Thrombin and its precursor in human cerebrospinal fluid.

The blood coagulation cascade proteolytic enzyme, thrombin, affects many cell types, including neurons and astrocytes, in which it prevents process outgrowth and induces significant morphological degeneration and even cell death. Since thrombin may contribute significantly to pathological conditions in the central nervous system (CNS), where it is synthesized locally, we measured the levels of thrombin and its precursor, prothrombin, in the cerebrospinal fluid (CSF) of 67 individuals from 6 groups: non-neurologic controls (NNC); spinal degenerative disease (SDD); peripheral nerve disease (PND); cerebrovascular, neuroimmune and seizure disorders and tumor (CNSD); traumatic brain injury (TBI) and neurodegenerative disorders (NDD). We employed a sensitive chromogenic assay utilizing the thrombin specific tripeptide substrate, S-2238, to evaluate CSF levels of thrombin and prothrombin. The latter estimated after its conversion to active enzyme by the snake venom prothrombinase, ecarin. No measurable active thrombin was detected in these CSF samples. However, activatable prothrombin was measured in all groups. The mean activatable prothrombin concentrations (in nM) were 7.26 +/- 3.39 (NNC); 8.85 +/- 3.09 (SDD); 6.78 +/- 2.58 (PND); 6.33 +/- 3.87 (CNSD); 5.10 +/- 1.86 (TBI), and 7.80 +/- 3.27 (NDD). Duncan's multiple comparison test showed significant reduction (p <0.05) in prothrombin levels of the TBI group. Our data suggests that the prothrombin zymogen gains access to the CSF, likely across either an intact or compromised blood-brain barrier (BBB), in increased amounts with age. Reduced levels in TBI patients may have diagnostic and/or prognostic value.