The delayed genotoxic effect of N-nitroso N-propoxur insecticide in mammalian cells

Assessment of transplacental and lactational genotoxicity of tembotrione in Wistar rats at different developmental stages by alkaline comet assay

This paper assessed the potential of trans-placental and -lactational genotoxicity and oxidative stress induction of tembotrione, a naturally derived allelopathic herbicide. Several treatment protocols were applied to measure primary DNA damage by alkaline comet assay in leucocytes and liver. To address the oxidative stress induction, TBARS, ROS, SOD, CA, GSH-Px activity were recorded. The dams were treated from the first gestation day and pups sacrificed after birth. The second treatment protocol comprised treating the dams during gestation and lactation and sacrificing the pups at weaning. The third group of pups comprised offspring of dams that were treated in gestation and lactation and sacrificed in puberty. To address translactational genotoxicity, dams were treated in lactation only. Dams treated in gestation and lactation were sacrificed after reentering the estrous cycle and analyzed for DNA damage and oxidative stress. Tembotrione doses encountered in everyday human exposure, as estimated by the EFSA, were applied in dam treatment in consecutive days (ADI: 0.0004 mg/kg b.w./day, AOEL: 0.0007 mg/kg b.w./day, 1/500 LD₅₀ 4.0 mg/kg b.w./day). Although we observed mitigated DNA integrity at the dose of 4.0 mg/kg/b.w./day in female pubertal rats, we can conclude that at the conditions employed in the study low doses of tembotrione do not pose a risk for DNA damage of the offspring of treated dams. Contrary to this, the highest dose significantly affected all the oxidative stress parameters in the liver and plasma of pubertal females, CAT and GSH-Px in the liver of males and ROS and CAT of dams.

Conserved Metabolic and Evolutionary Themes in Microbial Degradation of Carbamate Pesticides

Carbamate pesticides are widely used as insecticides, nematicides, acaricides, herbicides and fungicides in the agriculture, food and public health sector. However, only a minor fraction of the applied quantity reaches the target organisms. The majority of it persists in the environment, impacting the non-target biota, leading to ecological disturbance. The toxicity of these compounds to biota is mediated through cholinergic and non-cholinergic routes, thereby making their clean-up cardinal. Microbes, specifically bacteria, have adapted to the presence of these compounds by evolving degradation pathways and thus play a major role in their removal from the biosphere. Over the past few decades, various genetic, metabolic and biochemical analyses exploring carbamate degradation in bacteria have revealed certain conserved themes in metabolic pathways like the enzymatic hydrolysis of the carbamate ester or amide linkage, funnelling of aryl carbamates into respective dihydroxy aromatic intermediates, C1 metabolism and nitrogen assimilation. Further, genomic and functional analyses have provided insights on mechanisms like horizontal gene transfer and enzyme promiscuity, which drive the evolution of degradation phenotype. Compartmentalisation of metabolic pathway enzymes serves as an additional strategy that further aids in optimising the degradation efficiency. This review highlights and discusses the conclusions drawn from various analyses over the past few decades; and provides a comprehensive view of the environmental fate, toxicity, metabolic routes, related genes and enzymes as well as evolutionary mechanisms associated with the degradation of widely employed carbamate pesticides. Additionally, various strategies like application of consortia for efficient degradation, metabolic engineering and adaptive laboratory evolution, which aid in improvising remediation efficiency and overcoming the challenges associated with in situ bioremediation are discussed.

Screening of Pesticides with the Potential of Inducing DSB and Successive Recombinational Repair

A study was realized to ascertain whether eight selected pesticides would induce double strand breaks (DSB) in lymphocyte cultures and whether this damage would induce greater levels of proteins Rad51 participating in homologous recombination or of p-Ku80 participating in nonhomologous end joining. Only five pesticides were found to induce DSB of which only glyphosate and paraoxon induced a significant increase of p-Ku80 protein, indicating that nonhomologous end joining recombinational DNA repair system would be activated. The type of gamma-H2AX foci observed was comparable to that induced by etoposide at similar concentrations. These results are of importance since these effects occurred at low concentrations in the micromolar range, in acute treatments to the cells. Effects over longer exposures in actual environmental settings are expected to produce cumulative damage if repeated events of recombination take place over time.

Assessment of genotoxicity of Lannate-90® and its plant and animal metabolites in human lymphocyte cultures

This study evaluated direct and metabolic genotoxic effects caused by Lannate-90®, a methomyl-based formulation (90 % active ingredient), in human lymphocyte cultures using sister chromatid exchange assay (SCE). Two processes were used for the plant promutagens evaluation: in vivo activation, applying the insecticide systemically in plants for 4 h and subsequently adding plant metabolites containing extracts to lymphocyte cultures; and in vitro activation, where the insecticide was incubated with Vicia faba S10 mix plus human lymphocyte culture. Direct treatment with the insecticide significantly increased SCE frequency in human lymphocytes (250-750 mgL-1), with cellular death observed at 1000 mgL-1 concentration. Using the extracts of Vicia faba treated with Lannate-90® to treat human lymphocytes, a dose-response relationship was observed. In lymphocyte cultures treated directly with the insecticide for 2 h, a negative response was obtained. When S10 mix was added, SCE frequency did not change significantly. Meanwhile, a mixture of S9 mammalian metabolic mix and Lannate-90® increased the SCE frequency, with an observed concentration-dependent response. Although Lannate-90® induced cellular death at the highest concentrations, it did not cause a delay in cell proliferation in any of the treatments, confirming its genotoxic action. This study is one of the first to evaluate and compare the direct effect of Lannate-90® in two bioassays, animal and vegetal, and the effect of plant and animal metabolism on its genotoxic potential.

SIRT3 mediates decrease of oxidative damage and prevention of ageing in porcine fetal fibroblasts

AIMS

Sirtuin 3 (SIRT3) is a mitochondria-specific protein required for the deacetylation of metabolic enzymes and the action of oxidative phosphorylation by acting as a nicotinamide adenine dinucleotide (NAD⁺)-dependent deacetylase. SIRT3 increases oxidative stress resistance and prevents mitochondrial decay associated with ageing in response to caloric restriction. However, the effects of SIRT3 on oxidative damage and ageing are not well understood. We investigated the physiological functions of porcine SIRT3 on the damage and ageing in porcine fetal fibroblasts (PFFs).

MAIN METHODS

Overexpression and knockdown of SIRT3 were confirmed by quantitative real-time polymerase chain reaction (qRT-PCR) and western blot analysis, respectively. All cells were treated with three different stress reagents 12-o-tetradecanoylphorbol-13-acetate (TPA), methanesulfonic acid methylester (MMS), and tert-butylhydroperoxide (t-BHP), respectively, and then examined by flow cytometry following JC-1 (5, 5', 6, 6'-tetrachloro-1, 1', 3, 3'-tetraethylbenzimidazol-carbocyanine iodide) staining.

KEY FINDINGS

SIRT3 overexpression enhanced the ability of superoxide dismutase 2 (SOD2) to reduce cellular reactive oxygen species (ROS), which further decreased the damage to the membranes and the organelles of the cells, especially to mitochondria. It inhibited the initial decrease of mitochondrial membrane potential, and prevented the decrease of adenosine triphosphate (ATP) production and activity of Nampt. In contrast, SIRT3 knockdown reduced the ability of SOD2 to increase cellular ROS which was directly correlated with stress-induced oxidative damage and ageing in PFFs.

SIGNIFICANCE

Our findings identify one function of SIRT3 in PFFs was to dampen cytotoxicity, and, therefore, to decrease oxidative damage and attenuate ageing possibly by enhancing the activity of SOD2.

Carbofuran alters centrosome and spindle organization, and delays cell division in oocytes and mitotic cells

Although many countries banned of its usage, carbofuran (CF) is still one of the most commonly used carbamate derivative insecticides against insects and nematodes in agriculture and household, threatening the human and animal health by contaminating air, water, and food. Our goal was to evaluate the potential toxic effects of CF on mammalian oocytes besides mitotic cells. Caspase-dependent apoptotic pathway was assessed by immunofluorescence and western blot techniques. Alterations in the meiotic spindle formation after CF exposure throughout the in vitro maturation of mice oocyte-cumulus complexes (COCs) were analyzed by using a 3D confocal laser microscope. Maturation efficiency and kinetics were assessed by direct observation of the COCs. Results indicated that the number of TUNEL-positive cells increased in CF-exposed groups, particularly higher doses (>250 µM) in a dose-dependent fashion. The ratio of anticleaved caspase-3 labeled cells in those groups positively correlated with TUNEL-positivity. Western blot analysis confirmed a significant increase in active caspase-3 activity. CF caused a dose-dependent accumulation of oocytes at prometaphase-I (PM-I) of meiosis. Partial loss of spindle microtubules (MTs) was noted, which consequently gave rise to a diamond shape spindle. Aberrant pericentrin foci were noted particularly in PM-I and metaphase-I (M-I) stages. Conclusively, CF (1) induces programmed cell death in a dose-dependent manner, and (2) alters spindle morphology most likely through a mechanism that interacts with MT assembly and/or disorientation of pericentriolar proteins. Overall, data suggest that CF could give rise to aneuploidy or cell death in higher doses, therefore reduce fertilization and implantation rates.

Cell cycle deregulation by methyl isocyanate: Implications in liver carcinogenesis

Liver is often exposed to plethora of chemical toxins. Owing to its profound physiological role and central function in metabolism and homeostasis, pertinent succession of cell cycle in liver epithelial cells is of prime importance to maintain cellular proliferation. Although recent evidence has displayed a strong association between exposures to methyl isocyanate (MIC), one of the most toxic isocyanates, and neoplastic transformation, molecular characterization of the longitudinal effects of MIC on cell cycle regulation has never been performed. Here, we sequentially delineated the status of different proteins arbitrating the deregulation of cell cycle in liver epithelial cells treated with MIC. Our data reaffirms the oncogenic capability of MIC with elevated DNA damage response proteins pATM and γ-H2AX, deregulation of DNA damage check point genes CHK1 and CHK2, altered expression of p53 and p21 proteins involved in cell cycle arrest with perturbation in GADD-45 expression in the treated cells. Further, alterations in cyclin A, cyclin E, CDK2 levels along with overexpression of mitotic spindle checkpoints proteins Aurora A/B, centrosomal pericentrin protein, chromosomal aberrations, and loss of Pot1a was observed. Thus, MIC impacts key proteins involved in cell cycle regulation to trigger genomic instability as a possible mechanism of developmental basis of liver carcinogenesis.

Carbamate insecticide methomyl confers cytotoxicity through DNA damage induction

Carbamate insecticide methomyl could induce genotoxic effects, including micronuclei, chromosome aberrations and sister-chromatid exchanges. However, methomyl induction of cytotoxicity through DNA damage is largely unknown. Here we identify cytotoxicity and potential genotoxicity of methomyl in vitro. We have employed alkaline comet assay, γH2AX foci formation and DNA ladder assay to detected DNA damage and apoptosis of Drosophila S2, HeLa and HEK293 cells. The alkaline comet assay was used to evaluate total DNA single strand breaks (SSBs) in the target cells exposed in vitro to sublethal concentrations of methomyl. As expected, methomyl induced significant concentration-dependent increases in DNA damage of target cells compared with the negative control, as measured by increases in tail length (μm), tail DNA (percentage of the comet tail) and tail moment (arbitrary units). In agreement with the comet assay data, the percentage of γH2AX positive reaction in HeLa cells also revealed methomyl caused DNA double strand breaks (DSBs) in a time-dependent manner. Moreover, methomyl induced a significant increase of apoptosis in Drosophila S2, HeLa and HEK293 cells in a concentration- and time-dependent manner, as determined by Urea PAGE DNA fragmentation analysis. In conclusion, methomyl is a strongly genotoxic agent that induces cell DNA damage and apoptosis in vitro at these sublethal concentrations.

Sublethal propoxur toxicity to juvenile common carp (Cyprinus carpio L., 1758): biochemical, hematological, histopathological, and genotoxicity effects

The sublethal toxicological and genotoxic potential of propoxur, a widely used carbamate insecticide against household pests, in veterinary medicine, and in public health, was evaluated on carp as a model species (Cyprinus carpio L., 1758) using the erythrocyte micronucleus test. Based on the 96-h lethal concentration, 50% (LC50) data from the U.S. Environmental Protection Agency ECOTOX Database (10 mg/L), a sublethal exposure concentration of 5 mg/L was used under static bioassay laboratory conditions. Histopathological evaluation showed no significant changes in spleen, intestine, muscle, or skin tissues. However, the following conditions were recorded: hyperemia, branchitis in primary lamella, and telangiectasis, hyperplasia, fusion, epithelial lifting, and epithelial desquamation in secondary lamella of gill tissues; hemorrhage, destruction, prenephritis, and inflammation and desquamation in the tubules; edema in the kidney; passive hyperemia, albumin, and hydropic degeneration in the liver; and hyperemia, chromatolysis, and glial proliferation in brain tissues. No statistically significant increases in micronuclei frequencies were found. Hematological parameters showed decreased hematocrit values and mean corpuscular volume values, as well as increased erythrocyte and leukocyte counts compared with the control group (p < 0.01). Plasma glucose, cholesterol, triglycerides, phosphorus, sodium, total plasma protein, chloride, and aspartate aminotransferase levels were increased (p < 0.01). Only plasma calcium and potassium levels decreased in the experimental group. Propoxur has an ecotoxicological potential on fish, a nontarget organism.

Mitochondrial oxidative stress elicits chromosomal instability after exposure to isocyanates in human kidney epithelial cells

The role of oxidative stress is often attributed in environmental renal diseases. Isocyanates, a ubiquitous chemical group with diverse industrial applications, are known to undergo bio-transformation reactions upon accidental and occupational exposure. This study delineates the role of isocyanate-mediated mitochondrial oxidative stress in eliciting chromosomal instability in cultured human kidney epithelial cells. Cells treated with 0.005 microM concentration of methyl isocyanate displayed morphological transformation and stress-induced senescence. Along the time course, an increase in DCF fluorescence indicative of oxidative stress, depletion of superoxide dismutase (SOD) and glutathione reductase (GR) and consistent accumulation of 8-oxo-dG were noticed. Thus, endogenous oxidative stress resulted in aberrant expression of p53, p21, cyclin E and CDK2 proteins, suggestive of deregulated cell cycle, chromosomal aberrations, centromeric amplification, aneuploidy and genomic instability.

Sister chromatid exchanges and chromosomal aberrations in Chinese hamster ovary (CHO-K1) cells treated with the insecticide pirimicarb

Pirimicarb and its formulation Aficida (50% pirimicarb) effects were studied on CHO-K1 cells employing sister chromatid exchange (SCE), chromosomal aberrations (CA), cell-cycle progression and mitotic index analyses. Continuous treatments were performed within 10-300 microg/ml concentration-range. Pirimicarb, but not Aficida, induced a concentration-dependent increase of abnormal cells. Pirimicarb induced a greater frequency of chromatid/isochromatid breaks than Aficida did. Regression analyses showed a concentration-dependent increase in the frequency of chromatid-type breaks for both compounds whereas only the frequency of isochromatid-type breaks did in those pirimicarb-treated cultures. SCEs in pirimicarb- or Aficida-treated cultures were significantly higher than control values with concentrations of 100-200 microg/ml. Both test compounds induced equivalent frequency of SCEs. A delay in cell-cycle kinetics was observed for pirimicarb and Aficida within 100-300 and 200-300 microg/ml concentration-range, respectively. An inhibition of MI was observed for both chemicals regardless of tested concentrations. Finally, the CAs appears to be a higher sensitive bioassay to detect DNA damage at lower concentrations of pirimicarb than SCEs does. The results demonstrated that pirimicarb and Aficida exert geno-cytotoxicity, at least in CHO-K1 cells.

Effect of N-metylcarbamate pesticide bendiocarb on cattle lymphocytes after in vitro exposure

Bendiocarb is a carbamate broad-spectrum insecticide used to control disease vectors such as mosquitoes and flies, as well as household and agricultural pests. Nowadays, only few papers reporting cytogenetic or possible genotoxic effect of this insecticide on mammalian cells are available. In the present study 24-hour exposure to bendiocarbamate at concentrations ranging from 20 to 160 μg/ml was used for investigation of unstable chromosomal aberrations (CA), sister chromatid exchanges (SCE) and stable chromosomal aberration induction in cultured bovine peripheral lymphocytes. The slight but no significant increase of chromatide breaks frequency was observed after the exposure of lymphocytes to 80 μg/ml of bendiocarb. At the highest concentration added to the cell cultures (160 μg/ml) mitotic index decrease was shown in both donors (p < 0.05; p < 0.01). Both statistically significant elevation of SCEs (p < 0.05) and a reduction of proliferative indices (PI) (p < 0.01) were shown at a dose of 80 μg/ml. By means of two fluorescent-labelled whole chromosome-painting probes, stable aberrations such as bovine chromosome 1 and 5 translocation as well as numerical aberrations (polyploidies, heteroploidies) were visualised under fluorescent microscope in some examined metaphases.

Analysis of cellular response to isocyanate using N-succinimidyl N-methylcarbamate exposure in cultured mammalian cells

Isocyanates (R--N==C==O), one of the highly reactive industrial intermediates, possess the capability to modulate the bio-molecules by forming toxic metabolites and adducts which may cause adverse health effects. Some of their toxic degradations have previously been unknown and overlooked; of which, molecular repercussions underlying their genetic hazards upon occupational/accidental exposures still remain as an intricate issue and are hitherto unknown. To assess the genotoxic potential of methyl isocyanate in cultured mammalian cells after in vitro exposure, we performed a study in three different normal cell lines MM55.K (mouse kidney epithelial), B/CMBA.Ov (mouse ovarian epithelial), and NIH/3T3 (primary mouse embryonic fibroblast). Cellular DNA damage response was studied for qualitative phosphorylation states of ATM, gammaH2AX proteins and quantitative state of p53 phosphorylation; DNA cell cycle analysis and measure of cellular apoptotic index before and after treatment were also investigated. Our results demonstrate that methyl isocyanate by negatively regulating the DNA damage response pathway, might promote cell cycle arrest, and apoptosis in cultured mammalian cells suggestive of causing genetic alterations. We anticipate that these data along with other studies reported in the literature would help to design better approaches in risk assessment of occupational and accidental exposure to isocyanates. We also predict that increasing knowledge on DNA damage-triggered signaling leading to cell death could provide new strategies for investigating the effects of DNA repair disorders and decreased repair capacity on the toxicity and carcinogenic properties of environmental toxins.