Research on communication between glia and neurons has increased in the past decade. The onset of neuropathic pain, a major clinical problem that is not resolved by available therapeutics, involves activation of spinal cord glia through the release of proinflammatory cytokines in acute animal models of neuropathic pain. Here, we demonstrate for the first time that the spinal action of the proinflammatory cytokine, interleukin 1 (IL-1) is involved in maintaining persistent (2 months) allodynia induced by chronic-constriction injury (CCI). The anti-inflammatory cytokine IL-10 can suppress proinflammatory cytokines and spinal cord glial amplification of pain. Given that IL-1 is a key mediator of neuropathic pain, developing a clinically viable means of long-term delivery of IL-10 to the spinal cord is desirable. High doses of intrathecal IL-10-gene therapy using naked plasmid DNA (free pDNA-IL-10) is effective, but the dose required limits its potential clinical utility. Here we show that intrathecal gene therapy for neuropathic pain is improved sufficiently using two, distinct synthetic polymers, poly(lactic-co-glycolic) and polyethylenimine, that substantially lower doses of pDNA-IL-10 are effective. In conclusion, synthetic polymers used as i.t. gene-delivery systems are well-tolerated and improve the long-duration efficacy of pDNA-IL-10 gene therapy.

Introduction Current research indicates that chronic peripheral neuropathic pain includes a role for glia and the actions of proinflammatory factors. This review briefly discusses the glial and cytokine responses that occur following peripheral nerve damage in support of utilizing anti-inflammatory cytokine interleukin-10 therapy to suppress chronic peripheral neuropathic pain. Spinal Non-viral Interleukin-10 Gene Therapy IL-10 is one of the most powerful endogenous counter-regulators of pro-inflammatory cytokine function that acts in the nervous system. Subarachnoid (intrathecal) spinal injection of the gene encoding IL-10 delivered by non-viral vectors has several advantages over virally-mediated gene transfer methods and leads to profound pain relief in several animal models. Non-viral gene delivery Lastly, data are reviewed that non-viral DNA encapsulated by a biologically safe co-polymer, poly(lactic-co-glycolic) acid (PLGA), thought to protect DNA, leads to significantly improved therapeutic gene transfer in animal models, which additionally and significantly extends pain relief. Conclusions The impact of these early studies exploring anti-inflammatory genes emphasizes the exceptional therapeutic potential of new biocompatible intrathecal non-viral gene delivery approaches such as PLGA microparticles. Ultimately, ongoing expression of therapeutic genes are a viable option to treat chronic neuropathic pain in the clinic.

Purpose Interleukin-10 (IL-10) is an anti-inflammatory molecule that has achieved interest as a therapeutic for neuropathic pain. In this work, the potential of plasmid DNA-encoding IL-10 (pDNA-IL-10) slowly released from biodegradable microparticles to provide long-term pain relief in an animal model of neuropathic pain was investigated. Methods PLGA microparticles encapsulating pDNA-IL-10 were developed and assessed both in vitro and in vivo. Results In vitro, pDNA containing microparticles activated macrophages, enhanced the production of nitric oxide, and increased the production of IL-10 protein relative to levels achieved with unencapsulated pDNA-IL-10. In vivo, intrathecally administered microparticles embedded in meningeal tissue, induced phagocytic cell recruitment to the cerebrospinal fluid, and relieved neuropathic pain for greater than 74 days following a single intrathecal administration, a feat not achieved with unencapsulated pDNA. Therapeutic effects of microparticle-delivered pDNA-IL-10 were blocked in the presence of IL-10-neutralizing antibody, and elevated levels of plasmid-derived IL-10 were detected in tissues for a prolonged time period post-injection (>28 days), demonstrating that therapeutic effects are dependent on IL-10 protein production. Conclusions These studies demonstrate that microparticle encapsulation significantly enhances the potency of intrathecally administered pDNA, which may be extended to treat other disorders that require intrathecal gene therapy.

Background Importance of the field Therapeutic proteins and DNA constructs offer promise for the treatment of central nervous system disorders, yet significant biological barriers limit the ability of these molecules to reach the central nervous system from the bloodstream. Direct administrations to the cerebrospinal fluid (intrathecal administration) comprise an emerging field to facilitate the efficient delivery of these biological macromolecules to central nervous system tissues. Areas covered in this review Previous reports from 1990 to the present time describing the interactions and turnover of the cerebrospinal fluid within the intrathecal space, characterizations of the effects that therapeutic proteins and DNA have exhibited after intrathecal delivery via a lumbar route, and reports of emerging technologies to address the limitations of intrathecally administered macromolecules are reviewed. What the reader will gain This review provides an overview of the limitations that must be overcome for intrathecally administered biological macromolecules and the recent advances and promising approaches for surmounting these limitations. Take home message Emerging approaches that stabilize and sustain the delivery of intrathecally administered biological macromolecules may substantially enhance the clinical relevance of promising therapeutic proteins and DNA constructs for the treatment of various central nervous system disorders.

Brain-derived neurotrophic factor (BDNF) was covalently attached to polyethylene glycol (PEG) in order to enhance delivery to the spinal cord via the cerebrospinal fluid (intrathecal administration). By varying reaction conditions, mixtures of BDNF covalently attached to one (primary), two (secondary), three (tertiary) or more (higher order) PEG molecules were produced. The biological activity of each resulting conjugate mixture was assessed with the goal of identifying a relationship between the number of PEG molecules attached to BDNF and biological activity. A high degree of in vitro biological activity was maintained in mixtures enriched in primary and secondary conjugate products, while a substantial reduction in biological activity was observed in mixtures with tertiary and higher order conjugates. When a biologically active mixture of PEG-BDNF was administered intrathecally, it displayed a significantly improved half-life in the cerebrospinal fluid and an enhanced penetration into spinal cord tissue relative to native BDNF. Results from these studies suggest a PEGylation strategy that preserves the biological activity of the protein while also improving the half-life of the protein in vivo. Furthermore, PEGylation may be a promising approach for enhancing intrathecal delivery of therapeutic proteins with potential for treating disease and injury in the spinal cord.