Promotion of oxidative damage to arachidonic acid and alpha 1-antiproteinase by anti-inflammatory drugs in the presence of the haem proteins myoglobin and cytochrome C

Iron and atherosclerosis: Lessons learned from rabbits relevant to human disease

The role of iron in promoting atherosclerosis, and hence the cardiovascular, neurodegenerative and other diseases that result from atherosclerosis, has been fiercely controversial. Many studies have been carried out on various rodent models of atherosclerosis, especially on apoE-knockout (apoE-/-) mice, which develop atherosclerosis more readily than normal mice. These apoE-/- mouse studies generally support a role for iron in atherosclerosis development, although there are conflicting results. The purpose of the current article is to describe studies on another animal model that is not genetically manipulated; New Zealand White (NZW) rabbits fed a high-cholesterol diet. This may be a better model than the apoE-/- mice for human atherosclerosis, although it has been given much less attention. Studies on NZW rabbits support the view that iron promotes atherosclerosis, although some uncertainties remain, which need to be resolved by further experimentation.

Acetaminophen inhibits cytochrome c redox cycling induced lipid peroxidation

Cytochrome (cyt) c can uncouple from the respiratory chain following mitochondrial stress and catalyze lipid peroxidation. Accumulating evidence shows that this phenomenon impairs mitochondrial respiratory function and also initiates the apoptotic cascade. Therefore, under certain conditions a pharmacological approach that can inhibit cyt c catalyzed lipid peroxidation may be beneficial. We recently showed that acetaminophen (ApAP) at normal pharmacologic concentrations can prevent hemoprotein-catalyzed lipid peroxidation in vitro and in vivo by reducing ferryl heme to its ferric state. We report here, for the first time, that ApAP inhibits cytochrome c-catalyzed oxidation of unsaturated free fatty acids and also the mitochondrial phospholipid, cardiolipin. Using isolated mitochondria, we also showed that ApAP inhibits cardiolipin oxidation induced by the pro-apoptotic protein, tBid. We found that the IC(50) of the inhibition of cardiolipin oxidation by ApAP is similar in both intact isolated mitochondria and cardiolipin liposomes, suggesting that ApAP penetrates well into the mitochondria. Together with our previous results, the findings presented herein suggest that ApAP is a pleiotropic inhibitor of peroxidase catalyzed lipid peroxidation. Our study also provides a potentially novel pharmacological approach for inhibiting the cascade of events that can result from redox cycling of cyt c.

Effects of Ascorbic Acid on Oxidative System and Transient Evoked Otoacoustic Emissions in Rabbits Exposed to Noise

OBJECTIVES/HYPOTHESIS

The objective was to investigate the effects of both noise exposure and ascorbic acid on oxidative status and hearing thresholds of rabbits.

STUDY DESIGN

Randomized prospective animal study comparing oxidative parameters and otoacoustic emissions in two rabbit groups exposed to noise. One group was given ascorbic acid, the other group was not given any treatment.

METHODS

Two groups of rabbits were used in the study; each group had six rabbits. The six rabbits in the first group were not given any treatment, whereas 500 mg intramuscular ascorbic acid twice daily for 2 1/2 days was given to the six rabbits in the second group. Transient evoked otoacoustic emissions were recorded in all animals before and after noise exposure. Total protein sulfhydryl groups, carbonyl contents, and malondialdehyde levels, as well as erythrocyte glutathione, superoxide dismutase, and catalase enzyme levels, were measured in all rabbits. All the rabbits were exposed to noise (100 dB sound pressure level, 1000 Hz, 1 h), and transient evoked otoacoustic emissions were recorded again.

RESULTS

When oxidative parameters before noise exposure were compared, erythrocyte glutathione and catalase enzyme levels were detected to be higher in the second group (P <.05). In the first group of rabbits after noise exposure, total protein sulfhydryl groups were found to be reduced (P <.05), whereas plasma carbonyl contents and malondialdehyde levels were elevated significantly (P <.05). In this group, erythrocyte glutathione, superoxide dismutase, and catalase enzyme levels were low (P <.05). In the second group, which was given ascorbic acid, total protein sulfhydryl groups were reduced (P <.05), whereas plasma carbonyl contents and malondialdehyde levels did not change (P >.05) following noise exposure. In the second group, erythrocyte glutathione and catalase enzyme levels were reduced (P <.05), but superoxide dismutase levels did not change (P >.05). Transient evoked otoacoustic emissions after noise exposure were weak in both groups, but reproducibility and signal-to-noise ratios were higher in the second group (P <.05).

CONCLUSION

Ascorbic acid treatment inhibited both lipid peroxidation and oxidative damage of proteins in rabbits exposed to noise. The study data suggest, at least, that oxidative status should be included in the physiopathology of noise-induced hearing loss; in addition, a brief application of ascorbic acid before noise exposure appeared to play a protective role for cochlea.

Inactivation of ?1-Antiproteinase Induced by Phenylbutazone: Participation of Peroxyl Radicals and Hydroperoxide

To clarify the action of a side-effect of phenylbutazone, we investigated the inactivation of alpha(1)-antiproteinase induced by phenylbutazone in the presence of horseradish peroxidase (HRP) and H(2)O(2) (HRP-H(2)O(2)). The activity of alpha(1)-antiproteinase was rapidly lost during the interaction of phenylbutazone with HRP-H(2)O(2) under aerobic conditions. Phenylbutazone showed a marked spectral change under aerobic conditions but not under anaerobic conditions. Spin trap agents were very effective in inhibiting alpha(1)-antiproteinase inactivation induced by phenylbutazone. Oxidation of phenylbutazone was stopped by catalase, but the inactivation reaction of alpha(1)-antiproteinase proceeded even after removal of H(2)O(2) in the reaction mixture. Formation of the peroxidative product from phenylbutazone was detected by iodometric assay. These results indicate that both peroxyl radicals and the peroxidative product of phenylbutazone participated in the inactivation of alpha(1)-antiproteinase. Other anti-inflammatory drugs did not inactivate alpha(1)-antiproteinase during interaction with HRP-H(2)O(2). Inactivation of alpha(1)-antiproteinase may contribute to serious side effects of phenylbutazone.

Role of hydrogen peroxide in the aetiology of Alzheimer's disease: implications for treatment

Hydrogen peroxide (H(2)O(2)) is a stable, uncharged and freely diffusable reactive oxygen species (ROS) and second messenger. The generation of H(2)O(2) in the brain is relatively high because of the high oxygen consumption in the tissue. Alzheimer's disease is a neurodegenerative disorder characterised by the appearance of amyloid-beta (Abeta)-containing plaques and hyperphosphorylated tau-containing neurofibrillary tangles. The pathology of Alzheimer's disease is also associated with oxidative stress and H(2)O(2) is implicated in this and the neurotoxicity of the Abeta peptide. The ability for Abeta to generate H(2)O(2), and interactions of H(2)O(2) with iron and copper to generate highly toxic ROS, may provide a mechanism for the oxidative stress associated with Alzheimer's disease. The role of heavy metals in Alzheimer's disease pathology and the toxicity of the H(2)O(2) molecule may be closely linked. Drugs that prevent oxidative stress include antioxidants, modifiers of the enzymes involved in ROS generation and metabolism, metal chelating agents and agents that can remove the stimulus for ROS generation. In Alzheimer's disease the H(2)O(2) molecule must be considered a therapeutic target for treatment of the oxidative stress associated with the disease. The actions of H(2)O(2) include modifications of proteins, lipids and DNA, all of which are effects seen in the Alzheimer's disease brain and may contribute to the loss of synaptic function characteristic of the disease. The effectiveness of drugs to target this component of the disease pathology remains to be determined; however, metal chelators may provide an effective route and have the added bonus in the case of clioquinol of potentially reducing the Abeta load. Future research and development of agents that specifically target the H(2)O(2) molecule or enzymes involved in its metabolism may provide the future route to Alzheimer's disease therapy.

Inactivation of creatine kinase during the interaction of mefenamic acid with horseradish peroxidase and hydrogen peroxide: participation by the mefenamic acid radical

Creatine kinase (CK) was used as a marker molecule to examine the side effects of damage to tissues by mefenamic acid, an effective drug to treat rheumatic and arthritic diseases, with horseradish peroxidase and hydrogen peroxide (HRP-H(2)O(2)). Mefenamic acid inactivated CK during its interaction with HRP-H(2)O(2). Also, diphenylamine and flufenamic acid caused a loss of CK activity, indicating the imino group, not substituent groups, in the phenyl rings have a crucial role in CK inactivation. Rapid change in mefenamic acid spectra was detected, suggesting that mefenamic acid is efficiently oxidized by HRP-H(2)O(2). Peroxidases oxidize xenobiotics to free radicals by a one-electron transfer. However, direct detection of mefenamic acid radicals by electron spin resonance (ESR) was unsuccessful. Reduced glutathione and 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) in the reaction mixture containing mefenamic acid with HRP-H(2)O(2) produced ESR signals consistent with a DMPO-glutathionyl radical adduct. These results suggest that inactivation of CK is probably caused through formation of mefenamic acid radicals. Sulfhydryl groups and tryptophan residues of CK were diminished by mefenamic acid with HRP-H(2)O(2). Other SH enzymes, including alcohol dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase, were very sensitive to mefenamic acid with HRP-H(2)O(2). Inactivation of SH enzymes may explain some deleterious actions of mefenamic acid.

Role of free radicals in the neurodegenerative diseases: therapeutic implications for antioxidant treatment

Free radicals and other so-called 'reactive species' are constantly produced in the brain in vivo. Some arise by 'accidents of chemistry', an example of which may be the leakage of electrons from the mitochondrial electron transport chain to generate superoxide radical (O2*-). Others are generated for useful purposes, such as the role of nitric oxide in neurotransmission and the production of O2*- by activated microglia. Because of its high ATP demand, the brain consumes O2 rapidly, and is thus susceptible to interference with mitochondrial function, which can in turn lead to increased O2*- formation. The brain contains multiple antioxidant defences, of which the mitochondrial manganese-containing superoxide dismutase and reduced glutathione seem especially important. Iron is a powerful promoter of free radical damage, able to catalyse generation of highly reactive hydroxyl, alkoxyl and peroxyl radicals from hydrogen peroxide and lipid peroxides, respectively. Although most iron in the brain is stored in ferritin, 'catalytic' iron is readily mobilised from injured brain tissue. Increased levels of oxidative damage to DNA, lipids and proteins have been detected by a range of assays in post-mortem tissues from patients with Parkinson's disease, Alzheimer's disease and amyotrophic lateral sclerosis, and at least some of these changes may occur early in disease progression. The accumulation and precipitation of proteins that occur in these diseases may be aggravated by oxidative damage, and may in turn cause more oxidative damage by interfering with the function of the proteasome. Indeed, it has been shown that proteasomal inhibition increases levels of oxidative damage not only to proteins but also to other biomolecules. Hence, there are many attempts to develop antioxidants that can cross the blood-brain barrier and decrease oxidative damage. Natural antioxidants such as vitamin E (tocopherol), carotenoids and flavonoids do not readily enter the brain in the adult, and the lazaroid antioxidant tirilazad (U-74006F) appears to localise in the blood-brain barrier. Other antioxidants under development include modified spin traps and low molecular mass scavengers of O2*-. One possible source of lead compounds is the use of traditional remedies claimed to improve brain function. Little is known about the impact of dietary antioxidants upon the development and progression of neurodegenerative diseases, especially Alzheimer's disease. Several agents already in therapeutic use might exert some of their effects by antioxidant action, including selegiline (deprenyl), apomorphine and nitecapone.

Lipid peroxidation induced by phenylbutazone radicals

Lipid peroxidation was investigated to evaluate the deleterious effect on tissues by phenylbutazone (PB). PB induced lipid peroxidation of microsomes in the presence of horseradish peroxidase and hydrogen peroxide (HRP-H2O2). The lipid peroxidation was completely inhibited by catalase but not by superoxide dismutase. Mannitol and dimethylsulfoxide had no effect. These results indicated no paticipation of superoxide and hydroxyl radical in the lipid peroxidation. Reduced glutathione (GSH) efficiently inhibited the lipid peroxidation. PB radicals emitted electron spin resonance (ESR) signals during the reaction of PB with HRP-H2O2. Microsomes and arachidonic acid strongly diminished the ESR signals, indicating that PB radicals directly react with unsaturated lipids of microsomes to cause thiobarbituric acid reactive substances. GSH sharply diminished the ESR signals of PB radicals, suggesting that GSH scavenges PB radicals to inhibit lipid peroxidation. Also, 2-methyl-2-nitrosopropan strongly inhibited lipid peroxidation. R-Phycoerythrin, a peroxyl radical detector substance, was decomposed by PB with HRP-H2O2. These results suggest that lipid peroxidation of microsomes is induced by PB radicals or peroxyl radicals, or both.

Bioflavonoid rescue of ascorbate at a membrane interface

In aqueous solution, ascorbate potently prevents bleaching of cytochrome c on exposure to excess H2O2 or t-butyl hydroperoxide. Ascorbate failed to protect cytochrome c in the presence of liposomes of mitochondrial membranelike composition. Like the redox mediator N,N,N,'N'-tetramethyl-p-phenylenediamine (TMPD), however, the bioflavonoids epicatechin and quercetin restored the protection afforded by ascorbate in the presence of liposomes and gave further protection. The quercetin glycoside, rutin, was much less effective, as was the vitamin E analog Trolox. In the presence of liposomes, quercetin alone was relatively ineffective, but cooperated with ascorbate to extend protection synergistically. The results bear specific implications in antioxidant protection of cytochrome c and in moderation of its hydroperoxidase activities in biological membranes. The data also reveal a situation where ascorbate is without effect except in the presence of a bioflavonoid, and substantiate a possibly vital role for certain bioflavonoids in mediating electron transfer from ascorbate into a hydrophobic environment.

Trypanosoma cruzi trypanothione reductase is inactivated by peroxidase-generated phenothiazine cationic radicals

Trypanosoma cruzi trypanothione reductase (TR) was irreversibly inhibited by peroxidase/H2O2 /phenothiazine (PTZ) systems. TR inactivation depended on (a) time of incubation with the phenothiazine system; (b) the peroxidase nature and (c) the PTZ structure and concentration. With the most effective systems, TR inactivation kinetics were biphasic, with a relatively fast initial phase during which about 75% of the enzyme activity was lost, followed by a slower phase leading to total enzyme inactivation. GSH prevented TR inactivation by the peroxidase/H2O2/PTZ+* systems. Production of PTZ+* cation radicals by PTZ peroxidation was essential for TR inactivation. Horseradish peroxidase, leukocyte myeloperoxidase (MPO) and the pseudo-peroxidase myoglobin (Mb) were effective catalysts of PTZ+* production. Promazine, thioridazine, chlorpromazine, propionylpromazine prochlorperazine, perphenazine and trimeprazine were effective constituents of the HRP/H2O2 /PTZ system. The presence of substituents at the PTZ nucleus position 2 exerted significant influence on PTZ activity, as shown by the different effects of 2-trifluoromethyl and 2-H or 2-chlorophenothiazines. The PTZ+* cation radicals disproportionation regenerated the non-radical PTZ molecule and produced the PTZ sulfoxide that was inactive on TR. Thiol compounds including GSH interacted with PTZ+* cation radicals transferring an electron from the sulfide anion to the PTZ+*, thus nullifying the PTZ+* biological and chemical activities.

Phenylbutazone radicals inactivate creatine kinase

Creatine kinase (CK) was used as a marker molecule to examine the side effect of damage to tissues by phenylbutazone (PB), an effective drug to treat rheumatic and arthritic diseases, with horseradish peroxidase and hydrogen peroxide (HRP-H(2)O2). PB inactivated CK during its interaction with HRP-H(2) O(2), and inactivated CK in rat heart homogenate. PB carbon-centered radicals were formed during the interaction of PB with HRP-H(2)O2. The CK efficiently reduced electron spin resonance signals of the PB carbon-centered radicals. The spin trap agent 2-methyl-2-nitrosopropane strongly prevented CK inactivation. These results show that CK was inactivated through interaction with PB carbon-centered radicals. Sulfhydryl groups and tryptophan residues in CK were lost during the interaction of PB with HRP-H(2)O2, suggesting that cysteine and tryptophan residues are oxidized by PB carbon-centered radicals. Other enzymes, including alcohol dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, but not lactate dehydrogenase, were also inactivated. Sulfhydryl enzymes seem to be sensitive to attack by PB carbon-centered radicals. Inhibition of SH enzymes may explain some of the deleterious effects induced by PB.

Oxidative signaling pathway for externalization of plasma membrane phosphatidylserine during apoptosis

Active maintenance of membrane phospholipid asymmetry is universal in normal cell membranes and its disruption with subsequent externalization of phosphatidylserine is a hallmark of apoptosis. Externalized phosphatidylserine appears to serve as an important signal for targeting recognition and elimination of apoptotic cells by macrophages, however, the molecular mechanisms responsible for phosphatidylserine translocation during apoptosis remain unresolved. Studies have focused on the function of aminophospholipid translocase and phospholipid scramblase as mediators of this process. Here we present evidence that unique oxidative events, represented by selective oxidation of phosphatidylserine, occur during apoptosis that could promote phosphatidylserine externalization. We speculate that selective phosphatidylserine oxidation could affect phosphatidylserine recognition by aminophospholipid translocase and/or directly result in enzyme inhibition. The potential interactions between the anionic phospholipid phosphatidylserine and the redox-active cationic protein effector of apoptosis, cytochrome c, are presented as a potential mechanism to account for selective oxidation of phosphatidylserine during apoptosis. Thus, cytochrome c-mediated phosphatidylserine oxidation may represent an important component of the apoptotic pathway.

Free radicals and hearing. Cause, consequence, and criteria

Reactive oxygen and nitrogen species, including free radicals, are produced in the human body in both health and disease. In health, they may arise as regulatory mechanisms, intercellular signaling species, or as bacteriocidal agents. Their production is normally controlled by the antioxidant defense mechanisms that include intracellular enzymes--for example, glutathione peroxidase and superoxide dismutase--and low molecular-mass compounds such as vitamin E or ascorbic acid. Although repair mechanisms exist, some steady-state basal oxidative damage occurs in all individuals. Oxidative stress arises when there is a marked imbalance between the production and removal of reactive oxygen and nitrogen species. This may originate from an overproduction of these substances or from a depletion in the antioxidant defenses. Certain drugs may induce oxidative stress by forming drug-derived radicals that can not only deplete the antioxidant defenses but can also react directly with biomolecules. To be able to assess whether oxidative stress is occurring in a particular tissue, reliable biomarkers of oxidative damage are required. Since oxidative stress can damage all major biomolecules in vitro and probably in vivo, biomarkers for DNA, protein, and lipid damage are being developed which, when taken with an assessment of the antioxidant status of the individual, will allow evaluation of the involvement of oxidative stress in the etiology of disease and in the side effects of drugs. There is some evidence to suggest that free radical-mediated damage may be involved in the ototoxicity of aminoglycosides and cisplatin derivatives. Whether this is a cause or consequence of the toxic insult to the sensory hair cells of the inner ear remains to be determined.

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).

Antioxidant properties of S-adenosyl-L-methionine: a proposed addition to organ storage fluids

Glutathione (GSH) depletion adversely affects the survival of organ grafts. Supplementation of commercial organ preservation solutions with GSH is complicated by the ease of oxidation of its thiol group and its ability to act as a pro-oxidant under certain conditions. Alternative sulphur-containing compounds such as S-adenosyl-L-methionine (SAM) can reduce ischaemia-reperfusion injury, possibly by acting as glutathione precursors, and are effective when added to preservation solutions. Although the antioxidant properties of GSH are known in some detail, there is little information on the ability of SAM to interact directly with reactive oxygen species (ROS) produced during ischaemia-reperfusion injury. This work compares the interaction of SAM and GSH with several ROS which may be formed during ischaemia-reperfusion. In a variety of lipid peroxidation systems, SAM and GSH had little effect except at high concentrations (5 mM) where they became pro-oxidant. Scavenging of O2.- by both species was slow. SAM was less effective than GSH at preventing damage by peroxynitrite or HOCl. In contrast, SAM was more effective than GSH in scavenging hydroxyl radicals (.OH) and in chelating iron ions to inhibit .OH generation. Unlike GSH, SAM did not stimulate .OH formation at low concentrations. The beneficial effects of SAM in preservation solutions could therefore include direct radical scavenging as well as acting as a precursor for intracellular GSH.

Vitamin C: antioxidant or pro-oxidant in vivo?

Ascorbic acid has a multiplicity of antioxidant properties, but it can exert pro-oxidant effects in vitro, usually by interaction with transition metal ions. It is as yet uncertain that these pro-oxidant effects have any biological relevance: some of the available data are summarized.

Characterization of drugs as antioxidant prophylactics

There is growing interest in the evaluation of drugs (prescription only medicines and over-the-counter medicines) as antioxidant prophylactics. Although free radical mechanism in human degenerative diseases is now generally recognised, the mechanisms of tissue injury in humans are very complex and it may not be possible to clearly identify the role played by free radicals in the process. This review examines the current evidence to support the notion that drugs for a particular therapeutic category might possess useful antioxidant capacity hence minimising tissue injury due to free radicals.