Parenteral N,N-diethyldithiocarbamate produces segmental demyelination in the rat that is not dependent on cysteine carbamylation

Abstract

Disulfiram, a dithiocarbamate drug used in alcohol aversion therapy, produces a peripheral neuropathy characterized in rats as segmental demyelination accompanied by generation of S-(diethylaminocarbonyl)cysteine (DETC-Cys) adducts. N,N-Diethyldithiocarbamate (DEDC) is a major metabolite of disulfiram that can undergo methylation and oxidation to S-methyl- N,N-diethylthiocarbamate (MeDETC) sulfoxide and sulfone, thought to be responsible for carbamylation of sulfhydryl functions by disulfiram. To assess the role of cysteine carbamylation in disulfiram toxicity, DEDC and MeDETC were administered parenterally to male Sprague–Dawley rats for 4 and 8 weeks. The roles of the disulfide linkage in disulfiram and of carbamylated glutathione metabolites were assessed by administering S-(diethylaminodithiocarbonyl) N-acetylcysteine (DS-NAC) and S-(diethylaminocarbonyl)- N-acetylcysteine (DETC-NAC), respectively, parenterally for 12 weeks. Following exposure, spinal cord-derived neurofilament preparations and hemoglobin were isolated and analyzed by RP–HPLC and LC/MS/MS for the presence of DETC-Cys adducts. Peripheral nerve sections were also obtained and examined by light and electron microscopy for morphological lesions. RP–HPLC analysis of globin preparations from DEDC-, MeDETC-, and DS-NAC-exposed animals demonstrated a late-eluting peak, identical to that reported for disulfiram-generated DETC-Cys adducts on the β 3-globin chain. DETC-NAC exposure did not result in detectable globin modification by RP–HPLC. The quantity of DETC-Cys adducts produced on globin and neurofilament preparations determined by LC/MS/MS was twofold greater for MeDETC than DEDC following equimolar doses of each compound. Primary myelin lesions consisting of demyelinated axons and myelin splitting were observed in peripheral nerves following exposure to DEDC for 8 weeks. No lesions were detected following exposure to MeDETC, DS-NAC, or DETC-NAC at any time point or dose level. These results are consistent with DEDC, but not the other metabolites, being a demyelinating agent and thus a potential proximate toxic species for disulfiram-mediated demyelination. The production of significantly greater levels of DETC-Cys adducts by MeDETC relative to DEDC in the absence of neurotoxicity for MeDETC is consistent with cysteine carbamylation not contributing to the demyelination produced by disulfiram and DEDC.