Lifetime exposure to benzophenone-3 at an environmentally relevant concentration leads to female-biased social behavior and cognition deficits in zebrafish.

Benzophenone-3 (BP3) is an organic UV filter widely used in the commercial formulations of various personal care products. It has been detected ubiquitously in the environment and human tissues. Recently, BP3-induced neurotoxicity has been identified as the main health risk to humans and aquatic organisms. However, most research has been focused on embryonic development, and few studies explore chronic lifetime exposure. In the present study, we evaluated the neurotoxicity of lifetime exposure to an environmentally relevant concentration of BP3 in zebrafish. Our findings revealed that continuous BP3 exposure at 10 µg/L (0.04 µM) from 6 h post fertilization (hpf) to adulthood at 5 months led to female-biased social behavioral deficits and learning and memory impairment. These neurobehavioral effects were characterized by decreased prosocial activities in the social preference test and mirror biting assay, and reduced learning and memory in a T-maze test. Furthermore, these effects were accompanied by female-specific decreases in brain weight and brain dopamine concentration, female-biased decrease of neurogenesis in the telencephalon as well as female-specific increases in apoptotic cells and expression levels of genes and proteins related to the apoptosis pathway in the brain. Our results suggest that BP3-induced social behavior and learning/memory deficits are correlated to the cell loss in the telencephalon region of the zebrafish brain.

Transient MPTP exposure at a sensitive developmental window altered gut microbiome and led to male-biased motor and social behavioral deficits in adult zebrafish.

Zebrafish is an economical alternative model for developmental neurotoxicity (DNT) testing. DNT studies in zebrafish have been focused on acute effects; few studies explore enduring neurotoxicity in adults. More recently, gut microbiome has emerged as an important modulator between chemical exposure and neurotoxicity, rendering its necessity to be included in DNT testing. The present study used a well-known dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) as a model chemical to explore long-lasting neurotoxicity in adults after transient exposure during early development. We demonstrated that transient MPTP exposure at 1 µM during a sensitive developmental window of 48-96 h post-fertilization (hpf) altered gut microbiome and led to male-biased locomotion and behavioral deficits in adult fish. The locomotion deficit was manifested as hypoactivity observed in adult males under light conditions or specifically the reduction of fast swim bouts. The social behavioral deficits were characterized by the reduced number of times fish crossed the mirror zone in the mirror response assay and the reduced percent time fish spent at the area proximal to conspecific fish shoal in the social preference test. Gut microbiome analysis revealed that transient MPTP exposure during early development might render fish more susceptible to the colonization of the pathogenic Vibrio. In conclusion, our study revealed that transient MPTP exposure during early development could lead to long-lasting neurotoxicity in adult fish and cause altered gut microbiome composition in both larval and adult fish.

Characterization of Developmental Neurobehavioral Toxicity in a Zebrafish MPTP-Induced Model: A Novel Mechanism Involving Anemia.

Zebrafish represent an economical alternative to rodents for developmental neurotoxicity (DNT) testing. Mechanistic understanding is the key to successfully translating zebrafish findings to humans. In the present study, we used a well-known dopaminergic (DA) neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) as a model chemical to uncover the molecular pathways for observed DNT effects. To enhance the specificity of potential molecular targets, we restricted our exposure to a concentration that is nonteratogenic yet exhibits high DNT effects and an exposure window sensitive to MPTP. Our DNT assessment based on a battery of motor and social behavioral tests revealed an effective concentration of 1 µM and a sensitive window of 48-96 h postfertilization (hpf) for MPTP-induced hypoactivity. It is worth noting that this hypoactivity persisted into later larval development until 28 dpf. We observed increased cell apoptosis, oxidative stress, and decreased ATP levels in larvae immediately after exposure at 96 hpf. Significant reductions of DA neurons were found in the retina at 72, 96, and 120 hpf. No visible deformity was found in motoneurons at 72, 96, and 120 hpf. Transcriptome analysis uncovered a novel pathway manifested by significant upregulation of genes enriched with erythropoiesis. Sensitive window exposure of MPTP and other DA neurotoxins rotenone and paraquat exhibited a concentration-dependent effect on transcriptional changes of embryonic hemoglobins and anemia. Given that anemia is a significant risk factor for Parkinson's disease and MPTP is known to cause parkinsonism in humans, we concluded that anemia resulting from dysregulation of primitive erythropoiesis during embryonic development might serve as a common mechanism underlying DA neurotoxin-induced DNT effects between zebrafish and humans.

Polymorphisms of Cytochromes P450 and Glutathione S-Transferases Synergistically Modulate Risk for Parkinson's Disease.

Background: Environmental substances such as pesticides are well-known in link with Parkinson's disease (PD) risk. Enzymes including cytochromes P450 (CYPs), esterases and glutathione S-transferases (GSTs) are responsible for the xenobiotic metabolism and may functionally compensate each other for subtypes in the same class. We hypothesize that the genetic effects of each class modulate PD risk stronger in a synergistic way than individually. Methods: We selected 14 polymorphic loci out of 13 genes which encode enzymes in the classes of CYP, esterase, and GST, and recruited a cohort of 1,026 PD and control subjects from eastern China. The genotypes were identified using improved multiplex ligation detection reaction and analyzed using multiple models. Results: A total of 13 polymorphisms remained after Hardy-Weinberg equilibrium analysis. None of the polymorphisms were independently associated with PD risk after Bonferroni correction either by logistic regression or genetic models. In contrast, interaction analyses detected increased resistance to PD risk in individuals carrying the rs12441817/CC (CYP1A1) and rs2070676/GG + GC (CYP2E1) genotypes (P = 0.002, OR = 0.393, 95% CI = 0.216-0.715), or carrying the GSTM1-present, GSTT1-null, rs156697/AG + GG (GSTO2) and rs1695/AA (GSTP1) genotypes (P = 0.003, OR = 0.348, 95% CI = 0.171-0.706). The synergistic effect of GSTs on PD was primarily present in females (P = 0.003). No synergistic effect was observed within genotypes of esterases. Conclusion: We demonstrate a presence of synergistic but not individual impact on PD susceptibility in polymorphisms of CYPs and GSTs. The results indicate that the genetic interplay leads the way to PD development for xenobiotic metabolizing enzymes.

An antisense Alu transposon insertion/deletion polymorphism of ALDH1A1 may functionally associate with Parkinson's disease.

BACKGROUND: Aldehyde dehydrogenase 1 (encoded by ALDH1A1) has been shown to protect against Parkinson's disease (PD) by reducing toxic metabolites of dopamine. We herein revealed an antisense Alu element insertion/deletion polymorphism in intron 4 of ALDH1A1, and hypothesized that it might play a role in PD.  METHODS: A Han Chinese cohort comprising 488 PD patients and 515 controls was recruited to validate the Alu insertion/deletion polymorphism following a previous study of tag-single nucleotide polymorphisms, where rs7043217 was shown to be significantly associated with PD. Functional analyses of the Alu element insertion were performed. RESULTS: The Alu element of ALDH1A1 was identified to be a variant of Yb8 subfamily and termed as Yb8c4. The antisense Yb8c4 insertion/deletion polymorphism (named asYb8c4ins and asYb8c4del, respectively) appeared to be in a complete linkage disequilibrium with rs7043217 and was validated to be significantly associated with PD susceptibility with asYb8c4ins serving as a risk allele (P = 0.030, OR = 1.224, 95% CI = 1.020-1.470). Multiple functional analyses including ALDH1A1 mRNA expression in blood cells of carriers, and reporters of EGFP and luciferase showed that the asYb8c4ins had a suppressive activity on gene transcription. Mechanistic explorations suggested that the asYb8c4ins induced no changes in CpG methylation and mRNA splicing of ALDH1A1 and appeared no binding of transcription factors. CONCLUSIONS: Our results consolidate an involvement of ALDH1 in PD pathogenesis. The asYb8c4 polymorphism may be a functional output of its linkage disequilibrium-linked single nucleotide polymorphisms.

Autoimmune Disease Associated CLEC16A Variants Convey Risk of Parkinson's Disease in Han Chinese.

CLEC16A is a membrane-associated endosomal protein implicated in regulating autophagy and antigen presentation. Its genetic variants are broadly associated with multiple autoimmune diseases. Parkinson's disease (PD), which undergoes autophagy disruption and neuroinflammation, has been clinically observed, for an extensive amount of time, to be associated with autoimmune diseases. In this study, we aimed to understand whether the autoimmune disease associated CLEC16A variants pleiotropically modulate PD risk. Five of such CLEC16A variants, including rs6498169, rs12708716, rs12917716, rs7200786, and rs2903692, were selected and analyzed in a Han Chinese cohort comprising 515 sporadic PD patients and 504 controls. Results showed that rs6498169 and rs7200786 were significantly associated with PD susceptibility (p = 0.005 and 0.004, respectively; recessive model, p = 0.002 and 0.001, respectively). Rs6498169 was also associated with the PD subtype of postural instability/gait difficulty (p = 0.002). Haplotype analysis showed that the AAG module in order of rs6498169, rs12708716, and rs2903692 was associated with the highest risk for PD (p = 0.0047, OR = 1.42, 95% CI = 1.11-1.82). Functional annotation analyses suggested that rs6498169 had high probability to affect transcription factor binding and target gene expression. In summary, the current study demonstrates that the autoimmune disease associated CLEC16A variants convey risk of PD in Han Chinese. Our findings suggest a pleiotropic role of CLEC16A and strengthen the link between PD and autoimmune diseases.

Developmental titanium dioxide nanoparticle exposure induces oxidative stress and neurobehavioral changes in zebrafish.

The widespread commercial application of titanium dioxide nanoparticles (TiO2 NPs) leads to ubiquitous presence of TiO2 NPs in the aquatic environment, which highlights the necessity to determine their potential adverse effects on aquatic organisms. The developing nerve system is particularly susceptible to environment perturbation. However, few studies have explored the developmental neurobehavioral toxicity of TiO2 NPs, especially at smaller particle size ranges (≤20 nm) that have relatively longer retention time in the water column. In this study, zebrafish embryos were exposed to non-teratogenic concentrations of 0.1 and 1 mg/L TiO2 NPs (average size of 14-20 nm) from 8 to 108 h post-fertilization (hpf) followed by various assessments at different time points up to 12 days post-fertilization (dpf). Our findings revealed that 1 mg/L TiO2 NPs perturbed the motor and social behaviors in larval zebrafish. These behavioral changes were characterized by decreased swimming speed in a locomotor response test at 5 dpf, increased travel distance in a flash stimulus test at 5 dpf, increased preference to the light zone in a light/dark preference test at 10 dpf, and increased mirror attack and percent time spent in the mirror zone in a mirror stimulus response assay at 12 dpf. Mechanistic examinations at 5 dpf revealed elevated cell apoptosis and oxidative stress. Cell apoptosis was characterized by increased acridine orange (AO) positive cells in the olfactory region and neuromasts of the lateral line system. Oxidative stress was characterized by increased lipid peroxidation, increased ROS production, and upregulated catalase (cat) gene expression. In addition, TiO2 NP exposure also upregulated genes associated with the developmental nervous system such as the growth associated protein 43 (gap43) and proliferating cell nuclear antigen (pcna). Our results suggest that the neurobehavioral changes in larvae exposed to 1 mg/L TiO2 NPs during early development may result from cell apoptosis and oxidative stress induced neuronal damages.

Early life stage transient aristolochic acid exposure induces behavioral hyperactivity but not nephrotoxicity in larval zebrafish.

Aristolochic acids (AA) are nitrophenanthrene carboxylic acids found in plants of the Aristolochiaceae family. Humans are exposed to AA by deliberately taking herbal medicines or unintentionally as a result of environmental contamination. AA is notorious for its nephrotoxicity, however, fewer studies explore potential neurotoxicity associated with AA exposure. The developing nervous system is vulnerable to xenobiotics, and pregnant women exposed to AA may put their fetuses at risk. In the present study, we used the embryonic zebrafish model to evaluate the developmental neurotoxicity associated with AA exposure. At non-teratogenic concentrations (≤ 4 µM), continuous AA exposure from 8 to 120 hours post fertilization (hpf) resulted in larval hyperactivity that was characterized by increased moving distance, elevated activity and faster swimming speeds in several behavioral assays. Further analysis revealed that 8-24 hpf is the most sensitive exposure window for AA-induced hyperactivity. AA exposures specifically increased motor neuron proliferation, increased apoptosis in the eye, and resulted in cellular oxidative stress. In addition, AA exposures increased larval eye size and perturbed the expression of vision genes. Our study, for the first time, demonstrates that AA is neurotoxic to the developmental zebrafish with a sensitive window distinct from its well-documented nephrotoxicity.

Environmental relevant concentrations of benzophenone-3 induced developmental neurotoxicity in zebrafish.

Benzophenone-3 (BP3 or oxybenzone) is an organic UV filter that has been widely used in personal care products. Its frequent detection in the environment and humans as well as its structural similarity to estradiol have prompted most research focus on its endocrine effect. However, these effects are usually associated with concentrations 10-100 fold higher than its environmental relevant concentrations. Few studies explore its adverse effects at environmental relevant concentrations. In the present study, we evaluated the developmental neurotoxic (DNT) effects of low concentration BP3 exposure during a sensitive developmental window in zebrafish. Our findings revealed that BP3 exposure at 10 µg/L (0.04 µM) during 6-24 h post fertilization (hpf) led to various DNT effects such as increased spontaneous movement at 21 and 24 hpf, decreased touch response at 27 hpf, heightened hyperactivity in locomotor response at 5 day post fertilization (dpf), decreased shoaling behavior at 11 dpf and decreased mirror attacks at 12 dpf. These effects were accompanied with decreased axonal growth at 27 hpf, decreased cell proliferation and increased cell apoptosis in the head region of larval zebrafish immediately after BP3 exposure at 24 hpf, and increased expression of retinoid X receptor gene rxrgb at 5 dpf. Interestingly, rxrgb knockdown through morpholino injection largely restored most of BP3-induced DNT effects, axonal growth delay, cell proliferation and cell apoptosis, suggesting that BP3-induced DNT effects are likely mediated through the Rxrgb receptor. In considering with recent findings on the endocrine effects of BP3, we conclude that BP3 at environmental relevant concentrations has limited estrogenic effect, but is neurotoxic to developing embryos in zebrafish.

Cryopreservation disrupts lipid rafts and heat shock proteins in yellow catfish sperm.

Lipid rafts and associated membrane proteins (flotillin, caveolin) play important roles in cell signaling and sperm fertilization while heat shock proteins (Hsp) ensure properly protein folding to fulfill their physiological functions. The markedly reduced fertility in thawed sperm after cryopreservation could result from disrupted membrane lipid rafts and these proteins. To explore the effect of sperm cryopreservation on lipid rafts and heat shock proteins, we compared lipid raft integrity, and the expression levels of lipid raft associated proteins (Flot-1, Flot-2, Cav-1) as well as heat shock proteins (Hsp90, Hsp70) in fresh and thawed sperm cryopreserved under different scenarios in yellow catfish. We found higher lipid raft integrity, higher protein expression levels of Flot-1, Flot-2, Cav-1, Hsp90, and Hsp70 in fresh sperm samples than in thawed sperm samples, in thawed sperm samples cryopreserved with optimal cooling rate than those cryopreserved with sub-optimal cooling rate, and in thawed sperm samples cryopreserved with extenders supplemented with cholesterol than those supplemented with methyl-ß-cyclodextrin (for cholesterol removal). Our findings indicate that lipid raft integrity, and expression levels of Flot-1, Flot-2, Cav-1, Hsp90, and Hsp70 are clearly associated with sperm quality, and together they may play a cumulative role in reduced fertility associated with thawed sperm in aquatic species.