Journal Article

SHORT COMMUNICATION: Time-Related introduction of DNA repair synthesis in rat hepatocytes following <i>in vivo</i> treatment with cyproterone acetate

P. Kasper and L. Mueller

in Carcinogenesis

Volume 17, issue 10, pages 2271-2274
Published in print October 1996 | ISSN: 0143-3334
Published online October 1996 | e-ISSN: 1460-2180 | DOI: http://dx.doi.org/10.1093/carcin/17.10.2271
SHORT COMMUNICATION: Time-Related introduction of DNA repair
                    synthesis in rat hepatocytes following in vivo treatment with
                    cyproterone acetate

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Cyproterone acetate (CPA), a synthetic steroid hormone widely used as a human pharmaceutical, has recently been shown to induce unscheduled DNA synthesis (UDS) in vitro in primary cultures of rat and human hepatocytes. In the present study CPA was evaluated for its ability to initiate UDS in the liver of female rats in vivo by means of the in vivo/in vitro hepatocyte DNA repair test. Using the standard sampling time of 16 h after single oral dosing, a dose-related UDS responce at >50 mg CPA/kg body wt was observed. In order to examine the time course of CPA induced UDS, different sampling times (4, 16, 48, 72, 96, and 144 h) after a single oral administration of 100 mg CPA/kg body wt were used. Whereas no UDS was induced in liver cells isolated 4 h after treatment, continuous DNA repair activity was observed after 16 h, with a maximum effect of ∼10 net nuclear grains on day 4 after dosing. After a post-application period of 6 days the net grain counts returned to near control level. In contrast to the data with CPA, DNA damage induced by the positive control compound 2-acetylaminofluorene was removed much faster, within 2 days after administration. The time course of UDS activity during the first 4 days after administration of CPA parallels the previously reported time course of DNA adduct formation. However, a subsequent decrease and final cessation of UDS on day 6 takes place, although significant levels of CPA-DNA adducts have been reported to occur at that time point in rat liver cells. Whereas the time-related onset of UDS is suggested to reflect the pharmacokinetics of the activation of CPA to DNA-reactive intermediates, it remains unclear why the excision repair of DNA adducts did not continue. In addition to DNA repair synthesis, CPA was also shown to clearly increase the incidence of S phase cells under the test conditions applied, conforming the known mitogenic potential of CPA in rat liver.

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Subjects: Clinical Cytogenetics and Molecular Genetics

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