Acrolein as a novel therapeutic target for spinal cord injury induced neuropathic pain

Despite years of research, post-spinal cord injury (SCI) chronic neuropathic pain remains refractory to treatment and drastically impairs quality of life for SCI victims beyond paralysis. Although inflammation and free radicals contribute to neuropathic pain in SCI, the mechanism is not completely clear. We have recently demonstrated that acrolein, a product and catalyst of lipid peroxidation, induces a vicious cycle of oxidative stress, amplifying its effects and perpetuating oxidative stress and inflammation. In the current study, we have confirmed that acrolein is elevated significantly at least two weeks post-SCI which coincides with the emergence of hyperalgesia (mechanical, cold and thermal). Furthermore, anti-acrolein treatment hydalazine can reverse pain behavior. Consistent with this, acrolein is a known ligand that directly excites transient receptor potential ankyrin 1 receptor (TRPA1) in DRG nociceptive neurons to transmit pain sensation. In addition, we have observed a significant increase of monocyte chemoattractant protein-1 (MCP1), a pro-inflammatory chemokine that is also known be increased upon acrolein stimulation and capable of sensitizing TRPA1 following SCI. Similarly, we observed a heightened excitatory response of DRG sensory neurons to current stimulation in the presence of acrolein, indicating an enhanced sensitivity of DRG cells to acrolein post SCI. In summary, acrolein may play an important role in the post SCI hyperalgesia through greater direct binding to TRPA1 and enhanced sensitivity of DRG to acrolein via MCP1-mediated pathway

Polycistronic Delivery of IL-10 and NT-3 Promotes Oligodendrocyte Myelination and Functional Recovery in a Mouse Spinal Cord Injury Model.

One million estimated cases of spinal cord injury (SCI) have been reported in the United States and repairing an injury has constituted a difficult clinical challenge. The complex, dynamic, inhibitory microenvironment postinjury, which is characterized by proinflammatory signaling from invading leukocytes and lack of sufficient factors that promote axonal survival and elongation, limits regeneration. Herein, we investigated the delivery of polycistronic vectors, which have the potential to coexpress factors that target distinct barriers to regeneration, from a multiple channel poly(lactide-co-glycolide) (PLG) bridge to enhance spinal cord regeneration. In this study, we investigated polycistronic delivery of IL-10 that targets proinflammatory signaling, and NT-3 that targets axonal survival and elongation. A significant increase was observed in the density of regenerative macrophages for IL-10+NT-3 condition relative to conditions without IL-10. Furthermore, combined delivery of IL-10+NT-3 produced a significant increase of axonal density and notably myelinated axons compared with all other conditions. A significant increase in functional recovery was observed for IL-10+NT-3 delivery at 12 weeks postinjury that was positively correlated to oligodendrocyte myelinated axon density, suggesting oligodendrocyte-mediated myelination as an important target to improve functional recovery. These results further support the use of multiple channel PLG bridges as a growth supportive substrate and platform to deliver bioactive agents to modulate the SCI microenvironment and promote regeneration and functional recovery. Impact statement Spinal cord injury (SCI) results in a complex microenvironment that contains multiple barriers to regeneration and functional recovery. Multiple factors are necessary to address these barriers to regeneration, and polycistronic lentiviral gene therapy represents a strategy to locally express multiple factors simultaneously. A bicistronic vector encoding IL-10 and NT-3 was delivered from a poly(lactide-co-glycolide) bridge, which provides structural support that guides regeneration, resulting in increased axonal growth, myelination, and subsequent functional recovery. These results demonstrate the opportunity of targeting multiple barriers to SCI regeneration for additive effects

Acrolein involvement in sensory and behavioral hypersensitivity following spinal cord injury in the rat

Growing evidence suggests that oxidative stress, as associated with spinal cord injury (SCI), may play a critical role in both neuroinflammation and neuropathic pain conditions. The production of the endogenous aldehyde acrolein, following lipid peroxidation during the inflammatory response, may contribute to peripheral sensitization and hyperreflexia following SCI via the TRPA1-dependent mechanism. Here we report that there are enhanced levels of acrolein and increased neuronal sensitivity to the aldehyde for at least 14 days after SCI. Concurrent with injury-induced increases in acrolein concentration is an increased expression of TRPA1 in the lumbar (L3-L6) sensory ganglia. As proof of the potential pronociceptive role for acrolein, intrathecal injections of acrolein revealed enhanced sensitivity to both tactile and thermal stimuli for up to 10 days, supporting the compound’s pro-nociceptive functionality. Treatment of SCI animals with the acrolein scavenger hydralazine produced moderate improvement in tactile responses as well as robust changes in thermal sensitivity for up to 49 days. Taken together, these data suggests that acrolein directly modulates SCI-associated pain behavior, making it a novel therapeutic target for preclinical and clinical SCI as an analgesic

Reducing neuroinflammation by delivery of IL‐10 encoding lentivirus from multiple‐channel bridges

The spinal cord is unable to regenerate after injury largely due to growth‐inhibition by an inflammatory response to the injury that fails to resolve, resulting in secondary damage and cell death. An approach that prevents inhibition by attenuating the inflammatory response and promoting its resolution through the transition of macrophages to anti‐inflammatory phenotypes is essential for the creation of a growth permissive microenvironment. Viral gene delivery to induce the expression of anti‐inflammatory factors provides the potential to provide localized delivery to alter the host inflammatory response. Initially, we investigated the effect of the biomaterial and viral components of the delivery system to influence the extent of cell infiltration and the phenotype of these cells. Bridge implantation reduces antigen‐presenting cell infiltration at day 7, and lentivirus addition to the bridge induces a transient increase in neutrophils in the spinal cord at day 7 and macrophages at day 14. Delivery of a lentivirus encoding IL‐10, an anti‐inflammatory factor that inhibits immune cell activation and polarizes the macrophage population towards anti‐inflammatory phenotypes, reduced neutrophil infiltration at both day 7 and day 28. Though IL‐10 lentivirus did not affect macrophages number, it skewed the macrophage population toward an anti‐inflammatory M2 phenotype and altered macrophage morphology. Additionally, IL‐10 delivery resulted in improved motor function, suggesting reduced secondary damage and increased sparing. Taken together, these results indicate that localized expression of anti‐inflammatory factors, such as IL‐10, can modulate the inflammatory response following spinal cord injury, and may be a key component of a combinatorial approach that targets the multiple barriers to regeneration and functional recovery.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134909/1/btm210018.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134909/2/btm210018_am.pd

Reducing inflammation through delivery of lentivirus encoding for anti-inflammatory cytokines attenuates neuropathic pain after spinal cord injury.

Recently, many clinical trials have challenged the efficacy of current therapeutics for neuropathic pain after spinal cord injury (SCI) due to their life-threatening side-effects including addictions. Growing evidence suggests that persistent inflammatory responses after primary SCI lead to an imbalance between anti-inflammation and pro-inflammation, resulting in pathogenesis and maintenance of neuropathic pain. Conversely, a variety of data suggest that inflammation contributes to regeneration. Herein, we investigated long-term local immunomodulation using anti-inflammatory cytokine IL-10 or IL-4-encoding lentivirus delivered from multichannel bridges. Multichannel bridges provide guidance for axonal outgrowth and act as delivery vehicles. Anti-inflammatory cytokines were hypothesized to modulate the pro-nociceptive inflammatory niche and promote axonal regeneration, leading to neuropathic pain attenuation. Gene expression analyses demonstrated that IL-10 and IL-4 decreased pro-nociceptive genes expression versus control. Moreover, these factors resulted in an increased number of pro-regenerative macrophages and restoration of normal nociceptors expression pattern. Furthermore, the combination of bridges with anti-inflammatory cytokines significantly alleviated both mechanical and thermal hypersensitivity relative to control and promoted axonal regeneration. Collectively, these studies highlight that immunomodulatory strategies target multiple barriers to decrease secondary inflammation and attenuate neuropathic pain after SCI

Reducing inflammation through delivery of lentivirus encoding for anti-inflammatory cytokines attenuates neuropathic pain after spinal cord injury.

Recently, many clinical trials have challenged the efficacy of current therapeutics for neuropathic pain after spinal cord injury (SCI) due to their life-threatening side-effects including addictions. Growing evidence suggests that persistent inflammatory responses after primary SCI lead to an imbalance between anti-inflammation and pro-inflammation, resulting in pathogenesis and maintenance of neuropathic pain. Conversely, a variety of data suggest that inflammation contributes to regeneration. Herein, we investigated long-term local immunomodulation using anti-inflammatory cytokine IL-10 or IL-4-encoding lentivirus delivered from multichannel bridges. Multichannel bridges provide guidance for axonal outgrowth and act as delivery vehicles. Anti-inflammatory cytokines were hypothesized to modulate the pro-nociceptive inflammatory niche and promote axonal regeneration, leading to neuropathic pain attenuation. Gene expression analyses demonstrated that IL-10 and IL-4 decreased pro-nociceptive genes expression versus control. Moreover, these factors resulted in an increased number of pro-regenerative macrophages and restoration of normal nociceptors expression pattern. Furthermore, the combination of bridges with anti-inflammatory cytokines significantly alleviated both mechanical and thermal hypersensitivity relative to control and promoted axonal regeneration. Collectively, these studies highlight that immunomodulatory strategies target multiple barriers to decrease secondary inflammation and attenuate neuropathic pain after SCI