Interaction of diuron and related substituted phenylureas with the Ah receptor pathway

Direct additive-free N-formylation and N-acylation of anilines and synthesis of urea derivatives using green, efficient, and reusable deep eutectic solvent ([ChCl][ZnCl2]2)

In the current report, we introduce a simple, mild efficient and green protocol for N-formylation and N-acetylation of anilines using formamide, formic acid, and acetic acid as inexpensive, nontoxic, and easily available starting materials just with heating along stirring in [ChCl][ZnCl2]2 as a durable, reusable deep eutectic solvent (DES), which acts as a dual catalyst and solvent system to produce a wide range of formanilides and acetanilides. Also, a variety of unsymmetrical urea derivatives were synthesized by the reaction of phenyl isocyanate with a range of amine compounds using this benign DES in high to excellent yields. [ChCl][ZnCl2]2 showed good recycling and reusability up to four runs without considerable loss of its catalytic activity.

Co-occurrence of antiseptic triclocarban and chiral anti-inflammatory ibuprofen in environment: Association between biological effect in sediment and risk to human health

Residues of antiseptics and drugs have been ubiquitously detected in aquatic water-sediment systems, and are thus considered emerging contaminants that threaten our global environment. To investigate the potential risk of ibuprofen and triclocarban in sediment, effects of enzyme activity on the enantioselective degradation in sediment were investigated. Enantioselective fate of rac-ibuprofen was observed in sediment with R-enantiomer exhibiting preferential degradation. Enzyme evidence showed that high levels of triclocarban could significantly inhibit activities of catalase and urease activities in sediment, as well as increase the half-life of ibuprofen (from 5.8 d to 10.1 d). Cytotoxicity data suggested that cell growth processes were significantly affected by ibuprofen and triclocarban co-exposure, which was consistent with apoptosis results. Additionally, the expression of several proteins (Cyto-c, Nrf2, p62, Keap1, NQO1, and Pink1) were markedly induced upon exposure to ibuprofen in the presence of triclocarban. In conclusion, these findings illustrated that co-occurrence of ibuprofen and triclocarban residues have synergistic adverse effects to the environment and synergistically threaten human health.

Sub-lethal toxicity assessment of the phenylurea herbicide linuron in developing zebrafish (Danio rerio) embryo/larvae

Due to run-off and rain events, agrochemicals can enter water catchments, exerting endocrine disruption effects and toxicity to aquatic organisms. Linuron is a phenylurea herbicide used to control a wide variety of vegetative weeds in agriculture in addition to residential applications. However, there are few studies that quantify its toxicity to early developmental stages of fish. The objectives of this study were to assess the acute toxicity of linuron to zebrafish embryos/larvae by measuring mortality, morphological deformities, oxidative respiration, gene expression, and locomotor activity via the Visual Motor Response test. Zebrafish embryos at ~6-h post-fertilization (hpf) were exposed to either embryo rearing medium (ERM), or one dose of 0.625, 1.25, 2.5, 5, and 10 μM linuron for up to 7 days post-fertilization (dpf) depending on the assay. Zebrafish larvae exposed to linuron displayed pericardial edema, yolk sac edema, and spinal curvature. Oxidative respiration assessments in embryos using the Agilent XF^e24 Flux Analyzer revealed that linuron decreased mean basal respiration and oligomycin-induced ATP-linked respiration in 30 hpf embryos at 20 μM after a 24-hour exposure. In 7 dpf larvae, transcript abundance was determined for 6 transcripts that have a role in oxidative respiration (atp06, cox1, cox4-1, cox5a1, cytb, and nd1); the relative abundance of these transcripts was not altered with linuron treatment. A Visual Motor Response test was conducted on 7 dpf larvae to determine whether linuron (0.625 to 5 μM) impaired locomotor activity. Larval activity in the dark period decreased in a dose dependent manner and there were indications of hypoactivity as low as 1.25 μM. Transcript abundance was thus determined for tyrosine hydroxylase (th1) and glutamic acid decarboxylase 67 (gad1b), two rate limiting enzymes that control the production of dopamine and gamma-aminobutyric acid respectively. The mRNA levels of gad1b (p = 0.019) were reduced with increasing concentrations of linuron while th1 (p = 0.056) showed a similar decreasing trend, suggesting that neurotransmitter biosynthesis may be altered with exposure to linuron. This study improves knowledge related to the toxicity mechanisms for linuron and is the first to demonstrate that this anti-androgenic chemical impairs oxidative respiration and exerts neurotoxic effects associated with neurotransmitter biosynthesis during early development. These data are significant for environmental risk assessment of agrochemicals.

Map and model-moving from observation to prediction in toxicogenomics

BACKGROUND

Chemicals induce compound-specific changes in the transcriptome of an organism (toxicogenomic fingerprints). This provides potential insights about the cellular or physiological responses to chemical exposure and adverse effects, which is needed in assessment of chemical-related hazards or environmental health. In this regard, comparison or connection of different experiments becomes important when interpreting toxicogenomic experiments. Owing to lack of capturing response dynamics, comparability is often limited. In this study, we aim to overcome these constraints.

RESULTS

We developed an experimental design and bioinformatic analysis strategy to infer time- and concentration-resolved toxicogenomic fingerprints. We projected the fingerprints to a universal coordinate system (toxicogenomic universe) based on a self-organizing map of toxicogenomic data retrieved from public databases. Genes clustering together in regions of the map indicate functional relation due to co-expression under chemical exposure. To allow for quantitative description and extrapolation of the gene expression responses we developed a time- and concentration-dependent regression model. We applied the analysis strategy in a microarray case study exposing zebrafish embryos to 3 selected model compounds including 2 cyclooxygenase inhibitors. After identification of key responses in the transcriptome we could compare and characterize their association to developmental, toxicokinetic, and toxicodynamic processes using the parameter estimates for affected gene clusters. Furthermore, we discuss an association of toxicogenomic effects with measured internal concentrations.

CONCLUSIONS

The design and analysis pipeline described here could serve as a blueprint for creating comparable toxicogenomic fingerprints of chemicals. It integrates, aggregates, and models time- and concentration-resolved toxicogenomic data.

Isolated and mixed effects of diuron and its metabolites on biotransformation enzymes and oxidative stress response of Nile tilapia (Oreochromis niloticus)

Diuron is one of the most used herbicide in the world, and its field application has been particularly increased in Brazil due to the expansion of sugarcane crops. Diuron has often been detected in freshwater ecosystems and it can be biodegraded into three main metabolites in the environment, the 3,4-dichloroaniline (DCA), 3,4-dichlorophenylurea (DCPU) and 3,4-dichlorophenyl-N-methylurea (DCPMU). Negative effects under aquatic biota are still not well established for diuron, especially when considering its presence in mixture with its different metabolites. In this study, we evaluated the effects of diuron alone or in combination with its metabolites, DCPMU, DCPU and 3,4-DCA on biochemical stress responses and biotransformation activity of the fish Oreochromis niloticus. Results showed that diuron and its metabolites caused significant but dispersed alterations in oxidative stress markers and biotransformation enzymes, except for ethoxyresorufin-O-deethylase (EROD) activity, that presented a dose-dependent increase after exposure to either diuron or its metabolites. Glutathione S-transferase (GST) activity was significant lower in gills after exposure to diuron metabolites, but not diuron. Diuron, DCPMU and DCA also decreased the multixenobiotic resistance (MXR) activity. Lipid peroxidation levels were increased in gill after exposure to all compounds, indicating that the original compound and diuron metabolites can induce oxidative stress in fish. The integration of all biochemical responses by the Integrated Biomarker Response (IBR) model indicated that all compounds caused significant alterations in O. niloticus, but DCPMU caused the higher alterations in both liver and gill. Our findings imply that diuron and its metabolites may impair the physiological response related to biotransformation and antioxidant activity in fish at field concentrations. Such alterations could interfere with the ability of aquatic animals to adapt to environments contaminated by agriculture.

Development of Species-Specific Ah Receptor-Responsive Third Generation CALUX Cell Lines with Enhanced Responsiveness and Improved Detection Limits

The Ah receptor (AhR)-responsive CALUX (chemically activated luciferase expression) cell bioassay is commonly used for rapid screening of samples for the presence of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin), dioxin-like compounds, and AhR agonists/antagonists. By increasing the number of AhR DNA recognition sites (dioxin responsive elements), we previously generated a novel third generation (G3) recombinant AhR-responsive mouse CALUX cell line (H1L7.5c3) with a significantly enhanced response to DLCs compared to existing AhR-CALUX cell bioassays. However, the elevated background luciferase activity of these cells and the absence of comparable G3 cell lines derived from other species have limited their utility for screening purposes. Here, we describe the development and characterization of species-specific G3 recombinant AhR-responsive CALUX cell lines (rat, human, and guinea pig) that exhibit significantly improved limit of detection and dramatically increased TCDD induction response. The low background luciferase activity, low minimal detection limit (0.1 pM TCDD) and enhanced induction response of the rat G3 cell line (H4L7.5c2) over the H1L7.5c3 mouse G3 cells, identifies them as a more optimal cell line for screening purposes. The utility of the new G3 CALUX cell lines were demonstrated by screening sediment extracts and a small chemical compound library for the presence of AhR agonists. The improved limit of detection and increased response of these new G3 CALUX cell lines will facilitate species-specific analysis of DLCs and AhR agonists in samples with low levels of contamination and/or in small sample volumes.

Nrf2 upregulates ATP binding cassette transporter expression and activity at the blood-brain and blood-spinal cord barriers

Activation of nuclear factor E2-related factor-2 (Nrf2), a sensor of oxidative stress, is neuroprotective in animal models of cerebral ischemia, traumatic brain injury, subarachnoid hemorrhage, and spinal cord injury. We show here that Nrf2 activation with sulforaphane (SFN) in vivo or in vitro increases expression and transport activity of three ATP-driven drug efflux pumps at the blood-brain barrier [P-glycoprotein, ATP binding cassette b1 (Abcb1); multidrug resistance-associated protein-2 (Mrp2), Abcc2; and breast cancer resistance protein (Bcrp), Abcg2]. Dosing rats with SFN increased protein expression of all three transporters in brain capillaries and decreased by 50% brain accumulation of the P-glycoprotein substrate verapamil. Exposing rat or mouse brain capillaries to SFN increased P-glycoprotein, Bcrp, and Mrp2 transport activity and protein expression; SFN increased P-glycoprotein activity in mouse spinal cord capillaries. Inhibiting transcription or translation abolished upregulation of P-glycoprotein activity. No such effects were seen in brain capillaries from Nrf2-null mice, indicating Nrf2 dependence. Nrf2 signaled indirectly to increase transporter activity/expression. The p53 inhibitor pifithrin abolished the SFN-induced increase in transporter activity/expression, and the p53-activator nutlin-3 increased P-glycoprotein activity. SFN did not alter P-glycoprotein transport activity in brain and spinal cord capillaries from p53-null mice. Inhibitors of p38 MAPK and nuclear factor κB (NF-κB) blocked the effects of SFN and nutlin-3 on P-glycoprotein activity. These results implicate Nrf2, p53, and NF-κB in the upregulation of P-glycoprotein, Bcrp, and Mrp2 at blood-CNS barriers. They imply that the barriers are tightened selectively (efflux transporter upregulation) by oxidative stress, providing increased neuroprotection, but also reduced penetration of many therapeutic drugs.

Early life triclocarban exposure during lactation affects neonate rat survival

Triclocarban (3,4,4'-trichlorocarbanilide; TCC), an antimicrobial used in bar soaps, affects endocrine function in vitro and in vivo. This study investigates whether TCC exposure during early life affects the trajectory of fetal and/or neonatal development. Sprague Dawley rats were provided control, 0.2% weight/weight (w/w), or 0.5% w/w TCC-supplemented chow through a series of 3 experiments that limited exposure to critical growth periods: gestation, gestation and lactation, or lactation only (cross-fostering) to determine the susceptible windows of exposure for developmental consequences. Reduced offspring survival occurred when offspring were exposed to TCC at concentrations of 0.2% w/w and 0.5% w/w during lactation, in which only 13% of offspring raised by 0.2% w/w TCC dams survived beyond weaning and no offspring raised by 0.5% w/w TCC dams survived to this period. In utero exposure status had no effect on survival, as all pups nursed by control dams survived regardless of their in utero exposure status. Microscopic evaluation of dam mammary tissue revealed involution to be a secondary outcome of TCC exposure rather than a primary effect of compound administration. The average concentration of TCC in the milk was almost 4 times that of the corresponding maternal serum levels. The results demonstrate that gestational TCC exposure does not affect the ability of dams to carry offspring to term but TCC exposure during lactation has adverse consequences on the survival of offspring although the mechanism of reduced survival is currently unknown. This information highlights the importance of evaluating the safety of TCC application in personal care products and the impacts during early life exposure.

Common commercial and consumer products contain activators of the aryl hydrocarbon (dioxin) receptor

Activation of the Ah receptor (AhR) by halogenated aromatic hydrocarbons (HAHs), such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin), can produce a wide variety of toxic and biological effects. While recent studies have shown that the AhR can bind and be activated by structurally diverse chemicals, how widespread of these AhR agonists are in environmental, biological and synthetic materials remains to be determined. Using AhR-based assays, we demonstrate the presence of potent AhR agonists in a variety of common commercial and consumer items. Solvent extracts of paper, rubber and plastic products contain chemicals that can bind to and stimulate AhR DNA binding and/or AhR-dependent gene expression in hepatic cytosol, cultured cell lines, human epidermis and zebrafish embryos. In contrast to TCDD and other persistent dioxin-like HAHs, activation of AhR-dependent gene expression by these extracts was transient, suggesting that the agonists are metabolically labile. Solvent extracts of rubber products produce AhR-dependent developmental toxicity in zebrafish in vivo, and inhibition of expression of the metabolic enzyme CYP1A, significantly increased their toxic potency. Although the identity of the responsible AhR-active chemicals and their toxicological impact remain to be determined, our data demonstrate that AhR active chemicals are widely distributed in everyday products.

Should autism be considered a canary bird telling that Homo sapiens may be on its way to extinction?

There has been a dramatic enhancement of the reported incidence of autism in different parts of the world over the last 30 years. This can apparently not be explained only as a result of improved diagnosis and reporting, but may also reflect a real change. The causes of this change are unknown, but if we shall follow T.C. Chamberlin's principle of multiple working hypotheses, we need to take into consideration the possibility that it partly may reflect an enhancement of the average frequency of responsible alleles in large populations. If this hypothesis is correct, it means that the average germline mutation rate must now be much higher in the populations concerned, compared with the natural mutation rate in hominid ancestors before the agricultural and industrial revolutions. This is compatible with the high prevalence of impaired human semen quality in several countries and also with what is known about high levels of total exposure to several different unnatural chemical mutagens, plus some natural ones at unnaturally high levels. Moreover, dietary deficiency conditions that may lead to enhancement of mutation rates are also very widespread, affecting billions of people. However, the natural mutation rate in hominids has been found to be so high that there is apparently no tolerance for further enhancement of the germline mutation rate before the Eigen error threshold will be exceeded and our species will go extinct because of mutational meltdown. This threat, if real, should be considered far more serious than any disease causing the death only of individual patients. It should therefore be considered the first and highest priority of the best biomedical scientists in the world, of research-funding agencies and of all medical doctors to try to stop the express train carrying all humankind as passengers on board before it arrives at the end station of our civilization.

Ecotoxicological effects of diuron and chlorotoluron nitrate-induced photodegradation products: monospecific and aquatic mesocosm-integrated studies

The ecotoxicological impact of nitrate-induced photodegradation products of diuron and chlorotoluron was studied through monospecific biotests conducted in conjunction with experiments in outdoor aquatic mesocosms. Organisms representing three trophic levels were used: two heterotrophic microorganisms, the luminescent bacterium Vibrio fischeri and the ciliated protozoa Tetrahymena pyriformis, and one metazoa, the gastropod Lymnaea stagnalis. Among the variety of the phenylurea photoproducts, the N-formylated ones appeared clearly more toxic than the parent compounds towards the microorganisms, whereas the nitroderivatives showed a similar toxicity. Using photodegraded solutions of diuron, toxicity was maintained or even increased during disappearance of the initial herbicide, demonstrating that some of the photoproducts may have an impact additively or in synergy. Enzymatic biomarker assays performed on Lymnaea stagnalis exposed under monospecific conditions showed significant effects, due to the combination of nitrate with the pesticide and its photoproducts. A positive impact on snail fecundity was observed with chlorotoluron both under monospecific laboratory and integrated mesocosm conditions. Oviposition stimulation took place when first- and second-generation photoproducts were predominant.

In vitro screening for aryl hydrocarbon receptor agonistic activity in 200 pesticides using a highly sensitive reporter cell line, DR-EcoScreen cells, and in vivo mouse liver cytochrome P450-1A induction by propanil, diuron and linuron

The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that regulates genes involved in xenobiotic metabolism, cellular proliferation and differentiation. In this study, we have developed a highly sensitive AhR-mediated reporter cell line, DR-EcoScreen cells, which are mouse hepatoma Hepa1c1c7 cells stably transfected with a reporter plasmid containing seven copies of dioxin-responsive element. Using these DR-EcoScreen cells, we performed the reporter gene assay and characterized the AhR agonistic activities of 200 pesticides (29 organochlorines, 11 diphenyl ethers, 56 organophosphorus pesticides, 12 pyrethroids, 22 carbamates, 12 acid amides, 7 triazines, 6 ureas, and 45 others). Eleven of the 200 pesticides (acifluorfen-methyl, bifenox, chlorpyrifos, isoxathion, quinalphos, chlorpropham, diethofencarb, propanil, diuron, linuron, and prochloraz) showed AhR-mediated transcriptional activity. In particular, three herbicides (propanil, diuron, and linuron) have a common chemical structure and showed more potent agonistic activity than other pesticides. To investigate the in vivo effects, we examined the gene expression of AhR-inducible cytochrome P450 1As (CYP1As) in the liver of female C57BL/6 mice intraperitoneally injected with these three herbicides (300 mg kg(-1)) by quantitative RT-PCR, resulting in induction of significant high levels of CYP1A1 and CYP1A2 mRNAs. This indicates that propanil, diuron and linuron possess AhR-mediated transactivation effect in vivo as well as in vitro. Through the present study, we demonstrated that DR-EcoScreen cells are useful for sensitive, rapid and simple identification of AhR agonists among a large number of environmental chemicals.

In vitro biologic activities of the antimicrobials triclocarban, its analogs, and triclosan in bioassay screens: receptor-based bioassay screens

BACKGROUND

Concerns have been raised about the biological and toxicologic effects of the antimicrobials triclocarban (TCC) and triclosan (TCS) in personal care products. Few studies have evaluated their biological activities in mammalian cells to assess their potential for adverse effects.

OBJECTIVES

In this study, we assessed the activity of TCC, its analogs, and TCS in in vitro nuclear-receptor-responsive and calcium signaling bioassays.

MATERIALS AND METHODS

We determined the biological activities of the compounds in in vitro, cell-based, and nuclear-receptor-responsive bioassays for receptors for aryl hydrocarbon (AhR), estrogen (ER), androgen (AR), and ryanodine (RyR1).

RESULTS

Some carbanilide compounds, including TCC (1-10 muM), enhanced estradiol (E(2))-dependent or testosterone-dependent activation of ER- and AR-responsive gene expression up to 2.5-fold but exhibited little or no agonistic activity alone. Some carbanilides and TCS exhibited weak agonistic and/or antagonistic activity in the AhR-responsive bioassay. TCS exhibited antagonistic activity in both ER- and AR-responsive bioassays. TCS (0.1-10 muM) significantly enhanced the binding of [(3)H]ryanodine to RyR1 and caused elevation of resting cytosolic [Ca(2+)] in primary skeletal myotubes, but carbanilides had no effect.

CONCLUSIONS

Carbanilides, including TCC, enhanced hormone-dependent induction of ER- and AR-dependent gene expression but had little agonist activity, suggesting a new mechanism of action of endocrine-disrupting compounds. TCS, structurally similar to noncoplanar ortho-substituted poly-chlorinated biphenyls, exhibited weak AhR activity but interacted with RyR1 and stimulated Ca(2+) mobilization. These observations have potential implications for human and animal health. Further investigations are needed into the biological and toxicologic effects of TCC, its analogs, and TCS.

Fate of triclosan and evidence for reductive dechlorination of triclocarban in estuarine sediments

The biocides triclosan and triclocarban are wastewater contaminants whose occurrence and fate in estuarine sediments remain unexplored. We examined contaminant profiles in 137Cs/7Be-dated sediment cores taken near wastewater treatment plants in the Chesapeake Bay watershed (CB), Maryland and Jamaica Bay(JB), New York. In JB, biocide occurrences tracked the time course of biocide usage and wastewater treatment strategies employed, first appearing in the 1950s (triclocarban) and 1960s (triclosan), and peaking in the late 1960s and 1970s (24 +/- 0.54 and 0.8 +/- 0.4 mg/kg dry weight, respectively). In CB, where the time of sediment accumulation was not as well constrained by 137Cs depth profiles, triclocarban was only measurable in 137Cs-bearing sediments, peaking at 3.6 +/- 0.6 mg/ kg midway through the core and exceeding 1 mg/kg in recent deposits. In contrast, triclosan concentrations were low or not detectable in the CB core. Analysis of CB sediment by tandem mass spectrometry produced the first evidence for complete sequential dechlorination of triclocarban to the transformation products dichloro-, monochloro-, and unsubstituted carbanilide, which were detected at maxima of 15.5 +/- 1.8, 4.1 +/- 2.4, and 0.5 +/- 0.1 mg/kg, respectively. Concentrations of all carbanilide congeners combined were correlated with heavy metals (R2 > 0.64, P < 0.01), thereby identifying wastewater as the principal pathway of contamination. Environmental persistence over the past 40 years was observed for triclosan and triclocarban in JB, and for triclocarban's diphenylurea backbone in CB sediments.