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Biomedical subjects

B Halliwell

Publications and source records attributed to B Halliwell.

At least 163 records · Page 9Linked to original sources
PubMed1996

Evaluation of the pro-oxidant and antioxidant actions of L-DOPA and dopamine in vitro: implications for Parkinson's disease.

The antioxidant and pro-oxidant properties of L-DOPA and dopamine were investigated in vitro. Both compounds inhibited the peroxidation of ox-brain phospholipids, with IC50 values of 8.5 microM for dopamine and 450 microM for L-DOPA. Dopamine and L-DOPA reacted with trichloromethyl peroxyl radicals (CCl3O2.) with rate constants of 2.1 x 10(7)M-1s-1 and 1.3 x 10(7)M-1s-1 respectively. The effects of dopamine and L-DOPA on iron ion-dependent hydroxyl radical generation from H2O2 were complex. In general, low concentrations stimulated OH. formation in the presence of ferric-EDTA and, in the case of L-DOPA, ferric-ADP and ferric citrate chelates. Both compounds also reacted with superoxide radical and hypochlorous acid. The products of the reaction with HOCl could still inhibit alpha 1-antiproteinase and appear to be 'long lived' chloramine-type oxidizing species. Our results suggest that L-DOPA and dopamine might have a complex mixture of pro- and anti- oxidant effects, which could contribute to tissue damage due to oxidative stress in Parkinson's disease and other neurological disorders.

Animals↗
PubMed1996

Oxidative damage and motor neurone disease difficulties in the measurement of protein carbonyls in human brain tissue.

It has been suggested in the literature that elevated oxidative protein damage, measured as protein carbonyls, is present in the nervous system of patients with sporadic motor neurone disease (MND). However, the actual reported levels of brain protein carbonyls vary over a wide range. We show here that this is probably due to the use of the different protocols for the carbonyl assay; results differ depending on when the dinitrophenylhydrazine reagent is added and at what stage in the procedure protein is assayed for the calculation of carbonyls on a unit protein basis. Using a range of different procedures, we were unable to confirm reports of elevated protein carbonyls in motor cortex from brains of patients with MND. We also measured thiobarbituric acid-reactive material in the brain samples using an HPLC-based TBA test in the presence of butylated hydroxytoluene. In general, there was no significant elevation of TBARS in MND motor cortex. However, four patients showed values higher than any of the control patients (both 'normal' control and 'disease control'). There was no correlation of TBARS with protein carbonyl values. We suggest that oxidative damage in motor cortex in sporadic MND, if it occurs, may be confined to a small group of patients and may affect different molecular targets in each patient.

Adult↗
PubMed1996

Oxidative stress, nutrition and health. Experimental strategies for optimization of nutritional antioxidant intake in humans.

Reactive oxygen species and reactive nitrogen species are formed in the human body. Endogenous antioxidant defences are inadequate to scavenge them completely, so that ongoing oxidative damage to DNA, lipids, proteins and other molecules can be demonstrated and may contribute to the development of cancer, cardiovascular disease and possibly neurodegenerative disease. Hence diet-derived antioxidants may be particularly important in protecting against these diseases. Some antioxidants (e.g. ascorbate, certain flavonoids) can exert pro-oxidant actions in vitro, often by interaction with transition metal ions. The physiological relevance of these effects is uncertain, as is the optimal intake of most diet-derived antioxidants. In principle, these questions could be addressed by examining the effects of dietary composition and/or antioxidant supplementation upon parameters of oxidative damage in vivo. The methods available for measuring steady-state damage (i.e. the balance between damage and repair or replacement of damaged molecules) and the actual rate of damage to DNA, proteins and lipids are reviewed, highlighting areas in which further methodological development is urgently required.

Antioxidants↗
PubMed1996

Are whole extracts and purified glucosinolates from cruciferous vegetables antioxidants?

Fruits and vegetables contain several classes of compounds that can potentially contribute to antioxidant activity, including vitamins, simple and complex phenolics, sulphur-containing compounds and glucosinolates. The glucosinolates are found in high concentration in many cruciferous vegetables, and it is well established that their breakdown products induce endogenous antioxidant defences such as quinone reductase and glutathione S-transferase in cells and in vivo. Despite the anticarcinogenic effect of these compounds in animal models, the direct antioxidant properties of this class of compounds have not been systematically studied. We therefore examined the free radical-scavenging properties of representative extracts and of purified glucosinolates from cruciferous vegetables, by measuring their effect on ascorbate- or NADPH/iron-induced peroxidation of human liver microsomes, ascorbate/iron-induced peroxidation on phospholipid liposomes, iron chelation and hydroxyl radical scavenging using the deoxyribose assay, total antioxidant potential using ABTS (2,2'-azinobis(3-ethyl-benzothiazoline-6-sulphonate)) and the bleomycin assay. Most of the extracts from cruciferous vegetables exhibited some antioxidant properties, although extracts from cooked Brussels sprouts increased the rate of microsomal lipid peroxidation. The effects in these assays were dependent upon processing and species of crucifer, and the glucosinolate content appeared to play a minor role in these effects, since purified glucosinolates exhibited only weak antioxidant properties. The total antioxidant activities of extracts from cooked and autolysed Brussels sprouts were identical within experimental error. This is probably due to the content of phenolics which is unaltered by autolysis, despite the differences between these samples in other assays especially NADPH-iron-induced lipid peroxidation of human liver microsomes. The results demonstrate that glucosinolates are unlikely to account for the direct antioxidant effects of extracts from cruciferous vegetables.

Antioxidants↗
PubMed1996

Protection against peroxynitrite-dependent tyrosine nitration and alpha 1-antiproteinase inactivation by ascorbic acid. A comparison with other biological antioxidants.

Peroxynitrite, formed by reaction of superoxide and nitric oxide, appears to be an important tissue-damaging species generated at sites of inflammation. In this paper, we compare the abilities of several biological antioxidants to protect against peroxynitrite-dependent inactivation of alpha 1-antiproteinase, and to inhibit tyrosine nitration upon addition of peroxynitrite. GSH and ascorbate protected efficiently in both systems. Uric acid inhibited tyrosine nitration but not alpha 1-antiproteinase inactivation. The possibility that ascorbic acid is an important scavenger of reactive nitrogen species in vivo is discussed.

Antioxidants↗
PubMed1996

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.

Antioxidants↗
PubMed1996

Mechanisms involved in the generation of free radicals.

Free radicals are constantly formed in the human body, both by "accidents of chemistry" and for useful metabolic purposes. Their action is opposed by a balanced and co-ordinated system of antioxidant defences. Upsetting this balance causes oxidative stress, which can lead to cell injury and death.

Humans↗
PubMed1995

DNA damage in human respiratory tract epithelial cells: damage by gas phase cigarette smoke apparently involves attack by reactive nitrogen species in addition to oxygen radicals.

Treatment of human respiratory tract tracheobronchial epithelial cells with gas-phase cigarette smoke led to dose-dependent DNA strand breakage that was highly correlated with multiple chemical modifications of all four DNA bases. The pattern of base damage suggests attack by hydroxyl radicals (OH.). However, by far the most important base damage in quantitative terms was formation of xanthine and hypoxanthine, presumably resulting from deamination of guanine and adenine respectively. Hence, DNA damage by cigarette smoke may involve reactive nitrogen species as well as reactive oxygen species.

Adenine↗
PubMed1995

DNA strand breakage and base modification induced by hydrogen peroxide treatment of human respiratory tract epithelial cells.

Treatment of human respiratory tract epithelial cells with H2O2 led to concentration-dependent DNA strand breakage that was highly-correlated with multiple chemical modifications of all four DNA bases, suggesting that damage is due to hydroxyl radical, OH. However, the major base damage occurred to adenine. Hence, conclusions made about the occurrence and the extent of oxidative DNA damage on the basis only of changes in 8-hydroxyguanine should be approached with caution.

Bronchi↗
PubMed1995

Nitric oxide rapidly scavenges tyrosine and tryptophan radicals.

By utilizing a pulse-radiolytic technique, we demonstrate for the first time that the rate constant for the reaction of nitric oxide (.NO) with biologically relevant tyrosine and tryptophan radicals (Tyr. and Trp. respectively) in amino acids, peptides and proteins is of the order of (1-2) x 10(9) M-1.s-1. We also show that .NO effectively interferes with electron-transfer processes between tryptophan and tyrosine residues in proteins subjected to pulse radiolysis. The near diffusion-controlled rates of these reactions, coupled with the increasingly recognized role of protein radicals in enzyme catalysis and oxidative damage, suggest that Tyr. and Trp. are likely and important targets for .NO generated in vivo.

Dipeptides↗
PubMed1995

Nitric oxide and oxygen radicals: a question of balance.

The production of superoxide and nitric oxide individually has been associated with the development of several diseases but only recently has it been realised that interactions between them may also be important in disease pathology. The central hypothesis which is emerging is that the balance between nitric oxide and superoxide generation is a critical determinant in the aetiology of many human diseases including atherosclerosis, neurodegenerative disease, ischaemia-reperfusion and cancer. These ideas are discussed in this short overview and placed in the context of the current and future status of therapies which could modulate the balance between nitric oxide and superoxide.

Cardiovascular Diseases↗
PubMed1995

Presence of iron catalytic for free radical reactions in patients undergoing chemotherapy: implications for therapeutic management.

We investigated the kinetics of generation of iron 'catalytic' for free radical reactions in children with diagnosed acute lymphoblastic leukaemia (ALL) who received high-dose methotrexate infusions. In 76% of the chemotherapy courses studied, 'catalytic' iron appeared in plasma in the concentration range from 0.1 to 3 mumol/l. Positive correlations between maximum levels of 'catalytic' iron and plasma hepatic enzymes could be established in the majority of cases and in one subset of patients (low and medium risk ALL) mean 'catalytic' iron levels correlated well to clinically observable toxicities. The damaging potential of 'catalytic' iron was also demonstrated experimentally: oxidative damage to proteins was significantly (P < 0.05) higher in plasma samples showing the presence of 'catalytic' iron and in addition a strong correlation (r = 0.95, P < 0.02) was seen between plasma concentration of 'catalytic' iron and the ability of the plasma to stimulate lipid peroxidation. Our data show that chemotherapy releases 'catalytic' iron which may relate to toxic side effects. Hence binding this 'catalytic' iron by judicious co-administration of iron chelating agents could be beneficial in minimizing the iatrogenic adverse effects of chemotherapy of acute leukaemia.

Adolescent↗
PubMed1995

Superoxide-dependent depletion of reduced glutathione by L-DOPA and dopamine. Relevance to Parkinson's disease.

The mechanism of nigral cell death in Parkinson's disease (PD) remains unknown, but it is increasingly proposed that free radical reactions are important in the disease pathology. One of the most striking features of PD is an approximate 40% decrease in the levels of reduced glutathione (GSH) which occurs early in the development of the disease. We describe a possible mechanism of GSH depletion which results from the reaction of L-DOPA and dopamine with the superoxide free radical (O2.-) and leads to a very rapid loss of GSH.

Dopamine↗
PubMed1995

DNA damage and cancer: measurement and mechanism.

There is currently great interest in the possible role of reactive nitrogen species and reactive oxygen species in causing DNA damage that leads to cancer. It appears likely that certain reactive oxygen species can act as complete carcinogens. However, the development of human cancer will depend on other factors such as the extent of DNA damage, antioxidant levels and DNA repair systems. The true picture will only be seen if we have reliable and sensitive techniques for the measurement of DNA damage. In this article we outline various methods for measuring DNA damage base, with special emphasis on HPLC and GC-MS based systems.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1995

The chemical modification of glycosaminoglycan structure by oxygen-derived species in vitro.

The effect of reactive oxygen species (ROS) on the chemical structure of glycosaminoglycans (GAG) was studied in order to consider their role in connective tissue damage during an inflammatory disease state such as periodontal disease. GAG were exposed to a radical generating system for 1 h and analysed by gel filtration for fragmentation and chemically with respect to uronic acid, hexosamine and sulfate content. Non-sulfated GAG, hyaluronan and chondroitin, were most susceptible to depolymerisation and chemical modification of uronic acid and hexosamine residues by ROS. Depolymerisation and chemical modification of sulfated GAG, chondroitin 4-sulfate, dermatan sulfate and heparan sulfate was significantly less than for non-sulfated GAG. The highly sulfated GAG heparin showed minimal depolymerisation by ROS, but uronic acid residues were readily modified. Analysis of the ROS-exposed residues suggests that uronic acid is capable of degrading to a 3-carbon aldehyde, malondialdehyde. Chondroitin sulfate exposed to ROS resulted in marginal desulfation. The results suggest that the presence of sulfate on the GAG chain may protect the molecule against ROS attack. However, chemical modification of GAG may affect proteoglycan function and be of importance in considering connective tissue destruction in a variety of pathological situations, including periodontal disease.

Chondroitin Sulfates↗
PubMed1995

Tyrosine modification by reactive nitrogen species: a closer look.

Peroxynitrite (ONOO-) is a powerful oxidant and cytotoxic species formed by the rapid reaction between nitrogen monoxide (nitric oxide, .NO) and superoxide (O2.-). At neutral pH ONOO- is partly protonated and this protonated form, peroxynitrous acid (ONOOH), decomposes rapidly to nitrate, forming (an) intermediate(s) with reactivity similar to .OH and .NO2. Peroxynitrite can hydroxylate and nitrate aromatic rings, and aromatic nitration of phenols such as tyrosine by ONOOH is proposed to proceed via a radical mechanism, with intermediate formation of .NO2. Modification of tyrosine by .NO2 also involves nitration via a radical mechanism. Aromatic nitration of phenols by ONOO- has been shown to be enhanced by superoxide dismutase or Fe(3+)-EDTA, which were proposed to catalyze heterolytic cleavage of ONOOH to form a nitrating species similar to the nitronium ion (NO2+). We investigated possible mechanisms of tyrosine modification by various reactive nitrogen species, including ONOO-, 3-morpholinosydnonimine (SIN-1), and .NO2. Reaction of tyrosine with ONOO- leads to formation of 3-nitrotyrosine and dityrosine, indicating intermediate formation of tyrosyl radicals. The pH dependence of formation of both 3-nitrotyrosine and dityrosine by ONOO- suggests that intermediate formation of ONOOH is required. Qualitatively similar results were obtained when ONOOH was generated continuously by H2O2 and NaNO2 at mildly acidic pH or with SIN-1, a compound which at neutral pH releases both .NO and O2.-, presumably producing ONOO-. However, relatively low yields of nitrotyrosine were obtained with SIN-1, possibly because of competing reactions of tyrosyl radicals with .NO or O2.-. Possible involvement of .NO2 in tyrosine modification by ONOO- was studied using hydroxyl radical scavengers, which can increase the radical yield during decomposition of ONOOH and thereby enhance generation of .NO2. Hydroxyl radical scavengers did not affect tyrosine modification by .NO2 directly and slightly inhibited tyrosine modification by authentic ONOO-. However, when ONOO- was produced at a slower rate, either by SIN-1 or by H2O2/NaNO2 at acidic pH, hydroxyl radical scavengers were found to significantly enhance tyrosine nitration. Our results suggest that ONOO- or ONOO(-)-generating systems induce nitration of tyrosine (or tyrosine residues in proteins) via intermediate formation of tyrosyl radicals and .NO2.

Free Radicals↗
PubMed1995

Characterization of the potential antioxidant and pro-oxidant actions of some neuroleptic drugs.

It has been suggested in the literature that neuroleptic drugs may be able to exert antioxidant and/or pro-oxidant actions in vivo. The feasibility of this was tested by measuring the ability of chlorpromazine, prochlorperazine, metoclopramide, methotrimeprazine and haloperidol to scavenge biologically relevant oxygen-derived species in vitro. None of the drugs reacted with superoxide radical at a significant rate. Chlorpromazine, prochlorperazine, metoclopramide and methotrimeprazine were very powerful scavengers of hydroxyl radicals, reacting at almost a diffusion-controlled rate. Chlorpromazine showed some ability to inhibit iron ion-dependent hydroxyl radical formation. Chlorpromazine, methotrimeprazine, promethazine and prochlorperazine were powerful inhibitors of iron ion-dependent liposomal lipid peroxidation, scavengers of organic peroxyl radicals and inhibitors of haem protein/hydrogen peroxide-dependent peroxidation of arachidonic acid. Chlorpromazine, prochlorperazine, metoclopramide, methotrimeprazine and haloperidol were powerful scavengers of hypochlorous acid. Haloperidol showed no ability to inhibit lipid peroxidation or to scavenge peroxyl radicals, and reproducibly increased lipid peroxidation catalysed by haem proteins, in both the presence and absence of hydrogen peroxide. The relevance of these in vitro observations to events in vivo is discussed.

Antioxidants↗