Drugs online research references
Pharmacology. 1995 Feb;50(2):111-18.
Inhibitory action of hydrogen peroxide on a high-resistance epithelium.
Alarcon JM, Quevedo L, Reyes P.
Department of Physiological Sciences, Faculty of Biological Sciences, University of Concepcion, Chile.
The present study describes the action of H2O2 on active transporting epithelium, and the partial blockade of this action by antioxidants. The addition of increasing concentrations of H2O2 (0.80; 8.0 and 24.0 mmol/l) to the mucosal surface of isolated toad skin causes an irreversible and dose-dependent inhibition of the short circuit current (SCC) and potential difference (PD). Quantitative determination of the parameters of the electrical equivalent circuit of the skin, by means of Isaacson's amiloride test, shows that the most affected parameters were the SCC, PD and shunt conductance. When the skins were preincubated with mannitol and vitamin E, the inhibition elicited by H2O2 was partially blocked; on the other hand, when the skins were preincubated with superoxide dismutase or allopurinol, this inhibition remains unchanged. The thiobarbituric acid method was used as an indirect quantification of lipid peroxidation. The inhibitory action of H2O2 in terms of the equivalent electrical circuit and the parallel production of lipid peroxidation points to free-radical formation. Furthermore, the significant blockade of this action by some enzymatic antioxidants is in agreement with this hypothesis.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7716174&dopt=Abstract
J Dermatol Sci. 1997 Mar;14(3):207-16.
Increased generation of hydrogen peroxide possibly from mitochondrial respiratory chain after UVB irradiation of murine fibroblasts.
Masaki H, Sakurai H.
Shiga Central Laboratories, Noevir Co., Ltd., Japan.
The purpose of this study is to detect the generation of active oxygens in UVB-irradiated murine fibroblasts and to propose new mechanisms. Decreased survival of fibroblasts under UVB irradiation was partially recovered by addition of catalase, DMSO or deferoxamine, suggesting the contribution of several types of active oxygen species. Then we examined the formation of active oxygen species and found that fibroblasts under UVB irradiation generated superoxide anion radicals (.O2-), intracellular H2O2, and hydroxyl radicals as estimated by the ESR-spin trapping method. Addition of thenoyltrifluoroacetone, which is an inhibitor of the mitochondrial respiratory chain, decreased 29% of the intracellular H2O2 levels in UVB-irradiated cells, but allopurinol, which is an inhibitor of xanthine oxidase, had no effect on them. On the basis of these results, we propose a a possible mechanism for damage of murine fibroblasts exposed to UVB in terms of generation of active oxygen species. The mitochondrial respiratory chain reaction stimulated by UVB irradiation enhances the generation of .O2-, which is in turn dismutated to H2O2 and O2 by superoxide dismutase. H2O2 is then converted to hydroxyl radicals, catalyzed by trace elements such as iron, as suggested by Fenton-like reaction. Thus, hydroxyl radicals with higher reaction rate-constants than those of other active oxygen species to biomolecules are indicated to be responsible for the cytotoxicity in cells under UV irradiation.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9138478&dopt=Abstract
Acta Biochim Pol. 1984;31(1):161-72.
Unusual hypoxanthine hydroxylation system in hepatopancreas of Helix pomatia (Gastropoda).
Jezewska MM, Kaminski ZW.
The enzymatic system in hepatopancreas of H. pomatia (terrestrial purinotelic gastropod) hydroxylates hypoxanthine to xanthine and uric acid but fails to hydroxylate adenine, nicotinic acid and 3-methyl-6- hydroxypurine ; allopurinol is hydroxylated to oxypurinol 7 times faster than hypoxanthine to xanthine; at concentration of 10(-6) M it inhibits hydroxylation of hypoxanthine by 55%. Two protein fractions [precipitated at 0-0.30 (I) and 0.30-0.45 (II) saturation with (NH4)2 SO4] hydroxylate hypoxanthine with NAD+ as a cosubstrate but only fraction I, predominating during the active life, hydroxylates also xanthine and is inhibited by NADH. Protein fraction II, dominant during winter sleep, does not hydroxylate xanthine and its hypoxanthine-hydroxylating activity is not inhibited by NADH. The latter property may enable continuous operation of the protein catabolic pathway under anaerobiosis.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=6547015&dopt=Abstract
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