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Biomedical subjects

R B Cundall

Publications and source records attributed to R B Cundall.

At least 19 recordsLinked to original sources
PubMed1994

One-electron oxidation of C(2) and C(3) methyl substituted 5,6-dihydroxyindoles: model pathways of melanogenesis.

One-electron oxidation of a series of C(2)- and C(3)-methyl substituted analogues of 5,6-dihydroxyindole (DHI), in the pH range 5-9, was studied using the technique of pulse radiolysis with spectrophotometric detection. This investigation was undertaken to further our understanding of the involvement of free radical species in the polymerization processes leading to melanin formation. The optical absorption spectra of the protonated indole semiquinone radicals resulting from the one-electron oxidation of C(2)- and C(3)-methyl substituted indoles were similar to those of their corresponding hydroxylated indoles. From this similarity, it is inferred that methylation at C(2) and C(3) of DHI has little or no effect upon the initial radicals. The semiquinone radicals of these analogues subsequently decay to yield the corresponding quinone methide/imine. However, methyl substitution at C(2) and C(3) of the quinone methide derived from these analogues results in their stabilization. This stabilization contracts with the reactivity of the corresponding quinone methide from DHI. Further, these stabilized quinone methides do not interact with the azide ion (N3-), in contrast to the reaction of N3- with the quinone methide of DHI. It is concluded that methylation at C(2) and C(3) of DHI will modify the pathways so that the polymerization processes are less effective than those with DHI.

Catechol O-Methyltransferase Inhibitors↗
PubMed1992

Xanthine oxidase/dehydrogenase activity in intact cultured cells (in situ analysis).

The measured ratio of xanthine oxidase activity to the total activity of xanthine oxidase and dehydrogenase showed higher values in intact cells than when similar cells were homogenized. The total activity was the same for both systems. The xanthine oxidase ratio was 90, 60, 50, 50, 60% in V79, RIF/Ha3, SCC7, KHT intact cells and freshly extracted murine peritoneal macrophages respectively while the corresponding ratios measured were 25, 40, 38, 35, 22% when the cells were lysed by homogenization. Superoxide radical O2-. production by addition of xanthine to intact or homogenized cells to activate intracellular xanthine oxidase was higher in intact than homogenized cells. Homogenization of cells and tissues in the presence of dithioerythritol (DTE) can evidently lead to a considerable under-estimation of the xanthine oxidase ratio. The effect of hypoxia on cells has also been examined.

Animals↗
PubMed1991

Effects of hypoxia and reoxygenation on the conversion of xanthine dehydrogenase to oxidase in Chinese hamster V79 cells.

The effects of hypoxia and reoxygenation on the conversion of xanthine dehydrogenase to the free radical-producing xanthine oxidase in Chinese hamster V79 cells have been investigated using a newly developed fluorimetric enzyme assay. Hypoxia caused an increase in xanthine oxidase activity from 25% to 80% of the total activity of xanthine oxidase and dehydrogenase. The ratio returned to normal levels within 24 h of aerobic incubation. Hypoxia caused the release of xanthine oxidase in the medium of V79 cells and an increase in total protein concentration in the medium. There was an early change induced in lipid peroxidation markers and this was inhibited by allopurinol. The effects of glucose deprivation and calcium blockers were also investigated. Fura-2 AM was found to interact with V79 cells, making it impossible to determine intracellular calcium levels in V79 cells by this reagent.

Allopurinol↗
PubMed1990

Influence of fluorocarbon emulsions on porphyrin-sensitised oxidation of histidine.

The influence of fluorocarbon emulsions on the efficiency of photosensitized oxidation of histidine in solution has been studied, using haematoporphyrin and dihaematoporphyrin derivatives as sensitisers. It is shown that the fluorocarbon emulsions at low concentrations efficiently disaggregate porphyrins, and thereby enhance photosensitised oxidation. The high solubility of oxygen in fluorocarbon emulsions maintains solution oxygen tension, optimising photooxidative damage. It is suggested that fluorocarbon emulsions might find a role in photodynamic therapy, both as carriers for sensitising dyes, and also to maintain tissue oxygenation in hypoxic regions of solid tumours.

Emulsions↗
PubMed1990

The interactions of pyrenylmethyl tributylphosphonium bromide with single strand polynucleotides.

The binding of the water soluble derivative of pyrene, pyrenylmethyl tri-n-butylphosphonium bromide (PMTP), to single strand polynucleotides has been characterised by changes in the absorption spectra, fluorescence spectra, the fluorescence lifetime and the time-resolved fluorescence anisotropy of PMTP. For polyguanylic acid at low ionic strength, there are two modes of binding; external ionic binding and intercalation between the bases. The former results in PMTP excimer formation and the latter involves a charge-transfer complex between PMTP and guanine bases. Polyadenylic acid and polyinosinic acid show only external binding and poly[C] exhibits an interaction which is a combination of external binding and partial intercalation. Single strand DNA binds PMTP by intercalation and external binding at low ionic strength. In the presence of 0.2 M sodium chloride, only binding by intercalation between the bases occurs for poly[G]. Single strand DNA bound PMPT by partial intercalation, as well as full intercalation between the bases, but polyadenylic acid, polycytidylic acid and polyinosinic acid showed no significant binding in the presence of 0.2 M sodium chloride. The differences in the binding of PMTP are attributed to variations in the rigidity and form the structures of single strand polynucleotides adopt in solution. A full analysis of the binding isotherms has been made using methods based on Scatchard plots and the McGhee and von Hippel approach, which are critically compared.

DNA↗
PubMed1989

Radiosensitization of E. coli B/r by arylhydrazonopropanedinitriles.

Several arylhydrazonopropanedinitriles and an arylhydrazonopropane-diethyl ester (derivatives of well-known uncouplers of oxidative phosphorylation) have been studied with respect to their ability to radiosensitize E. coli B/r under oxic and hypoxic conditions. Of the compounds studied, 2-carboxyphenylhydrazono-propanedinitrile and 2-carboxyphenylhydrazonopropanediethylester were found to be the most efficient radiosensitizers under hypoxia, whilst the former compound was also found to provide radiosensitization under oxic conditions. Increased radiosensitization by 4-carboxyphenylhydrazonopropanedinitrile was observed on decreasing the pH of the irradiation incubation medium. The results are discussed with respect to the physicochemical properties of these compounds and their reactivity with thiols, for which data are presented.

Acetylcysteine↗
PubMed1986

In vitro neutralization of heparin in plasma prior to the activated partial thromboplastin time test: an assessment of four heparin antagonists and two anion exchange resins.

This study was carried out to investigate the effects on the activated partial thromboplastin time test (APTT) when heparin in plasma was neutralized with protamine, Polybrene(R), poly-DL-lysine, or heparin neutralizing activity (HNA) extracted from platelets; or removed by means of the anion exchange resins TEAE cellulose or ECTEOLA cellulose. The effect on the APTT of adding the polycations protamine, Polybrene or poly-DL-lysine to citrated plasma was examined. The formation of heparin/polycation complexes was studied by means of their light scattering properties. The low yields of platelet HNA obtained excluded this from practical use as an in vitro heparin antagonist. ECTEOLA cellulose was unable to remove plasma heparin at levels as low as 1 U/ml by the technique employed. TEAE cellulose was able to efficiently remove at least 40 U of heparin from 1 ml of plasma but also caused a non-specific prolongation of the APTT. The polycations protamine, Polybrene, and poly-DL-lysine, possessed clot promoting activity at low concentrations and acted as anticoagulants in their own right at higher concentrations. At a plasma heparin concentration of 4 U/ml, protamine was the most efficient neutralizer of heparin, while at 10 U/ml, Polybrene was the most effective in this respect. It was concluded that care must be taken in the interpretation of the APTT after heparin neutralization or removal as heparin antagonist induced non-specific effects may be present.

Anion Exchange Resins↗
PubMed1986

Free radical reactions with alpha-tocopherol and N-stearoyl tryptophan methyl ester in micellar solutions.

The rate constants have been measured for one-electron oxidation by N3. and Br2-. of N-stearoyl tryptophan methyl ester (STME) and alpha-tocopherol (alpha-T) in micelles of sodium dodecyl sulphate (SDS) or tetradecyl trimethyl ammonium bromide (TTAB). Compared with analogous reactions of tryptophan and Trolox C in aqueous solution, the rate constants for oxidation in micellar solution by N3. are reduced by 30-70%. The micellar charge increased the rate of oxidation of STME by Br2-. in TTAB micelles by almost an order of magnitude, compared with the reaction of Br2-. with tryptophan in aqueous solution. In SDS micelles the rate of oxidation of STME by Br2-. was reduced more than 30-fold. Quenching of fluorescence from STME in micelles by acrylamide confirmed the accessibility of the indole ring to the aqueous solvent. The rate of repair of the neutral STME radical by alpha-T in TTAB micelles was found to be accelerated by a factor of at least 27, compared with the similar reaction between Trolox C and tryptophan radicals in aqueous solution.

Free Radicals↗
PubMed1985

Transverse location of the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene in model lipid bilayer membrane systems by resonance excitation energy transfer.

A fluorescent phospholipid derivative, the fluoresceinthiocarbamyl adduct of a natural phosphatidylethanolamine, has been synthesized and incorporated into sonicated single-bilayer vesicles of egg lecithin and dipalmitoyllecithin. The surface location of this probe has been confirmed by using extrinsic fluorescence quenching studies together with steady-state emission anisotropy measurements. Electronic excitation energy transfer between 1,6-diphenyl-1,3,5-hexatriene incorporated within the hydrophobic core of the bilayer and the novel derivative has been investigated to estimate the depth within the bilayer at which the former is located. Efficiencies have been measured for two different phospholipids, egg lecithin and dipalmitoyllecithin, in the latter case both above and below the phospholipid phase transition, with and without added cholesterol. The observed dependence of the transfer efficiency on the acceptor concentration was compared with that calculated according to Förster theory applied to random two-dimensional distributions of donor and acceptor molecules in parallel planes for various interplanar separations, taking into account orientational effects. The Förster R0 of about 45 A for this donor-acceptor pair is particularly well suited to such studies since it is of the order of the width of the bilayer. The experiments showed that energy-transfer spectroscopy can provide useful quantitative information as to the transverse location of diphenylhexatriene in homogeneous phospholipid bilayers and may also reflect lateral partitioning of donor or of both donor and acceptor into different phases in systems exhibiting phase separations.

Diphenylhexatriene↗
PubMed1985

Photo-oxidation of tetracycline adsorbed on hydroxyapatite in relation to the light-induced staining of teeth.

In an attempt to understand the chemistry of the light-induced staining of children's teeth by tetracycline, we studied the photo-chemical behavior of tetracycline adsorbed on hydroxyapatite, as a simple model of enamel. Tetracycline was strongly bound by hydroxyapatite to give a pale yellow material which, under ultraviolet light, showed a bright yellow fluorescence (lambda max 525 nm). On exposure of this material to the radiation from a medium-pressure mercury lamp, the fluorescence gradually disappeared, and a red-purple product was formed. Photo-acoustic spectroscopy was employed to follow the disappearance of tetracycline and the concomitant formation of the red-purple product, the spectrum of which (lambda max 530 nm) led to the conclusion that it was 4 alpha, 12 alpha-anhydro-4-oxo-4-dedimethylaminotetracycline (AODTC). This assignment was supported by the observation that 1 mole of oxygen was absorbed per mole of adsorbed tetracycline converted to the red-purple product. It is suggested that the formation of AODTC on hydroxyapatite probably takes place by a mechanism of photo-oxidation similar to that already proposed for solutions of tetracycline, and that the formation of AODTC in children's teeth is responsible for the light-induced staining caused by tetracycline.

Child↗
PubMed1984

Repair of amino acid radicals by a vitamin E analogue.

Free radicals derived from one-electron oxidation of the amino acids tryptophan, tyrosine, methionine and histidine have been found to be rapidly (k = 10(7) -10(9) dm3 mol-1 s-1) and efficiently repaired by Trolox C, a vitamin E analogue. The reactions form a relatively stable phenoxyl radical of Trolox C (lambda max = 440 nm; epsilon = 5.4 X 10(3) mol dm-3 cm-1). The radical cation of tryptophan is more rapidly repaired than the neutral tryptophan radical. Repair of tryptophanyl radicals in the enzyme lysozyme has also been observed. The results suggest that a function of alpha-tocopherol in membranes may be the repair of radicals of integral membrane proteins.

Amino Acids↗
PubMed1984

The inactivation of papain by high LET radiations.

The effect of varying LET over a wide range (0.2-1570 eV/nm) on the radiation-induced inactivation of the enzyme papain in dilute aqueous solution has been investigated. Measurements of total, reparable and non-reparable inactivation G values in oxygen, nitrous oxide and argon saturated solutions have allowed the contributions to inactivation from radicals and hydrogen peroxide to be evaluated. At high LET the results demonstrate an increasing component due to reaction of the superoxide radical, formed from oxygen produced in the track as a primary radiolysis product. This effect was not observed in our previous study with ribonuclease due to the insensitivity of ribonuclease to inactivation by superoxide and hydrogen peroxide. The results obtained with papain clearly demonstrate a maximum in G (H2O2) at an LET of approximately 140 eV/nm. Generation of O2 within the track as a primary radiolysis product at high LET now appears to be confirmed as an important mechanism leading to reduction in the oxygen enhancement ratio for cellular systems exposed to high LET radiations (Baverstock and Burns 1981).

Energy Transfer↗
PubMed1981

Free radical reactions with proteins and enzymes. The inactivation of bovine carbonic anhydrase B.

A comparison of the inactivation of bovine carbonic anhydrase B (carbonate hydro-lyase, EC 4.2.1.1) by OH, (SCN)(2) and Br(2) shows that the enzyme contains one or more essential tryptophan residues. Direct oxidation of histidine and tyrosine residues by the radicals is less important in causing inactivation of the enzyme. The effectiveness of all these radicals in inactivating carbonic anhydrase decreases with increasing pH in the region where the activity-linked ionizable group dissociates. Differences between the rates of reaction of Br(2) and SCN(2) with the holo- and apo-enzyme and between the resulting transient product spectra indicate that access to the reactive tyrosine and tryptophan residues is diminished by the presence of Zn2+ in the active site region.

Animals↗
PubMed1981

The inhibition by anion binding of reactions of inorganic radical anions with bovine carbonic anhydrase B.

Reactions of the inorganic radical anions, Br(2) and (SCN)2, with bovine carbonic anhydrase (carbonate hydrolyase, EC 4.2.1.1) have been studied by pulse radiolysis. Reaction is almost completely inhibited by the binding of Br-, SCN- and ClO4- to an electrophilic site at the active centre of the enzyme. Dissociation constants for anion binding calculated from the reduction in free radical reactivity agree well with inhibition constants for these anions. The anions OCN- and CN-, although potent inhibitors of carbonic anhydrase activity, have relatively little effect on the reactivity of radical anions with the enzyme. Reaction of radical anions occurs mainly with tryptophan and tyrosine residues in the hydrophobic core of the enzyme, through a channel at the active site. This channel is closed by the anions in accord with their position in the lyotropic series.

Animals↗