Mechanisms of neurotoxicity of organophosphates, carbamates, and alkylating agents

Abstract

Identifying molecular targets and mechanisms of neuronal toxicity has long been a goal in the fields of pharmacology and toxicology. The literature is filled with singular examples of any one drug having an effect on one gene, one time point, on one particular pathway. The advent of DNA microarray technology has changed this singular approach to a more comprehensive and systematic one. In this new microarray experimental paradigm, the expression levels of thousands of genes can be studied in a single experiment. This is important because the rate of the discovery process can increase, and, more importantly, multiple rather than single biomarkers can be found for any particular drug or toxicant. This research focuses on studying the genotoxicity of three selected groups of compounds using a neuronal cell line as a model. These groups are: the organophosphates (chlorpyrifos, chlorpyrifos oxon, diisopropylfluorophosphate, tri-o-cresyl phosphate), the carbamates (pyridostigmine, physostigmine, neostigmine), and the alkylating agents (melphalan, chlorambucil, nitrogen mustard). The hypothesis to be tested is that there are unique genes that can differentiate the aforementioned groups. The specific aims of this proposal are: (1) Complete concentration-response curves for each compound in order to determine which concentration is appropriate for microarray experiments (2) Expose the SK-N-SH neuroblastoma cell line to each compound and isolate mRNA (3) Carry out cDNA microarray studies on all compounds and (4) Determine expression markers for a particular class of toxicants. The relative order for the concentration-response curves, reported from lowest (most toxic) to highest (least toxic) EC 50 is: Melphalan>Nitrogen Mustard>Chlorambucil>TOCP>CPF>CPO>Physostigmine>DFP>Pyridostigmine>Neostigmine. In terms of gene expression analysis, cDNA microarray studies showed that the most statistically significant pathways affected were related to cellular death and cell proliferation.