Structural:• Absence of fenestrations• More extensive tight junctions. Functional:• Impermeable to most substances• Sparse pinocytic vesicular transport• Increased expression of transport and carrier proteins: receptor mediated endocytosis • No gap junctions, only tight junctions • Limited paracellular and transcellular transport receptors for numerous hormones and neurotransmitters Differentiation of the endothelium into a barrier layer begins during embryonic angiogenesis and in the adult is largely maintained by a close inductive association especially with foot process of of astrocytic glial cells.

1. BLOOD BRAIN BARRIER
DR VISHAL SINGH
NEUROSURGERY RESIDENT
DR. R.M.L HOSPITAL

2.  Blood-brain barrier (BBB) restrict movement of certain substances into and out of
brain.
 It mediates a complex system of exchange, transport, and clearance.
 It ensures adequate concentration of essential compounds such as oxygen and
glucose and at the same time protects the brain from toxic substances in the
peripheral circulation
 History
 1882 - Paul Ehlrich – Typan Blue dye Intravenous injection.
 1913 - Edwin Goldmann ( Ehlrich’s student ) – injected water-soluble dyes into CNS

3. Anatomy of Blood Brain Barrier
The blood-brain barrier (BBB), an important
component of the neurovascular unit.
• made of specialized endothelial cells.
• basement membrane.
• neuroglial structures: astrocytes, pericytes,
and microglia.
• Neurons.

4. Characteristics of endothelial layer of BBB
 Structural:
• Absence of fenestrations
• More extensive tight junctions.
 Functional:
• Impermeable to most substances
• Sparse pinocytic vesicular transport
• Increased expression of transport and carrier proteins: receptor mediated endocytosis
• No gap junctions, only tight junctions
• Limited paracellular and transcellular transport
 receptors for numerous hormones and neurotransmitters
 Differentiation of the endothelium into a barrier layer begins during embryonic angiogenesis and
in the adult is largely maintained by a close inductive association especially with foot process of of
astrocytic glial cells.

5. Tight junction
• CLAUDINS make up the backbone of the tight junction
strands, form dimers, and bind homotypically to claudins on
adjacent cells to produce the primary seal of the tight
junction
• OCCLUDIN functions as a dynamic regulatory protein whose
presence at the BBB is correlated with increased
transendothelial electrical resistance and decreased
paracellular permeability
• Junctional adhesion molecules (JAMs) are localized at the
tight junction and, in association with platelet endothelial
cellular adhesion molecule-1 (PECAM), regulate leukocyte
migration across the BBB
• Adherens junctions are not specific for cerebral endothelial
junctions.
• Several other accessory proteins also contribute to its
structural support, such as zona occludens-1 (ZO- 1) to ZO-
3, cingulin, and 7H6.

6. Pericytes
 Pericytes with smooth muscle- like properties that reside adjacent to capillaries
 Cover 22-32% of endothelium
 regulation of endothelium proliferation , angiogenesis & inflammatory processes
 Regulate BBB specific gene expression patterns in endothelial cells
 Induce polarisation of astrocyte end feet surrounding CNS blood vessels
 In the absence of pericytes, There will be abnormal vasculogenesis, endothelial
hyperplasia and INCREASED permeability in the brain

7. Characteristics of Astrocytic foot
processes
 the star shaped astrocytic foot processes
Ensheath >95% of the abluminal vessel surface
 Do not directly produce a permeability barrier, they provide the signals which induce the
endothelial cells to form the BBB
 work cooperatively with the endothelial cells to regulate the cerebrospinal fluid (CSF), potassium
concentration.

8. Locatin of Blood Brain
Barrier :
 All over CNS including brain, spinal cord and peripheral nerves, except
 Circumventricular organs:-
Posterior pituitary,
median eminence,
organum vasculosum of the lamina terminalis (OVLT),
subfornical organs,
area postrema and
pineal gland.
the CVO permeable capillaries are the point of bidirectional blood–brain
communication for neuroendocrine function
In these areas the capillary endothelial cells are fenestrated and have
incomplete tight junctions, permitting molecules to pass

9. Sensory CVOs
These enable rapid detection of circulating signals in systemic blood
 Area postrema - Vomiting center:
 when a toxic substance enters the bloodstream it will get to the area postrema and
induce vomiting.
 Subfornical organ
 chemoreceptive area monitoring blood angiotensin II level
 Important for the regulation of body fluids.
 Organum vasculosum of the lamina terminalis
 A chemosensory area that detects peptides and other molecules.

10. Secretory CVOs
These facilitate transport of brain-derived signals into the circulating blood.
 Pineal body
 Secretes melatonin and neuroactive peptides.
 Associated with circadian rhythms.
 Neurohypophysis (posterior pituitary)
 Releases neurohormones like oxytocin and vasopressin
 Median eminence
 Regulates anterior pituitary through release of neurohormones like regulatory
hormones.

11. Blood Brain
Barrier
Transport:

12.  Paracellular aqueous diffusion.
Small water-soluble molecules can pass through this extracellular pathway, which is regulated by TJs.
 Transcellular lipophilic diffusion.
Substances cross the BBB at a rate proportional to their molecular weight and lipid solubility.
 Adsorptive transcytosis.
This endocytic process is mediated by clathrin-coated pits and, to a lesser extent, caveolae. It is generally selective
for cationic molecules and is the predominant mechanism for passage of HIV-1 into the brain. This process is being
investigated as a possible pathway for therapeutic drug delivery to the CNS.
 Saturable transport :
 Receptor-mediated transcytosis is the transport of solutes through receptor-binding and subsequent
endocytosis. This can occur against a concentration gradient but requires energy.
 Channel-mediated transport is a saturable mode of transit that mediates influx and efflux via transport proteins.
 Efflux pumps like P- glycoprotein.

13. FUNCTIONS OF BBB
 Ion regulation
 Stable environment for neural function
 combination of specific ion channels and transporters keeps the ionic composition optimal for synaptic
signalling function.
 concentration of [K+] in plasma is approximately 4.5 mM, but in CSF and brain ISF –> ∼2.5–2.9 mM, in
spite of changes that can occur in plasma [K+]
 following exercise or a meal, imposed experimentally, or resulting from pathology
 Ca2+, Mg2+ and pH are also actively regulated at the BBB
 Water traverses the plasma membranes by facilitated diffusion through water channels called
aquaporins The primary water channel in the CNS is AQP4, which is predominately expressed by
astrocyte

14.  Neurotransmitters
 Blood plasma contains high levels of the neuroexcitatory amino acid glutamate which fluctuate
significantly after the ingestion of food. If glutamate is released into the brain ISF in an uncontrolled
manner, as for example from hypoxic neurons during ischemic stroke, considerable and permanent
neurotoxic /neuroexcitatory damage can occur to neural tissue.
 Since the central and peripheral nervous systems use many of the same neurotransmitters, the BBB
also helps to keep the central and peripheral transmitter pools separate.

15.  Macromolecules
 BBB prevents many macromolecules from entering the brain.
 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 apoptosis
 Thrombin and plasmin if present in brain ISF can initiate cascades resulting in seizures,
glial activation, glial cell division and scarring, and cell death
 Leakage of these large molecular weight serum proteins into brain across a damaged
BBB can have serious pathological consequences.

16.  Neurotoxins
 Shields the CNS from neurotoxic substances circulating in the blood.
 Neurotoxins may be endogenous metabolites or proteins, ingested in the diet or
otherwise acquired from the environment.
 Several Energy-dependent efflux transporters (ATP- binding cassette transporters)
actively pump many of these agents out of the brain like P-Glycoprotein .

17.  Brain nutrition
 BBB allow low passive permeability to many essential water- soluble nutrients and
metabolites required by nervous tissue.
 Glucose
 GLUT-1(glucose transporter 1) present in high concentration in the ECs of arterioles, venules,
and capillaries and facilitates movement of glucose from the peripheral circulation to the brain.
 Insulin Independent GLUT.
 Function of GLUT-1altered with processes such as hypoglycaemia, diabetes, epilepsy, trauma,
and tumours.

18. PATHOLOGIC CHANGES IN THE BLOOD-
BRAIN BARRIER
Many factors that regulate permeability under normal conditions are altered during pathologic conditions
and result in enhanced vascular permeability and oedema formation
 Trauma
 Following traumatic brain injury, the BBB is known to disrupt, leading to focal oedema and altered extracellular
composition.
 BBB disruption is a pathological hallmark of severe TBI and is associated with neuroinflammatory events
contributing to brain edema and cell death.
 There is a strong temporal and spatial association between the degree of BBB disruption and the ability of
circulating inflammatory cells to quickly migrate to the area of CNS injury.

19. BBB and Brain Tumors
 Affect BBB permeability in at least two ways:
 directly, through invasion or mechanical interference,
 indirectly, by the production of diffusible molecules that act at a distance from tumour cells.
 Meningiomas and brain metastases do not contain the astrocytes and do not have a true BBB.
 The capillary endothelium within brain tumours have been named the “blood-brain tumor barrier”. The tumor capillaries
are surrounded by large collagen-filled extracellular spaces with gaps in the basal lamina and absence of glial processes.
 In primary brain tumors, the abnormal capillaries are found in the more malignant tumors and have cellular
fenestrations, wide junctions, pinocytotic vesicles and infolding of luminal surfaces.
 BBB in tumor is extremely heterogeneous and is frequently more permeable in the center of a malignant tumor, whereas
the well-vascularized, actively proliferating, infiltrating edge, which is sometimes referred to as the brain tissue adjacent
to the tumor, exhibits a variable degree of BBB integrity .These different permeabilities result in sharply reduced
concentrations of chemotherapeutic agents at the rapidly growing periphery, because of limited diffusion from the
central leaky hypoxic tumor. . This is termed the sink effect, and it can contribute to chemotherapy failure.
 In addition, because the bulk of a tumor gradually decreases with treatment, BBB integrity often recovers.

20.  Capillary permeability in gliomas is regionally variable, and can be 10–30 times that of the normal
brain. Malignant gliomas, actively degrade tight junctions by secreting soluble factors, eventually
leading to BBB disruption within invaded brain tissue.
 Vascular endothelial growth factor (VEGF) appears to be involved in tumorigenesis, neovascularization,
and edema production. VEGF is a mitogen for endothelial cells and has extremely potent effects on
microvascular permeability.
 vasogenic cerebral edema of tumor effects on brain metabolism and functions is primarily due to
alterations in the neuronal environment, collapse of microvessels by edema fluid, tissue hypoxia and
the cellular effect of the extravasating serum proteins.
 The metastatic tumors have capillary properties similar to that of the derivative tissue. These changes
lead to increased permeability - higher uptake of isotopes and contrast media.
 Radiotherapy can also alter BBB; changes may be seen many years after exposure.

21. BBB in CNS infection
 The integrity BBB is compromised, and leukocyte infiltration occurs in infection.
 Contrast enhancement in CT and MRI scans is due to BBB breakdown.
 When treatment becomes effective, BBB returns to normal.
 Antibiotics:
 The ideal compound to treat CNS infections is small, is moderately lipophilic, low level of plasma protein binding,
has a volume of distribution of around 1 liter/kg, and is not a strong ligand of P-gp or another efflux pump
located at the blood-brain or blood-CSF barrier.
 Drugs like isoniazid, pyrazinamide, linezolid, metronidazole, fluconazole, and some fluoroquinolones are
extremely valuable drugs for the treatment of CNS infections with susceptible pathogens.
 Direct – Intrathecal / Intraventricular route can be used.

22. Epilepsy and BBB
 Acute rise in blood pressure and blood flow that follows a seizure is associated
with increase in the number and volume of pinocytic vesicles of the brain
capillaries with deranged tight cell junctions are responsible for increased
movement of normally excluded substances.
 BBB is restored in about 1 hour.
 Reduction of blood pressure, steroids and pentobarbitones appear to protect and
restore BBB.
 Delayed neurodegeneration and functional impairment occur following the
development of the epileptic focus in the BBB permeable cerebral cortex

23. Clinical applications
 Restoration of Blood-Brain Barrier
 Corticosteroids are thought to decrease the permeability of CNS capillaries, thereby
protecting BBB function, and reversing the effect of influences acting to disrupt the BBB
in brain tumours.
 Antioxidants such as lipoic acid may be able to stabilize a weakening BBB. Lipoic acid
affects cellular migration into the CNS and stabilizes BBB integrity. Preferred in CNS
infections.
 Pharmacological Measures to Overcome Blood-Brain Barrier Blood
 As blood brain barrier is the single most important obstacle for effective dose delivery
of chemotherapeutic agents when given by intravenous route. Pharmacologically, the
drugs are administered in solvents such as ethanol or dimethyl sulfoxide (DMSO)

24. Methods – Drug delivery to CNS
 Disruption of Blood-Brain Barrier
 blood-tumor barrier limits adequate delivery of antitumor agents to tumor and the immediately adjacent brain.
Systemic toxicity has usually been the dose limiting factor in brain tumor chemotherapy.
 Goal of BBB disruption is maximizing delivery of agents to the brain while preserving neurocognitive function and
quality of life and minimizing systemic toxicity.
 Can be done by
 Osmotic shock- by injecting a hyperosmotic agent (mannitol) intra-arterially in the carotid or the vertebral arteries. The
infusion of mannitol causes osmotic shrinkage of capillary endothelial cells, with resultant separation of the tight junctions
between the cells.
 MRI Guided Focused Ultrasound.

25.  Bypass Blood brain Barrier
 Circumventing the Blood-Brain Barrier
 Intrathecal therapy is invasive procedure. Side effects include aseptic meningitis, chemotherapy-related
leukoencephalopathy. Effective in leptomeningeal diseases.
 Convection-Enhanced Delivery
 chemotherapy is infused into the brain tumor under constant pressure to deliver drug by bulk flow through
catheters placed into the tumor bed .
 Local Delivery of Polymer-Infused Chemotherapy
 A craniotomy must be performed to implant the drug wafers into the tumor resection cavity.

26.  Efflux inhibitors / modulators :
 aims to augment the diffusion of a drug across the BBB via the inhibition of efflux pumps that mediate its
active removal from the brain.
 Examples include inhibitors include tariquidar, elacridar, and reserpine
 Carrier mediated , Transcytotic approach:
 This delivery system includes freely soluble drug molecules that bind to expressed transporters or surface
molecules, drug-delivery vehicles such as liposomes or exosomes, or nanoparticles. I
 mportantly, these drug-delivery methods often incorporate transporter or receptor substrates or
molecular probes for targeting to specific structures at the BBB/BBTB.

27. THANK YOU