Vinclozolin--no transgenerational inheritance of anti-androgenic effects after maternal exposure during organogenesis via the intraperitoneal route

Epigenetics Research in Evolutionary Biology: Perspectives on Timescales and Mechanisms

Epigenetics research in evolutionary biology encompasses a variety of research areas, from regulation of gene expression to inheritance of environmentally mediated phenotypes. Such divergent research foci can occasionally render the umbrella term "epigenetics" ambiguous. Here I discuss several areas of contemporary epigenetics research in the context of evolutionary biology, aiming to provide balanced views across timescales and molecular mechanisms. The importance of epigenetics in development is now being assessed in many nonmodel species. These studies not only confirm the importance of epigenetic marks in developmental processes, but also highlight the significant diversity in epigenetic regulatory mechanisms across taxa. Further, these comparative epigenomic studies have begun to show promise toward enhancing our understanding of how regulatory programs evolve. A key property of epigenetic marks is that they can be inherited along mitotic cell lineages, and epigenetic differences that occur during early development can have lasting consequences on the organismal phenotypes. Thus, epigenetic marks may play roles in short-term (within an organism's lifetime or to the next generation) adaptation and phenotypic plasticity. However, the extent to which observed epigenetic variation occurs independently of genetic influences remains uncertain, due to the widespread impact of genetics on epigenetic variation and the limited availability of comprehensive (epi)genomic resources from most species. While epigenetic marks can be inherited independently of genetic sequences in some species, there is little evidence that such "transgenerational inheritance" is a general phenomenon. Rather, molecular mechanisms of epigenetic inheritance are highly variable between species.

Unaltered hepatic wound healing response in male rats with ancestral liver injury

The possibility that ancestral environmental exposure could result in adaptive inherited effects in mammals has been long debated. Numerous rodent models of transgenerational responses to various environmental factors have been published but due to technical, operational and resource burden, most still await independent confirmation. A previous study reported multigenerational epigenetic adaptation of the hepatic wound healing response upon exposure to the hepatotoxicant carbon tetrachloride (CCl4) in male rats. Here, we comprehensively investigate the transgenerational effects by repeating the original CCl4 multigenerational study with increased power, pedigree tracing, F2 dose-response and suitable randomization schemes. Detailed pathology evaluations do not support adaptive phenotypic suppression of the hepatic wound healing response or a greater fitness of F2 animals with ancestral liver injury exposure. However, transcriptomic analyses identified genes whose expression correlates with ancestral liver injury, although the biological relevance of this apparent transgenerational transmission at the molecular level remains to be determined. This work overall highlights the need for independent evaluation of transgenerational epigenetic inheritance paradigms in mammals.

Effects of the endocrine disruptor vinclozolin in male reproduction: a systematic review and meta-analysis†

Endocrine-disrupting chemicals have become an issue of scientific and public discussion. Vinclozolin (VNZ) is a fungicide that competitively antagonizes the binding of natural androgens to their receptor, disturbing the function of tissues that are sensitive to these hormones, as is the case of the male reproductive organs. A systematic review with meta-analyses of rodent studies was conducted to answer the following question: Does exposure to VNZ affect sperm parameters and testicular/epididymal weight? The methodology was prespecified according to the Cochrane Handbook for Systematic Reviews and PRISMA recommendations. Sixteen articles met the inclusion criteria, comprising a total of 1189 animals. The risk of publication bias was assessed using the Trim and Fill adjustment, funnel plot, and Egger regression test. Heterogeneity and inconsistency across the findings were tested using the Q-statistic and I2 of Higgins, respectively. Sensitivity was also analyzed. Statistical analysis was performed on Comprehensive Meta-Analysis software (Version 2.0), using random models and weighted mean differences along with a 95% confidence interval. Sperm motility, counts, daily sperm production (evidence of publication bias), and epididymis weight were decreased in VNZ-treated animals. Exposure length and dose, as well as the time point of exposure, influenced the obtained results. Despite the moderate/high heterogeneity observed, the sensitivity analysis overall demonstrated the robustness of the findings. The quality scores of the included studies were superior to 4 in a total of 9, then classified as good. The obtained data corroborate the capability of VNZ exposure to disrupt spermatogenic output and compromise male fertility.

Pesticides and transgenerational inheritance of pathologies: Designing, analysing and reporting rodent studies

Single-centre studies examining the transgenerational inheritance of pathologies in rodents exposed to pesticides have not always taken important design and analysis issues into account. This paper examines these methodological and statistical issues in detail. Its particular focus is on the estimation of 'litter effects': the tendency for rodents within a litter to be more alike than rodents in different litters. Appropriate statistical models were fitted to published data from a series of widely reported studies carried out at Washington State University. These studies were amalgamated into a single dataset in order to estimate these litter effects and associated treatment effects. Litter effects varied by outcome and were often substantial. Consequently, the effective sample size was often substantially less than the number of observations with implications for the power of the studies. Moreover, the reported precision of the estimates of treatment effects was too low. These problems are exacerbated by unexplained missing data across generations. Researchers in the life sciences could be more cognisant of the guidelines established in medicine for reporting randomised controlled trials, particularly cluster randomised trials. More attention should be paid to the design and analysis of multi-generational rodent studies; their imperfections have important implications for assessments of the evidence relating to the risks of pesticides for public health.

Transgenerational Effects of Endocrine-Disrupting Chemicals on Male and Female Reproduction

Endocrine-disrupting chemicals are known to interfere with normal reproductive function and hormone signaling. Phthalates, bisphenol A, pesticides, and environmental contaminants such as polychlorinated biphenyls and dioxins are known endocrine-disrupting chemicals that have been shown to negatively affect both male and female reproduction. Exposure to these chemicals occurs on a daily basis owing to these compounds being found in plastics, personal care products, and pesticides. Recently, studies have shown that these chemicals may cause transgenerational effects on reproduction in both males and females. This is of concern because exposure to these chemicals prenatally or during adult life can negatively impact the reproductive health of future generations. This mini-review summarizes the endocrine-disrupting chemicals that humans are exposed to on a daily basis and what is known about the transgenerational effects that these chemicals may have on male and female reproduction.

Passing experiences on to future generations: endocrine disruptors and transgenerational inheritance of epimutations in brain and sperm

All animals have body burdens of polychlorinated biphenyls (PCBs) despite their ban decades ago. These and modern endocrine-disrupting chemicals (EDCs) such as the fungicide vinclozolin (VIN) perturb hormone signaling and lead to dysfunctions following prenatal exposures. Beyond direct exposures, transgenerational disease phenotypes can persist for multiple generations without subsequent exposure. The mechanisms of action of these EDCs differ: VIN is anti-androgenic while the PCB mixture Aroclor 1221 (A1221) is weakly estrogenic. Based on limited evidence for the inheritance of epimutations in germline, we measured DNA methylation in brain and sperm of rats. Pregnant dams were exposed from day 8-18 of gestation to low dosages of VIN, A1221, or the vehicle. To produce paternal lineages, exposed F1 males were bred with untreated females, creating the F2 and subsequently F3 generations. In adult F1 and F3 males, mature sperm was collected, and brain nuclei involved in anxiety and social behaviors (CA3 of the hippocampus; central amygdala) were selected for assays of epimutations in CpG islands using reduced representation bisulfite sequencing. In F1 sperm, VIN and PCBs induced differential methylation in 215 and 284 CpG islands, respectively, compared to vehicle. The majority of effects were associated with hypermethylation. Fewer epimutations were detected in the brain. A subset of differentially methylated regions were retained from the F1 to the F3 generation, suggesting a common mechanism of EDC and germline epigenome interaction. Thus, EDCs can cause heritable epimutations in the sperm that may embody the future phenotype of brain-behavior disorders caused by direct or transgenerational exposures.

Human and animal evidence of potential transgenerational inheritance of health effects: An evidence map and state-of-the-science evaluation

BACKGROUND

An increasing number of reports suggest early life exposures result in adverse effects in offspring who were never directly exposed; this phenomenon is termed "transgenerational inheritance." Given concern for public health implications for potential effects of exposures transmitted to subsequent generations, it is critical to determine how widespread and robust this phenomenon is and to identify the range of exposures and possible outcomes.

OBJECTIVES

This scoping report examines the evidence for transgenerational inheritance associated with exposure to a wide range of stressors in humans and animals to identify areas of consistency, uncertainty, data gaps, and to evaluate general risk of bias issues for the transgenerational study design.

METHODS

A protocol was developed to collect and categorize the literature into a systematic evidence map for transgenerational inheritance by health effects, exposures, and evidence streams following the Office of Health Assessment and Translation (OHAT) approach for conducting literature-based health assessments.

RESULTS

A PubMed search yielded 63,758 unique records from which 257 relevant studies were identified and categorized into a systematic evidence map by evidence streams (46 human and 211 animal), broad health effect categories, and exposures. Data extracted from the individual studies are available in the Health Assessment Workspace Collaborative (HAWC) program. There are relatively few bodies of evidence where multiple studies evaluated the same exposure and the same or similar outcomes. Studies evaluated for risk of bias generally had multiple issues in design or conduct.

CONCLUSIONS

The evidence mapping illustrated that risk of bias, few studies, and heterogeneity in exposures and endpoints examined present serious limitations to available bodies of evidence for assessing transgenerational effects. Targeted research is suggested to addressed inconsistencies and risk of bias issues identified, and thereby establish more robust bodies of evidence to critically assess transgenerational effects - particularly by adding data on exposure-outcome pairs where there is some evidence (i.e., reproductive, metabolic, and neurological effects).

DNA methylation as a genomic marker of exposure to chemical and environmental agents

Recent progress in interpreting comprehensive genetic and epigenetic profiles for human cellular states has contributed new insights into the developmental origins of disease, elucidated novel signalling pathways and enhanced drug discovery programs. A similar comprehensive approach to decoding the epigenetic readouts from chemical challenges in vivo would yield new paradigms for monitoring and assessing environmental exposure in model systems and humans.

Linking inter-individual variability to endocrine disruptors: insights for epigenetic inheritance

Endocrine disrupting chemicals (EDCs) can induce a myriad of adverse health effects. An area of active investigation is the multi- and transgenerational inheritance of EDC-induced adverse health effects referring to the transmission of phenotypes across multiple generations via the germline. The inheritance of EDC-induced adverse health effects across multiple generations can occur independent of genetics, spurring much research into the transmission of underlying epigenetic mechanisms. Epigenetic mechanisms play important roles in the development of an organism and are responsive to environmental exposures. To date, rodent studies have demonstrated that acquired epigenetic marks, particularly DNA methylation, that are inherited following parental EDC exposure can escape embryonic epigenome reprogramming. The acquired epimutations can lead to subsequent adult-onset diseases. Increasing studies have reported inter-individual variations that occur with epigenetic inheritance. Factors that underlie differences among individuals could reveal previously unidentified mechanisms of epigenetic transmission. In this review, we give an overview of DNA methylation and posttranslational histone modification as the potential mechanisms for disease transmission, and define the requirements for multi- and transgenerational epigenetic inheritance. We subsequently evaluate rodent studies investigating how acquired changes in epigenetic marks especially DNA methylation across multiple generations can vary among individuals following parental EDC exposure. We also discuss potential sources of inter-individual variations and the challenges in identifying these variations. We conclude our review discussing the challenges in applying rodent generational studies to humans.

Assessing multigenerational effects of prednisolone to the freshwater snail, Physa acuta (Gastropoda: Physidae)

Prednisolone (PDS), a potent synthetic glucocorticoid is widely prescribed for its exceptional anti-inflammatory properties. Several studies have detected the environmental presence of PDS in water bodies which has led to an ecological concern for its toxicity to non-target aquatic biota. The present study investigated the effects of exposure to PDS on different life-cycle stages and generations of the freshwater snail, Physa acuta. This continuous exposure over a period of multiple generations resulted in generational impairments at measured endpoints. LOEC values (p<0.001) for PDS exposure ranged from 32 to 4μg/L in exposed F0-F2 generations. Global DNA methylation (% 5-methyl cytosine) of adult progeny was found to be affected at higher test concentrations in comparison to the parent snails. Partially formed to completely missed growth components of shell structure and shell thinning in abnormally underdeveloped PDS exposed snails of F1 and F2 generation, was also observed in this multigenerational exposure experiment. The multigenerational study confirmed P. acuta as a promising bioindicator since critical effects of the long term glucocorticoid exposure opens up the way for further investigations on transgenerational toxicity in environmental toxicology and risk assessment and to monitor glucocorticoid pollution in aqueous ecosystem.

Recent advances in understanding/assessing toxicity to the epigenome

The ability of non-genotoxic agents to induce cancer has been documented and clearly requires a reassessment of testing for environmental and human safety. Drug safety testing has historically relied on test batteries designed to detect DNA damage leading to mutation and cancer. The standard genetic toxicology testing battery has been a reliable tool set to identify small molecules/chemicals as hazards that could lead to genetic changes in organisms and induction of cancer. While pharmaceutical companies and regulatory agencies have extensively used the standard battery, it is not suitable for compounds that may induce epigenetic changes. Additionally, many pharmaceutical companies have changed their product portfolios to include peptides and/or other biological molecules, which are not expected to be genotoxic in their own right. If we are to best use our growing knowledge regarding chemicals and biomolecules that induce heritable changes via epigenetic mechanisms, then we must ask what changes may be needed in our testing paradigm to predict long-term downstream effects through epigenetic mechanisms.

Environmentally induced epigenetic toxicity: potential public health concerns

Throughout our lives, epigenetic processes shape our development and enable us to adapt to a constantly changing environment. Identifying and understanding environmentally induced epigenetic change(s) that may lead to adverse outcomes is vital for protecting public health. This review, therefore, examines the present understanding of epigenetic mechanisms involved in the mammalian life cycle, evaluates the current evidence for environmentally induced epigenetic toxicity in human cohorts and rodent models and highlights the research considerations and implications of this emerging knowledge for public health and regulatory toxicology. Many hundreds of studies have investigated such toxicity, yet relatively few have demonstrated a mechanistic association among specific environmental exposures, epigenetic changes and adverse health outcomes in human epidemiological cohorts and/or rodent models. While this small body of evidence is largely composed of exploratory in vivo high-dose range studies, it does set a precedent for the existence of environmentally induced epigenetic toxicity. Consequently, there is worldwide recognition of this phenomenon, and discussion on how to both guide further scientific research towards a greater mechanistic understanding of environmentally induced epigenetic toxicity in humans, and translate relevant research outcomes into appropriate regulatory policies for effective public health protection.

Developmental origins of epigenetic transgenerational inheritance

Environmental factors can induce epigenetic alterations in the germ cells that can potentially be transmitted transgenerationally. This non-genetic form of inheritance is termed epigenetic transgenerational inheritance and has been shown in a variety of species including plants, flies, worms, fish, rodents, pigs, and humans. This phenomenon operates during specific critical windows of exposure, linked to the developmental biology of the germ cells (sperm and eggs). Therefore, concepts of the developmental origins of transgenerational inheritance of phenotypic variation and subsequent disease risk need to include epigenetic processes affecting the developmental biology of the germ cell. These developmental impacts on epigenetic transgenerational inheritance, in contrast to multigenerational exposures, are the focus of this Perspective.

Elusive inheritance: Transgenerational effects and epigenetic inheritance in human environmental disease

Epigenetic mechanisms involving DNA methylation, histone modification, histone variants and nucleosome positioning, and noncoding RNAs regulate cell-, tissue-, and developmental stage-specific gene expression by influencing chromatin structure and modulating interactions between proteins and DNA. Epigenetic marks are mitotically inherited in somatic cells and may be altered in response to internal and external stimuli. The idea that environment-induced epigenetic changes in mammals could be inherited through the germline, independent of genetic mechanisms, has stimulated much debate. Many experimental models have been designed to interrogate the possibility of transgenerational epigenetic inheritance and provide insight into how environmental exposures influence phenotypes over multiple generations in the absence of any apparent genetic mutation. Unexpected molecular evidence has forced us to reevaluate not only our understanding of the plasticity and heritability of epigenetic factors, but of the stability of the genome as well. Recent reviews have described the difference between transgenerational and intergenerational effects; the two major epigenetic reprogramming events in the mammalian lifecycle; these two events making transgenerational epigenetic inheritance of environment-induced perturbations rare, if at all possible, in mammals; and mechanisms of transgenerational epigenetic inheritance in non-mammalian eukaryotic organisms. This paper briefly introduces these topics and mainly focuses on (1) transgenerational phenotypes and epigenetic effects in mammals, (2) environment-induced intergenerational epigenetic effects, and (3) the inherent difficulties in establishing a role for epigenetic inheritance in human environmental disease.

Importance of investigating epigenetic alterations for industry and regulators: An appraisal of current efforts by the Health and Environmental Sciences Institute

Recent technological advances have led to rapid progress in the characterization of epigenetic modifications that control gene expression in a generally heritable way, and are likely involved in defining cellular phenotypes, developmental stages and disease status from one generation to the next. On November 18, 2013, the International Life Sciences Institute (ILSI) Health and Environmental Sciences Institute (HESI) held a symposium entitled "Advances in Assessing Adverse Epigenetic Effects of Drugs and Chemicals" in Washington, D.C. The goal of the symposium was to identify gaps in knowledge and highlight promising areas of progress that represent opportunities to utilize epigenomic profiling for risk assessment of drugs and chemicals. Epigenomic profiling has the potential to provide mechanistic information in toxicological safety assessments; this is especially relevant for the evaluation of carcinogenic or teratogenic potential and also for drugs that directly target epigenetic modifiers, like DNA methyltransferases or histone modifying enzymes. Furthermore, it can serve as an endpoint or marker for hazard characterization in chemical safety assessment. The assessment of epigenetic effects may also be approached with new model systems that could directly assess transgenerational effects or potentially sensitive stem cell populations. These would enhance the range of safety assessment tools for evaluating xenobiotics that perturb the epigenome. Here we provide a brief synopsis of the symposium, update findings since that time and then highlight potential directions for future collaborative efforts to incorporate epigenetic profiling into risk assessment.

Bisphenol A and phthalate endocrine disruption of parental and social behaviors

Perinatal exposure to endocrine disrupting chemicals (EDCs) can induce promiscuous neurobehavioral disturbances. Bisphenol A and phthalates are two widely prevalent and persistent EDCs reported to lead to such effects. Parental and social behaviors are especially vulnerable to endocrine disruption, as these traits are programmed by the organizational-activational effects of testosterone and estrogen. Exposure to BPA and other EDCs disrupts normal maternal care provided by rodents and non-human primates, such as nursing, time she spends hunched over and in the nest, and grooming her pups. Paternal care may also be affected by BPA. No long-term study has linked perinatal exposure to BPA or other EDC and later parental behavioral deficits in humans. The fact that the same brain regions and neural hormone substrates govern parental behaviors in animal models and humans suggests that this suite of behaviors may also be vulnerable in the latter. Social behaviors, such as communication, mate choice, pair bonding, social inquisitiveness and recognition, play behavior, social grooming, copulation, and aggression, are compromised in animal models exposed to BPA, phthalates, and other EDCs. Early contact to these chemicals is also correlated with maladaptive social behaviors in children. These behavioral disturbances may originate by altering the fetal or adult gonadal production of testosterone or estrogen, expression of ESR1, ESR2, and AR in the brain regions governing these behaviors, neuropeptide/protein hormone (oxytocin, vasopressin, and prolactin) and their cognate neural receptors, and/or through epimutations. Robust evidence exists for all of these EDC-induced changes. Concern also exists for transgenerational persistence of such neurobehavioral disruptions. In sum, evidence for social and parental deficits induced by BPA, phthalates, and related chemicals is strongly mounting, and such effects may ultimately compromise the overall social fitness of populations to come.

Early-life Exposure to Endocrine Disrupting Chemicals and Later-life Health Outcomes: An Epigenetic Bridge?

A growing body of evidence demonstrates that adverse events early in development, and particularly during intrauterine life, may program risks for diseases in adult life. Increasing evidence has been accumulated indicating the important role of epigenetic regulation including DNA methylation, histone modifications and miRNAs in developmental programming. Among the environmental factors which play an important role in programming of chronic pathologies, the endocrine-disrupting chemicals (EDCs) that have estrogenic, anti-estrogenic, and anti-androgenic activity are of specific concern because the developing organism is extremely sensitive to perturbation by substances with hormone-like activity. Among EDCs, there are many substances that are constantly present in the modern human environment or are in widespread use, including dioxin and dioxin-like compounds, phthalates, agricultural pesticides, polychlorinated biphenyls, industrial solvents, pharmaceuticals, and heavy metals. Apart from their common endocrine active properties, several EDCs have been shown to disrupt developmental epigenomic programming. The purpose of this review is to provide a summary of recent research findings which indicate that exposure to EDCs during in-utero and/or neonatal development can cause long-term health outcomes via mechanisms of epigenetic memory.

Are we ready to consider transgenerational epigenetic effects in human health risk assessment?

Recently, there has been a growing concern that chemically or nutritionally mediated epigenetic changes might lead to adverse health outcomes. The natural question is whether the existing chemical safety assessment paradigm is or is not protective of epigenetic-mediated effects, and if there is a need to incorporate new endpoints to specifically address epigenetics. Of particular interest are transgenerational epigenetic effects, which can be passed on through multiple generations. To investigate these questions, a comparison was performed between OECD guideline rat toxicology studies versus several rat transgenerational epigenetic studies. This analysis focused on vinclozolin owing to the availability of a comprehensive suite of dose-response data (NOAEL, reference dose, and human exposure estimates) for both conventional and epigenetic endpoints. This analysis revealed that vinclozolin transgenerational effects were demonstrated at a dose level (100 mg/kg/day) that was: (1) ∼40-fold higher than the overall lowest-observed-adverse-effect level (LOAEL) from rat guideline studies, (2) ∼80-fold higher than the lowest NOAEL from rat guideline studies, (3) ∼80,000-fold higher than the reference dose for the molecule, and (4) ∼1.2-million fold above human exposure estimates. Through this analysis, we conclude that additional research across a spectrum of doses is necessary to elucidate the interplay between epigenetics and apical endpoints before considering epigenetics in human health risk assessment. Therefore, we recommend focusing future research toward (1) examining for potential causal relationships between epigenetic alterations and adverse apical endpoints, and (2) understanding the dose-response relationship of these causal epigenetic alterations when compared with those of the apical endpoints.

Vinclozolin exposure throughout pregnancy and its developmental toxicity

Vinclozolin administration effects: placenta, fetal tissues and skeletal measurements during pregnancy.

RNA: a possible contributor to the 'missing heritability'

A number of human pathologies have a transmission pattern that does not obey Mendelian segregation rules. This type of heredity is defined as non-Mendelian and is based on mechanisms of transgenerational epigenetic inheritance. Comprehensive information on the molecular mechanisms of it is still lacking. However, recent evidence from distantly related species including Caenorhabditis elegans, Drosophila, and mouse, points towards a role for non-coding RNA molecules in such a pattern of inheritance. While it would be too hasty to conclude that RNA molecules are at work in the transgenerational non-genetic inheritance of human pathologies, a growing number of studies seem to strongly support such a speculation.