Genetic effects of combined chemical-X-ray treatments in male mouse germ cells

Mouse dominant lethal and sperm abnormality studies with combined exposure to X-rays and mitomycin C

The induction of dominant lethal effects and sperm abnormalities in Pzh:Swiss male mice after treatments with X-rays and mitomycin C (MMC) was investigated. Combinations of high (1.00 Gy + 5.25 mg/kg bw MMC) and low (0.25 Gy + 1.75 mg/kg bw MMC) doses of both agents were used. Exposure to high doses of X-rays + MMC induced an increased rate of dominant lethal mutations in spermatogonia and late spermatocytes. Combined treatment with low doses of X-rays and MMC was not mutagenic in any stage of spermatogenesis. MMC increased the frequency of abnormal spermatozoa after exposure alone and in combination with X-rays. Treatment with two high doses (1.00 Gy + 5.25 mg/kg bw MMC) induced 58.4% abnormal spermatozoa. After combined exposure to low doses of both agents 35.7% spermatozoa with malformations were observed.

Induction of dominant lethal mutations by combined X-ray-acrylamide treatment in male mice

The induction of mutations following combined treatment with acrylamide (AA) plus X-rays has been determined using the dominant lethal mutations test in Pzh:SFISS male mice. Combinations of a mutagenic dose of both agents (1.00 Gy, 125 mg/kg b.w.) and a non-mutagenic dose, i.e., a dose that alone does not produce dominant lethals (0.25 Gy, 25 mg/kg b.w.), were used. For the discussion of the effects of combined action of X-rays and acrylamide the term 'enhancement in risk' was used whenever the effects observed after combined exposure significantly exceeded the sum of the effects produced separately by the agents. Such an enhanced risk has been observed in late spermatids after combined action of X-rays and AA at non-mutagenic doses, and in spermatozoa, spermatids and late spermatocytes after exposure to mutagenic doses.

Induction of chromosomal aberrations in male mouse germ cells by uranyl fluoride containing enriched uranium

Cytogenetic damage induced by a wide range of concentrations of uranyl fluoride injected into mouse testes was evaluated by determining the frequencies of chromosomal aberrations in spermatogonia and primary spermatocytes. Breaks, gaps and polyploids were observed in spermatogonia. The frequencies of the significant type of aberration, breaks, were induced according to the injected doses of uranyl fluoride. Primary spermatocytes were examined for fragments, univalents and multivalents. The multivalents observed in this study resulted either from chromatid interchanges or from reciprocal translocations. The reciprocal translocations were induced in spermatogonia and recorded in primary spermatocytes. For primary spermatocytes the incidence of aberrant cells largely depended on the administered dose. Sampling time after treatment could affect the frequencies of chromosomal aberrations in male mouse germ cells.

Induction of specific locus mutations in mouse spermatogonial stem cells by combined chemical X-ray treatments

Data that demonstrate how the biology of spermatogenesis plays an important role in determining the yield of genetic damage from ionizing radiation are briefly reviewed. It is suggested that for valid extrapolations of data from mouse mutation experiments to man detailed knowledge of the spermatogonial stem cell systems in the two species is required. Two new sets of mouse specific mutation data are presented. (1) When a 2 mg/kg dose of triethylenemelamine (TEM) was used as a conditioning dose and followed 24 h later by 6 Gy X-rays, the mutation yield from spermatogonial stem cells was over twice as high (30.20 X 10(-5)/locus/gamete) as that when the X-ray dose was given alone (13.75 X 10(-5)/locus/gamete). No such effect was found when the TEM was given only 3 h prior to the X-irradiation. Since TEM at the dose used is inefficient at inducing specific-locus mutations, an augmentation of the X-ray response is indicated. It has therefore been concluded that the augmented mutation responses obtained with equal 24 h X-ray fractionations at high doses are attributable to mutation induction by the second dose. The responsive cells would be the formerly resistant component of the stem cell population that had survived the TEM treatment and that had been 'triggered' into a radiosensitive phase by the population depletion. (2) When 2 doses of 500 mg/kg hydroxyurea (HU) were given 3 h apart 3 h prior to 6 Gy X-rays to reduce the numbers of stem cells in the S and G2 phases of the cell cycle exposed to the radiation, the mutation responses was greatly enhanced to a level that is the highest yet recorded per unit X-ray dose (7.10 X 10(-5)/locus/gamete/Gy). No such effect was obtained when the intervals between the HU and X-ray treatments were either shorter (less than 0.5 h) or longer (24 h). It was concluded that X-ray-induced specific-locus mutations derive principally from stem cells in the G1 phase of the cell cycle. The reasons why the X-ray-induced mutation-yields from repopulating stem cells (with a short cell cycle and, hence, short G1 phase) are similar to those from undamaged stem cell populations, in contrast to translocation yields, therefore remains unresolved.

Induction of specific-locus and dominant-lethal mutations by cyclophosphamide and combined cyclophosphamide-radiation treatment in male mice

Cyclophosphamide is the most widely used antineoplastic agent. It is also used to condition patients for bone-marrow transplantations. Because of the general interest of this compound we initiated a systematic study of the induction of dominant-lethal and specific-locus mutations in male mice. In addition, we investigated the induction of specific-locus mutations by the combined treatment of cyclophosphamide and ionizing radiation. A dose of 40 mg/kg bw of cyclophosphamide caused dominant-lethal mutations in male mice only in the 1st and 2nd week after treatment. A dose of 120 mg/kg induced dominant-lethal mutations in the mating intervals 1-21 days posttreatment. No dominant lethal mutations were observed after the 3rd week. The same differential spermatogenic response was observed for the induction of specific-locus mutations. Cyclophosphamide induced recessive mutations exclusively in spermatozoa and spermatids. No mutations were recovered from treated spermatocytes and spermatogonia. In contrast to cyclophosphamide, radiation induces specific-locus mutations in all germ-cell stages. The pretreatment with cyclophosphamide 24 h before radiation enhanced the frequency of specific-locus mutations in spermatogonia. The distribution of the observed mutations among the 7 loci and their viability supports the hypothesis that these mutations were induced by radiation rather than by cyclophosphamide. The compound causes an immediate inhibition of DNA and RNA synthesis in spermatogonia. The inhibition very likely interferes with the repair process. The disturbance of the repair process is probably the cause of the synergistic effect for the induction of specific-locus mutations in spermatogonia of mice after pretreatment with cyclophosphamide 24 h before irradiation.

Radiation-induced translocations in spermatogonial stem cells of Macaca fascicularis and Macaca mulatta

3 adult monkeys, one Macaca fascicularis and two Macaca mulatta, were whole-body irradiated with 1 Gy gamma-rays (60 Co). Reciprocal translocations induced in spermatogonial stem cells were scored as translocation multivalents in primary spermatocytes from 7.5 to 27.5 months after exposure. The translocation yields ranged from 4.1% at the earliest to 1.8% at the latest sampling interval. No significant differences were observed in the responses of the individual animals. A decline in the translocation frequencies with time after treatment was found in all 3 animals. The present data are different from those reported for testicular X-irradiation of the rhesus monkey Macaca mulatta (van Buul, 1980; Lyon et al., 1976) in that the translocation yields are higher. They are consistent with the results reported for testicular gamma-irradiation of the crab-eating monkey Macaca fascicularis (Matsuda et al., 1984, 1985). In view of the present results it appears unlikely that a species difference exists within the genus Macaca in the sensitivity of spermatogonial stem cells to the induction of translocations by ionizing radiation.