Characterizing Compartmental Neuroinflammatory Responses to Traumatic Brain Injury & Celastrol Administration

Introduction: Biomarkers are promising tools for understanding post traumatic brain injury (TBI) disease pathophysiology, but their biodistribution post-TBI is less understood, highlighting the need for comprehensive animal studies. Neuroinflammation contributes to post-TBI dysfunction and is a potential therapeutic target. Celastrol, a plant-derived triterpene, has documented neuroprotective and anti-inflammatory properties in hemorrhagic rat brain models. We hypothesize that experimental TBI elevates neuroinflammatory biomarkers in cerebrospinal fluid (CSF), serum, and ipsilateral hippocampal tissue (lysate), and that Celastrol attenuates the neuroinflammatory response across these compartments post-TBI.

Methods: 24 male Sprague-Dawley rats (275-300g) were separated into groups of 6 for analysis of biomarkers in CSF, serum, and lysate 48 hours after injury. In each group, anesthetized rats received a controlled cortical impact (CCI at 6m/s, 2.7 mm depth, 6mm tip diameter, 150 ms dwelling time) injury or sham surgery. A 0.5 mg/kg dose of Celastrol or 0.9% saline (vehicle) was administered beginning 24 hours post-CCI. CSF, serum and lysate were terminally collected 48 hours post-injury.

Serum, CSF, lysate concentrations of biomarkers (IFN-γ, IL-1β, IL-4, IL-5, IL-6, IL-10, IL-13, KC/GRO, TNF-a), and lysate concentrations of brain injury marker Glial fibrillary acidic protein (GFAP) were analyzed via multiplex immunoassay. Changes in multicompartment distribution ratios of each analyte were analyzed for injury and treatment effects by the Mann-Whitney U Test.

Results: Vehicle groups demonstrated significantly diminished serum to lysate concentrations of KC/GRO (-81%, p=0.016), TNF-a (-91%, p=0.016) in response to injury, compared to non-injured groups. Injured groups demonstrated significantly increased serum to lysate concentrations of IL-6 (+587%, p=0.016), KC/GRO (+708%, p=0.016), TNF-a (+224%, p=0.032) in response to Celastrol treatment, compared to vehicle groups.

Conclusion : KC/GRO and TNF-a present as meaningful serum analyte markers for inflammatory state of hippocampal tissue ipsilateral to TBI. Celastrol significantly modulates compartmental distribution of inflammatory markers IL-6, KC/GRO, TNF-a between serum and hippocampal tissue ipsilateral to TBI.