Comparison of Absolute Protein Abundances of Transporters and Receptors among Blood–Brain Barriers at Different Cerebral Regions and the Blood–Spinal Cord Barrier in Humans and Rats

This
work was designed to clarify the absolute abundances of transporters
and receptors at different cerebral regions of the blood–brain
barriers (BBB) and blood–spinal cord barrier (BSCB) in humans
and rats, using physiologically relevant units (pmol/g tissue and
fmol/cm2); 39 and 29 proteins including tight-junction
proteins and markers were quantified in human and rat capillary samples,
respectively. Protein expression levels of almost all proteins were
identical within a 2-fold range between BBB and BSCB in rats, while
many proteins showed >2-fold smaller expression levels in BSCB
than
BBB in humans. Protein expression levels of transporters and receptors
in humans were remarkably smaller than those in rats in both BBB and
BSCB in units of pmol/g tissue and fmol/cm2. Protein expression
levels (fmol/cm2) of MDR1 and BCRP at the BBB in humans
were 9.88-fold and 5.23-fold smaller than those in rats, respectively.
GLUT1 expression (pmol/g tissue) at cortical BBB in a human was 2.49-
and 3.76-fold greater than that at white matter BBB and BSCB, respectively.
INSR and LRP1 proteins were detected at cortical BBB, but not at white
matter BBB or BSCB in humans. These findings throw light on regional
differences and species differences in pharmacokinetics and physiological
functions in the central nervous system.