Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.17.3.2 (xanthine oxidase)
 8,383 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In purified system zinc has been shown to have an antioxidant role. Its effects on the resistance of cultured cells towards oxidative stress in vitro were examined. Diploid human skin fibroblasts were grown for 21 d in culture media (RPMI 1640 containing 15% fetal calf serum) added with different zinc (Zn) concentrations (100, 125, and 150 microM as Zinc chlorur ZnCl2). In comparison, cell controls were grown in standard culture media (6.5 microM Zn). The intracellular zinc levels of treated fibroblasts increased from 3- to 7-fold (2330 +/- 120 ng/mg protein in 150-microM Zn-treated cells versus 331 +/- 21 ng/mg protein in control cells). The intracellular copper increased 3- fold whereas the iron content slightly but not significantly decreased. The index of basal lipid peroxidation measured as thiobarbituric acid reactants (TBARs) of zinc-supplemented cells was lower than that of non zinc supplemented controls (0.89 mumol/g protein in 150 microM Zn-treated cells versus 1.59 mumol/g protein in controls). At these high doses of zinc, fibroblasts expressed lower antioxidant metalloenzymes activities. Diminished TBARs in Zn treated cells tends to support that Zn acts protectively against free radical mediated damage. However when the cells were challenged with extracellular oxidant stresses mediated by hypoxanthine/xanthine oxidase or hydrogen peroxide (H2O2), an increased toxicity in Zn-supplemented cells was observed. When we applied an intracellular oxidative stress as UV-B or UV-A radiation, Zn-treated fibroblasts were more resistant than cells grown in normal medium. If Zn has shown antioxidant effect in some in vitro or in vivo systems our observations clearly demonstrate that this role is not mediated by antioxidant metalloenzymes.
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PMID:Effect of zinc supplementation on resistance of cultured human skin fibroblasts toward oxidant stress. 768 32

Methotrexate, an important agent in the treatment of childhood acute lymphoblastic leukaemia, has generally failed to induce dose-dependent cytotoxicity of patient-derived leukaemic blasts when tested in the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. This effect is apparently due to salvage from the medium, by surviving leukaemic cells, of metabolites such as hypoxanthine and thymidine. In an attempt to address this problem, we have examined the effect, on leukaemic cell populations, of enzymatically depleting these metabolites from the culture medium employed during the MTT assay, using xanthine oxidase and thymidine phosphorylase. Specifically we have assessed methotrexate cytotoxicity in the paediatric acute lymphoblastic T cell leukaemia, GKTL, which is maintained as a xenograft, and like primary leukaemias, has poor viability in vitro. Although little cytotoxicity of GKTL cells was observed when the MTT assay was performed in supplemented RPMI-1640 medium, dose-dependent cytotoxicity of these cells was clearly apparent when the same medium was enzymatically depleted. In contrast, the ID50 for methotrexate of control CCRF-CEM cells was unaltered in enzymatically depleted medium. In the absence of methotrexate, enzymatic depletion of the medium did not affect leukaemic cell survival. We are currently investigating the general applicability of this approach for assaying the response to methotrexate of primary leukaemia samples.
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PMID:Methotrexate cytotoxicity determination using the MTT assay following enzymatic depletion of thymidine and hypoxanthine. 844 66