http://http://dspace.unitus.it:80 The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. 2013-05-22T23:08:30Z http://hdl.handle.net/2067/1346 Title: In vitro cytogenetic results supporting a DNA nonreactive mechanism for ochratoxin A, potentially relevant for its carcinogenicity Authors: Mosesso, Pasquale; Cinelli, Serena; Piñero, Joaquin; Bellacima, Raffaela; Pepe, Gaetano Abstract: 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. Description: The present paper is dedicated to Prof. A. T. Natarajan on the occasion of his 80th birthday.; L'articolo è disponibile sul sito dell'editore: http://pubs.acs.org/ 2007-12-31T23:00:00Z http://hdl.handle.net/2067/1348 Title: Relationship between chromatin structure, DNA damage and repair following X-irradiation of human lymphocytes Authors: Mosesso, Pasquale; Palitti, Fabrizio; Pepe, Gaetano; Piñero, Joaquin; Bellacima, Raffaela; Ahnström, Gunnar; Natarajan, Adayapalam T. Abstract: Earlier studies using the technique of premature chromosome condensation (PCC) have shown that in human lymphocytes, exchange type of aberrations are formed immediately following low doses (<2 Gy) of X-rays, whereas at higher doses these aberrations increase with the duration of recovery. This reflects the relative roles of slow and fast repair in the formation of exchange aberrations. The underlying basis for slow and fast repairing components of the DNA repair may be related to differential localization of the initial damage in the genome, i.e., between relaxed and condensed chromatin. We have tried to gain some insight into this problem by (a) X-irradiating lymphocytes in the presence of dimethyl sulfoxide (DMSO) a potent scavenger of radiation-induced .OH radicals followed by PCC and (b) probing the damage and repair in two specific chromosomes, 18 and 19, which are relatively poor and rich in transcribing genes by COMET-FISH, a combination of Comet assay and fluorescence in situ hybridization (FISH) techniques. Results obtained show (a) that both fast appearing and slowly formed exchange aberrations seem to take place in relaxed chromatin, since they are affected to a similar extent by DMSO, (b) significant differential DNA breakage of chromosome 18 compared to chromosome 19 in both G0 and G1 phases of the cell cycle as detected by Comet assay, indicating that relaxed chromatin containing high densities of transcriptionally active genes shows less fragmentation due to fast repair (chromosome 19) compared to chromosome 18, and (c) that relaxed chromatin is repaired or mis-repaired faster than more compact chromatin Description: L'articolo é disponibile sul sito dell'editore: http://www.sciencedirect.com 2009-12-31T23:00:00Z