Electron paramagnetic resonance study of the generation of reactive oxygen species catalysed by transition metals and quinoid redox cycling by inhalable ambient particulate matter.

A range of epidemiological studies in the 1990s showed that exposure to ambient particulate matter (PM) is associated with adverse health effects in the respiratory system and increased morbidity and mortality rates. Oxidative stress has emerged as a pivotal mechanism that underlies the toxic pulmonary effects of PM. A key question from a variety of studies was whether the adverse health effects of PM are mediated by the carbonaceous particles of their reactive chemical compounds adsorbed into the particles. Experimental evidence showed that PM contains redox-active transition metals, redox cycling quinoids and polycyclic aromatic hydrocarbons (PAHs) which act synergistically to produce reactive oxygen species (ROS). Fine PM has the ability to penetrate deep into the respiratory tree where it overcomes the antioxidant defences in the fluid lining of the lungs by the oxidative action of ROS. From a previous study [Valavanidis A, Salika A, Theodoropoulou A. Generation of hydroxyl radicals by urban suspended particulate air matter. The role of iron ions. Atmospher Environ 2000; 34 : 2379-2386], we established that ferrous ions in PM play an important role in the generation of hydroxyl radicals in the presence of hydrogen peroxide (H2O2). In the present study, we investigated the synergistic effect of transition metals and persistent quinoid and semiquinone radicals for the generation of ROS without the presence of H2O2. We experimented with airborne particulate matter, such as TSPs (total suspended particulates), fresh automobile exhaust particles (diesel, DEP and gasoline, GEP) and fresh wood smoke soot. Using electron paramagnetic resonance (EPR), we examined the quantities of persistent free radicals, characteristic of a mixture of quinoid radicals with different structures and a carbonaceous core of carbon-centred radicals. We extracted, separated and analysed the quinoid compounds by EPR at alkaline solution (pH 9.5) and by TLC. Also, we studied the direct production of superoxide anion and the damaging hydroxyl radical in aqueous and in DMSO suspensions of PM without H2O2. From these results, it is suggested that the cytotoxic and carcinogenic potential of PM can be partly the result of redox cycling of persistent quinoid radicals, which generate large amounts of ROS. In the second phase, the water-soluble fraction of PM elicits DNA damage via reactive transition metal-dependent formation of hydroxyl radicals, implicating an important role for hydrogen peroxide. Together, these data indicate the importance of mechanisms involving redox cycling of quinones and Fenton-type reactions by transition metals in the generation of ROS. These results are supported by recent studies indicating cytotoxic effects, especially mitochondrial damage, by PM extracts and differential mechanisms of cell killing by redox cycling quinones.

A comparative study by electron paramagnetic resonance of free radical species in the mainstream and sidestream smoke of cigarettes with conventional acetate filters and 'bio-filters'.

Tobacco smoking is the most important extrinsic cause, after the diet, for increasing morbidity and mortality in humans. Unless current tobacco smoking patterns in industrialised and non-industrialised countries change, cigarettes will kill prematurely 10 million people a year by 2025. Greece is at the top of the list of European countries in cigarette consumption. In 1997, a Greek tobacco company introduced a new 'bio-filter' (BF) claiming that it reduces substantially the risks of smoking. In a recent publication [Deliconstantinos G, Villiotou V, Stavrides J. Scavenging effects of hemoglobin and related heme containing compounds on nitric oxide, reactive oxidants and carcinogenic volatile nitrosocompounds of cigarette smoke. A new method for protection against the dangerous cigarette constituents. Anticancer Res 1994; 14: 2717-2726] it was claimed that the new 'bio-filter' (activated carbon impregnated with dry hemoglobin) reduces certain toxic substances and oxidants (like NO, CO, NOx, H2O2, aldehydes, trace elements and nitroso-compounds) in the gas-phase of the mainstream smoke. We have investigated by electron paramagnetic resonance (EPR) the mainstream and sidestream smoke of the BF cigarette, in comparison with three other cigarettes with similar tar and nicotine contents, that have conventional acetate filters. We found that BF cigarette smoke has similar tar radical species with the same intensity EPR signals to those of the other cigarettes. The ability of the aqueous cigarette tar extracts to produce hydroxyl radicals (HO*), which were spin trapped by DMPO, was very similar to, or even higher than, the other 3 brands. The gas-phase of the mainstream smoke of the BF cigarette showed a 30-35% reduction in the production of oxygen-centered radicals (spin trapped with PBN). In the case of the sidestream smoke, BF cigarettes produced substantially higher concentrations of gas-phase radicals, compared to the other brands. These results suggest that BF is partially effective at removing some of the gas-phase oxidants but not effective in the reduction of tar and its radical species in the mainstream and sidestream smoke. It is well known from epidemiological studies that tar content is strongly associated with increasing risk to smokers of lung cancer. In our experiments, BF cigarettes produce a higher amount of tar and stable free radical species than the other 3 brands in the sidestream smoke (between puffs), thus potentially increasing risk to the smoker and passive smoker.

Reaction of uric acid with peroxynitrite and implications for the mechanism of neuroprotection by uric acid.

Peroxynitrite, a biological oxidant formed from the reaction of nitric oxide with the superoxide radical, is associated with many pathologies, including neurodegenerative diseases, such as multiple sclerosis (MS). Gout (hyperuricemic) and MS are almost mutually exclusive, and uric acid has therapeutic effects in mice with experimental allergic encephalomyelitis, an animal disease that models MS. This evidence suggests that uric acid may scavenge peroxynitrite and/or peroxynitrite-derived reactive species. Therefore, we studied the kinetics of the reactions of peroxynitrite with uric acid from pH 6.9 to 8.0. The data indicate that peroxynitrous acid (HOONO) reacts with the uric acid monoanion with k = 155 M(-1) s(-1) (T = 37 degrees C, pH 7.4) giving a pseudo-first-order rate constant in blood plasma k(U(rate))(/plasma) = 0.05 s(-1) (T = 37 degrees C, pH 7.4; assuming [uric acid](plasma) = 0.3 mM). Among the biological molecules in human plasma whose rates of reaction with peroxynitrite have been reported, CO(2) is one of the fastest with a pseudo-first-order rate constant k(CO(2))(/plasma) = 46 s(-1) (T = 37 degrees C, pH 7.4; assuming [CO(2)](plasma) = 1 mM). Thus peroxynitrite reacts with CO(2) in human blood plasma nearly 920 times faster than with uric acid. Therefore, uric acid does not directly scavenge peroxynitrite because uric acid can not compete for peroxynitrite with CO(2). The therapeutic effects of uric acid may be related to the scavenging of the radicals CO(*-)(3) and NO(*)(2) that are formed from the reaction of peroxynitrite with CO(2). We suggest that trapping secondary radicals that result from the fast reaction of peroxynitrite with CO(2) may represent a new and viable approach for ameliorating the adverse effects associated with peroxynitrite in many diseases.

A study of the synergistic interaction of asbestos fibers with cigarette tar extracts for the generation of hydroxyl radicals in aqueous buffer solution.

Several models attempt to explain the synergistic increase in lung cancer among workers exposed to asbestos fibers, who were smokers at the same time. It is known that reactive oxygen species (ROS) are important mediators in asbestos-induced diseases, especially cancer. We studied quantitatively the formation of ROS (by spin trapping with DMPO) in aqueous buffer suspensions containing crocidolite (UICC), chrysotile (UICC and commercial, long fibers) alone, and in combination with aqueous cigarette tar extracts. It was observed that asbestos and cigarette tar act in a cooperative or synergistic way in the generation of hydroxyl radical spin adducts. Grinding of asbestos fibers and addition of EDTA (iron chelator) enhanced the intensity of the ESR signal. This enhancement progressed with time, probably due to the reaction of the extracted iron with the slow released hydrogen peroxide from tar extracts. It was observed a fivefold increase in the ESR signal (for crocidolite and aqueous tar extracts) in the formation of hydroxyl radicals via an iron-catalyzed Fenton reaction. These experimental results are suggest to be strong evidence to the fact that lung cancer has been found in asbestos workers exposed to high concentrations of fibers in the working environment who were smokers, and only rarely in nonsmokers.

Studies in vivo by electron spin resonance of free radical mechanisms implicated in UV-induced skin photocarcinogenesis.

Synopsis Solar ultraviolet radiation (UVR) is implicated in many types of skin damage, such as photodermatoses, photoageing, erythema, pigmentation, skin cancer etc. Free radicals and reactive oxygen species are considered to play an important role in cutaneous photocarcinogenesis. But skin is endowed with photoprotective agents, namely melanins and antioxidant enzymatic and non-enzymatic mechanisms. In this study we describe the in vivo electron spin resonance (ESR) signals of melanins after UVR exposure, using skin specimens of various types of mice, which were taken from different parts of their bodies. The ESR signals were used as a model for testing the antioxidant properties of butylated hydroxyanisole, tocopherol acetate, and octyl p-methoxycinnamate with butyl methoxy dibenzoyl methane and superoxide dismutase (SOD). Additional UVB radiation was applied to the skin samples in situ (in the cavity of the ESR spectrometer). Suppression of ESR signals of melanins was observed in all cases. Etudes in vivo par resonance paramagnetique electronique, après exposition au rayonnement UV, des méchanismes radicalans impliqués a la photocarcinogénèse cutanée.

Synthesis, molecular structure determination, and antitumor activity of platinum(II) and palladium(II) complexes of 2-substituted benzimidazole.

The complexes of 2-aminomethyl benzimidazole, 2-(beta-aminoethyl)benzimidazole, and 2-(alpha-aminoethy-l)benzimidazole with Pt(II) and Pd(II) have been prepared. The molecular structure of the free ligands and their complexes were studied by IR and 1H NMR. It was concluded that the substituted benzimidazole derivatives behave as bidentate ligands, being bound to the metal atoms via the nitrogen of the -N = group and the amino group of the side chain of the benzimidazole ring. The metal complexes were tested for antineoplastic activity both in cultures of neoplastic cells (MEL-745, K-562, Colon 205, IMP-32, SK-N-SH) and in vivo in rodents bearing L-1210 leukemia. The antiproliferative activity of these agents was compared to that of cis-platin.