An investigation of male-mediated F1 effects in mice treated acutely and sub-chronically with urethane

Abstract

In order to investigate the alleged potential of paternally administered urethane to cause foetal abnormalities and heritable tumours, male CD‐1 mice were treated with urethane, either acutely by intraperitoneal injection at doses of 1.25 and 1.75 g/kg bodyweight (bwt) or sub‐chronically in the drinking water at 1.25 for 10 weeks and 3.75 mg/ml for 9 weeks or vehicle for the control groups. They were mated to untreated females 1 week later. Uterine contents of half the pregnant females were examined just before full term, while the remaining females were allowed to deliver their litters. The resulting F1 offspring were observed for approximately 18 months and 12 months for acute and sub‐chronic exposures respectively and subjected to necropsy examination. Some of the mice treated acutely with 1.75 g/kg bwt exhibited partial infertility but none of those treated with 1.25 g/kg bwt had an adverse effect on their reproductive ability. There was no genetic effect of acute urethane treatment on male germ cells as indicated by dominant lethality. After birth, there was an increase (P <0.05) in post‐implantation deaths possibly due to perinatal mortality. There was an increased incidence and earlier onset of liver tumours induced in F1 male offspring from Fo males treated with 1.75 g/kg bwt, (20.7% vs. 10.1%, P=0.026) but not in the female offspring. F1 males from both treatment groups had mean bodyweights significantly higher than controls (P <0.01). Some males from each dose group of the acute study were examined using the restriction site mutation assay involving analysis of exon sequences. No mutations were identified in testes, liver or spleen of DNA isolated from the urethane‐treated animals. No reproductive or genetic effects were seen with sub‐chronic treatment at either 1.25 or 3.75 mg/ml urethane nor was there any predisposition of F1 animals to tumours although observation times were shorter. Teratogenesis Carcinog. Mutagen. 19:87–103, 1999. © 1999 Wiley‐Liss, Inc.

Male-mediated developmental toxicity

“…48 However, for urethane, there were negative results for dominant lethality and congenital malformations after subchronic exposure in the drinking water, although an increase in tumors in males was observed after acute intraperitoneal treatment. 49 A Japanese study in ICR mice after acute intraperitoneal treatment also reported negative results for dominant lethal mutations, confirming results by other workers, but demonstrated an increase in congenital malformations, tumors in the F1 generation and transmitted tumors in the F2 and F3 generations. 50 It is assumed that such effects outlined above have been produced as a result of alterations induced in the male germ cells because of their heritability through the generations.…”

“…By using this type of study design, we have examined the following compounds using chronic and acute exposure: cyclophosphamide, 1,3-butadiene and urethane (ethyl carbamate) ( Table 1). [42][43][44][45][46][47][48][49] Cyclophosphamide was positive for all endpoints in the rat after chronic gavage exposure. 43,44 This effect has also been shown by others 45 and led to the belief that chronic exposure might be a more realistic model than acute exposure, as man is chronically exposed in the workplace and environmentally.…”

“…[102][103][104] Ethnicities and the associated different dietary and cultural habits can affect congenital anomaly rates. 105 The large animal studies of the 1980s and 1990s demonstrated that damage could be transmitted through the father to both the first [42][43][44][46][47][48][49] and second generation. 50 It was originally assumed that this transmission was limited to genetically-based inheritance.…”

“…The study demonstrated that fathers can transmit DNA damage (single-strand breaks as measured in the Comet assay and double-strand breaks as measured by gH2AX) to their babies. 5 As tumors can manifest without dominant lethal mutations, 49 the different endpoints may be independent genetic (germ cell transmissible) events and might be species-and/or strain-dependent. The question of acute vs chronic exposure might also be agent/ compound-dependent.…”

“…They can be measured and scored in the same way as teratogenic defects after in utero exposure of females. [42][43][44][46][47][48][49] A1b: If delayed effects in the offspring are considered as childhood cancers, cognitive developmental defects, growth disorders and the like, then in humans after radiation it was thought that exposed fathers had given rise to leukemia in their children. 63,64 However, the case was thrown out of court because it foundered on 'the balance of probabilities' .…”