Cristina Rota

Antioxidant activity of carotenoids: An electron-spin resonance study on ?-carotene and lutein interaction with free radicals generated in a chemical system

β‐Carotene is thought to be a chain‐breaking antioxidant, even though we have no information about the mechanism of its antioxidant activity. Using electron‐spin resonance (ESR) spectroscopy coupled to the spin‐trapping technique, we have studied the effect of β‐carotene and lutein on the radical adducts of the spin‐trap PBN (N‐t ‐butyl‐α‐phenylnitrone) generated by the metal‐ion breakdown of different tert ‐butyl hydroperoxide (t BOOH) concentrations in methylene chloride. The peroxyl radical, along with an oxidation product of PBN (the PBNOx), trapped at room temperature from the breakdown of high concentration of t BOOH (1 M), were quenched by β‐carotene or lutein, in competition with the spin‐trapping agent. However, carotenoids were not able to quench the alkoxyl and methyl radicals generated in the reaction carried out in the presence of low t BOOH concentration (1 mM). The reaction between carotenoids and the peroxyl radical was also carried out in the absence of the spin trap, at 77 K: Under these different experimental conditions, we did not detect any radical species deriving from carotenoids. In the same system, a further evidence of the peroxyl radical quenching by β‐carotene and lutein was obtained. The antioxidant activity of vitamin E was also tested, for comparison with the carotenoids. In the presence of α‐tocopherol, peroxyl and alkoxyl radicals were quenched, and the tocopheroxyl radical was detected. Our data provide the first direct evidence that carotenoids quench peroxyl radicals. Under our experimental conditions, we did not detect any carotenoid radical species that could derive from the interaction with the peroxyl radical. The radical‐trapping activity of β‐carotene and lutein demonstrated in this chemical reaction contributes to our understanding carotenoid antioxidant action in biological systems.

N-Acetylcysteine Negatively Modulates Nitric Oxide Production in Endotoxin-Treated Rats Through Inhibition of NF-κB Activation

N-Acetylcysteine (NAC) has a wide spectrum of biological activities, either related to the ability to increase intracellular thiols or directly acting as an antioxidant. We used an in vivo animal model to study NAC modulation of nitric oxide (NO) production in response to lipopolysaccharide treatment. A comparison was made between NAC and the N-[3-(aminomethyl)benzyl] acetamidine (1400W), an inhibitor of the inducible NO synthase (iNOS). Both inhibit NO production, although NAC lacks any effect if given when iNOS is already induced; this indicates that the decrease of NO generation is not due to an effect on iNOS activity. We found that the DNA binding activity of nuclear transcription factor-kappaB in peripheral blood cells was inhibited by NAC given before lipopolysaccharide, whereas tumor necrosis factor-alpha secretion was not affected.

Detection of a stable nitroxide during chemical depolymerization of heparin

The use of low-molecular-weight heparins (LMWHs) has become common, since compared to unfractionated heparin (UFH), they have a much longer plasma half-life and lower incidence of side effects. LMWHs are derived from the depolymerization of UFH, obtained either chemically, physically or enzymatically. We employed electron spin resonance (ESR) spectroscopy to study the depolymerization of UFH by copper in the presence of hydrogen peroxide. A stable nitroxide radical was detected. This could be generated by the hydroxyl radical attack either to the N-SO−3 group or to free amino groups present in the UFH preparation.

Antioxidant effect of FeAOX-6 on free radical species produced during iron catalyzed breakdown of tert-butyl hydroperoxide

There is a body of evidences demonstrating, in biological systems, a cooperative interaction between tocopherols and carotenoids. FeAOX-6 is a novel antioxidant that combines the chroman head of α-tocopherol and a fragment of the isoprenyl chain of lycopene. We have tested its antioxidant effect on different radical species generated in a chemical system, where peroxyl, alkoxyl and methyl radicals are generated by the ferrous ion-mediated decomposition of tert-butyl hydroperoxide. We found that FeAOX-6 has the same effectiveness of α-tocopherol in quenching peroxyl radical with no contribution by lycopene. The antioxidant activity of FeAOX-6 on alkoxyl and methyl radicals is comparable to that of the equimolar mixture of the parent compounds. Lycopene is able to quench alkoxyl radical, while it has no effect on peroxyl radical, showing a different antioxidant activity compared to other carotenoids, such as β-carotene and lutein.

α-Tocopherol amplifies benzoyl peroxide free radical decomposition in a chemical system

Benzoyl peroxide is commonly used in the treatment of acne, even though some adverse effects have been reported, probably mediated by the formation of peroxide-derived free radicals and the depletion of antioxidants. In the present work we have studied, in a chemical system, the effect of α-tocopherol on benzoyl peroxide radical decomposition to analyse the presence of an interaction between these two compounds, leading to an enhanced peroxide-cytotoxicity, as we have previously reported. Under our experimental conditions α-tocopherol strongly amplified the peroxide free radical decomposition occurring either in the presence or in the absence of UV irradiation, and lead to the formation of an unknown radical species in addition to benzoyloxy, phenyl and tocopheroxyl free radicals. The results of this study show that the enhancement of benzoyl peroxide toxicity in cells exposed simultaneously to this peroxide and α-tocopherol, is likely due to the generation of the detected radical species.