Studies of early hepatocellular proliferation and peroxisomal proliferation in Wistar rats treated with herbicide diclofop

Characterization of two novel hydrolases from Sphingopyxis sp. DBS4 for enantioselective degradation of chiral herbicide diclofop-methyl

Diclofop-methyl, an aryloxyphenoxypropionate (AOPP) herbicide, is a chiral compound with two enantiomers. Microbial detoxification and degradation of various enantiomers is garnering immense research attention. However, enantioselective catabolism of diclofop-methyl has been rarely explored, especially at the molecular level. This study cloned two novel hydrolase genes (dcmA and dcmH) in Sphingopyxis sp. DBS4, and characterized them for diclofop-methyl degradation. DcmA, a member of the amidase superfamily, exhibits 26.1-45.9% identity with functional amidases. Conversely, DcmH corresponded to the DUF3089 domain-containing protein family (a family with unknown function), sharing no significant similarity with other biochemically characterized proteins. DcmA exhibited a broad spectrum of substrates, with preferential hydrolyzation of (R)-(+)-diclofop-methyl, (R)-(+)-quizalofop-ethyl, and (R)-(+)-haloxyfop-methyl. DcmH also preferred (R)-(+)-quizalofop-ethyl and (R)-(+)-haloxyfop-methyl degradation while displaying no apparent enantioselective activity towards diclofop-methyl. Using site-directed mutagenesis and molecular docking, it was determined that Ser175 was the fundamental residue influencing DcmA's activity against the two enantiomers of diclofop-methyl. For the degradation of AOPP herbicides, DcmA is an enantioselective amidase that has never been reported in research. This study provided novel hydrolyzing enzyme resources for the remediation of diclofop-methyl in the environment and deepened the understanding of enantioselective degradation of chiral AOPP herbicides mediated by microbes.

Effect of Pesticides on Peroxisome Proliferator-Activated Receptors (PPARs) and Their Association with Obesity and Diabetes

Obesity and diabetes mellitus are considered the most important diseases of the XXI century. Recently, many epidemiological studies have linked exposure to pesticides to the development of obesity and type 2 diabetes mellitus. The role of pesticides and their possible influence on the development of these diseases was investigated by examining the relationship between these compounds and one of the major nuclear receptor families controlling lipid and carbohydrate metabolism: the peroxisome proliferator-activated receptors (PPARs), PPARα, PPARβ/δ, and PPARγ; this was possible through in silico, in vitro, and in vivo assays. The present review aims to show the effect of pesticides on PPARs and their contribution to the changes in energy metabolism that enable the development of obesity and type 2 diabetes mellitus.

Agrochemicals and obesity

Obesity has become a very large concern worldwide, reaching pandemic proportions over the past several decades. Lifestyle factors, such as excess caloric intake and decreased physical activity, together with genetic predispositions, are well-known factors related to obesity. There is accumulating evidence suggesting that exposure to some environmental chemicals during critical windows of development may contribute to the rapid increase in the incidence of obesity. Agrochemicals are a class of chemicals extensively used in agriculture, which have been widely detected in human. There is now considerable evidence linking human exposure to agrochemicals with obesity. This review summarizes human epidemiological evidence and experimental animal studies supporting the association between agrochemical exposure and obesity and outlines possible mechanistic underpinnings for this link.

Two dcm Gene Clusters Essential for the Degradation of Diclofop-methyl in a Microbial Consortium of Rhodococcus sp. JT-3 and Brevundimonas sp. JT-9

The metabolism of widely used aryloxyphenoxypropionate herbicides has been extensively studied in microbes. However, the information on the degradation of diclofop-methyl (DCM) is limited, with no genetic and biochemical investigation reported. The consortium L1 of Rhodococcus sp. JT-3 and Brevundimonas sp. JT-9 was able to degrade DCM through a synergistic metabolism. To elaborate the molecular mechanism of DCM degradation, the metabolic pathway for DCM was first investigated. DCM was initially transformed by strain JT-3 to diclofop acid and then by strain JT-9 to 2-(4-hydroxyphenoxy) propionic acid as well as 2,4-dichlorophenol. Subsequently, the two dcm gene clusters, dcmAE and dcmB1B2CD, involved in further degradation of 2,4-dichlorophenol, were successfully cloned from strain JT-3, and the functions of each gene product were identified. DcmA, a glutathione-dependent dehalogenase, was responsible for catalyzing the reductive dehalogenation of 2,4-dichlorophenol to 4-chlorophenol, which was then converted by the two-component monooxygenase DcmB1B2 to 4-chlorocatechol as the ring cleavage substrate of the dioxygenase DcmC. In this study, the overall DCM degradation pathway of the consortium L1 was proposed and, particularly, the lower part on the DCP degradation was characterized at the genetic and biochemical levels.

Modulatory effects of quercetin on liver histopathological, biochemical, hematological, oxidative stress and DNA alterations in rats exposed to graded doses of score 250

This study investigated the morphological, biochemical and molecular aspects of liver injury in rats after the exposure to difenoconazole and the protective effects of quercetin against hepatotoxicity and genotoxicity induced by this fungicide. Rats were given graded doses of difenoconazole associated or not to quercetin daily for 20 days. Our results showed a significant increase in PLT (platelets) and WBC (white blood cells) in rats treated with higher doses of difenoconazole (1/38 and 1/9 of LD50). However, a significant decrease in Hb (hemoglobin) rate and RBC (red blood cells) number in rats treated with higher doses of difenoconazole (1/38 and 1/9 of LD50) was obtained. Besides, difenoconazole treatment caused an increase in hepatic enzyme activities of alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP) and lactate dehydrogenase (LDH). Difenoconazole increased the levels of malondialdehyde (MDA) and advanced oxidation protein products (AOPPs), and decreased superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) activities and vitamin C levels in liver tissues compared to the control group. We also noted a degradation of nucleic acids, testifying difenoconazole genotoxicity. Changes in hepatic tissues were confirmed by histological findings. Co-administration of quercetin (20 mg/kg) improved hematological and biochemical parameters and showed a significant liver protective effect by decreasing MDA levels and producing advanced oxidation protein, along with increased antioxidative enzyme activities and vitamin C levels. Results were confirmed by the improvement of histological impairments. Thus, it appears that quercetin was effective in preventing acute liver injury induced by exposure to difenoconazole.

Endocrine disruptors: from endocrine to metabolic disruption

Synthetic chemicals currently used in a variety of industrial and agricultural applications are leading to widespread contamination of the environment. Even though the intended uses of pesticides, plasticizers, antimicrobials, and flame retardants are beneficial, effects on human health are a global concern. These so-called endocrine-disrupting chemicals (EDCs) can disrupt hormonal balance and result in developmental and reproductive abnormalities. New in vitro, in vivo, and epidemiological studies link human EDC exposure with obesity, metabolic syndrome, and type 2 diabetes. Here we review the main chemical compounds that may contribute to metabolic disruption. We then present their demonstrated or suggested mechanisms of action with respect to nuclear receptor signaling. Finally, we discuss the difficulties of fairly assessing the risks linked to EDC exposure, including developmental exposure, problems of high- and low-dose exposure, and the complexity of current chemical environments.

Environmental behavior of the chiral aryloxyphenoxypropionate herbicide diclofop-methyl and diclofop: enantiomerization and enantioselective degradation in soil

In this study, the degradation of diclofop-methyl (DM) and its main metabolite, diclofop (DC), in two soils under aerobic and anaerobic conditions were investigated using enantioselective HPLC. Under aerobic or anaerobic conditions, rapid hydrolysis to the corresponding acid diclofop (DC)was observed. The results from this study revealed that the degradation of DM in the two soils is not enantioselective, and the calculated half-lives (t(1/2)) for the two soils were both less than 1 day. However, the degradation of DC in the two soils is enantioselective both under aerobic and anaerobic conditions, and the S-(-)-DC was preferentially degraded, resulting in relative enrichment of the R-(+)-form. The calculated t(1/2) values of the enantiomers of DC ranged between 8.7 and 43.3 days for aerobic incubation experiments and between 14.7 and 77.0 days for anaerobic incubation experiments, respectively. The enantiopure S-(-)- and R-(+)-DC were incubated under aerobic conditions, and it revealed significant enantiomerization with inversion of the S-(-)-enantiomer into R-(+)-enantiomer, and vice versa, and the S-(-)-DC showed a significantly higher inversion tendency than the R-(+)-DC.

Enantioselective effects of chiral herbicide diclofop acid on rice Xiushui 63 seedlings

In this study, the acute toxicity (72-h EC50 values) of chiral diclofop acid towards rice Xiushui 63 seedlings and its effects on the Hill reaction activities of chloroplasts were determined. Significant differences were observed between the two enantiomers in 72-h EC50 values and in both in vivo and in vitro relative Hill reaction activities. These observations indicate that the enantiomers of diclofop acid pose different toxicities to rice seedlings: the S-enantiomer is more toxic to leaves and the R-enantiomer is more toxic to roots. These enantioselective toxic effects on rice seedlings should be taken into account in chiral herbicide application.

Time-dependent degradation and toxicity of diclofop-methyl in algal suspensions : emerging contaminants

BACKGROUND, AIM, AND SCOPE

As emerging contaminants, transformation products of the pollutants via various environmental processes are rather unknown, and some may predominantly contribute to the environmental risks of the parent compounds. Hence, studies on transformation products complement the assessment of the environmental safety of the parent compounds. In this study, degradation experiments and toxicity tests using diclofop-methyl (DM), a widely used herbicide, and selected major transformation products were carried out in algal cultures to assess the time course of DM toxicity and its relevance in the formation of new breakdown products.

METHODS

The alga Chlorella vulgaris was maintained in the algal growth medium HB IV. The inhibition of algal growth was determined by measuring optical density at 680 nm (OD(680)). Initially, DM and two selected breakdown products were added to the algal cultures, and following degradation experiments analyses were carried out by high performance liquid chromatography. In addition, the possible relationship between DM degradation and toxicity was assessed, based on physico-chemical properties of the compounds and their toxicity.

RESULTS

DM was rapidly absorbed onto the surface of the algal cells where it was hydrolyzed to diclofop (DC). Further degradation to 4-(2, 4-dichlorophenoxy) phenol (DP) occurred in the cells. However, only a minor amount of DC was degraded to DP under the same conditions when DC was initially added to the algal culture. When C. vulgaris was exposed to these compounds for 96 h, the determined EC(50) showed that DC was about ten times less toxic than DM (EC(50) = 0.42 mg/L) and that DP (EC(50) = 0.20 mg/L) was the most toxic.

DISCUSSION

Due to strong hydrophobicity and rare dissociation, DM has tendency toward absorption as compared to DC. The higher average degradation rates of DC initially treated by DM revealed the damage of the cell membranes caused by the DM and, thus, enhanced movement of DC into the cells. Following occurrence of phenolic breakdown products, DP suggested that DC should be intracellularly degraded to DP, which had a more potent mode of action and a higher acute toxicity. Moreover, the results for EC(50) at various intervals were in accordance with degradation processes of the initial compounds, in which rapid formation of DP was attributed to an increasing toxicity of DM.

CONCLUSIONS

The toxicity of DM in algal suspensions increased with time due to its degradation to DP, which contributed significantly to the determined toxicity. These results indicate that the toxicity of the pesticide probably depends significantly on degradation. It is thus important to consider the time-dependent environmental processes when evaluating the toxicological effects of pesticides for proper risk assessment.

RECOMMENDATIONS AND PERSPECTIVES

Increasing transformation products of these contaminants are identified in the environment, although they seem to be unknown in terms of the lacking studies on environmental behavior and ecotoxicity concerning them. Certain breakdown products probably greatly contribute to the apparent toxicity of the parent compounds, which is ascribed to the parent compounds in general studies ignoring the dependence of their toxicity on various transformation pathways. These studies that identify new intermediates and assess their toxicity via the environmental processes will be helpful to distinguish the nature of toxicity of the parent contaminants.

Selective Oxidative Stress in Brain Areas of Neonate Rats Exposed to 2,4-Dichlorophenoxyacetic Acid Through Mother's Milk

2,4-Dichlorophenoxyacetic acid (2,4-D) induced disparate alterations on enzymatic activities of the defensive mechanism and/or modifications of the reactive oxygen species levels in specific neonate rat brain regions. The midbrain, striatum, and prefrontal cortex were the areas where the alterations were more remarkable and with similar tendency. The hippocampus did not suffer many alterations, and the hypothalamus was the area where no changes were observed. The current results suggest that the developing brain areas have different susceptibilities to the adverse effect of the herbicide, especially those areas related to the dopaminergic system, and that oxidative stress is one 2,4-D mechanism of toxicity.

Enantioselective degradation and ecotoxicity of the chiral herbicide diclofop in three freshwater alga cultures

Aryloxyphenoxypropanoates are a class of chiral herbicides. They have a pair of enantiomers, only the R(+) form of which is herbicidally active. Diclofop, the model compound of these herbicides, is commercialized as the racemate of the ester form, diclofop-methyl, consisting of a 1:1 mixture of the enantiomers. This study evaluated the enantioselectivity in aquatic toxicity and biodegradation of diclofop and diclofop-methyl. The herbicidally inactive S(-) enantiomers of both diclofop-methyl and diclofop were similar to or higher than the corresponding R(+) forms in toxicity to algae, depending on specific species. Although no enantiomeric conversion occurred for diclofop-methyl and diclofop, the difference in the enantioselective degradation of these herbicides observed in algae cultures suggested that their application forms were an important factor determining their enantioselective environmental behavior. The cell permeability and heat treatment of algae revealed that the enantioselective degradation of diclofop in algae cultures was governed primarily by the facilitated uptake by algae, whereas the enantioselective toxicity was primarily governed by the passive uptake. These results suggested that the acute toxicity test such as the 96 h EC 50 was insufficient to assess the ecological risk of chiral pesticides because of the differential degradation as well as possibly differential action sites of enantiomers. From this study, it was concluded that the enantioselective degradation and toxicity of chiral herbicides may result in their ecotoxicological effects being difficult to predict and that specific attention should thus be paid to currently used racemic pesticides as less active or inactive enantiomers may pose higher ecological risks.

In vitro screening of 200 pesticides for agonistic activity via mouse peroxisome proliferator-activated receptor (PPAR)alpha and PPARgamma and quantitative analysis of in vivo induction pathway

Peroxisome proliferator-activated receptors (PPARs) are ligand-dependent transcription factors and key regulators of lipid metabolism and cell differentiation. However, there have been few studies reporting on a variety of environmental chemicals, which may interact with these receptors. In the present study, we characterized mouse PPARalpha and PPARgamma agonistic activities of 200 pesticides (29 organochlorines, 11 diphenyl ethers, 56 organophosphorus pesticides, 12 pyrethroids, 22 carbamates, 11 acid amides, 7 triazines, 8 ureas and 44 others) by in vitro reporter gene assays using CV-1 monkey kidney cells. Three of the 200 pesticides, diclofop-methyl, pyrethrins and imazalil, which have different chemical structures, showed PPARalpha-mediated transcriptional activities in a dose-dependent manner. On the other hand, none of the 200 pesticides showed PPARgamma agonistic activity at concentrations <or =10(-5) M. To investigate the in vivo effects of diclofop-methyl, pyrethrins and imazalil, we examined the gene expression of PPARalpha-inducible cytochrome P450 4As (CYP4As) in the liver of female mice intraperitoneally injected with these compounds (< or =300 mg/kg). RT-PCR revealed significantly high induction levels of CYP4A10 and CYP4A14 mRNAs in diclofop-methyl- and pyrethrins-treated mice, whereas imazalil induced almost no gene expressions of CYP4As. In particular, diclofop-methyl induced as high levels of CYP4A mRNAs as WY-14643, a potent PPARalpha agonist. Thus, most of the 200 pesticides tested do not activate PPARalpha or PPARgamma in in vitro assays, but only diclofop-methyl and pyrethrins induce PPARalpha agonistic activity in vivo as well as in vitro.

Inhibition of cytokine production by the herbicide atrazine. Search for nuclear receptor targets

The hematological toxicity of the commonly used triazine herbicides is a cause for concern. In a search for molecular targets of these compounds, as their effects paralleled those seen with dexamethasone (DEX), we first looked for interaction with the glucocorticoid receptor. In contrast to the effects on proliferation and cytokine production of DEX, those induced by atrazine were not prevented by the glucocorticoid antagonist RU486. Also, whereas DEX was able to inhibit the promoter activity of genes regulated by NF-kappaB, atrazine failed to do so. We next looked for interaction with members of the peroxisome proliferator-activated receptor (PPAR) family. No peroxisome proliferation was observed in the liver or kidneys of mice treated with atrazine. Moreover, no PPAR-mediated induction of promoter activity was seen on targets of PPARalpha, PPARgamma, or PPARdelta. Similarly, neither atrazine nor simazine were able to stimulate RORalpha-mediated promoter activity. Finally, no binding of atrazine to the AR was observed. In conclusion, the effects of atrazine-type herbicides most probably do not result from interaction with the above-mentioned nuclear receptors.

Hepatocellular peroxisome proliferation and DNA synthesis in Wistar rats treated with herbicide fluazifop

The aim of this study was to determine the effect of herbicide fluazifop, on the early occurring changes in rat liver regarded as hepatic markers of peroxisome proliferators (PPs). Fluazifop was administered orally to male Wistar rats at increasing doses from 5.6 to 891 mg/kg body weight per day for 1, 2, 4, 7 and 14 consecutive days and peroxisome proliferation, induction of some peroxisome-associated enzymes and mitogenesis (S-phase, M-phase and percentage of binucleated hepatocytes) were studied. Short-term treatment of rats with fluazifop resulted in hepatomegaly due to time dependent proliferation of smooth endoplasmic reticulum (SER) and peroxisomes. The increase in the number of peroxisomes in the hepatocytes was supported by an increase in peroxisomal palmitoyl-CoA oxidation and catalase activity. In contrast to other PPs fluazifop induced low rate of rcplicative DNA synthesis and did not affect mitoses (M-phase). DNA synthesis was accompanied by the appearance of binucleated hepatocytes. Thus, we can conclude that fluazifop produces in male Wistar rats hepatomegaly due to cellular hypertrophy. The threshold dose for palmitoyl-CoA oxidation and DNA synthesis was 112 and 223 mg/kg body weight per day, respectively. The value for hepatomegaly and catalase activity was 56 mg/kg body weight per day. The results presented in this paper demonstrated that fluazifop can be classified as a weak rodent PPs.