title: Selective ascorbate toxicity in malignant mesothelioma: a redox Trojan mechanism.
abstract: We studied the mechanism of ascorbate toxicity in malignant mesothelioma (MMe) cells. Neutral red uptake showed that ascorbate, but not dehydroascorbate, was highly toxic in the MMe cell lines REN and MM98, and less toxic in immortalized (human mesothelial cells-htert) and primary mesothelial cells. Ascorbate transport inhibitors phloretin, sodium azide, and ouabain did not reduce ascorbate toxicity. Ascorbate promoted the formation of H(2)O(2) in the cell medium, and its toxicity was suppressed by extracellular catalase, but the concentration of endogenous catalase was higher in MMe cells than in normal cells. The confocal imaging of cells loaded with the dihydrhodamine 123 reactive oxygen species probe showed that ascorbate caused a strong increase of rhodamine fluorescence in MMe cells, but not in mesothelial cells. MMe cells showed a higher production of superoxide and NADPH oxidase (NOX)4 expression than did mesothelial cells. Two inhibitors of cellular superoxide sources (apocynin and rotenone) reduced ascorbate toxicity and the ascorbate-induced rise in rhodamine fluorescence. NOX4 small interfering RNA also reduced ascorbate toxicity in REN cells. Taken together, the data indicate that ascorbate-induced extracellular H(2)O(2) production induces a strong oxidative stress in MMe cells because of their high rate of superoxide production. This explains the selective toxicity of ascorbate in MMe cells, and suggests its possible use in the clinical treatment of malignant mesothelioma.
authors.affiliation: Department of Environment and Life Sciences, DiSAV, University of Piemonte Orientale Amedeo Avogadro, Viale T. Michel 11, Alessandria, Italy. ranzato@mfn.unipmn.it
authors.forename: Elia
authors.initials: E
authors.lastname: Ranzato
authors.forename: Stefano
authors.initials: S
authors.lastname: Biffo
authors.forename: Bruno
authors.initials: B
authors.lastname: Burlando
mesh_terms: D000970:Antineoplastic Agents / Q000378:metabolism / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D001205:Ascorbic Acid / Q000378:metabolism / Q000494:pharmacology*; D002374:Catalase / Q000378:metabolism; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D051272:Glucose Transporter Type 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D020128:Inhibitory Concentration 50; D008654:Mesothelioma / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D018613:Microscopy, Confocal; D009154:Mutation; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases / Q000235:genetics / Q000378:metabolism; D009336:Necrosis; D029363:Organic Anion Transporters, Sodium-Dependent / Q000037:antagonists & inhibitors / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000187:drug effects*; D010693:Phloretin / Q000494:pharmacology; D034622:RNA Interference; D019810:Sodium Azide / Q000494:pharmacology; D013481:Superoxides / Q000378:metabolism; D027981:Symporters / Q000037:antagonists & inhibitors / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D051272:Glucose Transporter Type 1; D029363:Organic Anion Transporters, Sodium-Dependent; C495677:SLC2A1 protein, human; D027981:Symporters; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D013481:Superoxides; D010042:Ouabain; D019810:Sodium Azide; D006861:Hydrogen Peroxide; D002374:Catalase; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases; C498910:NOX4 protein, human; D001205:Ascorbic Acid; D010693:Phloretin