Cardiac ischemia/reperfusion, aging, and redox-dependent alterations in mitochondrial function

Purinergic signaling in myocardial ischemia-reperfusion injury

Purines and their derivatives, extensively distributed in the body, act as a class of extracellular signaling molecules via a rich array of receptors, also known as purinoceptors (P1, P2X, and P2Y). They mediate multiple intracellular signal transduction pathways and participate in various physiological and pathological cell behaviors. Since the function in myocardial ischemia-reperfusion injury (MIRI), this review summarized the involvement of purinergic signal transduction in diversified pathological processes, including energy metabolism disorder, oxidative stress injury, calcium overload, inflammatory immune response, platelet aggregation, coronary vascular dysfunction, and cell necrosis and apoptosis. Moreover, increasing evidence suggests that purinergic signaling also mediates the prevention and treatment of MIRI, such as ischemic conditioning, pharmacological intervention, and some other therapies. In conclusion, this review exhibited that purinergic signaling mediates the complex processes of MIRI which shows its promising application and prospecting in the future.

Role of Oxidative Stress in Cardiac Dysfunction and Subcellular Defects Due to Ischemia-Reperfusion Injury

Ischemia-reperfusion (I/R) injury is well-known to be associated with impaired cardiac function, massive arrhythmias, marked alterations in cardiac metabolism and irreversible ultrastructural changes in the heart. Two major mechanisms namely oxidative stress and intracellular Ca²⁺-overload are considered to explain I/R-induced injury to the heart. However, it is becoming apparent that oxidative stress is the most critical pathogenic factor because it produces myocardial abnormalities directly or indirectly for the occurrence of cardiac damage. Furthermore, I/R injury has been shown to generate oxidative stress by promoting the formation of different reactive oxygen species due to defects in mitochondrial function and depressions in both endogenous antioxidant levels as well as regulatory antioxidative defense systems. It has also been demonstrated to adversely affect a wide variety of metabolic pathways and targets in cardiomyocytes, various resident structures in myocardial interstitium, as well as circulating neutrophils and leukocytes. These I/R-induced alterations in addition to myocardial inflammation may cause cell death, fibrosis, inflammation, Ca²⁺-handling abnormalities, activation of proteases and phospholipases, as well as subcellular remodeling and depletion of energy stores in the heart. Analysis of results from isolated hearts perfused with or without some antioxidant treatments before subjecting to I/R injury has indicated that cardiac dysfunction is associated with the development of oxidative stress, intracellular Ca²⁺-overload and protease activation. In addition, changes in the sarcolemma and sarcoplasmic reticulum Ca²⁺-handling, mitochondrial oxidative phosphorylation as well as myofibrillar Ca²⁺-ATPase activities in I/R hearts were attenuated by pretreatment with antioxidants. The I/R-induced alterations in cardiac function were simulated upon perfusing the hearts with oxyradical generating system or oxidant. These observations support the view that oxidative stress may be intimately involved in inducing intracellular Ca²⁺-overload, protease activation, subcellular remodeling, and cardiac dysfunction as a consequence of I/R injury to the heart.

The dinoflagellate Alexandrium affine acutely induces significant modulations on innate immunity, hepatic function, and antioxidant defense system in the gill and liver tissues of red seabream

Alexandrium affine is a global harmful algal bloom (HAB)-forming dinoflagellate. In this study, the effect of non-toxin-producing A. affine on the gill and liver tissues of red seabream, Pagrus major, was analyzed over 24 h exposure and 2 h depuration phases. After exposure to three concentrations of A. affine (4,000, 6,000, and 7,000 cells mL^-1), survival rates, respiration rates, immunities (lysozyme, total Ig), hepatic biomarkers (alanine aminotransferase, ALT; aspartate aminotransferase, AST; and alkaline phosphatase, ALP), lipid peroxidation (malondialdehyde, MDA), and antioxidant defense systems (glutathione, GSH; catalase, CAT; superoxide dismutase, SOD; glutathione peroxidases, GPx; and glutathione reductase, GR) were analyzed in gill and liver tissues. Dose-dependent decreases in survival and respiration rates were detected in red seabream. A. affine levels of to 6,000 and 7,000 cells mL^-1 induced immunosuppression and hepatic impairment in both tissues, as measured by significant decreases in lysozyme activity, total Ig level, ALT, AST, and ALP content. The levels of GSH, CAT, SOD, GPx, and GR were significantly decreased in the gills and liver in response to 7,000 cells mL^-1 of A. affine at 24 h, and MDA was elevated. However, different response patterns were observed between tissues in response to 4,000 cells mL^-1. Activity of antioxidant defense enzymes was significantly elevated in the liver but decreased in the gills. This suggests that the gills were more vulnerable than the liver. In the case of 6,000 and 7,000 cells mL^-1 treatments, higher susceptibility was also detected at 3 h in the gill compared to the overall responses of each parameter measured in liver. Taken together, direct attachment of A. affine to the gill tissue strongly affects immunity and antioxidant capacity of red seabream even after a short exposure period. These results could be helpful for understanding HAB-mediated effects in marine fish.

Intermittent hypoxia leads to functional reorganization of mitochondria and affects cellular bioenergetics in marine molluscs

Fluctuations in oxygen (O2) concentrations represent a major challenge to aerobic organisms and can be extremely damaging to their mitochondria. Marine intertidal molluscs are well-adapted to frequent O2 fluctuations, yet it remains unknown how their mitochondrial functions are regulated to sustain energy metabolism and prevent cellular damage during hypoxia and reoxygenation (H/R). We used metabolic control analysis to investigate the mechanisms of mitochondrial responses to H/R stress (18 h at <0.1% O2 followed by 1 h of reoxygenation) using hypoxia-tolerant intertidal clams Mercenaria mercenaria and hypoxia-sensitive subtidal scallops Argopecten irradians as models. We also assessed H/R-induced changes in cellular energy balance, oxidative damage and unfolded protein response to determine the potential links between mitochondrial dysfunction and cellular injury. Mitochondrial responses to H/R in scallops strongly resembled those in other hypoxia-sensitive organisms. Exposure to hypoxia followed by reoxygenation led to a strong decrease in the substrate oxidation (SOX) and phosphorylation (PHOS) capacities as well as partial depolarization of mitochondria of scallops. Elevated mRNA expression of a reactive oxygen species-sensitive enzyme aconitase and Lon protease (responsible for degradation of oxidized mitochondrial proteins) during H/R stress was consistent with elevated levels of oxidative stress in mitochondria of scallops. In hypoxia-tolerant clams, mitochondrial SOX capacity was enhanced during hypoxia and continued rising during the first hour of reoxygenation. In both species, the mitochondrial PHOS capacity was suppressed during hypoxia, likely to prevent ATP wastage by the reverse action of FO,F1-ATPase. The PHOS capacity recovered after 1 h of reoxygenation in clams but not in scallops. Compared with scallops, clams showed a greater suppression of energy-consuming processes (such as protein turnover and ion transport) during hypoxia, indicated by inactivation of the translation initiation factor EIF-2α, suppression of 26S proteasome activity and a dramatic decrease in the activity of Na(+)/K(+)-ATPase. The steady-state levels of adenylates were preserved during H/R exposure and AMP-dependent protein kinase was not activated in either species, indicating that the H/R exposure did not lead to severe energy deficiency. Taken together, our findings suggest that mitochondrial reorganizations sustaining high oxidative phosphorylation flux during recovery, combined with the ability to suppress ATP-demanding cellular functions during hypoxia, may contribute to high resilience of clams to H/R stress and help maintain energy homeostasis during frequent H/R cycles in the intertidal zone.

Thioredoxin Uses a GSH-independent Route to Deglutathionylate Endothelial Nitric-oxide Synthase and Protect against Myocardial Infarction

Reversible glutathionylation plays a critical role in protecting protein function under conditions of oxidative stress generally and for endothelial nitric-oxide synthase (eNOS) specifically. Glutathione-dependent glutaredoxin-mediated deglutathionylation of eNOS has been shown to confer protection in a model of heart damage termed ischemia-reperfusion injury, motivating further study of eNOS deglutathionylation in general. In this report, we present evidence for an alternative mechanism of deglutathionylation. In this pathway thioredoxin (Trx), a small cellular redox protein, is shown to rescue eNOS from glutathionylation during ischemia-reperfusion in a GSH-independent manner. By comparing mice with global overexpression of Trx and mice with cardiomyocyte-specific overexpression of Trx, we demonstrate that vascular Trx-mediated deglutathionylation of eNOS protects against ischemia-reperfusion-mediated myocardial infarction. Trx deficiency in endothelial cells promoted eNOS glutathionylation and reduced its enzymatic activity, whereas increased levels of Trx led to deglutathionylated eNOS. Thioredoxin-mediated deglutathionylation of eNOS in the coronary artery in vivo protected against reperfusion injury, even in the presence of normal levels of GSH. We further show that Trx directly interacts with eNOS, and we confirmed that Cys-691 and Cys-910 are the glutathionylated sites, as mutation of these cysteines partially rescued the decrease in eNOS activity, whereas mutation of a distal site, Cys-384, did not. Collectively, this study shows for the first time that Trx is a potent deglutathionylating protein in vivo and in vitro that can deglutathionylate proteins in the presence of high levels of GSSG in conditions of oxidative stress.

Effects of intermittent hypoxia on oxidative stress and protein degradation in molluscan mitochondria

Oxygen fluctuations represent a common stressor in estuarine and intertidal environments and can compromise the mitochondrial integrity and function in marine organisms. We assessed the role of mitochondrial protection mechanisms (ATP-dependent and ATP-independent mitochondrial proteases, and antioxidants) in tolerance to intermittent hypoxia or anoxia in three species of marine bivalves: the hypoxia tolerant hard clams (Mercenaria mercenaria) and oysters (Crassostrea virginica), and a hypoxia-sensitive subtidal scallop (Argopecten irradians). In clams and oysters, mitochondrial tolerance to hypoxia (18 h at 5% O2), anoxia (18 h at 0.1% O2) and subsequent reoxygenation was associated with the ability to maintain the steady-state activity of ATP-dependent and ATP-independent mitochondrial proteases and an anticipatory upregulation of the total antioxidant capacity (TAOC) under the low oxygen conditions. No accumulation of end-products of lipid or protein peroxidation was found during intermittent hypoxia or anoxia in clams and oysters (except for an increase in protein carbonyl concentration after hypoxia-reoxygenation in oysters). In contrast, hypoxia/anoxia and reoxygenation strongly suppressed activity of the ATP-dependent mitochondrial proteases in hypoxia-sensitive scallops. This suppression was associated with accumulation of oxidatively damaged mitochondrial proteins (including carbonylated proteins and proteins conjugated with a lipid peroxidation product malondialdehyde) despite high TAOC levels in scallop mitochondria. These findings highlight a key role of mitochondrial proteases in protection against hypoxia-reoxygenation stress and adaptations to frequent oxygen fluctuations in intertidal mollusks.

Altered FoF1 ATP synthase and susceptibility to mitochondrial permeability transition pore during ischaemia and reperfusion in aging cardiomyocytes

Aging is a major determinant of the incidence and severity of ischaemic heart disease. Preclinical information suggests the existence of intrinsic cellular alterations that contribute to ischaemic susceptibility in senescent myocardium, by mechanisms not well established. We investigated the role of altered mitochondrial function in the adverse effect of aging. Isolated perfused hearts from old mice (> 20 months) displayed increased ischaemia-reperfusion injury as compared to hearts from adult mice (6 months) despite delayed onset of ischaemic rigor contracture. In cardiomyocytes from aging hearts there was a more rapid decline of mitochondrial membrane potential (Δψm) as compared to young ones, but ischaemic rigor shortening was also delayed. Transient recovery of Δψm observed during ischaemia, secondary to the reversal of mitochondrial FoF1 ATP synthase to ATPase mode, was markedly reduced in aging cardiomyocytes. Proteomic analysis demonstrated increased oxidation of different subunits of ATP synthase. Altered bionergetics in aging cells was associated with reduced mitochondrial calcium uptake and more severe cytosolic calcium overload during ischaemia-reperfusion. Despite attenuated ROS burst and mitochondrial calcium overload, mitochondrial permeability transition pore (mPTP) opening and cell death was increased in reperfused aged cells. In vitro studies demonstrated a significantly reduced calcium retention capacity in interfibrillar mitochondria from aging hearts. Our results identify altered FoF1 ATP synthase and increased sensitivity of mitochondria to undergo mPTP opening as important determinants of the reduced tolerance to ischaemia-reperfusion in aging hearts. Because ATP synthase has been proposed to conform mPTP, it is tempting to hypothesise that oxidation of ATP synthase underlie both phenomena.

HS-1793, a recently developed resveratrol analogue protects rat heart against hypoxia/reoxygenation injury via attenuating mitochondrial damage

Resveratrol is known to exert a cardioprotective effect against hypoxia/reoxygenation (H/R) injury. HS-1793 is a novel, more stable resveratrol analog, but its cardioprotective effects were unknown. The present study aimed to test the cardioprotective effect of HS-1793 against H/R injury and investigate the role of mitochondria in Sprague Dawley rat heart damage using an ex vivo Langendorff system. HS-1793 ameliorated H/R-induced mitochondrial dysfunction by reducing mitochondrial reactive oxygen species production, improving mitochondrial oxygen consumption and suppressing mitochondrial calcium (Ca(2+)) overload during reperfusion. Moreover, HS-1793-treated rat heart showed reduced infarct size. Our data suggest that HS-1793 can protect cardiac against mitochondrial damage following H/R, thereby suppressing injury.

Protective effects of taurine against oxidative stress in the heart of MsrA knockout mice

Taurine has been shown to have potent anti-oxidant properties under various pathophysiological conditions. We reported previously a cellular dysfunction and mitochondrial damage in cardiac myocytes of methionine sulfoxide reductase A (MsrA) gene knockout mice (MsrA(-/-)). In the present study, we have explored the protective effects of taurine against oxidative stress in the heart of MsrA(-/-) mice with or without taurine treatment. Cardiac cell contractility and Ca(2+) dynamics were measured using cell-based assays and in vivo cardiac function was monitored using high-resolution echocardiography in the tested animals. Our data have shown that MsrA(-/-) mice exhibited a progressive cardiac dysfunction with a significant decrease of ejection fraction (EF) and fraction shortening (FS) at age of 8 months compared to the wild type controls at the same age. However, the dysfunction was corrected in MsrA(-/-) mice treated with taurine supplement in the diet for 5 months. We further investigated the cellular mechanism underlying the protective effect of taurine in the heart. Our data indicated that cardiac myocytes from MsrA(-/-) mice treated with taurine exhibited an improved cell contraction and could tolerate oxidative stress better. Furthermore, taurine treatment reduced significantly the protein oxidation levels in mitochondria of MsrA(-/-) hearts, suggesting an anti-oxidant effect of taurine in cardiac mitochondria. Our study demonstrates that long-term treatment of taurine as a diet supplement is beneficial to a heart that is vulnerable to environmental oxidative stresses.

Cross talk between mitochondria and NADPH oxidases

Reactive oxygen species (ROS) play an important role in physiological and pathological processes. In recent years, a feed-forward regulation of the ROS sources has been reported. The interactions between the main cellular sources of ROS, such as mitochondria and NADPH oxidases, however, remain obscure. This work summarizes the latest findings on the role of cross talk between mitochondria and NADPH oxidases in pathophysiological processes. Mitochondria have the highest levels of antioxidants in the cell and play an important role in the maintenance of cellular redox status, thereby acting as an ROS and redox sink and limiting NADPH oxidase activity. Mitochondria, however, are not only a target for ROS produced by NADPH oxidase but also a significant source of ROS, which under certain conditions may stimulate NADPH oxidases. This cross talk between mitochondria and NADPH oxidases, therefore, may represent a feed-forward vicious cycle of ROS production, which can be pharmacologically targeted under conditions of oxidative stress. It has been demonstrated that mitochondria-targeted antioxidants break this vicious cycle, inhibiting ROS production by mitochondria and reducing NADPH oxidase activity. This may provide a novel strategy for treatment of many pathological conditions including aging, atherosclerosis, diabetes, hypertension, and degenerative neurological disorders in which mitochondrial oxidative stress seems to play a role. It is conceivable that the use of mitochondria-targeted treatments would be effective in these conditions.

Drosophila models of cardiac disease

The fruit fly Drosophila melanogaster has emerged as a useful model for cardiac diseases, both developmental abnormalities and adult functional impairment. Using the tools of both classical and molecular genetics, the study of the developing fly heart has been instrumental in identifying the major signaling events of cardiac field formation, cardiomyocyte specification, and the formation of the functioning heart tube. The larval stage of fly cardiac development has become an important model system for testing isolated preparations of living hearts for the effects of biological and pharmacological compounds on cardiac activity. Meanwhile, the recent development of effective techniques to study adult cardiac performance in the fly has opened new uses for the Drosophila model system. The fly system is now being used to study long-term alterations in adult performance caused by factors such as diet, exercise, and normal aging. The fly is a unique and valuable system for the study of such complex, long-term interactions, as it is the only invertebrate genetic model system with a working heart developmentally homologous to the vertebrate heart. Thus, the fly model combines the advantages of invertebrate genetics (such as large populations, facile molecular genetic techniques, and short lifespan) with physiological measurement techniques that allow meaningful comparisons with data from vertebrate model systems. As such, the fly model is well situated to make important contributions to the understanding of complicated interactions between environmental factors and genetics in the long-term regulation of cardiac performance.

Tourniquet-induced acute ischemia-reperfusion injury in mouse skeletal muscles: Involvement of superoxide

Although arterial limb tourniquet is one of the first-line treatments to prevent exsanguinating hemorrhage in both civilian pre-hospital and battlefield casualty care, prolonged application of a limb tourniquet can lead to serious ischemia-reperfusion injury. However, the underlying pathomechanisms of tourniquet-induced ischemia-reperfusion injury are still poorly understood. Using a murine model of acute limb ischemia-reperfusion, we investigated if acute limb ischemia-reperfusion injury is mediated by superoxide overproduction and mitochondrial dysfunction. Hind limbs of C57/BL6 mice were subjected to 3h ischemia and 4h reperfusion via placement and release of a rubber tourniquet at the greater trochanter. Approximately 40% of the gastrocnemius muscle suffered infarction in this model. Activities of mitochondrial electron transport chain complexes including complex I, II, III, and IV in the gastrocnemius muscle were decreased in the ischemia-reperfusion group compared to sham. Superoxide production was increased while activity of manganese superoxide dismutase (MnSOD, the mitochondria-targeted SOD isoform) was decreased in the ischemia-reperfusion group compared to the sham group. Pretreatment with tempol (a SOD mimetic, 50mg/kg) or co-enzyme Q(10) (50mg/kg) not only decreased the superoxide production, but also reduced the infarct size and normalized mitochondrial dysfunction in the gastrocnemius muscle. Our results suggest that tourniquet-induced skeletal muscle ischemia-reperfusion injuries including infarct size and mitochondrial dysfunction may be mediated via superoxide overproduction and reduced antioxidant activity. In the future, this murine ischemia-reperfusion model can be adapted to mechanistically evaluate anti-ischemic molecules in tourniquet-induced skeletal muscle injury.

Glutathione peroxidase 1 protects mitochondria against hypoxia/reoxygenation damage in mouse hearts

Glutathione peroxidase 1 (GPx1) plays an important role in preventing cardiac dysfunction following ischemia-reperfusion injury. However, its role in protecting cardiac mitochondria against reoxygenation-induced reactive oxygen species (ROS) generation in vivo is unclear. We examined the role of GPx1 in protecting cardiac mitochondria against hypoxia-reoxygenation (HR) damage by testing for alterations in cardiac mitochondrial function. We used a two-dimensional gel electrophoresis proteomics analysis to examine the effects of reoxygenation on cardiac protein in wild-type (GPx1(+/+)) and GPx1 knockout (GPx1(-/-)) mouse hearts. We identified 42 protein spots showing differential expression in the two groups. Sixteen of the proteins identified were located in mitochondria and were involved in a number of key metabolic pathways. To verify our proteomics findings functionally, we performed NADH autofluorescence measurements and ATP production assays. The reduced expression of oxidative phosphorylation proteins in GPx1(-/-) mice following HR treatment resulted in loss of the mitochondrial membrane potential and decreased mitochondrial respiration. Mitochondrial ROS production and oxidative mtDNA damage were increased markedly during reoxygenation in GPx1(-/-) hearts. We also found morphological abnormalities in cardiac mitochondria and myocytes in HR-treated GPx1(-/-). This is the first report of the role of GPx1 in protecting cardiac mitochondria against reoxygenation damage in vivo. These findings will help clarify the mechanisms of HR injury and will aid in the development of antioxidant therapies to prevent cardiac mitochondrial dysfunction associated with reoxygenation.

Neuroprotective effect of Scutellaria baicalensis on spinal cord injury in rats

Inflammation has been known to play an important role in the pathogenesis after spinal cord injury (SCI). Microglia are activated after injury and produce a variety of proinflammatory factors such as tumor necrosis factor-alpha, interleukin-1beta, cyclooxygenase-2, and reactive oxygen species leading to apoptosis of neurons and oligodendrocytes. In this study, we examined the neuroprotective effects of total ethanol extract of Scutellaria baicalensis (EESB), after SCI. Using primary microglial cultures, EESB treatment significantly inhibited lipopolysaccharide-induced expression of such inflammatory mediators as tumor necrosis factor-alpha, IL-1beta, IL-6, cyclooxygenase-2, and inducible nitric oxide synthase. Furthermore, reactive oxygen species and nitric oxide production were significantly attenuated by EESB treatment. For in vivo study, rats that had received a moderate spinal cord contusion injury at T9 received EESB orally at a dose of 100 mg/kg. EESB inhibited expression of proinflammatory factors and protein carbonylation and nitration after SCI. EESB also inhibited microglial activation at 4 h after injury. Furthermore, EESB significantly inhibited apoptotic cell death of neurons and oligodendrocytes and improved functional recovery after SCI. Lesion cavity and myelin loss were also reduced following EESB treatment. Thus, our data suggest that EESB significantly improve functional recovery by inhibiting inflammation and oxidative stress after injury.

Mitochondrial superoxide production and respiratory activity: biphasic response to ischemic duration

Long bouts of ischemia are associated with electron transport chain deficits and increases in free radical production. In contrast, little is known regarding the effect of brief ischemia on mitochondrial function and free radical production. This study was undertaken to examine the relationship between the duration of ischemia, effects upon electron transport chain activities, and the mitochondrial production of free radicals. Rat hearts were subjected to increasing ischemic durations, mitochondria were isolated, and superoxide production and electron transport chain activities were measured. Results indicate that even brief ischemic durations induced a significant increase in superoxide production. This rate was maintained with ischemic durations less than 15 min, and then increased further with longer ischemic times. Mechanistically, brief ischemia was accompanied by an increase in NADH oxidase activity, reflected by a specific increase in complex IV activity. In contrast, longer ischemic durations were accompanied by a decrease in NADH oxidase activity, reflected by deficits in complexes I and IV activities.

Near infrared light protects cardiomyocytes from hypoxia and reoxygenation injury by a nitric oxide dependent mechanism

Photobiomodulation with near infrared light (NIR) provides cellular protection in various disease models. Previously, infrared light emitted by a low-energy laser has been shown to significantly improve recovery from ischemic injury of the canine heart. The goal of this investigation was to test the hypothesis that NIR (670 nm) from light emitting diodes produces cellular protection against hypoxia and reoxygenation-induced cardiomyocyte injury. Additionally, nitric oxide (NO) was investigated as a potential cellular mediator of NIR. Our results demonstrate that exposure to NIR at the time of reoxygenation protects neonatal rat cardiomyocytes and HL-1 cells from injury, as assessed by lactate dehydrogenase release and MTT assay. Similarly, indices of apoptosis, including caspase 3 activity, annexin binding and the release of cytochrome c from mitochondria into the cytosol, were decreased after NIR treatment. NIR increased NO in cardiomyocytes, and the protective effect of NIR was completely reversed by the NO scavengers carboxy-PTIO and oxyhemoglobin, but only partially blocked by the NO synthase (NOS) inhibitor L-NMMA. Mitochondrial metabolism, measured by ATP synthase activity, was increased by NIR, and NO-induced inhibition of oxygen consumption with substrates for complex I or complex IV was reversed by exposure to NIR. Taken together these data provide evidence for protection against hypoxia and reoxygenation injury in cardiomyocytes by NIR in a manner that is dependent upon NO derived from NOS and non-NOS sources.

Proteomic profiling of aging in the mouse heart: Altered expression of mitochondrial proteins

Using two-dimensional gel electrophoresis and liquid chromatography-tandem mass spectrometry, we have used a systems biology approach to study the molecular basis of aging of the mouse heart. We have identified 8 protein spots whose expression is up-regulated due to aging and 36 protein spots whose expression is down-regulated due to aging (p0.05 as judged by Wilcoxon Rank Sum test). Among the up-regulated proteins, we have characterized 5 protein spots and 2 of them, containing 3 different enzymes, are mitochondrial proteins. Among the down-regulated proteins, we have characterized 27 protein spots and 16 of them are mitochondrial proteins. Mitochondrial damage is believed to be a key factor in the aging process. Our current study provides molecular evidence at the level of the proteome for the alteration of structural and functional parameters of the mitochondria that contribute to impaired activity of the mouse heart due to aging.

The differential effects of superoxide anion, hydrogen peroxide and hydroxyl radical on cardiac mitochondrial oxidative phosphorylation

The involvement of reactive oxygen species (ROS) in cardiac ischemia-reperfusion injuries is well-established, but the deleterious effects of hydrogen peroxide (H(2)O(2)), hydroxyl radical (HO*) or superoxide anion (O(2)*(-) ) on mitochondrial function are poorly understood. Here, we report that incubation of rat heart mitochondria with each of these three species resulted in a decline of the ADP-stimulated respiratory rate but not substrate-dependent respiration. These three species reduced oxygen consumption induced by an uncoupler without alteration of the respiratory chain complexes, but did not modify mitochondrial membrane permeability. HO* slightly decreased F1F0-ATPase activity and HO* and O(2)*(-) partially inhibited the activity of adenine nucleotide translocase; H(2)O(2) failed to alter these targets. They inhibited NADH production by acting specifically on aconitase for O(2)*(-) and alpha-ketoglutarate dehydrogenase for H(2)O(2) and HO*. Our results show that O(2)*(-), H(2)O(2) and HO* act on different mitochondrial targets to alter ATP synthesis, mostly through inhibition of NADH production.

Keeping the engine primed: HIF factors as key regulators of cardiac metabolism and angiogenesis during ischemia

Myocardial ischemia, the most common cause of cardiac hypoxia in clinical medicine, occurs when oxygen delivery cannot meet myocardial metabolic requirements in the heart. This deficiency can result from either a reduced supply of oxygen (decreased coronary bloodflow) or an increased myocardial demand for oxygen (increased wall stress or afterload). Patients with stable coronary artery disease as well as patients experiencing acute myocardial infarction can experience episodes of severe ischemia. Although hypoxia is an obligatory component, it is not the sole environmental stress experienced by the ischemic heart. Reperfusion after ischemia is associated with increased oxidative stress as the heart reverts to aerobic respiration and thereby generates toxic levels of reactive oxygen species (ROS). During mild ischemia, mitochondrial function is partially compromised and substrate preferences adapt to sustain adequate ATP generation. With severe ischemia, mitochondrial function is markedly compromised and anaerobic metabolism must provide energy no matter what the cost in generation of toxic ROS adducts. Ischemia produces a variety of environmental stresses that impair cardiovascular function. As a result, multiple signaling pathways are activated in mammalian cells during ischemia/reperfusion injury in an attempt to minimize cellular injury and maintain cardiac output. Amongst the transcriptional regulators activated are members of the hypoxia inducible factor (HIF) transcription factor family. HIF factors regulate a variety of genes that affect a myriad of cellular processes including metabolism, angiogenesis, cell survival, and oxygen delivery, all of which are important in the heart. In this review, we will focus on the metabolic and angiogenic aspects of HIF biology as they relate to the heart during ischemia. We will review the metabolic requirements of the heart under normal as well as hypoxic conditions, the effects of preconditioning and its regulation as it pertains to HIF biology, the apparent roles of HIF-1 and HIF-2 in intermediary metabolism, and translational applications of HIF-1 and HIF-2 biology to cardiac angiogenesis. Increased understanding of the role of HIFs in cardiac ischemia will ultimately influence clinical cardiovascular practice.

Sequential opening of mitochondrial ion channels as a function of glutathione redox thiol status

Mitochondrial membrane potential (DeltaPsi(m)) depolarization contributes to cell death and electrical and contractile dysfunction in the post-ischemic heart. An imbalance between mitochondrial reactive oxygen species production and scavenging was previously implicated in the activation of an inner membrane anion channel (IMAC), distinct from the permeability transition pore (PTP), as the first response to metabolic stress in cardiomyocytes. The glutathione redox couple, GSH/GSSG, oscillated in parallel with DeltaPsi(m) and the NADH/NAD(+) redox state. Here we show that depletion of reduced glutathione is an alternative trigger of synchronized mitochondrial oscillation in cardiomyocytes and that intermediate GSH/GSSG ratios cause reversible DeltaPsi(m) depolarization, although irreversible PTP activation is induced by extensive thiol oxidation. Mitochondrial dysfunction in response to diamide occurred in stages, progressing from oscillations in DeltaPsi(m) to sustained depolarization, in association with depletion of GSH. Mitochondrial oscillations were abrogated by 4'-chlorodiazepam, an IMAC inhibitor, whereas cyclosporin A was ineffective. In saponin-permeabilized cardiomyocytes, the thiol redox status was systematically clamped at GSH/GSSG ratios ranging from 300:1 to 20:1. At ratios of 150:1-100:1, DeltaPsi(m) depolarized reversibly, and a matrix-localized fluorescent marker was retained; however, decreasing the GSH/GSSG to 50:1 irreversibly depolarized DeltaPsi(m) and induced maximal rates of reactive oxygen species production, NAD(P)H oxidation, and loss of matrix constituents. Mitochondrial GSH sensitivity was altered by inhibiting either GSH uptake, the NADPH-dependent glutathione reductase, or the NADH/NADPH transhydrogenase, indicating that matrix GSH regeneration or replenishment was crucial. The results indicate that GSH/GSSG redox status governs the sequential opening of mitochondrial ion channels (IMAC before PTP) triggered by thiol oxidation in cardiomyocytes.

beta1-Adrenoreceptor activation contributes to ischemia-reperfusion damage as well as playing a role in ischemic preconditioning

Protein kinase A (PKA) activation has been implicated in early-phase ischemic preconditioning. We recently found that during ischemia PKA activation causes inactivation of cytochrome-c oxidase (CcO) and contributes to myocardial damage due to ischemia-reperfusion. It may be that beta-adrenergic stimulation during ischemia via endogenous catecholamine release activates PKA. Thus beta-adrenergic stimulation may mediate both myocardial protection and damage during ischemia. The present studies were designed to determine the role of the beta(1)-adrenergic receptor (beta(1)-AR) in myocardial ischemic damage and ischemic preconditioning. Langendorff-perfused rabbit hearts underwent 30-min ischemia by anterior coronary artery ligation followed by 2-h reperfusion. Occlusion-reperfusion damage was evaluated by delineating the nonperfused volume of myocardium at risk and volume of myocardial necrosis after 2-h reperfusion. In some hearts ischemic preconditioning was accomplished by two 5-min episodes of global low-flow ischemia separated by 10 min before coronary occlusion-reperfusion. Orthogonal electrocardiograms were recorded, and coronary flow was monitored by a drip count. Three hearts from each experimental group were used to determine mitochondrial CcO and aconitase activities. Two-hour reperfusion after occlusion caused an additional decrease in CcO activity vs. that after 30-min occlusion alone. Blocking the beta(1)-AR during occlusion-reperfusion reversed CcO activity depression and preserved myocardium at risk for necrosis. Similarly, mitochondrial aconitase activity exhibited a parallel response after occlusion-reperfusion as well as for the other interventions. Furthermore, classic ischemic preconditioning had no effect on CcO depression. However, blocking the beta(1)-AR during preconditioning eliminated the cardioprotection. If the beta(1)-AR was blocked after preconditioning, the myocardium was preserved. Interestingly, in both of the latter cases the depression in CcO activity was reversed. Thus the beta(1)-AR plays a dual role in myocardial ischemic damage. Our findings may lead to therapeutic strategies for preserving myocardium at risk for infarction, especially in coronary reperfusion intervention.

Growth-hormone-releasing peptide 6 (GHRP6) prevents oxidant cytotoxicity and reduces myocardial necrosis in a model of acute myocardial infarction

Therapies aimed at enhancing cardiomyocyte survival following myocardial injury are urgently required. As GHRP6 [GH (growth hormone)-releasing peptide 6] has been shown to stimulate GH secretion and has beneficial cardiovascular effects, the aim of the present study was to determine whether GHRP6 administration reduces myocardial infarct size following acute coronary occlusion in vivo. Female Cuban Creole pigs were anaesthetized, monitored and instrumented to ensure a complete sudden left circumflex artery occlusion for 1 h, followed by a 72 h reperfusion/survival period. Animals were screened clinically before surgery and assigned randomly to receive either GHRP6 (400 μg/kg of body weight) or normal saline. Hearts were processed, and the area at risk and the infarct size were determined. CK-MB (creatine kinase MB) and CRP (C-reactive protein) levels and pathological Q-wave-affected leads were analysed and compared. Evaluation of the myocardial effect of GHRP6 also included quantitative histopathology, local IGF-I (insulin-growth factor-I) expression and oxidative stress markers. GHRP6 treatment did not have any influence on mortality during surgery associated with rhythm and conductance disturbances during ischaemia. Infarct mass and thickness were reduced by 78% and 50% respectively, by GHRP6 compared with saline (P<0.01). More than 50% of the GHRP6-treated pigs did not exhibit pathogological Q waves in any of the ECG leads. Quantitative histopathology and CK-MB and CRP serum levels confirmed the reduction in GHRP6-mediated necrosis (all P<0.05). Levels of oxidative stress markers suggested that GHRP6 prevented myocardial injury via a decrease in reactive oxygen species and by the preservation of antioxidant defence systems (all P<0.05). Myocardial IGF-I transcription was not amplified by GHRP6 treatment compared with the increase induced by the ischaemic episode in relation to expression in intact hearts (P<0.01). In conclusion, GHRP6 exhibits antioxidant effects which may partially contribute to reduce myocardial ischaemic damage.

Cardiac aging

Health care for the elderly in western society has emerged as an increasingly important economic and political issue in recent years. As the elderly proportion of western populations continues to expand, maintaining health and wellness of the aged will continue to be an important research priority in the near future. This review will attempt to briefly highlight what is known about age-related changes in cardiac performance in humans, then focus on recent work on cellular mechanisms of cardiac deterioration in vertebrate models. The final section will discuss the implications of work done in the nascent fruit fly model system for aging cardiac function and conclude by outlining potential future uses for invertebrate cardiac model systems.

Purification and properties of glutathione reductase from liver of the anoxia-tolerant turtle, Trachemys scripta elegans

Glutathione reductase (GR) is a homodimeric flavoprotein that catalyzes the reduction of oxidized glutathione (GSSG) using NADPH as a cofactor. The enzyme is a major component of cellular defense mechanisms against oxidative injury. In this study, GR was purified from the liver of the anoxia-tolerant turtle, Trachemys scripta elegans. The overall fold purifications were 13.3- and 12.1-fold with final specific activities of 5.5 and 1.44 U/mg of protein for control and anoxic turtle GR, respectively. SDS-PAGE of purified turtle liver GR showed a single protein band at approximately 55 kDa. Reverse phase HPLC of turtle GR revealed a single peak that had the same retention time as yeast GR. No new isoform of GR was detected in liver of T. s. elegans during anoxia. The K (m) values of turtle GR for GSSG and NADPH was 44.6 and 6.82 microM, respectively, suggesting a substantially higher affinity of turtle GR toward GSSG than most other vertebrates. Unlike other human GR, NADP(+ )did not inhibit turtle GR activity. The activation energy of turtle GR, calculated from the slope of the Arrhenius plot, was 32.2 +/- 2.64 kJ/mol. Turtle GR had high activity under a broad pH range (having activity between pHs 4 and 10; optimal activity at pH 6.5) and the enzyme maintains activity under the pH drop that occurs under anoxic conditions. The high affinity of turtle GR suggests that turtles have high redox buffering capacity of tissues to protect against oxidative stress encountered during anoxia/reoxygenation.

HFE mutations and risk of coronary heart disease in middle-aged women

BACKGROUND

Although heterozygosity for the C282Y mutation in the HFE gene has been associated with an increased risk of cardiovascular events, epidemiological studies remain inconclusive. The aim of the present study was to obtain further evidence as to whether HFE mutations are associated with risk of coronary heart disease (CHD) in middle-aged women. We used data of a cohort of 15 236 Dutch middle-aged women to investigate whether C282Y carriers and H63D carriers are at increased risk of coronary heart disease compared with non-carriers.

MATERIALS AND METHODS

Women were included in the study between 1993 and 1997 and were followed until 1 January 2000 for cardiovascular events. HFE genotyping was performed on all 211 coronary heart disease cases and a randomly selected sample from the baseline cohort (n = 1526). A weighted Cox proportional hazards model was used to estimate crude, age-adjusted and multivariate adjusted hazard ratios for C282Y and H63D carriership in relation to coronary heart disease.

RESULTS

Compared with non-carriers, those that carried the C282Y allele were not at increased risk for CHD (HR = 1.25, 95% CI = 0.74-2.09). Neither did we find an association between the H63D mutation and CHD risk (HR = 0.73, 95% CI = 0.43-1.24).

CONCLUSIONS

Our results are in accordance with similar studies to date, for which we present a meta-analysis. HFE mutations appear not to affect the risk of coronary heart disease.

Alterations in mitochondrial and cytosolic methionine sulfoxide reductase activity during cardiac ischemia and reperfusion

During cardiac ischemia/reperfusion, proteins are targets of reactive oxygen species produced by the mitochondrial respiratory chain resulting in the accumulation of oxidatively modified protein. Sulfur-containing amino acids are among the most sensitive to oxidation. Certain cysteine and methionine oxidation products can be reversed back to their reduced form within proteins by specific repair enzymes. Oxidation of methionine in protein produces methionine-S-sulfoxide and methionine-R-sulfoxide that can be catalytically reduced by two stereospecific enzymes, methionine sulfoxide reductases A and B, respectively. Due to the importance of the methionine sulfoxide reductase system in the maintenance of protein structure and function during conditions of oxidative stress, the fate of this system during ischemia/reperfusion was investigated. Mitochondrial and cytosolic methionine sulfoxide reductase activities are decreased during ischemia and at early times of reperfusion, respectively. Partial recovery of enzyme activity was observed upon extended periods of reperfusion. Evidence indicates that loss in activity is not due to a decrease in the level of MsrA but may involve structural modification of the enzyme.

Preconditioning prevents loss in mitochondrial function and release of cytochrome c during prolonged cardiac ischemia/reperfusion

Loss in mitochondrial function and induction of mitochondrial-mediated apoptosis occur as a result of cardiac ischemia/reperfusion. Brief and repeated cycles of ischemia/reperfusion, termed ischemic preconditioning, prevent or minimize contractile dysfunction and apoptosis associated with prolonged episodes of cardiac ischemia and reperfusion. The effects of preconditioning on various indices of ischemia/reperfusion-induced alterations in mitochondrial function and structure were therefore explored. Utilizing an in vivo rat model data is provided indicating that preconditioning completely prevents cardiac ischemia/reperfusion-induced: (1) loss in the activity of the redox sensitive Krebs cycle enzyme alpha-ketoglutarate dehydrogenase; (2) declines in NADH-linked ADP-dependent mitochondrial respiration; (3) insertion of the pro-apoptotic Bcl-2 protein Bax into the mitochondrial membrane; and (4) release of cytochrome c into the cytosol. The results of the current study indicate that preconditioning prevents specific alterations in mitochondrial structure and function that are known to impact cellular viability and provide insight into the collective benefits of preconditioning.

Protective effects of melatonin in experimental free radical-related ocular diseases

Melatonin (N-acetyl-5-methoxytryptamine) is an indoleamine with a range of antioxidative properties. Melatonin is endogenously produced in the eye and in other organs. Current evidence suggests that melatonin may act as a protective agent in ocular conditions such as photo-keratitis, cataract, glaucoma, retinopathy of prematurity and ischemia/reperfusion injury. These diseases are sight-threatening and they currently remain, for the most part, untreatable. The pathogenesis of these conditions is not entirely clear but oxidative stress has been proposed as one of the causative factors. Elevated levels of various reactive oxygen and nitrogen species have been identified in diseased ocular structures. These reactants damage the structure and deplete the eye of natural defense systems, such as the antioxidant, reduced glutathione, and the antioxidant enzyme superoxide dismutase. Oxidative damage in the eye leads to apoptotic degeneration of retinal neurons and fluid accumulation. Retinal degeneration decreases visual sensitivity and even a small change in the fluid content of the cornea and crystalline lens is sufficient to disrupt ocular transparency. In the eye, melatonin is produced in the retina and in the ciliary body. Continuous regeneration of melatonin in the eye offers a frontier antioxidative defense for both the anterior and posterior eye. However, melatonin production is minimal in newborns and its production gradually wanes in aging individuals as indicated by the large drop in circulating blood concentrations of the indoleamine. These individuals are possibly at risk of contracting degenerative eye diseases that are free radical-based. Supplementation with melatonin, a potent antioxidant, in especially the aged population should be considered as a prophylaxis to preserve visual functions. It may benefit many individuals worldwide, especially in countries where access to medical facilities is limited.

Targeting an antioxidant to mitochondria decreases cardiac ischemia-reperfusion injury

Mitochondrial oxidative damage contributes to a wide range of pathologies, including cardiovascular disorders and neurodegenerative diseases. Therefore, protecting mitochondria from oxidative damage should be an effective therapeutic strategy. However, conventional antioxidants have limited efficacy due to the difficulty of delivering them to mitochondria in situ. To overcome this problem, we developed mitochondria-targeted antioxidants, typified by MitoQ, which comprises a lipophilic triphenylphosphonium (TPP) cation covalently attached to a ubiquinol antioxidant. Driven by the large mitochondrial membrane potential, the TPP cation concentrates MitoQ several hundred-fold within mitochondria, selectively preventing mitochondrial oxidative damage. To test whether MitoQ was active in vivo, we chose a clinically relevant form of mitochondrial oxidative damage: cardiac ischemia-reperfusion injury. Feeding MitoQ to rats significantly decreased heart dysfunction, cell death, and mitochondrial damage after ischemia-reperfusion. This protection was due to the antioxidant activity of MitoQ within mitochondria, as an untargeted antioxidant was ineffective and accumulation of the TPP cation alone gave no protection. Therefore, targeting antioxidants to mitochondria in vivo is a promising new therapeutic strategy in the wide range of human diseases such as Parkinson's disease, diabetes, and Friedreich's ataxia where mitochondrial oxidative damage underlies the pathology.

Reversible redox-dependent modulation of mitochondrial aconitase and proteolytic activity during in vivo cardiac ischemia/reperfusion

Prooxidents can induce reversible inhibition or irreversible inactivation and degradation of the mitochondrial enzyme aconitase. Cardiac ischemia/reperfusion is associated with an increase in mitochondrial free radical production. In the current study, the effects of reperfusion-induced production of prooxidants on mitochondrial aconitase and proteolytic activity were determined to assess whether alterations represented a regulated response to changes in redox status or oxidative damage. Evidence is provided that ATP-dependent proteolytic activity increased during early reperfusion followed by a time-dependent reduction in activity to control levels. These alterations in proteolytic activity paralleled an increase and subsequent decrease in the level of oxidatively modified protein. In vitro data supports a role for prooxidants in the activation of ATP-dependent proteolytic activity. Despite inhibition during early periods of reperfusion, aconitase was not degraded under the conditions of these experiments. Aconitase activity exhibited a decline in activity followed by reactivation during cardiac reperfusion. Loss and regain in activity involved reversible sulfhydryl modification. Aconitase was found to associate with the iron binding protein frataxin exclusively during reperfusion. In vitro, frataxin has been shown to protect aconitase from [4Fe-4S](2+) cluster disassembly, irreversible inactivation, and, potentially, degradation. Thus, the response of mitochondrial aconitase and ATP-dependent proteolytic activity to reperfusion-induced prooxidant production appears to be a regulated event that would be expected to reduce irreparable damage to the mitochondria.

A mitochondrial oscillator dependent on reactive oxygen species

We describe a unique mitochondrial oscillator that depends on oxidative phosphorylation, reactive oxygen species (ROS), and mitochondrial inner membrane ion channels. Cell-wide synchronized oscillations in mitochondrial membrane potential (Delta Psi(m)), NADH, and ROS production have been recently described in isolated cardiomyocytes, and we have hypothesized that the balance between superoxide anion efflux through inner membrane anion channels and the intracellular ROS scavenging capacity play a key role in the oscillatory mechanism. Here, we formally test the hypothesis using a computational model of mitochondrial energetics and Ca(2+) handling including mitochondrial ROS production, cytoplasmic ROS scavenging, and ROS activation of inner membrane anion flux. The mathematical model reproduces the period and phase of the observed oscillations in Delta Psi(m), NADH, and ROS. Moreover, we experimentally verify model predictions that the period of the oscillator can be modulated by altering the concentration of ROS scavengers or the rate of oxidative phosphorylation, and that the redox state of the glutathione pool oscillates. In addition to its role in cellular dysfunction during metabolic stress, the period of the oscillator can be shown to span a wide range, from milliseconds to hours, suggesting that it may also be a mechanism for physiological timekeeping and/or redox signaling.

Differential sensitivity of Kir2 inward-rectifier potassium channels to a mitochondrial uncoupler: identification of a regulatory site

The aim of this study was to gain insight into the mechanism by which members of the K(ir)2 subfamily are differentially sensitive to agents that inhibit mitochondrial function by identifying responsible site(s) in K(ir)2 proteins. K(ir)2 channels were expressed in Xenopus laevis oocytes and assayed by two-electrode voltage clamp and patch clamp. Incubation of oocytes in carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP), a mitochondrial uncoupler, inhibited K(ir)2.2 and K(ir)2.3, but not K(ir)2.1. Replacement of the first 44 amino acids of K(ir)2.2 the or of first 19 K(ir)2.3 with the first 45 of K(ir)2.1 did not affect the sensitivity of the channels to FCCP. In contrast, a larger substitution of K(ir)2.1 N-terminal sequence (1-78) into K(ir)2.2 or K(ir)2.3 produced channels that were resistant to FCCP. Sequence alignment between residues 46 and 78 (K(ir)2.1 numbering) revealed four residues that are the same in K(ir)2.2 and K(ir)2.3 but different in K(ir)2.1. Each of these four residues in the resistant chimera was converted back to the K(ir)2.2/K(ir)2.3 amino acid. Three of the mutants (D51N, I59A, and G65S) were not sensitive to FCCP, but the H53Q mutant was sensitive. K(ir)2.1-H53A and K(ir)2.1-H53E were also sensitive. In contrast, K(ir)2.1-H53R and K(ir)2.1-H53K were recovered during resistant. K(ir)2.2 and K(ir)2.3 currents perfusion of inside-out patches from FCCP-treated oocytes. FCCP was without effect on K(ir)2.2 and K(ir)2.3 when applied directly to inside-out patches. Together, these results suggest inhibition of K(ir)2.2 and K(ir)2.3 by a ligand that bears a positive charge and is produced by an intracellular action of FCCP.

PPAR-gamma activation fails to provide myocardial protection in ischemia and reperfusion in pigs

Peroxisome proliferator-activated receptor (PPAR)-gamma modulates substrate metabolism and inflammatory responses. In experimental rats subjected to myocardial ischemia-reperfusion (I/R), thiazolidinedione PPAR-gamma activators reduce infarct size and preserve left ventricular function. Troglitazone is the only PPAR-gamma activator that has been shown to be protective in I/R in large animals. However, because troglitazone contains both alpha-tocopherol and thiazolidinedione moieties, whether PPAR-gamma activation per se is protective in myocardial I/R in large animals remains uncertain. To address this question, 56 pigs were treated orally for 8 wk with troglitazone (75 mg x kg(-1) x day(-1)), rosiglitazone (3 mg x kg(-1) x day(-1)), or alpha-tocopherol (73 mg x kg(-1) x day(-1), equimolar to troglitazone dose) or received no treatment. Pigs were then anesthetized and subjected to 90 min of low-flow regional myocardial ischemia and 90 min of reperfusion. Myocardial expression of PPAR-gamma, determined by ribonuclease protection assay, increased with troglitazone and rosiglitazone compared with no treatment. Rosiglitazone had no significant effect on myocardial contractile function (Frank-Starling relations), substrate uptake, or expression of proinflammatory cytokines during I/R compared with untreated pigs. In contrast, preservation of myocardial contractile function and lactate uptake were greater and cytokine expression was attenuated in pigs treated with troglitazone or alpha-tocopherol compared with untreated pigs. Multivariate analysis indicated that presence of an alpha-tocopherol, but not a thiazolidinedione, moiety in the test compound was significantly related to greater contractile function and lactate uptake and lower cytokine expression during I/R. We conclude that PPAR-gamma activation is not protective in a porcine model of myocardial I/R. Protective effects of troglitazone are attributable to its alpha-tocopherol moiety. These findings, in conjunction with prior rat studies, suggest interspecies differences in the response to PPAR-gamma activation in the heart.

Inhibition of Cardiac Mitochondrial Respiration by Salicylic Acid and Acetylsalicylate

Acetylsalicylate, the active ingredient in aspirin, has been shown to be beneficial in the treatment and prevention of cardiovascular disease. Because of the increasing frequency with which salicylates are used, it is important to more fully characterize extra- and intracellular processes that are altered by these compounds. Evidence is provided that treatment of isolated cardiac mitochondria with salicylic acid and to a lesser extent acetylsalicylate resulted in an increase in the rate of uncoupled respiration. In contrast, both compounds inhibited ADP-dependent NADH-linked (state 3) respiration to similar degrees. Under the conditions of our experiments, loss in state 3 respiration resulted from inhibition of the Krebs cycle enzyme alpha-ketoglutarate dehydrogenase (KGDH). Kinetic analysis indicates that salicylic acid acts as a competitive inhibitor at the alpha-ketoglutarate binding site. In contrast, acetylsalicylate inhibited the enzyme in a noncompetitive fashion consistent with interaction with the alpha-ketoglutarate binding site followed by enzyme-catalyzed acetylation. The effects of salicylic acid and acetylsalicylate on cardiac mitochondrial function may contribute to the known cardioprotective effects of therapeutic doses of aspirin, as well as to the toxicity associated with salicylate overdose.

Calcium, ATP, and ROS: a mitochondrial love-hate triangle

The mitochondrion is at the core of cellular energy metabolism, being the site of most ATP generation. Calcium is a key regulator of mitochondrial function and acts at several levels within the organelle to stimulate ATP synthesis. However, the dysregulation of mitochondrial Ca2+homeostasis is now recognized to play a key role in several pathologies. For example, mitochondrial matrix Ca2+overload can lead to enhanced generation of reactive oxygen species, triggering of the permeability transition pore, and cytochrome c release, leading to apoptosis. Despite progress regarding the independent roles of both Ca2+and mitochondrial dysfunction in disease, the molecular mechanisms by which Ca2+can elicit mitochondrial dysfunction remain elusive. This review highlights the delicate balance between the positive and negative effects of Ca2+and the signaling events that perturb this balance. Overall, a “two-hit” hypothesis is developed, in which Ca2+plus another pathological stimulus can bring about mitochondrial dysfunction.

Oxygen free radicals and redox biology of organelles

The presence and supposed roles of reactive oxygen species (ROS) were reported in literature in a myriad of instances. However, the breadth and depth of their involvement in cellular physiology and pathology, as well as their relationship to the redox environment can only be guessed from specialized reports. Whatever their circumstances of formation or consequences, ROS seem to be conspicuous components of intracellular milieu. We sought to verify this assertion, by collecting the available evidence derived from the most recent publications in the biomedical field. Unlike other reviews with similar objectives, we centered our analysis on the subcellular compartments, namely on organelles, grouped according to their major functions. Thus, plasma membrane is a major source of ROS through NAD(P)H oxidases located on either side. Enzymes of the same class displaying low activity, as well as their components, are also present free in cytoplasm, regulating the actin cytoskeleton and cell motility. Mitochondria can be a major source of ROS, mainly in processes leading to apoptosis. The protein synthetic pathway (endoplasmic reticulum and Golgi apparatus), including the nucleus, as well as protein turnover, are all exquisitely sensitive to ROS-related redox conditions. The same applies to the degradation pathways represented by lysosomes and peroxisomes. Therefore, ROS cannot be perceived anymore as a mere harmful consequence of external factors, or byproducts of altered cellular metabolism. This may explain why the indiscriminate use of anti-oxidants did not produce the expected "beneficial" results in many medical applications attempted so far, underlying the need for a deeper apprehension of the biological roles of ROS, particularly in the context of the higher cellular order of organelles.

Role of oxidative stress in neurodegeneration: recent developments in assay methods for oxidative stress and nutraceutical antioxidants

Reactive oxygen species (ROS) are produced in the course of normal metabolism and they serve important physiological functions. However, because of their high reactivity, accumulation of ROS beyond the immediate needs of the cell may affect cellular structure and functional integrity, by bringing about oxidative degradation of critical molecules, such as the DNA, proteins, and lipids. Although cells possess an intricate network of defense mechanisms to neutralize excess ROS and reduce oxidative stress, some tissues, especially the brain, are much more vulnerable to oxidative stress because of their elevated consumption of oxygen and the consequent generation of large amounts of ROS. For the same reason, the mitochondrial DNA (mtDNA) of brain cells is highly susceptible to structural alterations resulting in mitochondrial dysfunction. Several lines of evidence strongly suggest that these effects of ROS may be etiologically related to a number of neurodegenerative disorders. Nutraceutical antioxidants are dietary supplements that can exert positive pharmacological effects on specific human diseases by neutralizing the negative effects of ROS. The present communication concentrates on a review of recent concepts and methodological developments, some of them based on the results of work from our own laboratory, on the following aspects: (1) the complex interactions and complementary interrelationships between oxidative stress, mitochondrial dysfunction, and various forms of neural degeneration; (2) fractionation and isolation of substances with antioxidant properties from plant materials, which are extensively used in the human diet and, therefore, can be expected to be less toxic in any pharmacological intervention; (3) recent developments in methodologies that can be used for the assay of oxidative stress and determination of biological activities of exogenous and endogenous antioxidants; and (4) presentation of simple procedures based on polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) of the resulting amplicon for investigations of structural alterations in mtDNA.