摘要:

It is not commonly realised that symmetrical Fe(III) complexes are expected to have EPR spectra dominated by a symmetrical narrow line close to the free-spin g-value. The aim of this note is to stress that such features can be mistakenly identified as the spectra for stable organic radicals. This situation is a particular problem in studies of animal or plant tissue samples.

ISSN:1071-5762    

DOI:10.3109/10715769609145650

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

L-Lysine is shown to yield an adduct with the quinone methide intermediate formed during the horseradish peroxidase (HRP)-catalyzed aerobic oxidation of eugenol (4-allyl-2-methoxyphenol). Adduct formation is evidenced by (i) lysine quenching of the characteristic quinone methide absorption band measured at 350 ran; arginine and 7-aminobutyric acid, but not alanine or propionic acid showed similar behaviour (ii) lysine-promoted a 400 mV decrease of the eugenol oxidation voltammetric wave (1.00 V), concomitantly with an increase in current intensity and (iii) reverse phase HPLC isolation of the lysine eugenol adduct, followed by GC-MS analysis. The MS spectrum is consistent with a 2:1 lysineæugenol adduct (MW = 455). If operativein vivo, binding of lysine to eugenol might lead to protein inactivation and possibly be involved in eugenol toxicity.

ISSN:1071-5762    

DOI:10.3109/10715769609145651

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Sonodynamic therapy, a promising new approach to cancer treatment, is based on synergistic cell killing by combination of certain drugs (sonosensitizers) and ultrasound. Although the mechanism of sonodynamic action is not understood, the role of free radicals produced from sonosensitizers by ultrasound is implicated. In this work, we studied formation of free radicals during the decomposition of several water-soluble azo compounds by 50 kHz ultrasound in aqueous solutions. Using the spin trap 3, 5-dibromo-4-nitrosobenzene sulfonate (DBNBS) tertiary carbon-centered radicals from 2, 2′-azobis (N,N′-dimethyl-eneisobutyramidine) dihydrochloride (VA-044), 2-(carbamoylazo)-isobutyronitrile (V-30), and 2, 2′-azobis (2-amidinopropane) dihydrochloride (AAPH) and CH3 radicals from 1, 1′-azobis (N,N′-dimethylformamide) (ADMF) were detected in argonsaturated solutions and the corresponding oxygen-centered radicals (alkoxyl and peroxyl) from VA-044, V-30, and AAPH were identified using the spin trap 5, 5′-dimethyl-l-pyrroline-N-oxide (DMPO) in aerated sonicated solutions. No free radicals from 4, 4′-dihydroxyazobenzene-3, 3′-dicarboxylic acid, disodium salt (DHAB) could be found in either system. While VA-044 and AAPH could also be readily decomposed by heat (42.5°C and 80°C), V-30 decomposition only occurred in the ultrasound-exposed solutions. The most likely mechanism of decomposition of azo compounds by ultrasound is their thermolysis in the heated shell of the liquid surrounding ca vita ting bubbles driven by ultrasound and/or by pyrolysis inside these bubbles. Experiments using scavengers of·OH and·H, which are produced by sonolysis in aqueous solutions, demonstrated that these radicals are not involved in the ultrasound-mediated radical production from the azo compounds. Due to the known cytotoxic potential of free radicals produced from azo compounds, the use of these compounds as ultrasound sensitizers appears to be a promising approach for sonodynamic cell killing.

ISSN:1071-5762    

DOI:10.3109/10715769609145652

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Products of the reaction of 4-hydroxy-2-nonenal (4HNE) with native and heat-denaturedLeuconostoc mesenteroidesglucose-6-phosphate dehydrogenase (G6PDH) were analyzed to determine the structure and position of the protein modifications. Matrix assisted laser desorption time-of-flight mass spectrometry was used to measure molecular weights of the modified proteins and determine mass maps of peptides formed by digestion with cyanogen bromide. The molecular weight data show that one to two 4HNE molecules add to each subunit of native enzyme while approximately nineteen 4HNE molecules add to each subunit of heat-denatured enzyme. Peptides are observed in the cyanogen bromide mass map of modified native G6PDH that are consistent with selective modification of two segments of the amino acid sequence. One modified segment contains Lysine-182 that has been found to be part of the enzyme active site. Peptides are observed in the cyanogen bromide mass map of modified heat-denatured enzyme that are consistent with extensive modification of several segments of the amino acid sequence. The magnitude of the mass differences between modified and unmodified peptides were approximately 156 Da, consistent with a 1, 4-addition of 4HNE. These results support the conclusion that 4HNE inactivates G6PDH by selectively modifying only two or three sites in the protein by a 1, 4-addition reaction and that some aspect of the tertiary structure of the enzyme directs those modification reactions.

ISSN:1071-5762    

DOI:10.3109/10715769609145653

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Recent studies suggest that oxygen-derived free radicals are involved in mediating renal reperfusion injury. EPR spectroscopy and spin trapping with the spin traps DMPO and PBN, were used to detect and quantitate the formation of hydroxyl radicals in rat kidney after ischaemia-reperfusionin vivoandin vitroin the isolated rat kidney perfused in the absence of leucocytes. EPR analysis of homogenised kidneys and of venous samples did not detect radical adducts with either spin trap. With PBN, radical adducts were not detectedin vitro. When DMPO was used as the spin trap in kidneys perfused without albumin in the perfusate, EPR signals characteristic of hydroxyl and carbon-centred radical adducts were detected during early reperfusion following ischaemia. These studies confirm the generation of hydroxyl radicals during ischaemia-reperfusion in kidney. During reperfusion the total DMPO adduct concentration reached 4.35°1.05 nmol/g kidney/3 min, p<0.05. In control kidneys total adduct were present at lower concentration (2.55°1.1 nmol/g kidney/3 min). Addition of 15 mM dimethylthiourea abolished formation of these adducts following ischaemia-reperfusion but did not prevent a reduction in glomerular filtration rate. These results indicate that significant levels of hydroxyl and carbon-centred radicals are formed in the absence of circulating neutrophils during early renal reperfusion following ischaemia.

ISSN:1071-5762    

DOI:10.3109/10715769609145654

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

In this paper we have proposed a novel approach for studying the reaction of lipid oxidation by using the simplest chemical system available. Neat linoleic acid was incubated for 24 hours at 37°C in the air. The course of lipid oxidation was followed by measuring simultaneously by HPLC with a diode array detector 1) linoleic acid decrease, 2) the products formed by radical attack, namely four hydroperoxy-octadecadienoic acid (HPODE) isomers, two c,t (c,t) and two trans, trans (t,t). 3) the byproducts formed by HPODE degradations, the four oxo-octadeca-dienoic acid (oxoODE) isomers. In HPODEs the presence of conjugated diene chromophore was confirmed by second derivative spectrophotometry. c,t HPODEs were also identified for their positional isomerism, while for t,t molecules the lack of suitable reference compound makes unfeasible the identification of their positional isomerism. As in the case of the latter two c,t and two t,t oxo-ODE isomers were characterized. This simple system appears to be useful for studying the activity exherted by lipophilic molecules that, likeα-tocopherol, may act as antioxidants and/or as hydrogen atom donating molecules. The presence ofα-tocopherol in different concentration for 24 hours in the reaction environment, shifts the reaction of linoleic acid autoxidation towards different byproduct formations. From the results obtained it is evident thatα-tocopherol acts as hydrogen atom donor at all concentration tested, shifting the reaction toward a prevalent formation of c,t isomer of both HPODEs and oxo-ODEs. At concentration lower than 40 nmoles, when the ratio betweenα-tocopherol and linoleic acid was 1:100, the reaction of autoxidation is strongly inhibited, while at higher concentrationα-tocopherol acted as a prooxidant. In these experimental conditions,α-tocopherylquinone was spectrophoto-metrically identified as the predominant oxidation product ofα-tocopherol.

ISSN:1071-5762    

DOI:10.3109/10715769609145655

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Reactive oxygen species and reactive nitrogen species are formed in the human body. Endogenous antioxidant defences are inadequate to scavenge them completely, so that ongoing oxidative damage to DNA, lipids, proteins and other molecules can be demonstrated and may contribute to the development of cancer, cardiovascular disease and possibly neurodegenerative disease. Hence diet-derived antioxidants may be particularly important in protecting against these diseases. Some antioxidants (e.g. ascorbate, certain flavonoids) can exert pro-oxidant actionsin vitro, often by interaction with transition metal ions. The physiological relevance of these effects is uncertain, as is the optimal intake of most diet-derived antioxidants. In principle, these questions could be addressed by examining the effects of dietary composition and/or antioxidant supplementation upon parameters of oxidative damagein vivo. The methods available for measuring steady-state damage (i.e. the balance between damage and repair or replacement of damaged molecules) and the actual rate of damage to DNA, proteins and lipids are reviewed, highlighting areas in which further methodological development is urgently required.

ISSN:1071-5762    

DOI:10.3109/10715769609145656

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Fruits and vegetables contain several classes of compounds that can potentially contribute to antioxidant activity, including vitamins, simple and complex phenolics, sulphur-containing compounds and glucosinolates. The glucosinolates are found in high concentration in many cruciferous vegetables, and it is well established that their breakdown products induce endogenous antioxidant defences such as quinone reductase and glutathione S-transferase in cells andin vivo. Despite the anticarcinogenic effect of these compounds in animal models, the direct antioxidant properties of this class of compounds have not been systematically studied. We therefore examined the free radical-scavenging properties of representative extracts and of purified glucosinolates from cruciferous vegetables, by measuring their effect on ascorbate- or NADPH/iron-induced peroxidation of human liver microsomes, ascorbate/iron-induced peroxidation on phospholipid liposomes, iron chelation and hydroxyl radical scavenging using the deoxyribose assay, total antioxidant potential using ABTS (2, 2′-azinobis(3-ethyl-benzothiazoline-6-sulphonate)) and the bleomycin assay. Most of the extracts from cruciferous vegetables exhibited some antioxidant properties, although extracts from cooked Brussels sprouts increased the rate of microsomal lipid peroxidation. The effects in these assays were dependent upon processing and species of crucifer, and the glucosinolate content appeared to play a minor role in these effects, since purified glucosinolates exhibited only weak antioxidant properties. The total antioxidant activities of extracts from cooked and autolysed Brussels sprouts were identical within experimental error. This is probably due to the content of phenolics which is unaltered by autolysis, despite the differences between these samples in other assays especially NADPH-iron-induced lipid peroxidation of human liver microsomes. The results demonstrate that glucosinolates are unlikely to account for the direct antioxidant effects of extracts from cruciferous vegetables.

ISSN:1071-5762    

DOI:10.3109/10715769609145657

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Exposure of 3T3 fibroblasts to Fe reveals a concentration-dependent inhibition of cell proliferation compared to control cells, the apparent threshold for this iron-mediated effect being 5μM FeII. The inhibition of cell proliferation was accompanied by an enhancement of total malondialdehyde (MDA) levels (as detected directly by hplc) in the cells at higher iron concentrations. The co-supplementation of Fe with varying concentrations of ascorbic acid over the range 5μM to 240μM had no significant effect on the threshold for iron toxicity or lipid peroxidation. These results show that there is neither a significant exacerbation of the pro-oxidant effect of FeIInor any protective effect of ascorbate when cultures of 3T3 mouse fibroblasts are exposed to co-supplementation regimes of iron with ascorbic acid.

ISSN:1071-5762    

DOI:10.3109/10715769609145658

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Analysis of Free Radicals in Biological Systems Edited by A. Favier, J. Cadet, B. Kalyanaraman, M. Fontecave and J.-L. PierreBirkhauser Verlag AG, Basel,1995. DM 178Essays in Biochemistry Volume 291995 Edited by DK Apps and KF Tipton

ISSN:1071-5762    

DOI:10.3109/10715769609145659

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor