NEU 490 BBB

Question 1

Blood–CSF barriers - fenestrated?
VS
Blood–brain barrier (BBB) - Made up of?

Answer 1

Blood–CSF barriers: Choroid plexus in our neurons epithelial cells (vascular tissue found in our ventricles made up of capillary enveloped by ependymal cells and unlike the capillary for BBB choroid capillary do not have tight junctions are fenestrated means things leak out we want plasma to leak out to make CSF) (control movement into ventricles is by tight junctions in ependymal cells which has specific channels and transport that allow for movement of things to make CSF) (CSF plasma from blood leak out to circulate brain and spinal cord but for BBB want nothing to leak in)

Blood–brain barrier (BBB):
Made up of brain endothelial cells, basement membrane, pericytes, astrocytes, neurons

Question 2

What is the blood-brain barrier?

Brain consumes blank % of energy Source but only makes up blank % of body weight and has blank surface area ~20 m2

Capillary within blank μm of every brain cell

Vessels possess unique properties?

Answer 2

A highly selective semi-permeable barrier separating the circulating blood from the brain and spinal cord

Brain consumes 20% of energy Source but only makes up 2% of body weight and has Vascular surface area ~20 m2

Capillary within 25 μm of every brain cell

Vessels possess unique properties: isolation can’t be complete bc need nutrients and have neuroendocrine communication via blood. Precise control of CNS homeostasis allows for proper neuronal function and protected neural tissue so alteration so these barrier properties are actually a common component of a lot of neurological diseases.
- Tightly regulate the movement of ions, molecular, and cells
- Many common things neuroactive - includes K, Na, amino acids like glutamate, hormones, durg
- These substances many are ubiquitous so concertante can drastically change so constantly circulating (systemic circulation)

Question 3

BBB exists throughout the central nervous system

EXCEPTIONS TO THE RULE:

Circumventricular organs (CVOs) are?

Sensory systems? Area postrema, Subfornical organ, Vascular organ of

Secretory: body fluid homeostasis for thirst

Answer 3

EXCEPTIONS TO THE RULE: Brain areas not covered by BBB for the circumventricular organs - contrast to capillaries located throughout the brain, blood micro vessels in things called CVO do not have barrier properties, these endothelial cells fenstra which allow for free diffusion of substance between blood and CNS

Circumventricular organs (CVOs) are structures in the brain characterized by their extensive and highly permeable capillaries - facilitate special types of communication between the CNS and blood stream important in the neuro endocrine, peptides and hormones

Sensory systems:
- Area postrema - vomiting
- Subfornical organ - fluid balance, BV
- Vascular organ of lamina terminalis - regulates fuel balance and blood volume for drinking and appetite - these are all important for quick communication of survival to make the body do something

Secretory: body fluid homeostasis for thirst
- secrete hormones and glycoproteins into the peripheral blood using feedback from both the brain environment and external stimuli
- Subcommissural organ, Posterior pituitary gland, Intermediate lobe of pituitary gland, Pineal gland, Median eminence - neuroendocrine functions like HPA axis and fight or flight (fast direct communication via circulatory systems)

Question 4

Barrier - Discovery 1885

Ehrlich injected dye into blood stream but didn’t stain brain - Argued what?

Goldmann (Ehrlich’s student) injected dye into ventricles - hypothesized what?

2 possibilities said what and solved how?

Answer 4

Ehrlich injected dye into blood stream but didn’t stain brain - Argued can’t dissolve in brain

Goldmann (Ehrlich’s student) injected dye into ventricles -
Dye stained brain but didn’t leave - hypothesized barrier at vessels so can dissolve but it can cross

2 possibilities:
1. Physical astrocyte barrier
2. different capillary types having different intrinsic properties

Solve problem with Electronic microscopy saw astrocytes, different types of capillary and other cells types (pericytes)

Question 5

Blood Brain Barrier: not your standard capillary(luminal diameter of less than 10 mM)

BBB?

Capillary:

Typical Capillary:

Gliovascular Unit Brain:

Answer 5

BBB: tight-junction brain capillary endothelial cells that precludes entrance of substances into the brain

Capillary: Separates plasma from brain interstitial fluid (CSF + ECF)

Typical Capillary: Peripheral capillaries like endothelial cells do no not have tight junctions - think areas. Anything lipid soluble can travel directly through endothelial japs. Fenestra thin areas can easily leave through here

Gliovascular Unit Brain: brain tissue - brain capillaries - endothelial cells have tight junctions

Question 6

Peripheral vs. Cerebral Capillaries

Answer 6

Though capillaries form the physical barrier, BBB properties are not intrinsic to these cells themselves… Other components of the neurovascular unit are necessary!

BECs, astrocytes, pericytes, basement membrane, neurons

Question 7

Which of the following are some circumventricular organs not covered by the BBB?

Answer 7

Subfornical organ, Area postrema, and Pineal gland

Question 8

True or False: Tight junction are inherent qualities of endothelial cells in capillaries

Answer 8

False

Question 9

Cellular constituents of the BBB - not just capillaries important

What makes A“neurovascular unit”:

Answer 9

1) Brain endothelial cells
2) Basement membrane
3) Pericytes
4) Astrocytes
5) Neurons

Question 10

Basement membrane / basal lamina

Surrounds and organized?

What kind of support?

Composition mixture of?

BECs, astrocytes, and pericytes all bind to the BM via?

Laminins for?

Collagen type IV(4)?

Matrix metalloproteinases (MMPs)?

Answer 10

Surrounds Brain endothelial cells (BECs) - organized protein sheet surrounds BECs(brain endothelial cells and Pericytes)

Provides structural support/ integrity
20-200 nm thick - highly dynamic and maintenance of integrity

Composition: mixture of different(secreted by endothelial cells and pericytes) composed of extracellular matrix proteins
- structural (collagen type IV)
- adhesion proteins (laminin, fibronectin)
- heparan sulfate proteoglycans (perlecan, agrin)
- Growth factors and enzymes

BECs, astrocytes, and pericytes all bind to the BM via specific receptors

Laminins - organizing and scaffolding

Collagen type IV(4) stability of basement membrane (BM)

Matrix metalloproteinases (MMPs) activated by pathological insults which disrupt BBB integrity by impairment of TJ functional activity tight proteins

Question 11

Pericytes what are they? where are they? named how? take up how much %?

a lot pericytes in the brain vascular unit than periphery - what is the ratio?

Functions include?

Answer 11

Named with respect to their unique localization in the perivascular space of brain vessels – located between endothelial cells and astrocyte endfeet and embedded in basements membrane so physically separated from endothelial cells and astrocyte endfeet
- Peri (surrounding) cytes (cells)
- Location and pathology specific so could take up 22-90%

1 pericyte : 5 BEC ratio - a lot pericytes in the brain vascular unit than periphery
(compared to 1:100 in skeletal muscle capillaries!)

Functions include: induce formation of TJs between brain endothelial cells
- Vessel formation, sprouting, and stabilization - provide physical support for growing vasculature
- Vessel diameter and CBF - contribute to regulation of blood flow by controlling lumniar
- BBB integrity and transport of substances into pericyte – pericyte regulate
- Produce extracellular matrix proteins
- Regulation of endothelial cell proliferation migration and differentiation
- Clearance of toxins

Question 12

Pericytes(induce endothelial differentiation) signal to BECs - community via direct contact or paracrine signing

Cross-talk and functional coupling between pericytes and BECs is the result of?

Essential for what four things?

Platelet-derived growth factor B (PDGF-B) → expressed by endothelial cells, stimulates?

Transforming growth factor-β (TGF-β)?

Notch? what promote? which notch for survival? if notch inhbited then?

Answer 12

Cross-talk and functional coupling between pericytes and BECs is the result of several signal transduction cascades

Essential for recruitment, proliferation, migration, and attachment during angiogenesis (the process of new blood vessels forming from existing ones)

Platelet-derived growth factor B (PDGF-B) → expressed by endothelial cells, stimulates migration and proliferation of pericytes (knockout of this PDGF-B reduced pericyte converge of microvessels

Transforming growth factor-β (TGF-β) - cytokine expressed by BECs and control proliferation and differentiation of BECs which alters pericytes contractibility and motility reduced number of pericytes so loss of TGFB leads to increase endothelial proliferation

Notch - key signaling mechanism and plays role in blood vessel formation
- Promote cell differentiation
- Pericytes express Notch 1 and 3 and important for pericyte survival and adhesion to endothelium + limiting invasive behavior - mammals express four transmembrane notch receptors and five membrane bound ligands
- Inhibit notch in pericytes will develop severe AVM (arteriovenous malformation) + pericytes deficiencies in low numbers

Above are soluble mediators: growth, platelte, notch

Question 13

What happens if there aren’t pericytes?

Answer 13

Researchers used pericyte deficient mice
Regulating BBB specific gene expression in endothelial cells so tight junctions

Accumulation of intravenously injected tracers in the brain parenchyma and endothelium, indicating no effective barrier

Inducing polarization of astrocyte endfeet

Increase in permeability of BB to H20 and a range of low molecular mass and high molecular mass tracers which increase permeability occurs bc of endothelial transcytosis

Question 14

Which is true regarding pericytes? 4 things

Answer 14

They induce tight junctions between endothelial cells, contribute to regulation of blood flow, they regulate movement of substances into parenchyma, they affect endothelial cell proliferation

Question 15

Astrocytic Endfeet - surround capillary

abundant?

surround and are contiguous with who?

Answer 15

Most abundant cell type in brain

Perivascular endfeet of astrocytes surround BECs and are contiguous with the basal lamina - can bind directly via receptors

Close apposition of endothelial cells and astrocytes led researchers to further investigate the role of astrocytes in BBB function - orchestrate of BBB properties and barrier maturation also maintenance of BB integrity and functional + anatomical support

Question 16

Inhibition of which factors can lead to low number of pericytes?

Answer 16

Notch and TGF-beta

Question 17

Astrocytes BLANK surround brain endothelial cells/vasculature and are contiguous with the basement membrane. BLANK induces the polarization of these components.

Answer 17

Endfeet, pericyte

Question 18

Astrocytes Cover BLANK% of the surface of the BBB

Research has found that astrocytes contribute to both the BLANK and BLANK of the BBB

Answer 18

90-95%

the induction(give rise) and maintenance

Question 19

Germ Layers of Developing Embryo
Germ layers are primary layers of cells that form during embryonic development
Vertebrates have three germ layers, the endoderm, mesoderm, and ectoderm

Blastocysts?

Microglia which layer?

Ectoderm?

Mesoderm?

The endoderm?

Answer 19

Blastocysts are rapidly dividing, and can turn into a variety of things depending on which layer of developing tissue it ends up in -
Blastocyst which layer its in determine its fate

Microglia - yolk sac endoderm and primitive gut

Ectoderm make outside like skin, hair, eyes, and neural tube

Mesoderm middle layer like red blood cells muscle and heart cells

The endoderm: the innermost of the three primary germ layers of an embryo that is the source of the epithelium of the digestive tract and its derivatives and of the lower respiratory tract.

Question 20

Which layer of a developing embryo differentiates into neural tissue?

Answer 20

Ectoderm

Question 21

Neural tissue induces BBB characteristics experiment - Endothelial cells were transplanted into different environments during development

Transplanted avascular embryonic brain fragments to the coelomic cavity: show?

Transplanted avascular embryonic mesodermal tissue fragments to the brain: show?

Conclusion from this study: ?

Answer 21

Transplanted avascular embryonic brain fragments to the coelomic cavity:
Endothelial cells of new vasculature developing in the brain tissue show BBB characteristics

Transplanted avascular embryonic mesodermal tissue fragments to the brain:
Endothelial cells of new vasculature developing in the mesodermal tissue do NOT show BBB characteristics

Conclusion from this study: BBB characteristics of endothelial cells were induced in the presence of neural, but not non-neural, tissue
Influenced by the tissue it is growing within

Question 22

Astrocytes specifically induce BBB properties of non-neural endothelial cells study

Method: In vitro co-culture system
Rat fetal brain astrocytes cultivated on one surface of a porous membrane
Human umbilical vein EC on the opposite surface

cultures without the astrocytes and with?

Conclusion from this study:?

Answer 22

Astrocytes pass their endfeet through the pores, making contact with endothelial cells and TJs - this did not occur in cultures without the astrocytes

mRNAs (q-PCR) for representative BBB markers upregulated in endothelial cells co-cultured with astrocytes
Including transferrin receptor, P-gp, and GLUT-1

Conclusion from this study: Astrocytes are capable of differentiating non-neural EC(peripheral) into BECs through contact with their endfeet, endowing them with the BBB properties and TJs, transports + specific receptors - phenotype was change

Question 23

Three main functions of BBB: ?

Answer 23

Physical barrier, metabolic barrier, and transport barrier

Question 24

Physical Barrier:

Electrical resistance of?

Endothelial cells transport and carrier?

Thin or Thick?

Function?

Linked together by a complex of?

Answer 24

Electrical resistance of our endothelial cells and high 1800

Endothelial cells transport and carrier proteins (proper trafficking) and enzymes break down metabloism

Thin yet effective physical barrier
Cells are arranged in a single cell layer, just 500 nm thick

Function: To restrict the transport of many substances, while permitting essential molecules access to the brain

Linked together by a complex of proteins(membrane spanning and systolic) which span the inter-endothelial space( between two endothelial cells like capillary walls - walls of blood vessels) creating Tight Junctions

Question 25

Endothelial cells

In CNS? connected how? transport which?

Periphery? transport? arrangement? permeability? vesicles?

Answer 25

CNS:
- No fenestrations
- Connected via tight junctions, no or limited paracellular, Impermeable to most substances, Limited paracellular transport
- Express a variety of transporters, both toprovide the CNS with specific nutrients, and also to efflux potential toxins
- CNS Limited transcellular transport - through endothelial cells

Periphery:
- Fenestrated(in latin means windows) - up to 50 nm wide
- Paracellular transport may occur between endothelial cells
- Transcytotic vesicles
- High permeability

Question 26

Tight Junctions

TJs are one mode of?

Consist of what to make “TJ strands.” ?

Individual TJ strands then laterally and tightly associate with?

Components - Formed via the interaction between integral membrane proteins: ?
3 things and each has subtypes

Answer 26

TJs are one mode of cell-cell adhesion, sealing the aqueous paracellular diffusion pathway between endothelial cells.

Consist of integral membrane proteins which aggregate linearly to constitute “TJ strands.”

Individual TJ strands then laterally and tightly associate with strands in the apposing membrane of adjacent cells to form paired strands, intercellular distance becomes nonexistent “kissing points.”

Components - Formed via the interaction between integral membrane proteins:

Membrane-spanning proteins
- Claudins
Occludin
- Junctional Adhesion Molecules JAMs

Cytosolic Scaffolding proteins
- Zonulae Occludins

Adherens Junctions
- Cadherin

Question 27

Membrane Spanning: Claudins

increase what two things?

major constituent of? expression is?

Extracellular loops allow for?
Binding can either form a what or what?

Intracellular loops can?
primary type?

Answer 27

Claudin - 5 ko - increase paracellular transport and increase permeability of BBB to small molecules

Claudin is a major constituent of TJ strands
- There are 27 members of claudins, but Claudin 1, 3, and 5 are most involved in TJs - BBB
- Expression of claudins is tissue specific

Extracellular loops allow for binding between claudins located on adjacent endothelial cells
- Binding can either form a pore with charge-selectivity, or can form a barrier

Intracellular loops can interact with membrane-associated proteins - allow for anchoring and stability
Barrier forming claudins - primary type in BBB

Question 28

Membrane Spanning: Occludin

Occludin is the first what?

Increased occludin expression reduces?

Dephosphorylation of occludin causes?
a way to have active?

knockout analyses in mice, revealed that TJ strands can be?

Answer 28

Occludin is the first TJ transmembrane protein described - controls paracellular transport strongly

Increased occludin expression reduces paracellular diffusion - over expression

Dephosphorylation of occludin causes BBB failure - unwinding of extracellular loop contraction and phosphorylate is a way to have active interaction of two adjacent occludin

Several studies, including gene knockout analyses in mice, revealed that TJ strands can be formed without occludin - although occludin essential to effective BBB function it is not alone responsible for forming BBB

Question 29

Membrane Spanning: Junctional Adhesion Molecules

interact with what?

JAM, with a single transmembrane domain, was shown to?

It is a member of what family?

Located on a number of what cells?

Interacts with a variety of intracellular?

Answer 29

JAM 1-3 Interact with claudin and occludin

JAM, with a single transmembrane domain, was shown to associate laterally with TJ strands

It is a member of the immunoglobulin superfamily IgSF – a group of proteins involved in the recognition, binding, or adhesion of cells

Located on a number of immune and circulatory cells, in addition to epithelial and endothelial cells

Interacts with a variety of intracellular scaffolding proteins - leukocyte adhesion and transport into parenchym so immune function and allow for anchoring to membrane

Question 30

Let’s explore the structure of membrane spanning TJ proteins further. What is an N-terminus(free amine) and a C-terminus(free carboxylic acid) of a protein? Are they intracellular or extracellular in Tight junctions? What do the extracellular loops do? TELL ME ABOUT EXTRA AND INTRA

Research: what is a disorder that is linked to dysfunction of the extracellular loop portion of tight junction proteins?

Answer 30

Barrier or pone undergo cell to cell interaction so phosphorylation

Congenital sensorineural hearing loss and 2EC loop so MS BBB increase permeability and immune cell infiltratio

Extracellular loops allow for binding between claudins located on adjacent endothelial cells tj
Binding can either form a pore with charge-selectivity for ions, or can form a barrier
N and C terminus
binding of Intracellular components like Cytosolic Zonulae Occludins to intracellular portion to bind that to the actin cytoskeleton — intra inside cytosol in cell
exrracullar means outside cells in fluid where inneract
Intracellular loops can interact with membrane-associated proteins - allow for anchoring and stability cysoktal

Question 31

Cytosolic Scaffolding: Zonulae Occludins

ZO proteins are?
attach to? link those to?

Provide link between?

Decrease in ZO-1, ZO-2, and ZO-3 found in conditions where? what is there function?

Enriched in brain?

Answer 31

ZO proteins are scaffolding proteins providing the basis for assembly of multiprotein complexes at the cytoplasmic surface of TJs - attach to claudins, occludin, and JAM - link those to our actin cytoskeleton in order to anchor

Provide link between integral membrane proteins and cytoskeleton

Decrease in ZO-1, ZO-2, and ZO-3 found in conditions where BBB breakdowns - function primary structural, help regulate cell growth and proliferation

Enriched in brain endothelial capillaries

Question 32

Adherens Junctions: Cadherin - provide adhesion tension lower the difficulty of these two cells becoming adhered to one another

Cadherin dimers form what kind of adhesion?

What is critical for the normal functioning of cadherin?

What breaks the dimer/reduction of what?

Cadherins are linked to actin via? to do what? interfacial tension can signal to?

Adhesive cell-cell contact found in?

VE - Cadherin is span?

Answer 32

Cadherin dimers form cell-cell adhesion

Calcium is critical for the normal functioning of cadherins, which have a calcium binding site in their extracellular domain

Reduction of extracellular calcium leads to dissociation of cadherin-cadherin linkage, disruption of cytoskeletal integrity, and loss of cell-cell adhesion - breaks the dimer

Cadherins are linked to actin via α-, β-, and γ-catenin - ability of the adjacent EC to bind/adhere together and reduce interfacial tension which can signal to action cytoskeletal

Adhesive cell-cell contact found in many tissues

VE - Cadherin is span intercellular cleft which is linked to cytoplasm by alpha, beta, gamma catenin

Question 33

What if different components are missing? Experiment

Experiment: Wild-type and Cldn 5-/- embryos injected with a low molecular mass tracer (<800 Da)

Finding: Wild-type mice (Cldn 5+/+) excluded tracer from CNS, whereas Cldn 5-/- mice showed signs of tracer throughout CNS parenchyma.

Looking for serum albumin protein (68kDa)- found known in either animal had leaked into the CNS from blood vessels. - leakage of large molecules into CNS tissue

conclusions??

Answer 33

Authors conclusions: BBB is loosened in a size-selective manner in Cldn 5-/- mice.

Cells lacking claudins vs cells lacking claudins and JAM-A

Question 34

Transport - Main molecular traffic routes across the BBB

1) Transcellular Diffusion
includes?

2) Transport Proteins
includes?

3) Transcytosis
includes?

Answer 34

1) Transcellular Diffusion
i. (passive diffusion)

2) Transport Proteins
i. Solute Carriers
ii. ABC Efflux Transporters

3) Transcytosis
i. Receptor-mediated
ii. Adsorptive

Question 35

Passive diffusion is most dependent on what characteristic of the molecules?

What other factors could affect diffusion?

Answer 35

Lipid solubility

Size concentration gradient, charge

Question 36

Transcellular (passive) diffusion is most dependent upon lipid solubility

High oil/water partitioning coefficient?

Lipid Solubility: ?

Size: ?

Charge: ?

Easiest to cross: ?

Concentration of molecule in oil vs water ?

Answer 36

High oil/water partitioning coefficient - how we calculate how lipid soluble something is

Lipid Solubility: Hydrophobic (i.e., lipophilic) compounds can enter (but wait……)

Size: Partitioning into lipid membranes decreases exponentially with increasing cross-sectional areas - read a higher concentration of the substance to overcome its large size

Charge: Molecules that are negatively charged are excluded whereas(repelled from surface) those with positive charge are slowed.

Easiest to cross: lipid-soluble small, nonpolar, high concentration

Concentration of molecule in oil vs water - higher coeff more lipid soluble

Question 37

Transport Proteins: Solute carriers - expressed on our endothelial cells

What molecules? what soluble?

Allows access for molecules essential for?

Facilitative transporters - does not require what? so allows solutes to?
—- example of positively charged amino acids?

Secondary active transporters: ?
—- example of System A amino acid uptake?

Answer 37

Polar molecules, non-lipid soluble

Allows molecules essential for metabolism CNS access

Facilitative transporters (does not require ATP): allow solutes to flow downhill with their electrochemical gradient - High to low concentration
——-E.g. Cationic amino acid system (Y+) - Lysine, arginine, and ornithine - positively charged amino acids

Secondary active transporters: Ion-coupled transporters and exchangers that do not require ATP - exchange NA to traffic in molecule, exchange different molecules
—– E.g. System A - Na+-dependent neutral amino acid uptake
Glut-1(can pair with co transporter) - uptake of D-glucose so exchange Na to traffic in glucose

Question 38

Transcellular diffusion is dependent upon lipid solubility BUT it’s not that simple

Circulate as organic what to turn them what?

exchange?

Substrate for?

Answer 38

Circulate as organic anion metabolized by p450s - turns them into lipid soluble

Simple diffusion and saturable, carrier-mediated transport - exchange

Substrate for ABC Efflux

Question 39

Transport proteins: ATP-binding cassette (ABC) efflux transporters

Located on what?

Use ATP to actively eject what?

At least how many have been identified?

P-glycoprotein (P-gp)?

Answer 39

Located on luminal membrane of the BBB - endothelial cells

Use ATP to actively eject a range of substances, including both xenobiotics and endogenous toxic molecules (outside substances)

At least 48 have been identified - transport out toxic things
– Breast cancer resistance protein (BCRP)
– Multidrug resistance protein (MRP)

P-glycoprotein (P-gp)
– Diverse substrate list, including endogenous molecules such as steroid (estrogen, cholesterol) hormones, phenobarbital and cytokines
– The specificity of P-gp prevents many therapeutic drugs from reaching their target site, thus preventing their effective use - it is a target for decreased activity in order to keep solve meds in brain

Question 40

Transcytosis: Receptor-mediated

Primary route of transport for some what?
Including?

Requires what receptor binding?

example?

Nearly all iron in plasma is bound to what?

Answer 40

hydrophobic means “water-fearing” and refers to a molecule’s tendency to not mix with water, while lipophilic means “lipid-loving”

Primary route of transport for some essential peptides and signaling molecules - larger
— Including insulin(high concentration dependent), leptin, and transferrin

Requires ligand-receptor binding, followed by endocytosis and exocytosis

example: Iron-bound transferrin - internalized and trafficked in a vesicle to the brain paradigm can be released

Nearly all iron in plasma is bound to hydrophilic transferrin. This in turn is taken up in endocytic compartments via the transferrin receptor - traffick iron into brain

• on cell membrane in endothelial - internalized and trafficked in a vesicle to the brain tissue can be released - concentration dependent
  Primary route of transport for some essential peptides and signaling molecules - larger
  Including insulin(high concentration dependent), leptin, and transferrin
  Requires ligand-receptor binding, followed by endocytosis and exocytosis
  E.g., Iron-bound transferrin -
  Nearly all iron in plasma is bound to hydrophilic transferrin. This in turn is taken up in endocytic compartments via the transferrin receptor - traffick iron into brain

Question 41

Transcytosis: Adsorptive-mediated

Primary route of transport for? ex?

Cations > Anions - requires excess what?
– BECs carry an overall negative what?

No receptor required so use?

Answer 41

Primary route of transport for many plasma proteins
Example - Albumin

Cations > Anions - requires excess positive charge on molecule and interact with cell surface binding sites
– BECs carry an overall negative surface charge on their luminal membrane due to heparan sulfate proteoglycans

No receptor required - endocytosis and exocytosis only so charge selective

Question 42

Metabolic - BBB as an enzymatic barrier - liver is primary location of enzymatic breakdown

Presence of what enzymes?

Endobiotics such as? transported in via?

These are nurturism metabolizing enzymes and break down excess NT circulating? 4 of them

Xenobiotics via?

Phase 1 and
Phase II?

Answer 42

Presence of metabolizing enzymes in BECs

Endobiotics (e.g., L-DOPA, dopamine, serotonin, norepinephrine, melatonin, acetylcholine) - transported in via L-type transporter, a lot of these have relatively low lipid solubility

These are nurturism metabolizing enzymes and break down excess NT circulating:
Aromatic amino acid decarboxylase
Monoamine oxidase
Cholinesterase

Xenobiotics (chemicals which are foreign to life) via drug metabolizing enzymes - enzyme and L-DOPA decarboxylase - high dose to overcome for toxins of parkinsons

P450 drug metabolizing enzymes - Phase 1 catalase oxidoreductase reactions
Phase II Enzymes - transferease

Question 43

Given what you’ve learned so far about the BBB, if you were designing a drug to cross the BBB, what are some strategies you might employ?

• Adding something to increase lipid solubility
• Small molecules and nanoparticles
• MR ultrasound
• CSF

Answer 43

CSF

Question 44

How do we bypass the BBB?

An estimated what % of potential drug treatments for brain disorders are what?

As a result, patients are left with?

Scientists are currently developing novel techniques to?

Answer 44

Developing drugs that can penetrate the BBB

An estimated 98% of potential drug treatments for brain disorders are unable to penetrate the blood-brain barrier

As a result, patients are left with limited options - can affect outcomes and increase mortality

Scientists are currently developing novel techniques to disrupt the BBB and deliver therapeutic agents…

Question 45

Crossing the barrier

What agent for osmotic disruption? Example?

Trojan-horse method?

Magnetic resonance-guided focused ultrasound (MRgFUS) with intravenous microbubbles (MBs) can do what?

Answer 45

Administration of hyperosmolar agent - osmotic disruption
Ex: Mannitol - through an I.V

Trojan-horse method:
Receptor-mediated transcytosis (ex. Utilizing transferrin receptor)

Magnetic resonance-guided focused ultrasound (MRgFUS) with intravenous microbubbles (MBs)
— Locally disrupts BBB, therapeutic agents can be loaded into MBs