-imaging to quantify renal mitochondrial bioenergetics dysfunction after 13 Gy leg-out partial body irradiation (PBI). Furthermore, the mitigating effects of lisinopril (lisino), an anti-hypertensive angiotensin converting enzyme inhibitor, is assessed in renal radiation-induced injuries. Around day 150 post-irradiation, kidneys are harvested for cryo-imaging. The 3D images of the metabolic indices (NADH, nicotinamide adenine dinucleotide, and FAD, flavin adenine dinucleotide) are acquired, and the mitochondrial redox states of the irradiated and irradiated + lisino kidneys are quantified by calculating the volumetric mean redox ratio (NADH/FAD). PBI oxidized renal mitochondrial redox state by 78%. The kidneys from the irradiated + lisino rats showed mitigation of mitochondrial redox state by 93% compared to the PBI group. The study provides evidence for an altered bioenergetics and energy metabolism in the rat model of irradiation-induced kidney damage. In addition, the results suggest that lisinopril mitigates irradiation damage by attenuating the oxidation of mitochondria leading to increase redox ratio.

Telomerase Deficiency Predisposes to Heart Failure and Ischemia-Reperfusion Injury

Introduction: Elevated levels of mitochondrial reactive oxygen species (ROS) contribute to the development of numerous cardiovascular diseases. TERT, the catalytic subunit of telomerase, has been shown to translocate to mitochondria to suppress ROS while promoting ATP production. Acute overexpression of TERT increases survival and decreases infarct size in a mouse model of myocardial infarct, while decreased telomerase activity predisposes to mitochondrial defects and heart failure. In the present study, we examined the role of TERT on cardiac structure and function under basal conditions and conditions of acute or prolonged stress in a novel rat model of TERT deficiency. Methods: Cardiac structure and function were evaluated via transthoracic echocardiogram. Langendorff preparations were used to test the effects of acute global ischemia reperfusion injury on cardiac function and infarction. Coronary flow and left ventricular pressure were measured during and after ischemia/reperfusion (I/R). Mitochondrial DNA integrity was measured by PCR and mitochondrial respiration was assessed in isolated mitochondria using an Oxygraph. Angiotensin II infusion was used as an established model of systemic stress. Results: No structural changes (echocardiogram) or coronary flow/left ventricle pressure (isolated hearts) were observed in TERT-/- rats at baseline; however, after I/R, coronary flow was significantly reduced in TERT-/- compared to wild type (WT) rats, while diastolic Left Ventricle Pressure was significantly elevated (n = 6 in each group; p < 0.05) in the TERT-/-. Interestingly, infarct size was less in TERT-/- rats compared to WT rats, while mitochondrial respiratory control index decreased and mitochondrial DNA lesions increased in TERT-/- compared to WT. Angiotensin II treatment did not alter cardiac structure or function; however, it augmented the infarct size significantly more in TERT-/- compared to the WT. Conclusion: Absence of TERT activity increases susceptibility to stress like cardiac injury. These results suggest a critical role of telomerase in chronic heart disease.

Late sodium channel blockade improves angina and myocardial perfusion in patients with severe coronary microvascular dysfunction: Women's Ischemia Syndrome Evaluation-Coronary Vascular Dysfunction ancillary study

BACKGROUND

In a prior trial of late sodium channel inhibition (ranolazine) among symptomatic subjects without obstructive coronary artery disease (CAD) and limited myocardial perfusion reserve index (MPRI), we observed no improvement in angina or MPRI, overall. Here we describe the clinical characteristics and myocardial perfusion responses of a pre-defined subgroup who had coronary flow reserve (CFR) assessed invasively.

METHODS

Symptomatic patients without obstructive CAD and limited MPRI in a randomized, double-blind, crossover trial of ranolazine vs. placebo were subjects of this prespecified substudy. Because we had previously observed that adverse outcomes and beneficial treatment responses occurred in those with lower CFR, patients were subgrouped by CFR <2.5 vs ≥2.5. Symptoms were assessed using the Seattle Angina Questionnaire and the SAQ-7, and left-ventricular volume and MPRI were assessed by magnetic resonance imaging (MRI). Coronary angiograms, CFR, and MRI data were analyzed by core labs masked to treatment and patient characteristics.

RESULTS

During qualifying coronary angiography, 81 patients (mean age 55 years, 98% women) had invasively determined CFR 2.69 ± 0.65 (mean ± SD; range 1.4-5.5); 43% (n = 35) had CFR <2.5. Demographic and symptomatic findings did not differ comparing CFR subgroups. Those with low CFR had improved angina (p = 0.04) and midventricular MPRI (p = 0.03) with ranolazine vs placebo. Among patients with low CFR, reduced left-ventricular end-diastolic volume predicted a beneficial angina response.

CONCLUSIONS

Symptomatic patients with CFR <2.5 and no obstructive CAD had improved angina and myocardial perfusion with ranolazine, supporting the hypothesis that the late sodium channel is important in management of coronary microvascular dysfunction.

TRIAL REGISTRATION

clinicaltrials.gov Identifier NCT01342029.

Expression and Activation of BKCa Channels in Mice Protects Against Ischemia-Reperfusion Injury of Isolated Hearts by Modulating Mitochondrial Function

Aims: Activation and expression of large conductance calcium and voltage-activated potassium channel (BK_Ca) by pharmacological agents have been implicated in cardioprotection from ischemia-reperfusion (IR) injury possibly by regulating mitochondrial function. Given the non-specific effects of pharmacological agents, it is not clear whether activation of BK_Ca is critical to cardioprotection. In this study, we aimed to decipher the mechanistic role of BK_Ca in cardioprotection from IR injury by genetically activating BK_Ca channels. Methods and Results: Hearts from adult (3 months old) wild-type mice (C57/BL6) and mice expressing genetically activated BK_Ca (Tg-BK_Ca ^R207Q, referred as Tg-BK_Ca) along with wild-type BK_Ca were subjected to 20 min of ischemia and 30 min of reperfusion with or without ischemic preconditioning (IPC, 2 times for 2.5 min interval each). Left ventricular developed pressure (LVDP) was recorded using Millar's Mikrotip® catheter connected to ADInstrument data acquisition system. Myocardial infarction was quantified by 2,3,5-triphenyl tetrazolium chloride (TTC) staining. Our results demonstrated that Tg-BK_Ca mice are protected from IR injury, and BK_Ca also contributes to IPC-mediated cardioprotection. Cardiac function parameters were also measured by echocardiography and no differences were observed in left ventricular ejection fraction, fractional shortening and aortic velocities. Amplex Red® was used to assess reactive oxygen species (ROS) production in isolated mitochondria by spectrofluorometry. We found that genetic activation of BK_Ca reduces ROS after IR stress. Adult cardiomyocytes and mitochondria from Tg-BK_Ca mice were isolated and labeled with Anti-BK_Ca antibodies. Images acquired via confocal microscopy revealed localization of cardiac BK_Ca in the mitochondria. Conclusions: Activation of BK_Ca is essential for recovery of cardiac function after IR injury and is likely a factor in IPC mediated cardioprotection. Genetic activation of BK_Ca reduces ROS produced by complex I and complex II/III in Tg-BK_Ca mice after IR, and IPC further decreases it. These results implicate BK_Ca-mediated cardioprotection, in part, by reducing mitochondrial ROS production. Localization of Tg-BK_Ca in adult cardiomyocytes of transgenic mice was similar to BK_Ca in wild-type mice.

Mitochondrial bioenergetics and cardiolipin alterations in myocardial ischemia-reperfusion injury: implications for pharmacological cardioprotection

Mitochondrial dysfunction plays a central role in myocardial ischemia-reperfusion (I/R) injury. Increased reactive oxygen species production, impaired electron transport chain activity, aberrant mitochondrial dynamics, Ca²⁺ overload, and opening of the mitochondrial permeability transition pore have been proposed as major contributory factors to mitochondrial dysfunction during myocardial I/R injury. Cardiolipin (CL), a mitochondria-specific phospholipid, plays a pivotal role in multiple mitochondrial bioenergetic processes, including respiration and energy conversion, in mitochondrial morphology and dynamics as well as in several steps of the apoptotic process. Changes in CL levels, species composition, and degree of oxidation may have deleterious consequences for mitochondrial function with important implications in a variety of pathophysiological conditions, including myocardial I/R injury. In this review, we focus on the role played by CL alterations in mitochondrial dysfunction in myocardial I/R injury. Pharmacological strategies to prevent myocardial injury during I/R targeting mitochondrial CL are also examined.

CaMKII-dependent late Na+ current increases electrical dispersion and arrhythmia in ischemia-reperfusion

The mechanisms underlying Ca²⁺/calmodulin-dependent protein kinase II (CaMKII)-induced arrhythmias in ischemia-reperfusion (I/R) are not fully understood. We tested the hypothesis that CaMKII increases late Na⁺ current ( I_Na,L) via phosphorylation of Na_v1.5 at Ser⁵⁷¹ during I/R, thereby increasing arrhythmia susceptibility. To test our hypothesis, we studied isolated, Langendorff-perfused hearts from wild-type (WT) mice and mice expressing Na_v channel variants Na_v1.5-Ser571E (S571E) and Na_v1.5-Ser571A (S571A). WT hearts showed a significant increase in the levels of phosphorylated CaMKII and Na_v1.5 at Ser⁵⁷¹ [p-Na_v1.5(S571)] after 15 min of global ischemia (just before the onset of reperfusion). Optical mapping experiments revealed an increase in action potential duration (APD) and APD dispersion without changes in conduction velocity during I/R in WT and S571E compared with S571A hearts. At the same time, WT and S571E hearts showed an increase in spontaneous arrhythmia events (e.g., premature ventricular contractions) and an increase in the inducibility of reentrant arrhythmias during reperfusion. Pretreatment of WT hearts with the Na⁺ channel blocker mexiletine (10 μM) normalized APD dispersion and reduced arrhythmia susceptibility during I/R. We conclude that CaMKII-dependent phosphorylation of Na_v1.5 is a crucial driver for increased I_Na,L, arrhythmia triggers, and substrate during I/R. Selective targeting of this CaMKII-dependent pathway may have therapeutic potential for reducing arrhythmias in the setting of I/R. NEW & NOTEWORTHY Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) phosphorylation of Na_v1.5 at Ser⁵⁷¹ leads to a prolongation of action potential duration (APD), increased APD dispersion, and increased arrhythmia susceptibility after ischemia-reperfusion in isolated mouse hearts. Genetic ablation of the CaMKII-dependent phosphorylation site Ser⁵⁷¹ on Na_v1.5 or low-dose mexiletine (to inhibit late Na⁺ current) reduced APD dispersion, arrhythmia triggers, and ventricular tachycardia inducibility.

Antihyperglycemic and Metabolic Effects of Ranolazine in Patients With Diabetes Mellitus

The antianginal drug ranolazine, because of its unique mechanism of action, has been shown to have antihyperglycemic effects. Here, we review the reports on the antihyperglycemic and metabolic effects of ranolazine. MEDLINE was searched from 2000 to October 1, 2016 using the terms ranolazine, antihyperglycemic, diabetes, cardiology, and antianginal. Studies and reviews were included if they were in English and provided relevant data to inform practicing clinicians. Ranolazine has been shown to be effective as an antihyperglycemic while utilized as monotherapy or in combination with traditional diabetic regimens. A total of 6 studies were included in this review, with 5 being randomized controlled trials and 1 being a retrospective study. Of the 6 studies, 4 directly measured differences between baseline hemoglobin A1c (HbA1c), another measured endothelium function, and lastly the retrospective study evaluated outpatient clinic visit utilization, all-cause emergency department visits, inpatient admissions, and length of stay in a cohort of patients with angina and diabetes. In conclusion, ranolazine, because of its unique mechanism of action, may have a niche in therapy for patients with chronic stable angina pectoris and diabetes mellitus. Ranolazine has been shown to have positive antihyperglycemic and metabolic effects in patients with uncontrolled HbA1c.

Optical metabolic imaging of irradiated rat heart exposed to ischemia-reperfusion injury

Whole thoracic irradiation (WTI) is known to cause deterioration in cardiac function. Whether irradiation predisposes the heart to further ischemia and reperfusion (IR) injury is not well known. The aim of this study is to examine the susceptibility of rat hearts to IR injury following a single fraction of 15 Gy WTI and to investigate the role of mitochondrial metabolism in the differential susceptibility to IR injury. After day 35 of irradiation, ex vivo hearts from irradiated and nonirradiated rats (controls) were exposed to 25-min global ischemia followed by 60-min IR, or hearts were perfused without IR for the same protocol duration [time controls (TC)]. Online fluorometry of metabolic indices [redox state: reduced nicotinamide adenine dinucleotide (NADH), oxidized flavin adenine dinucleotide (FAD), and NADH/FAD redox ratio] and functional variables [systolic left ventricular pressure (LVP), diastolic LVP (diaLVP), coronary flow (CF), and heart rate were recorded in the beating heart; developed LVP (dLVP) and rate pressure product (RPP)] were derived. At the end of each experimental protocol, hearts were immediately snap frozen in liquid N2 for later three-dimensional imaging of the mitochondrial redox state using optical cryoimaging. Irradiation caused a delay in recovery of dLVP and RPP after IR when compared to nonirradiated hearts but recovered to the same level at the end of reperfusion. CF in the irradiated hearts recovered better than the control hearts after IR injury. Both fluorometry and 3-D cryoimaging showed that in WTI and control hearts, the redox ratio increased during ischemia (reduced) and decreased on reperfusion (oxidized) when compared to their respective TCs; however, there was no significant difference in the redox state between WTI and controls. In conclusion, our results show that although irradiation of rat hearts compromised baseline cardiovascular function, it did not alter cardiac mitochondrial redox state and induce greater susceptibility of these hearts to IR injury.

Endogenous and Agonist-induced Opening of Mitochondrial Big Versus Small Ca2+-sensitive K+ Channels on Cardiac Cell and Mitochondrial Protection

Both big (BKCa) and small (SKCa) conductance Ca-sensitive K channels are present in mammalian cardiac cell mitochondria (m). We used pharmacological agonists and antagonists of BKCa and SKCa channels to examine the importance of endogenous opening of these channels and the relative contribution of either or both of these channels to protect against contractile dysfunction and reduce infarct size after ischemia reperfusion (IR) injury through a mitochondrial protective mechanism. After global cardiac IR injury of ex vivo perfused Guinea pig hearts, we found the following: both agonists NS1619 (for BKCa) and DCEB (for SKCa) improved contractility; BKCa antagonist paxilline (PAX) alone or with SKCa antagonist NS8593 worsened contractility and enhanced infarct size; both antagonists PAX and NS8593 obliterated protection by their respective agonists; BKCa and SKCa antagonists did not block protection afforded by SKCa and BKCa agonists, respectively; and all protective effects by the agonists were blocked by scavenging superoxide anions (O2) with Mn(III) tetrakis (4-benzoic acid) porphyrin (TBAP). Contractile function was inversely associated with global infarct size. In in vivo rats, infusion of NS8593, PAX, or both antagonists enhanced regional infarct size while infusion of either NS1619 or DCEB reduced infarct size. In cardiac mitochondria isolated from ex vivo hearts after IR, combined SKCa and BKCa agonists improved respiratory control index and Ca retention capacity compared with IR alone, whereas the combined antagonists did not alter respiratory control index but worsened Ca retention capacity. Although the differential protective bioenergetics effects of endogenous or exogenous BKCa and SKCa channel opening remain unclear, each channel likely responds to different sensing Ca concentrations and voltage gradients over time during oxidative stress-induced injury to individually or together protect cardiac mitochondria and myocytes.

Metabolic Recovery of the Failing Heart: Emerging Therapeutic Options

Heart failure has mortality rates that parallel those of breast cancer. Current management strategies include neurohormonal blockade, rate control measures, natriuretic peptide preservation, implantation of mechanical assist devices, and heart transplantation. Despite these strategies, however, the failing myocardium remains energy depleted. New strategies to promote metabolic recovery are being developed to potentially augment current treatment guidelines. For example, an unexpected finding of our own studies showed that mechanical unloading with assist devices in advanced-stage heart failure restored metabolic flux. Unfortunately, at that point it is too late for myocardial recovery. Traditional metabolic therapies addressing hyperglycemia have had limited long-term outcome benefit. Now, new therapeutic options are emerging based on increased understanding of the molecular mechanisms underlying energy depletion. Metabolic cardiac imaging combined with laboratory diagnostics could guide the design of individual therapeutic strategies. To date, agents that show benefit in select individuals include mimetics that stimulate glucagon-like peptide-1, inhibitors of sodium-glucose cotransporter receptors, drugs that limit fatty acid oxidation, and hormonal therapy in select individuals. This review will summarize mechanisms and investigations related to these metabolic approaches to heart failure.

Mitochondrial VDAC1: A Key Gatekeeper as Potential Therapeutic Target

Mitochondria are the key source of ATP that fuels cellular functions, and they are also central in cellular signaling, cell division and apoptosis. Dysfunction of mitochondria has been implicated in a wide range of diseases, including neurodegenerative and cardiac diseases, and various types of cancer. One of the key proteins that regulate mitochondrial function is the voltage-dependent anion channel 1 (VDAC1), the most abundant protein on the outer membrane of mitochondria. VDAC1 is the gatekeeper for the passages of metabolites, nucleotides, and ions; it plays a crucial role in regulating apoptosis due to its interaction with apoptotic and anti-apoptotic proteins, namely members of the Bcl-2 family of proteins and hexokinase. Therefore, regulation of VDAC1 is crucial not only for metabolic functions of mitochondria, but also for cell survival. In fact, multiple lines of evidence have confirmed the involvement of VDAC1 in several diseases. Consequently, modulation or dysregulation of VDAC1 function can potentially attenuate or exacerbate pathophysiological conditions. Understanding the role of VDAC1 in health and disease could lead to selective protection of cells in different tissues and diverse diseases. The purpose of this review is to discuss the role of VDAC1 in the pathogenesis of diseases and as a potentially effective target for therapeutic management of various pathologies.

Dl-3-n-butylphthalide protects the heart against ischemic injury and H9c2 cardiomyoblasts against oxidative stress: involvement of mitochondrial function and biogenesis

Background

Myocardial infarction (MI) is an acute and fatal condition that threatens human health. Dl-3-n-butylphthalide (NBP) has been used for the treatment of acute ischemic stroke. Mitochondria may play a protective role in MI injury. However, there are few reports on the cardioprotective effect of NBP or the potential mitochondrial mechanism for the NBP-induced protection against cardiac ischemia injury. We investigated the therapeutic effects of NBP in an in vivo MI model and an in vitro oxidative stress model, as well as the potential mitochondrial mechanism.

Methods

This study comprised two different experiments. The aim of experiment 1 was to determine the protective effects of NBP on MI and the underlying mechanisms in vivo. In part 1, myocardial infarct size was measured by staining with 2,3,5-triphenyltetrazoliumchloride (TTC). Myocardial enzymes and mitochondrial enzymes were assayed. The aim of experiment 2 was to investigate the role of NBP in H₂O₂-induced myocardial ischemic injury in H9c2 cells and to determine the potential mechanism. In part 2, H9c2 cell viability was evaluated. ROS levels, mitochondrial morphology, and mitochondrial membrane potential of H9c2 cells were measured. ATP levels were evaluated using an assay kit; mitochondrial DNA (mtDNA), the expressions of NRF-1 and TFAM, and mitochondrial biogenesis factors were determined.

Results

NBP treatment significantly reduced the infarct ratio, as observed by TTC staining, decreased serum myocardial enzymes in MI, and restored heart mitochondrial enzymes (isocitrate dehydrogenase (ICDH), succinate dehydrogenase (SDH), malate dehydrogenase (MDH), and a-ketoglutarate dehydrogenase (a-KGDH) activities after MI. Moreover, in in vitro studies, NBP significantly increased the viability of H9c2 cells in a dose-dependent manner, reduced cell apoptosis, protected mitochondrial functions, elevated the cellular ATP levels, and promoted H₂O₂-induced mitochondrial biogenesis in H9c2 cardiomyoblasts.

Conclusion

Collectively, the results from both the in vivo and in vitro experiments suggested that NBP exerted a cardioprotective effect on cardiac ischemic injury via the regulation of mitochondrial function and biogenesis.

Mitochondrial Cx43 hemichannels contribute to mitochondrial calcium entry and cell death in the heart

Mitochondrial connexin 43 (Cx43) plays a key role in cardiac cytoprotection caused by repeated exposure to short periods of non-lethal ischemia/reperfusion, a condition known as ischemic preconditioning. Cx43 also forms calcium (Ca²⁺)-permeable hemichannels that may potentially lead to mitochondrial Ca²⁺ overload and cell death. Here, we studied the role of Cx43 in facilitating mitochondrial Ca²⁺ entry and investigated its downstream consequences. To that purpose, we used various connexin-targeting peptides interacting with extracellular (Gap26) and intracellular (Gap19, RRNYRRNY) Cx43 domains, and tested their effect on mitochondrial dye- and Ca²⁺-uptake, electrophysiological properties of plasmalemmal and mitochondrial Cx43 channels, and cell injury/cell death. Our results in isolated mice cardiac subsarcolemmal mitochondria indicate that Cx43 forms hemichannels that contribute to Ca²⁺ entry and may trigger permeability transition and cell injury/death. RRNYRRNY displayed the strongest effects in all assays and inhibited plasma membrane as well as mitochondrial Cx43 hemichannels. RRNYRRNY also strongly reduced the infarct size in ex vivo cardiac ischemia-reperfusion studies. These results indicate that Cx43 contributes to mitochondrial Ca²⁺ homeostasis and is involved in triggering cell injury/death pathways that can be inhibited by RRNYRRNY peptide.

Spinosad induces programmed cell death involves mitochondrial dysfunction and cytochrome C release in Spodoptera frugiperda Sf9 cells

Spinosad, a reduced-risk insecticide, acts on the nicotinic acetylcholine receptors and the gamma-aminobutyric acid receptor in the nervous system of target insects. However, its mechanism of action in non-neural insect cells is unclear. This study aimed to evaluate mitochondrial functional changes associated with spinosad in Spodoptera frugiperda (Sf9) insect cells. Our results indicate that in Sf9 cells, spinosad induces programmed cell death and mitochondrial dysfunction through enhanced reactive oxygen species production, mitochondrial permeability transition pore (mPTP) opening, and mitochondrial membrane potential collapse, eventually leading to cytochrome C release and apoptosis. The cytochrome C release induced by spinosad treatment was partly inhibited by the mPTP inhibitors cyclosporin A and bongkrekic acid. Subsequently, we found that spinosad downregulated Bcl-2 expression and upregulated p53 and Bax expressions, activated caspase-9 and caspase-3, and triggered PARP cleavage in Sf9 cells. These findings suggested that spinosad-induced programmed cell death was modulated by mitochondrial dysfunction and cytochrome C release.

Late sodium current and intracellular ionic homeostasis in acute ischemia

Blockade of the late Na⁺ current (I _NaL) protects from ischemia/reperfusion damage; nevertheless, information on changes in I _NaL during acute ischemia and their effect on intracellular milieu is missing. I _NaL, cytosolic Na⁺ and Ca²⁺ activities (Na_cyt, Ca_cyt) were measured in isolated rat ventricular myocytes during 7 min of simulated ischemia (ISC); in all the conditions tested, effects consistently exerted by ranolazine (RAN) and tetrodotoxin (TTX) were interpreted as due to I _NaL blockade. The results indicate that I _NaL was enhanced during ISC in spite of changes in action potential (AP) contour; I _NaL significantly contributed to Na_cyt rise, but only marginally to Ca_cyt rise. The impact of I _NaL on Ca_cyt was markedly enhanced by blockade of the sarcolemmal(s) Na⁺/Ca²⁺ exchanger (NCX) and was due to the presence of (Na⁺-sensitive) Ca²⁺ efflux through mitochondrial NCX (mNCX). sNCX blockade increased Ca_cyt and decreased Na_cyt, thus indicating that, throughout ISC, sNCX operated in the forward mode, in spite of the substantial Na_cyt increment. Thus, a robust Ca²⁺ source, other than sNCX and including mitochondria, contributed to Ca_cyt during ISC. Most, but not all, of RAN effects were shared by TTX. (1) The paradigm that attributes Ca_cyt accumulation during acute ischemia to decrease/reversal of sNCX transport may not be of general applicability; (2) I _NaL is enhanced during ISC, when the effect of Na_cyt on mitochondrial Ca²⁺ transport may substantially contribute to I _NaL impact on Ca_cyt; (3) RAN may act mostly, but not exclusively, through I _NaL blockade during ISC.

Mitochondrial Dysfunction and Myocardial Ischemia-Reperfusion: Implications for Novel Therapies

Mitochondria have emerged as key participants in and regulators of myocardial injury during ischemia and reperfusion. This review examines the sites of damage to cardiac mitochondria during ischemia and focuses on the impact of these defects. The concept that mitochondrial damage during ischemia leads to cardiac injury during reperfusion is addressed. The mechanisms that translate ischemic mitochondrial injury into cellular damage, during both ischemia and early reperfusion, are examined. Next, we discuss strategies that modulate and counteract these mechanisms of mitochondrial-driven injury. The new concept that mitochondria are not merely stochastic sites of oxidative and calcium-mediated injury but that they activate cellular responses of mitochondrial remodeling and cellular reactions that modulate the balance between cell death and recovery is reviewed, and the therapeutic implications of this concept are discussed.

Influence of trimetazidine and ranolazine on endothelial function in patients with ischemic heart disease

OBJECTIVE

Endothelial dysfunction is an independent predictor of atherosclerosis progression and cardiovascular events in patients with ischemic heart disease. Ranolazine and trimetazidine are novel drugs that reduce angina symptoms in the above-mentioned patients. The aim of this study was to compare the effects of ranolazine and trimetazidine on flow-mediated (FMD) and nitroglycerine-induced (GTN) dilation of the brachial artery.

METHODS

In a prospective, double-blind study, 56 men between 32 and 65 years of age with chronic ischemic heart disease were randomized and subjected to 12 weeks of treatment with either trimetazidine (35 mg twice daily) or ranolazine. Ranolazine was administered at a dose of 375 mg twice daily for 4 weeks and was increased to 500 mg twice daily for the rest of the study. FMD and GTN were measured using high-resolution ultrasound before and after treatment.

RESULTS

FMD increased from 3.5±7.4 to 13.8±9.4% (P<0.013; 294%) in the trimetazidine group and from 2.4±4.3 to 9.5±7.7% (P<0.037; 296%) in the ranolazine group, with no difference between the groups (P=0.444). GTN increased from 16.1±9.2 to 21.2±19.3% (P<0.022; 32%) in the trimetazidine group and from 13.8±9.6 to 21.7±13.7% (P<0.006; 57%) in the ranolazine group, with no difference between the groups (P=0.309).

CONCLUSION

Both trimetazidine and ranolazine led to an improvement in FMD and GTN of the brachial artery in patients with ischemic heart disease, with no statistically significant difference between the groups.

Optical Cryoimaging Reveals a Heterogeneous Distribution of Mitochondrial Redox State in ex vivo Guinea Pig Hearts and Its Alteration During Ischemia and Reperfusion

Oxidation of substrates to generate ATP in mitochondria is mediated by redox reactions of NADH and FADH2. Cardiac ischemia and reperfusion (IR) injury compromises mitochondrial oxidative phosphorylation. We hypothesize that IR alters the metabolic heterogeneity of mitochondrial redox state of the heart that is only evident in the 3-D optical cryoimaging of the perfused heart before, during, and after IR. The study involved four groups of hearts: time control (TC: heart perfusion without IR), global ischemia (Isch), global ischemia followed by reperfusion (IR) and TC with PCP (a mitochondrial uncoupler) perfusion. Mitochondrial NADH and FAD autofluorescence signals were recorded spectrofluorometrically online in guinea pig ex vivo-perfused hearts in the Langendorff mode. At the end of each specified protocol, hearts were rapidly removed and snap frozen in liquid N2 for later 3-D optical cryoimaging of the mitochondrial NADH, FAD, and NADH/FAD redox ratio (RR). The TC hearts revealed a heterogeneous spatial distribution of NADH, FAD, and RR. Ischemia and IR altered the spatial distribution and caused an overall increase and decrease in the RR by 55% and 64%, respectively. Uncoupling with PCP resulted in the lowest level of the RR (73% oxidation) compared with TC. The 3-D optical cryoimaging of the heart provides novel insights into the heterogeneous distribution of mitochondrial NADH, FAD, RR, and metabolism from the base to the apex during ischemia and IR. This 3-D information of the mitochondrial redox state in the normal and ischemic heart was not apparent in the dynamic spectrofluorometric data.