Disulfiram neurotoxicity in the rat: Characterization of peripheral nerve lesions and evaluation of carbon disulfide, N,N-diethyldithiocarbamate, and S-methyl-N,N,-diethylthiocarbamate as proximate toxic metabolites

Disulfiram is a dithiocarbamate drug used clinically for treatment of alcoholism that produces peripheral neuropathy in humans by an unknown mechanism. The goal of this work was to characterize the peripheral nerve lesions produced by disulfiram in the rat and evaluate three metabolites of disulfiram as proximate toxicants. The metabolites evaluated were carbon disulfide (CS₂), which has been demonstrated to effect covalent cross-linking of proteins and the development of a neurofilamentous axonopathy, S-methyl- N,N-diethyldithiocarbamate (MeDETC), that can be bioactivated to a sulfoxide that carbamylates protein cysteine residues, and N,N-diethyldithiocarbamate (DEDC), than can chelate copper and transport it into the nervous system.{09} The neurotoxicity and ability of disulfiram and these metabolites to form protein modifications was assessed by administration to rats either orally in the diet or ip via osmotic infusion pump. Oral administration of disulfiram was shown to produce peripheral nerve lesions seen by light and electron microscopy consistent with Schwann cell injury and segmental demyelination in peripheral nerves, rather than a CS₂-induced axonpathy. Evidence of CS₂-mediated protein cross-linking was also absent. Formation of an S-(diethylaminocarbonyl)cysteine (DETC-Cys) adduct on hemoglobin and spinal cord proteins prior to formation of lesions was identified by mass spectrometry, consistent with carbamylation by McDETC sulfoxide. However, although ip administration of McDETC resulted in high levels of DETC-Cys adducts, no peripheral neurotoxicity was observed. DEDC was shown to produce peripheral nerve demyelination similar to disulfiram when administered ip and resulted in elevated copper in the sciatic nerve, liver, and brain, presumably due to chelation and transport of copper by DEDC. Feeding an elevated copper diet did not modulate the toxicity of DEDC, but also did not increase copper levels in peripheral nerve tissue over DEDC administration alone. The conclusion of this work is that disulfiram produces a segmental demyelination in the rat that does not result from carbon disulfide-mediated covalent cross-linking or from DETC-Cys adducts on proteins, but instead may be due to alterations in copper storage by the copper-chelating metabolite DEDC.