‘Mobilized pools’ of metal ions are important in accelerating damaging free radical reactions. A major part of extracellular antioxidant defence is to keep ionic iron largely sequestered in proteins. Metal-chelating agents can inhibit radical reactions in vivo and in vitro.
<p>Increased damage by ROS plays a role in the development of neurodegenerative diseases, especially Alzheimer’s Disease and other dementias, and diets rich in antioxidants (high intake of fruits and vegetables) seem neuroprotective (as well as being protective against many other age-related diseases). However, attempts to treat/prevent such diseases by giving high doses of antioxidants such as vitamins E and C and carotenoids have, overall, been unsuccessful. Reasons for this will be discussed. A major focus of our work is a unique diet-derived thiol/thione with antioxidant properties, namely ergothioneine (ET). Low blood levels of ET are a risk factor for the development of neurodegenerative and cardiovascular diseases, frailty, eye disease, pre-eclampsia and age-related diseases generally. We have identified “adequate levels” of plasma ET in humans, levels below which are associated with increased disease occurrence, and the reasons leading to these low levels are under investigation. In animal studies, ET has exhibited the ability to modulate inflammation, scavenge certain ROS, protect against acute respiratory distress syndrome, decrease brain damage in models of Parkinson and Alzheimer diseases and stroke, prevent endothelial dysfunction, protect against ischemia-reperfusion injury, counteract iron dysregulation, hinder lung and liver fibrosis, and mitigate damage to the lungs, kidneys, liver, gastrointestinal tract, and testis. ET may also influence the gut microbiome. There is evidence that ET is specifically accumulated at sites of tissue injury, so we have called it an “adaptive antioxidant” that may not interfere with the normal physiological roles of ROS. But does low ET predispose to age-related diseases or is it a spurious correlation? Extensive cell and animal studies strongly suggest the former. Caveats in the use of ergothioneine supplements to prevent/ameliorate aged-related diseases include its potential to generate trimethylamine-N-oxide by the action of ergothionase enzymes in gut bacteria and its ability to be taken up by many bacteria, a few of which are pathogenic (e.g. <i>H. pylori, M. tuberculosis</i>). These caveats will be discussed.</p>
Mutations in Cu,Zn‐superoxide dismutase (SOD‐1) are associated with some familial cases of amyotrophic lateral sclerosis (ALS), but it is not known how they result in cell death. We examined effects of overexpression of wild‐type SOD‐1 or the G37R or G85R mutations on the accumulation of ubiquitinated and nitrated proteins, and on loss of cell viability induced by the proteasome inhibitor, lactacystin. Wild‐type SOD‐1 had no effect on proteasomal activity, but the mutants decreased it somewhat. Treatment with lactacystin (1 µ m ) caused only limited cell viability loss, even though it induced a marked inhibition of proteasomal activities. However, viability loss due to apoptosis was substantial in response to lactacystin when cells were overexpressing a mutant SOD‐1. The frequency of cells showing immunoreactivity against ubiquitinated‐ or nitrated‐proteins was enhanced when wild‐type and mutant SOD‐1 s were overexpressed. Ubiquitinated or nitrated α‐tubulin, SOD‐1, α‐synuclein and 68K neurofilaments were observed in the aggregates. Similar aggregates were observed in cells overexpressing mutant parkin (Del3–5, T240R and Q311′X). The nitric oxide synthase inhibitor, l ‐NAME, decreased viability loss and aggregation, suggesting that nitration of proteins may play an important role in aggregation and in the cell death accompanying it.
Highly reactive hydroxyl radicals (OH·) attack the amino acid phenylalanine to give ortho-, meta-, and para-tyrosines. An improved HPLC-based separation of these products is described. Both D- and L-phenylalanine are attacked by OH·, although only the latter is a substrate for the enzyme phenylalanine hydroxylase. Use of this improved aromatic hydroxylation assay to detect OH· is illustrated by measuring OH· in ozonized aqueous solutions at pH 7.4, and by showing that blood from some premature babies appears to be capable of catalyzing OH· formation.
OXY-RADICALS IN MOLECULAR BIOLOGY AND PATHOLOGY ED. by P.A. CERUTTI, I. FRIDOVICH and J.M. McCORD Alan R Liss Inc, New York, 1988BAILLIÈRE'S CLINICAL HAEMATOLOGY April 1989 IRON CHELATING THERAPY Guest Editor C. HERSHKO (Baillière Tindall, London)
The presence of hydrogen peroxide, at levels sometimes exceeding 100 μM, in human urine samples was established by three different assay methods: 2-oxoglutarate decarboxylation and the ferrous oxidation–xylenol orange (FOX) assay and an oxygen electrode. Detected levels of H2O2 were decreased by addition of superoxide dismutase. We conclude that urine contains autooxidizable molecules that, upon exposure to 21% O2, undergo rapid superoxide-dependent autooxidation reactions to generate H2O2. The exposure of human tissues to hydrogen peroxide may be greater than is commonly supposed, which has implications in relation to the proposed role of this species in cell signaling.
Peroxynitrite (ONOO − ) is a cytotoxic species formed in vivo. There is considerable interest in the development of ONOO − `scavengers' as therapeutic agents; several thiols have been suggested to fulfil this role. One protein inactivated by ONOO − is α 1 ‐antiproteinase (α 1 AP), the major inhibitor of serine proteinases in human body fluids. At low thiol:ONOO − concentration ratios, several thiols (captopril, penicillamine, cysteine, cystine and penicillamine disulphide) aggravated inactivation of α 1 AP by ONOO − , whereas GSH, GSSG, homocysteine, ergothioneine, N ‐acetylcysteine, lipoate and dihydrolipoate did not. We suggest that sulphur‐containing radicals are produced by reaction of certain thiols/disulphides with ONOO − or ONOO − ‐derived products and could mediate biological damage, including inactivation of α 1 AP. This must be considered in attempts to use thiols as `peroxynitrite scavengers'.
Abstract: Radicals are species containing one or more unpaired electrons, such as nitric oxide (NO •− ). The oxygen radical superoxide (O 2 •− ) and the nonradical hydrogen peroxide (H 2 O 2 ) are produced during normal metabolism and perform several useful functions. Excessive production of O 2 •‐ and H 2 O 2 can result in tissue damage, which often involves generation of highly reactive hydroxyl radical ( •− OH) and other oxidants in the presence of “catalytic” iron or copper ions. An important form of antioxidant defense is the storage and transport of iron and copper ions in forms that will not catalyze formation of reactive radicals. Tissue injury, e.g., by ischemia or trauma, can cause increased metal ion availability and accelerate free radical reactions. This may be especially important in the brain because areas of this organ are rich in iron and CSF cannot bind released iron ions. Oxidative stress on nervous tissue can produce damage by several interacting mechanisms, including increases in intracellular free Ca 2+ and, possibly, release of excitatory amino acids. Recent suggestions that free radical reactions are involved in the neurotoxicity of aluminum and in damage to the substantia nigra in patients with Parkinson's disease are reviewed. Finally, the nature of antioxidants is discussed, it being suggested that antioxidant enzymes and chelators of transition metal ions may be more generally useful protective agents than chain‐breaking antioxidants. Careful precautions must be used in the design of antioxidants for therapeutic use.
