Mark J. Burkitt

ESR SPIN TRAPPING STUDIES INTO THE NATURE OF THE OXIDIZING SPECIES FORMED IN THE FENTON REACTION PITFALLS ASSOCIATED WITH THE USE OF 5,5-DIMETHYL- 1-PYRROLINE-N-OXIDE IN THE DETECTION OF THE HYDROXYL RADICAL

Several investigators have challenged the widely held view that the hydroxyl radical is the primary oxidant formed in the reaction between the ferrous ion and hydrogen peroxide. In recent studies, using the ESR spin trapping technique. Yamazaki and Piette found that the stoichiometry of oxidant formation in the reaction between Fe2+ and H2O2 often shows a marked deviation from the expected value of 1:1 (I. Yamazaki and L. H. Piette (1990) J. Am. Chem. Soc. 113, 7588-7593). In order to account for these observations, it was suggested that additional oxidizing species are formed, such as the ferryl ion (FeO2+), particularly when iron is present at high concentration and chelated to EDTA. In this paper it is shown that secondary reactions, involving the redox cycling of iron and the oxidation of the hydroxyl radical adduct of the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) by iron, operate under the reaction conditions employed by Yamazaki and Piette. Consequently, the stoichiometry of oxidant formation can be rationalized without the need to envisage the formation of oxidizing species other than the hydroxyl radical. It is also demonstrated that the iron(III) complex of DETAPAC can react directly with DMPO to form the DMPO hydroxyl radical adduct (DMPO/OH) in the absence of hydrogen peroxide. Therefore, to avoid the formation of (DMPO/OH) as an artefact, it is suggested that DETAPAC should not be used as a reagent to inactivate containing adventitious iron in experiments using DMPO.

Hydroxyl radical formation from Cu(II)‐trolox mixtures: insights into the pro‐oxidant properties of α‐tocopherol

Although widely recognised as the most important chain‐breaking antioxidant of the lipid phase, α‐tocopherol has also been reported to exert pro‐oxidant activity, particularly during the Cu(II)‐stimulated oxidation of low density lipoproteins (LDL). In the present communication, we demonstrate that hydroxyl radicals are generated following the interaction of Cu(II) with the α‐tocopherol model compound Trolox, involving the reduction of Cu(II) by Trolox and the subsequent reduction of molecular oxygen by Cu(I). We suggest, therefore, that the hydroxyl radical may be the species responsible for the initiation of fatty acid oxidation during the Cu(II)‐stimulated oxidation of hydroperoxide‐free LDL.

Role of Mitochondria in Radical Generation and Toxicity of τ-Butylhydroperoxide Towards Cultured Human Endothelial Cells

The structural integrity of the endothelium is of critical importance in the maintenance of normal vascular function. Damage to the endothelial layer can result in loss of several critical functions, including maintenance of vascular tone, control of clotting and production of essential mediators. It has been proposed that oxidant-induced injury to the endothelium is an important component of the damage which leads to atherosclerotic plaque formation (Hefner & Repine, 1989). Oxidatively modified lipids and lipoproteins can alter a variety of endothelial functions including pinocytosis and PDGF production (Borsum et al, 1985; Fox et al, 1987). Oxidised low density lipoprotein (LDL) can also enhance monocyte adhesion to endothelial cells (Berliner et al, 1990), and stimulate production of prostacyclins (Triau et al, 1988), colony-stimlation factors (Rajavashisth et al, 1990) and tissue factor (Drake et al, 1991). Lipid hydroperoxides are a major component of oxidised LDL and have many cytotoxic properties in their own right. Linoleic acid hydroperoxide can induce metalloproteinases (Sasaguri et al, 1993) and activate protein kinase C (Taher et al, 1993) in cultured endothelial cells, while injection into laboratory animals leads to injury of aortic endothelium (Yagi et al, 1981). The mechanism of induction of endothelial damage by lipid hydroperoxides is largely unknown, but has been suggested to involve production of reactive oxygen species that are capable of rapid reaction with important biomolecules (Yagi et al, 1991; Yagi et al, 1993).