N,N-Diethyldithiocarbamate Produces Copper Accumulation, Lipid Peroxidation, and Myelin Injury in Rat Peripheral Nerve

Abstract

Previous studies have demonstrated the ability of the dithiocarbamate, disulfiram, to produce a peripheral neuropathy in humans and experimental animals and have also provided evidence that N,N-diethyldithiocarbamate (DEDC) is a proximate toxic species of disulfiram. The ability of DEDC to elevate copper levels in the brain suggests that it may also elevate levels of copper in peripheral nerve, possibly leading to oxidative stress and lipid peroxidation from redox cycling of copper. The study presented here investigates the potential of DEDC to promote copper accumulation and lipid peroxidation in peripheral nerve. Rats were administered either DEDC or deionized water by ip osmotic pumps and fed a normal diet or diet containing elevated copper, and the levels of metals, isoprostanes, and the severity of lesions in peripheral nerve and brain were assessed by ICP-AES/AAS, GC/MS, and light microscopy, respectively. Copper was the only metal that demonstrated any significant compound-related elevations relative to controls, and total copper was increased in both brain and peripheral nerve in animals administered DEDC on both diets. In contrast, lesions and elevated F2-isoprostanes were significantly increased only in peripheral nerve for the rats administered DEDC on both diets. Autometallography staining of peripheral nerve was consistent with increased metal content along the myelin sheath, but in brain, focal densities were observed, and a periportal distribution occurred in liver. These data are consistent with the peripheral nervous system being more sensitive to DEDC-mediated demyelination and demonstrate the ability of DEDC to elevate copper levels in peripheral nerve. Additionally lipid peroxidation appears to either be a contributing event in the development of demyelination, possibly through an increase of redox active copper, or a consequence of the myelin injury.

Copper accumulation and lipid oxidation precede inflammation and myelin lesions in N,N-diethyldithiocarbamate peripheral myelinopathy

“…In contrast, although liver copper levels were significantly elevated at the two-week exposure period, there appeared to be no further increase with longer exposures to DEDC. Furthermore, the magnitude of the increase in liver was similar to that observed previously (Tonkin et al, 2004) and was substantially below what would be expected to effect hepatotoxicity (Cisternas et al, 2005). Thus the cumulative increases in copper levels in the nervous system appear to be a direct and specific effect of DEDC.…”

“…The copper levels within the nervous system were positively correlated to the duration of exposure (p < 0.05 by the Pearson correlation test, r 2 = 0.99 brain and r 2 = 0.85 nerve). As observed in previous studies, the magnitude of the increase in total copper was substantially greater for the CNS relative to the PNS (Tonkin et al, 2004). In contrast, although liver copper levels were significantly elevated at the two-week exposure period, there appeared to be no further increase with longer exposures to DEDC.…”

“…Previous investigations have demonstrated that DEDC produces significant elevations of copper in the central (CNS) and peripheral (PNS) nervous systems (Delmaestro and Trombetta, 1995;Tonkin et al, 2004), and that the ability of DEDC to disrupt metal homeostasis appears specific for copper and predominantly affects the nervous system (Tonkin et al, 2004;Valentine et al, 2006). The current study supplements those previous studies through demonstrating that significant elevations in copper substantially precede the onset of myelin structural changes produced by DEDC in peripheral nerve.…”

“…Globin isolation and analysis to quantify adduct formation was performed as previously described Tonkin, 2004). Blood was separated into plasma and red blood cells, the cells lysed to produce hemolysate, and 100 μL of 1 N ascorbic acid added to each 1 mL hemolysate.…”

“…However, the molecular processes underlying the myelinopathy are not well defined. Previous studies have reported increased levels of copper and lipid oxidation to be associated with dithiocarbamate induced neurotoxicity (Calviello, 2005;Delmaestro, 1995;Tonkin, 2004) and correlative data have shown a relationship between copper levels in peripheral nerve and the severity of myelin injury produced by pyrrolidine dithiocarbamate and N,Ndiethyldithiocarbamate (DEDC) in rodent models (Valentine et al, 2006;Valentine et al, 2007). Additionally, proteomic analysis of sciatic nerve proteins using this animal model has demonstrated significant elevations in expression levels of glutathione transferase isozymes within Schwann cells consistent with activation of the antioxidant response element pathways subsequent to DEDC exposure (Viquez et al, 2007).…”