Abstract

My colleagues and I investigated the sites and mechanisms of aluminum (Al) and manganese (Mn) distribution through the blood-brain barrier (BBB) . Microdialysis was used to sample non-protein-bound Al in the extracellular fluid (ECF) of blood (plasma) and brain. Brain ECF Al appearance after intravenous Al citrate injection was too rapid to attribute to diffusion or to transferrin-receptor-mediated endocytosis, suggesting another carrier-mediated process. The brain:blood ECF Al concentration ratio was 0.15 at constant blood and brain ECF Al concentrations, suggesting carrier-mediated brain Al efflux. Pharmacological manipulations suggested the efflux carrier might be a monocarboxylate transporter (MCT) . However, the lack of Al ¹⁴C-citrate uptake into rat erythrocytes suggested it is not a good substrate for isoform MCT1 or for the band 3 anion exchanger. Al ¹⁴C-citrate uptake into murine-derived brain endothelial cells appeared to be carrier mediated, Na independent, pH independent, and energy dependent. Uptake was inhibited by substrate/inhibitors of the MCT and organic anion transporter families. Determination of ²⁶Al in rat brain at various times after intravenous ²⁶Al suggested a prolonged brain ²⁶Al half-life. It appears that Al transferrin and Al citrate cross the BBB by different mechanisms, that much of the Al entering brain ECF is rapidly effluxed, probably as Al citrate, but that some Al is retained for quite some time. Brain influx of the Mn²⁺ ion and Mn citrate, determined with the in situ brain perfusion technique, was greater than that attributable to diffusion, suggesting carrier-mediated uptake. Mn citrate uptake was approximately 3-fold greater than the Mn²⁺ ion, suggesting it is a primary Mn species entering the brain. After Mn²⁺ ion, Mn citrate, or Mn transferrin injection into the brain, brain Mn efflux was not more rapid than that predicted from diffusion. The BBB permeation of Al and Mn is mediated by carriers that may help regulate their brain concentrations. Key words: aluminum, b.End5 cells, blood-brain barrier, brain efflux, brain endothelial cells, brain influx, in situ brain perfusion, manganese, microdialysis, rat. Environ Health Perspect 110(suppl 5) :699-704 (2002) .

http://ehpnet1.niehs.nih.gov/docs/2002/suppl-5/699-704yokel/abstract.html