Polyol pathway mediates iron-induced oxidative injury in ischemic-reperfused rat heart

Polyol pathway exacerbated ischemia/reperfusion-induced injury in steatotic liver

BACKGROUND

The polyol pathway, a bypass pathway of glucose metabolism initiated by aldose reductase (AR), has been shown to play an important role in mediating tissue ischemia/reperfusion (I/R) impairment recently. Here, we investigated how and why this pathway might affect the fatty liver following I/R.

METHODS

Two opposite models were created: mice with high-fat-diet-induced liver steatosis were treated with aldose reductase inhibition (ARI) and subsequent I/R; and AR-overexpressing L02 hepatocytes were sequentially subjected to steatosis and hypoxia/reoxygenation. We next investigated (a) the hepatic injuries, including liver function, histology, and hepatocytes apoptosis/necrosis; (b) the NAD(P)(H) contents, redox status, and mitochondrial function; and (c) the flux through the caspase-dependent apoptosis pathway.

RESULTS

AR-inhibition in vivo markedly attenuated the I/R-induced liver injuries, maintained the homeostasis of NAD(P)(H) contents and redox status, and suppressed the caspase-dependent apoptosis pathway. Correspondingly, AR overexpression in vitro presented the opposite effects.

CONCLUSION

The flux through the polyol pathway may render steatotic liver greater vulnerability to I/R. Interventions targeting this pathway might provide a novel adjunctive approach to protect fatty liver from ischemia.

Impairment of calcium ATPases by high glucose and potential pharmacological protection

The review deals with impairment of Ca(2+)-ATPases by high glucose or its derivatives in vitro, as well as in human diabetes and experimental animal models. Acute increases in glucose level strongly correlate with oxidative stress. Dysfunction of Ca(2+)-ATPases in diabetic and in some cases even in nondiabetic conditions may result in nitration of and in irreversible modification of cysteine-674. Nonenyzmatic protein glycation might lead to alteration of Ca(2+)-ATPase structure and function contributing to Ca(2+) imbalance and thus may be involved in development of chronic complications of diabetes. The susceptibility to glycation is probably due to the relatively high percentage of lysine and arginine residues at the ATP binding and phosphorylation domains. Reversible glycation may develop into irreversible modifications (advanced glycation end products, AGEs). Sites of SERCA AGEs are depicted in this review. Finally, several mechanisms of prevention of Ca(2+)-pump glycation, and their advantages and disadvantages are discussed.

Differential effects of pharmacological HIF preconditioning of donors versus recipients in rat cardiac allografts

Ischemia-reperfusion injury (IRI) induces hypoxia-inducible factor-1 (HIF-1) in the myocardium, but the consequences remain elusive. We investigated HIF-1 activation during cold and warm ischemia and IRI in rat hearts and cardiac syngrafts. We also tested the effect of HIF-α stabilizing prolyl hydroxylase inhibitor (FG-4497) on IRI or allograft survival. Ex vivo ischemia of the heart increased HIF-1α expression in a time- and temperature-dependent fashion. Immunohistochemistry localized HIF-1α to all cardiac cell types. After reperfusion, HIF-1α immunoreactivity persisted in smooth muscle cells and cardiomyocytes in the areas with IRI. This was accompanied with a transient induction of protective HIF-1 downstream genes. Donor FG-4497 pretreatment for 4 h enhanced IRI in cardiac allografts as evidenced by an increase in cardiac troponin T release, cardiomyocyte apoptosis, and activation of innate immunity. Recipient FG-4497 pretreatment for 4 h decreased infiltration of ED1(+) macrophages, and mildly improved the long-term allograft survival. In syngrafts donor FG-4497 pretreatment increased activation of innate immunity, but did not induce myocardial damage. We conclude that the HIF-1 pathway is activated in heart transplants. We suggest that pharmacological HIF-α preconditioning of cardiac allografts donors would not lead to clinical benefit, while in recipients it may result in antiinflammatory effects and prolonged allograft survival.

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.

Aldose reductase, oxidative stress, and diabetic mellitus

Diabetes mellitus (DM) is a complex metabolic disorder arising from lack of insulin production or insulin resistance (Diagnosis and classification of diabetes mellitus, 2007). DM is a leading cause of morbidity and mortality in the developed world, particularly from vascular complications such as atherothrombosis in the coronary vessels. Aldose reductase (AR; ALR2; EC 1.1.1.21), a key enzyme in the polyol pathway, catalyzes nicotinamide adenosine dinucleotide phosphate-dependent reduction of glucose to sorbitol, leading to excessive accumulation of intracellular reactive oxygen species (ROS) in various tissues of DM including the heart, vasculature, neurons, eyes, and kidneys. As an example, hyperglycemia through such polyol pathway induced oxidative stress, may have dual heart actions, on coronary blood vessel (atherothrombosis) and myocardium (heart failure) leading to severe morbidity and mortality (reviewed in Heather and Clarke, 2011). In cells cultured under high glucose conditions, many studies have demonstrated similar AR-dependent increases in ROS production, confirming AR as an important factor for the pathogenesis of many diabetic complications. Moreover, recent studies have shown that AR inhibitors may be able to prevent or delay the onset of cardiovascular complications such as ischemia/reperfusion injury, atherosclerosis, and atherothrombosis. In this review, we will focus on describing pivotal roles of AR in the pathogenesis of cardiovascular diseases as well as other diabetic complications, and the potential use of AR inhibitors as an emerging therapeutic strategy in preventing DM complications.

Protective effects of deferoxamine mesylate preconditioning on pancreatic tissue in orthotopic liver autotransplantation in rats

BACKGROUND

Deferoxamine mesylate is known to ameliorate tissue ischemia-reperfusion injury. This study was designed to explore the impact of deferoxamine mesylate preconditioning (DMP) on pancreatic tissue and its possible effects during orthotopic liver autotransplantation.

METHODS

A modified orthotopic liver autotransplantation model was used to simulate pancreatic ischemia-reperfusion injury. Sprague-Dawley rats (0.25-0.30 kg) were randomly divided into normal control, autotransplantation (AT), systemic deferoxamine mesylate preconditioning (SDMP), and partial deferoxamine mesylate conditioning (PDMC) groups. The SDMP group was injected with deferoxamine mesylate (75-90 mg; 300 mg/kg), via the celiac artery at 24 and 48 hours before surgery. During surgery, the PDMC group underwent liver perfusion by means of deferoxamine mesylate solution (20 ml; 0.6 mmol/L) rather than Ringer's lactate solution, with no prior preconditioning. At 6, 24, and 48 hours after surgery, the rats were sacrificed to sample their pancreatic tissues for the expression of hypoxia-inducible factor-1α (HIF-1α) and malondialdehyde (MDA) content. The samples were subjected to blood chemistry analyses, light and transmission electron microscopic morphological studies, and quantitative measurement of HIF-1α expression.

RESULTS

The serum levels of amylase, lipase, and MDA in SDMP and PDMC groups were significantly lower than those in the AT group at 6, 24, and 48 hours after orthotopic liver autotransplantation (P < .05). Light and electron microscopic analyses showed much more severe pancreatic injury in the autotransplantation than in the SDMP and PDMC groups. The HIF-1α expression was increased in the SDMP and PDMC groups more than in the autotransplantation group (P < .05).

CONCLUSIONS

Deferoxamine mesylate preconditioning protected pancreatic tissue in orthotopic liver autotransplantation in rats. Inhibition of oxidative toxic reactions and up-regulated expression of HIF-1α protein are possible mechanisms.

Hepcidin is involved in iron regulation in the ischemic brain

Oxidative stress plays an important role in neuronal injuries caused by cerebral ischemia. It is well established that free iron increases significantly during ischemia and is responsible for oxidative damage in the brain. However, the mechanism of this ischemia-induced increase in iron is not completely understood. In this report, the middle cerebral artery occlusion (MCAO) rat model was performed and the mechanism of iron accumulation in cerebral ischemia-reperfusion was studied. The expression of L-ferritin was significantly increased in the cerebral cortex, hippocampus, and striatum on the ischemic side, whereas H-ferritin was reduced in the striatum and increased in the cerebral cortex and hippocampus. The expression level of the iron-export protein ferroportin1 (FPN1) significantly decreased, while the expression of transferrin receptor 1 (TfR1) was increased. In order to elucidate the mechanisms of FPN1 regulation, we studied the expression of the key regulator of FPN1, hepcidin. We observed that the hepcidin level was significantly elevated in the ischemic side of the brain. Knockdown hepcidin repressed the increasing of L-ferritin and decreasing of FPN1 invoked by ischemia-reperfusion. The results indicate that hepcidin is an important contributor to iron overload in cerebral ischemia. Furthermore, our results demonstrated that the levels of hypoxia-inducible factor-1α (HIF-1α) were significantly higher in the cerebral cortex, hippocampus and striatum on the ischemic side; therefore, the HIF-1α-mediated TfR1 expression may be another contributor to the iron overload in the ischemia-reperfusion brain.

Aldose reductase inhibition prevents hypoxia-induced increase in hypoxia-inducible factor-1alpha (HIF-1alpha) and vascular endothelial growth factor (VEGF) by regulating 26 S proteasome-mediated protein degradation in human colon cancer cells

The development of intratumoral hypoxia, a hallmark of rapidly progressing solid tumors, renders tumor cells resistant to chemotherapy and radiation therapy. We have recently shown that inhibition of aldose reductase (AR), an enzyme that catalyzes the reduction of lipid aldehydes and their glutathione conjugates, prevents human colon cancer cell growth in culture as well as in nude mouse xenografts by inhibiting the NF-κB-dependent activation of oxidative stress-mediated inflammatory and carcinogenic markers. However, the role of AR in mediating hypoxic stress signals is not known. We therefore investigated the molecular mechanisms by which AR inhibition prevents the hypoxia-induced human colon cancer cells growth and invasion. Our results indicate that AR inhibition by the pharmacological inhibitor fidarestat or ablation by AR-specific siRNA prevents hypoxia-induced proliferation of HT29, SW480, and Caco-2 colon cancer cells. Furthermore, hypoxia-induced increase in the level of HIF-1α in colon cancer cells was significantly decreased by AR inhibition. During hypoxic conditions, treatment of HT29 cells with the AR inhibitor fidarestat significantly decreased the expression of vascular endothelial growth factor, a down target of HIF-1α, at both mRNA and protein levels and also prevented the activation of PI3K/AKT, GSK3β, Snail, and lysyl oxidase. Furthermore, inhibition of hypoxia-induced HIF-1α protein accumulation by AR inhibition was abolished in the presence of MG132, a potent inhibitor of the 26 S proteasome. In addition, AR inhibition also prevented the hypoxia-induced inflammatory molecules such as Cox-2 and PGE2 and expression of extracellular matrix proteins such as MMP2, vimentin, uPAR, and lysyl oxidase 2. In conclusion, our results indicate that AR mediates hypoxic signals, leading to tumor progression and invasion.

Aldose reductase pathway contributes to vulnerability of aging myocardium to ischemic injury

Aging men and women display both increased incidence of cardiovascular disease and complications of myocardial infarction and heart failure. We hypothesized that altered glucose metabolism, in particular, flux of glucose via the polyol pathway (PP) may be responsible, in part, for the enhanced vulnerability of aging myocardium to ischemic injury, even in the absence of superimposed disease processes linked to PP flux, such as diabetes. To test our hypothesis, we determined the expression and products of PP enzymes aldose reductase (AR) and sorbitol dehydrogenase (SDH) in hearts from Fischer 344 aged (26 months) and young (4 months) rats subjected to global ischemia followed by reperfusion in the presence or absence of blockers of PP and the measures of ischemic injury and functional recovery were determined. Expression and activities of AR and SDH were significantly higher in aged vs. young hearts, and induction of ischemia further increased AR and SDH activity in the aged hearts. Myocardial ischemic injury was significantly greater in aged vs. young hearts, and blockade of AR reduced ischemic injury and improved cardiac functional recovery on reperfusion in aged hearts. These data indicate that innate increases in activity of the PP enzymes augment myocardial vulnerability to I/R injury in aging, and that blockers of PP protect the vulnerable aging hearts.

Advances in iron chelation: an update

INTRODUCTION

Oxidative stress (caused by excess iron) can result in tissue damage, organ failure and finally death, unless treated by iron chelators. The causative factor in the etiology of a variety of disease states is the presence of iron-generated reactive oxygen species (ROS), which can result in cell damage or which can affect the signaling pathways involved in cell necrosis-apoptosis or organ fibrosis, cancer, neurodegeneration and cardiovascular, hepatic or renal dysfunctions. Iron chelators can reduce oxidative stress by the removal of iron from target tissues. Equally as important, removal of iron from the active site of enzymes that play key roles in various diseases can be of considerable benefit to the patients.

AREAS COVERED

This review focuses on iron chelators used as therapeutic agents. The importance of iron in oxidative damage is discussed, along with the three clinically approved iron chelators.

EXPERT OPINION

A number of iron chelators are used as approved therapeutic agents in the treatment of thalassemia major, asthma, fungal infections and cancer. However, as our knowledge about the biochemistry of iron and its role in etiologies of seemingly unrelated diseases increases, new applications of the approved iron chelators, as well as the development of new iron chelators, present challenging opportunities in the areas of drug discovery and development.

Salvianolic acid A displays cardioprotective effects in in vitro models of heart hypoxia/reoxygenation injury

Oxidative stress induced by overproduction of reactive oxygen species (ROS) plays an important role in hypoxia/reoxygenation (H/R) injury. In the present study, effects of salvianolic acid A (1) on heart H/R injury through its antioxidant activity were examined, using a molecule-based ROS scavenging system and cardiomyocyte model of H/R injury, as well as isolated rat heart model. As a result, 1 showed a potent antioxidant activity, scavenging all of the tested ROS and DPPH (2,2-diphenyl-1-picrylhydrazyl). The antioxidant effect of 1 was also observed in cardiomyocytes exposed to H/R. Compound 1 remarkably decreased dihydroethidium and dichlorofluorescein fluorescence and increased cell viability and mitochondrial membrane potential, ΔΨ(m), when compared to the H/R group. In isolated rat hearts exposed to H/R, 1 markedly increased the coronary flow, the peak of pressure development and the valley of pressure development, and significantly reduced the left ventricular end diastolic pressure when compared to the H/R group. These results suggested that 1 had significant protective effects against H/R-induced myocardial injury through its antioxidant activity.

Hypoxia inducible factor 1 (HIF-1) and cardioprotection

Since its discovery in early 1990s, hypoxia inducible factor 1 (HIF-1) has been increasingly recognized for its key role in transcriptional control of more than a hundred genes that regulate a wide-spectrum of cellular functional events, including angiogenesis, vasomotor control, glucose and energy metabolism, erythropoiesis, iron homeostasis, pH regulation, cell proliferation and viability. Evidence accumulated during the past 7 years suggests a critical role for HIF-1alpha in mediating cardioprotection. The purpose of our present article is to provide an updated overview on this important regulator of gene expression in the cellular stress-responsive and adaptive process. We have particularly emphasized the involvement of HIF-1 in the induction of cardioprotective molecules, such as inducible nitric oxide synthase (iNOS), hemeoxygenase 1 (HO-1), and erythropoietin (EPO), which in turn alleviate myocardial damages caused by harmful events such as ischemia-reperfusion injury. Despite these advances, further in-depth studies are needed to elucidate the possible coordination or interaction between HIF-1alpha and other key transcription factors in regulating protein expression that leads to cardioprotection.

Cardiac contractile dysfunction during acute hyperglycemia due to impairment of SERCA by polyol pathway-mediated oxidative stress

Hyperglycemia is an indication of poor outcome for heart attack patients, even for nondiabetic patients with stress-induced hyperglycemia. Previous studies showed that inhibition of aldose reductase, the first and rate-limiting enzyme of the polyol pathway, attenuated contractile dysfunction in diabetic animals, but the mechanism is unclear. We therefore wanted to find out whether the polyol pathway also contributes to acute hyperglycemia-induced cardiac contractile dysfunction, and determine the mechanism involved. Rat hearts were isolated and retrogradely perfused with Krebs buffer containing either normal or high concentrations of glucose for 2 h. Short exposure to high-glucose medium led to contractile dysfunction as indicated by decreased -dP/dt(max), as well as elevation in left ventricular end-diastolic pressure. Cardiomyocytes incubated in high-glucose medium showed abnormal Ca2+ signaling, most likely because of decreased activity of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) inactivated by oxidative stress. Inhibition of aldose reductase or sorbitol dehydrogenase, the second enzyme in the polyol pathway, ameliorated contractile dysfunction, attenuated oxidative stress, and normalized Ca2+ signaling and SERCA activity caused by high glucose, indicating that the polyol pathway is the major contributor to acute hyperglycemia-induced oxidative stress leading to the inactivation of SERCA and contractile dysfunction.

Aldose reductase and cardiovascular diseases, creating human-like diabetic complications in an experimental model

Hyperglycemia and reduced insulin actions affect many biological processes. One theory is that aberrant metabolism of glucose via several pathways including the polyol pathway causes cellular toxicity. Aldose reductase (AR) is a multifunctional enzyme that reduces aldehydes. Under diabetic conditions AR converts glucose into sorbitol, which is then converted to fructose. This article reviews the biology and pathobiology of AR actions. AR expression varies considerably among species. In humans and rats, the higher level of AR expression is associated with toxicity. Flux via AR is increased by ischemia and its inhibition during ischemia reperfusion reduces injury. However, similar pharmacological effects are not observed in mice unless they express a human AR transgene. This is because mice have much lower levels of AR expression, probably insufficient to generate toxic byproducts. Human AR expression in LDL receptor knockout mice exacerbates vascular disease, but only under diabetic conditions. In contrast, a recent report suggests that genetic ablation of AR increased atherosclerosis and increased hydroxynonenal in arteries. It was hypothesized that AR knockout prevented reduction of toxic aldehydes. Like many in vivo effects found in genetically manipulated animals, interpretation requires the reproduction of human-like physiology. For AR, this will require tissue specific expression of AR in sites and at levels that approximate those in humans.

Novel role for aldose reductase in mediating acute inflammatory responses in the lung

Exaggerated inflammatory responses and the resultant increases in alveolar-capillary permeability underlie the pathogenesis of acute lung injury during sepsis. This study examined the functions of aldose reductase (AR) in mediating acute lung inflammation. Transgenic mice expressing human AR (ARTg) were used to study the functions of AR since mice have low intrinsic AR activity. In a mild cecal ligation and puncture model, ARTg mice demonstrated an enhanced AR activity and a greater inflammatory response as evaluated by circulating cytokine levels, neutrophil accumulation in the lungs, and activation of Rho kinase in lung endothelial cells (ECs). Compared with WT lung cells, ARTg lung cells produced more IL-6 and showed augmented JNK activation in response to LPS stimulation ex vivo. In human neutrophils, AR activity was required for fMLP-included CD11b activation and up-regulation, respiratory burst, and shape changes. In human pulmonary microvascular ECs, AR activity was required for TNF-alpha-induced activation of the Rho kinase/MKK4/JNK pathway and IL-6 production, but not p38 activation or ICAM-1 expression. Importantly, AR activity in both human neutrophils and ECs was required for neutrophil adhesion to TNF-alpha-stimulated ECs. These data demonstrate a novel role for AR in regulating the signaling pathways leading to neutrophil-EC adhesion during acute lung inflammation.

Polyol pathway and RAGE: a central metabolic and signaling axis in diabetic complications

There are multiple metabolic and molecular consequences of hyperglycemia. This review will focus on the roles of the polyol pathway and the receptor for advanced glycation end products (RAGE) in the pathogenesis of diabetic complications. The lead enzyme of the polyol pathway, aldose reductase, transduces maladaptive effects of hyperglycemia by multiple mechanisms, at least in part via the generation of the products of nonenzymatic glycation of proteins, the advanced glycation end products (AGEs). Furthermore, seminal shifts in metabolic flux in the intracellular space stimulated by aldose reductase action activate signal transduction pathways, which alter gene expression and change cellular phenotype. Among the ligands of the multi-ligand receptor RAGE are the AGEs. AGE-RAGE stimulation mediates vascular and target cell dysfunction. The intersection and interdependence of the polyol pathway-RAGE connection suggest that targeting this axis may provide benefit in reducing the complications of diabetes.

Polyol pathway impairs the function of SERCA and RyR in ischemic-reperfused rat hearts by increasing oxidative modifications of these proteins

A number of studies have shown that the polyol pathway, consisting of aldose reductase (AR) and sorbitol dehydrogenase (SDH), contributes to ischemia-reperfusion (I/R)-induced myocardial infarction due to depletion of ATP. In this report we show that the polyol pathway in I/R heart also contributes to the impairment of sacro/endoplasmic reticulum Ca(2+)-ATPase (SERCA) and ryanodine receptor (RyR), two key players in Ca(2+) signaling that regulate cardiac contraction. Rat hearts were isolated and retrogradely perfused with either Krebs' buffer containing 1 microM AR inhibitor, zopolrestat, or 200 nM SDH inhibitor, CP-170,711, and challenged by 30 min of regional ischemia and 45 min of reperfusion. We found that post-ischemic contractile function of the isolated perfused hearts was improved by pharmacological inhibition of the polyol pathway. I/R-induced contractile dysfunction is most likely due to impairment in Ca(2+) signaling and the activities of SERCA and RyR. All these abnormalities were significantly ameliorated by treatment with ARI or SDI. We showed that the polyol pathway activities increase the level of peroxynitrite, which enhances the tyrosine nitration of SERCA and irreversibly modifies it to form SERCAC674-SO(3)H. This leads to reduced level of S-glutathiolated SERCA, contributing to its inactivation. The polyol pathway activities also deplete the level of GSH, leading to decreased active RyR, the S-glutathiolated RyR. Thus, in I/R heart, inhibition of polyol pathway improved the function of SERCA and RyR by protecting them from irreversible oxidation.

Intranasal deferoxamine provides increased brain exposure and significant protection in rat ischemic stroke

Deferoxamine (DFO) is a high-affinity iron chelator approved by the Food and Drug Administration for treating iron overload. Preclinical research suggests that systemically administered DFO prevents and treats ischemic stroke damage and intracerebral hemorrhage. However, translation into human trials has been limited, probably because of difficulties with DFO administration. A noninvasive method of intranasal administration has emerged recently as a rapid way to bypass the blood-brain barrier and target therapeutic agents to the central nervous system. We report here that intranasal administration targets DFO to the brain and reduces systemic exposure, and that intranasal DFO prevents and treats stroke damage after middle cerebral artery occlusion (MCAO) in rats. A 6-mg dose of DFO resulted in significantly higher DFO concentrations in the brain (0.9-18.5 microM) at 30 min after intranasal administration than after intravenous administration (0.1-0.5 microM, p < 0.05). Relative to blood concentration, intranasal delivery increased targeting of DFO to the cortex approximately 200-fold compared with intravenous delivery. Intranasal administration of three 6-mg doses of DFO did not result in clinically significant changes in blood pressure or heart rate. Pretreatment with intranasal DFO (three 6-mg doses) 48 h before MCAO significantly decreased infarct volume by 55% versus control (p < 0.05). In addition, post-treatment with intranasal administration of DFO (six 6-mg doses) immediately after reperfusion significantly decreased infarct volume by 55% (p < 0.05). These experiments suggest that intranasally administered DFO may be a useful treatment for stroke, and a prophylactic for patients at high risk for stroke.

Aldose reductase mediates myocardial ischemia-reperfusion injury in part by opening mitochondrial permeability transition pore

Aldose reductase (AR), a member of the aldo-keto reductase family, has been demonstrated to play a central role in mediating myocardial ischemia-reperfusion (I/R) injury. Recently, using transgenic mice broadly overexpressing human AR (ARTg), we demonstrated that AR is an important component of myocardial I/R injury and that inhibition of this enzyme protects heart from I/R injury (20-22, 48, 49, 56). To rigorously delineate mechanisms by which AR pathway influences myocardial ischemic injury, we investigated the role played by reactive oxygen species (ROS), antioxidant enzymes, and mitochondrial permeability transition (MPT) pore opening in hearts from ARTg or littermates [wild type (WT)] subjected to I/R. MPT pore opening after I/R was determined using mitochondrial uptake of 2-deoxyglucose ratio, while H2O2 was measured as a key indicator of ROS. Myocardial 2-deoxyglucose uptake ratio and calcium-induced swelling were significantly greater in mitochondria from ARTg mice than in WT mice. Blockade of MPT pore with cyclosphorin A during I/R reduced ischemic injury significantly in ARTg mice hearts. H2O2 measurements indicated mitochondrial ROS generation after I/R was significantly greater in ARTg mitochondria than in WT mice hearts. Furthermore, the levels of antioxidant GSH were significantly reduced in ARTg mitochondria than in WT. Resveratrol treatment or pharmacological blockade of AR significantly reduced ROS generation and MPT pore opening in mitochondria of ARTg mice hearts exposed to I/R stress. This study demonstrates that MPT pore opening is a key event by which AR pathway mediates myocardial I/R injury, and that the MPT pore opening after I/R is triggered, in part, by increases in ROS generation in ARTg mice hearts. Therefore, inhibition of AR pathway protects mitochondria and hence may be a useful adjunct for salvaging ischemic myocardium.