J P Spencer

King's College London, Londinium, England, United Kingdom

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Publications (12)38.98 Total impact

  • K Zhao, M Whiteman, J P Spencer, B Halliwell
    Methods in Enzymology 02/2001; 335:296-307. · 2.00 Impact Factor
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    ABSTRACT: No modification of purine or pyrimidine bases was observed when isolated DNA was incubated with 1 mM nitrite at pH 7.4. However, exposure of human bronchial epithelial cells in culture medium at pH 7.4 to nitrite at concentrations of 100 microM or greater led to deamination of purine bases in cellular DNA. Deamination was more extensive in cells exposed to lower extracellular pH values and higher nitrite concentrations. Significant increases in the levels of xanthine and hypoxanthine, putative deamination products of guanine and adenine, respectively, were observed in DNA from nitrite-treated cells but no rise in any base oxidation products such as 8-hydroxyguanine. This pattern of damage suggests that exposure of cells to nitrite (even at pH 7.4) leads to intracellular generation of "reactive nitrogen species" capable of deaminating purines in DNA. In addition, significant DNA strand breakage occurred in nitrite-treated cells. The time course of base damage suggested that the repair of deaminated purine lesions in these cells is slow. By contrast, DNA isolated from cells exposed to hypochlorous acid (HOCl) has significant oxidation of pyrimidine bases and chlorination of cytosine but little oxidation of purines. Exposure of cells to both species (NO(2)(-) plus HOCl) potentiated the oxidative DNA base damage observed but decreased the extent of deamination. We hypothesize that this is due to the formation of nitryl chloride (NO(2)Cl) from reaction of HOCl with *NO(2)(-). The relevance of our observations to events in the stomach and respiratory tract, at sites of inflammation, and in ischemic tissues is discussed.
    Free Radical Biology and Medicine 05/2000; 28(7):1039-50. · 5.27 Impact Factor
  • O I Aruoma, J P Spencer, N Mahmood
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    ABSTRACT: The natural antioxidant ergothioneine (EGT) was tested for its ability to inhibit cell death caused by hydrogen peroxide (H2O2) and to inhibit DNA oxidation by peroxynitrite (ONOO-) in human neuronal hybridoma cell line (N-18-RE-105). High concentrations of EGT (5 mM) were tolerated by the N-18-RE-105 cells. N-acetylcysteine (NAC) was not well tolerated by the cells at concentrations greater than 3 mM (cell viability averaged 50%). Increasing concentrations of EGT increases cell viability in the presence of NAC. EGT at concentrations up to 2 mM weakly improved cell viability in the presence of H2O2. NAC at concentrations up to 2 mM weakly decreased, but not significantly, the viability of the cells. At a higher concentration of 5 mM, NAC weakly protected the neuronal cells against the H2O2-induced cell death. The protection was significantly enhanced by preincubation with EGT. Ergothioneine inhibited ONOO(-)-induced oxidative damage in isolated calf thymus DNA and DNA in N-18-RE-105 cells. The concentration of EGT in human and mammalian tissue has been estimated to be 1-2 mM, which suggests that EGT may serve as a non-toxic thiol buffering antioxidant in vivo and may find applications in pharmaceutical preparations where oxidative stability is desired.
    Food and Chemical Toxicology 12/1999; 37(11):1043-53. · 3.01 Impact Factor
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    ABSTRACT: Chronic inflammation results in increased nitric oxide formation and nitrite (NO-2) accumulation. Activated phagocytes release myeloperoxidase generating the cytotoxic agent hypochlorous acid (HOCl). Reaction of HOCl with NO-2 results in the formation of nitryl chloride (NO2Cl), a potent oxidising, nitrating and chlorinating species. Exposure of DNA to NO-2 alone (up to 250 microM) at pH 7.4 did not induce oxidative DNA base damage. However, incubation of DNA with NO-2 in the presence of HOCl led to increases in thymine glycol, 5-hydroxyhydantoin, 8-hydroxyadenine and 5-chlorouracil to levels higher than those achieved by HOCl alone. No significant increases in 8-hydroxyguanine, xanthine, hypoxanthine, 2-hydroxyadenine, FAPy guanine, FAPy adenine and 8-chloroadenine were observed. HOCl-induced depletion of FAPy guanine and 8-hydroxyguanine was reduced in the presence of NO-2. Modification of DNA by HOCl/NO-2 (presumably generating NO2Cl) produces a pattern of DNA base damage products in isolated DNA that is similar to the pattern produced by HOCl but not other reactive species.
    Biochemical and Biophysical Research Communications 05/1999; 257(2):572-6. · 2.41 Impact Factor
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    ABSTRACT: Hydroxytyrosol is one of the o-diphenolic compounds in extra virgin olive oil and has been suggested to be a potent antioxidant. The superoxide radical (O2*-) and nitric oxide (NO*) can react very rapidly to form peroxynitrite (ONOO ), a reactive tissue damaging species thought to be involved in the pathology of several chronic diseases. Hydroxytyrosol was highly protective against the peroxynitrite-dependent nitration of tyrosine and DNA damage by peroxynitrite in vitro. Given that extra virgin olive oil is consumed daily by many humans, hydroxytyrosol derived from this diet could conceivably provide a defense against damage by oxidants in vivo. The biological activity of hydroxytyrosol in vivo will depend on its intake, uptake and access to cellular compartments.
    Free Radical Biology and Medicine 04/1999; 26(5-6):762-9. · 5.27 Impact Factor
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    ABSTRACT: Oxidation of L-3,4-dihydroxyphenylalanine (L-DOPA) and dopamine (DA) to generate semiquinones/quinones, oxygen radicals, and other reactive oxygen species may play a role in neuronal cell death in Parkinson's disease (PD). In particular, semiquinones/quinones can form conjugates with thiol compounds such as GSH and cysteine. Exposure of L-DOPA, DA, and other catecholamines to a system generating O2.- radical led to O2(.-)-dependent depletion of added GSH (or cysteine), accompanied by the formation of thiol-DA or -DOPA adducts as detected by HPLC. Superoxide could additionally cause destruction of these adducts. Iron or copper ions could also promote conjugate formation between GSH or cysteine and DA and L-DOPA, especially if H2O2 was present. We applied HPLC to measure glutathionyl and cysteinyl conjugates of L-DOPA, DA, and 3,4-dihydroxyphenylacetic acid (DOPAC) in postmortem brain samples from PD patients and normal control subjects. Conjugates were detected in most brain areas examined, but levels were highest in the substantia nigra and putamen. In most regions, adduct levels were lower in PD, but there were significant increases in cysteinyl adducts of L-DOPA, DA, and DOPAC in PD substantia nigra, suggesting that acceleration of L-DOPA/DA oxidation occurs in PD, although we cannot say if this is a primary feature of the disease or if it is related to therapy with L-DOPA. In vitro, conjugate formation could be inhibited by the dithiol dihydrolipoate but not by its oxidised form, lipoic acid.
    Journal of Neurochemistry 12/1998; 71(5):2112-22. · 3.97 Impact Factor
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    ABSTRACT: When human respiratory tract epithelial cells were exposed to 100 microM H2O2, there was rapid induction of DNA strand breakage and chemical modifications to all 4 DNA bases suggestive of attack by OH.. The major products were FAPy-adenine, FAPy-guanine, and 8-OH-guanine. Some of the base modifications were removed very quickly from the DNA (e.g., 8-OH-guanine), whereas others persisted for longer (e.g., thymine glycol), probably due to differential activity of different repair enzymes. By contrast, strand breaks continued to increase over the time course of the experiment, perhaps because strand breakage is also implicated in the repair process. One should therefore be cautious in using strand breakage as a sole measure of oxidative DNA damage, and when drawing conclusions about the pattern and biological significance of oxidative DNA damage in cells the relative persistence of different lesions must be considered.
    Biochemical and Biophysical Research Communications 08/1996; 224(1):17-22. · 2.41 Impact Factor
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    ABSTRACT: Extracts of herbs and spices are increasingly of interest in the food industry because they retard oxidative degradation of lipids. There is also increasing interest in the antiviral activity of plant products. A liquid, deodorized rosemary extract and an oily extract of a mixture of Provençal herbs were tested for antioxidant and antiviral action in vitro. The rosemary extract (Herbor 025) and the extract of Provençal herbs (Spice Cocktail) inhibited peroxidation of phospholipid liposomes with 50% inhibition concentration values of 0.0009% (v/v) and 0.0035% (v/v), respectively. Herbor 025 and the spice cocktail (at 0.2%, v/v) reacted with trichloromethylperoxyl radical with calculated rates of 2.7 x 10(4) s-1 and 1.5 x 10(3) s-1, respectively. The main active components in the herbal preparations, carnosol and carnosic acid, at 0.05% (v/v) react with rate constants of (1-3) x 10(6) M-1 sec-1 and 2.7 x 10(7) M-1 sec-1, respectively. Both extracts show good antioxidant activity in the Rancimat test, especially in lard. Herbor 025 and the spice cocktail inhibited human immunodeficiency virus (HIV) infection at very low concentrations which were also cytotoxic. However, purified carnosol exhibited definite anti-HIV activity at a concentration (8 microM) which was not cytotoxic. Both preparations promoted some DNA damage in the copper-phenanthroline and the bleomycin-iron systems. The two herbal preparations possess antioxidant properties that may make them useful in the food matrix.
    Food and Chemical Toxicology 06/1996; 34(5):449-56. · 3.01 Impact Factor
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    ABSTRACT: 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.
    Free Radical Research 03/1996; 24(2):95-105. · 3.28 Impact Factor
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    ABSTRACT: Exposure of isolated calf thymus DNA and human skin epidermal keratinocytes to peroxynitrite or the peroxynitrite generator, 3-morpholinosydnonimine (SIN-1), led to extensive DNA base modification. Large increases in xanthine and hypoxanthine, possible deamination products of guanine and adenine, respectively, and in 8-nitroguanine were observed, but only small changes in some oxidized base products were seen. This pattern of damage suggests that hydroxyl radicals were not major contributors to base modification caused by peroxynitrite, as OH is known to cause multiple oxidative modifications to all four DNA bases. Instead, it seems that reactive nitrogen species play a much greater role in the mechanism of base damage, producing both nitration and deamination of purine bases when DNA or whole cells are exposed to peroxynitrite. If this pattern of damage is unique to peroxynitrite, it might act as a marker of cellular damage by this species in vivo.
    Chemical Research in Toxicology 01/1996; 9(7):1152-8. · 3.67 Impact Factor
  • J P Spencer, P Jenner, B Halliwell
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    ABSTRACT: 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.
    Neuroreport 08/1995; 6(11):1480-4. · 1.40 Impact Factor
  • Free Radical Research 03/1995; 22(2):187-90. · 3.28 Impact Factor