Acute exposure to 4-OH-A, not PCB1254, alters brain aromatase activity but does not adversely affect growth in zebrafish

Acute developmental exposure to pharmaceuticals or environmental contaminants can have deleterious, long lasting effects. Many of these compounds are endocrine disruptors (EDCs) that target estrogen signaling, with effects on reproductive and non-reproductive tissues. We recently reported that zebrafish larvae transiently exposed to the pharmaceutical EDC 4-OH-A display visual deficits as adults. Here, we examine whether these long-term effects are due to compound-induced morphological and/or cellular changes. Zebrafish aged 24 h, 48 h, 72 h, or 7 days post-fertilization (larvae) or 3-4mos (adults) were exposed to either 4-OH-A or PCB₁₂₅₄ for 24 h. After that time, notochord length, eye diameter, inter-eye distance, and heart rate were measured from larvae; and aromatase (estrogen synthase) activity was measured in homogenates of adult brain tissue. In general, indices of larval growth and development were not altered by 24 h exposure to either compound. 4-OH-A potently inhibited aromatase activity, while PCB₁₂₅₄ did not, with inhibition continuing even after removal from treatment. These results support differential function of EDCs and indicate that developmental exposure to 4-OH-A causes sustained inhibition of aromatase, which could be associated with altered adult behaviors.

First evidence on the occurrence and dynamics of Dehalococcoides mccartyi PCB-dechlorinase genes in marine sediment during Aroclor1254 reductive dechlorination

The present study evaluates the PCB-dehalorespiring capabilities and dynamics of indigenous Dehalococcoides mccartyi population in a PCB contaminated marine sediment. Specialized PCB-dechlorinase genes pcbA1, pcbA4 and pcbA5 previously characterized in pure cultures of D. mccartyi, were here found for the first time in environmental samples. Reductive dechlorination was stimulated by spiking Aroclor1254 to the sediment and by imposing strictly anaerobic conditions both with and without bioaugmentation with a Dehalococcoides mccartyi enrichment culture. In line with the contaminant dechlorination kinetics, Dehalococcoides population increased during the entire incubation period showing growth yields of 4.94E+07 Dehalococcoides per μmolCl^-1 and 7.30E+05 Dehalococcoides per μmolCl^-1 in the marine sediment with and without bioaugmentation respectively. The pcbA4 and pcbA5 dechlorinase genes, and to a lesser extent pcbA1 gene, were enriched during the anaerobic incubation suggesting their role in Aroclor1254 dechlorination under salinity conditions.

Induction of oxidative stress and the transcription of genes related to apoptosis in rare minnow (Gobiocypris rarus) larvae with Aroclor 1254 exposure

Polychlorinated biphenyls (PCBs) are a group of environmental contaminants widely dispersed in aquatic system. Recent data have shown that Aroclor 1254 (a highly chlorinated PCB mixture) has the potential to induce oxidative stress. The antioxidant genes are usually up-regulated in response to the oxidative stress. However, the mechanisms underlying the modulation are little known. We hypothesized that nuclear factors erythroid 2-related factor 2 (Nrf2) and nuclear factor-kappa B (NF-κB) might be involved in the regulation. In this study, rare minnow (Gobiocypris rarus) larvae were exposed to the Aroclor 1254 at four concentrations (5, 50, 500 and 5000μg/L) for 7 days. We found that the mRNA expressions of antioxidant genes (Cu/Zn-sod, Mn-sod, Cat, Gpx1 and Gclc) were strongly enhanced by Aroclor 1254 at high concentrations. H2O2 was significantly induced by 500 and 5000μg/L Aroclor 1254 exposure and protein thiol significantly decreased with 5000μg/L Aroclor 1254 exposure. The expression of Nrf2 and NF-κB were significantly up-regulated. Taken together, we proposed that the activation of Nrf2 and NF-κB by ROS might be a potential mechanism underlying the antioxidant gene expression induction in G. rarus larvae by Aroclor 1254. Furthermore, we investigated that the expression of genes related with apoptosis. The gene expression patterns reveal that waterborne Aroclor 1254-induced apoptosis is probably through DNA damage (p53 and p53 upregulated modulator of apoptosis (Puma)), disrupting mitochondrial membrane integrity (B-cell lymphoma 2 (Bcl-2) and Bcl-2-associated X (Bax)) and c-jin N-terminal kinase (JNK)-mediated apoptotic pathway (thioredoxin 1 (Trx1) and c-jun N-terminal kinase (JNK)). Aroclor 1254 at 5μg/L did not cause any changes in G. rarus. The findings will help us to understand the toxicological mechanism of Aroclor 1254 in fish and properly assess the risk of the environmental contaminant.

YY162 prevents ADHD-like behavioral side effects and cytotoxicity induced by Aroclor1254 via interactive signaling between antioxidant potential, BDNF/TrkB, DAT and NET

Methylphenidate (MP) has become the primary drug of choice for treatment of attention-deficit/hyperactivity disorder (ADHD). However, its psychotropic effects severely hamper long-term clinical use. We evaluated the effects of YY162, which consists of terpenoid-strengthened Ginkgo biloba and ginsenoside Rg3, on the ADHD-like condition induced by Aroclor1254, because both components have been suggested to modulate oxidative stress, dopaminergic neurotransmission, and brain-derived neurotrophic factor (BDNF) signaling, which may be critical targets for understanding the pathogenesis of ADHD. YY162 attenuated the increase in reactive oxygen species (ROS) and decrease in BDNF levels induced by Aroclor1254 in SH-SY5Y neuroblastoma cells. YY162 significantly attenuated Aroclor1254-induced ADHD-like behavior and oxidative stress in ICR mice. Furthermore, YY162 attenuated reductions in p-TrkB, BDNF, dopamine transporter (DAT) and norepinephrine transporter (NET) expression. These attenuating effects of YY162 were comparable to those of MP. Importantly, K252a, a TrkB antagonist, counteracted the protective effects of YY162. Our results suggest that YY162 possesses significant protective activities against ADHD-like conditions with negligible behavioral side effects, and that interactive signaling between antioxidant potential and BDNF/TrkB receptor for the positive modulation of the DAT and NET is important for YY162-mediated neuroprotective activity.

Polychlorinated biphenyls impair dibutyryl cAMP-induced astrocytic differentiation in rat C6 glial cell line

In the central nervous system, alteration of glial cell differentiation can affect brain functions. Polychlorinated biphenyls (PCBs) are persistent environmental chemical contaminants that exert neurotoxic effects in glial and neuronal cells. We examined the effects of a commercial mixture of PCBs, Aroclor1254 (A1254) on astrocytic differentiation of glial cells, using the rat C6 cell line as in vitro model. The exposure for 24 h to sub-toxic concentrations of A1254 (3 or 9 μM) impaired dibutyryl cAMP-induced astrocytic differentiation as showed by the decrease of glial fibrillary acidic protein (GFAP) protein levels and inhibition in change of cell morphology toward an astrocytic phenotype. The A1254 inhibition was restored by the addition of a protein kinase C (PKC) inhibitor, bisindolylmaleimide (bis), therefore indicating that PCBs disturbed the cAMP-induced astrocytic differentiation of C6 cells via the PKC pathway. The phosphorylation of signal transducer and activator of transcription 3 (STAT3) is essential for cAMP-induced transcription of GFAP promoter in C6 cells. Our results indicated that the exposure to A1254 (3 or 9 μM) for 24 h suppressed cAMP-induced STAT3 phosphorylation. Moreover, A1254 reduced cAMP-dependent phosphorylation of STAT3 requires inhibition of PKC activity. Together, our results suggest that PCBs induce perturbation in cAMP/PKA and PKC signaling pathway during astrocytic differentiation of glial cells.