Abstract
BackgroundAβ transport (flux) across the blood-brain barrier (BBB) is thought to contribute to the pathogenesis of Alzheimer’s disease as well as to elimination of toxic amyloid from the brain by immunotherapy. Several BBB transporters have been implicated in Aβ exchange between brain parenchyma and the circulation, including efflux transporters P-glycoprotein/ABCB1 and BCRP/ABCG2. Here we describe an application of in vivo optical imaging methods to study Aβ transport across the BBB in wild-type or animals deficient in specific efflux transporters.Methods/DesignSynthetic human Aβ1-40 or scrambled Aβ40-1 peptides were labeled with the near-infrared fluorescent tracer, Cy5.5. The free tracer or Cy5.5-labeled peptides were injected intravenously into Abcb1-KO or Abcg2-KO mice or their corresponding wild-type controls. The animals were imaged prospectively at different time points over a period of 8 hours using eXplore Optix small animal imager. At the end of the observation, animals were sacrificed by perfusion, their brains were imaged ex-vivo and sectioned for immunofluorescence analyses.DiscussionAfter appropriate circulation time, the fluorescence concentration in the head ROI measured in vivo was close to background values in both wild-type and Abcb1-KO or Abcg2-KO mice injected with either free dye or scrambled Aβ40-1-Cy5.5. In animals injected with Aβ1-40-Cy5.5, the deficiency in either Abcb1 or Abcg2 resulted in significant increases in fluorescence concentration in the head ROIs 2 hours after injection compared to wild-type animals. Fluorescence decay (elimination rate) over 2–8 hours after injection was similar between wild-type (t1/2 = 1.97 h) and Abcg2-KO (t1/2 = 2.34 h) and was slightly faster (t1/2 = 1.38 h) in Abcb1-KO mice. In vivo time-domain imaging method allows prospective, dynamic analyses of brain uptake/elimination of fluorescently-labeled compounds, including Aβ. Deficiency of either of the two major efflux pumps, Abcb1 and Abcg2, implicated in Aβ trafficking across the BBB, resulted in increased accumulation of peripherally-injected Aβ1-40 in the brain.
Highlights
Aβ transport across the blood-brain barrier (BBB) is thought to contribute to the pathogenesis of Alzheimer’s disease as well as to elimination of toxic amyloid from the brain by immunotherapy
In animals injected with Aβ1-40-Cy5.5, the deficiency in either Abcb1 or Abcg2 resulted in significant increases in fluorescence concentration in the head region of interest (ROI) 2 hours after injection compared to wild-type animals
Is Cy5.5 a substrate for mdr-1 P-glycoprotein or ABCG2? To enable prospective in vivo optical imaging of the distribution of peripherally-injected Aβ peptides, the peptides were labeled with the near-infrared fluorescent dye Cy5.5
Summary
Aβ transport (flux) across the blood-brain barrier (BBB) is thought to contribute to the pathogenesis of Alzheimer’s disease as well as to elimination of toxic amyloid from the brain by immunotherapy. Aβ peptides form oligomers, aggregates and plaques which are thought to contribute to synaptic dysfunction, Mechanistic studies have generated a substantial body of evidence that brain accumulation of Aβ peptides is not solely due to their increased production in the brain, and to reduced brain clearance and/or increased uptake from peripheral circulation [5,6]. Both latter processes are controlled by the polarized blood-brain barrier (BBB) receptors and transporters [7,8,9,10]. It is important to note that shuttling of Aβ across the BBB occurs by receptor/transporter-mediated processes that require the intact tertiary structure of the peptide that interacts with the carrier receptor(s)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
