Nitrite-Nitric Oxide Signaling and Cardioprotection. In: Santulli G, editor. Mitochondrial Dynamics in Cardiovascular Medicine. Cham: Springer International Publishing; 2017. pp. 335-46. [DOI: 10.1007/978-3-319-55330-6_18]

S-Nitroso Human Serum Albumin Enhances Left Ventricle Hemodynamic Performance and Reduces Myocardial Damage after Local Ischemia-Reperfusion Injury

Endothelial nitric oxide (NO) production is crucial in maintaining vascular homeostasis. However, in the context of ischemia-reperfusion (I/R) injury, uncoupled endothelial nitric oxide synthase (eNOS) can exacerbate reactive oxygen species (ROS) generation. Supplementation with S-nitroso human serum albumin (S-NO-HSA) offers a potential solution by mitigating eNOS uncoupling, thereby enhancing NO bioavailability. In a study conducted at the University of Verona, male rats underwent thoracotomy followed by 30 min left anterior descendant coronary (LAD) occlusion and subsequent reperfusion. Hemodynamic parameters were meticulously assessed using a conductance catheter inserted via the carotid artery. The rats were stratified into two main groups based on reperfusion duration and the timing of drug infusion, with the effects of S-NO-HSA evaluated after 2 or 24 h. Remarkably, intravenous administration of S-NO-HSA, initiated before or during ischemia, exhibited notable benefits. It significantly improved left ventricular function, safeguarded energetic substrates such as phosphocreatine and ATP, and sustained glutathione levels akin to basal conditions, indicative of diminished oxidative stress. The data from this study strongly suggest a protective role for S-NO-HSA in mitigating I/R injury induced by LAD artery occlusion, a phenomenon observed at both 2 and 24 h post-reperfusion. These findings underscore the promising therapeutic potential of NO supplementation in alleviating myocardial damage subsequent to ischemic insult.

Improvement of restless leg syndrome in maintenance hemodialysis patients with limb ischemic preconditioning: a single-center randomized controlled clinical trial

OBJECTIVE

This study evaluated the efficacy and safety of limb ischemic preconditioning (LIPC) in treating restless leg syndrome (RLS) in maintenance hemodialysis (MHD) patients.

METHODS

A total number of 45 patients participated in the study. They were randomly divided into LIPC group and control group. The LIPC was performed by inflating the limb ischemic preconditioning training device in the patient's thigh to 200 mmHg to create transient ischemia, whereas control group inflated the device to 20 mmHg. International Restless Legs Syndrome (IRLS), Clinical Global Impression Scale (CGI-S), and Medical Outputs Study Sleep Scale were employed to evaluate LIPC effectiveness. The primary endpoint was the 'rate of clinical improvement in RLS severity', defined as the percentage of patients who had an IRLS score decrease of ≥5 points in each group.

RESULTS

After intervention, the rate of clinical improvement in RLS severity was 56.5% in the LIPC group and 13.6% in the control group (13 (56.5) vs 3 (13.6), p = 0.003). In addition, the LIPC group's IRLS, CGI-S scores, the sleep disturbance and somnolence scores showed a significant downward trend compared to the control group (-5.5 ± 5.3 vs - 1.0 ± 3.8, p = 0.002; -1.7 ± 1.2 vs - 0.5 ± 1.4, p = 0.003; -15.5 ± 17.8 vs 3.7 ± 12.0, p < 0.001; -9.9 ± 18.8 vs - 2.4 ± 8.6, p = 0.003). During the study, there were no serious adverse event in any of the patients.

CONCLUSIONS

LIPC could be employed to effectively and safely alleviate the RLS symptoms in MHD patients.

Modeling Heart Diseases on a Chip: Advantages and Future Opportunities

Heart disease is a significant burden on global health care systems and is a leading cause of death each year. To improve our understanding of heart disease, high quality disease models are needed. These will facilitate the discovery and development of new treatments for heart disease. Traditionally, researchers have relied on 2D monolayer systems or animal models of heart disease to elucidate pathophysiology and drug responses. Heart-on-a-chip (HOC) technology is an emerging field where cardiomyocytes among other cell types in the heart can be used to generate functional, beating cardiac microtissues that recapitulate many features of the human heart. HOC models are showing great promise as disease modeling platforms and are poised to serve as important tools in the drug development pipeline. By leveraging advances in human pluripotent stem cell-derived cardiomyocyte biology and microfabrication technology, diseased HOCs are highly tuneable and can be generated via different approaches such as: using cells with defined genetic backgrounds (patient-derived cells), adding small molecules, modifying the cells' environment, altering cell ratio/composition of microtissues, among others. HOCs have been used to faithfully model aspects of arrhythmia, fibrosis, infection, cardiomyopathies, and ischemia, to name a few. In this review, we highlight recent advances in disease modeling using HOC systems, describing instances where these models outperformed other models in terms of reproducing disease phenotypes and/or led to drug development.

Empagliflozin attenuates cardiac microvascular ischemia/reperfusion injury through improving mitochondrial homeostasis

BACKGROUND

Empagliflozin has been reported to protect endothelial cell function, regardless of diabetes status. However, the role of empagliflozin in microvascular protection during myocardial ischemia reperfusion injury (I/R) has not been fully understood.

METHODS

Electron microscopy, western blots, immunofluorescence, qPCR, mutant plasmid transfection, co-immunoprecipitation were employed to explore whether empagliflozin could alleviate microvascular damage and endothelial injury during cardiac I/R injury.

RESULTS

In mice, empagliflozin attenuated I/R injury-induced microvascular occlusion and microthrombus formation. In human coronary artery endothelial cells, I/R injury led to adhesive factor upregulation, endothelial nitric oxide synthase inactivation, focal adhesion kinase downregulation, barrier dysfunction, cytoskeletal degradation and cellular apoptosis; however, empagliflozin treatment diminished these effects. Empagliflozin improved mitochondrial oxidative stress, mitochondrial respiration and adenosine triphosphate metabolism in I/R-treated human coronary artery endothelial cells by preventing the phosphorylation of dynamin-related protein 1 (Drp1) and mitochondrial fission 1 protein (Fis1), thus repressing mitochondrial fission. The protective effects of empagliflozin on mitochondrial homeostasis and endothelial function were abrogated by the re-introduction of phosphorylated Fis1, but not phosphorylated Drp1, suggesting that Fis1 dephosphorylation is the predominant mechanism whereby empagliflozin inhibits mitochondrial fission during I/R injury. Besides, I/R injury induced Fis1 phosphorylation primarily by activating the DNA-dependent protein kinase catalytic subunit (DNA-PKcs) pathway, while empagliflozin inactivated this pathway by exerting anti-oxidative effects.

CONCLUSIONS

These results demonstrated that empagliflozin can protect the microvasculature by inhibiting the DNA-PKcs/Fis1/mitochondrial fission pathway during myocardial I/R injury.

Effects of Remote Ischaemic Preconditioning on the Internal Thoracic Artery Nitric Oxide Synthase Isoforms in Patients Undergoing Coronary Artery Bypass Grafting

Remote ischaemic preconditioning (RIPC) is a medical procedure that consists of repeated brief periods of transient ischaemia and reperfusion of distant organs (limbs) with the ability to provide internal organ protection from ischaemia. Even though RIPC has been successfully applied in patients with myocardial infarction during coronary revascularization (surgery/percutaneous angioplasty), the underlying molecular mechanisms are yet to be clarified. Thus, our study aimed to determine the role of nitric oxide synthase (NOS) isoforms in RIPC-induced protection (3 × 5 min of forearm ischaemia with 5 min of reperfusion) of arterial graft in patients undergoing urgent coronary artery bypass grafting (CABG). We examined RIPC effects on specific expression and immunolocalization of three NOS isoforms — endothelial (eNOS), inducible (iNOS) and neuronal (nNOS) in patients’ internal thoracic artery (ITA) used as a graft. We found that the application of RIPC protocol leads to an increased protein expression of eNOS, which was further confirmed with strong eNOS immunopositivity, especially in the endothelium and smooth muscle cells of ITA. The same analysis of two other NOS isoforms, iNOS and nNOS, showed no significant differences between patients undergoing CABG with or without RIPC. Our results demonstrate RIPC-induced upregulation of eNOS in human ITA, pointing to its significance in achieving protective phenotype on a systemic level with important implications for graft patency.

Inorganic nitrate alleviates irradiation-induced salivary gland damage by inhibiting pyroptosis

Over 80% of patients undergoing radiotherapy (RT) for head and neck cancer (HNC) suffer reduced saliva secretion and dry mouth symptoms due to salivary gland damage. Although therapeutic interventions to alleviate such RT-induced damage are available, long-term hypofunction remains a significant issue. Therefore, novel therapeutic solutions to prevent irradiation (IR)-induced salivary gland damage are required. This study explored the protective effect of inorganic nitrate in preventing IR-induced salivary gland injury via pyroptosis suppression, both in vivo and in vitro. In the treatment group, C57BL/6 mice were pretreated with 2 mmol/L NaNO₃ supplied in drinking water one week before a single-dose of 15 Gy IR in the submandibular gland (SMG) region. Human vein endothelial cells (HUVECs) and mice SMG cells were treated with 10 μmol/L or 100 μmol/L NaNO₃ 2 h before a single-dose of 8 Gy IR. In vivo, IR-induced decreased saliva flow rate and body weight loss could be alleviated by nitrate supplementation. Nitrate prevented acinar and microvascular endothelial cell loss. Moreover, nitrate improved mitochondrial function and significantly decreased pyroptosis-related indexes. In vitro, nitrate supplementation reduced reactive oxygen species (ROS) generation by preserving mitochondrial homeostasis to inhibit NLPR3 inflammasome-mediated pyroptosis both in HUVECs and SMG cells. Nitrate showed potential as an oral protective agent to prevent IR-induced salivary gland damage; prospective insight into the underlying molecular mechanisms is presented.

Protection of multiple ischemic organs by controlled reperfusion

Reperfusion injury (RI) is a harmful complication that takes place during recanalization treatment of ischemic organs. Currently, there are no efficacious treatments for protecting the organs against RI. Therefore, it is necessary to discover new strategies to prevent RI. As a novel intervention technique, controlled reperfusion has promising effects on protecting multiple organs from RI, and it is done by adjusting physical parameters of blood flow or chemical compositions of the reperfusion liquid. In this brief review, the status of various controlled reperfusion methods is presented, as well as their application in the protection of ischemic organs.

Photobiomodulation therapy preconditioning modifies nitric oxide pathway and oxidative stress in human-induced pluripotent stem cell-derived ventricular cardiomyocytes treated with doxorubicin

Doxorubicin (DOX) is an anthracycline antibiotic that exhibits high heart toxicity. Human-induced pluripotent stem cell-derived ventricular cardiomyocytes (hiPSC-vCMs) are important in vitro models for testing drug cardiotoxicity. Photobiomodulation therapy (PBMT) is a non-invasive therapy that stimulates cells growth and self-repair using light irradiation. This study aimed to investigate the in vitro effects of PBMT preconditioning on cardiotoxicity induced by DOX. HiPSC-vCMs were treated with PBMT for 500 s, followed by the addition of 2 μM DOX. LED irradiation preconditioning parameters were at 660 nm with an irradiance of 10 mW/cm², performing 5 J/cm², followed by 24-h DOX exposure (2 μM). Human iPSC-vCMs treated with 2 μM DOX or irradiated with PBMT composed the second and third groups, respectively. The control group did neither receive PBMT preconditioning nor DOX and was irradiated with a white standard lamp. Cells from all groups were collected to perform mRNA and miRNA expressions quantification. PBMT, when applied before the DOX challenge, restored the viability of hiPSC-vCMs and reduced ROS levels. Although downregulated by DOX, myocardial UCP2 mRNA expression presented marked upregulation after PBMT preconditioning. Expression of eNOS and UCP2 mRNA and NO production were decreased after DOX exposure, and PBMT preconditioning before the DOX challenge reversed these changes. Moreover, our data indicated that PBMT preconditioning lowered the miR-24 expression. Our data suggested that PBMT preconditioning ameliorated in vitro DOX-induced cardiotoxicity on transcription level, restoring NO levels and reducing oxidative stress.

Nitrite in breast milk: roles in neonatal pathophysiology

Dietary nitrate has beneficial effects on health maintenance and prevention of lifestyle-related diseases in adulthood by serving as an alternative source of nitric oxide (NO) through the enterosalivary nitrate-nitrite-NO pathway, particularly when endogenous NO generation is lacking due to vascular endothelial dysfunction. However, this pathway is not developed in the early postnatal period due to a lack of oral commensal nitrate-reducing bacteria and less saliva production than in adults. To compensate for the decrease in nitrite during this period, colostrum contains the highest amount of nitrite compared with transitional, mature, and even artificial milk, suggesting that colostrum plays an important role in tentatively replenishing nitrite, in addition to involving a nutritional aspect, until the enterosalivary nitrate-nitrite-NO pathway is established. Increasing evidence demonstrates that breast milk rich in nitrite can be effective in the prevention of neonatal infections and gastrointestinal diseases such as infantile hypertrophic pyloric stenosis and necrotizing enterocolitis, suggesting that breastfeeding is advantageous for newborns at risk, given the physiological role of nitrite in the early postnatal period. IMPACT: The aim of this review is to discuss the physiological roles of nitrite in breast milk and its implications for neonates. Nitrite in breast milk may compensate for the decrease in nitrite during the early neonatal period until the enterosalivary nitrate-nitrite-nitric oxide pathway is established. Breast milk rich in nitrite may be effective in the prevention of neonatal infections and gastrointestinal diseases by providing nitric oxide bioavailability.

Hypothermic, oxygenated perfusion (HOPE) provides cardioprotection via succinate oxidation prior to normothermic perfusion in a rat model of donation after circulatory death (DCD)

In donation after circulatory death (DCD), cardiac grafts are subjected to warm ischemia in situ, prior to a brief period of cold, static storage (CSS) at procurement, and ex situ, normothermic, machine perfusion (NMP) for transport and graft evaluation. Cold ischemia and normothermic reoxygenation during NMP could aggravate graft injury through continued accumulation and oxidation, respectively, of mitochondrial succinate, and the resultant oxidative stress. We hypothesized that replacing CSS with hypothermic, oxygenated perfusion (HOPE) could provide cardioprotection by reducing cardiac succinate levels before NMP. DCD was simulated in male Wistar rats. Following 21 minutes in situ ischemia, explanted hearts underwent 30 minutes hypothermic storage with 1 of the following: (1) CSS, (2) HOPE, (3) hypothermic deoxygenated perfusion (HNPE), or (4) HOPE + AA5 (succinate dehydrogenase inhibitor) followed by normothermic reperfusion to measure cardiac and metabolic recovery. After hypothermic storage, tissue ATP/ADP levels were higher and succinate concentration was lower in HOPE vs CSS, HNPE, and HOPE + AA5 hearts. After 60 minutes reperfusion, cardiac function was increased and cellular injury was decreased in HOPE compared with CSS, HNPE, and HOPE + AA5 hearts. HOPE provides improved cardioprotection via succinate oxidation prior to normothermic reperfusion compared with CSS, and therefore is a promising strategy for preservation of cardiac grafts obtained with DCD.

Novel Insights Regarding Nitric Oxide and Cardiovascular Diseases

Nitric oxide (NO) is a powerful mediator with biological activities such as vasodilation and prevention of vascular smooth muscle cell proliferation as well as functional regulation of cardiac cells. Thus, impaired production or reduced bioavailability of NO predisposes to the onset of different cardiovascular (CV) diseases. Alterations in the redox balance associated with excitation-contraction coupling have been identified in heart failure (HF), thus contributing to contractile abnormalities and arrhythmias. For its ability to influence cell proliferation and angiogenesis, NO may be considered a therapeutic option for the management of several CV diseases. Several clinical studies and trials investigated therapeutic NO strategies for systemic hypertension, atherosclerosis, and/or prevention of in stent restenosis, coronary heart disease (CHD), pulmonary arterial hypertension (PAH), and HF, although with mixed results in long-term treatment and effective dose administered in selected groups of patients. Tadalafil, sildenafil, and cinaguat were evaluated for the treatment of PAH, whereas vericiguat was investigated in the treatment of HF patients with reduced ejection fraction. Furthermore, supplementation with hydrogen sulfide, tetrahydrobiopterin, and nitrite/nitrate has shown beneficial effects at the vascular level.

Nutraceuticals in Chronic Coronary Syndromes: Preclinical Data and Translational Experiences

Non-pharmacological treatments have always been considered important in the management of Chronic Coronary Syndromes. Nutraceuticals ("Nutrition" + "Pharmaceutical") could fall both under the definition of non-pharmacological treatment and pharmacological one or, probably more correctly, in the middle of these two kinds of therapies. However, the word "nutraceuticals" never appears in the latest guidelines on this issue. This is probably determined by the fact that evidences on this topic are scarce and most of the published articles are based on preclinical data while translational experiences are available only for some molecules. In this review we will focus on nutraceutical strategies that act on the ischemic myocardium itself and not only on the cardiovascular risk factors. As demonstrated by the important number of papers published in recent years, this is an evolving topic and evaluated substances principally act on two mechanisms (cardiac energetics and ischemia-reperfusion damage) that will be also reviewed.

The Role Of Amino Acid Arginine And Nitric Oxide System In Implementing Cardioprotective Effect Of Non-Opioid Analogue Of Leu-Enkephalin In Newborn Albino Rats After Intrauterine Hypoxia

Objective ― to evaluate the role of the amino acid arginine in the structure of the non-opioid analogue of leu-enkephalin (NALE) and the involvement of the nitric oxide system in the implementation of its cardioprotective effect in newborn albino rats subjected to intrauterine hypoxia. Material and Methods ― Pregnant female rats were subjected daily to 4-hour hypobaric hypoxia (oxygen partial pressure – 65 mm Hg) on days 15-19 of their gestation. The 7-day-old offspring of hypoxified female rats were examined. The progeny of intact animals served the control. We studied body and heart weights; activity of proliferative processes and autophagy in the myocardium of subendocardial parts of the left ventricle, expressed via the immunohistochemical detection of Ki-67 and Beclin-1 proteins, respectively; karyometric and nucleolometric indicators of cardiomyocytes (CMC); intensity of free radical processes in the tissues of the heart by chemiluminescence parameters. Correction of post-hypoxic changes in newborn rats was carried out by intraperitoneal injection of two peptides (Phe–D-Ala–Gly–Phe–Leu–Arg – non-opioid analogue of leu-enkephalin, or NALE, and Phe–D-Ala–Gly–Phe–Leu–Gly – G peptide) daily from day 2 through day 6 of their lives at a dose of 100 μg/kg. To assess the involvement of the nitric oxide system in the implementation of the NALE effects, the NO synthase inhibitor – N-nitro-L-arginine methyl ester (L-NAME) was additionally administered at a dose of 50 mg/kg. Results ― Intrauterine hypoxia led to a decrease in body weights of 7-day-old animals, an increase in the number of CMC expressing the Beclin-1 protein, reduction in the size of CMC nuclei, activation of free radial oxidation, and a decrease in antiradical protection in the heart tissues. The administration of NALE to newborn animals, subjected to intrauterine hypoxia (IUH), normalized their body weight and size of the CMC nuclei, and partially corrected changes in Beclin-1 expression and in chemiluminescence parameters. In 7-day-old animals, subjected to IUH and neonatal administration of NALE and L-NAME, a lower body weight was observed than in the control. Against the background of nitric oxide blockade, the antioxidant effect of NALE diminished, but the corrective effect of NALE on the karyometric index and Beclin-1 expression remained. G peptide, which differs from NALE by the substitution of the C-terminal amino acid Arg for the amino acid Gly, exhibited a corrective effect similar to NALE on the consequences of IUH. Conclusion ― Administration of NALE and G peptides to newborn albino rats after IUH has a pronounced cardioprotective effect. The mechanisms of the NALE peptide effects are, in part, associated with the activation of the NOS-NO system. However, the affinity of this peptide for opioid-like receptors may be of greater importance.

Mouse models of atherosclerosis and their suitability for the study of myocardial infarction

Atherosclerotic plaques impair vascular function and can lead to arterial obstruction and tissue ischaemia. Rupture of an atherosclerotic plaque within a coronary artery can result in an acute myocardial infarction, which is responsible for significant morbidity and mortality worldwide. Prompt reperfusion can salvage some of the ischaemic territory, but ischaemia and reperfusion (IR) still causes substantial injury and is, therefore, a therapeutic target for further infarct limitation. Numerous cardioprotective strategies have been identified that can limit IR injury in animal models, but none have yet been translated effectively to patients. This disconnect prompts an urgent re-examination of the experimental models used to study IR. Since coronary atherosclerosis is the most prevalent morbidity in this patient population, and impairs coronary vessel function, it is potentially a major confounder in cardioprotective studies. Surprisingly, most studies suggest that atherosclerosis does not have a major impact on cardioprotection in mouse models. However, a major limitation of atherosclerotic animal models is that the plaques usually manifest in the aorta and proximal great vessels, and rarely in the coronary vessels. In this review, we examine the commonly used mouse models of atherosclerosis and their effect on coronary artery function and infarct size. We conclude that none of the commonly used strains of mice are ideal for this purpose; however, more recently developed mouse models of atherosclerosis fulfil the requirement for coronary artery lesions, plaque rupture and lipoprotein patterns resembling the human profile, and may enable the identification of therapeutic interventions more applicable in the clinical setting.

Ischemia Reperfusion Injury: Opportunities for Nanoparticles

Ischemia reperfusion (IR)-induced oxidative stress, accompanied by inflammatory responses, contributes to morbidity and mortality in numerous diseases such as acute coronary syndrome, stroke, organ transplantation, and limb injury. Ischemia results in profound hypoxia and tissue dysfunction, whereas subsequent reperfusion further aggravates ischemic tissue damage through inducing cell death and activating inflammatory responses. In this review, we highlight recent studies of therapeutic strategies against IR injury. Furthermore, nanotechnology offers significant improvements in this area. Hence, we also review recent advances in nanomedicines for IR therapy, suggesting them as potent and promising strategies to improve drug delivery to IR-injured tissues and achieve protective effects.

The Healthy, Aging, and Diseased Kidney: Relationship with Cardiovascular Disease

The cardiovascular and renal systems share an intimate physiological relationship, wherein a perturbance in one system may have an adverse effect on the other. Since the burden of renal disease increases with age, there is a considerable interest in the pathophysiology of kidney disease in the geriatric patient population. This review will explore the physiological dynamics behind the increased susceptibility to kidney disease in this population. A better understanding of these pathophysiological changes may lead to improved prevention and management strategies.

Cardioprotection of pharmacological postconditioning on myocardial ischemia/reperfusion injury

Acute myocardial infarction is associated with high rates of morbidity and mortality and can cause irreversible myocardial damage. Timely reperfusion is critical to limit infarct size and salvage the ischemic myocardium. However, reperfusion may exacerbate lethal tissue injury, a phenomenon known as myocardial ischemia/reperfusion (I/R) injury. Pharmacological postconditioning (PPC), a strategy involving medication administration before or during the early minutes of reperfusion, is more efficient and flexible than preconditioning or ischemic conditioning. Previous studies have shown that various mechanisms are involved in the effects of PPC. In this review, we summarize the relative effects and potential underlying mechanisms of PPC to provide a foundation for future research attempting to develop novel treatments against myocardial I/R injury.

Mitochondrial quality control mechanisms as molecular targets in cardiac ischemiareperfusion injury

Mitochondrial damage is a critical contributor to cardiac ischemia/reperfusion (I/R) injury. Mitochondrial quality control (MQC) mechanisms, a series of adaptive responses that preserve mitochondrial structure and function, ensure cardiomyocyte survival and cardiac function after I/R injury. MQC includes mitochondrial fission, mitochondrial fusion, mitophagy and mitochondria-dependent cell death. The interplay among these responses is linked to pathological changes such as redox imbalance, calcium overload, energy metabolism disorder, signal transduction arrest, the mitochondrial unfolded protein response and endoplasmic reticulum stress. Excessive mitochondrial fission is an early marker of mitochondrial damage and cardiomyocyte death. Reduced mitochondrial fusion has been observed in stressed cardiomyocytes and correlates with mitochondrial dysfunction and cardiac depression. Mitophagy allows autophagosomes to selectively degrade poorly structured mitochondria, thus maintaining mitochondrial network fitness. Nevertheless, abnormal mitophagy is maladaptive and has been linked to cell death. Although mitochondria serve as the fuel source of the heart by continuously producing adenosine triphosphate, they also stimulate cardiomyocyte death by inducing apoptosis or necroptosis in the reperfused myocardium. Therefore, defects in MQC may determine the fate of cardiomyocytes. In this review, we summarize the regulatory mechanisms and pathological effects of MQC in myocardial I/R injury, highlighting potential targets for the clinical management of reperfusion.

Improved collateral flow and reduced damage after remote ischemic perconditioning during distal middle cerebral artery occlusion in aged rats

Circulation through cerebral collaterals can maintain tissue viability until reperfusion is achieved. However, collateral circulation is time limited, and failure of collaterals is accelerated in the aged. Remote ischemic perconditioning (RIPerC), which involves inducing a series of repetitive, transient peripheral cycles of ischemia and reperfusion at a site remote to the brain during cerebral ischemia, may be neuroprotective and can prevent collateral failure in young adult rats. Here, we demonstrate the efficacy of RIPerC to improve blood flow through collaterals in aged (16-18 months of age) Sprague Dawley rats during a distal middle cerebral artery occlusion. Laser speckle contrast imaging and two-photon laser scanning microscopy were used to directly measure flow through collateral connections to ischemic tissue. Consistent with studies in young adult rats, RIPerC enhanced collateral flow by preventing the stroke-induced narrowing of pial arterioles during ischemia. This improved flow was associated with reduced early ischemic damage in RIPerC treated aged rats relative to controls. Thus, RIPerC is an easily administered, non-invasive neuroprotective strategy that can improve penumbral blood flow via collaterals. Enhanced collateral flow supports further investigation as an adjuvant therapy to recanalization therapy and a protective treatment to maintain tissue viability prior to reperfusion.

Sevoflurane Preconditioning Prevents Septic Myocardial Dysfunction in Lipopolysaccharide-Challenged Mice

Myocardial dysfunction accompanied by severe sepsis could significantly increase the mortality rate of septic patients. This study investigated the effects and the potential mechanisms of sevoflurane preconditioning on septic myocardial dysfunction, which was induced by lipopolysaccharide (LPS; from Escherichia coli O55:B5; 18 mg/kg) in mice. Results indicated that 1 hour after the administration, LPS induced a significant increase in cell-surface Toll-like receptor 4 (TLR4), cytoplasmic IKKα protein expression, and nuclear translocation of nuclear factor kappa-B (NF-κB) protein (P < 0.05), which was attenuated by preconditioning with sevoflurane. Two hours after the administration, inhalation of sevoflurane significantly reduced the serum levels of tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1β, and IL-10 (P < 0.05). Twelve hours after administration, LPS caused pathological damage to the heart and elevated the serum levels of lactate dehydrogenase (LDH) and creatine kinase-MB (P < 0.05). Echocardiography indicated that sevoflurane preconditioning significantly improved systolic and diastolic function. The inhalation of sevoflurane inhibited increases in myeloperoxidase (MPO), macrophage inflammatory protein-2 (MIP-2), TNF-α, and IL-1β levels (P < 0.05) induced by endotoxemia, whereas IL-6 release was facilitated. Sevoflurane attenuated the myocardial levels of nitric oxide (P < 0.05) without an apparent influence on malondialdehyde (MDA) or superoxide dismutase (P > 0.05). In conclusion, our study indicates that exposure to 2% sevoflurane before LPS challenge is protective against myocardial dysfunction. Sevoflurane preconditioning may attenuate neutrophil infiltration and the release of inflammatory mediators during endotoxemia.

Total body irradiation-induced colon damage is prevented by nitrate-mediated suppression of oxidative stress and homeostasis of the gut microbiome

Inorganic dietary nitrate plays vital roles in biological functions via the exogenous NO3^-/NO2^-/NO pathway under hypoxia and ischemia. We previously verified the antioxidative effects of inorganic nitrate in a mouse model of total body irradiation (TBI). Accordingly, in this study, we evaluated the effects of inorganic nitrate on prevention of TBI-induced colon injury and dysbiosis of the gut microbiome. Nitrate significantly rescued the abnormal biological indexes (body weight, white blood cell, red blood cell, platelet, hemoglobin level and intestinal canal lengths) induced by TBI. Then, we detected oxidative stress and DNA damage indexes (phospho-histone H2AX and p53 binding protein 1), which were both increased by irradiation (IR) and alleviated by nitrate. IR-induced apoptosis and senescence were ameliorated by inorganic nitrate. The distribution of the gut microbiome differed for mice with TBI and those receiving inorganic nitrate. The average abundance of Lactobacillus significantly increased, and that of Bacteroidales decreased at the genus level in the nitrate group compared with that in the IR alone group. At 30 days after TBI, the abundances of Bacteroides and Faecalibaculum decreased, whereas that of Lactobacillus increased in the IR + nitrate group compared with that in the IR alone group. Inorganic nitrate efficiently prevents TBI-induced colon epithelium injury and maintains the homeostasis of the gut microbiome. Thus, our results showed that inorganic nitrate might be a promising treatment for TBI induced colon injury.

A systemic review on the antioxidant and anti-inflammatory effects of resveratrol, curcumin, and dietary nitric oxide supplementation on human cardiovascular health

The potential benefits of supplemental nutrients and dietary interventions against cardiovascular morbidity and mortality have been extensively investigated throughout the years. Numerous supplements claim cardioprotection and reduction of cardiovascular risk factors, but the roles of many supplements have not been determined. In the vast number of supplements on the market asserting cardioprotective effects, only 3 have been thoroughly evaluated and consistently reported as effective by our clinic patients. They have used supplements such as fish oil, multivitamins, and calcium, but many had not known of the benefits of resveratrol, curcumin, and nitric oxide as supplements for improving cardiovascular health. The cardioprotective effects of these dietary supplements in both animal models and humans have been explored with proposed mechanisms of action mostly attributed to antioxidant and anti-inflammatory properties. Resveratrol is one of the most studied polyphenols with established cardiovascular benefits. Preclinical studies have demonstrated these effects exerted via improved inflammatory markers, atherogenic profile, glucose metabolism, and endothelial function and are further supported by clinical trials. Curcumin has a well-established anti-inflammatory role by regulating numerous transcription factors and cytokines linked to inflammation. Inflammation is an underlying pathology in cardiovascular diseases, rendering curcumin a potential therapeutic compound. Similarly, nitric oxide supplementation has demonstrated cardiovascular benefits by normalizing blood pressure; enhancing blood flow; and reducing inflammation, immune dysfunction, and oxidative stress. A comprehensive review was performed evaluating the cardioprotective effects of these 3 dietary supplements with hope to provide updated information, promote further awareness of these supplements, and inspire future studies on their effects on cardiovascular health.

Hyperbaric oxygenation improves redox control and reduces mortality in the acute phase of myocardial infarction in a rat model

Among the mechanisms of action of hyperbaric oxygenation (HBO), the chance of reducing injury by interfering with the mechanisms of redox homeostasis in the heart leads to the possibility of extending the period of viability of the myocardium at risk. This would benefit late interventions for reperfusion to the ischemic area. The objective of the present study was to investigate the changes in the redox system associated with HBO therapy maintained during the first hour after coronary occlusion in an acute myocardial infarction (MI) rat model. Surviving male rats (n=105) were randomly assigned to one of three groups: Sham (SH=26), myocardial infarction (MI=45) and infarction+hyperbaric therapy (HBO=34, 1 h at 2.5 atm). After 90 min of coronary occlusion, a sample of the heart was collected for western blot analysis of total protein levels of superoxide dismutase, catalase, peroxiredoxin and 3‑nitrotyrosine. Glutathione was measured by enzyme‑linked immunosorbent assay (ELISA). The detection of the superoxide radical anion was carried out by oxidation of dihydroethidium analyzed with confocal microscopy. The mortality rate of the MI group was significantly higher than that of the HBO group. No difference was noted in the myocardial infarction size. The oxidized/reduced glutathione ratio and peroxiredoxin were significantly higher in the SH and MI when compared to the HBO group. Superoxide dismutase enzymes and catalase were significantly higher in the HBO group compared to the MI and SH groups. 3‑Nitrotyrosine and the superoxide radical were significantly lower in the HBO group compared to these in the MI and SH groups. These data demonstrated that hyperbaric oxygenation therapy decreased mortality by improving redox control in the hearts of rats in the acute phase of myocardial infarction.

Dietary Nitrate Protects Against Skin Flap Ischemia-Reperfusion Injury in Rats via Modulation of Antioxidative Action and Reduction of Inflammatory Responses

Dietary nitrate, found abundant in green vegetables, can be absorbed into the blood and be converted to nitric oxide (NO) in the body. Dietary nitrate has been proved to have many positive physiological functions in the body. Here, we evaluated the therapeutic effects of dietary nitrate on skin flap recovery following ischemia reperfusion (IR). Wistar rats were pretreated with nitrate from one week prior to ischemia to the end of reperfusion. It was found that oral administration of nitrate increased serum nitrate and nitrite levels, protected cells from apoptosis, and attenuated flap tissue edema. In the meantime, the oxidative stress marker malondialdehyde was reduced, while the activities of antioxidant enzymes were restored after nitrate treatment. Moreover, the macrophage and neutrophil infiltration in the flap was significantly attenuated by nitrate supplementation, as were the pro-inflammatory cytokines. In sum, we found that oral administration of nitrate can attenuate skin flap IR injury through the regulation of oxidative stress and inflammatory response.

Biochemical parameters of rat blood in the models of chronic heart failure and chronic kidney disease at the administration of nitric oxide donor

In modern veterinary medicine, the simultaneous occurrence of chronic heart failure and chronic kidney disease is often found. However, the cause and effect often exchange places, which creates great difficulties in the animals’ treatment. Chlofusan acts on both systems. It improves cardiac and renal functions by means of providing cardioprotective and nephroprotective effects. Models of chronic heart failure and chronic kidney disease in rats provide important information on the pathophysiology of these diseases in other animal species, and the assessment of changes in the biochemical analysis of blood makes it possible to assess the state of the heart and kidneys in the study. In the course of research, the results of rat biochemical analysis were studied on models of chronic heart and kidney failure with the introduction of an exogenous nitric oxide donor. Chlofuzan contributes to a partial balance restoration of biochemical blood parameters in rats, which indicates the restoration of the mutual work of the heart and kidneys.

KLF2 regulates eNOS uncoupling via Nrf2/HO-1 in endothelial cells under hypoxia and reoxygenation

Kruppel-like factor 2 (KLF2) regulates endothelial functions by modulating endothelial nitric oxide synthase (eNOS)/nitric oxide (NO) pathway. Tetrahydrobiopterin (BH₄) and S-glutathionylation of eNOS play essential roles in eNOS uncoupling and activation. However, the influence of KLF2 on eNOS uncoupling and the mechanism of eNOS activation still remain unknown. A hypoxia and reoxygenation (H/R) model of human umbilical vein endothelial cells (HUVECs) was utilized in this study. Cell viability and the eNOS uncoupling-related oxidative stress index were measured. The Nrf2 inhibitor ML385 and HO-1 siRNA were used to elucidate the mechanism of activation. The results show that overexpression of KLF2 increased the cell viability, reduced the lactate dehydrogenase leakage rate, downregulated the generation of O₂^•- and ONOO^-, and increased NO levels and eNOS activity. Overexpression of KLF2 also increased the BH₄/BH₂ ratio and the GSH/GSSG ratio, thus significantly improving eNOS uncoupling in the H/R model. KLF2 has no regulatory effect on the upstream-associated proteins in eNOS activation. However, when combined with the Nrf2 inhibitor or HO-1 siRNA, the regulatory effect of KLF2 on eNOS uncoupling was strongly reduced. These results suggest that KLF2 could improve eNOS uncoupling via Nrf2/HO-1 in H/R-induced endothelial injury.

Influence of Luehea divaricata Mart. extracts on peripheral vascular resistance and the role of nitric oxide and both Ca+2-sensitive and Kir6.1 ATP-sensitive K+ channels in the vasodilatory effects of isovitexin on isolated perfused mesenteric beds

BACKGROUND

Luehea divaricata Mart. (Malvaceae) is an important medicinal species widely used by indigenous and riverside populations of the Brazilian Pantanal region. It has been shown that the several extracts obtained from leaves of this species have important cardioprotective effects. Nevertheless, the secondary metabolites responsible for this activity, as well as the molecular mechanisms responsible for their pharmacological effects remain unknown.

PURPOSE

To carry out a biomonitoring study to identify possible active metabolites present in different ESLD fractions and evaluate the mechanisms responsible for the vasodilatory effects on isolated perfused mesenteric beds.

METHODS

First, ESLD was obtained from L. divaricata leaves and a liquid-liquid fractionation was performed. The resulting fractions were analyzed by liquid chromatography-mass spectrometry. Then, the possible vasodilatory effects of ESLD, chloroform, ethyl acetate, n-butanolic and aqueous fractions on perfused arterial mesenteric vascular beds were evaluated. Finally, the molecular mechanisms involved in vasodilator responses of the aqueous fraction and its chemical component, isovitexin, on the mesenteric arteriolar tone were also investigated.

RESULTS

In preparations with functional endothelium ESLD, n-butanolic, aqueous fraction and isovitexin dose-dependently reduced the perfusion pressure in mesenteric vascular beds. Endothelium removal or inhibition of nitric oxide synthase enzymes by L-NAME reduced the vasodilatory effects induced by aqueous fraction and isovitexin. Perfusion with nutritive solution containing 40 mM KCl abolished the vasodilatory effect of all aqueous fractions and Isovitexin doses. Treatment with glibenclamide, a Kir6.1 (ATP-sensitive) potassium channels blocker, tetraethylammonium, a non-selective KCa (calcium-activated) potassium channels blocker, or apamin, a potent blocker of small conductance Ca²⁺-activated (SK KCa) potassium channels reduced by around 70% vasodilation induced by all aqueous fractions and isovitexin doses. In addition, association of tetraethylammonium and glibenclamide, or L-NAME and glibenclamide, fully inhibited aqueous fraction and Isovitexin -induced vasodilation.

CONCLUSION

This study showed that AqueFr obtained from Luehea divaricata and its metabolite - isovitexin - has important vasodilatory effects on MVBs. Apparently, these effects are dependent on endothelium-NO release and both SK KCa K⁺ channels and Kir6.1 ATP-sensitive K⁺ channels activation in the vascular smooth muscle.

Combination therapy profoundly improved skin flap survival by modulating KATP channels and nitric oxide

PURPOSE

A potential therapeutic approach on skin flap necrosis is to target parallel pathways involved in necrosis. Azelaic Acid, Minoxidil and Caffeine combination was tried on skin flap survival by their possible interaction with ATP sensitive potassium (KATP) channels and nitric oxide pathway.

MATERIAL AND METHODS

Sprauge-Dawley rats were divided into 8 groups for skin flap surgery. Azelaic acid, minoxidil, caffeine, or their combination were applied topically in different groups. Two additional groups were treated with L-NAME or glibenclamide in addition to the combination therapy. Percentage of flap necrosis was calculated and flap samples were removed to measure tissue malondialdehyde (MDA) and nitric oxide (NO) and expression of inducible nitric oxide synthase (iNOS), Bcl-2 and Bax proteins.

RESULTS

Combination therapy profoundly decreased skin flap necrosis, tissue MDA contents, and expression of the pro-apoptotic protein Bax (p < 0.05 vs. single treatments). These effects were reversed by L-NAME and glibenclamide pre-treatments. Further evaluations showed combination therapy increases flap tissue NO content and iNOS expression (p < 0.05 vs. single treatments).

CONCLUSION

Beneficial effect of the combination therapy with azelaic acid, minoxidil and caffeine therapy on rescuing the flap from necrosis by targeting parallel signaling pathways suggested potential applications in clinical practice.

Adenosine A1 receptors and mitochondria: targets of remote ischemic preconditioning

Adenosine is involved in classic preconditioning in most species and acts especially through adenosine A₁ and A₃ receptors. The aim of the present study was to evaluate whether remote ischemic preconditioning (rIPC) activates adenosine A₁ receptors and improves mitochondrial function, thereby reducing myocardial infarct size. Isolated rat hearts were subjected to 30 min of global ischemia and 60 min of reperfusion [ischemia-reperfusion (I/R)]. In a second group, before isolation of the heart, a rIPC protocol (3 cycles of hindlimb I/R) was performed. Infarct size was measured with tetrazolium staining, and Akt/endothelial nitric oxide (NO) synthase (eNOS) expression/phosphorylation and mitochondrial function were evaluated after ischemia at 10 and 60 min of reperfusion. As expected, rIPC significantly decreased infarct size. This beneficial effect was abolished only when 8-cyclopentyl-1,3-dipropylxanthine (adenosine A₁ receptor blocker) and N^G-nitro-l-arginine methyl ester (NO synthesis inhibitor) were administered during the reperfusion phase. At the early reperfusion phase, rIPC induced significant Akt and eNOS phosphorylation, which was abolished by the perfusion with an adenosine A₁ receptor blocker. I/R led to impaired mitochondrial function, which was attenuated by rIPC and mediated by adenosine A₁ receptors. In conclusion, we demonstrated that rIPC limits myocardial infarct by activation of adenosine A₁ receptors at early reperfusion in the isolated rat heart. Interestingly, rIPC appears to reduce myocardial infarct size by the Akt/eNOS pathway and improves mitochondrial function during myocardial reperfusion. NEW & NOTEWORTHY Adenosine is involved in classic preconditioning and acts especially through adenosine A₁ and A₃ receptors. However, its role in the mechanism of remote ischemic preconditioning is controversial. In this study, we demonstrated that remote ischemic preconditioning activates adenosine A₁ receptors during early reperfusion, inducing Akt/endothelial nitric oxide synthase phosphorylation and improving mitochondrial function, thereby reducing myocardial infarct size.

Endothelium-Dependent Effects of Echinodorus grandiflorus (Cham. & Schltdl.) Micheli Mediated by M3-Muscarinic and B2-Bradykininergic Receptors on Peripheral Vascular Resistance and Its Modulatory Effects on K+ Channels in Mesenteric Vascular Beds

This work provides the first demonstration that ethanolic extract (EEEG) obtained from Echinodorus grandiflorus leaves (EEEG) and its butanolic fraction (ButFr) has important vasodilatory effects on isolated mesenteric vascular beds (MVBs). First, the EEEG was obtained and a liquid-liquid fractionation was performed. EEEG and its resulting fractions were analyzed by high-performance liquid chromatography. Then, the vasodilatory effects of EEEG and their respective fractions were evaluated. Finally, the molecular mechanisms involved in the vasodilator responses of the EEEG and ButFr were also investigated. EEEG vasodilator response was estimated at ~11 and 18 mm Hg at doses of 0.1 and 0.3 mg, respectively. Moreover, it was found that ButFr was able to induce an expressive dose-dependent vasodilator response in MVBs. The PP reduction values for doses of 0.1 and 0.3 mg were ~10 and 28 mm Hg, respectively. Endothelium removal or inhibition of nitric oxide and prostaglandin synthase (by L-NAME plus indomethacin) inhibited the vasodilatory effects induced by ButFr or EEEG. The peak effect of ButFr and EEEG doses (0.1 and 0.3 mg) was decreased by ~100% (p < 0.001). The association of atropine plus HOE-140 fully inhibited EEEG and ButFr-induced vasodilation (p < 0.001). Moreover, perfusion with nutritive solution containing 40 mM KCl or previous treatment with tetraethylammonium completely blocked vasodilation induced by ButFr (p < 0.001). This study showed that EEEG and its ButFr have important vasodilatory effects by endothelial M3-muscarinic and B2-bradykininergic receptors inducing nitric oxide and prostacyclin release followed by K+ channels activation in the vascular smooth muscle.

Reprint of "The interaction between environmental triggers and epigenetics in autoimmunity"

Systemic lupus erythematosus flares when genetically predisposed people encounter environmental agents that cause oxidative stress, such as infections and sunlight. How these modify the immune system to initiate flares is unclear. Drug induced lupus models demonstrate that CD4+ T cells epigenetically altered with DNA methylation inhibitors cause lupus in animal models, and similar T cells are found in patients with active lupus. How infections and sun exposure inhibit T cell DNA methylation is unclear. DNA methylation patterns are replicated each time a cell divides in a process that requires DNA methyltransferase one (Dnmt1), which is upregulated as cells enter mitosis, as well as the methyl donor S-adenosylmethionine, created from dietary sources. Reactive oxygen species that inhibit Dnmt1 upregulation, and a diet poor in methyl donors, combine to cause lupus in animal models. Similar changes are found in patients with active lupus, indicating a mechanism contributing to lupus flares.

Inorganic Nitrate Alleviates Total Body Irradiation-Induced Systemic Damage by Decreasing Reactive Oxygen Species Levels

PURPOSE

To evaluate the protective effect of inorganic nitrate against systemic damage in a mouse model of total body gamma irradiation (TBI).

METHODS AND MATERIALS

C57BL/6 mice in the irradiation (IR) + NaNO₃ group were pretreated with 2 mmol/L NaNO₃ in their drinking water for 1 week before receiving 5 Gy irradiation. Animals that received only 5 Gy irradiation were designated as the IR group. Survival and body weight were monitored. The peripheral blood lymphocytes, heart, liver, lung, and submandibular gland were harvested and assessed. Reactive oxygen species (ROS) were measured in the lung and submandibular gland. We examined phosphorylated histone H2AX (p-H2AX) and p53-binding protein 1 (53BP1) as markers of early-stage DNA damage and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and Bax/caspase 3 mRNA expression as markers of apoptosis.

RESULTS

No improvement of survival was observed in the IR + NaNO₃ group after TBI, but body weight loss after 5 Gy TBI was significantly attenuated in the IR + NaNO₃ group. The levels of peripheral blood erythrocytes, leukocytes, and platelets at 7 days postirradiation recovered with nitrate treatment; moreover, the p-H2AX level in the peripheral blood lymphocytes was much lower in the IR + NaNO₃ group at 2 and 4 hours post irradiation. In the lung and submandibular gland, the levels of p-H2AX, 53BP1 and ROS as well as TUNEL staining were significantly decreased in the IR + NaNO₃ group compared with those in the IR group. Gene expression of Bax and caspase 3 was decreased in both the lung and submandibular gland with nitrate treatment, indicating attenuation of apoptosis.

CONCLUSION

Inorganic nitrate delivery could effectively prevent TBI-induced systemic damage. Nitrate-mediated decreases in ROS levels may contribute to this systemic protective effect.

Cardioprotective effect of 2,3-dehydrosilybin preconditioning in isolated rat heart

2,3-dehydrosilybin (DHS) is a minor component of silymarin, Silybum marianum seed extract, used in some dietary supplements. One of the most promising activities of this compound is its anticancer and cardioprotective activity that results, at least partially, from its cytoprotective, antioxidant, and chemopreventive properties. The present study investigated the cardioprotective effects of DHS in myocardial ischemia and reperfusion injury in rats. Isolated hearts were perfused by the Langendorff technique with low dose DHS (100 nM) prior to 30 min of ischemia induced by coronary artery occlusion. After 60 min of coronary reperfusion infarct size was determined by triphenyltetrazolium staining, while lactatedehydrogenase activity was evaluated in perfusate samples collected at several timepoints during the entire perfusion procedure. Signalosomes were isolated from a heart tissue after reperfusion and involved signalling proteins were detected. DHS reduced the extent of infarction compared with untreated control hearts at low concentration; infarct size as proportion of ischemic risk zone was 7.47 ± 3.1% for DHS versus 75.3 ± 4.8% for ischemia. This protective effect was comparable to infarct limitation induced by ischemic preconditioning (22.3 ± 4.5%). Selective inhibition of Src-family kinases with PP2 (4-Amino-3-(4-chlorophenyl)-1-(t-butyl)-1H-pyrazolo[3,4-d]pyrimidine) abrogated the protection afforded by DHS. This study provides experimental evidence that DHS can mediate Src-kinase-dependent cardioprotection against myocardial damage produced by ischemia/reperfusion injury.

Cardioprotective signalling: Past, present and future

A few decades ago, cardiac muscle was discovered to possess signalling pathways that, when activated, protect the myocardium against the damage induced by ischaemia-reperfusion. The ability of cardiac muscle to protect itself against injury has been termed 'cardioprotection'. Many compounds and procedures can trigger cardioprotection including conditionings (exposure to brief episodes of ischaemia-reperfusion to protect against sustained ischaemia-reperfusion), hypoxia, adenosine, acetylcholine, adrenomedullin, angiotensin, bradykinin, catecholamines, endothelin, estrogens, phenylephrine, opioids, testosterone, and many more. These triggers activate many intracellular signalling factors including protein kinases, different enzymes, transcription factors and defined signalling pathways to target structures in mitochondria, sarcoplasmic reticulum, nucleus and sarcolemma to mediate cardioprotection. Although a lot of information about cardioprotection has been acquired, there are still two major outstanding issues to be addressed in the future 1) better understanding of spatio-temporal relationships between signalling elements, and; 2) devising therapeutic strategies against myocardial diseases based on cardioprotective signalling. Further research is required to paint integral picture of cardioprotective signalling and more clinical studies are required to properly test clinical efficacy and safety of potential cardioprotective strategies. Therapies against cardiac diseases based on cardioprotective strategies would be a perfect adjunct to current therapeutic strategies based on restitution of coronary blood flow and regulation of myocardial metabolic demands.

Connexins and Nitric Oxide Inside and Outside Mitochondria: Significance for Cardiac Protection and Adaptation

Irreversible myocardial damage happens in the presence of prolonged and severe ischemia. Several phenomena protect the heart against myocardial infarction and other adverse outcomes of ischemia and reperfusion (IR), namely: hibernation related to stunned myocardium, ischemic preconditioning (IPC), ischemic post-conditioning, and their pharmacological surrogates. Ischemic preconditioning consists in the induction of a brief IR to reduce damage of the tissue caused by prolonged and severe ischemia. Nitric oxide (NO) signaling plays an essential role in IPC. Nitric oxide-sensitive guanylate cyclase/cyclic guanosine-3′,5′-monophosphate (cGMP)-dependent protein kinase type I-signaling pathway protects against the IR injury during myocardial infarction. Mitochondrial ATP-sensitive and Ca²⁺-activated K⁺ channels are involved in NO-mediated signaling in IPC. Independently of the cGMP-mediated induction of NO production, S-nitrosation represents a regulatory molecular mechanism similar to phosphorylation and is essential for IPC. Unlike conditioning phenomena, the mechanistic basis of myocardial stunning and hibernation remains poorly understood. In this review article, we hypothesize that the disruption of electrical syncytium of the myocardium may underly myocardial stunning and hibernation. Considering that the connexins are the building blocks of gap junctions which represent primary structural basis of electrical syncytium, we discuss data on the involvement of connexins into myocardial conditioning, stunning, and hibernation. We also show how NO-mediated signaling is involved in myocardial stunning and hibernation. Connexins represent an essential element of adaptation phenomena of the heart at the level of both the cardio- myocytes and the mitochondria. Nitric oxide targets mitochondrial connexins which may affect electrical syncytium continuum in the heart. Mitochondrial connexins may play an essential role in NO-dependent mechanisms of myocardial adaptation to ischemia.

Heart Disease and Relaxin: New Actions for an Old Hormone

The hormone relaxin has long been recognized for its involvement in maternal adaptation during pregnancy. However, discoveries during the past two decades on the mechanism of action of relaxin, its family of receptors, and newly described roles in attenuating ischemia/reperfusion (I/R) injury, inflammation, and arrhythmias have prompted vast interest in exploring its therapeutic potential in cardiovascular disease. These observations inspired recently concluded clinical trials in patients with acute heart failure. This review discusses our current understanding of the protective signaling pathways elicited by relaxin in the heart, and highlights important new breakthroughs about relaxin signaling that may pave the way to more carefully designed future trials.

The GTN patch: a simple and effective new approach to cardioprotection?

There remains a significant un-met need to reduce the extent of myocardial injury caused by ischaemia and reperfusion injury in patients experiencing an ST-elevation MI. Although nitric oxide is central to many cardioprotective strategies currently undergoing investigation, cardioprotection from the delivery of nitrates/nitrites has been inconsistently observed. The route of administration appears to be a critical variable. The glyceryl trinitrate (GTN) patch is commonly used as a simple and practical means of delivering nitric oxide to patients with ischaemic heart disease, but whether acute cardioprotection can be achieved by application of a GTN patch has not been investigated before. Here, we use a mouse model to demonstrate that a GTN patch is highly cardioprotective when applied immediately prior to 40 min occlusion of the left anterior coronary artery followed by 2 h reperfusion, reducing infarct size from 54 ± 4% in control mice, to 28 ± 4% (P < 0.001, N = 7). The degree of protection was similar to that achieved with a standard remote ischaemic preconditioning protocol. Furthermore, and of greater potential clinical relevance, a GTN patch was also protective when applied well after the initiation of ischaemia and 15 min prior to reperfusion (28 ± 4 vs 59 ± 4%; P < 0.01, N = 5). Confirmatory experiments verified the expected effect increase in plasma nitrite levels and decrease in blood pressure. The simplicity and rapidity of GTN patch application (easily applied in an ambulance or cardiac catheterization laboratory), and low cost (potentially relevant to low-income countries), make it attractive for further investigation.

The interaction between environmental triggers and epigenetics in autoimmunity

Systemic lupus erythematosus flares when genetically predisposed people encounter environmental agents that cause oxidative stress, such as infections and sunlight. How these modify the immune system to initiate flares is unclear. Drug induced lupus models demonstrate that CD4+ T cells epigenetically altered with DNA methylation inhibitors cause lupus in animal models, and similar T cells are found in patients with active lupus. How infections and sun exposure inhibit T cell DNA methylation is unclear. DNA methylation patterns are replicated each time a cell divides in a process that requires DNA methyltransferase one (Dnmt1), which is upregulated as cells enter mitosis, as well as the methyl donor S-adenosylmethionine, created from dietary sources. Reactive oxygen species that inhibit Dnmt1 upregulation, and a diet poor in methyl donors, combine to cause lupus in animal models. Similar changes are found in patients with active lupus, indicating a mechanism contributing to lupus flares.