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.

Activities of metabolizing enzymes in human placenta.

In addition to the transfer across the placenta, placenta displays hormonal and xenobiotic metabolism, as well as enzymatic defense against oxidative stress. We analyzed aromatase (CYP19A1), uridine 5'-diphospho-glucuronyltransferase (UGT), glutathione-S-transferase (GST) and catalase (CAT) activities in over 70 placentas from nonsmokers stored at -80 °C from former perfusion studies. A wide interindividual variation in all activities was found. Longterm storage at -80 °C did not affect the activities. Ethoxyresorufin-O-deethylase (EROD, CYP1A1) was not detected in any of the studied placentas perfused with chemicals. Several compounds in placental perfusion changed statistically significantly the enzyme activities in placental tissue. Melamine and nicotine increased CYP19A1, melamine increased UGT and GST, PhIP with ethanol decreased CYP19A1 and increased GST, and PhIP with buprenorphine decreased CAT. Antipyrine in 100 µg/ml also changed the studied enzyme activities, but not statistically significantly. Because antipyrine is a reference compound in placental perfusions, its potential effects must be taken into account in human placental perfusion. Enzyme activities deserve further studies as biomarkers of placental toxicity. Finally, enzyme activities deserve further studies as biomarkers of placental toxicity.

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.