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Type: Journal article
Title: Cylindrospermopsin genotoxicity and cytotoxicity: Role of cytochrome P-450 and oxidative stress
Author: Humpage, A.
Fontaine, F.
Froscio, S.
Burcham, P.
Falconer, I.
Citation: Journal of Toxicology and Environmental Health Part A: Current Issues, 2005; 68(9):739-753
Publisher: Taylor & Francis Ltd
Issue Date: 2005
ISSN: 1528-7394
Abstract: Cylindrospermopsin (CYN) is a cyanobacterial toxin found in drinking-water sources world wide. It was the likely cause of human poisonings in Australia and possibly Brazil. Although CYN itself is a potent protein synthesis inhibitor, its acute toxicity appears to be mediated by cytochrome p-450 (CYP450)-generated metabolites. CYN also induces genotoxic effects both in vitro and in vivo, and preliminary evidence suggests that tumors are generated by oral exposure to CYN. To understand the role of CYP450-activated CYN metabolites on in vitro genotoxicity, this study quantified the process in primary mouse hepatocytes using the COMET assay in both the presence and absence of CYP450 inhibitors known to block acute CYN cytotoxicity. CYN was cytotoxic at concentrations above 0.1 microM (EC50 = 0.5 microM) but produced significant increases in Comet tail length, area, and tail moment at 0.05 microM and above; hence genotoxicity is unlikely to be secondary to metabolic disruption due to toxicity. The CYP450 inhibitors omeprazole (100 microM) and SKF525A (50 microM) completely inhibited the genotoxicity induced by CYN. The toxin also inhibits production of glutathione (GSH), a finding confirmed in this study. This could potentiate cytotoxicity, and by implication genotoxicity, via reduced reactive oxygen species (ROS) quenching. The lipid peroxidation marker, malondialdehyde (MDA) was quantified in CYN-treated cells, and the effect of the reduced glutathione (GSSG) reductase (GSSG-rd.) inhibitor 1,3-bis(chloroethyl)-l-nitrosourea (BCNU) on both MDA production and lactate dehydrogenase (LDH) leakage was examined. MDA levels were not elevated by CYN treatment, and block of GSH regeneration by BCNU did not affect lipid peroxidation or cytotoxicity. It therefore seems likely that CYP450-derived metabolites are responsible for both the acute cytotoxicity and genotoxicity induced by CYN.
Keywords: Hepatocytes
Reactive Oxygen Species
Cytochrome P-450 Enzyme System
Bacterial Toxins
Comet Assay
Mutagenicity Tests
Lipid Peroxidation
Oxidative Stress
Cytochrome P-450 Enzyme Inhibitors
Cyanobacteria Toxins
DOI: 10.1080/15287390590925465
Appears in Collections:Aurora harvest 6
Environment Institute publications
Pharmacology publications

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