In vitro metabolism of chlorotriazines: characterization of simazine, atrazine, and propazine metabolism using liver microsomes from rats treated with various cytochrome P450 inducers

Pharmacokinetics of the Recalcitrant Drug Lamotrigine: Identification and Distribution of Metabolites in Cucumber Plants

Treated wastewater is an important source of water for irrigation. As a result, irrigated crops are chronically exposed to wastewater-derived pharmaceuticals, such as the anticonvulsant drug lamotrigine. Lamotrigine is known to be taken up by plants, but its plant-derived metabolites and their distribution in different plant organs are unknown. This study aimed to detect and identify metabolites of lamotrigine in cucumber plants grown for 35 days in a hydroponic solution by using LC-MS/MS (Orbitrap) analysis. Our data showed that 96% of the lamotrigine taken up was metabolized. Sixteen metabolites possessing a lamotrigine core structure were detected. Reference standards confirmed two; five were tentatively identified, and nine molecular formulas were assigned. The data suggest that lamotrigine is metabolized via N-carbamylation, N-glucosidation, N-alkylation, N-formylation, N-oxidation, and amidine hydrolysis. The metabolites LTG-N2-oxide, M284, M312, and M370 were most likely produced in the roots and were translocated to the leaves. Metabolites M272, M312, M314, M354, M368, M370, and M418 were dominant in leaves. Only a few metabolites were detected in the fruits. With an increasing exposure time, lamotrigine leaf concentrations decreased because of continuous metabolism. Our data showed that the metabolism of lamotrigine in a plant is fast and that a majority of metabolites are concentrated in the roots and leaves.

Using in vitro derived enzymatic reaction rates of metabolism to inform pesticide body burdens in amphibians

Understanding how pesticide exposure to non-target species influences toxicity is necessary to accurately assess the ecological risks these compounds pose. To assess the potential metabolic activation of broad use pesticides in amphibians, in vitro and in vivo metabolic rate constants were derived from toad (Anaxyrus terrestris) livers in experiments measuring the depletion of atrazine (ATZ), triadimefon (TDN), and fipronil (FIP) as well as formation of their metabolites. To determine the predictability of these in vitro derived rate constants, Fowler's toads (Anaxyrus fowleri) were exposed to soil contaminated with each of the pesticides at maximum application rate. Desethyl atrazine (DEA) and deisopropyl atrazine (DIA), both metabolites of ATZ, exhibited similar velocities (V_max) while the K_M constant for DIA was two times higher than DEA. TDN was metabolized into two diastereomers of triadimenol (TDL A and TDL B), where TDL B had a V_max around two times higher than TDL A. The metabolite fipronil sulfone's V_max and K_M were 150 pmol min^-1 mg^-1 and 29 μM, respectively. While intrinsic clearance rates for the pesticides ranged from 0.54 to 38.31 mL min^-1 kg^-1. Thus, gaining knowledge on differences in metabolism of pesticides within amphibians is important in estimating risk to these non-target species since the inherent toxicity of metabolites can differ from the parent compound.

Changes in hepatic phase I and phase II biotransformation enzyme expression and glutathione levels following atrazine exposure in female rats

1. To determine the effects of repeated atrazine (ATR) treatment on hepatic phase I and II enzymes, adult female rats were treated with vehicle or 100 mg/kg of ATR for 1, 2, 3 or 4 days. Glutathione-s-transferases (GST) mRNA expression, protein levels (mu, pi, alpha, omega), and activity (cytosolic and microsomal), along with bioavailable glutathione (GSH) were assayed. 2. GST expression, concentrations and activity were increased, along with GSH levels, in animals treated with ATR for 3 and 4 days. 3. A subsequent study was performed with animals treated with vehicle, 6.5, 50 or 100 mg/kg/day for 4, 8 or 14 days. Expression of hepatic phase I CYP 450 enzymes was evaluated in conjugation with GST expression, protein and activity. Nineteen of the 45 CYP enzymes assayed displayed increased mRNA levels after eight days of treatment in animals treated with 50 or 100 mg/kg/day. After 14 days of treatment, all CYP expression levels returned to control levels except for CYP2B2, CYP2B3, CYP2C7, CYP2C23, CYP2E1, CYP3A9, CYP4A3 and CYP27A1, which remained elevated. 4. Results indicate that there may be a habituation or adaptation of liver phase I and phase II expression following repeated ATR treatment.

Atrazine and its main metabolites alter the locomotor activity of larval zebrafish (Danio rerio)

Atrazine (ATZ) and its main chlorometabolites, i.e., diaminochlorotriazine (DACT), deisopropylatrazine (DIP), and deethylatrazine (DE), have been widely detected in aquatic systems near agricultural fields. However, their possible effects on aquatic animals are still not fully understood. In this study, it was observed that several developmental endpoints such as the heart beat, hatchability, and morphological abnormalities were influenced by ATZ and its metabolites in different developmental stages. In addition, after 5 days of exposure to 30, 100, 300 μg L(-1) ATZ and its main chlorometabolites, the swimming behaviors of larval zebrafish were significantly disturbed, and the acetylcholinesterase (AChE) activities were consistently inhibited. Our results also demonstrate that ATZ and its main chlorometabolites are neuroendocrine disruptors that impact the expression of neurotoxicity-related genes such as Ache, Gap43, Gfap, Syn2a, Shha, Mbp, Elavl3, Nestin and Ngn1 in early developmental stages of zebrafish. According to our results, it is possible that not only ATZ but also its metabolites (DACT, DIP and DE) have the same or even more toxic effects on different endpoints of the early developmental stages of zebrafish.

Atrazine biodegradation efficiency, metabolite detection, and trzD gene expression by enrichment bacterial cultures from agricultural soil

Atrazine is a selective herbicide used in agricultural fields to control the emergence of broadleaf and grassy weeds. The persistence of this herbicide is influenced by the metabolic action of habituated native microorganisms. This study provides information on the occurrence of atrazine mineralizing bacterial strains with faster metabolizing ability. The enrichment cultures were tested for the biodegradation of atrazine by high-performance liquid chromatography (HPLC) and mass spectrometry. Nine cultures JS01.Deg01 to JS09.Deg01 were identified as the degrader of atrazine in the enrichment culture. The three isolates JS04.Deg01, JS07.Deg01, and JS08.Deg01 were identified as efficient atrazine metabolizers. Isolates JS04.Deg01 and JS07.Deg01 produced hydroxyatrazine (HA) N-isopropylammelide and cyanuric acid by dealkylation reaction. The isolate JS08.Deg01 generated deethylatrazine (DEA), deisopropylatrazine (DIA), and cyanuric acid by N-dealkylation in the upper degradation pathway and later it incorporated cyanuric acid in their biomass by the lower degradation pathway. The optimum pH for degrading atrazine by JS08.Deg01 was 7.0 and 16S rDNA phylogenetic typing identified it as Enterobacter cloacae strain JS08.Deg01. The highest atrazine mineralization was observed in case of isolate JS08.Deg01, where an ample amount of trzD mRNA was quantified at 72 h of incubation with atrazine. Atrazine bioremediating isolate E. cloacae strain JS08.Deg01 could be the better environmental remediator of agricultural soils and the crop fields contaminated with atrazine could be the source of the efficient biodegrading microbial strains for the environmental cleanup process.

Endocrine disruption caused by oral administration of atrazine in European quail (Coturnix coturnix coturnix)

The widely used herbicide atrazine (ATZ) has been reported to exhibit reproductive toxicity in rats, fish and amphibians, with an avian LD(50) of 5000 mg/kg. In the present work, ATZ was administered as a single oral dose of 25 or 100 mg/kg to female European quail (Coturnix coturnix coturnix) at days 0, 5 and 10 of the experiment, being the animals sampled at days 15, 30 and 45. ATZ significantly increased the expression of hepatic estrogen receptor α (ERα) at both doses at day 30. An important increase was also observed in plasma 17β-estradiol (E2) concentrations. ATZ at 100 mg/kg increased the circulating concentration of vitellogenin (Vtg), but this effect was not related with an increase in hepatic Vtg mRNA levels. ATZ had no effect on the hepatic expression of both cytochrome P450 1A4 (CYP1A4) or the related biotransformation activity ethoxyresorufin-O-deethylase (EROD). These results led to the conclusion that ATZ provokes an estrogenic effect in sexually mature females of European quail. Further studies are necessary to establish the effect on sexual development or reproduction of female and male birds in the wild.

In-vitro metabolism of glycyrrhetinic acid by human and rat liver microsomes and its interactions with six CYP substrates

Objectives

Glycyrrhetinic acid is the main metabolite of glycyrrhizin and the main active component of Licorice root. This study was designed to investigate the in-vitro metabolism of glycyrrhetinic acid by liver microsomes and to examine possible metabolic interactions that glycyrrhetinic acid may have with other cytochrome P450 (CYP) substrates.

Methods

Glycyrrhetinic acid was incubated with rat liver microsomes (RLM) and human liver microsomes (HLM). Liquid chromatography tandem mass spectrometry was used for glycyrrhetinic acid or substrates identification and quantification.

Key findings

The Km and Vmax values for HLM are 33.41 µm and 2.23 nmol/mg protein/min, respectively; for RLM the Km and Vmax were 24.24 µm and 6.86 nmol/mg protein/min, respectively. CYP3A4 is likely to be the major enzyme responsible for glycyrrhetinic acid metabolism in HLM while CYP2C9 and CYP2C19 are considerably less active. Other human CYP isoforms have minimal or no activity toward glycyrrhetinic acid. The interactions of glycyrrhetinic acid and six CYP substrates, such as phenacetin, diclofenac, (S)-mephenytoin, dextromethorphan, chlorzoxazone and midazolam were also investigated. The inhibitory action of glycyrrhetinic acid was observed in CYP2C9 for 4-hydroxylation of diclofenac, CYP2C19 for 4′-hydroxylation of (S)-mephenytoin and CYP3A4 for 1′-hydroxylation of midazolam with half maximal inhibitory concentration (IC50) values of 4.3-fold, 3.8-fold and 9.6-fold higher than specific inhibitors in HLM, respectively. However, glycyrrhetinic acid showed relatively little inhibitory effect (IC50 > 400 µm) on phenacetin O-deethylation, dextromethorphan O-demethylation and chlorzoxazone 6-hydroxylation.

Conclusions

The study indicated that CYP3A4 is likely to be the major enzyme responsible for glycyrrhetinic acid metabolism in HLM while CYP2C9 and CYP2C19 are considerably less active. The results suggest that glycyrrhetinic acid has the potential to interact with a wide range of xenobiotics or endogenous chemicals that are CYP2C9, CYP2C19 and CYP3A4 substrates.

Effects of long-term exposure to simazine in real concentrations on common carp (Cyprinus carpio L.)

The effects of a 90 day simazine exposure at concentrations of 0.06 (reported concentration in Czech rivers), 1, 2, and 4 μg L⁻¹ were assessed in one-year-old common carp (Cyprinus carpio L.). Its influence on biometric parameters, hematology, blood biochemistry, liver biomarkers, and histology was investigated. Biometric parameters of common carp exposed to simazine at 0.06 μg L⁻¹ showed no differences from untreated fish. Simazine concentrations of 1, 2, and 4 μg L⁻¹ caused significant (p<0.01) increase of hepatosomatic indices relative to controls. Hematological profiles showed significant (p<0.01) decrease in leukocyte count relative to controls at all concentrations. Biochemical profiles of common carp exposed to simazine at all concentrations showed significant (p<0.01) increase in activity of alkaline phosphatase. In addition, at concentrations of 1 and 2 μg L⁻¹, there was a significant increase in alanine aminotransferase (p<0.05), and, at 4 μg L⁻¹, a significant increase in total protein (p<0.05), albumins (p<0.05), and alanine aminotransferase (p<0.05) compared with controls. Renal histology revealed severe hyaline degeneration of the epithelial cells of caudal kidney tubules in fish at all exposure levels compared to controls. Chronic exposure of common carp to simazine caused significant shifts in hematological, biochemical, and biometric profiles, and histopathological changes. The results of this study indicate that chronic exposure of simazine has altered multiple physiological indices in fish hematology and biochemistry, which potentially may be a biomarker of simazine toxicity; however, before these parameters are used as special biomarkers for monitoring residual simazine in aquatic environment, more detailed experiments in laboratory need to be performed in the future.

Metabolism of xenobiotics of human environments

Xenobiotics have been defined as chemicals to which an organism is exposed that are extrinsic to the normal metabolism of that organism. Without metabolism, many xenobiotics would reach toxic concentrations. Most metabolic activity inside the cell requires energy, cofactors, and enzymes in order to occur. Xenobiotic-metabolizing enzymes can be divided into phase I, phase II, and transporter enzymes. Lipophilic xenobiotics are often first metabolized by phase I enzymes, which function to make xenobiotics more polar and provide sites for conjugation reactions. Phase II enzymes are conjugating enzymes and can directly interact with xenobiotics but more commonly interact with metabolites produced by phase I enzymes. Through both passive and active transport, these more polar metabolites are eliminated. Most xenobiotics are cleared through multiple enzymes and pathways. The relationship between chemical concentrations, enzyme affinity and quantity, and cofactor availability often determine which metabolic reactions dominate in a given individual.

A physiologically based pharmacokinetic model for atrazine and its main metabolites in the adult male C57BL/6 mouse

Atrazine (ATR) is a chlorotriazine herbicide that is widely used and relatively persistent in the environment. In laboratory rodents, excessive exposure to ATR is detrimental to the reproductive, immune, and nervous systems. To better understand the toxicokinetics of ATR and to fill the need for a mouse model, a physiologically based pharmacokinetic (PBPK) model for ATR and its main chlorotriazine metabolites (Cl-TRIs) desethyl atrazine (DE), desisopropyl atrazine (DIP), and didealkyl atrazine (DACT) was developed for the adult male C57BL/6 mouse. Taking advantage of all relevant and recently made available mouse-specific data, a flow-limited PBPK model was constructed. The ATR and DACT sub-models included blood, brain, liver, kidney, richly and slowly perfused tissue compartments, as well as plasma protein binding and red blood cell binding, whereas the DE and DIP sub-models were constructed as simple five-compartment models. The model adequately simulated plasma levels of ATR and Cl-TRIs and urinary dosimetry of Cl-TRIs at four single oral dose levels (250, 125, 25, and 5mg/kg). Additionally, the model adequately described the dose dependency of brain and liver ATR and DACT concentrations. Cumulative urinary DACT amounts were accurately predicted across a wide dose range, suggesting the model's potential use for extrapolation to human exposures by performing reverse dosimetry. The model was validated using previously reported data for plasma ATR and DACT in mice and rats. Overall, besides being the first mouse PBPK model for ATR and its Cl-TRIs, this model, by analogy, provides insights into tissue dosimetry for rats. The model could be used in tissue dosimetry prediction and as an aid in the exposure assessment to this widely used herbicide.

Oxidative stress induced by atrazine in rat erythrocytes: mitigating effect of vitamin E

The present study investigates the propensity of atrazine to induce oxidative stress and its possible attenuation by vitamin E in rat erythrocytes, which is a convenient model to understand the oxidative damage induced by various xenobiotics. Experimental animals were administered atrazine (300 mg/kg body weight, daily) and/or vitamin E (100 mg/kg body weight, daily) orally for a period of 7, 14, and 21 days. Results indicated that the reduced glutathione (GSH) content of the erythrocytes of atrazine treated rats was significantly decreased as compared to the control group. Co-administration of vitamin E along with atrazine restored the GSH content of erythrocytes nearly to control levels. The activities of antioxidant enzymes such as superoxide dismutase, catalase, glutathione peroxidase, and glutathione-s-transferase were found to be increased significantly in the erythrocytes accompanied by a decrease in the activity of the glucose-6-phosophate dehydrogenase, following atrazine exposure. On the other hand, when vitamin E was co-administered along with atrazine, activities of these enzymes were found to be restored significantly. In conclusion, results of the study demonstrated that atrazine induced oxidative stress in rat erythrocytes, in terms of increased activities of the various antioxidant enzymes, and decreased content of reduced glutathione. However, vitamin E administration ameliorated the effects of atrazine, suggesting that vitamin E is a potential antioxidant against atrazine-induced oxidative stress.

Disposition of the herbicide 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (Atrazine) and its major metabolites in mice: a liquid chromatography/mass spectrometry analysis of urine, plasma, and tissue levels

2-Chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine, ATR) is a toxicologically important and widely used herbicide. Recent studies have shown that it can elicit neurological, immunological, developmental, and biochemical alterations in several model organisms, including in mice. Because disposition data in mice are lacking, we evaluated ATR's metabolism and tissue dosimetry after single oral exposures (5-250 mg/kg) in C57BL/6 mice using liquid chromatography/mass spectrometry (Ross and Filipov, 2006). ATR was metabolized and cleared rapidly; didealkyl ATR (DACT) was the major metabolite detected in urine, plasma, and tissues. Plasma ATR peaked at 1 h postdosing and rapidly declined, whereas DACT peaked at 2 h and slowly declined. Most ATR and metabolite residues were excreted within the first 24 h. However, substantial amounts of DACT were still present in 25- to 48-h and 49- to 72-h urine. ATR reached maximal brain levels (0.06-1.5 microM) at 4 h (5-125 mg/kg) and 1 h (250 mg/kg) after dosing, but levels quickly declined to <0.1 microM by 12 h in all the groups. In contrast, strikingly high concentrations of DACT (1.5-50 microM), which are comparable with liver DACT levels, were detectable in brain at 2 h. Brain DACT levels slowly declined, paralleling the kinetics of plasma DACT. Our findings suggest that in mice ATR is widely distributed and extensively metabolized and that DACT is a major metabolite detected in the brain at high levels and is ultimately excreted in urine. Our study provides a starting point for the establishment of models that link target tissue dose to biological effects caused by ATR and its in vivo metabolites.

Styrene monomer primarily induces CYP2B1 mRNA in rat liver

To determine the cytochrome P450 (CYP) primarily expressed after styrene exposure, seven forms of hepatic CYP mRNA in rats treated with 600 mg kg(-1) styrene were examined. CYP1A2, CYP2B1/2, CYP2E1 and CYP3A2 mRNA were observed using real-time LightCycler PCR. The amount of CYP2B1 mRNA was significantly increased, 47-fold compared with controls, suggesting that this CYP is the primary cytochrome P450 in rats exposed to styrene. Significant increases in the amount of CYP2E1, CYP1A2 and CYP2B2 mRNA were also observed after styrene exposure, and their increase levels were 3.1-, 1.7- and 1.7-fold higher than controls, respectively. Western blot analysis also indicated that the protein levels of CYP2B1, CYP2B2, CYP2E1 and CYP1A2 showed clear increases after styrene treatment, corresponding to their mRNA expression. CYP2C11 mRNA decreased significantly in rats after styrene exposure. CYP1A1 was detected at the mRNA level in rat liver, but it was not detected at the protein level. The expression of epoxide hydrolase (EH), involved in Phase I drug metabolism, was also examined. EH mRNA increased 2-fold compared with controls after styrene exposure. Styrene thus appears to be a chemical compound that induces multiple CYPs. The results demonstrate that CYP2B1 is the primarily induced CYP form by styrene treatment to rats at acute toxic level.

Metabolic conversion of dietary quercetin from its conjugate to active aglycone following the induction of hepatocarcinogenesis in fisher 344 rats

Quercetin exhibits a potent anticarcinogenic activity. However, ingested quercetin circulates as the glucuronide/sulfate conjugates, which are less active compared to the aglycone in healthy individuals. This study aimed to develop further understandings of the cancer-preventing mechanism with dietary quercetin. According to a two-stage hepatocarcinogenesis model with N-diethylnitrosamine (DEN) and phenobarbital (PB), preneoplasms were induced specifically in the liver of Fisher 344 rats. In the liver, glutathione S-transferase placental form (GST-P) positive foci were produced 14 weeks later. beta-Glucuronidase activity increased significantly in the liver by 1.2-fold in the DEN/PB group compared to the activity in a saline group. In the kidney, thymus, lung, heart, and plasma, the activities were similar between both groups. When quercetin was dosed intragastrically 15 min before sacrifice, the aglycone level of quercetin in liver was significantly 1.9-fold higher in the DEN/PB group than in the saline group. On the other hand, quercetin was dosed to rats 3 times a week for 14 weeks. The treatment kept the aglycone level of quercetin at a significantly higher level and tended to suppress the formation of GST-P positive foci. The increase in beta-glucuronidase activity with carcinogenesis induction became insignificant following the frequent doses of quercetin. It was considered that quercetin aglycone played a preventative role and, thus, the conjugates were converted to the active aglycone by beta-glucuronidase that was induced by the generation of preneoplasms.

Oral absorption and oxidative metabolism of atrazine in rats evaluated by physiological modeling approaches

Atrazine (ATRA) is metabolized by cytochrome P450s to the chlorinated metabolites, 2-chloro-4-ethylamino-6-amino-1,3,5-triazine (ETHYL), 2-chloro-4-amino-6-isopropylamino-1, 3, 5-triazine (ISO), and diaminochlorotriazine (DACT). Here, we develop a set of physiologically based pharmacokinetic (PBPK) models that describe the influence of oral absorption and oxidative metabolism on the blood time course curves of individual chlorotriazines (Cl-TRIs) in rat after oral dosing of ATRA. These models first incorporated in vitro metabolic parameters to describe time course plasma concentrations of DACT, ETHYL, and ISO after dosing with each compound. Parameters from each individual model were linked together into a final composite model in order to describe the time course of all 4 Cl-TRIs after ATRA dosing. Oral administration of ISO, ETHYL and ATRA produced double peaks of the compounds in plasma time courses that were described by multiple absorption phases from gut. An adequate description of the uptake and bioavailability of absorbed ATRA also required inclusion of additional oxidative metabolic clearance of ATRA to the mono-dealkylated metabolites occurring in GI a tract compartment. These complex processes regulating tissue dosimetry of atrazine and its chlorinated metabolites likely reflect limited compound solubility in the gut from dosing with an emulsion, and sequential absorption and metabolism along the GI tract at these high oral doses.

Estimating constants for metabolism of atrazine in freshly isolated rat hepatocytes by kinetic modeling

This study estimated the kinetic constants for oxidative metabolism of atrazine (ATRA) and its chlorotriazine (Cl-TRI) metabolites, 2-chloro-4-ethylamino-6-amino-1,3,5-triazine (ETHYL), 2-chloro-4-amino-6-isopropylamino-1,3,5-triazine (ISO), and diaminochlorotriazine (DACT), using freshly isolated rat hepatocytes. Hepatocytes were incubated with 1.74, 44, 98, and 266 microM ATRA. Disappearance of ATRA and formation of the Cl-TRI metabolites were quantified over 90 min. At all incubation concentrations, ATRA was preferentially metabolized to ETHYL, producing ETHYL concentrations approximately 6 times higher than those of ISO. DACT concentrations peaked at 44 microM ATRA and decreased with increasing incubation concentrations, indicating non-linear metabolic behavior of ATRA with respect to DACT formation. A series of kinetic models were developed from these data to describe the dose and time-dependent oxidative metabolism of ATRA and the Cl-TRI metabolites. An integrated model for all the chloro-triazines included multi-substrate competitive inhibition of metabolism to describe the non-linear behavior of DACT production in relation to ATRA while simultaneously simulating the time-course behavior of the Cl-TRIs at all four ATRA concentrations. The maximal metabolic rate (V(max)) of ATRA metabolism and the Michaelis-Menten constant (K(M)) for the reaction were 1.6 microM/min and 30 microM, respectively. V(max) and K(M) values for ETHYL and ISO metabolism to DACT were also estimated using this modeling approach.

Metabolic activation of herbicide products by Vicia faba detected in human peripheral lymphocytes using alkaline single cell gel electrophoresis

Ametryn and metribuzin S-triazines derivatives and EPTC thiocarbamate are herbicides used extensively in Mexican agriculture, for example in crops such as corn, sugar cane, tomato, wheat, and beans. The present study evaluated the DNA damage and cytotoxic effects of three herbicides after metabolism by Vicia faba roots in human peripheral lymphocytes using akaline single cell gel electrophoresis. Three parameters were scored as indicators of DNA damage: tail length, percentage of cells with DNA damage (with comet), and level DNA damage. The lymphocytes were treated for 2 h with 0.5-5.0 microg/ml ametryn or metribuzin and 1.5-10 microg/ml EPTC. Lymphocytes also were coincubated for 2 h with 20 microl V. faba roots extracts that had been treated for 4 h with 50-500 mg/l of the two triazines or with the thiocarbamate herbicide or with ethanol (3600 mg/l), as positive control. The lymphocytes treated with three pesticides without in vivo metabolic activation by V. faba root did not show significant differences in the mean values between genotoxic parameters compared with negative control. But when human cells were exposed to three herbicides after they had been metabolized the frequency of cell comet, tail length and level DNA damage all increased. At highest concentrations of the three herbicides produced severe DNA damage compared with S10 fraction and negative control. The linear regression analysis of the tail length values of three herbicides indicated that there was genotoxic effect concentration-response relationship with ametryn and ametribuzin but no EPTC. The ethanol induced major increase DNA damage compared with S10 fraction and the three pesticides. There were not effects in cell viability with treatment EPTC and metribuzin whether or not it had been metabolized. High concentrations of ametryn alone and after it had been metabolized decreased cell viability compared with the negative control. The results demonstrated that the three herbicides needed to be activated by the V. faba root metabolism to produce DNA damage in human peripheral lymphocyte. The alkaline comet technique is a rapid and sensitive assay, to quickly evaluate DNA damage the metabolic activation of herbicide products by V. faba root in human cells in vitro.

Preliminary examination of short-term cellular toxicological responses of the coral Madracis mirabilis to acute Irgarol 1051 exposure

Irgarol 1051 is an s-triazine herbicide formulated with Cu2O in antifouling paints. Recent studies have shown that Irgarol 1051 inhibits coral photosynthesis at environmentally relevant concentrations, consistent with its mode of action as a photosystem II inhibitor. Related toxicologic effects of this herbicide on coral cellular physiology have not yet been investigated. We used cellular diagnostics to measure changes in 18 toxicologic cellular parameters in endosymbiotic algal (dinoflagellate) and cnidarian (host) fractions of the common branching coral Madracis mirabilis associated with in vivo 8- and 24-hour exposures to a nominal initial Irgarol 1051 concentration of 10 microg L(-1). Responses measured were (1) xenobiotic response, which includes total and dinoflagellate multixenobiotic resistance (MXR), cnidarian cytochrome (CYP) P450-3 and P450-6 classes, cnidarian, and dinoflagellate glutathione-s-transferase (GST); (2) oxidative damage and response, which includes cnidarian and dinoflagellate Cu/Zn and Mn superoxide dismutase (SOD), cnidarian and dinoflagellate glutathione peroxidase (GPx), cnidarian catalase, and total protein carbonyl); (3) metabolic homeostasis, which includes chloroplast and invertebrate small heat-shock proteins (sHsp), cnidarian protoporphyrinogen oxidase IX (PPO), cnidarian ferrochelatase, and cnidarian heme oxygenase; and (4) protein metabolic condition, which includes cnidarian and dinoflagellate heat shock proteins (hsp70 and hsp60), total ubiquitin, and cnidarian ubiquitin ligase. Acute responses to Irgarol 1051 exposure included significant increases in total and dinoflagellate MXR, dinoflagellate Cu/Zn SOD, dinoflagellate chloroplast sHsp, and cnidarian PPO. Irgarol 1051 exposure resulted in decreases in cnidarian GPx, cnidarian ferrochelatase, cnidarian catalase, and cnidarian CYP 450-3 and -6 classes. Related implications of Irgarol 1051 exposure to coral cellular condition are discussed.

Sediment TCDD-EQs and EROD and MROD activities in Ranid frogs from agricultural and nonagricultural sites in Michigan (USA)

In vitro studies have demonstrated atrazine-mediated induction of 7-ethoxyresorufin O-deethylase (EROD) activity. EROD is an enzyme active in the metabolism of many compounds, including many xenobiotics. These studies have suggested that atrazine may affect reproductive function by altering steroid metabolism. The goal of this study was to determine whether relationships could be detected between measured atrazine concentrations in surface waters and the liver-somatic index (LSI) and EROD and 7-methoxyresorufin O-deethylase (MROD) activities in the livers of ranid frogs. In addition, sediment dioxin toxic equivalents (TCDD-EQs) were determined using the H4IIE-luc cell bioassay. Adult and juvenile green frogs (Rana clamitans), bullfrogs (R. catesbeiana), and Northern leopard frogs (R. pipiens) were collected from areas with extensive corn cultivation and areas where there was little agricultural activity in south central Michigan in the summer of 2003. Atrazine concentrations at nonagricultural sites ranged from less than the limit of quantification (0.17 microg atrazine/L) to 0.23 microg atrazine/L and did not exceed 1.2 microg atrazine/L at agricultural sites. Sediment TCDD-EQs were measurable only at one agricultural site. Of the measured parameters, only LSI values in adult male frogs differed significantly between agricultural and nonagricultural sites, with greater values observed at agricultural sites. In green frogs, EROD and MROD activities were measurable in both adult and juvenile frogs and were similar among sites. Median EROD activities ranged from 13 to 21 pmol/min/mg protein in adult male green frogs and from 5 to 13 pmol/min/mg protein in adult female green frogs. Juvenile frogs had greater EROD and MROD activities than adult frogs. Bullfrogs and leopard frogs had greater activities than did green frogs. Atrazine concentrations were significantly and negatively correlated with MROD activity in adult male green frogs (Spearman R = -0.800). LSI and EROD and MROD activities of adult female or juvenile green frogs were not significantly correlated with atrazine concentrations. These results suggest that atrazine does not appear to have a consistent association with EROD or MROD activities in wild-caught green frogs.

The Steroid Hormone Biosynthesis Pathway as a Target for Endocrine-Disrupting Chemicals

Various chemicals found in the human and wildlife environments have the potential to disrupt endocrine functions in exposed organisms. Increasingly, the enzymes involved in the steroid biosynthesis pathway are being recognized as important targets for the actions of various endocrine-disrupting chemicals. Interferences with steroid biosynthesis may result in impaired reproduction, alterations in (sexual) differentiation, growth, and development and the development of certain cancers. Steroid hormone synthesis is controlled by the activity of several highly substrate-selective cytochrome P450 enzymes and a number of steroid dehydrogenases and reductases. Particularly aromatase (CYP19), the enzyme that converts androgens to estrogens, has been the subject of studies into the mechanisms by which chemicals interfere with sex steroid hormone homeostasis and function, often related to (de)feminization and (de)masculinazation processes. Studies in vivo and in vitro have focussed on ovarian and testicular function, with less attention given to other steroidogenic organs, such as the adrenal cortex. This review aims to provide a comprehensive overview of the state of knowledge regarding the mechanisms by which chemicals interfere with the function of steroidogenic enzymes in various tissues and organisms. The endocrine toxicities and mechanisms of action related to steroidogenesis of a number of classes of drugs and environmental contaminants are discussed. In addition, several potential in vitro bioassays are reviewed for their usefulness as screening tools for the detection of chemicals that can interfere with steroidogenesis. Analysis of the currently scattered state of knowledge indicates that still relatively little is known about the underlying mechanisms of interference of chemicals with steroidogenesis and their potential toxicity in steroidogenic tissues, neither in humans nor in wildlife. Considerably more detailed and systematic research in this area of (endocrine) toxicology is required for a better understanding of risks to humans and wildlife.

Determination of herbicides and a metabolite in human urine by liquid chromatography-electrospray ionization mass spectrometry

A method was developed to determine simazine, atrazine and their metabolite, 2-chloro-4,6-diamino-1,3,5-triazine, in urine. The presence of these herbicides in urine may reflect possible exposure to pesticides. Sample preparation involved protein precipitation and solid-phase extraction. The samples were analyzed by high-performance liquid chromatography-mass spectrometry. The detection limits were 0.4 microg/l and the analytes have a linear response in the interval 6-800 microg/l. The precision of the method was reflected in the RSD of < 2.4% for the herbicides studied. Based on the detectable herbicide levels from spiked urine samples collected from unexposed volunteers, this method can be used to determine the low levels necessary for establishing reference values of the selected herbicides and the metabolite.

Is cytochrome P450 CYP2D activity present in pig liver?

The presence of CYP2D in pig livers has been studied using different strains of pig, different CYP2D test substrates and monoclonal and polyclonal antibodies. The results of the studies lacked consistency, therefore the aim of this study was to identify the reasons for these inconsistencies. Liver microsomes isolated from conventional pigs and minipigs were tested in Western blotting using both monoclonal and polyclonal antibodies against human CYP2D6. The microsomes were also incubated with three different CYP2D tes t substrates.'The immunoblotting only gave a positive response when hybridised with polyclonal antibody. The pig microsomes did not metabolise debrisoquine, but metabolised two other test substrates, dextromethorphan and bufuralol. No correlation was found between the two enzyme assays and CYP2D apoprotein level. On the other hand positive correlations were found between dextromethorphan and bufuralol metabolism and the CYP2B immunochemical protein level, indicating that the CYP2B isoenzyme may be involved in the metabolism of these substrates. Further, assays using immunoinhibition and chemical inhibition of these reactions were performed. No response was obtained in the immunoinhibition assay. When using chemical inhibition, however, an average inhibition percentage of 83 were obtained with orphenadrine, a human CYP2B inhibitor. Average Ki values of 26.9 microM and 43.6 microM for orphenadrine indicate that it was a potent inhibitor. A rat and a mouse CYP2B inhibitor, resveratrol and pilocarpine, inhibited the reaction with an average of 40 and 70 percentage respectively. Orphenadrine did not inhibit CYPIA, CYP2A, CYP2E and CYP3A activities up to more than maximum 12 percentage, showing that it was almost selective for dextromethorphan metabolism. These results indicate that dextromethorphan and bufuralol metabolism may be catalysed by CYP2B and not CYP2D.

Effect of alachlor on hepatic cytochrome P450 enzymes in rats

Alachlor ((2-chloro-N-methoxymethyl)-N-(2,6-diethylphenyl)acetamide) is a widely used preemergence herbicide which has been classified by the USEPA as a probable human carcinogen. The herbicide has been suggested to be metabolized by hepatic cytochrome P450 system. We examined the effects of alachlor on cytochrome P450 enzymes in rat liver microsomes. Rats were treated intraperitoneally with alachlor daily for 5 days, at doses of 25, 50 and 100 mg/kg. Among the cytochrome P450-dependent monooxygenase activities, 7-pentoxyresorufin O-depentylase, which is associated with CYP2B1, was dose-dependently increased by alachlor. The induction relative to control activity was 1.7-4.2-fold. The activities of CYP1A-dependent monooxygenases such as 7-ethoxy-resorufin O-deethylase and acetanilide 4-hydroxylase were also significantly increased by alachlor at doses of 50 and 100 mg/kg (1.7-2.1-fold). Furthermore, immunoblotting showed that alachlor significantly increased CYP2B1/2 and CYP1A1/2 protein levels by 4.2-6.3- and 1.8-fold, respectively. Although 7-ethoxycoumarin O-deethylase, bufuralol 1'-hydroxylase and 4-nitrophenol 2-hydroxylase activities were significantly increased by alachlor at higher doses (> or = 50 mg/kg), the induction ratios were less than 1.6-fold. The activities of other cytochrome P450-dependent monooxygenases, namely testosterone 7 alpha-hydroxylase, testosterone 2 alpha-hydroxylase, testosterone 6 beta-hydroxylase and lauric acid omega-hydroxylase, were not affected by alachlor at any dose. In addition, there was no significant change in the protein levels of CYP2C11/6, CYP2D1, CYP2E1, CYP3A2/1 and CYP4A1/2/3. These results suggest that alachlor selectively induces cytochrome P450 isoforms of the CYP1A and CYP2B subfamilies in rat liver microsomes, and that the expression of these isoforms is closely related to the toxicity of alachlor.

Determination of UDP-glucuronosyltransferase UGT1A6 activity in human and rat liver microsomes by HPLC with UV detection

A simple and sensitive method for the determination of UDP-glucuronosyltransferase UGT1A6 activity using 4-methylumbelliferone (4-MU) and 4-nitrophenol (4-NP) as substrates in human and rat liver microsomes by high-performance liquid chromatography (HPLC) with uv detection is reported. The method was validated for the determination of 4-methylumbelliferyl beta-D-glucuronide (4-MUG) and 4-nitrophenyl beta-D-glucuronide (4-NPG) with respect to specificity, linearity, detection limit, recovery, stability, precision and accuracy. There was no interference from matrix and non-enzymatic reactions. Calibration curves for 4-MUG and 4-NPG are linear from 0.5 to 500 microM. Average recoveries ranged from 98 to 100% in spiked liver microsomes samples. 4-MUG and 4-NPG were stable at 4 degrees C for at least 72 h in spiked liver microsomes samples. The method was found to be more sensitive than previous methods using a spectrophotometer, a spectrofluorometer and HPLC. The detection limit for 4-MUG and 4-NPG (signal-to-noise ratio of 3) was 14 and 23 nM, respectively. The intra- and inter-day precision (relative S.D. (RSD)) and accuracy (relative mean error (RME)) was <5 and 9%, respectively. The intra- and inter-day reproducibility (RSD) of UGT1A6 enzyme assay in liver microsomes was <6%. With this improved sensitivity, the kinetics of UGT activities toward 4-MU and 4-NP in human and rat liver microsomes could be determined more precisely. In addition, the method could determine the non-inducible, and 3-methylcholanthrene- and phenobarbital-inducible activities of UGT1A6 in rat liver microsomes under the same assay conditions. Therefore, this method is applicable to in vivo and in vitro studies on the interaction of xenobiotic chemicals with UGT1A6 isoform in mammals using small amounts of biological samples.

Determination of cytochrome P450 1A activities in mammalian liver microsomes by high-performance liquid chromatography with fluorescence detection

A sensitive method for the determination of cytochrome P450 (P450 or CYP) 1A activities such as ethoxyresorufin O-deethylase (EROD) and methoxyresorufin O-demethylase (MROD) in liver microsomes from human, monkey, rat and mouse by high-performance liquid chromatography with fluorescence detection is reported. The newly developed method was found to be more sensitive than previous methods using a spectrofluorimeter and fluorescence plate reader. The detection limit for resorufin (signal-to-noise ratio of 3) was 0.80 pmol/assay. Intra-day and inter-day precisions (expressed as relative standard deviation) were less than 6% for both enzyme activities. With this improved sensitivity, the kinetics of EROD and MROD activities in mammalian liver microsomes could be determined more precisely. EROD activities in human and monkey liver microsomes, and MROD activities in liver microsomes from all animal species exhibited a monophasic kinetic pattern, whereas the pattern of EROD activities in rat and mouse liver microsomes was biphasic. In addition, the method could determine the non-inducible and 3-methylcholanthrene-inducible activities of EROD and MROD in rat and mouse liver microsomes under the same assay conditions. Therefore, this method is applicable to in vivo and in vitro studies on the interaction of xenobiotic chemicals with cytochrome CYP1A isoforms in mammals.