Blood Brain Barrier

Question 1

Why is there barrier between the blood and the brain.

Answer 1

Evolutionary necessity to prevent neuronal death and damage as well as to maintain brain homeostasis.

Question 2

Draw the difference between the blood and brain extracellular fluid ion concentrations.

Answer 2

Question 3

How is the BBB formed (PeriodT Mum)
PeriodT Mum

Answer 3

Physical barrier: adherens and tight junctions, lack of fenestrations.
Transport barrier: Small lipophilic molecules can penetrate the BBB. Transcellular movement of water is allowed owing to small size.
efflux transporters (P-gp, BCRP, MRP-1).

Metabolic barrier: CYP enzymes (CYP1B1, CY2J2, CYP2U1).

Question 4

What are the characteristic of the physical BBB. What are the effects of this physical barrier.

Answer 4

Continuous endothelium, absent of fenestrate, one cell thin with established tight junctions and adherens between endothelial cells. Impedes interendothlial diffusion of hydrophilic molecules.

Question 5

Patient X has disease that destroys astrocyte processes, what are the clinical implications.

Answer 5

Tight junctions are only formed when astrocytes are present. Astrocyte feet secrete factors which induce tight junction formation. Absence of this means NO tight junctions will be formed leading to leaky BBB.

Question 6

What are tight junctions made up of.

Answer 6

Occludens, Zona occludens and Claudins.

Question 7

Astrocytes are part of the BBB.
(a) TRUE
(b) FALSE

Answer 7

(b)false, they form the BBB but not itself a member of the BBB.

Question 8

How would you characterise the tightness of the blood brain barrier (endothelial).

Answer 8

Blood brain barrier capillaries have a high transendothelial electrical resistance at 8000 Ωcm2. Therefore endothelium is highly restricted and has controlled permeability to plasmatic compound, and ions.

Question 9

From this list what molecules can’t get through the BBB and why.
a. Methotrexate
b. Chloramphenicol
c. Ethanol
d. Water
e. Diazepam

Answer 9

(a) Methotrexate is hydrophilic and only small molecules <400 Da and lipid soluble molecules LogP >-1 (+gases) can pass through BBB.

Question 10

What can get through the BBB.

Answer 10

Small molecules <400 Da.
Lipid soluble molecules LogP>-1

Question 11

Name the efflux transporters that form the transport barrier BBB.

Answer 11

P-glycoprotein (P-gp)
Breast Cancer Resistant Protein (BCRP)
Multi-drug resistant efflux protein (MRP)

Question 12

What is the function the efflux transporters.

Answer 12

To prevent large lipophilic molecules entering in the brain.

Question 13

What is the clinical significance of efflux transporters.

Answer 13

While they keep toxins out of the brain such as pesticides, it limits therapeutic agents entry into the brain such as chemotherapy for brain tumours.

Question 14

What is the phenomena that describes the how efflux pumps up regulate their activity in the presence of drug.

Answer 14

CNS resistance.

Question 15

What classes of drugs are effluxes from the brain.

Answer 15

Antibiotics,
Chemotherapeutics
Anti-viral drugs
Vitamins

Question 16

Give the name of the drugs effluxed by the pump (recall the Venn diagram).

Answer 16

Paclitaxel is removed by P-gp (ABCB1) and cisplatin is removed by MRP1
(ABCC1). The most notably removed chemotherapeutic agent is Doxorubicin
which is removed by all three transporters… (BCRP ABCG2 EFFLUX TRANSPORTER).

Question 17

What metabolising enzyme is found in the astrocytes end foot processes.
a. CYP1B1 + CYP2U1
b. CYP1B1+ CYP2J2
c. CYP2J2 +CYP2U1
d. CYP1A1 + CYP2D6

Answer 17

(c) CYP2J2 +CYP2U1 although CYP1A1 also is present in the astrocyte cell.

Question 18

What metabolising enzyme is found in the endothelial

a. CYP1B1 + CYP2U1
b. CYP1B1+ CYP2J2
c. CYP2J2 +CYP2U1
d. CYP1A1 + CYP2D6

Answer 18

(a) CYP1B1 and CYP2U1, CYP2D6 is expressed also but very weakly.

Question 19

What are the clinical implications of inducible enzymes found at the BBB.

Answer 19

Drug won’t pass into the neuronal tissue or pass through endothelial because they are metabolised on the surface of endothelial and at the astrocytes end foot processes. Also clinically there will inter individual variability when prescribing an agent so varying therapeutic response will be seen.

Question 20

Function of CYP2J2

Answer 20

Metabolises arachidonic acid to active vasodilator and helps increase blood flow to brain.

Question 21

What can induce CYPs

Answer 21

Dexamethasone (CYP2D6)
Pollutant, alcohol, nicotine.

Question 22

How do things such a small hydrophilic molecules and large macromolecules get into the brain. Explain briefly how it works with examples.

Answer 22

For small hydrophilic molecules:
1. Polarised transporters (carrier-mediated transport) allows for unidirectional transport of specific molecules into the brain. E.g. Glut 1 for glucose, Mct1 for Lactate and Lat1 for leucine (neutral amino acid).
For larger molecules: peptides, proteins
2. Receptor mediated transcytosis (RMT): Macromolecular ligands bind to specific receptors on the surface of the endothelium and trigger endocytotic event.
3. Adsorptive mediated transcytosis (AMT): Excessively positive charge on the molecule (cations), adsorb to the surface of endothelium and undergo endocytosis and eventually exocytosis.

Question 23

What transport system does L-dopa take to get into the brain.

Answer 23

Carrier mediated transport: L-system large neutral amino acid transporter

Question 24

How does the neurons communicate to the blood brain barrier (Please Ask).

Answer 24

The neurovascular unit system consists of Pericytes and Astrocytes.

Question 25

Function of pericytes and astrocytes in the neurovascular unit.

Answer 25

Astrocytes are type glial cells that participate in ionic equilibrium, pH. Sequesters potassium from brain interstitial fluid. Take part in the synthesis, release and removal of glutamate and GABA from the synapse. Pericytes are on the external wall of the small vessels can control capillary diameter.

Question 26

If neuron doesn’t exhibit high energy demand the neurovascular unit will not increase the blood flow to the site.
a. True
b. False

Answer 26

(A) true, neurones exhibiting high activity will have neurotransmitter released in the synaptic space that the astrocytes will sense and act accordingly.

Question 27

What is the clinical significance if neurones or astrocytes are dying to the neurovascular unit.
(a) Blood flow is reduced and slows local drug delivery
(b) Blood flow is increased and increase local drug delivery
(c) Blood flow increase and slows down local drug delivery.

Answer 27

(a) Blood flow is reduced and slows local drug delivery

Question 28

How would we detect the small changes in blood flow in patient?

Answer 28

Functional MRI to identify regions of neuronal (brain) activity.

Question 29

What part of the brain makes the CSF and forms the Blood-CSF-barrier.

Answer 29

Choroid plexus located in the lateral ventricles (x2), 3rd ventricles and 4th ventricle.

Question 30

Label the diagram

Answer 30

Question 31

Describe the structure of the blood-CSF-barrier

Answer 31

Capillary endothelial is leaky, similar to peripheral capillaries.
Secretory Epithelial cells around the capillaries have tight junctions between them.

Question 32

Describe the similarities between BBB and Blood-CSF-barrier.

Answer 32

Question 33

What is the main functions choroid plexuses Blood-CSF-barrier.

Answer 33

Production of Cerebrospinal fluid (CSF).

Question 34

Describe briefly the production of CSF fluid.

Answer 34

Water from blood, follows ions transported from blood to ventricles. Ion transport set up by Na+/K+ ATPase in secretory epithelial cells.

Question 35

The volume of CSF produced in a day
a. 150 mL
b. 800 mL
c. 600 mL
d. 200 mL

Answer 35

(c) 600 mL is made every day, 150mL x4

Question 36

Describe the CSF composition

Answer 36

Low protein content (0.5%), glucose and amino acid is low, some electrolytes are low such as potassium and calcium.

Question 37

Where does the CSF fluid travel and go into the venules

Answer 37

Unidirectional flow CSF goes down the neuroaxis through the ventricles (lateral, third and fourth ventricles), goes out through hindbrain foramina into the cisterna magna and then the subarchnoid space to bathe the surface of the brain. When fluid builds up the valves open and lets CSF drain into the venous system.

Question 38

The CSF flows and drains into venous blood which is the major way that metabolites/waste/toxin are cleared.
(a) True
(b) False

Answer 38

(a) true.

Question 39

CSF flows over the …(a) .. along the (b)…. Of the blood vessels which is the …(c).. route. CSF can move into brain, and brain …(d)…. Can move out of the brain via the …(e) .. route.

Answer 39

(a) surface of the brain
(b) outside
(c) perivascular
(d) interstitial fluid
(e) perivascular route.

Question 40

What disease state is characterised by the build up of CSF fluid in the brain. +clinical implication with drug delivery.

Answer 40

Hydrocephalus —> drug metabolite may accumulate in area.

Question 41

Explain the function of the CSF

Answer 41

1. Excretion/drainage and clearance of toxic metabolites, large molecules and drugs (acts as lymphatic system for brain clearing).
2. Provides buoyancy to brain, reduces crushing spinal nerves (brain weight reduced from 1400g to 50g),
3. Distributes nutrients to brain (including vitamin C, folate, riboflavin).
4. Distributes hormonal secretion (IGF, leptin) through the CNS.

Question 42

When is drug c clearance by cerebrospinal fluid (CSF) the highest.
A. 12:00
B. 00:00
C. 1:30
D. 08:00

Answer 42

B. 00:00 CSF fluid production is the highest.

Question 43

What is the peak production volume of CSF fluid.
A. 42 ml/hr
B. 8 mL/hr
C. 84 ml/hr
D. 34 ml/hr

Answer 43

(A) 42 ml/hr peak production is highest at midnight.

Question 44

Patient X asked you if he should take his L-dopa at night. Should he?

Answer 44

No, Patient X should administer L-dopa in the morning as CSF fluid clearance is highest at night (peak production of CSF fluid at 00:00).