Concentration of microtubule associated protein tau (MAPT) in urine and saliva as a potential biomarker of traumatic brain injury in relationship with blood-brain barrier disruption in postmortem examination

Abstract

Traumatic brain injury (TBI) constitutes a frequent finding in medico-legal practice, including forensic autopsy and neuropathological examination. Despite clinico-scientific advances there is a need for identification of novel biomarkers considered for TBI diagnostics in ante- and postmortem cases. The role of MAPT protein as a biomarker in case of TBI was investigated in previous studies by examination of blood and cerebrospinal fluid obtained during forensic autopsies whereas less is known concerning its liberation and occurrence in other biofluids. The aim of this study was to elucidate and identify if elevated MAPT levels in other biofluids, such as urine, saliva, and vitreous body are also seen in TBI cases in population-based autopsy screening. The study was carried out using cases (n = 14) of severe head injury suspected as the cause of death and control cases (n = 13) of sudden death in the mechanism of cardiopulmonary failure. The biofluids, such as urine, saliva, and vitreous body were collected within ∼24 h after death and compared using ELISA test. Tissue specimens including brain and kidney were similarly collected during forensic autopsies. Brain specimens were stained immunohistologically with anti-Vimentin (V9) antibody and histologically using Mallory's trichrome method (to assess structural damage to blood-brain barrier elements) whereas kidney specimens were stained immunohistologically with anti-MAPT antibody (to assess the suitability of such a study in the diagnosis of TBI). In our study, we observed the elevated concentration levels of MAPT in saliva and urine. These changes were accompanied by damage to the structural elements of the blood-brain barrier (damage to the vascular endothelium and vascular basement membrane). According to this elevated cencentration levels of MAPT in this biofluids should be considered as TBI marker in postmortem examination even in cases where the head injury was not supposed to consist the direct cause of death.

Keywords: Biomarker; Blood–brain barrier; Microtubule associated protein tau; Saliva; Traumatic brain injury; Urine.