Search PubMed⌕ Search

Biomedical subjects

B Halliwell

Publications and source records attributed to B Halliwell.

At least 127 records · Page 7Linked to original sources
PubMed1997

Relationships between plasma measures of oxidative stress and metabolic control in NIDDM.

Diabetes mellitus may be associated with increased lipid peroxidation which may contribute to long-term tissue damage. To test this hypothesis, we measured hydroperoxides (ROOHs) as well as alpha-tocopherol in plasma from healthy subjects and individuals with non-insulin-dependent diabetes mellitus (NIDDM) (n = 41 and 87, respectively). ROOHs were analysed using the ferrous oxidation with xylenol orange version II (FOX2) assay in conjunction with a specific ROOH reductant, triphenylphosphine, alpha-Tocopherol was analysed by HPLC with fluorimetric detection. NIDDM patients had lower cholesterol standardised alpha-tocopherol levels as compared to control subjects (3.3 +/- 1.0 vs 5.1 +/- 2.3 (mumol/l)/(mmol/l); p < 0.0005, Mann-Whitney test): range (1.5-6.5 vs 1.9-13.0, respectively). Plasma ROOHs were substantially higher in the diabetic subjects compared to those of the control subjects (9.4 +/- 3.3 vs 4.1 +/- 2.2 mumol/l; p < 0.0005 Mann-Whitney test: range 2.7-16.8 vs 0.4-10.3, respectively). ROOH/cholesterol standardised alpha-tocopherol ratio was significantly higher in the diabetic patients compared to control subjects (3.2 +/- 1.6 vs 0.9 +/- 0.6; p < 0.0005, Mann-Whitney test: range 0.7-8.3 and 0.1-2.7, respectively). Plasma levels of ROOHs and alpha-tocopherol were similar in diabetic patients with or without complications as well as in smokers and non-smokers. The present study confirms previous findings from this laboratory that NIDDM is associated with increased oxidative stress as assessed by plasma ROOHs. Increased oxidative stress in diabetic patients appears to be related to the underlying metabolic abnormalities in diabetes, rather than to the complications of this disease. We therefore suggest that oxidative stress is an early stage in the disease pathology, which may contribute to the development of complications.

Adolescent↗
PubMed1997

Thiourea and dimethylthiourea inhibit peroxynitrite-dependent damage: nonspecificity as hydroxyl radical scavengers.

Thiourea and, more recently, dimethylthiourea, have been used as hydroxyl radical (OH.) scavengers in experiments both in vitro and in vivo. We show that both compounds can inhibit nitration of the amino acid tyrosine on addition of peroxynitrite, and also the inactivation of alpha1-antiproteinase by peroxynitrite. Hence, protective effects of (dimethyl) thiourea could be due to inhibition of peroxynitrite-dependent damage as well as to OH. scavenging, and these compounds must not be regarded as specific OH. scavengers.

Enzyme Inhibitors↗
PubMed1997

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.

Antioxidants↗
PubMed1997

Hypochlorous acid-induced base modifications in isolated calf thymus DNA.

Exposure of calf thymus DNA to hypochlorous acid/hypochlorite leads to extensive DNA base modification. Large concentration-dependent increases in pyrimidine oxidation products [thymine glycol (cis/trans), 5-hydroxycytosine, 5-hydroxyuracil, 5-hydroxyhydantoin] but not purine oxidation products (8-hydroxyguanine, 2- and 8-hydroxyadenine, FAPy guanine, FAPy adenine) were observed at pH 7.4. In addition, large increases in 5-chlorouracil (probably formed from 5-chlorocytosine during sample preparation), a novel chlorinated base, were observed. Addition of HOCl to DNA already damaged by .OH generated by a mixture of ascorbate, copper(II) chloride, and hydrogen peroxide showed that hypochlorous acid led to a loss of 8-hydroxyguanine, 2- and 8-hydroxyadenine, FAPy guanine, FAPy adenine, and 5-hydroxycytosine in a concentration- and pH-dependent manner. Nevertheless, time course studies suggested that the formation of purine oxidation products in isolated DNA by hypochlorous acid was not a major oxidation pathway. If this pattern of damage, especially the production of 5-chlorocytosine, is unique to hypochlorous acid, it might act as a "fingerprint" of damage to DNA by HOCl.

Animals↗
PubMed1997

Effect of peroxynitrite on plasma extravasation, microvascular blood flow and nociception in the rat.

1. Peroxynitrite (ONOO-) is a cytotoxic species, formed by the reaction between nitric oxide and superoxide free radicals, that may be involved in inflammation. In this study we have investigated the effect of peroxynitrite on plasma extravasation and microvascular blood flow in the dorsal skin and on nociceptive responses in the hind paw of the rat. 2. Male Wistar rats were anaesthetized and their dorsal skin shaved. Plasma extravasation was measured by the extravascular accumulation of 125I-labelled albumin over 0-45 min and 0-240 min. Blood flow was measured by laser-Doppler flowmetry over 0-240 min. Studies in the hind paw were carried out in the conscious rat. Hind paw weight changes were determined by volume displacement and nociception by a mechanical hyperalgesia technique. 3. Intradermal (i.d.) peroxynitrite (100-200 nmol site-1) produced a significant (P < 0.01) dose-dependent increase in plasma extravasation in dorsal skin over 0-45 min which was not increased over 45-240 min. Plasma extravasation was significantly (P < 0.001) decreased in rats pretreated with the anti-inflammatory steroid dexamethasone (1 mg kg-1, i.v.; -180 min), but not modulated by treatment with the hydrogen peroxide deactivator catalase (2200 u site-1), or the superoxide scavenger superoxide dismutase (500 u site-1), effective doses of the tachykinin NK1 antagonist SR140333 (1 nmol site-1), the cyclo-oxygenase inhibitor indomethacin (358 mumol site-1), or combined pretreatment with mepyramine (histamine H1-receptor antagonist; 2.8 nmol site-1) and methysergide (5-HT antagonist; 1.9 nmol site-1). 4. Microvascular blood flow was significantly (P < 0.05) increased 30 and 120 min after i.d. peroxynitrite (100 nmol site-1) in dorsal skin and remained raised until the end of the recording period (240 min). The increase in blood flow was unaffected by dexamethasone (1 mg kg-1, i.v.; -180 min) or indomethacin (10 mg kg-1, s.c.; -30 min). 5. Hind paw volume was significantly (P < 0.001) increased 30 min after intraplantar peroxynitrite (87.5 and 175 nmol paw-1) and remained raised for the duration of the experiment (360 min). By comparison, nociception was not altered by intraplantar peroxynitrite. 6. These data indicate that peroxynitrite can cause an increase in both plasma extravasation and blood flow, suggesting that peroxynitrite could be of biological relevance to microvascular responses. These findings may be of importance in the pathology of inflammatory diseases in which peroxynitrite formation occurs.

Animals↗
PubMed1997

Scavenging of hydroxyl radicals but not of peroxynitrite by inhibitors and substrates of nitric oxide synthases.

1. The nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) is widely used to study the role of NO. in physiological and pathological processes, including its role in the generation of the cytotoxic species peroxynitrite (ONOO-) and of reactive oxygen radicals such as hydroxyl (OH.). Often L-NAME is applied to tissues at mM concentrations. At such high concentrations, it might act as a free radical scavenger. A similar possibility might apply to the use of high levels of arginine to study the role of NO. in atherogenesis. 2. We therefore examined the rate of scavenging of OH. by L-NAME and found that L-NAME reacts more quickly with OH. than the established 'OH. scavenger' mannitol and the widely used 'OH. trap' salicylate. However, D-NAME can scavenge OH. at rates equal to L-NAME. Both L- and D-arginine were also good OH. scavengers, comparable in effectiveness to mannitol. 3. Neither L-NAME, D-NAME, L-arginine nor D-arginine was able to inhibit ONOO(-)-dependent nitration of tyrosine, suggesting that they are unlikely to be scavengers of ONOO(-)-derived nitrating species. 4. Neither L-NAME, D-NAME, L-arginine nor D-arginine was able to inhibit the inactivation of alpha 1-antiproteinase by ONOO-, suggesting that they cannot prevent direct oxidations by peroxynitrite. 5. We conclude that L-NAME has sufficient activity as an OH. scavenger to confound certain pharmacological experiments. However, this explanation of its biological effects can be ruled out if control experiments show that D-NAME has no effect and that L-arginine (also a free radical scavenger) antagonizes the action of L-NAME.

Dose-Response Relationship, Drug↗
PubMed1997

An assessment of oxidative damage to proteins, lipids, and DNA in brain from patients with Alzheimer's disease.

Oxidative stress may contribute to neuronal loss in Alzheimer's disease (AD). The present study compares the levels of oxidative damage to proteins, lipids, and DNA bases from seven different brain areas of AD and matched control tissues by using a range of techniques. No differences in levels of lipid peroxidation were found in any of the brain regions by using two different assay systems. Overall, there was a trend for protein carbonyl levels to be increased in AD in frontal, occipital, parietal, and temporal lobe, middle temporal gyrus, and hippocampus, but a significant difference was found only in the parietal lobe. Gas chromatography-mass spectrometry was used to measure products of damage to all four DNA bases. Increased levels of some (8-hydroxyadenine, 8-hydroxyguanine, thymine glycol, Fapy-guanine, 5-hydroxyuracil, and Fapy-adenine), but not all, oxidized DNA bases were observed in parietal, temporal, occipital, and frontal lobe, superior temporal gyrus, and hippocampus. The baseline level of oxidative DNA damage in the temporal lobe was higher than in other brain regions in both control and AD brain. The finding of increased oxidative damage to protein and DNA strengthens the possibility that oxidative damage may play a role in the pathogenesis of AD in at least some key brain regions.

Aged↗
PubMed1997

Oxidative DNA damage in the parkinsonian brain: an apparent selective increase in 8-hydroxyguanine levels in substantia nigra.

Oxidative damage has been implicated in the pathology of Parkinson's disease (PD), e.g., rises in the level of the DNA damage product, 8-hydroxy-2'-deoxyguanosine, have been reported. However, many other products result from oxidative DNA damage, and the pattern of products can be diagnostic of the oxidizing species. Gas chromatography/mass spectrometry was used to examine products of oxidation and deamination of all four DNA bases in control and PD brains. Products were detected in all brain regions examined, both normal and PD. Analysis showed that levels of 8-hydroxyguanine (8-OHG) tended to be elevated and levels of 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FAPy guanine) tended to be decreased in PD. The most striking difference was a rise in 8-OHG in PD substantia nigra (p = 0.0002); rises in other base oxidation/deamination products were not evident, showing that elevation in 8-OHG is unlikely to be due to peroxynitrite (ONOO-) or hydroxyl radicals (OH.), or to be a prooxidant effect of treatment with L-Dopa. However, some or all of the rise in 8-OHG could be due to a change in 8-OHG/FAPy guanine ratios rather than to an increase in total oxidative guanine damage.

Aged↗
PubMed1997

A generalised increase in protein carbonyls in the brain in Parkinson's but not incidental Lewy body disease.

The degeneration of neurones in Parkinson's disease (PD) may involve oxidative stress. Previously, increased lipid peroxidation and oxidative DNA damage have been reported in parkinsonian substantia nigra. In the present study the protein carbonyl assay was used to assess oxidative protein damage in postmortem brain tissue from patients with PD and age-matched controls. In brain areas associated with PD, such as substantia nigra, caudate nucleus, and putamen, there was a significant increase in carbonyl levels. However, increased carbonyl levels were also found in areas of the brain not thought to be affected in PD. This perhaps suggests that protein carbonyl formation is related to therapy with L-DOPA, which can exert prooxidant properties in vitro. Consistent with this possibility, brain regions from individuals with incidental Lewy body disease (putative presymptomatic PD) showed no rise in carbonyls in any brain areas. Our data show that either oxidative protein damage occurs widely but late in PD brain, and/or that L-DOPA treatment contributes to protein oxidation.

Adult↗
PubMed1997

Hydroxylation of salicylate and phenylalanine as assays for hydroxyl radicals: a cautionary note visited for the third time.

Hydroxylation of salicylate to 2,3- and 2,5-dihydroxy-benzoates (DHBs) is widely used as an index of hydroxyl radical (OH.) formation in vivo and in vitro. Several recent studies indicate that peroxynitrite can lead to generation of DHBs from salicylate and it is uncertain as to whether or not OH. is involved. A similar problem may occur in the use of phenylalanine as an OH. detector. Hence formation of hydroxylation products from salicylate (or phenylalanine) may not in itself be a definitive index of OH. generation, especially in cases where such generation in physiological systems is decreased by inhibitors of nitric oxide synthase. Determination of salicylate (or phenylalanine) nitration products can allow distinction between peroxynitrite-dependent aromatic hydroxylation and that involving "real" OH..

Animals↗
PubMed1997

Prevention of peroxynitrite-dependent tyrosine nitration and inactivation of alpha1-antiproteinase by antibiotics.

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 antibiotics to protect against peroxynitrite-dependent inactivation of alpha1-antiproteinase, and to inhibit tyrosine nitration by peroxynitrite, in vitro. Tetracycline, minocycline, doxycycline, rifamycin and rifampicin were highly protective in both assay systems, whereas several other antibiotics tested were not. The possibility that antibiotics could affect tissue injury at sites of inflammation by scavenging peroxynitrite is discussed.

Anti-Bacterial Agents↗