Diuron metabolites and urothelial cytotoxicity: in vivo, in vitro and molecular approaches

Diuron and its metabolites induce mitochondrial dysfunction-mediated cytotoxicity in urothelial cells

In the environment, or during mammalian metabolism, the diuron herbicide (3-(3,4-dichlorophenyl)-1,1-dimethylurea) is transformed mainly into 3-(3,4-dichlorophenyl)-1-methylurea (DCPMU) and 3,4-dichloroaniline (DCA). Previous research suggests that such substances are toxic to the urothelium of Wistar rats where, under specific exposure conditions, they may induce urothelial cell degeneration, necrosis, hyperplasia, and eventually tumors. However, the intimate mechanisms of action associated with such chemical toxicity are not fully understood. In this context, the purpose of the current in vitro study was to analyze the underlying mechanisms involved in the urothelial toxicity of those chemicals, addressing cell death and the possible role of mitochondrial dysfunction. Thus, human 1T1 urothelial cells were exposed to six different concentrations of diuron, DCA, and DCPMU, ranging from 0.5 to 500 µM. The results showed that tested chemicals induced oxidative stress and mitochondrial damage, cell cycle instability, and cell death, which were more expressive at the higher concentrations of the metabolites. These data corroborate previous studies from this laboratory and, collectively, suggest mitochondrial dysfunction as an initiating event triggering urothelial cell degeneration and death.

The Silent Threat: Exploring the Ecological and Ecotoxicological Impacts of Chlorinated Aniline Derivatives and the Metabolites on the Aquatic Ecosystem

The growing concern over the environmental impacts of industrial chemicals on aquatic ecosystems has prompted increased attention and regulation. Aromatic amines have drawn scrutiny due to their potential to disturb aquatic ecosystems. 4-chloroaniline and 3,4-dichloroaniline are chlorinated derivatives of aniline used as intermediates in the synthesis of pharmaceuticals, dyes, pesticides, cosmetics, and laboratory chemicals. While industrial applications are crucial, these compounds represent significant risks to aquatic environments. This article aims to shed light on aromatic amines' ecological and ecotoxicological impacts on aquatic ecosystems, given as examples 4-chloroaniline and 3,4-dichloroaniline, highlighting the need for stringent regulation and management to safeguard water resources. Moreover, these compounds are not included in the current Watch List of the Water Framework Directive, though there is already some information about aquatic ecotoxicity, which raises some concerns. This paper primarily focuses on the inherent environmental problem related to the proliferation and persistence of aromatic amines, particularly 4-chloroaniline and 3,4-dichloroaniline, in aquatic ecosystems. Although significant research underscores the hazardous effects of these compounds, the urgency of addressing this issue appears to be underestimated. As such, we underscore the necessity of advancing detection and mitigation efforts and implementing improved regulatory measures to safeguard the water bodies against these potential threats.

N-acetylation of toxic aromatic amines by fungi: Strain screening, cytotoxicity and genotoxicity evaluation, and application in bioremediation of 3,4-dichloroaniline

Aromatic amines (AA) are one of the most commonly used classes of compounds in industry and the most common pollutants found in both soil and water. 3,4-Dichloaniline (3,4-DCA) is a persistent residue of the phenylurea herbicide in the environment. In this study, we used a colorimetric method as a new approach to screen 12 filamentous fungal strains of the genera Aspergillus, Chaetomium, Cladosporium, and Mucor to assess their capacity to perform AA N-acetylation since it is considered a potential tool in environmental bioremediation. Subsequently, the selected strains were biotransformed with different AA substrates to evaluate the product yield. The strains Aspergillus niveus 43, Aspergillus terreus 31, and Cladosporium cladosporioides showed higher efficiencies in the biotransformation of 3,4-DCA at 500 µM into its N-acetylated product. These fungal strains also showed great potential to reduce the phytotoxicity of 3,4-DCA in experiments using Lactuca sativa seeds. Furthermore, N-acetylation was shown to be effective in reducing the cytotoxic and genotoxic effects of 3,4-DCA and other AA in the immortalized human keratinocyte (HaCaT) cell line. The isolated products after biotransformation showed that fungi of the genera Aspergillus and Cladosporium appeared to have N-acetylation as the first and main AA detoxification mechanism. Finally, A. terreus 31 showed the highest 3,4-DCA bioremediation potential, and future research can be carried out on the application of this strain to form microbial consortia with great potential for the elimination of toxic AA from the environment.

Toxic Effects Induced by Diuron and Its Metabolites in Caenorhabditis elegans

The toxicity of diuron herbicide and its metabolites has been extensively investigated; however, their precise toxic mechanisms have yet to be fully appreciated. In this context, we evaluated the toxic mechanism of diuron, 3,4-dichloroaniline (DCA) and 3-(3,4-dichlorophenyl)-1-methylurea (DCPMU), using Caenorhabditis elegans (C. elegans) in the L1 larval stage. For this purpose, worms were acutely exposed to the test chemicals with a preliminary concentration range of 0.5 to 500 μM and first analyzed for lethality (%). Next, the highest concentration (500 μM) was considered for survival (%), reactive oxygen and nitrogen species (RONS), glutathione (GSH) and ATP levels, autophagy index, behavior, and dopaminergic neurodegeneration parameters. Interestingly, increased lethality (%) was found for all chemicals at the higher concentrations tested (100 and 500 μM), with significant differences at 500 μM DCA (p < 0.05). A decrease in the median survival was observed mainly for DCA. Although no changes were observed in RONS production, GSH levels were significantly increased upon diuron and DCA treatment, likely reflecting an attempt to restore the redox status. Moreover, diuron and its metabolites impaired ATP levels, suggesting an alteration in mitochondrial function. The latter may trigger autophagy as an adaptive survival mechanism, but this was not observed in C. elegans. Dopaminergic neurotoxicity was observed upon treatment with all the tested chemicals, but only diuron induced alterations in the worms' locomotor behavior. Combined, these results indicate that exposure to high concentrations of diuron and its metabolites elicit distinct adverse outcomes in C. elegans, and DCA in particular, plays an important role in the overall toxicity observed in this experimental model.

Molecular Responses and Degradation Mechanisms of the Herbicide Diuron in Rice Crops

Diuron [DU; 3-(3,4-dichlorophenyl)-1,1-dimethylurea], a widely used herbicide for weed control, arouses ecological and health risks due to its environment persistence. Our findings revealed that DU at 0.125-2.0 mg L^-1 caused oxidative damage to rice. RNA-sequencing profiles disclosed a globally genetic expression landscape of rice under DU treatment. DU mediated downregulated gene encoding photosynthesis and biosynthesis of protein, fatty acid, and carbohydrate. Conversely, it induced the upregulation of numerous genes involved in xenobiotic metabolism, detoxification, and anti-oxidation. Furthermore, 15 DU metabolites produced by metabolic genes were identified, 7 of which include two Phase I-based and 5 Phase II-based derivatives, were reported for the first time. The changes of resistance-related phytohormones, like JA, ABA, and SA, in terms of their contents and molecular-regulated signaling pathways positively responded to DU stress. Our work provides a molecular-scale perspective on the response of rice to DU toxicity and clarifies the biotransformation and degradation fate of DU in rice crops.

Aryl hydrocarbon receptor agonist diuron and its metabolites cause reproductive disorders in male marine medaka (Oryzias melastigma)

Diuron, a widely used phenylurea herbicide, has been frequently detected in marine organism and seawater all over the world. But the understanding of potential damage of diuron on reproduction in marine fish is currently not enough. Herein, marine medaka (Oryzias melastigma) were continuously exposed to 0, 5, 50, 500, and 5000 ng/L diuron from embryo (0 dpf) to adult (180 dpf) stage. The results suggested that diuron had an adverse influence on male reproduction for marine medaka, including decreased gonado somatic index, histological changes of testes, decreased mobility of sperm, and reduced fecundity through disrupting the balance of sex hormone and genes expression related to hypothalamus-pituitary-gonadal-liver (HPGL) axis. The reduced fecundity was reflected in abnormal sexual behaviors, further inhibited growth and development of F1 embryo and larvae. Moreover, the proportion of diuron metabolites (DCPMU and DCPU) was increased in fish, but the proportion of diuron was decreased with the increasing of exposure concentration. Diuron, DCPMU, and DCPU was identified as aryl hydrocarbon receptor agonist (AhR) agonist using in silico and in vivo models. DCPMU and DCPU induced the gene expression of AhR signaling and metabolizing enzymes (such as cyp1a1) in the livers. A great deal of major metabolites affected various organs related to HPGL axis of male marine medaka and led to serious reproductive disorders. Consequently, it reveals that long-term exposure to environmentally relevant concentrations of diuron and even AhR agonist pesticides pose a potential ecological risk for marine fish.

Molecular signatures associated with diuron exposure on rat urothelial mitochondria

Diuron, 3- (3,4-dichlorophenyl)-1,1-dimethylurea, is a worldwide used herbicide whose biotransformation gives rise to the metabolites, 3-(3,4-dichlorophenyl)-1-methylurea (DCPMU) and 3,4-dichloroaniline (DCA). Previous studies indicate that diuron and/or its metabolites are toxic to the bladder urothelium of the Wistar rats where, under certain conditions of exposure, they may induce successively urothelial cell degeneration, necrosis, hyperplasia and eventually tumors. The hypothesis was raised that the molecular initiating event (MIE) of this Adverse Outcome Pathway (AOP) is the mitochondrial toxicity of those compounds. Therefore, this study aimed to investigate in vitro the metabolic alterations resulting from urothelial mitochondria isolated from male Wistar rats exposure to diuron, DCPMU and DCA at 10 and 100 µM. A non-targeted metabolomic analysis using mass spectrometry showed discriminative clustering among groups and alterations in the intensity abundance of membrane-associated molecules phosphatidylcholine (PC), phosphatidylinositol (PI) and phosphatidylserine (PS), in addition to methylhexanoyl-CoA and, particularly for diuron 100 µM, dehydro-L-gulonate, all of them involved in critical mitochondrial metabolism. Collectively, these data indicate the mitochondrial dysfunction as a MIE that triggers cellular damage and death observed in previous studies.

Emerging Strategies for the Bioremediation of the Phenylurea Herbicide Diuron

Diuron (DUR) is a phenylurea herbicide widely used for the effective control of most annual and perennial weeds in farming areas. The extensive use of DUR has led to its widespread presence in soil, sediment, and aquatic environments, which poses a threat to non-target crops, animals, humans, and ecosystems. Therefore, the removal of DUR from contaminated environments has been a hot topic for researchers in recent decades. Bioremediation seldom leaves harmful intermediate metabolites and is emerging as the most effective and eco-friendly strategy for removing DUR from the environment. Microorganisms, such as bacteria, fungi, and actinomycetes, can use DUR as their sole source of carbon. Some of them have been isolated, including organisms from the bacterial genera Arthrobacter, Bacillus, Vagococcus, Burkholderia, Micrococcus, Stenotrophomonas, and Pseudomonas and fungal genera Aspergillus, Pycnoporus, Pluteus, Trametes, Neurospora, Cunninghamella, and Mortierella. A number of studies have investigated the toxicity and fate of DUR, its degradation pathways and metabolites, and DUR-degrading hydrolases and related genes. However, few reviews have focused on the microbial degradation and biochemical mechanisms of DUR. The common microbial degradation pathway for DUR is via transformation to 3,4-dichloroaniline, which is then metabolized through two different metabolic pathways: dehalogenation and hydroxylation, the products of which are further degraded via cooperative metabolism. Microbial degradation hydrolases, including PuhA, PuhB, LibA, HylA, Phh, Mhh, and LahB, provide new knowledge about the underlying pathways governing DUR metabolism. The present review summarizes the state-of-the-art knowledge regarding (1) the environmental occurrence and toxicity of DUR, (2) newly isolated and identified DUR-degrading microbes and their enzymes/genes, and (3) the bioremediation of DUR in soil and water environments. This review further updates the recent knowledge on bioremediation strategies with a focus on the metabolic pathways and molecular mechanisms involved in the bioremediation of DUR.

Embryonic toxicity of 3,4-dichloroaniline (3,4-DCA) on Javanese medaka (Oryzias javanicus Bleeker, 1854)

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The 96 h LC₅₀ of 3,4-dichloroaniline in Javanese medaka embryo is 32.87 mg.L⁻¹.

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3,4-DCA lowers heart rate of developing Javanese medaka embryos.

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The sublethal concentration of 3,4-DCA delays hatching in Javanese medaka embryo.

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The LOEC for deformities in embryos of Javanese medaka was 0.5 mg.L⁻¹.

Early-life exposure to toxic chemicals causes irreversible morphological and physiological abnormalities that may last for a lifetime. The present study aimed to determine the toxicity effect of 3,4-Dichloroaniline (3,4-DCA) on Javanese medaka (Oryzias javanicus) embryos. Healthy embryos were exposed to various 3,4-DCA concentrations for acute toxicity (5, 10, 25, 50, and 100 mg.L⁻¹) and sublethal toxicity (0.10, 0.50, 1.25, 2.50, and 5.00 mg.L⁻¹) for 96 h and 20 days respectively. Acute toxicity test revealed that the median lethal concentration (96h-LC₅₀) was 32.87 mg.L⁻¹ (95 % CI = 27.90–38.74, R² = 0.95). Sublethal exposure revealed that 1.25 mg.L^-1 at 3 days post-exposure (3 dpe) has a significant lower heartrate (120 ± 12.3 beats/min., p < 0.01), while at 7 dpe those exposed to 5 mg.L⁻¹ (141.8 ± 8.3 beats/min) had significantly (p < 0.01) lower heart rate compared to other treatments. Likewise, at 13 dpe, 5.00 mg.L⁻¹ (110.4 ± 17.3 beats/min) and 2.5 mg.L^-1 (130.4 ± 8.3 beats/min) were significantly lower (p < 0.001) compared to control. None of the embryos in 5.00 mg.L⁻¹ and 2.50 mg.L^-1 treatment groups survived at the end of the experiment. The results indicated a concentration-dependent response. The lowest observed effect concentration (LOEC) that exerted developmental deformities was 0.5 mg.L⁻¹. Javanese medaka embryo have low sensitivity to acute toxicity of 3,4-DCA, but developmental abnormalities at sublethal concentrations were observed.

Toxicity of diuron metabolites in human cells

Diuron, a highly used herbicide worldwide, is metabolized into several toxic metabolites. DCA (3,4-dichloroaniline), DCPU [3-(3, 4-dichlorophenyl)urea] and DCPMU [3-(3,4-dichlorophenyl)-1-methyl urea] reduced viability of human placental choriocarcinoma BeWo, human breast adenocarcinoma MCF-7 and human colon adenocarcinoma Caco-2 cells as judged by the MTT assay, where color formation is dependent on functional mitochondria in viable cells. Based on the IC₅₀ values in BeWo cells the order of cytotoxicity was DCA > DCPU > diuron > DCPMU, and in Caco-2 cells DCPMU > DCPU > DCA, diuron. In MCF-7 cells, only DCPU had an IC₅₀ within the range of the concentrations used. In the PI-digitonin viability assay, only the highest concentration (200 μM) of DCPU caused a statistically significant decrease in viability in any cell line. There was no correlation between cytotoxicity and ROS production. This indicates that diuron metabolites are toxic in cells of human origin with mitochondria as the target, but ROS not the likely mechanism.

Cytotoxicity of organic and inorganic compounds to primary cell cultures established from internal tissues of Chelonia mydas

Chemical contaminants have been found in the tissues of sea turtles from all over the world; however, very little is known about the effects. Recently, in vitro alternatives to live animal testing have been applied to sea turtles due to their ethical and practical benefits. While primary skin fibroblasts have been established for several species of sea turtle, cells from internal organs are lacking, though they may be more relevant due to the well documented accumulation of contaminants within internal tissues. This study established primary cell cultures from the small intestine, heart, liver, ovary and skin of green turtles (Chelonia mydas). Cells were exposed to ten contaminants typically found in sea turtles to examine potential variations in sensitivity among cells established from different organs. Differences between cells established from different animals were also examined, including a comparison of cells established from a turtle with fibropapillomatosis (FP) and healthy turtles. Loggerhead (Caretta caretta) primary skin cells were also included for species comparisons. Significant differences were found between the organ types, with liver and heart being the least sensitive, and skin being the most sensitive. Overall, variation between the organ types was low. Primary skin fibroblasts may be a suitable and representative cell type for in vitro turtle toxicology research, as it is relatively easy to obtain from healthy live animals. Skin cultures provide a more sensitive indication of effect, and could be used as an early warning of the potential effects of chemical contamination. Some species differences were found but no differences were found between cell cultures from an FP turtle and healthy turtles. When EC₅₀ values were compared to accumulation values from the literature, inorganic contaminants, such as Zn, Cd, Cr, Hg, and Cu were identified as posing a potential risk to sea turtle populations around the world.

Transplacental transfer and metabolism of diuron in human placenta

Diuron is a broad-spectrum phenylurea derived herbicide which is commonly used across the globe. Diuron is toxic to the reproductive system of animals and carcinogenic to rat urothelium, and recently found to be genotoxic in human cells. In in vivo, it is metabolized predominately into 3-(3,4-dichlorophenyl)-1-methyl urea (DCPMU) in humans and 3-(3, 4-dichlorophenyl)urea (DCPU) in animals. Information on diuron toxicokinetics and related toxicity in human placenta is absent. We have investigated the toxicokinetics of diuron in ex vivo human placental perfusion and in in vitro human placental microsomes and human trophoblastic cancer cells (BeWo). Diuron crossed human placenta readily in placental perfusion. Furthermore, diuron was metabolized into DCPMU in perfused placenta and in in vitro incubations using microsomes from placentas of smokers. In incubations with placental microsomes from non-smokers, and in BeWo cells, metabolism to DCPMU was detected but only with the highest used diuron concentration (100 μM). Diuron metabolism was inhibited upon addition of α-naphthoflavone, a CYP1A1 inhibitor, underscoring the role of CYP1A1 in the metabolism. In conclusion, it is evident that diuron crosses human placenta and diuron can be metabolized in the placenta to a toxic metabolite via CYP1A1. This implicates in vivo fetal exposure to diuron if pregnant women are exposed to diuron, which may result in fetotoxicity.

Influence of Temperature on the Thyroidogenic Effects of Diuron and Its Metabolite 3,4-DCA in Tadpoles of the American Bullfrog (Lithobates catesbeianus)

Temperature is a key variable affecting the timing of amphibian metamorphosis from tadpoles to tetrapods, through the production and subsequent function of thyroid hormones (TH). Thyroid function can be impaired by environmental contaminants as well as temperature. Tadpoles can experience large temperature fluctuations in their habitats and many species are distributed in areas that may be impacted by agriculture. Diuron is a widely used herbicide detected in freshwater ecosystems and may impact endocrine function in aquatic organisms. We evaluated the influence of temperature (28 and 34 °C) on the action of diuron and its metabolite 3,4-dichloroaniline (3,4-DCA) on thyroid function and metamorphosis in tadpoles of Lithobates catesbeianus. Exposure to both compounds induced more pronounced changes in gene expression and plasma 3,3',5-triiodothyronine (T₃) concentrations in tadpoles treated at higher temperature. T₃ concentrations were increased in tadpoles exposed to 200 ng/L of diuron at 34 °C and an acceleration of metamorphosis was observed for the same group. Transcriptomic responses included alteration of thyroid hormone induced bZip protein (thibz), deiodinases (dio2, dio3), thyroid receptors (trα, trβ) and Krüppel-like factor 9 (klf9), suggesting regulation by temperature on TH-gene expression. These results suggest that environmental temperature should be considered in risk assessments of environmental contaminants for amphibian species.

Estrogenic activities of diuron metabolites in female Nile tilapia (Oreochromis niloticus)

Some endocrine disrupting chemicals (EDCs) can alter the estrogenic activities of the organism by directly interacting with estrogen receptors (ER) or indirectly through the hypothalamus-pituitary-gonadal axis. Recent studies in male Nile tilapia (Oreochromis niloticus) indicated that diuron may have anti-androgenic activity augmented by biotransformation. In this study, the effects of diuron and three of its metabolites were evaluated in female tilapia. Sexually mature female fish were exposed for 25 days to diuron, as well as to its metabolites 3,4-dichloroaniline (DCA), 3,4-dichlorophenylurea (DCPU) and 3,4-dichlorophenyl-N-methylurea (DCPMU), at concentrations of 100 ng/L. Diuron metabolites caused increases in E2 plasma levels, gonadosomatic indices and in the percentage of final vitellogenic oocytes. Moreover, diuron and its metabolites caused a decrease in germinative cells. Significant differences in plasma concentrations of the estrogen precursor and gonadal regulator17α-hydroxyprogesterone (17α-OHP) were not observed. These results show that diuron metabolites had estrogenic effects potentially mediated through enhanced estradiol biosynthesis and accelerated the ovarian development of O. niloticus females.

Anti-androgenic activities of diuron and its metabolites in male Nile tilapia (Oreochromis niloticus)

Diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea) is a widely used herbicide which has been frequently detected in surface waters throughout the world. In vivo bioassay guided fractionation studies indicated that diuron may have estrogenic activity augmented by biotransformation. This study evaluated the effects of diuron and three of its metabolites on plasma hormone concentrations and spermatogenesis of the freshwater fish Nile tilapia (Oreochromis niloticus). Sexually mature male fish were exposed for 25 days to diuron, as well to its metabolites 3,4-dichloroaniline (DCA), 3,4-dichlorophenylurea (DCPU) and 3,4-dichlorophenyl-N-methylurea (DCPMU), at concentrations of 200ng/L. Testosterone levels were decreased by diuron, but had limited effects on gonadal histology. Diuron metabolites, however, caused significant decreases in testosterone and in 11-ketotestosterone, gonadosomatic index, diameter of seminiferous tubules and in the mean percentages of germ cells (spermatids and spermatozoa). We conclude that these metabolites have antiandrogenic activity to male Nile tilapia, potentially causing reproductive impairment in male fish.