Mechanism of depression in cardiac sarcolemmal Na+-K+-ATPase by hypochlorous acid

Modification of Ischemia/Reperfusion-Induced Alterations in Subcellular Organelles by Ischemic Preconditioning

It is now well established that ischemia/reperfusion (I/R) injury is associated with the compromised recovery of cardiac contractile function. Such an adverse effect of I/R injury in the heart is attributed to the development of oxidative stress and intracellular Ca²⁺-overload, which are known to induce remodeling of subcellular organelles such as sarcolemma, sarcoplasmic reticulum, mitochondria and myofibrils. However, repeated episodes of brief periods of ischemia followed by reperfusion or ischemic preconditioning (IP) have been shown to improve cardiac function and exert cardioprotective actions against the adverse effects of prolonged I/R injury. This protective action of IP in attenuating myocardial damage and subcellular remodeling is likely to be due to marked reductions in the occurrence of oxidative stress and intracellular Ca²⁺-overload in cardiomyocytes. In addition, the beneficial actions of IP have been attributed to the depression of proteolytic activities and inflammatory levels of cytokines as well as the activation of the nuclear factor erythroid factor 2-mediated signal transduction pathway. Accordingly, this review is intended to describe some of the changes in subcellular organelles, which are induced in cardiomyocytes by I/R for the occurrence of oxidative stress and intracellular Ca²⁺-overload and highlight some of the mechanisms for explaining the cardioprotective effects of IP.

Involvement of Oxidative Stress in the Development of Subcellular Defects and Heart Disease

It is now well known that oxidative stress promotes lipid peroxidation, protein oxidation, activation of proteases, fragmentation of DNA and alteration in gene expression for producing myocardial cell damage, whereas its actions for the induction of fibrosis, necrosis and apoptosis are considered to result in the loss of cardiomyocytes in different types of heart disease. The present article is focused on the discussion concerning the generation and implications of oxidative stress from various sources such as defective mitochondrial electron transport and enzymatic reactions mainly due to the activation of NADPH oxidase, nitric oxide synthase and monoamine oxidase in diseased myocardium. Oxidative stress has been reported to promote excessive entry of Ca²⁺ due to increased permeability of the sarcolemmal membrane as well as depressions of Na⁺-K⁺ ATPase and Na⁺-Ca²⁺ exchange systems, which are considered to increase the intracellular of Ca²⁺. In addition, marked changes in the ryanodine receptors and Ca²⁺-pump ATPase have been shown to cause Ca²⁺-release and depress Ca²⁺ accumulation in the sarcoplasmic reticulum as a consequence of oxidative stress. Such alterations in sarcolemma and sarcoplasmic reticulum are considered to cause Ca²⁺-handling abnormalities, which are associated with mitochondrial Ca²⁺-overload and loss of myofibrillar Ca²⁺-sensitivity due to oxidative stress. Information regarding the direct effects of different oxyradicals and oxidants on subcellular organelles has also been outlined to show the mechanisms by which oxidative stress may induce Ca²⁺-handling abnormalities. These observations support the view that oxidative stress plays an important role in the genesis of subcellular defects and cardiac dysfunction in heart disease.

Effects of Alprazolam and Melatonin Used for Premedication on Oxidative Stress, Glicocalyx Integrity and Neurocognitive Functions

Objective

The purpose of this investigation was to compare the effect of alprazolam and melatonin on oxidative stress, glicocalyx integrity and neurocognitive function in patients undergoing coronary artery bypass grafting (CABG).

Methods

Overall, 42 patients undergoing CABG were retrospectively included in this study. Blood samples which preserved at -70°C for a previous study were used for this study. The participants were divided into two groups. Patients in the Group A were administered alprazolam before the operation, whereas melatonin was used for premedication in the Group M. Blood samples were collected at three time points [T0: before anaesthesia induction, T1: admittance to intensive care unit (ICU), T2: 24 h after ICU admission], and oxidative stress parameters and glicocalyx integrity were evaluated. Furthermore, Mini-Mental State Examination was recorded to measure neurocognitive function.

Results

The total thiol levels which were measured as an antioxidant parameter were significantly higher, and free Hb values were significantly lower in the Group M compared to the Group A (p<0.05). No significant differences were found in order to oxidative stress parameter levels, extubation time, length of hospital stay, durations of cross-clamp, cardiopulmonary bypass and operation and Mini-Mental State Examination results between the two groups (p>0.05).

Conclusion

In light of positive effects on oxidatif stress parameters, melatonin may be considered as a good and safe premedication agent with its anxiolytic, antioxidant and minimal haemodynamic and respiratory effects.

Effects of Off-Pump Versus On-Pump Coronary Artery Bypass Grafting: Apoptosis, Inflammation, and Oxidative Stress

<strong>Background</strong>: It has been suggested that off-pump coronary<br />artery bypass grafting (CABG) surgery reduces myocardial<br />ischemia-reperfusion injury, postoperative systemic<br />inflammatory response, and oxidative stress. The aim of this<br />study was to measure serum malondialdehyde (MDA), highsensitivity<br />C-reactive protein (hs-CRP), M30, and M65 levels<br />and to investigate the relationship between M30 levels and<br />oxidative stress and inflammation in patients undergoing onand<br />off-pump CABG surgery.<br /><strong>Methods</strong>: Fifty patients were randomly assigned to onpump<br />or off-pump CABG surgery (25 patients off-pump and<br />25 on-pump CABG surgery), and blood samples were collected<br />prior to surgery, and 30 minutes, 60 minutes, 6 hours,<br />and 24 hours after CABG surgery.<br /><strong>Results</strong>: Compared to the on-pump group, serum MDA<br />levels at 30 minutes, 60 minutes, 6 hours, and 24 hours after<br />the CABG surgery were significantly lower in the off-pump<br />group (P = .001, P = .001, P = .001, and P = .001, respectively).<br />Serum M30 levels were found to be elevated in both groups,<br />returning to baseline at 24 hours. When compared to baseline,<br />the hs-CRP level reached its peak at 24 hours at 13.28 ±<br />5.32 mg/dL in the on-pump group, and 15.44 ± 4.02 mg/dL<br />in the off-pump group.<br /><strong>Conclusion</strong>: CABG surgery is associated with an increase<br />in inflammatory markers and serum M30 levels, indicating<br />epithelial/endothelial apoptosis in the early period.

Heart protective effects and mechanism of quercetin preconditioning on anti-myocardial ischemia reperfusion (IR) injuries in rats

In this study, we investigated the effects and mechanism of quercetin preconditioning on anti-myocardial ischemia reperfusion (IR) injuries in vivo. Meanwhile, their potential anti-oxidative stress and anti-inflammation effect were assessed. SD rats were orally given quercetin 250 mg/kg. Myocardium apoptosis was determined with TUNEL staining. The biomarkers related to myocardial ischemia injury were determined. Simultaneously, hemodynamic parameters were monitored as left ventricular systolic pressure (LVSP), LV end-diastolic pressure (LVEDP) and maximal rate of increase and decrease of left ventricular pressure (dP/dtmax). The oxidative stress indicators and inflammatory factors were also evaluated. Western blot method was used for analysis of PI3K, Akt, p-Akt, Bax and Bcl-2 protein expressions. The results showed that quercetin significantly reduced apoptosis rate, improved cardiac function, decreased levels of creatine kinase (CK), aspartate aminotransferase (AST) and lactate dehydrogenase (LDH). Quercetin also restrained the oxidative stress related to myocardial ischemia injury as evidenced by decreased malondialdehyde (MDA), and elevated GSH, superoxide dismutase (SOD), catalase (CAT), glutathione-peroxidase (GSH-Px), glutathione reductase (GR) activity. Meanwhile, the inflammatory cascade was inhibited as evidenced by decreased cytokines such as tumor necrosis factor-α (TNF-α), C-reactive protein (CRP) and interleukin-1β (IL-1β). Our results still showed that quercetin pretreatment significantly inhibited the apoptosis by decreasing the number of apoptotic cells, decreasing the level of cleaved Bax, and increasing the level of Bcl-2 in rats subjected to I/R injury. Simultaneously, quercetin pretreatment markedly increased the phosphorylation of Akt. Blockade of PI3K activity by LY294002, dramatically abolished its anti-apoptotic effect and lowered Akt phosphorylation level. It can be concluded that quercetin pretreatment was protected against myocardium IR injury by decreasing oxidative stress, repressing inflammatory cascade, inhibiting apoptosis in vivo and PI3K/Akt pathway involved in the anti-apoptotic effect.

Beta-thromboglobulin as a marker of perioperative myocardial infarction in patients undergoing coronary artery bypass grafting following aspirin discontinuation

Perioperative myocardial infarction (PMI) following coronary artery bypass grafting (CABG) is associated with significant morbidity and mortality. The aim of this study was to assess platelet activation and oxidative stress in the setting of PMI in patients undergoing CABG. We studied 108 consecutive patients who stopped taking low-dose aspirin 7-10 days prior to elective isolated on- or off-pump CABG. β-thromboglobulin (β-TG), thromboxane B2 (TXB2) and 8-iso-prostaglandin F2α (8-iso-PGF2α), a marker of oxidative stress, were measured at the baseline and 5-7 days postoperatively. Aspirin (150 mg/d) was administered every morning since 12 hours after CABG. Mean baseline β-TG was 58.5 ± 10.3 IU/ml, TXB2 was 143.6 ± 28.5 ng/ml and 8-iso-PGF2α was 355.2 ± 40.7 pg/ml. Postoperatively, after administration of 4-6 doses of aspirin, β-TG increased by 16.7% and 8-iso-PGF2α increased by 17.2% 5-7 days after surgery (p = 0.005 and p < 0.001, respectively). TXB2 decreased by 99.7% to 410.3 ± 52.1 pg/ml (p < 0.001). Nine patients (8.3%) developed PMI. Baseline β-TG and TXB2, together with postoperative β-TG and 8-iso-PGF2α were higher in PMI patients than in the remaining subjects (all, p < 0.05). Multivariate analysis showed that baseline β-TG (OR: 1.28; 95% CI: 1.05-1.57, p = 0.015) was the only independent predictor of PMI. In conclusion, we demonstrated that increased platelet activation and thromboxane production, observed in patients not taking aspirin till the day of CABG, contribute to the occurrence of PMI in early postoperative period.

The effect of preoperative melatonin on nuclear erythroid 2-related factor 2 activation in patients undergoing coronary artery bypass grafting surgery

During and after coronary artery bypass grafting (CABG), oxidative stress occurs. Finding an effective way to improve antioxidant response is important in CABG surgery. It has been shown that patients with coronary heart disease have a low Melatonin production rate. The present study aimed to investigate the effects of Melatoninon nuclear erythroid 2-related factor 2(Nrf2) activity in patients undergoing CABG surgery. Thirty volunteers undergoing CABG were randomized to receive 10 mg oral Melatonin (Melatonin group, n = 15) or placebo (placebo group, n = 15) before sleeping for 1 month before surgery. The activated Nrf2 was measured twice by DNA-based ELISA method in the nuclear extract of peripheral blood mononuclear cells of patients before aortic clumps and 45 minutes after CABG operation. Melatonin administration was associated with a significant increase in both plasma levels of Melatonin and Nrf2 concentration in Melatonin group compared to placebo group, respectively (15.2 ± 4.6 pmol/L, 0.28 ± 0.01 versus 1.1 ± 0.59 pmol/L, 0.20 ± 0.07, P < 0.05). The findings of the present study provide preliminary data suggesting that Melatonin may play a significant role in the potentiation of the antioxidant defense and attenuate cellular damages resulting from CABG surgery via theNrf2 pathway.

Lipid oxidation by hypochlorous acid: chlorinated lipids in atherosclerosis and myocardial ischemia

Leukocytes, containing myeloperoxidase (MPO), produce the reactive chlorinating species, HOCl, and they have important roles in the pathophysiology of cardiovascular disease. Leukocyte-derived HOCl can target primary amines, alkenes and vinyl ethers of lipids, resulting in chlorinated products. Plasmalogens are vinyl ether-containing phospholipids that are abundant in tissues of the cardiovascular system. The HOCl oxidation products derived from plasmalogens are α-chlorofatty aldehyde and unsaturated molecular species of lysophosphatidylcholine. α-chlorofatty aldehyde is the precursor of both α-chlorofatty alcohol and α-chlorofatty acid. Both α-chlorofatty aldehyde and α-chlorofatty acid accumulate in activated neutrophils and have disparate chemotactic properties. In addition, α-chlorofatty aldehyde increases in activated monocytes, human atherosclerotic lesions and rat infarcted myocardium. This article addresses the pathways for the synthesis of these lipids and their biological targets.

Phospholipase C as a potential target for cardioprotection during oxidative stressThis review is one of a selection of papers published in a Special Issue on Oxidative Stress in Health and Disease

Cardiac dysfunction due to ischemia–reperfusion (I/R) is associated with marked changes in membrane function and subsequent Ca2+-handling abnormalities in cardiomyocytes. The membrane abnormalities in hearts subjected to I/R arise primarily from oxidative stress as a consequence of increased formation of reactive oxygen species and other oxidants, as well as reduced antioxidant defenses. Little is known, however, about the nature and mechanisms of the sarcolemmal membrane changes with respect to phospholipase C (PLC)-related signaling events. In addition, the mechanisms involved in protection of the postischemic myocardium and in ischemic preconditioning with respect to PLC function need to be established. Accordingly, this article reviews the historical and current information on PLC-mediated signal transduction mechanisms in I/R, as well as outlining future directions that should be addressed. Such information will extend our knowledge of ischemic heart disease and help improve its therapy.

Potential role and mechanisms of subcellular remodeling in cardiac dysfunction due to ischemic heart disease

Several studies have revealed varying degrees of changes in sarcoplasmic reticular and myofibrillar activities, protein content, gene expression and intracellular Ca-handling during cardiac dysfunction due to ischemia-reperfusion (I/R); however, relatively little is known about the sarcolemmal and mitochondrial alterations, as well as their mechanisms in the I/R hearts. Because I/R is associated with oxidative stress and intracellular Ca-overload, it has been indicated that changes in subcellular activities, protein content and gene expression due to I/R are related to both oxidative stress and Ca-overload. Intracellular Ca-overload appears to induce changes in subcellular activities, protein contents and gene expression (subcellular remodeling) by activation of proteases and phospholipases, as well as by affecting the genetic apparatus, whereas oxidative stress is considered to cause oxidation of functional groups of different subcellular proteins in addition to modifying the genetic machinery. Ischemic preconditioning, which is known to depress the development of both intracellular Ca-overload and oxidative stress due to I/R, was observed to attenuate the I/R-induced subcellular remodeling and improve cardiac performance. It is suggested that a combination therapy with antioxidants and interventions, which reduce the development of intracellular Ca-overload, may improve cardiac function by preventing or attenuating the occurrence of subcellular remodeling due to ischemic heart disease. It is proposed that defects in the activities of subcellular organelles may serve as underlying mechanisms for I/R-induced cardiac dysfunction under acute conditions, whereas subcellular remodeling due to alterations in gene expression may explain the impaired cardiac performance under chronic conditions of I/R.

2,3-Butanedione monoxime does not protect cardiomyocytes under oxidative stress

Heart muscle ischemia-reperfusion provokes a pronounced cardiomyocyte oxidative stress. In the present study, we examined a possible protective effect of the cardioprotective drug, 2,3-butanedione monoxime (BDM), on the cultured neonatal cardiac myocytes exposed to oxidative stress induced by hypochlorous acid (HOCl), that may be formed by activated polymorphonuclear neutrophils in myocardium ischemic-reperfusion areas, and a useful model oxidant, tert-butyl hydroperoxide (tBHP). Using isolated rat cardiomyocytes substantial cytotoxicity of HOCl and tBHP was demonstrated: The concentrations of HOCl and tBHP causing a 50% decrease of cardiomyocyte cell viability were estimated to be 55 +/- 5 microM and 36 +/- 6 microM, respectively. The cell viability measured immediately after the tBHP oxidative treatment was significantly higher than that measured after 22 h of cell post-incubation in a fresh culture medium. This showed delayed cell death after removing tBHP. Hypochlorous acid treatment of cardiomyocytes did not change cellular viability during the cellular post-incubation in a fresh medium. Even a long-term (22 h) incubation of oxidatively damaged cardiomyocytes with BDM (5 mM) added after the HOCl removal did not recover the viability of the HOCl-exposed cells. In the presence of BDM, the cytotoxicity of HOCl significantly increased probably due to a direct reaction of both compounds and toxic chlorinated derivative formation. 2,3-Butanedione monoxime (5 mM) did not reduce cytotoxicity of tBHP, either. Such well-known antioxidative agents as melatonin or glutathione considerably prevented oxidant-induced cell death in a concentration-dependent manner.

Hypochlorous acid induces apoptosis of cultured cortical neurons through activation of calpains and rupture of lysosomes

3-Chlorotyrosine, a bio-marker of hypochlorous acid (HOCl) in vivo, was reported to be substantially elevated in the Alzheimer's disease (AD) brains. Thus, HOCl might be implicated in the development of AD. However, its effect and mechanism on neuronal cell death have not been investigated. Here, we report for the first time that HOCl treatment induces an apoptotic-necrotic continuum of concentration-dependent cell death in cultured cortical neurons. Neurotoxicity caused by an intermediate concentration of HOCl (250 microm) exhibited several biochemical markers of apoptosis in the absence of caspase activation. However, the involvement of calpains was demonstrated by data showing that calpain inhibitors protect cortical neurons from apoptosis and the formation of 145/150 kDa alpha-fodrin fragments. Moreover, an increase in cytosolic Ca2+ concentration was associated with HOCl neurotoxicity and Ca2+ channel antagonists, and Ca2+ chelators prevented cleavage of alpha-fodrin and the induction of apoptosis. Finally, we found that calpain activation ruptured lysosomes. Stabilization of lysosomes by calpain inhibitors or imidazoline drugs, as well as inhibition of cathepsin protease activities, rescued cells from HOCl-induced neurotoxicity. Our results showed for the first time that HOCl induces apoptosis in cortical neurons, and that the cell death process involves calpain activation and rupture of lysosomes.

Association of hypoglutathionemia with reduced Na+/K+ ATPase activity in type 2 diabetes and microangiopathy

OBJECTIVE

Although recent studies link altered cellular redox state to protein dysfunction in various disease-states, such associations are least studied in clinical diabetes. Therefore, this study assessed the levels of reduced glutathione (GSH) and Na(+)/K(+) ATPase activities in type 2 diabetic patients with and without microangiopathy.

METHODS

The study group comprised of a total of 160 subjects, which included non-diabetic healthy controls (n = 40) and type 2 diabetic patients without (n = 60) and with microangiopathy (n = 60), defined as presence of retinopathy with or without nephropathy. Erythrocyte Na(+)/K(+) ATPase activity and GSH levels were estimated spectrophotometrically and fluorometry was used to determine the plasma thiobarbituric acid reactive substances (TBARS) and serum advanced glycation end products (AGEs).

RESULTS

GSH levels in diabetic subjects without (4.8+/- 0.15 mumol/g Hb) and with microangiopathy (5.2+/- 0.14 micromol/g Hb) were significantly lower (p < 0.001) compared to control subjects (6.3 +/- 0.14 mumol/g Hb). Erythrocyte Na(+)/K(+) ATPase activity was significantly reduced (p < 0.001) in diabetes subjects with (272 +/- 7 nmol Pi/mg protein/h) and without microangiopathy (304 +/- 8) compared to control (374 +/- 6) subjects. TBARS were significantly higher (p < 0.001) in diabetes subjects with (10.65 +/- 0.81 nM/ml) and without microangiopathy (9.90 +/- 0.5 nM/ml) compared to control subjects (5.18 +/- 0.18 nM/ml). Advanced glycation end product levels were also significantly (p < 0.001) elevated in diabetic subjects with microangiopathy (8.2+/- 1.8 AU) when compared to diabetes subjects without microangiopathy (7.0 +/- 2.0 AU) and control subjects (4.6 +/- 1.9 AU). On multivariate regression analysis, GSH levels showed a positive association with the Na(+)/K(+) ATPase activity and negative association with TBARS and AGE levels.

CONCLUSION

Hypoglutathionemia and increased oxidative stress appears to be early biochemical aberrations in diabetes, and through protein alterations, oxidative stress and redox modifications may contribute to pathogenesis of diabetic microangiopathy.

Functional consequences of oxidative membrane damage

The interaction of reactive oxygen species with biological membranes is known to produce a great variety of different functional modifications. Part of these modifications may be classified as direct effects. They are due to direct interaction of the reactive species with the molecular machinery under study with a subsequent chemical and functional modification of these molecules. An important part of the observed functional modifications are, however, indirect effects. They are the consequence of an oxidative modification of the environment of biological macromolecules. Lipid peroxidation-via its generation of chemically reactive products-contributes to the loss of cellular functions through the inactivation of membrane enzymes and even of cytoplasmic (i.e., water soluble) proteins. Oxidation of membrane lipids may, however, also increase the efficiency of membrane functions. This was observed for a series of transport systems. Lipid peroxidation was accompanied by activation of certain types of ion channels and ion carriers. The effect is due to an increase of the polarity of the membrane interior by accumulation of polar oxidation products. The concomitant change of the dielectric constant, which may be detected via the increase of the membrane capacitance, facilitates the opening of membrane channels and lowers the inner membrane barrier for the movement of ions across the membrane. The predominant effect, however, at least at a greater extent of lipid peroxidation, is the inhibition of membrane functions. The strong increase of the leak conductance contributes to the depolarization of the membrane potential, it destroys the barrier properties of the membrane and it may finally lead, via an increase of cytoplasmic Ca(2+) concentration, to cell death. The conclusions were derived from experiments performed with different systems: model systems in planar lipid membranes, native ion channels either reconstituted in lipid membranes or investigated in their natural environment by the patch-clamp method, and two important ion pumps, the Na/K-ATPase and the sarcoplasmic reticulum (SR) Ca-ATPase.

Photodynamic inactivation of the Na,K-ATPase occurs via different pathways

The photodynamic, i.e., the light-induced, inactivation of the Na,K-ATPase in the presence of the sensitizer rose bengal was studied under different conditions. The shape of inactivation curves of the enzyme activity was analyzed as well as partial reactions of the pump cycle. Both experimental approaches showed the existence of two different time constants of inactivation of the ion pump, which reflect two pathways of a photodynamic modification. This is supported by the following observations: (1) The amplitude of the initial fast decay of enzyme activity was enhanced in the presence of D2O and reduced in the presence of the singlet oxygen scavenger imidazole. (Similar results were found for the SR Ca-ATPase.) (2) Contrary to the fast enzyme inactivation the slow process shows an inverse dose-rate behavior. (3) Inactivation of the partial reactions of Na+ -binding and of K+-binding to the membrane domain of the Na,K-ATPase showed only a single time constant, which corresponded to the slower time constant of enzyme inactivation. In the presence of high concentrations of singlet oxygen the fast time constant dominated the inactivation of the ATP-induced partial reaction for which the cytoplasmic domains of the enzyme play an important role. The data support the conclusion that fast inactivation is due to modification of the cytoplasmic domains and slow inactivation due to modifications of the membrane domain of the ion pumps.

Neutrophil-mediated accumulation of 2-ClHDA during myocardial infarction: 2-ClHDA-mediated myocardial injury

The pathophysiological sequelae of myocardial infarction include neutrophil infiltration into the infarct zone that contributes to additional damage to viable tissue and removal of cellular debris from necrosed tissue. Reactive chlorinating species produced by myeloperoxidase amplify the oxidant capacity of activated neutrophils. Plasmalogens are a major phospholipid subclass of both endothelial cells and cardiac myocytes. Recent studies have shown that plasmalogens are targeted by neutrophil-derived reactive chlorinating species that lead to the production of alpha-chloro fatty aldehydes. Results herein demonstrate that the alpha-chloro fatty aldehyde 2-chlorohexadecanal (2-ClHDA) accumulates in rat hearts subjected to left anterior descending coronary artery occlusion. Myocardia from rats subjected to surgical infarction had increased 2-ClHDA and neutrophil infiltration levels compared with myocardia from rats subjected to sham surgery. Additionally, infarcted myocardia from rats rendered neutropenic by treatments with an anti-neutrophil antibody had diminished 2-ClHDA and neutrophil infiltration levels compared with infarcted myocardia from normopenic rats; 2-ClHDA was shown to elicit myocardial damage as determined by lactate dehydrogenase release in isolated perfused rat hearts. Additionally, 2-ClHDA treatment of hearts resulted in decreased heart rate and ventricular performance. Taken together, the present results demonstrate a novel neutrophil-dependent myeloperoxidase-based mechanism that results in 2-ClHDA production in response to regional myocardial infarction that may also contribute to cardiac dysfunction.

Role of oxidative stress in ischemia-reperfusion-induced changes in Na+,K(+)-ATPase isoform expression in rat heart

The aim of this study was to assess whether depression of cardiac Na+,K(+)-ATPase activity during ischemia/reperfusion (I/R) is associated with alterations in Na+,K(+)-ATPase isoforms, and if oxidative stress participates in these I/R-induced changes. Na+,K(+)-ATPase alpha1, alpha2, alpha3, beta1, beta2, and beta3 isoform contents were measured in isolated rat hearts subjected to I/R (30 min of global ischemia followed by 60 min of reperfusion) in the presence or absence of superoxide dismutase plus catalase (SOD+CAT). Effects of oxidative stress on Na+,K(+)-ATPase isoforms were also examined by perfusing the hearts for 20 min with 300 microM hydrogen peroxide or 2 mM xanthine plus 0.03 U/ml xanthine oxidase (XXO). I/R significantly reduced the protein levels of all alpha and beta isoforms. Treatment of I/R hearts with SOD+CAT preserved the levels of alpha2, alpha3, beta1, beta2, and beta3 isoforms, but not that of the alpha1 isoform. Perfusion of hearts with hydrogen peroxide and XXO depressed all Na+,K(+)-ATPase alpha and beta isoforms, except for alpha1. These results indicate that the I/R-induced decrease in Na+,K(+)-ATPase may be due to changes in Na+,K(+)-ATPase isoform expression and that oxidative stress plays a role in this alteration. Antioxidant treatment attenuated the I/R-induced changes in expression of all isoforms except alpha1, which appears to be more resistant to oxidative stress.

Gold sodium thiomalate improves membrane potential impaired by high-frequency stimulation

Effects of gold sodium thiomalate (GSTM) on membrane potential and tetanus tension were examined to elucidate whether the gold compound improves mechanical and electrical muscle dysfunction produced by continuous repeated stimulation of frog skeletal muscles. Continuous stimulation (50 Hz for 2 min, 0.05 ms pulse duration) to the sartorius muscle depolarized the membrane, decreased action potential amplitude, and prolonged action potential duration. GSTM (0.1 mM), unlike thiomalic acid (0.1 mM), markedly decreased impairment of these electrical parameters produced during the stimulation period. In the presence of 500 units/mL of catalase, fatigue stimulation still lengthened by 1.5-fold the half-duration of the action potential after a 5-min rest. The prolongation was, however, smaller than that in controls (no catalase). Application of both catalase and GSTM led to no further changes in action potential compared with the application of catalase alone. GSTM did not affect resting tension of single toe muscle fibers though it suppressed the maximum tension after continuous stimulation. These findings suggest that GSTM can inhibit excitable dysfunction of skeletal muscles subjected to continuous stimulation and that such protective effects of GSTM may be partially mediated by H2O2.Key words: gold sodium thiomalate, catalase, continuous stimulation, resting and action potentials, force, frog skeletal muscle.

Ischemia-reperfusion alters gene expression of Na+-K+ ATPase isoforms in rat heart

The present study investigated whether oxidative stress plays a role in ischemia-reperfusion-induced changes in cardiac gene expression of Na(+)-K(+) ATPase isoforms. The levels of mRNA for Na(+)-K(+) ATPase isoforms were assessed in the isolated rat heart subjected to global ischemia (30 min) followed by reperfusion (60 min) in the presence or absence of superoxide dismutase (5 x 10(4)U/L) plus catalase (7.5 x 10(4)U/L), an antioxidant mixture. The levels of mRNA for the alpha(2), alpha(3), and beta(1) isoforms of Na(+)-K(+) ATPase were significantly reduced in the ischemia-reperfusion hearts, unlike the alpha(1) isoform. Pretreatment with superoxide dismutase+catalase preserved the ischemia-reperfusion-induced changes in alpha(2), alpha(3), and beta(1) isoform mRNA levels of the Na(+)-K(+) ATPase, whereas the alpha(1) mRNA levels were unaffected. In order to test if oxidative stress produced effects similar to those seen with ischemia-reperfusion, hearts were perfused with an oxidant, H(2)O(2) (300 microM), or a free radical generator, xanthine (2mM) plus xanthine oxidase (0.03 U/ml) for 20 min. Perfusion of hearts with H(2)O(2) or xanthine/xanthine oxidase depressed the alpha(2), alpha(3), and beta(1) isoform mRNA levels of the Na(+)-K(+) ATPase, but had lesser effects on alpha(1) mRNA levels. These results indicate that Na(+)-K(+) ATPase isoform gene expression is altered differentially in the ischemia-reperfusion hearts and that antioxidant treatment appears to attenuate these changes. It is suggested that alterations in Na(+)-K(+) ATPase isoform gene expression by ischemia-reperfusion may be mediated by oxidative stress.

Hypochlorous acid-induced membrane pore formation in red blood cells

The hyperproduction of hypochlorous acid (HOCl), an extremely toxic biological oxidant generated by neutrophils and monocytes, is involved in the pathogenesis of many diseases. In these studies, we attempted to determine the membrane and cellular events associated with HOCl-induced erythrocyte impairment and haemolysis. In vitro human erythrocyte exposure to HOCl (0.1-1.0 mM) resulted in rapid oxidation of reduced glutathione, an increase in cell osmotic fragility and the formation of transient membrane pores. The process of glutathione oxidation depended on the [oxidant]/[cell number] ratio. The HOCl-induced haemolysis observed was apparently mediated by pore formation and altered membrane electrolyte permeability. The estimated pore radius was approximately 0.7 nm and the average number per cell was 0.01. The rate constant of HOCl-produced haemolysis depended on pH. There were significant differences in haemolysis of HOCl-treated erythrocytes which had maximal stability at pH 7.2-7.3.

Reduced activity of muscle Na(+)-K(+)-ATPase after prolonged running in rats

The purpose of this study was to investigate the hypothesis that Na(+)-K(+)-ATPase activity is reduced in muscle of different fiber composition after a single session of aerobic exercise in rats. In one experiment, untrained female Sprague-Dawley rats (weight 275 +/- 21 g; means +/- SE; n = 30) were run (Run) on a treadmill at 21 m/min and 8% grade until fatigue, or to a maximum of 2 h, which served as control (Con), or performed an additional 45 min of low-intensity exercise at 10 m/min (Run+). In a second experiment, utilizing rats of similar characteristics (weight 258 +/- 18 g; n = 32), Run was followed by passive recovery (Rec). Directly after exercise, rats were anesthetized, and tissue was extracted from Soleus (Sol), red vastus lateralis (RV), white vastus lateralis (WV), and extensor digitorum longus (EDL) and frozen for later analysis. 3-O-methylfluorescein phosphatase activity (3-O-MFPase) was determined as an indicator of Na(+)-K(+)-ATPase activity, and glycogen depletion identified recruitment of each muscle during exercise. 3-O-MFPase was decreased (P < 0.05) at Run+ by an average of 12% from Con in all muscles (P < 0.05). No difference was found between Con and Run. Glycogen was lower (P < 0.05) by 65, 57, 44, and 33% (Sol, EDL, RV, and WV, respectively) at Run, and there was no further depletion during the continued low-intensity exercise period. No differences in Na(+)-K(+)-ATPase activity was observed between Con and Rec. The results of this study indicate that inactivation of Na(+)-K(+)-ATPase can be induced by aerobic exercise in a volume-dependent manner and that the inactivation that occurs is not specific to muscles of different fiber-type composition. Inactivation of Na(+)-K(+)-ATPase suggests intrinsic structural modifications by mechanisms that are unclear.

Vitamin C protects against hypochlorous Acid-induced glutathione depletion and DNA base and protein damage in human vascular smooth muscle cells

Hypochlorous acid (HOCl), generated by myeloperoxidase released from activated macrophages, is thought to contribute to vascular dysfunction and oxidation of low density lipoproteins (LDLs) in atherogenesis. We have previously shown that HOCl exposure can cause chlorination and oxidation of isolated DNA and that vitamin C protects human arterial smooth muscle cells against oxidized LDL-mediated damage. We report in the present study that vitamin C attenuates HOCl-induced DNA base and protein damage and depletion of intracellular glutathione (GSH) and ATP in human arterial smooth muscle cells. Cells were pretreated in the absence or presence of 100 micromol/L vitamin C (24 hours) and then exposed to HOCl (0 to 500 micromol/L, 0 to 60 minutes) in the absence of vitamin C. Intracellular GSH and ATP levels were depleted by HOCl treatment, and gas chromatography-mass spectroscopy revealed a concentration- and time-dependent increase in DNA base oxidation and protein damage (measured as 3-chlorotyrosine). Pretreatment of smooth muscle cells with vitamin C significantly reduced the extent of HOCl-induced DNA and protein damage and attenuated decreases in intracellular ATP and GSH. Our findings suggest that physiological levels of vitamin C provide an important antioxidant defense against HOCl-mediated injury in atherosclerosis.

Human neuromuscular fatigue is associated with altered Na+-K+-ATPase activity following isometric exercise

The purpose of this study was to investigate the hypothesis that reductions in Na+-K+- ATPase activity are associated with neuromuscular fatigue following isometric exercise. In control (Con) and exercised (Ex) legs, force and electromyogram were measured in 14 volunteers [age, 23.4 +/- 0.7 (SE) yr] before and immediately after (PST0), 1 h after (PST1), and 4 h after (PST4) isometric, single-leg extension exercise at ~60% of maximal voluntary contraction for 30 min using a 0.5 duty cycle (5-s contraction, 5-s rest). Tissue was obtained from vastus lateralis muscle before exercise in Con and after exercise in both the Con (PST0) and Ex legs (PST0, PST1, PST4), for the measurements of Na+-K+-ATPase activity, as determined by the 3-O-methylfluorescein phosphatase (3-O-MFPase) assay. Voluntary (maximal voluntary contraction) and elicited (10, 20, 50, 100 Hz) force was reduced 30-55% (P < 0.05) at PST0 and did not recover by PST4. Muscle action potential (M-wave) amplitude and area (measured in the vastus medialis) and 3-O-MFPase activity at PST0-Ex were less than that at PST0-Con (P < 0.05) by 37, 25, and 38%, respectively. M-wave area at PST1-Ex was also less than that at PST1-Con (P < 0.05). Changes in 3-O-MFPase activity correlated to changes in M-wave area across all time points (r = 0.38, P < 0.05, n = 45). These results demonstrate that Na+-K+- ATPase activity is reduced by sustained isometric exercise in humans from that in a matched Con leg and that this reduction in Na+-K+-ATPase activity is associated with loss of excitability as indicated by M-wave alterations.

Hypochlorous acid damages erythrocyte membrane proteins and alters lipid bilayer structure and fluidity

Treatment of human erythrocyte membranes with active forms of chlorine (hypochlorous acid and chloramine T) resulted in a concentration-dependent inhibition of the membrane Na(+), K(+)- and Mg(2+)-ATPases. Membrane protein thiol group oxidation was consistent with inactivation of enzymes and preceded oxidation of tryptophan residues and chloramine formation. Erythrocyte exposure to hypochlorous acid led to complex changes of cell membrane rigidity and cell morphological transformations: cell swelling, echinocyte formation, and haemolysis. The inhibition of ion pump ATPases of human erythrocyte membranes may be due to direct oxidation of essential residues of enzyme (thiol groups) and structural rearrangement of the membrane.