Lipid peroxidation in rat tissue homogenates: Interaction of iron and ascorbic acid as the normal catalytic mechanism

Role of antioxidants and a nutrient rich diet in Alzheimer's disease

The joint attack on the body by metabolic acidosis and oxidative stress suggests that treatment in degenerative diseases, including Alzheimer's disease (AD), may require a normalizing of extracellular and intracellular pH with simultaneous supplementation of an antioxidant combination cocktail at a sufficiently high dose. Evidence is also accumulating that combinations of antioxidants may be more effective, taking advantage of synergistic effects of appropriate antioxidants as well as a nutrient-rich diet to prevent and reverse AD. This review focuses on nutritional, nutraceutical and antioxidant treatments of AD, although they can also be used in other chronic degenerative and neurodegenerative diseases.

Ferroptosis is associated with oxygen-glucose deprivation/reoxygenation-induced Sertoli cell death

Sertoli cell death contributes to spermatogenesis impairment, which is associated with male infertility. Testicular ischemia‑reperfusion (I/R) injury induces the cell death of germ cells and Sertoli cells, whereas inhibition of cell death ameliorates acute testicular I/R damage. The aim of the present study was to investigate the mechanism of I/R stress-induced cell death in TM4 cells. Oxygen‑glucose deprivation and reoxygenation (OGD/R) was demonstrated to induce I/R injury and cell death in TM4 cells. Cell death was blocked by the reactive oxygen species (ROS) inhibitor N‑acetylcysteine, as well as lipid peroxidation inhibitors Liproxstatin‑1 and iron chelator deferoxamine; however, inhibitors of apoptosis, necrosis or autophagy had no effect. It was also demonstrated that iron and lipid ROS levels were elevated in I/R injury and that mitochondria decreased in size and increased in membrane density, which is indicative of ferroptosis. Furthermore, the generation of lipid ROS suggests iron accumulation and glutathione (GSH) depletion. The expression of ferroportin (Fpn) protein and mRNA was decreased in TM4 cells. Notably, overexpression of Fpn inhibited ferroptosis, lipid ROS generation and iron accumulation. In addition, GSH‑dependent peroxidase 4 (GPX4) was inactivated via GSH depletion following I/R injury, whereas GPX4 activation blocked I/R‑induced ferroptosis by reducing lipid ROS levels. The mitogen‑activated protein kinase (MAPK) pathway was also investigated in the present study; it was observed that I/R‑induced ferroptosis was blocked by inhibiting p38 MAPK activation. The results of the present study demonstrate that ferroptosis is a pervasive and dynamic type of cell death induced by OGD/R injury in Sertoli cells. This may provide a novel insight into the application of cytoprotection in testicular I/R damage‑induced cell loss.

The effect of antioxidants on sperm motility activation in the Booroolong frog

Motile sperm can generate high levels of reactive oxygen species (ROS) post activation, and ROS can quickly accumulate to levels that impair motility and fertilising ability. The addition of antioxidants to sperm suspensions has been suggested as a means of reducing oxidative stress and enhancing sperm motility during and after sperm storage. Despite this, very few studies have attempted to experimentally test the effects of antioxidants on sperm motility activation in animals that use an external mode of fertilisation, espcially in amphibians. The present study aimed to investigate the effect of vitamin C and vitamin E on sperm motility activation in the Booroolong frog. Spermatozoa were activated in media containing either vitamin C (0, 0.05, 0.10, 0.15, 0.20, 0.25μgμL^-1) or vitamin E (0, 0.25, 0.50, 0.75, 1.0, 1.25 1.50, 1.75μgμL^-1). Sperm performance parameters (percent motility and velocity) were assessed using CASA at 0, 1, 2, 3, 4, 5 and 6h post-activation. Contrary to expectations, vitamin C supplementation was detrimental to sperm motility across all tested concentrations, while vitamin E had no effect. Further investigation on the endogenous antioxidant system of anuran sperm is required to ascertain whether alternative antioxidants may be more suitable at reducing ROS produced during sperm activation and improving sperm motility activation in vitro.

ReviewGenetics, lifestyle and the roles of amyloid β and oxidative stress in Alzheimer’s disease

This paper reviews a wide range of recent studies that have linked AD-associated biochemical and physiological changes with oxidative stress and damage. Some of these changes include disruptions in metal ion homeostasis, mitochondrial damage, reduced glucose metabolism, decreased intracellular pH and inflammation. Although the changes mentioned above are associated with oxidative stress, in most cases, a cause and effect relationship is not clearcut, as many changes are interlinked. Increases in the levels of Abeta peptides, the main protein components of the cerebral amyloid deposits of AD, have been demonstrated to occur in inherited early-onset forms of AD, and as a result of certain environmental and genetic risk factors. Abeta peptides have been shown to exhibit superoxide dismutase activity, producing hydrogen peroxide which may be responsible for the neurotoxicity exhibited by this peptide in vitro. This review also discusses the biochemical aspects of oxidative stress, antioxidant defence mechanisms, and possible antioxidant therapeutic measures which may be effective in counteracting increased levels of oxidative stress. In conclusion, this review provides support for the theory that damage caused by free radicals and oxidative stress is a primary cause of the neurodegeneration seen in AD with Abeta postulated as an initiator of this process.

Acidic pH amplifies iron-mediated lipid peroxidation in cells

The goal of our study was to investigate the mechanism by which changes in extracellular pH influence lipid peroxidation processes. Ferrous iron can react with hydroperoxides, via a Fenton-type reaction, to initiate free radical chain processes. Iron is more soluble at lower pH values, therefore we hypothesized that decreasing the environmental pH would lead to increased iron-mediated lipid peroxidation. We used Photofrin, a photosensitizer that produces singlet oxygen, to introduce lipid hydroperoxides into leukemia cells (HL-60, K-562, and L1210). Singlet oxygen reacts with the PUFA of cells producing lipid hydroperoxides. Using EPR spin trapping with POBN, free radical formation from HL-60 cells was only detected when Photofrin, light, and ferrous iron were present. Free radical formation increased with increasing iron concentration; in the absence of extracellular iron, radical formation was below the limit of detection and lipid hydroperoxides accumulated in the membrane. In the presence of iron, lipid-derived radical formation in cells is pH dependent; the lower the extracellular pH (7.5-5.5), the higher the free radical flux; the lower the pH, the greater the membrane permeability induced in K-562 cells, as determined by trypan blue dye exclusion. These data demonstrate that lipid peroxidation processes, mediated by iron, are enhanced with decreasing extracellular pH. Thus, acidic pH not only releases iron from "safe" sites, but this iron will also be more damaging.

Human sperm motility and lipid peroxidation in different ascorbic acid concentrations: an in vitro analysis

Human spermatozoal motility, viability and lipid peroxidation (LPO) have been assessed in Ringer-Tyrode supplemented with different concentrations of ascorbic acid (AA) ranging from 50 to 4000 microM. Ascorbic acid in concentrations below 1000 microM protects spermatozoa from free radical damage as evidenced from improvement in their motility and viability. Concomitantly, there is also witnessed depletion of malondialdehyde generation (an end product of LPO) following AA treatment. Ascorbic acid at 1000 microM concentration and above, however, is not protective, as evidenced by abrupt fall in sperm motility and viability and concomitant increase in LPO.

Free radical production by azomethine H: effects on pancreatic and hepatic tissues

The antimalarial properties of azomethine H represent the basis for its use as a chemotherapeutic agent. This work was carried out in order to verify the biological side effects of azomethine H and to clarify the contribution of reactive oxygen species (ROS) in this process. It was shown that azomethine H increased serum activities of amylase, alanine transaminase (ALT) and the TBARS concentrations, in rats. No changes were observed in glutathione peroxidase and catalase activities. The drug-induced tissue damage might be due to superoxide radicals (O2.-), since Cu-Zn superoxide dismutase activities were increased by azomethine H treatment. This study allows tentative conclusions to be drawn regarding which reactive oxygen metabolites play a role in azomethine H activity. We concluded that (O2.-) maybe produced as a mediator of azomethine H action.

Alpha-tocopherol inhibits agonist-induced monocytic cell adhesion to cultured human endothelial cells

Antioxidants have been proposed to be anti-atherosclerotic agents; however, the mechanisms underlying their beneficial effects are poorly understood. We have examined the effect of alpha-tocopherol (alpha-tcp) on one cellular event in atherosclerotic plaque development, monocyte adhesion to stimulated endothelial cells (ECs). Human umbilical vein ECs were pretreated with alpha-tcp before stimulation with known agonists of monocyte adhesion: IL-1 (10 ng/ml), LPS (10 ng/ml), thrombin (30 U/ml), or PMA (10 nM). Agonist-induced monocytic cell adhesion, but not basal adhesion, was inhibited in a time- and concentration-dependent manner by alpha-tcp. The IC50 of alpha-tcp on an IL-1-induced response was 45 microM. The inhibition correlated with a decrease in steady state levels of E-selectin mRNA and cell surface expression of E-selectin which is consistent with the ability of a monoclonal antibody to E-selectin to inhibit monocytic cell adhesion in this system. Probucol (50 microM) and N-acetylcysteine (20 mM) also inhibited agonist-induced monocytic cell adhesion; whereas, several other antioxidants had no significant effect. Protein kinase C (PKC) does not appear to play a role in the alpha-tcp effect since no suppression of phosphorylation of PKC substrates was observed. Activation of the transcription factor NF-kappa B is reported to be necessary but not sufficient for E-selectin expression in EC. Electrophoretic mobility shift assays failed to show an alpha-tcp-induced decrease in activation of this transcription factor after cytokine stimulation. It has been hypothesized that alpha-tcp acts as an anti-atherosclerotic molecule by inhibiting generation of oxidized LDL--a putative triggering molecule in the atherosclerotic process. Our results point to a novel alternative mechanism of action of alpha-tcp.

Oxidative stress in some dementia types

By analogy to some pathologies (such as demyelinating diseases, arthritis and inflammatory processes) where the loss of cellular integrity is the starting point of tissue oxidative damage, it is proposed that some dementia types could be derived from a similar mechanism. The following oxidative events are proposed: (a) different agents could alter capillary or neuron integrity with the subsequent leakage of oxidases, proteases and transition metals from cellular compartments; (b) the persistence of the damaging agent, possible depletion of antioxidative defenses and concomitant loss of neuron function; (c) alteration of adjacent cells in the same manner; and (d) finally localized brain necrosis and progression of the dementia.

Antioxidative activity of synthetic melanins. Cardiolipin liposome model

The inhibiting effect of melanin synthesized from dihydroxyphenylalanine (DOPA), dopamine, adrenaline and adrenolutin on the ultraviolet- or the Fe(2+)-ascorbic acid-induced peroxidation of cardiolipin liposomes has been studied. All these melanins are able to inhibit both the ultraviolet- and the Fe(2+)-ascorbic acid-induced lipid peroxidation. Antioxidative activity of melanins enhances in the order: dopamine-melanin less than melanin synthesized from dopamine in the presence of Cu(2+) less than DOPA--melanin less than melanin synthesized from adrenaline in the presence of Cu(2+) approximately equal to adrenolutin-melanin, and correlates with their ability to scavenge superoxide anion radical. The optical screening effect of the investigated melanins in the inhibition of lipid peroxidation was not higher than 15% for the most active melanins.

MRI in tardive dyskinesia: shortened left caudate T2

High-resolution magnetic resonance imaging of the brain was performed on 18 male schizophrenic patients, 14 with a cumulative exposure to neuroleptics of more than 1 year and 4 with less than 3 months of exposure. Calculated T2 relaxation time values were obtained for the basal ganglia. Patients with tardive dyskinesia (n = 9) had significantly shortened left caudate T2 relaxation times when compared to patients without tardive dyskinesia (n = 5). The group of four patients with fewer than 3 months' exposure to neuroleptics demonstrated a significantly greater variability of their left caudate T2 values. T2 relaxation time shortening may be related to iron levels in the basal ganglia and may be of predictive value in evaluating risk of tardive dyskinesia.

Ascorbate is an outstanding antioxidant in human blood plasma

We have shown recently that the temporal order of antioxidant consumption in human blood plasma exposed to a constant flux of aqueous peroxyl radicals is ascorbate = protein thiols greater than bilirubin greater than urate greater than alpha-tocopherol and that detectable lipid peroxidation starts only after ascorbate has been consumed completely. In this paper, we show that it is indeed ascorbate that completely protects plasma lipids against detectable peroxidative damage induced by aqueous peroxyl radicals and that ascorbate is the only plasma antioxidant that can do so. Plasma devoid of ascorbate, but no other endogenous antioxidant, is extremely vulnerable to oxidant stress and susceptible to peroxidative damage to lipids. The plasma proteins' thiols, although they become oxidized immediately upon exposure to aqueous peroxyl radicals, are inefficient radical scavengers and appear to be consumed mainly by autoxidation. Our data demonstrate that ascorbate is the most effective aqueous-phase antioxidant in human blood plasma and suggest that in humans ascorbate is a physiological antioxidant of major importance for protection against diseases and degenerative processes caused by oxidant stress.

Haemoglobin and myoglobin as inhibitors of hydroxyl radical generation in a model system of "iron redox" cycle

Methionine was oxidized to ethylene by an "Iron Redox" system containing H2O2, Fe-EDTA and ascorbate, generating hydroxyl radicals or another species of similar reactivity. Oxy or met forms of haemoglobin and myoglobin were found to inhibit methionine oxidation. Methionine oxidation was elevated in the "Iron Redox" system by increasing ascorbic acid concentration. However, in the presence of metmyoglobin or methaemoglobin, the increases in ascorbic acid did not lower the haemproteins' inhibitory effects but rather increased them. The pro-oxidative or anti-oxidative activities of haemproteins in biological oxidative reactions seem to be dependent on compartmentalization and on the presence and concentrations of reducing compounds and H2O2.

Hemoglobin-mediated oxidant damage to the central nervous system requires endogenous ascorbate

Hemorrhage within the central nervous system (CNS) may be associated with subsequent development of seizure states or paralysis. Prior investigations indicate that hemoglobin, released from extravasated erythrocytes, may be toxic to the CNS by promoting peroxidation of lipids and inhibition of Na,K-ATPase. These deleterious effects are blocked both in vitro and in vivo by the Fe3+ chelator, desferrioxamine, indicating the involvement of free iron derived from hemoglobin. We now report that the Fe2+ chelator, ferene, also inhibits methemoglobin- and ferric iron-mediated CNS lipid oxidation, reflecting the reduction of Fe3+ by some component of the CNS. This reduction is apparent in the accumulation of the highly chromophoric ferene: Fe2+ chelate after the addition of Fe3+ salts to supernatants of murine brain homogenates. Because large amounts of ascorbic acid occur in mammalian CNS, we suspected that this reducing substance might be responsible. Indeed, the peroxidative effects of hemoglobin and iron on murine brain are blocked by washing of CNS membranes or by preincubation of crude homogenates with ascorbate oxidase. Furthermore, the addition of ascorbate to washed CNS membranes fully restores hemoglobin/iron-driven peroxidation. We conclude that posthemorrhagic CNS dysfunction may stem from damaging redox reactions between hemoglobin iron, ascorbic acid, and oxidizable components of the nervous system.

An antioxidative role of ocular screening pigments

The action of ocular screening pigments of vertebrates (melanins) as well as those of invertebrates (ommochromes) on lipid peroxidation has been studied. Lipid peroxidation has been induced by one of the following systems: Fe2+ + ascorbic acid; Fe2+ + NADPH + liver microsomes; xanthine + xanthine oxidase; u.v. illumination; intense visible light, high concentration of O2. Measurements of the lipid peroxidation rate, as estimated from the accumulation of malonic dialdehyde, showed a sharp decrease of the lipid peroxidation rate in the presence of either melanosomes or ommochromes. Synthetic DOPA melanin was also found to exert a strong inhibiting effect on lipid peroxidation. A comparative study of lipid peroxidation in retinal pigment epithelium (RPE) of pigmented and albino rabbits demonstrated that the latter tissue is more sensitive to the effect of the above mentioned prooxidant systems. Apparently this finding is related to the presence of melanin-containing granules in the pigmented tissue rather than to differences in efficiency of other endogenous antioxidant systems. The activities of superoxide dismutase and glutathione peroxidase are practically equal in the RPE of pigmented and albino rabbits whereas the alpha-tocopherol content is higher in albinos. Possible mechanisms of inhibition of lipid peroxidation by melanosomes and ommochromes are discussed. It is proposed that their antioxidant function is one of the most important physiological features of melanins (vertebrate eye) and ommochromes (invertebrate eye).

Initiation of lipid peroxidation in biological systems

The direct oxidation of PUFA by triplet oxygen is spin forbidden. The data reviewed indicate that lipid peroxidation is initiated by nonenzymatic and enzymatic reactions. One of the first steps in the initiation of lipid peroxidation in animal tissues is by the generation of a superoxide radical (see Figure 16), or its protonated molecule, the perhydroxyl radical. The latter could directly initiate PUFA peroxidation. Hydrogen peroxide which is produced by superoxide dismutation or by direct enzymatic production (amine oxidase, glucose oxidase, etc.) has a very crucial role in the initiation of lipid peroxidation. Hydrogen peroxide reduction by reduced transition metal generates hydroxyl radicals which oxidize every biological molecule. Hydrogen peroxide also activates myoglobin, hemoglobin, and other heme proteins to a compound containing iron at a higher oxidation state, Fe(IV) or Fe(V), which initiates lipid peroxidation even on membranes. Complexed iron could also be activated by O2- or by H2O2 to ferryl iron compound, which is supposed to initiate PUFA peroxidation. The presence of hydrogen peroxide, especially hydroperoxides, activates enzymes such as cyclooxygenase and lipoxygenase. These enzymes produce hydroperoxides and other physiological active compounds known as eicosanoids. Lipid peroxidation could also be initiated by other free radicals. The control of superoxide and perhydroxyl radical is done by SOD (a) (see Figure 16). Hydrogen peroxide is controlled in tissues by glutathione-peroxidase, which also affects the level of hydroperoxides (b). Hydrogen peroxide is decomposed also by catalase (b). Caeruloplasmin in extracellular fluids prevents the formation of free reduced iron ions which could decompose hydrogen peroxide to hydroxyl radical (c). Hydroxyl radical attacks on target lipid molecules could be prevented by hydroxyl radical scavengers, such as mannitol, glucose, and formate (d). Reduced compounds and antioxidants (ascorbic acid, alpha-tocopherol, polyphenols, etc.) (e) prevent initiation of lipid peroxidation by activated heme proteins, ferryl ion, and cyclo- and lipoxygenase. In addition, cyclooxygenase is inhibited by aspirin and nonsteroid drugs, such as indomethacin (f). The classical soybean lipoxygenase inhibitors are antioxidants, such as nordihydroguaiaretic acid (NDGA) and others, and the substrate analog 5,8,11,14 eicosatetraynoic acid (ETYA), which also inhibit cyclooxygenase (g). In food, lipoxygenase is inhibited by blanching. Initiation of lipid peroxidation was derived also by free radicals, such as NO2. or CCl3OO. This process could be controlled by antioxidants (e).(ABSTRACT TRUNCATED AT 400 WORDS)

Regional lipid peroxidation in rat brain in vitro: possible role of endogenous iron

Lipoperoxidative capacity of various brain areas of aging rats was examined in vitro using the thiobarbituric acid test. Significant regional differences in the generation of lipid peroxides were found in freshly prepared homogenates from different areas of brain incubated under air. Incubation under oxygen resulted in marked stimulation of lipid peroxidation, with highest increases in hypothalamus (144%). Addition of exogenous Fe2+ and ascorbic acid resulted in stimulation of lipid peroxidation ranging from 10-fold in cortex to 20-fold in hypothalamus homogenates during incubation in air. A linear relationship was found between endogenous iron content in brain regions and their ability to produce lipid peroxides in vitro under oxygen for all areas except striatum. Several iron chelating agents effectively inhibited lipid peroxidation under hyperbaric oxygen whereas oxygen-free radical scavengers, as well as catalase and superoxide dismutase were not effective. It is concluded that regional differences in lipoperoxidative capacity of brain areas in vitro are in part governed by local endogenous iron content and may indicate regional susceptibility to oxidative damage.

Autoxidation of Acholeplasma laidlawii membranes

Autoxidation of Acholeplasma laidlawii membranes (with equimolar ratio of palmitic and linoleic acid) lacks an obvious induction period, and the overall rate of disappearance of substrate does not follow closely that of typical autocatalytic kinetics. Throughout the course of autoxidation, the major oxygenated products isolated were hydroperoxides (as hydroxy esters) and compounds that gave rise to trihydroxy esters. The yield of trihydroxy esters was appreciable even at the early stage of the oxidation and eventually grew to surpass that of hydroperoxides. The positions of the three hydroxyl groups in the trihydroxy esters were determined to be mostly of the 1,2,5-type rather than 1,2,3-type arrangement. To a lesser extent, some degraded products, including dimethyl nonanedioate, methyl myristate, methyl pentadecanoate, methyl hexadecadienoate and methyl heptadecadienoate also were obtained. Dimethyl nonanedioate was a previously known degradation product from 9-hydroperoxide. The shorter chain esters presumably arise from the cleavage of alpha-hydroperoxides of palmitate and linoleate moieties.

Interaction of metals and carbon tetrachloride on lipid peroxidation and hepatotoxicity

Rats were administered ferrous sulfate, cadmium chloride, or sodium vanadate alone and in combination with carbon tetrachloride (CCl4) to determine if lipid peroxidation is associated with the toxicity of the three metals and to determine if there is an interaction between these metals and CCl4 in producing lipid peroxidation and hepatotoxicity. Expired ethane was used as an index of lipid peroxidation while serum alanine aminotransferase (ALT) and histopathology were used to assess liver damage. Lipid peroxidation did not appear to be associated with the hepatotoxicity of cadmium since no measurable increase in ethane production was observed when serum ALT concentrations were doubled relative to controls. Cadmium did not increase ethane when administered with CCl4 and the increase in ALT was additive. Iron and vanadate produced small significant increases in ethane production but no increase in ALT and only minor histopathologic changes, yet potentiated lipid peroxidation and liver damage when administered with CCl4. Thus, Cd did not produce lipid peroxidation and did not potentiate the lipid peroxidation and hepatotoxicity of CCl4, while iron or vanadate which produced lipid peroxidation alone potentiated the lipid peroxidation and hepatotoxicity of CCl4.

Evaluation of lipid peroxidation of human erythrocyte hemolysates

Lipid peroxidation of human erythrocyte hemolysates was evaluated by determining thiobarbituric acid reactive substance by fluorospectrophotometer. Because of the non-linear relationship between malondialdehyde formation and hemoglobin concentration, a constant hemoglobin concentration is required to obtain reproducible results. Disruption of the hemolysate by sonication and the presence of formed elements are necessary to induce the reaction, the optimal pH of which was found to be limited to the region of 7.4. Either ferric or ferrous ions are essential for the reaction to proceed, but if both are present, their catalytic activity is abolished. The present method will be useful in the investigation of the mechanism of oxidative damage to erythrocytes under various pathological conditions.

Macrophage radiosensitivity in culture as a function of exposure to ionic iron

The effects of various concentrations of Fe3+ (30-125 microM) and various doses of X-irradiation (10 to 30 Gy) on the survival of mouse peritoneal macrophages in culture was tested and compared with the effect of combinations of both Fe3+ and X-irradiation. Exposure of the cells to 30 microM Fe3+ or 10 Gy did not significantly alter the survival pattern, as compared with control cells. Greater dosages of iron or X-irradiation caused increasing cellular degeneration and death. When the combined effect of 30 microM Fe3+ and 10 Gy was tested a pronounced decrease in survival time was noted. The production of malondialdehyde (MDA) was studied in cells cultured with and without iron and after exposure to X-irradiation. The results indicated an increasing peroxidative capacity in parallel with increasing dose and extent of exposure to iron and irradiation. Combinations of 30 microM Fe3+ and 10 Gy resulted in enhanced MDA production as compared with these treatments alone (in which levels of MDA did not differ from those in controls). The findings support the theory that cells containing iron-loaded lysosomes are abnormally sensitive to X-irradiation due to the catalytic activity of the Fe2+ in equilibrium with Fe3+ redox system on lipid peroxidation. The postulated mechanism involves disruption of lysosomal membranes as a consequence of increased lipid peroxidation, resulting in leakage of potent lytic enzymes into the cell sap causing cellular degeneration and death.

Inhibition of lipid peroxidation in spinal cord homogenates by various drugs

The extent and kinetic profiles of lipid peroxidation induced with Fe2+-ascorbic acid in a homogenate of spinal cord from greyhound dogs were ascertained by measurement of the formation of malondialdehyde (MDA) and chemiluminescence in the presence of four drugs. Changes in MDA and chemiluminescence were correlated as a function of the activator or inhibitors. The kinetic profiles of chemiluminescence which were observed for 25 min after addition of the activator and individual inhibitors were similar regardless of the type of inhibitor studied. The most effective inhibition was by disulfiram which was approximately 11 and 33 times more effective than two other inhibitors, propyl gallate and promethazine, respectively, and 11,000 times more effective than D-alpha-tocopherol.

Inhibition of enzymic and non-enzymic lipid peroxidation of flounder muscle sarcoplasmic reticulum by pretreatment with phospholipase A2

Sarcoplasmic reticulum, isolated from the muscle of winter flounder (Pseudopleuronectes americanus), was preincubated with phospholipase A2 to determine the effects of enzymic and non-enzymic lipid-peroxidation systems. Eicosapentaenoic acid (20:5) was preferentially released by phospholipase A2, but the percentage of docosahexaenoic acid (22:6) in the free fatty acids was similar to the percentage in membrane total fatty acids. A decrease in the production of both thiobarbituric acid-reactive substances and lipid hydroperoxides was observed in both the enzymic and non-enzymic peroxidation systems upon preincubation with phospholipase A2. Addition of palmitic acid or lysophosphatidylcholine did not inhibit either peroxidation system. Non-enzymic peroxidation was inhibited by the addition of beta-glycerophosphate, but enzymic peroxidation was apparently unaffected. A model is proposed to explain the inhibitory effect of phospholipid hydrolysis on lipid peroxidation in both systems, suggesting that fatty acids are structurally realigned upon hydrolysis, leading to decreased free-radical chain propagation. Additional factors appear to contribute to inhibition of enzymic peroxidation.

Phospholipid degradation and cellular edema induced by free radicals in brain cortical slices

Cellular edema and increased lactate production were induced in rat brain cortical slices by xanthine oxidase and xanthine, in the presence of ferric dialdehyde, was increased 174%. Among the various subcellular fractions of brain cortex, xanthine oxidase-stimulated lipid peroxidation was highest in myelin, mitochondria, and synaptosomes, followed by microsomes and nuclei. Antioxidants, catalase, chlorpromazine, and butylated hydroxytoluene inhibited lipid peroxidation in both homogenates and synaptosomes, indicating H2O2 and radicals were involved. Further, several free fatty acids, especially oleic acid (18:1), arachidonic acid (20:4), and docosahexaenoic acid (22:6) were released from the phospholipid pool concomitant with the degradation of membrane phospholipids in xanthine oxidase-treated synaptosomes. These data suggest that lipases are activated by free radicals and lipid peroxides in the pathogenesis of cellular swelling.

Enzymic lipid peroxidation in the microsomal fraction of rat brain

An enzymic lipid peroxidation system has been demonstrated in the microsomal fraction of rat brain and the requirements and optimal conditions for assay determined. The involvement of NADPH-cytochrome c reductase was demonstrated in vesicles reconstituted with lipids extracted from the brain microsomal fraction. Further characterization of the system made use of substances shown to inhibit the liver microsomal system. alpha-Tocopherol was shown to be an effective inhibitor of lipid peroxidation in the brain microsomal system, whereas Na2SO3 had no effect, which is indicative that free radical transfer occurs only in the hydrophobic regions. Neither superoxide dismutase nor catalase inhibited lipid peroxidation. The implications of an NADPH-cytochrome c reductase-dependent lipid peroxidation system that is not linked to a drug hydroxylation system and appears to differ from the liver microsomal system in a number of other ways are discussed.

Hydrogen peroxide and corneal endothelium

Because of recent evidence of low levels of hydrogen peroxide in the aqueous humor, studies were performed to determine levels of corneal endothelial toxicity as well as factors modifying toxicity. Perfusion of cornea endothelial cells for 3 h with varying concentrations of hydrogen peroxide demonstrated a threshold of toxicity at a concentration between 0.3 and 0.5 mM H2O2. The toxic effect resulted in rapid corneal swelling as well as disruption of endothelial cell cytoplasm and organelles. Both the physiologic and anatomic toxic effects of 0.5 mM H2O2 could be blocked with 5400 U/ml catalase. Exposure of corneas to 20 mM H2O2 for 10 min in the presence of EDTA - Fe+3 resulted in an enhancement of corneal swelling rate more rapid than that which resulted from a 10 min exposure to 20 mM H2O2 alone. Neither the presence of ascorbic acid nor the absence of glutathione and adenosine had and effect on the cornea swelling rate which occurred during a 3 h perfusion of endothelium with 0.3 mM H2O2. Chelated iron had no effect on the corneal swelling induced by phototactivation of rose bengal presensitized cornea endothelial cells.

Free radical initiation in proteins and amino acids by ionizing and ultraviolet radiations and lipid oxidation--part III: free radical transfer from oxidizing lipids

Parallels and similarities in chemical and functional damage to proteins by ionizing and uv radiations and oxidizing lipids have been recognized for some time. However, only recently have oxidizing lipids been shown directly by electron spin resonance to be radiomimetic also in their capacity for protein free radical production. Free radicals play a key role in the transformation of energy to molecular and cellular damage. It is thus of critical importance to elucidate the general mechanisms of free radical formation and reactions in proteins in order to understand protein involvement in various pathological conditions and in food deterioration. Accordingly, this review is a detailed comparison of gamma-radiation, UV radiation, and lipid oxidation for what is presently known concerning (1) the specific modes of energy deposition and free radical formation, (2) the free radicals formed in proteins and amino acids, and (3) the typical damage correlating with these radicals.

Growth-related lipid peroxidation in tumour microsomal membranes and mitochondria

Microsomes and mitochondria isolated from Morris hepatomas 3924A (fast-growing) and 44 (slow-growing) and Ehrlich ascites tumour cells exhibit a NADPH-dependent peroxidation of endogenous lipids lower than that of the corresponding fractions from rat liver. Moreover, the O2- and ascorbate-dependent lipid peroxidations are decreased in microsomes from the two Morris hepatomas. The peroxidative activity appears to be inversely related to the growth rate of the tumours. It is suggested that the low susceptibility of tumour membranes to peroxidative agents may be a factor responsible for the high mitotic activity of this tissue.

Autoxidation of fatty acid monolayers adsorbed on silica gel: I. Nature of adsorption sites

An unsaturated fatty acid monolayer deposited on a silica gel surface has been chosen as a model for studying non-enzymatic autoxidation of membrane lipids. Studies to determine the suitability of this system as a model for biomembranes were conducted to define the nature of the monolayers, particularly with respect to the factors determining the concentration of the fatty acid molecule on unit area of the surface. The results from adsorption isotherm, high temperature dehydroxylation, and infrared spectra studies show that adsorption of a monomolecular layer of fatty acids occurs and that the number of molecules absorbed corresponds to the number of isolated, non-hydrogen-bonded silanol groups. It is presumed the binding is by hydrogen bonding of the carboxyl groups to silanol groups. The packing density of the fatty acid molecules is 1.25 molecule/100 A2 which is similar to the density of the isolated silanol sites on the surface.

Formation of lipid peroxides in isolated rat liver microsomes by singlet molecular oxygen

Rat liver microsomes were incubated in neutral aqueous solution of potassium peroxychromate, a system which generates singlet molecular oxygen. Such incubation resulted both in a rapid decline in NADPH-cytochrome c reductase activity, and in an increase in formation of lipid peroxides. These reactions were not inhibited by either superoxide dismutase (SOD) or mannitol, nor were they entirely duplicated by incubating microsomes with hydrogen peroxide. However, a high concentration of 1,4-diazabicyclo-[2,2,2]octane (DABCO), a known scavenger of singlet oxygen, prevented both decline in reductase activity and formation of lipid peroxides. These results suggest that the observed effects are, in fact, attributable to singlet oxygen, and not to hydrogen peroxide, superoxide radical, or hydroxyl radical.

[Breakdown of linoleic and linolenic acid hydroperoxides in the presence of ascorbic acid analysis of the volatile aldehydes (author's transl)]

Hydroperoxide emulsions with 10(-3) mol ascorbic acid were stored for 19 h at 22 degrees C. Volatile aldehydes were formed in the presence of oxygen and traces of metals. The main compounds were identified as follows (mol-%): 2-pentenal [51] and 2-hexenal [22] from 13-hydroperoxioctadeca-9,11,15-trienoic acid; propanol [38] and 2-hexenal [25] from 9-hydroperoxioctadeca-10,12,15-trienoic acid; hexanal [82] respectively [66] from 13-hydroperoxioctadeca-9,11-respectively 9-hydroperoxioctadeca-10,12-dienoic acid. C9 and C10 aldehydes were only detected in very low concentrations as fragments of the 9-hydroperoxides.

Oxidative damage of retinal rod outer segment membranes and the role of vitamin E

Highly purified bovine rod outer segment membranes show loss of structural integrity under an air atmosphere. Obvious ultrastructural changes are preceded by increases in absorbance below 400 nm. These changes are inhibited by Ar or N2 atmospheres and appear to be due primarily to oxidative damage to the polyunsaturated fatty acids of the membrane lipids. Loss of polyunsaturated fatty acids, formation of malonaldehyde and fluorescent products characteristic of lipid oxidation accompany the spectral alterations. The elevated ultraviolet absorbance can largely be removed from the membranes by gentle extraction of the lipids using phospholipase C and hexane without changing the visible absorbance of rhodopsin. We have found a large seasonal variation in the endogenous level of alpha-tocopherol (vitamin E) in the bovine rod outer segment preparations. For much of the year we find that the rod outer segment membranes contain higher levels of alpha-tocopherol than have been previously reported in biological membranes. Rod outer segments which are low in endogenous tocopherol can be protected from oxygen damage by adding exogenous tocopherol. The rod outer segments are extremely susceptible to oxygen damage due to the unusually high content of polyunsaturated fatty acids in the membrane lipids. The presence of tocopherol inhibits oxygen damage but does not eliminate it. The tocopherol in the rod outer segments is consumed in air, thus complete protection from peroxidation in vitro requires an inert atmosphere as well as high levels of tocopherol. This work suggests that extensive precautions against oxidative degradation should also be employed in studies of other membrane systems where important deleterious effects of oxygen may be less obvious.