From the Cover: Teratogenic Effects of in Utero Exposure to Di-(2-Ethylhexyl)-Phthalate (DEHP) in B6:129S4 Mice

Modulation of fetoplacental growth, development and reproductive function by endocrine disrupters

Maternal endocrine homeostasis is vital to a successful pregnancy, regulated by several hormones such as human chorionic gonadotropin, estrogen, leptin, glucocorticoid, insulin, prostaglandin, and others. Endocrine stress during pregnancy can modulate nutrient availability from mother to fetus, alter fetoplacental growth and reproductive functions. Endocrine disrupters such as bisphenols (BPs) and phthalates are exposed in our daily life's highest volume. Therefore, they are extensively scrutinized for their effects on metabolism, steroidogenesis, insulin signaling, and inflammation involving obesity, diabetes, and the reproductive system. BPs have their structural similarity to 17-β estradiol and their ability to bind as an agonist or antagonist to estrogen receptors to elicit an adverse response to the function of the endocrine and reproductive system. While adults can negate the adverse effects of these endocrine-disrupting chemicals (EDCs), fetuses do not equip themselves with enzymatic machinery to catabolize their conjugates. Therefore, EDC exposure makes the fetoplacental developmental window vulnerable to programming in utero. On the one hand prenatal BPs and phthalates exposure can impair the structure and function of the ovary and uterus, resulting in placental vascular defects, inappropriate placental expression of angiogenic growth factors due to altered hypothalamic response, expression of nutrient transporters, and epigenetic changes associated with maternal endocrine stress. On the other, their exposure during pregnancy can affect the offspring's metabolic, endocrine and reproductive functions by altering fetoplacental programming. This review highlights the latest development in maternal metabolic and endocrine modulations from exposure to estrogenic mimic chemicals on subcellular and transgenerational changes in placental development and its effects on fetal growth, size, and metabolic & reproductive functions.

The exposure levels of phthalates in pregnant women and impact factors of fetal malformation

METHODS

Urine samples were collected from 157 women with fetal malformations (case group) and 147 women with normal fetuses (control group). High-performance liquid chromatography-mass spectrometry (HPLC-MS) was used to detect the content of eight metabolites of phthalate compounds in urine, including monoethyl phthalate (MEP), mononbutyl phthalate (MBP), monoisobutyl phthalate (MiBP), mono-(2-ethylhexyl) phthalate (MEHP), mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), mono-(2-ethyl-5-carboxypentyl) phthalate (MECPP), mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP), and mono-benzyl phthalate (MBzP). Demographic data were collected from questionnaires administered in specimen collection.

RESULTS

The exposure level of MEOHP and MEHP in the case group was higher than the others. And there were significant differences between structural malformations and chromosomal malformations in the levels of MEHHP and MEOHP. Pregnant women with low income, high body mass index (BMI), frequent plastic contact, and low nutrients intake were at risk of suffering from fetal malformation.

CONCLUSION

This study provides evidence for the correlation between the concentration of phthalates and fetal malformation. In addition, decreasing plastic exposure and supplementing nutrients may reduce the incidence of fetal malformations.

Epi-mutations for spermatogenic defects by maternal exposure to di(2-ethylhexyl) phthalate

Exposure to environmental factors during fetal development may lead to epigenomic modifications in fetal germ cells, altering gene expression and promoting diseases in successive generations. In mouse, maternal exposure to di(2-ethylhexyl) phthalate (DEHP) is known to induce defects in spermatogenesis in successive generations, but the mechanism(s) of impaired spermatogenesis are unclear. Here, we showed that maternal DEHP exposure results in DNA hypermethylation of promoters of spermatogenesis-related genes in fetal testicular germ cells in F1 mice, and hypermethylation of Hist1h2ba, Sycp1, and Taf7l, which are crucial for spermatogenesis, persisted from fetal testicular cells to adult spermatogonia, resulting in the downregulation of expression of these genes. Forced methylation of these gene promoters silenced expression of these loci in a reporter assay. These results suggested that maternal DEHP exposure-induced hypermethylation of Hist1h2ba, Sycp1, and Taf7l results in downregulation of these genes in spermatogonia and subsequent defects in spermatogenesis, at least in the F1 generation.

Diethylhexyl phthalate induces teratogenic effects through oxidative stress response in a chick embryo model

Diethylhexyl phthalate (DEHP) is known as a persistent environmental pollutant. However, the possible effects of DEHP on human neural tube defects (NTDs) remain elusive. We set out to investigate the exposure of DEHP in human and explore the association of DEHP and NTDs. The level of DEHP in maternal urine was measured and analyzed by GC-MS. To further validate the results in human NTDs, chick embryos were used as animal models. Viability, reactive oxygen species (ROS) level, oxidative stress indicators and apoptosis were detected in DEHP-treated chick embryos. Our research revealed that the detection ratio of positive DEHP and its metabolites in maternal urine were observed dramatically higher in NTDs population than that in normal controls (P < 0.01, P < 0.05, respectively). Moreover, DEHP treatment (10^-6 M) led to developmental toxicity in chick embryos via accelerating oxidative stress response and cell apoptosis, and changing the level of oxidative stress-related indicators. Moreover, high dose choline (100 μg/μl) could partially restrain the toxicity effects induced by DEHP. Our data collectively imply that the incidence of NTDs may closely associate with DEHP exposure, which disturbs the development of neural tubes by enhancing oxidative stress.

All-trans Retinoic Acid Disrupts Development in Ex Vivo Cultured Fetal Rat Testes. II: Modulation of Mono-(2-ethylhexyl) Phthalate Toxicity

Humans are universally exposed to low levels of phthalate esters (phthalates), which are used to plasticize polyvinyl chloride. Phthalates exert adverse effects on the development of seminiferous cords in the fetal testis through unknown toxicity pathways. To investigate the hypothesis that phthalates alter seminiferous cord development by disrupting retinoic acid (RA) signaling in the fetal testis, gestational day 15 fetal rat testes were exposed for 1-3 days to 10-6 M all-trans retinoic acid (ATRA) alone or in combination with 10-6-10-4 M mono-(2-ethylhexyl) phthalate (MEHP) in ex vivo culture. As previously reported, exogenous ATRA reduced seminiferous cord number. This effect was attenuated in a concentration-dependent fashion by MEHP co-exposure. ATRA and MEHP-exposed testes were depleted of DDX4-positive germ cells but not Sertoli cells. MEHP alone enhanced the expression of the RA receptor target Rbp1 and the ovary development-associated genes Wnt4 and Nr0b1, and suppressed expression of the Leydig cell marker, Star, and the germ cell markers, Ddx4 and Pou5f1. In co-exposures, MEHP predominantly enhanced the gene expression effects of ATRA, but the Wnt4 and Nr0b1 concentration-responses were nonlinear. Similarly, ATRA increased the number of cells expressing the granulosa cell marker FOXL2 in testis cultures, but this induction was attenuated by addition of MEHP. These results indicate that MEHP can both enhance and inhibit actions of ATRA during fetal testis development and provide evidence that RA signaling is a target for phthalate toxicity in the fetal testis.

Prenatal exposure to an environmentally relevant phthalate mixture disrupts testicular steroidogenesis in adult male mice

Endocrine disrupting chemicals (EDCs) in the environment are considered to be a contributing factor to the decline in the sperm quality. With growing evidence of the harmful effects of EDCs on the male reproductive system, we tested the hypothesis that prenatal exposure to an environmentally relevant phthalate mixture adversely affects reproductive outcomes and androgen synthesis. In this study, an environmentally relevant composition of phthalates (15% DiNP, 21% DEHP, 36% DEP, 15% DBP, 8% DiBP, and 5% BBzP) that were detected in urine samples of pregnant women in Illinois, United States, was used. Pregnant CD-1 mice (F0) were orally dosed with a vehicle or the phthalate mixtures (20 µg/kg/day, 200 µg/kg/day, 200 mg/kg/day, or 500 mg/kg/day) from gestational day 10.5 to the day of birth. Then, the indices of the reproductive function of the F1 males born to these dams were assessed. Those male mice prenatally exposed to the phthalate mixture had smaller gonads, prostates and seminal vesicles, especially in the 20 µg/kg/day and 500 mg/kg/day phthalate mixture groups, compared to the controls. Importantly, at the age of 12 months, those prenatally exposed mice had significantly lower serum testosterone concentrations accompanied by the decreased mRNA expression of testicular steroidogenic genes (StAR, Cyp11, and Cyp17) and impaired spermatogenesis. Taken together, this study found that prenatal exposure to environmentally relevant doses of a phthalate mixture caused a life-long impact on the reproduction in male mice.

Di(2-Ethylhexyl) Phthalate Exposure During Prenatal Development Causes Adverse Transgenerational Effects on Female Fertility in Mice

Di(2-ethylhexyl) phthalate (DEHP) is a ubiquitous environmental toxicant and endocrine disrupting chemical, but little is known about its effects on female reproduction. Thus, we tested the hypothesis that prenatal exposure to DEHP accelerates the onset of puberty, disrupts estrous cyclicity, disrupts birth outcomes, and reduces fertility in the F1, F2, and F3 generations of female mice. Pregnant CD-1 mice were orally dosed with corn oil (vehicle control) or DEHP (20 and 200 µg/kg/day and 500 and 750 mg/kg/day) from gestation day 10.5 until birth. F1 females were mated with untreated males to obtain the F2 generation. F2 females were mated with untreated males to produce the F3 generation. In all generations, the onset of puberty, estrous cyclicity, select birth outcomes, and fertility-related indices were evaluated. In the F1 generation, prenatal DEHP exposure (200 µg/kg/day) accelerated the onset of puberty, it (200 µg and 500 mg/kg/day) disrupted estrous cyclicity, and it (20 and 200 µg/kg/day) decreased fertility-related indices. In the F2 generation, ancestral DEHP exposure (500 mg/kg/day) accelerated the onset of puberty, it (20 and 200 µg/kg/day) disrupted estrous cyclicity, it (20 µg and 500 mg/kg/day) increased litter size, and it (500 mg/kg/day) decreased fertility-related indices. In the F3 generation, ancestral DEHP exposure (20, 200 µg, and 500 mg/kg/day) accelerated the onset of puberty, it (20 µg/kg/day) disrupted estrous cyclicity, and it (750 mg/kg/day) decreased female pup anogenital index. Collectively, these data indicate that prenatal DEHP exposure causes female reproductive problems in a multigenerational and transgenerational manner.

Independent and combined effects of diethylhexyl phthalate and polychlorinated biphenyl 153 on sperm quality in the human and dog

A temporal decline in human and dog sperm quality is thought to reflect a common environmental aetiology. This may reflect direct effects of seminal chemicals on sperm function and quality. Here we report the effects of diethylhexyl phthalate (DEHP) and polychlorinated biphenyl 153 (PCB153) on DNA fragmentation and motility in human and dog sperm. Human and dog semen was collected from registered donors (n = 9) and from stud dogs (n = 11) and incubated with PCB153 and DEHP, independently and combined, at 0x, 2x, 10x and 100x dog testis concentrations. A total of 16 treatments reflected a 4 × 4 factorial experimental design. Although exposure to DEHP and/or PCB153 alone increased DNA fragmentation and decreased motility, the scale of dose-related effects varied with the presence and relative concentrations of each chemical (DEHP.PCB interaction for: DNA fragmentation; human p < 0.001, dog p < 0.001; Motility; human p < 0.001, dog p < 0.05). In both human and dog sperm, progressive motility negatively correlated with DNA fragmentation regardless of chemical presence (Human: P < 0.0001, r = −0.36; dog P < 0.0001, r = −0.29). We conclude that DEHP and PCB153, at known tissue concentrations, induce similar effects on human and dog sperm supporting the contention of the dog as a sentinel species for human exposure.