Quantitative Analysis of Similarities and Differences in Neurotoxicities Caused by Adenosine and 2′‐Deoxyadenosine in Sympathetic Neurons

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Abstract
These experiments characterize the nucleoside transport and quantify the neurotoxicity of adenosine and 2'-deoxyadenosine (dAdo) in chick sympathetic neurons. We show that [3H]adenosine transport was sensitive to low temperature, specific inhibitors of nucleoside transport, and an excess concentration of adenosine. However, many of these treatments had a marginal effect on [3H]dAdo transport. Total retention of [3H]dAdo over short and long periods was approximately 10 times less than that of [3H]adenosine. These data suggest that adenosine and dAdo enter sympathetic neurons by different routes. Uptake of (3H]norepinephrine ([3H]NE) decreased in neurons damaged by nucleosides and increased to control levels when neurons were protected by various agents against adenosine or dAdo toxicity. These results indicate that [3H]NE uptake serves as a quantitative index of toxicity by the nucleosides. Using this approach we demonstrate that phosphorylation of both nucleosides is essential for their lethal action. For example, iodotubercidin prevented nucleoside-induced neuronal death, but the effect was much more pronounced in the case of dAdo toxicity (IC50 of 0.83 +/- 0.4 vs. 30 +/- 1.6 nM). Another kinase inhibitor, 5'-amino 5'-deoxyadenosine, was effective in protecting neurons against dAdo but had no effect against adenosine toxicity. These results suggest that specific kinases are associated with the phosphorylation of adenosine and dAdo in sympathetic neurons to produce toxic metabolic products. Finally, neurons were susceptible to dAdo toxicity from the time of plating to 4 weeks in culture but were resistant to adenosine toxicity 8 h after plating. In conclusion, our results highlight major differences in the mechanism of neurotoxicity by adenosine and dAdo and provide insights for identification of biochemical pathways leading to neuronal death.

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