Electrochemical Analysis Reveals Chlorpyrifos-Induced Dysregulation of Net Astrocytic Glutamate Uptake

Abstract

Chlorpyrifos (CPF), an organophosphate pesticide widely used on food crops and in households, has been a critical public health concern due to its neurotoxic effects. Investigations of CPF-induced neurotoxicity have focused on dysregulation of acetylcholinergic signaling but recent work suggests that alterations in glutamatergic neurotransmission and astrocytic glutamate metabolism may occur. L-glutamate is a major excitatory neurotransmitter that is mostly removed from the synaptic cleft by astrocytic glutamate transporters. Here we assessed the effects of CPF on net glutamate uptake by human-induced pluripotent stem cell derived astrocytes using electrochemical analysis. Our microclinical analyzer (µCA) paired with screen-printed electrodes (SPE) offers an automated sensing system that can be used to monitor cellular metabolism and signaling. In this work, a platinum based SPE combined with the µCA was used to electrochemically quantify glutamate uptake in human astrocytes. Immobilized glutamate oxidase on electrode surfaces provided stable and sensitive glutamate detection. The temperature modification of these electrodes (37°C) led to a nearly four-fold improvement in sensitivity (0.84±0.04 nA/µM), with low limits of detection (2.8±0.1 µM), and quantitation (9.3±0.5 µM). The linear range of the sensor (1-667 µM) is on the same order as typical extracellular glutamate concentrations. These sensors were used to assess the net glutamate uptake efficiency by using escalating concentrations of glutamate (10-200 µM). Glutamate uptake was most efficient when astrocytes were exposed to 50 µM glutamate for 30min (50% net uptake). We are investigating acute and chronic effects of net glutamate uptake using sublethal doses of CPF (0-100 µM). Identifying these cellular mechanisms affected by CPF is critical for the understanding of the impact of organophosphate toxicity.