Herbicide and Local Anesthetic Toxicity: Physiological Characterization, Targeted Proteomics, Metabolomics, and Protein Dynamics

Mechanisms of xenobiotic toxicity and detoxification are diverse. The goal of the current work was to identify and characterize these mechanisms using the model organism Saccharomyces cerevisiae grown to stationary phase on aerobic carbon sources. After initial screening of roughly a dozen xenobiotics at LC50 potency the xenobiotics selected for further study and characterization were 2,4-dichlorophenoxyacetic acid (2,4-D) and lidocaine. These xenobiotics were chosen due to distinct differences in physiological aberrations, generation of reactive oxygen species (ROS), and cell death pathways. In addition, 2,4-D and lidocaine are the most widely used xenobiotics for their respective applications, they both effect the central nervous system (CNS), and current knowledge of their biochemical mechanism(s) leading to toxicity and cellular demise is lacking. Due to their pro-oxidant effect, hydrogen peroxide was used as a positive control. Temporal assessment of physiological aberrations revealed that 2,4-D causes initial mitochondrial depolarization and an increased oxidative cellular environment that is partially restored to control levels at later time points. Lidocaine exposure causes persistent mitochondrial depolarization, an increased oxidative cellular environment, and temporal increase in intracellular calcium. Examination of metabolic pathways indicates that lidocaine has extreme effects on carbohydrate metabolism and general bioenergetics; causing carbon to cycle through the pentose phosphate pathway (PPP) and the preparatory phase of glycolysis. 2,4-D causes initial decrease in TCA cycle input from glycolysis and oxidatively modified monooxygenase enzymes involved in protein folding and ubiquinone biosynthesis. Phosphatidylserine externalization assay and genetic knockout screen implied that lidocaine induces metacaspase dependent apoptosis; 2,4-D induces cell death through Atg12 dependent autosis. Aggregation prone protein, α-synuclein in S. cerevisiae and Caenorhabditis elegans models displayed that lidocaine induces α-synuclein membrane dissociation, cleavage, aggregation, and dopaminergic neuron cell death. While 2,4-D had little effect on α-synuclein dynamics in the S. cerevisiae model, it did have temporally different, yet similar effects of aggregation, and dopaminergic neuron cell death in C. elegans models. Collectively, this work revealed unique biochemical alterations upon exposure to toxic levels 2,4-D and lidocaine that lead to cellular demise