Action of w-chloroacetophenon on several enzymes.
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Alcohol Oxidoreductases↗
Biomedical subjects
J A Castro
Publications and source records attributed to J A Castro.
Reactions of nifurtimox with critical sulfhydryl-containing biomolecules: their potential toxicological relevance.
Nifurtimox (Nfx) is a drug used in the treatment of Chagas' disease, an endemic parasitic disease from Latin American countries. It produces undesirable side-effects in patients, frequently forcing the treatment to be stopped. Its toxic mechanism is not fully understood. In this work we describe purely chemical reactions of Nfx with relevant cellular sulfhydryl (SH) compounds. The compounds tested were glutathione (GSH), cysteine (RSH), lipoic acid (LA) and coenzyme A (CoA). All reacted with Nfx to give nitrite (NO(-) (2)). The relative reaction rates were CoA>LA>GSH>RSH. In studies with GSH and RSH the formation of nitrite was accompanied by decreases in Nfx concentration and increases in the formation of a reaction product revealed by HPLC. We failed to show the presence of liver cytosolic GST (GSH transferase activity)-mediated formation of NO2- from Nfx. These NO(-) (2)-releasing processes occurred under in vivo conditions in Nfx-treated Sprague-Dawley male rats (240-260 g body weight) at a dose of 100 mg Nfx kg(-1) p.o. In urine samples NO(-) (2) excretion was accompanied by unchanged drug and two unidentified more polar metabolites detectable by HPLC. The Nfx reactions with critical SH from molecules such as GSH, RSH, LA and CoA, and potentially others containing SH residues (e.g. enzymes or structural proteins), might have toxicological relevance not only for the Nfx side-effects but also for the chemotherapeutic effects on Trypanosoma cruzi. In addition, Nfx reactions with GSH might be crucial in Nfx detoxification.
Animals↗
Hydroxyl and 1-hydroxyethyl free radical detection using spin traps followed by derivatization and gas chromatography-mass spectrometry.
Detection of hydroxyl free radicals is frequently performed by electron spin resonance (ESR) following spin trapping of the radical using 5,5-dimethylpyrroline N-oxide (DMPO) to generate a stable free radical having a characteristic ESR spectrum. The necessary ESR equipment is expensive and not readily available to many laboratories. In the present study, a specific and sensitive gas chromatography-mass spectrometry (GC/MS) method for detection of hydroxyl and hydroxyethyl free radicals is described. The DMPO or N-t-butyl-alpha-phenylnitrone (PBN) radical adducts are extracted and derivatized by trimethylsylilation and analyzed by GC/MS. To standardize the method, .OH and 1-hydroxyethyl radicals were generated in two different systems: 1) a Fenton reaction in a pure chemical system in the absence or presence of ethanol and 2) in liver microsomal suspensions where ethanol is metabolized in the presence of NADPH. In the Fenton system both radicals were easily detected and specifically identified using DMPO or PBN. In microsomal suspensions DMPO proved better for detection of .OH radicals and PBN more suitable for detection of 1-hydroxyethyl radicals. The procedure is specific, sensitive and potentially as useful as ESR.
Cyclic N-Oxides↗
Prevention of benznidazole-induced prolonging effect on the pentobarbital sleeping time of rats using different thiol-containing compounds.
Benznidazole (BZ) is a nitroimidazolic chemotherapeutic agent employed against the acute and indeterminate phase of Chagas' disease, a tropical sickness afflicting more than twenty million people in Latin America. BZ has serious toxic side effects forcing people to stop treatment. These effects were attributed to the nitroreductive metabolic activation of BZ to a hydronitroxide radical or the hydroxylamine, which would covalently bind to cellular components. One of these deleterious effects is the prolongation on the pentobarbital sleeping time of rats. This results from the covalent binding of BZ reactive metabolites, arisen during its nitroreductive metabolism, to the phospholipid component of the mixed function oxidase which biotransform the barbiturate. In this study, the potential ability of different thiol containing drugs to trap BZ reactive metabolites and to prevent BZ effect on the pentobarbital sleeping time was tested. Our HPLC studies evidenced that cysteine, N-acetylcysteine, penicillamine and glutathione were able to trap BZ reactive metabolites in vitro to produce one or two adducts. Reduced lipoic acid instead, decreased the intensity of the nitroreductive process without leading to detectable adducts. The in vivo administration of the thiol drugs, at dosage regimes available in literature, was able to markedly prevent the BZ prolongation effect on the sleeping time. Whether these thiols might prevent other BZ toxic effects without harming its chemotherapeutic actions remains to be established.
Animals↗
Induction of rat liver drug-metabolizing enzymes by promethazine.
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Aniline Hydroxylase↗
Dithiothreitol tetraacetate S-acetyl esterase activity in blood and in different tissues of male rats.
Dithiothreitol is known to be effective in vitro to prevent or even revert effects of oxidative stress and radiation in biological systems. However, its use in in vivo conditions has been hampered by its chemical instability and toxicity. Dithiothreitol tetraacetate is stable and less toxic than dithiothreitol. In this work, GLC-MS evidence is presented that dithiothreitol tetraacetate is hydrolyzed in vivo to give dithiothreitol. The activity of a dithiothreitol tetraacetate thiol esterase in blood and in different organs was determined and found to be: small intestine >> liver > pancreas >> testes approximately kidney > or = brain approximately adrenals approximately bone marrow approximately colon approximately lung > plasma approximately heart > total blood. These results suggest that dithiothreitol tetraacetate might be a suitable source of more stable and less toxic dithiothreitol in vivo, and that its production is due to an hydrolytic process requiring a dithiothreitol tetraacetate thiol esterase present in different organs and in blood.
Acetylesterase↗