A study of the age-related effects of lactational atrazine exposure

Aging disrupts the coordination between mRNA and protein expression in mouse and human midbrain

Age-related dopamine (DA) neuron loss is a primary feature of Parkinson's disease. However, it remains unclear whether similar biological processes occur during healthy aging, albeit to a lesser degree. We therefore determined whether midbrain DA neurons degenerate during aging in mice and humans. In mice, we identified no changes in midbrain neuron numbers throughout aging. Despite this, we found age-related decreases in midbrain mRNA expression of tyrosine hydroxylase (Th), the rate limiting enzyme of DA synthesis. Among midbrain glutamatergic cells, we similarly identified age-related declines in vesicular glutamate transporter 2 (Vglut2) mRNA expression. In co-transmitting Th +/Vglut2 + neurons, Th and Vglut2 transcripts decreased with aging. Importantly, striatal Th and Vglut2 protein expression remained unchanged. In translating our findings to humans, we found no midbrain neurodegeneration during aging and identified age-related decreases in TH and VGLUT2 mRNA expression similar to mouse. Unlike mice, we discovered diminished density of striatal TH+ dopaminergic terminals in aged human subjects. However, TH and VGLUT2 protein expression were unchanged in the remaining striatal boutons. Finally, in contrast to Th and Vglut2 mRNA, expression of most ribosomal genes in Th + neurons was either maintained or even upregulated during aging. This suggests a homeostatic mechanism where age-related declines in transcriptional efficiency are overcome by ongoing ribosomal translation. Overall, we demonstrate species-conserved transcriptional effects of aging in midbrain dopaminergic and glutamatergic neurons that are not accompanied by marked cell death or lower striatal protein expression. This opens the door to novel therapeutic approaches to maintain neurotransmission and bolster neuronal resilience.

Use of computational toxicology models to predict toxicological points of departure: A case study with triazine herbicides

BACKGROUND

Atrazine simazine and propazine, widely used triazine herbicides on food crops and in residential areas, disrupt the neuroendocrine system raising human health concerns. USEPA developed a PBPK model based on triazine common Mode of Action (MOA)-suppression of luteinizing hormone surge in female rats-to generate human regulatory points of departure (POD: mg/kg/day). We compared triazine Human Administered Equivalent Dose (AED_Human mg/kg/day) predictions from open access computational tools to the PBPK PODs to assess concordance.

METHODS

Computational tools were the following: ToxCast/Tox21 in vitro assays; Toxicogenomic databases to assess concordance with ToxCast/Tox21 targets; integrated chemical environment (ICE) models with ToxCast/Tox21 inputs to predict AED_Human PODs and population-based age-refined high throughput toxicokinetics (HTTK-Pop) to compare to age-related PBPK PODs.

RESULTS

ToxCast/Tox21 assays identified critical targets in the triazine common MOA and gene databases; ICE AED_Human predictions were mainly concordant with the USEPA PBPK PODs quantitatively. Low fold-differences between PBPK POD and ICE AED_Human predictions indicated that the ICE models are health-protective. HTTK-Pop age-refinements were within 10-fold of the USEPA PBPK PODs.

CONCLUSIONS

CompTox tools were used to identify assay targets in the MOA and identify potential molecular initiating targets in the adverse outcome pathway for potential use in risk assessment.

Mitochondrial dysfunction due to in vitro exposure to atrazine and its metabolite in striatum

Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) has been described as a potential toxic for dopaminergic metabolism both in vivo and in vitro. Its main metabolite diamino-chloro triazine (DACT) has been shown to achieve higher levels in brain tissue than atrazine. The aim of this study was to evaluate the in vitro effects of atrazine and DACT on striatal mitochondrial function, active oxygen species generation, and nitric oxide (NO) content. Incubation of mitochondria with atrazine (10 µM) was not able to modify oxygen consumption. However, a 50% increase in malate-glutamate state 4 respiratory rates was observed after DACT treatment (100 µM) without changes in respiratory state 3. Atrazine was able to inhibit complex I-III activity by 30% and DACT induced a tendency to decrease by 17% in the striatum. Regarding reactive oxygen species (ROS), DACT increased H₂ O₂ production by 43%. Also, superoxide anion levels were higher (14%) after atrazine exposure than in control mitochondria. Incubation of striatal mitochondria with atrazine and DACT induced membrane depolarization by 15% and 19%, respectively. Also, atrazine increased NO content by 10% but no significant changes were observed after exposure of mitochondria to DACT. Glutathione peroxidase activity was inhibited (56%) by DACT and atrazine inhibited superoxide dismutase activity by 60%. Also, cardiolipin oxidation (15%) was observed after atrazine treatment. Summing up, the obtained results suggest that in vitro atrazine and DACT induce ROS production affecting striatal mitochondrial function. The atrazine effects would be attributed to a direct effect on the mitochondrial respiratory chain and superoxide dismutase activity while DACT appears to disturb glutathione-related enzyme system.

Toxicological effects, environmental behaviors and remediation technologies of herbicide atrazine in soil and sediment: A comprehensive review

Atrazine has become one of the most popular applied triazine herbicides in the world due to its high herbicidal efficiency and low price. With its large-dosage and long-term use on a global scale, atrazine can cause widespread and persistent contamination of soil and sediment. This review systematically evaluates the toxicological effects, environmental risks, environmental behaviors (adsorption, transport and transformation, and bioaccumulation) of atrazine, and the remediation technologies of atrazine-contaminated soil and sediment. For the adsorption behavior of atrazine on soil and sediment, the organic matter content plays an extremely important role in the adsorption process. Various models and equations such as the multi-media fugacity model and solute transport model are used to analyze the migration and transformation process of atrazine in soil and sediment. It is worth noting that certain transformation products of atrazine in the environment even have stronger toxicity and mobility than its parent. Among various remediation technologies, the combination of microbial remediation and phytoremediation for atrazine-contaminated soil and sediment has wide application prospects. Although other remediation technologies such as advanced oxidation processes (AOPs) can also efficiently remove atrazine from soil, some potential problems still need to be further clarified. Finally, some related challenges and prospects are proposed.

Bioassays to screen the toxicity in drinking water samples collected in Brazilian rural area

Agriculture activities have increased the concentration of pesticides and metals in the environment. The excessive use of pesticides can generate an environmental impact and contribute to the development of human diseases. This study aimed to determine the presence of pesticides and metals in water samples collected in the Brazilian rural area in two different periods (before and after pesticide application) and to evaluate the alternative bioassays Lactuca sativa, Allium cepa, and Caenorhabditis elegans to monitoring toxicity in human drinking water samples. Eight sites in the rural area were selected and water samples were collected in two different periods of the year (before and after pesticide application). The presence of the pesticides was determinated by ultra-high performance liquid chromatography-tandem mass spectrometry and metals by inductively coupled plasma mass spectrometry. The potential toxicity of the water samples was performed with three different alternatives in vivo models (L. sativa, A. cepa, and C. elegans). Fifty-seven pesticides were analyzed and, according to the results, the most found ones were clomazone, atrazine, tebuconazole, metconazole, pyrimethanil, and carbofuran-3-hydroxide, which is a metabolic degradation product of insecticide carbofuran. The most detected metals were Cu, Cr, Mg, Fe, and Mn. The assays with L. sativa and A. cepa showed alterations in the period after pesticide application, while C. elegans presented changes in both periods compared to the same collection sites. These results indicate that bioassays, especially C. elegans, could be complementary and useful tools for monitoring the toxicity in drinking water samples.

Evaluation of atrazine neurodevelopment toxicity in vitro-application of hESC-based neural differentiation model

Atrazine is one of the widely used herbicides in the world and most of the current researches on atrazine neurodevelopment toxicity have focused on rodents or zebrafish models in vivo, resulting in relatively high cost, time consumption, and lower translational value to identify its hazard for the developing brain. Major international initiatives have pushed forward to convert the traditional animal-based developmental toxicity tests to in vitro assays using human cells to detect and predict chemical health hazards. In this study, we presented a human neural differentiation model based on human embryonic stem cells (hESC) that can be used to test toxicity at different stages of neural differentiation in vitro. hESC were differentiated into neural stem cells (NSC) and then terminally differentiated towards mixed neurons and glial cells for 21 days. Cell survival, proliferation, cell cycle, apoptosis, and gene expression levels were examined. Our results demonstrated that atrazine inhibited the proliferation of hESC and NSC, and showed different toxic sensitivity on these two kinds of cells. Also, atrazine blocked the NSC cell cycle G1 phase via down-regulating CCND1, CDK2, and CDK4, with no obvious effect on apoptosis. In addition, atrazine curbed EB spontaneous differentiation and NSC-induced neurons and glia cells differentiation. Atrazine altered genes expression levels of PAX6, TUBB3, NCAM1, GFAP, TH, NR4A1, and GRIA1. From the data we obtained, we recognized that the dopaminergic system was not the only target of atrazine neurotoxicity, glutamatergic neurons and astrocytes were also adversely affected.

Injury to dopaminergic neurons development via the Lmx1a/Wnt1 autoregulatory loop induced by simazine

Simazine is a kind of persistent organic pollutant that is detected in both ground and water and has several routes of exposure. Here, we explored the mechanisms underlying simazine-related effects on dopaminergic neurons via development-related factors using mouse embryos and embryonic mesencephalic hybrid cell line (MN9D cells). We treated pregnant mice with 50 μg/kg bw, 200 μg/kg bw simazine from the 0.5 day to the 10.5 day of embryonic phase and MN9D cells with 600 μM simazine for 24 h to research the mechanism of dopaminergic neurons acute respond to simazine through preliminary experiments. Protein expressions of LIM homeobox transcription factor 1-alpha (Lmx1a) and LIM homeobox transcription factor 1-beta (Lmx1b) displayed a dose- and time-dependent increase after the exposure to simazine. In the 200 μg/kg bw of embryos and the 24h-600 μM of MN9D cells, protein levels of dopaminergic developmental factors were significantly upregulated, and dopaminergic function was significantly damaged for the abnormal expression of Dyt5b. We demonstrated simazine induced the injury to dopaminergic neurons via the Lmx1a/wingless-related integration site 1 (Wnt1) and Lmx1b pathways. In the transfection experiments, we knocked down Lmx1a and Lmx1b of cells to verify the potential target of simazine-induced injury to dopaminergic neurons, respectively. We detected the protein and mRNA levels of development-related genes of dopaminergic neurons and intracellular dopamine levels in different treatment groups. Based on our experiments' results, we demonstrated an acute response to 24 h-600 μM simazine treatment, the simazine-induced injury to dopaminergic neuronal which leads to abnormal dopamine levels and dopaminergic impairment is via the activation of the Lmx1a/Wnt1 autoregulatory loop. Lmx1a is a promising target in the search for the mechanisms underlying simazine-induced dopaminergic injury.

Brain alterations in GABA, glutamate and glutamine markers after chronic atrazine exposure in the male albino rat

Atrazine (ATR; 2-chloro-4-ethylamino-6-isopropylamino-s-triazine) is an herbicide widely used to kill annual grasses and broadleaf weeds in crops such as corn, sorghum, and sugarcane. Studies in rodents have shown that chronic ATR exposure is associated with alterations in the nigrostriatal dopaminergic pathway such as hyperactivity, decreased striatal dopamine levels, and diminished numbers of tyrosine hydroxylase positive cells in substantia nigra pars compacta. However, the effects of ATR on neurotransmitters such as GABA and glutamate have been scarcely studied. To evaluate the impact of ATR on motor and anxiety tasks, tissue levels of GABA, glutamate, glutamine, and extracellular and potassium-evoked release of glutamate in the striatum, we daily exposed Sprague-Dawley male rats to 1 or 10 mg ATR/kg of body weight for 12-14 months. As previously reported, chronic ATR exposure causes hyperactivity in the group exposed to 10 mg ATR/kg and increased anxiety in both groups exposed to ATR. GABA, glutamate, and glutamine levels were differentially altered in brain regions related to nigrostriatal and mesolimbic systems, the amygdala, and the prefrontal cortex. The groups exposed to 10 mg ATR/kg showed increased extracellular levels and release of glutamate in the striatum. These neurochemical alterations could underlie the behavioral changes observed in rats. These results indicate that chronic exposure to the herbicide ATR disrupts the neurochemistry of several brain structures and could be a risk factor for the development of neurodegenerative diseases.

Profiling epigenetic changes in human cell line induced by atrazine exposure

How environmental chemicals can affect and exert their toxic effect at a molecular level has gained significant interest in recent years, not only for understanding their immediate health implications over exposed individuals, but also for their subsequent progeny. Atrazine (ATZ) is a commonly used herbicide in the U.S. and a long-suspected endocrine disrupting chemical. The molecular mechanism conferring long-term adverse health outcomes, however, remain elusive. Here, we explored changes in epigenetic marks that arise after exposure to ATZ at selected doses using image-based analysis coupled with data clustering. Significant decreases in methylated CpG (^meCpG) and histone 3 lysine 9 tri-methylated (H3K9me3) were observed in the selected human cell line with a clear spatial preference. Treating cells with ATZ leads to the loss of a subpopulation of cells with high ^meCpG levels as identified in our clustering and histogram analysis. A similar trend was observed in H3K9me3 potentially attributing to the cross-talking between ^meCpG and H3K9me3. Changes in ^meCpG are likely to be associated with alterations in epigenetic enzyme expression levels regulating ^meCpG and persist after the removal of ATZ source which collectively provide a plausible mechanism for long-term ATZ-induced toxicity.