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Biomedical subjects

M Kuwabara

Publications and source records attributed to M Kuwabara.

At least 253 records · Page 14Linked to original sources
PubMed1984

Identification of bile alcohols in urine from healthy humans.

Bile alcohols present in urine from healthy adults were studied. Urine was extracted with octadecylsilane-bonded silica gel, and a neutral fraction and a glucuronide fraction were isolated by ion exchange chromatography on piperidinohydroxypropyl Sephadex LH-20. Following hydrolysis of the glucuronide fraction with beta-glucuronidase and purification by silica gel column chromatography, the bile alcohols were analyzed by a combined gas-liquid chromatography-mass spectrometry. By direct comparison with reference standards, the structures of four major bile alcohols were elucidated as follows: 27-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,24,25- pentol ; 5 beta-cholestane-3 alpha,7 alpha,12 alpha,24, 25- pentol ; 5 beta-cholestane-3 alpha,7 alpha,12 alpha,25,26- pentol ; and 5 beta-cholestane-3 alpha,7 alpha,12 alpha,26,27- pentol . The daily excretion of these four bile alcohols in urine was 0.5-1.0 mumoles. After purification by silica gel column chromatography, the neutral fraction was analyzed by a combined gas-liquid chromatography-mass spectrometry. The major bile alcohol excreted in urine as the unconjugated form was 27-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,24,25- pentol . The daily excretion of the unconjugated C26 pentol (0.02-0.05 mumoles) was far lower than that of the conjugated C26 pentol (0.34-0.86 mumoles).

Adult↗
PubMed1983

Reactions of the hydrated electron with pyrimidine nucleosides halogenated at the sugar moiety: e.s.r. and spin-trapping with 2-methyl-2-nitrosopropane.

Free radicals produced by the reactions of hydrated electrons with pyrimidine nucleosides halogenated at the sugar moiety (2'-chloro-2'-deoxyuridine and 2'-chlorothymidine) were studied by e.s.r. and spin-trapping. 2-Methyl-2-nitrosopropane was used as the spin-trap. The usual spin-trapping technique was extended to frozen and deoxygenated systems to avoid contamination of the trapped radicals with side-products by spin-trapping 2-methyl-2-nitrosopropane itself. When this method was applied to 2'-chloro-2'-deoxyuridine, a free radical at the C-2' position of the sugar moiety was spin-trapped together with a free radical at the C-5 position of the base moiety. This indicates that hydrated electrons both add to the base moiety and eliminate halogen anions from the halogenated sugar moiety. In the case of 2'-chlorothymidine, however, only a free radical attributed to H-addition at the C-6 position of the thymine base was observed. No radicals produced by the reaction of hydrated electrons with the halogenated sugar could be spin-trapped.

Deoxyuridine↗
PubMed1982

E.S.R. of spin-trapped radicals in aqueous solutions of pyrimidine nucleosides and nucleotides. Reactions of the hydroxyl radical.

Free radicals produced by the reactions of OH radicals with ribose phosphates, pyrimidine nucleosides and nucleotides in aqueous solutions have been investigated by e.s.r. and spin-trapping techniques. OH radicals were generated by U.V. -photolysis of hydrogen peroxide and short-lived free radicals of the samples were spin-trapped by t-nitrosobutane and identified by e.s.r. spectroscopy. For ribose-5'-phosphate and 2' -deoxyribose-5' -phosphate, e.s.r. spectra observed consisted mainly of singles due to -C(5')H2 radicals which were initiated by H-abstraction from the sugar at the C-4' position and formed by the radical transfer to the C-5' position. It has also been shown that OH radicals abstract a hydrogen atom from the sugar at C-1' and C-5' positions. For cytidine, deoxycytidine, 5'-CMP, 3' -CMP and 5' -dCMP, four radicals have been observed and for uridine, deoxyuridine, 5' -UMP, 3' -UMP and 5' -dUMP, the existence of at least three radical species have been established. In contrast to the case of ribose phosphates, no signals due to -C(5')H2 radicals were detected for pyrimidine nucleosides and nucleotides. The results are discussed in relation to a recent mechanism which described OH-induced strand breaks of DNA.

Electron Spin Resonance Spectroscopy↗
PubMed1981

E.S.R. of spin-trapped radicals in gamma-irradiated polycrystalline nucleic acid constituents and their halogenated derivatives.

Free radicals in gamma-irradiated polycrystalline nucleic acid constituents and their 5-halogenated derivatives have been studied by e.s.r. and spin-trapping. After gamma-irradiation at room temperature, the polycrystalline samples were dissolved in aqueous solutions of t-nitrosobutane (tNB) in the absence or presence of oxygen. For many of the nucleic acid constituents, two types of radicals, -C(5)RH-C(6)H- and -C(5)R-C(6)H2-, formed by H-addition to the double bond [-C(5)R=C(6)H-] of the base, were observed, where R is -CH3 or -H. In addition, radicals formed on the sugar moiety were found for some nucleosides. When oxygen was present in the tNB solution, the relative stability of trapped radicals was changed, and thus the presence of more than one radical species could be established. For halogenated bases, the radical produced by H-abstraction from N(1) was observed, and an additional radical species formed by H-addition to the C(6) position was found for 5-fluorouracil. For halogenated nucleosides, the same spectrum was observed in all compounds except the 5-fluoroderivatives, and was assigned to the radicals produced on the sugar moiety. For 5-fluorodeoxyuridine and 5-fluorouridine, the radical formed by H-addition to the C(6) position of the base was observed. In general, the present results are in good agreement with those of previous single crystal studies, but in the case of halogenated compounds other than the 5-fluoroderivatives, it was not possible to spin-trap the alpha-halo radicals which were the most prominent radicals formed from gamma-irradiation of single crystals at room temperature.

Cobalt Radioisotopes↗
PubMed1981

E.S.R. of spin-trapped radicals in aqueous solutions of 5-halo derivatives of nucleic acid constituents: reactions of hydrated electrons, hydroxyl radicals and U.V. photolysis.

In order to obtain information concerning the mechanism of radio- and photosensitization due to 5-halogen substituted nucleic acid constituents, the free radicals produced in iodo-, bromo-, chloro- and fluoro-derivatives of uracil, uridine and deoxyuridine by reaction with hydrated electrons and with hydroxyl radicals and by direct U.V. photolysis have been studied by e.s.r. and spin-trapping. t-Nitrosobutane was used as the spin-trap. From 5-halogenated bases (except 5-fluorouracil) U.V. photolysis and reactions with hydrated electrons produced the uracilyl radical which was subsequently spin-trapped. When hydroxyl radical reactions were studied, the free radical at the N(1) position of the base was identified. From 5-fluorouracil U.V. photolysis generated the alpha-halo radical at the C(5) position of the base. For 5-halogenated ribonucleosides and deoxyribonucleosides, free radicals located on the sugar moiety were observed for reactions with hydrated electrons, hydroxyl radicals and for U.V. photolysis. The implications of these results for understanding the mechanism of radio- and photosensitization by 5-halogenated nucleic acids are discussed.

Electron Spin Resonance Spectroscopy↗