Polystyrene Nanoplastics Toxicity to Zebrafish: Dysregulation of the Brain–Intestine–Microbiota Axis

Abstract

In animal species, the brain–gut axis is a complex bidirectional network between the gastrointestinal (GI) tract and the central nervous system (CNS) consisting of numerous microbial, immune, neuronal, and hormonal pathways that profoundly impact organism development and health. Although nanoplastics (NPs) have been shown to cause intestinal and neural toxicity in fish, the role of the neurotransmitter and intestinal microbiota interactions in the underlying mechanism of toxicity, particularly at environmentally relevant contaminant concentrations, remains unknown. Here, the effect of 44 nm polystyrene nanoplastics (PS-NPs) on the brain–intestine–microbe axis and embryo–larval development in zebrafish (Danio rerio) was investigated. Exposure to 1, 10, and 100 μg/L PS-NPs for 30 days inhibited growth and adversely affected inflammatory responses and intestinal permeability. Targeted metabolomics analysis revealed an alteration of 42 metabolites involved in neurotransmission. The content of 3,4-dihydroxyphenylacetic acid (DOPAC; dopamine metabolite formed by monoamine oxidase activity) was significantly decreased in a dose-dependent manner after PS-NP exposure. Changes in the 14 metabolites correlated with changes to 3 microbial groups, including Proteobacteria, Firmicutes, and Bacteroidetes, as compared to the control group. A significant relationship between Firmicutes and homovanillic acid (0.466, Pearson correlation coefficient) was evident. Eight altered metabolites (l-glutamine (Gln), 5-hydroxyindoleacetic acid (5-HIAA), serotonin, 5-hydroxytryptophan (5-HTP), l-cysteine (Cys), l-glutamic acid (Glu), norepinephrine (NE), and l-tryptophan (l-Trp)) had a negative relationship with Proteobacteria although histamine (His) and acetylcholine chloride (ACh chloride) levels were positively correlated with Proteobacteria. An Associated Network analysis showed that Firmicutes and Bacteroidetes were highly correlated (0.969). Furthermore, PS-NPs accumulated in the gastrointestinal tract of offspring and impaired development of F1 (2 h post-fertilization) embryos, including reduced spontaneous movements, hatching rate, and length. This demonstration of transgenerational deficits is of particular concern. These findings suggest that PS-NPs cause intestinal inflammation, growth inhibition, and restricted development of zebrafish, which are strongly linked to the disrupted regulation within the brain–intestine–microbiota axis. Our study provides insights into how xenobiotics can disrupt the regulation of brain–intestine–microbiota and suggests that these end points should be taken into account when assessing environmental health risks of PS-NPs to aquatic organisms.

Zebrafish (Danio rerio) Reproduction Is Affected by Life-Cycle Exposure to Differently Charged Polystyrene Nanoplastics with Sex-Specific Responses

“…In this study, life-cycle exposure of parental zebrafish to environmentally realistic concentrations of differently charged PS altered spontaneous movements at 24 hpf and heart rate at 48 hpf for offspring. These results are consistent with previous results reported for zebrafish exposed for 30 days to PS–NPs, which resulted in adverse effects on the development of offspring through dysregulation of the brain-intestine-microbiota axis . These results demonstrate transgenerational effects of exposure to differently charged PS that result in adverse effects on reproduction through epigenetics, which could affect the development of the F1 generation due to lower concentrations of VTG and alterations of expressions of genes through methylation of DNA.…”

“…These results are consistent with previous results reported for zebrafish exposed for 30 days to PS−NPs, which resulted in adverse effects on the development of offspring through dysregulation of the brain-intestine-microbiota axis. 31 These results demonstrate transgenerational effects of exposure to differently charged PS that result in adverse effects on reproduction through epigenetics, which could affect the development of the F1 generation due to lower concentrations of VTG and alterations of expressions of genes through methylation of DNA. The reproductive endocrine system is complex and can be affected and modulated by interacting factors.…”

“…Total RNA was isolated with TRIzol reagent (Tiangen, Beijing, China), and 2 μg of RNA was used for reverse transcription using the First-Strand cDNA Biosynthesis Kit. Expressions of mRNA for genes were quantified by real-time polymerase chain reaction (RT-PCR) with an ABI 7500 PCR system (Advanced Biosystems, Foster City, CA) and calculated according to previous studies. , …”

“…Expressions of mRNA for genes were quantified by real-time polymerase chain reaction (RT-PCR) with an ABI 7500 PCR system (Advanced Biosystems, Foster City, CA) and calculated according to previous studies. 31,32 Statistical Analysis. Differences between propiconazoletreated groups and the control were conducted by the Dunnett post hoc test with one-way analysis of variance (ANOVA) using IBM SPSS Statistic 19.0 version (IBM).…”

Nanoplastic toxicity towards freshwater organisms

“…Interestingly, several recent studies focused on the potential effects induced by NPLs in the intestinal microbiome of freshwater secondary consumers. It has been found that both MPs and NPLs may cause dysbiosis in the zebrafish gut at very low concentrations (1 µg/L), but NPLs can also increase the presence of pathogenic genera, such as Aeromonas [131] . It has also been found that PS-NPLs at concentrations ≤ 0.1 mg/L affected the brain-intestine-microbiota axis of zebrafish, causing reduced growth, inflammatory responses, and altered intestinal permeability, even inducing transgenerational effects such as NPL accumulation in the gastrointestinal tract of the offspring [132] .…”