In vivo hyperoxic preconditioning protects against rat-heart ischemia/reperfusion injury by inhibiting mitochondrial permeability transition pore opening and cytochrome c release

Cardiolipin in myocardial ischaemia-reperfusion injury: From molecular mechanisms to clinical strategies

Myocardial reperfusion injury occurs when blood flow is restored after ischemia, an essential process to salvage ischemic tissue. However, this phenomenon is intricate, characterized by various harmful effects. Tissue damage in ischemia-reperfusion injury arises from various factors, including the production of reactive oxygen species, the sequestration of proinflammatory immune cells in ischemic tissues, the induction of endoplasmic reticulum stress, and the occurrence of postischemic capillary no-reflow. Secretory phospholipase A2 (sPLA2) plays a crucial role in the eicosanoid pathway by releasing free arachidonic acid from membrane phospholipids' sn-2 position. This liberated arachidonic acid serves as a substrate for various eicosanoid biosynthetic enzymes, including cyclooxygenases, lipoxygenases, and cytochromes P450, ultimately resulting in inflammation and an elevated risk of reperfusion injury. Therefore, the activation of sPLA2 directly correlates with the heightened and accelerated damage observed in myocardial ischemia-reperfusion injury (MIRI). Presently, clinical trials are in progress for medications aimed at sPLA2, presenting promising avenues for intervention. Cardiolipin (CL) plays a crucial role in maintaining mitochondrial function, and its alteration is closely linked to mitochondrial dysfunction observed in MIRI. This paper provides a critical analysis of CL modifications concerning mitochondrial dysfunction in MIRI, along with its associated molecular mechanisms. Additionally, it delves into various pharmacological approaches to prevent or alleviate MIRI, whether by directly targeting mitochondrial CL or through indirect means.

Endothelial Function and Hypoxic–Hyperoxic Preconditioning in Coronary Surgery with a Cardiopulmonary Bypass: Randomized Clinical Trial

A hypoxic–hyperoxic preconditioning (HHP) may be associated with cardioprotection by reducing endothelial damage and a beneficial effect on postoperative outcome in patients undergoing cardiac surgery with cardiopulmonary bypass (CPB). Patients (n = 120) were randomly assigned to an HHP and a control group. A safe, inhaled oxygen fraction for the hypoxic preconditioning phase (10–14% oxygen for 10 min) was determined by measuring the anaerobic threshold. At the hyperoxic phase, a 75–80% oxygen fraction was used for 30 min. The cumulative frequency of postoperative complications was 14 (23.3%) in the HHP vs. 23 (41.1%), p = 0.041. The nitrate decreased after surgery by up to 20% in the HHP group and up to 38% in the control group. Endothelin-1 and nitric oxide metabolites were stable in HHP but remained low for more than 24 h in the control group. The endothelial damage markers appeared to be predictors of postoperative complications. The HHP with individual parameters based on the anaerobic threshold is a safe procedure, and it can reduce the frequency of postoperative complications. The endothelial damage markers appeared to be predictors of postoperative complications.

An overview of hyperbaric oxygen preconditioning against ischemic stroke

Ischemic stroke (IS) has become the second leading cause of morbidity and mortality worldwide, and the prevention of IS should be given high priority. Recent studies have indicated that hyperbaric oxygen preconditioning (HBO-PC) may be a protective nonpharmacological method, but its underlying mechanisms remain poorly defined. This study comprehensively reviewed the pathophysiology of IS and revealed the underlying mechanism of HBO-PC in protection against IS. The preventive effects of HBO-PC against IS may include inducing antioxidant, anti-inflammation, and anti-apoptosis capacity; activating autophagy and immune responses; upregulating heat shock proteins, hypoxia-inducible factor-1, and erythropoietin; and exerting protective effects upon the blood-brain barrier. In addition, HBO-PC may be considered a safe and effective method to prevent IS in combination with stem cell therapy. Although the benefits of HBO-PC on IS have been widely observed in recent research, the implementation of this technique is still controversial due to regimen differences. Transferring the results to clinical application needs to be taken carefully, and screening for the optimal regimen would be a daunting task. In addition, whether we should prescribe an individualized preconditioning regimen to each stroke patient needs further exploration.

Mitochondrial Dysfunction and Cardiovascular Disease: Pathophysiology and Emerging Therapies

Mitochondria ensure the supply of cellular energy through the production of ATP via oxidative phosphorylation. The alteration of this process, called mitochondrial dysfunction, leads to a reduction in ATP and an increase in the production of reactive oxygen species (ROS). Mitochondrial dysfunction can be caused by mitochondrial/nuclear DNA mutations, or it can be secondary to pathological conditions such as cardiovascular disease, aging, and environmental stress. The use of therapies aimed at the prevention/correction of mitochondrial dysfunction, in the context of the specific treatment of cardiovascular diseases, is a topic of growing interest. In this context, the data are conflicting since preclinical studies are numerous, but there are no large randomized studies.

Apoptosis inhibition is involved in improvement of sevoflurane-induced cognitive impairment following normobaric hyperoxia preconditioning in aged rats

Sevoflurane, a commonly used anesthetic agent has been confirmed to induce cognitive impairment in aged rats. Normobaric hyperoxia preconditioning has been demonstrated to induce neuroprotection in rats. The present study aimed to determine whether normobaric hyperoxia preconditioning could ameliorate cognitive deficit induced by sevoflurane and the possible mechanism by which it may exert its effect. A total of 66, 20-month-old male Sprague-Dawley rats were randomly divided into 3 groups (n=22 each): Rats in the control (C) and sevoflurane anesthesia (S) groups received no normobaric hyperoxia preconditioning before sevoflurane exposure, rats in the normobaric hyperoxia pretreatment (HO) group received normobaric hyperoxia preconditioning before sevoflurane exposure (95% oxygen for 4 continuous h daily for 6 consecutive days). The anesthesia rats (S and HO groups), were exposed to 2.5% sevoflurane for 5 h, while the sham anesthesia rats (C group) were exposed to no sevoflurane. The neurobehavioral assessment was performed using a Morris water maze test, the expressions of the apoptosis proteins were determined using western blot analysis, and the apoptosis rate and cytosolic calcium concentration were measured by flow cytometry. Normobaric hyperoxia preconditioning improved prolonged escape latency and raised the number of platform crossings induced by sevoflurane in the Morris water maze test, increased the level of bcl-2 protein, and decreased the level of bax and active caspase-3 protein, the apoptosis rate and cytosolic calcium concentration in the hippocampus 24 h after sevoflurane exposure. The findings of the present study may imply that normobaric hyperoxia preconditioning attenuates sevoflurane-induced spatial learning and memory impairment, and this effect may be partly related to apoptosis inhibition in the hippocampus. In conclusion, normobaric hyperoxia preconditioning may be a promising strategy against sevoflurane-induced cognitive impairment by inhibiting the hippocampal neuron apoptosis.

Mitochondrial dysfunction in cardiovascular disease: Current status of translational research/clinical and therapeutic implications

Mitochondria provide energy to the cell during aerobic respiration by supplying ~95% of the adenosine triphosphate (ATP) molecules via oxidative phosphorylation. These organelles have various other functions, all carried out by numerous proteins, with the majority of them being encoded by nuclear DNA (nDNA). Mitochondria occupy ~1/3 of the volume of myocardial cells in adults, and function at levels of high-efficiency to promptly meet the energy requirements of the myocardial contractile units. Mitochondria have their own DNA (mtDNA), which contains 37 genes and is maternally inherited. Over the last several years, a variety of functions of these organelles have been discovered and this has led to a growing interest in their involvement in various diseases, including cardiovascular (CV) diseases. Mitochondrial dysfunction relates to the status where mitochondria cannot meet the demands of a cell for ATP and there is an enhanced formation of reactive-oxygen species. This dysfunction may occur as a result of mtDNA and/or nDNA mutations, but also as a response to aging and various disease and environmental stresses, leading to the development of cardiomyopathies and other CV diseases. Designing mitochondria-targeted therapeutic strategies aiming to maintain or restore mitochondrial function has been a great challenge as a result of variable responses according to the etiology of the disorder. There have been several preclinical data on such therapies, but clinical studies are scarce. A major challenge relates to the techniques needed to eclectically deliver the therapeutic agents to cardiac tissues and to damaged mitochondria for successful clinical outcomes. All these issues and progress made over the last several years are herein reviewed.

Influence of Hypoxic and Hyperoxic Preconditioning on Endothelial Function in a Model of Myocardial Ischemia-Reperfusion Injury with Cardiopulmonary Bypass (Experimental Study)

The aim of the experiment was to evaluate the effect of preconditioning based on changes in inspiratory oxygen fraction on endothelial function in the model of ischemia-reperfusion injury of the myocardium in the condition of cardiopulmonary bypass. The prospective randomized study included 32 rabbits divided into four groups: hypoxic preconditioning, hyperoxic preconditioning, hypoxic-hyperoxic preconditioning, and control group. All animals were anesthetized and mechanically ventilated. We provided preconditioning, then started cardiopulmonary bypass, followed by induced acute myocardial infarction (ischemia 45 min, reperfusion 120 min). We investigated endothelin-1, nitric oxide metabolites, asymmetric dimethylarginine during cardiopulmonary bypass: before ischemia, after ischemia, and after reperfusion. We performed light microscopy of myocardium, kidney, lungs, and gut mucosa. The endothelin-1 level was much higher in the control group than in all preconditioning groups after ischemia. The endothelin-1 even further increased after reperfusion. The total concentration of nitric oxide metabolites was significantly higher after all types of preconditioning compared with the control group. The light microscopy of the myocardium and other organs revealed a diminished damage extent in the hypoxic-hyperoxic preconditioning group as compared to the control group. Hypoxic-hyperoxic preconditioning helps to maintain the balance of nitric oxide metabolites, reduces endothelin-1 hyperproduction, and enforces organ protection.

Melatonin against Myocardial Ischemia-Reperfusion Injury: A Meta-analysis and Mechanism Insight from Animal Studies

Aims

Myocardial reperfusion damage after severe ischemia was an important issue during a clinical practice. However, the exacted pathogenesis involved remained unclear and also lacks effective interventions. Melatonin was identified to exert protective effects for alleviating the myocardial I/R injury. This meta-analysis was determined to evaluate the efficacy of melatonin treatment against reperfusion insult and further summarize potential molecular and cellular mechanisms.

Methods and Results

15 eligible studies with 211 animals (108 received melatonin and 103 received vehicle) were included after searching the databases of PubMed, MEDLINE, Embase, and Cochrane. Pretreatment with melatonin was associated with a significant lower infarct size in comparison with vehicle in myocardial I/R damage (WMD: -20.45, 95% CI: -25.43 to -15.47, p < 0.001; I² = 91.4%, p < 0.001). Evidence from subgroup analyses and sensitivity analysis indicated the robust and consistent cardioprotective effect of melatonin, while the metaregression also did not unmask any significant interactions between the pooled estimates and covariates (i.e., sample size, state, species, study type, route of administration, and duration of reperfusion, along with timing regimen of pretreatment). Accordingly, melatonin evidently increased EF (WMD: 17.19, 95% CI: 11.08 to 23.29, p < 0.001; I² = 77.0%, p < 0.001) and FS (WMD: 14.18, 95% CI: 11.22 to 17.15, p < 0.001; I² = 3.5%, p = 0.387) in the setting of reperfusion damage.

Conclusions

Melatonin preadministration conferred a profound cardioprotection against myocardial I/R injury in preclinical studies.

Sevoflurane Preconditioning Confers Delayed Cardioprotection by Upregulating AMP-Activated Protein Kinase Levels to Restore Autophagic Flux in Ischemia-Reperfusion Rat Hearts

Background

Volatile anesthetic preconditioning confers delayed cardioprotection against ischemia/reperfusion injury (I/R). AMP-activated protein kinase (AMPK) takes part in autophagy activation. Furthermore, autophagic flux is thought to be impaired after I/R. We hypothesized that delayed cardioprotection can restore autophagic flux by activating AMPK.

Material/Methods

All male rat hearts underwent 30-min ischemia and 120-min reperfusion with or without sevoflurane exposure. AMPK inhibitor compound C (250 μg/kg, iv) was given at the reperfusion period. Autophagic flux blocker chloroquine (10 mg/kg, ip) was administrated 1 h before the experiment. Myocardial infarction, nicotinamide adenine dinucleotide (NAD⁺) content, and cytochrome c were measured. To evaluate autophagic flux, the markers of microtubule-associated protein 1 light chain 3 (LC3) I and II, P62 and Beclin 1, and lysosome-associated membrane protein-2 (LAMP 2) were analyzed.

Results

The delayed cardioprotection enhanced post-ischemic AMPK activation, reduced infarction, CK-MB level, NAD⁺ content loss and cytochrome c release, and compound C blocked these effects. Sevoflurane restored impaired autophagic flux through a lower ratio of LC3II/LC3I, downregulation of P62 and Beclin 1, and higher expression in LAMP 2. Consistently, compound C inhibited these changes of autophagy flux. Moreover, chloroquine pretreatment abolished sevoflurane-induced infarct size reduction, CK-MB level, NAD⁺ content loss, and cytochrome c release, with concomitant increase the ratios of LC3II/LC3I and levels of P62 and Beclin 1, but p-AMPK expression was not downregulated by chloroquine.

Conclusions

Sevoflurane exerts a delayed cardioprotective effects against myocardial injury in rats by activation of AMPK and restoration of I/R-impaired autophagic flux.

Melatonin and Nicotinamide Mononucleotide Attenuate Myocardial Ischemia/Reperfusion Injury via Modulation of Mitochondrial Function and Hemodynamic Parameters in Aged Rats

Ischemic heart diseases are the major reasons for disability and mortality in elderly individuals. In this study, we tried to examine the combined effects of nicotinamide mononucleotide (NMN) preconditioning and melatonin postconditioning on cardioprotection and mitochondrial function in ischemia/reperfusion (I/R) injury of aged male rats. Sixty aged Wistar rats were randomly allocated to 5 groups, including sham, control, NMN-receiving, melatonin-receiving, and combined therapy (NMN+melatonin). Isolated hearts were mounted on Langendorff apparatus and then underwent 30-minue ligation of left anterior descending coronary artery to induce regional ischemic insult, followed by 60 minutes of reperfusion. Nicotinamide mononucleotide (100 mg/kg/d intraperitoneally) was administered for every other day for 28 days before I/R. Melatonin added to perfusion solution, 5 minutes prior to the reperfusion up to 15 minutes early reperfusion. Myocardial hemodynamic and infarct size (IS) were measured, and the left ventricles samples were obtained to evaluate cardiac mitochondrial function and oxidative stress markers. Melatonin postconditioning and NMN had significant cardioprotective effects in aged rats; they could improve hemodynamic parameters and reduce IS and lactate dehydrogenase release compared to those of control group. Moreover, pretreatment with NMN increased the cardioprotection by melatonin. All treatments reduced oxidative stress and mitochondrial reactive oxygen species (ROS) levels and improved mitochondrial membrane potential and restored NAD⁺/NADH ratio. The effects of combined therapy on reduction of mitochondrial ROS and oxidative status and improvement of mitochondrial membrane potential were greater than those of alone treatments. Combination of melatonin and NMN can be a promising strategy to attenuate myocardial I/R damages in aged hearts. Restoration of mitochondrial function may substantially contribute to this cardioprotection.

Vitamin D Deficiency: Effects on Oxidative Stress, Epigenetics, Gene Regulation, and Aging

Recent advances in vitamin D research indicate that this vitamin, a secosteroid hormone, has beneficial effects on several body systems other than the musculoskeletal system. Both 25 dihydroxy vitamin D [25(OH)₂D] and its active hormonal form, 1,25-dihydroxyvitamin D [1,25(OH)₂D] are essential for human physiological functions, including damping down inflammation and the excessive intracellular oxidative stresses. Vitamin D is one of the key controllers of systemic inflammation, oxidative stress and mitochondrial respiratory function, and thus, the aging process in humans. In turn, molecular and cellular actions form 1,25(OH)₂D slow down oxidative stress, cell and tissue damage, and the aging process. On the other hand, hypovitaminosis D impairs mitochondrial functions, and enhances oxidative stress and systemic inflammation. The interaction of 1,25(OH)₂D with its intracellular receptors modulates vitamin D–dependent gene transcription and activation of vitamin D-responsive elements, which triggers multiple second messenger systems. Thus, it is not surprising that hypovitaminosis D increases the incidence and severity of several age-related common diseases, such as metabolic disorders that are linked to oxidative stress. These include obesity, insulin resistance, type 2 diabetes, hypertension, pregnancy complications, memory disorders, osteoporosis, autoimmune diseases, certain cancers, and systemic inflammatory diseases. Vitamin D adequacy leads to less oxidative stress and improves mitochondrial and endocrine functions, reducing the risks of disorders, such as autoimmunity, infections, metabolic derangements, and impairment of DNA repair; all of this aids a healthy, graceful aging process. Vitamin D is also a potent anti-oxidant that facilitates balanced mitochondrial activities, preventing oxidative stress-related protein oxidation, lipid peroxidation, and DNA damage. New understandings of vitamin D-related advances in metabolomics, transcriptomics, epigenetics, in relation to its ability to control oxidative stress in conjunction with micronutrients, vitamins, and antioxidants, following normalization of serum 25(OH)D and tissue 1,25(OH)₂D concentrations, likely to promise cost-effective better clinical outcomes in humans.

[Role of mitochondrial permeability transition pore in mediating the effect of endomorphin-1 postconditioning against myocardial ischemia-reperfusion injury in rats]

OBJECTIVE

To investigate the role of mitochondrial permeability transition pore (MPTP) opening in mediating the effect of endomorphine-1 postconditioning to alleviate myocardial ischemia-reperfusion (IR) injury in rats.

METHODS

Forty-five male SD rats were randomized equally for sham operation, myocardial IR injury, endomorphin-1 postconditioning, atractyloside (a MPTP opener) postconditioning, or endomorphin-1 + atractyloside postconditioning. The hemodynamic param-eters of the rats were monitored in real time via carotid artery cannulation to the left ventricle. After reperfusion, plasma samples were collected for biochemical analyses. The size of myocardial infarct area was detected using Evans blue and TTC double staining, and the myocardial expressions of apoptosis-related proteins Bax, Bcl-2 and cleaved caspase-3 were analyzed using Western blotting.

RESULTS

Myocardial IR injury resulted in significantly decreased heart rate and blood pressure in the rats (P<0.05). Compared with those in IR group, the rats with endomorphin-1 postconditioning showed significantly increased heart rate and blood pressure (P<0.05), lowered contents or activities of LDH, CK-MB, cTnI, IL-6, TNF-α, Cyt-C and MDA in the plasma (P<0.05), increased plasma SOD activity (P<0.05), reduced size of myocardial infarction, decreased myocardial expression of Bax and cleaved caspase-3 protein (P<0.05), and increased myocardial expression of Bcl-2 protein (P<0.05). All these changes induced by endomorphin-1 were obviously reversed by atractyloside postconditioning (P<0.05).

CONCLUSION

Endomorphin-1 postconditioning protects against myocardial IR injury in rats probably by inhibiting the opening of MPTP and reducing cardiac myocyte apoptosis via down-regulating cleaved caspase-3 expression.

Neuroprotective effects of allicin on ischemia-reperfusion brain injury

BACKGROUND

Ischemia-reperfusion brain injury (IRBI) is an important cause for mortality and morbidity. Studies on humans and animals showed that oxidative stress (OS) plays a crucial role in ischemic stroke with or without reperfusion. Allicin is reported to be able to attenuate OS and has neuroprotective effects on rabbits' ischemia-reperfusion spinal cord injury.

AIM

To explore whether Allicin pretreatment has neuroprotective effects on IRBI in mice.

METHODS AND RESULTS

Transient middle cerebral artery occlusion (MCAO) was conducted to induce IRBI in mice. The mice were pretreated with either Allicin (MCAOA) or normal saline in the same volume (MCAONS). Sham-operated groups [Allicin group (SOA) and normal saline group (SONS)] were also set. Blood pressure and cerebral blood flow measurements revealed comparable hemodynamics. Via brain MRI and neuronal nuclear antigen (NeuN) immune-histochemical staining, MCAOA mice had a significantly reduced stroke size than MCAONS mice (P < 0.05, n = 15). Allicin pretreatment could attenuate the OS, the activity of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, inflammation, dysfunction of mitochondrial respiratory chain, and apoptosis (all P < 0.05, n = 15). Furthermore, Allicin also increased the activities of endogenous antioxidant enzymes, including catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPX), and glutathione S-transferase (GST), and promoted the angiogenesis in the peri-infarct zone (all P < 0.05, n = 15).

CONCLUSION

We showed that Allicin could protect mice from IRBI through a series of mechanisms. Allicin represents a new therapeutic direction of IRBI.

Myocardial Protection against Ischemic and Reperfusion Injuries (Experimental Study)

The effects of hypoxic, hyperoxic, and hypoxic-hyperoxic preconditioning were examined in the prospective study on narcotized and artificially ventilated rabbits. Under artificial circulation, acute myocardial ischemia was modeled by ligation of anterior descending coronary artery, which was followed by reperfusion. The degree of ventricular arrhythmias was assessed, and the ischemic area was evaluated in percent of the area at risk. Microscopic characterization of the myocardium was employed to assess the cardioprotective effect of hypoxic and/or hyperoxic preconditioning. According to Kruskal-Wallis test, the greatest resistance of the myocardium to ischemic and reperfusion injury was observed after hypoxic-hyperoxic preconditioning (H=42.459; p=0.009). The rabbits subjected to this type of preconditioning demonstrated the least damaged myocardium in comparison with nonconditioned controls.

Melatonin, mitochondria and hypertension

Melatonin, due to its multiple means and mechanisms of action, plays a fundamental role in the regulation of the organismal physiology by fine tunning several functions. The cardiovascular system is an important site of action as melatonin regulates blood pressure both by central and peripheral interventions, in addition to its relation with the renin-angiotensin system. Besides, the systemic management of several processes, melatonin acts on mitochondria regulation to maintain a healthy cardiovascular system. Hypertension affects target organs in different ways and cellular energy metabolism is frequently involved due to mitochondrial alterations that include a rise in reactive oxygen species production and an ATP synthesis decrease. The discussion that follows shows the role played by melatonin in the regulation of mitochondrial physiology in several levels of the cardiovascular system, including brain, heart, kidney, blood vessels and, particularly, regulating the renin-angiotensin system. This discussion shows the putative importance of using melatonin as a therapeutic tool involving its antioxidant potential and its action on mitochondrial physiology in the cardiovascular system.

Proteomic analysis of mitochondrial proteins in the guinea pig heart following long-term normobaric hyperoxia

Normobaric hyperoxia is applied for the treatment of a wide variety of diseases and clinical conditions related to ischemia or hypoxia, but it can increase the risk of tissue damage and its efficiency is controversial. In the present study, we analyzed cardiac mitochondrial proteome derived from guinea pigs after 60 h exposure to 100% molecular oxygen (NBO) or O₂ enriched with oxygen cation (NBO+). Two-dimensional gel electrophoresis followed by MALDI-TOF/TOF mass spectrometry identified twenty-two different proteins (among them ten nonmitochondrial) that were overexpressed in NBO and/or NBO+ group. Identified proteins were mainly involved in cellular energy metabolism (tricarboxylic acid cycle, oxidative phosphorylation, glycolysis), cardioprotection against stress, control of mitochondrial function, muscle contraction, and oxygen transport. These findings support the viewpoint that hyperoxia is associated with cellular stress and suggest complex adaptive responses which probably contribute to maintain or improve intracellular ATP levels and contractile function of cardiomyocytes. In addition, the results suggest that hyperoxia-induced cellular stress may be partially attenuated by utilization of NBO+ treatment.

Sevoflurane post-conditioning reduces rat myocardial ischemia reperfusion injury through an increase in NOS and a decrease in phopshorylated NHE1 levels

The protective effects of sevoflurane post-conditioning against myocardial ischemia/reperfusion (I/R) injury (MIRI) have been previously reported. However, the mechanisms responsible for these protective effects remain elusive. In this study, in order to investigate the molecular mechanisms responsible for the protective effects of sevoflurane post-conditioning on isolated rat hearts subjected to MIRI, Sprague-Dawley rat hearts were randomly divided into the following 6 groups: i) the sham-operated control; ii) 2.5% sevoflurane; iii) ischemia/reperfusion (I/R); iv) 2.5% sevoflurane post-conditioning plus I/R; v) 2.5% sevoflurane post-conditioning + NG-nitro-L-arginine methyl ester (L-NAME) plus I/R; and vi) L-NAME plus I/R. The infarct size was measured using 2,3,5-triphenyl tetrazolium chloride (TTC) staining. Additionally, the myocardial nitric oxide (NO), NO synthase (NOS) and nicotinamide adenine dinucleotide (NAD⁺) levels were determined. Autophagosomes and apoptosomes in the myocardium were detected by transmission electron microscopy. The levels of Bcl-2, cleaved caspase-3, Beclin-1, microtubule-associated protein light chain 3 (LC3)-I/II, Na⁺/H⁺ exchanger 1 (NHE1) and phosphorylated NHE1 protein were measured by western blot analysis. NHE1 mRNA levels were measured by reverse transcription-quantitative polymerase chain reaction. Compared with the I/R group, 15 min of exposure to 2.5% sevoflurane during early reperfusion significantly decreased the myocardial infarct size, the autophagic vacuole numbers, the NHE1 mRNA and protein expression of cleaved caspase-3, Beclin-1 and LC3-I/II. Post-conditioning with 2.5% sevoflurane also increased the NO and NOS levels and Bcl-2 protein expression (P<0.05 or P<0.01). Notably, the cardioprotective effects of sevoflurane were partly abolished by the NOS inhibitor, L-NAME. The findings of the present study suggest that sevoflurane post-conditioning protects the myocardium against I/R injury and reduces the myocardial infarct size. The underlying protective mechanisms are associated with the inhibition of mitochondrial permeability transition pore opening, and with the attenuation of cardiomyoctye apoptosis and excessive autophagy. These effects are mediated through an increase in NOS and a decrease in phopshorylated NHE1 levels.

Cardiovascular effects of hyperoxia during and after cardiac surgery

During and after cardiac surgery with cardiopulmonary bypass, high concentrations of oxygen are routinely administered, with the intention of preventing cellular hypoxia. We systematically reviewed the literature addressing the effects of arterial hyperoxia. Extensive evidence from pre-clinical experiments and clinical studies in other patient groups suggests predominant harm, caused by oxidative stress, vasoconstriction, perfusion heterogeneity and myocardial injury. Whether these alterations are temporary and benign, or actually affect clinical outcome, remains to be demonstrated. In nine clinical cardiac surgical studies in low-risk patients, higher oxygen targets tended to compromise cardiovascular function, but did not affect clinical outcome. No data about potential beneficial effects of hyperoxia, such as reduction of gas micro-emboli or post-cardiac surgery infections, were reported. Current evidence is insufficient to specify optimal oxygen targets. Nevertheless, the safety of supraphysiological oxygen suppletion is unproven. Randomised studies with a variety of oxygen targets and inclusion of high-risk patients are needed to identify optimal oxygen targets during and after cardiac surgery.

Mitochondria: a multimodal hub of hypoxia tolerance

Decreased oxygen availability impairs cellular energy production and, without a coordinated and matched decrease in energy consumption, cellular and whole organism death rapidly ensues. Of particular interest are mechanisms that protect brain from low oxygen injury, as this organ is not only the most sensitive to hypoxia, but must also remain active and functional during low oxygen stress. As a result of natural selective pressures, some species have evolved molecular and physiological mechanisms to tolerate prolonged hypoxia with no apparent detriment. Among these mechanisms are a handful of responses that are essential for hypoxia tolerance, including (i) sensors that detect changes in oxygen availability and initiate protective responses; (ii) mechanisms of energy conservation; (iii) maintenance of basic brain function; and (iv) avoidance of catastrophic cell death cascades. As the study of hypoxia-tolerant brain progresses, it is becoming increasingly apparent that mitochondria play a central role in regulating all of these critical mechanisms. Furthermore, modulation of mitochondrial function to mimic endogenous neuroprotective mechanisms found in hypoxia-tolerant species confers protection against otherwise lethal hypoxic stresses in hypoxia-intolerant organs and organisms. Therefore, lessons gleaned from the investigation of endogenous mechanisms of hypoxia tolerance in hypoxia-tolerant organisms may provide insight into clinical pathologies related to low oxygen stress.

Intermittent hypoxia protects cerebral mitochondrial function from calcium overload

Hypoxia leads to Ca(2+) overload and results in mitochondrial uncoupling, decreased ATP synthesis, and neuronal death. Inhibition of mitochondrial Ca(2+) overload protects mitochondrial function after hypoxia. The present study was aimed to investigate the effect of intermittent hypoxia on mitochondrial function and mitochondrial tolerance to Ca(2+) overload. Wistar rats were divided into control and intermittent hypoxia (IH) groups. The IH group was subject to hypoxia for 4 h daily in a hypobaric cabin (5,000 m) for 7 days. Brain mitochondria were isolated on day 7 following hypoxia. The baseline mitochondrial functions, such as ST3, ST4, and respiratory control ratio (RCR = ST3/ST4), were measured using a Clark-type oxygen electrode. Mitochondrial adenine nucleotide concentrations were measured by HPLC. Mitochondrial membrane potential was determined by measuring rhodamine 123 (Rh-123) fluorescence in the absence and presence of high Ca(2+) concentration (0.1 M), which simulates Ca(2+) overload. Our results revealed that IH did not affect mitochondrial respiratory functions, but led to a reduction in AMP and an increase in ADP concentrations in mitochondria. Both control and IH groups demonstrated decreased mitochondrial membrane potential in the presence of high Ca(2+) (0.1 M), while the IH group showed a relative higher mitochondrial membrane potential. These results indicated that the neuroprotective effect of intermittent hypoxia was resulted partly from preserving mitochondrial membrane potential, and increasing mitochondrial tolerance to high calcium levels. The increased ADP and decreased AMP in mitochondria following intermittent hypoxia may be a mechanism underlying this protection.

Effect of HEMADO on Level of CK-MB and LDH Enzymes after Ischemia/Reperfusion Injury in Isolated Rat Heart

INTRODUCTION

Ischemia/Reperfusion (IR) injury mainly causes the increase of enzymes involved in myocytes injury including CK-MB (creatine kinase-MB) isoenzyme and LDH (lactate dehydrogenase). Leakage of CK-MB isoenzyme and LDH from myocardial tissues to blood is indicator of acute myocardial infarction. The aim of this study was to assess the effect of HEMADO on IR injury and its relationship with mitochondrial ATP-sensitive K+ channels (mitoKATP) in rat heart.

METHODS

Twenty eight male Wistar rats (250-300g) were divided into four groups (seven members in each group): control (without ischemia), I/R (with ischemia+without HEMADO), ischemia received HEMADO (HEMADO), ischemia received HEMADO and 5-HD (5-hydroxydecanoate, specific mitoKATP channel blocker) (HEMADO+5-HD). The animals were anesthetized and the hearts were quickly removed and mounted on Langendorff apparatus and perfused by Krebs-Henseleit solution under constant pressure and temperature of 37ºC. After 20 minutes of stabilization, ischemic groups were exposed to 40 minutes of global ischemia and consecutive 90 minutes of reperfusion.

RESULTS

IR injury increased the level of LDH and CK-MB in the collected coronary flow during 5 minutes since start of reperfusion. HEMADO reduced the enzymes' levels and using 5-HD abolished the effect of HEMADO.

CONCLUSION

Our findings indicated that HEMADO could protect the heart against ischemia-reperfusion injury by decreasing the CK-MB and LDH levels. The cardioprotective effect of HEMADO may be mediated in part by mitoKATP.

Molecular mechanisms of ischemia-reperfusion injury in brain: pivotal role of the mitochondrial membrane potential in reactive oxygen species generation

Stroke and circulatory arrest cause interferences in blood flow to the brain that result in considerable tissue damage. The primary method to reduce or prevent neurologic damage to patients suffering from brain ischemia is prompt restoration of blood flow to the ischemic tissue. However, paradoxically, restoration of blood flow causes additional damage and exacerbates neurocognitive deficits among patients who suffer a brain ischemic event. Mitochondria play a critical role in reperfusion injury by producing excessive reactive oxygen species (ROS) thereby damaging cellular components, and initiating cell death. In this review, we summarize our current understanding of the mechanisms of mitochondrial ROS generation during reperfusion, and specifically, the role the mitochondrial membrane potential plays in the pathology of cerebral ischemia/reperfusion. Additionally, we propose a temporal model of ROS generation in which posttranslational modifications of key oxidative phosphorylation (OxPhos) proteins caused by ischemia induce a hyperactive state upon reintroduction of oxygen. Hyperactive OxPhos generates high mitochondrial membrane potentials, a condition known to generate excessive ROS. Such a state would lead to a "burst" of ROS upon reperfusion, thereby causing structural and functional damage to the mitochondria and inducing cell death signaling that eventually culminate in tissue damage. Finally, we propose that strategies aimed at modulating this maladaptive hyperpolarization of the mitochondrial membrane potential may be a novel therapeutic intervention and present specific studies demonstrating the cytoprotective effect of this treatment modality.

Neuroprotective effects of allicin on spinal cord ischemia-reperfusion injury via improvement of mitochondrial function in rabbits

Allicin, the active substance of garlic, exerts a broad spectrum of pharmacological activities and is considered to have potential therapeutic applications. The present study was designed to investigate the beneficial effects of allicin against spinal cord ischemia-reperfusion (I/R) injury and its associated mechanisms. Male New Zealand white rabbits were pretreated with allicin (1, 10 and 50 mg/kg) for two weeks, and exposed to infrarenal aortic occlusion-induced spinal cord I/R injury. We found that allicin significantly reduced the volume of the spinal cord infarctions, improved the histopathologic features and increased the number of motor neurons in a dose-dependent manner. This protection was associated with an improvement in neurological function, which was measured by the hind-limb motor function scores. Furthermore, allicin also significantly suppressed the accumulations of protein and lipid peroxidation products, and increased the activities of endogenous antioxidant enzymes, including catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPX) and glutathione S-transferase (GST). In addition, allicin treatment preserved the function of mitochondria respiratory chain complexes and inhibited the production of ROS and the release of mitochondrial cytochrome c in the spinal cord of this model. Collectively, these findings demonstrated that allicin exerts neuroprotection against spinal cord I/R injury in rabbits, which may be associated with the improvement of mitochondrial function.

Nicotinamide pretreatment protects cardiomyocytes against hypoxia-induced cell death by improving mitochondrial stress

BACKGROUND/AIMS

Nicotinamide plays a protective role in hypoxia-induced cardiomyocyte dysfunction. However, the underlying molecular mechanisms remain poorly understood. The purpose of this study was to investigate these and the effect of nicotinamide pretreatment on hypoxic cardiomyocytes.

METHODS

Cultured rat cardiomyocytes were pretreated with nicotinamide, subjected to hypoxia for 6 h, and then cell necrosis and apoptosis were examined. The effects of nicotinamide pretreatment on hypoxia-induced reactive oxygen species (ROS) formation, antioxidant enzyme expression, nicotinamide adenine dinucleotide (NAD(+)) and nicotinamide adenine dinucleotide phosphate (NADP(+)) levels, adenosine triphosphate (ATP) production and mitochondrial membrane potential were tested to elucidate the underlying mechanisms.

RESULTS

Based on the findings that nicotinamide treatment decreased protein expression of receptor-interacting protein (RIP; a marker for cell necrosis) and cleaved caspase-3 (CC3; a marker for cell apoptosis) in normoxic cardiomyocytes, we found that it dramatically reduced hypoxia-induced necrosis and apoptosis in cardiomyocytes. The underlying mechanisms of these effects are associated with the fact that it increased protein expression of superoxide dismutase and catalase, increased intracellular levels of NAD(+) and ATP concentration, decreased mitochondrial ROS generation and prevented the loss of mitochondrial membrane potential.

CONCLUSION

All of these results indicate that nicotinamide pretreatment protects cardiomyocytes by improving mitochondrial stress. Our study provides a new clue for the utilization of nicotinamide in therapies for ischemic heart disease.

Hyperoxia during colon surgery is associated with a reduction of xanthine oxidase activity and oxidative stress in colonic mucosa

BACKGROUND

Gut manipulation during surgery may induce local oxidative stress. Supplemental inspired oxygen increases arterial and tissue oxygen partial pressures. This study examined whether a 0.80 fraction of inspired oxygen (FiO(2)) attenuates the oxidative stress, reducing xanthine oxidase (XO) activity in colonic mucosa as a possible mechanism during colon surgery.

METHODS

Twenty-four cancer patients who underwent elective colon resection were randomly assigned to either 0.30 FiO(2) or 0.80 FiO(2) during surgery. Malondialdehyde (MDA) and oxidized glutathione (GSSG) levels were measured in blood plasma. We also determined the enzymatic activities of XO and xanthine dehydrogenase (XDH) in the colonic mucosa after resection of the piece of colon.

RESULTS

Oxygen partial pressure in arterial blood was higher in the 0.80 FiO(2) group than in the 0.30 FiO(2) group (P<0.001). MDA and GSSG levels measured in blood plasma as well as MDA measured in colonic mucosa were lower in the 0.80 FiO(2) group than in the 0.30 FiO(2) group. Otherwise, XO enzymatic activity and XO/(XO+XDH) ratio in colonic mucosa were lower in the 0.80 FiO(2) group than in the 0.30 FiO(2) group.

CONCLUSIONS

XO may be a major source of reactive oxygen species in patients during colon surgery. Inspiring 0.80 oxygen during colon surgery increases arterial partial pressure and this treatment was associated with reduced XO activity and levels of oxidative stress in colonic mucosa.

Application of medical gases in the field of neurobiology

Medical gases are pharmaceutical molecules which offer solutions to a wide array of medical needs. This can range from use in burn and stroke victims to hypoxia therapy in children. More specifically however, gases such as oxygen, helium, xenon, and hydrogen have recently come under increased exploration for their potential theraputic use with various brain disease states including hypoxia-ischemia, cerebral hemorrhages, and traumatic brain injuries. As a result, this article will review the various advances in medical gas research and discuss the potential therapeutic applications and mechanisms with regards to the field of neurobiology.