Stimulated human neutrophils damage cardiac sarcoplasmic reticulum function by generation of oxidants

Bromofatty aldehyde derived from bromine exposure and myeloperoxidase and eosinophil peroxidase modify GSH and protein

α-Chlorofatty aldehydes (α-ClFALDs) and α-bromofatty aldehydes (α-BrFALDs) are produced in activated neutrophils and eosinophils. This study investigated the ability of α-BrFALD and α-ClFALD to react with the thiols of GSH and protein cysteinyl residues. Initial studies showed that 2-bromohexadecanal (2-BrHDA) and 2-chlorohexadecanal (2-ClHDA) react with GSH producing the same fatty aldehyde-GSH adduct (FALD-GSH). In both synthetic and cellular reactions, FALD-GSH production was more robust with 2-BrHDA compared with 2-ClHDA as precursor. NaBr-supplemented phorbol myristate acetate (PMA)-activated neutrophils formed more α-BrFALD and FALD-GSH compared with non-NaBr-supplemented neutrophils. Primary human eosinophils, which preferentially produce hypobromous acid and α-BrFALD, accumulated FALD-GSH following PMA stimulation. Mice exposed to Br₂ gas had increased levels of both α-BrFALD and FALD-GSH in the lungs, as well as elevated systemic plasma levels of FALD-GSH in comparison to mice exposed to air. Similar relative reactivity of α-ClFALD and α-BrFALD with protein thiols was shown using click analogs of these aldehydes. Collectively, these data demonstrate that GSH and protein adduct formation are much greater as a result of nucleophilic attack of cysteinyl residues on α-BrFALD compared with α-ClFALD, which was observed in both primary leukocytes and in mice exposed to bromine gas.

Hypochlorous acid as a precursor of free radicals in living systems

Hypochlorous acid (HOCl) is produced in the human body by the family of mammalian heme peroxidases, mainly by myeloperoxidase, which is secreted by neutrophils and monocytes at sites of inflammation. This review discusses the reactions that occur between HOCl and the major classes of biologically important molecules (amino acids, proteins, nucleotides, nucleic acids, carbohydrates, lipids, and inorganic substances) to form free radicals. The generation of such free radical intermediates by HOCl and other reactive halogen species is accompanied by the development of halogenative stress, which causes a number of socially important diseases, such as cardiovascular, neurodegenerative, infectious, and other diseases usually associated with inflammatory response and characterized by the appearance of biomarkers of myeloperoxidase and halogenative stress. Investigations aimed at elucidating the mechanisms regulating the activity of enzyme systems that are responsible for the production of reactive halogen species are a crucial step in opening possibilities for control of the development of the body's inflammatory response.

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.

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.

The ability of mineral dusts and fibres to initiate lipid peroxidation. Part II: relationship to different particle-induced pathological effects

Exposure to pathogenic mineral dusts and fibres is associated with pulmonary changes including fibrosis and cancer. Investigations into aetiological mechanisms of these diseases have identified modifications in specific macromolecules as well as changes in certain early processes, which have preceded fibrosis and cancer. Peroxidation of lipids is one such modification, which is observed following exposure to mineral dusts and fibres. Their ability to initiate lipid peroxidation and the parameters that determine this ability have recently been reviewed. Part II of this review examines the relationship between the capacity of mineral dusts and fibres to initiate lipid peroxidation and a number of pathological changes they produce. The oxidative modification of polyunsaturated fatty acids is a major contributor to membrane damage in cells and has been implicated in a great variety of pathological processes. In most pathological conditions where an induction of lipid peroxidation is observed it is assumed to be the consequence of disease, without further establishing if the induction of lipid peroxidation may have preceded or accompanied the disease. In the great majority of instances, however, despite the difficulty in proving this association, a causal relationship between lipid peroxidation and disease cannot be ruled out.

Tissue and concentration-dependent effects of sodium selenite on muscle contraction

In this study, we demonstrated that sodium selenite with high doses (> or = 10(-3) M) were potent in inducing a contracture type effect on heart and smooth muscles. Selenite (Se), at a concentration of 10(-3) M, caused a contracture effect in heart preparations. Also, low Se concentrations did not have any significant effect. Although low concentrations of Se (> or = 10(-5) M) had a biphasic effects on acetylcholine (ACh) induced and spontaneous ileum contractions, 10(-3) M selenite enhanced once more a contracture effect similar to that of the heart preparations. Replacing Ca2+ concentration of the bathing solution by twofold Ca2+ or Ca2+-free did not change the effects of selenite (10(-5) M) on contractility of ileum preparations. In vascular smooth muscle, low concentration of selenite (< 10(-4)) had no significant effects on KCl, and phenylephrine-induced contractions and acetylcholine-induced endothelium-dependent relaxations of isolated rabbit aorta. However, the contractions induced by phenylephrine and the relaxations induced by acetylcholine in rabbit aorta were depressed significantly by high concentration of selenite (10(-3) M). The results obtained by selenite exposure from these three different types of tissue preparations first suggest that the high concentration of selenite exposure induces some alterations in the functions of muscles and endothelium in a tissue- and dose-dependent manner. Second, this observed irreversible type of dysfunction of tissues induced by 10(-3) M selenite is not directly dependent on the Ca2+ entrance into the cytosol, but might be induced by the increase of intracellular Ca2+ with the disturbance of Ca2+ regulation.

Aging-related changes in calcium oscillations in fertilized mouse oocytes

Aging of oocytes, being not fertilized after ovulation for a prolonged time, considerably affects normal development of the fertilized oocyte. We examined effects of the aging on a series of highly repetitive Ca2+ transients commonly seen in fertilized mouse oocytes (Ca2+ oscillations). Frequency of Ca2+ oscillations in the aged oocyte [20 hrs after induction of superovulation by i.p. human chorionic gonadotropin (hCG)] was significantly higher (34.1 +/- 5.8 l/hr) than the fresh oocyte (14 hr post-hCG, 21.8 +/- 7.9 l/hr). Rates of rise and fall of individual Ca2+ transient in the aged oocyte were significantly slower than the fresh oocyte, whereas durations of individual Ca2+ transients were similar. When extracellular Ca2+ was raised from 2.04 mM to 5.00 mM, aged oocytes showed significant prolongation of the duration of individual Ca2+ transient, that resulted in a sustained elevation of intracellular Ca2+ ([Ca2+]i) in 33% of the aged oocyte. Transient increase in [Ca2+]i by photolysis of a caged Ca2+, Nitr-5, injected into cytoplasm was completely restored in the fresh oocyte [fluorescence intensity of [Ca2+]i indicator dye Fluo-3 (F480) returned to 97 +/- 2% of the control level, time constant = 37 +/- 9 sec]. In contrast, in the aged oocyte, restoration of F480 following Nitr-5 photolysis was incomplete (115 +/- 12% of the control) and slow (time constant = 64 +/- 23 sec). Because inhibition of the Ca2+ pump of the endoplasmic reticulum (ER) by 5 microM thapsigargin almost completely inhibited restoration of F480 following Nitr-5 photolysis in the fresh oocyte, we conclude that the aging-related changes in Ca2+ oscillations may be accounted for by dysfunction of intracellular Ca2+ regulation, presumably of the Ca2+ pump of the ER.

Membrane phosphorylation protects the cardiac sarcoplasmic reticulum Ca(2+)-ATPase against chlorinated oxidants in vitro

OBJECTIVE

The calcium (Ca) pump of cardiac sarcoplasmic reticulum (SR) membranes is vulnerable to oxidation and hence likely to be damaged by chlorinated compounds, specifically hypochlorite (NaOCl) and monochloramine (NH2Cl), the most potent oxidants produced upon neutrophil activation. This could occur during prolonged ischemia or myocardial infarction when tissue levels of catecholamines are high. Phospholamban (PLN), the phosphorylatable regulator of the Ca pump, plays a central role in the effects of beta-adrenergic agonists on the heart. The purpose of this study was to investigate a possible role of PLN in determining the pump's sensitivity to NaOCl and NH2Cl.

METHODS

Ca-uptake and Ca(2+)-ATPase activities in purified phosphorylated and control canine cardiac microsomes, incubated at increasing concentrations of NaOCl or NH2Cl, were related to the extent of PLN phosphorylation by protein kinase A, which was quantitated by PhosphorImager analysis.

RESULTS AND CONCLUSIONS

Our data indicate that microsomal phosphorylation protects the Ca pump fully against 10 microM NaOCl or NH2Cl, which inhibit Ca-uptake by 21-41% when assayed at 25 or 37 degrees C and saturating Ca2+ in unphosphorylated microsomes, and protects partially at higher oxidant concentrations. The protective effect of protein kinase A on Ca-uptake is proportional to the amount of phosphorylated PLN. No comparable protection against similar oxidative damage of the Ca pump is observed when light fast skeletal muscle microsomes, which lack PLN, are incubated under conditions favorable for phosphorylation nor when PLN's inhibition of the cardiac Ca pump is relieved by proteolytic cleavage of its cytoplasmic domain. Our findings contribute toward an understanding of possible endogenous protective mechanisms that may promote calcium homeostasis in myocardial cells in inflammatory states associated with neutrophil activation and may suggest an approach toward development of protective strategies against oxidative damage in the heart.

Alteration in cardiac sarcolemmal ATP receptors by oxyradicals

We previously demonstrated that cardiac sarcolemmal membranes bind [35S]ATP gamma S at both low and high affinity binding sites. In this study we examined the effects of some P2-purinoceptor antagonists as well as of two oxidants (H2O2 and HOCl) on the high affinity ATP-binding sites under in vitro conditions. It was found that putative P2-purinoceptor antagonists such as Cibacron blue, suramin, and 4,4'-diisothiocyanatostilbene 2-2 acid markedly inhibited specific ATP-binding with sarcolemmal membrane. H2O2 produced a biphasic effect (first increase and then decrease) on the specific ATP-binding with cardiac sarcolemma in a time- and concentration-dependent manner; these effects were prevented by catalase. On the other hand, HOCl markedly inhibited ATP-binding; this inhibition was prevented by l-methionine. These results suggest that the high affinity ATP-binding sites in cardiac sarcolemma may represent the P2-purinoceptors, which are susceptible to modification by oxidative stress under pathophysiological conditions including myocardial ischemia-reperfusion injury.

Immunologic detection and measurement of hypochlorite-modified LDL with specific monoclonal antibodies

Oxidation of LDL is thought to contribute to the early stages of atherogenesis. Because myeloperoxidase is present in atherosclerotic lesions and can produce the strong oxidant hypochlorous acid (HOCl), which converts LDL into its high-uptake atherogenic form in vitro, we raised polyclonal and monoclonal antibodies (MoAbs) against HOCl-modified LDL (HOCl-LDL). Characterization of the polyclonal anti-human HOCl-LDL Abs showed that they cross-reacted strongly with 4-hydroxynonenal-, malondialdehyde-, and Cu(2+)-oxidized LDL. Similarly, polyclonal and some monoclonal Abs against aldehyde- and Cu(2+)-modified LDL cross-reacted with HOCl-LDL. In contrast to the polyclonal Abs, two selected hybridoma cell line supernatants containing MoAbs raised against HOCl-LDL (MoAb-A and MoAb-B) did not cross-react with either native LDL or aldehyde- or Cu(2+)-modified LDL. MoAb-A (clone 1B10A11, subtype IgG1 kappa) recognized an epitope that appeared to be specific for HOCl-LDL and depended on the tertiary structure of the (lipo)protein, as judged by a lack of cross-reactivity with HOCl-modified human and bovine serum albumin and a loss of reactivity associated with lipoprotein denaturation. MoAb-B (clone 2D10G9, subtype IgG2b kappa), on the other hand, gave identical titration curves with HOCl-LDL and HOCl-modified albumins, suggesting that this antibody recognized epitopes that are commonly generated on proteins that have been oxidized with HOCl. Thus, MoAb-A and MoAb-B may be useful tools for the investigation of a possible role for HOCl-mediated damage to (lipo)proteins in atherosclerosis and other inflammatory diseases.

Inhibition by activated neutrophils of the Ca2+ pump ATPase of intact red blood cells

Human neutrophils, activated by phorbol myristate acetate in the presence of intact red blood cells (RBCs), caused inhibition of the Ca2+ pump ATPase of the RBCs and fragmentation of the enzyme as well as other membrane proteins. Inhibition of the Ca2+ pump ATPase of intact RBCs was directly related to the neutrophil concentration and the time of incubation. Ca2+ pump ATPase activity was partially protected by the addition of exogenous glutathione-glutathione peroxidase, but not by superoxide dismutase. The addition of sodium azide, a potent inhibitor of endogenous RBC catalase, enhanced inhibition of the Ca2+ pump ATPase of intact RBCs. Examination by SDS-polyacrylamide gel electrophoresis of membrane proteins isolated from RBCs preincubated with activated neutrophils showed gross changes in banding patterns as compared to controls. Thus, a significant amount of methemoglobin appeared to be associated with the membrane proteins, and, in general, protein bands appeared to be more diffuse and less defined than proteins in control lanes. In addition, there was an increase in the low molecular weight protein bands. Using a monoclonal antibody to the Ca2+ pump ATPase, it was shown that the 140 kDa band representing the Ca2+ pump ATPase decreased, with concomitant appearance of two low molecular weight bands running at 8.2 and 6.8 kDa in the membrane proteins from RBCs preincubated with activated neutrophils. The data are interpreted to suggest that inhibition of the Ca2+ pump ATPase in intact RBCs under these conditions occurred as a result of: neutrophil-derived superoxide, dismutation of superoxide, to H2O2, diffusion of H2O2 into RBCs, a Fenton type reaction between oxyhemoglobin, and H2O2 producing hydroxyl radical and/or a ferryl radical capable of promoting protein fragmentation of RBC membrane proteins, including the plasma membrane Ca2+ pump ATPase.

Involvement of thiol groups in the impairment of cardiac sarcoplasmic reticular phospholipase D activity by oxidants

Considerable phospholipase D (PLD) activity is localized in myocardial sarcoplasmic reticular (SR) membranes, where it may take part in the regulation of Ca2+ movements. In this study, we examined thiol group dependence as a possible regulatory mechanism for SR PLD. SR membranes isolated from rat heart were exposed to four types of thiol group modifiers, which all induced a decrease in SR PLD activity that was prevented by dithiothreitol. Furthermore, since abnormalities in thiol status and Ca2+ homeostasis are characteristic for the myocardial cell damage induced by oxidative stress, we also studied the effects of oxidants on the SR PLD activity. The enzyme was not affected by xanthine-xanthine oxidase, but was depressed by hydrogen peroxide and by hypochlorous acid. These inhibitory effects were prevented by catalase as well as by methionine and dithiothreitol, respectively. Furthermore, reduced glutathione protected against the hydrogen peroxide-induced depression, whereas oxidized glutathione inhibited SR PLD. The results indicate that SR PLD activity is inhibited by nonradical oxidants, hydrogen peroxide and hypochlorous acid, through reversible modification of associated thiol groups. Thus, the enzyme may be controlled by the glutathione redox status of the cardiac cell.

Multi-agent therapy in the treatment of sepsis-induced microvascular injury

Cyclo-oxygenase inhibition (with ibuprofen) combined with histamine (H1, H2) receptor antagonism (with diphenhydramine and cimetidine) attenuates microvascular leak injury in sepsis syndromes. Ibuprofen reduces microvascular injury by limiting oxygen radical production by neutrophils. Histamine is known to inhibit this oxygen radical production, an effect antagonized by cimetidine. In the present study neutrophils isolated from pigs made septic with Pseudomonas organisms exhibited a significant (P < 0.05) increase in the production of the oxygen radicals, superoxide anion (O2-, 133 per cent) and hypochlorous acid (HOCl, 38 per cent). Ibuprofen used alone attenuated this sepsis-stimulated overproduction. Addition of the antihistamines cimetidine and diphenhydramine produced a significant increase in oxygen radical production (P < 0.05), by 122 per cent (O2-) and 47 per cent (HOCl), equivalent to that in untreated septic animals. This coincided with a significant deterioration in pulmonary compliance (P < 0.05) compared with that found in control animals and those treated with ibuprofen alone, and a significant accumulation of extravascular lung water (P < 0.05) at 240 and 300 min versus baseline. Histamine receptor antagonism may inadvertently enhance microvascular injury in sepsis.

Oxygen free radicals and calcium homeostasis in the heart

Many experiments have been done to clarify the effects of oxygen free radicals on Ca2+ homeostasis in the hearts. A burst of oxygen free radicals occurs immediately after reperfusion, but we have to be reminded that the exact levels of oxygen free radicals in the hearts are yet unknown in both physiological and pathophysiological conditions. Therefore, we should give careful consideration to this point when we perform the experiments and analyze the results. It is, however, evident that Ca2+ overload occurs when the hearts are exposed to an excess amount of oxygen free radicals. Through ATP-independent Ca2+ binding is increased, Ca2+ influx through Ca2+ channel does not increase in the presence of oxygen free radicals. Another possible pathway through which Ca2+ can enter the myocytes is Na(+)-Ca2+ exchanger. Although, the activities of Na(+)-K+ ATPase and Na(+)-H(+) exchange are inhibited by oxygen free radicals, it is not known whether intracellular Na(+) level increases under oxidative stress or not. The question has to be solved for the understanding of the importance of Na(+)-Ca2+ exchange in Ca2+ influx process from extracellular space. Another question is 'which way does Na(+)-Ca2+ exchange work under oxidative stress? Net influx or efflux of Ca2+?' Membrane permeability for Ca2+ may be maintained in a relatively early phase of free radical injury. Since sarcolemmal Ca(2+)-pump ATPase activity is depressed by oxygen free radicals, Ca2+ extrusion from cytosol to extracellular space is considered to be reduced. It has also been shown that oxygen free radicals promote Ca2+ release from sarcoplasmic reticulum and inhibit Ca2+ sequestration to sarcoplasmic reticulum. Thus, these changes in Ca2+ handling systems could cause the Ca2+ overload due to oxygen free radicals.

Effects of the reactive oxygen species hypochlorous acid and hydrogen peroxide on force production and calcium sensitivity of rat cardiac myofilaments

Neutrophil activation occurs after myocardial infarction/ischaemia. They produce the reactive oxygen species (ROS) hypochlorous acid (HOCl) and hydrogen peroxide (H2O2) which could contribute to contractile dysfunction upon reperfusion. The myofilaments of 'skinned' rat cardiac muscle were exposed to ROS in various states of activation. Isometric force was measured at controlled degrees of activation. A single application of 10 microM HOCl for 1 min increased log [Ca2+] for half-maximal activation (log K1/2) from 5.23 to 5.32, initial maximum Ca-activated force (FCa, max) was reduced by 18.8 +/- 5.8% and resting tension increased to 15.4 +/- 8.0% of FCa, max. At 50 microM, a 1-min exposure to HOCl produced a greater increase in Ca-sensitivity (log K1/2 increased from 5.23 to 5.47), a greater reduction in FCa, max (falling by 42.3 +/- 23.2%) and a greater increase in resting tension (to 25 +/- 10.7% of FCa, max). The nature of the resting tension rise was examined by reducing pH before and during exposure to HOCl; the results are consistent with 'rigor-like' cross-bridges being involved. H2O2 was without effect on the myofilaments at physiologically relevant (< 10 microM) concentrations. These results suggest that ROS associated with inflammation could contribute to post-ischaemic myocardial dysfunction.

Oxygen free radicals and calcium homeostasis in the heart

Many experiments have been done to clarify the effects of oxygen free radicals on Ca2+ homeostasis in the hearts. A burst of oxygen free radicals occurs immediately after reperfusion, but we have to be reminded that the exact levels of oxygen free radicals in the hearts are yet unknown in both physiological and pathophysiological conditions. Therefore, we should give careful consideration to this point when we perform the experiments and analayze the results. It is, however, evident that Ca2+ overload occurs when the hearts are exposed to an excess amount of oxygen free radicals. Though ATP-independent Ca2+ binding is increased, Ca2+ influx through Ca2+ channel does not increase in the presence of oxygen free radicals. Another possible pathway through which Ca2+ can enter the myocytes is Na(+)-Ca2+ exchanger. Although, the activities of Na(+)-K+ ATPase and Na(+)-Ca2+ exchanger. Although, the activities of Na(+)-H+ exchange are inhibited by oxygen free radicals, it is not known whether intracellular Na+ level increases under oxidative stress or not. The question has to be solved for the understanding of the importance of Na(+)-Ca2+ exchange in Ca2+ influx process from extracellular space. Another question is 'which way does Na(+)-Ca2+ exchange work under oxidative stress? Net influx or efflux of Ca2+?' Membrane permeability for Ca2+ may be maintained in a relatively early phase of free radical injury. Since sarcolemmal Ca(2+)-pump ATPase activity is depressed by oxygen free radicals, Ca2+ extrusion from cytosol to extracellular space is considered to be reduced. It has also been shown that oxygen free radicals promote Ca2+ release from sarcoplasmic reticulum and inhibit Ca2+ sequestration to sarcoplasmic reticulum. Thus, these changes in Ca2+ handling systems could cause the Ca2+ overload due to oxygen free radicals.

Effects of minimally invasive surgery on hypochlorous acid production by neutrophils

The production of chlorinated oxidants such as hypochlorous acid is a central antimicrobial and immunoregulatory function of neutrophils. Neutrophil hypochlorous acid production was compared in patients undergoing uncomplicated laparoscopic surgery (group 1) and those submitted to conventional open surgery (group 2). Preoperative peak hypochlorous acid production was similar in the two groups (mean(s.e.m.) 0.60(0.05) versus 0.69(0.06) nmol/min respectively). In group 2, mean(s.e.m.) neutrophil hypochlorous acid production fell significantly on day 1 after surgery (0.36(0.05) nmol/min; P < 0.01) but this did not occur in group 1 (0.63(0.07) nmol/min). By day 6 hypochlorous acid kinetics had returned to preoperative levels in both groups. Minimally invasive surgery is less disruptive of neutrophil function than conventional open procedures.

Reduction of myocardial infarct size in rat by IRFI-048, a selective analogue of vitamin E

The effects of IRFI-048 (2,3-dihydro-5-methoxy-4,6,7-trimethyl-2-benzofuranyl acetic acid), a selective analogue of Vitamin E, on myocardial tissue injury were examined in anaesthetized rats subjected to 60-min occlusion of the left coronary artery followed by 60-min reperfusion. Infarct size (Evan's blue and tetrazolium stain), serum creatinphosphokinase (CPK), plasma malonaldehyde (MAL), cardiac myeloperoxidase (MPO) activity, and ST-segment of electrocardiogram (ECG) and survival rate were evaluated. Postischaemic reperfusion produced severe cardiac necrosis, caused neutrophil (PMNs) infiltration (evaluated by MPO activity) in the jeopardized tissue, increased serum CPK and plasma MAL, raised ST-segment of ECG, and decreased survival rate. IRFI-048, (200 and 400 mg/kg o.s.) given to the rats 6 h before occlusion, caused a reduction of necrotic area expressed as a percentage of either the area at risk or the total left ventricle, decreased MPO activity both in the area at risk (from 3.2 +/- 0.3 U x 10(-3)/g tissue to 1.1 +/- 0.4 U x 10(-3)/g tissue; p < .005) and in the necrotic area (from 5.7 +/- 0.9 U x 10(-3)/g tissue to 1.8 +/- 0.5 U x 10(-3)/g tissue; p < .001), attenuated the rise of ST-segment of ECG (from 0.51 +/- 0.14 mV in the vehicle group to 0.28 +/- 0.11 mV in the treated group; p < .005), reduced the increase of plasma MAL and serum CPK during reperfusion (from 42 +/- 5.3 nmol/ml to 15 +/- 3.1 nmol/ml and 139 +/- 13 IU/100 ml to 58 +/- 7.5 IU/100 ml, respectively; p < .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Hypochlorous acid-induced zinc release from thiolate bonds: a potential protective mechanism towards biomolecules oxidant damage during inflammation

It has been proposed that metalloprotein zinc mobilization mediated by hypochlorous acid (HOCl) may induce cell injury (see H. Fliss and M. Ménard (1991), Archives of Biochemistry and Biophysics, 287, 175-179). In the present paper, we have demonstrated using a dimercaptopropanol-zinc complex that, once released from thiolate bonds by HOCl, zinc can exert a significant antioxidant effect on both linolenic acid and deoxyribose oxidation induced by iron. In these experimental conditions, however, the antagonism towards deoxyribose oxidation is notably less than that towards linolenic acid peroxidation, thus suggesting a more specific inhibitory effect of zinc on iron-mediated oxidant damage when polyunsaturated fatty acids represent the oxidizable substrate. The antioxidant effects of zinc are strictly related to the "free" form; indeed, the dimercaptopropanol-zinc complex per se is stimulatory even on biomolecules oxidant damage, apparently as a result of the prooxidant prooxidant interaction of the thiol compound with iron. In light of these results, it may be proposed that the zinc released from thiolate bonds by HOCl could specifically limit tissue oxidative burden in pathological conditions involving neutrophil accumulation and activation, such as inflammation and ischemia-reperfusion.

Thyroid hormones and regulation of cell reliability systems

Data and arguments are presented that provide evidence of a role played by thyroid hormones (TH) in cell reliability improvement. This role may be determined by synergistic TH action on the following key cell reliability systems: (1) reactive oxygen species (ROS) attack inhibition, and (2) genetic structure repair from injuries inflicted in the course of endogenous and induced mutagenesis. (1) New approaches to ROS oxidation defence were examined. It has been shown that Ca(2+)-ATPase and, probably, regulatory proteins of cell membranes may be the main target for oxidative attack. Protein phosphorylation as well as use of dithiothreitol will lead to a protective action against Ca2+ transport damaging in aorta smooth muscle sarcoplasmic reticulum under oxidation by HOCl, the most toxic ROS of activated neutrophils, whereas thyroxine (T4) and 3,5,3'-triiodothyronine (T3) validly inhibit chemiluminescence in human neutrophils activated by pyrogenal, a lipopolysaccharide from Salmonella typhi cell wall. As this takes place, TH most likely block neutrophil stimulation at the receptor-ligand interaction level. In this case L-T4 and L-T3 antioxidative effect is greater than that of DL-thyroxine and much greater than that produced by such a potent antioxidant as 4-methyl-2,6-diisobutyl phenol. (2) T4 acts as reparogen in rat liver cells under X-ray irradiation when a dose measuring one-half of daily hormone production by the normally functioning thyroid gland is administered to animals. Ionizing radiation dose reduction factor reached 1.3-1.4 following T4 administration. Reparogenic effect of T4 persists for at least 2 months from the moment the hormone has been administered and can be reduced in the presence of dinitrophenol. It is important to note that antioxidant and reparogenic TH potential can manifest itself within the range of physiologic concentrations of these hormones. Therefore, stimulation of cell reliability systems with TH may prove to be important for correcting conditions caused by errors in energy- and Ca(2+)-dependent DNA repair under extensive ROS attack. In particular, taking into account different responsiveness of normal and neoplastic tissues to TH, the use of TH reparogenic as well as antioxidant potential may contribute significantly to the improvement of antitumor radiotherapy efficacy.

The effect of hypochlorous acid and hydrogen peroxide on coronary flow and arrhythmogenesis in myocardial ischemia and reperfusion

The purpose of this study was to investigate the effect of the oxidants hypochlorous acid (HOCl) and hydrogen peroxide (H2O2) on the vulnerability of the myocardium to reperfusion-induced arrhythmias following global ischemia. After a 15 min equilibration period with or without experimental intervention, isolated perfused rat hearts in the Langendorff mode were made globally ischemic for 5 min by cross-clamping the aortic line. No dysrhythmias were evoked upon reperfusion at the 5 min global ischemia time period. HOCl or H2O2 were added to the perfusate 5 min into the equilibration period with a total exposure of 10 min. Global ischemia was then induced for 5 min followed by 10 min of reperfusion. A dose-response curve for HOCl (50-200 microM) indicated the development of idioventricular rhythms, in a concentration-dependent way. Furthermore, coronary flow of the hearts exposed to 100 and 200 microM HOCl, at 5 min post-reperfusion, was decreased; methionine (10 microM to 1 mM), an accepted scavenger for HOCl, prevented the responses to 200 microM HOCl, in a concentration-dependent manner. All hearts exposed to 200 microM H2O2 developed ventricular dysrhythmias during the reperfusion period. Coronary flow increased after 5 min of exposure to 200 microM H2O2 and remained elevated during reperfusion. It is concluded that toxic oxygen derived products are capable of increasing the susceptibility of the myocardium to reperfusion induced arrhythmias, and that although the electrical responses to exposure to those two oxidants were similar, the effects on the vasculature were not the same.

Oxidant-induced mobilization of zinc from metallothionein

Neutrophils which accumulate at sites of inflammation secrete a number of injurious oxidants which are highly reactive with protein sulfhydryls. The present study examined the possibility that this reactivity with thiols may cause protein damage by mobilizing zinc from cellular metalloproteins in which the metal is bound to cysteine. The ability of the three principal neutrophil oxidants, hypochlorous acid (HOCl), superoxide (.O2-), and hydrogen peroxide (H2O2), to cleave thiolate bonds and mobilize complexed zinc was compared using two model compounds (2,3-dimercaptopropanol and metallothionein peptide fragment 56-61), as well as metallothionein. With all compounds, 50 microM HOCl caused high rates of Zn2+ mobilization as measured spectrophotometrically with the metallochromic indicator 4-(2-pyridylazo)resorcinol. Xanthine (500 microM) plus xanthine oxidase (30 mU), which produced a similar concentration of .O2-, also effected a rapid rate of Zn2+ mobilization which was inhibited by superoxide dismutase but not catalase, indicating that .O2- is also highly reactive with thiolate bonds. In contrast, H2O2 alone was much less reactive at comparable concentrations. These data suggest that HOCl and .O2- can cause damage to cellular metalloproteins through the mobilization of complexed zinc. In view of the essential role played by zinc in numerous cellular processes, Zn2+ mobilization by neutrophil oxidants may cause significant cellular injury at sites of inflammation.

Singlet oxygen interaction with Ca(2+)-ATPase of cardiac sarcoplasmic reticulum

We investigated the role of singlet oxygen (generated from photoactivation of rose bengal) on the calcium transport and Ca(2+)-ATPase activity of cardiac sarcoplasmic reticulum (SR). Isolated cardiac SR exposed to rose bengal (10 nM) irradiated at 560 nm resulted in significant inhibition of Ca2+ uptake (from 2.27 +/- 0.05 to 0.62 +/- 0.05 mumol Ca2+/mg.min [mean +/- SEM], p less than 0.01) and Ca(2+)-ATPase activity (from 2.08 +/- 0.05 to 0.28 +/- 0.04 mumol Pi/min.mg [mean +/- SEM], p less than 0.01). The inhibition of calcium uptake and Ca(2+)-ATPase activity by rose bengal-derived activated oxygen (singlet oxygen) was dependent on the duration of exposure and intensity of light. Singlet oxygen scavengers ascorbic acid and histidine significantly protected SR Ca(2+)-ATPase against rose bengal-derived activated oxygen species, but superoxide dismutase and catalase did not attenuate the inhibition. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of SR exposed to photoactivated rose bengal for up to 14 minutes demonstrated complete loss of the Ca(2+)-ATPase monomer band, which was significantly protected by histidine. The addition of dithiothreitol (5 mM) had a slight protective effect, showing that new disulfide bond formation was not a major cause of aggregation. The results were also confirmed by high-performance liquid chromatography of the SR exposed to irradiated rose bengal. Irradiation of rose bengal also caused an 18% loss of total sulfhydryl groups of SR. On the other hand, superoxide radical (generated from xanthine oxidase action on xanthine) and hydroxyl radical (in the presence of Fe(3+)-EDTA or 0.5 mM H2O2 plus Fe(2+)-EDTA) as well as H2O2 (0.25-12 mM) were without any effect on the 97,000-d Ca(2+)-ATPase band of SR. Generation of radical species (superoxide and hydroxyl radical) from rose bengal was studied by electron paramagnetic resonance spectroscopy using the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). The results showed that irradiation of rose bengal formed a 1:2:2:1 quartet, characteristic of the DMPO-OH adduct, which was scavenged by ethanol but not by superoxide dismutase, catalase, or histidine. No radical species could be detected from irradiated rose bengal or irradiated DMPO under the assay conditions used. Peroxy adducts of DMPO might be produced but would be observed only at very low temperatures. Similarly, we could not detect any measurable.O2- anion from irradiation of rose bengal as indicated by either cytochrome c reduction at 550 nm or nitro blue tetrazolium reduction at 560 nm. These results show that SR is damaged most likely by singlet oxygen derived from rose bengal.(ABSTRACT TRUNCATED AT 400 WORDS)

Stunning: a radical re-view

The recovery from trauma, whether ischemia or some other form of tissue injury, is never instantaneous; time is always required for repair and the return of normal metabolism and function. To what extent the delay in recovery of contractile activity (stunning) after a brief period of ischemia represents convalescence from ischemia-induced injury, as opposed to the expression of reperfusion-induced injury, is perhaps not as clear as the proponents of stunning would hope. Definitive evidence for a distinct reperfusion-induced pathology, which compromises the recovery of contractile function from the depressed state induced by ischemia, is elusive. If reperfusion-induced injury accounts for a significant proportion of stunning, then the molecular mechanisms responsible for initiating the event and those responsible for orchestrating the event at the level of the contractile protein are far from clear. Perturbations of calcium homeostasis are frequently cited as responsible for the depressed contractile state, however, some metabolic derangement must precede any pathologically induced ionic disturbance. In this connection, evidence indicates that free-radical-induced oxidant stress, during the early moments of reperfusion, may modify the activity of a number of thiol-regulated proteins that are directly, or indirectly, responsible for controlling the movement of calcium. Sarcolemmal sodium-calcium exchange and the calcium release channel of the sarcoplasmic reticulum may be activated, whereas the sarcolemmal calcium pump and sodium-potassium ATPase, together with the calcium pump of the sarcoplasmic reticulum, may be inhibited. Under the conditions prevailing during ischemia and reperfusion, this would be expected to promote an early intracellular calcium overload. It is difficult to reconcile such a change with the decreased inotropic state that characterizes stunning; however, it seems likely that the calcium overload is transient and that the stunned myocardium rapidly reestablishes normal levels of intracellular calcium. It is still difficult to explain adequately the reduced inotropic state; clearly, the mechanism of stunning is not quite as simple as its definition.

Free radical-induced alterations of myocardial membrane proteins

Rat myocardial membranes exposed to the free radical-generating systems, Fe2+/ascorbate, Cu2+/t-butylhydro-peroxide, linoleic acid hydroperoxide, and soybean lipoxygenase (Type I) undergo lipid peroxidation. This is evidenced by the accumulation of thiobarbituric acid-reactive substances and the loss of both extractable phospholipids and their polyunsaturated acyl groups. Lipid peroxidation is accompanied by alterations of membrane proteins including the general loss of polypeptides and accumulation of high-molecular weight material. The most sensitive protein is a polypeptide with a molecular weight of 28 kDa. At low levels of oxidation, this protein moves incrementally to slightly higher apparent molecular weight. At higher oxidant levels or longer periods of oxidation, the protein disappears completely from the SDS-PAGE gel. The "28K reaction" occurs prior to the massive, oxidant-induced lipid alterations and may thus indicate specific adduct formation between this protein and certain peroxidized membrane phospholipids.

Alterations in cardiac contractile proteins due to oxygen free radicals

In view of the potential role of free radicals in the genesis of cardiac abnormalities under different pathophysiological conditions and the importance of contractile proteins in determining heart function, this study was undertaken to examine the effects of oxygen free radicals on the rat heart myofibrils. Xanthine plus xanthine oxidase (X + XO) which is known to generate superoxide anions (O2-) and hydrogen peroxide (H2O2), an activated species of oxygen, was found to decrease Ca(2+)-stimulated ATPase activity, increase Mg(2+)-ATPase activity and reduce sulfhydryl (SH) group contents in myofibrils; these effects were completely prevented by superoxide dismutase (SOD) plus catalase (CAT). Both H2O2 and hypochlorous acid (HOCl), an oxidant, produced actions on cardiac myofibrils similar to those observed by X + XO. The effects of H2O2 and HOCl were prevented by CAT and L-methionine, respectively. N-ethylmaleimide (NEM) and 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), inhibitors of SH groups, also produced effects similar to those seen with X + XO. Dithiothreitol (DTT), a well known sulfhydryl-reducing agent, prevented the actions of X + XO, H2O2, HOCl, NEM and DTNB. These results suggest that marked changes in myofibrillar ATPase activities by different species of oxygen free radicals may be mediated by the oxidation of SH groups.

Hypochlorous acid-induced mobilization of zinc from metalloproteins

Hypochlorous acid (HOCl), a neutrophil oxidant, can contribute to tissue injury at sites of inflammation by its reactivity with protein sulfhydryls. The present study shows that physiological concentrations (50-200 microM) of HOCl can displace Zn2+ from metalloproteins, such as metallothionein and alcohol dehydrogenase, in which the metal is bound to sulfhydryls by means of thiolate (S-Zn) bonds. No mobilization of Zn2+ was observed from superoxide dismutase in which the metal is not bound to cysteine, suggesting that HOCl reacts selectively with thiolate bonds. Zn2+ mobilization, measured spectrophotometrically with the metallochromic indicator 4-(2-pyridylazo)resorcinol, was also observed from complexes of this metal with other thiol-containing compounds such as 2,3-dimercaptopropanol and metallothionein fragment 56-61. HOCl cleavage of the thiolate bonds was confirmed by the decrease in absorbance at 250 nm. This study shows for the first time that HOCl can mobilize protein-bound Zn2+ and suggests that neutrophil oxidant injury may be partially mediated by the mobilization of cellular Zn2+.

Ibuprofen attenuates hypochlorous acid production from neutrophils in porcine acute lung injury

Hypochlorous acid (HOCl), a neutrophil-generated oxidant, has been implicated in tissue destruction in sepsis-induced acute lung injury (ALI). Ibuprofen, a cyclooxygenase inhibitor, successfully attenuates many of the physiological derangements in ALI. The aim of this study was to examine the role of PMN hypochlorous acid in sepsis-induced ALI and evaluate the effect of ibuprofen therapy. Neutrophils from three groups of young (15-25 kg), anesthetized swine were studied: controls (C, n = 7) received 0.9% NaCl, septic animals (Ps, n = 8) received live Pseudomonas aeruginosa (5 x 10(8) CFU/ml at 0.3 ml/20 kg/min) for 60 min, and ibuprofen-treated animals (Ps + I, n = 6) received Ps plus ibuprofen 12.5 mg/kg administered at 0 and 120 min. Neutrophils were isolated from peripheral blood at 0, 60, and 300 min and the rate and total production of HOCl were assessed on the basis of the ability of the amino acid taurine to trap HOCl.

RESULTS

Septic (Ps) PMNs produce 32% more HOCl, P less than 0.01, at 300 min than at baseline which was associated with a marked increase in both extravascular lung water (6.44 +/- 0.8 ml/kg, t = 0 vs 16.03 +/- 2.6 ml/kg, t = 300, P less than 0.01) and bronchoalveolar protein content (115 +/- 13 micrograms/ml, t = 0 vs 633 +/- 104 micrograms/ml, t = 300, P less than 0.01). Ibuprofen significantly attenuated (P less than 0.05) HOCl production when compared to Ps, in conjunction with significantly (P less than 0.05) reduced levels of extravascular lung water and bronchoalveolar lavage protein.

The antioxidants of human extracellular fluids

The antioxidants in the aqueous phase of human plasma include ceruloplasmin, albumin (the protein itself and possibly also albumin-bound bilirubin), ascorbic acid, transferrin, haptoglobin, and hemopexin. Assays that attempt to answer the question "what is the most important antioxidant?" are compared, it being concluded that the answer is different depending on the nature of the prooxidant stress imposed in the assay.

Calcium in lipid peroxidation: does calcium interact with superoxide?

Using a pulse radiolysis approach to generate and observe superoxide anions (O2-.) in the absence and presence of calcium, we have attempted to verify the recent hypothesis of Babizhayev (Arch. Biochem. Biophys. 266, 446-451, 1988) of a Ca2(+)-O2-. interaction during lipid peroxidation. We could not observe rapid scavenging of O2-. or complex formation with Ca2+ to account for an inhibitory effect of this cation on lipid peroxidation. Neither could we agree that the stimulatory effect is due to liberation of catalytic ferrous iron from weak complexes by Ca2+. Drawing on reports in the literature, we propose an alternate explanation for the apparent stimulation of lipid peroxidation by low Ca2+ concentrations. In our view, this is not a direct effect, but reflects independently initiated processes of lipid peroxidation and Ca2+ translocation, which interact subsequently in a synergistic manner. The reported inhibition at high Ca2+ concentrations is considered an artifact as it was observed at levels far in excess of those relevant to animal systems (but not necessarily in some plant compartments).

How to characterize a biological antioxidant

An antioxidant is a substance that, when present at low concentrations compared to those of an oxidizable substrate, significantly delays or prevents oxidation of that substrate. Many substances have been suggested to act as antioxidants in vivo, but few have been proved to do so. The present review addresses the criteria necessary to evaluate a proposed antioxidant activity. Simple methods for assessing the possibility of physiologically-feasible scavenging of important biological oxidants (superoxide, hydrogen peroxide, hydroxyl radical, hypochlorous acid, haem-associated ferryl species, radicals derived from activated phagocytes, and peroxyl radicals, both lipid-soluble and water-soluble) are presented, and the appropriate control experiments are described. Methods that may be used to gain evidence that a compound actually does function as an antioxidant in vivo are discussed. A review of the pro-oxidant and anti-oxidant properties of ascorbic acid that have been reported in the literature leads to the conclusion that this compound acts as an antioxidant in vivo under most circumstances.

Scavenging of hypochlorous acid and of myoglobin-derived oxidants by the cardioprotective agent mercaptopropionylglycine

Mercaptopropionylglycine (MPG) has a marked cardioprotective action in several model systems of ischaemia-reoxygenation injury. Suggested mechanisms of action include scavenging of hydroxyl radical and of hypochlorous acid and reacting with an oxidant formed by reaction of myoglobin with H2O2, thereby slowing lipid peroxidation stimulated by myoglobin-H2O2 mixtures. This oxidant seems not to be singlet O2 or hydroxyl radical. Studies in vitro show that scavenging of hypochlorous acid is a feasible mechanism of cardioprotective action for MPG in vivo in ischaemia/reperfusion systems to which neutrophil-mediated injury contributes. However, the poor ability of MPG to inhibit lipid peroxidation stimulated by myoglobin/H2O2 mixtures and its ability to increase iron ion release from myoglobin in the presence of a large excess of H2O2 suggests that MPG is unlikely to protect the myocardium by interfering with oxidants produced by the myoglobin-H2O2 system.

Prevention of reperfusion injury in ischemic-reperfused hearts by oxypurinol and allopurinol

We investigated the effects of the xanthine oxidase inhibitor allopurinol and its metabolite oxypurinol on isolated rabbit hearts. To assess the potential role of these drugs in preventing reperfusion injury, hearts were perfused using Langendorff techniques, held globally ischemic for 3 h at 15 degrees C, and then reperfused. During perfusion, hearts received Krebs-Henseleit solution maintained at 37 degrees C. Aortic perfusion pressure was held constant at 80 cm H2O. Prior to ischemia, hearts were arrested with a constant volume of KCl cardioplegia. Using a left ventricular (LV) balloon, developed pressures were measured prior to and following global ischemia. In addition, coronary circulation (CC) was measured before and after ischemia. All hearts were paced at 260 beats/min. We studied four groups: group 1 received 1 mM allopurinol, group 2 received 1 mM oxypurinol, group 3 received 90 IU/ml superoxide dismutase (SOD) plus 8085 IU/ml catalase (CAT), and group 4 received no treatment and served as a control. Each group consisted of 8 animals. Hearts receiving drug treatment did so during the first 5 min of reperfusion. Displaying all data as a function of LV volume, postischemic values were compared to preischemic values. Multivariate analysis and Tukey tests were used to detect significant differences between groups. When compared to the control group, all drug-treated groups significantly recovered end-diastolic function. Peak systolic pressure decreased significantly in the SOD/CAT group as compared to all other groups.(ABSTRACT TRUNCATED AT 250 WORDS)