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

Selective inhibition of class I but not class IIb histone deacetylases exerts cardiac protection from ischemia reperfusion

While inhibition of class I/IIb histone deacetylases (HDACs) protects the mammalian heart from ischemia reperfusion (IR) injury, class selective effects remain unexamined. We hypothesized that selective inhibition of class I HDACs would preserve left ventricular contractile function following IR in isolated hearts. Male Sprague Dawley rats (n=6 per group) were injected with vehicle (dimethylsulfoxide, 0.63mg/kg), the class I/IIb HDAC inhibitor trichostatin A (1mg/kg), the class I HDAC inhibitor entinostat (MS-275, 10mg/kg), or the HDAC6 (class IIb) inhibitor tubastatin A (10mg/kg). After 24h, hearts were isolated and perfused in Langendorff mode for 30min (Sham) or subjected to 30min global ischemia and 120min global reperfusion (IR). A saline filled balloon attached to a pressure transducer was placed in the LV to monitor contractile function. After perfusion, LV tissue was collected for measurements of antioxidant protein levels and infarct area. At the conclusion of IR, MS-275 pretreatment was associated with significant preservation of developed pressure, rate of pressure generation, rate of pressure relaxation and rate pressure product, as compared to vehicle treated hearts. There was significant reduction of infarct area with MS-275 pretreatment. Contractile function was not significantly restored in hearts treated with trichostatin A or tubastatin A. Mitochondrial superoxide dismutase (SOD2) and catalase protein and mRNA in hearts from animals pretreated with MS-275 were increased following IR, as compared to Sham. This was associated with a dramatic enrichment of nuclear FOXO3a transcription factor, which mediates the expression of SOD2 and catalase. Tubastatin A treatment was associated with significantly decreased catalase levels after IR. Class I HDAC inhibition elicits protection of contractile function following IR, which is associated with increased expression of endogenous antioxidant enzymes. Class I/IIb HDAC inhibition with trichostatin A or selective inhibition of HDAC6 with tubastatin A was not protective. This study highlights the need for the development of new strategies that target specific HDAC isoforms in cardiac ischemia reperfusion.

Finding the missing link: disulfide-containing proteins via a high-throughput proteomics approach

Top-down proteomics have recently started to gain attention as a novel method to provide insight into the structure of proteins in their native state, specifically the number and location of disulfide bridges. However, previous techniques still relied on complex and time-consuming protein purification and reduction reactions to yield useful information. In this issue of Proteomics, Zhao et al. (high-throughput screening of disulfide-containing proteins in a complex mixture, Proteomics 2013, 13, 3256-3260) devise a clever and rapid method for high-throughput determination of disulfides in proteins via reduction by tris(2-carboxyethyl)phosphine. Their work provides the foundation necessary to undertake more complex experiments in biological samples.

Interleukin-37 ameliorates myocardial ischaemia/reperfusion injury in mice

Innate immune and inflammatory responses are involved in myocardial ischaemia/reperfusion (I/R) injury. Interleukin (IL)-37 is a newly identified member of the IL-1 family, and functions as a fundamental inhibitor of innate immunity and inflammation. However, its role in myocardial I/R injury remains unknown. I/R or sham operations were performed on male C57BL/6J mice. I/R mice received an injection of recombinant human IL-37 or vehicle, immediately before reperfusion. Compared with vehicle treatment, mice treated with IL-37 showed an obvious amelioration of the I/R injury, as demonstrated by reduced infarct size, decreased cardiac troponin T level and improved cardiac function. This protective effect was associated with the ability of IL-37 to suppress production of proinflammatory cytokines, chemokines and neutrophil infiltration, which together contributed to a decrease in cardiomyocyte apoptosis and reactive oxygen species (ROS) generation. In addition, we found that IL-37 inhibited the up-regulation of Toll-like receptor (TLR)-4 expression and nuclear factor kappa B (NF-kB) activation after I/R, while increasing the anti-inflammatory IL-10 level. Moreover, the administration of anti-IL-10R antibody abolished the protective effects of IL-37 in I/R injury. In-vitro experiments further demonstrated that IL-37 protected cardiomyocytes from apoptosis under I/R condition, and suppressed the migration ability of neutrophils towards the chemokine LIX. In conclusion, IL-37 plays a protective role against mouse myocardial I/R injury, offering a promising therapeutic medium for myocardial I/R injury.

Blood pressure-targeted stepwise resuscitation for hemorrhagic shock in rats

BACKGROUND

Generation of reactive oxygen species (ROS) is an important mechanism of ischemia-reperfusion injury. Abrupt reoxygenation compared with slow reoxygenation has been known to increase ROS generation. Thus, slow and stepwise reperfusion can reduce ROS generation and subsequent ischemia-reperfusion injury. This study investigated the effect of slow reperfusion by blood pressure-targeted stepwise resuscitation (PSR) in hemorrhagic shock.

METHODS

Pressure-controlled hemorrhagic shock was induced in male Sprague-Dawley rats for 1 hour. Rats were then allocated to one of three groups (no-resuscitation group, n = 14; PSR group, n = 15; rapid normalization of blood pressure (RR) group, n = 15). Survival time and hemodynamic changes were recorded and compared. Blood samples and liver tissue were harvested after 6 hours of resuscitation in surviving rats.

RESULTS

All of the rats in the no-resuscitation group were expired before the end of the 6-hour observation period. Survival times were significantly longer in the PSR group than in the RR group (survival rates, 11 of 15 vs. 5 of 15, log rank p = 0.032). Plasma amino alanine transferase, histologic liver injury, and ROS generation in the liver tissue were significantly lower in the PSR group than in the RR group (all findings significant, p < 0.05). In addition, PSR significantly decreased plasma nitric oxide, liver interleukin 1β, and liver interleukin 6 compared with rapid resuscitation in addition to augmenting Akt survival pathways (all p < 0.05).

CONCLUSION

Slow reperfusion by PSR decreased mortality, ROS generation, and liver injury in rats undergoing hemorrhagic shock. Stepwise resuscitation also decreased inflammatory cytokine production and augmented Akt survival pathways.

The roles of reactive oxygen species and autophagy in mediating the tolerance of tumor cells to cycling hypoxia

Tumor hypoxia (low oxygenation) causes treatment resistance and poor patient outcome. A substantial fraction of tumor cells experience cycling hypoxia, characterized by transient episodes of hypoxia and reoxygenation. These cells are under a unique burden of stress, mediated by excessive production of reactive oxygen species (ROS). Cellular components damaged by ROS can be cleared by autophagy, rendering cycling hypoxic tumor cells particularly vulnerable to inhibition of autophagy and its upstream regulatory pathways. Activation of the PERK-mediated signaling arm of the unfolded protein response during hypoxia plays a critical role in the defense against ROS, both by stimulating glutathione synthesis pathways and through promoting autophagy.

Effects of ethyl pyruvate on cardiac function recovery and apoptosis reduction after global cold ischemia and reperfusion

The present study used an in vitro model of cold cardioplegia in isolated working rat hearts to evaluate the possible role of ethyl pyruvate (EP) in promoting cardiac function and preventing apoptosis. Two groups of rats were evaluated; the EP (2 mM EP; n=8) and control (n=8) groups. Isolated rat hearts were perfused with Krebs-Henseleit buffer (KHB) for 30 min, arrested with cardioplegic solution and stored for 4 h in B21 solution at 4°C. The hearts were reperfused with KHB for 45 min. EP was added to the cardioplegic and storage solutions and also to KHB for reperfusion. Cardiac parameters of the heart rate, including left ventricular systolic pressure, left ventricular end-diastolic pressure, left ventricular developed pressure and maximal rise rate of the left ventricular pressure, were monitored. In addition, coronary flow, adenosine triphosphate (ATP) levels and malondialdehyde (MDA) content were recorded and apoptotic cell determination was detected. The functional parameters in the EP group were significantly higher compared with those in the control group during the reperfusion period (P<0.05). In addition, ATP levels were higher in the EP group than in the control group and the content of MDA was lower in the EP group than in the control group. A concentration of 2 mM EP significantly reduced the number of apoptotic cells in the EP group compared with that of the control group (P<0.05). Therefore, EP significantly preserved cardiac function, enhanced tissue ATP levels, attenuated myocardial oxidative injury and markedly reduced apoptosis following myocardial ischemia in an in vitro model of 4 h of cold cardioplegia and reperfusion.

Uncoupling of increased cellular oxidative stress and myocardial ischemia reperfusion injury by directed sarcolemma stabilization

Myocardial ischemia/reperfusion (I/R) injury is a major clinical problem leading to cardiac dysfunction and myocyte death. It is widely held that I/R causes damage to membrane phospholipids, and is a significant mechanism of cardiac I/R injury. Molecular dissection of sarcolemmal damage in I/R, however, has been difficult to address experimentally. We studied here cardiac I/R injury under conditions targeting gain- or loss-of sarcolemma integrity. To implement gain-in-sarcolemma integrity during I/R, synthetic copolymer-based sarcolemmal stabilizers (CSS), including Poloxamer 188 (P188), were used as a tool to directly stabilize the sarcolemma. Consistent with the hypothesis of sarcolemmal stabilization, cellular markers of necrosis and apoptosis evident in untreated myocytes were fully blocked in sarcolemma stabilized myocytes. Unexpectedly, sarcolemmal stabilization of adult cardiac myocytes did not affect the status of myocyte-generated oxidants or lipid peroxidation in two independent assays. We also investigated the loss of sarcolemmal integrity using two independent genetic mouse models, dystrophin-deficient mdx or dysferlin knockout (Dysf KO) mice. Both models of sarcolemmal loss-of-function were severely affected by I/R injury ex vivo, and this was lessened by CSS. In vivo studies also showed that infarct size was significantly reduced in CSS-treated hearts. Mechanistically, these findings support a model whereby I/R-mediated increased myocyte oxidative stress is uncoupled from myocyte injury. Because the sarcolemma stabilizers used here do not transit across the myocyte membrane this is evidence that intracellular targets of oxidants are not sufficiently altered to affect cell death when sarcolemma integrity is preserved by synthetic stabilizers. These findings, in turn, suggest that sarcolemma destabilization, and consequent Ca(2+) mishandling, as a focal initiating mechanism underlying myocardial I/R injury.

Oxidative stress and autophagy in cardiovascular homeostasis

SIGNIFICANCE

Autophagy is an evolutionarily ancient process of intracellular protein and organelle recycling required to maintain cellular homeostasis in the face of a wide variety of stresses. Dysregulation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) leads to oxidative damage. Both autophagy and ROS/RNS serve pathological or adaptive roles within cardiomyocytes, depending on the context.

RECENT ADVANCES

ROS/RNS and autophagy communicate with each other via both transcriptional and post-translational events. This cross talk, in turn, regulates the structural integrity of cardiomyocytes, promotes proteostasis, and reduces inflammation, events critical to disease pathogenesis.

CRITICAL ISSUES

Dysregulation of either autophagy or redox state has been implicated in many cardiovascular diseases. Cardiomyocytes are rich in mitochondria, which make them particularly sensitive to oxidative damage. Maintenance of mitochondrial homeostasis and elimination of defective mitochondria are each critical to the maintenance of redox homeostasis.

FUTURE DIRECTIONS

The complex interplay between autophagy and oxidative stress underlies a wide range of physiological and pathological events and its elucidation holds promise of potential clinical applicability.

Effects of exogenous recombinant APC in mouse models of ischemia reperfusion injury and of atherosclerosis

Activated protein C (APC) is a serine protease that has both anticoagulant and cytoprotective properties. The cytoprotective effects are protease activated receptor 1 (PAR-1) and endothelial protein C receptor (EPCR) dependent and likely underlie protective effects of APC in animal models of sepsis, myocardial infarction and ischemic stroke. S360A-(A)PC, a variant (A)PC that has no catalytic activity, binds EPCR and shifts pro-inflammatory signaling of the thrombin-PAR-1 complex to anti-inflammatory signaling. In this study we investigated effects of human (h)wt-PC, hS360A-PC, hwt-APC and hS360A-APC in acute (mouse model of acute myocardial ischemia/reperfusion (I/R) injury) and chronic inflammation (apoE-/- mouse model of atherosclerosis). All h(A)PC variants significantly reduced myocardial infarct area (p<0.05) following I/R injury. IL-6 levels in heart homogenates did not differ significantly between sham, placebo and treatment groups in I/R injury. None of the h(A)PC variants decreased number and size of atherosclerotic plaques in apoE-/- mice. Only hS360A-APC slightly affected phenotype of plaques. IL-6 levels in plasma were significantly (p<0.001) decreased in hwt-APC and hS360A-PC treated mice. In the last group levels of monocyte chemotactic protein 1 (MCP-1) were significantly increased (p<0.05). In this study we show that both hwt and hS360A-(A)PC protect against acute myocardial I/R injury, which implies that protection from I/R injury is independent of the proteolytic activity of APC. However, in the chronic atherosclerosis model hwt and hS360-(A)PC had only minor effects. When the dose, species and mode of (A)PC administration will be adjusted, we believe that (A)PC will have potential to influence development of chronic inflammation as occurring during atherosclerosis as well.

Cardiac sympathetic innervation and PGP9.5 expression by cardiomyocytes after myocardial infarction: effects of central MR blockade

Central mechanisms involving mineralocorticoid receptor (MR) activation contribute to an increase in sympathetic tone after myocardial infarction (MI). We hypothesized that this central mechanism also contributes to cardiac sympathetic axonal sprouting and that central MR blockade reduces cardiac sympathetic hyperinnervation post-MI. Post-MI, tyrosine hydroxylase (TH) and norepinephrine transporter protein content in the noninfarcted base of the heart remained unaltered. In contrast, protein gene product (PGP)9.5 protein was increased twofold in the base of the heart and sixfold in the peri-infarct area at 1 wk post-MI and was associated with increased ubiquitin expression. These changes persisted to a lesser extent at 4 wk post-MI and were no longer present at 12 wk. Cardiac myocytes rather than sympathetic axons were the main source of this elevated PGP9.5 expression. At 7–10 days post-MI, in the peri-infarct area, sympathetic hyperinnervation was observed with a fourfold increase in growth-associated protein 43, a twofold increase in TH, and a 50% increase in PGP9.5-positive fibers compared with the epicardial side of the left ventricle in sham rats. Central infusion of the MR blocker eplerenone markedly attenuated these increases in nerve densities but did not affect overall cardiac PGP9.5 and ubiquitin protein overexpression. We conclude that central MR activation contributes to sympathetic hyperinnervation, possibly by decreasing cardiac sympathetic activity post-MI, or by affecting other mechanisms, such as the expression of nerve growth factor. Marked PGP9.5 expression occurs in cardiomyocytes early post-MI, which may contribute to the increase in ubiquitin.

Regulation of heat shock proteins 27 and 70, p-Akt/p-eNOS and MAPKs by Naringin Dampens myocardial injury and dysfunction in vivo after ischemia/reperfusion

Naringin has antioxidant properties that could improve redox-sensitive myocardial ischemia reperfusion (IR) injury. This study was designed to investigate whether naringin restores the myocardial damage and dysfunction in vivo after IR and the mechanisms underlying its cardioprotective effects. Naringin (20–80 mg/kg/day, p.o.) or saline were administered to rats for 14 days and the myocardial IR injury was induced on 15^th day by occluding the left anterior descending coronary artery for 45 min and subsequent reperfusion for 60 min. Post-IR rats exhibited pronounced cardiac dysfunction as evidenced by significantly decreased mean arterial pressure, heart rate, +LVdP/dt_max (inotropic state), -LVdP/dt_max (lusitropic state) and increased left ventricular end diastolic pressure as compared to sham group, which was improved by naringin. Further, on histopathological and ultrastructural assessments myocardium and myocytes appeared more normal in structure and the infarct size was reduced significantly in naringin 40 and 80 mg/kg/day group. This amelioration of post-IR-associated cardiac injury by naringin was accompanied by increased nitric oxide (NO) bioavailability, decreased NO inactivation to nitrotyrosine, amplified protein expressions of Hsp27, Hsp70, β-catenin and increased p-eNOS/eNOS, p-Akt/Akt, and p-ERK/ERK ratio. In addition, IR-induced TNF-α/IKK-β/NF-κB upregulation and JNK phosphorylation were significantly attenuated by naringin. Moreover, western blotting and immunohistochemistry analysis of apoptotic signaling pathway further established naringin cardioprotective potential as it upregulated Bcl-2 expression and downregulated Bax and Caspase-3 expression with reduced TUNEL positivity. Naringin also normalized the cardiac injury markers (lactate dehydrogenase and creatine kinase-MB), endogenous antioxidant activities (superoxide dismutase, reduced glutathione and glutathione peroxidase) and lipid peroxidation levels. Thus, naringin restored IR injury by preserving myocardial structural integrity and regulating Hsp27, Hsp70, p-eNOS/p-Akt/p-ERK signaling and inflammatory response.

Protective effects of low-frequency magnetic fields on cardiomyocytes from ischemia reperfusion injury via ROS and NO/ONOO-

Background. Cardiac ischemia reperfusion (I/R) injury is associated with overproduction of reactive oxygen species (ROS). Low frequency pulse magnetic fields (LFMFs) have been reported to decrease ROS generation in endothelial cells. Whether LFMFs could assert protective effects on myocardial from I/R injury via ROS regulation remains unclear. Methods. To simulate in vivo cardiac I/R injury, neonatal rat cardiomyocytes were subjected to hypoxia reoxygenation (H/R) with or without exposure to LFMFs. Cell viability, apoptosis index, ROS generation (including O₂⁻ and ONOO⁻), and NO production were measured in control, H/R, and H/R + LFMF groups, respectively. Results. H/R injury resulted in cardiomyocytes apoptosis and decreased cell viability, whereas exposure to LFMFs before or after H/R injury significantly inhibited apoptosis and improved cell viability (P < 0.05). LFMFs treatment could suppress ROS (including O₂⁻ and ONOO⁻) generation induced by H/R injury, combined with decreased NADPH oxidase activity. In addition, LFMFs elevated NO production and enhanced NO/ONOO⁻ balance in cardiomyocytes, and this protective effect was via the phosphorylation of endothelial nitric oxide synthase (eNOS). Conclusion. LFMFs could protect myocardium against I/R injury via regulating ROS generation and NO/ONOO⁻ balance. LFMFs treatment might serve as a promising strategy for cardiac I/R injury.

Superoxide release from contracting skeletal muscle in pulmonary TNF-α overexpression mice

Chronic obstructive pulmonary disease (COPD) often results in increased levels of tumor necrosis factor-α (TNF-α), a proinflammatory cytokine, which circulates in the blood. However, it is not clear whether pulmonary TNF-α overexpression (a COPD mimic) induces excessive reactive oxygen species (ROS) formation in skeletal muscle and thereby may contribute to the muscle impairment often seen in COPD. We hypothesized that ROS generation in contracting skeletal muscle is elevated when there is TNF-α overproduction in the lung and that this can induce muscle dysfunction. Cytochrome c (cyt c) in the perfusate was used to assay superoxide (O2(·-)) release from isolated contracting soleus muscles from transgenic mice of pulmonary TNF-α overexpression (Tg(+)) and wild-type (WT) mice. Our results showed that Tg(+) muscle released significantly higher levels of O2(·-) than WT during a period of intense contractile activity (in nmol/mg wt; 17.5 ± 2.3 vs. 4.4 ± 1.3, respectively; n = 5; P < 0.05). In addition, the soleus muscle demonstrated a significantly reduced fatigue resistance in Tg(+) mice compared with WT mice. Perfusion of the contracting soleus muscle with superoxide dismutase, which specifically scavenges O2(·-) in the perfusate, resulted in significantly less cyt c reduction, thereby indicating that the type of ROS released from the Tg(+) muscles is O2(·-). Our results demonstrate that pulmonary TNF-α overexpression leads to a greater O2(·-) release from contracting soleus muscle in Tg(+) compared with WT and that the excessive formation of O2(·-) in the contracting muscle of Tg(+) mice leads to earlier fatigue.

Exercise-induced cardioprotection is impaired by anabolic steroid treatment through a redox-dependent mechanism

High doses of anabolic androgenic steroids (AAS) impair the cardioprotective effects of exercise against ischemia/reperfusion (I/R) insult, possibly through cellular redox imbalance. Here, the effect of nandrolone decanoate (DECA) treatment on heart redox metabolism was investigated during I/R in sedentary and exercised rats. DECA treatment significantly reduced superoxide dismutase and glutathione reductase activities in exercised rats after heart reperfusion. Catalase and glutathione peroxidase activities were not affected by DECA in both sedentary and trained rats, regardless the I/R period. DECA also induced myocardial oxidative stress, as evidenced by the reduced levels of total reduced thiols after heart reperfusion in exercised rats treated with the anabolic steroid. These results indicate that cardiotoxic effects of supraphysiological doses of AAS involve reduced heart antioxidant capacity.

Achyranthes bidentata polypeptides reduces oxidative stress and exerts protective effects against myocardial ischemic/reperfusion injury in rats

Achyranthes bidentata, a Chinese medicinal herb, is reported to be neuroprotective. However, its role in cardioprotection remains largely unknown. Our present study aimed to investigate the effects of Achyranthes bidentata polypeptides (ABPP) preconditioning on myocardial ischemia/reperfusion (MI/R) injury and to test the possible mechanisms. Rats were treated with ABPP (10 mg/kg/d, i.p.) or saline once daily for one week. Afterward, all the animals were subjected to 30 min of myocardial ischemia followed by 4 h of reperfusion. ABPP preconditioning for one week significantly improved cardiac function following MI/R. Meanwhile, ABPP reduced infarct size, plasma creatine kinase (CK)/lactate dehydrogenase (LDH) activities and myocardial apoptosis at the end of reperfusion in rat hearts. Moreover, ABPP preconditioning significantly inhibited superoxide generation, gp91^phox expression, malonaldialdehyde formation and enhanced superoxide dismutase activity in I/R hearts. Furthermore, ABPP treatment inhibited PTEN expression and increased Akt phosphorylation in I/R rat heart. PI3K inhibitor wortmannin blocked Akt activation, and abolished ABPP-stimulated anti-oxidant effect and cardioprotection. Our study demonstrated for the first time that ABPP reduces oxidative stress and exerts cardioprotection against MI/R injury in rats. Inhibition of PTEN and activation of Akt may contribute to the anti-oxidant capacity and cardioprotection of ABPP.

Polyphenols: benefits to the cardiovascular system in health and in aging

Numerous studies have demonstrated the importance of naturally occurring dietary polyphenols in promoting cardiovascular health and emphasized the significant role these compounds play in limiting the effects of cellular aging. Polyphenols such as resveratrol, epigallocatechin gallate (EGCG), and curcumin have been acknowledged for having beneficial effects on cardiovascular health, while some have also been shown to be protective in aging. This review highlights the literature surrounding this topic on the prominently studied and documented polyphenols as pertaining to cardiovascular health and aging.

Characterization of oxygen radical formation mechanism at early cardiac ischemia

Myocardial ischemia–reperfusion (I/R) causes severe cardiac damage. Although the primary function of oxymyoglobin (Mb) has been considered to be cellular O₂ storage and supply, previous research has suggested that Mb is a potentially protective element against I/R injury. However, the mechanism of its protective action is still largely unknown. With a real-time fluorescent technique, we observed that at the onset of ischemia, there was a small burst of superoxide (O₂^•–) release, as visualized in an isolated rat heart. Thus, we hypothesize that the formation of O₂^•– correlates to Mb due to a decrease in oxygen tension in the myocardium. Measurement of O₂^•– production in a Langendorff apparatus was performed using surface fluorometry. An increase in fluorescence was observed during the onset of ischemia in hearts perfused with a solution of hydroethidine, a fluorescent dye sensitive to intracellular O₂^•–. The increase of fluorescence in the ischemic heart was abolished by a superoxide dismutase mimic, carbon monoxide, or by Mb-knockout gene technology. Furthermore, we identified that O₂^•– was not generated from the intracellular endothelium but from the myocytes, which are a rich source of Mb. These results suggest that during the onset of ischemia, Mb is responsible for generating O₂^•–. This novel mechanism may shed light on the protective role of Mb in I/R injury.

Basis for sensitive and selective time-delayed luminescence detection of hydroxyl radical by lanthanide complexes

Molecular probes for the detection of hydroxyl radical (HO•) by time-delayed luminescence spectroscopy directly in water at neutral pH with high sensitivity and selectivity are presented. The bimolecular probes consist of a lanthanide complex with open coordination sites and a reactive pre-antenna composed of an aromatic acid or amide; the latter binds to and sensitizes terbium emission upon hydroxylation by HO•. These probes exhibit long luminescence lifetimes compatible with time-delayed measurements that remove interfering background fluorescence from the sample. Six different reactive pre-antenna (benzoate, benzamide, isophthalate, isophthalamide, trimesate, and trimesamide) and two different terbium complexes [Tb-(1,4,7,10-tetraazacyclododecane-1,4,7-tris(acetic acid)) (Tb-DO3A) and Tb-(1,4,7,10-tetraazacyclododecane-1,7-bis(acetic acid)) (Tb-DO2A)] were evaluated. Of these the trimesamide/Tb-DO3A system enables the most sensitive detection of HO• with an about 1000-fold increase in metal-centered time-delayed emission upon hydroxylation of the pre-antenna to 2-hydroxytrimesamide. Excellent selectivity for both the trimesamide/Tb-DO3A and trimesate/Tb-DO3A systems over other reactive oxygen and nitrogen species are observed. Notably, the increase in metal-centered luminescence intensity is not associated with a decrease in the hydration number (q) of Tb-DO3A, suggesting that the antenna is interacting with the lanthanide via a second sphere coordination environment or that coordination by the antenna occurs by displacement of one or more of the carboxylate arms of DO3A. Formation of a weak ternary complex Tb-DO3A•hydroxytrimesamide was confirmed by temperature-dependent titration and a decrease in K(app) with increasing temperature.

Role of oxygen consumption in hypoxia protection by translation factor depletion

The reduction of protein synthesis has been associated with resistance to hypoxic cell death. Which components of the translation machinery control hypoxic sensitivity and the precise mechanism has not been systematically investigated, although a reduction in oxygen consumption has been widely assumed to be the mechanism. Using genetic reagents in Caenorhabditis elegans, we examined the effect on organismal survival after hypoxia of knockdown of 10 factors functioning at the three principal steps in translation. Reduction-of-function of all 10 translation factors significantly increased hypoxic survival to varying degrees, not fully accounted for by the level of translational suppression. Measurement of oxygen consumption showed that strong hypoxia resistance was possible without a significant decrease in oxygen consumption. Hypoxic sensitivity had no correlation with lifespan or reactive oxygen species sensitivity, two phenotypes associated with reduced translation. Resistance to tunicamycin, which produces misfolded protein toxicity, was the only phenotype that significantly correlated with hypoxic sensitivity. Translation factor knockdown was also hypoxia protective for mouse primary neurons. These data show that translation factor knockdown is hypoxia protective in both C. elegans and mouse neurons and that oxygen consumption does not necessarily determine survival; rather, mitigation of misfolded protein toxicity is more strongly associated with hypoxic protection.

Protective effects of osthole against myocardial ischemia/reperfusion injury in rats

Osthole, a bioactive simple coumarin derivative extracted from a number of medicinal plants, such as Cnidium monnieri and Angelica pubescens, has been shown to exert a variety of pharmacological activities and is considered to have potential therapeutic applications. In this study, we investigated the protective effects of osthole against myocardial ischemia/reperfusion (I/R) injury in rats. Male Sprague-Dawley rats were randomly assigned to 1 of 5 groups: the sham-oeprated control group (control), the vehicle group (vehicle), and 3 treatment groups, which were treated with osthole at the concentration of 1, 10 or 50 mg/kg (intraperitoneally), respectively, upon the initiation of myocardial ischemia. Treatment with osthole suppressed the formation of lipid peroxidation products, enhanced the capacities of antioxidant enzymes and inhibited the expression of inflammatory cytokines following myocardial I/R injury. Moreover, treatment with osthole reduced high-mobility group box protein 1 (HMGB1) and phosphorylated nuclear factor (NF)-κB expression in ischemic myocardial tissue. These results demonstrate the protective effects of osthole against myocardial I/R injury in rats and suggest that these effects may be associated with its antioxidant and anti-inflammatory activities.

Cardioprotection by the TSPO ligand 4'-chlorodiazepam is associated with inhibition of mitochondrial accumulation of cholesterol at reperfusion

AIMS

The translocator protein (TSPO) is located on the outer mitochondrial membrane where it is responsible for the uptake of cholesterol into mitochondria of steroidogenic organs. TSPO is also present in the heart where its role remains uncertain. We recently showed that TSPO ligands reduced infarct size and improved mitochondrial functions after ischaemia-reperfusion. This study, thus, sought to determine whether cholesterol could play a role in the cardioprotective effect of TSPO ligands.

METHODS AND RESULTS

In a model of 30 min coronary occlusion/15 min reperfusion in Wistar rat, we showed that reperfusion induced lipid peroxidation as demonstrated by the increase in conjugated diene and thiobarbituric acid reactive substance formation and altered mitochondrial function (decrease in oxidative phosphorylation and increase in the sensitivity of mitochondrial permeability transition pore opening) in ex-vivo isolated mitochondria. This was associated with an increase in mitochondrial cholesterol uptake (89.5 ± 12.2 vs. 39.9 ± 3.51 nmol/mg protein in controls, P < 0.01) and a subsequent strong generation of auto-oxidized oxysterols, i.e. 7α- and 7β-hydroxycholesterol, 7-ketocholesterol, cholesterol-5α,6α-epoxide, and 5β,6β-epoxide (+173, +149, +165, +165, and +193% vs. controls, respectively; P < 0.01). Administration of the selective TSPO ligand 4'-chlorodiazepam inhibited oxidative stress, improved mitochondrial function, and abolished both mitochondrial cholesterol accumulation and oxysterol production. This was also observed with the new TSPO ligand TRO40303.

CONCLUSION

These data suggest that 4'-chlorodiazepam inhibits oxidative stress and oxysterol formation by reducing the accumulation of cholesterol in the mitochondrial matrix at reperfusion and prevents mitochondrial injury. This new and original mechanism may contribute to the cardioprotective properties of TSPO ligands.

γ-Aminobutyric acid-mediated neurotransmission in cerebellar-hypothalamic circuit attenuates gastric mucosal injury induced by ischemia-reperfusion

BACKGROUND

Excessive greater splanchnic nerve (GSN) activation contributes to the progression of gastric ischemia-reperfusion (GI-R) injury. This study was designed to investigate the protective mechanism of cerebellar fastigial nucleus (FN) stimulation against GI-R injury.

METHODS

The GI-R injury model was induced in rats by clamping the celiac artery for 30 min, and then reperfusion for 30 min, 1, 3, 6, or 24 h, respectively.

KEY RESULTS

Microinjection of L-Glu (3, 6, 12 μg) into the FN dose-dependently attenuated GI-R injury and GSN activity. In addition, there was an enhancement of gastric mucosal blood flow in GI-R rats. Pretreatment with the glutamic acid decarboxylase antagonist into the FN, the GABAA receptor antagonist into the lateral hypothalamic area or lesion of superior cerebellar peduncle all reversed the protective effects of the FN stimulation. Furthermore, the FN stimulation reduced the TUNEL-positive gastric mucosal cell and Bax-positive gastric mucosal cell in GI-R rats.

CONCLUSIONS & INFERENCES

These results indicate that the protective effects of the FN stimulation against GI-R injury may be mediated by attenuation of the excessive GSN activation, gastric mucosal cell apoptosis, and Bax expression in GI-R rats.

Cardioprotective Effects of Quercetin in Cardiomyocyte under Ischemia/Reperfusion Injury

Quercetin, a polyphenolic compound existing in many vegetables, fruits, has antiinflammatory, antiproliferation, and antioxidant effect on mammalian cells. Quercetin was evaluated for protecting cardiomyocytes from ischemia/reperfusion injury, but its protective mechanism remains unclear in the current study. The cardioprotective effects of quercetin are achieved by reducing the activity of Src kinase, signal transducer and activator of transcription 3 (STAT3), caspase 9, Bax, intracellular reactive oxygen species production, and inflammatory factor and inducible MnSOD expression. Fluorescence two-dimensional differential gel electrophoresis (2D-DIGE) and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) can reveal the differentially expressed proteins of H9C2 cells treated with H₂O₂ or quercetin. Although 17 identified proteins were altered in H₂O₂-induced cells, these proteins such as alpha-soluble NSF attachment protein (α-SNAP), Ena/VASP-like protein (Evl), and isopentenyl-diphosphate delta-isomerase 1 (Idi-1) were reverted by pretreatment with quercetin, which correlates with kinase activation, DNA repair, lipid, and protein metabolism. Quercetin dephosphorylates Src kinase in H₂O₂-induced H9C2 cells and likely blocks the H₂O₂-induced inflammatory response through STAT3 kinase modulation. This probably contributes to prevent ischemia/reperfusion injury in cardiomyocytes.

Upregulation of phase II enzymes through phytochemical activation of Nrf2 protects cardiomyocytes against oxidant stress

Increased production of reactive oxygen species has been implicated in the pathogenesis of cardiovascular disease (CVD), and enhanced endogenous antioxidants have been proposed as a mechanism for regulating redox balance. Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is a transcriptional regulator of phase II antioxidant enzymes, and activation of Nrf2 has been suggested to be an important step in attenuating oxidative stress associated with CVD. A well-defined combination of five widely studied medicinal plants derived from botanical sources (Bacopa monniera, Silybum marianum (milk thistle), Withania somnifera (Ashwagandha), Camellia sinensis (green tea), and Curcuma longa (turmeric)) has been shown to activate Nrf2 and induce phase II enzymes through the antioxidant response element. The purpose of these experiments was to determine if treatment of cardiomyocytes with this phytochemical composition, marketed as Protandim, activates Nrf2, induces phase II detoxification enzymes, and protects cardiomyocytes from oxidant-induced apoptosis in a Nrf2-dependent manner. In cultured HL-1 cardiomyocytes, phytochemical treatment was associated with nuclear accumulation of Nrf2, significant induction of phase II enzymes, and concomitant protection against hydrogen peroxide-induced apoptosis. The protection against oxidant stress was abolished when Nrf2 was silenced by shRNA, suggesting that our phytochemical treatment worked through the Nrf2 pathway. Interestingly, phytochemical treatment was found to be a more robust activator of Nrf2 than oxidant treatment, supporting the use of the phytochemicals as a potential treatment to increase antioxidant defenses and protect heart cells against an oxidative challenge.

Oxidative stress and myocardial injury in the diabetic heart

Reactive oxygen or nitrogen species play an integral role in both myocardial injury and repair. This dichotomy is differentiated at the level of species type, amount and duration of free radical generated. Homeostatic mechanisms designed to prevent free radical generation in the first instance, scavenge, or enzymatically convert them to less toxic forms and water, playing crucial roles in the maintenance of cellular structure and function. The outcome between functional recovery and dysfunction is dependent upon the inherent ability of these homeostatic antioxidant defences to withstand acute free radical generation, in the order of seconds to minutes. Alternatively, pre-existent antioxidant capacity (from intracellular and extracellular sources) may regulate the degree of free radical generation. This converts reactive oxygen and nitrogen species to the role of second messenger involved in cell signalling. The adaptive capacity of the cell is altered by the balance between death or survival signal converging at the level of the mitochondria, with distinct pathophysiological consequences that extends the period of injury from hours to days and weeks. Hyperglycaemia, hyperlipidaemia and insulin resistance enhance oxidative stress in the diabetic myocardium that cannot adapt to ischaemia-reperfusion. Altered glucose flux, mitochondrial derangements and nitric oxide synthase uncoupling in the presence of decreased antioxidant defence and impaired prosurvival cell signalling may render the diabetic myocardium more vulnerable to injury, remodelling and heart failure.

Role of sirtuins in ischemia-reperfusion injury

Ischemia-reperfusion injury (IRI) remains an unresolved and complicated situation in clinical practice, especially in the case of organ transplantation. Several factors contribute to its complexity; the depletion of energy during ischemia and the induction of oxidative stress during reperfusion initiate a cascade of pathways that lead to cell death and finally to severe organ injury. Recently, the sirtuin family of nicotinamide adenine dinucleotide-dependent deacetylases has gained increasing attention from researchers, due to their involvement in the modulation of a wide variety of cellular functions. There are seven mammalian sirtuins and, among them, the nuclear/cytoplasmic sirtuin 1 (SIRT1) and the mitochondrial sirtuin 3 (SIRT3) are ubiquitously expressed in many tissue types. Sirtuins are known to play major roles in protecting against cellular stress and in controlling metabolic pathways, which are key processes during IRI. In this review, we mainly focus on SIRT1 and SIRT3 and examine their role in modulating pathways against energy depletion during ischemia and their involvement in oxidative stress, apoptosis, microcirculatory stress and inflammation during reperfusion. We present evidence of the beneficial effects of sirtuins against IRI and emphasize the importance of developing new strategies by enhancing their action.

Changes in the mitochondrial permeability transition pore in aging and age-associated diseases

Aging is a biological process associated with impairment of mitochondrial bioenergetic function, increased oxidative stress, attenuated ability to respond to stresses and increased risk in contracting age-associated diseases. When mitochondria are subjected to oxidative stress, accompanied by calcium overload and ATP depletion, they undergo "a permeability transition", characterized by sudden induced change of the inner mitochondrial membrane permeability for water as well as for low-molecular weight solutes (≤1.5kDa), resulting in membrane depolarization and uncoupling of oxidative phosphorylation. Research interest in the entity responsible for this phenomenon, the "mitochondrial permeability transition pore" (MPTP) has dramatically increased after demonstration that it plays a key role in the life and death decision in cells. The molecular structure and identity of MPTP is not yet known, although the pore is thought to exist as multiprotein complex. Some evidence indicate that the sensitivity of mitochondria to Ca(2+)-induced MPTP opening increases with aging; however the basis of this difference is unknown. Changes in MPTP structure and/or function may have important implications in the aging process and aged-associated diseases. This article examines data relevant to this issue. The important role of a principal lipidic counter-partner of the MPTP, cardiolipin, will also be discussed.

Methanol Extract of Cassia mimosoides var. nomame Attenuates Myocardial Injury by Inhibition of Apoptosis in a Rat Model of Ischemia-Reperfusion

Interruption of blood flow through coronary arteries and its subsequent restoration triggers the generation of a burst of reactive oxygen species (ROS), leading to myocardial cell death. In this study, we determined whether a methanol extract of Cassia mimosoides var. nomame Makino could prevent myocardial ischemia-reperfusion injury. When radical scavenging activity of the extract was measured in vitro using its α,α-diphenyl-β-picrylhydrazyl (DPPH) radical quenching ability, the extract showed an activity slightly lower than that of ascorbic acid. Three days after oral administration of the extract (400 mg/kg/day) to rats, myocardial ischemia/reperfusion injury was generated by 30 min of ligation of the left anterior descending coronary artery (LAD), followed by 3 hr reperfusion. Compared with the vehicle-treated group, administration of the extract significantly reduced infarct size (IS) (ratio of infarct area to area at risk) in the extract-treated group by 28.3%. Reduction in the cellular injury was mediated by attenuation of Bax/Bcl-2 ratio by 33.3%, inhibition of caspase-3 activation from procas-pase-3 by 40%, and subsequent reduction in the number of apoptotic cells by 66.3%. These results suggest that the extract attenuates myocardial injury in a rat model of ischemia-reperfusion by scavenging ROS, including free radicals, and consequently blocking apoptotic cascades. Therefore, intake of Cassia mimosoides var. nomame Makino might be beneficial for preventing ischemic myocardial injury.

Cell biology of ischemia/reperfusion injury

Disorders characterized by ischemia/reperfusion (I/R), such as myocardial infarction, stroke, and peripheral vascular disease, continue to be among the most frequent causes of debilitating disease and death. Tissue injury and/or death occur as a result of the initial ischemic insult, which is determined primarily by the magnitude and duration of the interruption in the blood supply, and then subsequent damage induced by reperfusion. During prolonged ischemia, ATP levels and intracellular pH decrease as a result of anaerobic metabolism and lactate accumulation. As a consequence, ATPase-dependent ion transport mechanisms become dysfunctional, contributing to increased intracellular and mitochondrial calcium levels (calcium overload), cell swelling and rupture, and cell death by necrotic, necroptotic, apoptotic, and autophagic mechanisms. Although oxygen levels are restored upon reperfusion, a surge in the generation of reactive oxygen species occurs and proinflammatory neutrophils infiltrate ischemic tissues to exacerbate ischemic injury. The pathologic events induced by I/R orchestrate the opening of the mitochondrial permeability transition pore, which appears to represent a common end-effector of the pathologic events initiated by I/R. The aim of this treatise is to provide a comprehensive review of the mechanisms underlying the development of I/R injury, from which it should be apparent that a combination of molecular and cellular approaches targeting multiple pathologic processes to limit the extent of I/R injury must be adopted to enhance resistance to cell death and increase regenerative capacity in order to effect long-lasting repair of ischemic tissues.