RESUMEN
In the present work we aimed to standardise the alkaline comet assay with erythrocytes of the cyprinodont, Mediterranean Killifish, Aphanius fasciatus. The aims of the study were to explore the suitability of this fish to assess biomarkers of genotoxic effects and as a sentinel organism to detect complex genotoxic mixtures in coastal lagoon ecosystems. Following proper optimisation, the application and effectiveness of the comet assay in erythrocytes of A. fasciatus were tested by measuring the tail DNA (%) induced by (a) in vivo exposure of individual fish to X-rays (dose, 3Gy) and (b) following in vitro challenge of erythrocytes with restriction endonucleases Fok-I and Eco-RI, which selectively induce double-strand breaks with cohesive and blunt termini, respectively. Furthermore, in order to evaluate whether circulating fish blood contained actively proliferating cells that could influence the extent of DNA damage in control (untreated) fish, we measured the number of "comets" positive for 5-bromo-2'-deoxyuridine (BrdU) by the use of anti-BrdU antibody and immuno-histochemical methods. Both treatments (i.e. with X-rays and restriction endonucleases) induced statistically significant increases in tail DNA (%) values compared with the relevant untreated controls, indicating the effectiveness of the comet assay in the erythrocytes of A. fasciatus to detect different types of DNA lesions. Results from anti-BrdU antibody labelling of erythrocytes indicated a very low percentage (5%) of "comets" positive for BrdU. Following optimisation and validation of the assay under laboratory conditions, fish were collected in the Orbetello lagoon (Tuscany, Italy), considered to be a significantly polluted site. The results showed statistically significant increases for tail DNA (%) compared with corresponding values observed in erythrocytes of fish caught in the unpolluted reference site "Saline di Tarquinia". The effects of physico-chemical parameters of the water (i.e., salinity, pH and oxygen content) did not significantly influence the induction of DNA damage. These results indicate that the comet assay provides a reliable parameter and that A. fasciatus is a promising "sentinel organism" to detect the genotoxic impact of complex mixtures in coastal lagoon ecosystems.
Asunto(s)
Ensayo Cometa/métodos , Peces Killi , Contaminantes Químicos del Agua/toxicidad , Animales , Mezclas Complejas/toxicidad , Daño del ADN/efectos de los fármacos , Daño del ADN/efectos de la radiación , Ecosistema , Eritrocitos , Italia , Peces Killi/genéticaRESUMEN
Ochratoxin A (OTA) is a widespread mycotoxin of cereals and many agricultural products and causes high incidences of renal tumors in rodents. Although its carcinogenic properties have been known since the eighties, the precise mechanism of action is still relatively undefined. At present, increasing evidence suggests that OTA does not act with a direct genotoxic mechanism, opposed to other previous evidence where the formation of DNA adducts by 32P-postlabeling was observed. The genotoxic activity of OTA assessed in a variety of in vitro and in vivo studies was very low if genotoxic at all. In this study, we clearly show that OTA does not bear any clastogenic or aneugenic activity based on the absence of the induction of chromosome aberrations, sister chromatid exchanges, and micronuclei in human lymphocytes and V79 cells in vitro in both the absence and the presence of S9 metabolism. Alternatively, cytogenetic analyses evidenced significant increases in endoreduplicated cells and highly condensed metaphases with separated chromatids. This implies that OTA or its possible metabolites do not covalently bind DNA through the formation of adducts since structural chromosome aberrations are a very sensitive end points to detect chemical carcinogens with electrophilic substituents. Alternatively, induction of endoreduplication and chromatid separation provides strong evidence for a DNA nonreactive mechanism of OTA carcinogenicity involving the disruption of mitosis by interfering with key regulators of chromosome separation and progression of mitosis. This causes a temporary arrest of mitoses and premature exit from it (mitotic slippage) to generate endoreduplication and polyploidy accompanied by increased risk of aneuploidy and subsequent tumor formation.