Benzo[a]pyrene-induced multigenerational changes in gene expression, behavior, and DNA methylation are primarily influenced by paternal exposure

Clearing the Air on Pollutant Disruptions of the Gut-Brain Axis: Developmental Exposure to Benzo[a]pyrene Disturbs Zebrafish Behavior and the Gut Microbiome in Adults and Subsequent Generations

Developmental exposure to benzo[a]pyrene (BaP), a ubiquitous environmental pollutant, has been linked to various toxic effects, including multigenerational behavioral impairment. While the specific mechanisms driving BaP neurotoxicity are not fully understood, recent work highlights two important determinants of developmental BaP neurotoxicity: (1) the aryl hydrocarbon receptor (AHR), which induces host metabolism of BaP, and (2) the gut microbiome, which may interact with BaP to affect its metabolism, or be perturbed by BaP to disrupt the gut-brain axis. We utilized the zebrafish model to explore the role of AHR, the gut microbiome, and their interaction, on BaP-induced neurotoxicity. We tested (1) how developmental BaP exposure and AHR2 perturbation in zebrafish link to adult behavior, (2) how these variables associate with the structure and function of the adult zebrafish gut metagenome, and (3) whether these associations are multigenerational. Our findings reveal a reticulated axis of association between BaP exposure, developmental AHR2 expression, the zebrafish gut metagenome, and behavior. Results indicate that AHR2 is a key modulator of how BaP elicits neurotoxicity and microbiome dysbiosis. Additionally, this axis of association manifests generationally. These findings demonstrate the importance of studying pollutant-microbiome interactions and elucidate the role of specific host genes in neurotoxicity and dysbiosis.

Network-based investigation of petroleum hydrocarbons-induced ecotoxicological effects and their risk assessment

Petroleum hydrocarbons (PHs) are compounds composed mostly of carbon and hydrogen, originating from crude oil and its derivatives. PHs are primarily released into the environment through the diffusion of oils, resulting from anthropogenic activities like transportation and offshore drilling, and accidental incidents such as oil spills. Once released, these PHs can persist in different ecosystems and cause long-term detrimental ecological impacts. While the hazards associated with such PH contaminations are often assessed by the concentrations of total petroleum hydrocarbons in the environment, studies focusing on the risks associated with individual PHs are limited. In this study, different network-based frameworks were utilized to explore and understand the adverse ecological effects associated with PH exposure. First, a list of 320 PHs was systematically curated from published reports. Next, biological endpoint data from toxicological databases was systematically integrated, and a stressor-centric adverse outcome pathway (AOP) network, linking 75 PHs with 177 ecotoxicologically-relevant high confidence AOPs within AOP-Wiki, was constructed. Further, stressor-species networks, based on reported toxicity concentrations and bioconcentration factors data within ECOTOX, were constructed for 80 PHs and 28 PHs, respectively. It was found that crustaceans are documented to be affected by many of these PHs. Finally, the aquatic toxicity data within ECOTOX was used to construct species sensitivity distributions for PHs, and their corresponding hazard concentrations (HC05), that are harmful to 5% of species in the aquatic ecosystem, were derived. Further, the predicted no-effect concentrations (PNECs) and risk quotients for the US EPA priority polycyclic aromatic hydrocarbons (PAHs) were computed by using their environmental concentration data for Indian coastal and river waters. Overall, this study highlights the importance of using network-based approaches and risk assessment methods to understand the PH-induced toxicities effectively.

The Role of Oxidative Stress and DNA Hydroxymethylation in the Pathogenesis of Benzo[a]pyrene-Impaired Reproductive Function in Male Mice

Benzo[a]pyrene (BaP), a polycyclic aromatic hydrocarbon, is known to cause teratogenesis. Environmental exposure of BaP has led to wide public concerns due to their potential risk of reproductive toxicity. However, the exact mechanism is still not clear. We aimed to explore the alterations of oxidative stress and DNA hydroxymethylation during BaP-impaired reproductive function. BALB/c mice were intragastrically administered with different doses of BaP (0.01, 0.1, and 1 mg/kg/day, once a day), while control mice were administered with corn coil. Then, the reproductive function, alterations of oxidative stress, DNA methylation, and DNA hydroxymethylation of testis tissues were evaluated. We found that BaP caused obvious histopathological damages of testis tissues. As for sperm parameters after BaP administration, testis weight and the rate of teratosperm were increased, as well as sperm count and motility were decreased. In mechanism, BaP upregulated HO-1 and MDA levels and downregulated SOD and CAT activity and GSH content in testis tissues, indicating that oxidative stress was induced by BaP. Furthermore, a significant induction of hydroxymethylation and inhibition of methylation were observed in testis tissues after BaP exposure. Collectively, BaP-induced oxidative stress and hydroxymethylation were involved in impairing reproductive function, which may be the mechanism of the male infertility.

Genome-wide DNA methylation changes in Oryzias melastigma embryos exposed to the water accommodated fraction of crude oil

The water accommodated fraction (WAF) of crude oil exerts considerable impacts on marine fish during embryonic stage. Clarifying changes in epigenetic modifications is helpful for understanding the molecular mechanism underlying the toxicity of embryonic WAF exposure. The aim of this study was to explore genome-wide DNA methylation changes in Oryzias melastigma embryos after exposure to the nominal total petroleum hydrocarbon concentration of 500 μg/L in WAF for 7 days. Whole-genome bisulfite sequencing revealed that 8.47 % and 8.46 % of all the genomic C sites were methylated in the control and WAF-exposed groups, respectively. Among the three sequence contexts, methylated CG site had the largest number in both the two groups. The sequence preferences of nearby methylated cytosines were consistent between the two groups. A total of 4798 differentially methylated regions (DMRs) were identified in the promoter region. Furthermore, Gene Ontology analysis revealed that DMR-related genes were enriched mainly for functions related to development and nervous system. Additionally, the Kyoto Encyclopedia of Genes and Genomes pathways enriched in DMR-related genes were related to nervous system and endocrine system. These novel findings provide comprehensive insights into the genome-wide DNA methylation landscape of O. melastigma following embryonic WAF exposure, shedding light on the epigenetic regulatory mechanisms underlying WAF-induced toxicity.