monodehydroascorbate and 5-5-dimethyl-1-pyrroline-1-oxide

The potential of free radical formation in serum of beta-thalassemia/Hb E patients receiving a single oral dose of 25 mg/kg body weight of deferiprone, a bidentate orally active iron chelator, was evaluated using EPR/spin trapping technique. In the presence of ascorbic acid and tert-butylhydroperoxide, EPR signals of ascorbyl radical (aH=0.18 mT) and DMPO-carbon centred adduct (aH=2.37 mT, aN=1.65 mT) were detected. Shortly after deferiprone administration, EPR signal intensities decreased concomitant with an increase in serum levels of deferiprone. Unfortunately, enhanced EPR signal intensities were observed at 300 min after dosing in patients with serum molar ratio of deferiprone to iron less than 3, suggesting the formation of incomplete iron-deferiprone complexes and consequently free radical formation. To avoid adverse effects of deferiprone, a dosage regimen should be designed according to iron status of the patients and aimed at maintaining an adequate ratio of serum chelator-to-iron concentration.

Topics: Adult; beta-Thalassemia; Cyclic N-Oxides; Deferiprone; Dehydroascorbic Acid; Electron Spin Resonance Spectroscopy; Female; Free Radicals; Humans; Iron; Iron Chelating Agents; Male; Oxidants; Pyridones; Spin Trapping; Young Adult

Electron spin resonance (ESR) spin trapping was utilized to investigate the reaction of peroxynitrite with thiols and ascorbate at physiological pH. The spin trap used was 5,5-dimethyl-1-pyrroline N-oxide (DMPO). The reaction of peroxynitrite with DMPO generated 5,5-dimethylpyrrolidone-(2)-oxy-(1) (DMPOX). Formate enhanced the peroxynitrite decomposition but did not generate any detectable amount of formate-derived free radicals. Thus, the spin trapping measurements provided no evidence for hydroxyl (.OH) radical generation in peroxynitrite decomposition at physiological pH. Thiols (glutathione, cysteine, and penicillamine) and ascorbate reacted with peroxynitrite to generate the corresponding thiyl and ascorbyl radicals. The one-electron oxidation of thiols by peroxynitrite may be one of the important mechanisms for peroxynitrite-induced toxicity and ascorbate may provide a detoxification pathway.

Topics: Ascorbic Acid; Cyclic N-Oxides; Dehydroascorbic Acid; Electron Spin Resonance Spectroscopy; Free Radicals; Hydrogen-Ion Concentration; Models, Biological; Nitrates; Spin Labels; Sulfhydryl Compounds

The generation of free radicals from tumour-promoting organic peroxides applied to intact murine skin samples has been studied by EPR spectroscopy using two techniques: first direct observation of ascorbyl radicals produced from reactions of peroxide-related radicals with ascorbate, an important endogenous antioxidant, and secondly, observation of radical adducts produced by spin-trapping. Free radical generation from tumour-promoting organic peroxides can be seen to occur in intact skin tissue through a one-electron reductive pathway, and takes place at sites including the viable cells of the epidermis and/or dermis. This radical generation is dependent upon the penetration of the skin by the peroxides, with the stratum corneum representing a major diffusional barrier to their penetration of skin. The technique of using ascorbyl radical measurement by EPR spectroscopy as a means of studying and quantifying radical production in intact tissues, developed in this work, may prove of much use in the study of many free radicals and their reactions in a wide range of biological systems, particularly skin. When combined with appropriate spin-trapping techniques, which enable identification of radical species and elucidation of their mechanisms of production, this enables the direct, real-time observation of radical reactions and mechanisms not previously possible in intact tissue samples.

Topics: Animals; Ascorbic Acid; Cyclic N-Oxides; Dehydroascorbic Acid; Electron Spin Resonance Spectroscopy; Free Radicals; In Vitro Techniques; Male; Mice; Peroxides; Skin; Skin Neoplasms; Spin Labels