Blood brain barrier ajay

blood brain barrier

1. BLOOD BRAIN BARRIER DR. AJAY KUMAR SINGH DNB NEUROSURGERY VPIMS

2. HISTORY OVERVIEW & DEFINITION ANATOMY & PHYSIOLOGY PATHOLOGIC CHANGES DRUG ADMINISTRATION REFRENCES

3. HISTORY First experimental evidence - Paul Ehrlich, Water-soluble dyes injected into blood stained all organs except the brain & spinal cord (1885). 1913: Edwin Goldman (dye in CSF) : the cerebral capillaries provide anatomical basis for a physiological barrier between brain and the rest of the body Lewandowsky

4. Three barrier layers b/w blood and neural tissues: (1) A highly specialized endothelial cells (EC) layer comprising the blood–brain barrier (BBB) and partitioning the blood and brain interstitial fluid, (2) The blood-CSF barrier (BCSFB) with the choroid plexus epithelium. (3) The arachnoid epithelium separating the blood from the subarachnoid CSF.

5. TO DEFINE The blood-brain barrier (BBB) is a "neurovascular unit" composed of micro vascular endothelium, basement membrane, neurons, and neuroglial structures: astrocytes, pericytes, and microglia and extracellualr matrix.

6. Cellular components of the BBB • Principal components are: – Endothelial cells – Astrocytes – Pericytes • Other cellular components like neurons and microglia also play significant role (immune function) NEUROVASCULAR UNIT

7. Around penetrating vessels and venules there is some distance between EC and brain tissue forming the Virchow-Robin space in which perivascular macrophages, executing some of the immune functions of the CNS, are found.

8. ANATOMY OF THE BLOOD-BRAIN BARRIER Monolayer of microvascular ECs that line the intraluminal space of brain capillaries. The EC layer has a luminal (inside) and abluminal (outside) compartment separated by cytoplasm between the blood and brain. Composed of TJs, which consist of Occludin and Claudine; adherent junctions, including Catherin, catenins , vinculin, and actinin; and junctional adhesion molecules .

9. ANATOMY OF THE BLOOD-BRAIN BARRIER There is charge polarity between the abluminal and luminal surface of Ecs , which influences permeability of the barrier. Transporters: Alkaline phosphatase and 'Y-GTP, P- glycoprotein ( Pgp )—luminal surface Na+K-ATPase , (GLUT-1) -- abluminal side.

10. Enzymatic surveillance system that metabolizes drugs and other compounds bypassing the structural barrier- y- glutamyl transpeptidase (y-GTP) alkaline phosphatase aromatic acid decarboxylase

11. Neurovascular unit Endothelial cells of the BBB are distinguished from those in the periphery- Tight junctions ( zonulae occludens ) The absence of endothelial pores Paucity of pinocytic vesicles The high cellular profile of mitochondria Absence of class II MHC

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13. Pericytes regulating the growth of ECs. Help in phagocytosis, thereby acting as 2 nd barrier to Ecs . PDGFR (tyrosine kinase receptor) present on the surface pericyte , (GBM). Trauma or hypoxia, result in a significantly decreased pericyte concentration-Decrease permeability.

14. Microglia act as antigen- presenting cells by engulfing these substances and presenting them to activated T cells for destruction. It also secrete cytokines, or proinflammatory molecules, and rapidly proliferate to contain the offending agent. Extracellular Matrix physical stability to BBB.

15. Neurons , PET and functional MRI, are based on regional increases in cerebral blood flow and glucose and oxygen consumption, which are associated with regional increases in neuronal activity.

16. Integrity of BBB Tight Junctions Adherens Junctions Pericytes Astrocyte end feet

17. TIGHT JUNCTIONS BETWEEN BMEC Appear at sites of apparent fusion between outer leaflets of plasma membrane of endothelial cells Continuous Anastomosing Protein components Claudin Occludin Junction Adhesion Molecules Accessory proteins

18. Occludin Dynamic regulatory protein Directly related to substance permeability HIV and High grade Brain tumor Source: Ballabh et al

19. Claudin Backbone of strands Selectively permit entry of cation through TJs. Forms scaffold of TJs and Ocludin secure it. Anaplastic astrocytoma and GBM.

20. Junction Adhesion Molecules: Belongs to immunoglobulin IgG superfamily Localizes at tight junctions Involved in cell-to-cell adhesion and monocyte transmigration through BBB Regulates paracellular permeability and leukocyte migration

21. Adherens Junction Complex between membrane protein cadherin and intermediary proteins called catenins Cadherin-catenin complex joins to actin cytoskeleton Form adhesive contacts between cells. Assemble via homophilic interactions between extracellular domains of calcium ion dependent cadherins on surface of adjacent cells

22. NATURE OF BBB ANATOMICAL – As a barrier of diffusion PHYSIOLOGICAL – As a dynamic barrier Permitting active transport as well as active efflux

23. FUNCTIONS OF BBB Permeability barrier : prevents free exchange of substances between blood and the CNS e.g ,: vasogenic edema - albumin leaks in Supplier of nutrients e.g. Glucose, amino acid, anion transporters Modulates disease processes e.g. upregulation of cytokine transport related to neuroregeneration

24. TRANSPORT ACROSS THE BBB Simple diffusion -transport of solutes occurs down a concentration gradient. Lipid soluble agents. 2. Facilitated diffusion -solute binds to a specific membrane spanning protein and, like simple diffusion, travels down a concentration gradient.

25. 3. Simple diffusion via aqueous channel -charged ions and solutes are the principal compounds that cross the BBB by this mechanism. 4. Active transport via protein carriers -only one transported against a conc gradient; a change in affinity of the carrier for solute and expenditure of ATP are required for transport.

26. GLUCOSE : Via a glucose transporter. Sodium-independent-- GLUT-l (ECs), GLUT-3 (neurons), and GLUT-5 (microglia). Rate limiting step of primary energy acquisition. GLUT-l expression is three to four times higher on the abluminal membrane and is altered with processes such as diabetes, epilepsy, trauma, and tumors .

27. AMINO ACID : Delivery of amino acids across the BBB is achieved by carrier mediated transport across the abluminal and luminal memb . NEUROTRANSMITTERS Glutamate, aspartate , glycine , and GABA , levodopa , as precursur . Acid glutamate increase, eg , from hypoxic neurons during ischemic stroke, considerable and permanent neurotoxic / neuroexcitatory damage can occur to neural tissue, helps to keep the central and peripheral transmitter pools separate, minimising ‘crosstalk.

28. Ion regulation: The concentration of potassium in mammalian plasma is approx 4.5 mM , but in CSF and brain ISF this is maintained at ∼2.5–2.9 mM . Macromolecules The protein content of CSF is much lower than that of plasma. Plasma proteins such as albumin, pro-thrombin and plasminogen are damaging to nervous tissue, causing cellular activation which can lead to a poptosis

29. Factor Xa , converts prothrombin to thrombin, and the thrombin receptor PAR1 is in the CNS. TPA converts plasminogen to plasmin . Thrombin and plasmin if present in brain ISF can initiate cascades resulting in seizures, glial activation, glial cell division and scarring, and cell death

30. Multidrug resistance (MDR) : Pgp is an efflux transporter protein found in ECs, astrocytes , and microglia, over luminal surface of the endothelial membrane and glia and prevents toxins from entering the brain. Patient with deletion of Pgp have 100 fold increased sensitivity to chemotherpay and antiviral agent.

31. PROPERTIES TO CROSS BBB Small molecules generally cross the BBB in pharmacologically significant amounts 1) molecular mass of drug < 400-500 Da 2) forms less than 8-10 hydrogen bonds with solvent water. 3) high oil/water partition coefficients ie should be highly lipophilic

32. DECREASES BBB PERMEABILITY Intracellular cyclic adenosine monophosphate (AMP) Steroids Adrenomedullin Noradrenalin Glial -derived neurotrophic factor (GDNF) Basic fibroblastic growth factor ( bFGF ) Polyunsaturated fatty acids Transforming growth factor-13 (TGF-I3)

33. INCREASES BBB PERMEABILITY Bradykinin , Histamine Serotonin (5HT) Thrombin, Glutamate, ATP, ADP, AMP Endothelin-1, Adenosine Platelet-activating factor Phospholipase A2 Arachidonic acid Prostaglandins, Leukotriene Interleukins: IL-1a, IL-113, IL-6, Tumor necrosis factor-a (TNF-a) Macrophage inhibitory proteins: MIP-1 and MIP-2 Free radicals

34. Regions of brain not enclosed by BBB Circumventricular organs area postrema , median eminence, neurohypophysis , pineal gland, subfornical organ and lamina terminalis These are regions which need to respond to factors present in systemic circulation

35. CIRCUMVENTRICULAR ORGANS

36. “Windows of the brain” Lacks tight junction Fenestrated capillaries Large molecular weight and polar substances readily pass back and forth from blood to the perivascular spaces. Important homeostatic function.

37. ALTERATIONS OF BBB IN DISEASE

38. CNS pathologies in Brain Trauma – Bradykinin is produced and stimulates production and release of IL-6 from astrocyte leads to opening of BBB. Infection - Infectious agents cross the BBB by transcytosis . Bacterial protein (LPS) effects permeability of BBB tight in by free radical IL-6 and IL-1. Epilepsy - Transient opening of BBB in epilepticogenic foci.

39. Tumor - Break down of BBB downregulation of tight junction of protein claudin -3 Pain - Alter BBB right junction protein expression and permeability.

40. HIV-l --- adsorptive endocytosis , Because brain ECs lack CD4 and galactosylceramide receptors, they are protected from direct infection. HIV enters the CNS via infected WBC. The virus continues to proliferate in glial cells and is protected from therapy by the BBB. Subsequent degradation of TJs results in the release of cytokines, including interleukin-l ( lL -l), tumor necrosis factor (TNF), and MMPS.

41. In patients with bacterial meningitis, steroids are given in conjunction with antibiotics to minimize inflammation in the brain. Dexamethasone , may impede antibiotic permeability by tightening the BBB in the setting of meningitis. Herpes enters the CNS through olfactory nerves, whereas rabies enters through spinal nerves. In general, viruses upset the BBB less than bacterial infection does.

42. BBB Modification in the delivery of Antitumor Agents Selectivity– to limit the penetration on the basis of weight, charge, and lipid solubility. “Sink action” of CSF Reservoir for solutes that cross BBB Active removal by CSF bulk flow into venous blood prevents a diffusional equilibrium to set in.

43. Modes of drug administration to avoid BBB Intra-arterial Intrathecal CSF Perfusion Directly to tumor bed or tumor cyst Packaging in Liposomes

44. REFRENCES Youmans neurological surgery 6 th edition Article2009: Neurobiology of disease Article 2015: Seminar in cell and developmental biology

45. THANK YOU