Inhibition of the mitochondrial fission protein dynamin-related protein 1 improves survival in a murine cardiac arrest model

Targeting mitochondrial quality control: new therapeutic strategies for major diseases

Mitochondria play a crucial role in maintaining the normal physiological state of cells. Hence, ensuring mitochondrial quality control is imperative for the prevention and treatment of numerous diseases. Previous reviews on this topic have however been inconsistencies and lack of systematic organization. Therefore, this review aims to provide a comprehensive and systematic overview of mitochondrial quality control and explore the possibility of targeting the same for the treatment of major diseases. This review systematically summarizes three fundamental characteristics of mitochondrial quality control, including mitochondrial morphology and dynamics, function and metabolism, and protein expression and regulation. It also extensively examines how imbalances in mitochondrial quality are linked to major diseases, such as ischemia-hypoxia, inflammatory disorders, viral infections, metabolic dysregulations, degenerative conditions, and tumors. Additionally, the review explores innovative approaches to target mitochondrial quality control, including using small molecule drugs that regulate critical steps in maintaining mitochondrial quality, nanomolecular materials designed for precise targeting of mitochondria, and novel cellular therapies, such as vesicle therapy and mitochondrial transplantation. This review offers a novel perspective on comprehending the shared mechanisms underlying the occurrence and progression of major diseases and provides theoretical support and practical guidance for the clinical implementation of innovative therapeutic strategies that target mitochondrial quality control for treating major diseases.

Novel Strategies to Improve the Cardioprotective Effects of Cardioplegia

The use of cardioprotective strategies as adjuvants of cardioplegic solutions has become an ideal alternative for the improvement of post-surgery heart recovery. The choice of the optimal cardioplegia, as well as its distribution mechanism, remains controversial in the field of cardiovascular surgery. There is still a need to search for new and better cardioprotective methods during cardioplegic procedures. New techniques for the management of cardiovascular complications during cardioplegia have evolved with new alternatives and additives, and each new strategy provides a tool to neutralize the damage after ischemia/reperfusion events. Researchers and clinicians have committed themselves to studying the effect of new strategies and adjuvant components with the potential to improve the cardioprotective effect of cardioplegic solutions in preventing myocardial ischemia/reperfusion-induced injury during cardiac surgery. The aim of this review is to explore the different types of cardioplegia, their protection mechanisms, and which strategies have been proposed to enhance the function of these solutions in hearts exposed to cardiovascular pathologies that require surgical alternatives for their corrective progression.

Dynamin-related protein 1 is a critical regulator of mitochondrial calcium homeostasis during myocardial ischemia/reperfusion injury

Dynamin-related protein 1 (Drp1) is a cytosolic GTPase protein that when activated translocates to the mitochondria, meditating mitochondrial fission and increasing reactive oxygen species (ROS) in cardiomyocytes. Drp1 has shown promise as a therapeutic target for reducing cardiac ischemia/reperfusion (IR) injury; however, the lack of specificity of some small molecule Drp1 inhibitors and the reliance on the use of Drp1 haploinsufficient hearts from older mice have left the role of Drp1 in IR in question. Here, we address these concerns using two approaches, using: (a) short-term (3 weeks), conditional, cardiomyocyte-specific, Drp1 knockout (KO) and (b) a novel, highly specific Drp1 GTPase inhibitor, Drpitor1a. Short-term Drp1 KO mice exhibited preserved exercise capacity and cardiac contractility, and their isolated cardiac mitochondria demonstrated increased mitochondrial complex 1 activity, respiratory coupling, and calcium retention capacity compared to controls. When exposed to IR injury in a Langendorff perfusion system, Drp1 KO hearts had preserved contractility, decreased reactive oxygen species (ROS), enhanced mitochondrial calcium capacity, and increased resistance to mitochondrial permeability transition pore (MPTP) opening. Pharmacological inhibition of Drp1 with Drpitor1a following ischemia, but before reperfusion, was as protective as Drp1 KO for cardiac function and mitochondrial calcium homeostasis. In contrast to the benefits of short-term Drp1 inhibition, prolonged Drp1 ablation (6 weeks) resulted in cardiomyopathy. Drp1 KO hearts were also associated with decreased ryanodine receptor 2 (RyR2) protein expression and pharmacological inhibition of the RyR2 receptor decreased ROS in post-IR hearts suggesting that changes in RyR2 may have a role in Drp1 KO mediated cardioprotection. We conclude that Drp1-mediated increases in myocardial ROS production and impairment of mitochondrial calcium handling are key mechanisms of IR injury. Short-term inhibition of Drp1 is a promising strategy to limit early myocardial IR injury which is relevant for the therapy of acute myocardial infarction, cardiac arrest, and heart transplantation.

Status of Mitochondrial Oxidative Phosphorylation during the Development of Heart Failure

Mitochondria are specialized organelles, which serve as the "Power House" to generate energy for maintaining heart function. These organelles contain various enzymes for the oxidation of different substrates as well as the electron transport chain in the form of Complexes I to V for producing ATP through the process of oxidative phosphorylation (OXPHOS). Several studies have shown depressed OXPHOS activity due to defects in one or more components of the substrate oxidation and electron transport systems which leads to the depletion of myocardial high-energy phosphates (both creatine phosphate and ATP). Such changes in the mitochondria appear to be due to the development of oxidative stress, inflammation, and Ca2+-handling abnormalities in the failing heart. Although some investigations have failed to detect any changes in the OXPHOS activity in the failing heart, such results appear to be due to a loss of Ca2+ during the mitochondrial isolation procedure. There is ample evidence to suggest that mitochondrial Ca2+-overload occurs, which is associated with impaired mitochondrial OXPHOS activity in the failing heart. The depression in mitochondrial OXPHOS activity may also be due to the increased level of reactive oxygen species, which are formed as a consequence of defects in the electron transport complexes in the failing heart. Various metabolic interventions which promote the generation of ATP have been reported to be beneficial for the therapy of heart failure. Accordingly, it is suggested that depression in mitochondrial OXPHOS activity plays an important role in the development of heart failure.

Multifaceted functions of Drp1 in hypoxia/ischemia-induced mitochondrial quality imbalance: from regulatory mechanism to targeted therapeutic strategy

Hypoxic-ischemic injury is a common pathological dysfunction in clinical settings. Mitochondria are sensitive organelles that are readily damaged following ischemia and hypoxia. Dynamin-related protein 1 (Drp1) regulates mitochondrial quality and cellular functions via its oligomeric changes and multiple modifications, which plays a role in mediating the induction of multiple organ damage during hypoxic-ischemic injury. However, there is active controversy and gaps in knowledge regarding the modification, protein interaction, and functions of Drp1, which both hinder and promote development of Drp1 as a novel therapeutic target. Here, we summarize recent findings on the oligomeric changes, modification types, and protein interactions of Drp1 in various hypoxic-ischemic diseases, as well as the Drp1-mediated regulation of mitochondrial quality and cell functions following ischemia and hypoxia. Additionally, potential clinical translation prospects for targeting Drp1 are discussed. This review provides new ideas and targets for proactive interventions on multiple organ damage induced by various hypoxic-ischemic diseases.

Metformin preconditioning protects against myocardial stunning and preserves protein translation in a mouse model of cardiac arrest

Cardiac arrest (CA) causes high mortality due to multi-system organ damage attributable to ischemia-reperfusion injury. Recent work in our group found that among diabetic patients who experienced cardiac arrest, those taking metformin had less evidence of cardiac and renal damage after cardiac arrest when compared to those not taking metformin. Based on these observations, we hypothesized that metformin's protective effects in the heart were mediated by AMPK signaling, and that AMPK signaling could be targeted as a therapeutic strategy following resuscitation from CA. The current study investigates metformin interventions on cardiac and renal outcomes in a non-diabetic CA mouse model. We found that two weeks of metformin pretreatment protects against reduced ejection fraction and reduces kidney ischemia-reperfusion injury at 24 h post-arrest. This cardiac and renal protection depends on AMPK signaling, as demonstrated by outcomes in mice pretreated with the AMPK activator AICAR or metformin plus the AMPK inhibitor compound C. At this 24-h time point, heart gene expression analysis showed that metformin pretreatment caused changes supporting autophagy, antioxidant response, and protein translation. Further investigation found associated improvements in mitochondrial structure and markers of autophagy. Notably, Western analysis indicated that protein synthesis was preserved in arrest hearts of animals pretreated with metformin. The AMPK activation-mediated preservation of protein synthesis was also observed in a hypoxia/reoxygenation cell culture model. Despite the positive impacts of pretreatment in vivo and in vitro, metformin did not preserve ejection fraction when deployed at resuscitation. Taken together, we propose that metformin's in vivo cardiac preservation occurs through AMPK activation, requires adaptation before arrest, and is associated with preserved protein translation.

Exogenous mitochondrial transplantation improves survival and neurological outcomes after resuscitation from cardiac arrest

BACKGROUND

Mitochondrial transplantation (MTx) is an emerging but poorly understood technology with the potential to mitigate severe ischemia-reperfusion injuries after cardiac arrest (CA). To address critical gaps in the current knowledge, we test the hypothesis that MTx can improve outcomes after CA resuscitation.

METHODS

This study consists of both in vitro and in vivo studies. We initially examined the migration of exogenous mitochondria into primary neural cell culture in vitro. Exogenous mitochondria extracted from the brain and muscle tissues of donor rats and endogenous mitochondria in the neural cells were separately labeled before co-culture. After a period of 24 h following co-culture, mitochondrial transfer was observed using microscopy. In vitro adenosine triphosphate (ATP) contents were assessed between freshly isolated and frozen-thawed mitochondria to compare their effects on survival. Our main study was an in vivo rat model of CA in which rats were subjected to 10 min of asphyxial CA followed by resuscitation. At the time of achieving successful resuscitation, rats were randomly assigned into one of three groups of intravenous injections: vehicle, frozen-thawed, or fresh viable mitochondria. During 72 h post-CA, the therapeutic efficacy of MTx was assessed by comparison of survival rates. The persistence of labeled donor mitochondria within critical organs of recipient animals 24 h post-CA was visualized via microscopy.

RESULTS

The donated mitochondria were successfully taken up into cultured neural cells. Transferred exogenous mitochondria co-localized with endogenous mitochondria inside neural cells. ATP content in fresh mitochondria was approximately four times higher than in frozen-thawed mitochondria. In the in vivo survival study, freshly isolated functional mitochondria, but not frozen-thawed mitochondria, significantly increased 72-h survival from 55 to 91% (P = 0.048 vs. vehicle). The beneficial effects on survival were associated with improvements in rapid recovery of arterial lactate and glucose levels, cerebral microcirculation, lung edema, and neurological function. Labeled mitochondria were observed inside the vital organs of the surviving rats 24 h post-CA.

CONCLUSIONS

MTx performed immediately after resuscitation improved survival and neurological recovery in post-CA rats. These results provide a foundation for future studies to promote the development of MTx as a novel therapeutic strategy to save lives currently lost after CA.

Ginsenoside Rb1 Improves Post-Cardiac Arrest Myocardial Stunning and Cerebral Outcomes by Regulating the Keap1/Nrf2 Pathway

The prognosis of cardiac arrest (CA) is dismal despite the ongoing progress in cardiopulmonary resuscitation (CPR). ginsenoside Rb1 (Gn-Rb1) has been verified to be cardioprotective in cardiac remodeling and cardiac ischemia/reperfusion (I/R) injury, but its role is less known in CA. After 15 min of potassium chloride-induced CA, male C57BL/6 mice were resuscitated. Gn-Rb1 was blindly randomized to mice after 20 s of CPR. We assessed the cardiac systolic function before CA and 3 h after CPR. Mortality rates, neurological outcome, mitochondrial homeostasis, and the levels of oxidative stress were evaluated. We found that Gn-Rb1 improved the long-term survival during the post-resuscitation period but did not affect the ROSC rate. Further mechanistic investigations revealed that Gn-Rb1 ameliorated CA/CPR-induced mitochondrial destabilization and oxidative stress, partially via the activation of Keap1/Nrf2 axis. Gn-Rb1 improved the neurological outcome after resuscitation partially by balancing the oxidative stress and suppressing apoptosis. In sum, Gn-Rb1 protects against post-CA myocardial stunning and cerebral outcomes via the induction of the Nrf2 signaling pathway, which may offer a new insight into therapeutic strategies for CA.

Molecular Mechanisms of Mitochondrial Quality Control in Ischemic Cardiomyopathy

Ischemic cardiomyopathy (ICM) is a special type of coronary heart disease or an advanced stage of the disease, which is related to the pathological mechanism of primary dilated cardiomyopathy. Ischemic cardiomyopathy mainly occurs in the long-term myocardial ischemia, resulting in diffuse myocardial fibrosis. This in turn affects the cardiac ejection function, resulting in a significant impact on myocardial systolic and diastolic function, resulting in a decrease in the cardiac ejection fraction. The pathogenesis of ICM is closely related to coronary heart disease. Mainly due to coronary atherosclerosis caused by coronary stenosis or vascular occlusion, causing vascular inflammatory lesions and thrombosis. As the disease progresses, it leads to long-term myocardial ischemia and eventually ICM. The pathological mechanism is mainly related to the mechanisms of inflammation, myocardial hypertrophy, fibrosis and vascular remodeling. Mitochondria are organelles with a double-membrane structure, so the composition of the mitochondrial outer compartment is basically similar to that of the cytoplasm. When ischemia-reperfusion induces a large influx of calcium into the cell, the concentration of calcium ions in the mitochondrial outer compartment also increases. The subsequent opening of the membrane permeability transition pore in the inner mitochondrial membrane and the resulting calcium overload induces the homeostasis of cardiomyocytes and activates the mitochondrial pathway of apoptosis. Mitochondrial Quality Control (MQC), as an important mechanism for regulating mitochondrial function in cardiomyocytes, affects the morphological structure/function and lifespan of mitochondria. In this review, we discuss the role of MQC (including mitophagy, mitochondrial dynamics, and mitochondrial biosynthesis) in the pathogenesis of ICM and provide important evidence for targeting MQC for ICM.

Ketone Body Improves Neurological Outcomes after Cardiac Arrest by Inhibiting Mitochondrial Fission in Rats

Ketone bodies including β-hydroxybutyrate (β-HB) have been proved the therapeutic potential in diverse neurological disorders. However, the role of β-HB in the regulation of neurological injury after cardiac arrest (CA) remains unclear. We investigated the effect of β-HB on brain mitochondrial dysfunction and neurological function after CA. A rat model of CA was established by asphyxia. The rats were randomly divided into three groups: sham group, control group, and β-HB group. Animals received 200 mg/kg β-HB or same volume vehicle at 10 minutes after return of spontaneous circulation by intraperitoneal injection. Neurological function was evaluated by neurologic deficit score and Y-maze. Neuronal cell loss and apoptosis were detected through hematoxylin-eosin staining, Nissl staining, and TdT-mediated dUTP nick-end labeling assay. Oxidative stress levels were determined by immunohistochemical staining of 4-hydoxynonenal and 8-hydroxy-2′-deoxyguanosine. Furthermore, mitochondrial ultrastructure of brain cells was observed by transmission electron microscopy. In addition, the protein expression levels of Bak, caspase 3, gasdermin D, caspase 1, brain-derived neurotrophic factor, dynamin-related protein 1 (Drp1), and phospho-Drp1 (ser616) were measured. We found that neurological function and survival rate were significantly higher in the β-HB group compared with the control group. β-HB also reduced neurons death and neurological oxidative stress after CA. Moreover, β-HB reduced neurological injury from apoptosis and pyroptosis after CA. In addition, β-HB maintained the structural integrity of brain mitochondria, prevented mitochondrial fission, and increased brain energy metabolism after CA. In conclusion, β-HB beneficially affected the neurological function of rats after global cerebral ischemia, associated with decreased mitochondrial fission, and improved mitochondrial function. Our results suggest that β-HB might benefit patients suffering from neurological dysfunction after CA.

Real-Time Brain Monitoring by Near-Infrared Spectroscopy Predicts Neurological Outcome after Cardiac Arrest and Resuscitation in Rats: A Proof of Concept Study of a Novel Prognostic Measure after Cardiac Arrest

Clinical studies have demonstrated that dynamic changes in regional cerebral oxygen saturation (rSO₂) after cardiac arrest (CA) and cardiopulmonary resuscitation (CPR) have a role in predicting neurological outcomes after the return of spontaneous circulation (ROSC). Our study evaluated whether the timing of rSO₂ decline shortly after CPR reflects the severity of brain injury in a rat model of CA. Rats were subjected to different durations of asphyxia to produce variable severities of brain injury, due to CA. Time from ROSC to achieving the initial minimum rSO₂ was defined as T_nadir. A T_nadir cut-off of 24 min had optimal sensitivity and specificity for predicting good neurological outcomes at 72 h after ROSC (AUC, 0.88; sensitivity, 89%; specificity, 86%; p < 0.01). Immunohistochemistry at 72 h post-CA revealed that the number of Fluoro-Jade B positive degenerating neurons in the hippocampus CA1 sector were markedly higher in animals with T_nadir > 24 min than that in animals with T_nadir ≤ 24 min. There was no difference in the gene expressions of cytokines and mitochondrial fission proteins in the brain at 2 h after ROSC between rats with T_nadir > 24 min and with T_nadir ≤ 24 min. In conclusion, T_nadir can be a novel predictor of good neurological outcomes after CA/CPR.

SENP3 Promotes an Mff-Primed Bcl-x L -Drp1 Interaction Involved in Cell Death Following Ischemia

Dysregulation of the mitochondrial fission machinery has been linked to cell death following ischemia. Fission is largely dependent on recruitment of Dynamin-related protein 1 (Drp1) to the receptor Mitochondrial fission factor (Mff) located on the mitochondrial outer membrane (MOM). Drp1 is a target for SUMOylation and its deSUMOylation, mediated by the SUMO protease SENP3, enhances the Drp1-Mff interaction to promote cell death in an oxygen/glucose deprivation (OGD) model of ischemia. Another interacting partner for Drp1 is the Bcl-2 family member Bcl-x _L , an important protein in cell death and survival pathways. Here we demonstrate that preventing Drp1 SUMOylation by mutating its SUMO target lysines enhances the Drp1-Bcl-x _L interaction in vivo and in vitro. Moreover, SENP3-mediated deSUMOylation of Drp1 promotes the Drp1-Bcl-x _L interaction. Our data suggest that Mff primes Drp1 binding to Bcl-x _L at the mitochondria and that Mff and Bcl-x _L can interact directly, independent of Drp1, through their transmembrane domains. Importantly, SENP3 loss in cells subjected to OGD correlates with reduced Drp1-Bcl-x _L interaction, whilst recovery of SENP3 levels in cells subjected to reoxygenation following OGD correlates with increased Drp1-Bcl-x _L interaction. Expressing a Bcl-x _L mutant with defective Drp1 binding reduces OGD plus reoxygenation-evoked cell death. Taken together, our results indicate that SENP3-mediated deSUMOlyation promotes an Mff-primed Drp1-Bcl-x _L interaction that contributes to cell death following ischemia.

Sodium-Glucose Co-Transporter 2 Inhibition With Empagliflozin Improves Cardiac Function After Cardiac Arrest in Rats by Enhancing Mitochondrial Energy Metabolism

Empagliflozin is a newly developed antidiabetic drug to reduce hyperglycaemia by highly selective inhibition of sodium–glucose co-transporter 2. Hyperglycaemia is commonly seen in patients after cardiac arrest (CA) and is associated with worse outcomes. In this study, we examined the effects of empagliflozin on cardiac function in rats with myocardial dysfunction after CA. Non-diabetic male Sprague–Dawley rats underwent ventricular fibrillation to induce CA, or sham surgery. Rats received 10 mg/kg of empagliflozin or vehicle at 10 min after return of spontaneous circulation by intraperitoneal injection. Cardiac function was assessed by echocardiography, histological analysis, molecular markers of myocardial injury, oxidative stress, mitochondrial ultrastructural integrity and metabolism. We found that empagliflozin did not influence heart rate and blood pressure, but left ventricular function and survival time were significantly higher in the empagliflozin treated group compared to the group treated with vehicle. Empagliflozin also reduced myocardial fibrosis, serum cardiac troponin I levels and myocardial oxidative stress after CA. Moreover, empagliflozin maintained the structural integrity of myocardial mitochondria and increased mitochondrial activity after CA. In addition, empagliflozin increased circulating and myocardial ketone levels as well as heart β-hydroxy butyrate dehydrogenase 1 protein expression. Together, these metabolic changes were associated with an increase in cardiac energy metabolism. Therefore, empagliflozin favorably affected cardiac function in non-diabetic rats with acute myocardial dysfunction after CA, associated with reducing glucose levels and increasing ketone body oxidized metabolism. Our data suggest that empagliflozin might benefit patients with myocardial dysfunction after CA.

Role of GTPase-Dependent Mitochondrial Dynamins in Heart Diseases

Heart function maintenance requires a large amount of energy, which is supplied by the mitochondria. In addition to providing energy to cardiomyocytes, mitochondria also play an important role in maintaining cell function and homeostasis. Although adult cardiomyocyte mitochondria appear as independent, low-static organelles, morphological changes have been observed in cardiomyocyte mitochondria under stress or pathological conditions. Indeed, cardiac mitochondrial fission and fusion are involved in the occurrence and development of heart diseases. As mitochondrial fission and fusion are primarily regulated by mitochondrial dynamins in a GTPase-dependent manner, GTPase-dependent mitochondrial fusion (MFN1, MFN2, and OPA1) and fission (DRP1) proteins, which are abundant in the adult heart, can also be regulated in heart diseases. In fact, these dynamic proteins have been shown to play important roles in specific diseases, including ischemia-reperfusion injury, heart failure, and metabolic cardiomyopathy. This article reviews the role of GTPase-dependent mitochondrial fusion and fission protein-mediated mitochondrial dynamics in the occurrence and development of heart diseases.

Pharmacological Approach for Neuroprotection After Cardiac Arrest-A Narrative Review of Current Therapies and Future Neuroprotective Cocktail

Cardiac arrest (CA) results in global ischemia-reperfusion injury damaging tissues in the whole body. The landscape of therapeutic interventions in resuscitation medicine has evolved from focusing solely on achieving return of circulation to now exploring options to mitigate brain injury and preserve brain function after CA. CA pathology includes mitochondrial damage and endoplasmic reticulum stress response, increased generation of reactive oxygen species, neuroinflammation, and neuronal excitotoxic death. Current non-pharmacologic therapies, such as therapeutic hypothermia and extracorporeal cardiopulmonary resuscitation, have shown benefits in protecting against ischemic brain injury and improving neurological outcomes post-CA, yet their application is difficult to institute ubiquitously. The current preclinical pharmacopeia to address CA and the resulting brain injury utilizes drugs that often target singular pathways and have been difficult to translate from the bench to the clinic. Furthermore, the limited combination therapies that have been attempted have shown mixed effects in conferring neuroprotection and improving survival post-CA. The global scale of CA damage and its resultant brain injury necessitates the future of CA interventions to simultaneously target multiple pathways and alleviate the hemodynamic, mitochondrial, metabolic, oxidative, and inflammatory processes in the brain. This narrative review seeks to highlight the current field of post-CA neuroprotective pharmaceutical therapies, both singular and combination, and discuss the use of an extensive multi-drug cocktail therapy as a novel approach to treat CA-mediated dysregulation of multiple pathways, enhancing survival, and neuroprotection.

The nuclear sirtuin SIRT6 protects the heart from developing aging-associated myocyte senescence and cardiac hypertrophy

Sirtuins have been shown to regulate the aging process. We have previously demonstrated that Sirt6 blocks the pressure overload-induced cardiac hypertrophy in mice. Here, we show that Sirt6 can also mitigate aging-induced cardiomyocyte senescence and cardiac hypertrophy. We found that aging is associated with altered Sirt6 activity along with development of cardiac hypertrophy and fibrosis. Compared to young mice (4-months), the hearts of aged mice (24-months) showed increased levels of mitochondrial DNA damage, shortened telomere length, and increased accumulation of 8-oxo-dG adducts, which are hallmarks of aging. The aged hearts also showed reduced levels of NAD⁺ and altered levels of mitochondrial fusion-fission proteins. Similar characteristics were observed in the hearts of Sirt6 deficient mice. Additionally, we found that doxorubicin (Dox) induced cardiomyocyte senescence, as measured by expression of p16^INK4a, p53, and β-galactosidase, was associated with loss of Sirt6. However, Sirt6 overexpression protected cardiomyocytes from developing Dox-induced senescence. Further, compared to wild-type mice, the hearts of Sirt6.Tg mice showed reduced expression of aging markers, and the development of aging-associated cardiac hypertrophy and fibrosis. Our data suggest that Sirt6 is a critical anti-aging molecule that regulates various cellular processes associated with aging and protects the heart from developing aging-induced cardiac hypertrophy and fibrosis.

Haemodynamic-directed cardiopulmonary resuscitation promotes mitochondrial fusion and preservation of mitochondrial mass after successful resuscitation in a pediatric porcine model

Objective

Cerebral mitochondrial dysfunction is a key mediator of neurologic injury following cardiac arrest (CA) and is regulated by the balance of fusion and fission (mitochondrial dynamics). Under stress, fission can decrease mitochondrial mass and signal apoptosis, while fusion promotes oxidative phosphorylation efficiency. This study evaluates mitochondrial dynamics and content in brain tissue 24 h after CA between two cardiopulmonary resuscitation (CPR) strategies.

Interventions

Piglets (1 month), previously randomized to three groups: (1) Std-CPR (n = 5); (2) HD-CPR (n = 5; goal systolic blood pressure 90 mmHg, goal coronary perfusion pressure 20 mmHg); (3) Shams (n = 7). Std-CPR and HD-CPR groups underwent 7 min of asphyxia, 10 min of CPR, and standardized post-resuscitation care. Primary outcomes: (1) cerebral cortical mitochondrial protein expression for fusion (OPA1, OPA1 long to short chain ratio, MFN2) and fission (DRP1, FIS1), and (2) mitochondrial mass by citrate synthase activity. Secondary outcomes: (1) intra-arrest haemodynamics and (2) cerebral performance category (CPC) at 24 h.

Results

HD-CPR subjects had higher total OPA1 expression compared to Std-CPR (1.52; IQR 1.02-1.69 vs 0.67; IQR 0.54-0.88, p = 0.001) and higher OPA1 long to short chain ratio than both Std-CPR (0.63; IQR 0.46-0.92 vs 0.26; IQR 0.26-0.31, p = 0.016) and shams. Citrate synthase activity was lower in Std-CPR than sham (11.0; IQR 10.15-12.29 vs 13.4; IQR 12.28-15.66, p = 0.047), but preserved in HD-CPR. HD-CPR subjects had improved intra-arrest haemodynamics and CPC scores at 24 h compared to Std-CPR.

Conclusions

Following asphyxia-associated CA, HD-CPR exhibits increased pro-mitochondrial fusion protein expression, preservation of mitochondrial mass, improved haemodynamics and superior neurologic scoring compared to Std-CPR.

Institutional protocol number

IAC 16-001023.

Baicalin Improves Cardiac Outcome and Survival by Suppressing Drp1-Mediated Mitochondrial Fission after Cardiac Arrest-Induced Myocardial Damage

Myocardial injury after cardiac arrest (CA) often results in severe myocardial dysfunction and death involving mitochondrial dysfunction. Here, we sought to investigate whether baicalin, a natural flavonoid compound, exerts cardioprotection against CA-induced injury via regulating mitochondrial dysfunction. We subjected the rats to asphyxia CA after a daily baicalin treatment for 4 weeks. After the return of spontaneous circulation, baicalin treatment significantly improved cardiac function performance, elevated survival rate from 35% to 75%, prevented necrosis and apoptosis in the myocardium, which was accompanied by reduced phosphorylation of Drp1 at serine 616, inhibited Drp1 translocation to the mitochondria and mitochondrial fission, and improved mitochondrial function. In H9c2 cells subjected to simulated ischemia/reperfusion, increased phosphorylation of Drp1 at serine 616 and subsequently enhanced mitochondrial Drp1 translocation as well as mitochondrial fission, augmented cardiomyocyte death, increased reactive oxygen species production, released cytochrome c from mitochondria and injured mitochondrial respiration were efficiently improved by baicalin and Drp1 specific inhibitor with Mdivi-1. Furthermore, overexpression of Drp1 augmented excessive mitochondrial fission and abolished baicalin-afforded cardioprotection, indicating that the protective impacts of baicalin are linked to the inhibition of Drp1. Altogether, our findings disclose for the first time that baicalin offers cardioprotection against ischemic myocardial injury after CA by inhibiting Drp1-mediated mitochondrial fission. Baicalin might be a prospective therapy for the treatment of post-CA myocardial injury.

Pharmacological inhibition of mitochondrial fission attenuates cardiac ischemia-reperfusion injury in pre-diabetic rats

An increase in the number of fragmented mitochondria contributes to the pathogenesis of ischemia-reperfusion (I/R) injury. Also, mitochondrial fission has shown an increase in obese condition. However, the cardioprotective roles of a mitochondrial fission inhibitor in obesity with cardiac I/R injury are unclear. We hypothesized that a fission inhibitor (Mdivi-1) reduces cardiac dysfunction during I/R injury in pre-diabetic rats. Male Wistar rats (n = 40) were received a high-fat diet for 12 weeks to induce prediabetes. Then, rats underwent a 30-min coronary artery ligation was performed followed by reperfusion for 120 min. These I/R rats were given either: (1) vehicle or Mdivi-1 treatment at 3 time points relative to onset of ischemia: (2) pre-ischemia; (3) during ischemia; and (4) at onset of reperfusion. Cardiac function, myocardial infarct size, mitochondrial function and dynamic balance were determined. Interestingly, Mdivi-1 given at any time points effectively attenuated mitochondrial reactive oxygen species production, depolarization, swelling, and dynamic imbalance, resulting in reduced arrhythmias, myocardial cell death, infarct size and enhanced cardiac performance during I/R injury in pre-diabetic rats. Taken together, inhibition of mitochondrial fission effectively protected the heart against cardiac I/R injury regardless of the time of administration in pre-diabetic rats.

FK866 alleviates cerebral pyroptosis and inflammation mediated by Drp1 in a rat cardiopulmonary resuscitation model

OBJECTIVES

Dynamin-related protein 1 (Drp1) mediates mitochondrial fission and triggers NLRP3 inflammasome activation. FK866 (a NAMPT inhibitor) exerts a neuroprotective effect in ischemia/reperfusion injury through the suppression of mitochondrial dysfunction. We explored the effects of FK866 on pyroptosis and inflammation mediated by Drp1 in a cardiac arrest/cardiopulmonary resuscitation (CA/CPR) rat model.

METHODS

Healthy male Sprague-Dawley rats were subjected to 7 min CA by trans-esophageal electrical stimulation followed by CPR. The surviving rats were treated with FK866 (a selective inhibitor of NAMPT), Mdivi-1 (Drp1 inhibitor), FK866 + Mdivi-1, or vehicle and then underwent 24 h reperfusion. Hematoxylin and eosin staining and immunohistochemistry (to detect NSE) were used to evaluate brain injury. We performed immunofluorescent staining to analyze NLRP3 and GSDMD expression in microglia or astrocytes and western blot to determine expression of NLRP3, IL-1β, GSDMD, Drp1, and Mfn2. Transmission electron microscopy was used to observe mitochondria.

RESULTS

FK866 significantly decreased pathological damage to brain tissue, inhibited the activation of NLRP3 in microglia or astrocytes, downregulated the expression of NLRP3, IL-1β, GSDMD, p-Drp1 protein, upregulated Mfn2 and improve mitochondrial morphology.

CONCLUSIONS

Our results demonstrated that FK866 protects the brain against ischemia-reperfusion injury in rats after CA/CPR by inhibiting pyroptosis and inflammation mediated by Drp1.

Cdk5-mediated Drp1 phosphorylation drives mitochondrial defects and neuronal apoptosis in radiation-induced optic neuropathy

Radiation-induced optic neuropathy (RION) is a devastating complication following external beam radiation therapy (EBRT) that leads to acute vision loss. To date, no efficient, available treatment for this complication, due partly to the lack of understanding regarding the developmental processes behind RION. Here, we report radiation caused changes in mitochondrial dynamics by regulating the mitochondrial fission proteins dynamin-related protein 1 (Drp1) and fission-1 (Fis1). Concurrent with an excessive production of reactive oxygen species (ROS), both neuronal injury and visual dysfunction resulted. Further, our findings delineate an important mechanism by which cyclin-dependent kinase 5 (Cdk5)-mediated phosphorylation of Drp1 (Ser616) regulates defects in mitochondrial dynamics associated with neuronal injury in the development of RION. Both the pharmacological inhibition of Cdk5 by roscovitine and the inhibition of Drp1 by mdivi-1 inhibited mitochondrial fission and the production of ROS associated with radiation-induced neuronal loss. Taken together, these findings may have clinical significance in preventing the development of RION.

Acute metformin treatment provides cardioprotection via improved mitochondrial function in cardiac ischemia / reperfusion injury

Cardiac ischemia/reperfusion (I/R) injury following reperfusion therapy in acute myocardial infarction results in mitochondrial dynamic imbalance and cardiomyocyte apoptosis. Although diabetic patients taking metformin have been shown to have a lower risk of myocardial infarction, the efficacy of the cardioprotection conferred by metformin regarding the mitochondrial function and dynamic in cardiac I/R injury are still inconclusive. In addition, the comparative effects between different doses of metformin given acutely prior to cardiac I/R injury have never been investigated. Fifty 8-week-old male Wistar rats weighing 300-350 g were divided into sham-operated (n = 10) and cardiac I/R-operated (n = 40) groups. In the cardiac I/R group, rats underwent 30-min ischemia followed by 120-min reperfusion and were randomly divided into four subgroups (n = 10/group): control (received normal saline), metformin (100, 200, and 400 mg/kg). The arrhythmia score, cardiac function, infarct size, mortality rate, mitochondrial function and apoptosis, were determined. Metformin (200 mg/kg) exerted the highest level of cardioprotection through reduction in arrhythmia, infarct size, mitochondrial fission, and apoptosis, in addition to preservation of mitochondrial function, leading to the attenuation of cardiac dysfunction. Doses of metformin (100 and 400 mg/kg) also improved mitochondrial and cardiac function, but to a lesser extent than metformin (200 mg/kg). In conclusion, metformin exerts cardioprotection by attenuating mitochondrial dysfunction, mitochondrial dynamic imbalance, and apoptosis. These led to decreased infarct size and eventual improvement in cardiac function in rats with acute cardiac I/R injury. These findings indicate the potential clinical benefits of acute metformin treatment in acute myocardial infarction.

Mitochondrial scenario: roles of mitochondrial dynamics in acute myocardial ischemia/reperfusion injury

The main therapeutic strategy currently used for acute myocardial infarction (AMI) is to open occluded coronary arteries, a process defined as blood reperfusion. However, blood reperfusion will increase cardiac mortality, tissue damage and cardiac dysfunction in patients with AMI, which is mechanically defined as "ischemia/reperfusion (I/R) injury". It is currently believed that mitochondrial dynamics plays a key role in myocardial I/R, especially excessive mitochondrial fission, which is the main cause of cardiac dysfunction. Therefore, in the process of I/R injury, effective drug intervention and correct treatment strategies can be used to regulate mitochondrial dynamic balance to combat ischemia-reperfusion injury, which can play a huge role in improving the prognosis of patients. This review summarized the effects of mitochondrial fission and mitochondrial fusion balance on myocardial and mitochondrial functional changes during myocardial I/R injury. Finally, combined with the previous injury mechanisms, this review also briefly described some drug intervention that may be beneficial to clinical practice to improve the postoperative quality of life of patients with AMI.

Acute dapagliflozin administration exerts cardioprotective effects in rats with cardiac ischemia/reperfusion injury

BACKGROUND

A sodium-glucose co-transporter 2 (SGLT-2) inhibitor had favorable impact on the attenuation of hyperglycemia together with the severity of heart failure. However, the effects of acute dapagliflozin administration at the time of cardiac ischemia/reperfusion (I/R) injury are not established.

METHODS

The effects of dapagliflozin on cardiac function were investigated by treating cardiac I/R injury at different time points. Cardiac I/R was instigated in forty-eight Wistar rats. These rats were then split into 4 interventional groups: control, dapagliflozin (SGLT2 inhibitor, 1 mg/kg) given pre-ischemia, at the time of ischemia and at the beginning of reperfusion. Left ventricular (LV) function and arrhythmia score were evaluated. The hearts were used to evaluate size of myocardial infarction, cardiomyocyte apoptosis, cardiac mitochondrial dynamics and function.

RESULTS

Dapagliflozin given pre-ischemia conferred the maximum level of cardioprotection quantified through the decrease in arrhythmia, attenuated infarct size, decreased cardiac apoptosis and improved cardiac mitochondrial function, biogenesis and dynamics, leading to LV function improvement during cardiac I/R injury. Dapagliflozin given during ischemia also showed cardioprotection, but at a lower level of efficacy.

CONCLUSIONS

Acute dapagliflozin administration during cardiac I/R injury exerted cardioprotective effects by attenuating cardiac infarct size, increasing LV function and reducing arrhythmias. These benefits indicate its potential clinical usefulness.

Exercise training protects the heart against ischemia-reperfusion injury: A central role for mitochondria?

Ischemic heart disease is one of the main causes of morbidity and mortality worldwide. Physical exercise is an effective lifestyle intervention to reduce the risk factors for cardiovascular disease and also to improve cardiac function and survival in patients with ischemic heart disease. Among the strategies that contribute to reduce heart damages during ischemia and reperfusion, regular physical exercise is efficient both in rodent experimental models and in humans. However, the cellular and molecular mechanisms of the cardioprotective effects of exercise remain unclear. During ischemia and reperfusion, mitochondria are crucial players in cell death, but also in cell survival. Although exercise training can influence mitochondrial function, the consequences on heart sensitivity to ischemic insults remain elusive. In this review, we describe the effects of physical activity on cardiac mitochondria and their potential key role in exercise-induced cardioprotection against ischemia-reperfusion damage. Based on recent scientific data, we discuss the role of different pathways that might help to explain why mitochondria are a key target of exercise-induced cardioprotection.

Assessment of Brain Glucose Metabolism Following Cardiac Arrest by [18F]FDG Positron Emission Tomography

BACKGROUND

Cardiac arrest (CA) patients who survived by cardiopulmonary resuscitation (CPR) can present different levels of neurological deficits ranging from minor cognitive impairments to persistent vegetative state and brain death. The pathophysiology of the resulting brain injury is poorly understood, and whether changes in post-CA brain metabolism contribute to the injury are unknown. Here we utilized [¹⁸F]fluorodeoxyglucose (FDG)-Positron emission tomography (PET) to study in vivo cerebral glucose metabolism 72 h following CA in a murine CA model.

METHODS

Anesthetized and ventilated adult C57BL/6 mice underwent 12-min KCl-induced CA followed by CPR. Seventy-two hours following CA, surviving mice were intraperitoneally injected with [¹⁸F]FDG (~ 186 µCi/200 µL) and imaged on Molecubes preclinical micro-PET/computed tomography (CT) imaging systems after a 30-min awake uptake period. Brain [¹⁸F]FDG uptake was determined by the VivoQuant software on fused PET/CT images with the 3D brain atlas. Upon completion of Positron emission tomography (PET) imaging, remaining [¹⁸F]FDG radioactivity in the brain, heart, and liver was determined using a gamma counter.

RESULTS

Global increases in brain [¹⁸F]FDG uptake in post-CA mice were observed compared to shams and controls. The median standardized uptake value of [¹⁸F]FDG for CA animals was 1.79 versus sham 1.25 (p < 0.05) and control animals 0.78 (p < 0.01). This increased uptake was consistent throughout the 60-min imaging period and across all brain regions reaching statistical significance in the midbrain, pons, and medulla. Biodistribution analyses of various key organs yielded similar observations that the median [¹⁸F]FDG uptake for brain was 7.04%ID/g tissue for CA mice versus 5.537%ID/g tissue for sham animals, p < 0.05).

CONCLUSIONS

This study has successfully applied [¹⁸F]FDG-PET/CT to measure changes in brain metabolism in a murine model of asystolic CA. Our results demonstrate increased [¹⁸F]FDG uptake in the brain 72 h following CA, suggesting increased metabolic demand in the case of severe neurological injury. Further study is warranted to determine the etiology of these changes.

Perturbed mitochondrial dynamics, an emerging aspect of epithelial-microbe interactions

Mitochondria exist in a complex network that is constantly remodeling via the processes of fission and fusion in response to intracellular conditions and extracellular stimuli. Excessive fragmentation of the mitochondrial network because of an imbalance between fission and fusion reduces the cells' capacity to generate ATP and can be a forerunner to cell death. Given the critical roles mitochondria play in cellular homeostasis and innate immunity, it is not surprising that many microbial pathogens can disrupt mitochondrial activity. Here we note the putative contribution of mitochondrial dysfunction to gut disease and review data showing that infection with microbial pathogens can alter the balance between mitochondrial fragmentation and fusion, preventing normal remodeling (i.e., dynamics) and can lead to cell death. Current data indicate that infection of epithelia or macrophages with microbial pathogens will ultimately result in excessive fragmentation of the mitochondrial network. Concerted research efforts are required to elucidate fully the processes that regulate mitochondrial dynamics, the mechanisms by which microbes affect epithelial mitochondrial fission and/or fusion, and the implications of this for susceptibility to infectious disease. We speculate that the commensal microbiome of the gut may be important for normal epithelial mitochondrial form and function. Drugs designed to counteract the effect of microbial pathogen interference with mitochondrial dynamics may be a new approach to infectious disease at mucosal surfaces.

Neuregulin-1 promotes mitochondrial biogenesis, attenuates mitochondrial dysfunction, and prevents hypoxia/reoxygenation injury in neonatal cardiomyocytes

Neuregulin-1 (NRG-1)/erythroblastic leukaemia viral oncogene homologues (ErbB) pathway activation plays a crucial role in regulating the adaptation of the adult heart to physiological and pathological stress. In the present study, we investigate the effect of recombined human NRG-1 (rhNRG-1) on mitochondrial biogenesis, mitochondrial function, and cell survival in neonatal rat cardiac myocytes (NRCMs) exposed to hypoxia/reoxygenation (H/R). The results of this study showed that, in the H/R-exposed NRCMs, mitochondrial biogenesis was impaired, as manifested by the decrease of the expression of peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) and mitochondrial membrane proteins, the inner membrane (Tim23), mitofusin 1 (Mfn1), and mitofusin 2 (Mfn2). RhNRG-1 pretreatment effectively restored the expression of PGC-1α and these membrane proteins, upregulated the expression of the anti-apoptosis proteins Bcl-2 and Bcl-xL, preserved the mitochondrial membrane potential, and attenuated H/R-induced cell apoptosis. Blocking PGC-1 expression with siRNA abolished the beneficial role of rhNRG-1 on mitochondrial function and cell survival. The results of the present study strongly suggest that NRG-1/ErbB activation enhances the adaption of cardiomyocytes to H/R injury via promoted mitochondrial biogenesis and improved mitochondrial homeostasis. SIGNIFICANCE OF THE STUDY: The results of this research revealed for the first time the relationship between neuregulin-1 (NRG-1)/erythroblastic leukaemia viral oncogene homologues (ErbB) activation and mitochondrial biogenesis in neonatal cardiomyocytes and verified the significance of this promoted mitochondrial biogenesis in attenuating hypoxia/reoxygenation injury. This finding may open a new field to further understand the biological role of NRG-1/ErbB signalling pathway in cardiomyocyte.

Suppression of Superoxide-Hydrogen Peroxide Production at Site IQ of Mitochondrial Complex I Attenuates Myocardial Stunning and Improves Postcardiac Arrest Outcomes

OBJECTIVES

Cardiogenic shock following cardiopulmonary resuscitation for sudden cardiac arrest is common, occurring even in the absence of acute coronary artery occlusion, and contributes to high rates of postcardiopulmonary resuscitation mortality. The pathophysiology of this shock is unclear, and effective therapies for improving clinical outcomes are lacking.

DESIGN

Laboratory investigation.

SETTING

University laboratory.

SUBJECTS

C57BL/6 adult female mice.

INTERVENTIONS

Anesthetized and ventilated adult female C57BL/6 wild-type mice underwent a 4, 8, 12, or 16-minute potassium chloride-induced cardiac arrest followed by 90 seconds of cardiopulmonary resuscitation. Mice were then blindly randomized to a single IV injection of vehicle (phosphate-buffered saline) or suppressor of site IQ electron leak, an inhibitor of superoxide production by complex I of the mitochondrial electron transport chain. Suppressor of site IQ electron leak and vehicle were administered during cardiopulmonary resuscitation.

MEASUREMENTS AND MAIN RESULTS

Using a murine model of asystolic cardiac arrest, we discovered that duration of cardiac arrest prior to cardiopulmonary resuscitation determined postresuscitation success rates, degree of neurologic injury, and severity of myocardial dysfunction. Post-cardiopulmonary resuscitation cardiac dysfunction was not associated with myocardial necrosis, apoptosis, inflammation, or mitochondrial permeability transition pore opening. Furthermore, left ventricular function recovered within 72 hours of cardiopulmonary resuscitation, indicative of myocardial stunning. Postcardiopulmonary resuscitation, the myocardium exhibited increased reactive oxygen species and evidence of mitochondrial injury, specifically reperfusion-induced reactive oxygen species generation at electron transport chain complex I. Suppressor of site IQ electron leak, which inhibits complex I-dependent reactive oxygen species generation by suppression of site IQ electron leak, decreased myocardial reactive oxygen species generation and improved postcardiopulmonary resuscitation myocardial function, neurologic outcomes, and survival.

CONCLUSIONS

The severity of cardiogenic shock following asystolic cardiac arrest is dependent on the length of cardiac arrest prior to cardiopulmonary resuscitation and is mediated by myocardial stunning resulting from mitochondrial electron transport chain complex I dysfunction. A novel pharmacologic agent targeting this mechanism, suppressor of site IQ electron leak, represents a potential, practical therapy for improving sudden cardiac arrest resuscitation outcomes.

Vitexin attenuates myocardial ischemia/reperfusion injury in rats by regulating mitochondrial dysfunction induced by mitochondrial dynamics imbalance

Vitexin (VT) is a main bioactive flavonoid compound derived from the dried leaf of hawthorn (Crataegus pinnatifida), a widely used Chinese traditional folk medicine. Recent studies have shown that vitexin presents cardioprotective effects in vivo and in vitro. Mitochondrial dysfunction is a salient feature of myocardial ischemia/reperfusion (I/R) injury (MIRI), but the potential mechanism is still unclear. This study investigated the cardioprotective effect of vitexin against MIRI and its possible mechanism. Isolated SD rat hearts were subjected to MIRI in a Langendorff perfusion system, and H9c2 cells were subjected to hypoxia/reoxygenation (H/R) in vitro. Ex vivo experiments showed improved left ventricular function and reduced infarct size in the vitexin group. Transmission electron microscopy showed that I/R caused outer mitochondrial membrane rupture, cristae disappearance and vacuolation, while vitexin reduced mitochondrial damage and ultimately reduced cardiomyocyte apoptosis. In vitro, vitexin protected H9c2 cells from H/R-induced mitochondrial dysfunction, significantly reducing ROS levels; improving mitochondrial activity, mitochondrial membrane potential and ATP content; markedly increasing MFN2 expression and reducing the recruitment of Drp1 in mitochondria. These results suggest a new protective mechanism of vitexin for ischemic heart disease treatment.

A Metabolic Checkpoint for the Yeast-to-Hyphae Developmental Switch Regulated by Endogenous Nitric Oxide Signaling

The yeast Candida albicans colonizes several sites in the human body and responds to metabolic signals in commensal and pathogenic states. The yeast-to-hyphae transition correlates with virulence, but how metabolic status is integrated with this transition is incompletely understood. We used the putative mitochondrial fission inhibitor mdivi-1 to probe the crosstalk between hyphal signaling and metabolism. Mdivi-1 repressed C. albicans hyphal morphogenesis, but the mechanism was independent of its presumed target, the mitochondrial fission GTPase Dnm1. Instead, mdivi-1 triggered extensive metabolic reprogramming, consistent with metabolic stress, and reduced endogenous nitric oxide (NO) levels. Limiting endogenous NO stabilized the transcriptional repressor Nrg1 and inhibited the yeast-to-hyphae transition. We establish a role for endogenous NO signaling in C. albicans hyphal morphogenesis and suggest that NO regulates a metabolic checkpoint for hyphal growth. Furthermore, identifying NO signaling as an mdivi-1 target could inform its therapeutic applications in human diseases.

Identification of novel dynamin-related protein 1 (Drp1) GTPase inhibitors: Therapeutic potential of Drpitor1 and Drpitor1a in cancer and cardiac ischemia-reperfusion injury

Mitochondrial fission is important in physiological processes, including coordination of mitochondrial and nuclear division during mitosis, and pathologic processes, such as the production of reactive oxygen species (ROS) during cardiac ischemia-reperfusion injury (IR). Mitochondrial fission is mainly mediated by dynamin-related protein 1 (Drp1), a large GTPase. The GTPase activity of Drp1 is essential for its fissogenic activity. Therefore, we aimed to identify Drp1 inhibitors and evaluate their anti-neoplastic and cardioprotective properties in five cancer cell lines (A549, SK-MES-1, SK-LU-1, SW 900, and MCF7) and an experimental cardiac IR injury model. Virtual screening of a chemical library revealed 17 compounds with high predicted affinity to the GTPase domain of Drp1. In silico screening identified an ellipticine compound, Drpitor1, as a putative, potent Drp1 inhibitor. We also synthesized a congener of Drpitor1 to remove the methoxymethyl group and reduce hydrolytic lability (Drpitor1a). Drpitor1 and Drpitor1a inhibited the GTPase activity of Drp1 without inhibiting the GTPase of dynamin 1. Drpitor1 and Drpitor1a have greater potency than the current standard Drp1 GTPase inhibitor, mdivi-1, (IC50 for mitochondrial fragmentation are 0.09, 0.06, and 10 μM, respectively). Both Drpitors reduced proliferation and induced apoptosis in cancer cells. Drpitor1a suppressed lung cancer tumor growth in a mouse xenograft model. Drpitor1a also inhibited mitochondrial ROS production, prevented mitochondrial fission, and improved right ventricular diastolic dysfunction during IR injury. In conclusion, Drpitors are useful tools for understanding mitochondrial dynamics and have therapeutic potential in treating cancer and cardiac IR injury.

Mitochondrial Dysfunction: Metabolic Drivers of Pulmonary Hypertension

Significance: Pulmonary hypertension (PH) is a progressive disease characterized by pulmonary vascular remodeling and lung vasculopathy. The disease displays progressive dyspnea, pulmonary artery uncoupling and right ventricular (RV) dysfunction. The overall survival rate is ranging from 28-72%. Recent Advances: The molecular events that promote the development of PH are complex and incompletely understood. Metabolic impairment has been proposed to contribute to the pathophysiology of PH with evidence for mitochondrial dysfunction involving the electron transport chain proteins, antioxidant enzymes, apoptosis regulators, and mitochondrial quality control. Critical Issues: It is vital to characterize the mechanisms by which mitochondrial dysfunction contribute to PH pathogenesis. This review focuses on the currently available publications that supports mitochondrial mechanisms in PH pathophysiology. Future Directions: Further studies of these metabolic mitochondrial alterations in PH could be viable targets of diagnostic and therapeutic intervention.

Targeting Mitochondrial Fission Using Mdivi-1 in A Clinically Relevant Large Animal Model of Acute Myocardial Infarction: A Pilot Study

Background: New treatments are needed to reduce myocardial infarct size (MI) and prevent heart failure (HF) following acute myocardial infarction (AMI), which are the leading causes of death and disability worldwide. Studies in rodent AMI models showed that genetic and pharmacological inhibition of mitochondrial fission, induced by acute ischemia and reperfusion, reduced MI size. Whether targeting mitochondrial fission at the onset of reperfusion is also cardioprotective in a clinically-relevant large animal AMI model remains to be determined. Methods: Adult pigs (30-40 kg) were subjected to closed-chest 90-min left anterior descending artery ischemia followed by 72 h of reperfusion and were randomized to receive an intracoronary bolus of either mdivi-1 (1.2 mg/kg, a small molecule inhibitor of the mitochondrial fission protein, Drp1) or vehicle control, 10-min prior to reperfusion. The left ventricular (LV) size and function were both assessed by transthoracic echocardiography prior to AMI and after 72 h of reperfusion. MI size and the area-at-risk (AAR) were determined using dual staining with Tetrazolium and Evans blue. Heart samples were collected for histological determination of fibrosis and for electron microscopic analysis of mitochondrial morphology. Results: A total of 14 pigs underwent the treatment protocols (eight control and six mdivi-1). Administration of mdivi-1 immediately prior to the onset of reperfusion did not reduce MI size (MI size as % of AAR: Control 49.2 ± 8.6 vs. mdivi-1 50.5 ± 11.4; p = 0.815) or preserve LV systolic function (LV ejection fraction %: Control 67.5 ± 0.4 vs. mdivi-1 59.6 ± 0.6; p = 0.420), when compared to vehicle control. Similarly, there were no differences in mitochondrial morphology or myocardial fibrosis between mdivi-1 and vehicle control groups. Conclusion: Our pilot study has shown that treatment with mdivi-1 (1.2 mg/kg) at the onset of reperfusion did not reduce MI size or preserve LV function in the clinically-relevant closed-chest pig AMI model. A larger study, testing different doses of mdivi-1 or using a more specific Drp1 inhibitor are required to confirm these findings.

Age-Dependent Myocardial Dysfunction in Critically Ill Patients: Role of Mitochondrial Dysfunction

Myocardial dysfunction is common in septic shock and post-cardiac arrest but manifests differently in pediatric and adult patients. By conventional echocardiographic parameters, biventricular systolic dysfunction is more prevalent in children with septic shock, though strain imaging reveals that myocardial injury may be more common in adults than previously thought. In contrast, diastolic dysfunction in general and post-arrest myocardial systolic dysfunction appear to be more widespread in the adult population. A growing body of evidence suggests that mitochondrial dysfunction mediates myocardial depression in critical illness; alterations in mitochondrial electron transport system function, bioenergetic production, oxidative and nitrosative stress, uncoupling, mitochondrial permeability transition, fusion, fission, biogenesis, and autophagy all may play key pathophysiologic roles. In this review we summarize the epidemiologic and clinical phenotypes of myocardial dysfunction in septic shock and post-cardiac arrest and the multifaceted manifestations of mitochondrial injury in these disease processes. Since neonatal and pediatric-specific data for mitochondrial dysfunction remain sparse, conclusive age-dependent differences are not clear; instead, we highlight what evidence exists and identify gaps in knowledge to guide future research. Finally, since focal ischemic injury (with or without reperfusion) leading to myocardial infarction is predominantly an atherosclerotic disease of the elderly, this review focuses specifically on septic shock and global ischemia-reperfusion injury occurring after resuscitation from cardiac arrest.

Dynamin-1-Like Protein Inhibition Drives Megamitochondria Formation as an Adaptive Response in Alcohol-Induced Hepatotoxicity

Despite the growing global burden of alcoholic liver diseases, therapeutic options are limited, and novel targets are urgently needed. Accumulating evidence suggests that mitochondria adapt in response to ethanol and formation of megamitochondria in the livers of patients is recognized as a hallmark of alcoholic liver diseases. The processes involved in ethanol-induced hepatic mitochondrial changes, the impact on mitochondria-shaping proteins, and the significance of megamitochondria formation remain unknown. In this study, we investigated the mitochondrial and cellular response to alcohol in hepatoma cell line VL-17A. The mitochondrial architecture rapidly changed after 3 or 14 days of ethanol exposure with double-pronged presentation of hyperfragmentation and megamitochondria, and cell growth was inhibited. Dynamin-1-like protein (Drp1) was identified as the main mediator driving these mitochondrial alterations, and its genetic inactivation was determined to foster megamitochondria development, preserving the capacity of the cells to grow despite alcohol toxicity. The role of Drp1 in mediating megamitochondria formation in mice with liver-specific inactivation of Drp1 was further confirmed. Finally, when these mice were fed with ethanol, the presentation of hepatic megamitochondria was exacerbated compared with wild type fed with the same diet. Ethanol-induced toxicity was also reduced. Our study demonstrates that megamitochondria formation is mediated by Drp1, and this phenomenon is a beneficial adaptive response during alcohol-induced hepatotoxicity.

Mdivi-1 and mitochondrial fission: recent insights from fungal pathogens

Mitochondrial fission shows potential as a therapeutic target in non-infectious human diseases. The compound mdivi-1 was identified as a mitochondrial fission inhibitor that acts against the evolutionarily conserved mitochondrial fission GTPase Dnm1/Drp1, and shows promising data in pre-clinical models of human pathologies. Two recent studies, however, found no evidence that mdivi-1 acts as a mitochondrial fission inhibitor and proposed other mechanisms. In mammalian cells, Bordt et al. showed that mdivi-1 inhibits complex I in mitochondria (Dev Cell 40:583, 2017). In a second study, we have recently demonstrated that mdivi-1 does not trigger a mitochondrial morphology change in the human yeast pathogen Candida albicans, but impacts on endogenous nitric oxide (NO) levels and inhibits the key virulence property of hyphal formation (Koch et al., Cell Rep 25:2244, 2018). Here we discuss recent insights into mdivi-1’s action in pathogenic fungi and the potential and challenges for repurposing it as an anti-infective. We also outline recent findings on the roles of mitochondrial fission in human and plant fungal pathogens, with the goal of starting the conversation on whether the research field of fungal pathogenesis can benefit from efforts in other disease areas aimed at developing therapeutic inhibitors of mitochondrial division.

Balancing mitochondrial dynamics via increasing mitochondrial fusion attenuates infarct size and left ventricular dysfunction in rats with cardiac ischemia/reperfusion injury

An uncontrolled balance of mitochondrial dynamics has been shown to contribute to cardiac dysfunction during ischemia/reperfusion (I/R) injury. Although inhibition of mitochondrial fission could ameliorate cardiac dysfunction, modulation of mitochondrial fusion by giving a fusion promoter at different time-points during cardiac I/R injury has never been investigated. We hypothesized that giving of a mitochondrial fusion promoter at different time-points exerts cardioprotection with different levels of efficacy in rats with cardiac I/R injury. Forty male Wistar rats were subjected to a 30-min ischemia by coronary occlusion, followed by a 120-min reperfusion. The rats were then randomly divided into control and three treated groups: pre-ischemia, during-ischemia, and onset of reperfusion. A pharmacological mitochondrial fusion promoter-M1 (2 mg/kg) was used for intervention. Reduced mitochondrial fusion protein was observed after cardiac I/R injury. M1 administered prior to ischemia exerted the highest level of cardioprotection by improving both cardiac mitochondrial function and dynamics regulation, attenuating incidence of arrhythmia, reducing infarct size and cardiac apoptosis, which led to the preservation of cardiac function and decreased mortality. M1 given during ischemia and on the onset of reperfusion also exerted cardioprotection, but with a lower efficacy than when given at the pre-ischemia time-point. Attenuating a reduction in mitochondrial fusion proteins during myocardial ischemia and at the onset of reperfusion exerted cardioprotection by attenuating mitochondrial dysfunction and dynamic imbalance, thus reducing infarct size and improving cardiac function. These findings indicate that it could be a promising intervention with the potential to afford cardioprotection in the clinical setting of acute myocardial infarction.

Biventricular Increases in Mitochondrial Fission Mediator (MiD51) and Proglycolytic Pyruvate Kinase (PKM2) Isoform in Experimental Group 2 Pulmonary Hypertension-Novel Mitochondrial Abnormalities

Introduction: Group 2 pulmonary hypertension (PH), defined as a mean pulmonary arterial pressure ≥25 mmHg with elevated pulmonary capillary wedge pressure >15 mmHg, has no approved therapy and patients often die from right ventricular failure (RVF). Alterations in mitochondrial metabolism, notably impaired glucose oxidation, and increased mitochondrial fission, contribute to right ventricle (RV) dysfunction in PH. We hypothesized that the impairment of RV and left ventricular (LV) function in group 2 PH results in part from a proglycolytic isoform switch from pyruvate kinase muscle (PKM) isoform 1 to 2 and from increased mitochondrial fission, due either to upregulation of expression of dynamin-related protein 1 (Drp1) or its binding partners, mitochondrial dynamics protein of 49 or 51 kDa (MiD49 or 51).

Methods and Results: Group 2 PH was induced by supra-coronary aortic banding (SAB) in 5-week old male Sprague Dawley rats. Four weeks post SAB, echocardiography showed marked reduction of tricuspid annular plane systolic excursion (2.9 ± 0.1 vs. 4.0 ± 0.1 mm) and pulmonary artery acceleration time (24.3 ± 0.9 vs. 35.4 ± 1.8 ms) in SAB vs. sham rats. Nine weeks post SAB, left and right heart catheterization showed significant biventricular increases in end systolic and diastolic pressure in SAB vs. sham rats (LV: 226 ± 15 vs. 103 ± 5 mmHg, 34 ± 5 vs. 7 ± 1 mmHg; RV: 40 ± 4 vs. 22 ± 1 mmHg, and 4.7 ± 1.5 vs. 0.9 ± 0.5 mmHg, respectively). Picrosirius red staining showed marked biventricular fibrosis in SAB rats. There was increased muscularization of small pulmonary arteries in SAB rats. Confocal microscopy showed biventricular mitochondrial depolarization and fragmentation in SAB vs. sham cardiomyocytes. Transmission electron microscopy confirmed a marked biventricular reduction in mitochondria size in SAB hearts. Immunoblot showed marked biventricular increase in PKM2/PKM1 and MiD51 expression. Mitofusin 2 and mitochondrial pyruvate carrier 1 were increased in SAB LVs.

Conclusions: SAB caused group 2 PH. Impaired RV function and RV fibrosis were associated with increases in mitochondrial fission and expression of MiD51 and PKM2. While these changes would be expected to promote increased production of reactive oxygen species and a glycolytic shift in metabolism, further study is required to determine the functional consequences of these newly described mitochondrial abnormalities.

Mesenchymal Stem Cells Shift Mitochondrial Dynamics and Enhance Oxidative Phosphorylation in Recipient Cells

Mesenchymal stem cells (MSCs) are the most commonly used cells in tissue engineering and regenerative medicine. MSCs can promote host tissue repair through several different mechanisms including donor cell engraftment, release of cell signaling factors, and the transfer of healthy organelles to the host. In the present study, we examine the specific impacts of MSCs on mitochondrial morphology and function in host tissues. Employing in vitro cell culture of inherited mitochondrial disease and an in vivo animal experimental model of low-grade inflammation (high fat feeding), we show human-derived MSCs to alter mitochondrial function. MSC co-culture with skin fibroblasts from mitochondrial disease patients rescued aberrant mitochondrial morphology from a fission state to a more fused appearance indicating an effect of MSC co-culture on host cell mitochondrial network formation. In vivo experiments confirmed mitochondrial abundance and mitochondrial oxygen consumption rates were elevated in host tissues following MSC treatment. Furthermore, microarray profiling identified 226 genes with differential expression in the liver of animals treated with MSC, with cellular signaling, and actin cytoskeleton regulation as key upregulated processes. Collectively, our data indicate that MSC therapy rescues impaired mitochondrial morphology, enhances host metabolic capacity, and induces widespread host gene shifting. These results highlight the potential of MSCs to modulate mitochondria in both inherited and pathological disease states.

Mitochondrial quality control in cardiac cells: Mechanisms and role in cardiac cell injury and disease

Mitochondria play an important role in maintaining cardiac homeostasis by supplying the major energy required for cardiac excitation-contraction coupling as well as controlling the key intracellular survival and death pathways. Healthy mitochondria generate ATP molecules through an aerobic process known as oxidative phosphorylation (OXPHOS). Mitochondrial injury during myocardial infarction (MI) impairs OXPHOS and results in the excessive production of reactive oxygen species (ROS), bioenergetic insufficiency, and contributes to the development of cardiovascular diseases. Therefore, mitochondrial biogenesis along with proper mitochondrial quality control machinery, which removes unhealthy mitochondria is pivotal for mitochondrial homeostasis and cardiac health. Upon damage to the mitochondrial network, mitochondrial quality control components are recruited to segregate the unhealthy mitochondria and target aberrant mitochondrial proteins for degradation and elimination. Impairment of mitochondrial quality control and accumulation of abnormal mitochondria have been reported in the pathogenesis of various cardiac disorders and heart failure. Here, we provide an overview of the recent studies describing various mechanistic pathways underlying mitochondrial homeostasis with the main focus on cardiac cells. In addition, this review demonstrates the potential effects of mitochondrial quality control dysregulation in the development of cardiovascular disease.

Three-dimensional electron microscopy techniques for unravelling mitochondrial dysfunction in heart failure and identification of new pharmacological targets

A hallmark of heart failure is mitochondrial dysfunction leading to a bioenergetics imbalance in the myocardium. Consequently, there is much interest in targeting mitochondrial abnormalities to attenuate the pathogenesis of heart failure. This review discusses (i) how electron microscopy (EM) techniques have been fundamental for the current understanding of mitochondrial structure–function, (ii) the paradigm shift in resolutions now achievable by 3‐D EM techniques due to the introduction of direct detection devices and phase plate technology, and (iii) the application of EM for unravelling mitochondrial pathological remodelling in heart failure. We further consider the tremendous potential of multi‐scale EM techniques for the development of therapeutics, structure‐based ligand design and for delineating how a drug elicits nanostructural effects at the molecular, organelle and cellular levels. In conclusion, 3‐D EM techniques have entered a new era of structural biology and are poised to play a pivotal role in discovering new therapies targeting mitochondria for treating heart failure.

Linked Articles

This article is part of a themed section on Mitochondrial Pharmacology: Featured Mechanisms and Approaches for Therapy Translation. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.22/issuetoc

Inhibition of mitochondrial fission as a novel therapeutic strategy to reduce mortality upon myocardial infarction

Ischemia reperfusion (I/R) injury is a common event following myocardial infarction (MI) resulting in excessive oxidative stress, calcium overload, inflammation, and cardiomyocyte death. Mitochondrial homeostasis including their dynamics are imbalanced in cardiac I/R injury in favor of increased mitochondrial fission. Inhibition of mitochondrial fission prior to I/R injury is protective and improves cardiac function following MI. Clinically, patients with MI often receive treatment following initiation of the ischemic event. Thus, treatments with more realistic timing would have better translational value and are important to research. In a recent study published in Clinical Science, Maneechote et al. [Clin. Sci. (2018) 132, 1669-1683] examined the effect of inhibiting mitochondrial fission using the mitochondrial division inhibitor (Mdivi-1) at different time points, pre-ischemia, during-ischemia, and upon onset of reperfusion, in a rat cardiac I/R model. The findings showed the greatest cardiac function improvement with pre-ischemia treatment along with decreased mitochondrial fragmentation and increased mitochondrial function. Mdivi-1 given during ischemia and at onset of reperfusion also improved cardiac function, but to a lesser extent than pre-ischemia intervention. Maneechote et al. postulated that the LV protection by Mdivi-1 in cardiac I/R could be due to an improvement in mitochondrial dysfunction through attenuating excessive mitochondrial fission which then reduces apoptotic myocytes. Their findings provide new insights into future treatment of patients suffering acute MI which could consider targetting the excessive mitochondrial fission during cardiac ischemia or at onset of reperfusion. Here, we will further discuss the background of the study, potential molecular mechanisms of mitochondrial fission, consequences of the fission, and future research directions.

Differential temporal inhibition of mitochondrial fission by Mdivi-1 exerts effective cardioprotection in cardiac ischemia/reperfusion injury

Altered cardiac mitochondrial dynamics with excessive fission is a predominant cause of cardiac dysfunction during ischemia/reperfusion (I/R) injury. Although pre-ischemic inhibition of mitochondrial fission has been shown to improve cardiac function in I/R injury, the effects of this inhibitor given at different time-points during cardiac I/R injury are unknown. Fifty male Wistar rats were subjected to sham and cardiac I/R injury. For cardiac I/R injury, rats were randomly divided into pre-ischemia, during-ischemia, and upon onset of reperfusion group. A mitochondrial fission inhibitor, Mdivi-1 (mitochondrial division inhibitor 1) (1.2 mg/kg) was used. During I/R protocols, the left ventricular (LV) function, arrhythmia score, and mortality rate were determined. Then, the heart was removed to determine infarct size, mitochondrial function, mitochondrial dynamics, and apoptosis. Our results showed that Mdivi-1 given prior to ischemia, exerted the highest level of cardioprotection quantitated through the attenuated incidence of arrhythmia, reduced infarct size, improved cardiac mitochondrial function and fragmentation, and decreased cardiac apoptosis, leading to preserved LV function during I/R injury. Mdivi-1 administered during ischemia and upon the onset of reperfusion also improved cardiac mitochondrial function and LV function, but at a lower efficacy than when it was given prior to ischemia. Taken together, mitochondrial fission inhibition after myocardial ischemic insults still exerts cardioprotection by attenuating mitochondrial dysfunction and dynamic imbalance, leading to decreased infarct size and ultimately improved LV function after acute cardiac I/R injury in rats. These findings indicate its potential clinical usefulness.

Potential mechanisms responsible for cardioprotective effects of sodium-glucose co-transporter 2 inhibitors

Diabetes mellitus currently affects over 350 million patients worldwide and is associated with many deaths from cardiovascular complications. Sodium-glucose co-transporter 2 (SGLT-2) inhibitors are a novel class of antidiabetic drugs with cardiovascular benefits beyond other antidiabetic drugs. In the EMPA-REG OUTCOME trial, empagliflozin significantly decreases the mortality rate from cardiovascular causes [38% relative risk reduction (RRR)], the mortality rate from all-causes (32% RRR) and the rate of heart failure hospitalization (35% RRR) in diabetic patients with established cardiovascular diseases. The possible mechanisms of SGLT-2 inhibitors are proposed to be systemic effects by hemodynamic and metabolic actions. However, the direct mechanisms are not fully understood. In this review, reports concerning the effects of SGLT-2 inhibitors in models of diabetic cardiomyopathy, heart failure and myocardial ischemia from in vitro, in vivo as well as clinical reports are comprehensively summarized and discussed. By current evidences, it may be concluded that the direct effects of SGLT-2 inhibitors are potentially mediated through their ability to reduce cardiac inflammation, oxidative stress, apoptosis, mitochondrial dysfunction and ionic dyshomeostasis.

Increased Drp1-Mediated Mitochondrial Fission Promotes Proliferation and Collagen Production by Right Ventricular Fibroblasts in Experimental Pulmonary Arterial Hypertension

Introduction: Right ventricular (RV) fibrosis contributes to RV failure in pulmonary arterial hypertension (PAH). The mechanisms underlying RV fibrosis in PAH and the role of RV fibroblasts (RVfib) are unknown. Activation of the mitochondrial fission mediator dynamin-related protein 1 (Drp1) contributes to dysfunction of RV myocytes in PAH through interaction with its binding partner, fission protein 1 (Fis1). However, the role of mitochondrial fission in RVfib and RV fibrosis in PAH is unknown. Objective: We hypothesize that mitochondrial fission is increased in RVfib of rats with monocrotaline (MCT)-induced PAH. We evaluated the contribution of Drp1 and Drp1-Fis1 interaction to RVfib proliferation and collagen production in culture and to RV fibrosis in vivo. Methods: Vimentin (+) RVfib were enzymatically isolated and cultured from the RVs of male Sprague-Dawley rats that received MCT (60 mg/kg) or saline. Mitochondrial morphology, proliferation, collagen production, and expression of Drp1, Drp1 binding partners and mitochondrial fusion mediators were measured. The Drp1 inhibitor mitochondrial division inhibitor 1 (Mdivi-1), P110, a competitive peptide inhibitor of Drp1-Fis1 interaction, and siRNA targeting Drp1 were assessed. Subsequently, prevention and regression studies tested the antifibrotic effects of P110 (0.5 mg/kg) in vivo. At week 4 post MCT, echocardiography and right heart catheterization were performed. The RV was stained for collagen. Results: Mitochondrial fragmentation, proliferation rates and collagen production were increased in MCT-RVfib versus control-RVfib. MCT-RVfib had increased expression of activated Drp1 protein and a trend to decreased mitofusin-2 expression. Mdivi-1 and P110 inhibited mitochondrial fission, proliferation and collagen III expression in MCT-RVfib. However, P110 was only effective at high doses (1 mM). siDrp1 also reduced fission in MCT-RVfib. Despite promising results in cell therapy, in vivo therapy with P110 failed to prevent or regress RV fibrosis in MCT rats, perhaps due to failure to achieve adequate P110 levels or to the greater importance of interaction of Drp1 with other binding partners. Conclusion: PAH RVfib have increased Drp1-mediated mitochondrial fission. Inhibiting Drp1 prevents mitochondrial fission and reduces RVfib proliferation and collagen production. This is the first description of disordered mitochondrial dynamics in RVfib and suggests that Drp1 is a potential new antifibrotic target.

Inhibition of dynamin-related protein 1 has neuroprotective effect comparable with therapeutic hypothermia in a rat model of cardiac arrest

Dynamin-related protein 1 (Drp1) regulates mitochondrial fission, it has been proven that inhibition of Drp1 by mdivi-1 improves survival and attenuates cerebral ischemic injury after cardiac arrest. In this study, we compared the effects of Drp1 inhibition with therapeutic hypothermia on post-resuscitation neurologic injury in a rat model of cardiac arrest. Rats were randomized into 4 groups: mdivi-1 treatment group (n = 39), hypothermic group (n = 38), normothermic group (n = 41), and sham group (n = 12). The rats in the mdivi-1 treatment group were received intravenously 1.2 mg/kg of mdivi-1 at 1 minute after the return of spontaneous circulation (ROSC). In rats in hypothermia group, rapid cooling was initiated at 5 minutes after resuscitation, and the core temperature was maintained to 33 ± 0.5°C for 2 hours. The results showed that both Drp1 inhibition and therapeutic hypothermia increased 3-day survival time (all P <0.05) and improved neurologic function up to 72 hours post cardiac arrest. In addition, both Drp1 inhibition and therapeutic hypothermia decreased cell injury, apoptosis in hippocampal cornu ammonis 1 region and brain mitochondrial dysfunction including adenosine triphosphate production, reactive oxygen species and mitochondrial membrane potential after cardiac arrest. Moreover, therapeutic hypothermia decreased mitochondrial Drp1 expression and mitochondrial fission after cardiac arrest. In conclusion, inhibition of Drp1 has a similar effect to therapeutic hypothermia on neurologic outcome after resuscitation in this cardiac arrest rat model, and the neuroprotective effects of therapeutic hypothermia are associated with inhibition of mitochondrial fission.

Cardioprotection of dapagliflozin and vildagliptin in rats with cardiac ischemia-reperfusion injury

Sodium-glucose cotransporter 2 inhibitor (SGLT2-i) effects on cardiac ischemia/reperfusion (I/R) injury are unclear. Unlike SGLT2-i, dipeptidyl peptidase 4 inhibitors (DPP4-i) have shown effective cardioprotection in cardiac I/R injury. We aimed to investigate whether SGLT2-i reduces myocardial dysfunction and myocardial injury to a greater extent than DPP4-i in obese insulin-resistant rats with/without cardiac I/R injury. The high-fat (HF) diet-induced obese insulin-resistant rats were divided into 4 groups and received the following treatments for 28 days: vehicle (HFV); vildagliptin at a dosage of 3 mg/kg/day (HFVil); dapagliflozin at a dosage of 1 mg/kg/day (HFDa) and combination drugs (HFDaVil). At the end, I/R injury was induced by a 30-min left anterior descending coronary occlusion and 120-min reperfusion. Dapagliflozin showed a greater efficacy than vildagliptin in improving the metabolic impairments, low frequency/high frequency (LF/HF) ratio, systolic blood pressure and left ventricular (LV) function in comparison to HFV rats. In cardiac I/R injury, dapagliflozin had a greater efficacy than vildagiptin in decreasing mitochondrial DRP1, cleaved caspase 3, LV dysfunction and infarct size in comparison to HFV rats. However, the combined therapy showed the greatest efficacy in attenuating LV dysfunction, mitochondrial DRP1 and infarct size in comparison to HFV rats. In conclusion, dapagliflozin has a more pronounced effect than vildagliptin in obese insulin-resistant rats for the improvement of LV function. In rats with cardiac I/R injury, although dapagliflozin had a greater efficacy on cardioprotection than vildagliptin, the combined therapy exerted the highest cardioprotective effects potentially by reducing mitochondrial fission.

Dynamic Changes of Mitochondrial Fusion and Fission in Brain Injury after Cardiac Arrest in Rats

Mitochondria change their morphology dynamically by continual fusion and fission processes to fulfill their function. However, little is known about the effect of cardiac arrest on mitochondrial dynamics. This study aimed to investigate time-dependent change of the mitochondrial dynamics after brain ischemic injury in rats of cardiac arrest. After resuscitation, obvious neuronal injury, reduced adenosine triphosphate (ATP) levels, excessive reactive oxygen species (ROS) generation, decreased mitochondrial membrane potential (MMP), and increased release of mitochondrial cytochrome c were observed at 12 h and 24 h after cardiac arrest. Moreover, we found that elongation of mitochondria was observed at 4 h after cardiac arrest, whereas fragmented mitochondria were significantly increased, along with concomitant increase in the fission proteins Drp1 and Fis1 and a reduction in the fusion proteins Mfn1 and Mfn2 at 12 h and 24 h after cardiac arrest. Taken together, these findings suggest that imbalance in mitochondrial dynamics probably contributes to brain injury after cardiac arrest.