Oxidation of quinones by H2O2: formation of epoxy- and hydroxyquinone adducts and electronically excited states.
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Hydrogen Peroxide↗
Biomedical subjects
E Cadenas
Publications and source records attributed to E Cadenas.
Co-oxidation of salicylate and cholesterol during the oxidation of metmyoglobin by H2O2.
The reaction between metmyoglobin and H2O2 proceeds with oxidation of the hemo-protein iron to a higher valence state and consumption of the peroxide. This reaction is further associated with (a) O2 evolution; (b) hydroxylation of the aromatic compound salicylate to yield a set of dihydroxybenzoic acid derivatives (analyzed by HPLC with electrochemical detection); (c) autoxidation of cholesterol with formation of 3 beta-hydroxy-5-alpha-cholest-6-ene-5-hydroperoxide; and (d) formation of electronically excited states detected by low-level chemiluminescence. The heterolytic scission of the O-O bond of hydroperoxides by metmyoglobin causes the formation of an oxidizing equivalent capable of promoting peroxidation of linoleate and arachidonate (as indicated by the parallel formation of thiobarbituric acid-reactive material and an enhancement of chemiluminescence intensity). The identity of the oxidizing equivalent(s) is discussed in terms of the formation of a relatively stable higher state of oxidation of heme Fe (FeIV-OH or FeV = O) as well as on possible intermediate species derived during the decomposition of H2O2 by metmyoglobin, such as HO.and 1O2. These species might be involved either simultaneously or sequentially in the peroxidation of fatty acids as well as in the tissue damage associated with the formation of H2O2 in ischemic-reperfusion states.
Cholesterol↗
Reductive addition of glutathione to p-benzoquinone, 2-hydroxy-p-benzoquinone, and p-benzoquinone epoxides. Effect of the hydroxy- and glutathionyl substituents on p-benzohydroquinone autoxidation.
The reductive addition of GSH to p-benzoquinones, 2-hydroxy-p-benzoquinone, and 2,3-epoxy-p-benzoquinones with different degree of methyl substitution was studied in terms of absorption spectral changes and autoxidation reactions. The nucleophilic addition of GSH to p-benzoquinone yields a glutathionyl-p-benzohydroquinone product with maximal absorption at lambda 303nm. This compound autoxidizes slowly--but at a rate 8-fold higher than the parent hydroquinone--to glutathionyl-p-benzoquinone, which reveals maximal absorption at lambda 367 nm. The autoxidation of the glutathionyl derivative is accompanied by O2 consumption and H2O2 formation. The nucleophilic addition of GSH to either 2-hydroxy-p-benzoquinone or 2,3-epoxy-p-benzoquinone yields the same primary molecular product, 2-hydroxy-5-glutathionyl-p-benzohydroquinone, a compound that shows maximal absorption at lambda 300 nm and autoxidizes at rates substantially higher (44-fold) than the parent glutathionyl hydroquinone lacking a -OH substituent. The autoxidation product, 2-hydroxy-5-glutathionyl-p-benzoquinone, reveals maximal absorbance at lambda 343 nm as well as a resolved absorption band at longer wavelengths (lambda 520 nm), the latter contributed by the -OH substituent. The glutathionyl substituent exerted only minor changes in the reduction potential of the quinones, whereas the -OH substituent lowered significantly the half-wave reduction potential, as measured in aqueous solutions. The rate of autoxidation was markedly enhanced by both substituents as follows: hydroxy-glutathionyl-p-benzohydroquinone much greater than hydroxy-p-benzohydroquinone much greater than glutathionyl-p-benzohydroquinone greater than p-benzohydroquinone. Superoxide dismutase enhanced the rate of autoxidation of p-benzohydroquinone and its glutathionyl adduct, whereas it inhibited autoxidation of the hydroxy derivatives with or without glutathionyl substitution. The biochemical significance of these results is discussed in terms of the pro-oxidant character of the reductive addition of GSH to p-benzoquinones, alpha-hydroxyquinones, and quinone epoxides.
Benzoquinones↗
Reduction of ferryl- and metmyoglobin to ferrous myoglobin by menadione-glutathione conjugate. Spectrophotometric studies under aerobic and anaerobic conditions.
Both metmyoglobin (MbIII) and ferrylmyoglobin (MbIV) are reduced by the menadiol-glutathione conjugate (GS-Q2-) to oxymyoglobin (MbIIO2) or deoxymyoglobin (MbII), depending whether the assay is carried out under aerobic or anaerobic conditions, respectively. Under aerobic conditions, the reduction of MbIII to MbIIO2 by GS-Q2- is associated with O2 consumption. The latter process is accounted for by (a) the autoxidation of the conjugate yielding H2O2 and (b) the rapid binding of O2 to MbII to yield MbIIO2. The ratio [O2]consumed/[MbIIO2]formed is approximately 1.5 at the time when MbIIO2 formation is maximal (at about 0.8 min). This ratio, higher than the unit, indicates that there is more than one O2-consuming reaction in this experimental model. The ratio of initial rates of O2 consumption and MbIIO2 formation is close to the unit [(-dO2/dt)/(+ dMbIIO2/dt) = 1.1]. The formation of H2O2 originating during the autoxidation of the GS-Q2- is substantially lower in the presence of MbIII, probably due to the heterolytic cleavage of the O--O bond of the peroxide by the hemoprotein. Although the latter reaction should yield MbIV, this species is not observed in the absorption spectrum, probably due to its rapid reduction by GS-Q2-. MbIV is reduced to MbIIO2 by the GS-Q2-. Whether this reaction takes place in one-electron transfer steps, that is, the sequence: MbIV----MbIII----MbIIO2 is difficult to evaluate by absorption spectral analysis, due to the rapid rate of the [MbIV----MbIIO2] transition. Under anaerobic conditions, the reduction of either MbIII or MbIV by GS-Q2- yields MbII as a stable molecular product. Anaerobic conditions prevent any further interaction of MbII with intermediates of O2 reduction derived from GS-Q2- autoxidation.
Chemical Phenomena↗
Reduction of ferrylmyoglobin to metmyoglobin by quinonoid compounds.
Several quinoid compounds mediated the reduction of ferrylmyoglobin (MbIV) to metmyoglobin (MbIII). The efficiency of the MbIV reduction to MbIII was accomplished by the quinones in the following order: p-benzoquinone greater than 1,4-naphthoquinone greater than 2-OH-1,4-naphthoquinone greater than 2,3-epoxy-1,4-naphthoquinone. The quinone-mediated reduction of MbIV to MbIII had the following characteristics: (a) it was stoichiometrically--rather than catalytically--related to the number of cycles of the MbIV----MbIII transition involving the reduction of H2O2. (b) It proceeded with similar efficiencies under aerobic and anaerobic conditions. (c) It did not require the free radical form of MbIV(.MbIV), thus excluding a two-electron oxidation of the quinone. (d) the nucleophilic addition of--NH2 groups of the apoprotein on the quinone seemed not to be involved through an alternative pathway in the reduction of MbIV, especially since 2-OH-1,4-naphthoquinone, a compound which cannot undergo nucleophilic addition, also facilitated the reduction of the ferryl compound. (e) No two-electron oxidation products of the unsubstituted quinones, such as quinone epoxides, were detected in the spent reaction mixture analyzed by HPLC with electrochemical detection. On the basis of these observations, it is suggested that the reduction of MbIV to MbIII by the above quinonoid compounds is a one-electron transfer process, with electron abstraction being probably accomplished at some site in the benzo ring of the quinone.
Benzoquinones↗
Effect of superoxide dismutase on the autoxidation of various hydroquinones--a possible role of superoxide dismutase as a superoxide:semiquinone oxidoreductase.
The autoxidation of DT-diaphorase-reduced 1,4-naphthoquinone, 2-OH-1,4-naphthoquinone, and 2-OH-p-benzoquinone is efficiently prevented by superoxide dismutase. This effect was assessed in terms of an inhibition of NADPH oxidation (over the amount required to reduce the available quinone), O2 consumption, and H2O2 formation. Superoxide dismutase also affects the distribution of molecular products -hydroquinone/quinone-involved in autoxidation, by favoring the accumulation of the reduced form of the above quinones. In contrast, the rate of autoxidation of DT-diaphorase-reduced 1,2-naphthoquinone is enhanced by superoxide dismutase, as shown by increased rates of NADPH oxidation, O2 consumption, and H2O2 formation and by an enhanced accumulation of the oxidized product, 1,2-naphthoquinone. These findings suggest that superoxide dismutase can either prevent or enhance hydroquinone autoxidation. The former process would imply a possible new activity displayed by superoxide dismutase involving the reduction of a semiquinone by O2-.. This activity is probably restricted to the redox properties of the semiquinones under study, as indicated by the failure of superoxide dismutase to prevent autoxidation of 1,2-naphthohydroquinone.
Hydroquinones↗
DT-diaphorase-catalyzed two-electron reduction of various p-benzoquinone- and 1,4-naphthoquinone epoxides.
The oxidation of various quinones by H2O2 results in quinone epoxide formation. The yield of epoxidation is inversely related to the degree of methyl substitution of the quinone and seems not to be dependent on the redox potential of the quinones studied. The following order of H2O2-mediated epoxidation of quinones was found: p-benzoquinone greater than or equal to 1,4-naphthoquinone greater than 2-methyl-p-benzoquinone greater than 2,6-dimethyl-p-benzoquinone greater than or equal to 2-methyl-1,4-naphthoquinone greater than 2,3-dimethyl-1,4-naphthoquinone. DT-Diaphorase reduces several quinone epoxides at different rates. The rate of quinone epoxide reduction cannot be related to either the redox potential of the quinone epoxide (as reflected by the half-wave potential calculated from the corresponding hydrodynamic voltamograms) or the degree of substitution of the quinone epoxide. It appears, however, that a quinone epoxide redox potential more negative than -0.5 to -0.6 volts settles a threshold for the electron transfer reaction. This does not exclude that specificity requirements, i.e. the formation of the quinone epoxide substrate-enzyme complex may chiefly determine the rate of reduction of quinone epoxides by DT-diaphorase. DT-diaphorase-catalyzed two-electron transfer to quinone epoxides--resulting in epoxide ring opening--yields 2-OH-p-benzohydroquinone or 2-OH-1,4-naphthohydroquinone products. These hydroxy-derivatives show a higher rate of autoxidation than do the parent hydroquinones lacking the OH substituent.
Benzoquinones↗
One-electron transfer reactions of diquat radical to different reduction intermediates of oxygen. Formation of hydroxyl radical and electronically excited states.
The one-electron transfer activation of DQ++ by microsomal fractions comprises an aerobic phase and an anaerobic phase. The aerobic phase is characterized by O2 consumption, formation of electronically excited states with main emission below 600 nm, and H2O2 formation. The anaerobic phase is characterized by H2O2 consumption, DQ+ accumulation, HO. formation, and also electronically excited state formation with main emission beyond 600 nm. Superoxide dismutase abolishes the photoemission during the aerobic phase, whereas it has no effect on the photoemission originating during the anaerobic phase. The hydroxylation products of the aromatic compound salicylate, mainly 2,3- and 2,5-dihydroxybenzoic acids--indicative of the occurrence of HO.-, were detected by h.p.l.c. with oxidative electrochemical detection during the anaerobic phase, but not during the aerobic phase. Neither H2O2 consumption nor HO. are prevented by desferrioxamine. These experimental observations are interpreted on the grounds of two main electron-transfer reactions of DQ.+: under aerobic conditions, two one-electron transfer steps to molecular O2 and O2.- to yield H2O2. Under anaerobic conditions, one-electron transfer step to contaminating iron or any ferrioxamine formed to a ferrous complex which can support a Fenton-like reduction of H2O2 with formation of HO.. The toxicological relevance for the occurrence of such reactions is also discussed in terms of the formation of electronically excited states.
Animals↗
The potential intermediate role of lysosomes in oxygen free radical pathology. Review article.
The term "free radical" refers to atoms or groups of atoms containing a single unpaired electron occupying an outer orbital. This unpaired electron lends the molecule distinct chemical and physical properties such as its high reactivity and magnetic moment, respectively. Some relevant advances in medical research have encompassed O2 radicals and other toxic derivatives of O2. These reactive O2 species were shown to play a significant role in a wide spectrum of pathological states (see Halliwell & Gutteridge, 1985; Flohé 1986; Kensler & Taffe, 1986; McCord, 1986), though the measurement of free radical activity in clinically-accesible material has been unsatisfactory (Dormandy, 1986). This overview provides only a framework of information to assist the reader on some relevant topics on free radical pathology, which by no means can cover the multiple aspects of the medical literature in this context. The reader is referred to several articles which cover particular features of free radical biology and medicine (Chance et al., 1979; Pryor, 1976-1984; Fridovich, 1983; Jamieson et al., 1986; Kensler & Taffe, 1986; McCord, 1986; Weiss, 1986).
Animals↗
Hydroperoxide-induced chemiluminescence in rabbit lungs: role of arachidonic acid enzymes.
Low-level chemiluminescence (C) is thought to be an index of oxidant stress. We measured the relationship between low-level C, pulmonary arterial pressure, and perfusate concentration of thromboxane B2 (TxB2) in isolated perfused rabbit lungs during challenge with tert-butyl hydroperoxide (t-bu-OOH). We also measured glutathione release as another index of oxidant stress. We found that C was correlated with each variable, suggesting that oxidant stress measured by C and by glutathione release stimulated TxB2 production and pulmonary vasoconstriction. We also investigated the contribution of active O2 metabolites produced by prostaglandin (PG) peroxidase to oxidant stress by studying the effects of t-bu-OOH before and after the use of cyclooxygenase and lipoxygenase inhibitors. We found that C was augmented after inhibition, perhaps due to metabolism of t-bu-OOH by peroxidases of both arachidonic acid (AA) metabolic pathways in the absence of their normal substrates. We studied phenylbutazone, thought to inhibit peroxidases, and AA. C during t-bu-OOH administration was not augmented after phenylbutazone and was markedly inhibited after AA administration perhaps because AA competes with t-bu-OOH. To further study the role of peroxidases we pretreated the lungs with the antioxidant dithiothreitol, which inhibits peroxidases involved in both the cyclooxygenase and lipoxygenase pathways. Dithiothreitol nearly abolished C produced by t-bu-OOH and also prevented the increased light caused by eicosatetrynoic acid. We directly tested the hypothesis that C occurred as a result of the interaction of t-bu-OOH and the cyclooxygenase and lipoxygenase enzymes; we measured C when t-bu-OOH was added to purified PGH2 synthase or soybean lipoxygenase. The combination of t-bu-OOH with PGH2 synthase or lipoxygenase led to C that was inhibited by dithiothreitol and by the antioxidant phenol. These results suggest that enzymes involved in AA metabolism can interact with t-bu-OOH and that the action of these enzymes on t-bu-OOH leads to C. The results may mean that lipid peroxides can indirectly contribute to tissue oxidant stress due to production of active O2 metabolites as by-products of their metabolism by AA peroxidases.
Animals↗
Inhibition of the mitochondrial F1-ATPase by rose bengal mediated photooxidation. Interaction of the Fe2+ chelate of bathophenanthroline with the sensitizer.
Rose Bengal mediated photooxidation of mitochondrial F1-ATPase and its beta-subunit resulted in inactivation and loss of about 50 and 60% of their histidine residues, respectively. The beta-subunit was not cleaved upon photooxidation. Photooxidation of histidine probably results in changes in the conformational stability of F1-ATPase leading to its inactivation. The participation of singlet molecular oxygen during the photooxidation process is suggested by the selective loss of histidine residues, while other amino acids, also sensitive to singlet oxygen attack, were not affected. Photochemical damage of F1-ATPase was prevented by various phenanthroline compounds, the order of efficiency being bathophenanthroline-Fe chelate greater than bathophenanthroline greater than orthophenanthroline-Fe chelate greater than bathophenanthroline-sulfonate-Fe chelate. The prevention by bathophenanthroline-Fe chelate of photochemical damage is interpreted on the basis of its interaction with the photosensitizer, Rose Bengal, probably implying a chemical reaction which decreases the actual concentration of the sensitizer and, thereby, the extent of photoinactivation.
Amino Acids↗
An experimental model system for leishmaniasis. Effects of porphyrin-compounds and menadione on Leishmania parasites engulfed by cultured macrophages.
In order to facilitate studies on the effects of chemotherapeutic agents on the host-parasite interactions in leishmaniasis, we have developed an experimental model for infecting human monocyte-derived- and mouse peritoneal macrophages in culture with recently-isolated Leishmania donovani promastigots (LDP). The chemotherapeutic agents studied were protoporphyrin, hematoporphyrin, menadione, and combinations of hematoporphyrin plus menadione. Since the Leishmania donovani amastigotes survived poorly in mouse macrophages and protoporphyrin was quite toxic to the latter, our investigations were focused on the effects of hematoporphyrin and menadione on amastigotes engulfed by human macrophages. Treatment of Leishmania donovani amastigotes-infested human macrophages with either 50 microM hematoporphyrin or 10 microM menadione did not influence significantly the survival of either Leishmania donovani amastigotes or the macrophages themselves. Larger individual doses of hematoporphyrin and menadione were toxic to both parasites and macrophages. The combination of 50 microM hematoporphyrin and 10 microM menadione, however, caused the destruction of the parasites without affecting the host macrophage. The enhanced deleterious effect from combined low doses of hematoporphyrin and menadione is discussed in terms of the production of reactive oxygen species, such as superoxide anion radical and hydrogen peroxide, originating from cellular redox cycling of menadione, and followed by decomposition of the formed hydrogen peroxide by hematoporphyrin to produce the more reactive hydroxyl radical.
Animals↗
Hydroperoxide metabolism in vitamin E-deficient hepatocytes. Studies on low-level chemiluminescence, lipid peroxidation, and glutathione status.
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Adenosine Diphosphate↗
Electronically excited state generation during the reaction of p-benzoquinone with H2O2. Relation to product formation: 2-OH- and 2,3-epoxy-p-benzoquinone. The effect of glutathione.
The reaction between H2O2 and p-benzoquinone proceeds with consumption of both reactants with second order rate constants of 1.66- and 0.77 M-1S-1, respectively. The process is mainly supported by oxygen addition reactions to the quinone resulting in the formation of both 2,3-epoxy-p-benzoquinone and 2-OH-p-benzoquinone. The former product accumulates in the assay mixture without participating in further reactions. The formation of the latter product implies free radical intermediates such as 2-OH-p-benzosemiquinone anion, which supports the generation of electronically excited states upon its oxidation by H2O2, presumably as part of an organic Fenton reaction. The relaxation of the excited state is accompanied by photoemission at 485-530 nm. Glutathione was found to counteract the oxidative aspects of the reaction between p-benzoquinone and H2O2 by a series of processes involving (a) a rapid reductive addition to the quinone with formation of a substituted p-benzohydroquinone; (b) an effective quenching of photoemission, which might be attributed to the deactivation of the excited state by the p-benzohydroquinone-glutathione adduct, and (c) the decomposition of the formed 2,3-epoxy-p-benzoquinone, also by reductive cleavage of the epoxide ring.
Benzoquinones↗
DT-diaphorase-catalyzed two-electron reduction of quinone epoxides.
DT-diaphorase catalyzes the two-electron reduction of the unsubstituted quinone epoxide, 2,3-epoxy-p-benzoquinone, at expense of NAD(P)H with formation of 2-OH-p-benzohydroquinone as the reaction product. The further conversion reactions of 2-OH-p-benzohydroquinone are influenced by the presence of O2 in the medium. Under aerobic conditions, 2-OH-p-benzohydroquinone undergoes autoxidation--probably with formation of 2-OH-semiquinone intermediates--to 2-OH-p-benzoquinone. The latter product is rapidly reduced by DT-diaphorase and, thus, its accumulation can be only observed upon exhaustion of NADPH. Under anaerobic conditions, 2-OH-p-benzohydroquinone does not undergo autoxidation and its accumulation is stoichiometrically (1:1) related to the amount of NADPH oxidized and epoxide substrate reduced. DT-diaphorase also catalyzes the reduction of the disubstituted quinone epoxide, 2,3-dimethyl-2,3-epoxy-1,4-naphthoquinone. Neither the aliphatic epoxide, trans-stilbene oxide, nor the aromatic epoxide, 4,5-epoxy-benzo[a]pyrene are substrates for DT-diaphorase. The reduction of 2,3-epoxy-p-benzoquinone is also catalyzed by the one-electron transfer enzyme, NADPH-cytochrome P450 reductase at a rate similar to that found with DT-diaphorase. However, this reaction differs from that catalyzed by DT-diaphorase in the distribution of molecular products as well as in the relative contribution of nonenzymatic reactions, i.e. semiquinone disproportionation and autoxidation.
Animals↗
Reactive oxygen intermediates in biochemistry.
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Cytochrome P-450 Enzyme System↗
The relation of free radical production to hyperoxia.
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Adaptation, Physiological↗
Oxidative stress: damage to intact cells and organs.
Oxidative cell damage can be monitored by detection of (a) photoemission of singlet molecular oxygen formed from radical interactions (so-called low-chemical chemiluminescence), (b) end products of lipid peroxidation, such as ethane, and (c) glutathione disulphide release. These methods, preferably used in a complementary fashion, provide insight into the pro-oxidant-antioxidant balance in the intact cell or organ. Recent work from this laboratory on the metabolism of hydroperoxides and aldehydes as well as on redox cycling of the quinone menadione is presented. The comparison of GSSG transport systems in liver and heart reveals a limitation of capacity in the latter, thus making GSSG export potentially critical in the heart. As part of an inter-organ feedback system between extrahepatic tissues and liver, the newly described hormone stimulation of GSH release from liver is also presented.
Aldehydes↗