Correlation between hydroperoxide-induced chemiluminescence of the heart and its function

A white paper on Phospholipid Hydroperoxide Glutathione Peroxidase (GPx4) forty years later

The purification of a protein inhibiting lipid peroxidation led to the discovery of the selenoperoxidase GPx4 forty years ago. Thus, the evidence of the enzymatic activity was reached after identifying the biological effect and unambiguously defined the relationship between the biological function and the enzymatic activity. In the syllogism where GPx4 inhibits lipid peroxidation and its inhibition is lethal, cell death is operated by lipid peroxidation. Based on this rationale, this form of cell death emerged as regulated iron-enforced oxygen toxicity and was named ferroptosis in 2012. In the last decades, we learned that reduction of lipid hydroperoxides is indispensable and, in cooperation with prooxidant systems, controls the critical steady state of lipid peroxidation. This concept defined the GPx4 reaction as both the target for possible anti-cancer therapy and if insufficient, as cause of degenerative diseases. We know the reaction mechanism, but the details of the interaction at the membrane cytosol interface are still poorly defined. We know the gene structure, but the knowledge about expression control is still limited. The same holds true for post-transcriptional modifications. Reverse genetics indicate that GPx4 has a role in inflammation, immunity, and differentiation, but the observations emerging from these studies need a more specifically addressed biochemical evidence. Finally, the role of GPx4 in spermatogenesis disclosed an area unconnected to lipid peroxidation. In its mitochondrial and nuclear form, the peroxidase catalyzes the oxidation of protein thiols in two specific aspects of sperm maturation: stabilization of the mid-piece and chromatin compaction. Thus, although available evidence converges to the notion that GPx4 activity is vital due to the inhibition of lipid peroxidation, it is reasonable to foresee other unknown aspects of the GPx4 reaction to be disclosed.

Intestinal and Hepatic Uptake of Dietary Peroxidized Lipids and Their Decomposition Products, and Their Subsequent Effects on Apolipoprotein A1 and Paraoxonase1

Both pro- and antiatherosclerotic effects have been ascribed to dietary peroxidized lipids. Confusion on the role of peroxidized lipids in atherosclerotic cardiovascular disease is punctuated by a lack of understanding regarding the metabolic fate and potential physiological effects of dietary peroxidized lipids and their decomposition products. This study sought to determine the metabolic fate and physiological ramifications of 13-hydroperoxyoctadecadienoic acid (13-HPODE) and 13-HODE (13-hydroxyoctadecadienoic acid) supplementation in intestinal and hepatic cell lines, as well as any effects resulting from 13-HPODE or 13-HODE degradation products. In the presence of Caco-2 cells, 13-HPODE was rapidly reduced to 13-HODE. Upon entering the cell, 13-HODE appears to undergo decomposition, followed by esterification. Moreover, 13-HPODE undergoes autodecomposition to produce aldehydes such as 9-oxononanoic acid (9-ONA). Results indicate that 9-ONA was oxidized to azelaic acid (AzA) rapidly in cell culture media, but AzA was poorly absorbed by intestinal cells and remained detectable in cell culture media for up to 18 h. An increased apolipoprotein A1 (ApoA1) secretion was observed in Caco-2 cells in the presence of 13-HPODE, 9-ONA, and AzA, whereas such induction was not observed in HepG2 cells. However, 13-HPODE treatments suppressed paraoxonase 1 (PON1) activity, suggesting the induction of ApoA1 secretion by 13-HPODE may not represent functional high-density lipoprotein (HDL) capable of reducing oxidative stress. Alternatively, AzA induced both ApoA1 secretion and PON1 activity while suppressing ApoB secretion in differentiated Caco-2 cells but not in HepG2. These results suggest oxidation of 9-ONA to AzA might be an important phenomenon, resulting in the accumulation of potentially beneficial dietary peroxidized lipid-derived aldehydes.

Comparison of Lipid Peroxidation and Myocardial Damage Induced by Adriamycin and 4′-Epiadriamycin in Mice

Adriamycin (ADM) and 4'-epiadriamycin (4'-ADM) were given to mice in a single dose of 15 mg/kg body weight (i.p.). Twenty-five mice were alloted to 3 groups. One group (Group I; n = 8) was given ADM; another group (Group II; n = 9) was similarly treated with 4'-ADM, and a control group (n = 8) received an equivalent volume of 0.9% NaCl solution. Mice were sacrificed 4 days after the described treatment. A complete autopsy was carried out in each animal. Hydroperoxide-initiated chemiluminescence and malonaldehyde formation were measured in mouse heart homogenates. Control mice showed a maximal photoemission of 52 +/- 2 (X 10(-3)) (mean values +/- S.E.M.) cpm/mg protein and a formation of 20 +/- 4 nmol malonaldehyde/g organ after a 2 hr-incubation. The ADM-treated mice showed a 24% enhanced hydroperoxide-initiated photoemission and a 370% increased malonaldehyde formation. The 4'-ADM-treated mice showed a 15% increased hydroperoxide-stimulated chemiluminescence and an 85% increased malonaldehyde formation. Vitamin A (5000 IU), vitamin E (85 IU) and vitamins A and E (same doses as before) given as a single dose i.p. 1 day before doxorubicin administration were able to decrease the hydroperoxide-initiated chemiluminescence by 24%, 26% and 44%, respectively. Microscopically, only scarce isolated microvacuolated subendocardial fibers were found in the ADM-treated animals. Our data showing that 4'-ADM lacks a statistically significant effect in increasing heart peroxidation as compared to ADM may explain its lower myocardial toxicity.

Singlet molecular oxygen generated by biological hydroperoxides

The chemistry behind the phenomenon of ultra-weak photon emission has been subject of considerable interest for decades. Great progress has been made on the understanding of the chemical generation of electronically excited states that are involved in these processes. Proposed mechanisms implicated the production of excited carbonyl species and singlet molecular oxygen in the mechanism of generation of chemiluminescence in biological system. In particular, attention has been focused on the potential generation of singlet molecular oxygen in the recombination reaction of peroxyl radicals by the Russell mechanism. In the last ten years, our group has demonstrated the generation of singlet molecular oxygen from reactions involving the decomposition of biologically relevant hydroperoxides, especially from lipid hydroperoxides in the presence of metal ions, peroxynitrite, HOCl and cytochrome c. In this review we will discuss details on the chemical aspects related to the mechanism of singlet molecular oxygen generation from different biological hydroperoxides.

Biophoton detection and low-intensity light therapy: a potential clinical partnership

Low-intensity light therapy (LILT) is showing promise in the treatment of a wide variety of medical conditions. Concurrently, our knowledge of LILT mechanisms continues to expand. We are now aware of LILT's potential to induce cellular effects through, for example, accelerated ATP production and the mitigation of oxidative stress. In clinical use, however, it is often difficult to predict patient response to LILT. It appears that cellular reduction/oxidation (redox) state may play a central role in determining sensitivity to LILT and may help explain variability in patient responsiveness. In LILT, conditions associated with elevated reactive oxygen species (ROS) production, e.g. diabetic hyperglycemia, demonstrate increased sensitivity to LILT. Consequently, assessment of tissue redox conditions in vivo may prove helpful in identifying responsive tissues. A noninvasive redox measure may be useful in advancing investigation in LILT and may one day be helpful in better identifying responsive patients. The detection of biophotons, the production of which is associated with cellular redox state and the generation of ROS, represents just such an opportunity. In this review, we will present the case for pursuing further investigation into the potential clinical partnership between biophoton detection and LILT.

Role of Ca2+ in radiation-induced damage in murine splenocytes

PURPOSE

To address the links between calcium, peroxidation, cell damage and death and the response of the enzymes involved in free radical metabolism, in splenocytes of mice irradiated with gamma-rays.

MATERIALS AND METHODS

Splenocytes of Swiss albino mice were irradiated with various doses (0-7 Gy) of gamma-rays (60Co) at a dose-rate of 0.0575 Gy s(-1). Membrane peroxidation and fluidity were determined by the thiobarbituric acid-reactive substances (TBARS) method, and fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH), respectively. Apoptosis was analysed by nucleosomal ladder formation and activity of NF-kappaB by electrophoretic mobility shift assay (EMSA). The specific activities of the antioxidant enzymes, lactate dehydrogenase (LDH), levels of nitric oxide (NO*) and glutathione were determined spectrophotometrically. Modulatory effects of Ca2+ were examined at 3 Gy using different concentrations (1, 3 and 5 mM) in the presence or absence of the ionophore A23187.

RESULTS

Irradiation of splenocytes resulted in enhanced peroxidative damage. membrane fluidity, apoptosis and DNA binding activity of NF-kappaB. The specific activities of LDH and antioxidant enzymes superoxide dismutase (SOD), DT-diaphorase (DTD), glutathione S-transferase (GST) and levels of glutathione (GSH) and NO* were increased with radiation dose up to 4Gy. Ca2+ augmented the radiation-induced responses. The presence of ionophore A23187 potentiated the modulatory effects of Ca2+.

CONCLUSIONS

These findings show that Ca2+ augments radiation damage and is more effective intracellularly. Ca2+, peroxidation, cellular damage and apoptosis are possibly interlinked through signals, as is evident from the increased activity of NF-kappaB and generation of NO*. The enhanced antioxidant status suggests an attempt made by the irradiated cells to maintain their normal functions.

Oxidative stress in mouse heart by antitumoral drugs: a comparative study of doxorubicin and mitoxantrone

Doxorubicin and mitoxantrone were given to mice in a single dose of 15 mg/kg body wt (i.p.). 'In situ' heart spontaneous chemiluminescence, hydroperoxide-initiated chemiluminescence and TBARS were measured in heart homogenates of treated and control animals at 2-5 days after injection. Heart spontaneous emission (control value: 45 +/- 5 cps/cm2) was increased by 10-fold in doxorubicin-treated mice 4 days after administration, whereas mitoxantrone did not produce any significant change. Administration of doxorubicin produced increases of 50% in hydroperoxide-initiated chemiluminescence and of 80% in TBARS levels 4 days after injection. Mitoxantrone did not induce significant changes in these parameters as compared with the controls. Cardiac reduced glutathione levels were not affected by mitoxantrone but were decreased (about 30%) by doxorubicin (control value: 0.98 +/- 0.08 mumol/g organ). Our data indicate that mitoxantrone does not induce an increase in the endogenous lipoperoxidation rate in heart tissue as doxorubicin does; this could contribute to the lower cardiotoxicity of mitoxantrone as compared with doxorubicin.

Vasoactive eicosanoids in the rat heart: clues to a contributory role of cardiac thromboxane to post-ischaemic hyperaemia

To assess the potential role of vasoactive cardiac eicosanoids in the modulation of coronary flow, we measure thromboxane(TX)B2, 6-keto-prostaglandin(PG)F1 alpha, PGE2 and sulphido-peptide leukotrienes (LTC4, D4, E4) in the coronary effluent of isolated perfused rat heart in both baseline and post-ischaemic conditions. Leukotrienes were undetectable. The order of production rate for the other eicosanoids was 6-keto-PGF1 alpha > TXB2 > PGE2. Production of such substances was increased about seven-fold over control after 5 min. global ischaemia; experiments with hypoxia showed that this was due to an actual increase in synthesis and not to a washout effect. A platelet source for TXB2 was excluded by 111In platelet labelling experiments. We assessed relative sensitivity to inhibition of cardiac TX synthesis relative to production of 6-keto-PGF1 alpha to inhibition by aspirin, ibuprofen, diclofenac and the specific thromboxane synthase inhibitor OKY-046. Aspirin, ibuprofen and diclofenac decreased 6-keto-PGF1 alpha production at a concentration always greater than required for a similar extent of TX inhibition. On the other hand a selective inhibition (> 90%) of TX was observed in the presence of OKY-046. Regression analysis of various 6-keto-PGF1 alpha/TXB2 ratios, as obtained in these different conditions, vs coronary flow, showed no correlation in baseline conditions, but a significant positive correlation (r = 0.59, P < 0.01) for post-ischaemic values. These data suggest a role for cardiac eicosanoids, including a non-platelet, cardiac-derived TX, in modulating the hyperaemic response in the isolated rat heart.

The effect of beta blocking drugs on lipid peroxidation in rat heartin vitro

Beta-adrenergic receptor blocking drugs include a structurally related class of drugs that are employed clinically to treat a variety of cardiovascular disorders. Since these drugs exert additional nonspecific effects including membrane stabilization, representative samples including atenolol, dilevolol, labetalol, metoprolol and propranolol were studied to determine their influence on lipid peroxidation. Homogenates or liposomes of adult rat hearts were incubated in the presence of various concentrations of propranolol or equivalent concentrations of dilevolol, labetalol, metoprolol or atenolol. Lipid peroxidation was stimulated with 50 microM FeSO4, 5 microM t-butyl hydroperoxide (homogenates) or 0.2 mM citrate FeSO4 (liposomes) plus O2. Lipid peroxidation, as assessed by both the thiobarbituric acid reaction and chemiluminescence, was reduced in a dose-dependent manner as the propranolol concentration was increased from 1 to 10 mM. The five beta-adrenergic receptor blocking drugs reduced lipid peroxidation both in crude homogenates and in liposomes; their effectiveness was related to their lipophilicity. Dilevolol, propranolol, labetalol and metoprolol at a concentration of 20 mM reduced lipid peroxidation by 45%, 37%, 35% and 28%, respectively. The hydrophilic blocker atenolol was ineffective in reducing lipid peroxidation even at elevated concentrations. Lipophilic beta-blocking drugs apparently are capable of exerting an antioxidant effect in protecting membrane lipids against peroxidation.

Enhanced chemiluminescence as a measure of oxygen-derived free radical generation during ischemia and reperfusion

It has been suggested that oxygen-derived free radicals may contribute to the myocardial injury associated with ischemia and reperfusion. As the presence of enhanced free radical generation is a prerequisite for such damage, several techniques have been used to provide evidence of increased oxygen free radical production during reperfusion; however, all such techniques have substantial limitations. In this study, we used enhanced chemiluminescence to evaluate oxygen free radical generation during ischemia and reperfusion in the isolated Langendorff-perfused rat heart. The chemiluminescent technique, which has high sensitivity and can monitor radical generation continuously, avoids some of the limitations of earlier methods. Chemiluminescence (expressed as counts per second) decreased from 219 +/- 11 at baseline to 142 +/- 9 during ischemia and markedly increased to a peak of 476 +/- 36 during the first 3-5 minutes of reperfusion. This was followed by a slow decline over 11-16 minutes to a steady-state level of 253 +/- 14 (each sequential change in chemiluminescence was highly significant; p less than 0.001). Superoxide dismutase (2,000 units/min) significantly decreased peak reperfusion chemiluminescence to 316 +/- 17 (p less than 0.01). Hearts subjected to a second period of ischemia and reperfusion had a higher peak chemiluminescence (626 +/- 62), which also was significantly attenuated by 1,000 units/min superoxide dismutase (398 +/- 16; p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Damage of Escherichia coli cells by t-butylhydroperoxide involves the respiratory chain but is independent of the presence of oxygen

The action of t-butylhydroperoxide (tBOOH) on Escherichia coli cells has been studied as a model system for organic peroxide toxicity. Exposure of E. coli cells to tBOOH led to progressive and irreversible impairment of the respiratory function, an effect which was dependent on the availability of substrate. The effect of tBOOH on growth of E. coli with different carbon sources and alternative terminal electron acceptors was investigated. It was found that the sensitivity of E. coli to tBOOH under diverse growth conditions implicating a functional respiratory chain was greater than when the bacterium grew by fermentation. Also the mutant E. coli SASX76, which requires exogenous 5-aminolevulinic acid to synthesize the cytochromes, was more resistant to tBOOH when lacking a functional respiratory chain. These data point to the respiratory chain as a major target in the in vivo action of tBOOH. Experiments with isolated membranes also showed a tBOOH-induced damage of the respiratory chain monitored by impairment of the NADH oxidase. The effect of tBOOH was produced even under anaerobiosis, indicating that development of cell damage was independent of oxygen and, therefore, that neither oxygen-derived radicals nor lipid peroxidation were involved.

The metabolic consequences of hydroperoxide perfusion on the isolated rat heart

Perfusion of rat hearts with Krebs-Henseleit bicarbonate buffer containing low concentrations of hydrogen peroxide or t-butylhydroperoxide (50-500 microM) caused an imbalance in the relative synthesis versus utilization rates of ATP, leading to a net hydrolysis of ATP and phosphocreatine. Hydrogen peroxide also caused an 80% inactivation of glyceraldehyde-3-phosphate dehydrogenase, resulting in an inhibition of glycolysis and a rapid accumulation of sugar phosphates as detected with 31P-NMR spectroscopy. This inhibition was partially reversible with peroxide-free perfusion, resulting in a cessation of high-energy-phosphate hydrolysis and a decrease in the accumulated inorganic phosphate and sugar phosphate. t-Butylhydroperoxide toxicity was irreversible. Providing an alternative, non-glycolytic substrate (butyrate) did not protect against the toxicity of hydrogen peroxide, but altered the relative importance of sugar phosphate formation versus ATP hydrolysis. Experiments with heart homogenates in vitro suggest that the inhibition of glyceraldehyde-3-phosphate dehydrogenase is a consequence of a direct reaction of the enzyme with hydrogen peroxide or one of its metabolites. Hearts subjected to total global ischemia (10-20 min), followed by reperfusion with oxygenated buffer, showed no detectable inactivation of glyceraldehyde-3-phosphate dehydrogenase, indicating that ischemia and reperfusion do not result in the production of high global concentrations of hydrogen peroxide.

Oxidative stress in the rat heart, studies on low-level chemiluminescence

Detection of ultraweak chemiluminescence (CL) emission from the surface of the organ is a sensitive and non-disruptive tool to evaluate the oxidative stress in rat heart. Indeed, an increased photon emission rate can be observed when cellular antioxidants such as glutathione or vitamin E are depleted, or when organic hydroperoxides are infused. We used CL recording to demonstrate in rat heart that: (i) different diets may lead to different heart sensitivity to an oxidative stress; and (ii) post-ischaemic reoxygenation induces an oxidative stress. CL emission induced by an oxidative stress is accompanied by an increased release of eicosanoids. However, while non-steroid anti-inflammatory drugs (aspirin, indomethacin and ibuprofen) prevented eicosanoid release, these compounds dramatically enhanced hydroperoxide-dependent CL. The nature of this phenomenon is still obscure, but the increase of steady-state concentration of excited species caused by anti-inflammatory drugs seems to be pathophysiologically relevant, since in all our experimental conditions tissue damage was proportional to CL emission rate.

Increased ultra weak chemiluminescence emission from rat heart at postischemic reoxygenation: protective role of vitamin E

Aim of this study was to confirm an increased free radical generation rate during ischemia-reoxygenation, by ultra-weak chemiluminescence detection at the surface of perfused rat heart. We observed that reoxygenation following 30 min global ischemia, induces an increase of ultraweak chemiluminescence emission in isolated perfused heart only if partial depletion of vitamin E is induced by dietary manipulation. Moreover, in normal diet fed rats, vitamin E is partially consumed during global ischemia, but not during reoxygenation. Since chemiluminescence increases during post-ischemic reperfusion, when vitamin E myocardial content is lowered, the most probable free radicals involved are the hydroperoxyl radical derivatives of lipids. These radicals, indeed, are known both to produce photoemission by disproportion and to react with vitamin E. On the other hand, the nature of the reaction that consumes vitamin E during ischemia is still obscure. Accordingly, the basal level of vitamin E myocardial content seems to be a key factor for protecting the heart against reoxygenation injury and its consumption during ischemia could be a determinant of myocardial sensitivity to oxidative stress during reperfusion.

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.

Regulatory aspects of low intensity photon emission

Photon emission from unicellular and multicellular organisms has been a subject of study for many decennia. In contrast to the well-known phenomenon of bioluminescence originating in luciferin-luciferase reactions, low intensity emission in the visible region of the electromagnetic spectrum has been found in almost every species studied so far. At present, the nomenclature of this phenomenon has not crystallized and it is referred to by a variety of names, such as mitogenetic radiation 29, dark luminescence 7, low-level chemiluminescence 20,36, and biophotons 57. Particular attention has been focussed on the relationship between photon emission and the regulation of various aspects of cellular metabolism, although in many cases quantitative data are still lacking. Throughout the history of this field of research the question of a functional biological role of the low intensity emission has been repeatedly raised; this is reflected, for instance, in the heterogeneity of the terms used to describe it. The discussion concerns the possible participation of photons of low intensity in intra- and intercellular communication. This paper reviews literature on the metabolic regulation of low intensity emission, as well as the regulation of photon emission initiated by external light. Furthermore, recent data are discussed with respect to a possible biocommunicative function of low intensity photon emission.

Spontaneous lung chemiluminescence upon paraquat administration

In vivo rat lung chemiluminescence was measured at different times after a single injection of either 30 or 60 mg paraquat/kg b.w. The lungs were isolated to determine myeloperoxidase (index of polymorphonuclear leukocytes), lung wet weight (lung edema) and malondialdehyde (lipid peroxidation). The highest chemiluminescence was reached 30 hours after injection of 30 mg/kg or 6 hours after a 60 mg/kg dose. The peak chemiluminescence was coincident with the maximum concentration of myeloperoxidase and lung wet weight suggesting that most chemiluminescence was the consequence of polymorphonuclear activation after migration to the injured areas.

Effect of dietary fats on hydroperoxide-induced chemiluminescence emission and eicosanoid release in the rat heart

The effect of diets supplemented with three different fats (olive oil, sunflower oil, pork fat) on the susceptibility of the rat heart to oxidative stress and on the rate of eicosanoid release were studied. Our results show that when fatty-acid unsaturation of heart lipids is increased or vitamin E is decreased, even to a low degree, a marked enhancement of the susceptibility to hydroperoxide-induced oxidative stress (measured by chemiluminescence emission) occurs, which is associated with an increase of eicosanoid release from the heart.

The role of lipid peroxidation in pathogenesis of arrhythmias and prevention of cardiac fibrillation with antioxidants

The present paper shows the arrhythmogenic effect of a direct induction of lipid peroxidation (LP) on isolated auricles; it is demonstrated that preendured stress potentiates this effect, while antioxidants prevent it. Subsequently, in studying the mechanism of the LP arrhythmogenic effect it was established that stress, like the LP induction, disorders the activity of Na, K-ATPase and accelerates thermodenaturation of this enzyme which plays a key role in maintaining the transmembrane potential and the electrical stability of the heart. Antioxidants prevent the enumerated shifts. Based on these data, the antioxidant BHT was successfully applied for prevention of the fall in cardiac fibrillation threshold in stress and experimental myocardial infarction, and also for prevention of cardiac fibrillation itself under acute ischemia and reoxygenation of the heart.

Interaction of lipid peroxidation and calcium in the pathogenesis of neuronal injury

The interactions between lipid peroxidation and calcium in mediating damage to central nervous system membranes have been examined in several in vitro systems. Using isolated rat brain synaptosomes, brain mitochondria, or cultured fetal mouse spinal cord neurons, Ca2+ was found to markedly enhance lipid peroxidation-induced disruption of membrane function. Gamma-aminobutyric acid (GABA) uptake by synaptosomes was inhibited 25% by either lipid peroxidation (induced with xanthine and xanthine oxidase) or Ca2+ alone, whereas inhibition was 46% with their combination. Ca2+ enhancement of lipid peroxidation-induced damage to synaptosomes was intensified by the Ca2+ ionophore, A23187, and was partially blocked by the Ca2+ channel blocker, verapamil. Similarly, inhibition of state 3 respiration in isolated rat brain mitochondria was observed with Ca2+ and a free radical generating system (xanthine and xanthine oxidase) under conditions where either insult alone failed to cause detectable damage. Na+,K+-ATPase activity of cultured fetal mouse spinal cord neurons was inhibited 32% when cells were incubated for 30 minutes in the presence of both A23187 and a free radical generating system. However, Na+,K+-ATPase was not affected during a 30 minute incubation with either A23187 or radical generating system alone. In further studies, peroxidation of rat brain synaptosomes by ferrous iron (Fe2+) and H2O2 was coupled with a rapid and large (2-7-fold) uptake of Ca2+ by synaptosomes. Fe2+ also enhanced Ca2+ uptake by spinal cord neurons in culture, an effect that was coincident with peroxidation of neuronal membranes and the release of arachidonic acid from cells. Iron-induced Ca2+ uptake was blocked by high concentrations of either desferrioxamine or methylprednisolone, whereas Ca2+ channel blockers did not affect Ca2+ uptake induced by Fe2+. Finally, peroxidation of membrane lipids by Fe2+ was stimulated by Ca2+. Concentrations of Ca2+ as low as 10(-9) M increased peroxidation reactions within brain synaptosomal membranes. The results of these studies indicate that lipid peroxidation and Ca2+ can synergistically act to damage biologic membranes. The findings suggest that Ca2+ and lipid peroxidation cannot be considered as separate entities in the pathophysiology of CNS trauma. A hypothesis proposing an inseparable interplay between lipid peroxidation and Ca2+ in the pathogenesis of traumatic and ischemic cell injury is presented.

Characteristics of lipid peroxidative conduction block induced by an organic hydroperoxide in axons of isolated frog nerve

The direct effects of lipid peroxidation on axonal conduction were investigated by application of tertiary-butyl hydroperoxide (t-BOOH) to the isolated common peroneal nerve of the frog (Rana catesbeiana). The powerful oxidizing agent t-BOOH caused a concentration-related (0.03-3.0%) block of action potential conduction. This effect, presumably due to axonal lipid peroxidation, was progressive, with the time required for the conduction impairment to occur also being a function of t-BOOH concentration. In contrast, tertiary butyl alcohol had no effect even at a 3.0% concentration. The gamma-fibers in the nerve were the most sensitive to t-BOOH conduction block, followed in order by the larger diameter beta-fibers and the even larger alpha-fibers. The rate of decrease in conduction was faster in nerves that were stimulated continuously (1 Hz) than in those that were activated only at specific measurement times, indicating an association between axonal depolarization and susceptibility to peroxidative conduction block. Recovery of conduction was observed particularly in alpha- and beta-fibers. The rate and extent of recovery were inversely proportional to the concentration of t-BOOH, suggesting that moderate peroxidative damage is potentially reversible. The possible relationship of these results to lipid peroxidative axonal damage in acute central nervous system injury is discussed.

Glutathione depletion increases chemiluminescence emission and lipid peroxidation in the heart

Diamide, CDNB and phorone were used to deplete glutathione in retrogradely perfused rat hearts. Following glutathione depletion the spontaneous chemiluminescence increased by 70%, irrespective of the agent used. The glutathione depletion and the chemiluminescence emission were associated to an increase of malondialdehyde content in the heart, as determined by HPLC. Under these conditions the heart function was impaired and histological examination showed a coagulative myocytolysis, a pattern already described in human and experimental pathology, where a key role is attributed to a Ca2+ homeostasis impairment.

Evidence for lipid peroxidation during the calcium paradox in vitamin E-deficient rat heart

Vitamin E is known to play an important role in the protective capacity of tissues as a free radical scavenger. Rats were made deficient in vitamin E, in order to demonstrate more clearly the formation of free radicals after exposing the rat heart to sudden changes in calcium homeostasis. The formation of malondialdehyde was taken as measure for lipid peroxidation. Malondialdehyde was detected in appreciable amounts both in heart tissue and coronary perfusate of vitamin E-deficient rat hearts after exposing them to the sudden changes in calcium concentration as seen during the calcium paradox. These findings emphasize a the hearts of normally fed rats no malondialdehyde could be detected in tissue or coronary perfusate after the calcium paradox. Therefore an essential role for vitamin E against oxidative stress in heart tissue is also indicated.