Serum Transthyretin Monomer as a Possible Marker of Blood-to-CSF Barrier Disruption

Abstract

The CNS is shielded from systemic influences by two separate barriers, the blood-brain barrier (BBB) and the blood-to-CSF barrier. Failure of either barrier bears profound significance in the etiology and diagnosis of several neurological diseases. Furthermore, selective opening of BBB tight junctions provides an opportunity for delivery of otherwise BBB impermeant drugs. Peripheral assessment of BBB opening can be achieved by detection in blood of brain-specific proteins that extravasate when these endothelial junctions are breached. We developed a proteomic approach to discover clusters of CNS-specific proteins with extravasation into serum that correlates with BBB openings. Protein profiles from blood samples obtained from patients undergoing iatrogenic BBB disruption (BBBD) with intra-arterial hyperosmotic mannitol were compared with pre-BBB opening serum. A low molecular weight protein (14 kDa) identified by mass spectroscopy as transthyretin (TTR) consistently correlated with BBBD. Protein gel electrophoresis and immunodetection confirmed that TTR was indeed extravasated in its monomeric form when CNS barriers were breached. The time course of TTR extravasation was compared with release from the brain of another BBB integrity marker, S-100beta (11 kDa). Kinetic analysis revealed that the appearance of S-100beta, presumably originating from perivascular astrocytic end feet, preceded extravasation of TTR by several minutes. Because TTR is localized primarily in choroid plexus and, as a soluble monomer, in CSF, we concluded that although S-100beta is a marker of BBB integrity, TTR instead may be a peripheral tracer of blood-to-cerebrospinal barrier.

Serum S100β

“…A second, more direct route is provided by disruptions on the capillary level that allow drainage of perivascular S100␤ directly into the circulation. 11,21 The second route is more likely in patients with brain tumors or other lesions. Finally, markers other than S100␤ may indicate CSF-to-BBB dysfunction better.…”

“…Blood samples were drawn before (10 minutes prior to mannitol injection), during (45 seconds, 1 minute, and 10 minutes after mannitol injection), and after (up to 6 hours) iatrogenic, selective, intraarterial osmotic opening of the BBB. 11,20,21 A total of 54 BBBD procedures in 6 patients were studied.…”

“…18,19 Although it is recognized that S100␤ originates from the central nervous system (CNS) and increases in cerebrospinal fluid (CSF) after injury, it remains unclear whether elevation of serum levels of S100␤ is a sign of bloodbrain barrier (BBB) dysfunction or neuronal/parenchymal damage. Our previous experience suggested that S100␤ levels reflected BBB dysfunction, 11,20,21 whereas recent work suggested that both BBB leakage and parenchymal lesions can be detected using this serum marker. 11 In these studies, BBB leakage was not assessed independently, although we hypothesized that contrast enhancement on neuroimaging would correlate with breaching of the BBB and, consequently, should demonstrate elevated serum S100␤ levels.…”

Separation of β2-Transferrin by Denaturing Gel Electrophoresis to Detect Cerebrospinal Fluid in Ear and Nasal Fluids

“…Our results are attributable to protein denaturation during SDS-PAGE, which hampers differentiation between the CSF-specific monomeric form and the tetrameric form present in blood (38 ). This distinction would require more sophisticated techniques (39 ) that are unlikely to become routine procedures but may be helpful in difficult situations, e.g., in the case of blood contamination.…”

Human body fluid proteome analysis

“…Failure of either barrier bears profound significance in the etiology and diagnosis of several neurological diseases. Comparative proteome analysis of sera from patients undergoing BBB disruption (BBBD) with pre-BBB opening serum indicated that alpha-2-macroglobulin (A2MG) and TTR were correlated with BBBD and may be a peripheral tracer of BCB [256,257]. In Alzheimer's disease (AD) patients, serum proteins such as HG, hemoglobin, vitronectin, alpha-1-acid glycoprotein (A1AG), apo B100, fragment of factor H, and histidine-rich glycoprotein were found at altered levels [258].…”