Characterization of transcriptional responses mediated by benzo[a]pyrene stress in a new marine fish model of goby, Mugilogobius chulae

Unraveling the protective role of Nrf2 in molluscs: Insights into mitochondrial and apoptosis pathways in the defense against Bap-induced oxidative stress

Benzopyrene (Bap) is a major constituent of petroleum pollutants commonly found in aquatic environments, and its mutagenic and carcinogenic properties have adverse effects on aquatic organisms' development, growth, and reproduction. The antioxidant defense system element, NF-E2-related factor 2 (Nrf2), has been linked to the oxidative stress response in marine invertebrates exposed to toxic substances. In a previous study, a novel Nrf2 homologue, McNrf2, was identified in mussel Mytilus coruscus, a significant model marine molluscs in ecotoxicology studies. McNrf2 showed the potential to trigger an antioxidant defense against oxidative stress induced by Bap. Here, we employed an Nrf2 overexpression and inhibition model using SFN and ML385 as Nrf2 inducer and inhibitor, respectively. Next, immunofluorescence technique was used to evaluate the nuclear activation of Nrf2 induced by Bap-mediated oxidative stress. Transmission electron microscopy revealed that overexpression of Nrf2 could maintain the quantity and structural integrity of mitochondria, while flow cytometry analysis showed that Nrf2 could alleviate Bap-induced cellular apoptosis. These findings suggest that Nrf2 can protect molluscs from Bap-induced oxidative stress through the mitochondria and apoptosis pathways, providing a novel perspective on Nrf2's antioxidant function.

Emerging bio-dispersant and bioremediation technologies as environmentally friendly management responses toward marine oil spill: A comprehensive review

Marine oil spills emanating from wells, pipelines, freighters, tankers, and storage facilities draw public attention and necessitate quick and environmentally friendly response measures. It is sometimes feasible to contain the oil with booms and collect it with skimmers or burn it, but this is impracticable in many circumstances, and all that can be done without causing further environmental damage is adopting natural attenuation, particularly through microbial biodegradation. Biodegradation can be aided by carefully supplying biologically accessible nitrogen and phosphorus to alleviate some of the microbial growth constraints at the shoreline. This review discussed the characteristics of oil spills, origin, ecotoxicology, health impact of marine oils spills, and responses, including the variety of remedies and responses to oil spills using biological techniques. The different bioremediation and bio-dispersant treatment technologies are then described, with a focus on the use of green surfactants and their advances, benefits/drawbacks. These technologies were thoroughly explained, with a timeline of research and recent studies. Finally, the hurdles that persist as a result of spills are explored, as well as the measures that must be taken and the potential for the development of existing treatment technologies, all of which must be linked to the application of integrated procedures.

Unravelling the molecular mechanism of mutagenic factors impacting human health

Environmental mutagens are chemical and physical substances in the environment that has a potential to induce a wide range of mutations and generate multiple physiological, biochemical, and genetic modifications in humans. Most mutagens are having genotoxic effects on the following generation through germ cells. The influence of germinal mutations on health will be determined by their frequency, nature, and the mechanisms that keep a specific mutation in the population. Early prenatal lethal mutations have less public health consequences than genetic illnesses linked with long-term medical and social difficulties. Physical and chemical mutagens are common mutagens found in the environment. These two environmental mutagens have been associated with multiple neurological disorders and carcinogenesis in humans. Thus in this study, we aim to unravel the molecular mechanism of physical mutagens (UV rays, X-rays, gamma rays), chemical mutagens (dimethyl sulfate (DMS), bisphenol A (BPA), polycyclic aromatic hydrocarbons (PAHs), 5-chlorocytosine (5ClC)), and several heavy metals (Ar, Pb, Al, Hg, Cd, Cr) implicated in DNA damage, carcinogenesis, chromosomal abnormalities, and oxidative stress which leads to multiple disorders and impacting human health. Biological tests for mutagen detection are crucial; therefore, we also discuss several approaches (Ames test and Mutatox test) to estimate mutagenic factors in the environment. The potential risks of environmental mutagens impacting humans require a deeper basic knowledge of human genetics as well as ongoing research on humans, animals, and their tissues and fluids.

Transcriptome aberration associated with altered locomotor behavior of zebrafish (Danio rerio) caused by Waterborne Benzo[a]pyrene

Waterborne Benzo[a]pyrene (B[a]P) pollution is a global threat to aquatic organisms. The exposure to waterborne B[a]P can disrupt the normal locomotor behavior of zebrafish (Danio rerio), however, how it affect the locomotor behavior of adult zebrafish remains unclear. Herein, B[a]P at two concentrations (0.8 μg/L and 2.0 μg/L) were selected to investigate the molecular mechanisms of the affected locomotor behavior of zebrafish by B[a]P based on transcriptome profiling. Adverse effects of B[a]P exposure affecting locomotor behavior in zebrafish were studied by RNA sequencing, and the locomotion phenotype was acquired. The gene enrichment results showed that the differentially highly expressed genes (atp2a1, cdh2, aurka, fxyd1, clstn1, apoc1, mt-co1, tnnt3b, and fads2) of zebrafish are mainly enriched in adrenergic signaling in cardiomyocytes (dre04261) and locomotory behavior (GO:0007626). The movement trajectory plots showed an increase in the locomotor distance and velocity of zebrafish in the 0.8 μg/L group and the opposite in the 2.0 μg/L group. The results showed that B[a]P affects the variety of genes in zebrafish, including motor nerves, muscles, and energy supply, and ultimately leads to altered locomotor behavior.

Effects of polycyclic aromatic hydrocarbons on biomarker responses in Gambusia yucatana, an endemic fish from Yucatán Peninsula, Mexico

Polycyclic aromatic hydrocarbons (PAHs) are petroleum components that, when dissolved in the aquatic environment, can disrupt normal animal physiological functions and negatively affect species populations. Gambusia yucatana is an endemic fish of the Yucatán Peninsula that seems to be particularly sensitive to the presence of PAHs dissolved in the water. Here, we examined PAH effects on gene expressions linked to endocrine disruption and biotransformation in this species. Specifically, we examined the expression of vitellogenin I (vtg1), vitellogenin II (vtg2), oestrogen receptor α (esr1), oestrogen receptor β (esr2), aryl hydrocarbon receptor (AhR) and the cytochrome P4503A (CYP3A) genes. We exposed G. yucatana to different concentrations of PAHs (3.89, 9.27, 19.51 μg/L) over a period of 72 h and found changes associated with reproduction, such as increases in hepatic expression of vtg, esr, AhR and CYP3A, mainly at concentrations of 9.27 and 19.51 μg/L. Our results also indicate that benzo[a]pyrene was probably the main PAH responsible for the observed effects. The genes examined here can be used as molecular markers of endocrine-disrupting compounds, as the PAHs, present in the environment, as gene expression increases could be observed as early as after 24 h. These biomarkers can help researchers and conservationists rapidly identify the impacts of oil spills and improve mitigation before the detrimental effects of environmental stressors become irreversible.

Genotoxicity detection of oil-containing drill cuttings by Comet assay based on a demersal marine fish Mugilogobius chulae

An enormous amount of oil-containing drill cuttings have been produced by the marine oil and gas industry. The environmental impacts of discharged drilling waste have been extensively studied. However, there is still an urgent need to develop alternative methods to identify the genotoxicity of untreated and treated drill waste in a timely manner before it is discharged. In this study, we developed a relatively rapid, sensitive, and accurate genotoxicity-detection method using Comet assay and the marine benthic goby Mugilogobius chulae. This goby is sensitive to a standard toxicant mitomycin C (MMC). The optimal exposure period for genotoxicity detection using M. chulae was determined. Three genotoxic indices (tail length (TL), tail DNA content (TD), and tail moment (TM)) were used to assess the effectiveness of high-temperature treatment of oil-contaminated waste. Untreated oil-containing drill cuttings exhibited the highest genotoxicity to goby cells. Genotoxicity was dramatically reduced after thermal treatment of drill cuttings at 350 °C and 500 °C. TD and TM exhibited significant correlation with the concentration of total petroleum hydrocarbons (TPHs)/total polycyclic aromatic hydrocarbons (PAHs) according to Pearson and Mantel correlation analyses (P values were <0.05). Using redundancy analysis (RDA) and variation partition analysis (VPA), the genotoxic effects of the drill cuttings were ascribed to total alkanes and specific groups of PAHs. In conclusion, this newly established biological model has the potential to be widely used to detect the genetic damage of untreated or treated oil-containing drill cuttings discharged into the marine environment.

Whole-genome sequencing reveals sex determination and liver high-fat storage mechanisms of yellowstripe goby (Mugilogobius chulae)

As a promising novel marine fish model for future research on marine ecotoxicology as well as an animal model of human disease, the genome information of yellowstripe goby (Mugilogobius chulae) remains unknown. Here we report the first annotated chromosome-level reference genome assembly for yellowstripe goby. A 20.67-cM sex determination region was discovered on chromosome 5 and seven potential sex-determining genes were identified. Based on combined genome and transcriptome data, we identified three key lipid metabolic pathways for high-fat accumulation in the liver of yellowstripe goby. The changes in the expression patterns of MGLL and CPT1 at different development stage of the liver, and the expansion of the ABCA1 gene, innate immune gene TLR23, and TRIM family genes may help in balancing high-fat storage in hepatocytes and steatohepatitis. These results may provide insights into understanding the molecular mechanisms of sex determination and high-fat storage in the liver of marine fishes.

Transcriptomic changes in western mosquitofish (Gambusia affinis) liver following benzo[a]pyrene exposure

Widely distributed western mosquitofish (Gambusia affinis) has been used as a new model species for hazard assessment of environmental stressors such as polycyclic aromatic hydrocarbons (PAHs). However, most of the PAH studies using G. affinis rely on targeted biomarker-based analysis, and thus may not adequately address the complexity of the toxic mechanisms of the stressors. In the present study, the whole transcriptional sequencing of G. affinis liver after exposure to a PAH model, benzo[a]pyrene (BaP) (100 μg/L), for 20 days was performed by using the HiSeq XTen sequencers. In total, 58,156,233 and 51,825,467 clean nucleotide reads were obtained in the control and BaP-exposed libraries, respectively, with average N50 lengths of 1419 bp. In addition, after G. affinis was exposed for 20 days, 169 genes were upregulated, and 176 genes were downregulated in liver. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were applied to all the genes to determine the genes' biological functions and processes. The results clearly showed that the differentially expressed genes were mainly related to immune pathways and metabolic correlation pathways. Interestingly, almost all the pathways related with the immunity were upregulated, while the metabolism pathways were downregulated. Lastly, quantitative real-time PCR (qRT-PCR) was performed to measure expressional levels of twelve genes confirmed through the DGE analysis. These results demonstrate that BaP damages immunity and enhances the consumption of all available energy storage to activate mechanisms of the detoxification in G. affinis. Up until now, the present study is the first time that a whole transcriptome sequencing analysis in the liver of G. affinis exposed to BaP has been reported.

Toxicities of Polycyclic Aromatic Hydrocarbons for Aquatic Animals

Polycyclic aromatic hydrocarbons (PAHs) are organic compounds that are widely distributed in the air, water, and soil. Recently, the amount of PAHs derived from fuels and from incomplete combustion processes is increasing. In the aquatic environment, oil spills directly cause PAH pollution and affect marine organisms. Oil spills correlate very well with the major shipping routes. Furthermore, accidental oil spills can seriously impact the marine environment toxicologically. Here, we describe PAH toxicities and related bioaccumulation properties in aquatic animals, including invertebrates. Recent studies have revealed the toxicity of PAHs, including endocrine disruption and tissue-specific toxicity, although researchers have mainly focused on the carcinogenic toxicity of PAHs. We summarize the toxicity of PAHs regarding these aspects. Additionally, the bioaccumulation properties of PAHs for organisms, including invertebrates, are important factors when considering PAH toxicity. In this review, we describe the bioaccumulation properties of PAHs in aquatic animals. Recently, microplastics have been the most concerning environmental problem in the aquatic ecosystem, and the vector effect of microplastics for lipophilic compounds is an emerging environmental issue. Here, we describe the correlation between PAHs and microplastics. Thus, we concluded that PAHs have a toxicity for aquatic animals, indicating that we should emphasize the prevention of aquatic PAH pollution.