The cellular and molecular origin of reactive oxygen species generation during myocardial ischemia and reperfusion

Anti-apoptotic and myocardial protective effects of ethyl pyruvate after regional ischaemia/reperfusion myocardial damage in an in vivo rat model

INTRODUCTION

The integration of reactive oxygen species is strongly associated with important pathophysiological mechanisms that mediate myocardial ischaemia/reperfusion (I/R) damage. Pyruvate is an efficacious scavenger of reactive oxygen species and a previous study has shown that ethyl pyruvate (EP) has a myocardial protective effect against regional I/R damage in an in vivo rat model. The purpose of this study was to determine whether the myocardial protective effect of EP is associated with anti-apoptosis.

METHODS

Rats were allocated to receive EP dissolved in lactated Ringer's solution or lactated Ringer's solution alone, via intraperitoneal infusion one hour before ischaemia. They were exposed to 30 minutes of ischaemia followed by reperfusion of the left coronary artery territory over two hours. Anti-apoptotic effects were checked using several biochemical parameters after two hours of reperfusion. Apoptosis was analysed using measured caspase-3 activity, Western blotting of B-cell lymphoma 2 (Bcl-2) family protein cleaved by caspase-3, and assessment of DNA laddering patterns and the terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) staining test.

RESULTS

In ischaemic myocardium, EP increased Bcl-2 expression, but reduced Bcl-2-associated X protein and cleaved caspase-3 expressions. EP reduced the expression of DNA laddering and the number of myocardial I/R-damaged TUNEL-positive cells.

CONCLUSION

This study demonstrated that EP has an anti-apoptotic effect after regional I/R damage in an in vivo rat heart model. The myocardial protective effect of EP may be related to its anti-apoptotic effect.

Altered Calcium Handling and Ventricular Arrhythmias in Acute Ischemia

Acute ischemia results in deadly cardiac arrhythmias that are a major contributor to sudden cardiac death (SCD). The electrophysiological changes involved have been extensively studied, yet the mechanisms of ventricular arrhythmias during acute ischemia remain unclear. What is known is that during acute ischemia both focal (ectopic excitation) and nonfocal (reentry) arrhythmias occur, due to an interaction of altered electrical, mechanical, and biochemical properties of the myocardium. There is particular interest in the role that alterations in intracellular calcium handling, which cause changes in intracellular calcium concentration and to the calcium transient, play in ischemia-induced arrhythmias. In this review, we briefly summarize the known contributors to ventricular arrhythmias during acute ischemia, followed by an in-depth examination of the potential contribution of altered intracellular calcium handling, which may include novel targets for antiarrhythmic therapy.

Ischemia/Reperfusion

Ischemic disorders, such as myocardial infarction, stroke, and peripheral vascular disease, are the most common causes of debilitating disease and death in westernized cultures. The extent of tissue injury relates directly to the extent of blood flow reduction and to the length of the ischemic period, which influence the levels to which cellular ATP and intracellular pH are reduced. By impairing ATPase-dependent ion transport, ischemia causes intracellular and mitochondrial calcium levels to increase (calcium overload). Cell volume regulatory mechanisms are also disrupted by the lack of ATP, which can induce lysis of organelle and plasma membranes. Reperfusion, although required to salvage oxygen-starved tissues, produces paradoxical tissue responses that fuel the production of reactive oxygen species (oxygen paradox), sequestration of proinflammatory immunocytes in ischemic tissues, endoplasmic reticulum stress, and development of postischemic capillary no-reflow, which amplify tissue injury. These pathologic events culminate in opening of mitochondrial permeability transition pores as a common end-effector of ischemia/reperfusion (I/R)-induced cell lysis and death. Emerging concepts include the influence of the intestinal microbiome, fetal programming, epigenetic changes, and microparticles in the pathogenesis of I/R. The overall goal of this review is to describe these and other mechanisms that contribute to I/R injury. Because so many different deleterious events participate in I/R, it is clear that therapeutic approaches will be effective only when multiple pathologic processes are targeted. In addition, the translational significance of I/R research will be enhanced by much wider use of animal models that incorporate the complicating effects of risk factors for cardiovascular disease. © 2017 American Physiological Society. Compr Physiol 7:113-170, 2017.

Transplantation and Damage-Associated Molecular Patterns (DAMPs)

Upon solid organ transplantation and during cancer immunotherapy, cellular stress responses result in the release of damage-associated molecular patterns (DAMPs). The various cellular stresses have been characterized in detail over the last decades, but a unifying classification based on clinically important aspects is lacking. Here, we provide an in-depth review of the most recent literature along with a unifying concept of the danger/injury model, suggest a classification of DAMPs, and review the recently elaborated mechanisms that result in the emission of such factors. We further point out the differences in DAMP responses including the release following a heat shock pattern, endoplasmic reticulum stress, DNA damage-mediated DAMP release, and discuss the diverse pathways of regulated necrosis in this respect. The understanding of various forms of DAMPs and the consequences of their different release patterns are prerequisite to associate serum markers of cellular stresses with clinical outcomes.

Oxidant Status following Cardiac Surgery with Phosphorylcholine-Coated Extracorporeal Circulation Systems

Introduction. Extracorporeal circulation (ECC) related systemic oxidative stress is a well-known entity but the underlying mechanisms are not clearly described. Our aim was to investigate the relation between the oxidative stress indices, inflammatory markers, and phosphorylcholine-coated (PCC) ECC systems. Patients and Methods. Thirty-two consecutive coronary artery bypass grafting (CABG) cases were randomly assigned to Group I (PCC, n = 18) and Group II (noncoated, n = 14) ECC circuits. Total Antioxidant Status (TAS), Total Oxidant Status (TOS), Tumor Necrosis Factor-α (TNF-α), Interleukin-1β (IL-β), Interleukin-6 (IL-6), Interleukin-8 (IL-8), Interleukin-10 (IL-10), and Procalcitonin (PCT) levels were measured at 5 different time points. The association between the oxidative indices levels and PCC system used was analyzed. Results. In Group I TOS and TAS statuses were increased at T1, T2, T3, and T4, while IL-10 and TNF-α levels accompanied those raises only at T2 (Group I-Group II, 4.73 ± 2.04 versus 2.79 ± 0.63, p = 0.002, and 30.56 ± 8.11 versus 23.97 ± 7.8, p = 0.031, resp.). In contrast, mean TAS and TOS levels were similar to baseline at all time points in Group II but IL-6 and IL-8 levels were increased at T2 (Group I-Group II, 16.84 ± 5.63 versus 44.81 ± 17.0, p = 0.001, and 38.88 ± 9.8 versus 46.14 ± 9.25, p = 0.038, resp.). Conclusion. Even coated ECC systems are still incapable of attenuating the inflammatory response to cardiopulmonary bypass (CPB).

Understanding pacing postconditioning-mediated cardiac protection: a role of oxidative stress and a synergistic effect of adenosine

We and others have demonstrated a protective role for pacing postconditioning (PPC) against ischemia/reperfusion (I/R) injury in the heart; however, the underlying mechanisms behind these protective effects are not completely understood. In this study, we wanted to further characterize PPC-mediated cardiac protection, specifically identify optimal pacing sites; examine the role of oxidative stress; and test the existence of a potential synergistic effect between PPC and adenosine. Isolated rat hearts were subjected to coronary occlusion followed by reperfusion. PPC involved three, 30 s, episodes of alternating left ventricular (LV) and right atrial (RA) pacing. Multiple pacing protocols with different pacing electrode locations were used. To test the involvement of oxidative stress, target-specific agonists or antagonists were infused at the beginning of reperfusion. Hemodynamic data were digitally recorded, and cardiac enzymes, oxidant, and antioxidant status were chemically measured. Pacing at the LV or RV but not at the heart apex or base significantly (P < 0.001) protected against ischemia-reperfusion injury. PPC-mediated protection was completely abrogated in the presence of reactive oxygen species (ROS) scavenger, ebselen; peroxynitrite (ONOO^-) scavenger, uric acid; and nitric oxide synthase inhibitor, L-NAME. Nitric oxide (NO) donor, snap, however significantly (P < 0.05) protected the heart against I/R injury in the absence of PPC. The protective effects of PPC were significantly improved by adenosine. PPC-stimulated protection can be achieved by alternating LV and RA pacing applied at the beginning of reperfusion. NO, ROS, and the product of their interaction ONOO^- play a significant role in PPC-induced cardiac protection. Finally, the protective effects of PPC can be synergized with adenosine.

Preoperative values of inflammatory markers predict clinical outcomes in patients after CABG, regardless of the use of cardiopulmonary bypass

Objective

The impact of systemic inflammation on clinical outcomes after CABG surgery is still controversial. In this study, we evaluated the impact of the markers of inflammation, endothelial damage and platelet activation on clinical outcomes after on- and off-pump CABG.

Methods

A group of 191 consecutive on- and off-pump CABG patients were prospectively studied. Blood samples were drawn before surgery, 18–36 h after the procedure and 5–7 days postoperatively and analyzed for 8-iso-prostaglandin F_2α (8-iso-PGF_2α), asymmetric dimethylarginine (ADMA) and β-thromboglobulin (β-TG). White blood count and C-reactive protein were measured twice, first before and then during the first 18–36 h after CABG. The primary clinical end-points were: low cardiac output syndrome (LCOS), postoperative myocardial infarction (PMI) and in-hospital cardiovascular death.

Results

Elevation of 8-iso-PGF_2α, ADMA and β-TG before surgery was associated with an increased risk of morbidity and mortality after CABG. There were no differences in analyzed markers and clinical outcomes between the on- and off-pump groups. Even during the uncomplicated postoperative course the inflammatory response was enhanced and still remained higher than baseline 5–7 days after surgery.

Conclusion

Links between preoperative 8-iso-PGF_2α, ADMA and β-TG and unfavorable early post-CABG outcomes suggest that these markers could be useful in identifying patients with increased risk of LCOS, PMI and in-hospital cardiovascular death following elective CABG.

Effect of Combination of Angiotensin-Converting Enzyme Inhibitors and Vitamin D Receptor Activators on Cardiac Oxidative Stress in Diabetic Rats

BACKGROUND

The principle mediator of diabetic myocardial injury is oxidative stress. The aim was to compare the effect of monotherapy with enalapril, angiotensin-converting enzyme inhibitor and paricalcitol (vitamin D receptor activator), to the combined therapy with both drugs on the cardiac oxidant-antioxidant balance in the type 2 diabetic rats.

MATERIALS AND METHODS

A total of 50 male Sprague-Dawley rats were divided into 5 groups, namely the normal control and diabetic, vehicle, enalapril, paricalcitol and paricalcitol and enalapril-treated groups. Enalapril was given at a dose of (25mg/L) in drinking water once daily and paricalcitol was given intraperitoneally (0.8μg/kg/3 × week) for 3 months. Glycemic status, cardiac oxidant-antioxidant parameters and histologic examination were determined.

RESULTS

Paricalcitol and combined treatment significantly (P < 0.01) reduced the level of fasting, postprandial blood glucose, homeostatic model assessment-insulin resistance, cardiac malondialdehyde and nitric oxide. Moreover, they significantly (P < 0.01) increased the levels of insulin and c-peptide compared to diabetic control rats. Combined treatment significantly (P < 0.01) raised the level of glutathione, glutathione S-transferase and catalase more than monotherapy.

CONCLUSION

The combination of angiotensin-converting enzyme inhibitors and vitamin D receptor activators has a superior effect on reducing cardiac oxidative stress by raising antioxidant activity than monotherapy in diabetic rats.

CD38 Deficiency Protects the Heart from Ischemia/Reperfusion Injury through Activating SIRT1/FOXOs-Mediated Antioxidative Stress Pathway

Ischemia/reperfusion (I/R) injury induces irreversible oxidative stress damage to the cardiac muscle. We previously observed that CD38 deficiency remarkably protects mouse embryonic fibroblasts (MEFs) from oxidative stress-induced injury. However, whether CD38 deficiency protects from I/R injury in the heart is not explored. Here, we showed that the hearts of CD38 deficient mice or wild type mice supplied with exogenous NAD were significantly protected from ischemia/reperfusion injury, seen as reduction of the myocardial infarct sizes when the mice were subjected to 30 min ischemia followed by 24 hours of reperfusion. Consistently, the protection of CD38 deficiency on hypoxia/reoxygenation (H/R) injury was confirmed with a CD38 knockdown H9c2 stable cell line. Furthermore, we observed that knockdown of CD38 remarkably inhibited ROS generation and intracellular Ca²⁺ overloading induced by H/R in H9c2 cells. The FOXO1 and FOXO3 expressions were significantly elevated by H/R injury in CD38 knockdown cells compared with normal H9c2 cells. The cell immunofluorescence assay showed that FOXO1 nuclear translocation was significantly increased in CD38 knockdown H9c2 cells. In addition, we demonstrated that the increase of FOXO1 nuclear translocation was associated with the increased expressions of antioxidant catalase and SOD2 and the attenuated expression of the ROS generation enzyme NOX4. In conclusion, our results provide new evidence that CD38 deficiency protects the heart from I/R injury through activating SIRT1/FOXOs-mediated antioxidative stress pathway.

A Mouse Model of Retinal Ischemia-Reperfusion Injury Through Elevation of Intraocular Pressure

Retinal ischemia-reperfusion (I/R) is a pathophysiological process contributing to cellular damage in multiple ocular conditions, including glaucoma, diabetic retinopathy, and retinal vascular occlusions. Rodent models of I/R injury are providing significant insights into mechanisms and treatment strategies for human I/R injury, especially with regard to neurodegenerative damage in the retinal neurovascular unit. Presented here is a protocol for inducing retinal I/R injury in mice through elevation of intraocular pressure (IOP). In this protocol, the ocular anterior chamber is cannulated with a needle, through which flows the drip of an elevated saline reservoir. Using this drip to raise IOP above systolic arterial blood pressure, a practitioner temporarily halts inner retinal blood flow (ischemia). When circulation is reinstated (reperfusion) by removal of the cannula, severe cellular damage ensues, resulting ultimately in retinal neurodegeneration. Recent studies demonstrate inflammation, vascular permeability, and capillary degeneration as additional elements of this model. Compared to alternative retinal I/R methodologies, such as retinal arterial ligation, retinal I/R injury by elevated IOP offers advantages in its anatomical specificity, experimental tractability, and technical accessibility, presenting itself as a valuable tool for examining neuronal pathogenesis and therapy in the retinal neurovascular unit.

Upregulation of microRNA-22 contributes to myocardial ischemia-reperfusion injury by interfering with the mitochondrial function

Mitochondrial oxidative damage is critically involved in cardiac ischemia reperfusion (I/R) injury. MicroRNA-22 (miR-22) has been predicted to potentially target sirtuin-1 (Sirt1) and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1α), both of which are known to provide protection against mitochondrial oxidative injury. The present study aims to investigate whether miR-22 is involved in the regulation of cardiac I/R injury by regulation of mitochondrial function. We found that miR-22 level was significantly increased in rat hearts subjected to I/R injury, as compared with the sham group. Intra-myocardial injection of 20 ug miR-22 inhibitor reduced I/R injury as evidenced by significant decreases in cardiac infarct size, serum lactate dehydrogenase (LDH) and creatine kinase (CK) levels and the number of apoptotic cardiomyocytes. H9c2 cardiomyocytes exposed to hypoxia/reoxygenation (H/R) insult exhibited an increase in miR-22 expression, which was blocked by reactive oxygen species (ROS) scavenger and p53 inhibitor. In addition, miR-22 inhibitor attenuated, whereas miR-22 mimic aggravated H/R-induced injury in H9c2 cardiomyocytes. MiR-22 inhibitor per se had no significant effect on cardiac mitochondrial function. Mitochondria from rat receiving miR-22 inhibitor 48h before ischemia were found to have a significantly less mitochondrial superoxide production and greater mitochondrial membrane potential and ATP production as compared with rat receiving miR control. In H9c2 cardiomyocyte, it was found that miR-22 mimic aggravated, whilst miR-22 inhibitor significantly attenuated H/R-induced mitochondrial damage. By using real time PCR, western blot and dual-luciferase reporter gene analyses, we identified Sirt1 and PGC1α as miR-22 targets in cardiomyocytes. It was found that silencing of Sirt1 abolished the protective effect of miR-22 inhibitor against H/R-induced mitochondrial dysfunction and cell injury in cardiomyocytes. Taken together, our findings reveal a novel molecular mechanism for cardiac mitochondrial dysfunction during myocardial I/R injury at the miRNA level and demonstrate the therapeutic potential of miR-22 inhibition for acute myocardial I/R injury by maintaining cardiac mitochondrial function.

The Ubiquitin-Like SUMO System and Heart Function: From Development to Disease

SUMOylation is a ubiquitin-related transient posttranslational modification pathway catalyzing the conjugation of small ubiquitin-like modifier (SUMO) proteins (SUMO1, SUMO2, and SUMO3) to lysine residues of proteins. SUMOylation targets a wide variety of cellular regulators and thereby affects a multitude of different cellular processes. SUMO/sentrin-specific proteases are able to remove SUMOs from targets, contributing to a tight control of SUMOylated proteins. Genetic and cell biological experiments indicate a critical role of balanced SUMOylation/deSUMOylation for proper cardiac development, metabolism, and stress adaptation. Here, we review the current knowledge about SUMOylation/deSUMOylation in the heart and provide an integrated picture of cardiac functions of the SUMO system under physiologic or pathologic conditions. We also describe potential therapeutic approaches targeting the SUMO machinery to combat heart disease.

Dityrosine as a marker of acute myocardial infarction? Experiments with the isolated Langendorff heart

The isolated Langendorff heart was used to evaluate dityrosine as a marker of acute myocardial infarctions. The animal model allowed the generation of local infarctions with defined survival times, as well as infarctions with and without reperfusion. The results showed that dityrosine, at least under the conditions of the animal model, occurs very shortly after early ischemia and infarctions, since positive staining results were already obtained after a survival time of only 5 min. Furthermore, it could be proved that the occurrence of dityrosine does not depend on a reperfusion of the ischemic muscle area and that there are no differences in the staining patterns of infarctions with and without reperfusion. Positive staining results for dityrosine in control hearts without infarctions had to be considered when evaluating the tissue samples of the study hearts. In part, the positive staining results of the control hearts seemed to be an artefact of the Langendorff system, easily identifiable by a distinctive staining pattern. Positive staining results in tissue samples of hearts that suffered from arrhythmia on the other hand implied that the occurrence of dityrosine is not specific for myocardial infarctions. Taking into account the results of previous works on human tissue samples, however, these findings did not question the use of dityrosine as a diagnostic tool; they simply showed that myocardial damage due to oxidative stress might occur under various pathologic conditions.

Sulforaphane improves oxidative status without attenuating the inflammatory response or cardiac impairment induced by ischemia–reperfusion in rats

Sulforaphane, a natural isothiocyanate, demonstrates cardioprotection associated with its capacity to stimulate endogenous antioxidants and to inhibit inflammation. The aim of this study was to investigate whether sulforaphane is capable of attenuating oxidative stress and inflammatory responses through the TLR4/MyD88/NFκB pathway, and thereby could modulate post-ischemic ventricular function in isolated rat hearts submitted to ischemia and reperfusion. Male Wistar rats received sulforaphane (10 mg·kg−1·day−1) or vehicle i.p. for 3 days. Global ischemia was performed using isolated hearts, 24 h after the last injection, by interruption of the perfusion flow. The protocol included a 20 min pre-ischemic period followed by 20 min of ischemia and a 20 min reperfusion. Although no changes in mechanical function were observed, sulforaphane induced a significant increase in superoxide dismutase and heme oxygenase-1 expression (both 66%) and significantly reduced reactive oxygen species levels (7%). No differences were observed for catalase and glutathione peroxidase expression or their activities, nor for thioredoxin reductase, glutaredoxin reductase and glutathione-S-transferase. No differences were found in lipid peroxidation or TLR4, MyD88, and NF-κB expression. In conclusion, although sulforaphane was able to stimulate endogenous antioxidants modestly, this result did not impact inflammatory signaling or cardiac function of hearts submitted to ischemia and reperfusion.

Compromised Wound Healing in Ischemic Type 2 Diabetic Rats

Ischemia is one of the main epidemic factors and characteristics of diabetic chronic wounds, and exerts a profound effect on wound healing. To explore the mechanism of and the cure for diabetic impaired wound healing, we established a type 2 diabetic rat model. We used an 8weeks high fat diet (HFD) feeding regimen followed by multiple injections of streptozotocin (STZ) at a dose of 10mg/kg to induce Wister rat to develop type 2 diabetes. Metabolic characteristics were assessed at the 5th week after the STZ injections to confirm the establishment of diabetes mellitus on the rodent model. A bipedicle flap, with length to width ratio 1.5, was performed on the back of the rat to make the flap area ischemic. Closure of excisional wounds on this bipedicle flap and related physiological and pathological changes were studied using histological, immunohistochemical, real time PCR and protein immunoblot approaches. Our results demonstrated that a combination of HFD feeding and a low dose of STZ is capable of inducing the rats to develop type 2 diabetes with noticeable insulin resistance, persistent hyperglycemia, moderate degree of insulinemia, as well as high serum cholesterol and high triglyceride levels. The excision wounds on the ischemic double pedicle flap showed deteriorative healing features comparing with non-ischemic diabetic wounds, including: delayed healing, exorbitant wound inflammatory response, excessive and prolonged ROS production and excessive production of MMPs. Our study suggested that HFD feeding combined with STZ injection could induce type 2 diabetes in rat. Our ischemic diabetic wound model is suitable for the investigation of human diabetic related wound repair; especically for diabetic chronic wounds.

Protective Effects of L-Malate against Myocardial Ischemia/Reperfusion Injury in Rats

Objective. To investigate the protective effects of L-malate against myocardial ischemia/reperfusion (I/R) injury in rats. Methods. Male Sprague-Dawley rats were randomly assigned to the following groups: sham (sham), an ischemia/reperfusion (I/R) model group (model), an DMF pretreated group (DMF), and 5 L-malate pretreated groups (15, 60, 120, 240, or 480 mg/kg, gavage) before inducing myocardial ischemia. Plasma LDH, cTn-I, TNF-α, hs-CRP, SOD, and GSH-PX were measured 3 h later I/R. Areas of myocardial infarction were measured; hemodynamic parameters during I/R were recorded. Hearts were harvested and Western blot was used to quantify Nrf2, Keap1, HO-1, and NQO-1 expression in the myocardium. Results. L-malate significantly reduced LDH and cTn-I release, reduced myocardial infarct size, inhibited expression of inflammatory cytokines, and partially preserved heart function, as well as increasing antioxidant activity after myocardial I/R injury. Western blot confirmed that L-malate reduced Kelch-like ECH-associated protein 1 in ischemic myocardial tissue, upregulated expression of Nrf2 and Nrf2 nuclear translocation, and increased expression of heme oxygenase-1 and NAD(P)H:quinone oxidoreductase 1, which are major targets of Nrf2. Conclusions. L-malate may protect against myocardial I/R injury in rats and this may be associated with activation of the Nrf2/Keap1 antioxidant pathway.

Mitochondrial oxidative metabolism and uncoupling proteins in the failing heart

Despite significant progress in cardiovascular medicine, myocardial ischemia and infarction, progressing eventually to the final end point heart failure (HF), remain the leading cause of morbidity and mortality in the USA. HF is a complex syndrome that results from any structural or functional impairment in ventricular filling or blood ejection. Ultimately, the heart's inability to supply the body's tissues with enough blood may lead to death. Mechanistically, the hallmarks of the failing heart include abnormal energy metabolism, increased production of reactive oxygen species (ROS) and defects in excitation-contraction coupling. HF is a highly dynamic pathological process, and observed alterations in cardiac metabolism and function depend on the disease progression. In the early stages, cardiac remodeling characterized by normal or slightly increased fatty acid (FA) oxidation plays a compensatory, cardioprotective role. However, upon progression of HF, FA oxidation and mitochondrial oxidative activity are decreased, resulting in a significant drop in cardiac ATP levels. In HF, as a compensatory response to decreased oxidative metabolism, glucose uptake and glycolysis are upregulated, but this upregulation is not sufficient to compensate for a drop in ATP production. Elevated mitochondrial ROS generation and ROS-mediated damage, when they overwhelm the cellular antioxidant defense system, induce heart injury and contribute to the progression of HF. Mitochondrial uncoupling proteins (UCPs), which promote proton leak across the inner mitochondrial membrane, have emerged as essential regulators of mitochondrial membrane potential, respiratory activity and ROS generation. Although the physiological role of UCP2 and UCP3, expressed in the heart, has not been clearly established, increasing evidence suggests that these proteins by promoting mild uncoupling could reduce mitochondrial ROS generation and cardiomyocyte apoptosis and ameliorate thereby myocardial function. Further investigation on the alterations in cardiac UCP activity and regulation will advance our understanding of their physiological roles in the healthy and diseased heart and also may facilitate the development of novel and more efficient therapies.

The effect of levosimendan on myocardial ischemia-reperfusion injury in streptozotocin-induced diabetic rats

Objective

Ischemia/reperfusion (I/R) injury is an important cause of myocardial damage by means of oxidative, inflammatory, and apoptotic mechanisms. The aim of the present study was to examine the potential cardio protective effects of levosimendan in a diabetic rat model of myocardial I/R injury.

Methods

A total of 18 streptozotocin-induced diabetic Wistar Albino rats (55 mg/kg) were randomly divided into three equal groups as follows: the diabetic I/R group (DIR) in which myocardial I/R was induced following left thoracotomy, by ligating the left anterior descending coronary artery for 60 min, followed by 2 h of reperfusion; the diabetic I/R levosimendan group (DIRL), which underwent I/R by the same method while taking levosimendan intraperitoneal 12 µg kg⁻¹; and the diabetic control group (DC) which underwent sham operations without tightening of the coronary sutures. As a control group (C), six healthy age-matched Wistar Albino rats underwent sham operations similar to the DC group. Two hours after the operation, the rats were sacrificed and the myocardial tissue samples were examined by light microscopy for evidence of myonecrosis and inflammatory cell infiltration.

Results

Myonecrosis findings were significantly different among groups (p=0.008). Myonecrosis was more pronounced in the DIR group compared with the C, DC, and DIRL groups (p=0.001, p=0.007 and p=0.037, respectively). Similarly, the degree of inflammatory cell infiltration showed significant difference among groups (p<0.0001). Compared with C, DC, and DIRL groups, the inflammatory cell infiltration was significantly higher among the DIR group (p<0.0001, p<0.0001, and p=0.020, respectively). Also, myocardial tissue edema was significantly different among groups (p=0.006). The light microscopic myocardial tissue edema levels were significantly higher in the DIR group than the C, DC, and DIRL groups (p=0.001, p=0.037, and p=0.014, respectively).

Conclusion

Taken together, our data indicate that levosimendan may be helpful in reducing myocardial necrosis, myocardial inflammation, and myocardial tissue edema resulting from ischemia–reperfusion injury.

Biological thiols-triggered hydrogen sulfide releasing microfibers for tissue engineering applications

By electrospinning of polycaprolactone (PCL) solutions containing N-(benzoylthio)benzamide (NSHD1), a H2S donor, fibrous scaffolds with hydrogen sulfide (H2S) releasing capability (H2S-fibers) are fabricated. The resultant microfibers are capable of releasing H2S upon immersion in aqueous solution containing biological thiols under physiological conditions. The H2S release peaks of H2S-fibers appeared at 2-4h, while the peak of donor alone showed at 45 min. H2S release half-lives of H2S-fibers were 10-20 times longer than that of donor alone. Furthermore, H2S-fibers can protect cells from H2O2 induced oxidative damage by significantly decreasing the production of intracellular reactive oxygen species (ROS). Finally, we investigated the H2S-fibers application as a wound dressing in vitro. Given that H2S has a broad range of physiological functions, H2S-fibers hold great potential for various biomedical applications.

STATEMENT OF SIGNIFICANCE

Hydrogen sulfide, as a gaseous messenger, plays a crucial role in many physiological and pathological conditions. Recent studies about functions of H2S suggests H2S-based therapy could be promising therapeutic strategy for many diseases, such as cardiovascular disease, arthritis, and inflammatory bowel disease. Although many H2S donors have been developed and applied for biomedical studies, most of H2S donors have the shortage that the H2S release is either too fast or uncontrollable, which poorly mimic the biological generation of H2S. By simply combining electrospinning technique with our designed biological thiols activated H2S donor, NSHD1, we fabricated H2S releasing microfibers (H2S-fibers). This H2S-fibers significantly prolonged the releasing time compared to H2S donor alone. By adjusting the electrospinning parameters, tunable releasing profiles can be achieved. Moreover, the H2S fibers can protect cardiac myoblasts H9c2 and fibroblast NIH 3T3 from oxidative damage and support their proliferation as cellular scaffolds. To our knowledge, this is the first report of electrospun fibers with H2S releasing capacity. We anticipate this H2S-releasing scaffold will have great potential for biomedical applications.

Reperfusion injury and reactive oxygen species: The evolution of a concept

Reperfusion injury, the paradoxical tissue response that is manifested by blood flow-deprived and oxygen-starved organs following the restoration of blood flow and tissue oxygenation, has been a focus of basic and clinical research for over 4-decades. While a variety of molecular mechanisms have been proposed to explain this phenomenon, excess production of reactive oxygen species (ROS) continues to receive much attention as a critical factor in the genesis of reperfusion injury. As a consequence, considerable effort has been devoted to identifying the dominant cellular and enzymatic sources of excess ROS production following ischemia-reperfusion (I/R). Of the potential ROS sources described to date, xanthine oxidase, NADPH oxidase (Nox), mitochondria, and uncoupled nitric oxide synthase have gained a status as the most likely contributors to reperfusion-induced oxidative stress and represent priority targets for therapeutic intervention against reperfusion-induced organ dysfunction and tissue damage. Although all four enzymatic sources are present in most tissues and are likely to play some role in reperfusion injury, priority and emphasis has been given to specific ROS sources that are enriched in certain tissues, such as xanthine oxidase in the gastrointestinal tract and mitochondria in the metabolically active heart and brain. The possibility that multiple ROS sources contribute to reperfusion injury in most tissues is supported by evidence demonstrating that redox-signaling enables ROS produced by one enzymatic source (e.g., Nox) to activate and enhance ROS production by a second source (e.g., mitochondria). This review provides a synopsis of the evidence implicating ROS in reperfusion injury, the clinical implications of this phenomenon, and summarizes current understanding of the four most frequently invoked enzymatic sources of ROS production in post-ischemic tissue.

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Reperfusion injury is implicated in a variety of human diseases and disorders.

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Evidence implicating ROS in reperfusion injury continues to grow.

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Several enzymes are candidate sources of ROS in post-ischemic tissue.

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Inter-enzymatic ROS-dependent signaling enhances the oxidative stress caused by I/R.

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Molecular Characterization of Reactive Oxygen Species in Myocardial Ischemia-Reperfusion Injury

Myocardial ischemia-reperfusion (I/R) injury is experienced by individuals suffering from cardiovascular diseases such as coronary heart diseases and subsequently undergoing reperfusion treatments in order to manage the conditions. The occlusion of blood flow to the tissue, termed ischemia, can be especially detrimental to the heart due to its high energy demand. Several cellular alterations have been observed upon the onset of ischemia. The danger created by cardiac ischemia is somewhat paradoxical in that a return of blood to the tissue can result in further damage. Reactive oxygen species (ROS) have been studied intensively to reveal their role in myocardial I/R injury. Under normal conditions, ROS function as a mediator in many cell signaling pathways. However, stressful environments significantly induce the generation of ROS which causes the level to exceed body's antioxidant defense system. Such altered redox homeostasis is implicated in myocardial I/R injury. Despite the detrimental effects from ROS, low levels of ROS have been shown to exert a protective effect in the ischemic preconditioning. In this review, we will summarize the detrimental role of ROS in myocardial I/R injury, the protective mechanism induced by ROS, and potential treatments for ROS-related myocardial injury.

Po2 cycling protects diaphragm function during reoxygenation via ROS, Akt, ERK, and mitochondrial channels

Po2 cycling, often referred to as intermittent hypoxia, involves exposing tissues to brief cycles of low oxygen environments immediately followed by hyperoxic conditions. After experiencing long-term hypoxia, muscle can be damaged during the subsequent reintroduction of oxygen, which leads to muscle dysfunction via reperfusion injury. The protective effect and mechanism behind Po2 cycling in skeletal muscle during reoxygenation have yet to be fully elucidated. We hypothesize that Po2 cycling effectively increases muscle fatigue resistance through reactive oxygen species (ROS), protein kinase B (Akt), extracellular signal-regulated kinase (ERK), and certain mitochondrial channels during reoxygenation. Using a dihydrofluorescein fluorescent probe, we detected the production of ROS in mouse diaphragmatic skeletal muscle in real time under confocal microscopy. Muscles treated with Po2 cycling displayed significantly attenuated ROS levels (n = 5; P < 0.001) as well as enhanced force generation compared with controls during reperfusion (n = 7; P < 0.05). We also used inhibitors for signaling molecules or membrane channels such as ROS, Akt, ERK, as well as chemical stimulators to close mitochondrial ATP-sensitive potassium channel (KATP) or open mitochondrial permeability transition pore (mPTP). All these blockers or stimulators abolished improved muscle function with Po2 cycling treatment. This current investigation has discovered a correlation between KATP and mPTP and the Po2 cycling pathway in diaphragmatic skeletal muscle. Thus we have identified a unique signaling pathway that may involve ROS, Akt, ERK, and mitochondrial channels responsible for Po2 cycling protection during reoxygenation conditions in the diaphragm.

NSAIDs and Cardiovascular Diseases: Role of Reactive Oxygen Species

Nonsteroidal anti-inflammatory drugs (NSAIDs) are the most commonly used drugs worldwide. NSAIDs are used for a variety of conditions including pain, rheumatoid arthritis, and musculoskeletal disorders. The beneficial effects of NSAIDs in reducing or relieving pain are well established, and other benefits such as reducing inflammation and anticancer effects are also documented. The undesirable side effects of NSAIDs include ulcers, internal bleeding, kidney failure, and increased risk of heart attack and stroke. Some of these side effects may be due to the oxidative stress induced by NSAIDs in different tissues. NSAIDs have been shown to induce reactive oxygen species (ROS) in different cell types including cardiac and cardiovascular related cells. Increases in ROS result in increased levels of oxidized proteins which alters key intracellular signaling pathways. One of these key pathways is apoptosis which causes cell death when significantly activated. This review discusses the relationship between NSAIDs and cardiovascular diseases (CVD) and the role of NSAID-induced ROS in CVD.

Functional electron paramagnetic resonance imaging of ischemic rat heart: Monitoring of tissue oxygenation and pH

PURPOSE

Electron paramagnetic resonance (EPR) imaging in the spectral-spatial domain with application of soluble paramagnetic probes provides an opportunity for spatially resolved functional measurements of living objects. The purpose of this study was to develop EPR methods for visualization of oxygenation and acidosis of ischemic myocardium.

METHODS

EPR oxygen measurements were performed using isotopically substituted (2) H,(15) N-dicarboxyproxyl. The radical has an EPR line width of 320 mG and oxygen-induced line broadening of 0.53 mG/mm Hg, providing oxygen sensitivity down to 5 μM. pH measurements were performed using previously developed pH-sensitive imidazoline nitroxide. The radical has an EPR spectrum with pH-dependable hyperfine splitting, pK = 6.6, providing pH sensitivity of approximately 0.05 U in the physiological range.

RESULTS

EPR imaging of isolated and perfused rat hearts was performed in the two-dimensional + spectral domain. The spatial resolution of the measurements was about 1.4 mm. Marked tissue hypoxia was observed in the ischemic area of the heart after occlusion of the left anterior descending coronary artery. Tissue oxygenation was partly restored upon reperfusion. EPR mapping of myocardial pH indicated acidosis of the ischemic area down to pH 6.7-6.8.

CONCLUSION

This study demonstrates the capability of low-field EPR and the nitroxide spin probes for mapping of myocardial oxygenation and pH. The developed approaches might be used for noninvasive investigation of microenvironment on living objects. Magn Reson Med 76:350-358, 2016. © 2015 Wiley Periodicals, Inc.

New perspectives on bioactivity of olive oil: evidence from animal models, human interventions and the use of urinary proteomic biomarkers

Olive oil (OO) is the primary source of fat in the Mediterranean diet and has been associated with longevity and a lower incidence of chronic diseases, particularly CHD. Cardioprotective effects of OO consumption have been widely related with improved lipoprotein profile, endothelial function and inflammation, linked to health claims of oleic acid and phenolic content of OO. With CVD being a leading cause of death worldwide, a review of the potential mechanisms underpinning the impact of OO in the prevention of disease is warranted. The current body of evidence relies on mechanistic studies involving animal and cell-based models, epidemiological studies of OO intake and risk factor, small- and large-scale human interventions, and the emerging use of novel biomarker techniques associated with disease risk. Although model systems are important for mechanistic research nutrition, methodologies and experimental designs with strong translational value are still lacking. The present review critically appraises the available evidence to date, with particular focus on emerging novel biomarkers for disease risk assessment. New perspectives on OO research are outlined, especially those with scope to clarify key mechanisms by which OO consumption exerts health benefits. The use of urinary proteomic biomarkers, as highly specific disease biomarkers, is highlighted towards a higher translational approach involving OO in nutritional recommendations.

Mesenchymal Stromal Cell Therapy in Ischemia/Reperfusion Injury

Ischemia/reperfusion injury (IRI) represents a worldwide public health issue of increasing incidence. IRI may virtually affect all organs and tissues and is associated with significant morbidity and mortality. Particularly, the duration of blood supply deprivation has been recognized as a critical factor in stroke, hemorrhagic shock, or myocardial infarction, as well as in solid organ transplantation (SOT). Pathophysiologically, IRI causes multiple cellular and tissular metabolic and architectural changes. Furthermore, the reperfusion of ischemic tissues induces both local and systemic inflammation. In the particular field of SOT, IRI is an unavoidable event, which conditions both short- and long-term outcomes of graft function and survival. Clinically, the treatment of patients with IRI mostly relies on supportive maneuvers since no specific target-oriented therapy has been validated thus far. In the present review, we summarize the current literature on mesenchymal stromal cells (MSC) and their potential use as cell therapy in IRI. MSC have demonstrated immunomodulatory, anti-inflammatory, and tissue repair properties in rodent studies and in preliminary clinical trials, which may open novel avenues in the management of IRI and SOT.

A novel function of nuclear nonmuscle myosin regulatory light chain in promotion of xanthine oxidase transcription after myocardial ischemia/reperfusion

Nuclear myosin regulates gene transcription and this novel function might be modulated through phosphorylation of the myosin regulatory light chain (p-MLC20). Nonmuscle MLC20 (nmMLC20) is also present in the nuclei of cardiomyocytes and a potential nmMLC20 binding sequence has been identified in the promoter of the xanthine oxidase (XO) gene. Thus, we investigated its function in the regulation of XO transcription after myocardial ischemia/reperfusion (IR). In a rat model of myocardial IR and a cardiomyocyte model of hypoxia/reoxygenation (HR) injury, the cardiac or cell injury, myosin light chain kinase (MLCK) content, XO expression and activity, XO-derived products, and level of nuclear p-nmMLC20 were detected. Coimmunoprecipitation (co-IP), chromatin immunoprecipitation, DNA pull-down, and luciferase reporter gene assays were used to decipher the molecular mechanisms through which nmMLC20 promotes XO expression. IR or HR treatment dramatically elevated nuclear p-nmMLC20 level, accompanied by increased XO expression, activity, and products (H2O2 and uric acid), as well as the IR or HR injury; these effects were ameliorated by inhibition of MLCK or knockdown of nmMLC20. Our findings from these experiments demonstrated that nuclear p-nmMLC20 binds to the consensus sequence GTCGCC in the XO gene promoter, interacts with RNA polymerase II and transcription factor IIB to form a transcription preinitiation complex, and hence activates XO gene transcription. These results suggest that nuclear p-nmMLC20 plays an important role in IR/HR injury by transcriptionally upregulating XO gene expression to increase oxidative stress in myocardium. Our findings demonstrate nuclear nmMLC20 as a potential new therapeutic target to combat cardiac IR injury.

Pretreatment of Adipose Derived Stem Cells with Curcumin Facilitates Myocardial Recovery via Antiapoptosis and Angiogenesis

The poor survival rate of transplanted stem cells in ischemic myocardium has limited their therapeutic efficacy. Curcumin has potent antioxidant property. This study investigates whether prior curcumin treatment protects stem cells from oxidative stress injury and improves myocardial recovery following cells transplantation. Autologous Sprague-Dawley rat adipose derived mesenchymal stem cells (ADSCs) were pretreated with or without curcumin. The hydrogen peroxide/serum deprivation (H2O2/SD) medium was used to mimic the ischemic condition in vitro. Cytoprotective effects of curcumin on ADSCs were evaluated. Curcumin pretreatment significantly increased cell viability and VEGF secretion, and decreased cell injury and apoptosis via regulation of PTEN/Akt/p53 and HO-1 signal proteins expression. The therapeutic potential of ADSCs implantation was investigated in myocardial ischemia-reperfusion injury (IRI) model. Transplantation of curcumin pretreated ADSCs not only resulted in better heart function, higher cells retention, and smaller infarct size, but also decreased myocardial apoptosis, promoted neovascularization, and increased VEGF level in ischemic myocardium. Together, priming of ADSCs with curcumin improved tolerance to oxidative stress injury and resulted in enhancement of their therapeutic potential of ADSCs for myocardial repair. Curcumin pretreatment is a promising adjuvant strategy for stem cells transplantation in myocardial restoration.

Transient receptor potential melastatin-4 is involved in hypoxia-reoxygenation injury in the cardiomyocytes

Ischemic heart disease still remains the most common cause of cardiac death. During ischemia-reperfusion (I/R), reactive oxygen species (ROS) are produced in excess in cardiac tissue, where they induce cell death. Our previous study showed that 9-phenanthrol (9-Phe), a specific inhibitor of the TRPM4 channel, preserves cardiac contractile function and protects the heart from I/R injury-related infarction in the excised rat heart. Accordingly, we hypothesized that TRPM4 channels are involved in the 9-Phe-mediated cardioprotection against ROS-induced injury. In rats, intravenous 9-Phe mitigated the development of myocardial infarction caused by the occlusion of the left anterior descending artery. Immunohistochemical analysis indicated that TRPM4 proteins are expressed in ventricular myocytes susceptible to I/R injury. Hydrogen peroxide (H₂O₂) is among the main ROS overproduced during I/R. In the cardiomyocyte cell line H9c2, pretreatment with 9-Phe prevented cell death induced by conditions mimicking I/R, namely 200 μM H₂O₂ and hypoxia-reoxygenation. Gene silencing of TRPM4 preserved the viability of H9c2 cardiomyocytes exposed to 200 μM H₂O₂. These results suggest that the cardioprotective effects of 9-Phe are mediated through the inhibition of the TRPM4 channels.

Apocynum venetum Leaf Attenuates Myocardial Ischemia/Reperfusion Injury by Inhibiting Oxidative Stress

Apocynum venetum, a Chinese medicinal herb, is reported to be neuroprotective. However, whether Apocynum venetum leaf extract (AVLE) protects against ischemic myocardium remains elusive. Our present study was aimed to observe the effects of AVLE preconditioning on myocardial ischemia/reperfusion (MI/R) injury and to investigate the possible mechanisms. Rats were treated with AVLE (500 mg/kg/d, o.g.) or distilled water once daily for one week. Afterward, all the animals were subjected to 30 min of myocardial ischemia followed by 4 h of reperfusion. AVLE preconditioning for one week significantly improved cardiac function following MI/R. Meanwhile, AVLE reduced infarct size, plasma creatine kinase (CK)/lactate dehydrogenase (LDH) activities and myocardial apoptosis at the end of reperfusion in rat hearts. Moreover, AVLE preconditioning significantly inhibited superoxide generation, gp91phox expression, malonaldialdehyde formation and enhanced superoxide dismutase (SOD) activity in I/R hearts. Furthermore, AVLE treatment increased Akt and extracellular regulated protein kinases 1/2 (ERK1/2) phosphorylations in I/R rat heart. Either the Phosphatidylinositide 3-kinase (PI3K) inhibitor wortmannin or the ERK1/2 inhibitor PD98059 blocked AVLE-stimulated anti-oxidative effects and cardioprotection. Our study demonstrated for the first time that AVLE reduces oxidative stress and exerts cardioprotection against MI/R injury in rats.

Role of TRP channels in the induction of heat shock proteins (Hsps) by heating skin

Transient receptor potential (TRP) channels in skin are crucial for achieving temperature sensitivity to maintain internal temperature balance and thermal homeostasis, as well as to protect skin cells from environmental stresses such as infrared (IR) or near-infrared (NIR) radiation via heat shock protein (Hsp) production. However, the mechanisms by which IR and NIR activate TRP channels and produce Hsps intracellularly have been independently reported. In this review, we discuss the relationship between TRP channel activation and Hsp production, and introduce the roles of several skin TRP channels in the regulation of HSP production by IR and NIR exposure.

N-acetylcysteine administration prevents nonthyroidal illness syndrome in patients with acute myocardial infarction: a randomized clinical trial

CONTEXT

The acute phase of the nonthyroidal illness syndrome (NTIS) is characterized by low T3 and high rT3 levels, affecting up to 75% of critically ill patients. Oxidative stress has been implicated as a causative factor of the disturbed peripheral thyroid hormone metabolism.

OBJECTIVE

The objective of the study was to investigate whether N-acetylcysteine (NAC), a potent intracellular antioxidant, can prevent NTIS in patients with acute myocardial infarction.

DESIGN

This was a randomized, multicenter clinical trial.

SETTINGS

Consecutive patients admitted to the emergency and intensive care units of two tertiary hospitals in southern Brazil were recruited. Patients and intervention included 67 patients were randomized to receive NAC or placebo during 48 hours. Baseline characteristics and blood samples for thyroid hormones and oxidative parameters were collected.

MAIN OUTCOME

Variation of serum T3 and rT3 levels was measured.

RESULTS

Baseline characteristics were similar between groups (all P > .05). T3 levels decreased in the placebo group at 12 hours of follow-up (P = .002) but not in NAC-treated patients (P = .10). Baseline rT3 levels were elevated in both groups and decreased over the initial 48 hours in the NAC-treated patients (P = .003) but not in the control group (P = .75). The free T4 and TSH levels were virtually identical between the groups throughout the study period (P > .05). Measurement of total antioxidant status and total carbonyl content demonstrated that oxidative balance was deranged in acute myocardial infarction patients, whereas NAC corrected these alterations (P < .001).

CONCLUSIONS

NAC administration prevents the derangement in thyroid hormone concentrations commonly occurring in the acute phase of acute myocardial infarction, indicating that oxidative stress is involved in the NTIS pathophysiology.

Carbon Monoxide-Releasing Molecules Attenuate Postresuscitation Myocardial Injury and Protect Cardiac Mitochondrial Function by Reducing the Production of Mitochondrial Reactive Oxygen Species in a Rat Model of Cardiac Arrest

The objective of this study is to examine whether carbon monoxide-releasing molecules (CORMs) can decrease the generation of excessive reactive oxygen species (ROS) in cardiac mitochondria, thereby protecting against postresuscitation myocardial injury and cardiac mitochondrial dysfunction after resuscitation in a rat model of ventricular fibrillation (VF), and further investigated the underlying mechanism. Rats suffered 8 minutes of untreated VF and resuscitation and were randomized into the control group with vehicle infusion and the CORM group with CO-releasing molecule 2 (CORM2) treatment. Animals in the Sham group were instrumented without induced VF and resuscitation. Effects of CORM2 on cardiac function, myocardial oxidative stress, cardiac mitochondrial function, and mitochondrial ROS generation were assessed. Moreover, to further evaluate the direct effect of CORM2 on cardiac mitochondria isolated from resuscitated rats, we measured mitochondrial function and ROS generation when isolated cardiac mitochondria were directly incubated with different concentrations of (CORM2). Compared with the Sham group, the control and CORM groups demonstrated impaired cardiac function, increased myocardial injury, and aggravated mitochondrial damage. CORM2 improved cardiac performance and attenuated myocardial damage and oxidative stress in resuscitated rats. Additionally, animals with CORM2 treatment showed the decreased generation of cardiac mitochondrial ROS, alleviated mitochondrial injury, and preserved mitochondrial function and complex activities when compared with the control group. In isolated cardiac mitochondria incubated with CORM2, low concentrations of CORM2 (20 μmol/L) mildly uncoupled mitochondrial respiration, leading to reduced mitochondrial ROS production. In contrast, high concentrations of CORM2 (60 μmol/L) resulted in the reverse effect presumably due to its excessive uncoupling action. These findings suggest that CORM2 attenuates oxidative stress of the heart and improves cardiac function after resuscitation. The mechanism was probably that CO, the product of CORM2, reduces the production of cardiac mitochondrial ROS and thereby attenuates mitochondrial injury and dysfunction during the postresuscitation period, due to the transient uncoupling of mitochondrial respiration.

PO2 cycling reduces diaphragm fatigue by attenuating ROS formation

Prolonged muscle exposure to low PO₂ conditions may cause oxidative stress resulting in severe muscular injuries. We hypothesize that PO₂ cycling preconditioning, which involves brief cycles of diaphragmatic muscle exposure to a low oxygen level (40 Torr) followed by a high oxygen level (550 Torr), can reduce intracellular reactive oxygen species (ROS) as well as attenuate muscle fatigue in mouse diaphragm under low PO₂. Accordingly, dihydrofluorescein (a fluorescent probe) was used to monitor muscular ROS production in real time with confocal microscopy during a lower PO₂ condition. In the control group with no PO₂ cycling, intracellular ROS formation did not appear during the first 15 min of the low PO₂ period. However, after 20 min of low PO₂, ROS levels increased significantly by ∼30% compared to baseline, and this increase continued until the end of the 30 min low PO₂ condition. Conversely, muscles treated with PO₂ cycling showed a complete absence of enhanced fluorescence emission throughout the entire low PO₂ period. Furthermore, PO₂ cycling-treated diaphragm exhibited increased fatigue resistance during prolonged low PO₂ period compared to control. Thus, our data suggest that PO₂ cycling mitigates diaphragm fatigue during prolonged low PO₂. Although the exact mechanism for this protection remains to be elucidated, it is likely that through limiting excessive ROS levels, PO₂ cycling initiates ROS-related antioxidant defenses.

1H-NMR metabolomic biomarkers of poor outcome after hemorrhagic shock are absent in hibernators

Background

Hemorrhagic shock (HS) following trauma is a leading cause of death among persons under the age of 40. During HS the body undergoes systemic warm ischemia followed by reperfusion during medical intervention. Ischemia/reperfusion (I/R) results in a disruption of cellular metabolic processes that ultimately lead to tissue and organ dysfunction or failure. Resistance to I/R injury is a characteristic of hibernating mammals. The present study sought to identify circulating metabolites in the rat as biomarkers for metabolic alterations associated with poor outcome after HS. Arctic ground squirrels (AGS), a hibernating species that resists I/R injury independent of decreased body temperature (warm I/R), was used as a negative control.

Methodology/principal findings

Male Sprague-Dawley rats and AGS were subject to HS by withdrawing blood to a mean arterial pressure (MAP) of 35 mmHg and maintaining the low MAP for 20 min before reperfusing with Ringers. The animals’ temperature was maintained at 37±0.5°C for the duration of the experiment. Plasma samples were taken immediately before hemorrhage and three hours after reperfusion. Hydrophilic and lipid metabolites from plasma were then analyzed via ¹H–NMR from unprocessed plasma and lipid extracts, respectively. Rats, susceptible to I/R injury, had a qualitative shift in their hydrophilic metabolic fingerprint including differential activation of glucose and anaerobic metabolism and had alterations in several metabolites during I/R indicative of metabolic adjustments and organ damage. In contrast, I/R injury resistant AGS, regardless of season or body temperature, maintained a stable metabolic homeostasis revealed by a qualitative ¹H–NMR metabolic profile with few changes in quantified metabolites during HS-induced global I/R.

Conclusions/significance

An increase in circulating metabolites indicative of anaerobic metabolism and activation of glycolytic pathways is associated with poor prognosis after HS in rats. These same biomarkers are absent in AGS after HS with warm I/R.

Reactive oxygen and nitrogen species in steatotic hepatocytes: a molecular perspective on the pathophysiology of ischemia-reperfusion injury in the fatty liver

SIGNIFICANCE

Hepatic ischemia-reperfusion (IR) injury results from the temporary deprivation of hepatic blood supply and is a common side effect of major liver surgery (i.e., transplantation or resection). IR injury, which in most severe cases culminates in acute liver failure, is particularly pronounced in livers that are affected by non-alcoholic fatty liver disease (NAFLD). In NAFLD, fat-laden hepatocytes are damaged by chronic oxidative/nitrosative stress (ONS), a state that is acutely exacerbated during IR, leading to extensive parenchymal damage.

RECENT ADVANCES

NAFLD triggers ONS via increased (extra)mitochondrial fatty acid oxidation and activation of the unfolded protein response. ONS is associated with widespread protein and lipid (per)oxidation, which reduces the hepatic antioxidative capacity and shifts the intracellular redox status toward an oxidized state. Moreover, activation of the transcription factor peroxisome proliferator-activated receptor α induces expression of mitochondrial uncoupling protein 2, resulting in depletion of cellular energy (ATP) reserves. The reduction in intracellular antioxidants and ATP in fatty livers consequently gives rise to severe ONS and necrotic cell death during IR.

CRITICAL ISSUES

Despite the fact that ONS mediates both NAFLD and IR injury, the interplay between the two conditions has never been described in detail. An integrative overview of the pathophysiology of NAFLD that renders steatotic hepatocytes more vulnerable to IR injury is therefore presented in the context of ONS.

FUTURE DIRECTIONS

Effective methods should be devised to alleviate ONS and the consequences thereof in NAFLD before surgery in order to improve resilience of fatty livers to IR injury.