Mechanistically distinct steps in the mitochondrial death pathway triggered by oxidative stress in cardiac myocytes

FDA approved L-type channel blocker Nifedipine reduces cell death in hypoxic A549 cells through modulation of mitochondrial calcium and superoxide generation

As hypoxia is a major driver for the pathophysiology of COVID-19, it is crucial to characterize the hypoxic response at the cellular and molecular levels. In order to augment drug repurposing with the identification of appropriate molecular targets, investigations on therapeutics preventing hypoxic cell damage is required. In this work, we propose a hypoxia model based on alveolar lung epithelial cells line using chemical inducer, CoCl₂ that can be used for testing calcium channel blockers (CCBs). Since recent studies suggested that CCBs may reduce the infectivity of SARS-Cov-2, we specifically select FDA approved calcium channel blocker, nifedipine for the study. First, we examined hypoxia-induced cell morphology and found a significant increase in cytosolic calcium levels, mitochondrial calcium overload as well as ROS production in hypoxic A549 cells. Secondly, we demonstrate the protective behaviour of nifedipine for cells that are already subjected to hypoxia through measurement of cell viability as well as 4D imaging of cellular morphology and nuclear condensation. Thirdly, we show that the protective effect of nifedipine is achieved through the reduction of cytosolic calcium, mitochondrial calcium, and ROS generation. Overall, we outline a framework for quantitative analysis of mitochondrial calcium and ROS using 3D imaging in laser scanning confocal microscopy and the open-source image analysis platform ImageJ. The proposed pipeline was used to visualize mitochondrial calcium and ROS level in individual cells that provide an understanding of molecular targets. Our findings suggest that the therapeutic value of nifedipine may potentially be evaluated in the context of COVID-19 therapeutic trials.

MicroRNA-210 repression facilitates advanced glycation end-product (AGE)-induced cardiac mitochondrial dysfunction and apoptosis via JNK activation

Hyperglycemia results in the formation of reactive oxygen species which in turn causes advanced glycation end products (AGEs) formation, leading to diabetic cardiomyopathy. Our previous study showed that AGE-induced reactive oxygen species-dependent apoptosis is mediated via protein kinase C delta (PKCδ)-enhanced mitochondrial damage in cardiomyocytes. By using microRNA (miRNA) database, miRNA-210 was predicted to target c-Jun N-terminal kinase (JNK), which were previously identified as downstream of PKCδ in regulating mitochondrial function. Therefore, we hypothesized that miR-210 mediates PKCδ-dependent upregulation of JNK to cause cardiac mitochondrial damage and apoptosis following AGE exposure. AGE-exposed cells showed activated cardiac JNK, PKCδ, and apoptosis, which were reversed by treatment with a JNK inhibitor and PKCδ-KD (deficient kinase). Cardiac miR-210 and mitochondrial function were downregulated following AGE exposure. Furthermore, JNK was upregulated and involved in AGE-induced mitochondrial damage. Interestingly, luciferase activity of the miR-210 mimic plus JNK WT-3'-untranslated region overexpressed group was significantly lower than that of miR-210 mimic plus JNK MT-3'UTR group, indicating that JNK is a target of miR-210. Moreover, JNK activation induced by AGEs was reduced by treatment with the miR-210 mimic and reversed by treatment with the miR-210 inhibitor, indicating the regulatory function of miR-210 in JNK activation following AGE exposure. Additionally, JNK-dependent mitochondrial dysfunction and apoptosis were reversed following treatment with the miR-210 mimic, while the miR-210 inhibitor showed no effect on JNK-induced mitochondrial dysfunction and apoptosis in AGE-exposed cardiac cells. Taken together, our study showed that PKCδ-enhanced JNK-dependent mitochondrial damage is mediated through the reduction of miR-210 in cardiomyocytes following AGE exposure.

Atypical antipsychotics and oxidative cardiotoxicity: review of literature and future perspectives to prevent sudden cardiac death

Oxidative stress is considered the principal mediator of myocardial injury under pathological conditions. It is well known that reactive oxygen (ROS) or nitrogen species (RNS) are involved in myocardial injury and repair at the same time and that cellular damage is generally due to an unbalance between generation and elimination of the free radicals due to an inadequate mechanism of antioxidant defense or to an increase in ROS and RNS. Major adverse cardiovascular events are often associated with drugs with associated findings such as fibrosis or inflammation of the myocardium. Despite efforts in the preclinical phase of the development of drugs, cardiotoxicity still remains a great concern. Cardiac toxicity due to second-generation antipsychotics (clozapine, olanzapine, quetiapine) has been observed in preclinical studies and described in patients affected with mental disorders. A role of oxidative stress has been hypothesized but more evidence is needed to confirm a causal relationship. A better knowledge of cardiotoxicity mechanisms should address in the future to establish the right dose and length of treatment without impacting the physical health of the patients.

Metabolic Control by Heat Stress Determining Cell Fate to Ferroptosis for Effective Cancer Therapy

Flexible manipulation of the fate of cancer cells through exogenous stimulation-induced metabolic reprogramming could handle the cellular plasticity-derived therapies resistance, which provides an effective paradigm for the treatment of refractory and relapsing tumors in clinical settings. Herein, we demonstrated that moderate heat (45 °C) could significantly regress the expression of antioxidants and trigger specific lipid metabolic reprogramming in cancer cells synergized with iron oxide nanoparticles (Fe₃O₄ NPs). This metabolic control behavior destroyed the tumor redox homeostasis and produced overwhelming lipid peroxides, consequently sensitizing the tumor to ferroptosis. Based on these findings, a heat-triggered tumor-specific ferroptosis strategy was proposed by the rational design of a polypeptide-modified and 1H-perfluoropentane (1H-PFP)-encapsulated Fe₃O₄-containing nanoformulation (GBP@Fe₃O₄). When irradiated by an 808 nm laser, the phase transition of 1H-PFP was triggered by localized moderate heat (45 °C), leading to burst release of Fe₃O₄in situ to produce potent reactive oxygen species through the Fenton reaction in the tumor microenvironment. Together with the antioxidant inhibition response and distinctive lipid metabolic reprogramming by heat stress, this oxidative damage was amplified to induce tumor ferroptosis and achieve sufficient antitumor effects. Importantly, we confirmed that ACSBG1, an acyl-CoA synthetase, was the key pro-ferroptotic factor in this heat-induced ferroptosis process. Moreover, knockout of this gene could realize cancer cell death fate conversion from ferroptosis to non-ferroptotic death. This work provides mechanistic insights and practical strategies for heat-triggered ferroptosis in situ to reduce the potential side effects of direct ferroptosis inducers and highlights the key factor in regulating cell fate under heat stress.

Norwogonin attenuates hypoxia-induced oxidative stress and apoptosis in PC12 cells

Background

Norwogonin is a natural flavone with three phenolic hydroxyl groups in skeletal structure and has excellent antioxidant activity. However, the neuroprotective effect of norwogonin remains unclear. Here, we investigated the protective capacity of norwogonin against oxidative damage elicited by hypoxia in PC12 cells.

Methods

The cell viability and apoptosis were examined by MTT assay and Annexin V-FITC/PI staining, respectively. Reactive oxygen species (ROS) content was measured using DCFH-DA assay. Lactate dehydrogenase (LDH), malondialdehyde (MDA) and antioxidant enzyme levels were determined using commercial kits. The expression of related genes and proteins was measured by real-time quantitative PCR and Western blotting, respectively.

Results

We found that norwogonin alleviated hypoxia-induced injury in PC12 cells by increasing the cell viability, reducing LDH release, and ameliorating the changes of cell morphology. Norwogonin also acted as an antioxidant by scavenging ROS, reducing MDA production, maintaining the activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx), and decreasing the expression levels of HIF-1α and VEGF. In addition, norwogonin prevented cell apoptosis via inhibiting the expression levels of caspase-3, cytochrome c and Bax, while increasing the expression levels of Bcl-2 and the ratio of Bcl-2/Bax.

Conclusions

Norwogonin attenuates hypoxia-induced injury in PC12 cells by quenching ROS, maintaining the activities of antioxidant enzymes, and inhibiting mitochondrial apoptosis pathway.

Mitochondrial dynamics modulation as a critical contribution for Shenmai injection in attenuating hypoxia/reoxygenation injury

ETHNOPHARMACOLOGICAL RELEVANCE

Shenmai injection (SMI) is a CFDA-approved and widely prescribed herbal medicine injection in China for treating cardiac dysfunction, especially myocardial ischemia and reperfusion (I/R) injury. However, despite of its known clinical efficacy, the cardioprotective mechanisms of SMI remain to be established.

AIM OF STUDY

The present study aimed to investigate the role of SMI on mitophagy and mitochondrial dynamics in cardiomyocytes with a hypoxia/reperfusion (H/R) injury setting.

MATERIALS AND METHODS

H9c2 cardiomyocytes were subjected to 12 h of hypoxia followed by 2 h of reoxygenation to induce cellular injury. Multi-parameter imaging analysis was performed using Operetta High Content Imaging System to detect changes in mitochondrial function and morphological texture. The mPTP opening was directly assessed by analyzing mitochondrial calcein release in H9c2 and by Ca²⁺-induced swelling of isolated cardiac mitochondria. Mitochondrial respiration was measured by XF 24 analyzer of Seahorse Bioscience. RT-PCR and Western blotting analyses were used to detect mitophagy, mitochondrial fusion and fission biomarkers at the gene and protein levels.

RESULTS

Pretreatment of SMI significantly improved myocardial cell survival and protected against H/R-induced deterioration of mitochondrial structure and function, as evidenced by decreased mitochondrial mass and cytosolic Ca²⁺, increased mitochondrial membrane potential (ΔΨ_m) and mitochondrial morphology by SER Texture analysis, inhibited mPTP opening in H9c2 cells and isolated cardiac mitochondria, and alleviated severely impaired mitochondrial respiration. Mechanistically, SMI attenuated H/R injury by inducing mitophagy and then modulated mitochondrial dynamics as indicated by a significantly increased expression of LC3, Beclin 1, Parkin and Pink, and the inhibition of excessive mitochondria fission and increased mitochondrial fusion. Finally, the cardioprotective effect of SMI was confirmed in a LAD-induced cardiac dysfunction model in vivo.

CONCLUSION

We found that alleviation of H/R injury by pretreatment with SMI may be attributable to inducing mitophagy and modulating mitochondrial dynamics in cardiomyocytes, thereby providing a rationale for future clinical applications and potential mitoprotective therapy for MI/R injury.

Screening and analysis of key active constituents in Guanxinshutong capsule using mass spectrum and integrative network pharmacology

Guanxinshutong capsule (GXSTC) is an effective and safe traditional Chinese medicine used in the treatment of cardiovascular diseases (CVDs) for many years. However, the targets of this herbal formula and the underlying molecular mechanisms of action involved in the treatment of CVDs are still unclear. In the present study, we used a systems pharmacology approach to identify the active ingredients of GXSTC and their corresponding targets in the calcium signaling pathway with respect to the treatment of CVDs. This method integrated chromatographic techniques, prediction of absorption, distribution, metabolism, and excretion, analysis using Kyoto Encyclopedia of Genes and Genomes, network construction, and pharmacological experiments. 12 active compounds and 33 targets were found to have a role in the treatment of CVDs, and four main active ingredients, including protocatechuic acid, cryptotanshinone, eugenol, and borneol were selected to verify the effect of (GXSTC) on calcium signaling system in cardiomyocyte injury induced by hypoxia and reoxygenation. The results from the present study revealed the active components and targets of GXSTC in the treatment of CVDs, providing a new perspective to enhance the understanding of the role of the calcium signaling pathway in the therapeutic effect of GXSTC.

Arginase II inhibition prevents interleukin-8 production through regulation of p38 MAPK phosphorylation activated by loss of mitochondrial membrane potential in nLDL-stimulated hAoSMCs

Arginase inhibition exhibits beneficial effects in vascular endothelial and smooth muscle cells. In human aortic smooth muscle cells (hAoSMCs), native low-density lipoprotein (nLDL) induced the production of interleukin-8 (IL-8) that is involved in the pathogenesis of cardiovascular diseases. Therefore, we examined the effect of arginase inhibition on IL-8 production and the underlying mechanism. In hAoSMCs, reverse transcription–PCR, western blotting and immunocytochemistry with MitoTracker confirmed that arginase II was confined predominantly to mitochondria. The mitochondrial membrane potential (MMP) was assessed using tetramethylrhodamine ethyl ester. The MMP decreased upon nLDL stimulation but was restored upon arginase inhibition. MMP loss caused by nLDL was prevented by treatment with the intracellular Ca²⁺ chelator BAPTA-AM. In mitochondrial Ca²⁺ measurements using Rhod-2 AM, increased mitochondrial Ca²⁺ levels by nLDL were inhibited upon preincubation with an arginase inhibitor. Among the polyamines, spermine, an arginase activity-dependent product, caused mitochondrial Ca²⁺ movement. The nLDL-induced MMP change resulted in p38 mitogen-activated protein kinase (MAPK) phosphorylation and IL-8 production and was prevented by the arginase inhibitors BAPTA and ruthenium 360. In isolated AoSMCs from ApoE^−/− mice fed a high-cholesterol diet, arginase activity, p38 MAPK phosphorylation, spermine and mitochondrial Ca²⁺ levels and keratinocyte-derived chemokine (KC) production were increased compared with wild-type (WT) mice. However, in AoSMCs isolated from arginase II-null mice, increases in MMP and decreases in mitochondrial Ca²⁺ levels were noted compared with WT and were associated with p38 MAPK activation and IL-8 production. These data suggest that arginase activity regulates the change in MMP through Ca²⁺ uptake that is essential for p38 MAPK phosphorylation and IL-8 production.

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.

A critical courier role of volatile oils from Dalbergia odorifera for cardiac protection in vivo by QiShenYiQi

Component-based Chinese medicine (CCM) is derived from traditional Chinese medicine but produced with modern pharmaceutical standard and clearer clinical indications. However, it still faces challenges of defining individual component contribution in the complex formula. Using QiShenYiQi (QSYQ) as a model CCM, we investigated the role of Dalbergia odorifera (DO), an herbal component, in preventing myocardial damage. We showed that in vitro, QSYQ exerted considerable protective activities on cardiomyocytes from H₂O₂-induced mitochondrial dysfunction with or without DO. However, in isolated rat hearts, myocardial protection by QSYQ was significantly weakened without DO. In everted gut sac model, DO significantly enhanced absorption of the major QSYQ ingredients in different regions of rat intestine. Finally, in in vivo mouse model of doxorubicin (DOX)-induced myocardial damage, only QSYQ, but not QiShenYiQi without DO (QSYQ-DO), exerted a full protection. Taken together, our results showed that instead of directly contributing to the myocardial protection, Dalbergia odorifera facilitates the major active ingredients absorption and increases their efficacy, eventually enhancing the in vivo potency of QSYQ. These findings may shed new lights on our understanding of the prescription compatibility theory, as well as the impacts of “courier herbs” in component-based Chinese medicine.

Identity and function of a cardiac mitochondrial small conductance Ca2+-activated K+ channel splice variant

We provide evidence for location and function of a small conductance, Ca2+-activated K+ (SKCa) channel isoform 3 (SK3) in mitochondria (m) of guinea pig, rat and human ventricular myocytes. SKCa agonists protected isolated hearts and mitochondria against ischemia/reperfusion (IR) injury; SKCa antagonists worsened IR injury. Intravenous infusion of a SKCa channel agonist/antagonist, respectively, in intact rats was effective in reducing/enhancing regional infarct size induced by coronary artery occlusion. Localization of SK3 in mitochondria was evidenced by Western blot of inner mitochondrial membrane, immunocytochemical staining of cardiomyocytes, and immunogold labeling of isolated mitochondria. We identified a SK3 splice variant in guinea pig (SK3.1, aka SK3a) and human ventricular cells (SK3.2) by amplifying mRNA, and show mitochondrial expression in mouse atrial tumor cells (HL-1) by transfection with full length and truncated SK3.1 protein. We found that the N-terminus is not required for mitochondrial trafficking but the C-terminus beyond the Ca2+ calmodulin binding domain is required for Ca2+ sensing to induce mK+ influx and/or promote mitochondrial localization. In isolated guinea pig mitochondria and in SK3 overexpressed HL-1 cells, mK+ influx was driven by adding CaCl2. Moreover, there was a greater fall in membrane potential (ΔΨm), and enhanced cell death with simulated cell injury after silencing SK3.1 with siRNA. Although SKCa channel opening protects the heart and mitochondria against IR injury, the mechanism for favorable bioenergetics effects resulting from SKCa channel opening remains unclear. SKCa channels could play an essential role in restraining cardiac mitochondria from inducing oxidative stress-induced injury resulting from mCa2+ overload.

Unique morphological characteristics of mitochondrial subtypes in the heart: the effect of ischemia and ischemic preconditioning

RATIONALE

Three subsets of mitochondria have been described in adult cardiomyocytes - intermyofibrillar (IMF), subsarcolemmal (SSM), and perinuclear (PN). They have been shown to differ in physiology, but whether they also vary in morphological characteristics is unknown. Ischemic preconditioning (IPC) is known to prevent mitochondrial dysfunction induced by acute myocardial ischemia/reperfusion injury (IRI), but whether IPC can also modulate mitochondrial morphology is not known.

AIMS

Morphological characteristics of three different subsets of adult cardiac mitochondria along with the effect of ischemia and IPC on mitochondrial morphology will be investigated.

METHODS

Mouse hearts were subjected to the following treatments (N=6 for each group): stabilization only, IPC (3x5 min cycles of global ischemia and reperfusion), ischemia only (20 min global ischemia); and IPC and ischemia. Hearts were then processed for electron microscopy and mitochondrial morphology was assessed subsequently.

RESULTS

In adult cardiomyocytes, IMF mitochondria were found to be more elongated and less spherical than PN and SSM mitochondria. PN mitochondria were smaller in size when compared to the other two subsets. SSM mitochondria had similar area to IMF mitochondria but their sphericity measures were similar to PN mitochondria. Ischemia was shown to increase the sphericity parameters of all 3 subsets of mitochondria; reduce the length of IMF mitochondria, and increase the size of PN mitochondria. IPC had no effect on mitochondrial morphology either at baseline or after ischemia.

CONCLUSION

The three subsets of mitochondria in the adult heart are morphologically different. IPC does not appear to modulate mitochondrial morphology in adult cardiomyocytes.

Four Main Active Ingredients Derived from a Traditional Chinese Medicine Guanxin Shutong Capsule Cause Cardioprotection during Myocardial Ischemia Injury Calcium Overload Suppression

Guanxin Shutong capsule is a traditional Chinese medicine for the treatment of myocardial ischemia (MI). Previous studies have shown that the formula has four main active ingredients (FMAI), protocatechuic acid, cryptotanshinone, borneol, and eugenol. However, the mechanisms of action of these FMAI against MI injury are still not well known. The aim of the present study was to evaluate the protective effects of the FMAI on MI in vitro and in vivo. In vitro, rat neonatal cardiomyocytes were isolated, the cell viability and apoptosis rate were, respectively, measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method and fluorescence activating cell sorter, and the intracellular calcium concentration ([Ca²⁺ ]_i ) and CaM and CaMKII δ mRNA as well as protein levels were determined. Meanwhile, their downstream targets of RyR2 and PLB were also measured by western blot. In vivo, a rat model of coronary artery ligation was used to evaluate the cardioprotective effects. Infarct sizes of heart tissues and levels of serum biochemical indicators, including creatine kinase, lactate dehydrogenase, superoxide dismutase, and glutamate oxaloacetic transaminase, were measured. The in vitro results showed that the FMAI inhibited cell apoptosis, reduced [Ca²⁺ ]_i , decreased the expression of CaM and CaMKII δ, and increased the expression of RyR2 and PLB. In vivo, the FMAI diminished infract size, reduced creatine kinase, lactate dehydrogenase, and aspartate aminotransferase levels, and enhanced superoxide dismutase activity. In conclusion, our data suggest that the FMAI suppressed calcium overload and exerted its protective effect via its antioxidant, antiinflammatory, and anti-apoptosis activities. Copyright © 2017 John Wiley & Sons, Ltd.

Inhibiting c-Jun N-terminal kinase partially attenuates caffeine-dependent cell death without alleviating the caffeine-induced reduction in mitochondrial respiration in C2C12 skeletal myotubes

Caffeine is a widely consumed stimulant that has previously been shown to promote cytotoxic stress and even cell death in numerous mammalian cell lines. Thus far there is little information available regarding the toxicity of caffeine in skeletal muscle cells. Our preliminary data revealed that treating C2C12 myotubes with 5 mM caffeine for 6 h increased nuclear fragmentation and reduced basal and maximal oxygen consumption rate (OCR) in skeletal myotubes. The purpose of this study was to further elucidate the pathways by which caffeine increased cell death and reduced mitochondrial respiration. We specifically examined the role of c-Jun N-terminal kinase (JNK), which has previously been shown to simultaneously increase caspase-dependent cell death and reduce mitochondrial respiration in other mammalian cell lines. We found that caffeine promoted a dose-dependent increase in cell death in multinucleated myotubes but did not in mononucleated myoblasts. The addition of 10 μM Z-DEVD-FMK, a specific inhibitor of executioner caspases, completely inhibited caffeine-dependent cell death. Further, the addition of 400 μM dantrolene, a specific ryanodine receptor (RYR) inhibitor, prevented the caffeine-dependent increase in cell death and the reduction in basal and maximal OCR. We also discovered that caffeine treatment significantly increased the phosphorylation of JNK and that the addition of 30 μM SP600125 (JNKi), a specific JNK inhibitor, partially attenuated caffeine-induced cell death without preventing the caffeine-dependent reduction in basal and maximal OCR. Our results suggest that JNK partially mediates the increase in caspase-dependent cell death but does not contribute to reduced mitochondrial respiration in caffeine-treated skeletal muscle cells. We conclude that caffeine increased cell death and reduced mitochondrial respiration in a calcium-dependent manner by activating the RYR and promoting reticular calcium release.

Partial contribution of mitochondrial permeability transition to t-butyl hydroperoxide-induced cell death

Mitochondrial permeability transition (MPT) is thought to determine cell death under oxidative stress. However, MPT inhibitors only partially suppress oxidative stress-induced cell death. Here, we demonstrate that cells in which MPT is inhibited undergo cell death under oxidative stress. When C6 cells were exposed to 250 μM t-butyl hydroperoxide (t-BuOOH), the loss of a membrane potential-sensitive dye (tetramethylrhodamine ethyl ester, TMRE) from mitochondria was observed, indicating mitochondrial depolarization leading to cell death. The fluorescence of calcein entrapped in mitochondria prior to addition of t-BuOOH was significantly decreased to 70% after mitochondrial depolarization. Cyclosporin A suppressed the decrease in mitochondrial calcein fluorescence, but not mitochondrial depolarization. These results show that t-BuOOH induced cell death even when it did not induce MPT. Prior to MPT, lactate production and respiration were hampered. Taken together, these data indicate that the decreased turnover rate of glycolysis and mitochondrial respiration may be as vital as MPT for cell death induced under moderate oxidative stress.

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Cell death was induced in C6 cells by 250 μM t-BuOOH.

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Mitochondrial permeability transition (MPT) occurred before cell death.

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MPT was confirmed by observing calcein fluorescence in mitochondria.

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MPT inhibition did not prevent depolarization of mitochondria and cell death.

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Contribution of MPT to cell death is partial under moderate oxidative stress.

Danhong injection protects cardiomyocytes against hypoxia/reoxygenation- and H2O2-induced injury by inhibiting mitochondrial permeability transition pore opening

ETHNOPHARMACOLOGICAL RELEVANCE

Danhong injection (DHI), a Chinese medical product extracted from Radix et Rhizoma Salviae Miltiorrhizae (Salvia miltiorrhiza Bge., Labiatae, Danshen in Chinese) and Flos Carthami (Carthamus tinctorius L., Compositae, Honghua in Chinese), has been widely used for the treatment of ischemic heart disease, and clinical and experimental studies have demonstrated the protective effects against myocardial ischemia/reperfusion injury. Nevertheless, the underlying cellular mechanisms responsible for this protective effect are poorly understood.

AIM OF THE STUDY

The present study aimed to examine the mechanism of DHI in regulating hypoxia/reoxygenation- and H2O2-induced cardiomyocytes injury.

MATERIALS AND METHODS

Neonatal rat cardiomyocytes were subjected to hypoxia (9h)-reoxygenation (2h) or H2O2 (100 μM) in the presence or absence of DHI (2.5, 5, 10 μg/mL). Intracellular reactive oxygen species (ROS), cytosolic and mitochondrial Ca(2+) concentrations, mitochondrial membrane potential (ΔΨm) and mitochondrial permeability transition pore (mPTP) opening were monitored using CMH2DCFDA, Fluo-4 and rhod-2, JC-1 and calcein, respectively. Cell survival was evaluated using the 2-(4,5-dimethylthiazol-2-yl)-2,5 -diphenyltetrazolium bromide (MTT) assay and apoptosis was detected by Annexin V/propidium iodide (PI) staining.

RESULTS

DHI improved cell survival following H/R and H2O2 injury and reduced H/R-induced cytochrome c release and apoptosis when compared with non-DHI treated cells. In addition, DHI attenuated H/R-induced ROS generation, H2O2-induced cytosolic and mitochondrial Ca(2+) overload, and cellular ROS generation when compared with H/R- and H2O2-only groups. Moreover, DHI significantly inhibited both mPTP opening and ΔΨm depolarization.

CONCLUSION

These data demonstrate that the protective mechanism of DHI against H/R- and H2O2-induced injury is mediated by the inhibition of mPTP opening via mitigating Ca(2+) overload and ROS generation.

The fruits of wampee inhibit H2O2-induced apoptosis in PC12 cells via the NF-κB pathway and regulation of cellular redox status

Wampee (Clausena lansium) fruits (CLS), whose pulp can be used to prepare fruit cups, desserts, jam, or jelly, can be eaten along with the peel. In this study, a PC12 cell model was built to observe the protective effect of CLS against H₂O₂-induced oxidative stress. We found that pretreatment with CLS increased cell viability and inhibited cytotoxicity, caspase-3 activity and DNA condensation. CLS also attenuated the increase in ROS production and MMP reduction. Moreover, we attempted to determine whether CLS suppressed the expression and phosphorylation of NF-κB. Western blot and immunostaining assay revealed that CLS inhibited H₂O₂-induced up-regulation of NF-κB p65 and pNF-κB p65. And CLS significantly suppressed the translocation of NF-κB p65 and pNF-κB p65 from cytoplasm to nuclear. Also, seven major compounds including a new flavanoid, luteolin-4'-O-β-d-gluco-pyranoside (3) and six known compounds 1,2, 4–7 were isolated and identified from CLS. Their antioxidative and H₂O₂-induced PC12 cell apoptosis-reversing activity were determined. These findings suggest that CLS and its major constituents (flavanoids) may be potential antioxidant agents and should encourage further research into their use as a functional food for neurodegenerative diseases.

Phosphodiesterase-5 inhibitor tadalafil attenuates oxidative stress and protects against myocardial ischemia/reperfusion injury in type 2 diabetic mice

Diabetic patients exhibit increased risk for the development of cardiovascular diseases primarily because of impaired nitric oxide (NO) bioavailability. The phosphodiesterase-5 (PDE-5) inhibitor sildenafil restores NO signaling and protects against ischemia/reperfusion (I/R) injury. In this study, we determined the effect of the long-acting PDE-5 inhibitor tadalafil on diabetes-associated complications and its role in attenuating oxidative stress after I/R injury in type 2 diabetic db/db mice. Adult male db/db mice (n=40/group) were randomized to receive dimethyl sulfoxide (10% DMSO, 0.2ml, ip) or tadalafil (1mg/kg in 10% DMSO, ip) for 28 days. After 28 days treatment, the hearts were isolated and subjected to 30min global ischemia followed by 60min reperfusion in the Langendorff mode. Infarct size was measured using computer morphometry of tetrazolium-stained sections. Cardiomyocytes were isolated from a subset of hearts and subjected to 40min simulated ischemia followed by 1h of reoxygenation (SI/RO). Dichlorodihydrofluorescein diacetate and JC-1 staining was used to measure reactive oxygen species (ROS) generation and mitochondrial membrane potential (Δψm), respectively. Another subset of hearts was used for the estimation of lipid peroxidation, glutathione, and the expression of myocardial pRac1, Rac1, gp91(phox), p47(phox), and p67(phox) by Western blot. Tadalafil treatment improved the metabolic status and reduced infarct size compared to the untreated db/db mice (21.2±1.8% vs 45.8±2.8%; p<0.01). The db/db mice showed enhanced oxidative stress in cardiomyocytes as indicated by a significant increase in ROS production. Cardiac NAD(P)H oxidase activity, lipid peroxidation, and oxidized glutathione were also increased in db/db mice compared to nondiabetic control animals. Tadalafil treatment in db/db mice suppressed oxidative stress, attenuated myocardial expression of pRac1 and gp91(phox), and also preserved the loss of Δψm in cardiomyocytes after SI/RO. In conclusion, these results demonstrate that chronic treatment with tadalafil attenuates oxidative stress and improves mitochondrial integrity while providing powerful cardioprotective effects in type 2 diabetes.

Mitochondria: A mirror into cellular dysfunction in heart disease

Cardiovascular (CV) disease is the single most significant cause of morbidity and mortality worldwide. The emerging global impact of CV disease means that the goals of early diagnosis and a wider range of treatment options are now increasingly pertinent. As such, there is a greater need to understand the molecular mechanisms involved and potential targets for intervention. Mitochondrial function is important for physiological maintenance of the cell, and when this function is altered, the cell can begin to suffer. Given the broad range and significant impacts of the cellular processes regulated by the mitochondria, it becomes important to understand the roles of the proteins associated with this organelle. Proteomic investigations of the mitochondria are hampered by the intrinsic properties of the organelle, including hydrophobic mitochondrial membranes; high proportion of basic proteins (pI greater than 8.0); and the relative dynamic range issues of the mitochondria. For these reasons, many proteomic studies investigate the mitochondria as a discrete subproteome. Once this has been achieved, the alterations that result in functional changes with CV disease can be observed. Those alterations that lead to changes in mitochondrial function, signaling and morphology, which have significant implications for the cardiomyocyte in the development of CV disease, are discussed.

Astragaloside IV inhibits oxidative stress-induced mitochondrial permeability transition pore opening by inactivating GSK-3β via nitric oxide in H9c2 cardiac cells

Objective. This study aimed to investigate whether astragaloside IV modulates the mitochondrial permeability transition pore (mPTP) opening through glycogen synthase kinase 3β (GSK-3β) in H9c2 cells. Methods. H9c2 cells were exposed to astragaloside IV for 20 min. GSK-3β (Ser⁹), Akt (Ser⁴⁷³), and VASP (Ser²³⁹) activities were determined with western blot. The mPTP opening was evaluated by measuring mitochondrial membrane potential (ΔΨ_m). Nitric oxide (NO) generation was measured by 4-amino-5-methylamino-2′, 7′-difluorofluorescein (DAF-FM) diacetate. Fluorescence images were obtained with confocal microscopy. Results. Astragaloside IV significantly enhanced GSK-3β phosphorylation and prevented H₂O₂-induced loss of ΔΨ_m. These effects of astragaloside IV were reversed by the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002, the NO sensitive guanylyl cyclase selective inhibitor ODQ, and the PKG inhibitor KT5823. Astragaloside IV activated Akt and PKG. Astragaloside IV was also shown to increase NO production, an effect that was reversed by L-NAME and LY294002. Astragaloside IV applied at reperfusion reduced cell death caused by simulated ischemia/reperfusion, indicating that astragaloside IV can prevent reperfusion injury. Conclusions. These data suggest that astragaloside IV prevents the mPTP opening and reperfusion injury by inactivating GSK-3β through the NO/cGMP/PKG signaling pathway. NOS is responsible for NO generation and is activated by the PI3K/Akt pathway.

Protection against cardiac injury by small Ca(2+)-sensitive K(+) channels identified in guinea pig cardiac inner mitochondrial membrane

We tested if small conductance, Ca(2+)-sensitive K(+) channels (SK(Ca)) precondition hearts against ischemia reperfusion (IR) injury by improving mitochondrial (m) bioenergetics, if O(2)-derived free radicals are required to initiate protection via SK(Ca) channels, and, importantly, if SK(Ca) channels are present in cardiac cell inner mitochondrial membrane (IMM). NADH and FAD, superoxide (O(2)(-)), and m[Ca(2+)] were measured in guinea pig isolated hearts by fluorescence spectrophotometry. SK(Ca) and IK(Ca) channel opener DCEBIO (DCEB) was given for 10 min and ended 20 min before IR. Either TBAP, a dismutator of O(2)()(-), NS8593, an antagonist of SK(Ca) isoforms, or other K(Ca) and K(ATP) channel antagonists, were given before DCEB and before ischemia. DCEB treatment resulted in a 2-fold increase in LV pressure on reperfusion and a 2.5 fold decrease in infarct size vs. non-treated hearts associated with reduced O(2)(-) and m[Ca(2+)], and more normalized NADH and FAD during IR. Only NS8593 and TBAP antagonized protection by DCEB. Localization of SK(Ca) channels to mitochondria and IMM was evidenced by a) identification of purified mSK(Ca) protein by Western blotting, immuno-histochemical staining, confocal microscopy, and immuno-gold electron microscopy, b) 2-D gel electrophoresis and mass spectroscopy of IMM protein, c) [Ca(2+)]-dependence of mSK(Ca) channels in planar lipid bilayers, and d) matrix K(+) influx induced by DCEB and blocked by SK(Ca) antagonist UCL1684. This study shows that 1) SK(Ca) channels are located and functional in IMM, 2) mSK(Ca) channel opening by DCEB leads to protection that is O(2)(-) dependent, and 3) protection by DCEB is evident beginning during ischemia.

Mapping of redox state of mitochondrial cytochromes in live cardiomyocytes using Raman microspectroscopy

This paper presents a nonivasive approach to study redox state of reduced cytochromes c, c1 and b of complexes II and III in mitochondria of live cardiomyocytes by means of Raman microspectroscopy. For the first time with the proposed approach we perform studies of rod- and round-shaped cardiomyocytes, representing different morphological and functional states. Raman mapping and cluster analysis reveal that these cardiomyocytes differ in the amounts of reduced cytochromes c, c1 and b. The rod-shaped cardiomyocytes possess uneven distribution of reduced cytochromes c, c1 and b in cell center and periphery. Moreover, by means of Raman spectroscopy we demonstrated the decrease in the relative amounts of reduced cytochromes c, c1 and b in the rod-shaped cardiomyocytes caused by H2O2-induced oxidative stress before any visible changes. Results of Raman mapping and time-dependent study of reduced cytochromes of complexes II and III and cytochrome c in cardiomyocytes are in a good agreement with our fluorescence indicator studies and other published data.

Chemical speciation of nanoparticles surrounding metal-on-metal hips

Spectromicroscopy of tissue surrounding failed CoCr metal-on-metal hip replacements detected corroded nanoscale debris in periprosthetic tissue in two chemical states, with concomitant mitochondrial damage. The majority of debris contained Cr(3+), with trace amounts of oxidised cobalt. A minority phase containing a core of metallic chromium and cobalt was also observed.

Mitochondrial K+ channels are involved in ischemic postconditioning in rat hearts

The mitochondrial calcium-activated potassium channel (mitoK(Ca)) and the mitochondrial ATP-sensitive potassium channel (mitoK(ATP)) are both involved in cardiac preconditioning. Here, we examined whether these two channels are also involved in ischemic or pharmacological postconditioning. Using Langendorff perfusion, rat hearts were made hypoxic for 45 min and then reoxygenated for 30 min. Ischemic postconditioning (IPT) was achieved through application of 3 cycles of 10 s of reperfusion and 10 s of ischemia before reoxygenation, with and without paxilline (Pax; a mitoK(Ca) blocker) or 5-hydroxydecanoate (5-HD; a mitoK(ATP) blocker). Pharmacological postconditioning was carried out for 5 min at the onset of reoxygenation using NS1619 (a mitoK(Ca) opener) or diazoxide (Dia; a mitoK(ATP) opener). Pax and 5-HD abolished IPT-induced cardioprotection from reoxygenation injury, whereas administration of NS1619 or Dia significantly improved cardiac contractile activity and reduced aspartate aminotransferase (an index of myocyte injury) release following reoxygenation. In addition, isolated rat myocytes were loaded with tetramethylrhodamine methyl ester (TMRE; fluorescent mitochondrial membrane potential indicator) and 2',7'-dichlorofluorescein [DCFH; fluorescent reactive oxygen species (ROS) indicator] or Fluo-4-acetoxymethyl ester (Fluo-4-AM; fluorescent calcium indicator). When TMRE-loaded myocytes were laser illuminated, the DCFH and Fluo-4 fluorescence increased, and TMRE fluorescence decreased. These effects were significantly inhibited by NS1619 and Dia. We therefore conclude that IPT may protect the heart through activation of mitoK(ATP) and mitoK(Ca) channels, and that opening of these channels at the onset of reoxygenation protects the heart from reoxygenation injury, most likely by reducing excess generation of ROS and the resultant Ca(2+) overload.

The Na+/H+ exchanger-1 inhibitor cariporide prevents glutamate-induced necrotic neuronal death by inhibiting mitochondrial Ca2+ overload

In the brain, Na+/H+ exchanger-1 (NHE-1) activation has a significant impact on ischemic injury, and, in recent studies, NHE-1 inhibition has been found to protect neurons from ischemic injury. This protective effect has been ascribed to the prevention of apoptosis, but neuronal cell death following ischemia is a consequence of both necrotic and apoptotic cell death. Here, we evaluated the ability of the potent NHE-1 inhibitor cariporide to prevent necrotic cell death in an in vitro model of excitotoxic neuronal death. Cariporide (100 nM) was found to reduce both glutamate-induced necrotic and apoptotic neuronal cell death. Ca2+ concentrations were observed to peak twice in cytosol and mitochondria in cultured neuronal cells after glutamate exposure, and cariporide was found to reduce the second Ca2+ concentration increase, but not the first. Furthermore, glutamate-mediated mitochondrial death pathways involving loss of mitochondrial membrane potential and reactive oxygen species (ROS) accumulation were found to be attenuated by cariporide. In addition, cariporide effectively prevented necrosis following exposure to glutamate and ameliorated the mitochondrial Ca2+ and ROS production increases implicated in necrotic cell death. These results suggest that NHE-1 participates in the necrotic cell death process and that its inhibition offers a means of preventing both necrosis and apoptosis.

Mitofusins and the mitochondrial permeability transition: the potential downside of mitochondrial fusion

Mitofusins (Mfn-1 and Mfn-2) are transmembrane proteins that bind and hydrolyze guanosine 5'-triphosphate to bring about the merging of adjacent mitochondrial membranes. This event is necessary for mitochondrial fusion, a biological process that is critical for organelle function. The broad effects of mitochondrial fusion on cell bioenergetics have been extensively studied, whereas the local effects of mitofusin activity on the structure and integrity of the fusing mitochondrial membranes have received relatively little attention. From the study of fusogenic proteins, theoretical models, and simulations, it has been noted that the fusion of biological membranes is associated with local perturbations on the integrity of the membrane that present in the form of lipidic holes which open on the opposing bilayers. These lipidic holes represent obligate intermediates that make the fusion process thermodynamically more favorable and at the same time induce leakage to the fusing membranes. In this perspectives article we present the relevant evidence selected from a spectrum of membrane fusion/leakage models and attempt to couple this information with observations conducted with cardiac myocytes or mitochondria deficient in Mfn-1 and Mfn-2. More specifically, we argue in favor of a situation whereby mitochondrial fusion in cardiac myocytes is coupled with outer mitochondrial membrane destabilization that is opportunistically employed during the process of mitochondrial permeability transition. We hope that these insights will initiate research on this new hypothesis of mitochondrial permeability transition regulation, a poorly understood mitochondrial function with significant consequences on myocyte survival.

Specific inhibition of mitochondrial oxidative stress suppresses inflammation and improves cardiac function in a rat pneumonia-related sepsis model

Using a mitochondria-targeted vitamin E (Mito-Vit-E) in a rat pneumonia-related sepsis model, we examined the role of mitochondrial reactive oxygen species in sepsis-mediated myocardial inflammation and subsequent cardiac contractile dysfunction. Sepsis was produced in adult male Sprague-Dawley rats via intratracheal injection of S. pneumonia (4 × 10(6) colony formation units per rat). A single dose of Mito-Vit-E, vitamin E, or control vehicle, at 21.5 μmol/kg, was administered 30 min postinoculation. Blood was collected, and heart tissue was harvested at various time points. Mito-Vit-E in vivo distribution was confirmed by mass spectrometry. In cardiac mitochondria, Mito-Vit-E improved total antioxidant capacity and suppressed H(2)O(2) generation, whereas vitamin E offered little effect. In cytosol, both antioxidants decreased H(2)O(2) levels, but only vitamin E strengthened antioxidant capacity. Mito-Vit-E protected mitochondrial structure and function in the heart during sepsis, demonstrated by reduction in lipid and protein oxidation, preservation of mitochondrial membrane integrity, and recovery of respiratory function. While both Mito-Vit-E and vitamin E suppressed sepsis-induced peripheral and myocardial production of proinflammatory cytokines (tumor necrosis factor-α, interleukin-1β, and interleukin-6), Mito-Vit-E exhibited significantly higher efficacy (P < 0.05). Stronger anti-inflammatory action of Mito-Vit-E was further shown by its near-complete inhibition of sepsis-induced myeloperoxidase accumulation in myocardium, suggesting its effect on neutrophil infiltration. Echocardiography analysis indicated that Mito-Vit-E ameliorated cardiac contractility of sepsis animals, shown by improved fractional shortening and ejection fraction. Together, our data suggest that targeted scavenging of mitochondrial reactive oxygen species protects mitochondrial function, attenuates tissue-level inflammation, and improves whole organ activities in the heart during sepsis.

Cardiomyocyte deletion of mitofusin-1 leads to mitochondrial fragmentation and improves tolerance to ROS-induced mitochondrial dysfunction and cell death

Molecular studies examining the impact of mitochondrial morphology on the mammalian heart have previously focused on dynamin related protein-1 (Drp-1) and mitofusin-2 (Mfn-2), while the role of the other mitofusin isoform, Mfn-1, has remained largely unexplored. In the present study, we report the generation and initial characterization of cardiomyocyte-specific Mfn-1 knockout (Mfn-1 KO) mice. Using electron microscopic analysis, we detect a greater prevalence of small, spherical mitochondria in Mfn-1 KO hearts, indicating that the absence of Mfn-1 causes a profound shift in the mitochondrial fusion/fission balance. Nevertheless, Mfn-1 KO mice exhibit normal left-ventricular function, and isolated Mfn-1 KO heart mitochondria display a normal respiratory repertoire. Mfn-1 KO myocytes are protected from mitochondrial depolarization and exhibit improved viability when challenged with reactive oxygen species (ROS) in the form of hydrogen peroxide (H(2)O(2)). Furthermore, in vitro studies detect a blunted response of KO mitochondria to undergo peroxide-induced mitochondrial permeability transition pore opening. These data suggest that Mfn-1 deletion confers protection against ROS-induced mitochondrial dysfunction. Collectively, we suggest that mitochondrial fragmentation in myocytes is not sufficient to induce heart dysfunction or trigger cardiomyocyte death. Additionally, our data suggest that endogenous levels of Mfn-1 can attenuate myocyte viability in the face of an imminent ROS overload, an effect that could be associated with the ability of Mfn-1 to remodel the outer mitochondrial membrane.

Brain mitochondria from rats treated with sulforaphane are resistant to redox-regulated permeability transition

Oxidative stress promotes Ca2+-dependent opening of the mitochondrial inner membrane permeability transition pore (PTP), causing bioenergetic failure and subsequent cell death in many paradigms, including those related to acute brain injury. One approach to pre-conditioning against oxidative stress is pharmacologic activation of the Nrf2/ARE pathway of antioxidant gene expression by agents such as sulforaphane (SFP). This study tested the hypothesis that administration of SFP to normal rats increases resistance of isolated brain mitochondria to redox-sensitive PTP opening. SFP or DMSO vehicle was administered intraperitoneally to adult male rats at 10 mg/kg 40 h prior to isolation of non-synaptic brain mitochondria. Mitochondria were suspended in medium containing a respiratory substrate and were exposed to an addition of Ca2+ below the threshold for PTP opening. Subsequent addition of tert-butyl hydroperoxide (tBOOH) resulted in a cyclosporin A-inhibitable release of accumulated Ca2+ into the medium, as monitored by an increase in fluorescence of Calcium Green 5N within the medium, and was preceded by a decrease in the autofluorescence of mitochondrial NAD(P)H. SFP treatment significantly reduced the rate of tBOOH-induced Ca2+ release but did not affect NAD(P)H oxidation or inhibit PTP opening induced by the addition of phenylarsine oxide, a direct sulfhydryl oxidizing agent. SFP treatment had no effect on respiration by brain mitochondria and had no effect on PTP opening or respiration when added directly to isolated mitochondria. We conclude that SFP confers resistance of brain mitochondria to redox-regulated PTP opening, which could contribute to neuroprotection observed with SFP.

Targeting the mitochondrial permeability transition: cardiac ischemia-reperfusion versus carcinogenesis

Cardiovascular diseases and cancer continue to be major causes of death worldwide, and despite intensive research only modest progress has been reached in reducing the morbidity and mortality of these awful diseases. Mitochondria are broadly accepted as the key organelles that play a crucial role in cell life and death. They provide cells with ATP produced via oxidative phosphorylation under physiological conditions, and initiate cell death through both apoptosis and necrosis in response to severe stress. Oxidative stress accompanied by calcium overload and ATP depletion induces the mitochondrial permeability transition (mPT) with formation of pathological, non-specific mPT pores (mPTP) in the mitochondrial inner membrane. Opening of the mPTP with a high conductance results in matrix swelling ultimately inducing rupture of the mitochondrial outer membrane and releasing pro-apoptotic proteins into the cytoplasm. The ATP level is the determining factor in deciding whether cells die through apoptosis or necrosis. Cardiac cells undergoing ischemia followed by reperfusion (IR) possess exactly the same conditions mentioned above to induce mPTP opening. Due to its critical role in cell death, inhibition of mPTP opening has been accepted as a major therapeutic approach to protect the heart against IR. In contrast to cardiac IR, cancer cells exhibit less sensitivity to pore opening which can be in part explained by increased expression of mPTP compounds/modulators and metabolic remodeling. Since the main goal of chemotherapy is to provoke apoptosis, mPT induction may represent an attractive approach for the development of new cancer therapeutics to induce mitochondria-mediated cell death and prevent cell differentiation in carcinogenesis. This review focuses on the role of the mPTP in cardiac IR and cancer, and pharmacological agents to prevent or initiate mPT-mediated cell death, respectively in these diseases.

Mitochondrial ROS production under cellular stress: comparison of different detection methods

Reactive oxygen species (ROS) are involved in the regulation of many physiological processes. However, overproduction of ROS under various cellular stresses results in cell death and organ injury and thus contributes to a broad spectrum of diseases and pathological conditions. The existence of different cellular sources for ROS and the distinct properties of individual ROS (their reactivity, lifetime, etc.) require adequate detection methods. We therefore compared different models of cellular stress and various ROS-sensitive dyes-2',7'-dichlorodihydrofluorescein diacetate (DCF-DA), MitoSOX™, and MitoTracker® red CM-H(2)XRos-using a confocal fluorescent imaging approach, which has the advantage of not only detecting but also of localizing intracellular sources for ROS. Confocal acquisition of DCF-DA fluorescence can be combined with ROS detection by the mitochondria-specific probes MitoSOX™ and MitoTracker® red CM-H(2)XRos. Specificity was controlled using various antioxidants such as Trolox and N-acetylcysteine. Using different fluorescent ROS-sensitive probes, we detected higher ROS production equally under cell starvation (IL-3 or serum depletion), hypoxia-reoxygenation, or treatment of cells with prooxidants. The detected increase in ROS was approximately threefold in IL-3-depleted 32D cells, approximately 3.5-fold in serum-deprived NIH cells, and 2.5-fold to threefold in hypoxic HL-1 cells, and these findings agree well with previously published spectrofluorometric measurements. In some cases, electron spin resonance (ESR) spectroscopy was used for the validation of results from confocal fluorescent imaging. Our data show that confocal fluorescent imaging and ESR data are in good agreement. Under cellular stress, mitochondrial ROS are released into the cytoplasm and may participate in many processes, but they do not escape from the cell.

Hypothermia protects H9c2 cardiomyocytes from H2O2 induced apoptosis

The purpose of our study was to investigate underlying basic mechanisms of hypothermia-induced cardioprotection during oxidative stress in a cardiomyocyte cell culture model. For hypothermic treatment we cooled H9c2 cardiomyocytes to 20°C, maintained 20min at 20°C during which short-term oxidative damage was inflicted with 2mM H(2)O(2,) followed by rewarming to 37°C. Later on, we analyzed lactate dehydrogenase (LDH), caspase-3 cleavage, reactive oxygen species (ROS), mitochondrial activity, intracellular ATP production, cytoprotective signal molecules as well as DNA damage. Hypothermia decreased H(2)O(2) damage in cardiomyocytes as demonstrated in a lower LDH release, less caspase-3 cleavage and less M30 CytoDeath staining. After rewarming H(2)O(2) damaged cells demonstrated a significantly higher reduction rate of intracellular ROS compared to normothermic H(2)O(2) damaged cardiomyocytes(.) This was in line with a significantly greater mitochondrial dehydrogenase activity and higher intracellular ATP content in cooled and rewarmed cells. Moreover, hypothermia preserved cell viability by up-regulation of the anti-apoptotic protein Bcl-2 and a reduction of p53 phosphorylation. DNA damage, proven by PARP-1 cleavage and H2AX phosphorylation, was significantly reduced by hypothermia. In conclusion, we could demonstrate that hypothermia protects cardiomyocytes during oxidative stress by preventing apoptosis via inhibiting mitochondrial dysfunction and DNA damage.

Proteomic profiling of cellular responses to Carvedilol enantiomers in vascular smooth muscle cells by iTRAQ-coupled 2-D LC-MS/MS

Carvedilol is a third-generation beta-blocker, with the S-enantiomer being more active than the R-enantiomer. Clinically, it has been used in the treatment of hypertension, congestive heart failure and angina pectoris. Each enantiomer of Carvedilol exhibits differential pharmacological effects. However, the cellular effects of individual enantiomer are not well understood. To gain insights into how each enantiomer affects cells, we analysed differential protein expression levels in vascular smooth muscle cells (A7r5) incubated separately with S- and R-Carvedilol by iTRAQ-coupled 2-D LC-MS/MS approach. Thirteen proteins were identified with statistically significant changes in cells incubated with S-Carvedilol, while the changes of most proteins incubated with R-Carvedilol were less significant. Among these proteins, actin in aortic smooth muscle (ACTA2), calmodulin, S100-A6, S100-A10, S100-A11, thioredoxin, lactadherin and heat-shock protein 105 kDa were found to be closely relevant with the clinical effects of Carvedilol. Furthermore, the changes in protein levels were validated by Western blot. Our findings thus provided molecular evidence on a comprehensive protein profile on Carvedilol-cell interaction, which may shed new light in molecular events underlying Carvedilol treatment.

Protective effects of steroids from Allium chinense against H2O2-induced oxidative stress in rat cardiac H9C2 cells

Allium chinense, a traditional herbal medicine, has been used for the treatment of cardiovascular diseases for hundreds of years. In this study, A. chinense steroids (ACSs) including three steroidal glycosides and their parent aglycones were isolated from the bulbs of A. chinense. For the first time, their cardioprotective effects were evaluated in cultured rat cardiac H9C2 cells by pretreatment with ACSs for 24 h before exposure to 0.2 mm H(2)O(2). The results showed the cell viability decreased markedly when H9C2 cells were incubated with 0.2 mm H(2)O(2) alone for 2 h, while the cell lipid peroxidation (estimated by the excessive production of nitric oxide and malondialdehyde) and intracellular free calcium concentration ([Ca(2+)](i)) increased significantly. The addition of 20 microm (below the toxic concentration) of ACSs notably attenuated the cellular injury induced by H(2)O(2). The effects of ACSs in our experiments were similar to those of nimodipine, a clinically applied calcium channel blocker. Preliminary analysis of the structure-activity relationship indicated that ACSs with a spirostane-type skeleton exhibited stronger protection than that with a furostane-type skeleton, and glycosylation of the steroids could substantially lower the protective activities. The above results suggested the protective effects of steroids originated from A. chinense on the oxidative injury of H9C2 cells and ACSs may have potential for preventing cardiac injuries induced by oxidative stress.

Burn serum causes a CD14-dependent mitochondrial damage in primary cardiomyocytes

Studies from animal models suggest that myocardial mitochondrial damage contributes to cardiac dysfunction after burn injury. In this report, we used an ex vivo model of primary cardiomyocyte culture to investigate the mechanisms of burn-induced mitochondrial impairment. Briefly, blood serum was collected from Sprague-Dawley (SD) rats subjected to 40% total body surface area burn and added (10% vol/vol) to primary cardiomyocytes prepared from SD rats. The effect of the burn serum on mitochondrial function and membrane integrity in the myocytes was analyzed. Exposure of myocytes to burn serum doubled the mitochondrial membrane damage measured by two independent assays. This treatment also significantly elevated mitochondrial oxidative stress, indicated by a more than 30% increase in lipid oxidation. Downregulation of mitochondrial antioxidant defense was also evident since the activities of the antioxidant enzymes superoxide dismutase and glutathione peroxidase were reduced by about 30% and 50%, respectively. Burn serum also induced deficiency of mitochondrial metabolism, indicated by a 30% decrease in the activity of cytochrome c oxidase. These mitochondrial dysfunctions appear to be generated by oxidative stress because burn serum induced a significant increase of mitochondrial oxygen species (mtROS) in cardiomyocytes, and pretreatment of cardiomyocytes with the antioxidant N-acetyl-cysteine prevented the mitochondrial damages induced by burn serum. Remarkably, the increase in mtROS was abolished by an antibody-mediated blockade of CD14. Furthermore, burn injury-induced mitochondrial damage in cardiomyocytes was prevented in CD14 knockout mice. Taken together, these data suggested that burn injury produces CD14-dependent mitochondrial damage via oxidative stress in myocardium.

Inhibition of glycogen synthase kinase 3beta prevents peroxide-induced collapse of mitochondrial membrane potential in rat ventricular myocytes

1. Preconditioning has been proposed to protect the myocardium by inhibiting glycogen-synthase kinase (GSK) 3beta. The aim of the present study was to test whether transfection of ventricular myocytes with inactive GSK3 beta would mimic preconditioning and whether a constitutively active form of GSK3 beta would prevent protection by an opioid receptor agonist. 2. Isolated ventricular myocytes from adult rats were infected with live adenovirus containing either a wild-type (wtGSK), constitutively active (caGSK) or dominant-negative (dnGSK) GSK3 beta plasmid. Cells were loaded with tetramethylrhodamine ethyl ester (TMRE) and exposed to H(2)O(2) (100 micromol/L) for 40 min before mitochondrial membrane potential (Delta Psi(m)) was assessed using flow cytometric analysis. 3. Fluorescence intensity was reduced in H(2)O(2)-treated cells compared with untreated cells, presumably because oxidant injury opened mitochondrial permeability transition pores, causing mitochondria to lose TMRE. The selective GSK3 beta inhibitor SB216763, as well as the delta-opioid receptor agonist [d-Ala(2)-D-Leu(5)]-enkephalin (DADLE) (1 micromol/L), protected cells against peroxide-induced loss of Delta Psi(m). 4. Cells transfected with dnGSK (1 micromol/L) were equally protected against peroxide stress, when given throughout the TMRE and H(2)O(2) treatment, confirming a protective effect of GSK3 beta with a highly selective inhibition. Cells transfected with wtGSK did not show any difference in responses to H(2)O(2), SB216763 or DADLE compared with untransfected cells, suggesting that adenovirus infection itself had no effect. In contrast, caGSK-transfected myocytes could no longer be protected with DADLE, suggesting a role for GSK3 beta between the surface receptor and the mitochondria. 5. These experiments confirm that inhibition of GSK3 beta protects the myocytes, but also that the preconditioning mimetic DADLE loses its protective effect when a constitutively active GSK3 beta is present.

Growth factor erv1-like modulates Drp1 to preserve mitochondrial dynamics and function in mouse embryonic stem cells

The relationship of mitochondrial dynamics and function to pluripotency are rather poorly understood aspects of stem cell biology. Here we show that growth factor erv1-like (Gfer) is involved in preserving mouse embryonic stem cell (ESC) mitochondrial morphology and function. Knockdown (KD) of Gfer in ESCs leads to decreased pluripotency marker expression, embryoid body (EB) formation, cell survival, and loss of mitochondrial function. Mitochondria in Gfer-KD ESCs undergo excessive fragmentation and mitophagy, whereas those in ESCs overexpressing Gfer appear elongated. Levels of the mitochondrial fission GTPase dynamin-related protein 1 (Drp1) are highly elevated in Gfer-KD ESCs and decreased in Gfer-overexpressing cells. Treatment with a specific inhibitor of Drp1 rescues mitochondrial function and apoptosis, whereas expression of Drp1-dominant negative resulted in the restoration of pluripotency marker expression in Gfer-KD ESCs. Altogether, our data reveal a novel prosurvival role for Gfer in maintaining mitochondrial fission-fusion dynamics in pluripotent ESCs.

Serum superoxide dismutase activity correlates with the components of metabolic syndrome or carotid artery intima-media thickness

The activities of the enzymes to eliminate reactive oxygen species prevent the progression of atherosclerosis. We conducted a cross-sectional study among 3234 people that underwent total health check-up service, and studied the relationship between the serum superoxide dismutase (SOD) activity and risk factors of atherosclerosis or carotid artery intima-media thickness (IMT). Serum SOD activity negatively correlated with body mass index (BMI), systolic and diastolic blood pressure, serum triglyceride (TG) concentration and serum glucose concentration. Low serum SOD activity positively correlated with the carotid IMT thickening. But on the other hand, existence of carotid artery plaque positively correlated with serum SOD activity especially among men. Serum SOD activity negatively correlated with the components of metabolic syndrome and low serum SOD activity seems to be an independent risk of the thickening of carotid IMT. On the other hand, serum SOD activity level seems to elevate limitedly but reactively to the status of increased oxidative stress, such as carotid plaque formation.

Cardioprotection of bradykinin at reperfusion involves transactivation of the epidermal growth factor receptor via matrix metalloproteinase-8

AIM

The endogenous autacoid bradykinin (BK) reportedly reduces myocardial infarct size when given exogenously at reperfusion. Muscarinic and opioid G-protein-coupled receptors are equally protective and have been shown to couple through a matrix metalloproteinase (MMP)-dependent transactivation of the epidermal growth factor receptor (EGFR). Here we test whether BK protects the rat heart through the EGFR by an MMP-dependent pathway.

METHODS

Infarct size was measured in isolated perfused rat hearts undergoing 30 min regional ischaemia followed by 120 min reperfusion. In additional studies HL-1 cardiomyocytes were loaded with tetramethylrhodamine ethyl to measure their mitochondrial membrane potential (Psim). Adding the calcium ionophore calcimycin, causes Psim-collapse presumably due to calcium-induced mitochondrial permeability transition.

RESULTS

As expected, BK (100 nmol L(-1)) started 5 min prior to reperfusion reduced infarct size from 38.9 +/- 2.0% of the ischaemic zone in control hearts to 22.2 +/- 3.3% (P < 0.001). Co-infusing the EGFR inhibitor AG1478, the broad-spectrum MMP-inhibitor GM6001, or a highly selective MMP-8 inhibitor abolished BK's protection, thus suggesting an MMP-8-dependent EGFR transactivation in the signalling. Eighty minutes of exposure to calcimycin reduced the mean cell fluorescence to 37.4 +/- 1.8% of untreated cells while BK could partly preserve the fluorescence and, hence, protect the cells (50.5 +/- 2.3%, P < 0.001). The BK-induced mitochondrial protection could again be blocked by AG1478, GM6001 and MMP-8 inhibitor. Finally, Western blotting revealed that BK's protection was correlated with increased phosphorylation of EGFR and its downstream target Akt.

CONCLUSION

These results indicate that BK at reperfusion triggers its protective signalling pathway through MMP-8-dependent transactivation of the EGFR.

The role of the mitochondrial permeability transition pore in heart disease

Like Dr. Jeckyll and Mr. Hyde, mitochondria possess two distinct persona. Under normal physiological conditions they synthesise ATP to meet the energy needs of the beating heart. Here calcium acts as a signal to balance the rate of ATP production with ATP demand. However, when the heart is overloaded with calcium, especially when this is accompanied by oxidative stress, mitochondria embrace their darker side, and induce necrotic cell death of the myocytes. This happens acutely in reperfusion injury and chronically in congestive heart failure. Here calcium overload, adenine nucleotide depletion and oxidative stress combine forces to induce the opening of a non-specific pore in the mitochondrial membrane, known as the mitochondrial permeability transition pore (mPTP). The molecular nature of the mPTP remains controversial but current evidence implicates a matrix protein, cyclophilin-D (CyP-D) and two inner membrane proteins, the adenine nucleotide translocase (ANT) and the phosphate carrier (PiC). Inhibition of mPTP opening can be achieved with inhibitors of each component, but targeting CyP-D with cyclosporin A (CsA) and its non-immunosuppressive analogues is the best described. In animal models, inhibition of mPTP opening by either CsA or genetic ablation of CyP-D provides strong protection from both reperfusion injury and congestive heart failure. This confirms the mPTP as a promising drug target in human cardiovascular disease. Indeed, the first clinical trials have shown CsA treatment improves recovery after treatment of a coronary thrombosis with angioplasty.

Mitochondrial permeability transition pore opening as a promising therapeutic target in cardiac diseases

In addition to their central role in ATP synthesis, mitochondria play a critical role in cell death. Oxidative stress accompanied by calcium overload, ATP depletion, and elevated phosphate levels induces mitochondrial permeability transition (MPT) with formation of nonspecific MPT pores (MPTP) in the inner mitochondrial membrane. Pore opening results in mitochondrial dysfunction with uncoupled oxidative phosphorylation and ATP hydrolysis, ultimately leading to cell death. For the past 20 years, three proteins have been accepted as key structural components of the MPTP: adenine nucleotide translocase (ANT) in the inner membrane, cyclophilin D (CyP-D) in the matrix, and the voltage-dependent anion channel (VDAC) in the outer membrane. However, most recent studies have questioned the molecular identity of the pores. Genetic studies have eliminated the VDAC as an essential component of MPTP and attributed a regulatory (rather than structural) role to ANT. Currently, the phosphate carrier appears to play a crucial role in MPTP formation. MPTP opening has been examined extensively in cardiac pathological conditions, including ischemia/reperfusion as well as heart failure. Accordingly, MPTP is accepted as a therapeutic target for both pharmacological and conditional strategies to block pore formation by direct interaction with MPTP components or indirectly by decreasing MPTP inducers. Inhibition of MPTP opening by reduction of CyP-D activity by nonimmunosuppressive analogs of cyclosporine A or sanglifehrin A, as well as attenuation of reactive oxygen species accumulation through mitochondria-targeted antioxidants, is the most promising. This review outlines our current knowledge of the structure and function of the MPTP and describes possible approaches for cardioprotection.

Mitochondrial reactive oxygen species production in excitable cells: modulators of mitochondrial and cell function

The mitochondrion is a major source of reactive oxygen species (ROS). Superoxide (O(2)(*-)) is generated under specific bioenergetic conditions at several sites within the electron-transport system; most is converted to H(2)O(2) inside and outside the mitochondrial matrix by superoxide dismutases. H(2)O(2) is a major chemical messenger that, in low amounts and with its products, physiologically modulates cell function. The redox state and ROS scavengers largely control the emission (generation scavenging) of O(2)(*-). Cell ischemia, hypoxia, or toxins can result in excess O(2)(*-) production when the redox state is altered and the ROS scavenger systems are overwhelmed. Too much H(2)O(2) can combine with Fe(2+) complexes to form reactive ferryl species (e.g., Fe(IV) = O(*)). In the presence of nitric oxide (NO(*)), O(2)(*-) forms the reactant peroxynitrite (ONOO(-)), and ONOOH-induced nitrosylation of proteins, DNA, and lipids can modify their structure and function. An initial increase in ROS can cause an even greater increase in ROS and allow excess mitochondrial Ca(2+) entry, both of which are factors that induce cell apoptosis and necrosis. Approaches to reduce excess O(2)(*-) emission include selectively boosting the antioxidant capacity, uncoupling of oxidative phosphorylation to reduce generation of O(2)(*-) by inducing proton leak, and reversibly inhibiting electron transport. Mitochondrial cation channels and exchangers function to maintain matrix homeostasis and likely play a role in modulating mitochondrial function, in part by regulating O(2)(*-) generation. Cell-signaling pathways induced physiologically by ROS include effects on thiol groups and disulfide linkages to modify posttranslationally protein structure to activate/inactivate specific kinase/phosphatase pathways. Hypoxia-inducible factors that stimulate a cascade of gene transcription may be mediated physiologically by ROS. Our knowledge of the role played by ROS and their scavenging systems in modulation of cell function and cell death has grown exponentially over the past few years, but we are still limited in how to apply this knowledge to develop its full therapeutic potential.

Methanolic extract of onion (Allium cepa) attenuates ischemia/hypoxia-induced apoptosis in cardiomyocytes via antioxidant effect

BACKGROUND

Although there is growing awareness of the beneficial potential of onion intake to lower the risk of cardiovascular disease, there is little information about the effect of onion on ischemic heart injury, one of the most common cardiovascular diseases.

AIM OF THE STUDY

This study investigates the effect of the methanol-soluble extract of onion on ischemic injury in heart-derived H9c2 cells in vitro and in rat hearts in vivo. The underlying mechanism is also investigated.

METHODS

To evaluate the effect of onion on ischemia-induced cell death, LDH release and TUNEL-positivity were assessed in H9c2 cells, and the infarct size was measured in a myocardial infarct model. To investigate the mechanism of the cardioprotection by onion, the reactive oxygen species (ROS) level and the mitochondrial membrane potential (DeltaPsi(m)) were measured using an imaging technique; the caspase-3 activity was assayed, and Western blotting was performed to examine cytochrome c release in H9c2 cells.

RESULTS

The methanolic extract of onion had a preventive effect on ischemia/hypoxia-induced apoptotic death in H9c2 cells in vitro and in rat heart in vivo. The onion extract (0.05 g/ml) inhibited the elevation of the ROS, mitochondrial membrane depolarization, cytochrome c release and caspase-3 activation during hypoxia in H9c2 cells. In the in vivo rat myocardial infarction model, onion extract (10 g/kg) significantly reduced the infarct size, the apoptotic cell death of the heart and the plasma MDA level.

CONCLUSION

In conclusion, the results of this study suggest that the methanolic extract of onion attenuates ischemia/hypoxia-induced apoptosis in heart-derived H9c2 cells in vitro and in rat hearts in vivo, through, at least in part, an antioxidant effect.

The molecular composition of the mitochondrial permeability transition pore

Uncontrolled cell death is a fundamental cause of organ disease in humans. However, despite the need for us to delineate the molecular machinery that underlies cardiomyocyte death, our knowledge of these lethal cellular processes is still limited. The discovery that mitochondrial dysfunction, and in particular the mitochondrial permeability transition (MPT) pore, is often a common cause of the cardiac cell mortality that underlies numerous cardiac diseases has been a first crucial step. The purpose of this review is to outline our current understanding of the molecular identity of the MPT pore and the many questions that still need to be answered.