Untargeted Lipidomics for Determining Cellular and Subcellular Responses in Zebrafish (Danio rerio) Liver Cells Following Exposure to Complex Mixtures in U.S. Streams

Understanding PFAS toxicity through cell culture metabolomics: Current applications and future perspectives

Per- and polyfluoroalkyl substances (PFAS), ubiquitous environmental contaminants, pose significant challenges to ecosystems and human health. While cell cultures have emerged as new approach methodologies (NAMs) in ecotoxicity research, metabolomics is an emerging technique used to characterize the small-molecule metabolites present in cells and to understand their role in various biological processes. Integration of metabolomics with cell cultures, known as cell culture metabolomics, provides a novel and robust tool to unravel the complex molecular responses induced by PFAS exposure. In vitro testing also reduces reliance on animal testing, aligning with ethical and regulatory imperatives. The current review summarizes key findings from recent studies utilizing cell culture metabolomics to investigate PFAS toxicity, highlighting alterations in metabolic pathways, biomarker identification, and the potential linkages between metabolic perturbations. Additionally, the paper discusses different types of cell cultures and metabolomics methods used for studies of environmental contaminants and particularly PFAS. Future perspectives on the combination of metabolomics with other advanced technologies, such as single-cell metabolomics (SCM), imaging mass spectrometry (IMS), extracellular flux analysis (EFA), and multi-omics are also explored, which offers a holistic understanding of environmental contaminants. The synthesis of current knowledge and identification of research gaps provide a foundation for future investigations that aim to elucidate the complexities of PFAS-induced cellular responses and contribute to the development of effective strategies for mitigating their adverse effects on human health.

Coupled Lipidomics and Digital Pathology as an Effective Strategy to Identify Novel Adverse Outcome Pathways in Eisenia fetida Exposed to MoS2 Nanosheets and Ionic Mo

Molybdenum disulfide (MoS₂) nanosheets are increasingly applied in several fields, but effective and accurate strategies to fully characterize potential risks to soil ecosystems are lacking. We introduce a coelomocyte-based in vivo exposure strategy to identify novel adverse outcome pathways (AOPs) and molecular endpoints from nontransformed (NTMoS₂) and ultraviolet-transformed (UTMoS₂) MoS₂ nanosheets (10 and 100 mg Mo/L) on the earthworm Eisenia fetida using nontargeted lipidomics integrated with transcriptomics. Machine learning-based digital pathology analysis coupled with phenotypic monitoring was further used to establish the correlation between lipid profiling and whole organism effects. As an ionic control, Na₂MoO₄ exposure significantly reduced (61.2-79.5%) the cellular contents of membrane-associated lipids (glycerophospholipids) in earthworm coelomocytes. Downregulation of the unsaturated fatty acid synthesis pathway and leakage of lactate dehydrogenase (LDH) verified the Na₂MoO₄-induced membrane stress. Compared to conventional molybdate, NTMoS₂ inhibited genes related to transmembrane transport and caused the differential upregulation of phospholipid content. Unlike NTMoS₂, UTMoS₂ specifically upregulated the glyceride metabolism (10.3-179%) and lipid peroxidation degree (50.4-69.4%). Consequently, lipolytic pathways were activated to compensate for the potential energy deprivation. With pathology image quantification, we report that UTMoS₂ caused more severe epithelial damage and intestinal steatosis than NTMoS₂, which is attributed to the edge effect and higher Mo release upon UV irradiation. Our results reveal differential AOPs involving soil sentinel organisms exposed to different Mo forms, demonstrating the potential of liposome analysis to identify novel AOPs and furthermore accurate soil risk assessment strategies for emerging contaminants.

Protective mechanisms of a microbial oil against hypercholesterolemia: evidence from a zebrafish model

A Western diet elevates the circulating lipoprotein and triglyceride levels which are the major risk factors in cardiovascular disease (CVD) development. Consumption of long-chain omega-3 fatty acids can stall the disease progression. Although these fatty acids can significantly impact the intestine under a hypercholesterolemic condition, the associated changes have not been studied in detail. Therefore, we investigated the alterations in the intestinal transcriptome along with the deviations in the plasma lipids and liver histomorphology of zebrafish offered DHA- and EPA-rich oil. Fish were allocated to 4 dietary treatments: a control group, a high cholesterol group and microbial oil groups with low (3.3%) and high (6.6%) inclusion levels. We quantified the total cholesterol, lipoprotein and triglyceride levels in the plasma. In addition, we assessed the liver histology, intestinal transcriptome and plasma lipidomic profiles of the study groups. The results suggested that higher levels of dietary microbial oil could control the CVD risk factor indices in zebrafish plasma. Furthermore, microbial oil-fed fish had fewer liver vacuoles and higher mRNA levels of genes involved in β-oxidation and HDL maturation. Analyses of the intestine transcriptome revealed that microbial oil supplementation could influence the expression of genes altered by a hypercholesterolemic diet. The plasma lipidomic profiles revealed that the higher level of microbial oil tested could elevate the long-chain poly-unsaturated fatty acid content of triglyceride species and lower the concentration of several lysophosphatidylcholine and diacylglycerol molecules. Our study provides insights into the effectiveness of microbial oil against dyslipidemia in zebrafish.

Single and combined genotoxicity of metals and fluoroquinolones to zebrafish embryos at environmentally relevant concentrations

Fluoroquinolones (FQs) are known to have genotoxicity to aquatic organisms. However, their genotoxicity mechanisms, individually and in combination with heavy metals, are poorly understood. Here, we investigated the single and joint genotoxicity of FQs, ciprofloxacin (CIP) and enrofloxacin (ENR), and metals (Cd and Cu) at environmentally relevant concentrations (0.2 µM) to zebrafish embryos. We found that FQs or/and metals induced genotoxicity (i.e., DNA damage and cell apoptosis) to zebrafish embryos. Compared with their single exposure, the combined exposure of FQs and metals elicited less ROS overproduction but higher genotoxicity, suggesting other toxicity mechanisms may also act in addition to oxidation stress. The upregulation of nucleic acid metabolites and the dysregulation of proteins confirmed the occurrence of DNA damage and apoptosis, and further revealed the inhibition of DNA repair by Cd and binding of DNA or DNA topoisomerase by FQs. This study deepens the knowledge on the responses of zebrafish embryos to exposure of multiple pollutants, and highlights the genotoxicity of FQs and heavy metals to aquatic organisms.

Physiological Responses of Methanosarcina barkeri under Ammonia Stress at the Molecular Level: The Unignorable Lipid Reprogramming

Acetotrophic methanogens' dysfunction in anaerobic digestion under ammonia pressure has been widely concerned. Lipids, the main cytomembrane structural biomolecules, normally play indispensable roles in guaranteeing cell functionality. However, no studies explored the effects of high ammonia on acetotrophic methanogens' lipids. Here, a high-throughput lipidomic interrogation deciphered lipid reprogramming in representative acetoclastic methanogen (Methanosarcina barkeri) upon high ammonia exposure. The results showed that high ammonia conspicuously reduced polyunsaturated lipids and longer-chain lipids, while accumulating lipids with shorter chains and/or more saturation. Also, the correlation network analysis visualized some sphingolipids as the most active participant in lipid-lipid communications, implying that the ammonia-induced enrichment in these sphingolipids triggered other lipid changes. In addition, we discovered the decreased integrity, elevated permeability, depolarization, and diminished fluidity of lipid-supported membranes under ammonia restraint, verifying the noxious ramifications of lipid abnormalities. Additional analysis revealed that high ammonia destabilized the structure of extracellular polymeric substances (EPSs) capable of protecting lipids, e.g., declining α-helix/(β-sheet + random coil) and 3-turn helix ratios. Furthermore, the abiotic impairment of critical EPS bonds, including C-OH, C═O-NH-, and S-S, and the biotic downregulation of functional proteins involved in transcription, translation, and EPS building blocks' supply were unraveled under ammonia stress and implied as the crucial mechanisms for EPS reshaping.

Effects of perfluorobutane sulfonate and perfluorooctane sulfonate on lipid homeostasis in mouse liver

Perfluorobutane sulfonate (PFBS), an alternative to perfluorooctane sulfonate (PFOS), has been increasingly used in recent years. However, emerging evidence has raised concerns about the potential health risks of PFBS. Here, the toxicityof low-dose PFBS on livers was explored and compared with that of PFOS. Adult C57BL/6 mice were exposed to 10 μg/L, 500 μg/L PFBS, or 500 μg/L PFOS for 28 days through drinking water. At the phenotypic level, no liver damage was observed in the 10 μg/L PFBS group. The cell apoptosis and decrease of CAT activities were observed in the 500 μg/L PFBS group, while accumulation of lipid droplets, increase of CAT activities and TAG levels were found in the 500 μg/L PFOS group. Lipidomics analysis revealed that 138, 238, and 310 lipids were significantly changed in the 10 μg/L, 500 μg/L PFBS and 500 μg/L PFOS groups, respectively. The two PFBS-treated groups induced similar global lipid changes in a dose-dependent manner, which were distinct from PFOS. Overall, PFBS exposure induced an increase in phosphatidylcholines and sphingomyelins, but a decrease in phosphatidylinositol. PFOS exposure caused an increase in triacylglycerols. This study provides more evidence on the health hazards caused by exposure to low-dose PFBS.

Subcellular-Level Mitochondrial Energy Metabolism Response in the Fat Body of the German Cockroach Fed Abamectin

Mitochondria are the leading organelle for energy metabolism. The toxic effects of environmental toxicants on mitochondrial morphology, energy metabolism, and their determination of cell fate have already been broadly studied. However, minimal research exists on effects of environmental toxicants such as pesticides on mitochondrial energy metabolism at in vitro subcellular level, particularly from an omics perspectives (e.g., metabolomics). Here, German cockroach (Blattella germanica) was fed diets with (0.01 and 0.001 mg/mL) and without abamectin, and highly purified fat body mitochondria were isolated. Swelling measurement confirmed abnormal mitochondrial swelling caused by abamectin stress. The activity of two key mitochondrial energy metabolism-related enzymes, namely succinic dehydrogenase and isocitrate dehydrogenase, was significantly affected. The metabolomic responses of the isolated mitochondria to abamectin were analyzed via untargeted liquid chromatography/mass spectrometry metabolomics technology. Fifty-two differential metabolites (DMs) were identified in the mitochondria between the 0.001 mg/mL abamectin-fed and the control groups. Many of these DMs were significantly enriched in pathways involved in ATP production and energy consumption (e.g., oxidative phosphorylation, TCA cycle, and pentose phosphate pathway). Nineteen of the DMs were typically related to energy metabolism. This study is valuable for further understanding mitochondrial toxicology under environmental toxicants, particularly its subcellular level.

Exposure to trace levels of metals and fluoroquinolones increases inflammation and tumorigenesis risk of zebrafish embryos

Exposure to trace-level heavy metals and antibiotics may elicit metabolic disorder, alter protein expression, and then induce pathological changes in zebrafish embryos, despite negligible physiological and developmental toxicity. This study investigated the single and combined developmental toxicity of fluoroquinolones (enrofloxacin [ENR] and ciprofloxacin [CIP]) (≤0.5 μM) and heavy metals (Cu and Cd) (≤0.5 μM) to zebrafish embryos, and molecular responses of zebrafish larvae upon exposure to the single pollutant (0.2 μM) or a binary metal-fluoroquinolone mixture (0.2 μM). In all single and mixture exposure groups, no developmental toxicity was observed, but oxidative stress, inflammation, and lipid depletion were found in zebrafish embryos, which was more severe in the mixture exposure groups than in the single exposure groups, probably due to increased metal bioaccumulation in the presence of ENR or CIP. Metabolomics analysis revealed the up-regulation of amino acids and down-regulation of fatty acids, corresponding to an active response to oxidative stress and the occurrence of inflammation. The up-regulation of antioxidase and immune proteins revealed by proteomics analysis further confirmed the occurrence of oxidative stress and inflammation. Furthermore, the KEGG pathway enrichment analysis showed a significant disturbance of pathways related to immunity and tumor, indicating the potential risk of tumorigenesis in zebrafish larvae. The findings provide molecular-level insights into the adverse effects of heavy metals and antibiotics (especially in chemical mixtures) on zebrafish embryos, and highlight the potential ecotoxicological risks of trace-level heavy metals and antibiotics in the environment.