To Cull or Not To Cull? Considerations for Studies of Endocrine-Disrupting Chemicals

Effects of a TAML catalyst on mice exposed during pregnancy and lactation

Tetra-amido macrocyclic ligands (TAMLs) are catalysts designed to mimic endogenous peroxidases that can degrade pollutants. Before TAMLs gain widespread use, it is first important to determine if they have endocrine disrupting properties. In this study, we evaluated the effects of the iron TAML, NT7, on hormone-sensitive outcomes in mice exposed during pregnancy and lactation, and on their litters prior to weaning. We administered NT7 at one of three doses to mice via drinking water prior to and then throughout pregnancy and lactation. Two hormonally active pharmaceuticals, ethinyl estradiol (EE2) and flutamide (FLUT), a known estrogen receptor agonist and androgen receptor antagonist, respectively, were also included. In the females, we measured pre- and post-parturition weight, length of pregnancy, organ weights at necropsy, and morphology of the mammary gland at the end of the lactational period. We also quantified maternal behaviors at three stages of lactation. For the offspring, we measured litter size, litter weights, and the achievement of other developmental milestones. We observed only one statistically significant effect of NT7, a decrease in the percentage of pups with ear opening at postnatal day 5. This contrasts with the numerous effects of EE2 on both the mother and the litter, as well as several modest effects of FLUT. The approach taken in this study could provide guidance for future studies that aim to evaluate novel compounds for endocrine disrupting properties.

On the basis of sex: male vs. female rat adenosine A1/A2A receptor affinity

OBJECTIVE

To ensure reproducibility in biomedical research, the biological variable sex must be reported; yet a reason for using male (instead of female) rodents is seldom given. In our search for novel adenosine receptor ligands, our research group routinely determines a test compound's binding affinities at male Sprague-Dawley rat (r) adenosine A1 and A2A receptors via in vitro radioligand binding studies. This pilot study compared the binding affinities of four adenosine receptor ligands (frequently used as reference standards) at male and female adenosine rA1 and rA2A receptors.

RESULTS

The inhibition constant (Ki) values determined using female rats correspond well to the values obtained using male rats and no markable difference could be observed in affinity and selectivity of reference standards. For example, DPCPX the selective adenosine A1 receptor antagonist: male rA1Ki: 0.5 ± 0.1 nM versus female rA1Ki: 0.5 ± 0.03 nM; male rA2AKi: 149 ± 23 nM versus female rA2AKi: 135 ± 29 nM. From the limited data at hand, we conclude that even when using female rats for in vitro studies without regard for the oestrous cycle, the obtained data did not vary much from their male counterparts.

Maternal acrylamide exposure changes intestinal epithelium, immunolocalization of leptin and ghrelin and their receptors, and gut barrier in weaned offspring

Acrylamide (ACR) is an amide formed as a byproduct in many heat-processed starchy-rich foods. In utero ACR exposure has been associated with restricted fetal growth, but its effects of postnatal functional development of small intestine is completely unknown. The current study investigated the time- and segment-dependent effects of prenatal ACR exposure on morphological and functional development of small intestine in weaned rat offspring. Four groups of pregnant female Wistar rats were exposed to ACR (3 mg/kg b.w./day) for 0, 5, 10 and 15 days during pregnancy. Basal intestinal morphology, immunolocalization of gut hormones responsible for food intake and proteins of intestinal barrier, activity of the intestinal brush border disaccharidases, apoptosis and proliferation in intestinal mucosa were analyzed in offspring at weaning (postnatal day 21). The results showed that in utero ACR exposure disturbs offspring gut structural and functional postnatal development in a time- and segment-depended manner and even a short prenatal exposure to ACR resulted in changes in intestinal morphology, immunolocalization of leptin and ghrelin and their receptors, barrier function, activity of gut enzymes and upregulation of apoptosis and proliferation. In conclusion, prenatal ACR exposure disturbed the proper postnatal development of small intestine.

Maternal behaviours and adult offspring behavioural deficits are predicted by maternal TNFα concentration in a rat model of neurodevelopmental disorders

Exposure to inflammatory stressors during fetal development is a major risk factor for neurodevelopmental disorders (NDDs) in adult offspring. Maternal immune activation (MIA), induced by infection, causes an acute increase in pro-inflammatory cytokines which can increase the risk for NDDs directly by inducing placental and fetal brain inflammation, or indirectly through affecting maternal care behaviours thereby affecting postnatal brain development. Which of these two potential mechanisms dominates in increasing offspring risk for NDDs remains unclear. Here, we show that acute systemic maternal inflammation induced by the viral mimetic polyinosinic:polycytidylic acid (poly I:C) on gestational day 15 of rat pregnancy affects offspring and maternal behaviour, offspring cognition, and expression of NDD-relevant genes in the offspring brain. Dams exposed to poly I:C elicited an acute increase in the pro-inflammatory cytokine tumour necrosis factor (TNF; referred to here as TNFα), which predicted disruption of key maternal care behaviours. Offspring of poly I:C-treated dams showed early behavioural and adult cognitive deficits correlated to the maternal TNFα response, but, importantly, not with altered maternal care. We also found interacting effects of sex and treatment on GABAergic gene expression and DNA methylation in these offspring in a brain region-specific manner, including increased parvalbumin expression in the female adolescent frontal cortex. We conclude that the MIA-induced elevation of TNFα in the maternal compartment affects fetal neurodevelopment leading to altered offspring behaviour and cognition. Our results suggest that a focus on prenatal pathways affecting fetal neurodevelopment would provide greater insights into the mechanisms underpinning the TNFα-mediated genesis of altered offspring behaviour and cognition following maternal inflammation.

Neonatal Behavioral Screen for Mouse Models of Neurodevelopmental Disorders

Behavioral phenotyping approaches for neonatal mice are important for investigating early alterations in brain development and function, relevant to neurodevelopmental disorders in humans. This chapter describes a behavioral screen that can provide an overall profile of function across the neonatal and preweaning period while also minimizing pup stress and disturbance of the maternal environment. Testing begins when mice are between 6 and 8 days in age, with additional evaluations at discrete time points until postnatal day (PD) 20-21, using tests for negative geotaxis, surface righting reflex, activity in an open field, acoustic startle responses and sensorimotor gating, and limb clasp.

Rodent models of metabolic disorders: considerations for use in studies of neonatal programming

Epidemiologically, metabolic disorders have garnered much attention, perhaps due to the predominance of obesity. The early postnatal life represents a critical period for programming multifactorial metabolic disorders of adult life. Though altricial rodents are prime subjects for investigating neonatal programming, there is still no sufficiently generalised literature on their usage and methodology. This review focuses on establishing five approach-based models of neonatal rodents adopted for studying metabolic phenotypes. Here, some modelled interventions that currently exist to avoid or prevent metabolic disorders are also highlighted. We also bring forth recommendations, guidelines and considerations to aid research on neonatal programming. It is hoped that this provides a background to researchers focused on the aetiology, mechanisms, prevention and treatment of metabolic disorders.

Postweaning positive modulation of α5GABAA receptors improves autism-like features in prenatal valproate rat model in a sex-specific manner

Autism spectrum disorder (ASD), as a common neurodevelopmental disorder that encompasses impairments in social communication and interaction, as well as repetitive and restrictive behavior, still awaits an effective treatment strategy. The involvement of GABAergic neurotransmission, and especially a deficit of GABA_A receptors that contain the α5 subunits, were implicated in pathogenesis of ASD. Therefore, we tested MP-III-022, a positive allosteric modulator (PAM) selective for α5GABAA receptors, in Wistar rats prenatally exposed to valproic acid, as an animal model useful for studying ASD. Postweaning rats of both sexes were treated for 7 days with vehicle or MP-III-022 at two doses pharmacokinetically determined as selective, and thereafter tested in a behavioral battery (social interaction test, elevated plus maze, spontaneous locomotor activity, and standard and reverse Morris water maze). Additional rats were used for establishing a primary neuronal culture and performing calcium imaging, and determination of hippocampal mRNA levels of GABRA5, NKCC1, and KCC2. MP-III-022 prevented impairments in many parameters connected with social, repetitive and restrictive behavioral domains. The lower and higher dose was more effective in males and females, respectively. Intriguingly, MP-III-022 elicited certain changes in control animals similar to those manifested in valproate animals themselves. Behavioral results were mirrored in GABA switch and spontaneous neuronal activity, assessed with calcium imaging, and also in expression changes of three genes analyzed. Our data support a role of α5GABAA receptors in pathophysiology of ASD, and suggest a potential application of selective PAMs in its treatment, that needs to be researched in a sex-specific manner. LAY SUMMARY: In rats prenatally exposed to valproate as a model of autism, a modulator of α5GABAA receptors ameliorated social, repetitive and restrictive impairments, and, intriguingly, elicited certain autism-like changes in control rats. Behavioral results were mirrored in GABA switch and spontaneous neuronal activity, and partly in gene expression changes. This shows a role of α5GABAA receptors in pathophysiology of ASD, and a potential application of their selective modulators in its treatment.

Roadbumps at the Crossroads of Integrating Behavioral and In Vitro Approaches for Neurotoxicity Assessment

With the appreciation that behavior represents the integration and complexity of the nervous system, neurobehavioral phenotyping and assessment has seen a renaissance over the last couple of decades, resulting in a robust database on rodent performance within various testing paradigms, possible associations with human disorders, and therapeutic interventions. The interchange of data across behavior and other test modalities and multiple model systems has advanced our understanding of fundamental biology and mechanisms associated with normal functions and alterations in the nervous system. While there is a demonstrated value and power of neurobehavioral assessments for examining alterations due to genetic manipulations, maternal factors, early development environment, the applied use of behavior to assess environmental neurotoxicity continues to come under question as to whether behavior represents a sensitive endpoint for assessment. Why is rodent behavior a sensitive tool to the neuroscientist and yet, not when used in pre-clinical or chemical neurotoxicity studies? Applying new paradigms and evidence on the biological basis of behavior to neurobehavioral testing requires expertise and refinement of how such experiments are conducted to minimize variability and maximize information. This review presents relevant issues of methods used to conduct such test, sources of variability, experimental design, data analysis, interpretation, and reporting. It presents beneficial and critical limitations as they translate to the in vivo environment and considers the need to integrate across disciplines for the best value. It proposes that a refinement of behavioral assessments and understanding of subtle pronounced differences will facilitate the integration of data obtained across multiple approaches and to address issues of translation.

Persistent autism-relevant behavioral phenotype and social neuropeptide alterations in female mice offspring induced by maternal transfer of PBDE congeners in the commercial mixture DE-71

Polybrominated diphenyl ethers (PBDEs) are ubiquitous persistent organic pollutants (POPs) that are known neuroendocrine disrupting chemicals with adverse neurodevelopmental effects. PBDEs may act as risk factors for autism spectrum disorders (ASD), characterized by abnormal psychosocial functioning, although direct evidence is currently lacking. Using a translational exposure model, we tested the hypothesis that maternal transfer of a commercial mixture of PBDEs, DE-71, produces ASD-relevant behavioral and neurochemical deficits in female offspring. C57Bl6/N mouse dams (F0) were exposed to DE-71 via oral administration of 0 (VEH/CON), 0.1 (L-DE-71) or 0.4 (H-DE-71) mg/kg bw/d from 3 wk prior to gestation through end of lactation. Mass spectrometry analysis indicated in utero and lactational transfer of PBDEs (in ppb) to F1 female offspring brain tissue at postnatal day (PND) 15 which was reduced by PND 110. Neurobehavioral testing of social novelty preference (SNP) and social recognition memory (SRM) revealed that adult L-DE-71 F1 offspring display deficient short- and long-term SRM, in the absence of reduced sociability, and increased repetitive behavior. These effects were concomitant with reduced olfactory discrimination of social odors. Additionally, L-DE-71 exposure also altered short-term novel object recognition memory but not anxiety or depressive-like behavior. Moreover, F1 L-DE-71 displayed downregulated mRNA transcripts for oxytocin (Oxt) in the bed nucleus of the stria terminalis (BNST) and supraoptic nucleus, and vasopressin (Avp) in the BNST and upregulated Avp1ar in BNST, and Oxtr in the paraventricular nucleus. Our work demonstrates that developmental PBDE exposure produces ASD-relevant neurochemical, olfactory processing and behavioral phenotypes that may result from early neurodevelopmental reprogramming within central social and memory networks.

The effects of perinatal fluoxetine exposure on emotionality behaviours and cortical and hippocampal glutamatergic receptors in female Sprague-Dawley and Wistar-Kyoto rats

RATIONALE

There is increasing concern regarding the use of selective serotonin reuptake inhibitors (SSRIs) in pregnancy. Animal studies repeatedly show increased anxiety- and depressive-like behaviours in offspring exposed perinatally to SSRIs, however much of this research is in male offspring.

OBJECTIVES

The primary aim of this study was to investigate the effects of perinatal SSRI exposure on emotionality-related behaviours in female offspring and associated glutamatergic markers, in Sprague-Dawley (SD) rats and in the Wistar-Kyoto (WKY) rat model of depression. Secondly, we sought to investigate the glutamatergic profile of female WKY rats that may underlie their depressive- and anxiety-like phenotype.

METHODS

WKY and SD rat dams were treated with the SSRI, fluoxetine (FLX; 10 mg/kg/day), or vehicle, throughout gestation and lactation (5 weeks total). Female adolescent offspring underwent behaviour testing followed by quantitative immunoblot of glutamatergic markers in the prefrontal cortex and ventral hippocampus.

RESULTS

Naïve female WKY offspring displayed an anxiety-like and depressive-like phenotype as well as reductions in NMDA and AMPA receptor subunits and PSD-95 in both ventral hippocampus and prefrontal cortex, compared to SD controls. Perinatal FLX treatment increased anxiety-like and forced swim immobility behaviours in SD offspring but did not influence behaviour in female WKY offspring using these tests. Perinatal FLX exposure did not influence NMDA or AMPA receptor subunit expression in female WKY or SD offspring; it did however have restricted effects on group I mGluR expression in SD and WKY offspring and reduce the glutamatergic synaptic scaffold, PSD-95.

CONCLUSION

These findings suggest female offspring of the WKY strain display deficits in glutamatergic markers which may be related to their depressive- and anxiety-like phenotype. While FLX exposed SD offspring displayed increases in anxiety-like and depressive-like behaviours, further studies are needed to assess the potential impact of developmental FLX exposure on the behavioural phenotype of female WKY rats.

Maternal obesity interrupts the coordination of the unfolded protein response and heat shock response in the postnatal developing hypothalamus of male offspring in mice

Maternal obesity malprograms offspring obesity and associated metabolic disorder. As a common phenomenon in obesity, endoplasmic reticulum (ER) stress also presents early prior to the development. Here, we investigate metabolic effect of early activated hypothalamic ER stress in offspring exposed to maternal obesogenic environment and the underlying mechanism in ICR mice model. We found higher body weight, hyperphagia and defective hypothalamic feeding-circuit in the offspring born to obese dams, with hypothalamic ER stress, and even more comprehensive cell proteotoxic stress were induced during the early postnatal period. However, neonatal inhibition of hypothalamic ER stress worsened the metabolic end. We believe that the uncoordinated interaction between the unfolded protein response and the heat shock response, regulated by heat shock protein 70, might be responsible for the malformed hypothalamic feeding circuit of the offspring exposure to maternal obesogenic conditions and were linked with deleterious metabolism in adulthood, especially when exposure to high-energy conditions.

Controlling litter effects to enhance rigor and reproducibility with rodent models of neurodevelopmental disorders

Research with rodents is crucial for expanding our understanding of genetic and environmental risk factors for neurodevelopmental disorders (NDD). However, there is growing concern about the number of animal studies that are difficult to replicate, potentially undermining the validity of results. These concerns have prompted funding agencies and academic journals to implement more rigorous standards in an effort to increase reproducibility in research. However, these standards fail to address a major source of variability in rodent research brought on by the “litter effect,” the fact that rodents from the same litter are phenotypically more similar to one other than rodents from different litters of the same strain. We show that the litter effect accounts for 30–60% of the variability associated with commonly studied phenotypes, including brain, placenta, and body weight. Moreover, we show how failure to control for litter-to-litter variation can mask a phenotype in Chd8^V986*/+ mice that model haploinsufficiency of CHD8, a high-confidence autism gene. Thus, if not properly controlled, the litter effect has the potential to negatively influence rigor and reproducibility of NDD research. While efforts have been made to educate scientists on the importance of controlling for litter effects in previous publications, our analysis of the recent literature (2015–2020) shows that the vast majority of NDD studies focused on genetic risks, including mutant mouse studies, and environmental risks, such as air pollution and valproic acid exposure, do not correct for litter effects or report information on the number of litters used. We outline best practices to help scientists minimize the impact of litter-to-litter variability and to enhance rigor and reproducibility in future NDD studies using rodent models.

Aging Induces Profound Changes in sncRNA in Rat Sperm and These Changes Are Modified by Perinatal Exposure to Environmental Flame Retardant

Advanced paternal age at fertilization is a risk factor for multiple disorders in offspring and may be linked to age-related epigenetic changes in the father's sperm. An understanding of aging-related epigenetic changes in sperm and environmental factors that modify such changes is needed. Here, we characterize changes in sperm small non-coding RNA (sncRNA) between young pubertal and mature rats. We also analyze the modification of these changes by exposure to environmental xenobiotic 2,2',4,4'-tetrabromodiphenyl ether (BDE-47). sncRNA libraries prepared from epididymal spermatozoa were sequenced and analyzed using DESeq 2. The distribution of small RNA fractions changed with age, with fractions mapping to rRNA and lncRNA decreasing and fractions mapping to tRNA and miRNA increasing. In total, 249 miRNA, 908 piRNA and 227 tRNA-derived RNA were differentially expressed (twofold change, false discovery rate (FDR) p ≤ 0.05) between age groups in control animals. Differentially expressed miRNA and piRNA were enriched for protein-coding targets involved in development and metabolism, while piRNA were enriched for long terminal repeat (LTR) targets. BDE-47 accelerated age-dependent changes in sncRNA in younger animals, decelerated these changes in older animals and increased the variance in expression of all sncRNA. Our results indicate that the natural aging process has profound effects on sperm sncRNA profiles and this effect may be modified by environmental exposure.

Effects of prenatal exposure to valproic acid or poly(I:C) on ultrasonic vocalizations in rat pups: The role of social cues

Sociocommunicative deficits commonly observed in autism spectrum disorder (ASD) can be experimentally modeled using rodents' ultrasonic vocalizations (USVs). For example, USVs emitted by pups, separated from their mothers and nest, serve as a useful tool to identify autistic-like behaviors during the early period of development. Being sensitive to social context, these neonatal calls may help to reveal reduced social attachment or abnormal processing of social information. The aim of the present study was to characterize quantitative and structural changes in USVs emitted during isolation by male and female rat pups prenatally exposed to either valproic acid (VPA) or poly(I:C). To determine whether those pups differed from controls in sensitivity to social stimuli, isolation-induced USVs were recorded under two bedding conditions, i.e., novel bedding and soiled bedding from their home cages. Our results demonstrated early communication deficits in both models of autism. We reported a reduced number of USVs emitted by both VPA- and poly(I:C)-exposed males and females. Moreover, compared to the controls, VPA (but not poly(I:C)) pups emitted shorter calls with a higher peak frequency. While VPA offspring demonstrated fewer USVs on the "safe" bedding imbued with maternal/nest odors, this calming effect was not observed in poly(I:C) males, suggesting a more specific deficit in social communication. The present results demonstrate that qualitative along with quantitative analyses of neonatal vocalizations are a useful tool for assessing early sociocommunicative deficits in ASD models. Notably, more specific changes in USV emission may be detected when introducing social context.

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.

Dose threshold for radiation induced fetal programming in a mouse model at 4 months of age: Hepatic expression of genes and proteins involved in glucose metabolism and glucose uptake in brown adipose tissue

Exposure to ionizing radiation contributing to negative health outcomes is a widespread concern. However, the impact of low dose and sub-lethal dose radiation (SLDR) exposures remain contentious, particularly in pregnant women who represent a vulnerable group. The fetal programming hypothesis states that an adverse in utero environment or stress during development of an embryo or fetus can result in permanent physiologic changes often resulting in progressive metabolic dysfunction with age. To assess changes in gene expression profiles of glucose/insulin signaling and lipid metabolism caused by radiation exposure in utero, pregnant C57Bl/6J mice were irradiated using a dose response ranging from low dose to SLDR and compared to a Sham-irradiated group. mRNA expression analysis in 16 week old offspring (n = 84) revealed that genes involved in metabolic function including glucose metabolism, insulin signaling and lipid metabolism were unaffected by prenatal radiation exposures up to 300 mGy. However, female offspring of dams exposed to 1000 mGy had upregulated expression of genes contributing to insulin resistance and gluconeogenesis. In a second cohort of mice, the effects of SLDR on fetal programming of hepatic SOCS3 and PEPCK protein expression were assessed. 4 month old female offspring of dams irradiated at 1000 mGy had: 1) increased liver weights, 2) increased hepatic expression of proteins involved in glucose metabolism and 3) increased ¹⁸F-fluorodeoxyglucose (FDG) uptake in interscapular brown adipose tissue (IBAT) measured by positron emission tomography (PET) (n = 25). The results of this study indicate that prenatal radiation exposure does not affect metabolic function up to 300 mGy and 1000 mGy may be a threshold dose for sex-specific alterations in glucose uptake and hepatic gene and protein expression of SOCS3, PEPCK, PPARGC1A and PPARGC1B. These findings suggest that SLDR doses alter glucose uptake in IBAT and hepatic gene and protein expression of offspring and these changes may progress with age.

Statistical modeling with litter as a random effect in mixed models to manage "intralitter likeness"

"Intralitter likeness," the possibility that the shared genetics and/or maternal environment in multiparous species causes strong similarity for outcome variables in littermates, violates a core statistical assumption, that of observation independence, when littermate outcomes are analyzed. Intralitter likeness has been of major concern to investigators for several decades. Despite consensus and guidance, many research reports in the rodent literature continue to ignore intralitter likeness. A historical review of the literature revealed that the long-preferred solution was to include litter as an effect in statistical models. Limitations in software development and computing capacity prior to 1990, however, appear to have led researchers and guidance authorities to endorse instead the method of using one value per litter. Here, the history of discussions regarding intralitter likeness in developmental neurotoxicological research is reviewed; growing knowledge regarding the biological bases and significance of intralitter likeness is discussed; principles underlying the use of litter as a random effect in mixed models are presented; statistical examples are provided illustrating the advantages and critical importance of including litter as a random effect in mixed models; and results using all data points (all pups from all litters) with litter as a random effect, are compared to results based on random selections of representative littermates. Mixed models with litter included as a random effect have distinct advantages for the analysis of clustered data. Modern computing capacity provides ready accessibility to mixed models for all researchers. Accessibility however does not preclude the need for appropriate expertise and consultation in the use of mixed (hierarchical) models.

Prenatal infection with Mycoplasma pulmonis in rats exaggerates the angiotensin II pressor response in adult offspring

Exposure to different stressors in utero is linked to adult diseases such as obesity and hypertension. In this study, the impact of prenatal infection (PNI) on adult body weight and cardiovascular function was evaluated using a naturally occurring rodent pathogen, Mycoplasma pulmonis (MP). Pregnant Sprague-Dawley rats were infected with MP on gestational day 14 and gave birth naturally. Adult PNI offspring weighed more than controls, but resting mean arterial pressure (MAP) was unchanged. Subcutaneous injection of angiotensin II (10 μg/kg) elicited a rise in MAP that was greater in both male and female PNI offspring compared with controls (P < 0.03). The accompanying reflex bradycardia was similar to the controls, suggesting that PNI induced baroreflex dysfunction. Subcutaneous nicotine administration, a potent cardiorespiratory stimulus, also elicited a transient rise in MAP that was generally greater in the PNI group, but the change in MAP from baseline was only significant in the PNI females compared with controls (P < 0.03). Elevated body weight and cardiovascular reactivity in the PNI offspring was associated with an increase in the ratio of hypothalamic corticotrophin-releasing hormone receptors type 1 to type 2 gene expression in both sexes compared with controls. These findings support previous studies demonstrating that PNI induces alterations in cardiovascular function and body weight. Yet, unlike previous studies utilizing other models of PNI (e.g., endotoxin), MP PNI did not induce resting hypertension. Thus, our study provides a foundation for future studies evaluating the cardiovascular risks of offspring exposed to microbial challenges in utero.

Rat liver epigenome programing by perinatal exposure to 2,2',4'4'-tetrabromodiphenyl ether

Perinatal exposures to polybrominated diphenyl ethers permanently reprogram liver metabolism and induce a nonalcoholic fatty liver disease-like phenotype and insulin resistance in rodents. Aim: To test if these changes are associated with altered liver epigenome. Materials & methods: Expression of small RNA and changes in DNA methylation in livers of adult rats were analyzed following perinatal exposure to 2,2',4,4'-tetrabromodiphenyl ether, the polybrominated diphenyl ether congener most prevalent in human tissues. Results: We identified 33 differentially methylated DNA regions and 15 differentially expressed miRNAs. These changes were enriched for terms related to lipid and carbohydrate metabolism, insulin signaling, Type-2 diabetes and nonalcoholic fatty liver disease. Conclusion: Changes in the liver epigenome are a likely candidate mechanism of long-term maintenance of an aberrant metabolic phenotype.

Exposure to low doses of oxybenzone during perinatal development alters mammary gland morphology in male and female mice

Oxybenzone (benzophenone-3) is an ultraviolet radiation filter commonly used in personal care products including sunscreens, textiles and inks, and food and beverage containers, among others. Due to its widespread use, human exposures to oxybenzone are widespread. Oxybenzone is considered an endocrine disrupting chemical due to its antiestrogenic and antiandrogenic properties. We evaluated the effects of oral exposures to oxybenzone on the growth and morphology of the mammary gland, body weight and anogenital distance in BALB/c mice exposed to 30, 212 or 3000 μg/kg/day in utero and during lactation. Developmental exposures to oxybenzone reduced the size and growth of mammary gland in males prior to and during puberty. In exposed females, oxybenzone reduced mammary cell proliferation, decreased the number of cells expressing estrogen receptor α, and altered mammary gland morphology in adulthood. These results suggest that even low doses of oxybenzone can disrupt hormone sensitive organs during critical windows of development.

Preclinical Models of Altered Early Life Nutrition and Development of Reproductive Disorders in Female Offspring

Early epidemiology studies in humans have and continue to offer valuable insight into the Developmental Origins of Health and Disease (DOHaD) hypothesis, which emphasises the importance of early-life nutritional and environmental changes on the increased risk of metabolic and reproductive disease in later life. Human studies are limited and constrained by a range of factors which do not apply to preclinical research. Animal models therefore offer a unique opportunity to fully investigate the mechanisms associated with developmental programming, helping to elucidate the developmental processes which influence reproductive diseases, and highlight potential biomarkers which can be translated back to the human condition. This review covers the use and limitations of a number of animal models frequently utilised in developmental programming investigations, with an emphasis on dietary manipulations which can lead to reproductive dysfunction in offspring.

Increased hepatic INSIG-SCAP-SREBP expression is associated with cholesterol metabolism disorder in assisted reproductive technology-conceived aged mice

Although most children conceived by assisted reproductive technology (ART) are healthy, there are concerns regarding the potential long-term health implications of ART. It has been reported that alterations in insulin-induced gene (INSIG), sterol regulatory element binding protein (SREBP), and SREBP cleavage-activating protein (SCAP) are involved in cardiometabolic changes. Thus, ART mouse models were established via in vitro fertilization (IVF), intracytoplasmic injection (ICSI), and in vitro oocyte maturation (IVM). A significantly higher systolic blood pressure was identified in the IVM aged female mice. In addition, abnormalities in the blood lipids and liver function were identified in the IVM- or ICSI-conceived elderly mice. Furthermore, ICSI or IVM significantly affected the hepatic expression and methylation of INSIG-SCAP-SREBP from a young to old age. Our animal data indicated that ICSI or IVM result in a higher risk of cholesterol metabolism dysfunction in older mice, which may be associated with long-term alterations of INSIG-SCAP-SREBP.

Effects of Perinatal Exposure to Dibutyltin Chloride on Fat and Glucose Metabolism in Mice, and Molecular Mechanisms, in Vitro

BACKGROUND

The organotin dibutyltin (DBT) is used in the manufacture of polyvinyl chloride (PVC) plastics, in construction materials, and in medical devices. Previous animal studies showed detrimental effects of DBT during in utero development at relatively high doses, but little was known about the effects of DBT exposure at environmentally relevant doses on endpoints such as obesity and metabolic disease.

OBJECTIVES

We tested the potential obesogenic effects of DBT using in vitro and in vivo models.

METHODS

We evaluated the effects of DBT on nuclear receptor activation and adipogenic potential using human and mouse multipotent mesenchymal stromal stem cells (MSCs). We also evaluated the effects of perinatal exposure to environmentally relevant doses of DBT in C57BL/6J mice.

RESULTS

DBT activated human and mouse PPARγ and RXRα in transient transfection assays, increased expression of adipogenic genes, promoted adipogenic differentiation and increased lipid accumulation in mouse and human MSCs, in vitro. DBT-induced adipogenic differentiation was abolished by the PPARγ antagonist T0070907, indicating that DBT was acting primarily through PPARγ. Perinatal exposure to low doses of DBT led to increased fat storage, decreased glucose tolerance, and increased circulating leptin levels in male, but not female, mice.

CONCLUSIONS

DBT acted as an obesogen by inducing lipid accumulation in human and mouse MSCs through a PPARγ-dependent pathway. In vivo exposure to biologically relevant doses of DBT during perinatal development led to increased fat storage, elevated leptin levels in plasma, and glucose intolerance in mice. Based on these findings, we posit that monitoring of DBT levels in human samples may aid in understanding and potentially preventing the rising rates of metabolic disorders in human populations. https://doi.org/10.1289/EHP3030.

Transcriptomic Analysis of Gonadal Adipose Tissue in Male Mice Exposed Perinatally to 2,2',4,4'-Tetrabromodiphenyl Ether (BDE-47)

For the majority of lipophilic compounds, adipose tissue is traditionally considered as a storage depot and only rarely as a target organ. Meanwhile, abnormalities in adipose tissue physiology induced by chemical exposure may contribute to the current epidemic of obesity and metabolic diseases. Polybrominated diphenyl ethers (PBDEs) are a group of lipophilic flame retardants found in the majority of human samples in North America. Their ability to alter the physiology of adipose tissue is unknown. We exposed pregnant mice to 0.2 mg/kg body weight/day of BDE-47 perinatally. Transcriptomic changes in gonadal adipose tissue were analyzed in male offspring using the RNA-seq approach with subsequent bioinformatic analysis. The expression of genes of coagulation and complement cascade, de novo lipogenesis, and xenobiotic metabolism was altered in response to BDE-47 exposure. The affected molecular network included the following hubs: PPARα, HNF1A, and HNF4. These findings suggest that adipose tissue should be considered a target tissue for BDE-47, in addition to its role as a storage depot. This study also builds a background for a targeted search of sensitive phenotypic endpoints of BDE-47 exposure, including lipid profile parameters and coagulation factors in circulation. Additional studies are needed to investigate the role of PBDEs as an obesogen.

Prenatal Exposure to Unconventional Oil and Gas Operation Chemical Mixtures Altered Mammary Gland Development in Adult Female Mice

Unconventional oil and gas (UOG) operations, which combine hydraulic fracturing (fracking) and directional drilling, involve the use of hundreds of chemicals, including many with endocrine-disrupting properties. Two previous studies examined mice exposed during early development to a 23-chemical mixture of UOG compounds (UOG-MIX) commonly used or produced in the process. Both male and female offspring exposed prenatally to one or more doses of UOG-MIX displayed alterations to endocrine organ function and serum hormone concentrations. We hypothesized that prenatal UOG-MIX exposure would similarly disrupt development of the mouse mammary gland. Female C57Bl/6 mice were exposed to ~3, ~30, ~ 300, or ~3000 μg/kg/d UOG-MIX from gestational day 11 to birth. Although no effects were observed on the mammary glands of these females before puberty, in early adulthood, females exposed to 300 or 3000 μg/kg/d UOG-MIX developed more dense mammary epithelial ducts; females exposed to 3 μg/kg/d UOG-MIX had an altered ratio of apoptosis to proliferation in the mammary epithelium. Furthermore, adult females from all UOG-MIX-treated groups developed intraductal hyperplasia that resembled terminal end buds (i.e., highly proliferative structures typically seen at puberty). These results suggest that the mammary gland is sensitive to mixtures of chemicals used in UOG production at exposure levels that are environmentally relevant. The effect of these findings on the long-term health of the mammary gland, including its lactational capacity and its risk of cancer, should be evaluated in future studies.

Developmental Exposure to 2,2',4,4'-Tetrabromodiphenyl Ether Permanently Alters Blood-Liver Balance of Lipids in Male Mice

Polybrominated diphenyl ethers (PBDEs) were used as flame-retardant additives starting 1965 and were recently withdrawn from commerce in North America and Europe. Approximately 1/5 of the total U.S. population were born when environmental concentrations of PBDE plateaued at their maximum. Accumulating evidence suggests that developmental exposures to PBDE may result in long-lasting programming of liver metabolism. In this study, CD-1 mice were exposed prenatally or neonatally to 1 mg/kg body weight of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), and changes in liver histology, transcriptome, and liver-blood balance of triglycerides were analyzed in 10 months old male offspring. In both exposure groups, long-term reprogramming of lipid metabolism was observed, including increased liver triglycerides and decreased blood triglycerides, and altered expression of metabolic genes in the liver. Significant upregulation of lipid influx transporter Cd36 2.3- and 5.7-fold in pre- and neonatal exposure groups, respectively was identified as a potential mechanism of blood/liver imbalance of triglycerides. Analysis of our and previously published all-genome gene expression data identified changes in expression of ribosomal protein genes as a transcriptomic signature of PBDE exposure. Further comparison of our new data and published data demonstrate that low doses (0.2 mg/kg body weight) of PBDE induce long-lasting up-regulation of ribosomal genes, suppression of Cd36 in liver and increase circulating triglycerides in blood, while moderated doses (≥1 mg/kg body weight) produce opposite long-lasting effects. To conclude, this study shows that an environmentally relevant developmental exposures to BDE-47 permanently alter lipid uptake and accumulation in the liver, with low and moderate doses having opposite effect on liver transcriptomics and triglyceride balance. Similar effects of pre- and neonatal exposures point at hepatocyte maturation as a sensitive window of the liver metabolism programming. These results suggest that PBDE exposure may be an important factor increasing risks of cardio-vascular disease and non-alcoholic fatty liver disease via modulation of liver/blood balance of lipids. The translational relevance of these findings for human remain to be studied.

Developmental Exposure to 2,2',4,4'-Tetrabromodiphenyl Ether Induces Long-Lasting Changes in Liver Metabolism in Male Mice

Polybrominated diphenyl ethers (PBDEs) were used as flame-retardant additives in a wide range of polymers. The generations born when environmental concentrations of PBDEs reached their maximum account in the United States for one-fifth of the total population. We hypothesized that exposure to PBDEs during sensitive developmental windows might result in long-lasting changes in liver metabolism. The present study was based on experiments with CD-1 mice and human hepatocellular carcinoma cells (human hepatoma cell line, HepG2). Pregnant mice were exposed to 0.2 mg/kg 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) from gestation day 8 until postnatal day 21. The metabolic health-related outcomes were analyzed on postnatal day 21 and postnatal week 20 in male offspring. Several groups of metabolic genes, including ribosomal and mitochondrial genes, were significantly upregulated in the liver at both points. Genes regulated via mechanistic target of rapamycin (mTOR) pathway, the gatekeeper of metabolic homeostasis, were whether up- or downregulated at both measurement points. On postnatal day 21, but not week 20, both mTOR complexes in the liver were activated, as measured by phosphorylation of their targets. mTOR complexes were also activated by BDE-47 in HepG2 cells in vitro. The following changes were observed at week 20: a decreased number of polyploid hepatocytes, suppressed cytoplasmic S6K1, twofold greater blood insulin-like growth factor-1 and triglycerides, and 2.5-fold lower expression of fatty acid uptake membrane receptor CD36 in liver tissue. Thus, perinatal exposure to environmentally relevant doses of BDE-47 in laboratory mice results in long-lasting changes in liver physiology. Our evidence suggests involvement of the mTOR pathway in the observed metabolic programming of the liver.

Bisphenol S (BPS) Alters Maternal Behavior and Brain in Mice Exposed During Pregnancy/Lactation and Their Daughters

Estrogenic endocrine disrupting chemicals have been shown to disrupt maternal behavior in rodents. We investigated the effects of an emerging xenoestrogen, bisphenol S (BPS), on maternal behavior and brain in CD-1 mice exposed during pregnancy and lactation (F0 generation) and in female offspring exposed during gestation and perinatal development (F1 generation). We observed different effects in F0 and F1 dams for a number of components of maternal behavior, including time on the nest, time spent on nest building, latency to retrieve pups, and latency to retrieve the entire litter. We also characterized expression of estrogen receptor α in the medial preoptic area (MPOA) and quantified tyrosine hydroxylase immunoreactive cells in the ventral tegmental area, 2 brain regions critical for maternal care. BPS-treated females in the F0 generation had a statistically significant increase in estrogen receptor α expression in the caudal subregion of the central MPOA in a dose-dependent manner. In contrast, there were no statistically significant effects of BPS on the MPOA in F1 dams or the ventral tegmental area in either generation. This work demonstrates that BPS affects maternal behavior and brain with outcomes depending on generation, dose, and postpartum period. Many studies examining effects of endocrine disrupting chemicals view the mother as a means by which offspring can be exposed during critical periods of development. Here, we demonstrate that pregnancy and lactation are vulnerable periods for the mother. We also show that developmental BPS exposure alters maternal behavior later in adulthood. Both findings have potential public health implications.

Sexually-dimorphic alterations in cannabinoid receptor density depend upon prenatal/early postnatal history

Recent research has demonstrated that the endogenous cannabinoid system is central to the brain's response to stress. As part of an ongoing collaboration, we sought to examine the effects of prenatal and early postnatal rearing and housing conditions on developing endocannabinoid systems. We compare brain cannabinoid receptors (CBR) in offspring of either prenatal vehicle intubated or non-treated dams (Experiment 1) or in rats derived from a vendor and shipped at weaning to a collaborating lab (Experiment 2). From postnatal day (PND) 23, all rats were either housed in isolated conditions or enriched conditions with 3 rats/cage and a variety of stimulus objects changed twice a week. All rats underwent 5days of handling as controls for a behavior study and all rats were sacrificed at approximately PND48-50 within 2hours of the last behavioral test. All brains were processed together for CB1 receptor binding using ³H CP55,940 in prefrontal cortex, striatum, amygdala and hippocampus. Conditions in the two labs were as similar as possible since the two studies were intentionally designed to be comparable and contemporary. Results show that 1) comparing offspring of non-treated dams to offspring of dams receiving daily vehicle intubations, males show decreased CB1 binding in most brain regions while females only showed alterations in the hippocampus and these were increases in the offspring of the vehicle-intubated dams. 2) When comparing offspring of non-treated dams in NY with those derived from a vendor, shipped and maintained in the collaborating lab, this latter group showed reduced CB1 binding in prefrontal cortex in males and increased binding in all four brain regions in females. Therefore, overall, both prenatal handling (intubations) and being vendor-derived, shipped and maintained in a collaborating facility reduced CB1 receptors in males and increased them in females in key limbic brain regions. Effects of environmental enrichment or isolation were minor with only the prefrontal cortex showing an increase in binding in the isolated animals that were offspring of the vehicle-intubated dams. These results support the ideas that prenatal/early postnatal conditions produce different effects in males and females and override the effects of enrichment/isolation on cannabinoid receptors. Behavioral responses to cannabinoid challenges would therefore be expected to vary depending on sex, prenatal/early postnatal history and postweaning conditions of the rats. Since exogenous cannabinoids act through the CBR, the present data may provide a molecular basis for discrepant behavioral effects reported across various labs in the literature as well as sex differences seen following stress and/or manipulation of the cannabinoid system.

Adverse Reproductive and Developmental Health Outcomes Following Prenatal Exposure to a Hydraulic Fracturing Chemical Mixture in Female C57Bl/6 Mice

Unconventional oil and gas operations using hydraulic fracturing can contaminate surface and groundwater with endocrine-disrupting chemicals. We have previously shown that 23 of 24 commonly used hydraulic fracturing chemicals can activate or inhibit the estrogen, androgen, glucocorticoid, progesterone, and/or thyroid receptors in a human endometrial cancer cell reporter gene assay and that mixtures can behave synergistically, additively, or antagonistically on these receptors. In the current study, pregnant female C57Bl/6 dams were exposed to a mixture of 23 commonly used unconventional oil and gas chemicals at approximately 3, 30, 300, and 3000 μg/kg·d, flutamide at 50 mg/kg·d, or a 0.2% ethanol control vehicle via their drinking water from gestational day 11 through birth. This prenatal exposure to oil and gas operation chemicals suppressed pituitary hormone concentrations across experimental groups (prolactin, LH, FSH, and others), increased body weights, altered uterine and ovary weights, increased heart weights and collagen deposition, disrupted folliculogenesis, and other adverse health effects. This work suggests potential adverse developmental and reproductive health outcomes in humans and animals exposed to these oil and gas operation chemicals, with adverse outcomes observed even in the lowest dose group tested, equivalent to concentrations reported in drinking water sources. These endpoints suggest potential impacts on fertility, as previously observed in the male siblings, which require careful assessment in future studies.