Radioactive iodine induces clastogenic and age-dependent aneugenic effects in lymphocytes of thyroid cancer patients as revealed by interphase FISH

Mutagenesis vol.12 no.6 pp.449-455, 1997 Radioactive iodine induces clastogenic and age-dependent aneugenic effects in lymphocytes of thyroid cancer patients as revealed by interphase FISH MJ.Ramfrez1, J.Surralles1, P.GalofrS2, A.Creus1 and R.Marcos1>3 'Grup dc Mutagenesi, Departament de Genetica i de Microbiologia, Edifici Cn, Universitat Autbnoma de Barcelona, 08193 Bellaterra and 2Servei de Medicina Nuclear, Ciutat Sanitaria 1 Universitaria Vail d'Hebron, Pg. Vail d'Hebron 119, 08035 Barcelona, Spain Introduction One of the major consequences of the Chernobyl nuclear power plant accident has been a high increase in the incidence of thyroid cancer in exposed children from both Belarus (Kazakov et al, 1992) and Ukraine (Likhtarev et al, 1995), with over a 100-fold increased frequency in some heavily contaminated regions (Rytomaa, 1996). The severe health consequences of the Chernobyl radioactive accident have been directly linked to high exposure to radioactive iodine, mainly I3I I (Likhtarev et al, 1995). Thyroid cancer and hyperthyroidism patients are usually treated with radioactive iodine (Spencer et al, 1985; Farrar and Toft, 1991) and, therefore, they provide us with an unfortunate, but nevertheless unique, opportunity to study cytogenetic damage induced by known doses of 13II in exposed people. The treatment of thyroid cancer patients usually consists of [131I]sodium iodide given orally to eliminate remaining tumour cells after total thyroidectomy. Around 90% of the radiation effects are a result of P-radiation, which has a mean track length in soft tissues of ~0.4 mm (Searle, 1983). The physical characteristics of this radionuclide make extra- The X chromosome is preferentially prone to aneuploidy, above all in older women (Guttenbach et al, 1994; Hando etal, 1994; Richard etal, 1994; Cataldn etal, 1995; Surralle's et al, 1996a,b). This feature would make the X chromosome especially useful to monitor genotoxic effects induced by aneugens. FISH with an X chromosome centromere-specific probe allows easy and specific detection of aneuploidy events, circumventing most technical limitations of metaphase analysis (Eastmond et al, 1995; Surrall6s et al, 1996a). ^To whom correspondence should be addressed. Tel: +34 3 5812052; Fax: +34 3 5812387; Email: © UK Environmental Mutagen Society/Oxford University Press 1997 449 After the Chernobyl nuclear accident, a dramatic 131Irelated Increase in the incidence of thyroid cancer has been reported in exposed children. However, little is known about the eventual genotoxic effects of 131I in exposed humans. Thyroid cancer patients are usually treated with 131 I and, therefore, they provide us with an opportunity to study cytogenetic damage induced by known doses of this radionuclide. FISH techniques have been employed to study the origin of micronuclei as well as X chromosome nondisjunction and X chromosome numerical abnormalities in lymphocytes from 131I-treated women suffering from thyroid cancer. Blood was sampled before and 1 week after 131 I treatment Cells were analysed with either pancentromeric FISH to classify micronuclei or X chromosome centromere-specific FISH in mononucleated and binucleated cells to evaluate X chromosome numerical abnormalities and non-disjunction respectively. Our data indicate that 131I-induced clastogenic and age-dependent aneugenic effects in the lymphocytes of exposed patients. The X chromosome was not preferentially involved in the aneugenic effect induced by 131I. It is concluded that besides its major clastogenic effect, 131I can also induce an X chromosome-independent aneugenic activity mainly in patients with spontaneous proneness to chromosome loss. thyroidal radiation apparently minimal and restricted to yemissions, suggesting that side effects such as secondary neoplastic and non-neoplastic malignancies would not usually be expected. However, in a study conducted with 10 552 hyperthyroidism patients treated with 131I an increased risk for some tumours was reported (Hall et al, 1993). However, the results of other studies on cancer incidence after radioactive iodine treatment are contradictory (Hoffman 1984; Ron et al, 1984). It is widely accepted that increased levels of chromosomal aberrations are predictive of future cancer risk (Hagmar et al, 1994). A cytological consequence of chromosomal aberration induction is the formation of micronuclei (MN). MN are chromosomal fragments or whole chromosomes that are left behind during mitotic division and appear in the cytoplasm of daughter cells as small additional nuclei. However, the MN assay lacks specificity due to the heterogeneous cytogenetic origin of the end point analysed. To overcome this problem, fluorescence in situ hybridization (FISH) with probes labelling the centromeric region of all human chromosomes has been used to unravel the content of MN (Becker et al, 1990). This approach is based on the widely accepted assumption that MN harbouring acentric chromosomal fragments will not be labelled by the probe, whereas MN harbouring whole chromosomes will be positively labelled. Although pancentromeric labelling of MN has been extensively used in in vitro experiments, to our knowledge only few biomonitoring studies using this approach have been published (Surralles et al, 1997). FISH coupled to the MN assay allows a quick and reliable identification of both aneugenic and clastogenic agents. This is especially relevant in the case of exposure to radioactive iodine since, besides its major clastogenic effect, ionizing radiation can also induce aneuploidy in vivo (reviewed by Natarajan et al, 1996). However, MN induction through aneugenic activity only reflects chromosome loss at anaphase. This is a potential limitation of the MN assay, because mitotic non-disjunction appears to be the prevalent mechanism for in vitro aneuploidy induction by ionizing radiation (KirschVolders et al, 1996) and chemical spindle poisons (Zijno et al, 1996b; Ramirez et al, 1997). This limitation can be circumvented using FISH with chromosome-specific centromeric probes in binucleated cells induced with cytochalasin B, allowing detection of all aneuploidy-related events, including chromosome loss and non-disjunction (Zijno et al, 1994). MJ.Ramfrcz et aL Although the possible cytogenetic damage induced by therapeutic exposure to I31I might be not detectable after a period of 1 year (Guti6rrez et ah, 1995), several investigations reported increases in the frequency of MN in patients with thyroid cancer and hyperthyroidism after radioiodine treatment (Livingston et al, 1993; Catena et al, 1994; Wuttke et al., 1996; Gutierrez etal, 1997). In the present study we investigate the nature of this increase by means of either pancentomeric or X chromosome centromere-specific FISH in lymphocytes from young and older thyroid cancer patients sampled before and 1 week after 131I treatment. Materials and methods Lymphocyte cultures and slide preparation Bloo (...truncated)