Seizurogenic effect of perfluorooctane sulfonate in zebrafish larvae.

While the developmental neurotoxicity of perfluorooctane sulfonate (PFOS) has been reported, its seizurogenic potential has not been investigated. Behavior assessment was conducted in zebrafish larvae exposed to PFOS at concentrations of 0, 0.1, 1, 5, 10, and 20 µM. Changes in electrophysiological signals and in the concentration of 20 neurochemicals were measured. Behavior assessment revealed that PFOS altered larval behaviors and significantly increased the counts and duration of bursting (an irregular high-speed movement). Electrophysiological analysis showed that the number of seizure-like events and duration of seizure-like signals were significantly increased, corresponding to results observed using pentylenetetrazol as a positive seizurogenic agent. The outbreak of seizures detected via abnormal electrophysiological signals was confirmed by the increased expression of c-fos and bdnf, which are typical seizure-related genes. Analysis of neurochemicals indicated that PFOS dysregulated overall neurotransmission systems, and aberrant endogenous concentrations of various neurochemicals in the amino acid, cholinergic, dopaminergic, serotonergic and kynurenergic, and GABAergic systems were associated with seizure-like behavior and signals. This study, the first to demonstrate that exposure to PFOS provokes a seizurogenic effect in developing zebrafish larvae, should stimulate further research on the association between PFOS exposure and neurodevelopmental toxicity or neurological disorders.

Effects of the chorion on the developmental toxicity of organophosphate esters in zebrafish embryos.

Many toxicological studies have utilized zebrafish embryos to investigate the developmental toxicity of organophosphate esters (OPEs). However, in respect of the presence or absence of the chorion, a consistent experimental methodology has yet to be developed. In this study, we used a fixed exposure scheme to compare the developmental toxicities of six major OPEs in chorionated and dechorionated zebrafish embryos. Removal of the chorion increased sensitivity to OPEs: we found higher incidence of mortality and malformation in dechorionated embryos. In a behavioral assay, the locomotive activity of zebrafish larvae was consistently inhibited by OPEs except tris (1-chloropropyl) phosphate regardless of chorion presence. However, at the molecular level, the expression of ZHE1 and mmp9 was affected by the presence of the chorion in zebrafish embryos exposed to tributyl phosphate and triphenyl phosphate (TPHP), respectively. Furthermore, in zebrafish embryos exposed to TPHP, the increased expression of miR-137 and miR-141 was abolished by the presence of the chorion. Our results demonstrate for the first time that the presence of the chorion influences phenotypic morbidity, organismal behavior, and gene expression in zebrafish embryos exposed to chemicals; thus, we suggest that dechorionation is desirable for exploring the toxicity mechanisms that underlie effects of chemical exposure.

miR-137 and miR-141 regulate tail defects in zebrafish embryos caused by triphenyl phosphate (TPHP).

Exposure to triphenyl phosphate (TPHP), an organophosphate flame retardants (OPFRs), caused developmental toxicity in zebrafish embryos. However, the underlying molecular mechanism at the epigenetic level is largely unknown. Based on developmental toxicity (i.e., mortality and malformation), we measured expression levels of mRNA genes and their targeted miRNA in zebrafish embryos exposed to TPHP. As a result, TPHP caused developmental delay beginning at the 17-somite stage linking to detrimental effects in the tail and even embryonic mortality. Abnormal tail development was found to be associated with down-regulation of mmp9 and sox9b in both qRT-PCR and whole in-situ hybridization analysis. Also, we identified two microRNAs (i.e., miR-137 and miR-141) and observed their differential over-expression in TPHP-exposed zebrafish embryos. In the microinjection of miR-137 and miR-141 inhibitors, the reduced expression of mmp9 and sox9b upon TPHP exposure was compensated, indicating that epigenetic deregulation of miRNAs modulated putative genes involved in phenotypic tail defects triggered by TPHP in developing zebrafish embryos. This study provides insight for future mechanistic research using teleost fish on function of miRNAs in environmental toxicology.