title: Uptake and transport of high-density lipoprotein (HDL) and HDL-associated alpha-tocopherol by an in vitro blood-brain barrier model.
abstract: The present study aimed to investigate pathways that contribute to uptake and transcytosis of high-density lipoproteins (HDLs) and HDL-associated alpha-tocopherol (alpha TocH) across an in vitro model of the blood-brain barrier (BBB). In primary porcine brain capillary endothelial cells HDL-associated alpha TocH was taken up in 10-fold excess of HDL holoparticles, indicating efficient selective uptake, a pathway mediated by scavenger receptor class B, type I (SR-BI). SR-BI was present in caveolae of brain capillary endothelial cells and expressed almost exclusively at the apical membrane. Disruption of caveolae with methyl-beta-cyclodextrin (CDX) resulted in (mis)sorting of SR-BI to the basolateral membrane. Immunohistochemistry of porcine brain cryosections revealed SR-BI expression on brain capillary endothelial cells and presumably astrocytic endfeet. HDL-associated [(14)C]alpha TocH taken up by brain capillary endothelial cells was recovered in sucrose gradient fractions containing the majority of cellular caveolin-1, the major caveolae-associated protein. During mass transfer studies using alpha TocH-enriched HDL, approximately 50% of cellular alpha TocH was recovered with the bulk of cellular caveolin-1 and SR-BI. Efflux experiments revealed that a substantial amount of cell-associated [(14)C]alpha TocH could be mobilized into the culture medium. In addition, apical-to-basolateral transport of HDL holoparticles and HDL-associated alpha TocH was saturable. Results from the present study suggest that part of cerebral apolipoprotein A-I and alpha TocH originates from plasma HDL transcytosed across the BBB and that caveolae-located SR-BI facilitates selective uptake of HDL-associated alpha TocH at the BBB.
authors.affiliation: Institute of Molecular Biology and Biochemistry, Medical University Graz, Graz, Austria.
authors.forename: Zoltan
authors.initials: Z
authors.lastname: Balazs
authors.forename: Ute
authors.initials: U
authors.lastname: Panzenboeck
authors.forename: Astrid
authors.initials: A
authors.lastname: Hammer
authors.forename: Andrea
authors.initials: A
authors.lastname: Sovic
authors.forename: Oswald
authors.initials: O
authors.lastname: Quehenberger
authors.forename: Ernst
authors.initials: E
authors.lastname: Malle
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Sattler
mesh_terms: D000818:Animals; D016632:Apolipoprotein A-I / Q000378:metabolism; D001692:Biological Transport / Q000502:physiology; D019921:Biotinylation; D001812:Blood-Brain Barrier / Q000166:cytology / Q000378:metabolism*; D001921:Brain / Q000166:cytology / Q000378:metabolism; D001923:Brain Chemistry; D018955:CD36 Antigens; D002196:Capillaries / Q000166:cytology / Q000378:metabolism; D021941:Caveolae / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D051242:Caveolin 1; D022461:Caveolins / Q000737:chemistry / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D002478:Cells, Cultured; D003505:Cyclodextrins / Q000737:chemistry; D042783:Endothelial Cells / Q000378:metabolism*; D008075:Lipoproteins, HDL / Q000737:chemistry / Q000378:metabolism*; D008954:Models, Biological; D011971:Receptors, Immunologic / Q000378:metabolism; D051116:Receptors, Scavenger; D051122:Scavenger Receptors, Class B; D013347:Subcellular Fractions / Q000737:chemistry; D013552:Swine; D024502:alpha-Tocopherol / Q000737:chemistry / Q000378:metabolism*; D047392:beta-Cyclodextrins
chemical_list: D016632:Apolipoprotein A-I; D018955:CD36 Antigens; D051242:Caveolin 1; D022461:Caveolins; D003505:Cyclodextrins; D008075:Lipoproteins, HDL; D011971:Receptors, Immunologic; D051116:Receptors, Scavenger; D051122:Scavenger Receptors, Class B; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; D024502:alpha-Tocopherol