Intracellular labile iron determines H2O2-induced apoptotic signaling via sustained activation of ASK1/JNK-p38 axis

Hydrogen peroxide (H2O2) acts as a second messenger in signal transduction participating in several redox regulated pathways, including cytokine and growth factor stimulated signals. However, the exact molecular mechanisms underlying these processes remain poorly understood and require further investigation. In this work, using Jurkat T lymphoma cells and primary human umbilical vein endothelial cells, it was observed that changes in intracellular "labile iron" were able to modulate signal transduction in H2O2-induced apoptosis. Chelation of intracellular labile iron by desferrioxamine rendered cells resistant to H2O2-induced apoptosis. In order to identify the exact points of iron action, we investigated selected steps in H2O2-mediated apoptotic pathway, focusing on mitogen activated protein kinases (MAPKs) JNK, p38 and ERK. It was observed that spatiotemporal changes in intracellular labile iron, induced by H2O2, influenced the oxidation pattern of the upstream MAP3K ASK1 and promoted the sustained activation of JNK-p38 axis in a defined time-dependent context. Moreover, we indicate that H2O2 induced spatiotemporal changes in intracellular labile iron, at least in part, by triggering the destabilization of lysosomal compartments, promoting a concomitant early response in proteins of iron homeostasis. These results raise the possibility that iron-mediated oxidation of distinct proteins may be implicated in redox signaling processes. Since labile iron can be pharmacologically modified in vivo, it may represent a promising target for therapeutic interventions in related pathological conditions.

The effects of propofol or sevoflurane on free radical production after tourniquet induced ischaemia-reperfusion injury during knee arthroplasty

BACKGROUND

We studied the effects of anesthesia with propofol or sevoflurane on the production of free oxygen radicals during total knee arthroplasty performed with the use of an ischemic tourniquet by measuring the levels of malondialdehyde (MDA).

METHODS

We studied two groups of patients (20 patients in each group) who underwent total knee arthroplasty. To maintain anesthesia we delivered 66% nitrous oxide plus sevoflurane or propofol. Blood samples for the determination of the MDA levels were drawn before the application of the ischemic tourniquet and 5 and 30 minutes after its release.

RESULTS

There were no differences between groups in regard to age, weight and duration of the tourniquet application. MDA levels decreased significantly in the propofol group 30 minutes after the release of the tourniquet (1.7 micromol litre(-1) vs 1.57 micromol litre(-1), Friedman's ANOVA, P = 0.007). In contrast, there was a small rise of the MDA levels in the sevoflurane group (1.82 micromol litre(-1) vs 1.96 micromol litre(-1), Friedman's ANOVA, P = 0.007).

CONCLUSION

Propofol may have anti-oxidant properties in orthopaedic surgery requiring tourniquet application, but sevoflurane needs further study.

Oxidative stress in hepatic ischemia-reperfusion injury: the role of antioxidants and iron chelating compounds

Ischemia-reperfusion (IR) injury is a multifactorial process triggered when the liver or other organs are transiently subjected to reduced blood supply followed by reperfusion. It has been shown that "reactive oxygen species" (ROS) are generated during ischemia and reperfusion and may represent pivotal mediators of the ensuing pathological complications. In some cases, however, moderate production of ROS may exert protective effects, a phenomenon presumably related to "ischemic preconditioning". This review will focus mainly on: a) describing the sources and the biochemical mechanisms of ROS generation during ischemia and reperfusion, b) discussing current developments in understanding the biochemical pathways by which ROS may induce toxic or protective effects, c) critically evaluating the results of previous attempts to counteract the toxic effects of ROS by using a variety of antioxidant and transition metal-chelating agents, and d) if feasible, proposing potential new pharmaceutical agents aimed at ameliorating ROS-inducing deleterious effects during reperfusion. It is concluded that ROS are generated from different sources, at different periods during IR, and may act by a variety of not well understood biochemical mechanisms which ultimately lead to cell damage and tissue failure.

Ageing research in Greece

Ageing research in Greece is well established. Research groups located in universities, research institutes or public hospitals are studying various and complementary aspects of ageing. These research activities include (a) functional analysis of Clusterin/Apolipoprotein J, studies in healthy centenarians and work on protein degradation and the role of proteasome during senescence at the National Hellenic Research Foundation; (b) regulation of cell proliferation and tissue formation, a nationwide study of determinants and markers of successful ageing in Greek centenarians and studies of histone gene expression and acetylation at the National Center for Scientific Research, Demokritos; (c) work on amyloid precursor protein and Presenilin 1 at the University of Athens; (d) oxidative stress-induced DNA damage and the role of oncogenes in senescence at the University of Ioannina; (e) studies in the connective tissue at the University of Patras; (f) proteomic studies at the Biomedical Sciences Research Center Alexander Fleming; (g) work on Caenorhabditis elegans at the Foundation for Research and Technology; (h) the role of ultraviolet radiation in skin ageing at Andreas Sygros Hospital; (i) follow-up studies in healthy elderly at the Athens Home for the Aged; and (j) socio-cultural aspects of ageing at the National School of Public Health. These research activities are well recognized by the international scientific community as it is evident by the group's very good publication records as well as by their direct funding from both European Union and USA. This article summarizes these research activities and discuss future directions and efforts towards the further development of the ageing field in Greece.

Intracellular iron, but not copper, plays a critical role in hydrogen peroxide-induced DNA damage

The role of intracellular iron, copper, and calcium in hydrogen peroxide-induced DNA damage was investigated using cultured Jurkat cells. The cells were exposed to low rates of continuously generated hydrogen peroxide by the glucose/glucose oxidase system, and the formation of single strand breaks in cellular DNA was evaluated by the sensitive method, single cell gel electrophoresis or "comet" assay. Pre-incubation with the specific ferric ion chelator desferrioxamine (0.1-5.0 mM) inhibited DNA damage in a time- and dose-dependent manner. On the other hand, diethylenetriaminepentaacetic acid (DTPA), a membrane impermeable iron chelator, was ineffective. The lipophilic ferrous ion chelator 1,10-phenanthroline also protected against DNA damage, while its nonchelating isomer 1,7-phenanthroline provided no protection. None of the above iron chelators produced DNA damage by themselves. In contrast, the specific cuprous ion chelator neocuproine (2,9-dimethyl-1,10-phenanthroline), as well as other copper-chelating agents, did not protect against H(2)O(2)-induced cellular DNA damage. In fact, membrane permeable copper-chelating agents induced DNA damage in the absence of H(2)O(2). These results indicate that, under normal conditions, intracellular redox-active iron, but not copper, participates in H(2)O(2)-induced single strand break formation in cellular DNA. Since BAPTA/AM (1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester), an intracellular Ca(2+)-chelator, also protected against H(2)O(2)-induced DNA damage, it is likely that intracellular Ca(2+) changes are involved in this process as well. The exact role of Ca(2+) and its relation to intracellular transition metal ions, in particular iron, needs to be further investigated.

Trimetazidine protects low-density lipoproteins from oxidation and cultured cells exposed to H(2)O(2) from DNA damage

Trimetazidine is a well-established anti-ischemic drug, which has been used for long time in the treatment of pathological conditions related with the generation of reactive oxygen species. However, although extensively studied, its molecular mode of action remains largely unknown. In the present study, the ability of trimetazidine to protect low-density lipoproteins (LDL) from oxidation and cultured cells from H(2)O(2)-induced DNA damage was investigated. Trimetazidine, tested at concentrations 0.02 to 2.20 mM, was shown to offer significant protection to LDL exposed to three different oxidizing systems, namely copper, Fe/ascorbate, and met-myoglobin/H(2)O(2). The oxidizability of LDL was estimated by measuring, (i) the lag period, (ii) the maximal rate of conjugated diene formation, (iii) the total amount of conjugated dienes formed, (iv) the electrophoretic migration of LDL protein in agarose gels (REM), and (v) the inactivation of the enzyme PAF-acetylhydrolase present in LDL. In addition, the presence of trimetazidine decreased considerably the DNA damage in H(2)O(2)-exposed Jurkat cells in culture. H(2)O(2) was continuously generated by the action of glucose oxidase at a rate of 11.8 +/- 1.5 microM per min (60 ng enzyme per 100 microl), and DNA damage was assessed by the single cell gel electrophoresis assay (also called comet assay). The protection offered by trimetazidine in this system (about 30% at best) was transient, indicating modification of this agent during its action. These results indicate that trimetazidine can modulate the action of oxidizing agents in different systems. Although its mode of action is not clarified, the possibility that it acts as a lipid barrier permeable transition metal chelator is considered.

SIN-1-induced DNA damage in isolated human peripheral blood lymphocytes as assessed by single cell gel electrophoresis (comet assay)

Human lymphocytes were exposed to increasing concentrations of SIN-1, which generates superoxide and nitric oxide, and the formation of single-strand breaks (SSB) in individual cells was determined by the single-cell gel electrophoresis assay (comet assay). A dose- and time-dependent increase in SSB formation was observed rapidly after the addition of SIN-1 (0.1-15 mM). Exposure of the cells to SIN-1 (5 mM) in the presence of excess of superoxide dismutase (0.375 mM) increased the formation of SSB significantly, whereas 1000 U/ml catalase significantly decreased the quantity of SSB. The simultaneous presence of both superoxide dismutase and catalase before the addition of SIN-1 brought the level of SSB to that of the untreated cells. Moreover, pretreatment of the cells with the intracellular Ca(2+)-chelator BAPTA/AM inhibited SIN-1-induced DNA damage, indicating the involvement of intracellular Ca(2+) changes in this process. On the other hand, pretreatment of the same cells with ascorbate or dehydroascorbate did not offer any significant protection in this system. The data suggest that H2O2-induced changes in Ca(2+) homeostasis are the predominant pathway for the induction of SSB in human lymphocytes exposed to oxidants.

Glucose oxidase-produced H2O2 induces Ca2+-dependent DNA damage in human peripheral blood lymphocytes

DNA of lymphocytes from human peripheral blood was analyzed by using the single cell gel electrophoresis technique (comet assay). The cells were used either as received from the donors or after treatment with various concentrations of the H2O2-generating enzyme glucose oxidase, in order to achieve a continuous flow of H2O2. The formation of single strand breaks (SSB) was dose-related but the time course of the induction of SSB by relatively low concentrations of glucose oxidase was of a biphasic mode with a fast increase 2 to 5 min after the addition of glucose oxidase followed by a gradual decrease toward the original base level during the next 35 to 60 min. This response of the cells appears to be based on the activation of already existing defense system(s) because it was shown that H2O2 is continuously released during the reaction time and the inhibition of protein synthesis does not affect the observed pattern. Supplementation of the growth medium with various antioxidants resulted in substantial protection only when the agents were taken up by the cells. The presence of the intracellular calcium chelator BAPTA protected the cells from H2O2-induced DNA damage in a dose-dependent manner. Only at the higher rate of H2O2-generation considerable DNA damage was observed in the presence of BAPTA. These results suggest that H2O2, at low concentrations induces DNA damage through intracellular Ca2+ -mediated processes, which lead to DNA strand breaks possibly by endonuclease activation.

Evidence for non-adaptive immune response in HIV infection

Increased levels of soluble forms of adhesion molecules such as intercellular adhesion molecule 1 (ICAM-1) and E-selectin have been found in the sera of HIV-infected patients and have been associated with disease progression. The aim of the present study was to investigate whether this phenomenon reflects activation of the non-adaptive immune response in HIV infection. Fifty-one patients with HIV infection (42 men, nine women) were classified into two subgroups: those with HIV infection but without evidence of AIDS indicator conditions (HIV infected non-AIDS cases, n = 27) and those with AIDS (AIDS cases, n = 24). The activation of non-adaptive immune response was evaluated as the production of reactive oxygen species that cause lipid peroxidation, which was assessed by measuring thiobarbituric reactive substances (TBARS) using the thiobarbituric acid assay (TBA). Plasma levels of von Willebrand factor (vWF), measured by rocket immunoelectrophoresis, were used to show activation of endothelial cells even in the absence of any other causative agent, in these patients. TBARS levels in non-AIDS cases were significantly higher than in control subjects (n = 17) or AIDS cases (P < 0.001). The mean vWF levels were higher in AIDS cases than in non-AIDS cases or normal subjects (P < 0.05). TBARS levels remained significantly higher in non-AIDS cases after adjusting for age, CD4 T-cell and neutrophil counts, antiretroviral therapy and vWF plasma levels. The above findings indicate that in HIV infection, the virus per se is responsible for the increased oxidative stress that in turn activates various transduction pathways, may be leading to endothelial cell activation and shedding of adhesion molecules from the cell surface.

On the molecular mechanism of metmyoglobin-catalyzed reduction of hydrogen peroxide by ascorbate

Hydrogen peroxide induces rapid oxidation of metmyoglobin with an apparent second order rate constant, k1 = 3.4 x 10(4) M-1 min-1. The product of this interaction is ferrylmyoglobin with an unstable free radical on the globin moiety. This activated form of myoglobin is able: (a) to initiate the peroxidation of erythrocyte membranes and (b) to form intra- and intermolecular covalent crosslinkings. The presence of ascorbic acid in amounts stoichiometric to H2O2 efficiently prevents all the above processes. Moreover, in the presence of ascorbic acid a cyclic process is taking place leading to H2O2 reduction, ascorbic acid oxidation, and unmodified metmyoglobin formation (reaction 1).

Safety and efficacy of recombinant gamma interferon in the treatment of systemic sclerosis

OBJECTIVE

To evaluate the safety and efficacy of recombinant gamma interferon (rIFN gamma) in the treatment of patients with systemic sclerosis.

METHODS

Sixteen patients with systemic sclerosis were treated with r-IFN gamma, 60 micrograms m-2 (low dose, n = 10) and 150 micrograms m-2 (high dose, n = 6), three times weekly in an open phase I/II trial of eight months duration. The patients were stratified in low and high dose according to the severity and the extent of scleroderma; the two groups were comparable.

RESULTS

The treatment was well tolerated. The most common side effects, almost certainly related to r-IFN gamma, were fever, chills, dizziness, headache, and severe flu-like syndrome with decreasing intensity with the time of treatment. Severe aphthous stomatitis (n = 1), ventricular tachycardia (n = 1), severe oesophageal ulcers due to gastro-oesophageal reflux (n = 1), disease exacerbation alone with frank arthritis and slight pericardial effusion (n = 1), and inability to conform to the requirements of the study (n = 1) were the reasons for discontinuing treatment. Side effects and degree of response were evident during the first five months of treatment. A significant decrease in mean skin thickness score was observed and was higher in the high dose group. Reactive oxygen species of peripheral neutrophils and soluble interleukin-2 receptor serum concentrations were higher than those of normal individuals at study entry and decreased in parallel with clinical improvement.

CONCLUSIONS

Treatment of systemic sclerosis patients with r-IFN gamma was relatively safe and well tolerated for doses as high as 150 micrograms m-2 three times weekly. Side effects and the degree of response can be seen during the first months of therapy and can be used as predictors of ultimate toxicity or response. The drug seems to be effective in treating cutaneous scleroderma.

Purification and properties of human placental ATP diphosphohydrolase

ATP diphosphohydrolase activity (ATP-DPH) has been previously identified in the particulate fraction of human term placenta [Papamarcaki, T. & Tsolas, O. (1990) Mol. Cell. Biochem. 97, 1-8]. In the present study we have purified to homogeneity and characterized this activity. A 260-fold purification has been obtained by solubilization of the particulate fraction and subsequent chromatography on DEAE Sepharose CL-6B and 5'-AMP Sepharose 4B. The preparation has been shown to be free of alkaline phosphatase even though the placental extract is rich in this activity. The purified enzyme is a glycoprotein and migrates as a single broad band of 82 kDa on SDS/PAGE. The same band is obtained after photoaffinity labeling of the enzyme with 8-azido-[alpha-32P]ATP. The enzyme has a broad substrate specificity, hydrolyzing triphosphonucleosides and diphosphonucleosides but not monophosphonucleosides or other phosphate esters. The activity is dependent on the addition of divalent cations Ca2+ or Mg2+. The Km values for ATP and ADP were determined to be 10 microM and 20 microM, respectively. Maximum activity was found at pH 7.0-7.5 with ATP as substrate, and pH 7.5-8.0 with ADP. The enzymic activity is inhibited by NaN3, NaF, adenosine 5'-[beta,gamma-imido]triphosphate and adenosine 5'-[alpha,beta-methylene]triphosphate. Protein sequence analysis showed ATP-DPH to be N-terminally blocked. Partial internal amino acid sequence information was obtained after chymotryptic cleavage and identified a unique sequence with no significant similarity to known proteins. ATP-DPH activity has been reported to be implicated in the prevention of platelet aggregation, hydrolysing ADP to AMP and thus preventing blood clotting.

Superoxide anion generation by human peripheral blood mononuclear cells in response to prothymosin alpha

The ability of human peripheral blood mononuclear cells to respond to highly purified prothymosin alpha by generating superoxide anion was investigated. The generation of superoxide anion was detected by measuring the superoxide dismutase-inhibitable reduction of oxidized cytochrome C. Prothymosin alpha was shown to stimulate weakly these cells. The dose-response curve displayed a biphasic bell-shaped superoxide generation profile with two specific concentration optima for each individual blood donor, but with variations in optimal concentrations between the donors. By using a counter current centrifugation (elutriation) system, the mononuclear cell population was separated into several fractions according to their volume and density. Selective stimulation of these fractions with prothymosin alpha revealed that different cell populations were responsible for the generation of superoxide at higher and lower concentrations of stimulant, respectively. The response to the stimulus was immediate and lasted for a time period of about 4 to 8 min during which approximately 0.7 nmol O2- per min/10(6) cells were generated. The superoxide generation was cell-number-dependent with an optimum at 1 x 10(6) cells and lower rates for both smaller and larger cell numbers. Staurosporine, a potent inhibitor of protein kinase C, at concentrations sufficient to inhibit totally PMA-induced O2- generation, failed to affect the response of the cells to prothymosin alpha, while chelation of the extracellular Ca2+ abolished the lower but not the higher peak of O2- generation. Finally, simultaneous addition of prothymosin alpha and PMA resulted in a approximately 40% decrease of the O2- generation induced by PMA alone. A putative role as cell injury indicator is proposed for prothymosin alpha.

Ferrylmyoglobin-catalyzed linoleic acid peroxidation

The addition of linoleic acid (18:2) to a solution containing oxymyoglobin (MbIIO2), metmyoglobin (MbIII), or metmyoglobin-azide complex (MbIII-N3-) resulted in the formation of a common complex with identical absorption spectral properties. The addition of H2O2 to a MbIII/linoleic acid mixture revealed a spectral profile with lambda max at 530 nm and different from that observed in the reaction of MbIII with H2O2 and identical to that of ferrylmyoglobin. This was accompanied by a progressive decrease in the absorption in the visible region, indicating heme degradation during the lipid peroxidation process. The oxidation products of linoleic acid during the MbIII/18:2/H2O2 interaction were assessed by HPLC under anaerobic and aerobic conditions. In both instances, the chromatograms at lambda 234 nm revealed the formation of a main peak with a retention time of 11.1 min, which cochromatographed with a standard of 9-hydroperoxide of linoleic acid. The latter adduct was not degraded by the oxoferryl complex of myoglobin. The conclusions originating from this research are two-fold. On the one hand, the identical spectral properties exhibited by the product originating from the reaction of either MbIIO2 or MbIII with linoleic acid bridge the apparent discrepancy between the different reactivities of MbIIO2 and MbIII toward H2O2 and their ability to promote lipid peroxidation. On the other hand, the pattern of oxidation products of linoleic acid observed during the MbIII/H2O2 interaction, i.e., the formation of a 9-hydroperoxide adduct as a major product, points to a specific binding character and a regioselectivity of the oxoferryl complex in the oxidation of unsaturated fatty acids or a catalytic preference for decomposition of the various isomeric hydroperoxides over that of the 9-hydroperoxide.

Redox cycling of myoglobin and ascorbate: a potential protective mechanism against oxidative reperfusion injury in muscle

Metmyoglobin catalyzes the decomposition of H2O2 as well as other hydroperoxides by using ascorbic acid as a substrate. The ratio of H2O2 reduced to ascorbate oxidized is close to one, whereas the rate of oxidation is directly proportional to both H2O2 and metmyoglobin concentrations. Ascorbate also prevents the protein modifications and the O2 evolution that accompany the reaction of metmyoglobin with hydroperoxides. In the absence of ascorbate, myoglobin and H2O2 promote the peroxidation of unsaturated fatty acids and, thus, may cause damage to cellular constituents. However, lipid peroxidation is inhibited in the presence of ascorbate and, for this reason, it is suggested that this heme protein functions in the opposite manner. The redox cycling of myoglobin by ascorbate may act as an important electron "sink" and defense mechanism against peroxides during oxidative challenge to muscle.

Mechanisms of reoxygenation injury in myocardial infarction: implications of a myoglobin redox cycle

The addition of ascorbate to ischemic rat hearts prevents the myocardial damage associated with reoxygenation. H2O2 oxidizes myoglobin (Mb+2) to higher oxidation states (Mb+4 and Mb+5) which are rapidly reduced by ascorbate. It is proposed that the operation of a myoglobin redox cycle, in which H2O2 causes the two-electron oxidation of myoglobin, is a critical determinant of reperfusion injury. Conversely, the reduction of myoglobin, in one-electron steps, may represent an essential protective mechanism against such injury in the heart.

Effect of ambient oxygen concentration on lipofuscin accumulation in cultured rat heart myocytes--a novel in vitro model of lipofuscinogenesis

The objective of this study was to elucidate the factors involved in the accumulation of lipofuscin in post-mitotic cells. The hypothesis that oxidative stress accelerates the rate of lipofuscin accumulation was tested by examining the effects of 5%, 20%, and 40% ambient oxygen concentration on lipofuscin content in cultured rat cardiac myocytes. Lipofuscin was quantified by microspectrofluorometry at 7 and 12 days of in vitro age. Lipofuscin-emitted yellow autofluorescence increased in direct relationship to ambient oxygen concentration with age. Transmission electron microscopic examination of the cells after 3, 8, and 12 days in culture indicated a progressive time and oxygen dependent increase in the frequency and size of lipofuscin organelles. The results are interpreted to suggest that oxidative stress is one of the causal factors in the accumulation of lipofuscin.

Glutathione-dependent reduction of peroxides during ferryl- and met-myoglobin interconversion: a potential protective mechanism in muscle

Met-myoglobin is oxidized both by H2O2 and other hydroperoxides to a species with a higher iron valency state and the spectral characteristics of ferryl-myoglobin. Glutathione (GSH) reduces the latter species back to met-myoglobin with parallel oxidation to its disulfide (GSSG) but cannot reduce met-myoglobin to ferrous myoglobin. Under aerobic conditions, the GSH-mediated reduction of ferry-myoglobin is associated with O2 consumption and amounts of GSSG are formed far in excess over that of the peroxide added. Under anaerobic conditions, this ratio is close to unity. These results are interpreted in terms of a one-electron redox process involving the reduction of ferryl-myoglobin to met-myoglobin and the one-electron oxidation of GSH to its thiyl radical. Further reactions of thiyl radicals are influenced by the presence of oxygen which will be the determining factor in the ratio H2O2 added/GSSG formed. It is suggested that, when oxygen is limiting, myoglobin may serve as a protector of muscle cells against peroxides and other oxidants.

Co-oxidation of salicylate and cholesterol during the oxidation of metmyoglobin by H2O2

The reaction between metmyoglobin and H2O2 proceeds with oxidation of the hemo-protein iron to a higher valence state and consumption of the peroxide. This reaction is further associated with (a) O2 evolution; (b) hydroxylation of the aromatic compound salicylate to yield a set of dihydroxybenzoic acid derivatives (analyzed by HPLC with electrochemical detection); (c) autoxidation of cholesterol with formation of 3 beta-hydroxy-5-alpha-cholest-6-ene-5-hydroperoxide; and (d) formation of electronically excited states detected by low-level chemiluminescence. The heterolytic scission of the O-O bond of hydroperoxides by metmyoglobin causes the formation of an oxidizing equivalent capable of promoting peroxidation of linoleate and arachidonate (as indicated by the parallel formation of thiobarbituric acid-reactive material and an enhancement of chemiluminescence intensity). The identity of the oxidizing equivalent(s) is discussed in terms of the formation of a relatively stable higher state of oxidation of heme Fe (FeIV-OH or FeV = O) as well as on possible intermediate species derived during the decomposition of H2O2 by metmyoglobin, such as HO.and 1O2. These species might be involved either simultaneously or sequentially in the peroxidation of fatty acids as well as in the tissue damage associated with the formation of H2O2 in ischemic-reperfusion states.

Reduction of ferryl- and metmyoglobin to ferrous myoglobin by menadione-glutathione conjugate. Spectrophotometric studies under aerobic and anaerobic conditions

Both metmyoglobin (MbIII) and ferrylmyoglobin (MbIV) are reduced by the menadiol-glutathione conjugate (GS-Q2-) to oxymyoglobin (MbIIO2) or deoxymyoglobin (MbII), depending whether the assay is carried out under aerobic or anaerobic conditions, respectively. Under aerobic conditions, the reduction of MbIII to MbIIO2 by GS-Q2- is associated with O2 consumption. The latter process is accounted for by (a) the autoxidation of the conjugate yielding H2O2 and (b) the rapid binding of O2 to MbII to yield MbIIO2. The ratio [O2]consumed/[MbIIO2]formed is approximately 1.5 at the time when MbIIO2 formation is maximal (at about 0.8 min). This ratio, higher than the unit, indicates that there is more than one O2-consuming reaction in this experimental model. The ratio of initial rates of O2 consumption and MbIIO2 formation is close to the unit [(-dO2/dt)/(+ dMbIIO2/dt) = 1.1]. The formation of H2O2 originating during the autoxidation of the GS-Q2- is substantially lower in the presence of MbIII, probably due to the heterolytic cleavage of the O--O bond of the peroxide by the hemoprotein. Although the latter reaction should yield MbIV, this species is not observed in the absorption spectrum, probably due to its rapid reduction by GS-Q2-. MbIV is reduced to MbIIO2 by the GS-Q2-. Whether this reaction takes place in one-electron transfer steps, that is, the sequence: MbIV----MbIII----MbIIO2 is difficult to evaluate by absorption spectral analysis, due to the rapid rate of the [MbIV----MbIIO2] transition. Under anaerobic conditions, the reduction of either MbIII or MbIV by GS-Q2- yields MbII as a stable molecular product. Anaerobic conditions prevent any further interaction of MbII with intermediates of O2 reduction derived from GS-Q2- autoxidation.

Effect of daunorubicin on subcellular pools of glutathione in cultured heart cells from neonatal rats

Alterations in cellular GSH and its compartmentation were investigated as a possible mechanism of toxicity of the anthracycline derivative daunorubicin in neonatal heart cells. Cultured beating heart cells from neonatal rats were exposed to daunorubicin at therapeutically relevant concentrations and the resulting changes in cellular GSH as well as cytosolic and mitochondrial pools of GSH were determined. Toxicity was estimated as an increased permeability of the plasma membrane to cytosolic enzymes, e.g., lactate dehydrogenase. Control heart cells were found to contain 12.2 +/- 1.8 nmoles GSH/10(6) cells. Daunorubicin caused a rapid initial decrease followed by a transient increase in cellular GSH. The extent of the latter increase was dependent on the concentration of daunorubicin. High concentrations of daunorubicin gave only a slight increase followed by a pronounced decrease in cellular GSH. By applying a digitonin-based method the effect of daunorubicin on the cytosolic and mitochondrial pools of GSH were separated. The concentration of cytosolic and mitochondrial reduced GSH was estimated to be 8.9 +/- 1.5 nmoles/10(6) cells and 3.3 +/- 0.6 nmoles/10(6) cells, respectively. The results indicate that daunorubicin caused a decrease of cytosolic GSH and, after a short lag period, a release of alctate dehydrogenase. No decrease of mitochondrial GSH occurred under these conditions indicating that daunorubicin influences selectively cytosolic GSH. No lipid peroxidation products were detected in DRB-treated cells under conditions when lactate dehydrogenase was released. Likewise, addition of the iron-chelator desferrioxamin did not influence the release of lactate dehydrogenase, whereas dithiothreitol offered partial protection.(ABSTRACT TRUNCATED AT 250 WORDS)

Toxic effects of daunorubicin on isolated and cultured heart cells from neonatal rats

Various aspects of the cardiotoxicity of the anthracycline derivative and antineoplastic drug daunorubicin were investigated using isolated and cultured cells from neonatal rat hearts as a model system. Treatment of the cells with concentrations of daunorubicin of the same order of magnitude as those used in chemotherapy was accompanied by marked toxic effects, e.g. a decreased or abolished contraction, and release of lactate dehydrogenase, pyruvate and oxidized glutathione to the medium. A decreased frequency of contraction appeared to be the most sensitive probe of daunorubicin toxicity, followed by release of pyruvate and oxidized glutathione/lactate dehydrogenase. Daunorubicin and/or its metabolites also bound to cellular protein and DNA. Exposure to daunorubicin was shown to be accompanied by a rapid induction of primarily DT-diaphorase and a slower induction of glutathione transferase. The latter observations are interpreted to indicate a protective role of quinone- and peroxide-metabolizing enzymes, respectively, and support the hypothesis that daunorubicin toxicity involves generation of free radical derivatives, which initiate lipid peroxidation. This conclusion is further substantiated by the demonstration that addition of daunorubicin leads to an increased oxygen consumption.

Accumulation of 99Tcm-gluconate in daunorubicin-treated neonatal heart cells in culture

The cardiotoxic effect of daunorubicin was investigated using cultured heart cells from neonatal rat hearts. Exposure of the cells to low but toxic concentrations of daunorubicin led to drastically altered permeability properties of the plasma membrane as measured by release of lactate dehydrogenase. Simultaneously, 99Tcm-gluconate, an isotope complex used in scintigraphic imaging of myocardial infarcts, was accumulated in the cells. The results suggest that daunorubicin-induced cardiac damage may be estimated by isotope uptake.

Enzyme induction by daunorubicin in neonatal heart cells in culture

The effect of the antineoplastic agent daunorubicin on beating heart cells from neonatal rats was investigated with respect to cell damage and induction of enzymes possibly involved in drug metabolism. Of the enzymes assayed DT-diaphorase and glutathione-S-transferase showed a two-to-four fold increase in activity: higher concentrations of daunorubicin inactivated glutathione-S-transferase. Daunorubicin toxicity increased in the presence of dicoumarol, a specific inhibitor of DT-diaphorase. These results indicate that both DT-diaphorase and glutathione-S-transferase may be involved in the metabolism of daunorubicin.

Binding of 99mTc-gluconate to heart mitochondria

99mTc-gluconate has previously been shown to bind to isolated rat heart mitochondria. In the presence of potassium cyanide this binding is enhanced several fold, an effect which has been shown to be correlated to the efficiency of the in vivo binding of the isotope complex in ischemic dog hearts. The present investigation shows that the potassium cyanide-induced binding was mainly localized to the mitochondrial inner membrane; in the presence of cyanide other organelles, e.g., nuclei and liver microsomes also showed some binding. Boiling, lipid extraction, or addition of N-ethylmaleimide caused a variable inhibition of the binding of 99mTc-gluconate to rat heart mitochondria, which also was markedly influenced by temperature, pH, time, and concentrations of protein and isotope complex, but not by conditions affecting energy levels or calcium transport. Fractionation of submitochondrial particles exposed to 99mTc-gluconate in the presence of potassium cyanide indicated that the 99mTc-gluconate-binding component cofractionated with cytochrome oxidase. It is postulated that a protein component localized in the mitochondrial inner membrane, possibly cytochrome oxidase, is responsible for the binding of 99mTc-gluconate.

Subcellular binding of 99Tcm-gluconate in infarcted myocardium in dogs

Binding of 99Tcm-gluconate on the subcellular level in myocardial infarct tissue in the dog was investigated by means of a fractionated centrifugation technique. High isotope activity/g protein was recorded in the mitochondrial fraction indicating the 99Tcm-gluconate binds preferentially to a protein structure localized in the mitochondria.

Improved methods for automatic monitoring of contracting heart cells in culture

The present communication describes improved methods for isolating and plating beating heart cells from neonatal rats using collagenase and collagen-coated petri dishes. The amplitude and frequency of contraction are continuously and simultaneously measured under well defined conditions and during prolonged periods of time with a highly sensitive and thermostated instrument. Additions, e.g. drugs and toxic agents, are made through an accessory pump system that involves extensive dilution of the added compound with medium; aliquots of medium can be withdrawn for estimation of metabolites. The system described is reliable and relatively inexpensive and allows a more extensive use of isolated heart cells, especially in studies of heart functions where small changes in amplitude and frequency of beating during prolonged periods of time are important.