Preconception omega-3 fatty acid supplementation of adult male mice with a history of developmental 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure prevents preterm birth in unexposed female partners

Exposure of ambient PM2.5 during gametogenesis period affects the birth outcome: Results from the project ELEFANT

Various environmental and behavioural factors influence neonatal health. Gamete formation (gametogenesis) is a crucial period which affects embryo development and neonatal health and ambient air pollution exposure at this stage may lead to an adverse birth outcome. Previous epidemiological and toxicological research demonstrated a strong association between maternal ambient air pollution exposure and adverse birth outcomes. However, the joint exposure-outcome of paternal exposure (76 days before the last menstruation and 14 days after the last menstruation) and maternal exposure (14 days after the last menstruation) when exploring the mechanism of the influence of air pollutants on pregnancy outcome and neonatal health remains unexplored. Here, in the Project Environmental and LifEstyle FActors iN metabolic health throughout life-course Trajectories (ELEFANT), we collected the data of 10,960 singleton pregnant women with 24-42 completed gestational weeks and included them in this study. A multinominal logistic regression model was applied to investigate the association between adverse birth outcomes and ambient PM_2.5 exposure levels during spermatogenesis and oogenesis. Results from the binary classification of ambient PM_2.5 exposure showed that the risk of abnormal birthweight was significantly greater when ambient PM_2.5 exposure was both higher during spermatogenesis and oogenesis, with RRs of 1.86 (95% CI: 1.02, 3.39). The risk of macrosomia (RR: 1.88 (95% CI: 1.13, 3.12)) increased significantly when ambient PM_2.5 levels were higher during spermatogenesis. Primiparity and primigravity are more likely to be influenced by higher ambient PM_2.5 levels during spermatogenesis. In conclusion, more attention should be paid to higher exposure level of ambient PM_2.5 during spermatogenesis.

A Paternal Fish Oil Diet Preconception Reduces Lung Inflammation in a Toxicant-Driven Murine Model of New Bronchopulmonary Dysplasia

New bronchopulmonary dysplasia (BPD) is a neonatal disease that is theorized to begin in utero and manifests as reduced alveolarization due to inflammation of the lung. Risk factors for new BPD in human infants include intrauterine growth restriction (IUGR), premature birth (PTB) and formula feeding. Using a mouse model, our group recently reported that a paternal history of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure increased his offspring's risk of IUGR, PTB, and new BPD. Additionally, formula supplementation of these neonates worsened the severity of pulmonary disease. In a separate study, we reported that a paternal preconception fish oil diet prevented TCDD-driven IUGR and PTB. Not surprisingly, eliminating these two major risk factors for new BPD also significantly reduced development of neonatal lung disease. However, this prior study did not examine the potential mechanism for fish oil's protective effect. Herein, we sought to determine whether a paternal preconception fish oil diet attenuated toxicant-associated lung inflammation, which is an important contributor to the pathogenesis of new BPD. Compared to offspring of standard diet TCDD-exposed males, offspring of TCDD-exposed males provided a fish oil diet prior to conception exhibited a significant reduction in pulmonary expression of multiple pro-inflammatory mediators (Tlr4, Cxcr2, Il-1 alpha). Additionally, neonatal lungs of pups born to fish oil treated fathers exhibited minimal hemorrhaging or edema. Currently, prevention of BPD is largely focused on maternal strategies to improve health (e.g., smoking cessation) or reduce risk of PTB (e.g., progesterone supplementation). Our studies in mice support a role for also targeting paternal factors to improve pregnancy outcomes and child health.

Associations of prenatal exposure to perfluoroalkyl substances with preterm birth: A family-based birth cohort study

Studies have investigated associations between maternal exposure to PFAS and preterm birth, but the impact of paternal and overall family exposure to PFAS mixtures on preterm birth remains unknown. To address this knowledge gap, a total of 355 preterm births and 481 controls were selected for a family-based birth cohort study in a coastal area of China, between 2016 and 2018. Seven PFAS, including perfluorobutanoic acid (PFBA), perfluorohexanoic acid (PFHxA), perfluorohexanesulfonic acid (PFHxS), perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), perfluorononanoic acid (PFNA) and perfluorodecanoic acid (PFDA), were quantified in maternal, paternal and neonatal sera. Preterm birth was defined as live delivery at <37 completed gestational weeks. Bayesian kernel machine regression (BKMR) model was used to inspect the combined effect of family PFAS mixtures. Latent class analysis was used to identify family-level PFAS exposure profiles. Multiple linear regression analysis showed higher odds of preterm birth in association with higher maternal PFBA (OR = 1.16, 95%CI:1.09, 1.25), PFOA (OR = 1.51, 95%CI:1.27, 1.80), PFOS (OR = 2.07, 95%CI:1.70, 2.52) and PFNA (OR = 1.36, 95%CI: 1.01, 1.83), and neonatal PFBA (OR = 1.16, 95%CI:1.05,1.29), PFHxA (OR = 1.46, 95%CI:1.32, 1.62), PFHxS (OR = 1.15, 95%CI:1.05, 1.26) and PFNA (OR = 1.30, 95%CI:1.09,1.56). The associations were reversed between individual paternal PFAS exposures and preterm birth. At the family level, higher PFAS mixture concentration was associated with higher odds of preterm birth. In particular, higher PFNA and PFDA exposure was associated with greater preterm birth risk (OR = 2.55, 95%CI:1.45, 4.50). The PFAS-preterm association was modified by family-level seafood consumption. Our results suggest that higher family-level PFNA and PFDA exposure was associated with greater preterm birth risk, although the results for individual paternal, maternal and neonatal PFAS exposures were contradictory. If replicated in other coastal areas, these findings highlight a need to focus on the family triad and to consider seafood consumption when assessing the reproductive toxicity of PFAS exposure.

A Paternal Fish Oil Diet Preconception Modulates the Gut Microbiome and Attenuates Necrotizing Enterocolitis in Neonatal Mice

Epidemiology and animal studies suggest that a paternal history of toxicant exposure contributes to the developmental origins of health and disease. Using a mouse model, our laboratory previously reported that a paternal history of in utero exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) increased his offspring’s risk of developing necrotizing enterocolitis (NEC). Additionally, our group and others have found that formula supplementation also increases the risk of NEC in both humans and mice. Our murine studies revealed that intervening with a paternal fish oil diet preconception eliminated the TCDD-associated outcomes that are risk factors for NEC (e.g., intrauterine growth restriction, delayed postnatal growth, and preterm birth). However, the efficacy of a paternal fish oil diet in eliminating the risk of disease development in his offspring was not investigated. Herein, reproductive-age male mice exposed to TCDD in utero were weaned to a standard or fish oil diet for one full cycle of spermatogenesis, then mated to age-matched unexposed females. Their offspring were randomized to a strict maternal milk diet or a supplemental formula diet from postnatal days 7–10. Offspring colon contents and intestines were collected to determine the onset of gut dysbiosis and NEC. We found that a paternal fish oil diet preconception reduced his offspring’s risk of toxicant-driven NEC, which was associated with a decrease in the relative abundance of the Firmicutes phylum, but an increase in the relative abundance of the Negativicutes class.

Associations of paternal serum dioxin-like polychlorinated biphenyl concentrations with IVF success: A pilot study

Dioxin-like polychlorinated biphenyls (DL-PCBs) are environmental pollutants that have been associated with impaired semen quality. However, research on the potential impact of paternal exposure to DL-PCBs and the risk of adverse pregnancy outcomes are limited. We examine the relationship between serum DL-PCB concentrations and IVF outcomes among 42 males seeking fertility treatment. Concentrations of 12 serum DL-PCBs were analyzed by high-resolution gas chromatography coupled to high-resolution mass spectrometry. Modified Poisson regressions, adjusted for confounders, were used to assess bivariate associations and to estimate risk ratios (RRs) between DL-PCBs and binary IVF outcomes. The median concentration (25th-75th percentiles) of the sum of the 12 DL-PCBs (∑DL-PCBs) obtained for the patients was 5.42 (3.78-7.78) ng/g lipid. No statistically significant association between DL-PCB levels and embryo quality was found. However, men with high serum PCB-77 concentrations present more probability of high-quality embryos (RR: 0.292; 95% CI: 0.090-0.942), whereas the opposite trend is observed for men with lower serum levels of PCB-156 (RR: 7.960; 95% CI: 1.020-62.100), who present increased odds of high-quality embryos. Serum concentrations of PCB-126 and PCB-114 were associated with decreased implantation rates (p < 0.05). Moreover, PCB-77 and ∑non-ortho PCBs were significantly associated with a lower likelihood of clinical pregnancy (p < 0.05). A lower likelihood of live birth was associated with higher levels of PCB-77, PCB-105, PCB-118, and recording significant differences for ∑non-ortho PCBs, ∑mono-ortho PCBs, and ∑DL-PCBs (p < 0.05). These findings suggest that paternal DL-PCB exposure before conception may be related to pregnancy endpoints. However, DL-PCB measurement were limited to male partners. Therefore, we propose that future studies with larger population sizes should include both maternal and paternal factors.

A Preconception Paternal Fish Oil Diet Prevents Toxicant-Driven New Bronchopulmonary Dysplasia in Neonatal Mice

New bronchopulmonary dysplasia is a developmental lung disease associated with placental dysfunction and impaired alveolarization. Risk factors for new BPD include prematurity, delayed postnatal growth, the dysregulation of epithelial-to-mesenchymal transition (EMT), and parental exposure to toxicants. Our group previously reported that a history of paternal toxicant exposure increased the risk of prematurity and low birth weight in offspring. A history of paternal toxicant exposure also increased the offspring's risk of new BPD and disease severity was increased in offspring who additionally received a supplemental formula diet, which has also been linked to poor lung development. Risk factors associated with new BPD are well-defined, but it is unclear whether the disease can be prevented. Herein, we assessed whether a paternal fish oil diet could attenuate the development of new BPD in the offspring of toxicant exposed mice, with and without neonatal formula feeding. We investigated the impact of a paternal fish oil diet preconception because we previously reported that this intervention reduces the risk of TCDD associated placental dysfunction, prematurity, and low birth weight. We found that a paternal fish oil diet significantly reduced the risk of new BPD in neonatal mice with a history of paternal toxicant exposure regardless of neonatal diet. Furthermore, our evidence suggests that the protective effects of a paternal fish oil diet are mediated in part by the modulation of small molecules involved in EMT.

Mapping the past, present and future research landscape of paternal effects

BACKGROUND

Although in all sexually reproducing organisms an individual has a mother and a father, non-genetic inheritance has been predominantly studied in mothers. Paternal effects have been far less frequently studied, until recently. In the last 5 years, research on environmentally induced paternal effects has grown rapidly in the number of publications and diversity of topics. Here, we provide an overview of this field using synthesis of evidence (systematic map) and influence (bibliometric analyses).

RESULTS

We find that motivations for studies into paternal effects are diverse. For example, from the ecological and evolutionary perspective, paternal effects are of interest as facilitators of response to environmental change and mediators of extended heredity. Medical researchers track how paternal pre-fertilization exposures to factors, such as diet or trauma, influence offspring health. Toxicologists look at the effects of toxins. We compare how these three research guilds design experiments in relation to objects of their studies: fathers, mothers and offspring. We highlight examples of research gaps, which, in turn, lead to future avenues of research.

CONCLUSIONS

The literature on paternal effects is large and disparate. Our study helps in fostering connections between areas of knowledge that develop in parallel, but which could benefit from the lateral transfer of concepts and methods.

Developmental 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure of either parent enhances the risk of necrotizing enterocolitis in neonatal mice

BACKGROUND

Necrotizing enterocolitis (NEC) is a rare, but potentially fatal intestinal inflammatory condition most often arising in premature infants. Infants provided formula are also at greater risk of developing this disease. Although the majority of formula-fed, preterm infants do not develop NEC, up to 30% of infants with the disease do not survive. Thus, identifying additional, currently unrecognized factors, which may predispose a specific infant to NEC development would be a significant clinical advancement. In this regard, we have previously reported that offspring of female or male mice with a history of developmental exposure to the environmental toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exhibit altered sensitivity to inflammatory challenges and are frequently born premature. Herein, we examined the possibility that, compared to unexposed mice (F1_NONE ), developmental TCDD exposure of either parent (maternal, F1M_TCDD , or paternal, F1P_TCDD ) would enhance the risk of NEC in offspring (F2_TCDD mice) in association with supplemental formula feeding.

METHODS

Beginning on postnatal day 7, all neonates were randomized to maternal milk only or maternal milk with up to 20 supplemental formula feedings. All pups remained with the Dams and were additionally allowed to nurse ad libitum.

RESULTS

Formula-fed F2_NONE pups rarely developed NEC while this disease was common in formula-fed F2M_TCDD and F2P_TCDD mice. Unexpectedly, 50% of F2M_TCDD pups that were not provided supplemental formula also developed NEC.

CONCLUSIONS

Our studies provide evidence that a history of parental TCDD exposure enhances the risk of NEC in offspring and suggest exposure to environmental immunotoxicants such as TCDD may also contribute to this inflammatory disease in humans.

Paternal developmental toxicant exposure is associated with epigenetic modulation of sperm and placental Pgr and Igf2 in a mouse model

Preterm birth (PTB), parturition prior to 37 weeks' gestation, is the leading cause of neonatal mortality. The causes of spontaneous PTB are poorly understood; however, recent studies suggest that this condition may arise as a consequence of the parental fetal environment. Specifically, we previously demonstrated that developmental exposure of male mice (F1 animals) to the environmental endocrine disruptor 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was associated with reduced sperm quantity/quality in adulthood and control female partners frequently delivered preterm. Reproductive defects persisted in the F2 and F3 descendants, and spontaneous PTB was common. Reproductive changes in the F3 males, the first generation without direct TCDD exposure, suggest the occurrence of epigenetic alterations in the sperm, which have the potential to impact placental development. Herein, we conducted an epigenetic microarray analysis of control and F1 male-derived placentae, which identified 2171 differentially methylated regions, including the progesterone receptor (Pgr) and insulin-like growth factor (Igf2). To assess if Pgr and Igf2 DNA methylation changes were present in sperm and persist in future generations, we assessed methylation and expression of these genes in F1/F3 sperm and F3-derived placentae. Although alterations in methylation and gene expression were observed, in most tissues, only Pgr reached statistical significance. Despite the modest gene expression changes in Igf2, offspring of F1 and F3 males consistently exhibited IUGR. Taken together, our data indicate that paternal developmental TCDD exposure is associated with transgenerational placental dysfunction, suggesting epigenetic modifications within the sperm have occurred. An evaluation of additional genes and alternative epigenetic mechanisms is warranted.

Paternal Environmental Toxicant Exposure and Risk of Adverse Pregnancy Outcomes

PURPOSE OF REVIEW

Current clinical efforts to predict and prevent preterm birth are primarily focused on the mother and have made minimal progress in improving outcomes. However, recent data indicate that paternal factors can also influence timing of birth. Herein, we will review recent human and murine data examining the contribution of the father to pregnancy outcomes with an emphasis on environmental exposures that can negatively impact fertility and the timing of birth.

RECENT FINDINGS

Human epidemiology studies now clearly indicate that a variety of paternal factors (age, race, weight, smoking status) can influence sperm quality, birth timing and, in some studies, offspring health. Utilizing a mouse model, our data have 57demonstrated that developmental exposure to the environmental toxicant TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) is associated with a transgenerational reduction in sperm number and quality and an increased risk of preterm birth in an unexposed partner.

SUMMARY

Toxicant exposure history can clearly influence sperm quality in men and mice. Murine data further indicate that exposures which negatively affect sperm quality also impair placental function, potentially leading to preterm birth and other adverse outcomes. Of particular concern, these changes have been linked to epigenetic alterations within the male germ cell which can then be transmitted across multiple generations. Since it is not possible to prevent an ancestral toxicant exposure in a human population, identifying lifestyle modifications that can be implemented during the preconception period to improve sperm quality should be explored for the therapeutic potential to reduce the incidence of PTB and its sequelae.

Sex-Dependent Influence of Developmental Toxicant Exposure on Group B Streptococcus-Mediated Preterm Birth in a Murine Model

Infectious agents are a significant risk factor for preterm birth (PTB); however, the simple presence of bacteria is not sufficient to induce PTB in most women. Human and animal data suggest that environmental toxicant exposures may act in concert with other risk factors to promote PTB. Supporting this "second hit" hypothesis, we previously demonstrated exposure of fetal mice (F1 animals) to the environmental endocrine disruptor 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) leads to an increased risk of spontaneous and infection-mediated PTB in adult animals. Surprisingly, adult F1_males also confer an enhanced risk of PTB to their control partners. Herein, we used a recently established model of ascending group B Streptococcus (GBS) infection to explore the impact of a maternal versus paternal developmental TCDD exposure on infection-mediated PTB in adulthood. Group B Streptococcus is an important contributor to PTB in women and can have serious adverse effects on their infants. Our studies revealed that although gestation length was reduced in control mating pairs exposed to low-dose GBS, dams were able to clear the infection and bacterial transmission to pups was minimal. In contrast, exposure of pregnant F1_females to the same GBS inoculum resulted in 100% maternal and fetal mortality. Maternal health and gestation length were not impacted in control females mated to F1_males and exposed to GBS; however, neonatal survival was reduced compared to controls. Our data revealed a sex-dependent impact of parental TCDD exposure on placental expression of Toll-like receptor 2 and glycogen production, which may be responsible for the differential impact on fetal and maternal outcomes in response to GBS infection.

Developmental exposure of mice to dioxin promotes transgenerational testicular inflammation and an increased risk of preterm birth in unexposed mating partners

TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin, commonly known as dioxin) is a ubiquitous environmental contaminant and known endocrine disruptor. Using a mouse model, we previously found that adult female mice exposed in utero to TCDD (F1 generation) as well as multiple subsequent generations (F2-F4) exhibited reduced fertility and an increased incidence of spontaneous preterm birth. Additional studies revealed that male F1 mice with a similar in utero/developmental TCDD exposure also exhibited diminished fertility and conferred an increased risk of preterm birth to their unexposed mating partners. Herein, we extend these previous observations, reporting that reduced fertility in male F1 mice is linked to testicular inflammation which coincides with apoptosis of developing spermatocytes, sub-fertility and an increased risk of preterm birth in their unexposed mating partners. Significantly, in the absence of additional toxicant exposure, testicular inflammation and reduced fertility persisted in F2 and F3 males and their control mating partners also frequently exhibited spontaneous preterm birth. Although a steady, global decline in male fertility has been noted over the last few decades, the reasons for these changes have not been firmly established. Likewise, the PTB rate in the U.S. and other countries has paralleled industrial development, suggesting a possible relationship between environmental toxicant exposure and adverse pregnancy outcomes. Most current clinical strategies to prevent preterm birth are focused solely on the mother and have yielded limited benefits. In contrast, our studies strongly suggest that the preconception testicular health of the father is a critical determinant of pregnancy outcomes in mice. Future clinical studies should examine the potential contribution of the male to gestation length in women and whether efforts to reduce the incidence of preterm birth should be initiated in both parents prior to pregnancy.

Do in utero events contribute to current health disparities in reproductive medicine?

Health disparities exist in reproductive medicine as discussed in detail in the subsequent articles of this issue; however, in most cases, the exact cause of these differences is unknown. Some of these disparities can be linked to environmental exposures such as alcohol and other hazardous toxic exposures (polycarbonate, pesticides, nicotine) in adults. In addition, low socioeconomic status, behavioral risk factors, and lack of education have been linked to poor obstetric and reproductive outcomes in minority groups. Aside from these various environmental exposures later in life, there is evidence that adverse events in utero could contribute to poor reproductive outcome in specific minority groups. We will focus on the developmental origins of health and disease as a possible causal mechanism for health disparities in reproductive diseases, as this perspective may suggest tractable solutions of how to address and eliminate these health disparities.

Racial and ethnic health disparities in reproductive medicine: an evidence-based overview

Racial and ethnic health disparities in reproductive medicine exist across the life span and are costly and burdensome to our healthcare system. Reduction and ultimate elimination of health disparities is a priority of the National Institutes of Health who requires reporting of race and ethnicity for all clinical research it supports. Given the increasing rates of admixture in our population, the definition and subsequent genetic significance of self-reported race and ethnicity used in health disparity research is not straightforward. Some groups have advocated using self-reported ancestry or carefully selected single-nucleotide polymorphisms, also known as ancestry informative markers, to sort individuals into populations. Despite the limitations in our current definitions of race and ethnicity in research, there are several clear examples of health inequalities in reproductive medicine extending from puberty and infertility to obstetric outcomes. We acknowledge that socioeconomic status, education, insurance status, and overall access to care likely contribute to the differences, but these factors do not fully explain the disparities. Epigenetics may provide the biologic link between these environmental factors and the transgenerational disparities that are observed. We propose an integrated view of health disparities across the life span and generations focusing on the metabolic aspects of fetal programming and the effects of environmental exposures. Interventions aimed at improving nutrition and minimizing adverse environmental exposures may act synergistically to reverse the effects of these epigenetic marks and improve the outcome of our future generations.

The Role of Endocrine Disruptors in the Epigenetics of Reproductive Disease and Dysfunction: Potential Relevance to Humans

In a murine model, we have linked early life toxicant exposure to reduced uterine sensitivity to progesterone, a phenotype we had previously associated with inflammation in endometriosis patients. Subsequent studies revealed that developmental toxicant exposure not only reduces fertility in male and female mice but also negatively impacts pregnancy leading to spontaneous preterm birth (PTB). An epigenetic alteration of the progesterone receptor gene correlated with reduced fertility and adverse pregnancy outcomes and persisted in multiple generations of mice in the absence of an additional toxicant exposure. Gene-environment interactions in women may explain why some patients "at risk" for PTB deliver at term while others without known risks deliver early. Our model provides a unique system to unravel the interactive influences of inflammation and reduced progesterone responsiveness on PTB and suggests that therapy needs to begin prior to pregnancy (and involve both partners) rather than once the inflammatory cascade has been initiated.

Environmental toxicants--induced epigenetic alterations and their reversers

Epigenetics has been emphasized in the postgenome era to clarify obscure health risks of environmental toxicants including endocrine disrupting chemicals (EDCs). In addition, mixed exposure in real life can modify health consequences of the toxicants. Particularly, some nutritional and dietary materials modify individual susceptibility through changes in the epigenome. Therefore, we focused on some environmental toxicants that induce epigenetic alterations, and introduced chemopreventive materials to reverse the toxicants-induced epigenetic alterations. Methodologically, we used global and specific DNA methylation as epigenetic end points and searched epigenetic modulators in food. We reviewed various epigenetic end points induced by environmental toxicants including alcohol, asbestos, nanomaterials, benzene, EDCs, metals, and ionizing radiation. The epigenetic end points can be summarized into global hypomethylation and specific hypermethylation at diverse tumor suppress genes. Exposure timing, dose, sex, or organ specificity should be considered to use the epigenetic end points as biomarkers for exposure to the epimutagenic toxicants. Particularly, neonatal exposure to the epimutagens can influence their future adult health because of characteristics of the epimutagens, which disrupt epigenetic regulation in imprinting, organogenesis, development, etc. Considering interaction between epimutagenic toxicants and their reversers in food, we suggest that multiple exposures to them can alleviate or mask epigenetic toxicity in real life. Our present review provides useful information to find new end points of environmental toxicants and to prevention from environment-related diseases.