Relationship between injury severity and serum tau protein levels in traumatic brain injured rats

Background: Although serum tau protein levels increase following TBI, the time course is unknown. The aim of the present study was to determine whether serum tau protein levels increased in both a severity-dependent and time-dependent manner in an experimental model of rat traumatic brain injury (TBI). Methods: A total of 24 Sprague-Dawley rats were subjected to varying grades of TBI using a contusion injury model on the right parietal cortex. Enzyme-linked Immunoabsorbent Assay (ELISA) analysis for serum was performed at 15. min pre-injury, 1, 6, 24, 48, and 168. h post-injury. Immunoblotting for serum tau protein, neurological evaluation and histological observation were also performed. Results: Tau protein levels rapidly increased after 1. h in both mild and severe TBI groups (p< 0.001), and declined after 6. h. In the sham-operated group, tau protein levels did not change significantly after TBI. Tau protein levels were severity-dependent at 1 and 6. h after TBI. The levels were higher in the severe TBI group than in the mild TBI group at 1. h (p< 0.001) and 6. h (p< 0.001). Conclusions: Serum tau protein levels were severity-dependent and time-dependent at 1 and 6. h after TBI. However, the serum tau protein may not be a useful marker 24. h after TBI.