Radiosensitivity Of Oocytes Research Articles

Molecular Mechanism and Prevention Strategy of Chemotherapy- and Radiotherapy-Induced Ovarian Damage.

Fertility preservation is an emerging discipline, which is of substantial clinical value in the care of young patients with cancer. Chemotherapy and radiation may induce ovarian damage in prepubertal girls and young women. Although many studies have explored the mechanisms implicated in ovarian toxicity during cancer treatment, its molecular pathophysiology is not fully understood. Chemotherapy may accelerate follicular apoptosis and follicle reservoir utilization and damage the ovarian stroma via multiple molecular reactions. Oxidative stress and the radiosensitivity of oocytes are the main causes of gonadal damage after radiation treatment. Fertility preservation options can be differentiated by patient age, desire for conception, treatment regimen, socioeconomic status, and treatment duration. This review will help highlight the importance of multidisciplinary oncofertility strategies for providing high-quality care to young female cancer patients.

The role of ionizing radiaton on ovulation rate and oocyte morphology in mouse

We investigated the effects of ionizing radiation on maturation ability and radiosensitivity of oocytes enclosed in preantral and antral follicles. Balb/c female mice received total body single dose gamma radiation (7.2 Gy) at the diestrous to proestrous transition period. In the first experiment, spontaneously ovulated oocytes were collected from irradiated animals. In the second experiment, irradiated animals were allowed to superovulate to assess the ovarian function. The spontaneous ovulation rate of the follicles exposed at antral stage was significantly lower than the sham-irradiated mice (p < 0.01), and most of the oocytes were found at the metaphase I stage. Oocyte morphology and the ovulation rate of the follicles exposed at preantral stage were similar to the sham-irradiated group. Minimal morphological abnormalities were observed in the oocytes and the polar body as well. The superovulation response of all the irradiated animals was lower than the respective control animals. The superovulation rate was significantly lower in the first ovulation after irradiation (p < 0.01). In conclusion, our findings indicate that total body gamma irradiation, on a basis of estrous cycle stages, leads to ovulation failure in the antral stage while causes abnormal oocyte morphology in the preantral stage follicles in mice.

Cytogenetic studies in mouse oocytes irradiated in vitro at different stages of maturation, by use of an early preantral follicle culture system

In vivo studies on X-irradiated mice have shown that structural chromosome aberrations can be induced in female germ cells and that the radiation-induced chromosomal damage strongly depends on the stage of maturation reached by the oocytes at the time of irradiation. In the present study, the sensitivity of oocytes to induction of chromosome damage by radiation was evaluated at two different stages, by use of a recently developed method of in vitro culture covering a crucial period of follicle/oocyte growth and maturation. A key feature of this system is that growth and development of all follicles is perfectly synchronized, due to the selection of a narrow class of follicles in the start-off culture. This allows irradiation of well-characterized and homogenous populations of follicles, in contrast to the situation prevailing in vivo. Follicles were X-irradiated with either 2 or 4Gy, on day 0 of culture (early preantral follicles with one to two cell layers) or on day 12, 3h after hormonal stimulation of ovulation (antral Graafian follicles). Ovulated oocytes, blocked in metaphase I (MI) by colchicine, were fixed 16h after hormonal stimulation and analyzed for chromosome aberrations. The results confirm the high radiosensitivity of oocytes at 2 weeks prior to ovulation and the even higher radiosensitivity of those irradiated a few hours before ovulation, underlining the suitability of the in vitro system for further studies on the genetic effects of ionising radiation in female mammals.

Cytogenetic effects of X-rays in the guinea pig female germ cells. II. The maturing oocyte

In a previous study, we showed that the guinea pig constitutes one of the best models to evaluate the genetic risk associated with an irradiation of the human female germ cells. Herewith, experiments were undertaken to evaluate the chromosomal radiosensitivity of oocytes of this species at two different stages of follicular development, separated by only 1 week. Female guinea pigs were X-irradiated on the ovaries, at either the beginning (day 3) or the middle (day 10) of the 17-day oestrous cycle. The doses delivered were 1 or 2 Gy. Meiotically competent oocytes were collected 1 week after irradiation (day 3) or immediately thereafter (day 10), and they were cultured to the metaphase of the first meiosis (MI) and examined for the presence of chromosome aberrations. Our data demonstrated a dramatic increase in the radiosensitivity of the oocyte during this short time interval: oocytes irradiated at the beginning of the oestrous cycle had a low frequency of chromosome aberrations, while those irradiated at the middle of the oestrous cycle (when growing Graafian follicles are clearly visible at the surface of the ovaries) exhibited heavy chromosome damage. However, we also found that oocytes irradiated at the middle of the oestrous cycle were eliminated from the ovaries in a few days, after their evolution to the MII stage. The stimulation of the first meiotic division by radiation required less than 24 h after doses of 1 or 2 Gy and was probably due to a rapid atresia of the large follicles containing the oocytes. On the basis of these results, it can be concluded that the radiosensitivity of the nearly mature guinea pig oocyte (1 week before ovulation) is clearly much higher than that of the corresponding stage in the mouse, both in terms of sensitivity to killing and to induction of chromosome aberrations.

Effects of neonatal ovarian X-irradiation in the Chinese hamster. II. Absence of chromosomal and developmental damages in surviving oocytes irradiated at the pachytene and resting dictyate stages.

Ovaries of Chinese hamsters were irradiated with 1 Gy of X-rays on day 0, 4, 8 and 14 after birth, and the late effects on pachytene and resting dictyate oocytes, which had been proven to be radioresistant and to survive acute oocyte-killing, were studied in the progeny of the irradiated females. Thirty hours after mating, fertilized ova were collected and female pronuclear chromosomes were karyotyped. On day 18.5 of gestation, the number of corpora lutea and implantation sites were counted and the live and dead fetuses were examined phenotypically. There was no increase of chromosome aberrations in female pronuclei of one-cell embryos of the irradiated groups. There was no significant difference in the incidences of pre- and postimplantation deaths and of congenital malformations between the irradiated groups and the non-irradiated controls. These findings indicated clearly that oocytes at the pachytene and resting dictyate stages which had survived the acute oocyte-killing effects of X-rays were also free from late deleterious effects on genetic and developmental abilities. The radiosensitivity of oocytes of the Chinese hamster was compared with that of the mouse with respect to chromosome aberrations, lethal mutations and congenital anomalies, and the difference between both species was discussed.

Dose-response relationship for induction of structural chromosome aberrations in Chinese hamster oocytes after X-irradiation

Recently, we determined the precise timing of changes of meiotic chromosomal radiosensitivity in oocytes during the spontaneous estrous cycle in the Chinese hamster, by assessing MII chromosomal lesions induced after 200 rad X-irradiation at various stages prior to ovulation (Mikamo et al., 1981). It was demonstrated that early diakinesis was the most radiosensitive phase, the incidence of oocytes with structural chromosome aberrations being 15 times higher than during dictyotene stages of diestrum. A high radiosensitivity was also found in mouse oocytes at a transitional stage from late dictyotene to diakinesis, although X-irradiation was restricted only to this single stage (Reichert et al., 1975). In the present work, we investigated the dose-response relationship for induction of chromosome aberrations in Chinese hamster oocytes at the most radiosensitive stage, and compared our results with those obtained previously in the mouse.

Radiation-induced dominant lethality in oocytes of Drosophila hydei, with emphasis on the differential sensitivity of the immature stages in class b

A brood-pattern analysis of radiation-induced damage in the oocytes of attached-X females of Drosophila hydei was carried out by the dominant lethal test. The methods used allow a refined description of the differential radiosensitivity of oocytes with respect to the stage succession in the oogenesis of this species. As in D. melanogaster , three levels of sensitivity, corresponding to classes A, B and C of oocytes, showed up. The differences in sensitivity led to clear-cut steps in the brood pattern of lethal frequencies, whereby class B is distinguised by an intermediate yield of induced damage. Eggs deposited on the first day after irradiation are not in every instance a pure sample of irradiated stage-14 oocytes, but may contain and admixture derived from less sensitive vitellogenic stages. For the previtellogenic stages, belonging to class B, it is proposed that it is the youngest group which exhibits the highest radiosensitivity. This agrees with earlier results from detachment of attached-X chromosomes in D. hydei . The brood patterns of lethal frequencies were not identical, but similar, when a distinction was made between induced early and late embryonic lethality. On certain assumptions, this is interpreted to mean that the stage-dependent differences in sensitivity observed are due to genetic causes, i.e. , are correlated with changes in the state of the oocyte nucleus during oogenesis.

Radiation-induced dominant lethality in oocytes of Drosophila hydei, with emphasis on differential sensitivity of the immature stages in class B

A brood-pattern analysis of radiation-induced damage in the oocytes of attached-X females of Drosophila hydei was carried out by the dominant lethal test. The methods used allow a refined description of the differential radiosensitivity of oocytes with respect to the stage succession in the oogenesis of this species. As in D. melanogaster, three levels of sensitivity, corresponding to classes A, B and C of oocytes, showed up. The differences in sensitivity led to clear-cut steps in the brood pattern of lethal frequencies, whereby class B is distinguised by an intermediate yield of induced damage. Eggs deposited on the first day after irradiation are not in every instance a pure sample of irradiated stage-14 oocytes, but may contain and admixture derived from less sensitive vitellogenic stages. For the previtellogenic stages, belonging to class B, it is proposed that it is the youngest group which exhibits the highest radiosensitivity. This agrees with earlier results from detachment of attached-X chromosomes in D. hydei. The brood patterns of lethal frequencies were not identical, but similar, when a distinction was made between induced early and late embryonic lethality. On certain assumptions, this is interpreted to mean that the stage-dependent differences in sensitivity observed are due to genetic causes, i.e., are correlated with changes in the state of the oocyte nucleus during oogenesis.

Radiosensitivity of oocytes of Drosophila. 3. Sensitivity of class-B oocytes of XX-O and X-X females.

SummaryClass-B oocytes of XX/O and X/X females of Drosophila melanogaster are equally radiosensitive. On the hypothesis that radiation-induced lethality in oocytes results from chromosomal damage in the oocyte nucleus, it would be expected that after x-irradiation of XX/O females, more lethality would be observed in the progeny with a maternal XX/II/III/IV chromosome complement than in the progeny with a maternal II/III/IV complement. This was not found for the class-B oocytes of XX/O females, which is in contrast to the results of comparable experiments with class-A oocytes of the same type of female. It is concluded that radiation-induced lethality observed after treatment of class-B oocytes results to a large extent from lethal damage induced in targets other than the chromosomes of the oocyte nucleus.

Radiosensitivity of oocytes of Drosophila. II. Sensitivity of class-B oocytes of X-X and XY-XY.

SummaryClass-B oocytes of X/X and XY/XY females are equally sensitive to the x-ray induction of lethal damage expressed after maturation and insemination (socalled embryonic lethality). On the other hand, class-A oocytes of the same types of female show a difference in sensitivity which can be attributed to the higher content of chromosomal material in the oocyte nuclei of XY/XY females than X/X females. This indicates that in class-B oocytes, radiation-induced damage located in targets other than the oocyte chromosomes is of significance in the induction of embryonic lethality by radiation.

Radiosensitivity of oocytes in post-natal guinea-pigs.

Radiosensitivity of oocytes in post-natal guinea-pigs.

The radio-sensitivity of oocytes at different stages of maturation

The viability of the zygote after fertile mating has been used as an index to assess the radio-sensitivity of oocytes in Graafian follicles at different times before expected ovulation, and at known stages of the maturation process. Radio-sensitivity increases as the interval between irradiation and expected ovulation decreases; the increase is progressive as the oocyte passes from the late dictyate (diplotene) phase through the successive stages of maturation, at least up to congression of chromo­somes at first metaphase. It is estimated that radio-sensitivity increases by about ten times between the earliest and the latest developmental stages studied, on the day of pro-oestrus. Oocytes in 'medium-sized’ follicles (irradiated 5 to 35 days before fertilization) are highly radio-resistant. The estimated LD 50 for oocytes at this stage is about three times higher than that for pre-ovulatory oocytes some 14 to 15 h before expected ovulation. The total differ­ence between the radio-sensitivity of oocytes in ‘medium-sized’ or growing follicles, and that of oocytes at first metaphase, is of the order of × 30. X-irradiation is followed by superovulation and a decrease in the mean size of the corpora lutea of pregnancy. In general, the number of corpora lutea is inversely correlated with their mean size. The degree of superovulation is partially dependent on ( a ) the dose of X -rays and ( b ) the developmental stage of the oocytes at the time of irradiation. The radio-sensitivity of the fertilized ovum, 8 to 12 h after ovulation, is lower than that of pre-ovulatory oocytes which have reached or passed first metaphase. Subsequently, the sensitivity of the zygote decreases with advancing age.