Assessment of oxidative stress responses and the cytotoxic and genotoxic potential of the herbicide tembotrione in HepG2 cells

The benefit of using in vitro bioassays to screen agricultural samples for oxidative stress: South Africa's case

Applied pesticides end up in non-target environments as complex mixtures. When bioavailable, these chemicals pose a threat to living organisms and can induce oxidative stress (OS). In this article, attention is paid to OS and the physiological role of the antioxidant defense system. South African and international literature was reviewed to provide extensive evidence of pesticide-induced OS in non-target organisms, in vivo and in vitro. Although in vitro approaches are used internationally, South African studies have only used in vivo methods. Considering ethical implications, the authors support the use of in vitro bioassays to screen environmental matrices for their OS potential. Since OS responses are initiated and measurable at lower cellular concentrations compared to other toxicity endpoints, in vitro OS bioassays could be used as an early warning sign for the presence of chemical mixtures in non-target environments. Areas of concern in the country could be identified and prioritized without using animal models. The authors conclude that it will be worthwhile for South Africa to include in vitro OS bioassays as part of a battery of tests to screen environmental matrices for biological effects. This will facilitate the development and implementation of biomonitoring programs to safeguard the South African environment.

Evaluation of Toxic Effects Induced by Sub-Acute Exposure to Low Doses of α-Cypermethrin in Adult Male Rats

To contribute new information to the pyrethroid pesticide α-cypermethrin toxicity profile, we evaluated its effects after oral administration to Wistar rats at daily doses of 2.186, 0.015, 0.157, and 0.786 mg/kg bw for 28 days. Evaluations were performed using markers of oxidative stress, cholinesterase (ChE) activities, and levels of primary DNA damage in plasma/whole blood and liver, kidney, and brain tissue. Consecutive exposure to α-cypermethrin affected the kidney, liver, and brain weight of rats. A significant increase in concentration of the thiobarbituric acid reactive species was observed in the brain, accompanied by a significant increase in glutathione peroxidase (GPx) activity. An increase in GPx activity was also observed in the liver of all α-cypermethrin-treated groups, while GPx activity in the blood was significantly lower than in controls. A decrease in ChE activities was observed in the kidney and liver. Treatment with α-cypermethrin induced DNA damage in the studied cell types at almost all of the applied doses, indicating the highest susceptibility in the brain. The present study showed that, even at very low doses, exposure to α-cypermethrin exerts genotoxic effects and sets in motion the antioxidative mechanisms of cell defense, indicating the potential hazards posed by this insecticide.

Evaluation of oxidative stress responses and primary DNA damage in blood and brain of rats exposed to low levels of tembotrione

Tembotrione is a rather novel pesticide, usually used for post-emergence weed control. Even though its use is rapidly growing, it is not followed by an adequate flow of scientific evidence regarding its toxicity towards non-target organisms. We evaluated the potential of low doses of tembotrione to induce oxidative stress and cytogenetic damage in blood and brain cells of adult male Wistar rats. Parameters of lipid peroxidation, glutathione levels, activities of antioxidant enzymes and primary DNA damage were assessed following 28-day repeated oral exposure to doses comparable with the currently proposed health-based reference values. The results of the alkaline comet assay showed that such low doses of tembotrione have the potency to inflict primary DNA damage in both peripheral blood leukocytes and brain of treated rats, even with only slight changes in the oxidative biomarker levels. The DNA damage in blood and brain cells of Wistar rats significantly increased at all applied doses, suggesting that tembotrione genotoxicity is mainly a result of direct interaction with DNA while the induction of oxidative stress responses contributes to DNA instability in a lesser extent. The findings of the present study call for further research using other sensitive biomarkers of effect and different exposure scenarios.

DNA damage in kidney and parenchymal and non-parenchymal liver cells of adult Wistar rats after subchronic oral treatment with tembotrione

DNA damage in the liver and kidney cells of adult male Wistar rats was studied using the comet assay after a 28-day oral administration of tembotrione at doses of 0.0007, 0.0013 and 0.7 mg/kg b.w./day [AOEL (acceptable operator exposure level), REL (residual exposure level) and 1000× AOEL]. As a descriptor of DNA damage, tail intensity was used. Antioxidant status was assessed by activity of glutathione peroxidase (GPx). Significant DNA damage was recorded in the kidney cells at all three doses as compared to negative control. In parenchymal liver cells, significant DNA damage was observed in AOEL and 1000× AOEL doses, while in non-parenchymal liver cells, only AOEL-treated group was significantly different compared to negative control. In both types of liver cells, REL and 1000× AOEL doses were significantly different from the AOEL dose. No significant changes in GPx activity compared to control were observed at any exposure level. The results of the present study suggest that repeated in vivo exposure to tembotrione led to low-level DNA instability in kidney and liver cells. Exposure to the highest tembotrione dose showed a relatively weak response with the alkaline comet assay. Further research should focus on the effects of this herbicide in other models along with different exposure scenarios.

Acute and subchronic effects of three herbicides on biomarkers and reproduction in earthworm Dendrobaena veneta

Earthworms are exposed to herbicides both through their skin and digestive system. Herbicides can influence earthworms' survival, physiology and reproduction. However, there is a lack of data on herbicide effects on earthworms as they are often regarded as low or non-toxic. The aim of our study was to investigate whether widely used commercial formulations of glyphosate (GLF), tembotrione (TBT) and nicosulfuron (NCS) each applied at three environmentally relevant concentrations have adverse effects on various biomarkers and reproduction in epigeic earthworm Dendrobaena veneta. The activities of measured biomarkers varied depending on the herbicide used and the exposure duration and suggest that oxidative stress plays an important role in the toxicity of tested herbicides. Namely, GLF caused an acetylcholinesterase (AChE) activity induction after seven days, and NCS after 28 days, while TBT caused an inhibition up to 47% (6.6 μg kgdw soil-1) after seven days. Only TBT caused a significant change (H2 = 13.96, p = 0.002) to catalase (CAT) after seven days of exposure. Malondialdehyde concentrations (MDA) were increased all the time after NCS exposure, but only after seven days in GLF and 28 days in TBT treatments, respectively. The tested herbicides did not have a significant effect on reproduction success, expect of NCS which increased the number of juveniles (p < 0.05).

Effects of the chloro-s-triazine herbicide terbuthylazine on DNA integrity in human and mouse cells

Terbuthylazine belongs to the chloro-s-triazine group of herbicides and acts primarily as a photosynthesis inhibitor. The mechanisms of action related to its exposure, relevant both in animals and humans, are still insufficiently investigated. This comprehensive study focused on the outcomes of terbuthylazine exposure at cell level in vitro, and a mice model in vivo. Experiments in vitro were conducted on whole human peripheral blood, isolated lymphocytes, and HepG2 cells exposed for 4 h to terbuthylazine at 8.00, 0.80, and 0.58 ng/mL, which is comparable with current reference values set by the European Commission in 2011. Terbuthylazine cytotoxicity was evaluated using dual fluorescent staining with ethidium bromide and acridine orange on lymphocytes, and CCK-8 colorimetric assay on HepG2 cells. The levels of DNA damage were measured using alkaline and hOGG1-modified comet assays. The potency of terbuthlyazine regarding induction of oxidative stress in vitro was studied using a battery of standard oxidative stress biomarkers. The in vivo experiment was conducted on Swiss albino mice exposed to terbuthlyazine in the form of an active substance and its formulated commercial product Radazin TZ-50 at a daily dose of 0.0035 mg/kg bw for 14 days. Following exposure, the DNA damage levels in leukocytes, bone marrow, liver, and kidney cells of the treated mice were measured using an alkaline comet assay. In vitro results suggested low terbuthylazine cytotoxicity in non-target cells. The highest tested concentration (8.00 ng/mL) reduced lymphocyte viability by 15%, mostly due to apoptosis, while cytotoxic effects in HepG2 cells at the same concentration were negligible. Acute in vitro exposure of human lymphocytes and HepG2 cells to terbuthylazine resulted in low-level DNA instability, as detected by the alkaline comet assay. Further characterization of the mechanisms behind the DNA damage obtained using the hOGG1-modified comet assay indicated that oxidative DNA damage did not prevail in the overall damage. This was further confirmed by the measured levels of oxidative stress markers, which were mostly comparable to control. Results obtained in mice indicate that both the active substance and formulated commercial product of terbuthylazine produced DNA instability in all of the studied cell types. We found that DNA in liver and kidney cells was more prone to direct toxic effects of the parent compound and its metabolites than DNA in leukocytes and bone marrow cells. The overall findings suggest the formation of reactive terbuthylazine metabolites capable of inducing DNA cross-links, which hinder DNA migration. These effects were most pronounced in liver cells in vivo and HepG2 cells in vitro. To provide a more accurate explanation of the observed effects, additional research is needed. Nevertheless, the present study provides evidence that terbuthylazine at concentrations comparable with current reference values possesses toxicological risk because it caused low-level DNA instability, both at cellular and animal organism level, which should be further established in forthcoming studies.

Redox imbalance caused by pesticides: a review of OPENTOX-related research

Pesticides are a highly diverse group of compounds and the most important chemical stressors in the environment. Mechanisms that could explain pesticide toxicity are constantly being studied and their interactions at the cellular level are often observed in well-controlled in vitro studies. Several pesticide groups have been found to impair the redox balance in the cell, but the mechanisms leading to oxidative stress for certain pesticides are only partly understood. As our scientific project "Organic pollutants in environment - markers and biomarkers of toxicity (OPENTOX)" is dedicated to studying toxic effects of selected insecticides and herbicides, this review is focused on reporting the knowledge regarding oxidative stress-related phenomena at the cellular level. We wanted to single out the most important facts relevant to the evaluation of our own findings from studies conducted on in vitro cell models.

Fate and ecotoxicological impact of new generation herbicides from the triketone family: An overview to assess the environmental risks

Triketones, derived chemically from a natural phytotoxin (leptospermone), are a good example of allelochemicals as lead molecules for the development of new herbicides. Targeting a new and key enzyme involved in carotenoid biosynthesis, these latest-generation herbicides (sulcotrione, mesotrione and tembotrione) were designed to be eco-friendly and commercialized fifteen-twenty years ago. The mechanisms controlling their fate in different ecological niches as well as their toxicity and impact on different organisms or ecosystems are still under investigation. This review combines an overview of the results published in the literature on β-triketones and more specifically, on the commercially-available herbicides and includes new results obtained in our interdisciplinary study aiming to understand all the processes involved (i) in their transfer from the soil to the connected aquatic compartments, (ii) in their transformation by photochemical and biological mechanisms but also to evaluate (iii) the impacts of the parent molecules and their transformation products on various target and non-target organisms (aquatic microorganisms, plants, soil microbial communities). Analysis of all the data on the fate and impact of these molecules, used pure, as formulation or in cocktails, give an overall guide for the assessment of their environmental risks.

4-Hydroxyphenylpyruvate Dioxygenase and Its Inhibition in Plants and Animals: Small Molecules as Herbicides and Agents for the Treatment of Human Inherited Diseases

This review mainly focuses on the physiological function of 4-hydroxyphenylpyruvate dioxygenase (HPPD), as well as on the development and application of HPPD inhibitors of several structural classes. Among them, one illustrative example is represented by compounds belonging to the class of triketone compounds. They were discovered by serendipitous observations on weed growth and were developed as bleaching herbicides. Informed reasoning on nitisinone (NTBC, 14), a triketone that failed to reach the final steps of the herbicidal design and development process, allowed it to become a curative agent for type I tyrosinemia (T1T) and to enter clinical trials for alkaptonuria. These results boosted the research of new compounds able to interfere with HPPD activity to be used for the treatment of the tyrosine metabolism-related diseases.