摘要:

The objective of this work is to reexamine the competitive degradation of deoxyribose by hydroxyl radicals (OH) produced by the reaction between H2O2and Fe2+-EDTA. The·OH radicals produced attack deoxyribose (D, rate constantkD) and eventually an·OH scavenger (S, rate constantkS). First, we examined the effect of [D], [H2O2], [Fe2+-EDTA], [EDTA]/[Fe2+] ratio and reaction time on the rate of D degradation, measured as the absorbance of the chromogen formed between the product of the reaction D +·OH (malondialdehyde) and thiobarbituric acid. In particular, it was showed that under our experimental conditions ([D] = 3 mM, [H2O2] =0.85 mM, [Fe2+]=0.13 mM), the rate of overall process is first order in Fe2+, zero order in H2O2and is maximal for a ratio [EDTA]/[Fe2+] = 1.1. Second, the kinetics of OH radical reaction in competition experiments between D and S (mannitol) was investigated. The results show that the ratio of the rates of D degradation in the absence (VD) and in the presence (VDS) of S should be represented by VD/VDS= 1 + /tS[S]/(kD[D] + kx) where kxaccounts for the rate of·OH reactions with other reagents such as Fe2+-EDTA, H2O2etc…After having determined kxfor each set of experimental conditions, we obtained the values ofkS/kDby determining the variations of VD/VDSas a function of [S] and [D]. By takingkD=1.9×109M−ls−1, a value ofkS=1.9×109M−1s−1was obtained, very close to that obtained by pulse radiolysis. Finally, the validity of the established relation was confirmed for other biomolecules (methionine,k =5.6×10 M−1s−1and alanine,k= 3.3×108M−Is_1). By constrast, it was not applicable to cysteine, thiourea and mercaptoethanol which was attributed to an interaction of the latter scavengers with Fe2+and/or H2O2.

ISSN:1071-5762    

DOI:10.3109/10715769409145635

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

4-Hydroxynonenal (HNE), a major aidchydic product of lipid peroxidation, is a chemoattractant for neutrophilic polymorphonuclear granulocytesin vitro. The question was studied, whether HNE is formed during the ingress of neutrophils in the Sephadex model of inflammation. The polydextrane Sephadex G-200, which causes an acute aseptic traumatic inflammation, was injected subcutaneously into rats. The implants were excised 6–36 hours later, and the neutrophils separated from the exsudate by centrifugation. After extraction with dichloromethane HNE was identified in the exsudate by non-derivative reversed phase HPLC in combination with on-line uv-spectroscopy. The concentration of HNE in the inflammatory focus did not correlate with the number of neutrophils present. While the peak of HNE coincided with the time point of the highest turnover rate of neutrophils (0.13μM at 6 hrs after implantation), the highest number of neutrophils (about 100 million cells) occurred not earlier than 18 hrs later (24 hrs after onset of inflammation).When neutrophils were isolated from the inflammatory focus and stimulated with Zymosan, they were able to produce HNEin vitrodepending on the time of isolation. The highest production of HNE (0.17μM) by phagocyting neutrophils was observed at the shortest inflammation time studied (3 hrs). In order to compare these results with the oxidative burst of neutrophils the formation of superoxide was also measured by the cytochrome c reduction assayin vitro. The maximum of the production rate of superoxide anion was observed at the same inflammation time (6 hrs), when the HNE maximum occurred. Cells which ingressed earliest (at 3 hrs) showed the highest production rate of superoxide per cell (307×10−18moles per cell and 30min).The ability of HNE to attract neutrophilsin vivowas studied by adding synthetic HNE to the Sephadex gel and measuring the ingression of neutrophils afterwards. The application of 1μM HNE in the focus did not change the number of neutrophils but 10μM HNE increased the cell number by a factor of 3.The results indicate that HNE is not only a chemoattractant for rat neutrophilsin vitrobut alsoin vivo. It is suggested that HNE is produced by selfdestruction of neutrophils during a traumatic inflammation and its production seems to be tightly connected to the oxidative burst of neutrophils. The idea of HNE as part of an autocatalytic cycle is supported whereby neutrophils which immigrate into an inflammatory focus produce HNE which stimulates the ingress of new neutrophils.

ISSN:1071-5762    

DOI:10.3109/10715769409145636

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

In order to evaluate different mitochondrial antioxidant systems, the depletion of alpha-tocopherol and the levels of the reduced and oxidized forms of CoQ were measured in rat liver mitochondria during Fe++/ascorbate and NADPH/ADP/Fe++induced lipid peroxidation. During the induction phase of malondialdehyde formation, alpha-tocopherol declined moderately to about 80% of initial contents, whereas the total CoQ pool remained nearly unchanged, but reduced CoQ9 continuously declined. At the start of massive malondialdehyde formation, CoQ9 reaches its fully oxidized state. At the same time alpha-tocopherol starts to decline steeply, but never becomes fully exhausted in both experimental systems. Evidently the oxidation of the CoQ9 pool constitutes a prerequisite for the onset of massive lipid peroxidation in mitochondria and for the subsequent depletion of alpha-tocopherol. Trapping of the GSH by addition of dinitrochlorbenzene (a substrate of the GSH transferase), results in a moderate acceleration of lipid peroxidation, but alpha-tocopherol and ubiquinol levels remained unchanged when compared with the controls. Addition of succinate to GSH depleted mitochondria effectively suppressed MDA formation as well as alpha-tocopherol and ubiquinol depletion. The data support the assumption that the protective effect of respiratory substrates against lipid peroxidation in the absence of mitochondrial GSH is mediated by the regeneration of the lipid soluble antioxidants CoQ and alpha-tocopherol.

ISSN:1071-5762    

DOI:10.3109/10715769409145637

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

2-(3-Aminopropyl-amino) ethaneperthiol (RSSH, the perthiol analogue of the thiol radioprotector, WR-1065) reacts with theα-hydroxy alkyl radical (CH3)2C.OH by donating a hydrogen atom as indicated by the characterization of perthiyl radicals (RSS.;λmax= 374 nm,≈374= 1680≈20 dm3mol−1cm−1) by pulse radiolysis. The perthiyl radical abstracts a hydrogen from the alcohol to establish a reversible hydrogen-transfer equilibrium. This equilibrium lies predominantly on the side of radical repair since the rate constants for the forward and reverse reactions at pH 4 are:k(RSSH + (CH3)2C−OH) = (2.4±0.1)±109dm3mol−1s_1andk(RSS−+ (CH3)2CHOH) = (3.8±0.3)×103dm3mol−1s−1respectively. The pKa, (RSSH←RSS−+ H+) = 6.2±0.1 was determined from the pH dependence of the rate of perthiol repair. Identical experiments have been performed with WR-1065 allowing a direct comparison of free-radical repair reactivity to be made with the parthiol analogue. At pH≈7.4 the reactivities of the thiol and perthiol were similar, both repairing the alcohol radical with a rate constant of∼(2.4±0.1)←108dm3mol−1s−1. However, at pH 5 whilst the hydrogen-donation rate of the thiol was 15–20% higher than at pH 7.4, the perthiol reactivity was over an order of magnitude higher. The thermodynamic driving force for the observed enhanced free-radical repair reactivity of RSSH compared to RSH is attributed to the resonance stabilization energy of 8.8 kJ mol−1within the RSS−radical. These results indicate a possible application of RSSH/RSS−as DNA-targeted antioxidants or chemoprotectors.

ISSN:1071-5762    

DOI:10.3109/10715769409145638

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

Diaryl tellurides carrying electron-donating substituents in theparapositions were found to efficiently inhibit peroxidation of rat hepatocytes, rat liver microsomes and a chlorobenzene solution of phosphatidylcholine. The most active compound in the microsomal assay, bis(4-dimethylaminophenyl) tellurite, showed an IC50-value of 30 nM. This compound also caused a dose-dependent delay of the onset of the linear phase of microsomal peroxidation stimulated by iron/ADP/ascorbate. The peak oxidation potentials of the diaryl tellurides (0.50–1.14 V in MeCN) correlated linearly with the IC50-values in this assay, with a point of inflection around 0.85 V. In the hepatocyte system, all compounds showed similar protective activity. It is proposed that diaryl tellurides exert an antioxidative effect by deactivating both peroxides and peroxyl radicals under the formation of telluroxides. These oxides may regenerate the active divalent organotellurides upon exposure to a suitable reducing agent.

ISSN:1071-5762    

DOI:10.3109/10715769409145639

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

ISSN:1071-5762    

DOI:10.3109/10715769409145640

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor