Thursday, September 29, 2022

What Cannot Pass Through The Blood Brain Barrier

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Tj Cytoplasmic Plaque Proteins

Medical Video Lecture, PHYSIOLOGY: Substances that cannot pass through Blood Brain Barrier

The most prominent subgroup of scaffolding proteins localizing to tight junctions is represented by the MAGUK proteins . The modular nature of MAGUK proteins was early recognized as they all share a common structural core consisting of one or several PDZ domains and an SH3 domain followed by a catalytically inactive guanylate kinase domain . Originally, MAGUKs only referred to a group of proteins including the mammalian synaptic scaffold protein Psd-95, the Drosophila tumor suppressor Dlg, and the tight junction protein ZO-1. Since then a large number of scaffold proteins belonging to this family have been identified. Generally, at junctions they serve as molecular hubs coordinating large protein assemblies which transduce the signals impinging on and emanating from the apical plasma membrane, thereby influencing diverse cellular processes, including the establishment and maintenance of cell polarity and cell-cell adhesion complexes, synaptic plasticity, and cell survival .

Taken together, the modular structure of a set of adaptor proteins allows the spatio-temporal assembly of multi-protein complexes at discrete regions of epithelial and endothelial cells through their interaction with clustered transmembrane TJ proteins, not only ensuring the structural integrity of the TJ, but also integrating various regulatory pathways at the cytoplasmic plaque which are pivotal for TJ physiology.

Ion And Fluid Transport At The Bloodbrain Barrier

The primary functions of the bloodbrain barrier are to allow ready access to the brain parenchyma of O2 and nutrients such as glucose and essential amino acids and ready removal from the brain of waste products like CO2, while at the same time providing a barrier to the movement of substances that should not be allowed to enter or leave the brain. The bloodbrain barrier also plays the principal role in long-term regulation of the ionic composition of ISF. Although astrocytes are very important in short-term control of ISF ionic composition, a process sometimes called physiological buffering, they cannot set or determine the long-term composition .

Unfortunately, it has not been possible to determine the composition of the fluid, if any, secreted by the bloodbrain barrier by direct sampling . However, if the fluid secretion rate were known, one could infer the composition because the net fluxes of solutes and water across the bloodbrain barrier plus the water produced by brain cell metabolism must replace the fluid that is lost by net outflow from the parenchyma after allowance for metabolic changes . The fluid lost is a nearly isosmotic solution with composition very close to that of CSF. Thus the net fluid transferred across the bloodbrain barrier into the brain must be either a hyperosmotic secretion or a hypoosmotic absorbate to make the net product, including the ~60 ml day1 of metabolic water, nearly isosmotic .

What Can Pass Through Blood

What can pass through blood-brain barrier? Only water, certain gases , and lipid-soluble substances can easily diffuse across the barrier .15 Sept 2015

What can and Cannot cross the blood-brain barrier? Such substances include lipid-soluble substances . Hydrophilic substances, for example, hydron and bicarbonate, are not permitted to pass through cells and across the blood-brain barrier.

What does the blood-brain barrier let in? The blood vessels that vascularize the central nervous system possess unique properties, termed the bloodbrain barrier, which allow these vessels to tightly regulate the movement of ions, molecules, and cells between the blood and the brain.

Can caffeine cross the blood-brain barrier? Passive diffusion: fat-soluble substances dissolve in the cell membrane and cross the barrier . Water-soluble substances such as penicillin have difficulty in getting through.

Also Check: Fluoride Officially Classified As A Neurotoxin

The Bbb Can Be Broken Down By:

  • Hypertension : highblood pressure opens the BBB.
  • Development: the BBB is present, but may be not fully formed at birth.
  • Hyperosmolitity: a high concentration of asubstance in the blood can open the BBB.
  • Microwaves: exposure to microwaves can openthe BBB.
  • Radiation: exposure to radiation can open theBBB.
  • Infection: exposure to infectious agents canopen the BBB.
  • Trauma, Ischemia, Inflammation, Pressure:injury to the brain can open the BBB.
  • Expression Of Ion Transporters


    The whole profile of transporters expressed in the choroid plexus has been the subject of major transcriptome studies comparing adult and embryonic tissue .

    Studies on the expression of specific transporters at the RNA and protein levels in adults have been reviewed recently . It has been found in these studies that ion transporters are expressed in choroid plexus epithelial cells at levels sufficiently high to allow clear detailed cellular localization by immunohistochemistry as illustrated in Fig. . Figure indicates the transporters present together with the ions they transport. From the known properties of these transporters together with careful measurements of electrical potentials and currents and from the results of techniques such as gene knockout, it is possible to describe the main features of solute transport involved in secretion as shown in the figure and described in Sect. . More extensive discussion and detailed referencing can be found in reviews by Brown et al. and Damkier et al. .

    Fig. 5

    Regulation of HCO3 transport across the choroid plexus and its interrelations with H+, CO2 and Cl transport are considered in Sect. .

    The indirect coupling of Cl fluxes to those of Na+ via the combination of NBCn2/NCBE and AE2 provides an explanation for the observation that net Cl transport across the epithelium can be against its electrochemical gradient .

    Role of carbonic anhydrase in HCO3 transport

    Pathways for K+ transport

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    Organic Anion Transporting Polypeptide

    Organic anion transporting polypeptides are members of the solute carrier organic anion transporter family . The OATPs accommodate the transport of a wide variety of amphipathic solutes, including bile salts, anionic peptides, steroid conjugates, thyroid hormones and an increasing number of pharmaceutical drugs and xenobiotics . Members of the OATP family, of which there are currently 11 known to be expressed in humans , share a great deal of amino acid sequence identity and transport solutes in a sodium independent manner .

    Our Brain Has A Barrier That Stops Drugs How Do We Get Past It

    A new drug for Alzheimer’s, stroke or brain injury might work well in the lab, but the crucial test is whether it can get to where it needs to be.

    Thats really the annoying challenge, because we have candidates that could do a good job if we could get them into the brain, said Professor Maria Tenje, a trained physicist turned engineer at Uppsala University, Sweden.

    The brain has a protective barrier that is designed to stop dangerous molecules and cells from entering. It acts as a filter between the brain and the blood vessels, allowing important nutrients, like oxygen, to enter while keeping out molecules that could upset the delicate, complex processes in the brain. Well, nearly all of them.

    When you have a beer, you can feel the pleasant effect because the ethanol has reached the brain, said Prof. Tenje.

    But if everything could just cross the lining and go into the brain then that would be the end of us because we have a lot of toxins, nanoparticles, and chemicals that should not go into the brain.

    From an engineering perspective its an interesting problem how can we have something that only allows passage of specific molecules and how can we control it? That is what we are trying to find out.

    ‘From an engineering perspective its an interesting problem how can we have something that only allows& nbsp passage of specific molecules and& nbsp how can we control it?’

    Prof. Maria Tenje, Uppsala University, Sweden


    New model


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    How To Get Into The Brain

    Morgan Sheng

    M.B.B.S., Ph.D. Vice President, Neuroscience, Genentech

    *While Morgan was an employee at the time this article was published, he has since left Genentech.

    The human brain is one of the most complex systems in the known universe. Nearly 100 billion brain cells, called neurons, make over 500 trillion connections. Given its profound importance, you can imagine that our brains have some pretty serious security measures.

    One of these security measures is the blood-brain barrier , a protective layer of cells that only allows certain molecules to pass through it from the blood into the brain itself. Other molecules, like most proteins and antibodies, cant pass through.

    The BBB is an important protective measure, but it also makes it very challenging to use biologic medicines for diseases of the brain, like Alzheimers disease. On top of that, our scientists have shown in preclinical models of Alzheimers disease that the BBB remains largely intact. This finding challenges a widely held belief that the BBB is compromised in Alzheimers disease, and that therapeutic antibodies can work themselves into the brain to treat the disease.

    Ultimately, what we need are new ways to overcome this fundamental problem in antibody delivery to the brain.

    To learn more about this new type of antibody that crosses the blood brain barrier, watch the video and read the papers from Genentech scientists below.

    Transport Pathways Across The Blood

    Blood Brain Barrier, Animation

    The BBB endothelial cells differ from those in peripheral microvessels by more intensive tight junctions, sparse pinocytic vesicular transport and much less fenestrations. The transport of substances from the capillary blood into the brain tissue depends on the molecular size, lipid solubility, binding to specific transporters and electrical charge . Figure 4.6 summarizes the transport routes across the BBB . Compared to the peripheral microvessel wall, the additional structure of the BBB and tighter endothelial junctions greatly restrict the transport of hydrophilic molecules through the gaps between the cells, i.e., the paracellular pathway of the BBB, route A in Fig. 4.6. In contrast, small hydrophobic molecules such as O2 and CO2 diffuse freely across plasma membranes following their concentration gradients, i.e., the transcellular lipophilic diffusion pathway, route C in Fig. 4.6. The permeability of the BBB to most molecules can be estimated on the basis of their octanol/water partition coefficients . For example, diphenhydramine , which has a high partition coefficient and can easily cross the BBB, whereas water-soluble loratadine is not able to penetrate the BBB and has little effect on the CNS .

    Figure 4.6. Transport pathways across the brain microvascular endothelial cell. Modified from .

    Amaldoss M J Newton, Sukhjinder Kaur, in, 2019

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    Function Of The Blood

    The core function of the blood-brain barrier is to keep harmful substances from gaining access to the sensitive, delicate matter of the brain and spinal cord. Examples of toxins include bacteria, parasites, poisons and similar others.

    But the blood-brain barrier is also responsible for choosing which substances to let into the inner sanctum of the brain and spinal cord interior. These approved elements include hormones, amino acids, key nutrients and similar others.

    Under ideal conditions, the blood-brain barrier will accurately identify each visitor, permitting entry only to those substances that are wanted and needed. Some substances may be granted automatic entry while others may need to be transported via hitching a ride with incoming proteins. The barrier can even control how quickly various visitors are allowed inside, as well as how quickly they reach their destination.

    The blood-brain barrier is what is called dynamic,which means it is always on the job. The interior cells are continually communicating with cells on the periphery that receive and respond to different incoming and outgoing signals. There are three main ways that visitors are restricted from crossing the barrier: size, polarity or fat insolubility.

    Gaba As A Safe Alternative To Xanax Naturally Reducing Symptoms Of Anxiety

    Xanax or generically known as Alprazolam, has been on the market since 1981 and used to treat panic disorder, which has made it a block buster drug in the United States. This particular drug falls into the benzodiazepine benzos class, which enhances the effect of the neurotransmitter gamma-aminobutyric acid at the GABA receptor. This causes a sedative effect that allows the body to relax. It is sleep inducing and may cause anterograde amnesia and dissociation.

    There is no doubt, that benzo drugs are powerful and can even be addicting, which is why they are generally used for short-term situations, and not for the daily management of anxiety and stress.

    So, what does a person do when they need to management their anxiety on a daily basis, but they dont want to be under the influence of heavy narcotics or prescription drugs? Along with prescription drugs comes a laundry list of side effects and drug interactions. Prescription drugs may not be the best choice for those who want a more natural approach to managing their anxiety while remaining productive and energetic, not sleepy and dysfunctional.

    Fortunately, there are some supplements on the market today that have an effect on the GABA receptor which have been proven to improve mood, anxiety, depression, PTD, social phobia, and even enhance neurological function. A few brands that have excellent research and reviews are Life Vitality Ultra Bliss, PureLife Gabatrol, and PureLife U4ea.

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    Molecular Components Of The Tight Junctions

    The tight junctions consist of both membrane proteins as well as cytoplasmic proteins . The integral membrane proteins are Claudins, Occludin and Junctional adhesion molecules . There are also several cytoplasmic accessory proteins that form a plaque and function as adapter proteins to link the membrane proteins to the actin cytoskeleton of the cell . These include Zonula occludens proteins , Cingulin, AF-6, 7H6 antigen and Symplekin. These tight junctional complexes are not static structures but rather very dynamic entities that can bend without breaking, thereby maintaining structural integrity .

    Figure 2.

    Schematic representation of proteins that are involved in the formation of the tight junction and adherens junctions in brain microvessel endothelial cells.

    Fa Transport Across The Bbb And Effects Of Fa On Bbb Permeability


    Fatty acids are key components of membranes and exhibit many biological functions in a variety of tissues, including the key energy source for mitochondrial -oxidation . Cells acquire fatty acids through de novo synthesis, hydrolysis of triglycerides or uptake from exogenous sources . Minimal amount of FA are derived from TG hydrolysis and most cells are dependent upon fatty acid uptake from the peripheral blood . FA from the diet are absorbed by enterocytes in the small intestine and packaged into chylomicrons as TG. The liver also produces very low density lipoprotein , a rich source of endogenously generated TG. Circulating chylomicrons and VLDL particles are hydrolyzed by lipoprotein lipase in the capillary lumen of tissues and the released FA from these lipoproteins may be taken up by tissues in the body . FA that enter into cells are then esterified and stored as TG or transported to the mitochondria for -oxidation. The importance of FA for the developing and adult brain has been recently reviewed . FA transport from blood into parenchymal neurons is much more difficult than other cells since the tight junctions of the BBB severely restrict passage into the brain. FA must first move via transcellular transport across both the luminal and abluminal membranes of the endothelial cells and then across the plasma membrane of the neural cells .

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    What Can Cross The Bbb And Enter The Brain

    The BBB is very restrictive, limiting what can access the brain. Glucose and other nutrients necessary to keep the brain healthy and functioning properly are allowed to cross the BBB and enter the brain.

    Typically, cells of the immune system are not able to cross the BBB. This helps prevent brain inflammation. Unfortunately, sometimes, pathogens damage the BBB, enabling them to leave the blood and enter the brain. As a result of the damage, immune cells also enter the brain in an attempt to kill the invading organisms. When this happens, the person may experience:

    • Meningitis Inflammation of the meninges, the outer membrane of the brain and spinal cord
    • Encephalitis – Inflammation of the brain

    Meningitis and encephalitis are serious conditions that typically require hospitalization and may lead to permanent brain damage or death.

    Different types of germs can cross the BBB and lead to serious infections:

    Overview Of Locations And Functions Of The Choroid Plexuses And The Bloodbrain Barrier

    The choroid plexuses constitute the interface between blood and cerebrospinal fluid in the ventricles. There are four such plexuses protruding into the ventricles, one in each of the lateral ventricles, one in the IIIrd and one in the IVth ventricle . As seen in the light microscope each choroid plexus has a frond-like shape with many villi, each with a layer of cuboidal epithelial cells overlying blood microvessels of the fenestrated type . Even on this scale the epithelial layer appears to have a large surface area. Furthermore the apical brush border and basolateral in foldings make the actual membrane area of the epithelial cells much greater still . As described in detail by Cserr and more recently by Damkier et al. the epithelial layer has all the hallmarks of a leaky secretory epithelium designed to produce a large volume of nearly isosmotic fluid.

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    Historical Origins Of Modern Concepts On Brain Drug Transport

    By the 1930s, studies with brain-penetrating basic vital dyes showed that the dye entered the brain from blood across the walls of capillaries perfusing brain parenchyma. Broman and Friedemann clearly observed that the BBB was localized to the capillary wall in brain, and that drug entry into the CSF across the choroid plexus was an entirely separate problem from drug transport across the BBB. Indeed, in his 1942 review on the BBB, Friedemann stated that, distribution between blood and CSF is an entirely different problem and remains outside the scope of this review.’ Nevertheless, the idea that the BBB and BCSFB are functionally equivalent, and that the CSF and ISF are functionally equivalent, is perpetuated in neuroscience text books. These ideas form the basis for bypassing the BBB with intrathecal drug delivery to the brain. In 2013, or 100 years after the publication of Goldman’s experiment defining the BBB, there are multiple ongoing clinical trials of intrathecal delivery to the human brain of drugs that do not cross the BBB.

    Cell Polarizationa Key Step Toward Barrier Formation

    Blood Brain Barrier – Structure & Function

    The Crumbs group localizes apically or at apical junctions and consists of the transmembrane Crb proteins and the large scaffolding proteins Pals1 and Patj through which the complex physically is connected to the Par group via Par6 . In ECs tight junction integrity is also maintained by angiomotin and angiomotin-like proteins , in part through the action of the associated RhoGEF Syx and loss of any of these proteins results in increased vascular permeability and/or reduced sprouting angiogenesis .

    One of the essential polarity regulators from yeast to man is the RhoGTPase Cdc42. In epithelial cells PTEN-mediated segregation of phosphoinositides has been shown to initiate polarization by recruiting Cdc42 to apical domains . Further, the small GTPase Rac1 has been shown to play an important role downstream of the Par complex . Independent of their polarity actions the best studied function of Rho GTPases is their role als molecular organizers of the actin cytoskeleton. These two processes are interconnected as cell polarization and the establishment of a functional TJ also entails a complex rearrangement of the actin cytoskeleton, microtubule organizing centers, and the establishment of a vesicle trafficking machinery, all together facilitating vectorial transport functions .

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