title: Clearance of albumin following ultrasound-induced blood-brain barrier opening is mediated by glial but not neuronal cells.
abstract: Ultrasound-mediated opening of the blood-brain barrier (BBB) in the presence of gas-filled microbubbles is a potential strategy for drug delivery across the blood-brain barrier to promote regeneration after ischemic stroke. However, related bioeffects and potential side-effects that could limit a translation into clinical application are poorly understood so far. We therefore examined the clearance of extravasated albumin following ultrasound-mediated BBB opening. Autofluorescence of albumin-bound Evans Blue dye indicated cellular albumin uptake as soon as 30min after insonation (2±0.72 cells/optical field). Cellular albumin uptake increased constantly over 24h (22±3.33 cells/optical field, p<0.05). Initially, the majority of albumin-positive cells were located in the periphery of brain capillaries. Most albumin phagocyting cells stained positive for CD163 and Iba-1, identifying them as activated microglia. Further, a small fraction of albumin-positive cells stained positive for the astroglial markers GFAP/S100B. Some perivascular cells with intracellular albumin were shown to express the endothelial marker protein EN4. Albumin uptaking cells stained negative for the neuronal TubulinIII. Thus, ultrasound-induced BBB opening leads to albumin extravasation which is phagocytized predominantly by activated microglia, astrocytes and endothelial cells. As albumin uptake into neurons has been shown to be neurotoxic, rapid albumin clearance by microglia might prevent neuronal cell death.
authors.affiliation: Department of Neurology, UniversitätsMedizin Mannheim, University of Heidelberg, Germany. alonso@neuro.ma.uni-heidelberg.de
authors.forename: Angelika
authors.initials: A
authors.lastname: Alonso
authors.forename: Eileen
authors.initials: E
authors.lastname: Reinz
authors.forename: Marc
authors.initials: M
authors.lastname: Fatar
authors.forename: Michael G
authors.initials: MG
authors.lastname: Hennerici
authors.forename: Stephen
authors.initials: S
authors.lastname: Meairs
mesh_terms: D000418:Albumins / Q000378:metabolism*; D000818:Animals; D001812:Blood-Brain Barrier / Q000166:cytology / Q000378:metabolism* / Q000528:radiation effects*; D004396:Coloring Agents; D003287:Contrast Media; D005070:Evans Blue; D005455:Fluorescent Antibody Technique; D007839:Functional Laterality / Q000502:physiology; D008297:Male; D018613:Microscopy, Confocal; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009457:Neuroglia / Q000502:physiology* / Q000528:radiation effects*; D009474:Neurons / Q000502:physiology* / Q000528:radiation effects*; D010587:Phagocytosis / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D014465:Ultrasonics
chemical_list: D000418:Albumins; D004396:Coloring Agents; D003287:Contrast Media; D009419:Nerve Tissue Proteins; D005070:Evans Blue