Regional blood-brain barrier transport of cationized bovine serum albumin in awake rats

Abstract

Regional blood-brain barrier permeability-surface area products (PAs) of cationized bovine serum albumin (cBSA) with isoelectric point (pI) approximately 8 or greater than or equal to 11 and of native bovine serum albumin (nBSA;pI approximately 4) were determined in awake male Sprague-Dawley rats after bolus intravenous injection. The albumins were labeled with 125I. Brain uptakes were assessed by autoradiography and by direct assay of radioactivity in brain regions. nBSA uptake into brain was statistically insignificant over 3 h, whereas cBSA uptake was significantly even at 6 min. Mean PA values of cBSA with pI approximately 11 (1.69-2.65 x 10(-5) ml.s-1.g-1) in most brain regions were twofold higher than PAs of cBSA with pI approximately 8 (0.98-1.37 x 10(-5) ml.s-1.g-1), whereas mean PA for nBSA did not differ significantly from zero. Autoradiographs of brain slices and net distributions in brain compartments at 6 and 30 min after injection suggested that cBSA entered the brain parenchyma via blood vessels and cerebrospinal fluid but that the former was the main route. The results quantitate for the first time regional brain PA values for cationized proteins and suggest specific mechanisms at cerebral blood vessels that distinguish transport of cationized from noncationized macromolecules.

Enhanced permeabilities of cationized‐bovine serum albumins at the blood‐nerve and blood‐brain barriers in awake rats

“…Similar findings were reported for the choroid plexus (Griffin and Giffels, 1982), and other organs (Shen and Ryser, 1978;Michel et al, 1985). We recently showed that the permeability of the BBB to cationized serum bovine albumin is proportional to the degree of its cationization (Shimon-Hophy et al, 1991) The vascular endothelial cells of the rat sciatic nerve, like the capillaries of the central nervous system, have anionic sites on their cell membranes and basal laminae (Bush and Allt, 1990). Whether these anionic domains influence the permeability of macromolecules, as they do at the BBB, is not known.…”

“…In brief, dialyzed nBSA (Fluka, Ronkonkoma, NY) was activated by carbodiimide (Fluka) and then treated with ethylene diamine (Fluka) at pH = 4.75, T = 23°C (Griffin and Giffels, 1982;Shimon-Hophy et al, 1991). The solution then was dialyzed against distilled water for 3 days, followed by lyophilization.…”

“…Surgical procedure. The surgical procedure has been described in detail (Wadhwani et al, 1990;Shimon-Hophy et al, 1991). In brief, a rat was anesthetized with Na pentobarbital i.p.…”

A developmentally regulated blood‐cerebrospinal fluid transfer mechanism for albumin in immature rats.

“…Thus it would seem that overall molecular charge alone is not the specific characteristic that determines the extent to which albumin is transferred across the immature blood-CSF barrier. This is in contrast to adult rats where cationization of albumin (Griffin & Griffels, 1982; Shimon-Hophy, Wadhwani, Chandrasekaran, Larson, Smith & Rapoport, 1991) and IgG (Triguero, Buciak, Yang & Pardridge, 1989) resulted in a substantial uptake of these proteins into brain and CSF. The transfer of albumin into CSF in the adult is probably only by diffusion (see above) and it is possible that cationization may in some way affect the molecular sieving of these proteins by a glycocalyx matrix as described for blood vessels (see Michel, 1975).…”

“…However, luminal cationic sites in rodent brain vessels do not develop until late postnatal life (12-24 days; Vorbrodt, Lossinsky, Dobrogowska & Wisniewski, 1990), indicating that the charge on cell surfaces is not involved in the transfer of albumin in the newborn period. The cationized proteins used by Griffen & Giffels (1982), Shimon-Hophy et al (1991) and Triguero et al (1989) all had pI values of 8 or more which is higher than the great majority of known plasma proteins in vivo (Putnam, 1975 & Saunders, 1988); one possibility seems to be that the overall high concentration of protein may exert sufficient colloid osmotic pressure across the CSF-brain interface for an osmotic increase in the volume of the ventricular system, around which the immature brain grows (Saunders, 1992). Given the well-known carrier properties of albumin, this may also be a mechanism for delivery of a wide range of molecules that are important for normal brain development.…”