Search PubMed⌕ Search

Biomedical subjects

S Pou

Publications and source records attributed to S Pou.

43 records · Page 3Linked to original sources
PubMed1989

Intracellular spin-trapping of oxygen-centered radicals generated by human neutrophils.

Phagocytosing neutrophils secrete superoxide into a vacuole generally inaccessible for direct study. However, the spin-trapping agent 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) enters the cytoplasm of several cell types where it can report free radical species including superoxide and hydroxyl radical. In the present study we employed a variety of experimental conditions to eliminate extracellular ESR signals and/or free radicals generated by stimulated neutrophils so that DMPO adducts reported events inside the cell. We identified a concentration of poly(ethylene glycol)-modified superoxide dismutase that permitted measurement of intracellular superoxide as determined by several criteria. It seems likely that poly(ethylene glycol)-modified superoxide dismutase is too large to enter the neutrophil phagosome. Under these conditions no hydroxyl radical was detected, as would be predicted from earlier studies with spin-trapping. Use of poly(ethylene glycol)-modified superoxide dismutase should allow on-line measurement of phagosomal events, thereby improving our understanding of microbicidal and inflammatory processes.

Cyclic N-Oxides↗
PubMed1989

Calcium chelator Quin 2 prevents hydrogen-peroxide-induced DNA breakage and cytotoxicity.

Exposure of cultured Chinese hamster ovary (CHO) cells to hydrogen peroxide results in the production of extensive DNA breakage which can be prevented by the intracellular calcium chelator Quin 2. This effect occurs at Quin 2 AM concentrations as low as 0.1 microM and is maximal at 1 microM. Addition of the extracellular calcium chelator, EGTA, does not affect the level of DNA breakage generated by H2O2. Quin 2 also significantly reduces cellular toxicity caused by the oxidant. Experiments with spin-trapping techniques demonstrate that Quin 2 does not affect the formation of hydroxyl radicals generated by the action of Fe2+ on H2O2. Quin 2 at high concentrations, similar to those reached within the cell, actually enhanced generation of hydroxyl radical in the absence of other iron chelators under our experimental conditions. These results suggest that H2O2 or H2O2-derived radicals do not directly induce DNA strand breakage in intact mammalian cells; rather, these radicals may disturb intracellular Ca2+ homeostasis which results in secondary reactions ultimately leading to DNA strand breakage. In addition to strand breakage, membrane and protein oxidation probably contribute to the cytotoxic effect of H2O2.

Aminoquinolines↗
PubMed1989

An electron spin resonance study of oxyradical generation in superoxide dismutase- and catalase-deficient mutants of Escherichia coli K-12.

The response of superoxide dismutase- and catalase-deficient strains of Escherichia coli to redox active compounds was examined by electron spin resonance. Levels of radicals formed in response to pyocyanine in situ were extremely low and were found to be predominantly extracellular, even in a strain completely deficient in both superoxide dismutase and catalase. In cell-free extracts of superoxide dismutase-minus strains incubated with NADPH and pyocyanine, the primary accumulating radical was the superoxide anion (O2-), although low levels of the hydroxyl radical (.OH) were also detected. In contrast, extracts from strains lacking catalase were found to accumulate higher levels of hydroxyl radicals.

Catalase↗
PubMed1987

Nitroxides as potential contrast enhancing agents for MRI application: influence of structure on the rate of reduction by rat hepatocytes, whole liver homogenate, subcellular fractions, and ascorbate.

With an eye toward the development of nitroxides as potential contrast enhancing agents for MRI applications, we have compared the rates of reduction of 24 nitroxides of diverse structures by rat whole liver homogenate, hepatocytes, subcellular fractions, and ascorbate (10 eq excess). Our results indicate that five-membered ring nitroxides and alpha-carboxy alpha-aryl tert-butyl nitroxides are significantly more resistant toward bioreduction than six-membered ring and heterocyclic-substituted nitroxides in all systems. In the case of six-membered ring nitroxides the presence of either negatively charged or positively charged groups increases the susceptibility toward ascorbate reduction. The presence of carboxylate groups tends to enhance the resistance of all the nitroxides toward reduction by liver homogenate, hepatocytes, and subcellular fractions. trans-Azethoxyl nitroxides exhibited the best overall resistance toward bioreduction. The T1 relaxants of selected nitroxides were measured and found to be similar.

Animals↗
PubMed1986

1,3-Di(2-[5-3H]tolyl)guanidine: a selective ligand that labels sigma-type receptors for psychotomimetic opiates and antipsychotic drugs.

Brain sigma-type receptors are thought to mediate hallucinogenic effects of certain benzomorphan opiates in humans. The biochemical characterization of sigma receptors has been difficult because of the lack of potent and selective ligands. We report here the synthesis and characterization of a tritiated, symmetrically substituted guanidine derivative, 1,3-di(2-[5-3H]tolyl)guanidine ([3H]Tol2Gdn), that binds with high affinity to a single population of binding sites in guinea pig brain membrane preparations. The [3H]Tol2Gdn binding site displays stereoselectivity for dextrorotatory optical isomers of benzomorphan opiates known to have sigma-type behavioral effects. Furthermore, the [3H]Tol2Gdn binding site has a high affinity for haloperidol and for phenothiazine antipsychotics, which have antihallucinatory properties in humans. The drug-selectivity profile of [3H]Tol2Gdn binding closely correlates with the drug-selectivity profile of tritiated (+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine [+)-[3H]3-PPP) binding to guinea pig brain membrane receptors. (+)-[3H]3-PPP has been proposed to be a selective sigma-receptor ligand [Largent, B. L., Gundlach, A. L. & Snyder, S. H. (1984) Proc. Natl. Acad. Sci. USA 82, 4983-4987]. Receptor autoradiography using [3H]Tol2Gdn on slide-mounted rat and guinea pig brain sections reveals a heterogeneous distribution pattern of enriched binding in limbic and sensorimotor structures of the brain. These results indicate that [3H]Tol2Gdn is a selective ligand for the sigma-site. Availability of this sigma-receptor probe should greatly facilitate the physiological, biochemical, and pharmacological characterization of sigma receptors in brain.

Animals↗
PubMed1985

Nitroxide-doped liposomes containing entrapped oxidant: an approach to the "reduction problem" of nitroxides as MRI contrast agents.

The purpose of this investigation is to test the feasibility of a nitroxide regeneration system involving liposomes as an approach toward solving the "reduction problem" when nitroxides are used as contrast enhancing agents in MRI applications. It is shown that the inclusion of an entrapped oxidant (K3Fe(CN)6) in the aqueous compartment of nitroxide-doped liposomes causes a 4-5-fold increase in the duration of the nitroxide ESR signal in the presence of the external reductant sodium ascorbate. Confirmation was obtained by monitoring the concentration of the internalized Fe(CN)6(3-) ion versus time by visible spectroscopy at 410 nm. Trans bilayer (flip-flop) motion of the long chain nitroxide ester is the likely mechanism of this nitroxide regeneration system.

Ascorbic Acid↗