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Biomedical subjects

G O Phillips

Publications and source records attributed to G O Phillips.

At least 19 recordsLinked to original sources
PubMed2006

Chain scission of hyaluronan by carbonate and dichloride radical anions: potential reactive oxidative species in inflammation?

The reactions of the carbonate and dichloride radical anions, CO3- and Cl2-, with the extracellular matrix glycosaminoglycan hyaluronan (HA) have been studied using the kinetic technique of pulse radiolysis and also by steady-state irradiation combined with gel permeation chromatography/multiangle laser light scattering(gpc/MALLS) to measure the rates of reaction with HA and the yield of HA chain scission, respectively. For comparison, the same measurements were made for the reactions of the free radicals *OH, Br2*-, and N3*. The carbonate and dichloride radical anions were found to react relatively quickly with HA (7.0 x 10(5) and 6.9 x 10(6) dm3 mol(-1) s(-1), respectively) although they are much less reactive than the hydroxyl radical, *OH. Significant yields (20 and 38%, respectively) of chain scission of HA by these radical anions were also determined from the gpc/MALLS experiments, providing some support for their potential participation in the depolymerization of HA in vivo. These results are compared with data obtained for the other free radicals (hydroxyl, azide radicals, and dibromide radical anions) investigated in this study in order to gain an insight into their mechanism of reaction with HA. Earlier chain scission yields of HA by hydroxyl radicals determined by the authors have also been revised using the gpc/MALLS technique employed in the current study. The yields of 52% (absence of air) and 44% (in air) are much lower than the previous values. In the current study, the effect of oxygen on the yields of HA chain breaks is discussed in terms of the reactivity of HA peroxyl radicals in the presence of superoxide radical anions. The relevance of the results of this study to mechanisms of inflammation is discussed.

Carbonates↗
PubMed2006

Butyrate modulates TGF-beta1 generation and function: potential renal benefit for Acacia(sen) SUPERGUM (gum arabic)?

Anecdotal evidence suggests that high fibre supplementation of dietary intake may have health benefits in renal disease related to alterations in circulating levels of short-chain fatty acids. The aim of the study was to examine the hypothesis that dietary manipulation may increase serum butyrate and thus have potential beneficial effects in renal disease. We examined the effect of dietary supplementation with a gum arabic sample of standardized molecular characteristics, Acacia(sen) SUPERGUM EM2 (SUPERGUM), on systemic levels of butyrate in normal human subjects. In an in vitro study, we also examined the potential role of butyrate in modifying the generation of the profibrotic cytokine transforming growth factor-beta (TGF-beta1) by renal epithelial cells. Following 8 weeks of dietary supplementation with 25 g/day of SUPERGUM, there was a two-fold increase in serum butyrate (n=7, P=0.03). In vitro work demonstrated that exposure of renal epithelial cells to elevated concentrations of butyrate suppressed both basal and stimulated TGF-beta1 synthesis. The action of butyrate was mediated by suppression of the extracellular signal-regulated kinase/mitogen-activated protein kinase signalling pathway. In addition, butyrate exposures reduced the response of renal epithelial cells to TGF-beta1 as assessed by luciferase activity of a TGF-beta-responsive reporter construct. Attenuation of TGF-beta1 signalling was associated with reduced phosphorylation of Smad 3 and decreased trafficking of TGF-beta1 receptors into signalling, non-lipid raft-associated membrane fractions. In conclusion, the data demonstrate that dietary supplementation with SUPERGU increased serum butyrate, which at least in vitro has beneficial effects on renal pro-fibrotic cytokine generation.

Butyrates↗
PubMed2003

Chain scission of hyaluronan by peroxynitrite.

The reaction of peroxynitrite with the biopolymer hyaluronan has been studied using stopped-flow techniques combined with detection of molecular weight changes using the combination of gel permeation chromatography and multiangle laser light scattering. From the effect of peroxynitrite on the yield of hyaluronan chain breaks, it was concluded that the chain breaks were caused by hydroxyl radicals which escape a cage containing the *OH NO*(2) radical pair. The yield of free hydroxyl radicals was determined as 5+/-1% (as a proportion of the total peroxynitrite concentration). At high peroxynitrite concentrations, it was observed that the yield of chain breaks leveled out, an effect largely attributable to the scavenging of hydroxyl radicals by nitrite ions present in the peroxynitrite preparation. These experiments also provided some support for a previous proposal that the adduct formed between ONOOH and ONOO(-) might itself produce hydroxyl radicals. The rate of this reaction would have to be of the order of 0.05 s(-1) to produce hydroxyl radical yields that would account quantitatively for chain break yields at high peroxynitrite concentrations. By carrying out experiments at higher hyaluronan concentrations, it was also concluded that an additional yield of chain breaks was produced by the bimolecular reaction of the polymer with ONOOH at a rate constant of about 10 dm(3)mol(-1)s(-1). At 5.3 x 10(-3)mol dm(-3) hyaluronan, this amounted to 3.5% chain breaks (per peroxynitrite concentration). These conclusions support the proposal that the yield of hydroxyl radicals arising from the isomerization of ONOOH to nitrate ions is relatively low.

Chromatography, Gel↗
PubMed2001

Comparative rheological behavior of hyaluronan from bacterial and animal sources with cross-linked hyaluronan (hylan) in aqueous solution.

Using a variety of rheological techniques, the behavior of hyaluronan (M(w) 0.8-2.2 x 10(6)), cross-linked hyaluronan (hylan) (M(w) 1.8-12.5 x 10(6)), and Healon (M(w) approximately 5 x 10(6)) (a proprietary hyaluronan) was studied over a large range of molecular weights. The object was to study the effect of the cross-links in hylan on the various rheological parameters, in comparison with linear hyaluronan. There are significant differences. The Huggins constant and the critical overlap parameter C*[eta] are considerably lower for hylan and an increase in moduli at low frequencies was observed for hylan compared with the hyaluronan samples at all molecular weights studied. The results point to a difference in structure in dilute solution for hylan due to the ability to form networks, which can be removed by pressure filtration. In contrast, we do not find an increase of the steady shear viscosity and elastic modulus at higher concentrations when a homogeneous entangled network is reached. We attribute this behavior to the semirigid character of the hyaluronan chain and to the predominance of entanglements over the cross-link points present in hylan in the semidilute domain. Due to the higher apparent molecular weights that are possible with hylan structures but not with the hyaluronans currently available, a wider range of applications can be achieved with hylans when viscoelasticity is required, particularly for the viscosupplementation of synovial fluid damaged by osteoarthritis.

Animals↗
PubMed2000

The effect of hydroxyl radicals on the rheological performance of hylan and hyaluronan.

Shear flow, dynamic oscillation and extensional viscosity measurements were used to compare the rheological performance of several hylan samples (M(v) 1.6, 3.2, 3.7, 4.7 and 5.6x10(6)) and hyaluronan (M(v) 1.4 and 1.8x10(6)) before and after hydroxyl radicals (*OH) induced degradation. It was found that the higher molecular weight cross-linked structure of hylan was more resistant to degradation than hyaluronan and that this superior stability was reflected in various rheological parameters. The *OH degradation of the initial hylan and hyaluronan samples produced a range of polysaccharides based on hylan and hyaluronan with molecular weight covering a range from 0.5-5.6x10(6). The rheological parameters associated with the polysaccharides could then also be studied. Zero shear values of the complex viscosity (eta*), dynamic viscosity (eta') and shear viscosity (eta) were calculated using the method of Morris(1) and shown to approach the same value at zero shear or frequency. An adaptation of the method of Gibbs et al. gave a 'master curve' for the storage and loss modulus of hyaluronan and hylan, which encompasses a 10-fold molecular weight and a 5-fold concentration variation. In all instances for hylan, the storage modulus predominates over the loss modulus, whereas for hyaluronan, the reverse is true, demonstrating the greater elasticity of hylan throughout the whole experimental range of molecular weights and concentrations.

Animals↗
PubMed1998

Acacia gum (Gum Arabic): a nutritional fibre; metabolism and calorific value.

Gum Arabic (Acacia gum, INS 414: E414) is extensively used as a food additive, but there is no regulatory or scientific consensus about its calorific value. It is a complex polysaccharide, primarily indigestible to both humans and animals, not degraded in the intestine, but fermented in the colon under the influence of microorganisms. Despite a range of animal studies, there are no usable data for humans which can quantify the utilizable energy of Gum Arabic. Estimates in the literature from animal experiments vary from 0 to 4 kcal/g. After certain allowances are made for the energy losses from volatile and gaseous fermentation products, an upper level of 2 kcal/g for rats has been set. The situation in man is demonstrably different, with greatly reduced amounts of such products, and the need to adapt for varying periods before Gum Arabic is attacked by colonic bacteria. In the absence of an agreed scientific assignment, the FDA in the USA insist upon 4 kcal/g in nutritional labelling, whereas in Europe, no value has been assigned to soluble dietary fibre, such as Gum Arabic. This review argues that based on present scientific knowledge only an arbitrary value can be used for regulatory purposes.

Animals↗
PubMed1993

E.s.r. study of the conformational transition of spin-labelled xanthan gum in aqueous solution.

The order to disorder transition of xanthan molecules in aqueous solutions has been studied using e.s.r. spectroscopy. Nitroxide spin-label was covalently attached to carboxyl groups on the xanthan side chains. The e.s.r. spectra obtained for aqueous spin-labelled xanthan solutions at varying ionic strengths contained both isotropic and anisotropic components at room temperature. The anisotropic component was attributed to the association of the side chains with the xanthan cellulosic backbone and was found to be present in greater proportions at increasing ionic strength. The spectra gradually changed with rising temperature and the proportion of anisotropic component decreased. This spectral change reflected the disruption of the side chain association with the backbone during the conformational change. Hysteresis effects were observed following sequential heating and cooling cycles suggesting that chain aggregation occurred.

Electron Spin Resonance Spectroscopy↗
PubMed1991

Effect of sugars and polyols on water in agarose gels.

Effects of ribose, glucose, sucrose, ethylene glycol, glycerin, propylene glycol, and sorbitol on water in concentrated agarose gels were studied by differential scanning calorimetry at low temperatures. Changes in the phase transition temperatures of 40% agarose gels, induced by the addition of these chemical reagents, are discussed, together with rheological and thermal data for the same systems at ambient and higher temperatures. Both sugars and polyols are believed to reduce the amount of freezable water and to promote plasticization and molecular mobility of agarose chains in gels, thus shifting the glass transition temperatures to lower temperatures. However, the effects of decreasing freezable water, and the direct effect on the junction zones, produced by sugars seem to be different from the effects produced by polyols.

Calorimetry, Differential Scanning↗
PubMed1989

One-electron reduction of 5-deazalumiflavin in aqueous solution: a pulse radiolysis study.

The one-electron reduction of 5-deazalumiflavin has been studied in aqueous solution in the acidity range H0 = -1 to pH 13 using the reducing species CO2-, e-aq and (CH3)2COH radicals. The spectral and other properties of the deazaflavin radicals formed were found to be independent of the reductant used. Four protolytic forms of the radical were distinguished with associated pKa values of 1.3 +/- 0.3, 6.0 +/- 0.3 and 10.7 +/- 0.3.

Electrons↗
PubMed1988

Superoxide radical reactions in aqueous solutions of pyrogallol and n-propyl gallate: the involvement of phenoxyl radicals. A pulse radiolysis study.

The reactions of O2-. in aqueous solutions of pyrogallol 1 and the antioxidant n-propyl gallate 2 have been studied. In both cases the initial reaction gives hydrogen peroxide and the corresponding phenoxyl radical (k(1 + O2-.) = 3.4 x 10(5), k(2 + O2-.) = 2.6 x 10(5) dm3 mol-1S-1). These phenoxyl radicals have been produced independently by reacting 1 and 2 with Br2-. and their spectra and first pKa values measured (pKa(phenoxyl radical from 1) = 5.1, pKa(phenoxyl radical from 2) = 4.1). It is necessary to correct the observed spectra for the contribution of the H-adducts, formed by the reaction of radiolytically produced H atoms with the substrates (k(1 + H) = 2.5 x 10(9), k(2 + H) = 3.8 x 10(9) dm3 mol-1 S-1). The H-adduct spectra are given. In the reactions of O2-. with the substrates the initial transient absorbances are characteristic of the phenoxyl radicals; however at longer times a new transient absorbing around 500 nm (epsilon congruent to 10(4) dm3 mol-1 cm-1) appears. This is believed to be the deprotonated hydroxy-orthoquinone, formed by the reaction of phenoxyl radicals with O2-. (k congruent to 1.5 x 10(8) dm3 mol-1 S-1, from kinetic curve-fitting). The absorbance due to the hydroxy-orthoquinones decays by first-order kinetics (1.6 x 10(2) in the case of 1 and 1.1 x 10(2) s-1 in the case of 2). This is thought to be mainly the result of the conversion of the hydroxy-orthoquinone into its hydrate. Similar experiments were carried out with catechol and ethyl protocatechuate. The chemistry appears to be similar to that of the pyrogallol derivatives. The rate constant for reaction of these compounds with O2-. is, however, only less than or equal to x 10(4) dm3 mol-1 s-1.

Gallic Acid↗
PubMed1987

The reactivity of various free radicals with hyaluronic acid: steady-state and pulse radiolysis studies.

The reactions of the primary water radicals with the biopolymer hyaluronic acid have been studied by pulse radiolysis. Bimolecular rate constants, expressed in terms of the disaccharide repeating sub-unit of hyaluronic acid, for OH., H. and eaq- were found to be 7 X 10(8) M-1 X s-1, 5 X 10(7) M-1 X s-1 and less than 5 X 10(6) M-1 X s-1, respectively. By comparing the viscosities of samples, gamma-irradiated in the steady state under a variety of conditions, with unirradiated controls, the efficiencies with which selected radicals cause chain breakage have been determined. Efficiencies of 30%, 15%, 0%, 0.2% and 5% were estimated for OH., H., eaq-, methanol radicals and tert-butanol radicals, respectively. The presence of oxygen during irradiation increased the extent of chain breakage by a factor of 1.75.

Electrons↗
PubMed1987

Evidence for the addition of the superoxide anion to the anti-oxidant n-propyl gallate in aqueous solution.

n-Propyl gallate reacts with the superoxide radical anion in aqueous solution (k = 5.1 x 10(5) mol-1 dm3 s-1). The spectrum of the transient species so formed has been measured (absorbance maximum at 550 nm, epsilon = 1360 mol-1 dm3 cm-1). Electron or H atom transfer processes as well as proton abstraction have been excluded as possible mechanisms, and it is proposed that an addition reaction takes place.

Antioxidants↗
PubMed1986

Quantitative analysis of a polysulfated xylan (SP54) in urine using gas-liquid chromatography.

A sensitive analytical method for the quantitation of a polysulfated xylan (SP54) in urine has been developed. SP54 and urinary glycosaminoglycans have been isolated from urine using cetylpyridinium chloride. This method removes all glycosaminoglycans with molecular weights less than 3000 Da. Following isolation, SP54 and urinary glycosaminoglycans have been selectively hydrolyzed under conditions (0.5 M HCl/105 degrees C/30 min) which produce an efficient yield of xylose from SP54 but not from the glycosaminoglycans. Xylose derived from SP54 has subsequently been determined using gas-liquid chromatography. Levels of SP54 down to 10 micrograms/ml have been determined using this technique.

Chromatography, Gas↗
PubMed1983

A study of factors influencing hydration of sodium hyaluronate from compressibility and high-precision densimetric measurements.

A study of the factors influencing the hydration of the biopolymer hyaluronic acid was made by compressibility and density measurements. The factors investigated were the hydration changes on glycosidic bond formation, and also the influence of counterion type, solution ionic strength and temperature. The results indicate that, with this biopolymer, the hydration of the glucuronate residue is significantly more than that of the N-acetylglucosamine residue, and further that the biopolymer is less hydrated than the sum of its component monosaccharide residues. Change of the counterion salt form of this polyelectrolyte from univalent to bivalent counterion type (Na+ to Ca2+) leads to a small though significant increase in the total hydration sheath surrounding the polymer. An increase in the background ionic strength of the solvent leads to a quantifiable lowering of the hydration of the polymer at physiological ionic strength compared with its value in salt-free aqueous solution. A decrease in hydration with increase in temperature in the range 20-50 degrees C is the opposite of previous reports, and was observed when the polymer was dissolved both in pure water and in 0.15 M-NaCl.

Acetylglucosamine↗