Effects of microplastics on head kidney gene expression and enzymatic biomarkers in adult zebrafish

Untargeted metabolomics and transcriptomics joint analysis of the effects of polystyrene nanoplastics on lipid metabolism in the mouse liver

BACKGROUND

Micro/nanoplastics (MNPs), as emerging environmental pollutants, are widely present in environments that are essential for human survival. They exist in vast quantities and possess stable properties, making them challenging to manage. Some reports indicated that there is a positive correlation between the production of MNPs and the incidence of obesity. The liver serves as both the central hub for lipid metabolism and a prime target for MNPs toxicity. These studies revealed that MNPs can lead to increased hepatic lipid accumulation, suggesting that they may be potential obesogens. However, the specific metabolic changes and possible mechanisms involved remain to be elucidated.

METHODS

This study focuses on the impact of nanoplastics (NPs) on liver lipid metabolism, using C57BL/6J mice (hereinafter referred to as C57 mice) as the research subjects, and exposing them to 100 nm NPs at 1000 µg/L continuously for 12 weeks.

RESULTS

The study revealed that (1) NPs led to nondietary weight gain together with an increase in fat volume and mass in mice. (2) NPs significantly increased serum total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) levels, with notable differences between groups. Notably, NPs exposure induced opposing effects on serum lipid profiles, elevating high-density lipoprotein cholesterol (HDL-C) concentrations while suppressing triglyceride (TG) levels, though intergroup differences failed to reach statistical significance. (3) NPs caused multiple inflammatory responses in the liver, with significant lipid deposition. (4) Untargeted metabolomics analysis indicated that NPs exposure led to significant alterations in various lipid metabolites, particularly glycerophospholipids. Additionally, transcriptomics reveals that differentially expressed genes (DEGs) triggered by NPs exposure are predominantly involved in metabolic routes including lipid metabolism and cytochrome P450 (CYP). Taken together, these findings suggested that alterations in lipid metabolism resulting from NPs exposure may involve arachidonic acid metabolism. Phosphatidylcholine (PC) could be the key substance, and the CYP gene family (Cyp2c23, Cyp2c40) might be the critical genes regulating liver lipid metabolism during NPs exposure.

CONCLUSIONS

This study has demonstrated that NPs exposure induced obesity and hepatic lipid accumulation in male mice independently of food intake. The integrated omics data identified dysregulated PC metabolism and CYP gene family expression, suggesting their involvement in arachidonic acid-associated pathways. These findings provided preliminary mechanistic clues linking NP exposure to hepatic lipid metabolism dysregulation and helped to elucidate the adverse effects of NPs on liver lipid metabolism.

Phenotypic and Gene Expression Alterations in Aquatic Organisms Exposed to Microplastics

The use of plastics, valued for its affordability, durability, and convenience, has grown significantly with the advancement of industry. Paradoxically, these very properties of plastics have also led to significant environmental challenges. Plastics are highly resistant to decomposition, resulting in their accumulation on land, where they eventually enter aquatic environments, due to natural processes or human activities. Among these plastics, microplastics, which are tiny plastic particles, are particularly concerning when they enter aquatic ecosystems, including rivers and seas. Their small size makes them easily ingestible by aquatic organisms, either by mistake or through natural feeding behaviors, which poses serious risks. Moreover, microplastics readily adsorb other pollutants present in aquatic environments, creating pollutant complexes that can have a synergistic impact, magnifying their harmful effects compared to microplastics or pollutants acting alone. As a result, extensive research has focused on understanding the effects of microplastics on aquatic organisms. Numerous studies have demonstrated that aquatic organisms exposed to microplastics, either alone or in combination with other pollutants, exhibit abnormal hatching, development, and growth. Additionally, many genes, particularly those associated with the antioxidant system, display abnormal expression patterns in these conditions. In this review, we examine these impacts, by discussing specific studies that explore changes in phenotype and gene expression in aquatic organisms exposed to microplastics, both independently and in combination with adsorbed pollutants.

Microplastics in freshwater ecosystems: probabilistic environmental risk assessment and current knowledge in occurrence and ecotoxicological studies

Ecotoxicological studies involving microplastics (MPs) conducted on a laboratory scale may not always accurately mirror real environmental conditions (types, sizes, shapes, and concentrations of MPs). This review primarily focused on examining studies that investigated the prevalence of MPs in freshwater environments and accumulation in organisms worldwide, considering important factors such as morphology, particle size, and the specific polymer types involved. This review also encompassed ecotoxicological studies related to MPs, and ecological risk analyses were carried out based on the obtained ecotoxicological data. Based on the extensive dataset collected, we determined the hazardous concentration for 5% of the tested organisms (HC5) and estimated for the first time a predicted noneffect concentration (PNEC) value for two distinct types of MPs polymers: polystyrene (PS) and polyethylene (PE), based on the species sensitive distribution (SSD) curves obtained from nonobserved concentration (NOEC) values, with 0.003 mg L-1 for PS and 0.011 mg L-1 for PE. Furthermore, another PNEC value for 7 types of MPs (PE, PS, polyvinyl chloride, PA6, polyester, polyethylene terephthalate, and ethylene acrylic acid copolymer (EEA copolymer)) was calculated (0.0027 mg L-1 or 2.61 particles L-1). Subsequently, the risk quotient (RQ) was computed utilizing data obtained from the measured environmental concentrations of 18 places. An RQ value of 0.094 was obtained, inferring that MPs have a low-risk potential globally. However, when the RQ values were examined for each country separately, they exhibited significant variability (RQ = 22.06 in Malaysia and 0.000008 in Australia). Overall, this review provides a comprehensive overview of the current knowledge on MP abundance in freshwater environments, the associated ecotoxicological research to reinforce the outcomes derived from the risk analysis, and their accumulation in biota.

Toxicity of Polystyrene Microplastics with Cadmium on the Digestive System of Rana zhenhaiensis Tadpoles

Microplastics pollution in freshwater systems is attracting increasing attention. However, our knowledge of its combined toxicity with heavy metals is scarce. In this study, Rana zhenhaiensis was used as the model animal to study the combined poisoning mechanism of cadmium or microplastics on the digestive systems of tadpoles in freshwater. Results showed that the exposure to cadmium and polystyrene increased the mortality and metamorphosis rate of R. zhenhaiensis tadpoles, and delayed their growth and development. Cadmium was detected in the livers and intestines, while polystyrene mainly accumulated in the gills and intestines of tadpoles. The individual exposure of cadmium or polystyrene can cause pathological damage to liver tissue, induce oxidative stress in liver, and change gene expression. Cadmium co-exposure with polystyrene can reduce the cadmium accumulation in the liver. While polystyrene can slightly increase cadmium accumulation in the intestine. Exposure to cadmium and polystyrene altered the abundance and community structure of intestinal microbiota, and polystyrene increased the dysregulation of the gut microbiome. In this study, the combined exposure of microplastics and cadmium had a negative impact on R. zhenhaiensis tadpoles, but the introduction of microplastics on the toxicity of cadmium on the tadpoles needs further investigation, due to the different characteristics of microplastics.

Ceratophyllum demersum alleviates microplastics uptake and physiological stress responses in aquatic organisms, an overlooked ability

It has been demonstrated that microplastics (MPs) may be inadvertently ingested by aquatic animals, causing harm to their physiological functions and potentially entering the food chain, thereby posing risks to human food safety. To achieve an environmentally friendly and efficient reduction of MPs in freshwater environments, this experiment investigates the depuration effect of C. demersum on MPs using three common aquatic animals: Macrobrachium nipponense, Corbicula fluminea, and Bellamya aeruginosa as research subjects. The amounts of MPs, digestive enzyme activity, oxidative stress index, and energy metabolism enzyme activity in the digestive and non-digestive systems of three aquatic animals were measured on exposure days 1, 3, and 7 and on depuration days 1 and 3. The results indicated that the depuration effect of C. demersum and the species interaction were significant for the whole individual. Concerning digestive tissue, C. demersum was the most effective in purifying B. aeruginosa. When subjected to short-term exposure to MPs, C. demersum displayed a superior depuration effect. Among non-digestive tissues, C. demersum exhibited the earliest purifying effect on C. fluminea. Additionally, C. demersum alleviated physiological responses caused by MPs. In conclusion, this study underscores C. demersum as a promising new method for removing MPs from aquatic organisms.

Exposure to virgin and marine incubated microparticles of biodegradable and conventional polymers modulates the hepatopancreas transcriptome of Mytilus galloprovincialis

Biodegradable polymers have been proposed as an alternative to conventional plastics to mitigate the impact of marine litter, but the research investigating their toxicity is still in its infancy. This study evaluates the potential ecotoxicological effects of both virgin and marine-incubated microparticles (MPs), at environmentally relevant concentration (0.1 mg/l), made of different biodegradable polymers (Polycaprolactone, Mater-Bi, cellulose) and conventional polymers (Polyethylene) on Mytilus galloprovincialis by using transcriptomics. This approach is increasingly being used to assess the effects of pollutants on organisms, obtaining data on numerous biological pathways simultaneously. Whole hepatopancreas de novo transcriptome sequencing was performed, individuating 972 genes differentially expressed across experimental groups compared to the control. Through the comparative transcriptomic profiling emerges that the preponderant effect is attributable to the marine incubation of MPs, especially for incubated polycaprolactone (731 DEGs). Mater-Bi and cellulose alter the smallest number of genes and biological processes in the mussel hepatopancreas. All microparticles, regardless of their polymeric composition, dysregulated innate immunity, and fatty acid metabolism biological processes. These findings highlight the necessity of considering the interactions of MPs with the environmental factors in the marine ecosystem when performing ecotoxicological evaluations. The results obtained contribute to fill current knowledge gaps regarding the potential environmental impacts of biodegradable polymers.

A review of cumulative toxic effects of environmental endocrine disruptors on the zebrafish immune system: Characterization methods, toxic effects and mechanisms

Environmental endocrine disrupting chemicals (EDCs), are a type of exogenous organic pollutants, are ubiquitous in natural aquatic environments. Currently, in addition to neurological, endocrine, developmental and reproductive toxicity, ecotoxicology studies on immunotoxicity are receiving increasing attention. In this review, the composition of immune system of zebrafish, the common indicators of immunotoxicity, the immunotoxicity of EDCs and their molecular mechanism were summarized. We reviewed the immunotoxicity of EDCs on zebrafish mainly in terms of immune organs, immunocytes, immune molecules and immune functions, meanwhile, the possible molecular mechanisms driving these effects were elucidated in terms of endocrine disruption, dysregulation of signaling pathways, and oxidative damage. Hopefully, this review will provide a reference for further investigation of the immunotoxicity of EDCs.

PLASTAMINATION: Outcomes on the Central Nervous System and Reproduction

BACKGROUND

Environmental exposures to non-biodegradable and biodegradable plastics are unavoidable. Microplastics (MPs) and nanoplastics (NPs) from the manufacturing of plastics (primary sources) and the degradation of plastic waste (secondary sources) can enter the food chain directly or indirectly and, passing biological barriers, could target both the brain and the gonads. Hence, the worldwide diffusion of environmental plastic contamination (PLASTAMINATION) in daily life may represent a possible and potentially serious risk to human health.

OBJECTIVE

This review provides an overview of the effects of non-biodegradable and the more recently introduced biodegradable MPs and NPs on the brain and brain-dependent reproductive functions, summarizing the molecular mechanisms and outcomes on nervous and reproductive organs. Data from in vitro, ex vivo, non-mammalian and mammalian animal models and epidemiological studies have been reviewed and discussed.

RESULTS

MPs and NPs from non-biodegradable plastics affect organs, tissues and cells from sensitive systems such as the brain and reproductive organs. Both MPs and NPs induce oxidative stress, chronic inflammation, energy metabolism disorders, mitochondrial dysfunction and cytotoxicity, which in turn are responsible for neuroinflammation, dysregulation of synaptic functions, metabolic dysbiosis, poor gamete quality, and neuronal and reproductive toxicity. In spite of this mechanistic knowledge gained from studies of non-biodegradable plastics, relatively little is known about the adverse effects or molecular mechanisms of MPs and NPs from biodegradable plastics.

CONCLUSION

The neurological and reproductive health risks of MPs/NPs exposure warrant serious consideration, and further studies on biodegradable plastics are recommended.

The effects of polyethylene microplastics on the growth, reproduction, metabolic enzymes, and metabolomics of earthworms Eisenia fetida

The existing data regarding the effects of polyethylene (PE) microplastics (MPs) smaller than 5 mm in size on earthworms are insufficient to fully comprehend their toxicity. In this study, earthworms Eisenia fetida were exposed to artificially added PE at a concentration ranging from 0.05 to 20 g/kg soil (0.005%-2%) for 60 days to determine the concentration range causing negative effects on earthworms and to uncover the potential toxic mechanisms. The individual growth, reproduction, and metabolic enzyme activities, including phase I enzymes (cytochrome P450 [CYP] 1A2, 2B6, 2C9, and 3A4), and phase II metabolic enzymes (superoxide dismutase (SOD), catalase (CAT), and glutathione sulfotransferase (GST)), and metabolomics were measured. The observed variations in responses of multiple cross-scale endpoints indicated that individual indices are less responsive to PE MPs than metabolic enzymes or metabolomics. Despite the absence of significant alterations in growth inhibition based on body weight, PE MPs at concentrations equal to or exceeding 2.5 g/kg were found to exert a toxic effect on earthworms, which was evidenced by significant changes in metabolic enzyme activities (CYP1A2, 2B6, 2C9, and 3A4, SOD, CAT, and GST) and important small molecule metabolites screened based on metabolomics, likely due to the bioaccumulation of PE. The toxicity of PE MPs to earthworms is inferred to be associated with neurotoxicity, oxidative damage, decreased detoxification capacity, energy metabolism imbalance, and impaired amino acid and purine metabolism due to bioaccumulation. The findings of this study will enhance our understanding of the molecular toxicity mechanisms of PE MPs and contribute to a more accurate assessment of the ecological risks posed by PE MPs in soil.

On the Novel Process of Pristine Microplastic Bio-fragmentation by Zebrafish (Danio rerio)

Microplastics are highly persistent particles that deliberately contaminate our ecosystem. These small-sized particles can pass through filtering systems into the water bodies, affecting various forms of aquatic and terrestrial life. However, little is known about their fragmentation process within the organism's body. In previous studies, commercially available microplastics were used that are rarely found in the environment naturally, hence they cannot mimic the effects on our surroundings. Therefore, using the zebrafish, Danio rerio we have evaluated the process of bio-fragmentation of ingested pristine polyethene microplastics which are widely used in our daily life. We have also examined their faecal pellets through Field Emission Scanning Electron Microscopy (FE-SEM) and Fourier transform infrared spectroscopy (FTIR). Our results show that zebrafish can potentially bio-fragment the pristine microplastic particles into nano-plastic within a short period of 24 h. Additionally, zebrafish cannot recognize the pristine microplastic particles and can ingest them as food. No mortality occurred during the experiment. Thus, we have identified a natural pathway of microplastic bio-fragmentation, introducing an emerging role of zebrafish in biogeochemical cycling and the fate of plastics.

Toxicity of microplastics and copper, alone or combined, in blackspot seabream (Pagellus bogaraveo) larvae

Plastics pose serious risks for fish productivity and a potential constraint for food security. Newly hatched blackspot seabream larvae were exposed to microplastics (MPs), copper (Cu, 10-810 µg/L) and their mixtures (Cu+MPs), during 3 and 9 days. Biochemical biomarkers and the expression of antioxidant and neurotoxicity-related genes were evaluated. In the 3-day exposure, catalase and glutathione-S-transferase activities decreased in MPs, Cu and Cu+MPs groups, followed by an increase of lipid peroxidation in the Cu270 and Cu270 +MPs exposed larvae. In the 9-day exposure, ROS levels increased in MPs and Cu30 groups, but no significant oxidative damage was observed, suggesting that the antioxidant system overcome the induced oxidative stress. However, the acetylcholinesterase transcript was downregulated in MPs, Cu and Cu10+MPs groups, indicating that MPs effects in cholinergic neurotransmission may arise after longer exposures. Overall, MPs and Cu can reduce survival, induce oxidative stress, lipid peroxidation, neurotoxicity, and impact negatively fish larvae fitness.