Combined effects of microcystin-LR and rice straw-derived biochar on the hepatic antioxidant capacity of zebrafish: Insights from LC-MS/MS-based metabolomics analysis

Joint effects of rice straw-derived biochar and microcystin-LR on splenic histopathological injuries, inflammation, and innate immune responses in male zebrafish

Microcystin-LR (MC-LR), a toxin produced by cyanobacterial blooms, poses a significant threat to aquatic animals and humans. Biochar (BC), known for its high adsorption capacity, is increasingly being utilized to remove hazardous pollutants from aquatic environment. In the present study, we conducted a full factorial experiment to investigate the potential immunotoxicity in male zebrafish (Danio rerio) exposed to environmentally relevant levels of MC-LR (0, 1, 5, 25 μg/L) and rice straw-derived BC (0, 100 μg/L) for 30 d. The findings revealed that subchronic MC-LR exposure caused concentration-dependent splenic histopathological injuries, characterized by an augmentation of melano-macrophage centers, edematous mitochondria, and vacuolation. While the presence of BC mitigated the inflammatory response and mitochondrial damage in the combined groups. Furthermore, in contrast to the group solely exposed to 25 μg/L MC-LR, decreased levels of interleukin 1β (IL1β), tumor necrosis factor α (TNFα), and interleukin 6 (IL6) as well as significant downregulation of inflammation and immune-related genes (tlr4a, myd88, p38a, tnfα) were noticed in the corresponding co-exposure group, which confirmed that BC can reduce MC-LR-induced inflammatory response. Concurrently, a significant increase in complement C3 (C3) content, along with higher splenic c3b expression levels, was observed in the MC-LR-co-BC group in relative to the group exposed solely to MC-LR, suggesting that BC alleviated MC-LR-induced innate immune inhibition. Our results also demonstrated that BC can decrease MC-LR contents in both water and spleen, thereby alleviating MC-LR-induced inflammation and innate immune inhibition via the MyD88-dependent toll-like receptor (TLR/MyD88) signaling pathway in male zebrafish. Our results underscore the potential of BC to mitigate the deleterious impacts of MC-LR on aquatic organisms in blooms-contaminated water.

Biochar alleviates nanoplastics and bisphenol A mediated immunological, neurological and gut microbial toxicity in channel catfish Ictaluruspunctatus

Nanoplastics (NPs) and bisphenol A (BPA), exhibit abundant industrial applications, are produced in large volumes and ubiquitously released into the environment, posing a serious threat to ecological and human health. Biochar has been extensively studied for its ability to mitigate the negative effects of contaminants on plants. Therefore, this study aims to investigate whether biochar co-exposure with polystyrene nanoplastics (PS-NPs, size 80 nm) and BPA mitigate their toxic impacts on Ictalurus punctatus and maintain its normal growth. The I. punctatus was exposed individually to PS-NPs (0.5 mg/L) and BPA (0.2 mg/L) as well as co-exposed to PS-NPs + biochar and BPA + biochar for 7 days. Results showed PS-NPs and BPA single exposure caused tissue damage in terms of hepatocyte swelling and gut villi diffusion, and induced oxidative stress. PS-NPs and BPA single exposures led to significant changes in enzymatic activities and genetic expressions of biomarkers related to the immune system, producing inflammatory response. It also led to dysregulation of neurotransmitter enzymes (ACH, ChAT, AChE) and overexpression of neuron genes, resulting in neurotoxicity. Moreover, there was an increase in the diversity and alteration in composition of the gut microbiota (Plesiomonas, Pseudomonas), resulting in dysbiosis of the gut microbiota. However, biochar presence (0.5 g/L) reduced the accumulation of PS-NPs and BPA in fish and contributed to various degrees of mitigation for the toxic impacts of PS-NPs and BPA. Overall, biochar helped to mitigate the negative effects of PS-NPs and BPA on oxidative stress, histopathology, immune system, neurological responses and gut microbiota. This study emphasized the potential of biochar to mitigate the negative impacts of NPs and BPA on aquatic organisms.

Female zebrafish are more affected than males under polystyrene microplastics exposure

Microplastics are ubiquitous in freshwater and can be absorbed into fish skin and gills, accumulate in the gut, and be transported to other tissues, thus posing a risk to fish health. Further studies are needed, however, to investigate effects such as endocrine disruption and multi-tissue toxicity. In this study, zebrafish were exposed to polystyrene (PS) microplastics and health-related indicators were measured, including skin mucus, gut damage, oxidative stress, stable isotope composition and reproduction as well as an assessment of changes to metabolites using a metabolomics approach. Results showed that concentrations of PS microplastics were higher in gills than those in the gut. Minimal impact to immunoglobulin M level and lysozyme activity in mucus indicated, however, that microplastic toxicity primarily stemmed from ingestion rather than disruption of skin mucus immunity. Female zebrafish were more affected by PS microplastics. Gut microbiota dysbiosis was induced, especially in females. Significant alterations in pathways associated with lipid and energy metabolism were observed in the liver of female fish. PS microplastics also induced sex steroid hormone disorder and reduced female egg production, possibly linked to the alteration of gut microbiota and hepatic metabolism. Combined, these results highlight the gender-specific toxicity of PS microplastics to zebrafish health, potentially harming their population.

LC-MS untargeted metabolomics reveals metabolic disturbance and ferroptosis in MWCNTs-induced hepatotoxicity of Cyprinus carpio

In recent years, there is a great concern about the potential adverse effects of carbon nanotubes (CNTs) on the aquatic systems due to their increasingly extensive application. In this study, juvenile Cyprinus carpio were exposed to multi-walled CNTs (MWCNTs) at concentrations of 0, 0.25, and 2.5 mg L-1 for 28 days. Then, oxidative stress indicators and metabolite profile of the livers were assessed. Results showed the significant increase of malondialdehyde (MDA) content and decrease of glutathione (GSH) activities in fish treated with 2.5 mg L-1 MWCNTs. LC-MS untargeted metabolomics demonstrated that 406 and 274 metabolites in fish treated with 2.5 mg L-1 MWCNTs were significantly up- and down-regulated, respectively. KEGG functional annotation analysis showed the disturbance of amino acid metabolism, lipid metabolism, and nucleotide metabolism. In addition, ferroptosis signaling pathway was detected. Therefore, iron content analysis and quantitative real-time RT-PCR assay were performed furtherly to validate the contribution of ferroptosis to MWCNTs-induced hepatotoxicity. The iron content increased significantly and the mRNA levels of ferroptosis-related genes including STEAP3, ACSL4, NCOA4, TFR1, NRF2, SLC3A2, SLC7A11, GPX4, and FPN1 were also obviously changed. Taken together, our study suggested that MWCNTs exposure-induced ferroptosis were associated with iron overload and lipid peroxidation via NRF2/SLC7A11/GSH/GPX4 axis. Our findings provide essential information to understand the mechanism of CNTs-induced hepatotoxicity in fish and explore potential biomarkers.

Unraveling the Red Sea soft coral Sarcophyton convolutum potentials against oxidative and inflammatory stresses in zebrafish

The Red Sea is one of the world's hotspots for biodiversity, and for marine natural products (MNPs) as well. These MNPs attract special interest for their capabilities to combat inflammatory and oxidative stress-related diseases, being some of the most serious health problems worldwide nowadays. The current study aimed to identify the bioactive ingredients of the Red Sea soft coral Sarcophyton convolutum, and to assess its protective potentials against oxidative and inflammatory stresses. Coral extract (CE) was analyzed using GC-MS and HPLC. In a protection trial, adult zebrafish were intraperitoneally injected with two doses of crab extract, i.e. 50 and 500 μg/fish in 1 % DMSO as a vehicle, then challenged with 30 μg L-1 of CuSO4 for 48 h. All groups, but the negative control one, were challenged with 30 μg L-1 of CuSO4. Total antioxidant activity, as well as mRNA levels of proinflammatory markers and antioxidant enzyme genes were measured. The results showed richness of S. convolutum extract with various bioactive ingredients, including phenolic compounds, flavonoids, alkanes, fatty acids, sesquiterpenes, and pheromone-like substances. CuSO4 significantly induced the expected signals of inflammatory and oxidative stress, reducing both the antioxidant activity and increasing proinflammatory marker genes. However, CE, especially the low dose, showed significant capability to reduce proinflammatory markers and elevating the total antioxidant activity. Therefore, we concluded that S. convolutum can be a promising source for future efforts of drug discovery and a wide spectrum of pharmaceutical products.