Exposure of female mice to perfluorooctanoic acid suppresses hypothalamic kisspeptin-reproductive endocrine system through enhanced hepatic fibroblast growth factor 21 synthesis, leading to ovulation failure and prolonged dioestrus

Insight into perfluorooctanoic acid-induced impairment of mouse embryo implantation via single-cell RNA-seq

Perfluorooctanoic acid (PFOA) is an environmentally persistent chemical that poses significant risks to human health. Studies have shown that PFOA affects female reproduction, but the specific impact on endometrial receptivity and the underlying mechanisms remain poorly understood. In this study, we investigated the effects of low-dose PFOA exposure through drinking water on endometrial receptivity in a murine model. Our results demonstrate that PFOA exposure significantly impaired endometrial receptivity, which led to a marked decrease in embryo implantation rates. Utilizing single-cell RNA sequencing technology, we conducted a comprehensive analysis that revealed specific mechanisms by which PFOA disrupts the function and development of endometrial epithelial cells. Notably, we identified dysregulation of the ANGPTL (angiopoietin-like) signaling pathway, which is critical for communication between endometrial stromal and epithelial cells, ultimately contributing to embryo implantation failure. These findings provide novel insights into the reproductive toxicity of PFOA and highlight potential targets for therapeutic interventions aimed at addressing infertility associated with environmental contaminants.

Exposure to Long- and Short-Chain Per- and Polyfluoroalkyl Substances in Mice and Ovarian-Related Outcomes: An in Vivo and in Vitro Study

BACKGROUND

The extensive use of per- and polyfluoroalkyl substances (PFAS) has led to environmental contamination and bioaccumulation of these substances. Previous research linked PFAS exposure to female reproductive disorders, but the mechanism remains elusive. Further, most studies focused on legacy long-chain PFOA and PFOS, yet the reproductive impacts of other long-chain PFAS and short-chain alternatives are rarely explored.

OBJECTIVES

We investigated the effects of long- and short-chain PFAS on the mouse ovary and further evaluated the toxic mechanisms of long-chain perfluorononanoic acid (PFNA).

METHODS

A 3D in vitro mouse ovarian follicle culture system and an in vivo mouse model were used, together with approaches of reverse transcription-quantitative polymerase chain reaction (RT-qPCR), enzyme-linked immunosorbent assay (ELISA), RNA sequencing (RNA-seq), pharmacological treatments, in situ zymography, histology, in situ hybridization, analytical chemistry, and benchmark dose modeling (BMD). Using these approaches, a wide range of exposure levels (1 - 250 μ M ) of long-chain PFAS (PFOA, PFOS, PFNA) and short-chain PFAS (PFHpA, PFBS, GenX) were first tested in cultured follicles to examine their effects on follicle growth, hormone secretion, and ovulation. We identified 250 μ M as the most effective concentration for further investigation into the toxic mechanisms of PFNA, followed by an in vivo mouse exposure model to verify the accumulation of PFNA in the ovary and its ovarian-disrupting effects.

RESULTS

In vitro cultured ovarian follicles exposed to long- but not short-chain PFAS showed poorer gonadotropin-dependent follicle growth, ovulation, and hormone secretion in comparison with control follicles. RT-qPCR and RNA-seq analyses revealed significant alterations in the expression of genes involved in follicle-stimulating hormone (FSH)-dependent follicle growth, luteinizing hormone (LH)-stimulated ovulation, and associated regulatory pathways in the PFNA-exposed group in comparison with the control group. The PPAR agonist experiment demonstrated that a peroxisome proliferator-activated receptor gamma (PPAR γ ) antagonist could reverse both the phenotypic and genotypic effects of PFNA exposure, restoring them to levels comparable to the control group. Furthermore, in vivo experiments confirmed that PFNA could accumulate in ovarian tissues and validated the in vitro findings. The BMD, in vitro, and in vivo extrapolation analyses estimated follicular rupture as the most sensitive end point and that observed effects occurred in the range of human exposure to long-chain PFAS.

DISCUSSION

Our study demonstrates that long-chain PFAS, particularly PFNA, act as a PPAR γ agonist in granulosa cells to interfere with gonadotropin-dependent follicle growth, hormone secretion, and ovulation; and exposure to high levels of PFAS may cause adverse ovarian outcomes. https://doi.org/10.1289/EHP14876.

Per- and Polyfluoroalkyl Substances and Female Health Concern: Gender-based Accumulation Differences, Adverse Outcomes, and Mechanisms

The deleterious health implications of perfluoroalkyl and polyfluoroalkyl substances (PFAS) are widely recognized. Females, in contrast to males, exhibit unique pathways for PFAS exposure and excretion, leading to complex health outcomes. The health status of females is largely influenced by hormone-related processes. PFAS have been reported to be associated with various aspects of female health, including reproductive system disorders and pregnancy-related diseases. In this article, we provide insights into the correlations between PFAS and female-prevalent diseases. Current epidemiological and toxicological evidence has demonstrated that the adverse effects of PFAS on the health of the female reproductive system are primarily attributed to the disruption of the hypothalamic-pituitary-gonadal (HPG) axis and hormonal homeostasis. However, these findings do not sufficiently elucidate the intricate associations between PFAS and specific diseases. Furthermore, autoimmune disorders, another category that is more prevalent in women compared to men, require additional investigation. Immune biomarkers pertinent to autoimmune disorders have been observed to be influenced by PFAS exposure, although epidemiological evidence is insufficient to substantiate these relations. Further thorough exploration encompassing epidemiological and toxicological studies is essential to elucidating the inherent influence of PFAS on human pathologies. Additionally, comprehensive investigations into female health issues beyond their reproductive functions is essential.

Reproductive and germ-cell mutagenic effects of poly-and perfluoroalkyl substances (PFAS) to Caenorhabditis elegans after multigenerational exposure

Per- and polyfluoroalkyl substances (PFAS) are a class of globally ubiquitous persistent organic pollutants (POPs). The developmental and reproductive toxicity of PFAS have attracted considerable attention. However, the influence of PFAS exposure on genomic stability of germ cells remains unexplored. In this study, we evaluated long-term reproductive toxicity of environmentally relevant levels of four long-chain PFAS compounds: perfluorooctanoic acid (PFOA, C8), perfluorononanoic acid (PFNA, C9), perfluorodecanoic acid (PFDA, C10), and perfluorooctanesulfonic acid (PFOS, C8), and examined their germ-cell mutagenicity in Caenorhabditis elegans. Our findings reveal that multigenerational exposure to PFAS exhibited minor impacts on development and reproduction of worms. Among all tested PFAS, PFNA significantly increased mutation frequencies of progeny by preferentially inducing T:A → C:G substitutions and small indels within repetitive regions. Further analysis of mutation spectra uncovered elevated frequencies of microhomology-mediated deletions and large deletions in PFOA-treated worms, indicating its potential activity in eliciting DNA double-strand breaks. This study provides the first comparative analysis of the genome-wide mutational profile of PFAS compounds, underscoring the importance of assessing germ-cell mutagenic actions of long-chain PFAS.

Exploring the sources, occurrence, transformation, toxicity, monitoring, and remediation strategies of per- and polyfluoroalkyl substances: a review

Per- and polyfluoroalkyl substances (PFAS), a class of man-made chemicals, possess unique properties that have rendered them indispensable in various industries and consumer goods. However, their extensive use and persistence in the environment have raised concerns about their potential repercussions on human health and the ecosystem. This review provides insights into the sources, occurrence, transformation, impacts, fate, monitoring, and remediation strategies for PFAS. Once released into the environment, these chemicals undergo intricate transformation processes, such as degradation, bioaccumulation, and biomagnification, which result in their far-reaching distribution and persistence. Their chemical stability results in persistent pollution, with far-reaching ecological and human health implications. Remediation strategies for PFAS are still in their infancy, and researchers are exploring innovative and sustainable methods for treating contaminated environments. Promising technologies such as adsorption, biodegradation, and electrochemical oxidation have shown the potential to remove PFAS from contaminated sites, yet the search for more efficient and sustainable solutions continues. In conclusion, this review emphasizes the urgent need for continued research and innovation to address the global environmental challenge posed by PFAS. As we move forward, it is imperative to prioritize sustainable solutions that minimize the detrimental consequences of these substances on human health and the environment.

Perfluoroalkyl and Polyfluoroalkyl Substances in Relation to the Participant-Reported Total Pregnancy and Live Birth Numbers among Reproductive-Aged Women in the United States

Perfluoroalkyl and polyfluoroalkyl substances (PFASs), widely utilized in various industries, may pose potential reproductive well-being risks. However, the research on the impact of PFAS exposures on pregnancy and live birth rates remains scarce. To address this gap, we conducted a cross-sectional study using the data from the United States National Health and Nutrition Examination Survey (NHANES) collected between 2013 and 2018. We focused on six PFAS compounds measured in the serum of women aged 20 to 50 years, employing the Poisson regression, Quantile G-composition (Qgcomp), and Weighted Quantile Sum (WQS) regression models. Adjusting for age, racial/ethnic origin, educational level, marital status, family income, body mass index (BMI), menarche age, birth control pill use, and other female hormone consumption, the Poisson regression identified significant negative associations between the individual PFAS exposures and pregnancy and live birth numbers (p < 0.05 for all 24 null hypotheses for which the slope of the trend line is zero). The Qgcomp analysis indicated that a one-quartile increase in the mixed PFAS exposures was associated with reductions of 0.09 (95% CI: -0.15, -0.03) in the pregnancy numbers and 0.12 (95% CI: -0.19, -0.05) in the live birth numbers. Similarly, the WQS analysis revealed that a unit increase in the WQS index corresponded to decreases of 0.14 (95% CI: -0.20, -0.07) in the pregnancy numbers and 0.14 (95% CI: -0.21, -0.06) in the live birth numbers. Among the six specific PFAS compounds we studied, perfluorononanoic acid (PFNA) had the most negative association with the pregnancy and live birth numbers. In conclusion, our findings suggest that PFAS exposures are associated with lower pregnancy and live birth numbers among women of reproductive age.

Per- and Polyfluoroalkyl Substances (PFASs) and Their Potential Effects on Female Reproductive Diseases

Per- and polyfluoroalkyl substances (PFASs) are a class of anthropogenic organic compounds widely present in the natural and human living environments. These emerging persistent pollutants can enter the human body through multiple channels, posing risks to human health. In particular, exposure to PFASs in women may cause a series of reproductive health hazards and infertility. Based on a review of the existing literature, this study preliminarily summarizes the effects of PFAS exposure on the occurrence and development of female reproductive endocrine diseases, such as polycystic ovary syndrome (PCOS), endometriosis, primary ovarian insufficiency (POI), and diminished ovarian reserve (DOR). Furthermore, we outline the relevant mechanisms through which PFASs interfere with the physiological function of the female ovary and finally highlight the role played by nutrients in reducing the reproductive health hazards caused by PFASs. It is worth noting that the physiological mechanisms of PFASs in the above diseases are still unclear. Therefore, it is necessary to further study the molecular mechanisms of PFASs in female reproductive diseases and the role of nutrients in this process.

PFAS association with kisspeptin and sex hormones in teenagers of the HBM4EU aligned studies

Exposure to Perfluoroalkyl acids (PFAS) can impair human reproductive function, e.g., by delaying or advancing puberty, although their mechanisms of action are not fully understood. We therefore set out to evaluate the relationship between serum PFAS levels, both individually and as a mixture, on the Hypothalamic-Pituitary-Gonadal (HPG) axis by analyzing serum levels of reproductive hormones and also kisspeptin in European teenagers participating in three of the HBM4EU Aligned Studies. For this purpose, PFAS compounds were measured in 733 teenagers from Belgium (FLEHS IV study), Slovakia (PCB cohort follow-up), and Spain (BEA study) by high performance liquid chromatography-tandem mass spectrometry (HPLC/MS) in laboratories under the HBM4EU quality assurance quality control (QA/QC) program. In the same serum samples, kisspeptin 54 (kiss-54) protein, follicle-stimulating hormone (FSH), total testosterone (TT), estradiol (E2), and sex hormone-binding globulin (SHBG) levels were also measured using immunosorbent assays. Sex-stratified single pollutant linear regression models for separate studies, mixed single pollutant models accounting for random effects for pooled studies, and g-computation and Bayesian kernel machine regression (BKMR) models for the mixture of the three most available (PFNA, PFOA, and PFOS) were fit. PFAS associations with reproductive markers differed according to sex. Each natural log-unit increase of PFOA, PFNA, and PFOS were associated with higher TT [18.41 (6.18; 32.31), 15.60 (7.25; 24.61), 14.68 (6.18; 24.61), respectively] in girls, in the pooled analysis (all studies together). In males, G-computation showed that PFAS mixture was associated with lower FSH levels [-10.51 (-18.81;-1.36)]. The BKMR showed the same patterns observed in G-computation, including a significant increase on male Kiss-54 and SHBG levels. Overall, effect biomarkers may enhance the current epidemiological knowledge regarding the adverse effect of PFAS in human HPG axis, although further research is warranted.

Hepatic and ovarian effects of perfluorooctanoic acid exposure differ in lean and obese adult female mice

Obesity and overweight cause poor oocyte quality, miscarriage, infertility, polycystic ovarian syndrome, and offspring birth defects and affects 40% and 20% of US women and girls, respectively. Perfluorooctanoic acid (PFOA), a per- and poly-fluoroalkyl substance (PFAS), is environmentally persistent and has negative female reproductive effects including endocrine disruption, oxidative stress, altered menstrual cyclicity, and decreased fertility in humans and animal models. PFAS exposure is associated with non-alcoholic fatty liver disease which affects ∼24-26% of the US population. This study investigated the hypothesis that PFOA exposure impacts hepatic and ovarian chemical biotransformation and alters the serum metabolome. At 7 weeks of age, female lean, wild type (KK.Cg-a/a) or obese (KK.Cg-Ay/J) mice received saline (C) or PFOA (2.5 mg/Kg) per os for 15 d. Hepatic weight was increased by PFOA exposure in both lean and obese mice (P < 0.05) and obesity also increased liver weight (P < 0.05) compared to lean mice. The serum metabolome was also altered (P < 0.05) by PFOA exposure and differed between lean and obese mice. Exposure to PFOA altered (P < 0.05) the abundance of ovarian proteins with roles in xenobiotic biotransformation (lean - 6; obese - 17), metabolism of fatty acids (lean - 3; obese - 9), cholesterol (lean - 8; obese - 11), amino acids (lean - 18; obese - 19), glucose (lean - 7; obese - 10), apoptosis (lean - 18; obese - 13), and oxidative stress (lean - 3; obese - 2). Use of qRT-PCR determined that exposure to PFOA increased (P < 0.05) hepatic Ces1 and Chst1 in lean but Ephx1 and Gstm3 in obese mice. Also, obesity basally increased (P < 0.05) Nat2, Gpi and Hsd17b2 mRNA levels. These data identify molecular changes resultant from PFOA exposure that may cause liver injury and ovotoxicity in females. In addition, differences in toxicity induced by PFOA exposure occurs in lean and obese mice.

Perfluorooctanoic acid exposure in vivo perturbs mitochondrial metabolic during oocyte maturation

Perfluorooctanoic acid (PFOA), a member of a group of polyfluorinated and perfluorinated alkyl substances (PFAS), is associated with adverse pregnancy outcomes in mammals. However, the effects of in vivo exposure to PFOA on the female reproductive system and the underlying mechanisms remain unclear. In our study, we constructed a mouse model to investigate whether low-dose PFOA (1 mg/kg/day) or high-dose PFOA (5 mg/kg/day) affect meiosis maturation of oocytes and the potential mechanisms that may be associated with oocyte maturation disorder. Our results indicate that low-dose and high-dose PFOA can lead to impaired oocyte maturation, which is manifested by decreased rate of embryonic foam rupture and first polar body extrusion. Moreover, PFOA exposure harmed the mitochondrial metabolic, resulting in low levels of ATP contents, high reactive oxygen species, aberrant mitochondrial membrane potential. In addition, the proportion of DNA damage marker γ-H2AX was also significantly increased in PFOA exposure oocytes. These changes lead to abnormal arrangements of the spindle and chromosomes during oocyte maturation. In conclusion, our results for the first time illustrated that exposure to PFOA in vivo in female mice impaired the meiosis maturation of oocytes, which provided a basis for studying the mechanism of PFOA reproductive toxicity in female mammals.

The effects of endocrine-disrupting chemicals on ovarian- and ovulation-related fertility outcomes

Exposure to endocrine-disrupting chemicals (EDCs) is unavoidable, which represents a public health concern given the ability of EDCs to target the ovary. However, there is a large gap in the knowledge about the impact of EDCs on ovarian function, including the process of ovulation. Defects in ovulation are the leading cause of infertility in women, and EDC exposures are contributing to the prevalence of infertility. Thus, investigating the effects of EDCs on the ovary and ovulation is an emerging area for research and is the focus of this review. The effects of EDCs on gametogenesis, uterine function, embryonic development, and other aspects of fertility are not addressed to focus on ovarian- and ovulation-related fertility issues. Herein, findings from epidemiological and basic science studies are summarized for several EDCs, including phthalates, bisphenols, per- and poly-fluoroalkyl substances, flame retardants, parabens, and triclosan. Epidemiological literature suggests that exposure is associated with impaired fecundity and in vitro fertilization outcomes (decreased egg yield, pregnancies, and births), while basic science literature reports altered ovarian follicle and corpora lutea numbers, altered hormone levels, and impaired ovulatory processes. Future directions include identification of the mechanisms by which EDCs disrupt ovulation leading to infertility, especially in women.

Reduced Birth Weight and Exposure to Per- and Polyfluoroalkyl Substances: A Review of Possible Underlying Mechanisms Using the AOP-HelpFinder

Prenatal exposure to per- and polyfluorinated substances (PFAS) may impair fetal growth. Our knowledge of the underlying mechanisms is incomplete. We used the Adverse Outcome Pathway (AOP)-helpFinder tool to search PubMed for studies published until March 2021 that examined PFAS exposure in relation to birth weight, oxidative stress, hormones/hormone receptors, or growth signaling pathways. Of these 1880 articles, 106 experimental studies remained after abstract screening. One clear finding is that PFAS are associated with oxidative stress in in vivo animal studies and in vitro studies. It appears that PFAS-induced reactive-oxygen species (ROS) generation triggers increased peroxisome proliferator-activated receptor (PPAR)γ expression and activation of growth signaling pathways, leading to hyperdifferentiation of pre-adipocytes. Fewer proliferating pre-adipocytes result in lower adipose tissue weight and in this way may reduce birth weight. PFAS may also impair fetal growth through endocrine effects. Estrogenic effects have been noted in in vivo and in vitro studies. Overall, data suggest thyroid-damaging effects of PFAS affecting thyroid hormones, thyroid hormone gene expression, and histology that are associated in animal studies with decreased body and organ weight. The effects of PFAS on the complex relationships between oxidative stress, endocrine system function, adipogenesis, and fetal growth should be further explored.

Construction of a ceRNA-based lncRNA–mRNA network to identify functional lncRNAs in premature ovarian insufficiency

Premature ovarian insufficiency, characterized by ovarian infertility and low fertility, has become a significant problem in developed countries due to its propensity for late delivery. It has been described that the vital role of lncRNA in the development and progression of POI. The aim of this work was to create a POI-based lncRNA–mRNA network (POILMN) to recognize key lncRNAs. Overall, differently expressed mRNAs (DEGs) and differently expressed lncRNAs (DELs) were achieved by using the AnnoProbe and limma R packages. POI-based lncRNA–mRNA network (POILMN) construction was carried out using the tinyarray R package and hypergeometric distribution. To identify key lncRNAs, we used CentiScaPe plug-in Cytoscape as a screening tool. In total, 244 differentially expressed lncRNAs (DELs) and 288 differentially expressed mRNAs (DEGs) were obtained in this study. Also, 177 lncRNA/mRNA pairs (including 39 lncRNAs and 86 mRNAs) were selected using the hypergeometric test. Finally, we identified four lncRNA (HCP5, NUTM2A-AS1, GABPB1-IT1, and SMIM25) intersections by topological analysis between two centralities (degree and betweenness), and we explored their subnetwork GO and KEGG pathway enrichment analysis. Here, we have provided strong evidence for a relationship with apoptosis, DNA repair damage, and energy metabolism terms and pathways in the key lncRNAs in our POI-based lncRNA–mRNA network. In addition, we evaluated the localization information of genes related to POI and found that genes were more distributed on chromosomes 15, 16, 17, and 19. However, more experiments are needed to confirm the functional significance of such predicted lncRNA/mRNA. In conclusion, our study identified four long non-coding RNA molecules that may be relevant to the progress of premature ovarian insufficiency.

Use of kisspeptin to trigger oocyte maturation during in vitro fertilisation (IVF) treatment

Infertility is a major global health issue and is associated with significant psychological distress for afflicted couples. In vitro fertilisation (IVF) utilises supra-physiological doses of stimulatory hormones to induce the growth of multiple ovarian follicles to enable surgical retrieval of several oocytes for subsequent fertilisation and implantation into the maternal endometrium. The supra-physiological degree of ovarian stimulation can lead to potential risks during IVF treatment, including ovarian hyperstimulation syndrome (OHSS) and multiple pregnancy. The choice of oocyte maturation trigger, such as human chorionic gonadotrophin (hCG) or gonadotrophin releasing hormone agonist (GnRHa), can impact both the efficacy of IVF treatment with a bearing on luteal phase hormonal dynamics and thus the degree of luteal phase support required to maintain optimal pregnancy rates, as well as on safety of treatment with particular respect to the risk of OHSS. Kisspeptin regulates gonadotrophin releasing hormone (GnRH) release and is therefore a key regulator of the hypothalamo-pituitary-gonadal (HPG) axis. Kisspeptin has been shown to be requisite for the occurrence of the physiological ovulatory luteinising hormone (LH) surge. In this review, we discuss the potential use of kisspeptin as a novel trigger of oocyte maturation.

Chronic exposure to perfluorohexane sulfonate leads to a reproduction deficit by suppressing hypothalamic kisspeptin expression in mice

Background

Perfluorohexane sulfonate (PFHxS) is a six-carbon perfluoroalkyl sulfonic acid found as an environmental contaminant. This study aims to investigate the effects of PFHxS exposure on female reproduction and the underlying mechanism in mice.

Methods

Eight-week-old ICR mice were divided randomly into four groups administered corn oil (vehicle) and PFHxS at doses of 0.5, 5, and 50 mg/kg/day for 42 days by intragastric administration. Body weight, ovarian weight, estrous cycle, follicle counts, and serum sex hormone levels were evaluated. The expression of kisspeptin and gonadotropin releasing hormone (GnRH) in the hypothalamus was also detected.

Results

Compared to vehicle exposure, 5 mg/kg/day PFHxS treatment prolonged the estrous cycle, especially the duration of diestrus, after 42 days of treatment. The numbers of secondary follicles, antral follicles and corpus lutea were significantly reduced in the PFHxS-treated mice. Moreover, compared with the control mice, the PFHxS-treated mice showed decreases in the serum levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), and estrogen (E2), and reduced GnRH mRNA levels, along with the lack of an LH surge. Furthermore, the PFHxS-treated mice had lower levels of kisspeptin immunoreactivity and kiss-1 mRNA in the arcuate nucleus (ARC) and anteroventral periventricular nucleus (AVPV) than the control mice. After intraventricular administration of kisspeptin-10, the numbers of secondary follicles, antral follicles and corpus lutea recovered, along with the levels of GnRH mRNA, FSH, and LH in the mice treated with 5 mg/kg/day PFHxS.

Conclusion

These results indicate that chronic exposure of mice to 5 mg/kg/day PFHxS affects reproductive functions by inhibiting kisspeptin expression in the ARC and AVPV regions, leading to deficits in follicular development and ovulation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13048-021-00903-z.

Fibroblast growth factor 21 in dairy cows: current knowledge and potential relevance

Fibroblast growth factor 21 (FGF21) has been identified as an important regulator of carbohydrate and lipid metabolism, which plays an important role for metabolic regulation, particularly under conditions of energy deprivation or stress conditions. Dairy cows are subjected to a negative energy balance and various kinds of stress particularly during the periparturient phase and during early lactation. It has been shown that the plasma concentration of FGF21 in dairy cows is dramatically increased at parturition and remains high during the first weeks of lactation. This finding suggests that FGF21 might exert similar functions in dairy cows than in other species, such as mice or humans. However, the role of FGF21 in dairy cows has been less investigated so far. Following a brief summary of the previous findings about the function of FGF21 in humans and mice, the present review aims to present the current state of knowledge about the role of FGF21 in dairy cows. The first part of the review deals with the tissue localization of FGF21 and with conditions leading to an upregulation of FGF21 expression in the liver of dairy cows. In the second part, the influence of nutrition on FGF21 expression and the role of FGF21 for metabolic diseases in dairy cows is addressed. In the third part, findings of exogenous FGF21 application on metabolism in dairy cows are reported. Finally, the potential relevance of FGF21 in dairy cows is discussed. It is concluded that FGF21 might be of great importance for metabolic adaptation to negative energy balance and stress conditions in dairy cows. However, further studies are needed for a better understanding of the functions of FGF21 in dairy cows.

Per- and Polyfluoroalkyl Substance Toxicity and Human Health Review: Current State of Knowledge and Strategies for Informing Future Research

Reports of environmental and human health impacts of per- and polyfluoroalkyl substances (PFAS) have greatly increased in the peer-reviewed literature. The goals of the present review are to assess the state of the science regarding toxicological effects of PFAS and to develop strategies for advancing knowledge on the health effects of this large family of chemicals. Currently, much of the toxicity data available for PFAS are for a handful of chemicals, primarily legacy PFAS such as perfluorooctanoic acid and perfluorooctane sulfonate. Epidemiological studies have revealed associations between exposure to specific PFAS and a variety of health effects, including altered immune and thyroid function, liver disease, lipid and insulin dysregulation, kidney disease, adverse reproductive and developmental outcomes, and cancer. Concordance with experimental animal data exists for many of these effects. However, information on modes of action and adverse outcome pathways must be expanded, and profound differences in PFAS toxicokinetic properties must be considered in understanding differences in responses between the sexes and among species and life stages. With many health effects noted for a relatively few example compounds and hundreds of other PFAS in commerce lacking toxicity data, more contemporary and high-throughput approaches such as read-across, molecular dynamics, and protein modeling are proposed to accelerate the development of toxicity information on emerging and legacy PFAS, individually and as mixtures. In addition, an appropriate degree of precaution, given what is already known from the PFAS examples noted, may be needed to protect human health. Environ Toxicol Chem 2021;40:606-630. © 2020 SETAC.