Glyphosate-containing herbicides are among the most widely-used in the world. Although glyphosate itself is relatively non-toxic, growing evidence suggests that commercial herbicide formulations may lead to increased oxidative stress and mitochondrial inhibition. In order to assess these mechanisms in vivo, we chronically (24h) exposed Caenorhabditis elegans to various concentrations of the glyphosate-containing herbicide TouchDown (TD). Following TD exposure, we evaluated the function of specific mitochondrial electron transport chain complexes. Initial oxygen consumption studies demonstrated inhibition in mid- and high-TD concentration treatment groups compared to controls. Results from tetramethylrhodamine ethyl ester and ATP assays indicated reductions in the proton gradient and ATP levels, respectively. Additional studies were designed to determine whether TD exposure resulted in increased reactive oxygen species (ROS) production. Data from hydrogen peroxide, but not superoxide or hydroxyl radical, assays showed statistically significant increases in this specific ROS. Taken together, these data indicate that exposure of Caenorhabditis elegans to TD leads to mitochondrial inhibition and hydrogen peroxide production.

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Mn/Zn ethylene-bis-dithiocarbamate (Mn/Zn-EBDC) fungicides are among some the most widely-used fungicides in the world. Although they have been available for over 50 years, little is known about their mechanism of action in fungi, or their potentially toxic mechanisms in humans. To determine if exposure of Caenorhabditis elegans (C. elegans) to a representative fungicide (Manzate; MZ) from this group inhibits mitochondria or produces reactive oxygen species (ROS), we acutely (30 min) exposed worms to various MZ concentrations. Initial oxygen consumption studies showed an overall statistically significant decrease in oxygen consumption associated with addition of Complex I- and/or II-substrate in treatment groups compared to controls (*p < 0.05). In order to better characterize the individual complex activity, further studies were completed that specifically assessed Complex II or Complex IV. Data indicated that neither of these two complexes were targets of MZ treatment. Results from tetramethylrhodamine ethyl ester (proton gradient) and ATP assays showed statistically significant reductions in both endpoints (*p < 0.05, **p < 0.01, respectively). Additional studies were completed to determine if MZ treatment also resulted in increased ROS production. These assays provided evidence that hydrogen peroxide, but not superoxide or hydroxyl radical levels were statistically significantly increased (*p < 0.05). Taken together, these data indicate exposure of C. elegans to MZ concentrations to which humans are exposed leads to mitochondrial inhibition and concomitant hydrogen peroxide production. Since mitochondrial inhibition and increased ROS are associated with numerous neurodegenerative diseases, we suggest further studies to determine if MZ catalyzes similar toxic processes in mammals.

Recent data demonstrate that chronic exposure of Caenorhabditis elegans (C. elegans) to a high-use glyphosate-containing herbicide, Touchdown (TD), potentially damages the adult nervous system. It is unknown, however, whether unhatched worms exposed to TD during the egg stage show abnormal neurodevelopment post-hatching. Therefore, we investigated whether early treatment with TD leads to aberrant neuronal or neurite development in C. elegans. Studies were completed in three different worm strains with green fluorescent protein (GFP)-tagged neurons to facilitate visual neuronal assessment. Initially, eggs from C. elegans with all neurons tagged with GFP were chronically exposed to TD. Visual inspection suggested decreased neurite projections associated with ventral nerve cord neurons. Data analysis showed a statistically significant decrease in overall green pixel numbers at the fourth larval (L4) stage (*p < 0.05). We further investigated whether specific neuronal populations were preferentially vulnerable to TD by treating eggs from worms that had all dopaminergic (DAergic) or γ-aminobutyric acid (GABAergic) neurons tagged with GFP. As before, green pixel number associated with these discrete neuronal populations was analyzed at multiple larval stages. Data analysis indicated statistically significant decreases in pixel number associated with DAergic, but not GABAergic, neurons (***p< 0.001) at all larval stages. Finally, statistically significant decreases (at the first larval stage, L1) or increases (at the fourth larval stage, L4) in superoxide levels, a developmental signaling molecule, were detected (*p < 0.05). These data suggest that early exposure to TD may impair neuronal development, perhaps through superoxide perturbation. Since toxic insults during development may late render individuals more vulnerable to neurodegenerative diseases in adulthood, these studies provide some of the first evidence in this model organism that early exposure to TD may adversely affect the developing nervous system.