In the presence of physiological concentrations of iron(III) salts, superoxide radical and hydrogen peroxide can interact to form the highly‐damaging hydroxyl radical. No specific added ‘chelator’ of iron salts is necessary for this reaction to occur.
The nitric oxide synthase inhibitor N G ‐nitro‐ l ‐arginine methyl ester ( l ‐NAME) is widely used to study the role of NO • in physiological and pathological processes, including its role in the generation of the cytotoxic species peroxynitrite (ONOO − ) and of reactive oxygen radicals such as hydroxyl (OH • ). Often l ‐NAME is applied to tissues at mM concentrations. At such high concentrations, it might act as a free radical scavenger. A similar possibility might apply to the use of high levels of arginine to study the role of NO . in atherogenesis. We therefore examined the rate of scavenging of OH • by l ‐NAME and found that l ‐NAME reacts more quickly with OH . than the established ‘OH . scavenger’ mannitol and the widely used ‘OH • trap’ salicylate. However, d ‐NAME can scavenge OH • at rates equal to l ‐NAME. Both l ‐ and d ‐arginine were also good OH • scavengers, comparable in effectiveness to mannitol. Neither l ‐NAME, d ‐NAME, l ‐arginine nor d ‐arginine was able to inhibit ONOO − ‐dependent nitration of tyrosine, suggesting that they are unlikely to be scavengers of ONOO − ‐derived nitrating species. Neither l ‐NAME, d ‐NAME, l ‐arginine nor d ‐arginine was able to inhibit the inactivation of α 1 ‐antiproteinase by ONOO − , suggesting that they cannot prevent direct oxidations by peroxynitrite. We conclude that l ‐NAME has sufficient activity as an OH • scavenger to confound certain pharmacological experiments. However, this explanation of its biological effects can be ruled out if control experiments show that d ‐NAME has no effect and that l ‐arginine (also a free radical scavenger) antagonizes the action of l ‐NAME.
Peroxidation of LDL is thought to be important in the pathogenesis of atherosclerosis, but the mechanism by which peroxidation is initiated is uncertain. Hydroxyl radical is an initiating species formed by the reaction of transition metal ions with hydrogen peroxide and of superoxide radical with nitric oxide. However, the role of the nitric oxide radical in macrophage-mediated LDL oxidation is still uncertain. In most in vitro experiments, reactions involving preformed peroxides in the LDL are being examined rather than first-chain initiation. Superoxide and transition metal ions (which are present in advanced human arteriosclerotic lesions) can lead to peroxide decomposition and propagate LDL peroxidation. The 'seeding' peroxides in LDL could be generated by lipoxygenases (other than 5-lipoxygenase), originate from dietary fats, or be formed by endogenous peroxidation, but the possibility of artefactual formation of peroxides during prolonged LDL isolation procedures must not be disregarded.
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1. A mixture of NADPH and ferrodoxin reductase is a convenient way of reducing adriamycin in vitro. Under aerobic conditions the adriamycin semiquinone reacts rapidly with O2 and superoxide radical is produced. 2. Superoxide generated either by adriamycin:ferredoxin reductase or by hypoxanthine: xanthine oxidase can promote the formation of hydroxyl radicals in the presence of soluble iron chelates. 3. Hydroxyl radicals produced by a hypoxanthine:xanthine oxidase system in the presence of an iron chelate cause extensive fragmentation in double-stranded DNA. Protection is offered by catalase, superoxide dismutase or desferrioxamine. 4. Addition of double-stranded DNA to a mixture of adriamycin, ferredoxin reductase, NADPH and iron chelate inhibits formation of both superoxide and hydroxyl radicals. This is not due to direct inhibition of ferredoxin reductase and single-stranded DNA has a much weaker inhibitory effect. It is concluded that adriamycin intercalated into DNA cannot be reduced.
Attack by .OH radicals, generated by a Fenton system, upon salicylate produces 2,3-dihydroxybenzoate and 2,5-dihydroxybenzoate as major products and catechol as a minor product. H.p.l.c. separation combined with electrochemical detection was used to identify and quantify 2,3-dihydroxybenzoate and 2,5-dihydroxybenzoate in human plasma and synovial fluid. We propose that conversion of salicylate into 2,3-dihydroxybenzoate, or of other aromatic compounds into specific hydroxylated products, may be a useful assay for .OH formation in the human body.
