Ochratoxin A-Induced Mutagenesis in Mammalian Cells Is Consistent with the Production of Oxidative Stress

Abstract

Ochratoxin A (OTA) is a widespread mycotoxin in food and a powerful nephrocarcinogen in rats. The mutagenicity of OTA has been extensively investigated but with conflicting results, thus leaving open the mechanistic question for OTA carcinogenicity. Here, we examined the mutagenicity of OTA by using well-standardized mutation assays such as the hypoxanthine-guanine phosphoribosyltransferase (HPRT) assay in Chinese hamster V79 cells and the thymidine kinase assay in mouse lymphoma LY5178 cells. OTA-induced HPRT mutations were characterized at the molecular level. In V79 cells, OTA produced a dose- and time-related decrease in cell number as a consequence of the transitory cytostatic effect mediated by G2/M cell cycle arrest. In both mutation assays, OTA was weakly mutagenic and this effect was independent of biotransformation. OTA-induced mutations were characterized by point mutations (48%) and a lack of a detectable reverse-transcription polymerase chain reaction product (52%). The pattern of OTA-induced point mutations was similar to that of spontaneous mutants, suggesting that OTA induced an increase of the endogenous oxidative metabolism but not covalent DNA adducts. Our data support a model where OTA is mutagenic via oxidative DNA damage induction.

Role of Environmental Toxins in Endemic (Balkan) Nephropathy

“…5,9 Oxidative DNA damage may account for some or all of these harmful effects. 16 Evidence supporting an oxidative mechanism was presented by Fuchs and Peraica (Zagreb, Croatia), who reported that levels of malondialdehyde and protein carbonyl were increased in renal tissue of male rats treated with low dosages (5 ng/kg) of ochratoxin A. Marin-Kuan and Schilter (Lausanne, Switzerland) used gene expression profiling to demonstrate ochratoxin A-induced disruption of pathways regulated by the transcription factor Nrf2, thereby reducing cellular defenses against oxidative stress. They proposed that a network of interacting epigenetic mechanisms, including protein synthesis inhibition, oxidative stress, and the activation of specific cell signaling pathways, may be responsible for renal cell tumors in rats treated with ochratoxin A.…”

Ochratoxin A induces DNA damage and G2 phase arrest in human esophageal epithelium Het-1A cells <i>in vitro </i>

“…Several studies have demonstrated that OTA could induce DNA damage in rat and human kidney cells, V79 Chinese hamster lung fibroblasts, rat hepatocytes, and the Chinese hamster ovary fibroblast cells (Robbiano et al, 2004;Palma et al, 2007;Cavin et al, 2009;Kamp et al, 2005a;Cosimi et al, 2009). DNA damage can cause an alteration in the genomic structure and then lead to cell death or the occurrence of mutations involved in tumorigenesis (Levy et al, 2011).…”

Possible Carcinogenic Mechanisms Underlying Renal Carcinogens in Food

“…Gene mutations derived from double strand breaks (DSBs) arise during the repair process, and there are two major pathways that mediate DNA repair, non-homologous end joining (NHEJ) and homologous recombination repair (HR) [96][97][98] with HR being more effective than NHEJ in the late S and G 2 phases of the cell cycle 99,100) . OTA induces G 2 /M arrest and increases cell proliferation through another functional mechanism, thereby increasing the ratio of cells in the S/G 2 phase [101][102][103] . Quantitative PCR analysis of mRNA expression also demonstrated that genes related to G 2 /M arrest (Chek1 and Wee1) and S/G 2 phase (Ccna2 and Cdk1) were significantly increased by OTA treatment in a dose-dependent manner 73) .…”