Mechanism Of Free Radical Formation Research Articles

Multi-phase CdS loaded on biochar for photocatalytic activation of peroxymonosulfate for thiamethoxam degradation: π-conjugation improves PMS adsorption

Mounting evidence highlights the negative impacts of thiamethoxam (THM) on non-target organisms and ecosystem. Herein, multi-phase cadmium sulfide loaded on biochar (CdS@BC) was used to photocatalytic activate peroxymonosulfate (PMS) to remove THM. The obtained CdS@BC significantly improved the photocatalytic performance of PMS on THM degradation with a superior rate constant of 0.165 min−1, 60 times more than that of BC. In addition, the catalyst displayed excellent stability and reusability. The mechanism of free radical formation by adsorption activation of PMS adsorbed on CdS@BC was characterized using active species detection and Density functional theory (DFT) calculations. According to the DFT study, the phase junction and π-conjugated structure contribute to the stable migration of π-electrons, thus effectively activating the PMS to produce active substances for the degradation of THM. The findings provide a theoretical basis for the design and synthesis of effective catalysts for AOPs to remove emerging organic contaminants from wastewater.

CyDEPMPOs: A class of stable cyclic DEPMPO derivatives with improved properties as mechanistic markers of stereoselective hydroxyl radical adduct formation in biological systems

The cis/trans diastereoisomeric composition of hydroxyl radical adducts to chiral cyclic nitrones can be used to approach mechanisms of free radical formation in biological systems. Such determination is greatly simplified when both diastereoisomers have ESR spectra with at least two non-overlapping lines. To achieve this prerequisite, a series of DEPMPO-derived spin traps bearing one unsubstituted or alkyl-substituted 2-oxo-1,3,2-dioxaphosphorinane ring were synthesized and their structures were confirmed by X-ray diffraction, 1H, 13C and 31P NMR. These CyDEPMPOs nitrones showed variable lipophilicities and LD 50 values on murine fibroblasts compatible with a safe use in biological spin trapping. All CyDEPMPOs formed persistent spin adducts with a series of free radicals, including superoxide and hydroxyl (i.e., CyDEPMPOs-OH) and the in vitro half-life times of these two latter were at least as extended as those of parent DEPMPO. Using four methods of CyDEPMPOs-OH formation, the cis-CyDEPMPOs-OH percentage was found significantly varied with substitution on the P-containing ring and, more interestingly, with the generating system.

Arsenic: toxicity, oxidative stress and human disease

Arsenic (As) is a toxic metalloid element that is present in air, water and soil. Inorganic arsenic tends to be more toxic than organic arsenic. Examples of methylated organic arsenicals include monomethylarsonic acid [MMA(V)] and dimethylarsinic acid [DMA(V)]. Reactive oxygen species (ROS)-mediated oxidative damage is a common denominator in arsenic pathogenesis. In addition, arsenic induces morphological changes in the integrity of mitochondria. Cascade mechanisms of free radical formation derived from the superoxide radical, combined with glutathione-depleting agents, increase the sensitivity of cells to arsenic toxicity. When both humans and animals are exposed to arsenic, they experience an increased formation of ROS/RNS, including peroxyl radicals (ROO•), the superoxide radical, singlet oxygen, hydroxyl radical (OH•) via the Fenton reaction, hydrogen peroxide, the dimethylarsenic radical, the dimethylarsenic peroxyl radical and/or oxidant-induced DNA damage. Arsenic induces the formation of oxidized lipids which in turn generate several bioactive molecules (ROS, peroxides and isoprostanes), of which aldehydes [malondialdehyde (MDA) and 4-hydroxy-nonenal (HNE)] are the major end products. This review discusses aspects of chronic and acute exposures of arsenic in the etiology of cancer, cardiovascular disease (hypertension and atherosclerosis), neurological disorders, gastrointestinal disturbances, liver disease and renal disease, reproductive health effects, dermal changes and other health disorders. The role of antioxidant defence systems against arsenic toxicity is also discussed. Consideration is given to the role of vitamin C (ascorbic acid), vitamin E (α-tocopherol), curcumin, glutathione and antioxidant enzymes such as superoxide dismutase, catalase and glutathione peroxidase in their protective roles against arsenic-induced oxidative stress.

Distribution of Stable Free Radicals among Amino Acids of Isolated Soy Proteins

Application of deuterium sulfide to powdered isolated soy proteins (ISP) was used to quench stable free radicals and produce a single deuterium label on amino acids where free radicals reside. The deuterium labels rendered increases of isotope ratio for the specific ions of radical-bearing amino acids. Isotope ratio measurements were achieved by gas chromatography/mass spectrometry (GC/MS) analyses after the amino acids were released by acidic hydrolysis and converted to volatile derivatives with propyl chloroformate. The isotope enrichment data showed the stable free radicals were located on Ala, Gly, Leu, Ile, Asx (Asp+Asn), Glx (Glu+Gln), and Trp but not on Val, Pro, Met, Phe, Lys, and His. Due to the low abundance of Ser, Thr, and Cys derivatives and the impossibility to accurately measure their isotope ratios, the radical bearing status for these amino acids remained undetermined even though their derivatives were positively identified from ISP hydrolysates. The relative isotope enrichment for radical-bearing amino acids Ala, Gly, Leu, Ile, Asx (Asp+Asn), Glx (Glu+Gln), and Trp were 8.67%, 2.96%, 2.90%, 3.94%, 6.03%, 3.91%, and 21.48%, respectively. Isotope ratio increase for Tyr was also observed but further investigation revealed such increase was mainly from nonspecific deuterium-hydrogen exchange not free radical quenching. The results obtained from the present study provide important information for a better understanding of the mechanisms of free radical formation and stabilization in "dry" ISP.

Involvement of inducible nitric oxide synthase in hydroxyl radical-mediated lipid peroxidation in streptozotocin-induced diabetes

Free radical production is implicated in the pathogenesis of diabetes mellitus, where several pathways and different mechanisms were suggested in the pathophysiology of the complications. In this study, we used electron paramagnetic resonance (EPR) spectroscopy combined with in vivo spin-trapping techniques to investigate the sources and mechanisms of free radical formation in streptozotocin-induced diabetic rats. Free radical production was directly detected in the diabetic bile, which correlated with lipid peroxidation in the liver and kidney. EPR spectra showed the trapping of a lipid-derived radical. Such radicals were demonstrated to be induced by hydroxyl radical through isotope-labeling experiments. Multiple enzymes and metabolic pathways were examined as the potential source of the hydroxyl radicals using specific inhibitors. No xanthine oxidase, cytochrome P450s, the Fenton reaction, or macrophage activation were required for the production of radical adducts. Interestingly, inducible nitric oxide synthase (iNOS) (apparently uncoupled) was identified as the major source of radical generation. The specific iNOS inhibitor 1400W as well as L-arginine pretreatment reduced the EPR signals to baseline levels, implicating peroxynitrite as the source of hydroxyl radical production. Applying immunological techniques, we localized iNOS overexpression in the liver and kidney of diabetic animals, which was closely correlated with the lipid radical generation and 4-hydroxynonenal-adducted protein formation, indicating lipid peroxidation. In addition, protein tyrosine nitration occurred in the diabetic target organs. Taken together, our studies support inducible nitric oxide synthase as a significant source of EPR-detectable reactive intermediates, which leads to lipid peroxidation and may contribute to disease progression as well.

Nitric oxide and MPP+-induced hydroxyl radical generation

Although neuroprotective effect of nitric oxide (NO) is discussed, NO has a role of pathogenesis of cellular injury. NO is synthesized from L-arginine by NO synthase (NOS). NO contributes to the extracellular potassium-ion concentration ([K(+)](o))-induced hydroxyl radical ((*)OH) generation. Cytotoxic free radicals such as peroxinitrite (ONOO(-)) and (*)OH may also be implicated in NO-mediated cell injury. NO activation was induced by K(+) depolarization. NO may react with superoxide anion (O(2) (-)) to form ONOO(-) and its decomposition generates (*)OH. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) metabolite 1-methyl-4-phenylpyridinium ion (MPP(+)) involve toxicity induced by NO. Intraneuronal Ca(2+) triggered by MPP(+) may be detrimental to the functioning of dopaminergic nerve terminals in the striatum. Although the [K(+)](o)-induced depolarization enhances the formation of (*)OH product due to MPP(+), the (*)OH generation via NOS activation may be unrelated the dopamine (DA)-induced (*)OH generation. Depolarization enhances the MPP(+)-induced (*)OH formation via NOS activation. NOS inhibition is associated with a protective effect due to suppression of depolarization-induced (*)OH generation. ONOO(-) has been implicated as a causative factor under conditions in which DA neurons are damaged. These findings may be useful in elucidating the actual mechanism of free radical formation in the pathogenesis of neurodegenerative brain disorders, including Parkinson's disease and traumatic brain injuries.

Free Radical Mechanisms of Aging Processes Under Physiological Conditions

Free radical theory of aging predicts crucial role for free radicals produced by external factors (environmental contamination, irradiation, etc.) or pathological disorders (hereditary diseases or infections) in the initiation of aging. Does it mean that under hypothetical completely physiological conditions aging processes could be fully suppressed? To answer this question, we will consider the possible mechanisms of free radical formation in such hypothetical state. There are two major mechanisms, which are responsible for free radical-mediated damage in a living organism: superoxide overproduction by mitochondria and nonenzymatic lipid peroxidation. Superoxide overproduction causes the inhibition of nitric oxide formation and bioavailability, one of principal characteristics of aging, while nonenzymatic lipid peroxidation, which is already demonstrated at physiological conditions, produces toxic isoprostanes. We suggest that major initiators of free radical-mediated damaging processes leading to aging at physiological state are oxidizable components of diet. The possibility of inhibition of aging processes by supplementation of nontoxic antioxidants and calorie restriction is discussed. Scheme demonstrating the potential mechanisms of starting the free radical-mediated aging processes is presented, which are discussed on the grounds of known literature data.

Dopamine efflux by MPTP and hydroxyl radical generation.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) produces a parkinsonian syndrome after its conversion to 1-methyl-4-phenylpyridine (MPP(+)) by B-form monoamine oxidase (MAO) in the brain, which is one of the most potent dopamine (DA)-releasing agents. MPP(+) perfusion into the striatum increases extracellular DA levels and this increase may concomitantly induce the formation of reactive free oxygen radicals, such as hydroxyl radical (.OH). These elevations seem to induce lipid peroxidation of striatum membranes, as detected by increases non-enzymatic formation of 2,3-dihydroxybenzoic acid (DHBA) levels. Sustained increase in striatal DA efflux by MAO inhibition produce.OH generation by products of monoamine. Therefore, reserpine-induced DA depletion clearly decreased MPP(+)-induced.OH formation. Neuromelanine synthesis from DA produce highly reactive free radicals. Nitric oxide (NO) contributes to produce MPP(+)-induced.OH generation via NO synthase (NOS) activation by depolarization. The antioxidation effect of angiotensin converting enzyme (ACE) inhibitor protects against MPP(+)-induced.OH generation due to the suppression of the Ca(2+)-dependent release of DA. These findings may be useful in elucidating the actual mechanism of free radical formation in the pathogenesis of neurodegenerative brain disorders, including Parkinson's disease and traumatic brain injuries. This review describes the free radicals mechanisms involved in MPTP toxicity and their possible involvement in the the pathogenesis of Parkinson's disease.

Environmental estrogen-like chemicals and hydroxyl radicals induced by MPTP in the striatum: a review.

Oxygen free radical formation has been implicated in lesions caused by the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and iron. Although MPTP produces a parkinsonian syndrome after its conversion to 1-methyl-4-phenylpyridine (MPP+) by type B monoamine oxidase (MAO) in the brain, the etiology of this disease remains obscure. This review focuses on the role of an environmental neurotoxin chemically related to MPP+-induced free radical generation in the pathogenesis of Parkinson's disease. Environmental-like chemicals, such as para-nonylphenol or bisphenol A, significantly stimulated hydroxyl radical (*OH) formation in the striatum. Allopurinol, a xanthine oxidase inhibitor, prevents para-nonylphenol and MPP+-induced *OH generation. Tamoxifen, a synthetic nonsteroidal antiestrogen, suppressed the *OH generation via dopamine efflux induced by MPP+. These results confirm that free radical production might make a major contribution at certain stages in the progression of the injury. Such findings may be useful in elucidating the actual mechanism of free radical formation in the pathogenesis of neurodegenerative brain disorders, including Parkinson's disease and traumatic brain injuries.

Free Radical Intermediates of Phenytoin and Related Teratogens: PROSTAGLANDIN H SYNTHASE-CATALYZED BIOACTIVATION, ELECTRON PARAMAGNETIC RESONANCE SPECTROMETRY, AND PHOTOCHEMICAL PRODUCT ANALYSIS

Phenytoin and related xenobiotics can be bioactivated by embryonic prostaglandin H synthase (PHS) to a teratogenic free radical intermediate. The mechanism of free radical formation was evaluated using photolytic oxidation with sodium persulfate and by EPR spectrometry. Characterization of the products by mass spectrometry suggested that phenytoin photolyzes to a nitrogen-centered radical that rapidly undergoes ring opening to form a carbon-centered radical. PHS-1 was incubated with teratogen (phenytoin, mephenytoin, trimethadione, phenobarbital, and major metabolites) or its vehicle and the free radical spin trap alpha-phenyl-N-t-butylnitrone, and incubations were analyzed by EPR spectrometry. There was no alpha-phenyl-N-t-butylnitrone radical adduct in control incubations. For phenytoin, a putative unstable nitrogen-centered radical adduct and a stable carbon-centered radical adduct were detected. Free radical spin adducts also were detected for all other teratogens and metabolites except carbamazepine. The PHS inhibitor eicosatetraynoic acid abolished the free radical EPR signal. Incubation of 2'-deoxyguanosine with phenytoin and PHS-1 resulted in a 5-fold increase in its oxidation to 8-hydroxy-2'-deoxyguanosine. This is the first direct chemical evidence for PHS-catalyzed bioactivation of phenytoin and related teratogens to a free radical intermediate that initiates DNA oxidation, which may constitute a common molecular mechanism of teratologic initiation.

Generation of nitro and superoxide radical anions from 2,4,6-trinitrobenzenesulfonic acid by rat gastrointestinal cells

Reactive oxygen and nitrogen species have been implicated in the inflammation of the gastrointestinal tract. The objective of this study was to investigate mechanisms of free radical formation from the colitis inducer 2,4,6-trinitrobenzene sulfonic acid (TNBS). We showed that TNBS was rapidly metabolized to TNBS nitro radical anion via metabolic reduction by flavinmononucleotide/NADPH, xanthine/xanthine oxidase as well as the rat small intestine and colon. TNBS nitro radical anion was directly detected with electron paramagnetic resonance (EPR) spectroscopy. EPR spectra of TNBS nitro radical anion showed hyperfine coupling constants from the proximal nitrogen, two hydrogens and the two distal nitrogens with respective magnitudes of a N(4)=9.7 G; a H(3,5)=3.2 G (2); and a N(2,6)=0.25 G. EPR spin trapping using 5,5-dimethyl-1-pyrroline N-oxide in aerobic incubations of isolated enterocytes (or colonocytes, or red blood cells) and TNBS, in the presence or absence of NADPH, produced radical adducts characteristic of superoxide and hydroxyl radicals. Our EPR data showing generation of TNBS nitro and superoxide radical anions demonstrate that one-electron reduction of TNBS may be an initial step in the cascade of the in vivo inflammatory events in TNBS-induced colitis.

Chemiluminescent measurement of increased free-radical formation after ischemia/reperfusion. Mechanisms of free radical formation in the liver

It has been proposed that xanthine oxidase-derived superoxide mediates reperfusion injury in the liver; however, there is a little direct evidence to support this hypothesis. In this paper we describe a model system to directly and noninvasively measure oxyradical formation and hepatic injury in isolated perfused rat liver. Using this sensitive chemiluminescent technique, we clearly demonstrate the theorized burst in oxygen radical production upon reperfusion of previously ischemic liver, without perturbing the system with chemical luminescence enhancers. This increase in chemiluminescence (CL) upon reperfusion was diminished by the free radical scavengers trolox and ascorbate, as well as N-2-mercaptoproprionyl-glycine (MPG), thereby confirming the oxyradical nature of this signal. Additionally, superoxide dismutase and the xanthine oxidase inhibitor allopurinol, but not catalase, attenuated the reperfusion effect, providing the most direct evidence so far that XOD derived superoxide anion is formed during liver reperfusion. Hepatic injury (AST release) did not appear to relate to increased CL, supporting the notion that the oxyradical flux may serve as a signal for other events leading to tissue injury. Further studies using this sensitive chemiluminescent technique should aid in delineating the detailed mechanism(s) of reperfusion injury.

Free Radical Chemistry of Nitric Oxide: Looking at the Dark Side

Pulmonary cells are both critical sources and targets of toxic reactive species, with the mechanisms of free radical formation and tissue target reactions poorly understood .NO can contribute to novel pathophysiologic reactions that can occur in lungs. The toxicology of inhaled .NO is poorly and incompletely described, and there is a limited mechanistic understanding of the significant contribution of .NO and O₂. to pulmonary pathologic conditions. Finally, antioxidant defense supplementation will be the most effective when the location and nature of toxic species contributing to tissue injury are revealed, and the antioxidants are site-directed.

Effects of antioxidants and free radical scavengers in three different models of acute pancreatitis.

The present studies were done to evaluate the therapeutic potential of several antioxidants and free radical scavengers in three different models of acute pancreatitis. (a) Edematous pancreatitis with acinar cells necrosis was induced by seven hourly intraperitoneal injections of 50 micrograms of caerulein per kg in mice. (b) Hemorrhagic pancreatitis was induced by feeding a choline-deficient, ethionine-supplemented (CDE) diet in mice. (c) Hemorrhagic pancreatitis was induced by retrograde infusion of 0.6 ml of 5% sodium taurocholate into the pancreatic duct in rats. The following antioxidants and free radical scavengers were given at various doses intravenously, subcutaneously, or intraperitoneally before the onset of pancreatitis: Ebselen [2-phenyl-1,2-benzisoselenazol-3(2H)-one], superoxide dismutase, catalase, deferoxamine (Desferal), dimethyl sulfoxide, or allopurinol. The severity of pancreatitis was assessed at various times after its onset by determination of serum amylase and pancreatic weight (edema), by grading of histological alterations, and by determination of survival (survival determined in models of hemorrhagic pancreatitis). In general, free radical scavengers and antioxidants ameliorated edema and inflammation to a greater degree than necrosis and the increase in serum amylase. Superoxide dismutase (as did Ebselen in previous studies) exerted beneficial effects on survival in diet-induced pancreatitis in the absence of marked effects on pancreatic necrosis, suggesting that these beneficial effects are due to amelioration of extrapancreatic complications that often contribute to mortality in acute pancreatitis. None of the antioxidants had major beneficial effects in taurocholate-induced hemorrhagic pancreatitis. Thus, formation of free radicals may be important for progression and outcome in diet-induced and, to a lesser degree, in caerulein-induced pancreatitis but not at all in taurocholate-induced pancreatitis. Different models of pancreatitis may, therefore, involve different degrees and mechanisms of free radical formation. Despite the amelioration of edema and the beneficial effects on mortality seen for some antioxidants in some of the models, antioxidants and free radical scavengers appear to have only a limited potential for treatment of acute pancreatitis.

Direct radiation action of heavy ions on DNA as studied by ESR-spectroscopy.

The effects of heavy ions on the mechanisms of free radical formation in DNA-constituents as compared to low-LET irradiation are investigated by means of Electron Spin Resonance (ESR) spectroscopy. Dose-yield curves were measured at low (T < 100 K) and ambient temperatures in order to obtain the G-value, that is number of radicals formed per 100 eV absorbed energy. These G-values show a characteristic LET-dependence and are one to two orders of magnitude lower than for low-LET irradiation. Measurements on 2'Deoxycytidine at 300 K using combined heavy ion and X-ray irradiation methods suggested that this effect can be partially explained by a destruction of radicals during the irradiation.

Radical migration as an elementary process in degradation

Abstract

On the mechanism of free radical formation during browning reaction of sugars with amino compounds.

To elucidate the formation mechanism of N,N′-dialkylpyrazine cation radical during browning reaction of sugars with amino compounds, main products in an early stage of the reaction were determined quantitatively by TLC and GLC. It was shown that the Schiff base, two-carbon fragmental product of sugar, the free radical and deoxyosone were successively produced prior to the browning. Polarographical measurements indicated that the radical formation was induced by the production of some reducing substances in the reaction mixture. These results suggest that the free radical was formed by the reduction of N,N′-dialkylpyrazinium; a compound, which demonstrated to have a strong activity to browning, might be formed by condensation of two-carbon enaminol followed by oxidation.

Free radical initiation in proteins and amino acids by ionizing and ultraviolet radiations and lipid oxidation--part III: free radical transfer from oxidizing lipids.

Parallels and similarities in chemical and functional damage to proteins by ionizing and uv radiations and oxidizing lipids have been recognized for some time. However, only recently have oxidizing lipids been shown directly by electron spin resonance to be radiomimetic also in their capacity for protein free radical production. Free radicals play a key role in the transformation of energy to molecular and cellular damage. It is thus of critical importance to elucidate the general mechanisms of free radical formation and reactions in proteins in order to understand protein involvement in various pathological conditions and in food deterioration. Accordingly, this review is a detailed comparison of gamma-radiation, UV radiation, and lipid oxidation for what is presently known concerning (1) the specific modes of energy deposition and free radical formation, (2) the free radicals formed in proteins and amino acids, and (3) the typical damage correlating with these radicals.

Free radical initiation in proteins and amino acids by ionizing and ultraviolet radiations and lipid oxidation--Part 22: ultraviolet radiation and photolysis.

Parallels and similarities in chemical and functional damage to proteins by ionizing and UV radiations and oxidizing lipids have been recognized for some time. However, only recently have oxidizing lipids been shown directly by electron spin resonance to be radiomimetic also in their capacity for protein free radical production. Free radicals play a key role in the transformation of energy to molecular and cellular damage. It is thus of critical importance to elucidate the general mechanisms of free radical formation and reactions in proteins in order to understand protein involvement in various pathological conditions and in food deterioration. Accordingly, this review is a detailed comparison of gamma radiation, UV radiation, and lipid oxidation for what is presently known concerning (1) the specific modes of energy deposition and free radical formation, (2) the free radicals formed in proteins and amino acids, and (3) the typical damage correlating with these radicals.

Free radical initiation in proteins and amino acids by ionizing and ultraviolet radiations and lipid oxidation--Part I: ionizing radiation.

Parallels and similarities in chemical and functional damage to proteins by ionizing and UV radiations and oxidizing lipids have been recognized for some time. However, only recently have oxidizing lipids been shown directly by electron spin resonance to be radiomimetic also in their capacity for protein free radical production. Free radicals play a key role in the transformation of energy to molecular and cellular damage. It is thus of critical importance to elucidate the general mechanisms of free radical formation and reactions in proteins in order to understand protein involvement in various pathological conditions and in food deterioration. Accordingly, this review is a detailed comparison of gamma radiation, UV radiation, and lipid oxidation for what is presently known concerning (1) the specific modes of energy deposition and free radical formation, (2) the free radicals formed in proteins and amino acids, and (3) the typical damage correlating with these radicals.