Nitric oxide protects the heart from ischemia-induced apoptosis and mitochondrial damage via protein kinase G mediated blockage of permeability transition and cytochrome c release

Vericiguat attenuates doxorubicin-induced cardiotoxicity through the PRKG1/PINK1/STING axis

Doxorubicin (DOX) is restricted due to its severe cardiotoxicity. There is still a lack of viable and effective drugs to prevent or treat DOX-induced cardiotoxicity(DIC). Vericiguat is widely used to treat heart failure with reduced ejection fraction. However, it is not clear whether vericiguat can improve DIC. In the present study, we constructed a DIC model using mice and neonatal rat cardiomyocytes and found that vericiguat ameliorated DOX-induced cardiac insufficiency in mice, restored DOX-induced mitochondrial dysfunction in neonatal rat cardiomyocytes, and inhibited the expression of inflammatory factors. Further studies showed that vericiguat improved mitochondrial dysfunction and reduced mtDNA leakage into the cytoplasm by up-regulating PRKG1, which activated PINK1 and then inhibited the STING/IRF3 pathway to alleviate DIC. These findings demonstrate for the first time that vericiguat has therapeutic potential for the treatment of DIC.

Bibliometric analysis of research progress on tetramethylpyrazine and its effects on ischemia-reperfusion injury

In recent decades, natural products have attracted worldwide attention and become one of the most important resources for pharmacological industries and medical sciences to identify novel drug candidates for disease treatment. Tetramethylpyrazine (TMP) is an alkaloid extracted from Ligusticum chuanxiong Hort., which has shown great therapeutic potential in cardiovascular and cerebrovascular diseases, liver and renal injury, as well as cancer. In this review, we analyzed 1270 papers published on the Web of Science Core Collection from 2002 to 2022 and found that TMP exerted significant protective effects on ischemia-reperfusion (I/R) injury that is the cause of pathological damages in a variety of conditions, such as ischemic stroke, myocardial infarction, acute kidney injury, and liver transplantation. TMP is limited in clinical applications to some extent due to its rapid metabolism, a short biological half-life and poor bioavailability. Obviously, the structural modification, administration methods and dosage forms of TMP need to be further investigated in order to improve its bioavailability. This review summarizes the clinical applications of TMP, elucidates its potential mechanisms in protecting I/R injury, provides strategies to improve bioavailability, which presents a comprehensive understanding of the important compound. Hopefully, the information and knowledge from this review can help researchers and physicians to better improve the applications of TMP in the clinic.

A multifactorial study of in situ antioxidant activity of modified GrO in myocardial reperfusion injury using the Langerdorff model

Carbon nanomaterials possess antioxidant properties that can be applied in biomedicine and clinics for the development of new highly effective treatments against oxidative stress-induced diseases like ischemic heart disease. We previously reported the usage of graphene oxide (GrO) as a precursor for the elaboration of such prototypes. The promising findings led to the development of two new modifications of GrO: nitrogen-doped (N-GrO) and l-cysteine functionalized (S-GrO) derivatives as possible antioxidant agents in ischemia-reperfusion (I/R) conditions. In this study, the cardioprotective and antioxidant potential of modified GrO as a pre-treatment in rats was evaluated for the first time. In Langendorff isolated rat heart I/R model, the left ventricle developed pressure (LVDP), the end-diastolic pressure (EDP), the maximal (dP/dtmax) and minimal (dP/dtmin) value of the first derivative of LVDP, and heart rate (HR) were measured. The oxidative-nitrosative markers, in particular, the rate of O2*- and H2O2 generation, the content of malonic dialdehyde, diene conjugates, and leukotriene as well as cNOS and iNOS activity were estimated. Obtained results show a significant restoration of cadiodynamic parameters at the reperfusion period. Simultaneously, all samples significantly reduced the rate of reactive oxygen species (ROS) and lipid peroxidation markers in cardiac homogenates and preserved cNOS activity at the preischemic level. This evidence makes GrO derivatives promising candidates for the correction of reperfusion disorders affecting myocardial function.

Potential Cardioprotective Role of Menaquinone-4 Against Cardiac Ischemia-reperfusion Injury

ABSTRACT

Myocardial infarction is among the leading causes of mortality. Menaquinone-4 (MK-4), a vitamin K2 analog, might play a role in rescuing cardiac ischemia/reperfusion (I/R) injury. This work aimed to discover the potential cardioprotective role of MK-4 against myocardial I/R injury in rats. Thirty-two rats were categorized into 3 groups: (I/R) control group: subjected to I/R protocol (received vehicle), MK-4 preconditioning group: MK-4 infusion for 20 minutes before the I/R protocol, and MK-4 postconditioning group: MK-4 infusion for 20 minutes at the start of the reperfusion phase. The hearts were placed in the Langendorff apparatus, and the left ventricular developed pressure (LVDP), heart rate (HR), + (LV dP/dt) max, - (LV dP/dt) max, and Tau were calculated. The necrotic mass was determined by staining it with nitro blue tetrazolium. Creatine kinase-MB (CK-MB), lactate dehydrogenase (LDH), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and C- reactive protein (CRP), as well as cardiac superoxide dismutase (SOD), nitric oxide (NOx), malondialdehyde (MDA), and glutathione (GSH) levels were all evaluated. MK-4 postconditioning significantly reduced myocardial infarct size; increased LVDP, + (LV dp/dt) max, - (LV dp/dt) max, and HR; reduced Tau, CK-MB, LDH, CRP, IL-6, TNF-α, MDA, and NOx levels; and increased SOD activity, whereas no significant difference in the GSH level was detected. In conclusion, these data imply that MK-4 may protect the heart from the consequences of I/R.

BNP protects against diabetic cardiomyopathy by promoting Opa1-mediated mitochondrial fusion via activating the PKG-STAT3 pathway

Brain natriuretic peptide (BNP) belongs to the family of natriuretic peptides, which are responsible for a wide range of actions. Diabetic cardiomyopathy (DCM) is often associated with increased BNP levels. This present research intends to explore the role of BNP in the development of DCM and the underlying mechanisms. Diabetes was induced in mice using streptozotocin (STZ). Primary neonatal cardiomyocytes were treated with high glucose. It was found that the levels of plasma BNP started to increase at 8 weeks after diabetes, which preceded the development of DCM. Addition of exogenous BNP promoted Opa1-mediated mitochondrial fusion, inhibited mitochondrial oxidative stress, preserved mitochondrial respiratory capacity and prevented the development of DCM, while knockdown of endogenous BNP exacerbated mitochondrial dysfunction and accelerated DCM. Opa1 knockdown attenuated the aforementioned protective action of BNP both in vivo and in vitro. BNP-induced mitochondrial fusion requires the activation of STAT3, which facilitated Opa1 transcription by binding to its promoter regions. PKG, a crucial signaling biomolecule in the BNP signaling pathway, interacted with STAT3 and induced its activation. Knockdown of NPRA (the receptor of BNP) or PKG blunted the promoting effect of BNP on STAT3 phosphorylation and Opa1-mediated mitochondrial fusion. The results of this study demonstrate for the first time that there is a rise in BNP during the early stages of DCM as a compensatory protection mechanism. BNP is a novel mitochondrial fusion activator in protecting against hyperglycemia-induced mitochondrial oxidative injury and DCM through the activation of NPRA-PKG-STAT3-Opa1 signaling pathway.

Proteomics as a Tool for the Study of Mitochondrial Proteome, Its Dysfunctionality and Pathological Consequences in Cardiovascular Diseases

The focus of this review is on the proteomic approaches applied to the study of the qualitative/quantitative changes in mitochondrial proteins that are related to impaired mitochondrial function and consequently different types of pathologies. Proteomic techniques developed in recent years have created a powerful tool for the characterization of both static and dynamic proteomes. They can detect protein-protein interactions and a broad repertoire of post-translation modifications that play pivotal roles in mitochondrial regulation, maintenance and proper function. Based on accumulated proteomic data, conclusions can be derived on how to proceed in disease prevention and treatment. In addition, this article will present an overview of the recently published proteomic papers that deal with the regulatory roles of post-translational modifications of mitochondrial proteins and specifically with cardiovascular diseases connected to mitochondrial dysfunction.

Molecular Signaling to Preserve Mitochondrial Integrity against Ischemic Stress in the Heart: Rescue or Remove Mitochondria in Danger

Cardiovascular diseases are one of the leading causes of death and global health problems worldwide, and ischemic heart disease is the most common cause of heart failure (HF). The heart is a high-energy demanding organ, and myocardial energy reserves are limited. Mitochondria are the powerhouses of the cell, but under stress conditions, they become damaged, release necrotic and apoptotic factors, and contribute to cell death. Loss of cardiomyocytes plays a significant role in ischemic heart disease. In response to stress, protective signaling pathways are activated to limit mitochondrial deterioration and protect the heart. To prevent mitochondrial death pathways, damaged mitochondria are removed by mitochondrial autophagy (mitophagy). Mitochondrial quality control mediated by mitophagy is functionally linked to mitochondrial dynamics. This review provides a current understanding of the signaling mechanisms by which the integrity of mitochondria is preserved in the heart against ischemic stress.

Current trends and future perspectives for heart failure treatment leveraging cGMP modifiers and the practical effector PKG

Cyclic guanosine monophosphate (cGMP), an intracellular second messenger molecule synthesized by guanylated cyclases (GCs), controls various myocardial properties, including cell growth and survival, interstitial fibrosis, endothelial permeability, cardiac contractility, and cardiovascular remodeling. These processes are mediated by the main cGMP effector protein kinase G (PKG) activation of which exerts intrinsic protective responses against the adverse effects of neurohormonal stimulation and pathological cardiac stress. Therapeutic strategies that enhance cGMP levels and PKG activation have been used for heart failure, which can be executed by reducing natriuretic peptide (NP) proteolysis, enhancing cGMP synthesis, or blocking cGMP hydrolysis. Among these, reducing NP clearance with neprilysin inhibitor combined with angiotensin receptor blocker has been shown to greatly improve the prognosis of patients with heart failure with reduced ejection fraction (HFrEF) compared to the prognosis of patients on standard therapy using angiotensin-converting enzyme inhibitors. Moreover, in a recent phase III clinical trial, soluble GC-derived cGMP generation was shown to have potential efficacy in the management of HFrEF. Despite the clinical significance of cGMP/PKG signaling activated by either soluble or particulate GCs in heart failure, the differential signaling events downstream of intracellular cGMP, which are precisely controlled not only by PKG activation but also by the changes in its targeting and compartmentalization depending on the pathophysiology of heart disease, are not yet completely understood. Hitherto, the importance of the latter PKG regulatory mechanisms in developing therapeutic strategies has not been elucidated. Further investigation of redox-based PKG modulation will aid in the successful development of clinical therapies and could also lead to the establishment of improved personalized treatments for patients with heart failure.

The mitochondrial NO-synthase/guanylate cyclase/protein kinase G signaling system underpins the dual effects of nitric oxide on mitochondrial respiration and opening of the permeability transition pore

The available data on the involvement of nitric oxide (NO) and mitochondrial calcium-dependent NO synthase (mtNOS) in the control of mitochondrial respiration and the permeability transition pore (mPTP) are contradictory. We have proposed that the mitochondrial mtNOS/guanylate cyclase/protein kinase G signaling system (mtNOS-SS) is also implicated in the control of respiration and mPTP, providing the interplay between NO and mtNOS-SS, which, in turn, may result in inconsistent effects of NO. Therefore, using rat liver mitochondria, we applied specific inhibitors of the enzymes of this signaling system to evaluate its role in the control of respiration and mPTP opening. Steady-state respiration was supported by pyruvate, glutamate, or succinate in the presence of hexokinase, glucose, and ADP. When applied at low concentrations, l-arginine (to 500 µm) and NO donors (to 50 µm) activated the respiration and increased the threshold concentrations of calcium and d,l-palmitoylcarnitine required for the dissipation of the mitochondrial membrane potential and pore opening. Both effects were eliminated by the inhibitors of NO synthase, guanylate cyclase, and kinase G, which denotes the involvement of mtNOS-SS in the activation of respiration and deceleration of mPTP opening. At high concentrations, l-arginine and NO donors inhibited the respiration and promoted pore opening, indicating that adverse effects induced by an NO excess dominate over the protection provided by mtNOS-SS. Thus, these results demonstrate the opposite impact of NO and mtNOS-SS on the respiration and mPTP control, which can explain the dual effects of NO.

Nitric Oxide Donor NOC-18-Induced Changes of Mitochondrial Phosphoproteome in Rat Cardiac Ischemia Model

Background and objective: Nitric oxide (NO) is known to exert cardioprotective effects against heart ischemic damage and may be involved in ischemic pre- and postconditioning. NO-triggered cardioprotective mechanisms are not well understood but may involve regulation of mitochondrial permeability transition pore (mPTP). In this study, we aimed to identify differentially phosphorylated mitochondrial proteins possibly involved in the NO/protein kinase G (PKG)/mPTP signaling pathway that can increase the resistance of cardiomyocytes to ischemic damage. Materials and methods: Isolated hearts from Wistar rats were perfused with NO donor NOC-18 prior to induction of stop–flow ischemia. To quantify and characterize the phosphoproteins, mitochondrial proteins were resolved and analyzed by two-dimensional gel electrophoresis followed by Pro-Q Diamond phosphoprotein gel staining, excision, trypsin digestions, and mass spectrometry. Quantitative proteomic analysis coupled with liquid chromatography–tandem mass spectrometry was also performed. Results: Mitochondrial protein phosphorylation patterns in NOC-18-pretreated ischemic hearts versus ischemic hearts were compared. Pretreatment of hearts with NOC-18 caused changes in mitochondrial phosphoproteome after ischemia which involved modifications of 10 mitochondrial membrane-bound and 10 matrix proteins. Among them, α-subunit of ATP synthase and adenine nucleotide (ADP/ATP) translocase 1, both of which are considered as potential structural components of mPTP, were identified. We also found that treatment of isolated non-ischemic mitochondria with recombinant PKG did not cause the same protein phosphorylation as pretreatment of hearts with NOC-18. Conclusions: Our study suggests that pretreatment of hearts with NOC-18 causes changes in mitochondrial phosphoproteome after ischemia which involves modifications of certain proteins thought to be involved in the regulation of mPTP opening and intracellular redox state. These proteins may be potential targets for pharmacological preconditioning of the heart.

Cardioprotective Effect of Isosorbide Dinitrate Postconditioning Against Rat Myocardial Ischemia-Reperfusion Injury In Vivo

BACKGROUND This study investigated the cardioprotective effect of isosorbide dinitrate (ISDN) postconditioning against rat myocardial ischemia/reperfusion injury in vivo and provided a theoretical basis for clinical application. MATERIAL AND METHODS We randomly divided 32 Wistar rats into 4 groups: sham group, I/R (ischemia/reperfusion) group, I-PostC group (with 3 cycles of 30 s reperfusion and 30 s reocclusion applied at the onset of reperfusion), and P-PostC group (nitrate postconditioning: isosorbide dinitrate (5mg/kg) was given 1 min before reperfusion). The left anterior descending artery (LAD) was occluded for 40 min, followed by a 180-min reperfusion. Relevant indicators were tested. The LAD was occluded again, then we determined the myocardial infarct size. Paraffinized sections were prepared and TUNEL detection was performed. RESULTS There were no significant differences in ischemic sizes between different groups. Compared with the I/R group, the levels of cTnI and myocardial infarct size in the I-PostC group and P-PostC group were significantly decreased (p<0.05). However, there were no significant difference between the I-PostC group and P-PostC group. Compared with the sham-operated group, the levels of cTnI and MDA in the I/R group, I-PostC group, and P-PostC group were significantly increased (p<0.05) and the levels of SOD were significantly decreased (p<0.05). Compared with the I/R group, I-PostC and P-PostC decreased the level of MDA and increased the level of SOD (both P<0.05). CONCLUSIONS ISDN postconditioning induces a similar cardioprotective effect as I-PostC. The potential mechanisms of cardioprotection of ISDN postconditioning might be via improvement of myocardial antioxidant capacity and reduced generation of reactive oxygen species.

Microglial activation and the nitric oxide/cGMP/PKG pathway underlie enhanced neuronal vulnerability to mitochondrial dysfunction in experimental multiple sclerosis

During multiple sclerosis (MS), a close link has been demonstrated to occur between inflammation and neuro-axonal degeneration, leading to the hypothesis that immune mechanisms may promote neurodegeneration, leading to irreversible disease progression. Energy deficits and inflammation-driven mitochondrial dysfunction seem to be involved in this process. In this work we investigated, by the use of striatal electrophysiological field-potential recordings, if the inflammatory process associated with experimental autoimmune encephalomyelitis (EAE) is able to influence neuronal vulnerability to the blockade of mitochondrial complex IV, a crucial component for mitochondrial activity responsible of about 90% of total cellular oxygen consumption. We showed that during the acute relapsing phase of EAE, neuronal susceptibility to mitochondrial complex IV inhibition is markedly enhanced. This detrimental effect was counteracted by the pharmacological inhibition of microglia, of nitric oxide (NO) synthesis and its intracellular pathway (involving soluble guanylyl cyclase, sGC, and protein kinase G, PKG). The obtained results suggest that mitochondrial complex IV exerts an important role in maintaining neuronal energetic homeostasis during EAE. The pathological processes associated with experimental MS, and in particular the activation of microglia and of the NO pathway, lead to an increased neuronal vulnerability to mitochondrial complex IV inhibition, representing promising pharmacological targets.

Immunobiology of Nitric Oxide and Regulation of Inducible Nitric Oxide Synthase

Nitric oxide (NO) is a bioactive gas that has multiple roles in innate and adaptive immune responses. In macrophages, nitric oxide is produced by inducible nitric oxide synthase upon microbial and cytokine stimulation. It is needed for host defense against pathogens and for immune regulation. This review will summarize the role of NO and iNOS in inflammatory and immune responses and will discuss the regulatory mechanisms that control inducible nitric oxide synthase expression and activity.

DPP-4 Inhibitor and Estrogen Share Similar Efficacy Against Cardiac Ischemic-Reperfusion Injury in Obese-Insulin Resistant and Estrogen-Deprived Female Rats

Estrogen deprivation aggravates cardiac injury after myocardial ischemia and reperfusion (I/R) injury. Although either estrogen or the dipeptidyl peptidase-4 (DPP-4) inhibitor, vildagliptin, reduces myocardial damage following cardiac I/R, their effects on the heart in obese-insulin resistant and estrogen deprived conditions remain unknown. Ovariectomized (O) rats (n = 36) were divided to receive either normal diet (NDO) or high-fat diet (HFO) for 12 weeks, followed by treatment with a vehicle, estrogen or vildagliptin for 4 weeks. The setting of in vivo cardiac I/R injury, 30-min ischemia and 120-min reperfusion, was performed. At 12 weeks after ovariectomy, both NDO and HFO rats exhibited an obese-insulin resistant condition. Both NDO and HFO rats treated with estrogen and vildagliptin showed reduced fasting plasma glucose, insulin and HOMA index. Both treatments improved cardiac function indicated by restoration of heart rate variability and increased %left ventricular ejection fraction (%LVEF). The treatments similarly protected cardiac mitochondrial function against I/R injury, leading to a reduction in the infarct size, oxidative stress and apoptosis in the ischemic myocardium. These findings demonstrate that vildagliptin effectively improves metabolic status, and shares similar efficacy to estrogen in reducing myocardial infarction and protecting cardiac mitochondrial function against I/R injury in estrogen-deprived obese-insulin resistant rats.

Neuroprotective Strategies during Cardiac Surgery with Cardiopulmonary Bypass

Aortocoronary bypass or valve surgery usually require cardiac arrest using cardioplegic solutions. Although, in principle, in a number of cases beating heart surgery (so-called off-pump technique) is possible, aortic or valve surgery or correction of congenital heart diseases mostly require cardiopulmonary arrest. During this condition, the heart-lung machine also named cardiopulmonary bypass (CPB) has to take over the circulation. It is noteworthy that the invention of a machine bypassing the heart and lungs enabled complex cardiac operations, but possible negative effects of the CPB on other organs, especially the brain, cannot be neglected. Thus, neuroprotection during CPB is still a matter of great interest. In this review, we will describe the impact of CPB on the brain and focus on pharmacological and non-pharmacological strategies to protect the brain.

Morphine stimulates nitric oxide release in human mitochondria

The expression of morphine by plants, invertebrate, and vertebrate cells and organ systems, strongly indicates a high level of evolutionary conservation of morphine and related morphinan alkaloids as required for life. The prototype catecholamine, dopamine, serves as an essential chemical intermediate in morphine biosynthesis, both in plants and animals. We surmise that, before the emergence of specialized plant and animal cells/organ systems, primordial multi-potential cell types required selective mechanisms to limit their responsiveness to environmental cues. Accordingly, cellular systems that emerged with the potential for recruitment of the free radical gas nitric oxide (NO) as a multi-faceted autocrine/paracrine signaling molecule, were provided with extremely positive evolutionary advantages. Endogenous morphinergic signaling, in concert with NO-coupled signaling systems, has evolved as an autocrine/paracrine regulator of metabolic homeostasis, energy metabolism, mitochondrial respiration and energy production. Basic physiological processes involving morphinergic/NO-coupled regulation of mitochondrial function, with special emphasis on the cardiovascular system, are critical to all organismic survival. Key to this concept may be the phenomenon of mitochondrial enslavement in eukaryotic evolution via endogenous morphine.

Increased Long-Term Mortality among Black CABG Patients Receiving Preoperative Inotropic Agents

The aim of this study was to examine racial differences in long-term mortality after coronary artery bypass grafting (CABG), stratified by preoperative use of inotropic agents. Black and white patients who required preoperative inotropic support prior to undergoing CABG procedures between 1992 and 2011 were compared. Mortality probabilities were computed using the Kaplan-Meier product-limit method. Hazard ratios (HR) and 95% confidence intervals (CI) were computed using a Cox regression model. A total of 15,765 patients underwent CABG, of whom 211 received preoperative inotropic agents within 48 hours of surgery. Long-term mortality differed by race (black versus white) among preoperative inotropic category (inotropes: adjusted HR = 1.6, 95% CI = 1.009–2.4; no inotropes: adjusted HR = 1.15, 95% CI = 1.08–1.2; P_interaction < 0.0001). Our study identified an independent preoperative risk-factor for long-term mortality among blacks receiving CABG. This outcome provides information that may be useful for surgeons, primary care providers, and their patients.

Poly (ADP‑ribose) polymerase‑ and cytochrome c‑mediated apoptosis induces hepatocyte injury in a rat model of hyperammonia‑induced hepatic failure

Hepatic failure (HF) is caused by several factors, which induce liver cell damage and dysfunction. However, the specific mechanism of HF remains to be fully elucidated. The present study aimed to investigate the underlying cause of hepatocyte injury and liver dysfunction. Liver cells were isolated from healthy female Sprague-Dawley rats, aged between 6 and 8 weeks, weighing ~230 g. The liver cells were cultured in RPMI-1640 medium containing 10% fetal bovine serum. An MTT assay was used to examine the inhibitory rate of liver growth in each group. Flow cytometric analysis was performed to detect liver cells undergoing apoptosis. The protein expression levels of poly (ADP-ribose) polymerase (PARP) and cytochrome c (Cyt C) were detected by western blotting. The level of calmodulin-dependent kinase (CaMK) was assessed using an ELISA. The results indicated that the growth inhibitory rate of rat liver cells was significantly increased following treatment with increasing concentrations of NH₄Cl. The results of flow cytometric analysis demonstrated that the apoptotic rate in the BAPTA-acetoxymethyl ester group was significantly lower compared with the NH₄Cl group (P<0.05). Treatment with NH₄Cl increased the protein expression levels of PARP and Cyt C in the liver cells. The mRNA expression of CaMK decreased gradually following treatment with increasing concentrations of NH₄Cl for 6, 12 and 24 h. The results suggested that hepatocyte injury and liver dysfunction may be caused by inducing apoptosis via the PARP and Cyt C pathways. Additionally, downregulation of CaMK may be associated with the apoptosis observed in hepatocyte injury.

Mitochondrial channels: ion fluxes and more

The field of mitochondrial ion channels has recently seen substantial progress, including the molecular identification of some of the channels. An integrative approach using genetics, electrophysiology, pharmacology, and cell biology to clarify the roles of these channels has thus become possible. It is by now clear that many of these channels are important for energy supply by the mitochondria and have a major impact on the fate of the entire cell as well. The purpose of this review is to provide an up-to-date overview of the electrophysiological properties, molecular identity, and pathophysiological functions of the mitochondrial ion channels studied so far and to highlight possible therapeutic perspectives based on current information.

Differential expression of transcription factors and inflammation-, ROS-, and cell death-related genes in organotypic cultures in the modiolus, the organ of Corti and the stria vascularis of newborn rats

Cells respond to injury and hypoxia by changing gene expression. To study how the main compartments of the cochlea, the stria vascularis (SV), the organ of Corti (OC), and the modiolus (MOD), respond to such stress, we analyzed the expression of selected genes using microarray analysis. Organotypic cultures of SV, OC, and MOD from newborn rats were used as an experimental model. In the present study, we compare the expression of a total of 50 genes involved in apoptosis and necrosis, reactive oxygen species (ROS) metabolism, inflammation as well as selected transcription factors (TF) and analyze their role for the different cell death patterns observed in the three regions. MOD, OC, and SV differ not only in their basal gene profiles but also in their ability to respond to injury and hypoxia. The results provide two coexpression clusters across the three regions, a Hif-1a coexpression cluster and a cluster around the cell death-associated transcripts Casp3, Capn1, Capn2, and Capns1. These clusters include the TF Jun, Bmyc, Nfyc, Foxd3, Hes1, the ROS-associated molecules Sod3, and Nos2, and the inflammatory chemokine Ccl20. The evidence of both clusters indicates the complex and regulated character of gene expression following injury and hypoxia across the three regions SV, OC, and MOD. The high vulnerability of spiral ganglion neurons in the MOD region, previously explained on the basis of the availability of neuro-trophic factors, is associated with the increased endogenous production of ROS and nitric oxide and inadequate activation of protective acting genes.

Conformational change of mitochondrial complex I increases ROS sensitivity during ischemia

AIMS

Myocardial ischemia/reperfusion (I/R) is associated with mitochondrial dysfunction and subsequent cardiomyocyte death. The generation of excessive quantities of reactive oxygen species (ROS) and resultant damage to mitochondrial enzymes is considered an important mechanism underlying reperfusion injury. Mitochondrial complex I can exist in two interconvertible states: active (A) and deactive or dormant (D). We have studied the active/deactive (A/D) equilibrium in several tissues under ischemic conditions in vivo and investigated the sensitivity of both forms of the heart enzyme to ROS.

RESULTS

We found that in the heart, t½ of complex I deactivation during ischemia was 10 min, and that reperfusion resulted in the return of A/D equilibrium to its initial level. The rate of superoxide generation by complex I was higher in ischemic samples where content of the D-form was higher. Only the D-form was susceptible to inhibition by H2O2 or superoxide, whereas turnover-dependent activation of the enzyme resulted in formation of the A-form, which was much less sensitive to ROS. The mitochondrial-encoded subunit ND3, most likely responsible for the sensitivity of the D-form to ROS, was identified by redox difference gel electrophoresis.

INNOVATION

A combined in vivo and biochemical approach suggests that sensitivity of the mitochondrial system to ROS during myocardial I/R can be significantly affected by the conformational state of complex I, which may therefore represent a new therapeutic target in this setting.

CONCLUSION

The presented data suggest that transition of complex I into the D-form in the absence of oxygen may represent a key event in promoting cardiac injury during I/R.

Effects of nitric oxide on cell proliferation: novel insights

Nitric oxide (NO) has been suggested to be a pathophysiological modulator of cell proliferation, cell cycle arrest, and apoptosis. In this context, NO can exert opposite effects under diverse conditions. Indeed, several studies have indicated that low relative concentrations of NO seem to favor cell proliferation and antiapoptotic responses and higher levels of NO favor pathways inducing cell cycle arrest, mitochondria respiration, senescence, or apoptosis. Here we report the effects of NO on both promotion and inhibition of cell proliferation, in particular in regard to cardiovascular disease, diabetes, and stem cells. Moreover, we focus on molecular mechanisms of action involved in the control of cell cycle progression, which include both cyclic guanosine monophosphate-dependent and -independent pathways. This growing field may lead to broad and novel targeted therapies against cardiovascular diseases, especially concomitant type 2 diabetes, as well as novel bioimaging NO-based diagnostic tools.

In the eye of the storm: mitochondrial damage during heart and brain ischaemia

We review research investigating mitochondrial damage during heart and brain ischaemia, focusing on the mechanisms and consequences of ischaemia-induced and/or reperfusion-induced: (a) inhibition of mitochondrial respiratory complex I; (b) release of cytochrome c from mitochondria; (c) changes to mitochondrial phospholipids; and (d) nitric oxide inhibition of mitochondria. Heart ischaemia causes inhibition of cytochrome oxidase and complex I, release of cytochrome c, and induction of permeability transition and hydrolysis and oxidation of mitochondrial phospholipids, but some of the mechanisms are unclear. Brain ischaemia causes inhibition of complexes I and IV, but other effects are less clear.

Essential role of nitric oxide in acute ischemic preconditioning: S-nitros(yl)ation versus sGC/cGMP/PKG signaling?

Nitric oxide (NO) plays an important role in acute ischemic preconditioning (IPC). In addition to activating soluble guanylyl cyclase (sGC)/cyclic guanosine monophosphate (cGMP)/protein kinase G (PKG) signaling pathways, NO-mediated protein S-nitros(yl)ation (SNO) has been recently shown to play an essential role in cardioprotection against ischemia-reperfusion (I/R) injury. In our previous studies, we have shown that IPC-induced cardioprotection could be blocked by treatment with either N-nitro-L-arginine methyl ester (L-NAME, a constitutive NO synthase inhibitor) or ascorbate (a reducing agent to decompose SNO). To clarify NO-mediated sGC/cGMP/PKG-dependent or -independent (i.e., SNO) signaling involved in IPC-induced cardioprotection, mouse hearts were Langendorff-perfused in the dark to prevent SNO decomposition by light exposure. Treatment with 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, a highly selective inhibitor of sGC) or KT5823 (a potent and selective inhibitor of PKG) did not abolish IPC-induced acute protection, suggesting that the sGC/cGMP/PKG signaling pathway does not play an important role in NO-mediated cardioprotective signaling during acute IPC. In addition, treatment with ODQ in IPC hearts provided an additional protective effect on functional recovery, in parallel with a higher SNO level in these ODQ+IPC hearts. In conclusion, these results suggest that the protective effect of NO is not related primarily to activation of the sGC/cGMP/PKG signaling pathway, but rather through SNO signaling in IPC-induced acute cardioprotection.

Cytosolic Ca2+-induced apoptosis in rat cardiomyocytes via mitochondrial NO-cGMP-protein kinase G pathway

Previously, we showed that in adult rat cardiomyocytes, nitric oxide (NO) donors stimulate mitochondrial cGMP production, followed by cytochrome c release, independently of the mitochondrial permeable transition pore. We investigated whether mitochondrial cGMP-induced cytochrome c release from cardiac mitochondria is Ca(2+)-sensitive. Mitochondria and primary cultured cardiomyocytes were prepared from left ventricles of male Wistar rats. The cytosolic Ca(2+) concentration was adjusted with Ca(2+)-EGTA buffers. Cytochrome c released from mitochondria was measured by Western blotting. Cardiomyocyte apoptosis was assessed by Annexin V staining. Cytochrome c release from cardiac mitochondria was evoked by buffered Ca(2+) (1 μM); this was inhibited by NO-cGMP pathway inhibitors such as N(G)-monomethyl-l-arginine monoacetate (inhibitor of NO synthase), 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (NO scavenger), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, NO-sensitive guanylyl cyclase inhibitor) and voltage-dependent anion channel (VDAC) inhibitor, 4,4'-diisothiocyano-2,2'-disulfonic acid stilbene, but not by cyclosporin A (mitochondrial permeable transition pore inhibitor). Furthermore, this release was significantly and dose dependently inhibited by 0.3-3 μM KT5823 (protein kinase G inhibitor). At the cellular level, intracellular perfusion of cardiomyocytes with buffered Ca(2+) (1 μM) also induced apoptosis, which was inhibited in the presence of ODQ. A membrane-permeable cGMP analog, 8-Br-cGMP, but not cGMP itself, mimicked buffered Ca(2+) actions in both cardiac mitochondria and cardiomyocytes. We further confirmed an increase in protein kinase G activity by adding cGMP in mitochondrial protein fraction. Our results suggest that mitochondrial NO-cGMP pathway-induced cytochrome c release from cardiac mitochondria, triggered by increased cytosolic Ca(2+), occurs through VDAC via the stimulation of an undiscovered mitochondrial protein kinase G.

Mitochondrial performance in heat acclimation--a lesson from ischemia/reperfusion and calcium overload insults in the heart

Long-term heat acclimation (LTHA; 30 days, 34°C) causes phenotypic adaptations that render protection against ischemic/reperfusion insult (I/R, 30 min global ischemia and 40 min reperfusion) via heat acclimation-mediated cross-tolerance (HACT) mechanisms. Short-term acclimation (STHA, 2 days, 34 °C), in contrast, is characterized by cellular perturbations, leading to increased susceptibility to insults. Here, we tested the hypothesis that enhanced mitochondrial respiratory function is part of the acclimatory repertoire and that the 30-day regimen is required for protection via HACT. We subjected isolated hearts and mitochondria from controls (C), STHA, or LTHA rats to I/R, hypoxia/reoxygenation, or Ca2+ overload insults. Mitochondrial function was assessed by measuring O2 consumption, membrane potential (ΔΨm), mitochondrial Ca2+ ([Ca2+]m), ATP production, respiratory chain complex activities, and molecular markers of mitochondrial biogenesis. Our results, combining physiological and biochemical parameters, confirmed that mitochondria from LTHA rats subjected to insults, in contrast to C, preserve respiratory functions (e.g., upon I/R, C mitochondria fueled by glutamate-malate, demonstrated decreases of 81%, 13%, 25%, and 50% in O2/P ratio, ATP production, ΔΨm, and complex I activity, respectively, whereas the corresponding LTHA parameters remained unchanged). STHA mitochondria maintained ΔΨm but did not preserve ATP production. LTHA [Ca2+]m was significantly higher than that of C and STHA and was not affected by the hypoxia/reoxygenation protocol compared with C. Enhanced mitochondrial biogenesis markers, switched-on during STHA coincidentally with enhanced membrane integrity (ΔΨm), were insufficient to confer intact respiratory function upon insult. LTHA was required for respiratory complex I adaptation and HACT. Stabilized higher basal [Ca2+]m and attenuated Ca2+ overload are likely connected to this adaptation.

Inhibition of the Mitochondrial Permeability Transition for Cytoprotection: Direct versus Indirect Mechanisms

Mitochondria are fascinating organelles, which fulfill multiple cellular functions, as diverse as energy production, fatty acid β oxidation, reactive oxygen species (ROS) production and detoxification, and cell death regulation. The coordination of these functions relies on autonomous mitochondrial processes as well as on sustained cross-talk with other organelles and/or the cytosol. Therefore, this implies a tight regulation of mitochondrial functions to ensure cell homeostasis. In many diseases (e.g., cancer, cardiopathies, nonalcoholic fatty liver diseases, and neurodegenerative diseases), mitochondria can receive harmful signals, dysfunction and then, participate to pathogenesis. They can undergo either a decrease of their bioenergetic function or a process called mitochondrial permeability transition (MPT) that can coordinate cell death execution. Many studies present evidence that protection of mitochondria limits disease progression and severity. Here, we will review recent strategies to preserve mitochondrial functions via direct or indirect mechanisms of MPT inhibition. Thus, several mitochondrial proteins may be considered for cytoprotective-targeted therapies.

Protective effect of ligustrazine against myocardial ischaemia reperfusion in rats: the role of endothelial nitric oxide synthase

1. The aim of the present study was to determine whether ligustrazine (2,3,5,6-tetramethylpyrazine; TMP) exerts a cardioprotective effect during myocardial ischaemia reperfusion (IR), and to investigate the underlying mechanisms and the role of endothelial nitric oxide synthase (eNOS) in cardioprotection. 2. Sprague-Dawley rats were divided into a sham group and five IR groups: IR control, TMP pretreated, TMP + wortmannin (a phosphatidylinositol 3-kinase (PI3K) inhibitor), N(G) -nitro-L-arginine methyl ester (L-NAME; a NOS inhibitor) and TMP + L-NAME. IR was produced by 35 min of regional ischaemia followed by 120 min of reperfusion. Myocardial infarct size, oxidative stress, myocardial apoptosis, nitric oxide (NO) production, and expression of phosphorylated protein kinase B (Akt) and eNOS were measured. 3. TMP markedly decreased infarct size and attenuated myocardial apoptosis, as evidenced by a decrease in the apoptotic index and reduced caspase-3 activity. TMP treatment caused a marked increase in NO production. Cotreatment with wortmannin or L-NAME completely blocked the TMP-induced NO increase. TMP induced phosphorylation of Akt at Ser 473 (1.61 ± 0.18 vs 0.79 ± 0.10 in the IR control group) and phosphorylation of eNOS at Ser1177 (1.87 ± 0.33 vs 0.94 ± 0.22 in the IR control group). Wortmannin abrogated the phosphorylation of Akt and eNOS induced by TMP. 4. These data suggest that ligustrazine has anti-apoptotic and cardioprotective effects against myocardial IR injury and that it acts through the PI3K/Akt pathway. In addition, the phosphorylation of eNOS with subsequent NO production was found to be an important downstream effector that contributes significantly to the cardioprotective effect of TMP.

Levosimendan modulates programmed forms of cell death through K(ATP) channels and nitric oxide

Levosimendan exerts cardioprotection through mitochondrial K(ATP) (mitoK(ATP)) channels opening. In addition, intracoronary levosimendan was found to modulate programmed forms of cell death by nitric oxide (NO) involvement. The aim of this study was to examine the role of mitoK(ATP) channels and NO in the effects of levosimendan on apoptosis/autophagy. In H9c2 cells treated with hydrogen peroxide apoptosis/autophagy, survival signaling, cell viability, mitochondrial membrane potential, and permeability transition pore opening were analyzed through Western blot and colorimetric and fluorescence assays. Pretreatment of H9c2 cells with levosimendan was able to counteract the oxidative injuries caused by hydrogen peroxide. The effects of levosimendan were potentiated by diazoxide and were similar to those elicited by the autophagic activator rapamycin. The autophagic inhibitor 3-methyladenine reduced the effects of levosimendan, whereas after the pan-caspases inhibitor N-Acetyl-Asp-Glu-Val-Asp-al (Z-VAD.FMK), cell survival and autophagy in response to levosimendan increased. Both the mitoK(ATP) channels inhibition and the NO synthase blocking attenuated the cardioprotection elicited by levosimendan. The results have shown that levosimendan protects H9c2 cells against oxidative injuries through the modulation of the interplay between autophagy and apoptosis and the activation of survival signaling. The mitoK(ATP) channels and NO may be involved in such cardioprotection through interference with mitochondrial functioning.

Nitric oxide signaling: classical, less classical, and nonclassical mechanisms

Although nitric oxide (NO) was identified more than 150 years ago and its effects were clinically tested in the form of nitroglycerine, it was not until the decades of 1970-1990 that it was described as a gaseous signal transducer. Since then, a canonical pathway linked to cyclic GMP (cGMP) as its quintessential effector has been established, but other modes of action have emerged and are now part of the common body of knowledge within the field. Classical (or canonical) signaling involves the selective activation of soluble guanylate cyclase, the generation of cGMP, and the activation of specific kinases (cGMP-dependent protein kinases) by this cyclic nucleotide. Nonclassical signaling alludes to the formation of NO-induced posttranslational modifications (PTMs), especially S-nitrosylation, S-glutathionylation, and tyrosine nitration. These PTMs are governed by specific biochemical mechanisms as well as by enzymatic systems. In addition, a less classical but equally important pathway is related to the interaction between NO and mitochondrial cytochrome c oxidase, which might have important implications for cell respiration and intermediary metabolism. Cross talk trespassing these necessarily artificial conceptual boundaries is progressively being identified and hence an integrated systems biology approach to the comprehension of NO function will probably emerge in the near future.

1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one induces cell cycle arrest and apoptosis in HeLa cells by preventing microtubule polymerization

1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) is known as a specific inhibitor of soluble guanylyl cyclase (sGC). Previously, however, ODQ was reported to induce cell death via sGC-dependent and sGC-independent means in a variety of cell types. The aim of this study was to investigate the mechanism by which ODQ induces cell death in HeLa cells. Treatment of HeLa cells with ODQ induced a concentration-dependent decrease in cell viability over the range from 10 to 100 μM. DNA fragmentation and fluorescence-activated cell sorting analysis using annexin V and propidium iodide staining revealed that ODQ triggered apoptosis at concentrations of 50 and 100 μM within 24 to 48 h. The addition of 8-Br-cGMP in the presence of ODQ failed to rescue HeLa cells from death, suggesting that the inhibition of sGC was not responsible for the pro-apoptotic action of ODQ. ODQ arrested the cell cycle at the G2/M phase and caused disassembly of the microtubule network. This process was reversed by dithiothreitol. In addition, ODQ was shown to inhibit the polymerization of purified tubulin, and this was also prevented by dithiothreitol. These results indicate that ODQ inhibits microtubule assembly by direct oxidation of tubulin, induces cell cycle arrest at the G2/M phase, and triggers apoptosis in HeLa cells.

Blockade of electron transport during ischemia preserves bcl-2 and inhibits opening of the mitochondrial permeability transition pore

Myocardial ischemia damages the electron transport chain and augments cardiomyocyte death during reperfusion. To understand the relationship between ischemic mitochondrial damage and mitochondrial-driven cell death, the isolated perfused heart underwent global stop-flow ischemia with and without mitochondrial protection by reversible blockade of electron transport. Ischemic damage to electron transport depleted bcl-2 content and favored mitochondrial permeability transition (MPT). Reversible blockade of electron transport preserved bcl-2 content and attenuated calcium-stimulated mitochondrial swelling. Thus, the damaged electron transport chain leads to bcl-2 depletion and MPT opening. Chemical inhibition of bcl-2 with HA14-1 also dramatically increased mitochondrial swelling, augmented by exogenous H(2)O(2) stress, indicating that bcl-2 depleted mitochondria are poised to undergo MPT during the enhanced oxidative stress of reperfusion.

Stress-induced opening of the permeability transition pore in the dystrophin-deficient heart is attenuated by acute treatment with sildenafil

Susceptibility of cardiomyocytes to stress-induced damage has been implicated in the development of cardiomyopathy in Duchenne muscular dystrophy, a disease caused by the lack of the cytoskeletal protein dystrophin in which heart failure is frequent. However, the factors underlying the disease progression are unclear and treatments are limited. Here, we tested the hypothesis of a greater susceptibility to the opening of the mitochondrial permeability transition pore (PTP) in hearts from young dystrophic ( mdx) mice (before the development of overt cardiomyopathy) when subjected to a stress protocol and determined whether the prevention of a PTP opening is involved in the cardioprotective effect of sildenafil, which we have previously reported in mdx mice. Using the 2-deoxy-[3H]glucose method to quantify the PTP opening in ex vivo perfused hearts, we demonstrate that when compared with those of controls, the hearts from young mdx mice subjected to ischemia-reperfusion (I/R) display an excessive PTP opening as well as enhanced activation of cell death signaling, mitochondrial oxidative stress, cardiomyocyte damage, and poorer recovery of contractile function. Functional analyses in permeabilized cardiac fibers from nonischemic hearts revealed that in vitro mitochondria from mdx hearts display normal respiratory function and reactive oxygen species handling, but enhanced Ca2+ uptake velocity and premature opening of the PTP, which may predispose to I/R-induced injury. The administration of a single dose of sildenafil to mdx mice before I/R prevented excessive PTP opening and its downstream consequences and reduced tissue Ca2+ levels. Furthermore, mitochondrial Ca2+ uptake velocity was reduced following sildenafil treatment. In conclusion, beyond our documentation that an increased susceptibility to the opening of the mitochondrial PTP in the mdx heart occurs well before clinical signs of overt cardiomyopathy, our results demonstrate that sildenafil, which is already administered in other pediatric populations and is reported safe and well tolerated, provides efficient protection against this deleterious event, likely by reducing cellular Ca2+ loading and mitochondrial Ca2+ uptake.

U50,488H postconditioning reduces apoptosis after myocardial ischemia and reperfusion

AIMS

Evidence has indicated U50,488H, a selective κ-opioid receptor (κ-OR) agonist, administered before ischemia attenuates apoptosis and infarction during ischemia and reperfusion (I/R). However, it remains unclear whether U50,488H postconditioning reduces apoptosis during I/R. This study was designed, therefore, to test the hypothesis that U50,488H administered at the onset of reperfusion inhibits cardiomyocyte apoptosis and to investigate the underlying mechanisms.

MAIN METHODS

Male Sprague-Dawley rats were subjected to myocardial ischemia and reperfusion(MI/R) and were randomized to receive either vehicle, U50,488H, U50,488H plus Nor-BNI, a selective κ-OR antagonist, U50,488H plus wortmannin, a specific inhibitor of phosphoinositide 3'-kinase (PI3K), or U50,488H plus L-NAME, a nitric oxide synthase inhibitor (NOS inhibitor), immediately prior to reperfusion. In vitro study was performed on cultured neonatal cardiomyocytes subjected to simulated ischemia/reperfusion.

KEY FINDINGS

Treatment with U50,488H resulted in increases in Akt and endothelial nitric oxide synthase (eNOS) phosphorylation with secondary NO production both in vivo and in vitro and these effect were completely blocked by wortmannin and specific Akt inhibitor(AI). L-NAME treatment had no effect on Akt and eNOS phosphorylation; but, significantly reduced NO production. Moreover, treatment with U50,488H markedly reduced myocardial apoptotic death. Treatment with wortmannin and specific Akt inhibitor abolished the anti-apoptotic effect of U50,488H. L-NAME also significantly attenuated the anti-apoptotic effect of U50,488H.

SIGNIFICANCE

These results demonstrate that U50,488H administered immediately prior to reperfusion increases Akt phosphorylation through a PI3-kinase-dependent mechanism and reduces postischemic myocardial apoptosis. Phosphorylation of eNOS with secondary NO production contribute significantly to the anti-apoptotic effect of U50,488H postconditioning.

Interactive effects of endogenous morphine, nitric oxide, and ethanol on mitochondrial processes

Positive evolutionary pressure has preserved the ability to synthesize chemically authentic morphine, albeit in homeopathic concentrations, throughout animal phyla. The prototype catecholamine dopamine (DA) serves as an essential chemical intermediate in morphine biosynthesis both in plants and animals, thereby providing considerable insight into the roles reciprocal "morphinergic" and catecholamine regulation of diverse physiological processes. Primordial, multi-potential cell types, before the emergence of specialized plant and animal cells/organ systems, required selective mechanisms to limit their responsiveness to environmental noise. Accordingly, cellular systems that emerged with the potential for recruitment of the free radical gas nitric oxide (NO) as a multi-faceted autocrine/paracrine signaling molecule were provided with extremely positive evolutionary advantages. Endogenous "morphinergic" in concert with NO-coupled signaling systems have evolved as autocrine/paracrine regulators of metabolic homeostasis, energy metabolism, mitochondrial respiration and energy production. Basic physiological processes involving "morphinergic"/NO-coupled regulation of cardiovascular mitochondrial function, with special emphasis on the interactive effects of ethanol, are discussed within the context of our review.