A novel, ultrasensitive assay for tau: potential for assessing traumatic brain injury in tissues and biofluids

Traumatic brain injury (TBI) is a cause of death and disability and can lead to tauopathy-related dementia at an early age. Pathologically, TBI results in axonal injury that is coupled to tau hyperphosphorylation, leading to microtubule instability and tau-mediated neurodegeneration. This suggests that the forms of this protein might serve as neuroinjury-related biomarkers for diagnosis of injury severity and prognosis of the neurological damage prior to clinical expression. We initially determined whether we could detect tau in body fluids using a highly sensitive assay. We used a novel immunoassay, enhanced immunoassay using multi-arrayed fiberoptics (EIMAF) either alone or in combination with rolling circle amplification (a-EIMAF) for the detection of total (T) and phosphorylated (P) tau proteins from brains and biofluids (blood, CSF) of rodents following controlled cortical impact (CCI) and human patients post severe TBI (sTBI). This assay technology for tau is the most sensitive to date with a detection limit of approximately 100 ag/mL for either T-tau and P-tau. In the rodent models, T-tau and P-tau levels in brain and blood increased following CCI during the acute phase and remained high during the chronic phase (30 d). In human CSF samples, T-tau and P-tau increased during the sampling period (5-6 d). T-tau and P-tau in human serum rose during the acute phase and decreased during the chronic stage but was still detectable beyond six months post sTBI. Thus, EIMAF has the potential for assessing both the severity of the proximal injury and the prognosis using easily accessible samples.