Reciprocal translocations in somatic and germ cells of mice chronically exposed by inhalation to ethylene oxide: implications for risk assessment

Abstract

Groups of male B6C3F1 mice were exposed by inhalation to 0, 25, 50, 100 or 200 p.p.m. ethylene oxide (EO) for up to 48 weeks (6 hours/day, 5 days/week). Animals were sacrificed at 6, 12, 24 and 48 weeks after the start of the exposure for analyses of reciprocal translocations in peripheral blood lymphocytes and germ cells. The frequency of the total chromosomal aberrations in the peripheral blood lymphocytes was significantly increased at the 100 and 200 p.p.m. exposure concentrations at the 12-week time point, at 50, 100 and 200 p.p.m. at the 24-week time point and at all EO concentrations at the 48-week time point. The frequency of stable reciprocal translocations, which can be used as biomarkers, was increased (P < 0.05) at 100 and 200 p.p.m. at the 12-week time point, at 100 and 200 p.p.m. at the 24-week time point and at 50, 100 and 200 p.p.m. at the 48-week time point. No statistically significant increase could be observed in translocation frequencies at the 6-week time point in the peripheral blood lymphocytes. The exposure-response curves were non-linear when the frequencies of translocations were plotted against EO exposure durations or against EO exposure concentrations. There was no effect of exposure concentration rate on reciprocal translocation frequency. Reciprocal translocations induced in spermatogonial stem cells (observed at the sprematocyte stage) showed significant increases in translocation frequencies over controls at all EO concentrations at 48 weeks. However, increases were small and they did not occur in a dose-responsive manner. The statistically significant increase observed at 12 weeks in the spermatocytes was equivocal. This study provides low-level chronic exposure somatic cytogenetic data generated in mice that can be used to support the shape of the tumour dose-response in rodents and humans The germ cell cytogenetic data are discussed in terms of its relevance for a threshold response for genetic effects at low exposures.

Dose and temporal evaluation of ethylene oxide‐induced mutagenicity in the lungs of male big blue mice following inhalation exposure to carcinogenic concentrations

“… If point mutations are arising secondary to other events, such as chromosome aberrations or reciprocal translocations, as suggested by the Donner et al [] data, that finding is consistent with the conclusion that EO does not initiate tumors via point mutations (since the other events happen first).…”

Comparison between two FISH techniques in the in vitro study of cytogenetic markers for low-dose X-ray exposure in human primary fibroblasts

“…Conversely the stable exchanges (i.e., balanced translocations), are maintained in the subsequent generations (Tucker and Luckinbill, 2011) and are detectable in the injured cell progeny even in case of highly-cycling cells, such as spermatogonial stem cells, for at least 1 year (Donner et al, 2010). Both stable and unstable aberrations can be markers of recent exposure, but only the stable ones can long report the chromosomal radio-induced damage (RID).…”

“…The lower sensitivity of the stable exchanges parameter (empirical and calculated threshold between 0.5 and 1 Gy) is rewarded by the fact that it shows potential as a retrospective reporter of exposures distant in time (Fucić et al, 2007; Donner et al, 2010). Note that this lower sensitivity is not due to a technique failure but to the X-ray damage induction mode: in this dose rage the exchange frequency seemed to be weak and approximately dependent on the square of the dose, and up to 0.5 Gy this kind of RID is negligible.…”

Chromosome translocations and assessing human exposure to adverse environmental agents

“…Similar results were seen in mice given cyclophosphamide or urethane [Director et al, 1998] in their drinking water; both of these agents are powerful clastogens. In contrast, inhalation of ethylene oxide was recently shown to induce translocations in peripheral blood and germ cells of mice [Donner et al, 2009]. This work led to the important realization, mentioned previously, that chemical clastogens are generally not potent inducers of translocations.…”

“…This stands in contrast to chemicals, where in vivo exposures to the well-known clastogens cyclophosphamide and ethyl carbamate (urethane), indicate that translocations are not readily formed even at doses that suppress bone marrow cell growth [Director et al, 1996[Director et al, , 1998]. However, recent work with ethylene oxide indicates that this chemical does induce translocations in peripheral blood lymphocytes and in spermatogonial stem cells following inhalation by mice [Donner et al, 2009], although the exposure-response curves in blood were nonlinear and the increases in germ cells were not dose responsive. The weak induction of translocations by chemicals may appear to be surprising in light of their wellestablished ability to induce single-strand chromosome breaks.…”