Fast repair of hydroxy radical purine deoxynucleotide adducts by phenylpropanoid glycosides and their derivatives from Chinese herbs

DNA damaged by oxygen radicals has been implicated as a causative event in a number of degenerative diseases, including cancer and aging. So it is very significant to look for ways in which either oxygen radicals are scavenged prior to DNA damage or damaged DNA is repaired to supplement the cells' inadequate repair capacity. The repair activities and reaction mechanism of phenylpropanoid glycosides (PPGs) and their derivatives, isolated from Chinese folk medicinal herbs, towards both dGMP-OH* adducts and dAMP-OH* adducts were studied with the pulse radiolytic technique. On pulse irradiation of nitrous oxide saturated 2 mM dGMP or dAMP aqueous solution containing one of the PPGs or their derivatives, the transient absorption spectra of the hydroxyl adduct of dGMP or dAMP decayed with the formation of that of phenoxyl radicals of PPGs or their derivatives within several decades of microseconds after electron pulse irradiation. The result indicated that dGMP or dAMP hydroxyl adducts can be repaired by PPGs or their derivatives. The rate constants of the repair reactions were deduced to be 0.641-1.28 x 10(9) M(-1) s(-1) for dGMP-OH* and 0.2-0.491 x 10(9) M(-1) s(-1) for dAMP-OH*, which positively correlated to the number of phenolic hydroxyl groups in the glycoside structure. A deeper understanding of this new repair mechanism may help researchers to design strategies to prevent and/or intervene more effectively in free radical related diseases.     

Fast repair of purine deoxynucleotide radical cations by rutin and quercetin

Repair effects of rutin and quercetin on purine deoxynucleotide radical cations were studied using pulse radiolysis technique. On electron pulse irradiation of N₂ saturated deoxynucleotide aqueous solution containing 20 mmol/L K₂S₂O₈, 200 mmol/Lt-BuOH and rutin or quercetin, the transient absorption spectra of the deoxynucleotide radical cations decayed quickly. At the same time, the spectra of flavonoid phenoxyl radicals formed within several dozen microseconds. The results indicated that deoxynucleotide radical cations can be repaired by flavonoids. The rate constants of the repair reactions were 3.8 ×10⁸-4.4 ×10⁸ mol⁻¹ · L · s⁻¹ and 1.3×10⁸-1.8×10⁸ mol⁻¹ · L · s⁻¹ for dAMP and dGMP radical cations, respectively.     

Fast repair of purine deoxynucleotide radical cations by rutin and quercetin

Repair effects of rutin and quercetin on purine deoxynucleotide radical cations were studied using pulse radiolysis technique. On electron pulse irradiation of N2 saturated deoxynucleotide aqueous solution containing 20 mmol/L K2S2O8, 200 mmol/L f-BuOH and rutin or quercetin, the transient absorption spectra of the deoxynucleotide radical cations decayed quickly. At the same time, the spectra of flavonoid phenoxyl radicals formed within several dozen microseconds. The results indicated that deoxynucleotide radical cations can be repaired by flavonoids. The rate constants of the repair reactions were 3.8 × 108-4.4×108 mol-1 · L · s-1 and 1.3×108-1.8×108 mol-1 · L · s-1 for dAMP and dGMP radical cations, respectively.     

Reaction of hydroxyl radical with phenylpropanoid glycoside and its derivatives by pulse radiolysis

The reaction of hydroxyl radical with 1 phenylpropanoid glycoside ( PPG), cistanoside C, and its 3 derivatives: 1-O-β-D-2-(p-hydroxyphenyl)-ethanyl-glucose, 6-O-(E)-feruloyl-glucose and 6-O-(E)-p-hydroxy-cinnamoylglucose isolated from folk medicinal herbs was investigated by pulse radiolysis technique respectively. The reaction rate constants were determined by analysis of built-up trace of absorption at λ_(max) of specific transient absorption spectra of PPG and its derivatives upon attacking·OH. All four compounds react with·OH at close to diffusion controlled rate (1.03×10~9—19.139×10~9 L·mol~(-1)·s~(-1)), suggesting that they are effective·OH scavengers. The results demonstrated that the numbers of phenolic hydroxyl groups of PPG and its derivatives are directly related to their scavenging activities. By comparing the reaction rates of·OH with 1-O-β-D-2-(p-hydroxyphenyl)-ethanyl-glucose, 6-O-(E)-feruloyl-glueose or 6-O-(E)-p-hydroxy-cinnomoyl-glucose, it is evident that the phenylethyl g     

Fast repair of dAMP radical anions by phenylpropanoid glycosides and their analogs

Repair effect on 2'-deoxyadenosine-5'-monophosphate (dAMP) radical anions by phenylpropanoid glycosides (PPGs) and their analogs, isolated from Chinese folk medicinal herb, was studied using pulse radiolysis technique. The radical anion of dAMP was formed by the reaction of hydrated electron with dAMP. On pulse irradiation of nitrogen-saturated dAMP aqueous solution containing 0.2 M t-BuOH and one of PPGs or their analogs, the transient absorption spectrum of the radical anion of dAMP decayed with the formation of that of the radical anion of PPGs or their analogs within several decades of microseconds after electron pulse irradiation. The results indicated that dAMP radical anions can be repaired by PPGs or their analogs. The rate constants of the repair reactions were deduced to be 1.6-4.5 x 10(8) M(-1) s(-1).     

Mechanism of the Photocatalytic Inactivation of Lactobacillus casei Phage PL-1 by Titania Thin Film

The mechanism of the inactivation of Lactobacillus casei phage PL-1 suspended in a phosphate buffer by black-light (BL) -catalytic titanium dioxide (TiO₂) thin film was studied. Generation of both superoxide anions (O₂ ⁻) and hydroxyl radicals ( · OH) was confirmed in the aqueous medium in which TiO₂ film was settled with BL irradiation under gentle shaking. With BL-irradiation alone without TiO₂ film, only O₂ ⁻ was generated to some extent. The genome DNA inside the phage particles was found to be fragmented by the treatment of PL-1 phages with BL-catalytic TiO₂ film. The phage inactivation by BL-catalytic TiO₂ film was inhibited by the addition of albumin in a concentration-dependent manner. BL-catalytic TiO₂ film was considered to cause primarily the damage to the capsid protein through the generation of active oxygen species such as · OH, followed by damage to the genome DNA inside the phage particles. Received: 11 August 2000 / Accepted: 30 August 2000     

Reduction in free-radical-induced DNA strand breaks and base damage through fast chemical repair by flavonoids

This paper provides evidence that dietary flavonoids can repair a range of oxidative radical damages on DNA, and thus give protection against radical-induced strand breaks and base alterations. We have irradiated dilute aqueous solutions of plasmid DNA in the absence and presence of flavonoids (F) in a “constant ^·OH radical scavenging environment”, k of 1.5 × 10⁷ s^-1 by decreasing the concentration of TRIS buffer in relation to the concentration of added flavonoids. We have shown that the flavonoids can reduce the incidence of single-strand breaks in double-stranded DNA as well as residual base damage (assayed as additional single-strand breaks upon post-irradiation incubation with endonucleases) with dose modification factors of up to 2.0 ± 0.2 at [F] < 100 μM by a mechanism other than through direct scavenging of ^·OH radicals. Pulse radiolysis measurements support the mechanism of electron transfer or H^· atom transfer from the flavonoids to free radical sites on DNA which result in the fast chemical repair of some of the oxidative damage on DNA resulting from ^·OH radical attack. These in vitro assays point to a possible additional role for antioxidants in reducing DNA damage.     

Fast repair of deoxynucleotide radical cations by phenylpropanoid glycosides (PPGs) and their analogs

The repair effects on deoxynucleotide radical cations of phenylpropanoid glycosides (PPGs) and their analogs, isolated from a Chinese folk medicinal herb, were studied using the pulse radiolysis technique. The radical cations of deoxynucleotides were formed by the reaction of SO4*- with deoxynucleotides. On pulse irradiation of a nitrogen saturated deoxynucleotide aqueous solution containing 20 mM K2S2O8, 200 mM t-BuOH and one of the PPGs or their analogs, the transient absorption spectra of the radical cations of nucleotide decayed with the formation of those of the radical cation of PPGs or their analogs within several tens of microseconds after electron pulse irradiation. The result indicates that deoxynucleotide radical cations can be repaired by PPGs or their analogs. The rate constants of the repair reactions were determined to be 0.48-1.1 x 10(9), 0.64-1.80 x 10(9) and 2.12-4.4 x 10(9) M(-1) s(-1) for dAMP, dGMP and dCMP radical cations respectively. It is obvious that the rate constants of the repair reaction depend on the number of phenolic hydroxyl groups contained in the PPGs and their analogs. A deeper understanding of this new repair mechanism will undoubtedly help researchers design strategies to prevent and/or intervene more effective in free radical related diseases.     

Reaction rate coefficients of hydroxyl radical-induced DNA single- and α-type double-strand breaks

With a model system of pBR322 plasmid DNA solution in vitro, the dose effects of radiation- induced single- and double-strand breaks (SSB and DSB) were measured and DSB was distinguished into α- and β-types. Under the condition of low scavenging capacity existing in the irradiated DNA solution, SSB and αDSB were mainly induced by hydroxyl radicals (^·OH). Moreover, a certain relationship was obtained between the SSB and αDSB yields and the DNA concentration. It was found that when the DNA solution was irradiated in the presence of 2.5 mmol dm^–3 mannitol, the reciprocals of G(SSB) and G(αDSB), respectively, were linearly related to the reciprocal of the DNA concentration, i.e. the competition reactions of DNA and mannitol for ^·OH radicals can be described by second-order kinetics. The rate coefficients and the efficiencies of the ^·OH radical inducing SSB were deduced. Also, the reaction rate coefficients and the efficiencies for the induction of αDSB from SSB by the ^·OH radical transfer mechanism, were first derived from the competition kinetics. Received: 27 October 1999 / Accepted: 15 March 2000     

Superoxide Dismutase Enhanced the Formation of Hydroxyl Radicals in a Reaction Mixture Containing Xanthone under UVA Irradiation

To clarify the effect of superoxide dismutase (SOD) on the formation of hydroxyl radical in a standard reaction mixture containing 15 μM of xanthone, 0.1 M of 5,5-dimethyl-1-pyrroline N-oxide (DMPO), and 45 mM of phosphate buffer (pH 7.4) under UVA irradiation, electron paramagnetic resonance (EPR) measurements were performed. SOD enhanced the formation of hydroxyl radicals. The formation of hydroxyl radicals was inhibited on the addition of catalase. The rate of hydroxyl radical formation also slowed down under a reduced oxygen concentration, whereas it was stimulated by disodium ethylenediaminetetraacetate (EDTA) and diethyleneaminepentaacetic acid (DETAPAC). Above findings suggest that O₂, H₂O₂, and iron ions participate in the reaction. SOD possibly enhances the formation of the hydroxyl radical in reaction mixtures of photosensitizers that can produce O₂ ^?·.     

Radiolysis of spin-labeled DNA: an electron spin resonance investigation

The reactions of free and DNA-bound 2,2,5,5-tetramethylpyrrolidine-N-oxyl (PROXYL) probes with radicals generated during radiolysis of dilute aqueous solutions of DNA were examined. For the free PROXYL probe in deaerated solution with each of the four nucleotides (dAMP, dCMP, dGMP, and TMP) it was found that the pyrimidine radicals were more reactive toward the probe than were the purine radicals. Reactions of the electron adduct of TMP and the hydroxyl radical adducts of dAMP, dGMP, and TMP with the probe resulted in little or no reduction of the probe. For TMP these results are consistent with the fact that both the protonated electron and hydroxyl radical adducts of TMP will covalently bind to the nitroxide function of the probe. Reduction of the PROXYL probe was observed in reactions with the hydroxyl radical adduct of dCMP and with the electron adducts of dAMP, dCMP, and dGMP. Results of the radiolysis of the free PROXYL probe in deaerated dilute solution of DNA suggest that the PROXYL probe protects the DNA from water radical attack as the ratio of DNA bases to PROXYL probe increases above 50:1. Reactions of DNA-bound probes are dependent on the depth of the nitroxide function in relation to the major groove of the DNA helix. Two probes with tether lengths which are less than the depth of the major groove show an expected increase in reactions with DNA base radicals as compared to a probe with a tether that extends beyond the groove. The longer probe is involved largely in reactions with sugar and water radicals along the periphery of the DNA helix. In the presence of oxygen, there is a dramatic decrease in the loss of both the free and DNA-bound probes due to the lack of reaction of these probes with peroxyl radicals formed by the addition of molecular oxygen to DNA radicals.     

Pulse-radiolytic investigations of catechols and catecholamines II. Reactions of Tiron with oxygen radical species

Transient spectra and kinetic data of Tiron (1,2-dihydroxybenzene-3,5-disulphonic acid) are reported, obtained after pulse-radiolytic oxidation by hydroxyl radicals (°OH), superoxide anions (O₂^?) or a combination of both oxygen radicals. The rate constant with °OH radicals was determined at 1.0·10⁹ M^?1·s^?1. Contrary to a previous report (Greenstock, C.L. and Miller, R.W. (1975) Biochim. Biophys. Acta 396, 11–16), the rate constant with O₂^? of 1.0·10⁷ M^?1·s^?1 is lower by one order of magnitude; also the semiquinone absorbs at 300 nm rather than at 400 nm. The ratio of the rate constants with °OH and O₂^? of 100 again demonstrates that any oxidation reaction by the latter radical is unspecific due to the more efficient reaction of °OH radicals, leading to the same products with catechol compounds.     

The participation of a tryptophan residue in the binding of ferric iron to pyrocatechase

The fast reaction technique of pulse radiolysis was used to produce free radicals in aqueous solution from alcohols, deoxyribose, cytosine, uracil, thymine, dihydrothymine and histidine. The electron transfer reactions from these radicals to p-benzoquinone was observed from the formation kinetics of the semiquinone anion ·BQ^? at 430 nm and the efficiency was found to be as high as 90% or more, with k～5×10⁹ M^?1sec^?1. In acid or neutral solutions in the presence of oxygen the peroxy radicals ·O₂RH formed do not essentially transfer an electron to BQ, and the efficiency is <10%. The significance of these results in the fixation of radiation damage in photobiology and radiation biology are indicated. The reactions of the superoxide ·O₂^? radical with BQ are also presented and discussed.     

Enhanced germicidal effects of pulsed UV‐LED irradiation on biofilms

Aims: The major objective of the study was to evaluate the enhanced germicidal effects of low‐frequency pulsed ultraviolet A (UVA)‐light‐emitting diode (LED) on biofilms. Methods and Results: The germicidal effects of UVA‐LED irradiation (365 nm, 0·28 mW cm^?2, in pulsed or continuous mode) on Candida albicans or Escherichia coli biofilms were evaluated by determining colony‐forming units. The morphological change of microbial cells in biofilms was observed using scanning electron microscopy. After 5‐min irradiation, over 90% of viable micro‐organisms in biofilms had been killed, and pulsed irradiation (1–1000 Hz) had significantly greater germicidal ability than continuous irradiation. Pulsed irradiation (100 Hz, 60 min) almost completely killed micro‐organisms in biofilm (>99·9%), and 20‐min irradiation greatly damaged both microbial species. Interestingly, few hyphae were found in irradiated Candida biofilms. Moreover, mannitol treatment, a scavenger of hydroxyl radicals (OH^?), significantly protected viable micro‐organisms in biofilms from UVA‐LED irradiation. Conclusions: The study demonstrated that pulsed UVA‐LED irradiation has a strong germicidal effect (maximum at 100 Hz, over 5‐min irradiation) and causes the disappearance of hyphal forms of Candida. Significance and Impact of the Study: This study can assist in developing a low‐frequency pulsed UVA‐LED system to be applied to pathogenic biofilms for disinfection.     

The adduct formation between the thioguanine-polyamine ligands and DNA with the AP site under UVA irradiated and non-irradiated conditions

The AP sites are representative of DNA damage and known as an intermediate in the base excision repair (BER) pathway which is involved in the repair of damaged nucleobases by reactive oxygen species, UVA irradiation, and DNA alkylating agents. Therefore, it is expected that the inhibition or modulation of the AP site repair pathway may be a new type of anticancer drug. In this study, we investigated the effects of the thioguanine-polyamine ligands (^SG-ligands) on the affinity and the reactivity for the AP site under UVA irradiated and non-irradiated conditions. The ^SG-ligands have a photo-reactivity with the A-F-C sequence where F represents a tetrahydrofuran AP site analogue. Interestingly, the ^SG-ligands promoted the β-elimination of the AP site followed by the formation of a covalent bond with the β-eliminated fragment without UVA irradiation.     

Oxygen radical-induced mitochondrial DNA damage and repair in pulmonary vascular endothelial cell phenotypes

Mitochondrial (mt) DNA is damaged by free radicals. Recent data also show that there are cell type-dependent differences in mtDNA repair capacity. In this study, we explored the effects of xanthine oxidase (XO), which generates superoxide anion directly, and menadione, which enhances superoxide production within mitochondria, on mtDNA in pulmonary arterial (PA), microvascular (MV), and pulmonary venous (PV) endothelial cells (ECs). Both XO and menadione damaged mtDNA in the EC phenotypes, with a rank order of sensitivity of (from most to least) PV > PA > MV for XO and MV = PV > PA for menadione. Dimethylthiourea and deferoxamine blunted menadione- and XO-induced mtDNA damage, thus supporting a role for the iron-catalyzed formation of hydroxyl radical. Damage to the nuclear vascular endothelial growth factor gene was not detected with either XO or menadione. PAECs and MVECs, but not PVECs, repaired XO-induced mtDNA damage quickly. Menadione-induced mtDNA damage was avidly repaired in MVECs and PVECs, whereas repair in PAECs was slower. Analysis of mtDNA lesions at nucleotide resolution showed that damage patterns were similar between EC phenotypes, but there were disparities between XO and menadione in terms of the specific nucleotides damaged. These findings indicate that mtDNA in lung vascular ECs is damaged by XO- and menadione-derived free radicals and suggest that mtDNA damage and repair capacities differ between EC phenotypes.     

Host-Cell Repair of Vaccinia Virus and of Double Stranded RNA of Encephalomyocarditis Virus

IN normal human cells DNA which has been damaged by ultraviolet radiation is repaired by excision of thymidine dimers and by repair replication. Patients suffering from xeroderma pigmentosum have a hereditary defect of the excision step and therefore their cells repair ultraviolet-induced lesions in their DNA less efficiently than do normal cells^1–4. An analogous situation has been well characterized in bacteria⁵.     

Quercetin and daidzein β-apo-14’-carotenoic acid esters as membrane antioxidants

Abstract

Esterification by β-apo-14’-carotenoic acid was found to have opposite effects on antioxidant activity of quercetin (at B4’, B3’ hydroxyl) as of daidzein (at A7 hydroxyl) in phosphatidylcholine liposomes. The daidzein ester had increased activity, while quercetin had a significant decreased activity. Quantum mechanical calculations using density function theory (DFT) indicate a modest decrease in bond dissociation enthalpy, BDE, for (weakest) hydrogen–oxygen phenolic bond in daidzein from 368.4 kJ·mol^{? 1} to 367.7 kJ·mol^{? 1} compared to a significant increase in quercetin from 329.5 kJ·mol^{? 1} to 356.6 kJ·mol^{? 1} upon derivatization. These opposite changes in tendency for hydrogen atom transfer from phenolic groups to lipid radicals combined with an increase in A-to-B dihedral angle from 0.0° to 36.4° and in dipole moment from 0.40 D to 6.01 D for quercetin upon derivatization, while less significant for daidzein (36.4°–36.7° and 3.26 D–7.87 D, respectively), together provide a rationale for the opposite effect of esterification on antioxidation.     

Modeling the scavenging activity of ellagic acid and its methyl derivatives towards hydroxyl, methoxy, and nitrogen dioxide radicals

The reaction mechanisms involved in the scavenging of hydroxyl (OH^·), methoxy (OCH₃ ^·), and nitrogen dioxide (NO₂ ^·) radicals by ellagic acid and its monomethyl and dimethyl derivatives were investigated using the transition state theory and density functional theory. The calculated Gibbs barrier energies associated with the abstraction of hydrogen from the hydroxyl groups of ellagic acid and its monomethyl and dimethyl derivatives by an OH· radical in aqueous media were all found to be negative. When NO₂ ^· was the radical involved in hydrogen abstraction, the Gibbs barrier energies were much larger than those calculated when the OH^· radical was involved. When OCH₃ ^· was the hydrogen-abstracting radical, the Gibbs barrier energies lay between those obtained with OH^· and NO₂ ^· radicals. Therefore, the scavenging efficiencies of ellagic acid and its monomethyl and dimethyl derivatives towards the three radicals decrease in the order OH^· >> OCH₃ ^· > NO₂ ^·. Our calculated rate constants are broadly in agreement with those obtained experimentally for hydrogen abstraction reactions of ellagic acid with OH· and NO₂· radicals.

Nature of the repair process associated with the recovery of Escherichia coli after exposure to Cd2+.

When different strains of $\text{Escherichia coli}$ are exposed to Cd²⁺, the cells accommodate after a long lag and proliferate. The time required for this response depends on the nature of the strain and the supplements in the growth medium. Immediately after exposure to Cd²⁺, considerable single strand breaks in the DNA are observed but the DNA is repaired prior to the initiation of cell proliferation. The finding that accommodation occurs in DNA polymerase I-deficient mutant cells suggests that DNA polymerase I may not be required for repair of damaged DNA in Cd²⁺-exposed cells. The recovery of Cd²⁺-exposed cells in a temperature-sensitive DNA ligase mutant cells at the permissive temperature (30° C) and failure to recover at the non-permissive temperature (42° C) indicates, however, that DNA ligase is involved in the repair of the single strand breaks associated with Cd²⁺-induced damage.