Toxicity studies of depleted uranium in primary rat cortical neurons and in Caenorhabditis elegans

Depleted Uranium (DU) is the major by-product of the uranium enrichment process for its more radioactive isotopes. DU still retains 60% of its natural radioactivity, but its properties as a pyrophoric and very dense metal have resulted in its usage in armor and ammunitions. Questions have been raised regarding possible neurotoxic effects of DU in humans based on follow-up studies in which there was decreased neurocognitive behavior in a small population of Gulf War veterans. Additional studies in rodent models indicate that DU can traverse the blood-brain barrier, accumulate in specific brain regions, and can result in increased oxidative stress, altered electrophysiological profiles, and sensorimotor deficits. To date, there have been limited studies into understanding the specific chemical effects of DU in the central nervous system (CNS) using reductionist methodologies. In the absence of focused molecular studies on cells of CNS origin, we have used primary rat cortical neuron cultures, and the nematode Caenorhabditis elegans (C. elegans ), to evaluate the effects of DU. We have also used the power of the C. elegans model as a quick screen to identify molecular targets of interest.In assessing the toxic potential of DU in primary rat cortical neurons, we evaluated a number of endpoints apart from cell viability and cytotoxicity. These endpoints included thiol metabolite levels, high energy phosphate levels, and isoprostane levels. We also used two C. elegans strains with green fluorescent protein labeled neurons, under the transcriptional control of neural-specific promoters, to assist in quantifying if there was any significant neurodegeneration following DU exposure. Together, our data specifically regarding the cells of CNS origin indicate that DU exhibits low neurotoxic potential, and results in minimal changes in thiol metabolism, high energy phosphates, and lipid peroxidation products.The nematode model provides numerous advantages, including a rapid replication cycle, sequenced genome, numerous genetic mutants freely available, ease of growth, maintainence, and manipulation. We harnessed the C. elegans model to screen through a number of different genetic strains using concentration-response profiles to identify molecular targets of interest. We then performed more focused studies to try and determine the molecular mechanism(s) by which DU causes shifts in the concentration-response profile. Our studies demonstrated that the metallothioneins, small thiol-rich proteins, appear to be protective against DU exposure, and that nematode death is not a result of increased uranium accumulation by the worms. Additionally, our studies with different metallothionein knockouts demonstrated that only one of the two forms, metallothionein-1, appears to be important for the ability to accumulate uranium in the worms.Overall, our studies have added to our understanding of the effects of DU exposure on cells of CNS origin, and in C. elegans. Although in vitro models may not fully recapitulate human health and disease, our focused studies indicate that cortical neurons can tolerate high doses of DU without significant oxidative injury or death. Altogether, the results of our studies in primary rat cortical neurons and in C. elegans demonstrate low neurotoxic potential of DU, and should alleviate some of the concern surrounding DU as a neurotoxin, and a chemical that may be responsible for Gulf War Syndrome.