Inhibition of the nitric oxide/cyclic guanosine monophosphate pathway limited the cardioprotective effect of post-conditioning in hearts with apical myocardial infarction

Novel drug design and repurposing: An opportunity to improve translational research in cardiovascular diseases?

Drug repurposing is defined as the use of approved therapeutic drugs for indications different from those for which they were originally designed. Repositioning diminishes both the time and cost for drug development by omitting the discovery stage, the analysis of absorption, distribution, metabolism, and excretion routes, as well as the studies of the biochemical and physiological effects of a new compound. Besides, drug repurposing takes advantage of the increased bioinformatics knowledge and availability of big data biology. There are many examples of drugs with repurposed indications evaluated in in vitro studies, and in pharmacological, preclinical, or retrospective clinical analyses. Here, we briefly review some of the experimental strategies and technical advances that may improve translational research in cardiovascular diseases. We also describe exhaustive research from basic science to clinical studies that culminated in the final approval of new drugs and provide examples of successful drug repurposing in the field of cardiology.

L-theanine abates oxidative stress and mitochondrial dysfunction in myocardial ischemia-reperfusion injury by positively regulating the antioxidant response

L-theanine (L-THE), a non-protein amino acid isolated from Camelia sinensis, has antioxidant properties that could prevent oxidative damage and mitochondrial dysfunction generated by myocardial ischemia and reperfusion (I/R) injury. The present study aimed to identify the effects of pretreatment with L-THE in rat hearts undergoing I/R. Wistar rats received vehicle or 250 mg/Kg L-THE intragastrically for 10 days. On day 11, hearts were removed under anesthesia and exposed to I/R injury in the Langendorff system. Measurement of left ventricular developed pressure and heart rate ex vivo demonstrates that L-THE prevents I/R-induced loss of cardiac function. Consequently, the infarct size of hearts subjected to I/R was significantly decreased when L-THE was administered. L-THE also mitigated I/R-induced oxidative injury in cardiac tissue by decreasing reactive oxygen species and malondialdehyde levels, while increasing the activity of antioxidant enzymes, SOD and CAT. Additionally, L-THE prevents oxidative phosphorylation breakdown and loss of inner mitochondrial membrane potential caused by I/R, restoring oxygen consumption levels, increasing respiratory control and phosphorylation efficiency, as well as buffering calcium overload. Finally, L-THE modifies the expression of genes involved in the antioxidant response through the overexpression of SOD1, SOD2 and CAT; as well as the transcriptional factors PPARα and Nrf2 in hearts undergoing I/R. In conclusion, L-THE confers cardioprotection against I/R injury by preventing oxidative stress, protecting mitochondrial function, and promoting overexpression of antioxidant genes. More studies are needed to place L-THE at the forefront of cardiovascular research and recommend its therapeutic use.

Pathways for Cardioprotection in Perspective: Focus on Remote Conditioning and Extracellular Vesicles

Despite the development of cutting-edge treatments, coronary artery disease (CAD) morbidity and mortality rates remain present at high levels. Therefore, new cardioprotective approaches are crucial to improve the health of patients. To date, experimental investigations of acute ischemia-reperfusion injury (IRI) have generally demonstrated the efficacy of local ischemic preconditioning and postconditioning cardioprotection techniques as well as of remote conditioning. However, application in clinical settings is still highly controversial and debated. Currently, remote ischemic conditioning (RIC) seems to be the most promising method for heart repair. Protective factors are released into the bloodstream, and protection can be transferred within and across species. For a long time, the cross-function and cross-transmission mechanisms of cardioprotection were largely unknown. Recently, it has been shown that small, anuclear, bilayered lipid membrane particles, known as extracellular vesicles (EVs), are the drivers of signal transduction in cardiac IRI and RIC. EVs are related to the pathophysiological processes of cardiovascular diseases (CVDs), according to compelling evidence. In this review, we will first review the current state of knowledge on myocardial IRI and cardioprotective strategies explored over the past 37 years. Second, we will briefly discuss the role of EVs in CVD and the most recent improvements on EVs as prognostic biomarkers, diagnostic, and therapeutic agents. We will discuss how EVs can be used as a new drug delivery mechanism and how they can be employed in cardiac treatment, also from a perspective of overcoming the impasse that results from neglecting confounding factors.

Mitochondrial Quality Control in Cardiac-Conditioning Strategies against Ischemia-Reperfusion Injury

Mitochondria are the central target of ischemic preconditioning and postconditioning cardioprotective strategies, which consist of either the application of brief intermittent ischemia/reperfusion (I/R) cycles or the administration of pharmacological agents. Such strategies reduce cardiac I/R injury by activating protective signaling pathways that prevent the exacerbated production of reactive oxygen/nitrogen species, inhibit opening of mitochondrial permeability transition pore and reduce apoptosis, maintaining normal mitochondrial function. Cardioprotection also involves the activation of mitochondrial quality control (MQC) processes, which replace defective mitochondria or eliminate mitochondrial debris, preserving the structure and function of the network of these organelles, and consequently ensuring homeostasis and survival of cardiomyocytes. Such processes include mitochondrial biogenesis, fission, fusion, mitophagy and mitochondrial-controlled cell death. This review updates recent advances in MQC mechanisms that are activated in the protection conferred by different cardiac conditioning interventions. Furthermore, the role of extracellular vesicles in mitochondrial protection and turnover of these organelles will be discussed. It is concluded that modulation of MQC mechanisms and recognition of mitochondrial targets could provide a potential and selective therapeutic approach for I/R-induced mitochondrial dysfunction.

Implications of Oxidative and Nitrosative Post-Translational Modifications in Therapeutic Strategies against Reperfusion Damage

Post-translational modifications based on redox reactions "switch on-off" the biological activity of different downstream targets, modifying a myriad of processes and providing an efficient mechanism for signaling regulation in physiological and pathological conditions. Such modifications depend on the generation of redox components, such as reactive oxygen species and nitric oxide. Therefore, as the oxidative or nitrosative milieu prevailing in the reperfused heart is determinant for protective signaling, in this review we defined the impact of redox-based post-translational modifications resulting from either oxidative/nitrosative signaling or oxidative/nitrosative stress that occurs during reperfusion damage. The role that cardioprotective conditioning strategies have had to establish that such changes occur at different subcellular levels, particularly in mitochondria, is also presented. Another section is devoted to the possible mechanism of signal delivering of modified proteins. Finally, we discuss the possible efficacy of redox-based therapeutic strategies against reperfusion damage.

Ischaemic post-conditioning in rats: Responder and non-responder differ in transcriptome of mitochondrial proteins

Ischaemic post‐conditioning (IPoC) is a clinical applicable procedure to reduce reperfusion injury. Non‐responsiveness to IPoC possibly caused by co‐morbidities limits its clinical attractiveness. We analysed differences in the expression of mitochondrial proteins between IPoC responder (IPoC‐R) and non‐responder (IPoC‐NR). Eighty rats were randomly grouped to sham, ischaemia/reperfusion (I/R), IPoC or ischaemic pre‐conditioning (IPC, as positive cardioprotective intervention) in vivo. Infarct sizes were quantified by plasma troponin I levels 60 minutes after reperfusion. After 7 days, rats were sacrificed and left ventricular tissue was taken for post hoc analysis. The transcriptome was analysed by qRT‐PCR and small RNA sequencing. Key findings were verified by immunoblots. I/R increased plasma troponin I levels compared to Sham. IPC reduced troponin I compared to I/R, whereas IPoC produced either excellent protection (IPoC‐R) or no protection (IPoC‐NR). Twenty‐one miRs were up‐regulated by I/R and modified by IPoC. qRT‐PCR analysis revealed that IPoC‐R differed from other groups by reduced expression of arginase‐2 and bax, whereas the mitochondrial uncoupling protein (UCP)‐2 was induced in IPC and IPoC‐R. IPoC‐R and IPoC‐NR synergistically increased the expression of non‐mitochondrial proteins like VEGF and SERCA2a independent of the infarct size. Cardiac function was more closely linked to differences in mitochondrial proteins than on regulation of calcium‐handling proteins. In conclusion, healthy rats could not always be protected by IPoC. IPoC‐NR displayed an incomplete responsiveness which is reflected by different changes in the mitochondrial transcriptome compared to IPoC‐R. This study underlines the importance of mitochondrial proteins for successful long‐term outcome.

Cardioprotective effects of Prolame and SNAP are related with nitric oxide production and with diminution of caspases and calpain-1 activities in reperfused rat hearts

Cardiac tissue undergoes changes during ischemia-reperfusion (I-R) that compromise its normal function. Cell death is one of the consequences of such damage, as well as diminution in nitric oxide (NO) content. This signaling molecule regulates the function of the cardiovascular system through dependent and independent effects of cyclic guanosine monophosphate (cGMP). The independent cGMP pathway involves post-translational modification of proteins by S-nitrosylation. Studies in vitro have shown that NO inhibits the activity of caspases and calpains through S-nitrosylation of a cysteine located in their catalytic site, so we propose to elucidate if the regulatory mechanisms of NO are related with changes in S-nitrosylation of cell death proteins in the ischemic-reperfused myocardium. We used two compounds that increase the levels of NO by different mechanisms: Prolame, an amino-estrogenic compound with antiplatelet and anticoagulant effects that induces the increase of NO levels in vivo by activating the endothelial nitric oxide synthase (eNOS) and that has not been tested as a potential inhibitor of apoptosis. On the other hand, S-Nitroso-N-acetylpenicillamine (SNAP), a synthetic NO donor that has been shown to decrease cell death after inducing hypoxia-reoxygenation in cell cultures. Main experimental groups were Control, I-R, I-R+Prolame and I-R+SNAP. Additional groups were used to evaluate the NO action pathways. Contractile function represented as heart rate and ventricular pressure was evaluated in a Langendorff system. Infarct size was measured with 2,3,5-triphenyltetrazolium chloride stain. NO content was determined indirectly by measuring nitrite levels with the Griess reaction and cGMP content was measured by Enzyme-Linked ImmunoSorbent Assay. DNA integrity was evaluated by DNA laddering visualized on an agarose gel and by Terminal deoxynucleotidyl transferase dUTP Nick-End Labeling assay. Activities of caspase-3, caspase-8, caspase-9 and calpain-1 were evaluated spectrophotometrically and the content of caspase-3 and calpain-1 by western blot. S-nitrosylation of caspase-3 and calpain-1 was evaluated by labeling S-nitrosylated cysteines. Our results show that both Prolame and SNAP increased NO content and improved functional recovery in post-ischemic hearts. cGMP-dependent and S-nitrosylation pathways were activated in both groups, but the cGMP-independent pathway was preferentially activated by SNAP, which induced higher levels of NO than Prolame. Although SNAP effectively diminished the activity of all the proteases, a correlative link between the activity of these proteases and S-nitrosylation was not fully established.

Protective effect of gastrodin on myocardial ischemia-reperfusion injury and the expression of Bax and Bcl-2

The protective effects of gastrodin on myocardial ischemia-reperfusion injury in rats and the underlying mechanism were investigated. Sprague Dawley (SD) rats were randomly divided into three groups, of which the gastrodin group was treated with gastrodin, and the other two groups were treated with normal saline. In the myocardial ischemia-reperfusion model group, myocardial ischemia was induced by ligation of the left anterior descending coronary artery, and myocardial reperfusion was performed by ligature removal. Only thread without ligation for the sham operation group was conducted. The rats were euthanized 8 days after surgery. Heart tissues were harvested and used for measurement of apoptotic rate and expression levels of apoptosis-related proteins. Serum levels of cytokines were measured also using blood samples. Compared with the myocardial ischemia-reperfusion model group, significant reduction of cardiomyocyte apoptosis was observed in the gastrodin group (P<0.05). In the gastrodin group, the protein and mRNA expression levels for Bax and activated caspase-3 decreased, while for Bcl-2 increased (P<0.05). Gastrodin can downregulate inflammatory cytokines (P<0.05) and upregulate anti-inflammatory cytokines such as IL-10 (P<0.05) in serum of SD rats. Therefore, gastrodin played a protective role in myocardial ischemia-reperfusion injury by regulating the expression levels of apoptosis-related signaling proteins and inflammatory cytokines.

Overexpression of inducible nitric oxide synthase in the diabetic heart compromises ischemic postconditioning

Ischemia postconditioning (PTC) can reduce myocardial ischemia/reperfusion injury. However, the effectiveness of PTC cardioprotection is reduced or lost in diabetes and the mechanisms are largely unclear. Hyperglycemia can induce overexpression of inducible nitric oxide synthesis (iNOS) in the myocardium of diabetic subjects. However, it is unknown whether or not iNOS especially its overexpression plays an important role in the loss of cardioprotection of PTC in diabetes. C57BL6 and iNOS^-/- mice were treated with streptozotocin to induce diabetes. Part of diabetic C57BL6 mice were also treated with an iNOS specific inhibitor, 1400 W. Mice were subjected to myocardial ischemia/ reperfusion with/without PTC. The hemodynamic parameters, plasma levels of cardiac troponin T (cTnT), TNF-α, IL-6 and nitric oxide (NO) were monitored. The myocardial infarct size, superoxide anion (O₂^-) generation, nitrotyrosine production and apoptosis were measured. The expression of phosphorylated Akt, endothelial NOS (eNOS), iNOS and Erk1/2 in ischemic heart were detected by immunoblot analysis. In diabetic C57BL6 and iNOS^-/- mice, the post-ischemic hemodynamics were impaired, the cTnT, TNF-α, IL-6 level, myocardial infarct size, apoptotic index, O₂^- and nitrotyrosine generation were increased and the Akt/eNOS signal pathways were inhibited. PTC improved hemodynamic parameters, reduced cTnT level, myocardial infarct size, apoptotic index, O₂^- and nitrotyrosine generation and activated Akt/eNOS and Erk1/2 signal pathways in both non-diabetic C57BL6 and iNOS^-/- mice as well as diabetic iNOS^-/- mice, but not in diabetic C57BL6 mice. PTC also increased NO production in both non-diabetic and diabetic C57BL6 and iNOS^-/- mice, and enhanced iNOS expression in non-diabetic C57BL6 mice. 1400 W restored the cardioprotection of PTC in diabetic C57BL6 mice. Our data demonstrated that PTC reduced myocardial ischemia/reperfusion injury in non-diabetic mice but not C57BL6 diabetic mice. Deletion of iNOS restored the cardioprotection of PTC in diabetic mice. Our findings suggest that iNOS plays a key role in the reduction of cardioprotection of PTC in diabetes and may provide a therapeutic target for diabetic patients.

Cardioprotective strategies preserve the stability of respiratory chain supercomplexes and reduce oxidative stress in reperfused ischemic hearts

Electron leakage from dysfunctional respiratory chain and consequent superoxide formation leads to mitochondrial and cell injury during ischemia and reperfusion (IR). In this work we evaluate if the supramolecular assembly of the respiratory complexes into supercomplexes (SCs) is associated with preserved energy efficiency and diminished oxidative stress in post-ischemic hearts treated with the antioxidant N-acetylcysteine (NAC) and the cardioprotective maneuver of Postconditioning (PostC). Hemodynamic variables, infarct size, oxidative stress markers, oxygen consumption and the activity/stability of SCs were compared between groups. We found that mitochondrial oxygen consumption and the activity of respiratory complexes are preserved in mitochondria from reperfused hearts treated with both NAC and PostC. Both treatments contribute to recover the activity of individual complexes. NAC reduced oxidative stress and maintained SCs assemblies containing Complex I, Complex III, Complex IV and the adapter protein SCAFI more effectively than PostC. On the other hand, the activities of CI, CIII and CIV associated to SCs assemblies were preserved by this maneuver, suggesting that the activation of other cardioprotective mechanisms besides oxidative stress contention might participate in maintaining the activity of the mitochondrial respiratory complexes in such superstructures. We conclude that both the monomeric and the SCs assembly of the respiratory chain contribute to the in vivo functionality of the mitochondria. However, although the ROS-induced damage and the consequent increased production of ROS affect the assembly of SCs, other levels of regulation as those induced by PostC, might participate in maintaining the activity of the respiratory complexes in such superstructures.

Mitochondria in Cardiac Postconditioning

Mitochondria play a pivotal role in cardioprotection. Here we report some fundamental studies which considered the role of mitochondrial components (connexin 43, mitochondrial KATP channels and mitochondrial permeability transition pore) in postconditioning cardioprotection. We briefly discuss the role of mitochondria, reactive oxygen species and gaseous molecules in postconditioning. Also the effects of anesthetics-used as cardioprotective substances-is briefly considered in the context of postconditioning. The role of mitochondrial postconditioning signaling in determining the limitation of cell death is underpinned. Issues in clinical translation are briefly considered. The aim of the present mini-review is to discuss in a historical perspective the role of main mitochondria mechanisms in cardiac postconditioning.

The opposing roles of NO and oxidative stress in cardiovascular disease

Nitric oxide (NO) plays a pivotal role in the maintenance of cardiovascular homeostasis. A reduction in the bioavailability of endogenous NO, manifest as a decrease in the production and/or impaired signaling, is associated with many cardiovascular diseases including hypertension, atherosclerosis, stroke and heart failure. There is substantial evidence that reactive oxygen species (ROS), generated predominantly from NADPH oxidases (Nox), are responsible for the reduced NO bioavailability in vascular and cardiac pathologies. ROS can compromise NO function via a direct inactivation of NO, together with a reduction in NO synthesis and oxidation of its receptor, soluble guanylyl cyclase. Whilst nitrovasodilators are administered to compensate for the ROS-mediated loss in NO bioactivity, their clinical utility is limited due to the development of tolerance and resistance and systemic hypotension. Moreover, efforts to directly scavenge ROS with antioxidants has had limited clinical efficacy. This review outlines the therapeutic utility of NO-based therapeutics in cardiovascular diseases and describes the source and impact of ROS in these pathologies, with particular focus on the interaction with NO. Future therapeutic approaches in the treatment of cardiovascular diseases are highlighted with a focus on nitroxyl (HNO) donors as an alternative to traditional NO donors and the development of novel Nox inhibitors.

Gastrodin Pretreatment Impact on Sarcoplasmic Reticulum Calcium Transport ATPase (SERCA) and Calcium Phosphate (PLB) Expression in Rats with Myocardial Ischemia Reperfusion

Background

Calcium overload, inflammation, and apoptosis play important roles in myocardial ischemia-reperfusion injury (MIRI). Gastrodin pretreatment can alleviate MIRI. This study observed sarcoplasmic reticulum calcium transport ATPase (Ca²⁺-ATPase, SERCA) and calcium phosphate (PLB) protein expression in the ventricular remodeling process after myocardial infarction to explore the effect of gastrodin pretreatment on MIRI.

Material/Methods

Healthy 7-week-old male SD rats were randomly divided into a sham group (A), a model group (B), and gastrodin pretreatment groups C, D, and E (100, 200, and 400 mg/kg, respectively) with 20 in each group. Anterior descending coronary artery ligation method was used to establish a rat MIRI model with 30-min ischemia and 120-min reperfusion. Cardiac electrophysiological activity was recorded. Serum IL-6 and IL10 levels were determined by ELISA. SERCA activity was tested by colorimetric phosphorus method. SERCA, PLB, and pSer-PLB protein expression were detected by Western blot.

Results

Compared with the sham group, IL-6 and IL-10 levels were elevated, SERCA2a expression was downregulated, and PLB protein was elevated in the model group (P<0.05). pSer16-PLB showed no significant difference among groups, and the ratio of pSer16-PLB/PLB obviously decreased (P<0.05). IL-6 level gradually declined and IL-10 increased in the gastrodin group following concentration elevation. SERCA 2a expression rose in the gastrodin group in a dose-dependent manner (P<0.05). Elevated PLB protein expression showed no significant difference, while pSer16-PLB protein increased (P<0.05), leading to elevated pSer16 PLB/PLB ratio (P<0.05).

Conclusions

Gastrodin pretreatment alleviates MIRI and inflammation injury by regulating SERCA and PLB expression to decrease calcium overload.

Altered Nitric Oxide System in Cardiovascular and Renal Diseases

Nitric oxide (NO) is synthesized by a family of NO synthases (NOS), including neuronal, inducible, and endothelial NOS (n/i/eNOS). NO-mediated effects can be beneficial or harmful depending on the specific risk factors affecting the disease. In hypertension, the vascular relaxation response to acetylcholine is blunted, and that to direct NO donors is maintained. A reduction in the activity of eNOS is mainly responsible for the elevation of blood pressure, and an abnormal expression of iNOS is likely to be related to the progression of vascular dysfunction. While eNOS/nNOS-derived NO is protective against the development of atherosclerosis, iNOS-derived NO may be proatherogenic. eNOS-derived NO may prevent the progression of myocardial infarction. Myocardial ischemia/reperfusion injury is significantly enhanced in eNOS-deficient animals. An important component of heart failure is the loss of coronary vascular eNOS activity. A pressure-overload may cause severer left ventricular hypertrophy and dysfunction in eNOS null mice than in wild-type mice. iNOS-derived NO has detrimental effects on the myocardium. NO plays an important role in regulating the angiogenesis and slowing the interstitial fibrosis of the obstructed kidney. In unilateral ureteral obstruction, the expression of eNOS was decreased in the affected kidney. In triply n/i/eNOS null mice, nephrogenic diabetes insipidus developed along with reduced aquaporin-2 abundance. In chronic kidney disease model of subtotal-nephrectomized rats, treatment with NOS inhibitors decreased systemic NO production and induced left ventricular systolic dysfunction (renocardiac syndrome).