Molecular characterization of PXR and two sulfotransferases and hepatic transcripts of PXR, two sulfotransferases and CYP3A responsive to bisphenol A in rare minnow Gobiocypris rarus

Exploring the binding mechanism of positive allosteric modulators in human metabotropic glutamate receptor 2 using molecular dynamics simulations

Positive allosteric modulators (PAMs) of human metabotropic glutamate receptor 2 (hmGlu₂) are well-known in the treatment of psychiatric disorders for their higher selectivity and lower tolerance risk. A variety of PAMs have been reported over the last decade and two compounds were in Phase II clinical trials for schizophrenia and anxiety. These trials were discontinued on account of the unsatisfactory therapeutic efficacy, but PAMs were explored as novel treatments for addiction and epilepsy. Thus, it is still important to explore novel hmGlu₂ PAMs in the near future. Nowadays, the challenges in optimizing drug potency and improving scaffold diversity for PAMs are the noncomprehensive character analyses of multiple scaffolds; the exploration of the binding modes of PAMs in the allosteric binding site have been proposed to reduce this difficulty. However, there has been no comprehensive research about the binding profiles of PAMs in the hmGlu₂ receptor. To address this issue, this work explores the binding characters of eight PAMs representing five chemical series by multiple computational methods. As a result, the shared binding modes of the eight studied PAMs interacting with 15 residues in the allosteric binding site were defined. In addition, the reduced hydrophobicity with low electronegativity of R₁, increased hydrophobicity with low negative electron density of R₂ and the electronegativity of the linker were identified as indicators that regulate the affinity of PAMs. This finding agrees well with the physicochemical properties of reported multiple series PAMs. This comprehensive work sheds additional light on the binding mechanism and physicochemical regularity underlining PAMs affinity and could be further utilized as a structural and energetic blueprint for discovering and assessing novel PAMs for hmGlu₂.

Molecular mechanisms of developmental toxicities of azoxystrobin and pyraclostrobin toward zebrafish (Danio rerio) embryos: Visualization of abnormal development using two transgenic lines

Azoxystrobin (AZ) and pyraclostrobin (PY) are strobilurin fungicides that inhibit fungal mitochondrial respiration. In this study, a representative model, zebrafish (Danio rerio), was used as a test species for acute and developmental toxicity. Survival and malformation rates were observed only PY-treated embryos, with an LC₅₀ value of 77.75 ppb accompanied by a dramatic decrease in hatching rate, while AZ did not show great mortality. Morphological changes were observed in PY-treated embryos with the occurrence of pericadial edema at 25 ppb. A delay in growth was observed after treatment with pyraclostrobin at 50 ppb. Use of genetically engineered Tg(cmlc:EGFP) allowed fluorescence observation during heart development. PY interfered with normal heart development via upregulation of the nppa gene responsible for the expression of natriuretic peptides. Heart function was dramatically reduced as indicated by reduced heart rates. Increased expression of the nppa gene was also seen in AZ-treated embryos. The expression level of cyp24a1 was also up-regulated, while ugt1a1 and sult1st6 were down-regulated after treatment of zebrafish embryos with AZ or PY. Overall, strobilurin fungicides might inhibit normal heart formation and function within the range of concentrations tested.

Acute toxicities of fluorene, fluorene-1-carboxylic acid, and fluorene-9-carboxylic acid on zebrafish embryos (Danio rerio): Molecular mechanisms of developmental toxicities of fluorene-1-carboxylic acid

In this study, fluorene (FL), FL-1-carboxylic acid (FC-1), and FL-9-carboxylic acid (FC-9) were investigated to understand their acute toxicity by measuring inhibitory effects on hatching rates and developmental processes of zebrafish embryos (Danio rerio). For exposure concentrations up to 3000 μg/L, FC-1 alone showed acute toxicity at 1458 μg/L for LC₅₀ value. FC-1 caused yolk sac and spinal deformities, and pericardial edema. Molecular studies were undertaken to understand FC-1 toxicity examining 61 genes after exposure to 5 μM (equivalent to LC₂₀ value of FC-1) in embryos. In the FC-1-treated embryos, the expression of the cyp7a1 gene, involved in bile acid biosynthesis, was dramatically decreased, while the expression of the Il-1β gene involved in inflammation was remarkably increased. In addition to these findings, in FC-1-treated embryos, the expression of nppa gene related to the differentiation of the myocardium was 3-fold increased. On the other hand, cyp1a, cyp3a, ugt1a1, abcc4, mdr1, and sult1st1 responsible for detoxification of xenobiotics were upregulated in FC-9-treated embryos. Taken together, carboxylation on carbon 1 of FL increased acute toxicity in zebrafish embryos, and its toxicity might be related to morphological changes with modification of normal biological functions and lowered defense ability.

Testicular transcriptome alterations in zebrafish (Danio rerio) exposure to 17β-estradiol

The hormone 17β-estradiol (E₂) can be found in rivers, effluents, and even drinking water. Researches have demonstrated that E₂ affects various metabolic pathways through gene activation and may cause reproductive toxicity in fish. Therefore, the aim of this study was to evaluate E₂-induced toxicity via testicular transcriptome of zebrafish (Danio rerio) exposed to different concentrations (10 ng L^-1, and 100 ng L^-1) of E₂. A total of >600 significant differentially expressed genes (DEGs) were enriched among the three treatments. Short time-series expression miner analysis revealed five KEGG pathways including drug metabolism, other enzymes, calcium signaling pathway, ECM-receptor interaction, gap junction, and cell adhesion molecules. Twenty genes were selected to verify the accuracy of RNA-Seq. Other reported genes related to sex differentiation, development, energy metabolism, and other processes were found. One set of genes significantly increased/decreased/fluctuated over time, especially 12 h after E₂ exposure. Genes associated with ovaries (zp3c), and development (bmp15, gdf9, and sycp2l) were significantly upregulated with increasing E₂ concentration. E₂ and testosterone was significantly decreased by 10 (except for T) and 100 ng L^-1 E₂ exposure at 12 h. The current study demonstrated that sex differentiation, development, energy metabolism, immunity, and ribosome biogenesis in male zebrafish were all significantly affected by 17β-estradiol exposure through transcriptional alterations.

Metabolic signatures of bisphenol A and genistein in Atlantic salmon liver cells

Screening has revealed that aquafeeds with high inclusion of plant material may contain small amounts of endocrine disrupting agricultural pesticides. In this work, bisphenol A (BPA) and genistein (GEN) were selected as model endocrine disrupting toxicants with impact on DNA methylation in fish. Atlantic salmon hepatocytes were exposed in vitro to four concentrations of BPA and GEN (0.1, 1.0, 10 and 100 μM) for 48 h. Toxicity endpoints included cytotoxicity, global DNA methylation, targeted transcriptomics and metabolomic screening (100 μM). GEN was not cytotoxic in concentrations up to 100 μM, whereas one out of two cell viability assays indicated a cytotoxic response to 100 μM BPA. Compared to the control, significant global DNA hypomethylation was observed at 1.0 μM BPA. Both compounds upregulated cyp1a1 transcription at 100 μM, while estrogenic markers esr1 and vtg1 responded strongest at 10 μM. Dnmt3aa transcription was downregulated by both compounds at 100 μM. Metabolomic screening showed that BPA and GEN resulted in significant changes in numerous biochemical pathways consistent with alterations in carbohydrate metabolism, indicating perturbation in glucose homeostasis and energy generation, and glutamate metabolism. Pathway analysis showed that while the superpathway of methionine degradation was among the most strongly affected pathways by BPA, GEN induced changes to uridine and pyrimidine biosynthesis. In conclusion, this mechanistic study proposes metabolites associated with glucose and glutamate metabolism, glucuronidation detoxification, as well as cyp1a1, vtg1, esr1, ar, dnmt3aa, cdkn1b and insig1 as transcriptional markers for BPA and GEN exposure in fish liver cells.

Effects of bisphenol A on lipid metabolism in rare minnow Gobiocypris rarus

As one of the most abundant endocrine disrupting compounds (EDCs), bisphenol A (BPA) exists ubiquitously in an aquatic environment. Many studies on fish have focused on the reproductive toxicity effects of BPA. However, few has involved the effects of BPA on lipid metabolism. To evaluate the effects of BPA on lipid metabolism, we determine the hepato-somatic index, triglyceride contents in the liver and serum, the activities of acetyl-CoA carboxylase (ACC), fatty acid synthase (FASN), carnitine palmitoyltransferase (CPT1), and glycerol-3-phosphate acyltransferase (GPAT) enzymes and the mRNA expression of acaca, acacb, fasn, gpat1 and cpt1α in Gobiocypris rarus after exposure to BPA for 28days. BPA induced increasing tendency of triglyceride contents in male fish, possibly due to up-regulated lipid synthesis. Although in this process, fatty acid β-oxidation was up-regulated, it might be compensated by increasing lipogenesis. Our result also revealed that the GPAT enzyme might play a key role in lipid metabolism disturbance by BPA in females. Besides, the effect of BPA on the fatty acid β-oxidation pathway might be gender-dependent in G. rarus. Further studies are needed to investigate BPA's effects on the signaling pathway of lipid metabolism.