Variations in phytoestrogen content between different mill dates of the same diet produces significant differences in the time of vaginal opening in CD-1 mice and F344 rats but not in CD Sprague-Dawley rats

Grain versus AIN: Common rodent diets differentially affect health outcomes in adult C57BL/6j mice

Semi-synthetic and grain-based diets are common rodent diets for biomedical research. Both diet types are considered nutritionally adequate to support breeding, growth, and long life, yet there are fundamental differences between them that may affect metabolic processes. We have characterized the effects of diet type on breeding outcomes, metabolic phenotype, and microbiota profile in adult mice. Healthy 8-week-old female and male C57BL/6J mice were fed a semi-synthetic or a grain-based diet for 12 weeks and changes in body weight and body composition were monitored. Breeding outcomes were determined. Body fat accumulation of female mice was lower on the semi-synthetic diet than on the grain-based diet. Pregnancy rate and newborn pup survival appeared to be lower in mice exposed to semi-synthetic diet compared to grain-based diet. Both female and male mice showed a profound change in fecal microbiota alpha and beta diversity depending on diet type. Our study shows that type of rodent diet may affect breeding outcomes whilst influencing metabolism and health of female laboratory mice. These factors have the potential to influence other experimental outcomes and the results suggest that semi-synthetic and grain-based diets are not interchangeable in research using rodent models. Careful consideration and increased understanding of the consequences of diet choice would lead to improvements in experimental design and reproducibility of study results.

Obesity III: Obesogen assays: Limitations, strengths, and new directions

There is increasing evidence of a role for environmental contaminants in disrupting metabolic health in both humans and animals. Despite a growing need for well-understood models for evaluating adipogenic and potential obesogenic contaminants, there has been a reliance on decades-old in vitro models that have not been appropriately managed by cell line providers. There has been a quick rise in available in vitro models in the last ten years, including commercial availability of human mesenchymal stem cell and preadipocyte models; these models require more comprehensive validation but demonstrate real promise in improved translation to human metabolic health. There is also progress in developing three-dimensional and co-culture techniques that allow for the interrogation of a more physiologically relevant state. While diverse rodent models exist for evaluating putative obesogenic and/or adipogenic chemicals in a physiologically relevant context, increasing capabilities have been identified for alternative model organisms such as Drosophila, C. elegans, zebrafish, and medaka in metabolic health testing. These models have several appreciable advantages, including most notably their size, rapid development, large brood sizes, and ease of high-resolution lipid accumulation imaging throughout the organisms. They are anticipated to expand the capabilities of metabolic health research, particularly when coupled with emerging obesogen evaluation techniques as described herein.

Diet effects on mouse meiotic recombination: a warning for recombination studies

Meiotic recombination is a critical process for sexually reproducing organisms. This exchange of genetic information between homologous chromosomes during meiosis is important not only because it generates genetic diversity, but also because it is often required for proper chromosome segregation. Consequently, the frequency and distribution of crossovers are tightly controlled to ensure fertility and offspring viability. However, in many systems it has been shown that environmental factors can alter the frequency of crossover events. Two studies in flies and yeast point to nutritional status affecting the frequency of crossing over. However, this question remains unexplored in mammals. Here we test how crossover frequency varies in response to diet in Mus musculus males. We use immunohistochemistry to estimate crossover frequency in multiple genotypes under two diet treatments. Our results indicate that while crossover frequency was unaffected by diet in some strains, other strains were sensitive even to small composition changes between two common laboratory chows. Therefore, recombination is both resistant and sensitive to certain dietary changes in a strain-dependent manner and, hence, this response is genetically determined. Our study is the first to report a nutrition effect on genome-wide levels of recombination. Moreover, our work highlights the importance of controlling diet in recombination studies and may point to diet as a potential source of variability among studies, which is relevant for reproducibility.

The Influence of Feed and Drinking Water on Terrestrial Animal Research and Study Replicability

For more than 50 years, the research community has made strides to better determine the nutrient requirements for many common laboratory animal species. This work has resulted in high-quality animal feeds that can optimize growth, maintenance, and reproduction in most species. We have a much better understanding of the role that individual nutrients play in physiological responses. Today, diet is often considered as an independent variable in experimental design, and specialized diet formulations for experimental purposes are widely used. In contrast, drinking water provided to laboratory animals has rarely been a consideration in experimental design except in studies of specific water-borne microbial or chemical contaminants. As we advance in the precision of scientific measurements, we are constantly discovering previously unrecognized sources of experimental variability. This is the nature of science. However, science is suffering from a lack of experimental reproducibility or replicability that undermines public trust. The issue of reproducibility/replicability is especially sensitive when laboratory animals are involved since we have the ethical responsibility to assure that laboratory animals are used wisely. One way to reduce problems with reproducibility/replicability is to have a strong understanding of potential sources of inherent variability in the system under study and to provide "…a clear, specific, and complete description of how the reported results were reached [1]." A primary intent of this review is to provide the reader with a high-level overview of some basic elements of laboratory animal nutrition, methods used in the manufacturing of feeds, sources of drinking water, and general methods of water purification. The goal is to provide background on contemporary issues regarding how diet and drinking water might serve as a source of extrinsic variability that can impact animal health, study design, and experimental outcomes and provide suggestions on how to mitigate these effects.

Choice of Laboratory Rodent Diet May Confound Data Interpretation and Reproducibility

The reproducibility of experimental data is challenged by many factors in both clinical and preclinical research. In preclinical studies, several factors may be responsible, and diet is one variable that is commonly overlooked, especially by those not trained in nutrition. In particular, grain-based diets contain complex ingredients, each of which can provide multiple nutrients, non-nutrients, and contaminants, which may vary from batch to batch. Thus, even when choosing the same grain-based diet used in the past by others, its composition will likely differ. In contrast, purified diets contain refined ingredients that offer the ability to control the composition much more closely and maintain consistency from one batch to the next, while minimizing the presence of non-nutrients and contaminants. In this article, we provide several different examples or scenarios showing how the diet choice can alter data interpretation, potentially affecting reproducibility and knowledge gained within any given field of study.

Effects of Rodent Diet Choice and Fiber Type on Data Interpretation of Gut Microbiome and Metabolic Disease Research

Poor diet reporting and improperly controlling laboratory animal diet continues to reduce our ability to interpret data effectively in animal studies. In order to make the best use of our resources and improve research transparency, proper reporting methods that include a diet design are essential to improving our understanding of the links between gut health and metabolic disease onset. This unit will focus on the importance of diet choice in laboratory animal studies, specifically as it relates to gut health, microbiome, and metabolic disease development. The two most commonly used diet types, grain-based (GB) diets, and purified ingredient diets, will each be described, with particular emphasis on their differences in dietary fiber. A further description of how these diet types and fiber can affect gut morphology and microbiota will be provided as well as how purified ingredient diets may be improved upon. © 2018 by John Wiley & Sons, Inc.

Effects of Low-Dose Developmental Bisphenol A Exposure on Metabolic Parameters and Gene Expression in Male and Female Fischer 344 Rat Offspring

BACKGROUND

Bisphenol A (BPA) is an endocrine-disrupting chemical that may contribute to development of obesity and metabolic disorders. Humans are constantly exposed to low concentrations of BPA, and studies support that the developmental period is particularly sensitive.

OBJECTIVES

The aim was to investigate the effects of low-dose developmental BPA exposure on metabolic parameters in male and female Fischer 344 (F344) rat offspring.

METHODS

Pregnant F344 rats were exposed to BPA via their drinking water, corresponding to 0.5 μg/kg BW/d (BPA0.5; n=21) or 50 μg/kg BW/d (BPA50; n=16), from gestational day (GD) 3.5 until postnatal day (PND) 22, and controls were given vehicle (n=26). Body weight (BW), adipose tissue, liver (weight, histology, and gene expression), heart weight, and lipid profile were investigated in the 5-wk-old offspring.

RESULTS

Males and females exhibited differential susceptibility to the different doses of BPA. Developmental BPA exposure increased plasma triglyceride levels (0.81±0.10 mmol/L compared with 0.57±0.03 mmol/L, females BPA50 p=0.04; 0.81±0.05 mmol/L compared with 0.61±0.04 mmol/L, males BPA0.5 p=0.005) in F344 rat offspring compared with controls. BPA exposure also increased adipocyte cell density by 122% in inguinal white adipose tissue (iWAT) of female offspring exposed to BPA0.5 compared with controls (68.2±4.4 number of adipocytes/HPF compared with 55.9±1.5 number of adipocytes/HPF; p=0.03) and by 123% in BPA0.5 females compared with BPA50 animals (68.2±4.4 number of adipocytes/high power field (HPF) compared with 55.3±2.9 number of adipocytes/HPF; p=0.04). In iWAT of male offspring, adipocyte cell density was increased by 129% in BPA50-exposed animals compared with BPA0.5-exposed animals (69.9±5.1 number of adipocytes/HPF compared with 54.0±3.4 number of adipocytes/HPF; p=0.03). Furthermore, the expression of genes involved in lipid and adipocyte homeostasis was significantly different between exposed animals and controls depending on the tissue, dose, and sex.

CONCLUSIONS

Developmental exposure to 0.5 μg/kg BW/d of BPA, which is 8-10 times lower than the current preliminary EFSA (European Food Safety Authority) tolerable daily intake (TDI) of 4 μg/kg BW/d and is within the range of environmentally relevant levels, was associated with sex-specific differences in the expression of genes in adipose tissue plasma triglyceride levels in males and adipocyte cell density in females when F344 rat offspring of dams exposed to BPA at 0.5 μg/kg BW/d were compared with the offspring of unexposed controls. https://doi.org/10.1289/EHP505.

Modeling month-season of birth as a risk factor in mouse models of chronic disease: from multiple sclerosis to autoimmune encephalomyelitis

Month-season of birth (M-SOB) is a risk factor in multiple chronic diseases, including multiple sclerosis (MS), where the lowest and greatest risk of developing MS coincide with the lowest and highest birth rates, respectively. To determine whether M-SOB effects in such chronic diseases as MS can be experimentally modeled, we examined the effect of M-SOB on susceptibility of C57BL/6J mice to experimental autoimmune encephalomyelitis (EAE). As in MS, mice that were born during the M-SOB with the lowest birth rate were less susceptible to EAE than mice born during the M-SOB with the highest birth rate. We also show that the M-SOB effect on EAE susceptibility is associated with differential production of multiple cytokines/chemokines by neuroantigen-specific T cells that are known to play a role in EAE pathogenesis. Taken together, these results support the existence of an M-SOB effect that may reflect seasonally dependent developmental differences in adaptive immune responses to self-antigens independent of external stimuli, including exposure to sunlight and vitamin D. Moreover, our documentation of an M-SOB effect on EAE susceptibility in mice allows for modeling and detailed analysis of mechanisms that underlie the M-SOB effect in not only MS but in numerous other diseases in which M-SOB impacts susceptibility.-Reynolds, J. D., Case, L. K., Krementsov, D. N., Raza, A., Bartiss, R., Teuscher, C. Modeling month-season of birth as a risk factor in mouse models of chronic disease: from multiple sclerosis to autoimmune encephalomyelitis.

Low dietary soy isoflavonoids increase hippocampal spine synapse density in ovariectomized rats

High dietary intake of plant estrogens (phytoestrogens) can affect brain structure and function. The effects of phytoestrogen intake within the range of normal animal and human dietary consumption, however, remain uncertain. The aim of the present study was to determine the effects of the isoflavonoids present in a standard low phytoestrogen laboratory rat chow on spine synapse density in the stratum radiatum of area CA1 of the hippocampus. Weanling rats (22days old) were fed either standard chow (Teklad 2018), a nutritionally comparable diet without soy (Teklad 2016) or a custom diet containing Teklad 2016 supplemented with the principal soy isoflavonoids, daidzein and genistein, for 40days. Rats were ovariectomized at 54days of age. Eight days later, spine synapse density on the apical dendrites of hippocampal pyramidal neurons in the stratum radiatum of area CA1 was measured by electron microscopic stereological analysis. Animals maintained on Teklad 2016 exhibited an approximately 60% lower CA1 spine synapse density than animals consuming Teklad 2018. Replacing genistein and daidzein in Teklad 2016 returned synapse density to levels indistinguishable from those in animals on Teklad 2018. These results indicate that the isoflavonoids in a standard laboratory rat diet exert significant effects on spine synapse density in the CA1 region of the hippocampus. Since changes in spine synapse density in this region of the hippocampus have been linked to cognitive performance and mood state, these data suggest that even relatively low daily consumption of soy phytoestrogens may be sufficient to influence hippocampal function.

Comparison of endpoints relevant to toxicity assessments in 3 generations of CD-1 mice fed irradiated natural and purified ingredient diets with varying soy protein and isoflavone contents

Diet is an important variable in toxicology. There are mixed reports on the impact of soy components on energy utilization, fat deposition, and reproductive parameters. Three generations of CD-1 mice were fed irradiated natural ingredient diets with varying levels of soy (NIH-41, 5K96, or 5008/5001), purified irradiated AIN-93 diet, or the AIN-93 formulation modified with ethanol-washed soy protein concentrate (SPC) or SPC with isoflavones (SPC-IF). NIH-41 was the control for pairwise comparisons. Minimal differences were observed among natural ingredient diet groups. F0 males fed AIN-93, SPC, and SPC-IF diets had elevated glucose levels and lower insulin levels compared with the NIH-41 group. In both sexes of the F1 and F2 generations, the SPC and SPC-IF groups had lower body weight gains than the NIH-41 controls and the AIN-93 group had an increased percent body fat at postnatal day 21. AIN-93 F1 pups had higher baseline glucose than NIH-41 controls, but diet did not significantly affect breeding performance or responses to glucose or uterotrophic challenges. Reduced testes weight and sperm in the AIN-93 group may be related to low thiamine levels. Our observations underline the importance of careful selection, manufacturing procedures, and nutritional characterization of diets used in toxicological studies.

Using the Collaborative Cross to Study the Role of Genetic Diversity in Cancer-Related Phenotypes

Human populations are genetically diverse and often a single mouse model can only represent a small subset of the human population. Studying genetic diversity directly can improve the predictive value of mouse models of cancer biology and research on the effects of carcinogens and therapeutics in humans. The collaborative cross is a panel of inbred mouse lines that captures 90% of the genetic diversity of the Mus musculus strain and can help identify regions of the genome that are responsible for variation in cancer phenotypes across the population. The appropriate procedure will depend on the mouse model used; here, three mouse cross designs are described as examples.

Impact of Low-Dose Oral Exposure to Bisphenol A (BPA) on Juvenile and Adult Rat Exploratory and Anxiety Behavior: A CLARITY-BPA Consortium Study

Bisphenol A (BPA) is a high volume production chemical and has been identified as an endocrine disruptor, prompting concern that developmental exposure could impact brain development and behavior. Rodent and human studies suggest that early life BPA exposure may result in an anxious, hyperactive phenotype but results are conflicting and data from studies using multiple doses below the no-observed-adverse-effect level are limited. To address this, the present studies were conducted as part of the CLARITY-BPA (Consortium Linking Academic and Regulatory Insights on BPA Toxicity) program. The impact of perinatal BPA exposure (2.5, 25, or 2500 µg/kg body weight (bw)/day) on behaviors related to anxiety and exploratory activity was assessed in juvenile (prepubertal) and adult NCTR Sprague-Dawley rats of both sexes. Ethinyl estradiol (0.5 µg/kg bw/day) was used as a reference estrogen. Exposure spanned gestation and lactation with dams gavaged from gestational day 6 until birth and then the offspring gavaged directly through weaning (n = 12/sex/group). Behavioral assessments included open field, elevated plus maze, and zero maze. Anticipated sex differences in behavior were statistically identified or suggested in most cases. No consistent effects of BPA were observed for any endpoint, in either sex, at either age compared to vehicle controls; however, significant differences between BPA-exposed and ethinyl estradiol-exposed groups were identified for some endpoints. Limitations of this study are discussed and include suboptimal statistical power and low concordance across behavioral tasks. These data do not indicate BPA-related effects on anxiety or exploratory activity in these developmentally exposed rats.

Segregated responses of mammary gland development and vaginal opening to prepubertal genistein exposure in Bscl2(-/-) female mice with lipodystrophy

Berardinelli-Seip congenital lipodystrophy 2-deficient (Bscl2(-/-)) mice recapitulate human BSCL2 disease with lipodystrophy. Bscl2-encoded seipin is detected in adipocytes and epithelium of mammary gland. Postnatal mammary gland growth spurt and vaginal opening signify pubertal onset in female mice. Bscl2(-/-) females have longer and dilated mammary gland ducts at 5-week old and delayed vaginal opening. Prepubertal exposure to 500ppm genistein diet increases mammary gland area and accelerates vaginal opening in both control and Bscl2(-/-) females. However, genistein treatment increases ductal length in control but not Bscl2(-/-) females. Neither prepubertal genistein treatment nor Bscl2-deficiency affects phospho-estrogen receptor α or progesterone receptor expression patterns in 5-week old mammary gland. Interestingly, Bscl2-deficiency specifically reduces estrogen receptor β expression in mammary gland ductal epithelium. In summary, Bscl2(-/-) females have accelerated postnatal mammary ductal development but delayed vaginal opening; they display segregated responses in mammary gland development and vaginal opening to prepubertal genistein treatment.

The effects of postnatal exposure to low-dose bisphenol-A on activity-dependent plasticity in the mouse sensory cortex

Bisphenol-A (BPA) is a monomer used in the production of polycarbonate plastics, epoxies and resins and is present in many common household objects ranging from water bottles, can linings, baby bottles, and dental resins. BPA exposure has been linked to numerous negative health effects throughout the body, although the mechanisms of BPA action on the developing brain are still poorly understood. In this study, we sought to investigate whether low dose BPA exposure during a developmental phase when brain connectivity is being organized can cause long-term deleterious effects on brain function and plasticity that outlast the BPA exposure. Lactating dams were orally exposed to 25 μg/kg/day of BPA (one half the U.S. Environmental Protection Agency's 50 μg/kg/day rodent dose reference) or vehicle alone from postnatal day (P)5 to P21. Pups exposed to BPA in their mother's milk exhibited deficits in activity-dependent plasticity in the visual cortex during the visual critical period (P28). To determine the possible mechanisms underlying BPA action, we used immunohistochemistry to examine histological markers known to impact cortical maturity and developmental plasticity and quantified cortical dendritic spine density, morphology, and dynamics. While we saw no changes in parvalbumin neuron density, myelin basic protein expression or microglial density in BPA-exposed animals, we observed increases in spine density on apical dendrites in cortical layer five neurons but no significant alterations in other morphological parameters. Taken together our results suggest that exposure to very low levels of BPA during a critical period of brain development can have profound consequences for the normal wiring of sensory circuits and their plasticity later in life.

Sex-specific Esr2 mRNA expression in the rat hypothalamus and amygdala is altered by neonatal bisphenol A exposure

Perinatal life is a critical window for sexually dimorphic brain organization, and profoundly influenced by steroid hormones. Exposure to endocrine-disrupting compounds may disrupt this process, resulting in compromised reproductive physiology and behavior. To test the hypothesis that neonatal bisphenol A (BPA) exposure can alter sex-specific postnatal Esr2 (Erβ) expression in brain regions fundamental to sociosexual behavior, we mapped Esr2 mRNA levels in the principal nucleus of the bed nucleus of the stria terminalis (BNSTp), paraventricular nucleus (PVN), anterior portion of the medial amygdaloid nucleus (MeA), super optic nucleus, suprachiasmatic nucleus, and lateral habenula across postnatal days (PNDs) 0-19. Next, rat pups of both sexes were subcutaneously injected with 10 μg estradiol benzoate (EB), 50 μg/kg BPA (LBPA), or 50 mg/kg BPA (HBPA) over the first 3 days of life and Esr2 levels were quantified in each region of interest (ROI) on PNDs 4 and 10. EB exposure decreased Esr2 signal in most female ROIs and in the male PVN. In the BNSTp, Esr2 expression decreased in LBPA males and HBPA females on PND 10, thereby reversing the sex difference in expression. In the PVN, Esr2 mRNA levels were elevated in LBPA females, also resulting in a reversal of sexually dimorphic expression. In the MeA, BPA decreased Esr2 expression on PND 4. Collectively, these data demonstrate that region- and sex-specific Esr2 expression is vulnerable to neonatal BPA exposure in regions of the developing brain critical to sociosexual behavior in rat.

Integrative rodent models for assessing male reproductive toxicity of environmental endocrine active substances

In the present review, we first summarize the main benefits, limitations and pitfalls of conventional in vivo approaches to assessing male reproductive structures and functions in rodents in cases of endocrine active substance (EAS) exposure from the postulate that they may provide data that can be extrapolated to humans. Then, we briefly present some integrated approaches in rodents we have recently developed at the organism level. We particularly focus on the possible effects and modes of action (MOA) of these substances at low doses and in mixtures, real-life conditions and at the organ level, deciphering the precise effects and MOA on the fetal testis. It can be considered that the in vivo experimental EAS exposure of rodents remains the first choice for studies and is a necessary tool (together with the epidemiological approach) for understanding the reproductive effects and MOA of EASs, provided the pitfalls and limitations of the rodent models are known and considered. We also provide some evidence that classical rodent models may be refined for studying the multiple consequences of EAS exposure, not only on the reproductive axis but also on various hormonally regulated organs and tissues, among which several are implicated in the complex process of mammalian reproduction. Such models constitute an interesting way of approaching human exposure conditions. Finally, we show that organotypic culture models are powerful complementary tools, especially when focusing on the MOA. All these approaches have contributed in a combinatorial manner to a better understanding of the impact of EAS exposure on human reproduction.

The role of neurokinin B signalling in reproductive neuroendocrinology

The KNDy neuropeptides, kisspeptin, neurokinin B (NKB) and dynorphin A (Dyn), have been implicated in regulating pulsatile luteinising hormone (LH) secretion. Studies of the interactions between KNDy signalling systems, however, are currently few. Although the stimulatory effect of kisspeptin and the inhibitory effect of Dyn on the gonadotropin-releasing hormone pulse generator are widely accepted, the effects of NKB in rodents are variable and sometimes controversial. Literature describing increased LH secretion in response to NKB receptor agonism predominates and is in line with human physiology, as well as the pathophysiology of pubertal failure associated with disruption of NKB signalling. However, the robust suppression of the LH pulse, induced by the same treatment under hypoestrogenic conditions, may hold clues as to the mechanisms of reproductive inhibition under pathological conditions. This review discusses the recent evidence for this paradox and outlines a revised working model incorporating the mechanisms by which KNDy neuropeptides modulate the reproductive axis.

Environmental epigenetics and phytoestrogen/phytochemical exposures

One of the most important environmental factors to promote epigenetic alterations in an individual is nutrition and exposure to plant compounds. Phytoestrogens and other phytochemicals have dramatic effects on cellular signaling events, so have the capacity to dramatically alter developmental and physiological events. Epigenetics provides one of the more critical molecular mechanisms for environmental factors such as phytoestrogens/phytochemicals to influence biology. In the event these epigenetic mechanisms become heritable through epigenetic transgenerational mechanisms the impacts on the health of future generations and areas such as evolutionary biology need to be considered. The current review focuses on available information on the environmental epigenetics of phytoestrogen/phytochemical exposures, with impacts on health, disease and evolutionary biology considered. This article is part of a Special Issue entitled 'Phytoestrogens'.

Voluntary exercise impairs initial delayed spatial alternation performance in estradiol treated ovariectomized middle-aged rats

Estrogens differentially modulate behavior in the adult female rodent. Voluntary exercise can also impact behavior, often reversing age associated decrements in memory processes. Our research group has published a series of papers reporting a deficit in the acquisition of an operant working memory task, delayed spatial alternation (DSA), following 17β-estradiol treatment to middle-aged ovariectomized (OVX) rats. The current study examined if voluntary exercise could attenuate the 17β-estradiol induced deficits on DSA performance. OVX 12-month old Long-Evans rats were implanted with a Silastic capsule containing 17β-estradiol (10% in cholesterol: low physiological range) or with a blank capsule. A subset of the 17β-estradiol and OVX untreated rats were given free access to a running wheel in their home cage. All rats were tested for 40 sessions on the DSA task. Surprisingly, we found running wheel access to impair initial acquisition of the DSA task in 17β-estradiol treated rats, an effect not seen in OVX untreated rats given running wheel access. This deficit was driven by an increase in perseverative responding on a lever no longer associated with reinforcement. We also report for the first time a 17β-estradiol induced impairment on the DSA task following a long intertrial delay (18-sec), an effect revealed following more extended testing than in our previous studies (15 additional sessions). Overall, running wheel access increased initial error rate on the DSA task in 17β-estradiol treated middle-aged OVX rats, and failed to prevent the 17β-estradiol induced deficits in performance of the operant DSA task in later testing sessions.

The estrogenic content of rodent diets, bedding, cages, and water bottles and its effect on bisphenol A studies

The lowest observed adverse effect level for bisphenol A (BPA) in mice and rats is currently poorly defined due to inconsistent study designs and results in published studies. The objectives of the current study were to (1) compare the estrogenic content of rodent diets, bedding, cages, and water bottles to evaluate their impact on the estrogenic activity of BPA and (2) review the literature on BPA to determine the most frequently reported diets, beddings, cages, and water bottles used in animal studies. Our literature review indicated that low-dose BPA animal studies have inconsistent results and that factors contributing to this inconsistency are the uses of high-phytoestrogen diets and the different routes of exposure. In 44% (76 of 172) of all reports, rodents were exposed to BPA via the subcutaneous route. Our literature review further indicated that the type of diet, bedding, caging, and water bottles used in BPA studies were not always reported. Only 37% (64 of 172) of the reports described the diet used. In light of these findings, we recommend the use of a diet containing low levels of phytoestrogen (less than 20 μg/g diet) and metabolizable energy (approximately 3.1 kcal/g diet) and estrogen-free bedding, cages, and water bottles for studies evaluating the estrogenic activity of endocrine-disrupting compounds such as BPA. The oral route of BPA exposure should be used when results are to be extrapolated to humans.

Working memory in bisphenol-A treated middle-aged ovariectomized rats

Over 90% of the U.S. population has detectable bisphenol-A (BPA) in their urine according to recent biomonitoring data. BPA is best known for its estrogenic properties, and most rodent research on the nervous system effects of BPA has focused on determining if chronic exposures during pre- and perinatal development have organizational effects on brain development and behavior. Estrogens also have important impacts on brain and behavior during adulthood, particularly in females during aging, but the impact of BPA on the adult brain is less studied. We have published a series of studies documenting that chronic exposure to various estrogens including 17β-estradiol, ERβ selective SERMs and soy phytoestrogens impairs performance of middle-aged female rats on an operant working memory task. The purpose of this study was to determine if chronic oral exposure to BPA would alter working memory on this same task. Ovariectomized (OVX) middle-aged Long Evans rats were tested on an operant delayed spatial alternation (DSA) task. Rats were treated for 8-10 weeks with either a 0 (vehicle control), 5 or 50 μg/kg bw/day oral bolus of BPA. A subset of the vehicle control rats was implanted with a Silastic implant containing 17β-estradiol (low physiological range) to serve as a positive control. All rats were tested for 25 sessions on the DSA task. BPA treatment did not influence performance accuracy on the DSA task, whereas 17β-estradiol significantly impaired performance, as previously reported. The results of this study suggest that chronic oral exposure to BPA does not alter working memory processes of middle-aged OVX rats assessed by this operant DSA task.

Estrogen-like disruptive effects of dietary exposure to bisphenol A or 17α-ethinyl estradiol in CD1 mice

Bisphenol A (BPA) is an endocrine disrupting chemical that is ubiquitous in wild and built environments. Due to variability in study design, the disruptive effects of BPA have proven difficult to experimentally replicate. This study was designed to assess the disruptive actions of dietary BPA exposure, while carefully controlling for known confounders. Parental CD1 mice were acclimated to defined diet containing BPA (0.03, 0.3, 3, 30, or 300 ppm) or 17α-ethinyl estradiol (EE; 0.0001, 0.001, and 0.01 ppm) and bred to produce progeny (F1) that were maintained through adulthood on the same diet as the parents. In F1 females, uterine weights were increased in all EE and the 30-ppm BPA-exposure groups, demonstrating model sensitivity and estrogen-like actions of BPA. In BPA-exposed females, no treatment-related differences were observed in parental reproductive function, or in the timing of puberty and metabolic function in female offspring. In F1 males, modest changes in body weight, adiposity and glucose tolerance, consistent with improved metabolic function, were observed. Associated with increased prolactin and increased circulating testosterone levels, balanopreputial separation was accelerated by 0.03 and 3.0 ppm BPA and anogenital distance at postnatal day 21 was increased in males by 0.03 ppm BPA. Sperm counts were also increased with 3.0 ppm BPA exposures. Overall, BPA was found to have modest, sex specific endocrine disruptive effects on a variety of end points below the established no observed adverse effect level. The dose response characteristics for many of the effects were nonmonotonic and not predictable from high-dose extrapolations.

Disrupted organization of RFamide pathways in the hypothalamus is associated with advanced puberty in female rats neonatally exposed to bisphenol A

Hypothalamic neurons, which produce the kisspeptin family of peptide hormones (Kp), are critical for initiating puberty and maintaining estrous cyclicity by stimulating gonadotropin-releasing hormone (GnRH) release. Conversely, RFamide-related peptide-3 (RFRP3) neurons inhibit GnRH activity. It has previously been shown that neonatal exposure to bisphenol A (BPA) can alter the timing of female pubertal onset and induce irregular estrous cycles or premature anestrus. Here we tested the hypothesis that disrupted ontogeny of RFamide signaling pathways may be a mechanism underlying advanced puberty. To test this, we used a transgenic strain of Wistar rats whose GnRH neurons express enhanced green fluorescent protein. Pups were exposed by daily subcutaneous injection to vehicle, 17beta-estradiol (E2), 50 μg/kg BPA, or 50 mg/kg BPA, from Postnatal Day (PND) 0 through PND 3, and then cohorts were euthanized on PNDs 17, 21, 24, 28, and 33 (5-8 animals per age per exposure; males were collected on PNDs 21 and 33). Vaginal opening was advanced by E2 and 50 μg/kg BPA. On PND 28, females exposed to E2 and 50 μg/kg BPA had decreased RFRP-3 fiber density and contacts on GnRH neurons. RFRP3 perikarya were also decreased in females exposed to 50 μg/kg BPA. Data suggest that BPA-induced premature puberty results from decreased inhibition of GnRH neurons.

Delayed reproductive dysfunction in female rats induced by early life exposure to low-dose diethylstilbestrol

A one-lifespan test was carried out to establish a test protocol for endocrine-disrupting chemicals (EDCs). Diethylstilbestrol was administered by oral gavage to neonatal rats at doses of 0.05, 0.5 and 5 μg/kg/day for 5 days after birth. Abnormal estrous cycles were observed throughout the study in all females from the 5 μg/kg group, and in 40% from the 0.5 μg/kg group from 24 weeks of age. The conception rate of 12-week-old females in the 5 μg/kg group was 0%, and that of the 23-week-old females in the 0.5 μg/kg group was 33.3%. No effect of DES was observed at the first parturition in any group, except for the 5 μg/kg group. However, litter size was significantly reduced in the 0.5 μg/kg group at the second parturition. These results indicated that a prolonged period of observation of reproductive function is necessary to determine EDCs reliably.

The estrogenic endocrine disrupting chemical bisphenol A (BPA) and obesity

There is increasing experimental and epidemiological evidence that fetal programming of genetic systems is a contributing factor in the recent increase in adult obesity and other components of metabolic syndrome. In particular, there is evidence that epigenetic changes associated with the use of manmade chemicals may interact with other factors that influence fetal and postnatal growth in contributing to the current obesity epidemic. The focus of this review is on the developmental effects of estrogenic endocrine disrupting chemicals (EDCs), and more specifically on effects of exposure to the estrogenic EDC bisphenol A (BPA), on adipocytes and their function, and the ultimate impact on adult obesity; BPA exposure also results in impaired reproductive capacity. We discuss the interaction of EDCs with other factors that impact growth during fetal and neonatal life, such as placental blood flow and nutrient transport to fetuses, and how these influence fetal growth and abnormalities in homeostatic control systems required to maintain normal body weight throughout life.

Testosterone impairs the acquisition of an operant delayed alternation task in male rats

The current study examined the effects of gonadectomy (GDX) and subsequent testosterone treatment of male Long-Evans rats on an operant variable delay spatial alternation task (DSA). Gonadally-intact rats (intact-B), GDX rats receiving implants that delivered a physiological level of testosterone (GDX-T), and GDX rats receiving blank implants (GDX-B) were tested for 25 sessions on a DSA task with variable inter-trial delays ranging from 0 to 18 s. Acquisition of the DSA task was found to be enhanced following GDX in a time and delay dependent manner. Both the GDX-T and the intact-B rats had lower performance accuracies across delays initially, relative to GDX-B rats, and this deficit persisted into subsequent testing sessions at longer delays. The GDX-T and intact-B rats also had a tendency to commit more perseverative errors during the early testing sessions, with both groups persisting in pressing a lever which had not been associated with reinforcement for at least two consecutive trials. However, both the GDX-T and intact-B groups were able to achieve performance accuracy similar to that of the GDX-B rats by the final sessions of testing. Overall, these results suggest that castration of adult male rats enhances their acquisition of an operant DSA task.

Effects of multiple daily genistein treatments on delayed alternation and a differential reinforcement of low rates of responding task in middle-aged rats

The use of extracts that are highly enriched in phytoestrogens, such as genistein, has become popular to promote various aspects of healthy aging, including maintenance of cognitive function. These compounds are promoted to menopausal women as safe, natural alternatives to traditional estrogen therapies, yet their safety and efficacy are poorly understood. Previous research in our lab found that once daily oral treatment of ovariectomized female Long-Evans (LE) rats with the soy phytoestrogen, genistein resulted in subtle deficits in performance on cognitive tasks assessing working memory and response inhibition/timing ability. The present study further modeled exposure of the menopausal woman to genistein by treating 14-month old ovariectomized female LE rats three times daily at a dose of genistein resulting in serum concentrations similar to those that could be achieved in humans consuming either a commercially available soy isoflavone supplement or a diet high in these phytoestrogens. Genistein (3.4 mg/kg) or sucrose control pellets were orally administered to animals daily, 30 min before behavioral testing, and again both 4 and 8 h after the first treatment. The test battery consisted of a delayed spatial alternation task (DSA) that tested working memory and a differential reinforcement of low rates of responding (DRL) task that tested inhibitory control/timing. Genistein treatment impaired DSA performance relative to sucrose controls. Performance on the DRL task was largely unaffected by genistein treatment. Although the impairment measured on DSA was less pronounced than that we have previously reported following chronic treatment with 17β-estradiol, the pattern of the deficit was very similar to that observed with 17β-estradiol.

Neonatal Bisphenol A exposure alters sexually dimorphic gene expression in the postnatal rat hypothalamus

Developmental exposure to Bisphenol A (BPA), a component of polycarbonate and epoxy resins, has been purported to adversely impact reproductive function in female rodents. Because neonatal life is a critical window for the sexual dimorphic organization of the hypothalamic-pituitary-gonadal (HPG) axis, interference with this process could underlie compromised adult reproductive physiology. The goal of the present study was to determine if neonatal BPA exposure interferes with sex specific gene expression of estrogen receptor alpha (ERα), ER beta (ERβ) and kisspeptin (Kiss1) in the anterior and mediobasal hypothalamus. Long Evans (LE) neonatal rats were exposed to vehicle, 10μg estradiol benzoate (EB), 50mg/kg BPA or 50μg/kg BPA by subcutaneous injection daily from postnatal day 0 (PND 0) to PND 2. Gene expression was assessed by in situ hybridization on PNDs 4 and 10. Within the anterior hypothalamus ERα expression was augmented by BPA in PND 4 females, then fell to male-typical levels by PND 10. ERβ expression was not altered by BPA on PND 4, but significantly decreased or eliminated in both sexes by PND 10. Kiss1 expression was diminished by BPA in the anterior hypothalamus, especially in females. There were no significant impacts of BPA in the mediobasal hypothalamus. Collectively, BPA effects did not mirror those of EB. The results show that neonatal hypothalamic ER and Kiss1 expression is sensitive to BPA exposure. This disruption may alter sexually dimorphic hypothalamic organization and underlie adult reproductive deficiencies. Additionally, the discordant effects of EB and BPA indicate that BPA likely disrupts hypothalamic organization by a mechanism other than simply acting as an estrogen mimic.

Impact of perinatal exposure to equol enantiomers on reproductive development in rodents

There is now considerable interest in the intestinally derived soy isoflavone metabolite, equol, which occurs in the enantiomeric forms, S-(-)equol and R-(+)equol, both differing in biological actions. Little is known about effects of either enantiomer on reproductive development, yet such knowledge is fundamental because of the recent commercialization of S-(-)equol as a dietary supplement. S-(-)equol and R-(+)equol were therefore investigated to determine their effects on reproductive development and fertility in the Sprague-Dawley rat. Neither enantiomer affected fertility, number of litters produced, number of pups per litter, number of male and female pups born, birth weight, anogenital distance, testicular descent or vaginal opening. Histological analysis showed no major abnormalities in ovary, testis, prostate or seminal vesicle tissue with dietary exposure to S-(-)equol or R-(+)equol, but both enantiomers triggered hyperplasia of uterine tissue. With R-(+)equol this stimulatory effect subsided after exposure was discontinued, but the effect of S-(-)equol was prolonged.

Sex-specific neuroendocrine and behavioral phenotypes in hypomorphic Type II Neuregulin 1 rats

Neuregulin 1 (NRG1) is an important growth factor involved in the development and plasticity of the central nervous system. Since its identification as a susceptibility gene for schizophrenia, several transgenic mouse models have been employed to elucidate the role NRG1 may play in the pathogenesis of psychiatric disease. Unfortunately very few studies have included females, despite the fact that some work suggests that the consequences of disrupted NRG1 expression may be sex-specific. Here, we used Nrg1 hypomorphic (Nrg1(Tn)) Fischer rats to demonstrate sex-specific changes in neuroendocrine and behavioral phenotypes as a consequence of reduced Type II NRG1 expression. We have previously shown that male Nrg1(Tn) rats have increased basal corticosterone levels, and fail to habituate to an open field despite normal overall levels of locomotor activity. The current studies show that, in contrast, female Nrg1(Tn) rats exhibit enhanced suppression of corticosterone levels following an acute stress, reduced locomotor activity, and enhanced habituation to novel environments. Furthermore, we also show that female, but not male, Nrg1(Tn) rats have impaired prepulse inhibition. Finally, we provide evidence that sex-specific changes are not likely attributable to major disruptions in the hypothalamic-pituitary-gonadal axis, as measures of pubertal onset, estrous cyclicity, and reproductive capacity were unaltered in female Nrg1(Tn) rats. Our results provide further support for both the involvement of NRG1 in the control of hypothalamic-pituitary-adrenal axis function and the sex-specific nature of this relationship.

Neonatal exposure to genistein adversely impacts the ontogeny of hypothalamic kisspeptin signaling pathways and ovarian development in the peripubertal female rat

Neonatal exposure to estrogenic endocrine disrupting compounds (EDCs) can advance pubertal onset and induce premature anestrous in female rats. It was recently discovered that hypothalamic kisspeptin (KISS) signaling pathways are sexually dimorphic and regulate both the timing of pubertal onset and estrous cyclicity. Thus we hypothesized that disrupted sex specific ontogeny of KISS signaling pathways might be a mechanism underlying these EDC effects. We first established the sex specific development of KISS gene expression, cell number and neural fiber density across peripuberty in the anteroventral periventricular nucleus (AVPV) and arcuate nucleus (ARC), hypothesizing that the sexually dimorphic aspects of KISS signaling would be most vulnerable to EDCs. We next exposed female rats to the phytoestrogen genistein (GEN, 1 or 10 mg/kg bw), estradiol benzoate (EB, 10 μg), or vehicle from post natal day (P) 0-3 via subcutaneous (sc) injection. Animals were sacrificed on either P21, 24, 28, or 33 (n=5-14 per group at each age). Vaginal opening was significantly advanced by EB and the higher dose of GEN compared to control animals and was accompanied by lower numbers of KISS immunoreactive fibers in the AVPV and ARC. Ovarian morphology was also assessed in all age groups for the presence of multiple oocyte follicles (MOFs). The number of MOFs decreased over time in each group, and none were observed in control animals by P24. MOFs were still present, however, in the EB and 10 mg/kg GEN groups beyond P24 indicating a disruption in the timing of ovarian development.

Altered health outcomes in adult offspring of Sprague Dawley and Wistar rats undernourished during early or late pregnancy

BACKGROUND

Birth weight in humans has been inversely associated with adult disease risk. Results of animal studies have varied depending on species, strain, and treatment.

METHODS

We compared birth weight and adult health in offspring following 50% maternal undernutrition on gestation days (GD) 1-15 (UN1-15) or GD 10-21 (UN10-21) in Sprague Dawley and Wistar rats. Offspring from food-deprived dams were weighed and cross-fostered to control dams. Litters were weighed during lactation and initiating at weaning males were fed either control or a high-fat diet. Young and mature adult offspring were evaluated for obesity, blood pressure (BP), insulin response to oral glucose, and serum lipids. Nephron endowment, renal glucocorticoid receptor, and renin-aldosterone-angiotensin system components were measured.

RESULTS

The UN10-21 groups had birth weights lower than controls and transient catch up growth by weaning. Neither strain demonstrated obesity or dyslipidemia following prenatal undernutrition, but long-term body weight deficits occurred in the UN groups of both strains. High-fat diet fed offspring gained more weight than control offspring without an effect of prenatal nutrition. Sprague Dawley were slightly more susceptible than Wistar rats to altered insulin response and increased BP following gestational undernutrition. Nephron endowment in Sprague Dawley but not Wistar offspring was lower in the UN10-21 groups. Glucocorticoid and renin-aldosterone-angiotensin system pathways were not altered.

CONCLUSIONS

The most consistent effect of maternal undernutrition was elevated BP in offspring. Long-term health effects occurred with undernutrition during either window, but the UN10-21 period resulted in lower birth weight and more severe adult health effects.

Choice of animal feed can alter fetal steroid levels and mask developmental effects of endocrine disrupting chemicals

Exposure of fetuses to endocrine disrupting chemicals (EDCs), such as the estrogenic drug diethylstilbestrol (DES), disrupts development of the reproductive system and affects other aspects of adult phenotype including diseases, consistent with the developmental origins of health and disease hypothesis. To determine whether diet could influence the effects of DES, we compared mice fed a commonly used combination of soy-based Purina 5008 (breeding and lactation) and 5001 (post-weaning) with mice fed soy-based Purina 5002 throughout life. We exposed fetal CD-1 mice (F1) in utero on different feeds to a 0 (controls), low (0.1 μg/kg/day) or high (50 μg/kg/day) dose of DES via feeding the dam (F0) on gestation days 11–17. Compared to 5008, 5002 feed significantly increased serum estradiol in control fetuses. On 5008 (but not 5002) feed, DES significantly increased fetal serum estradiol at a low dose and reduced it at a high dose. Diet influenced the effects of in utero DES on F1 female onset of puberty and the uterine response to estradiol (an inverted-U dose–response relationship seen for DES on uterine weight with 5008/5001 feed was not observed with 5002). Both low- and high-dose DES reduced daily sperm production (DSP) in adult F1 males on 5008/5001 feed, whereas males fed 5002 showed no DES-induced reduction in DSP. Thus, we observed a number of low-dose effects of in utero DES exposure on Purina 5008/5001 feed that were not observed using Purina 5002, a feed commonly used in industry-funded toxicological studies conducted for regulatory purposes.

Estradiol impairs response inhibition in young and middle-aged, but not old rats

Estrogens have been shown to have a strong influence on such cognitive domains as spatial memory, response learning, and several tasks of executive function, including both working memory and attention. However, the effects of estrogens on inhibitory control and timing behavior, both important aspects of executive function, have received relatively little attention. We examined the effects of estradiol on inhibitory control and timing behavior using a differential reinforcement of low rates of responding (DRL) task. Ovariectomized young (3 month), middle-aged (12 month), and old (18 month) Long-Evans rats were implanted with Silastic implants containing 0, 5 or 10% 17β-estradiol in cholesterol vehicle and were tested on a DRL task requiring them to wait 15s between lever presses to receive a food reinforcer. The ratio of reinforced to non-reinforced lever presses did not differ across age in the cholesterol vehicle group. Conversely, 17β-estradiol impaired learning of the DRL task in young and middle-aged rats, but the learning of old rats was not impaired relative to vehicle controls following either 5% or 10% 17β-estradiol treatment. Overall, old rats also made fewer lever presses than both the young and middle-aged rats. These results provide new evidence that estrogens impair inhibitory control, an important aspect of self regulation, and add to existing evidence that estrogens differentially affect cognition at different ages.

Dietary soy may not confound acute experimental stroke infarct volume outcomes in ovariectomized female rats

Oestrogen administration can alter experimental stroke outcomes. Soy as a source of phytoestrogens may therefore modulate responses in 'oestrogen-sensitive' stroke models, thus potentially confounding results. We evaluated the effects of dietary soy on acute infarct volumes in a pilot study using a rat focal stroke model. We hypothesized that ovariectomized (OVX) rats fed a soy-rich diet would have smaller acute infarct volumes than rats fed a soy-free diet. OVX rats were randomly assigned to a soy-free (n = 6) or a soy-rich (n = 6) diet for four weeks and weighed weekly. Following the dietary trial, rats underwent 2 h of middle cerebral artery occlusion (MCAO). Mean arterial blood pressure, rectal and temporalis muscle temperatures, arterial blood gases and blood glucose were recorded peri-ischaemia. Rats were euthanized 22 h following 2 h of MCAO. Brains were stained with 2,3,5-triphenyl tetrazolium chloride for acute infarct volume analysis. Uterine weight and histology were also evaluated as additional internal oestrogen-sensitive controls. Rats on the soy-free diet had greater gains in body weight (259 +/- 6% baseline body weight) than rats on the soy-rich diet (238 +/- 4% baseline body weight). No differences were seen in uterine weight and histology, peri-ischaemic physiological parameters and infarct volumes between the treatment groups. The results of this pilot study suggest that the dietary soy level tested may not alter acute infarct volumes in ischaemic female rat brain. More studies addressing the potential confounding effects of dietary soy in 'oestrogen-sensitive' stroke models are needed if investigators are to make informed choices regarding diets used in experimental stroke research.

Equol: history, chemistry, and formation

Equol, first isolated from equine urine in 1932 and identified 50 years later in human urine as a metabolite of the soy isoflavones, daidzin and daidzein, is produced by intestinal bacteria in some, but not all, adults. This observation led to the term equol-producers to define those adults that could make equol in response to consuming soy isoflavones and the hypothesis that the health benefits of soy-based diets may be greater in equol-producers than in equol nonproducers. By virtue of a chiral center, equol occurs as a diastereoisomer and intestinal bacteria are enantiospecific in synthesizing exclusively the S-(-)equol enantiomer, an enantiomer that has selective affinity for the estrogen receptor-beta. Both enantiomers are of interest from a clinical and pharmacological perspective and are currently being developed as nutraceutical and pharmacological agents. The wide range of biological activities these enantiomers possess warrants their investigation for the treatment of a number of hormone-related conditions involving estrogen-dependent and androgen-related conditions. The following review describes the history, chemistry, and factors governing the intestinal bacterial formation of equol.

Colitis causes delay in puberty in female mice out of proportion to changes in leptin and corticosterone

BACKGROUND

Inflammatory bowel disease that begins prior to puberty frequently causes a delay in puberty resulting in losses of growth, bone mineralization, and self esteem. A major cause of this pubertal delay is likely due in part to the effect of decreased levels of leptin on the function of the hypothalamic-pituitary-gonadal axis, though systemic inflammation is also thought to play a role.

METHODS

To investigate further whether low leptin levels alone were responsible for delayed puberty in colitis, we induced colitis in 23-day-old female mice using 3% dextran sodium sulfate (DSS), resulting in 10 days of worsening colitis. These mice were compared to controls that were free-feeding and food-restricted (FR) mice that were given only enough food to keep them the same weight as the DSS group. All groups were followed for the timing of vaginal opening until 33 days old, when they were euthanized and their serum collected.

RESULTS

DSS-treated mice exhibited later timing of vaginal opening relative to both of the other groups, as well as increased colonic inflammation by cytology and increased serum levels of interleukin (IL)-6 and tumor necrosis factor(TNF)-alpha. The difference in the timing of vaginal opening between the DSS and FR groups occurred despite equivalent serum levels of leptin between the groups and despite an increase in corticosterone in the FR group relative to both of the other groups.

CONCLUSIONS

We conclude that DSS colitis causes delay in puberty in sexually immature mice beyond what would be expected from decreases in weight and leptin levels.

Open- and closed-formula laboratory animal diets and their importance to research

Almost 40 y ago the scientific community was taking actions to control environmental factors that contribute to variation in the responses of laboratory animals to scientific manipulation. Laboratory animal diet was recognized as an important variable. During the 1970s, the American Institute of Nutrition, National Academy of Science, Institute of Laboratory Animal Resources, and Laboratory Animals Centre Diets Advisory Committee supported the use of 'standard reference diets' in biomedical research as a means to improve the ability to replicate research. As a result the AIN76 purified diet was formulated. During this same time, the laboratory animal nutritionist at the NIH was formulating open-formula, natural-ingredient diets to meet the need for standardized laboratory animal diets. Since the development of open-formula diets, fixed-formula and constant-nutrient-concentration closed-formula laboratory animal natural ingredient diets have been introduced to help reduce the potential variation diet can cause in research.

The pharmacokinetic behavior of the soy isoflavone metabolite S-(-)equol and its diastereoisomer R-(+)equol in healthy adults determined by using stable-isotope-labeled tracers

BACKGROUND

The nonsteroidal estrogen equol occurs as diastereoisomers, S-(-)equol and R-(+)equol, both of which have significant biological actions. S-(-)equol, the naturally occurring enantiomer produced by 20-30% of adults consuming soy foods, has selective affinity for estrogen receptor-beta, whereas both enantiomers modulate androgen action. Little is known about the pharmacokinetics of the diastereoisomers, despite current interest in developing equol as a nutraceutical or pharmaceutical agent.

OBJECTIVE

The objective was to compare the pharmacokinetics of S-(-)equol and R-(+)equol by using [13C] stable-isotope-labeled tracers to facilitate the optimization of clinical studies aimed at evaluating the potential of these diastereoisomers in the prevention and treatment of estrogen- and androgen-dependent conditions.

DESIGN

A randomized, crossover, open-label study in 12 healthy adults (6 men and 6 women) compared the plasma and urinary pharmacokinetics of orally administered enantiomeric pure forms of S-(-)[2-13C]equol, R-(+)[2-13C]equol, and the racemic mixture. Plasma and urinary [13C]R-equol and [13C]S-equol concentrations were measured by tandem mass spectrometry.

RESULTS

Plasma [13C]equol concentration appearance and disappearance curves showed that both enantiomers were rapidly absorbed, attained high circulating concentrations, and had a similar terminal elimination half-life of 7-8 h. The systemic bioavailability and fractional absorption of R-(+)[2-13C]equol were higher than those of S-(-)[2-13C]equol or the racemate. The pharmacokinetics of racemic (+/-)[2-13C]equol were different from those of the individual enantiomers: slower absorption, lower peak plasma concentrations, and lower systemic bioavailability.

CONCLUSIONS

The high bioavailability of both diastereoisomers contrasts with previous findings for the soy isoflavones daidzein and genistein, both of which have relatively poor bioavailability, and suggests that low doses of equol taken twice daily may be sufficient to achieve biological effects.

The bisphenol A experience: a primer for the analysis of environmental effects on mammalian reproduction

It is increasingly evident that environmental factors are a veritable Pandora's box from which new concerns and complications continue to emerge. Although previously considered the domain of toxicologists, it is now clear that an understanding of the effects of the environment on reproduction requires a far broader range of expertise and that, at least for endocrine-disrupting chemicals, many of the tenets of classical toxicology need to be revisited. Indeed, because of the wide range of reproductive effects induced by these chemicals, interest among reproductive biologists has grown rapidly: in 2000, the program for the annual Society for the Study of Reproduction meeting included a single minisymposium on the fetal origins of adult disease, one platform session on endocrine disruption, and 23 toxicology poster presentations. In contrast, environmental factors featured prominently at the 2009 meeting, with strong representation in the plenary, minisymposia, platform, and poster sessions. Clearly, a lot has happened in a decade, and environmental issues have become an increasingly important research focus for reproductive biologists. In this review, we summarize some of the inherent difficulties in assessing environmental effects on reproductive performance, focusing on the endocrine disruptor bisphenol A (BPA) to illustrate important emerging concerns. In addition, because the BPA experience serves as a prototype for scientific activism, public education, and advocacy, these issues are also discussed.

Effects of 4-vinylcyclohexene diepoxide on peripubertal and adult Sprague-Dawley rats: ovarian, clinical, and pathologic outcomes

Young rats treated daily with intraperitoneal 4-vinylcyclohexene diepoxide (VCD) undergo selective destruction of primordial follicles, resulting in gradual ovarian failure resembling the menopausal transition in women. To determine whether VCD has similar effects on ovaries of older rats, adult and peripubertal Sprague-Dawley rats were injected intraperitoneally daily for 30 d with vehicle or VCD at 40 or 80 mg/kg. Body weight, food intake, complete blood counts, and markers of liver injury and renal function were measured during VCD treatment. Complete gross necropsy and microscopic observations were performed on day 31, and ovarian follicles were counted. At 80 mg/kg, VCD destroyed primordial and primary follicles to a similar extent in both adult and peripubertal animals, although adult rats likely started with fewer follicles and therefore approached follicle depletion. Treatment with VCD did not affect body weight, but food intake was reduced in both adult and peripubertal rats treated with 80 mg/kg VCD. Adult rats treated with 80 mg/kg VCD had neutrophilia and increased BUN and creatinine; in addition, 4 of these rats were euthanized on days 25 or 26 due to peritonitis. VCD treatment did not increase alanine aminotransferase levels, a marker of liver injury, although the 80-mg/kg dose increased liver weights. In conclusion, VCD effectively destroys small preantral follicles in adult Sprague-Dawley rats, making them a suitable model of the menopausal transition of women. However, because adult rats were more sensitive to the irritant properties of VCD, the use of a lower dose should be considered.

Bisphenol A effects on the growing mouse oocyte are influenced by diet

Growing evidence suggests that exposure to bisphenol A (BPA) has the ability to disrupt several different stages of oocyte development. To date, most attention has focused on the effects of BPA on the periovulatory oocyte, and considerable variation is evident in the results of these studies. In our own laboratory, variation in the results of BPA studies conducted at different times appeared to correlate with changes in mill dates of animal feed. This observation, coupled with reports by others that dietary estrogens in feed are a confounding variable in studies of endocrine-disrupting chemicals, prompted us to evaluate the effect of diet on the results of BPA studies of the periovulatory oocyte. Genetically identical females were placed on a high- or low-phytoestrogen diet prior to mating. Their female offspring were exposed to BPA, oocytes collected, and meiotic spindle and chromosome characteristics compared between control and BPA-treated females. We observed significant diet-related variation in both the frequency of abnormalities in oocytes from untreated females and in the response to BPA. Our results demonstrate that the impact of BPA on meiosis depends, at least in part, on diet. We suggest that variation in the conclusions of recent BPA studies reflects differences in the diets used, as well as other methodological differences. Because meiotic disturbances are a feature of all studies to date, however, we conclude that low levels of BPA adversely affect the meiotic process.

Timing of supplementation of selenium and isoflavones determines prostate cancer risk factor reduction in rats

Background

High dietary intake of selenium or isoflavones reduces risk factors for prostate cancer. We tested whether combined supplementation of these two dietary components would reduce prostate cancer risk factors in rats more than supplementation of each component individually.

Methods

Male Noble rat pups were exposed from conception to diets containing an adequate (0.33–0.45 mg/kg diet) or high (3.33–3.45 mg/kg) concentration of selenium as Se-methylselenocysteine and a low (10 mg/kg) or high (600 mg/kg) level of isoflavones in a 2 × 2 factorial design. Pups consumed their respective diets until sacrifice at 35, 100, or 200 days. Male Noble rat breeders, whose exposure to the diets began after puberty, were sacrificed at 336 days. Rats were weighed biweekly. Blood was collected at the time of sacrifice and body fat and prostates were dissected and weighed. Serum levels of leptin, IGF-1, and testosterone were determined using ELISA kits. Serum levels of isoflavones were assayed by GC/MS. Liver activity of selenium-dependent glutathione peroxidase 1 was measured as an indicator of selenium status.

Results

Serum isoflavone concentrations were nearly 100-fold higher at 35 days of age (1187.1 vs. 14.4 ng/mL, mean ± SD) in pups fed the high vs. low isoflavone diets, and remained so at 100 and 200 days, and in breeders. There were no dietary differences in liver glutathione peroxidase activity in pups or breeders. High isoflavone intake significantly (p = 0.001–0.047) reduced body weight in rat pups from 35 days onward, but not in breeders. Body fat and leptin were likewise significantly reduced by high isoflavones in pups while effects in breeders were less pronounced but still significant. High intake of Se and isoflavones each decreased serum IGF-1 in pups at 100 and 200 days, but not in breeders. No consistent dietary effects were observed on serum testosterone or relative weights of prostates. In pups, the combination of high isoflavones and high selenium produced the lowest weight gain, the lowest serum leptin, and the lowest serum IGF-1 concentrations of all four diets.

Conclusion

Combined intake of high selenium and high isoflavones may achieve greater chemopreventive effects than either compound individually. The timing of supplementation may determine the significance of its effects.

Meeting report: batch-to-batch variability in estrogenic activity in commercial animal diets--importance and approaches for laboratory animal research

We report information from two workshops sponsored by the National Institutes of Health that were held to a) assess whether dietary estrogens could significantly impact end points in experimental animals, and b) involve program participants and feed manufacturers to address the problems associated with measuring and eliminating batch-to-batch variability in rodent diets that may lead to conflicting findings in animal experiments within and between laboratories. Data were presented at the workshops showing that there is significant batch-to-batch variability in estrogenic content of commercial animal diets, and that this variability results in differences in experimental outcomes. A combination of methods were proposed to determine levels of total estrogenic activity and levels of specific estrogenic constituents in soy-containing, casein-containing, and other soy-free rodent diets. Workshop participants recommended that researchers pay greater attention to the type of diet being used in animal studies and choose a diet whose estrogenic activity (or lack thereof) is appropriate for the experimental model and end points of interest. Information about levels of specific phytoestrogens, as well as estrogenic activity caused by other contaminants and measured by bioassay, should be disclosed in scientific publications. This will require laboratory animal diet manufacturers to provide investigators with information regarding the phytoestrogen content and other estrogenic compounds in commercial diets used in animal research.

Variations in phytoestrogen content between different mill dates of the same diet produces significant differences in the time of vaginal opening in CD-1 mice and F344 rats but not in CD Sprague-Dawley rats

BACKGROUND

The optimum test diet and rodent species/strain for evaluating endocrine-disrupting compounds (EDCs) are critical.

OBJECTIVES

We conducted studies to evaluate rodent species sensitivity and the effects of diets varying in phytoestrogen content on the time of vaginal opening (VO) in CD-1 mice, Fischer 344 (F344) rats, and CD Sprague-Dawley (S-D) rats.

METHODS

Mice were weaned on postnatal day (PND) 15 and rats on PND19 and randomly assigned to control or test diets. Body weights, food consumption, and time of VO were recorded.

RESULTS

The time of VO was significantly advanced in F344 rats fed diets containing daidzein and genistein, whereas these same diets did not advance VO in S-D rats. When animals were fed the AIN-76A diet spiked with genistein, time of VO was significantly advanced at all doses in CD-1 mice, at the two highest doses in F344 rats, and at the highest dose in S-D rats. The time of VO in F344 rats was more highly correlated with the phytoestrogen content than with the total metabolizable energy (ME) of 12 diets.

CONCLUSIONS

The S-D rat is less sensitive to dietary phytoestrogens compared with the F344 rat or the CD-1 mouse, suggesting that the S-D rat is not the ideal model for evaluating estrogenic activity of EDCs. The profound effects of dietary phytoestrogens on the time of VO, an estrogen-sensitive marker, indicate that a standardized open-formula phytoestrogen-free diet containing a low ME level should be used to optimize the sensitivity of estrogenic bioassays.