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Adenosine: Key to Blood Brain Barrier Regulation
Health Science Symposium (5/6/14)
Special thanks to the Organizers for the
Invitation
Margaret Bynoe, Ph.D.
Associate Professor,
Director of Graduate Studies
Cornell University, College of Veterinary Medicine
Ithaca, NY
Adenosine
1
Adenosine is a purine nucleoside: regulates inflammation,
immune cell migration
CD39
CD73
Four adenosine receptors:
A1
A2A
A2B
A3
Ado
10 Sec
Extracellular adenosine regulates the blood- brain barrier (BBB)
2
What is the blood brain barrier (BBB)?
The BBB: is a semi-permeable barrier that consists of a single layer of
endothelial cells that line cerebral vasculature
Blood vessel
Astrocytes
WEB OF VESSELS: The brain is
replete with blood vessels—
some 500 miles of them—. By
Megan Scudellari | November 1,
2013
By Marta Toran
The blood to brain barrier refers to a lack of direct communication between
the blood and peripheral tissues and the brain
3
•Adenosine receptors (ARs) are expressed on BBB cells
•Ecto-enzymes, CD39 and CD73 are expressed on BBB
cells
A1 and A2A ARs are expressed on
mouse brain endothelial cells
CD73 and CD39 expression on
mouse brain endothelial cells
CD39
CD73
4
The Scientific Problem
The blood brain barrier (BBB) hinders the delivery of therapeutic
drugs into the central nervous system (CNS).
The Challenge
To safely and effectively modulate the BBB to permit the entry
of therapeutic drugs into the CNS.
5
Modulation of adenosine receptor signaling
alters
blood brain barrier permeability
DMSO
NECA: (general AR agonist)
Mice treated with 10 mg/kg FITC-dextran and
DMSO or adenosine receptor modulator for 1 hr.
SCH58261: (A2AAR antagonist)
6
AR facilitates anti-beta amyloid antibody entry into the brain of
Alzheimer’s transgenic mice
•FDA-approved A2A agonist is more potent than NECA
Lexiscan vs NECA in Rats
7
A1 AR
A2A AR
GAPDH
HBMVECHCMEC-D3
Endothelial
Cell
Porous
membrane
Tight Junction
Molecule
AR Agonist
130
110
90
FITC-Dextran
Relative
Concentration
T cell
150
Relative TEER Changes (%)
An in vitro human BBB
Trans-endothelial electrical
resistance
Control
LEX 1uM
NECA 1uM
VEGF
S1P
8
Control
**
6
4 ** * **
2*
0 30 60 90
70
50
0
10
20
30
Minutes post- treatment
8
Lexiscan or NECA
Gemcitabine
Brain
endothelial
cell monolayer
Porous membrane
Glioblastoma
cells
5
15
30
60
Incubation of receiver chamber
for 4 days at 37 °C
Removal of donor chamber
(Minutes post treatment)
9
A2A AR activation permeabilized primary human brain
endothelial cell barrier to Gemcitabine passage
10
Approaches to CNS drug delivery technologies
Current approaches are either
-too invasive
Pro-Drug
Drug
Modification
to Cross
BBB
-painful
-result in permanent
brain damage
CNS
Lipidization
Modifications often
result in loss of
drug activity
Fusion
Protein
Collodial
Delivery
Endogenous
Control
-loss of drug efficacy
BBB
Modification/
Bypass
Disruption
Modulation of
BBB
• Invasive
• Costly
Mechanical
pump
• Non-patient
friendly
Intercranial
injection
• High probability of
causing permanent
brain damage11
Approaches to CNS drug delivery technologies
The use of adenosine signaling to modulate BBB permeability has many advantages over
other approaches to deliver therapeutics to the CNS:
1) It makes use of an endogenous mechanism for BBB control
2) It has the potential for precise time dependent control of BBB permeability
3) The process is reversible
4) ARs are located directly on BBB endothelial cells
5) Over 50 commercial reagents for ARs are available; some FDA-approved
6) Use of in vivo and in vitro model systems, there is great potential to gain molecular
mechanistic understanding; can lead to other targets
Adenosine
CNS
Delivery
Endogenous
Control
Modulation of BBB
Disadvantages of adenosine as a facilitator of BBB permeability:
-drug-drug interaction
-multifunctional properties of adenosine
12
Conclusion/s
We propose that blood brain barrier permeability is
mediated by A2A AR signaling
• The BBB, mediated by the A2A receptor operates as a DOOR “blood brain door”. Local adenosine concentration is the “key”.
• Differential modulation of adenosine receptor signaling represents a
“tunable” system that can be exploited for therapeutic purposes.
Opening the BBB to therapeutics:
Alzheimer’s disease
Closing the BBB to
damaging inflammatory cells:
Parkinson’s disease
Multiple sclerosis
Cancers of the CNS
Neurological manifestation of HIV-AIDS
Mental disorders
13
Work Presented today by Past and Present members of the lab:
Dr. Aaron Carman
Dr. Jeff Mills
Dr. Dogeun Kim (DVM)
Cindy Meuller
Special thanks to Philip Owh for many encouraging conversation
14