Publications

Interactions of a series of coumarins with reactive oxygen species

Sixteen plant-derived or synthetic coumarins with various hydroxyl and other substitutions were tested for their ability to inhibit lipid peroxidation and to scavenge hydroxyl radicals, superoxide radicals and hypochlorous acid. Seven unsubstituted or monosubstituted coumarins were essentially inactive in all tests except for ability to scavenge OH with rate constants ⪸1 × 109 M−1. sec−1. Of the remaining nine, six containing dihydroxy substitutions were effective inhibitors of Fe3+-ascorbate-dependent microsomal lipid peroxidation ( ic 50 < 20 μM), with ortho-dihydroxy + one additional substitution optimal ( ic 50 < 10 μM). ortho-Dihydroxylated coumarins were pro-oxidant (enhanced OH. generation) in the Fe3+-EDTA-H2O2 deoxyribose system but decreased OH generation in the Fe3+- ascorbate-H2O2 deoxyribose system, indicating that these compounds can both chelate iron ions and also readily donate electrons for redox cycling of Fe3+. The meta-dihydroxycoumarin did not show this behaviour, but was an effective scavenger of hypochlorous acid, a property shared by only one other compound. Several other coumarins with one or more hydroxyl substituents were also capable of effectively removing Superoxide anions (ic 50 3.7–72 μM), although some could not be quantified due to direct rapid reduction of cytochrome c. We conclude that several compounds, notably 5,7-dihydroxy-4-methylcoumarin, possess beneficial biochemical profiles of interest in relation to pathophysiological processes dependent upon reactive oxygen species.

Protection against Superoxide and Hydrogen Peroxide in Synovial Fluid from Rheumatoid Patients

1. On exposure of synovial fluid to superoxide and hydrogen peroxide, generated enzymically or by activated polymorphonuclear leucocytes, hyaluronic acid is depolymerized and the fluid loses its lubricating properties. The ability of synovial fluid from rheumatoid patients to scavenge superoxide and hydrogen peroxide was therefore examined. 2. Synovial fluid from a range of rheumatoid patients contained no superoxide dismutase activity, insufficient caeruloplasmin to scavenge any superoxide radical and little, if any, catalase activity. 3. Total ascorbate (reduced ascorbate + dehydroascorbate) concentrations in the plasma and synovial fluid of rheumatoid patients were similar in each case. The values are at the low end of the normal range. 4. These results are discussed in relation to the role of oxygen radicals in inflammatory joint disease.

Antioxidant and prooxidant abilities of foods and beverages

Effects of Lithium on Age-related Decline in Mitochondrial Turnover and Function in Caenorhabditis elegans

Aging has been associated with the accumulation of damages in molecules and organelles in cells, particularly mitochondria. The rate of damage accumulation is closely tied to the turnover of the affected cellular components. Perturbing mitochondrial turnover has been shown to significantly affect the rate of deterioration of mitochondrial function with age and to alter lifespan of model organisms. In this study, we investigated the effects of upregulating autophagy using lithium in Caenorhabditis elegans. We found that lithium treatment increased both the lifespan and healthspan of C. elegans without any significant change in the mortality rate and oxidative damages to proteins. The increase in healthspan was accompanied by improved mitochondrial energetic function. In contrast, mitochondrial DNA copy number decreased faster with age under lithium. To better understand the interactions among mitochondrial turnover, damage, and function, we created a mathematical model that described the dynamics of functional and dysfunctional mitochondria population. The combined analysis of model and experimental observations showed how preferential (selective) autophagy of dysfunctional mitochondria could lead to better mitochondrial functionality with age, despite a lower population size. However, the results of model analysis suggest that the benefit of increasing autophagy for mitochondrial function is expected to diminish at higher levels of upregulation due to a shrinking mitochondrial population.

FREE RADICALS, PROTEINS AND DNA. OXIDATIVE DAMAGE VERSUS REDOX REGULATION

Formation of Reactive Nitrogen Species during Peroxidase-catalyzed Oxidation of Nitrite

Involvement of peroxynitrite (ONOO-) in inflammatory diseases has been implicated by detection of 3-nitrotyrosine, an allegedly characteristic protein oxidation product, in various inflamed tissues. We show here that nitrite (NO2-), the primary metabolic end product of nitric oxide (NO·), can be oxidized by the heme peroxidases horseradish peroxidase, myeloperoxidase (MPO), and lactoperoxidase (LPO), in the presence of hydrogen peroxide (H2O2), to most likely form NO·2, which can also contribute to tyrosine nitration during inflammatory processes. Phenolic nitration by MPO-catalyzed NO2- oxidation is only partially inhibited by chloride (Cl-), the presumed major physiological substrate for MPO. In fact, low concentrations of NO2- (2-10 μM) catalyze MPO-mediated oxidation of Cl-, indicated by increased chlorination of monochlorodimedon or 4-hydroxyphenylacetic acid, most likely via reduction of MPO compound II. Peroxidase-catalyzed oxidation of NO2-, as indicated by phenolic nitration, was also observed in the presence of thiocyanate (SCN-), an alternative physiological substrate for mammalian peroxidases. Collectively, our results suggest that NO2-, at physiological or pathological levels, is a substrate for the mammalian peroxidases MPO and lactoperoxidase and that formation of NO2· via peroxidase-catalyzed oxidation of NO2- may provide an additional pathway contributing to cytotoxicity or host defense associated with increased NO· production. Involvement of peroxynitrite (ONOO-) in inflammatory diseases has been implicated by detection of 3-nitrotyrosine, an allegedly characteristic protein oxidation product, in various inflamed tissues. We show here that nitrite (NO2-), the primary metabolic end product of nitric oxide (NO·), can be oxidized by the heme peroxidases horseradish peroxidase, myeloperoxidase (MPO), and lactoperoxidase (LPO), in the presence of hydrogen peroxide (H2O2), to most likely form NO·2, which can also contribute to tyrosine nitration during inflammatory processes. Phenolic nitration by MPO-catalyzed NO2- oxidation is only partially inhibited by chloride (Cl-), the presumed major physiological substrate for MPO. In fact, low concentrations of NO2- (2-10 μM) catalyze MPO-mediated oxidation of Cl-, indicated by increased chlorination of monochlorodimedon or 4-hydroxyphenylacetic acid, most likely via reduction of MPO compound II. Peroxidase-catalyzed oxidation of NO2-, as indicated by phenolic nitration, was also observed in the presence of thiocyanate (SCN-), an alternative physiological substrate for mammalian peroxidases. Collectively, our results suggest that NO2-, at physiological or pathological levels, is a substrate for the mammalian peroxidases MPO and lactoperoxidase and that formation of NO2· via peroxidase-catalyzed oxidation of NO2- may provide an additional pathway contributing to cytotoxicity or host defense associated with increased NO· production.

DNA and Free Radicals

Oxidants are major contributors to cancer and aging. Part 1 Chemistry and measurement of damage to DNA by reactive oxygen species: chemistry of free radical damage to DNA and nucleoproteins DNA damage induced by photosensitization oxidative damage - meaning and measurement. Part 2 Mechanism of DNA damage by oxidative stress: hydrogen peroxide and DNA damage oxidative stress and calcium homeostasis lipid peroxidation and cancer the role of organic peroxyl radicals carcinogenesis. Part 3 Consequences of oxidative DNA damage: enzymes that repair oxidative damage to DNA sex as a response to oxidative DNA damage oxidative stress and cell proliferation in vitro ornithine decarboxylase and tumour promotion - a role for oxidants. Part 4 Pro-oxidants and DNA damage: redox cycling drugs and DNA damage role of reactive oxygen species the mutagenicity of complex mixtures of plant origin mineral fibres, cigarette smoke and oxidative DNA damage use of DNA damage as a measure of pro-oxidant actions of antioxidant food additives and nutrient components.

The Proteasome: Source and a Target of Oxidative Stress?

Iron and Oxygen: a Dangerous Mixture

During the chemical and biological evolution of the Earth, its atmosphere changed from a highly reducing state to the oxygen-rich state that we know today. Free molecular oxygen (dioxygen) probably appeared on the Earth's surface some 2 billion years ago as a result of photosynthetic microorganisms acquiring the ability to split water. Oxygen is now the most abundant element in the Earth's crust and the second most abundant element in the biosphere. The concentration of molecular oxygen (hereafter referred to as oxygen) in dry air has risen to 21%. Iron, the element of equal importance in this story, is the fourth most abundant element in the Earth's crust.

The novel neuromodulator hydrogen sulfide: an endogenous peroxynitrite ‘scavenger’?

Hydrogen sulfide (H 2 S) is a well‐known cytotoxic gas. Recently it has been shown to stimulate N ‐methyl‐ d ‐aspartate (NMDA) receptors to enhance long‐term potentiation suggesting a novel neuromodulatory role in vivo. Endogenous levels of H 2 S in the brain are reported to range between 10 and 160 µ m . Considerably lower H 2 S levels are reported in the brains of Alzheimer's disease (AD) patients, where levels of brain protein nitration (probably mediated by peroxynitrite) are markedly increased. Activation of NMDA receptors leads to intracellular tyrosine nitration by peroxynitrite. Because H 2 S and peroxynitrite are important mediators in brain function and disease, we investigated the effects of the H 2 S ‘donor’, sodium hydrogen sulfide (NaSH) on peroxynitrite‐mediated damage to biomolecules and to cultured human SH‐SY5Y cells. H 2 S significantly inhibited peroxynitrite‐mediated tyrosine nitration and inactivation of α 1 ‐antiproteinase to a similar extent to reduced glutathione at each concentration tested (30–250 µ m ). H 2 S also inhibited peroxynitrite‐induced cytotoxicity, intracellular protein nitration and protein oxidation in human neuroblastoma SH‐SY5Y cells. These data suggest that H 2 S has the potential to act as an inhibitor of peroxynitrite‐mediated processes in vivo and that the potential antioxidant action of H 2 S deserves further study, given that extracellular GSH levels in the brain are very low.

Formation of 4-hydroxynonenal in the supraventricular corpus callosum of postnatal rats

Lipid peroxidation is known to be associated with many neurodegenerative diseases and with trau- matic brain injury, but its occurrence in the normal de- veloping brain has not been reported. The present study was carried out using a specific antibody that recognises proteins modified by the end-product of lipid peroxide decomposition, 4-hydroxynonenal (HNE), to evaluate evaluate possible lipid peroxidation products in the brains of developing rats by immunocytochemistry and electron microscopy. Moderately dense labelling was observed in the supraventricular corpus callosum in the 7- and 8-day-old rats, whilst very dense labelling was observed in the same region, in the 9- and 10-day-old rats. Very little immunoreactivity was observed at 14 days, and no staining was observed in the corpus cal- losum in adult rats. HNE staining was not observed in neuronal cell bodies that give rise to callosal axons in the overlying cerebral cortex. Electron microscopy showed dense HNE staining on the basal laminae of blood vessels and on the plasma membranes of unmyeli- nated axons. Large numbers of rounded cells with fea- tures of oligodendrocyte precursor cells were labelled by Perl's stain in the supraventricular corpus callosum at postnatal day 7 and postnatal day 10, i.e. at times cor- responding to high levels of HNE immunoreactivity. In contrast, very few such cells were observed in the adult brain, corresponding to the very little or no Perl's stain- ing in the adult. These results suggest that lipid peroxi- dation observed in the supraventricular corpus callosum at postnatal day 10 could result from an accumulation of iron in this region, at this time.

Potential Problems of Ascorbate and Iron Supplementation: Pro-Oxidant Effect in Vivo?

Tell Me about Free Radicals, Doctor: A Review

No abstract is provided for this article.

Celebrating the 60th birthday of BBRC

Protection by albumin against the pro-oxidant actions of phenolic dietary components

Synthetic and natural phenolic compounds are increasingly used in food preservation. Carnosol and carnosic acid (active components of rosemary extract), flavonoids (morin, quercetin, fisetin, myricetin), other plant phenolics (gossypol) and propyl gallate may protect lipids against oxidative damage but have the potential to increase damage to non-lipid constituents of foods, such as carbohydrates and DNA. Thus, in the presence of ferric EDTA and H2O2, they can form highly reactive hydroxyl radicals that can degrade the sugar deoxyribose and/or accelerate DNA degradation by means of a ferricbleomycin complex. Human and bovine serum albumin afford considerable protection against damage to deoxyribose and DNA mediated by the above reactions. It is suggested that, given the fortification of foods with iron and EDTA and the use of phenolic substances as ‘antioxidant’ food additives, the addition of albumin might afford some protection.

Free radicals and food additives

No abstract is provided for this article.

Commentary on “Ascorbate kills breast cancer cells by rewiring metabolism via redox imbalance and energy crisis” by Ghanem et al. [Free Radic. Biol. Med. 163 (2021) 196–209]

Free Radicals in the Pathogenesis of Liver Injury