Assessment of the Acute Toxicity, Uptake and Biotransformation Potential of Benzotriazoles in Zebrafish (<i>Danio rerio</i>) Larvae Combining HILIC- with RPLC-HRMS for High-Throughput Identification

The current study reports on the toxicity, uptake, and biotransformation potential of zebrafish (embryos and larvae) exposed to benzotriazoles (BTs). Acute toxicity assays were conducted. Cardiac function abnormalities (pericardial edema and poor blood circulation) were observed from the phenotypic analysis of early life zebrafish embryos after BTs exposure. For the uptake and biotransformation experiment, extracts of whole body larvae were analyzed using liquid chromatography–high-resolution tandem mass spectrometry (UPLC-Q-TOF-HRMS/MS). The utility of hydrophilic interaction liquid chromatography (HILIC) as complementary technique to reversed phase liquid chromatography (RPLC) in the identification process was investigated. Through HILIC analyses, additional biotransformation products (bio-TPs) were detected, because of the enhanced sensitivity and better separation efficiency of isomers. Therefore, reduction of false negative results was accomplished. Both oxidative (hydroxylation) and conjugative (glucuronidation, sulfation) metabolic reactions were observed, while direct sulfation proved the dominant biotransformation pathway. Overall, 26 bio-TPs were identified through suspect and nontarget screening workflows, 22 of them reported for the first time. 4-Methyl-1-<i>H</i>-benzotriazole (4-MeBT) demonstrated the highest toxicity potential and was more extensively biotransformed, compared to 1-<i>H</i>-benzotriazole (BT) and 5-methyl-1-<i>H</i>-benzotriazole (5-MeBT). The extent of biotransformation proved particularly informative in the current study, to explain and better understand the different toxicity potentials of BTs

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<p>Zebrafish has emerged as a powerful model organism for high throughput drug screening. Several morphological criteria, transgenic lines and in situ expression screens have been developed to identify novel bioactive compounds and their mechanism of action. Here, we used the inhibition of melanogenesis during early zebrafish embryo development to identify natural compounds that block melanogenesis. We identified an extract from the Greek hawthorn Crataegus pycnoloba as a potent inhibitor of melanin synthesis and used activity based subfractionation to identify active subfractions and eventually three single compounds of the same family (dibenzofurans). These compounds show reversible inhibition of melanin synthesis and do not act via inhibition of tyrosinase. We also showed that they do not interfere with neural crest differentiation or migration. We identified via in silico modeling that the compounds can bind to the aryl hydrocarbon receptor (AHR) and verified activation of the Ahr signaling pathway showing the induction of the expression of target genes.</p

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<p>Zebrafish has emerged as a powerful model organism for high throughput drug screening. Several morphological criteria, transgenic lines and in situ expression screens have been developed to identify novel bioactive compounds and their mechanism of action. Here, we used the inhibition of melanogenesis during early zebrafish embryo development to identify natural compounds that block melanogenesis. We identified an extract from the Greek hawthorn Crataegus pycnoloba as a potent inhibitor of melanin synthesis and used activity based subfractionation to identify active subfractions and eventually three single compounds of the same family (dibenzofurans). These compounds show reversible inhibition of melanin synthesis and do not act via inhibition of tyrosinase. We also showed that they do not interfere with neural crest differentiation or migration. We identified via in silico modeling that the compounds can bind to the aryl hydrocarbon receptor (AHR) and verified activation of the Ahr signaling pathway showing the induction of the expression of target genes.</p

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<p>Zebrafish has emerged as a powerful model organism for high throughput drug screening. Several morphological criteria, transgenic lines and in situ expression screens have been developed to identify novel bioactive compounds and their mechanism of action. Here, we used the inhibition of melanogenesis during early zebrafish embryo development to identify natural compounds that block melanogenesis. We identified an extract from the Greek hawthorn Crataegus pycnoloba as a potent inhibitor of melanin synthesis and used activity based subfractionation to identify active subfractions and eventually three single compounds of the same family (dibenzofurans). These compounds show reversible inhibition of melanin synthesis and do not act via inhibition of tyrosinase. We also showed that they do not interfere with neural crest differentiation or migration. We identified via in silico modeling that the compounds can bind to the aryl hydrocarbon receptor (AHR) and verified activation of the Ahr signaling pathway showing the induction of the expression of target genes.</p

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<p>Zebrafish has emerged as a powerful model organism for high throughput drug screening. Several morphological criteria, transgenic lines and in situ expression screens have been developed to identify novel bioactive compounds and their mechanism of action. Here, we used the inhibition of melanogenesis during early zebrafish embryo development to identify natural compounds that block melanogenesis. We identified an extract from the Greek hawthorn Crataegus pycnoloba as a potent inhibitor of melanin synthesis and used activity based subfractionation to identify active subfractions and eventually three single compounds of the same family (dibenzofurans). These compounds show reversible inhibition of melanin synthesis and do not act via inhibition of tyrosinase. We also showed that they do not interfere with neural crest differentiation or migration. We identified via in silico modeling that the compounds can bind to the aryl hydrocarbon receptor (AHR) and verified activation of the Ahr signaling pathway showing the induction of the expression of target genes.</p

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<p>Zebrafish has emerged as a powerful model organism for high throughput drug screening. Several morphological criteria, transgenic lines and in situ expression screens have been developed to identify novel bioactive compounds and their mechanism of action. Here, we used the inhibition of melanogenesis during early zebrafish embryo development to identify natural compounds that block melanogenesis. We identified an extract from the Greek hawthorn Crataegus pycnoloba as a potent inhibitor of melanin synthesis and used activity based subfractionation to identify active subfractions and eventually three single compounds of the same family (dibenzofurans). These compounds show reversible inhibition of melanin synthesis and do not act via inhibition of tyrosinase. We also showed that they do not interfere with neural crest differentiation or migration. We identified via in silico modeling that the compounds can bind to the aryl hydrocarbon receptor (AHR) and verified activation of the Ahr signaling pathway showing the induction of the expression of target genes.</p

The “topology screen” assay.

<p>(<b>A</b>) Expression constructs. <i>hr3</i> enhancer, baculoviral (BmNPV) homologous region 3 enhancer sequence; pActin, <i>Bombyx mori</i> A3 cytoplasmic actin promoter; MCS, multiple cloning site; actin pA, 3′untranslated region of <i>B. mori</i> actin gene containing polyadenylation signals; Flag, epitope tag; OR; Odorant or opioid receptor ORF; THE, Tobacco etch virus protease recognition site; HR3, <i>Bombyx mori</i> hormone receptor 3. (<b>B</b>) Hypothetical model illustrating possible location of HR3 in both fusion constructs, with respect to the OR orientation (GPCR or not) in the membrane. RORE-bA, response element for retinoic acid receptor-related orphan receptor/basal actin promoter.</p

Co-localization of odorant receptors expressed in lepidopteran insect cells.

<p>(<b>A</b>) Expression constructs for N-terminally (mycOR1, mycOR2) or C-terminally tagged receptors (OR1myc) were transfected in Bm5 cells (in the absence/presence of OR7) and the localization of the expressed ORs was detected using anti-Myc antibody. Control indicates transfection with empty expression vector. (<b>B</b>) Co-localization of OR2 with the plasma membrane marker wheat germ agglutinin. Cells expressing OR2myc were double stained with WGA-Texas Red-X conjugate (b, e, f) and with anti-myc antibody (a, d, g) in the presence or absence of saponin (a-f and g-i, respectively). (<b>C</b>) Detection of ORs in the membrane fraction of stable cell lines coexpressing mycOR1 (lane 2) or mycOR2 (lane 3) along with flagOR7. Immunoblotting was performed with anti-Myc and anti-Flag antibodies (upper and lower panels, respectively). Membranes from Bm5 untransfected cells were used as a negative control (lane 1). (<b>D</b>) Co-localization of OR1 or OR2 with OR7. Bm5 cells were co-transfected with expression plasmids for N-terminally tagged mycOR1 or mycOR2 together with N-terminally tagged flagOR7 expression vector. Tagged ORs were detected with anti-Myc/anti-mouse fluorescein-labelled IgG and anti-Flag/anti-rabbit Alexa fluor-labelled IgG as indicated and counter-stained with DAPI. (<b>E</b>) Pull-down assays showing heteromerization between OR1 and OR7 or OR2 and OR7. Extracts containing C-terminally Myc-His-tagged OR7 were incubated with Ni²⁺-NTA beads and bound protein complexes were analyzed by Western blot by anti-Flag antibody (upper panel) for the presence of N-terminally Flag-tagged OR1 and OR2 or by anti-Myc antibody (lower panel) to detect OR7mychis.</p

Flow cytometric analysis of expression of Myc-tagged OR2 on the surface of Bm5 cells.

<p>(<b>A</b>) N- or (<b>B</b>) C-terminally Myc-tagged OR2 were stably expressed in Bm5 cells in the presence of flagOR7 and analyzed by FACS for the extracellular localization of the Myc tag. For each panel, the green tracing and number represent fluorescence values obtained from the staining of the cells with only the FITC labelled secondary antibodies, while the red tracing and number represent values obtained from cells incubated with both the primary anti-Myc and the FITC labelled secondary antibodies. Increased fluorescence intensity (2.59-fold over the background value) was observed for the C-terminally Myc-tagged receptor in comparison to the receptor that was Myc-tagged at the N-terminal end (1.43-fold over the background value). (<b>C</b>) Values (increases over background) indicated in this panel represent the mean ± S.E.M. of three independent experiments. (<b>D</b>) Western blot analyses of whole cell lysates from the stable cell lines used for FACS analysis and control, mock-transformed cells, probed with anti-Myc (upper) and anti- tubulin (lower) antibodies. (<b>E</b>) FACS analysis of cells expressing the N-terminally Myc-tagged µ-opioid receptor used as a positive control for the extracellular localization of the Myc tag. Green and red tracing/numbers are as in panels A and B. Inset shows the detection of µOR in these cells by western blotting with the anti-myc antibody. The arrowhead and the arrow point to major bands detected (putative monomer and dimer, respectively), while the positions of 50, 90 and 118-kDa molecular mass markers are indicated at left.</p

List of oligonucleotides used in PCR. Restriction sites are underlined; initiation and termination codons are in bold and italics, respectively.

<p>List of oligonucleotides used in PCR. Restriction sites are underlined; initiation and termination codons are in bold and italics, respectively.</p