Etelvino Bechara - Academia.edu (original) (raw)

Papers by Etelvino Bechara

Clinical Chemistry, Jul 1, 1997

ing, undergoes metal-catalyzed aerobic oxidation at physiological pH to yield reactive free radic... more ing, undergoes metal-catalyzed aerobic oxidation at physiological pH to yield reactive free radical species (O 2 . , HO ⅐ , and ALA ⅐ ). We analyzed the relationships between plasma ALA concentrations, blood concentrations of lead, protoporphyrin IX (PP-IX), superoxide dismutase (SOD), and methemoglobin (metHb), and urine chemiluminescence (CL) in samples collected from lead-exposed workers. All variables measured were substantially (P <0.01) higher (2-8-fold) in the lead-exposed workers (n ‫؍‬ 60). Plasma ALA concentrations were, on average, 6-fold higher in lead-exposed workers. We observed positive linear relationships between ALA and lead (r ‫؍‬ 0.992), ALA and PP-IX (r ‫؍‬ 0.891), ALA and metHb (r ‫؍‬ 0.984), lead and SOD (r ‫؍‬ 0.948), ALA and urine CL (r ‫؍‬ 0.987), and lead and PP-IX (r ‫؍‬ 0.993). These data are consistent with our free radical hypothesis for lead poisoning, where ALA distribution to and accumulation in several organs may trigger oxidative stress responses.

Chem Res Toxicol, 2004

Oxidative stress is believed to play a role in the pathogenesis of several diseases, including di... more Oxidative stress is believed to play a role in the pathogenesis of several diseases, including diabetes and inborn errors of metabolism. The types of oxidative damage observed in these pathologies have been attributed to the excessive production of reactive intermediates relating to the accumulation of toxic metabolites. The production of extremely oxidizing peroxynitrite can also be high in these pathologies. We study here the oxidation initiated by peroxynitrite of the ethyl esters of acetoacetate (EAA) and 2-methylacetoacetate (EMAA), metabolites that accumulate in diabetes and isoleucinemia, respectively. Oxygen consumption studies have confirmed that peroxynitrite promotes the aerobic oxidation of EAA and EMAA in phosphate buffer. These reactions were accompanied by ultraweak light emission, which probably arises from triplet carbonyl products formed by thermolysis of dioxetane intermediates. The kinetics of oxygen uptake and chemiluminescence by EAA and EMAA was strongly affected by the phosphate ion, known to catalyze carbonyl enolization and nucleophilic additions to carbonyls. The reaction pH profiles obtained by oxygen consumption and chemiluminescence measurements indicated that the peroxynitrite anion was the initiator of EAA and EMAA aerobic oxidation. EPR spin-trapping studies with the spin traps 3,5-dibromo-4-nitrosobenzenesulfonic acid and 2-methyl-2-nitrosopropane showed the intermediacy of methyl and a carbon-centered radical (•CH 2 COR) in the oxidation of EAA by peroxynitrite. In the case of EMAA, a tertiary carbon-centered radical (•EMAA) and an acyl radical were detected, the latter probably resulting from the cleavage of a triplet carbonyl product. Superstoichiometric formation of acetate from both substrates confirmed the occurrence of oxygen-dependent chain reactions, here proposed to be initiated by one-electron abstraction from the enolic form of the substrates. The free radicals and electronically excited species generated in the oxidation of EAA and EMAA may help shed further light on the molecular basis of these diseases.

Free Radical Biol Med, 2010

The α-aminoketone 1,4-diamino-2-butanone (DAB), a putrescine analogue, is highly toxic to various... more The α-aminoketone 1,4-diamino-2-butanone (DAB), a putrescine analogue, is highly toxic to various microorganisms, including Trypanosoma cruzi. However, little is known about the molecular mechanisms underlying DAB&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s cytotoxic properties. We report here that DAB (pK(a) 7.5 and 9.5) undergoes aerobic oxidation in phosphate buffer, pH 7.4, at 37°C, catalyzed by Fe(II) and Cu(II) ions yielding NH(4)(+) ion, H(2)O(2), and 4-amino-2-oxobutanal (oxoDAB). OxoDAB, like methylglyoxal and other α-oxoaldehydes, is expected to cause protein aggregation and nucleobase lesions. Propagation of DAB oxidation by superoxide radical was confirmed by the inhibitory effect of added SOD (50 U ml-1) and stimulatory effect of xanthine/xanthine oxidase, a source of superoxide radical. EPR spin trapping studies with 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) revealed an adduct attributable to DMPO-HO(•), and those with α-(4-pyridyl-1-oxide)-N-tert-butylnitrone or 3,5-dibromo-4-nitrosobenzenesulfonic acid, a six-line adduct assignable to a DAB(•) resonant enoyl radical adduct. Added horse spleen ferritin (HoSF) and bovine apo-transferrin underwent oxidative changes in tryptophan residues in the presence of 1.0-10 mM DAB. Iron release from HoSF was observed as well. Assays performed with fluorescein-encapsulated liposomes of cardiolipin and phosphatidylcholine (20:80) incubated with DAB resulted in extensive lipid peroxidation and consequent vesicle permeabilization. DAB (0-10 mM) administration to cultured LLC-MK2 epithelial cells caused a decline in cell viability, which was inhibited by preaddition of either catalase (4.5 μM) or aminoguanidine (25 mM). Our findings support the hypothesis that DAB toxicity to several pathogenic microorganisms previously described may involve not only reported inhibition of polyamine metabolism but also DAB pro-oxidant activity.

Cheminform, 2010

ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Free Radical Biol Med, 1993

Chem Res Toxicol, 2000

Peroxynitrite is shown here to promote the aerobic oxidation of isobutanal (IBAL) and 3-methyl-2,... more Peroxynitrite is shown here to promote the aerobic oxidation of isobutanal (IBAL) and 3-methyl-2,4-pentanedione (MP) in a pH 7.2 phosphate buffer into acetone plus formate and biacetyl plus acetate, respectively. These products are expected from dioxetane intermediates, whose thermolysis is known to be chemiluminescent (CL). Accordingly, the extent of total oxygen uptake by IBAL at different concentrations parallels the corresponding CL maximum intensities. The pH profile based on oxygen uptake data for the MP reaction matches the titration curve of peroxynitrous acid (pK(a) approximately 7), indicating that peroxynitrite anion is the oxidizing agent. Energy transfer studies with IBAL and the 9, 10-dibromoanthracene-2-sulfonate ion, a triplet carbonyl detector, indicates that triplet acetone (tau = 19 micros) is the energy donor. It is postulated that IBAL- or MP-generated triplet carbonyls are produced by the thermolysis of dioxetane intermediates, which are formed by the cyclization of alpha-hydroperoxide intermediates produced by insertion of dioxygen into the IBAL or MP enolyl radicals, followed by their reduction. Accordingly, EPR spin-trapping studies with 3,5-dibromo-4-nitrosobenzenesulfonic acid (DBNBS) and 2-methyl-2-nitrosopropane (MNP) revealed the intermediacy of carbon-centered radicals, as expected for one-electron abstraction from the enol forms of IBAL or MP by peroxynitrite. The EPR data obtained with IBAL also reveal formation of the isopropyl radical produced by competitive nucleophilic addition of ONOO(-) to IBAL, followed by homolytic cleavage of this adduct and beta-scission of the resulting Me(2)CHCH(O(-))O(*). Superstoichiometric formation of fragmentation products from IBAL or MP attests to the prevalence of an autoxidation chain reaction, here proposed to be initiated by one-electron abstraction by ONOO(-) from the substrate. This work reveals the potential role of peroxynitrite as a generator of electronically excited species that may contribute to deleterious and pathological processes associated with excessive nitric oxide and aldehyde production.

Annals of the Entomological Society of America, Apr 30, 1997

Seventeen Brazilian railroad-worm species in 8 genera (Phrixothrix, Stenophrixothrix, Mastinoceru... more Seventeen Brazilian railroad-worm species in 8 genera (Phrixothrix, Stenophrixothrix, Mastinocerus, Mastinomorphus, Taximastinocerus, Brasilocenis, Euryopa, Pseudophengodes) collected in southeastern and west central Brazil, near the Parque Nacional das Emas, were studied. The studied species generally inhabit pluvial tropical forests, but Mastinomorphus sp., was found in open marshy areas of west central cerrados. The life history of Brazilian phengodids resembles in many aspects that of the North American Zarhipis integripennis (LeConte). We detail here the life cycle of Mastinomorphus sp.) In larvae and in larviform females of the species studied, the bioluminescence ranges from yellow-green to red (A m . LX = 562-638 nm) for the head and from green to orange (A max = 535-592 nm) for the lateral lanterns. In adult males, the emission color varies from green to yellow (A max = 549-580 nm), except Euryopa spp., who emit orange light (A max = 592-598 nm). Luminescence was observed among all life stages of the species studied, in contrast to the North American Phengodini, whose adult males do not glow. Bioluminescence from the larval and female head lanterns may serve for illumination of the nearby environment, whereas the lateral lanterns of larvae and adult males and females seem to be important for self defense.

Quimica Nova, Dec 1, 2008

Free Radical Research, Nov 1, 2003

Aminoacetone (AA) is a threonine and glycine metabolite overproduced and recently implicated as a... more Aminoacetone (AA) is a threonine and glycine metabolite overproduced and recently implicated as a contributing source of methylglyoxal (MG) in conditions of ketosis. Oxidation of AA to MG, NH4+, and H2O2 has been reported to be catalyzed by a copper-dependent semicarbazide sensitive amine oxidase (SSAO) as well as by copper- and iron ion-catalyzed reactions with oxygen. We previously demonstrated that AA-generated O2*-. and enoyl radical (AA*) induce dose-dependent Fe(II) release from horse spleen ferritin (HoSF); no reaction occurs under nitrogen. In the present study we further explored the mechanism of iron release and the effect of AA on the ferritin apoprotein. Iron chelators such as EDTA, ATP and citrate, and phosphate accelerated AA-promoted iron release from HoSF, which was faster in horse spleen isoferritins containing larger amounts of phosphate in the core. Incubation of apoferritin with AA (2.5-50 mM, after 6 h) changes the apoprotein electrophoretic behavior, suggesting a structural modification of the apoprotein by AA-generated ROS. Superoxide dismutase (SOD) was able to partially protect apoferritin from structural modification whereas catalase, ethanol, and mannitol were ineffective in protection. Incubation of apoferritin with AA (1-10 mM) produced a dose-dependent decrease in tryptophan fluorescence (13-30%, after 5 h), and a partial depletion of protein thiols (29% after 24 h). The AA promoted damage to apoferritin produced a 40% decrease in apoprotein ferroxidase activity and an 80% decrease in its iron uptake ability. The current findings of changes in ferritin and apoferritin may contribute to intracellular iron-induced oxidative stress during AA formation in ketosis and diabetes mellitus.

Analytical Biochemistry, Jul 31, 1986

The present work describes an alternative technique for following the rate of oxygen uptake by ch... more The present work describes an alternative technique for following the rate of oxygen uptake by chemical and enzymatic systems. This method is based on spectrofluorometric monitoring of the well-known quenching effect of molecular oxygen on the emission of the photoexcited [Ru(bpy)3]2+ ion, added to the reaction mixtures. The rate of oxygen consumption determined using the present method agrees with that obtained by conventional polarographic techniques in all of the following systems: ascorbate/Cu2+, glucose/glucose oxidase (EC 1.1.3.4), and propanal/horseradish peroxidase (EC 1.11.1.7); in the last case, agreement was observed both in the presence and absence of serum albumin and of chloroplasts. Spectrofluorometric data for amphotericin autoxidation in dimethyl sulfoxide are in accord with the rate of decay of the ESR signal of a spin trap added to the reaction mixture. The advantages and limitations of the present spectrofluorometric technique relative to conventional polarographic monitoring of dissolved oxygen are discussed.

Free Radical Biol Med, 2011

Acetoacetate (AA) and 2-methylacetoacetate (MAA) are accumulated in metabolic disorders such as d... more Acetoacetate (AA) and 2-methylacetoacetate (MAA) are accumulated in metabolic disorders such as diabetes and isoleucinemia. Here we examine the mechanism of AA and MAA aerobic oxidation initiated by myoglobin (Mb)/H2O2. We propose a chemiluminescent route involving a dioxetanone intermediate whose thermolysis yields triplet α-dicarbonyl species (methylglyoxal and diacetyl). The observed ultraweak chemiluminescence increased linearly on raising the concentration of either Mb (10–500 μM) or AA (10–100 mM). Oxygen uptake studies revealed that MAA is almost a 100-fold more reactive than AA. EPR spin-trapping studies with MNP/MAA revealed the intermediacy of an α-carbon-centered radical and acetyl radical. The latter radical, probably derived from triplet diacetyl, is totally suppressed by sorbate, a well-known quencher of triplet carbonyls. Furthermore, an EPR signal assignable to MNP-AA• adduct was observed and confirmed by isotope effects. Oxygen consumption and α-dicarbonyl yield were shown to be dependent on AA or MAA concentrations (1–50 mM) and on H2O2 or tert-butOOH added to the Mb-containing reaction mixtures. That ferrylMb is involved in a peroxidase cycle acting on the substrates is suggested by the reaction pH profiles and immunospin-trapping experiments. The generation of radicals and triplet dicarbonyl products by Mb/H2O2/β-ketoacids may contribute to the adverse health effects of ketogenic unbalance.

Tetrahedron Asymmetry, 1999

Journal of Biological Chemistry