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  • 1
    Electronic Resource
    Electronic Resource
    Transformation of barbituric acid into alloxan by hydroxyl radicals: interaction with melatonin and with other hydroxyl radical scavengers (2002)
    Oxford, UK : Munksgaard International Publishers
    Journal of pineal research 33 (2002), S. 0 
    Details
    ISSN: 1600-079X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Barbituric acid (2,4,6-pyrimidinetrione) can be transformed by a non-enzymatic hydroxylation into alloxan (2,4,5,6-pyrimidinetetrone). This transformation can be used as a reaction indicating the formation of hydroxyl radicals (·OH). This conversion was detected using HPLC. Formation of ·OH was demonstrated by electron spin resonance (ESR) spectroscopy combined with spin-trapping techniques. It was shown that ·OH generated via the Fenton reaction abstracts first a hydrogen atom from barbituric acid (BA) and forms intermediately a paramagnetic derivative of BA. After a second attack by another ·OH, the BA radical is transformed into dialuric acid (DA), which autoxidizes via the alloxan radical (·ALX) to ALX. Superoxide radicals (·O2−) are formed during autoxidation of DA and ·ALX. They are able to regenerate ferrous ions. As a result, traces of iron salts are capable of catalyzing the conversion of large amounts of BA into ALX. Several scavengers of ·OH were tested with regard to their efficiency in preventing the transformation of BA into ALX. Of all the scavengers analyzed, melatonin was shown to be one of the most potent compounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1600-079X.2002.02936.x
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  • 2
    Electronic Resource
    Electronic Resource
    Alloxan acts as a prooxidant only under reducing conditions: influence of melatonin (1999)
    Springer
    Cellular and molecular life sciences 55 (1999), S. 487-493 
    Details
    ISSN: 1420-9071
    Keywords: Key words. Alloxan; free radicals; oxidative stress; diabetes; melatonin; antioxidant; prooxidant; lucigenin; NBT.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. Depending on the availability of suitable reducing agents, alloxan can be either a prooxidant or an antioxidant. Alloxan and its reduced derivative, dialuric acid, act as a redox couple, driven by reduced glutathione (GSH) or L-cysteine, generating in vitro in the presence of oxygen, both superoxide radical and hydrogen peroxide. The production of superoxide radicals was shown by the appearance of lucigenin chemiluminescence (CL) as well as by the generation of formazan from nitroblue tetrazolium (NBT). The lucigenin CL as well as the NBT reduction was inhibited by superoxide dismutase and partially by catalase. Melatonin inhibited alloxan-mediated CL. In contrast, in the absence of reducing agents, alloxan is a scavenger of superoxide radicals formed by other reactions. Because of the high content of reducing compounds in the cell (e.g. glutathione), it is suggested that alloxan acts in vivo mainly as a generator of reactive oxygen species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000180050305
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  • 3
    Electronic Resource
    Electronic Resource
    ‘Classical’ and ‘new’ diabetogens—comparison of their effects on isolated rat pancreatic islets in vitro (2000)
    Springer
    Cellular and molecular life sciences 57 (2000), S. 158-164 
    Details
    ISSN: 1420-9071
    Keywords: Key words. Alloxan; streptozotocin; xanthine oxidase/hypoxanthine; SNAP; reactive oxygen species.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. This study compares functional and morphological alterations caused by application of alloxan, streptozotocin, xanthine oxidase/hypoxanthine (generation of reactive oxygen species), or S-nitroso-N-acetyl-D,L-penicillamine (SNAP, liberation of nitric oxide) to isolated rat pancreatic islets in vitro. In perifusion experiments, membrane leakage—detected by non-stimulated insulin release—was found after application of all drugs, but showed a substance-specific time pattern. Twenty-four hours after application of the classical diabetogens (alloxan or streptozotocin), potassium chloride- and glucose-stimulated insulin secretion were markedly reduced, while a persistent reduction was observed neither after exposure to xanthine oxidase/hypoxanthine, nor to SNAP. Morphological analysis of the islets revealed that nearly all β-cells were destroyed following alloxan or streptozotocin treatment, while the majority of β-cells were configured regularly after application of xanthine oxidase/hypoxanthine or SNAP. Necrotic cells found after xanthine oxidase/hypoxanthine usually differed in morphology from those observed after application of the classical diabetogens. While the former cells were characterised by swollen nuclei, the latter had shrunken nuclei with irregular condensed chromatin. Apoptosis was found only following nitric oxide exposure. Due to these differences, it seems unlikely that alloxan, streptozotocin, xanthine oxidase/hypoxanthine, and nitric oxide have a common major feature in their toxic action.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000180050505
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    Paper (German National Licenses)
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