Copper transport to the brain by the blood-brain barrier and blood-CSF barrier

Abstract

The mechanism of copper (Cu) transport into the brain is unclear. This study evaluated the main species and route of Cu transport into the brain using in situ brain perfusion technique, and assessed the levels of mRNA encoding Cu transporters using real time RT-PCR. Free (64)Cu uptake in rat choroid plexus (CP), where the blood-cerebrospinal fluid barrier (BCB) is primarily located, is about 50 and 1000 times higher than (64)Cu-albumin and (64)Cu-ceruloplasmin uptake, respectively. The unidirectional transport rate constants (K(in)) for Cu in the CP and brain capillaries of the blood-brain barrier (BBB) were 1034 and 319 microl/s/g, respectively, while K(in) in CSF and capillary-depleted parenchyma were much reduced, 0.8 and 112 microl/s/g, respectively. The K(in) in cerebellum was significantly lower than that in hippocampus. The mRNAs encoding Cu transporter-1 (Ctr1) and ATP7A were higher in the CP than those in brain capillaries and parenchyma, whereas ATP7B mRNA was higher in brain capillaries than those in the CP and brain parenchyma. Taken together, these data suggest that the expression of Cu transporters is higher in brain barriers than in brain parenchyma; the Cu transport into the brain is mainly achieved through the BBB as a free Cu ion and the BCB may serve as a main regulatory site of Cu in the CSF.

Fig. 1

⁶⁴Cu uptake (as a volume of distribution, mL/g) into choroid plexus (CP), cerebrospinal fluid (CSF), brain capillaries (BC) and brain parenchyma (BP), after rat brain was perfused with free ⁶⁴Cu, ⁶⁴Cu-albumin (Alb) and ⁶⁴Cu-ceruloplasmin (CPN) for 2 min. Data represent mean ± SEM, n=4.

Fig. 2

Time courses of ⁶⁴Cu uptake into choroid plexus, CSF, brain capillaries and brain parenchyma after rat brain was perfused with only free ⁶⁴Cu. Data represent mean ± SEM, n=3–5.

Fig. 3

Time courses of ⁶⁴Cu uptake into various brain regions (i.e., frontal cortex, striatum, hippocampus, midbrain and cerebellum) after rat brain was perfused with only free ⁶⁴Cu. Data represent mean ± SEM, n=5.

Fig. 4

Relative abundance of mRNAs encoding Cu transporters (Ctr1, DMT1, ATP7A, ATP7B) in brain parenchyma and capillaries and choroid plexus by real time RT-PCR. Data represent mean ± SEM, n=7. Different letters (a, b, and c) above each bar indicate a significant difference between each other by ANAVA