Blood Brain Barrier and Its clinical application

1. BLOOD BRAIN BARRIER
PRESENTER
DR. PARTH JOSHI
RESIDENT DEPT OF
NEUROSURGERY
MODERATOR
DR.SUBODH RAJU
SENIOR CONSULTANT
DEPT. OF NEUROSURGERY

2. OUTILNE
• ANATOMY- PHYSICAL AND BIOCHEMICAL BARRIER
• TRANSPORT ACROSS BBB
• FUNCTIONS OF BBB
• BBB MODULATIONS- INCREASE AND DECREASE IN PERMEABILITY
• PATHOLOGICAL STATES INVOVING BBB BREAKDOWN /DISORDER
• THERAPEURTIC IMPLICATIONS

3. • WHAT IS BLOOD BRAIN BARRIER?
• It’s a neurovascular unit composed of
• 1) Microvascular Endothelium
• 2) Basement membrane
• 3) Neurological str.- Astrocytes, Pericytes, Microglia
• It’s a Dynamic Gatekeeper of brain – CARRIER AND BARRIER
• 1885-Paul Ehrlich- IV tryptan blue- stained all str. Except- Brain and Spine
• 1990- Lewandowsky – Blut-hirn-shrank- Blood Brain Cabinate

4. NEUROVASCULAR SYSTEM
• Critical for the brain function
• Every neuron has capillary
• Brain capillary total length ~ 650km – surface area for transport – 20 meter square
• In neurodegenerative diseases length of the capillaries decreased .i.e. Alzheimer's ds
• Vascular reduction-1) Diminished energy substrate/nutrients
2) Accumulation of toxic products due to decrease in clearance

5. ANATOMY OF THE BBB
Composed of
1. Capillary endothelium
2. BM of endothelium
3. Pericytes
4. Astrocytes
5. P glycoproteins
Microglia also plays an important role

6. ENDOTHELIAL CELLS
• Low permeability in part by Tight Junctions and Adhesion Junctions and partly as it lacks Fenestration
• 2 surfaces- luminal and abluminal
• 300-500 nm cytoplasm b/w Blood and brain
• Tight Junctions:
• Regulate Paracellular Transport
• Consist of OCCLUDIN, CLAUDIN , ADHERENCE MOLECULES
• Adhesion Junctions:
• Mediate cell spacing
• Transmit cytoskeletal signals
• Includes: CADHERIN, CATENINS, VINCULIN, ACTININS

7. DIFFERENCE OF CAPILLARIES IN PERIPHERY AND BRAIN
BRAIN CAPILLARY ENDOTHELIAL CELLS HAS
1) RARE PINOCYTE VESICLE
2) HIGH CONCENTRATION OF MITOCHONDRIA
3) TIGHT JUNCTIONS

8. TO STRENGTHEN STRUCTURAL INTEGRITY
• ENZYMATIC SURVILANCE SYSTEM
• It metabolizes drugs and compounds which manage to bypass BBB
• 3 main catalytic agents
1. Gamma GTP( glutamyl trans peptidase)
2. Alkaline Phosphatase
3. Aromatic Acid Decarboxylase
• this will also affect the response to drugs in certain condition where drug crosses BBB
• POLARITY BETWEEN LUMINAL AND ABLUMINAL SURFACE OF EC’S
• Influences permeability
• Maintained by Tight Junctions and Matrix proteins
• Cations usually passes through BBB if size permits (<450 kD)
• DIFFRENTIAL RECEPTOR EXPRESSION
• For glucose and ions and amino acids
• Na-K ATPase, Na-H exchanger, Na-AA transporter, GLUT-1- more on abluminal surface
• P-GP– by human MDR1 gene- also has more con. at abluminal surface

9. ASTROCYTES
• Reinforces barrier function
• Also maintains BBB polarity by AQP4 – which has role in H2O absorption and edema formation
• They have feet on BM surrounding the EC and TJs
• >90 % of astrocytes foot process surrounds EC
• They also have ADRENERGIC AND CHOLINERGIC TERMINALS
• Maintain BBB integrity indirectly by certain protein production rather than physical interaction
• E.g. PDGFR- PLt derived GF- also on Pericytes
• Act via TK receptor
Targated for Malig. Brain Tumors

10. NEURONS
• Modulate BBB by signaling
• Provide : Noradrenergic ,
• serotonergic,
• cholinergic,
• GABAergic
innervation to EC and Astrocytes

11. MICROGLIA
• Resident microphage of CNS
• Immune surveillance of perivascular spaces
• Act as APC
• Important role in sequel of STROKE, TRAUMA, MS, NEURODEGERATIVE D’S
• Role in clearing debris in Alzheimer's ds

12. PERICYTES
• Undifferentiated contractile connective tissue
• Localize to capillary wall
• Regulate the growth of EC
• Modulate integrity of capillary cells
• Act as SECONDARY BBB
• Lack in contractile ACTIN , although implicated in regulating CBF
• Cover 20-30% microvascular circumference
• Most abundant on venules
• Provide mechanical support
• Synthesize Extracellular matrix proteins- LAMININ, FIBRONECTIN

13. EXTRACELLULAR MATRIX
• Provide physical stability to BBB by – LAMININ, TYPE 4 COLLAGEN, INTEGRINS
• Mediate polarity at Astrocyte- EC interface
• MMP upregulate the Tight Junction protein expression
• PERMIABILITY OF THE BBB DETERMINED BY BOTH
1. TJ CONTROLLED PARACELLULAR PERMIABILITY
2. CAVEOLE MEDIATED TRANSCELLULAR PERMIABILITY

14. TO SUMMARIZE
• Brain microvasculature differ from peripheral EC in 3 primary way
1. BBB lack fenestration and characterized by low pinocytic activity – markedly impair fluid uptake
2. TJs are Ubiquitous in brain- impede Para cellular transport of large (>450kD) and Hydrophobic
molecules across BBB
3. Higher concentration of mitochondria for active transport

15. TRANSPORT ACROSS BBB
• 4 PRIMARY TRANSPORT MECHANISMS
1. PRIMARY AQUOUS DIFFUSION
2. TRANSCELLULAR LIPOPHILIC DIFFUSION
3. ADSORPTIVR TRANSCYTOSIS
4. SATURABLE TRANSPORT
1. RECEPTOR MEDIATED TRANSCYTOSIS
2. CHANNEL MEDIATED TRANSPORT

16. 1) PRIMARY AQUOUS DIFFUSION
• Small H20 soluble molecules pass through Extracellular pathway
• Regulated by TJs

17. 2) TRANSCELLULAR LIPOPHILIC DIFFUSION
• Diffusion of some substances across cell
• Its non Saturable and non competitive
• RULE- higher lipophilicity of substance with molecular weight <450kD will have greater diffusion
• If 2 subs identical in all other properties than one with less molecular weight will penetrate more
rapidly.
• Small inorganic molecules like- O2, CO2, NO  highly permeable across EC by dissolving into
Lipid plasma membrane.
• Important is Hydrogen Binding Property- if H+ and O2 atom total number </= 5 , it will have high
probability of entering the CNS

18. 3) ADSORPTIVE TRANSCYTOSIS
• Transcytosis is ATP dependent transport – ATP is required
• To bring substance to luminal surface
• Transport across EC
• For exocytosis
• High no. of Mitochondria of EC ( 5X than peripheral sites) helps here
• Mediated by 1) Clathrin coated Pits
2) Caveole – to lesser extent ( sites of endothelial TRANSCYTOSIS, ENDOCYTOSIS,
AND SIGNAL TRANSDUCTION)
• Selective for Cationic Molecules (+VE)
• eg. Albumin and other plasma proteins
• Predominant mechanism for HIV-1 passage in brain

19. 4) SATURABLE TRANSPORT-
A) RECEPTOR MEDIATED TRANSCYTOSIS
• Transport of solute through receptor binding and subsequent endocytosis
• E.g.: IGF 1,2
• AT 2
• ANP, BNP
• IL- 1
• Transferrin
• Insulin

20. 4) SATURABLE TRANSPORT-
B) CHANNEL / TRANSPORT PROTEIN MEDIATED TRANSPORT
• Saturable mode of transport
• Influx and efflux via transport proteins
• If against concentration gradient than ATP may require
• E.g. Glucose and Amino Acids, Nucleosides- bind to protein transporter
conformational changes in protein transport to other side
Vinca alkaloids
Cyclosporin A
AZT

21. EFFLUX PUMPS AND TRANSPORTERS

22. BBB MODULATION

23. FUNCTIONS OF BBB

24. BBB IN PATHOLOGICAL CONDITIONS
1) SROKE

25. STROKE…..

26. 2) TRAUMATIC BRAIN INJURY

27. 3) INFECTION/ INFLAMMATION

28. 4) MULTIPLE SCLEROSIS 5) HIV
- TJ DISRUPTION

29. 6) ALZHEIMER’S DISEASE AND 7) PARKINSON’S DS

30. 8) EPILEPSY

31. 9) BRAIN TUMORS

32. THERAPEUTIC IMPLICATIONS

34. POTENTIAL SOLUTION TO BBB PROBLEM

35. TARGETED THERAPY ACROSS BBB

36. TARGETED THERAPY ACROSS BBB
• 1) Enhancing Drug permeability through BBB
• Bradykinin administration Caveolin upregulation increases permeability of ECs increase in drug delivery
• Nanoparticle coated with AntiEGF Ab increases uptake in glioma cells
• Monoclonal antibodies as “Trojan Horses” molecules to carry genes and large molecules across BBB
• Carrier molecules – K6 Apo g
2) Temporary disruption of BBB
• Radiation induced focal disruption to reduce effect on normal vessels
• Hyperosmolar disruption by Mannitol- for Cyclophosphamide delivery
• MRI guided focused USG Disruption of TJs due to stress in cells microbubbles BBB disruption
used for delivery of : Doxorubicin, Carmustin, Trastuzumab

37. 3) Interstitial delivery of drug / Convection enhanced delivery
surgically placed catheter delivery of chemo agents into micro perfusion
4) Use of Polymers/microchips
Polymer wafers implanted at surgical cavity post op- local administration
used for Gliomas
5) P-gp targeting and modulation for primary CNS neoplasm

38. THANK YOU