Human exposure to dithiocarbamates occurs in agriculture, industry and medicine. Although an understanding of degradative and metabolic pathways is evolving, there is currently little knowledge on the molecular targets and mechanisms underlying the biological affects of dithiocarbamates. The long-range objectives of this project are to delineate the interactions of dithiocarbamates and their metabolites within biological systems and to determine the relevance of these interactions as mechanisms of toxicity and biomarkers. Previous studies revealed the ability of certain dithiocarbamates to produce selective Schwann cell toxicity accompanied by increased levels of copper and lipid peroxidation products in nerve. Investigations in this application are guided by the working hypothesis that these dithiocarbamates bind endogenous copper, form lipophilic complexes and accumulate within myelin resulting in increased lipid peroxidation, oxidative injury and demyelination. This hypothesis will be tested through two specific aims: 1) To determine if copper accumulation and oxidative stress are required for dithiocarbamate-mediated segmental demyelination and 2) To determine the molecular targets and cellular responses in dithiocarbamate-mediated peripheral nerve demyelination.
Aim 1 will be achieved through: a) synthesis of dithiocarbamates differing in their affinity for copper and their copper complex solubility and evaluating their relative potency for lipid peroxidation and demyelination in vivo, b) determining the ability of the non-dithiocarbamate copper chelating agent, cuprizone, to elevate copper and lipid peroxidation in nerve, c) determining if lipid peroxidation and copper accumulation are direct affects of dithiocarbamates through defining the dose response and temporal relationship of these affects to the onset of myelin injury and d) determining if transgenic models with compromised defense to oxidative injury and copper toxicity are more sensitive to dithiocarbamate-mediated demyelination.
Aim 2 will be achieved through a) determining changes in protein expression, b) identifying damaged proteins, c) measuring cuproenzyme activities and d) characterizing the location and chemical species of excess copper produced in nerve by dithiocarbamates. The significance of these studies lies in establishing structure-activity relationships useful for predicting agents that may act through similar mechanisms, identifying susceptible populations, developing mechanistically based exposure recommendations and predicting the affects of long term low level exposures.
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