Background: Peri-spinal subarachnoid (intrathecal; i.t.) injection of non-viral naked plasmid DNA encoding the\nanti-inflammatory cytokine, IL-10 (pDNA-IL-10) suppresses chronic neuropathic pain in animal models. However, two\nsequential i.t. pDNA injections are required within a discrete 5 to 72-hour period for prolonged efficacy. Previous reports\nidentified phagocytic immune cells present in the peri-spinal milieu surrounding the i.t injection site that may play a\nrole in transgene uptake resulting in subsequent IL-10 transgene expression.\nMethods: In the present study, we aimed to examine whether factors known to induce pro-phagocytic\nanti-inflammatory properties of immune cells improve i.t. IL-10 transgene uptake using reduced naked pDNA-IL-10\ndoses previously determined ineffective. Both the synthetic glucocorticoid, dexamethasone, and the hexose sugar,\nD-mannose, were factors examined that could optimize i.t. pDNA-IL-10 uptake leading to enduring suppression of\nneuropathic pain as assessed by light touch sensitivity of the rat hindpaw (allodynia).\nResults: Compared to dexamethasone, i.t. mannose pretreatment significantly and dose-dependently prolonged\npDNA-IL-10 pain suppressive effects, reduced spinal IL-1�Ÿ and enhanced spinal and dorsal root ganglia IL-10\nimmunoreactivity. Macrophages exposed to D-mannose revealed reduced proinflammatory TNF-a, IL-1�Ÿ, and nitric\noxide, and increased IL-10 protein release, while IL-4 revealed no improvement in transgene uptake. Separately,\nD-mannose dramatically increased pDNA-derived IL-10 protein release in culture supernatants. Lastly, a single i.t.\nco-injection of mannose with a 25-fold lower pDNA-IL-10 dose produced prolonged pain suppression in neuropathic rats.\nConclusions: Peri-spinal treatment with D-mannose may optimize naked pDNA-IL-10 transgene uptake for suppression\nof allodynia, and is a novel approach to tune spinal immune cells toward pro-phagocytic phenotype for improved\nnon-viral gene therapy
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