Identification of Sex-Specific Transcriptome Responses to Polychlorinated Biphenyls (PCBs)

Environmentally realistic concentrations of chlorinated, brominated, and fluorinated persistent organic pollutants induce the unfolded protein response as a shared stress pathway in the liver of Atlantic cod (Gadus morhua)

In the North Sea and North Atlantic coastal areas, fish experience relatively high background levels of persistent organic pollutants. This study aimed to compare the mode of action of environmentally relevant concentrations of mixtures of halogenated compounds in Atlantic cod. Juvenile male cod with mean weight of 840 g were exposed by gavage to dietary mixtures of chlorinated (PCBs, DDT analogs, chlordane, lindane, and toxaphene), brominated (PBDEs), and fluorinated (PFOS) compounds for 4 weeks. One group received a combined mixture of all three compound groups. The results showed that the accumulated levels of chemicals in cod liver after 4 weeks of exposure reflected concentrations found in wild fish in this region. Pathway analysis revealed that the treatment effects by each of the three groups of chemicals (chlorinated, brominated, and fluorinated) converged on activation of the unfolded protein response (UPR). Upstream regulator analysis predicted that almost all the key transcription factors (XBP1, ERN1, ATF4, EIF2AK3, and NFE2L2) regulating the UPR were significantly activated. No additive effect was observed in cod co-treated with all three compound groups. In conclusion, the genome-wide transcriptomic study suggests that the UPR pathway is a sensitive common target of halogenated organic environmental pollutants in fish.

A review of statistical strategies to integrate biomarkers of chemical exposure with biomarkers of effect applied in omic-scale environmental epidemiology

Humans are exposed to a growing list of synthetic chemicals, some of them becoming a major public health concern due to their capacity to impact multiple biological endpoints and contribute to a range of chronic diseases. The integration of endogenous (omic) biomarkers of effect in environmental health studies has been growing during the last decade, aiming to gain insight on the potential mechanisms linking the exposures and the clinical conditions. The emergence of high-throughput omic platforms has raised a list of statistical challenges posed by the large dimension and complexity of data generated. Thus, the aim of the present study was to critically review the current state-of-the-science about statistical approaches used to integrate endogenous biomarkers in environmental-health studies linking chemical exposures with health outcomes. The present review specifically focused on internal exposure to environmental chemical pollutants, involving both persistent organic pollutants (POPs), non-persistent pollutants like phthalates or bisphenols, and metals. We identified 42 eligible articles published since 2016, reporting 48 different statistical workflows, mostly focused on POPs and using metabolomic profiling in the intermediate layer. The outcomes were mainly binary and focused on metabolic disorders. A large diversity of statistical strategies were reported to integrate chemical mixtures and endogenous biomarkers to characterize their associations with health conditions. Multivariate regression models were the most predominant statistical method reported in the published workflows, however some studies applied latent based methods or multipollutant models to overcome the specific constraints of omic or exposure of data. A minority of studies used formal mediation analysis to characterize the indirect effects mediated by the endogenous biomarkers. The principles of each specific statistical method and overall workflow set-up are summarized in the light of highlighting their applicability, strengths and weaknesses or interpretability to gain insight into the causal structures underlying the triad: exposure, effect-biomarker and outcome.

Prenatal Exposure to Metabolism-Disrupting Chemicals, Cord Blood Transcriptome Perturbations, and Birth Weight in a Belgian Birth Cohort

Prenatal exposure to metabolism-disrupting chemicals (MDCs) has been linked to birth weight, but the molecular mechanisms remain largely unknown. In this study, we investigated gene expressions and biological pathways underlying the associations between MDCs and birth weight, using microarray transcriptomics, in a Belgian birth cohort. Whole cord blood measurements of dichlorodiphenyldichloroethylene (p,p'-DDE), polychlorinated biphenyls 153 (PCB-153), perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), and transcriptome profiling were conducted in 192 mother-child pairs. A workflow including a transcriptome-wide association study, pathway enrichment analysis with a meet-in-the-middle approach, and mediation analysis was performed to characterize the biological pathways and intermediate gene expressions of the MDC-birth weight relationship. Among 26,170 transcriptomic features, we successfully annotated five overlapping metabolism-related gene expressions associated with both an MDC and birth weight, comprising BCAT2, IVD, SLC25a16, HAS3, and MBOAT2. We found 11 overlapping pathways, and they are mostly related to genetic information processing. We found no evidence of any significant mediating effect. In conclusion, this exploratory study provides insights into transcriptome perturbations that may be involved in MDC-induced altered birth weight.

Sublethal, sex-specific, osmotic, and metabolic impairments in embryonic and adult round stingrays from a location exposed to environmental contamination in southern California, USA

Organic contaminants are known to affect a suite of physiological processes across vertebrate clades. However, despite their ancient lineage and important roles in maintaining healthy ecosystems, elasmobranchs (sharks, skates, and rays) are understudied with regard to sublethal effects of contaminant exposure on metabolic processes. Perturbations resulting from contaminant exposure can divert energy away from maintaining physiological homeostasis, particularly during energetically challenging life stages, such as pregnancy and embryonic development. Using the round stingray (Urobatis halleri) as a model elasmobranch species, we captured adult males and pregnant females (matrotrophic histotrophy) and their embryos from two populations differing in their environmental exposure to organic contaminants (primarily polychlorinated biphenyls (PCBs)). Pregnant females from the PCB-exposed population experienced significant decreases from early- to late-pregnancy in tissue mass and quality not seen in reference females. PCB-exposed pregnant females also failed to maintain plasma urea concentrations as pregnancy progressed, which was accompanied by a loss in muscle protein content. Despite the energetic demands of late-term pregnancy, females had significantly greater liver lipid content than reproductively inactive adult males. PCB-exposed adult males also had high metabolic capacity (i.e., enzyme activity) for most substrate groupings of all sex-site groups, suggesting that males may be even more negatively impacted by contaminant exposure than pregnant females. Evidence that in utero exposure to PCBs via maternal offloading impairs embryo outcomes is accumulating. Embryos from the PCB-contaminated site had lower tissue quality measures and indications that sex-based differences were manifesting in utero as males had higher metabolic capacities than females. This study indicates that accumulated PCB contaminants are not physiologically inert in the stingray.

In vitro effects of selected endocrine disruptors (DEHP, PCB118, BPA) on narrow-clawed crayfish (Astacus leptodactylus) primary cells

Environmental pollutants with endocrine-disrupting effect are of global importance due to their contribution to the aethiologies of variety of complex diseases. These lipophilic pollutants are persistent in the environment and able to bioaccummulate in nontarget organisms. BPA, DEHP and PCB118 (dioxin-like PCB) are associated with endocrine disruption effects, while information on their effects on aquatic invertebrates are limited. In the current study, the effects of these compounds, which are ubiqutous and present at low concentrations in the environment, are studied in the primary hepatopancreas, muscle, gill, intestine and gonadal cultures of narrow-clawed crayfish (Astacus leptodactylus Eschscholtz, 1823), a widely distributed freshwater crayfish in Turkey with high economic importance. IC50 values following MTT assay ranged 0.27-12.61 nM; when compared with other tissues, the gonads were more affected with lower IC50 values. PCB118 induced higher cytotoxicity, while DEHP was the least toxic compound. This is the first study on the primary culture of A. leptodactylus¸ and the toxic effects of these compounds in this organism providing mechanistic insights on the responses and detoxification capacity of the organs. This study provides basis to unravel the mechanism of action of the tested EDCs in crayfish and improvement of cell culture conditions for ecotoxicity and screening assays.

Transcriptome responses in blood reveal distinct biological pathways associated with arsenic exposure through drinking water in rural settings of Punjab, Pakistan

BACKGROUND

Groundwater Arsenic (As) contamination is a global public health concern responsible for various health implications and a neglected area of environmental health research in Pakistan. Because of interindividual differences in genetic predisposition, As-related health issues may not be equally distributed among the As-exposed population. However, till date, no studies have been conducted including multiple SNPs involved in As metabolism and disease risk using a linear mixed effect model approach to analyze peripheral blood transcriptomics results.

OBJECTIVES

In order to detect early responses on the gene expression level and to evaluate the impact of selected SNPs inferring disease risks associated with As exposure, we designed a systematic study to investigate blood transcriptomics profiles of 57 differentially exposed rural subjects living in drinking water As-contaminated settings of Lahore and Kasur districts in Punjab Province in southeast Pakistan. Exposure among the subjects was correlated with individual transcriptome responses applying urinary As profiles as the main biomarker for risk stratification.

METHODS

We performed whole genome gene expression analysis in blood of subjects using microarrays. Linear effect mixed models were applied for evaluating the combined impact of SNPs hypothetically increasing the risk for As exposure-induced health effects (GSTM1, GSTT1, As3MT, DNMT1, MTHFR, ERCC2 and EGFR).

RESULTS

Our findings confirmed important signaling, growth factor, cancer and other disease related pathways known to be associated with increased As exposure levels. In addition, upon implementing our integrative SNPs-based genetic risk factor, pathways associated with an increased risk of NAFLD and diabetes appeared significantly enhanced by down-regulation of genes NDUFV3, IKBKB, IL6R, ADIPOR1, PPARA, OGT and FOXO1.

CONCLUSION

We report the first comprehensive study applying state-of-the-art bioinformatics approaches to address multiple SNP-based inter-individual variability in adverse molecular responses among subjects exposed to drinking water As contamination in Pakistan thereby providing strong evidence of various gene expression targets associated with development of known As-related diseases.

Omics for Nurse Scientists Conducting Environmental Health Research

Nurse scientists are ideally positioned to perform environmental health research and it is critical that the role of omics in the complex relationships between environmental exposures and an individual's unique physiology in human health outcomes be appreciated. Importantly, omics can offer nurse scientists a tool to measure exposure, demonstrate molecular phenotypic changes associated with exposure, and potentially uncover mechanisms of exposure-related disease or negative health outcomes. The purpose of this summary is to serve as an overview of omics methodologies for nurse scientists conducting environmental health research and provides future directions of this work as well as exemplar funding opportunities that demonstrate the growing need and interest in this area. The intersection of nursing and exposure science will accelerate the work in environmental health and bring forth translation of research findings into clinical and community practice. Importantly, this information can better help us understand the variation in response to the environment and support environmental health policy change at the local, state, and federal level to improve community health and well-being.

Identification and characterization of a meta-cleavage product hydrolase involved in biphenyl degradation from Arthrobacter sp. YC-RL1

Polychlorinated biphenyls (PCBs) are a group of persistent organic pollutants (POPs) widely existing in the environment. Arthrobacter sp. YC-RL1 is a biphenyl-degrading bacterium that shows metabolic versatility towards aromatic compounds. A 2-hydroxy-6-oxo-6-phenylhexa-2, 4-dienoate (HOPDA) hydrolase (BphD) gene involved in the biodegradation of biphenyl was cloned from strain YC-RL1 and heterologously expressed in Escherichia coli BL21 (DE3). The recombinant BphD_YC-RL1 was purified and characterized. BphD_YC-RL1 showed the highest activity at 45 °C and pH 7. It was stable under a wide range of temperature (20-50 °C). The enzyme had a K_m value of 0.14 mM, K_cat of 11.61 s^-1, and V_max of 0.027 U/mg. Temperature dependence catalysis exhibited a biphasic Arrhenius Plot with a transition at 20 °C. BphD_YC-RL1 was inactivated by SDS, Tween 20, Tween 80, Trition X-100, DTT, CHAPS, NBS, PMSF, and DEPC, but insensitive to EDTA. Site-directed mutagenesis of the active-site residues revealed that the catalytic triad residues (Ser115, His275, and Asp247) of BphD_YC-RL1 were necessary for its activity. The investigation of BphD_YC-RL1 not only provides new potential enzyme resource for the biodegradation of biphenyl but also helps deepen our understanding on the catalytic process and mechanism.