57 - Evaluation of hydrogel-mediated drug delivery for mitigation of acute traumatic brain injury neuropathology in rats.

Abstract Text: There is no FDA-approved treatment traumatic brain injury (TBI) thus there is an interest in developing a point-of-injury treatment for the austere forward battlefield environments that can mitigate brain swelling and intracranial pressure. With exposed brain tissue, the lethality risk is significantly increased as the brain becomes susceptible to infections. Hydrogel-mediated drug delivery is a therapeutic strategy to provide physical barrier around the wounded tissue and administer a drug of choice directly to the site of injury which can minimize systemic exposure. This study evaluates the efficacy of providing a sustained delivery of dexamethasone (DX), a drug particularly effective against inflammation and edema, to prevent acute cerebral edema development following TBI. The polyethylene glycol (PEG)-based hydrogels used in this study are modified with ester linkages producing a photo-crosslinked polyethylene glycol-bis-acryloyloxy acetate (PEG-bis-AA) and integrated dexamethasone-conjugated hyaluronic acid (HA-DXM). The hydrogel allows for locally administered, low-dose dexamethasone release to the site of injury over 7 days as the native enzymes degrade the hydrogel. We hypothesize that the hydrogel will effectively deliver dexamethasone to the injury site during this period to mitigate the cerebral edema and neuroinflammation following TBI. Sprague-Dawley rats were divided into three treatment groups: Sham that received a craniotomy but no treatment, vehicle treated (VEH HYG) treated, and DX treated (DX HYG). VEH HYG and DX HYG groups received a controlled cortical impact (CCI, Depth = 2.5 mm, Velocity = 4 m/s, Dwell Time = 1 s) under anesthesia. Hydrogels were placed in the craniotomy site immediately after injury. The righting reflex, the time that the animal has righting on all four limbs, was recorded. Cerebral edema was evaluated in 6 brain regions: anterior, medial, and posterior for both the ipsilateral and contralateral hemispheres using the wet-dry method at 6hr, 24hr, 48hr, and 72hr timepoints post-injury. Histology was also performed to determine the hematoma and lesion size using hematoxylin and eosin (H&E), and GFAP and IBA1 for neuroinflammation. Hydrogels were recovered from the injury site and the remaining dexamethasone content was quantified using an enzyme-linked immunoassay. This study results show a significant increase in righting reflex for both VEH HYG and DX HYG compared to sham controls although there were no significant changes between both treatment groups. Results from the DX ELISA demonstrate that the hydrogels from later time points contained less DX, indicating constant delivery of the drug over the period tested. Cerebral edema results demonstrate a significant increase in brain water content between shams versus both treatment groups. In fact, DX HYG showed significant reduction in cerebral edema at the site of injury at the 48hr and 72hr time points compared to the VEH HYG controls, but there were no significant differences when compared to sham. GFAP and IBA1 results demonstrated DX HYG significantly decreased IBA1 at 24hr and 72hr post-injury in the hippocampal and striatum regions as well as GFAP at for 48hr and 72hr timepoints compared to VEH HYG. Overall, there is potential to utilize hydrogel biotechnology as an effective method for low-dose, localized delivery of drugs to the injured brain after TBI with improvements to edema and neuroinflammation with no significant adverse effects. PCR analysis may also reveal the potential to explore the effect of hydrogel DX delivery in inflammatory gene expression post-injury. In the future, this innovative platform can be used to expand upon the timepoints of delivery post-injury and alternative drugs that may yield the most effective results.

Keywords: Hydrogel, Neuroinflammation, Hematoma, Lesion, Dexamethasone, Edema, Histopathology, Enzyme-linked Immunoassay, Gene Expression