Effect of tamoxifen on sperm fertilising ability and preimplantation embryo development

Low-dose tamoxifen treatment in juvenile males has long-term adverse effects on the reproductive system: implications for inducible transgenics

The tamoxifen-inducible Cre system is a popular transgenic method for controlling the induction of recombination by Cre at a specific time and in a specific cell type. However, tamoxifen is not an inert inducer of recombination, but an established endocrine disruptor with mixed agonist/antagonist activity acting via endogenous estrogen receptors. Such potentially confounding effects should be controlled for, but >40% of publications that have used tamoxifen to generate conditional knockouts have not reported even the minimum appropriate controls. To highlight the importance of this issue, the present study investigated the long-term impacts of different doses of a single systemic tamoxifen injection on the testis and the wider endocrine system. We found that a single dose of tamoxifen less than 10% of the mean dose used for recombination induction, caused adverse effects to the testis and to the reproductive endocrine system that persisted long-term. These data raise significant concerns about the widespread use of tamoxifen induction of recombination, and highlight the importance of including appropriate controls in all pathophysiological studies using this means of induction.

Estrogen signaling, through estrogen receptor β, regulates DNA methylation and its machinery in male germ line in adult rats

Estrogen, through its receptors, regulates various aspects of spermatogenesis and male fertility. To understand the roles of estrogen receptors (ERα and ERβ) in male fertility, we have developed in vivo selective ER agonist administration models. Treatment of adult male rats with ERα or ERβ agonist for 60 d decreases fertility and litter size mainly due to increased pre- and post-implantation embryo loss. Since epigenetic mechanisms like DNA methylation play a crucial role in male fertility, we investigated the effects of the ER agonists on DNA methylation in spermatozoa. Treatment with ERβ agonist causes a significant decrease in DNA methylation both at the global level and at the H19 differentially methylated region (DMR). This could be due to decrease in DNA methyltransferases in the testis upon ERβ agonist treatment. The hypomethylation observed at the H19 DMR corroborates with aberrant expression of Igf2 and H19 imprinted genes in the resorbed embryos sired by ERβ agonist-treated males. Thus, our study demonstrates that ERβ regulates DNA methylation and methylating enzymes during adult rat spermatogenesis. Activation of estrogen signaling through ERβ could therefore cause DNA methylation defects leading to impaired male fertility. These results define a role for estrogen in epigenetic regulation of male germ line, suggesting that epigenetic insults by exposure to environmental estrogens could potentially affect male fertility.

Effect of estrogen receptor-subtype-specific ligands on fertility in adult male rats

Maintenance of normal male fertility relies on the process of spermatogenesis which is under complex endocrine control by mechanisms involving gonadotropin and steroid hormones. Although testosterone is the primary sex steroid in males, estrogen is locally produced in the testis and plays a very crucial role in male fertility. This is evident from presence of both the estrogen receptors alpha (ERα) and beta (ERβ) in the testis and their absence, as in the case of knockout mice models, leads to sterility. The present study was undertaken to understand individual roles of the two ERs in spermatogenesis and their direct contribution towards the maintenance of male fertility using receptor-subtype-specific ligands. Administration of ERα and β agonists to adult male rats for 60 days results in a significant decrease in fertility, mainly due to an increase in pre- and post-implantation loss and a concomitant decrease in litter size and sperm counts. Our results indicate that ERα is mainly involved in negative feedback regulation of gonadotropin hormones, whereas both ERs are involved in regulation of prolactin and testosterone production. Histological examinations of the testis reveal that ERβ could be involved in the process of spermiation since many failed spermatids were observed in stages IX-XI following ERβ agonist treatment. Our results indicate that overactivation of estrogen signaling through either of its receptors can have detrimental effects on the fertility parameters and that the two ERs have both overlapping and distinct roles in maintenance of male fertility.

Aberrant methylation of multiple imprinted genes in embryos of tamoxifen-treated male rats

Genomic imprinting is an epigenetic phenomenon known to regulate fetal growth and development. Studies from our laboratory have demonstrated that treatment of adult male rats with tamoxifen increased postimplantation loss around mid gestation. Further studies demonstrated the aberrant expression of transcripts of several imprinted genes in the resorbing embryos at days 11 and 13 of gestation including IGF2. In addition, decreased methylation at theIgf2–H19imprint control region was observed in spermatozoa and in resorbing embryos sired by tamoxifen-treated males. In this study, methylation analysis of the imprinted genes, which were found to be differentially expressed, was done using EpiTYPER in the spermatozoa of tamoxifen-treated rats and in postimplantation embryos sired by tamoxifen-treated rats. Differentially methylated regions (DMRs) for most imprinted genes have not been identified in the rats. Hence, initial experiments were performed to identify the putative DMRs in the genes selected for the study. Increased methylation at CpG islands present in the putative DMRs of a number of imprinted genes was observed in the resorbing embryos sired by tamoxifen-treated male rats. This increase in methylation is associated with the downregulation of most of these genes at the transcript level in resorbing embryos. No change in the methylation status of these genes was observed in spermatozoa. These observations suggest that a deregulation of mechanisms protecting unmethylated alleles from a wave ofde novomethylation occurs following implantation.

The impairment of metrial gland development in tamoxifen exposed rats

We examined the sequential histopathological changes in the placenta from rats exposed to tamoxifen. Tamoxifen was administered intraperitoneally at doses of 0 and 2 mg/kg/day on gestation days (GDs) 8, 9 and 10, and the placentas were sampled on GDs 11, 13, 15, 17, and 21. The fetal mortality rates in the tamoxifen group were increased up to 56%. However, there were no effects on the weights of live embryos/fetuses and their placentas. Histopathologically, the size of metrial gland in the tamoxifen group was reduced on all sampling times. The spiral arteries appeared less well developed in the hypoplastic metrial gland. A decrease in uterine natural killer (uNK) cells and mitotic uNK cells around the spiral arteries in the metrial gland was detected from GD 13 onward and on GDs 11 and 13, respectively. There were no obvious changes in the labyrinth zone or basal zone. We consider that the anti-estrogen effect of tamoxifen inhibits the proliferation of decidualized endometrial stromal cells in the metrial gland and leads to inhibition of the proliferative activity of uNK cells, followed by defective development of spiral arteries, and metrial gland hypoplasia. It is assumed that the metrial gland hypoplasia might be involved in the tamoxifen-induced embryo/fetus-toxicity.

Effects of 17beta-estradiol, and its metabolite, 4-hydroxyestradiol on fertilization, embryo development and oxidative DNA damage in sand dollar (Dendraster excentricus) sperm

Oxidative compounds have been demonstrated to decrease the fertilization capability and viability of offspring of treated spermatozoa. As estrogen and its hydroxylated metabolites readily undergo redox cycling, this study was undertaken to determine if estrogens and other oxidants could damage DNA and impair sperm function. Sperm was preexposed to either 17beta-estradiol (E2), 4-hydroxyestradiol (4OHE2) or the oxidant t-butyl hydroperoxide (t-BOOH), and allowed to fertilize untreated eggs. The fertilization rates and development of the larvae were assessed, as well as the amount of 8-oxodeoxyguanosine (8-oxodG) as an indication of oxidative DNA damage. All compounds caused significant decreases in fertilization and increases in pathological abnormalities in offspring, with 4OHE2 being the most toxic. Treatment with 4OHE2 caused a significant increase of 8-oxodG, but E2 failed to show any effect. Pathological abnormalities were significantly correlated (r(2)=0.44, p< or =0.05) with 8-oxodG levels in sperm treated with t-BOOH and 4OHE2, but not E2. 8-OxodG levels also were somewhat weakly correlated with impaired fertilization in 4OHE2-treated sperm (r(2)=0.33, p< or =0.05). The results indicate that biotransformation of E2 to 4OHE2 enhances oxidative damage of DNA in sperm, which can reduce fertilization and impair embryonic development, but other mechanisms of action may also contribute to these effects.

Effect of tamoxifen treatment on the semen quality and fertility of the male rat

OBJECTIVES

To determine the effects of tamoxifen treatment on the seminal quality and fertility of the male Wistar rat.

DESIGN

Experimental prospective study.

SETTING

Animal research and university laboratory facility.

SUBJECT(S)

Seventy-five-day-old male and female Wistar rats.

INTERVENTION(S)

Sperm quality parameters were assayed in seminal and epididymal sperm samples in control and treated rats at a dose of 0.4 mg tamoxifen/kg per day. In addition, mating studies were performed, and different fertility parameters were assayed.

RESULT(S)

Tamoxifen treatment significantly decreased sperm concentration and motility in seminal and epididymal sperm. Sperm viability and hypo-osmotic swelling test results were shown not to be altered. The copulatory plug was absent or severely impaired in tamoxifen-treated males. When mating experiments were performed, a significant decrease in the fertility index and increased percentages of preimplantation and postimplantation embryo loss were also observed.

CONCLUSION(S)

Tamoxifen treatment significantly altered sperm quality in seminal and epididymal sperm. These alterations were present in testis and epididymis, and additional negative effects on the sexual accessory glands were observed. Finally, these alterations were capable of seriously compromising fertility ability of these male rats.

Mechanism delineating differential effect of an antiestrogen, tamoxifen, on the serum LH and FSH in adult male rats

Tamoxifen, a synthetic non-steroidal antiestrogen with residual estrogenic activity, administered to adult male rats reduces their fertility. A decrease in the circulating LH and testosterone levels with a transient rise or no change in circulating FSH levels was observed. The present study was carried out to delineate the mechanism causing the differential effect of tamoxifen on circulating gonadotropins by correlating it to changes in the hypothalamic LHRH, pituitary gonadotropins and testicular inhibin/activin. Hypothalamus, pituitary-hypothalamus complex (PHC) and intact pituitary (PI) from control and tamoxifen-treated male rats were superfused in vitro, and pulsatile release of LHRH by hypothalamus and that of LH and FSH by the PHC and PI were studied. Concomitantly, testicular immunoexpression of alpha and betaB subunits of inhibin/activin were studied by immunohistochemistry and enzyme-linked immunosorbent assays (ELISA). At 0.4 mg/kg/day dose of tamoxifen a decrease in mean hypothalamic LHRH and LH pulse frequency from PHC construct was observed. FSH pulse frequency was not affected under the same experimental conditions. At the same dose of tamoxifen, testicular expression of both alpha and betaB subunits of inhibin/activin was upregulated. The study demonstrated that reduced circulating LH levels were due to a decrease in hypothalamic LHRH concentration and in LH pulsatility following tamoxifen treatment. The lack of effect on circulating FSH under the same experimental conditions was likely due to its modulation by inhibin and activin.

Reproductive toxicity assessment of lasofoxifene, a selective estrogen receptor modulator (SERM), in male rats

BACKGROUND

Lasofoxifene is a nonsteroidal selective estrogen receptor modulator (SERM) with greater than 100-fold selectivity against all other steroid receptors and is a potentially superior treatment for postmenopausal osteoporosis. The purpose of this study was to evaluate the effects of lasofoxifene on male reproduction in rats in light of the known effects of estrogen modulating compounds on male reproductive ability.

METHODS

Lasofoxifene was administered to adult male rats at doses of 0.1, 1, 10, and 100 mg/kg for 66-70 consecutive days. After 28 days of dosing, male rats were cohabited with untreated female rats. Female rats were euthanized on gestation day 14 and a uterine examination was carried out for evaluation of reproductive parameters and embryo viability. Male rats were euthanized after 66-70 days of dosing and epididymal sperm motility and concentration were assayed. The testes, epididymides, prostate, and seminal vesicles were weighed and microscopically examined.

RESULTS

The duration of cohabitation was increased for 100 mg/kg males by 0.7 days. The number of males copulating and the number of implantation sites produced per copulation were reduced in the 10 and 100 mg/kg groups. Weights of the seminal vesicles and epididymides were reduced for all groups, although the testes weight and epididymal sperm motility and concentration were not affected by treatment. There were no microscopic findings in the male reproductive tissues.

CONCLUSION

The changes in male fertility and reproductive tissue weights after exposure to lasofoxifene are consistent with those previously described for estrogen receptor-modulating compounds.

Effect of paternal tamoxifen on the expression of insulin-like growth factor 2 and insulin-like growth factor type 1 receptor in the post-implantation rat embryos

Nuclear transplantation studies demonstrated the importance of paternal contribution to embryogenesis. Paternal treatment with agents like cyclophosphamide and 5-azacytidine has been shown to cause an increase in pre-implantation loss (PIL) and post-implantation loss (POL). Studies from our laboratory have shown that paternal tamoxifen treatment increases PIL and POL. It was observed that the PIL occurred at day 2 of gestation (embryo at 2-4 cell stage) and the POL occurred around day 9 of gestation (mid-gestation). The insulin-like growth factor (IGF) system represents one of the major growth-controlling system expressed in the embryo. Several studies suggest that in rodents, insulin-like growth factor 2 (Igf2) signaling through the insulin-like growth factor type 1 receptor (Igf1r) modulates embryo growth at around days 9-11 of gestation (mid-gestation). The present study was undertaken to evaluate the expression of Igf2 and Igf1r transcript by RT-PCR in the post-implantation embryos obtained after paternal tamoxifen treatment. It was observed that both the genes were down regulated in resorbed embryos (POL). Since Igf2 is an imprinted gene and the imprint mark is established during spermatogenesis, the present study suggests that paternal tamoxifen treatment may have affected imprinting of the gene during spermatogenesis thereby decreasing its expression and leading to increase in POL. This is to our knowledge the first study correlating the increase in post-implantation embryo loss obtained after paternal drug treatment with the decrease in the expression of Igf2 in these embryos.

Effect of oral tamoxifen on semen characteristics and serum hormone profile in male bonnet monkeys

The effects of oral tamoxifen were studied at a dose of 0.4 mg/kg per day, on the serum hormones and semen parameters in adult male bonnet monkeys, for a period of 90 days. Honey was used as vehicle. Monkeys were treated with honey for 30 days, followed by tamoxifen from Day 30-120 (90 days). Thereafter the treatment was withdrawn until Day 150 of schedule. Blood samples were drawn at 12 and 24 clock hours at monthly intervals for the analysis of luteinizing hormone, follicle-stimulating hormone and testosterone. Semen samples were also collected for analysis once a month, from Day 0-150 of exposure. Tamoxifen treatment produced a transient but significant increase in circulating gonadotropins, at Day 90 of treatment schedule, corresponding to 60 days of treatment. Whilst serum testosterone levels were normal throughout treatment period, an increase was observed after 30 days of drug withdrawal. No effect of oral tamoxifen was evident on semen parameters, viz., volume, counts, morphology and motility. However, throughout the exposure period to honey, a significant increase was observed in sperm counts without any effect on testosterone levels. The present study suggests that oral tamoxifen has a transient antiestrogenic effect on the serum hormones and no effect on semen parameters of adult nonhuman primate males. It is concluded that bioefficacy of oral tamoxifen may have been reduced due to hepatic metabolism.

Effect of human dietary exposure levels of genistein during gestation and lactation on long-term reproductive development and sperm quality in mice

The objective of the present study was to determine the long-term reproductive effects of gestational and lactational exposure (0, 0.1, 0.5, 2.5 and 10 mg/kg/day) to genistein on male mice at levels comparable to or greater than human dietary exposures. Testicular growth, sperm count and motility, and sperm fertilizing ability in vitro was assessed in male offspring on postnatal days (PND) 105 and 315. Selected genes were also examined by real-time PCR to determine whether genistein caused changes in gene expression similar to those previously observed with diethylstilbestrol (DES). No significant treatment-related effects on male offspring body weight, anogenital distance, seminal vesicle weight or testis weight were observed. There were also no significant effects on sperm count, the percent of motile sperm or the number of motile sperm at any age. The in vitro fertilizing ability of epididymal sperm was increased significantly in the high-dose group approximately 17% (P < 0.001) on PND 105 and 315. The results indicate that developmental exposure of mice to genistein at human exposure levels does not induce adverse effects on sperm quality or changes in testicular gene expression similar to DES.

Estrogen receptor, calcium mobilization and rat sperm motility

Oral treatment with 0.4 mg/kg/day of tamoxifen citrate, an antiestrogen, has been reported to reduce the fertility of adult male rat, presumably through estrogen receptors expressed throughout the male reproductive tract. During the course of these studies, tamoxifen was observed to gradually alter the pattern of sperm motility in the cauda epididymides without reducing sperm counts. Studies were carried out to understand the mechanism involved in tamoxifen induced change in the sperm motility pattern. In order to study the direct effects of tamoxifen on motility, biochemical levels/activities of sperm calcium, cAMP, phosphodiesterase and dynein ATPase, normally implicated in sperm motility were studied In view of the fact that tamoxifen is a ligand of estrogen receptor, estrogen receptor alpha protein and transcript were localized on rat sperm membrane and the effect of tamoxifen studied. The present study demonstrated presence of estrogen receptor protein and mRNA in the rat sperm by immunofluorescence, western blotting and in situ hybridization respectively. Specificity of sperm estrogen receptors was confirmed by conventional binding studies using [3H]-estradiol. There was no effect of tamoxifen treatment on estrogen receptors in rat sperms. Biochemical analysis of the sperms from tamoxifen treated cauda epididymides revealed a significant increase in the levels of calcium and cAMP. A significant reduction was also apparent in the activity of dynein ATPase. Tamoxifen treatment did not alter phosphodiesterase activity. Estrogen receptors could be identified both in the control as well as tamoxifen treated rat sperms. It was concluded that tamoxifen treatment mobilized calcium from the intra- or extra-cellular pools with a concomitant increase in cAMP and presumably activation of PKA (protein kinase A). Tamoxifen altered the pattern of sperm motility through a calcium induced block in the activity of dynein ATPase, presumably through the activation of sperm phosphatase. The putative estrogen receptor mediated signal transduction pathway appears to be directly affected in the tamoxifen treated, sub-motile rat sperm.

Effect of paternal administration of an antiestrogen, tamoxifen on embryo development in rats

We have earlier reported that oral administration of tamoxifen causes a dose-dependent reduction in the fertility of adult male rats. The decrease in fertility was mainly due to an increase in pre-implantation loss without an effect on fertilizing ability. During the study, an increased incidence of post-implantation loss of conceptuses sired by tamoxifen-treated male rats was observed. A detailed study was undertaken to investigate dose-related changes in pre- and post-implantation loss and the stage(s) of development at which these losses occurred. The present study demonstrates that tamoxifen treatment produced few normal litters as well as significantly increased pre-implantation loss without affecting the rate of fertilization. Also a significant increase in the number of degenerating embryos at the 2-4-cell stage (days 1-2 of gestation), retrieved from the oviduct/uterus of females mated with tamoxifen-treated males was observed. Histology of the resorbed fetuses, in both control and treated groups, showed presence of trophoblast outgrowth indicative of early placenta formation, which normally occurs on days 8-9 of gestation. The present results suggest that pre-implantation loss occurred at the 2-4-cell stage and the post-implantation loss occurred around days 8-9 of gestation, i.e. around midgestation. The possible effects of paternal tamoxifen treatment on embryogenesis may be due to the reduction of androgens or by the blockage of the estrogen receptor by tamoxifen, thereby affecting germ cell maturation during spermatogenesis.