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

A comparative review of the toxicity mechanisms of perfluorohexanoic acid (PFHxA) and perfluorohexanesulphonic acid (PFHxS) in fish

Industrial and consumer goods contain diverse perfluoroalkyl substances (PFAS). These substances, like perfluorohexanoic acid (PFHxA) and perfluorohexanesulphonic acid (PFHxS), are under increased scrutiny due to their potential toxicity to aquatic organisms. However, our understanding of their biological impacts and mechanisms of action remains limited. The objectives of this review were to compare data for levels of PFHxA and PFHxS in aquatic environments and fish tissues, as well as toxicity mechanisms related to morphological, endocrine, metabolic, and behavioral endpoints. A computational assessment was also performed to identify putative mechanisms of toxicity and to characterize exposure biomarkers. Studies have shown that both PFHxA and PFHxS residues are present in diverse marine and freshwater fish tissues, suggesting the importance of monitoring these PFAS in aquatic organisms. In fish tissues, these chemicals have been reported to be as high as 37.5 ng/g for PFHxA and 1290 ng/g for PFHxS, but their persistence in aquatic environments and degradation in tissues requires further study. In terms of mechanisms of toxicity, both oxidative stress and endocrine disruption have been reported. Based on evidence for endocrine disruption, we modeled interactions of estrogen and androgen receptors of several fish species with PFHxA and PFHxS. Molecular docking revealed that PFHxS has a stronger affinity for interacting with the estrogen and androgen receptors of fish compared to PFHxA and that estrogen and androgen receptors of fathead minnow, zebrafish, Atlantic salmon, and largemouth bass show comparable binding affinities for each chemical except for salmon Esr2b, which was predicted to have lower affinity for PFHxA relative to Esr2a. While mechanistic data are lacking in fish in general for these chemicals, a computational approach revealed that PFHxA can perturb the endocrine system, nervous system, and is linked to changes in kidney and liver weight. Proteins associated with PFHxA and PFHxS exposures in fish include those related to lipid and glucose regulation, reproductive proteins like KISS metastasis suppressor, and proteins associated with the immune system (specifically RAG1, RAG2), all of which are potential biomarkers of exposure. Taken together, we synthesize current knowledge regarding the environmental fate and ecotoxicology of PFHxA/PFHxS in fish species.

Molecular insights into the effects of tetrachlorobisphenol A on puberty initiation in Wistar rats

Tetrachlorobisphenol A (TCBPA) is the chlorinated derivative of bisphenol A (BPA). Several studies have found that BPA adversely affects the reproductive activity largely through binding to estrogen receptors and the critical period of BPA exposure advances the vaginal opening time in the female offspring via the kisspeptin/G protein-coupled receptor 54 (KGG) system. However, whether TCBPA can affect puberty initiation via KGG and the roles of estrogen receptors in this process remain unknown. Therefore, this study investigated the influence of TCBPA on the onset time of puberty in Wistar rats and the related molecular mechanisms by combing in vitro GT1-7 cells and molecular docking. In female Wistar rats, TCBPA at ≥100 mg/kg bw/day (49.2 μmol/L in rat body) markedly advanced vaginal opening time and increased serum levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), and gonadotropin-releasing hormone (GnRH). It also increased the relative gene expression of LH receptor (LHR), GnRH1, and FSH receptor (FSHR) in hypothalamic-pituitary-gonadal (HPG) axis tissues. In GT1-7 cells, TCBPA increased genes and proteins associated with KGG pathway and activated the extracellular-regulated protein kinase 1/2 (Erk1/2) and phosphatidylinositol-3-kinase/protein kinase B (PI3K/Akt) pathways via G protein-coupled estrogen membrane receptor 1 (GPER1) and estrogen receptor alpha (ERα). Docking analyses supported its interactions with GPER1 and ERα, and treatment with specific inhibitors of ERα- and GPER1-modulated PI3K/Akt and Erk1/2 signaling suppressed its effects. Taken together, TCBPA-induced advancement of puberty initiation in Wistar rats thus results primarily from increased LH, GnRH, and FSH secretion together with GnRH1, FSHR, and LHR upregulation driven by ERα- and GPER1-modulated Erk1/2 and PI3K/Akt signaling. Our results provide new molecular insights into the reproductive toxicity of EDCs.

Effects of trichlorobisphenol A on the expression of proteins and genes associated with puberty initiation in GT1-7 cells and the relevant molecular mechanism

This study evaluated the effects of Cl3BPA on kisspeptin-G-protein coupled receptor 54 (GPR54)/gonadotropin-releasing hormone (GnRH) (KGG) signals and analyzed the roles of estrogen receptor alpha (ERɑ) and G-protein coupled estrogen receptor 1 (GPER1) in regulating KGG signals. The results showed that Cl3BPA at 50 μM increased the levels of intracellular reactive oxygen species (ROS) and GnRH, upregulated the protein levels of kisspeptin and the expression of fshr, lhr and gnrh1 genes related to KGG in GT1-7 cells. In addition, 50 μM Cl3BPA significantly upregulated the phosphorylation of extracellular regulated protein kinases 1/2 (Erk1/2), the protein levels of GPER1 and the expression of the gper1 as well as the most target genes associated with mitogen-activated protein kinase (MAPK)/Erk1/2 pathways. Specific signal inhibitor experiments found that Cl3BPA activated KGG signals by activating the GPER1-mediated MAPK/Erk1/2 signaling pathway at the mRNA level. A docking test further confirmed the interactions between Cl3BPA and GPER1. The findings suggest that Cl3BPA might induce precocious puberty by increasing GnRH secretion together with KGG signaling upregulation, which is driven by GPER1-mediated signaling pathway. By comparison, ClxBPAs with fewer chlorine atoms had more obvious effects on the expression of proteins and partial genes related to KGG signals in GT1-7 cells.

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.

Perfluorohexane sulfonate (PFHxS) disturbs the estrous cycle, ovulation rate, oocyte cell communication and calcium homeostasis in mice

Perfluoroalkyl substances are man-made chemicals with ample consumer and industrial applications. They are widely used and are resistant to environmental and metabolic degradation. Several studies have evaluated the effects of Perfluorohexane sulfonate on reproduction. However, there are few reports exploring the cell and molecular mechanisms of its toxicity in the ovary. The aim of this study was to investigate the effects of PFHxS exposure on the estrous cycle, ovulation rate, and the underlying mechanisms of action in female mice in vivo. The animals received a single sub-lethal dose of PFHxS (25.1 mg/kg, 62.5 mg/kg) or vehicle and were stimulated to obtain immature cumulus cell-oocyte complexes (COCs) from the ovaries, or superovulated to develop mature COCs. To evaluate oocyte physiology, Gap-junction intercellular communication (GJIC) was analyzed in immature COCs and calcium homeostasis was evaluated in mature oocytes. PFHxS exposure prolonged the estrous cycle and decreased ovulation rate in female mice. Connexins, Cx43 and Cx37, were downregulated and GJIC was impaired in immature COCs, providing a possible mechanism for the alterations in the estrous cycle and ovulation. No morphological abnormalities were observed in the mature PFHxS-exposed oocytes, but calcium homeostasis was affected. This effect is probably due, at least partially, to deregulation of the endoplasmic reticulum calcium modulator, Stim1. These mechanisms of ovarian injury could explain the reported correlation among PFHxS levels and subfertility in women undergoing fertility treatments.

Association between prenatal exposure to perfluoroalkyl substances and anogenital distance in female neonates

BACKGROUND

Perfluoroalkyl substances (PFASs) have been reported to exert reproductive toxicity. Anogenital distance (AGD) is a biomarker of intrauterine androgen exposure and an indicator of genital development. An animal study reported that female neonatal rats exposed to perfluorooctanoic acid or perfluorooctane sulfonate (PFOS) during postnatal days 1-5 exhibited a longer AGD, while epidemiological studies have shown inconsistent results. This study aimed to examine the effects of prenatal exposure to PFASs on the AGD in female neonates.

METHODS

PFAS levels were measured in plasma samples obtained from pregnant women at 12-16 gestational weeks using high-performance liquid chromatography/mass spectrometry. The AGD of each female neonate was measured within 3 days after delivery. The anogenital index (AGI), calculated as AGD divided by weight, was also determined. A total of 362 motherinfant pairs were included in this study. A multivariate linear regression model was used to examine the association between prenatal ln-transformed concentrations of PFASs and AGD/AGI. In addition, weighted quantile sum regression (WQSR) and Bayesian kernel machine regression (BKMR) models were used to assess the overall effects of a mixture of PFASs on the AGD/AGI and to identify important contributors to the overall effect.

RESULTS

There was a consistent pattern of association between maternal PFAS concentrations and increased AGDanus to posterior fourchette (AF), AGDanus to clitoris (AC), and AGIAF lengths at birth. Statistical significance was found between maternal ln-transformed concentrations of perfluorohexane sulfonate (PFHxS), perfluorododecanoic acid, and perfluorotridecanoic acid and AGDAF, with β values (95% confidence interval [CI]) of 0.83 (0.16, 1.51), 0.32 (0.05, 0.59), and 0.25 (0.00, 0.51) mm, respectively; between PFOS and AGDAC, with a β value (95% CI) of 0.63 (0.04, 1.21) mm; and between PFHxS and AGIAF, with a β value (95% CI) of 0.22 (0.02, 0.43) mm/kg. Similarly, the WQSR and BKMR models showed that an increase in the AGDAF/AGIAF at birth was associated with co-exposure to a mixture of PFASs.

CONCLUSION

High maternal concentrations of PFASs were associated with increased AGD in female neonates, indicating that PFASs may impair reproductive development in female offspring in early life.

The Role of Genetics in Central Precocious Puberty: Confirmed and Potential Neuroendocrine Genetic and Epigenetic Contributors and Their Interactions with Endocrine Disrupting Chemicals (EDCs)

Despite the growing prevalence of central precocious puberty (CPP), most cases are still diagnosed as “idiopathic” due to the lack of identifiable findings of other diagnostic etiology. We are gaining greater insight into some key genes affecting neurotransmitters and receptors and how they stimulate or inhibit gonadotropin-releasing hormone (GnRH) secretion, as well as transcriptional and epigenetic influences. Although the genetic contributions to pubertal regulation are more established in the hypogonadotropic hypogonadism (HH) literature, cases of CPP have provided the opportunity to learn more about its own genetic influences. There have been clinically confirmed cases of CPP associated with gene mutations in kisspeptin and its receptor (KISS1, KISS1R), Delta-like noncanonical Notch ligand 1 (DLK1), and the now most commonly identified genetic cause of CPP, makorin ring finger protein (MKRN3). In addition to these proven genetic causes, a number of other candidates continue to be evaluated. After reviewing the basic clinical aspects of puberty, we summarize what is known about the various genetic and epigenetic causes of CPP as well as discuss some of the potential effects of endocrine disrupting chemicals (EDCs) on some of these processes.