Bromate-induced Changes in p21 DNA Methylation and Histone Acetylation in Renal Cells

Changes in CpG Methylation of the Vitellogenin 1 Promoter in Adult Male Zebrafish after Exposure to 17α-Ethynylestradiol

Numerous pharmaceutical and industrial chemicals are classified as endocrine-disrupting chemicals (EDCs) that interfere with hormonal homeostasis, leading to developmental disorders and other pathologies. The synthetic estrogen 17α-ethynylestradiol (EE2) is used in oral contraceptives and other hormone therapies. EE2 and other estrogens are inadvertently introduced into aquatic environments through municipal wastewater and agricultural effluents. Exposure of male fish to estrogens increases expression of the egg yolk precursor protein vitellogenin (Vtg), which is used as a molecular marker of exposure to estrogenic EDCs. The mechanisms behind Vtg induction are not fully known, and we hypothesized that it is regulated via DNA methylation. Adult zebrafish were exposed to either dimethyl sulfoxide or 20 ng/L EE2 for 14 days. Messenger RNA (mRNA) expression and DNA methylation were assessed in male zebrafish livers at 0, 0.25, 0.5, 1, 4, 7, and 14 days of exposure; and those of females were assessed at 13 days (n ≥ 4/group/time point). To test the persistence of any changes, we included a recovery group that received EE2 for 7 days and did not receive any for the following 7 days, in the total 14-day study. Methylation of DNA at the vtg1 promoter was assessed with targeted gene bisulfite sequencing in livers of adult male and female zebrafish. A significant increase in vtg1 mRNA was observed in the EE2-exposed male fish as early as 6 h. Interestingly, DNA methylation changes were observed at 4 days. Decreases in the overall methylation of the vtg1 promoter in exposed males resulted in levels comparable to those in female controls, suggesting feminization. Importantly, DNA methylation levels in males remained significantly impacted after 7 days post-EE2 removal, unlike mRNA levels. These data identify an epigenetic mark of feminization that may serve as an indicator of not only estrogenic exposure but also previous exposure to EE2. Environ Toxicol Chem 2024;00:1-10. © 2024 SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Effects of prenatal and lactational exposure to iodoacetic acid on the F1 generation of mice†

Water disinfection can generate water disinfection byproducts (DBPs). Iodoacetic acid (IAA) is one DBP, and it has been shown to be an ovarian toxicant in vitro and in vivo. However, it is unknown if prenatal and lactational exposure to IAA affects reproductive outcomes in female offspring. This study tested the hypothesis that prenatal and lactational exposure to IAA adversely affects reproductive parameters in F1 female offspring. Adult female CD-1 mice were dosed with water (control) or IAA (10, 100, and 500 mg/L) in the drinking water for 35 days and then mated with unexposed males. IAA exposure continued throughout gestation. Dams delivered naturally, and pups were continuously exposed to IAA through lactation until postnatal day (PND) 21. Female pups were euthanized on PND 21 and subjected to measurements of anogenital distance, ovarian weight, and vaginal opening. Ovaries were subjected to histological analysis. In addition, sera were collected to measure reproductive hormone levels. IAA exposure decreased vaginal opening rate, increased the absolute weight of the ovaries, increased anogenital index, and decreased the percentage of atretic follicles in female pups compared to control. IAA exposure caused a borderline decrease in the levels of progesterone and follicle-stimulating hormone (FSH) and increased levels of testosterone in female pups compared to control. Collectively, these data show that prenatal and lactational exposure to IAA in drinking water affects vaginal opening, anogenital index, the weight of the ovaries, the percentage of atretic follicles, and hormone levels in the F1 generation in mice.

Effects of glufosinate-ammonium on male reproductive health: Focus on epigenome and transcriptome in mouse sperm

Glufosinate-ammonium (GLA) is a widely used herbicide with emerging concern over its neural and reproductive toxicity. To uncover potential effects of GLA on male reproductive health in mammals, adult male C57BL/6J mice were administered 0.2 mg/kg·d GLA for 5 weeks. After examination on fertility, testis histology and semen quality in the GLA group, we performed deep sequencing to identify repressive epigenetic marks including DNA methylation and histone modifications (H3K27me3 and H3K9me3), together with mRNA transcript levels in sperm. Then, we integrated multi-omics sequencing data to comprehensively explore GLA-induced epigenetic and transcriptomic alterations. We found no significant difference either on fertility, testis histology or semen quality-related indicators. As for epigenome, the protein level of H3K27me3 was significantly increased in GLA sperm. Next generation sequencing showed alterations of these epigenetic marks and extensive transcription inhibition in sperm. These differential repressive marks were mainly distributed at intergenic regions and introns. According to results by Gene Ontology enrichment analysis, both differentially methylated and expressed genes were mainly enriched in pathways related to synapse organization. Subtle differences in genomic imprinting were also observed between the two groups. These results suggested that GLA predominantly impaired sperm epigenome and transcriptome in mice, with little effect on fertility, testis histology or semen quality. Further studies on human sperm using similar strategies need to be conducted for a better understanding of the male reproductive toxicity of GLA.

Development of a rat and human PBPK model for bromate and estimation of human equivalent concentrations in drinking water

A physiologically based pharmacokinetic (PBPK) model was developed to described uptake, disposition and clearance of bromate in the rat using published experimental data in rat. The rodent bromate model was extrapolated to human using species-specific physiological parameters and standard interspecies scaling of rate constants. The bromate model is kinetically linear (i.e. AUC and Cmax) across the range of drinking water concentrations used in the cancer bioassays (15 to 500 ppm). This is likely the result of the poor oral bioavailability of bromate due to high reduction rates in the intestinal tract. The bromate PBPK model was used to assess the human equivalent drinking water concentration (HEC) consistent with average plasma concentrations in the rodent bioassays. At drinking water concentrations <500 mg/L, the predicted HEC was two to three fold lower than the bioassay concentration and was dependent on the reported drinking water intake reported in the bioassay.

Adapterama II: universal amplicon sequencing on Illumina platforms (TaggiMatrix)

Next-generation sequencing (NGS) of amplicons is used in a wide variety of contexts. In many cases, NGS amplicon sequencing remains overly expensive and inflexible, with library preparation strategies relying upon the fusion of locus-specific primers to full-length adapter sequences with a single identifying sequence or ligating adapters onto PCR products. In Adapterama I, we presented universal stubs and primers to produce thousands of unique index combinations and a modifiable system for incorporating them into Illumina libraries. Here, we describe multiple ways to use the Adapterama system and other approaches for amplicon sequencing on Illumina instruments. In the variant we use most frequently for large-scale projects, we fuse partial adapter sequences (TruSeq or Nextera) onto the 5' end of locus-specific PCR primers with variable-length tag sequences between the adapter and locus-specific sequences. These fusion primers can be used combinatorially to amplify samples within a 96-well plate (8 forward primers + 12 reverse primers yield 8 × 12 = 96 combinations), and the resulting amplicons can be pooled. The initial PCR products then serve as template for a second round of PCR with dual-indexed iTru or iNext primers (also used combinatorially) to make full-length libraries. The resulting quadruple-indexed amplicons have diversity at most base positions and can be pooled with any standard Illumina library for sequencing. The number of sequencing reads from the amplicon pools can be adjusted, facilitating deep sequencing when required or reducing sequencing costs per sample to an economically trivial amount when deep coverage is not needed. We demonstrate the utility and versatility of our approaches with results from six projects using different implementations of our protocols. Thus, we show that these methods facilitate amplicon library construction for Illumina instruments at reduced cost with increased flexibility. A simple web page to design fusion primers compatible with iTru primers is available at: http://baddna.uga.edu/tools-taggi.html. A fast and easy to use program to demultiplex amplicon pools with internal indexes is available at: https://github.com/lefeverde/Mr_Demuxy.

Persistent epigenetic changes in adult daughters of older mothers

Women of advanced maternal age account for an increasing proportion of live births in many developed countries across the globe. Offspring of older mothers are at an increased risk for a variety of subsequent health outcomes, including outcomes that do not manifest until childhood or adulthood. The molecular underpinnings of the association between maternal aging and offspring morbidity remain elusive. However, one possible mechanism is that maternal aging produces specific alterations in the offspring's epigenome in utero, and these epigenetic alterations persist into adulthood. We conducted an epigenome-wide association study (EWAS) of the effect of a mother's age on blood DNA methylation in 2,740 adult daughters using the Illumina Infinium HumanMethylation450 array. A false discovery rate (FDR) q-value threshold of 0.05 was used to identify differentially methylated CpG sites (dmCpGs). We identified 87 dmCpGs associated with increased maternal age. The majority (84%) of the dmCpGs had lower methylation in daughters of older mothers, with an average methylation difference of 0.6% per 5-year increase in mother's age. Thirteen genomic regions contained multiple dmCpGs. Most notably, nine dmCpGs were found in the promoter region of the gene LIM homeobox 8 (LHX8), which plays a pivotal role in female fertility. Other dmCpGs were found in genes associated with metabolically active brown fat, carcinogenesis, and neurodevelopmental disorders. We conclude that maternal age is associated with persistent epigenetic changes in daughters at genes that have intriguing links to health.