Festuca arundinacea,glutathione S-transferase and herbicide safeners: A preliminary case study to reduce herbicidal pollution

The expression of glutathione S-transferase (GST) activity in Festuca arundinacea was investigated in response to the following herbicide safeners: benoxacor, cloquintocet-mexyl, fenchlorazol-ethyl, fenclorim, fluxofenim and oxabetrinil. All the above compounds enhanced the GST activity tested towards the “model” substrate 1-chloro-2,4-dinitrobenzene (CDNB). Assays of GST activity towards the herbicides terbuthylazine (N ²-tert-butyl-6-chloro-N ⁴-ethyl-1,3,5-triazine-2,4-diamine) and butachlor (N-butoxymethyl-2-chloro-2′,6′-diethylacetanilide) as substrates also showed the ability of the safeners to enhance the enzyme activity towards both these herbicides, with the exception of cloquintocet-mexyl for the enzyme activity towards butachlor. As a consequence of the above effects at a macro-scale level, decreased herbicide accumulation and persistence were ascertained in response to the addition of the safener benoxacor to both terbuthylazine and butachlor treatments. These results are discussed in terms of capacity of benoxacor to induce herbicide detoxification in Festuca arundinacea with a view to utilizing them in reducing herbicide pollution.     

Effect of herbicides on glutathione S-transferases in the earthworm, <Emphasis Type="Italic">Eisenia fetida</Emphasis>

AIM AND BACKGROUND: Earthworms have been studied as a readily available, easily maintainable and cheap test species for assessing chemical pollution, and may be an alternative to in vivo rodent bioassays. The current investigation aims to characterize detoxification enzymes in Eisenia fetida and stress response against two herbicides with different modes of action, namely, fenoxaprop and metolachlor. METHODS: Herbicides were applied to soil containing earthworms. Animals were then collected, sacrificed and shock-frozen. Extracted protein was analyzed for glutathione S-transferase (GST) activity using CDNB (1-chloro-2,4-dinitrobenzene), DCNB (1,2-dichloro-4-nitrobenzene), pNBC (p-nitrobenzylchloride), PNOBC (p-nitrobenz-o-ylchloride) and selected herbicides. GST isoenzymes were partially purified by affinity chromatography and molecular weights were estimated by SDS-PAGE. RESULTS: In E. fetida protein extracts, GST activity towards model compounds ranked as CDNB>DCNB>PNBOC>PNBC. Fluorodifen was not conjugated at all, but fenoxaprop and metolachlor were conjugated at low rates. Furthermore, the GST isoenzyme pattern changed during the incubation with herbicides, either due to stress or as a defense reaction. After incubation with monochlorobimane, a strong fluorescence of the intestinal tract and the intersegments was observed, indicating organ-specific GST induction. DISCUSSION: According to the author's knowledge, here, for the first time, evidence is presented that E. fetida GST are also capable of conjugating a wider range of xenobiotic substrates. Different forms of GST were observed and changes in GST isoforms due to the herbicide treatment were also noticed. GST conjugation rates varied between different herbicides used in this experiment. It might be assumed that herbicides may well be detoxified by earthworms, to a certain extent, but that they are also potent stress factors influencing the detoxification system of the animal. High doses or long exposure might lead to deleterious effects on earthworms and limit their survival rate. The use of the animals as bioindicators for herbicides and herbicide residues seems very promising, but is surely influenced by the lack of detoxification for some compounds. CONCLUSIONS: Conjugation of several xenobiotics with model substances and herbicides is proven in the earthworm E. fetida. However, E. fetida has only limited capabilities of detoxifying herbicidal compounds. Different isoforms of GST were involved and altered in their activity after treatment. RECOMMENDATIONS AND PERSPECTIVES: The accumulation of GS-conjugates and their determination via fluorescence microscopy is a quick and secure, additional marker for exposure that should be further developed to complement existing biotests. The described methods and endpoints might help to understand the complex reaction of earthworms towards herbicides and lead to an adapted test methodology.     

Toxicity of abamectin and doramectin to soil invertebrates

This study aimed at determining the toxicity of avermectins to soil invertebrates in soil and in faeces from recently treated sheep. Abamectin was more toxic than doramectin. In soil, earthworms (Eisenia andrei) were most affected with LC50s of 18 and 228 mg/kg dry soil, respectively, while LC50s were 67-111 and >300 mg/kg for springtails (Folsomia candida), isopods (Porcellio scaber) and enchytraeids (Enchytraeus crypticus). EC50s for the effect on reproduction of springtails and enchytraeids were 13 and 38 mg/kg, respectively for abamectin, and 42 and 170 mg/kg for doramectin. For earthworms, NOEC was 10 and 8.4 mg/kg for abamectin and doramectin effects on body weight. When exposed in faeces, springtails and enchytraeids gave LC50s and EC50s of 1.0-1.4 and 0.94-1.1 mg/kg dry faeces for abamectin and 2.2->2.4 mg/kg for doramectin. Earthworm reproduction was not affected. This study indicates a potential risk of avermectins for soil invertebrates colonizing faeces from recently treated sheep.     

Quantum dots enhance Cu2+-induced hepatic L02 cells toxicity

As a new class of xenogenous nanoparticle,quantum dots (QDs) possess the potential to co-exist with Cu2+ in human liver.The combined toxicity is thus concerned.Considering QDs and Cu2+ are known ROS (reactive oxygen species) inducer,we investigated the combined oxidative stress and corresponding protective strategy using human hepatic L02 cells.The results demonstrated that the presence of a small amount of MPA-CdTe QDs (2 μg/mL) in a Cu2+ solution (2.5-20 μg/mL) resulted in a higher toxicity with up to 8-fold cell viability decrease,which was accompanied by cell morphology changes.The combined toxicity was then confirmed as ROS associated oxidative stress with up to 300% and 35% increase of the intracellular ROS level and glutathione S-transferase (GST) activity,respectively.N-acetylcysteine (NAC) can also provide almost complete protection against the induced toxicity.Therefore,the ROS associated oxidant injury might be responsible for the QDs-Cu2+/Cu2+ induced toxicity and could be balanced through cytoprotective antioxidant enzyme GST.     

Levels of plasma B-esterases and glutathione-S-transferase activities in three South American toad species

We determined the normal levels of butyrylcholinesterase (BChE), carboxylesterase (CbE), and glutathione S-transferases (GST) activities in three South American toad species in order to establish reference values for field pesticide monitoring purposes. Interspecies variations in B-esterase and GST activities were examined according to body mass. In addition, comparative inhibition of BChE and CbE activities using malaoxon, and chemical reactivation of malaoxon-inhibited BChE activity using pyridine-2-aldoxime methochloride (2-PAM) were investigated. Bufo fernandezae had average activity values for BChE: 17.31 mmol min^?1 ml^?1; CbE: 621.49 nmol min^?1 ml^?1 and GST: 1.94 mmol min^?1 ml^?1 while B. arenarum enzymatic average activities were BChE: 9.51 mmol min^?1 ml^?1; CbE: 270.07 nmol min^?1 ml^?1, and GST: 1.59 mmol min^?1 ml^?1; finally Bufo schneideri had enzymatic mean values of BChE: 2.08 mmol min^?1 ml^?1; CbE: 301.95 nmol min^?1 ml^?1, and GST: 1.60 mmol min^?1 ml^?1. Moreover, we found an allometric relationship between plasma BChE and CbE activities and body size for the three toad species. We suggest that B. fernandezae would be the species with a higher tolerance capacity to organophosphorous insecticides compared to the other toad species, while B. schneideri may be the most vulnerable toad species to field pesticide exposure, although some other factors (e.g., brain AChE sensitivity or pesticide metabolism by phosphotriesterases) should be also taken into account. The malaoxon-inhibited BChE activity of the three toad species was reactivated in the presence of 2-PAM, and it is recommended as a specific and sensitive methodology in the assessment of field exposure to OP insecticides together to compare BChE activity levels between OP-exposed and nonexposed individuals.     

Sublethal concentrations of azinphos-methyl induce biochemical and morphological alterations in Rhinella arenarum embryos

Considering that amphibians are good sentinels of environmental conditions, Rhinella arenarum embryos were used to investigate the effects of sublethal concentrations of the organophosphorus insecticide azinphos-methyl, focusing on its anticholinesterasic or pro-oxidant actions and its possible connection with the appearance of morphological alterations. Early amphibian embryos exposed to azinphos-methyl displayed a protective response through glutathione S-transferase induction, along with superoxide dismutase inhibition. At intermediate embryonic stages, embryos exposed to azinphos-methyl displayed superoxide dismutase inhibition and morphological alterations, although cholinesterase activity was not altered, suggesting that molecular targets other than cholinesterase were involved in the development of morphological alterations. At the end of embryonic development, decreases in reduced glutathione and cholinesterase inhibition were observed, along with a significant increase in the number of malformed embryos. The connection between biochemical alterations and the appearance of malformations was not evident in R. arenarum embryos. However, increased glutathione S-transferase and decreased superoxide dismutase activities could be considered as early markers of exposure to azinphos-methyl. The results obtained demonstrate that sublethal concentrations of azinphos-methyl are a serious threat to toad embryos in their natural habitats because biochemical and morphological alterations could impair their ability to deal with environmental stresses.     

壬基酚对赤子爱胜蚓的生态毒理学研究

环境激素对生态的影响越来越受到人们的重视。通过赤子爱胜蚓对壬基酚的滤纸接触法毒性试验,从分子水平揭示环境污染物对蚯蚓组织的毒性影响。在壬基酚对赤子爱胜蚓(Eiseniafoetida)的急性毒性试验中,测得72hLC50为0.908μg/cm2。在系列浓度的壬基酚暴露中,过氧化氢酶(Catalase,CAT),超氧化物歧化酶(Superoxidedismutase,SOD)和谷胱甘肽硫转移酶(GlutathioneS-transferase,GST)的敏感性依次为CAT>SOD>GST。实验结果表明,这三种酶均可作为早期NP污染预警指标。     

Growth, photosynthesis and antioxidant responses of two microalgal species, Chlorella vulgaris and Selenastrum capricornutum, to nonylphenol stress

The effect of nonylphenol (NP) on growth, photochemistry and biochemistry of two green microalgae, Chlorella vulgaris and Selenanstrum capricornutum, and their ability to degrade NP were compared. The 96 h EC₅₀ of C. vulgaris and S. capricornutum were greater than 4.0 and 1.0 mg L⁻¹ NP, respectively, suggesting that the former species was more tolerant to NP. Both microalgae acclimated to NP stress through down-regulating their photosynthetic activities, including antenna size (chlorophyll a content), maximal photochemistry (Fv/Fm) and the light absorbed by PSII (ABS/CS₀), but the dissipation of energy from reaction centres (DI₀/RC) increased with the increase of NP concentrations. In C. vulgaris, the changes of these parameters were more significant than in S. capricornutum and recovered completely after a 96 h exposure. The antioxidant responses, such as GSH content, CAT and POD activities in C. vulgaris increased with the increase of NP concentrations after a 24 h exposure, but these changes disappeared with exposure time and recovered to the control levels after 96 h. In S. capricornutum, although GSH content, CAT and POD activities also increased when exposed to low- to moderate-NP concentrations, these values were significantly reduced at a high concentration (4 mg L⁻¹) even after a 96 h exposure, indicating its antioxidant responses were significantly delayed. It is clear that the more NP-tolerant species, C. vulgaris, acclimated better with a faster recovery of its photosynthetic activity from the NP-induced damage, and exhibited more efficient and rapid responses to NP-induced oxidative stress. C. vulgaris also had a higher NP degradation ability than S. capricornutum.     

Carcinogen-Metabolizing Enzymes and Insecticides

Abstract

The present study was under taken to demonstrate the effect of some commonly used insecticides on the activity of cytochrome P450 system including cytochrome b5, aryl hydrocarbon [benzo(a)pyrene] hydroxylase (AHH), N-nirosodimethylamine N-demethylase I [NDMA-dI] and NADPH-cytochrome c reductase as phase I of drug oxidation. In addition, the activity of glutathione S-transferase (GST), glutathione reductase (GR), and the level of glutathione (GSH) were determined in the liver of male mice after oral administration of sumithion, dursban, chlordane, methoxychlor, heptachlor epoxide, and lindane as single (24 h) or as repeated doses for six consecutive days. Oral administration of sumithion, dursban, chlordane, methoxychlore, and heptachlor epoxide as repeated doses decreased: (i) the hepatic content of cytochrome P450 by 36, 37, 47, 37, and 67%, respectively, (ii) AHH activity by 28, 29, 70, 31, and 79%, respectively, (iii) NDMA-dI activity by 43, 44, 32, 27, and 31, respectively. On the other hand, sumithion, chlordane, and methoxychlore induced the activity of NADPH-cytochrome c reductase by 45, 62, and 43 respectively after repeated dose treatments. In addition, single and repeated-dose treatments of mice with lindane induced; (i) cytochrome P450 by 23 and 65%, respectively, (ii) cytochrome b5 by 49 and 131%, respectively, (iii) AHH activity by 64 and 50%, respectively. Repeated-dose treatments of mice with chlordane, methoxychlore, and heptachlor epoxide decreased the GSH level by 42, 38, and 68%, respectively and GST activity by 44, 44, and 55% respectively. Moreover, single- and repeated-dose treatments of mice with lindane decreased the GSH levels by 40 and 54%, respectively, and induced GST activity by 25 and 41%, respectively. Interestingly, single-dose treatments with chlordane, methoxychlore, and heptachlor epoxide decreased the activity of GR by 32, 38, and 31, respectively whereas repeated doses of these compounds induced such activity by 83, 50, and 64%, respectively. It is concluded that modifications in cytochrome P450 system by pesticides could potentiate the toxicity and carcinogenicity of environmental carcinogens such as polycyclic aromatic hydrocarbon and N-nirosodimethylamine (NDMA).     

Glutathione S-transferase activity in rats exposed to methyl parathion

Methyl parathion is an organophosphate insecticide that has been used in agriculture and the domestic sector for several years. This pesticide and others, arriving through different processes, exert significant effects on water quality with serious consequences for environmental and human health. The main objective of this study was to investigate the changes of Glutathione S-transferase enzyme activity in methyl parathion exposed rat tissues. For this purpose, wistar rats (Rattus norvegicus) were injected intraperitoneally with 7 mg kg^?1 dose of methyl parathion, while corn oil was applied to control groups in the same way. The liver, kidneys, brain and small intestine were quickly removed after 0, 2, 4, 8, 16, 32, 64, and 72 hours of injection of methyl parathion and the glutathione S-transferase activity was determined in these tissues. As a result it was seen that glutathione S-transferase activity increases in all tissues in the group of male and female rats to which methyl parathion was given. The increase of glutathione S-transferase activity may be a result of methyl parathion's toxic effect because it is one of the most important enzymes of detoxification metabolism.