The secondary injury cascade after spinal cord injury:an analysis of local cytokine/chemokine regulation

After spinal cord injury,there is an extensive infiltration of immune cells,which exacerbates the injury and leads to further neural degeneration.Therefore,a major aim of current research involves targeting the immune response as a treatment for spinal cord injury.Although much research has been performed analyzing the complex inflammatory process following spinal cord injury,there remain major discrepancies within previous literature regarding the timeline of local cytokine regulation.The objectives of this study were to establish an overview of the timeline of cytokine regulation for 2 weeks after spinal cord injury,identify sexual dimorphisms in terms of cytokine levels,and determine local cytokines that significantly change based on the severity of spinal cord injury.Rats were inflicted with either a mild contusion,moderate contusion,severe contusion,or complete transection,7 mm of spinal cord centered on the injury was harvested at varying times post-injury,and tissue homogenates were analyzed with a Cytokine/Chemokine 27-Plex assay.Results demonstrated pro-inflammatory cytokines including tumor necrosis factorα,interleukin-1β,and interleukin-6 were all upregulated after spinal cord injury,but returned to uninjured levels within approximately 24 hours post-injury,while chemokines including monocyte chemoattractant protein-1 remained upregulated for days post-injury.In contrast,several anti-inflammatory cytokines and growth factors including interleukin-10 and vascular endothelial growth factor were downregulated by 7 days post-injury.After spinal cord injury,tissue inhibitor of metalloproteinase-1,which specifically affects astrocytes involved in glial scar development,increased more than all other cytokines tested,reaching 26.9-fold higher than uninjured rats.After a mild injury,11 cytokines demonstrated sexual dimorphisms;however,after a severe contusion only leptin levels were different between female and male rats.In conclusion,pro-inflammatory cytokines initiate the inflammatory process and return to baseline within hours post-injury,chemokines continue to recruit immune cells for days post-injury,while anti-inflammatory cytokines are downregulated by a week post-injury,and sexual dimorphisms observed after mild injury subsided with more severe injuries.Results from this work define critical chemokines that influence immune cell infiltration and important cytokines involved in glial scar development after spinal cord injury,which are essential for researchers developing treatments targeting secondary damage after spinal cord injury.

Functional recovery after peripheral nerve injury via sustained growth factor delivery from mineral-coated microparticles

The gold standard for treating peripheral nerve injuries that have large nerve gaps where the nerves cannot be directly sutured back together because it creates tension on the nerve,is to incorporate an autologous nerve graft.However,even with the incorporation of a nerve graft,generally patients only regain a small portion of function in limbs affected by the injury.Although,there has been some promising results using growth factors to induce more axon growth through the nerve graft,many of these previous therapies are limited in their ability to release growth factors in a sustained manner and tailor them to a desired time frame.The ideal drug delivery platform would deliver growth factors at therapeutic levels for enough time to grow axons the entire length of the nerve graft.We hypothesized that mineral coated microparticles(MCMs)would bind,stabilize and release biologically active glial cell-derived neurotrophic factor(GDNF)and nerve growth factor(NGF)in a sustained manner.Therefore,the objective of this study was to test the ability of MCMs releasing growth factors at the distal end of a 10 mm sciatic nerve graft,to induce axon growth through the nerve graft and restore hind limb function.After sciatic nerve grafting in Lewis rats,the hind limb function was tested weekly by measuring the angle of the ankle at toe lift-off while walking down a track.Twelve weeks after grafting,the grafts were harvested and myelinated axons were analyzed proximal to the graft,in the center of the graft,and distal to the graft.Under physiological conditions in vitro,the MCMs delivered a burst release of NGF and GDNF for 3 days followed by a sustained release for at least 22 days.In vivo,MCMs releasing NGF and GDNF at the distal end of sciatic nerve grafts resulted in significantly more myelinated axons extending distal to the graft when compared to rats that received nerve grafts without growth factor treatment.The rats with nerve grafts incorporated with MCMs releasing NGF and GDNF also showed significant improvement in hind limb function starting at 7 weeks postoperatively and continuing through 12 weeks postoperatively when compared to rats that received nerve grafts without growth factor treatment.In conclusion,MCMs released biologically active NGF and GDNF in a sustained manner,which significantly enhanced axon growth resulting in a significant improvement of hind limb function in rats.The animal experiments were approved by University of Wisconsin-Madison Animal Care and Use Committee(ACUC,protocol#M5958)on January 3,2018.