Neurotoxicity and physiological stress in brain of zebrafish chronically exposed to tributyltin

Chronic exposure to tris (2-chloroethyl) phosphate (TCEP) induces brain structural and functional changes in zebrafish (Danio rerio): A comparative study on the environmental and LC50 concentrations of TCEP

Tris (2-chloroethyl) phosphate (TCEP) is a crucial organophosphorus flame retardant widely used in many industrial and commercial products. Available reports reported that TCEP could cause various toxicological effects on organisms, including humans. Unfortunately, toxicity data for TCEP (particularly on neurotoxicity) on aquatic organisms are lacking. In the present study, Danio rerio were exposed to different concentrations of TCEP for 42 days (chronic exposure), and oxidative stress, neurotoxicity, sodium, potassium-adenosine triphosphatase (Na+, K+-ATPase) activity, and histopathological changes were evaluated in the brain. The results showed that TCEP (100 and 1500 µg L-1) induced oxidative stress and significantly decreased the activities of antioxidant enzymes (SOD, CAT and GR) in the brain tissue of zebrafish. In contrast, the lipid peroxidation (LPO) level was increased compared to the control group. Exposure to TCEP inhibited the acetylcholinesterase (AChE) and Na+,K+-ATPase activities in the brain tissue. Brain histopathology after 42 days of exposure to TCEP showed cytoplasmic vacuolation, inflammatory cell infiltration, degenerated neurons, degenerated purkinje cells and binucleate. Furthermore, TCEP exposure leads to significant changes in dopamine and 5-HT levels in the brain of zebrafish. The data in the present study suggest that high concentrations of TCEP might affect the fish by altering oxidative balance and inducing marked pathological changes in the brain of zebrafish. These findings indicate that chronic exposure to TCEP may cause a neurotoxic effect in zebrafish.

Whole-Transcriptome Analysis Reveals the RNA Profiles in Mouse Bone Marrow Mesenchymal Stem Cells or Zebrafish Embryos After Exposure to Environmental Level of Tributyltin

To understand the underlying molecular mechanisms, mouse bone marrow mesenchymal stem cells (BMSCs) and zebrafish embryos were exposed to the control group and Tributyltin (TBT) group (10 ng/L, environmental concentration) for 48 h, respectively. The expression profiles of RNAs were investigated using whole-transcriptome analysis in mouse BMSCs or zebrafish embryos after TBT exposure. For mouse BMSCs, the results showed 2,449 differentially expressed (DE) mRNAs, 59 DE miRNAs, 317 DE lncRNAs, and 15 circRNAs. Similarly, for zebrafish embryos, the results showed 1,511 DE mRNAs, 4 DE miRNAs, 272 DE lncRNAs, and 28 circRNAs. According to KEGG pathway analysis showed that DE RNAs were mainly associated with immune responses, signaling, and cellular interactions. Competing endogenous RNA (ceRNA) network analysis revealed that the regulatory network of miRNA-circRNA constructed in zebrafish embryos was more complex compared to that of mouse BMSCs.

Environmental contaminants modulate transport activity of zebrafish (Danio rerio) multidrug and toxin extrusion protein 3 (Mate3/Slc47a2.1)

Zebrafish Mate3 is one of six co-orthologs of human multidrug and toxin extrusion proteins. It is highly expressed in the kidneys, intestine, testes, and brain of males. Initial interaction studies showed its interaction with xenobiotic compounds, suggesting a role in the efflux of toxic compounds. In this study, we aimed to test various environmental contaminants for their interaction with zebrafish Mate3. We developed a stable zebrafish Mate3 cell line and optimized a high-throughput screening assay using DAPI and ASP+ as fluorescent model substrates. To gain insight into the structure and function of the Mate3 protein and relate these to the results of the DAPI and ASP+ transport measurements, we predicted its 3D structure using the AlphaFold2 algorithm. A 3D structure with high per residue confidence scores with 13 transmembrane segments (TMs) was obtained, with topology and mutual positioning characteristic of the Mate protein family in a shape open to the extracellular part. Molecular docking methods were used to identify DAPI and ASP+ binding sites on the surface and in the center of the protein cavity. Because our kinetics experiments combined with molecular docking indicated that there may be additional active sites in zebrafish Mate3, additional cytotoxicity experiments were performed and highly potent Mate3 interactors were identified from a set of 55 different environmental contaminants. Our results suggest that some of the identified interactors may be of environmental concern, as their interaction with Mate3 could lead to an impairment of its normal efflux function, making fish more sensitive to harmful substances commonly released into the aquatic environment. Finally, the quality of zebrafish Mate3 structures predicted by the AlphaFold2 algorithm opens up the possibility of successfully using this tool for in silico research on transport preferences of other Mate proteins.

Embryonic exposure to environmentally relevant levels of tributyltin affects embryonic tributyltin bioaccumulation and the physiological responses of juveniles in cuttlefish (Sepia pharaonis)

Tributyltin (TBT) is a typical organic pollutant that persists in aquatic sediments due to its wide usage as an antifouling fungicide during the past few decades. Despite increased awareness of the serious negative consequences of TBT on aquatic species, studies on the effects of TBT exposure on cephalopod embryonic development and juvenile physiological performance are scarce. To investigate the lasting effects of TBT toxicity on Sepia pharaonis from embryo to hatchling, embryos (gastrula stage, 3-5 h post fertilization) were exposed to four levels of TBT until hatching: 0 (control), 30 (environmental level), 60, and 120 ng/L. Subsequently, juvenile growth performance endpoints and behavioral alterations were assessed over 15 days post-hatching. Egg hatchability was significantly reduced and embryonic development (i.e., premature hatching) was accelerated in response to 30 ng/L TBT exposure. Meanwhile, TBT-induced alterations in embryonic morphology primarily included yolk-sac lysis, embryonic malformations, and uneven pigment distributions. During the pre-middle stage of embryonic development, the eggshell serves as an effective barrier to safeguard the embryo from exposure to 30-60 ng/L TBT, according to patterns of TBT accumulation and distribution in the egg compartment. However, even environmental relevant levels of TBT (30 ng/L) exposure during embryonic development had a negative impact on juvenile behavior and growth, including slowing growth, shortening eating times, causing more irregular movements, and increasing inking times. These findings indicate that after TBT exposure, negative long-lasting effects on S. pharaonis development from embryo to hatchling persist, suggesting that long-lasting toxic effects endure from S. pharaonis embryos to hatchlings.

Neurotoxic effects of different sizes of plastics (nano, micro, and macro) on juvenile common carp (Cyprinus carpio)

Using common carp as a model, we assessed the effects of polyethylene (PE) plastics on the brain. We measured activity of acetylcholinesterase (AChE), monoamine oxidase (MAO), and the content of nitric oxide (NO) in carp brain following exposure to 100 mg/L of either macroplastics (MaP), microplastics (MPs), or nanoplastic (NPs) for 15 days compared to an unexposed group. Following exposure, each biochemical biomarker was reduced 30–40%, with a higher magnitude of change corresponding to the smaller size of the particles (NPs > MPs > MaPs). In the carp tectum, exposure for 15 days to plastic particles caused varying degrees of necrosis, fibrosis, changes in blood capillaries, tissue detachment, edema, degenerated connective tissues, and necrosis in large cerebellar neurons and ganglion cells. In the carp retina, there was evidence for necrosis, degeneration, vacuolation, and curvature in the inner layer. Here we provide evidence that exposure to plastic particles can be associated with neurotoxicity in common carp.

Metabolomics profiling of valproic acid-induced symptoms resembling autism spectrum disorders using 1H NMR spectral analysis in rat model

Prenatal exposure to valproic acid (VPA) has been implicated in the manifestation of autism spectrum disorder (ASD)-like behavioral and functional changes both in human and rodents including mice and rats. The objective of this study was to determine metabolomics profiling and biomarkers related to VPA-induced symptoms resembling ASD using proton nuclear magnetic resonance (1H-NMR) spectral data. VPA was administered to pregnant rats at gestation day 12.5 and effects measured subsequently in male 4-week-old offspring pups. The sociability of VPA-treated animals was significantly diminished and exhibited ASD-like behavior as evidenced by reduction of social adaptation disorder and lack of social interactions. To find biomarkers related to ASD, the following were collected prefrontal brain cortices, urine bladder and blood samples directly from heart puncture. In all samples, principal component analysis (PCA) and partial least-squares discriminant analysis (PLS-DA) displayed significant clustering pattern differences between control and treated groups. Valine, taurine, myo-inositol, 3-hydroxybutyrate and 1,3-dihydroxyacetone were significantly decreased in brain cortices in treated rats. Serum metabolites of glucose, creatine phosphate, lactate, glutamine and threonine were significantly increased in VPA-administered animals. Urinary metabolites of pimelate, 3-hydroxyisovalerate and valerate were significantly reduced in VPA-treated rat, whereas galactose and galactonate levels were elevated. Various metabolites were associated with mitochondrial dysfunction metabolism and central nervous system disorders. Data demonstrated that VPA-induced alterations in endogenous metabolites of serum, urine, and brain cortex which might prove useful as biomarkers for symptoms resembling ASD as a model of this disorder.

Tributyltin Alters Calcium Levels, Mitochondrial Dynamics, and Activates Calpains Within Dorsal Root Ganglion Neurons

Tributyltin (TBT) remains a global health concern. The primary route of human exposure to TBT is either through ingestion or skin absorption, but TBT's effects on the peripheral nervous system have still not been investigated. Therefore, we exposed in vitro sensory dorsal root ganglion (DRG) neurons to TBT at a concentration of 50-200 nM, which is similar to the observed concentrations of TBT in human blood samples. We observed that TBT causes extensive axon degeneration and neuronal death in the DRG neurons. Furthermore, we discovered that TBT causes an increase in both cytosolic and mitochondrial calcium levels, disrupts mitochondrial dynamics, decreases neuronal ATP levels, and leads to the activation of calpains. Additional experiments demonstrated that inhibition of calpain activation prevented TBT-induced fragmentation of neuronal cytoskeletal proteins and neuronal cell death. Thus, we conclude that calpain activation is the key executioner of TBT-induced peripheral neurodegeneration.