Information

How to make GABA pass the blood brain barrier?


I thought of methylating GABA at the gamma amino group in order to make it pass the blood brain barrier, but would it work?

The goal is to make a sedative. Like GHB or benzodiazepines (I know that benzos have a totally different structure)

Any ideas on how to make GABA pass the blood brain barrier?


Short answer
Chemical reversible shielding of the aminogroup in GABA seems to be sufficient to get it into the brain as a Trojan horse.

Background

Given that you ask

… how to make GABA pass the blood brain barrier?

I assume that

  • You wish to elevate GABA by exogenously administering a compound;
  • That compound has to cross the blood-brain barrier (BBB) and physically turn into GABA;
  • A drug indirectly elevating GABA through unknown (e.g., GHB) or known mechanisms (Gabapentin) does not suffice your needs.
  • If you are happy with indirect actions, the links above will help you out. Now on to the real stuff :-)

GABA (Fig. 1) has 3 hydrophylic groups that may prevent it to cross the blood-brain barrier (BBB), namely a hydroxyl-, a keto- and an amine-group. The BBB generally only permits passive entry of small hydrophobic molecules. The amino-group in turn is also prone to de-amination by mono-amino oxidase inhibitors.

An often-used method to get drugs into the brain is shielding of pesky hydrophilic and/or fragile chemical groups by certain molecules that are irreversibly bound to them. A well-known example of shielding a fragile amino-group is the B-methylation of phenetylamine compounds into their amphetamine analogues. Alpha-amination to a methamphetamine further stabilizes the essential amino-group. Amphetamines and methamphetamines are way more stable in the brain than their phenetylamine precursors and likely enter the BBB also more swiftly because they are more hydrophobic by shielding the amino group (Shulgin, 1990).

However, those methyl groups are irreversibly bound, so it's not an option here, as apparently you wish to increase GABA, and not an active derivative of it.

Now, another way is using a Trojan horse method (Pardridge, 2006); by reversibly shielding the essential amine group the drug can enter the brain, where it is converted back to its original compound. Picamilon does the job here. Smarter Nootropics say;

First developed in the early 1970s in the Soviet Union, picamilon (alongside phenibut) is an “enhanced” form of GABA that is capable of crossing the blood brain barrier when taken as a supplement.Inside the brain, picamilon is rapidly hydrolyzed into its constituent parts; niacin and GABA. Niacin helps to enhance brain blood flow through its vasodilatory properties [].


Fig. 1. GABA and Picamilon. source: Smarter Nootropics

Reference
- Pardridge, Discov Med (2006); 6(34):139-43
- Shulgin, PIHKAL, Transform Press, U.S. (1990)


How prions invade the brain

The spread of prions to the brain does not occur by direct transmission across the blood-brain barrier, according to a study published November 29 in the open-access journal PLOS Pathogens by Annika Keller and Adriano Aguzzi of the University Hospital Zürich, and colleagues. As noted by the authors, insights into how prions enter the brain could lead to the development of effective strategies to prevent neurodegeneration, even after infection outside the nervous system has already taken place.

Prion diseases or transmissible spongiform encephalopathies (TSEs) are incurable brain diseases caused by modifications of the prion protein. Prions can be transmitted through contaminated food, surgical instruments and blood. Transmission of prions has caused the kuru epidemic in humans and bovine spongiform encephalopathy in cattle, which in turn has caused variant Creutzfeldt-Jakob disease in humans. Furthermore, injection of prion-contaminated hormones has caused hundreds of TSE cases. In order to develop drugs to prevent the spread of prions into the brain after exposure via food or medical procedures, it is necessary to gain an understanding of how prions propagate from the site of entry to the brain.

In the new study, the researchers tested whether prions in blood may enter the brain via blood vessels. To do so, they used genetically modified mice with a highly permeable blood-brain barrier -- a network of blood vessels and tissue that is made up of closely spaced cells and helps keep harmful substances from reaching the brain. Both genetically modified and unmodified mice were similar in their survival rates after infection with prions. These surprising results suggest that passage of prions through the blood-brain barrier may not be relevant to the development of disease. Taken together with past findings, the new results suggest that prions likely reach the brain by traveling along nerves in other parts of the body, similar to rhabdoviruses and herpesviruses.

"Studies on mice possessing a permeable blood-brain barrier (BBB) add to the conjecture that prion spread from the periphery to the brain does not occur by direct transition across the BBB," adds Keller. "Besides their significance for the basic understanding of prion neuroinvasion, these results may be of relevance to the possibility of developing effective post-exposure prophylaxis of prion diseases, which may prevent neurodegeneration even after extraneural infection has already taken place."


Stress Essential Reads

It’s Time to Talk About the Privilege of Self-Care

Dealing With a Stressful Situation When All Alone

There’s relatively limited research on the direct benefits of supplemental GABA for sleep. Some recent research suggests that GABA produced in fermented food may increase sleep time and decrease the time it takes to fall asleep. Another recent study showed that a combination of GABA and 5-HTP may together improve sleep quality and increase sleep time. Given the importance of GABA to the body’s sleep patterns, more research into the effects of GABA supplements on sleep is sorely needed.

For stress and anxiety: As a natural chemical the body produces, GABA’s primary role is to diminish the activity of neurons in the brain and central nervous system, which puts the body in a greater state of relaxation and alleviates stress and anxiety. Supplemental GABA may benefit sleep by aiding relaxation and providing relief from anxiety and stress. There remains debate among researchers about supplemental GABA’s effectiveness in reducing anxiety and stress because of longstanding questions over supplemental GABA’s ability to enter the brain from the bloodstream. (It’s important to note that GABA, in supplement form, may have other ways of relaxing the body, including possibly through GABA’s activity in the gut microbiome.)

While the scientific debate goes on, some studies have shown GABA to be effective in lowering anxiety and boosting relaxation. One small study of 13 adults showed GABA to be effective as a relaxant and anxiety reliever, with slowed brain waves seen within an hour of taking the supplement. This study also found that a boost to the immune system also occurred with GABA, suggesting supplemental GABA may enhance immunity in people undergoing mental stress.

Another larger study investigated the effects of 100 milligrams of GABA among a group of people who’d recently undertaken a stressful mental task. Scientists measured a slowing down of brain waves in people who’d taken GABA, pointing to an alleviation of mental stress. Another study tested the effects of GABA in people who were about to take a stressful math test. Those who ate chocolate infused with GABA rebounded more quickly from test-related stress, including stress-lowering changes to heart-rate variability.

For high blood pressure: GABA supplements are sometimes used by people as a natural way to lower blood pressure. There is evidence indicating that GABA may work to reduce high blood pressure. In one study of people with borderline high blood pressure, 12 weeks of use of the supplement chlorella, a type of algae rich in GABA, significantly lowered blood pressure. In addition to being important on its own, maintaining healthy blood pressure can also help protect your sleep. A natural drop in blood pressure at night is one part of the body’s progression into sleep. High blood pressure can be a sign of hyperarousal, a state of physical alertness and vigilance that can make it difficult to fall asleep and stay asleep. Poor sleep and sleep disorders, particularly sleep apnea, contribute to high blood pressure, and can lead to the kind of hypertension that is difficult to treat.

What to know

Always consult your doctor before you begin taking a supplement or make any changes to your existing medication and supplement routine. This is not medical advice, but it is information you can use as a conversation starter with your physician.

The following doses are based on amounts that have been investigated in scientific studies. In general, it is recommended that users begin with the lowest suggested dose, and gradually increase as needed.

  • For sleep, stress and anxiety: 100-200 mg and higher doses, in scientific studies. Individual dosing and length of use will vary.
  • For high blood pressure: 10-20 mg, in scientific studies.

Possible side effects

GABA oral supplements are generally well tolerated by healthy adults. Some people may experience negative side effects, including:

  • Gastric distress.
  • Nausea.
  • Diminished appetite.
  • Constipation.
  • Burning throat.
  • Drowsiness and fatigue.
  • Muscle weakness.
  • Shortness of breath, at very high doses.

Interactions

These are commonly used medications and supplements that have scientifically-identified interactions with GABA. People who take these or any other medications and supplements should consult with a physician before beginning to use GABA as a supplement.

Interactions with medications

  • High blood pressure medications. GABA can lower blood pressure. If you take GABA in addition to taking blood pressure medication, your blood pressure may drop too low.
  • Antidepressant medications. People taking antidepressants should consult with their physician before taking GABA.
  • Neurally-active medications. People taking medications that affect brain activity should consult their physician before taking GABA.

Interactions with other supplements

  • Herbs and supplements that may lower blood pressure. Because GABA may lower your blood pressure, if you take GABA along with other herbs or supplements that also may lower blood pressure, the combination may lead to your blood pressure dropping too low.Herbs and supplements that lower blood pressure include, but are not limited to:
    • Cocoa.
    • Alpha-linolenic acid.
    • Blond psyllium, and other fiber supplements.
    • Cod liver oil.
    • Magnesium.
    • Calcium.
    • Potassium.
    • Folic acid.
    • Coenzyme Q10.
    • L-arginine.
    • Garlic. fatty acids.
    • Cocoa.
    • Alpha-linolenic acid.
    • Blond psyllium, and other fiber supplements.
    • Cod liver oil.
    • Magnesium.
    • Calcium.
    • Potassium.
    • Folic acid.
    • Coenzyme Q10.
    • L-arginine.
    • Garlic.
    • Omega-3 fatty acids.

    I’ve seen patients experience relief from anxiety, reduced stress, and improved sleep via the relaxing impact of supplemental GABA. I don’t think we’ve seen nearly enough research to have a sufficient understanding of how GABA supplements might affect stress, mood, and sleep, or other ways GABA as a supplement may benefit emotional, cognitive, and physical health. As we learn more—which I hope we do, soon—I’ll be sure to update you.


    A GABA-EEG test of the blood-brain barrier near epileptic foci

    The permeability of the blood-brain barrier (BBB) to gamma-aminobutyric acid (GABA) in the region of an epileptic focus may be assessed by infusing GABA and measuring a change in epileptic spike activity on the EEG. GABA does not cross the normal BBB but will suppress epileptic spike activity when it does cross where the BBB is damaged. 9 alumina-cobalt experimental epileptic foci were all initially suppressible, but 7 then became unsuppressible . When the foci were irradiated to lower the BBB, all 7 became temporarily suppressible. The experiments demonstrate that (1) epileptic foci can be equally active both with the BBB 'open' and 'closed' (2) the intravenous GABA-EEG test can detect whether the BBB near the epileptic focus is open to GABA, and (3) anatomic tests of BBB integrity (in these experiments intravenous trypan blue) cannot determine if whether BBB near the focus is 'open' to GABA. Since the intravenous GABA-EEG test reveals the permeability of the BBB in the immediate environment of the epileptic focus, it may be very useful in the selection of a susceptible therapeutic group for inhibitory amino acid therapy.


    What to know about GABA

    Gamma-aminobutyric acid (GABA) is a neurotransmitter, or chemical messenger, in the brain. It blocks specific signals in the central nervous system, slowing down the brain. This provides a protective and calming effect on the brain and body.

    The body produces GABA, and it may also be present in some fermented foods, such as kimchi, miso, and tempeh. These are not foods that most people include in their daily diets, so some people take GABA supplements to achieve the benefits.

    In this article, we examine how increased levels of GABA may impact the brain and body, and whether taking GABA supplements could have the same benefits.

    Share on Pinterest GABA activity can relieve stress, reduce stress, and improve sleep.

    The brain contains many neurotransmitters that trigger or inhibit specific reactions in the body.

    GABA is a neurotransmitter that inhibits or slows the brain’s functions. This activity produces effects such as:

    The brain naturally releases GABA at the end of a day to promote sleepiness and allow a person to rest. Some of the medications doctors prescribe to induce sleep and reduce anxiety may also increase the action of GABA.

    Some experts have suggested that increased levels of GABA may have benefits, but the evidence is not clear. According to a 2019 review, GABA has anti-microbial, anti-seizure, and antioxidant properties and may help treat and prevent conditions such as:

    Medications to increase GABA

    Doctors may prescribe medicines that increase the amount of GABA or stimulate the same neurotransmitters in the brain to treat some medical conditions, such as epilepsy.

    For example, benzodiazepines (Valium, Xanax) act on many of the same neurotransmitter receptors as GABA. According to one study, people who have depression may have reduced GABA levels in the brain. The use of benzodiazepines may be beneficial in those instances.

    Doctors also prescribe the medication gabapentin (Neurontin), which is chemically similar to GABA to reduce seizures and muscle pain.

    However, doctors are not clear whether the therapeutic effects of these medications are related to their effect on GABA receptors or whether they work in other ways.

    Some people take supplements of GABA for their supposed stress- and anxiety-relieving benefits.

    The Food and Drug Administration (FDA) has approved GABA for use as a supplement and as a food additive. Manufacturers may add GABA to:

    Manufacturers produce GABA supplements by fermenting a form of lactic acid bacteria.

    However, the FDA do not regulate dietary supplements in the same way as medications. Therefore, consumers should exercise caution as to where they purchase the product from and only buy from reputable vendors and companies.

    Some people may take a supplement in pill form, while others may add it to foods, such as protein drinks.

    Researchers have not established a daily recommended intake or a suggested upper limit for GABA. Anyone wanting to take GABA as a supplement should consider talking to their doctor first.

    At present, there is not enough research to evaluate the possible side effects of taking GABA supplements. However, if a person does experience side effects that might be GABA-related, they should discontinue the use of the supplement and contact their doctor.

    Some researchers have voiced concerns about the supposed positive benefits of taking GABA supplements. An article in the journal Frontiers in Psychology notes that experts remain unclear whether GABA offers real benefits or whether the effects that people report experiencing are a placebo response.

    Other researchers do not believe that GABA supplements cross the blood-brain barrier, which they would have to do to have any effect on the body.

    However, some studies report positive effects from taking GABA supplements. These include:

    Enhanced thinking and task performance abilities

    A study from 2015 found that taking 800 milligrams (mg) of GABA supplementation per day enhanced a person’s ability to prioritize and plan actions. Although the study was small, involving just 30 healthy volunteers, it showed how GABA supplementation might promote enhanced thinking.

    Stress reduction

    An older study from 2012 found that taking 100 mg of GABA daily helped reduce stress due to mental tasks. Like many other studies related to GABA, the study was small and involved just 63 participants.

    Workout recovery and muscle building

    A 2019 research study asked 21 healthy males to take a supplement with whey protein or whey protein plus GABA once a day for 12 weeks.

    The participants performed the same resistance training exercises twice a week, and the researchers measured the results. The researchers found that the combination of whey protein and GABA increased levels of growth hormone compared to whey protein alone.

    Although this was another small study, the researchers concluded that GABA supplements might help to build muscle and assist in workout recovery. They recommended that researchers conduct more studies.

    GABA naturally plays an essential role in promoting sleep, relieving anxiety, and protecting the brain.

    Scientists have not been able to prove the positive effects of GABA supplementation on a large scale, and their use may have limited effectiveness.

    If a person has received a diagnosis for conditions such as depression, anxiety, or attention deficit hyperactivity disorder, they may wish to talk to their doctor about medically-proven treatment before taking GABA supplements.


    How does the blood-brain barrier work?

    Only select chemicals can cross the blood-brain barrier. Dr Karl explains how your brain's amazing border security system works.

    The blood-brain barrier is not just a flyscreen with little holes in it, but a vital organ made of many different types of cells (Source: janulla/iStockphoto)

    Related Stories

    If there's one organ that truly makes us humans different from the rest of the animal kingdom, that organ is the brain.

    That 1,200 grams inside our skull is fed by some 650 kilometres of blood vessels. These blood vessels twist and loop around to make intimate contact with every single one of our 100 billion-or-so nerve cells.

    But these blood vessels are different from all the other blood vessels in our body. They are lined by a strange structure called the blood-brain barrier. It closely controls what is, and is not, allowed to leave the blood supply and enter the brain. It's your own personal customs and border security.

    We used to think of the blood-brain barrier as some kind of biological flyscreen. If the chemical was small enough (with a molecular weight of less than 500 daltons), it could get through the tiny holes and into the brain. But if the chemical was bigger than 500 daltons, it was excluded.

    But now we have new technology, the new so-called 'two photon' microscopes. For the first time, we are able to 'penetrate' and look into the living brain down to a depth of about one-third of a millimetre - while the brain is still functioning.

    We can now see that the blood-brain barrier is not just a flyscreen with little holes in it, but a vital organ made of many different types of cells.

    The anatomy and micro-anatomy is astonishing.

    The blood vessels in the brain (and in the spinal cord as well) are lined on the inside with specialised endothelial cells. These endothelial cells are stuck together very tightly, forming what are called 'tight junctions'.

    We used to think that the only way that a chemical could leave the blood and enter the nerves in the brain was by being small enough to sneak through these tight junctions.

    We now know that there are myriad molecular passageways actually embedded in the membrane of the endothelial cells — and these molecular passageways will block some chemicals, while actively pushing others across.

    The researchers have even seen enormous white blood cells slip out of the blood vessels and into the brain — and back again. They have found cells called astrocytes and pericytes surrounding the blood vessels, apparently helping to control the influx and eflux of chemicals. And orbiting, and cruising around, all of these are specialised immune system cells called 'microglia'.

    The microglia patrol the brain and spinal cord for invaders that are trying to get in, or that have already succeeded in getting inside. They also look for damaged or cancerous cells and remove them.

    There's a whole range of neuro-degenerative diseases — including Alzheimer's and Parkinson's — that now seem to involve defective microglia and/or a defective blood-brain barrier.

    For example, we know that Alzheimer's disease involves having too much of a chemical called beta-amyloid in the brain.

    The blood-brain barrier has two specific proteins involved in this process — one brings the beta-amyloid out of the bloodstream into the brain, while the other protein does the opposite. Perhaps keeping the beta amyloid out of the brain might be a prevention, or even a cure, for Alzheimer's disease.

    About 98 per cent of today's medications cannot cross the blood-brain barrier in significant quantities. Mind you, drugs such as most antipsychotics, sleeping aids and antidepressants are smaller than 500 daltons and can sneak through. But they're in the two per cent of drugs that can get through.

    Today neuroscientists have come up with a handful of ways of getting the other 98 per cent of therapeutic drugs across the blood-brain barrier.

    Let me give you a broad-brush explanation. One technique is to feed a tiny pipe into a blood vessel in the brain, right next to something that you want to treat (such as a cancer). You can then squirt in a tiny amount of mannitol, which shrivels up the endothelial cells. This then opens up the previously closed tight junctions. While the tight junctions are open, you can now squirt in (at least for an hour-or-two) the healing drug.

    Other methods of getting drugs into the brain involve encapsulating them in fat so that they can sneak through the body of the endothelial cells, or joining them onto the tail end of a chemical that already freely crosses the endothelial cells.

    The customs and border security agencies of the world could learn a lot from the blood-brain barrier .


    Introduction

    Gamma-aminobutyric acid (GABA) serves as the main inhibitory neurotransmitter in the human cortex (Roberts and Kuriyama, 1968 Petroff, 2002). In recent years it has become widely available as a food supplement. In Europe and the United States, GABA is considered a 𠇏ood constituent” and a 𠇍ietary supplement,” respectively. As such, manufacturers are not required to provide evidence supporting the efficacy of their products as long as they make no claims with regards to potential benefits in relation to specific diseases or conditions. These GABA food supplements can be purchased online via numerous websites, including web shop giants such as Amazon.com, with often very positive customer reviews. Hundreds of people report that these supplements have helped them alleviate anxiety and/or improve sleep quality, in addition to other beneficial effects. Interestingly, GABA has long been thought to be unable to cross the blood𠄻rain barrier (BBB), which raises questions about the mechanisms of action behind such beneficial effects (Roberts et al., 1958 Van Gelder and Elliott, 1958 Kuriyama and Sze, 1971 Knudsen et al., 1988). Through what mechanisms do these products exert their action? Do they rely on a placebo effect only? Do they exert an effect through peripheral effects outside of the brain? Or is GABA able to cross the BBB after all?

    The current paper aims to give a succinct overview of recent understanding of GABA’s BBB permeability (Blood𠄻rain Barrier Permeability), the role of GABA in treatment of diseases (GABA, Diseases, and Treatment), its role as a food supplement (GABA as a Food Supplement), and the possibility that this food supplement might affect the central nervous system through an effect on the enteric nervous system (Enteric Nervous System Effects of GABA).

    Blood𠄻rain Barrier Permeability

    The BBB protects most of the brain from toxins and ion abnormalities that find their way into vascular space through ingestion, infection, or other means (Purves et al., 2004). On the one hand, the BBB is important in keeping the brain safe from harmful substances. On the other hand it severely limits the passage of substances into the brain that might be beneficial to the individual, such as drugs to treat central nervous system disorders (Pardridge, 2005).

    The BBB is made up by neighboring capillary endothelial cells. These cells are connected via tight junctions, which are impermeable (Brightman and Reese, 1969). As a consequence, molecules need to enter via active uptake by specialized transporter molecules or diffusion into the cells of the BBB (Pardridge, 2005, 2007). Tight junctions are responsible for the brain’s high resistance to outside materials. These tight junctions are not present in the rest of the body, where much more ionic and molecular traffic is possible (see Figure 1 Purves et al., 2004). As a consequence, the diffusion of a substance depends on its ability to cross the cell membrane, which consists largely of a lipid bilayer. The ability of a substance to pass through this lipid bilayer (i.e., its lipophilicity) depends largely on basic chemical properties (Lipinski, 2000 Pardridge, 2005).

    Figure 1. The difference between capillaries as they are generally found in the body versus the ones in the brain and the possible ways for a substance to move across these capillaries.

    Initial studies from the fifties reported GABA’s inability to cross the BBB (Van Gelder and Elliott, 1958). Since then, several research groups have replicated this finding (Roberts et al., 1958 Kuriyama and Sze, 1971 Knudsen et al., 1988). However, a number of studies have reported that GABA does cross the BBB, albeit in small amounts (Frey and Löscher, 1980 Löscher, 1981 Löscher and Frey, 1982 Al-Sarraf, 2002 Shyamaladevi et al., 2002). This discrepancy could be the result of variation in chemical compounds, method of administration (i.e., oral versus injection), and the species used.

    With regards to the first factor, not every study has employed the same chemical compound. One study administered 4-amino-3-hydroxybutyric acid (Kuriyama and Sze, 1971). Although this compound has a different chemical structure than GABA (i.e., an extra OH group), this study is often cited as providing evidence for GABA’s inability to cross the BBB. In view of the role that simple chemical properties play in BBB permeation, it might be problematic to generalize findings with different chemical compounds to GABA as it is found in the central nervous system and its food supplement version. All other studies that have reported evidence for or against GABA’s BBB permeability either administered radioactively labeled GABA (which is chemically identical to GABA, see Figure 2), or did not further specify the kind of GABA they used.

    Figure 2. GABA’s chemical structure.

    A second factor that may, in principle, account for the discrepancy between animal studies concerns the significant variation in methods of GABA administration. GABA was administered either by intraperitoneal injection (Van Gelder and Elliott, 1958 Kuriyama and Sze, 1971 Frey and Löscher, 1980 Löscher, 1981 Shyamaladevi et al., 2002), intravenous injection (Roberts et al., 1958 Löscher and Frey, 1982 Knudsen et al., 1988), or the bilateral in situ brain perfusion technique (Al-Sarraf, 2002). However, there appears to be no systematic relationship between the method of administration and the research outcome positive and negative evidence has been found with all of these methods.

    Thirdly, the reported studies differ in the species of animals tested. Most studies used rats (Van Gelder and Elliott, 1958 Kuriyama and Sze, 1971 Al-Sarraf, 2002 Shyamaladevi et al., 2002), but mice (Roberts et al., 1958 Frey and Löscher, 1980), rabbits (Van Gelder and Elliott, 1958 Kuriyama and Sze, 1971), and dogs (Löscher and Frey, 1982) have also been used. As with the employed methodologies, both positive and negative evidence has been found with these different species.

    One limitation of this field is that there have been no studies with humans that directly assessed GABA’s BBB permeability. This is not so surprising given the limited number of methods for measuring GABA levels in the human brain. GABA levels have been determined in post-mortem tissue samples (Perry et al., 1973). Additionally, neocortical slices have been extracted from epileptic patients undergoing surgery (Errante et al., 2002), but these methods have not been employed to assess the effect of GABA administration on brain GABA levels. The obvious noninvasive candidate for such an assessment is magnetic resonance spectroscopy (MRS), but we are not aware of any MRS studies that assessed brain GABA levels after administration of GABA. Assessment of GABA concentrations in the brain using MRS requires a careful experimental design, since GABA is not only present in the brain, but also in blood vessels located outside of the BBB. Tissue fraction analyses estimating blood, CSF, gray matter and white matter presence within each volume of interest should therefore be incorporated (Draper et al., 2014).

    Interestingly, evidence has been found for the presence of a GABA-transporter in the BBB (Takanaga et al., 2001). The expression of such a transporter indicates that GABA can enter and/or exit the brain through facilitated transport. In mice, the brain efflux rate for GABA was found to be 17 times higher than the influx rate (Kakee et al., 2001). This complicates the interpretation of GABA concentrations in the brain, and it is possible that this may have led to an underestimation of the extent to which GABA is able to cross the BBB. That is, some studies may have found little evidence for GABA’s BBB permeability because of the high efflux rate.

    GABA, Diseases, and Treatment

    Increasing GABA in the brain has for years been the focus of drug development aiming to alleviate the severity of epileptic seizures (Hawkins and Sarett, 1957 Wood et al., 1979 Gale, 1989 Petroff et al., 1995). Initial studies examined the efficacy of administering GABA directly. One study reported a reduction in the amount of seizures in epileptic patients who were administered a very high dose of GABA (0.8 g/kg daily Tower, 1960). However, this result was found only in four out of twelve patients. Additionally, the patients in whom the administration of GABA did have an effect were children below the age of 15. This finding is in line with the suggestion that the BBB permeability to GABA decreases with age (Al-Sarraf, 2002). Perhaps more importantly, GABA’s half-life is about 17 min in mice (Kakee et al., 2001). If the half-life has a similar short duration in humans, direct administration of GABA is unsuitable as pharmacological treatment of epilepsy.

    The GABA analog gabapentin was developed as an anti-epileptic drug. Gabapentin functions by modulating enzymes involved in GABA synthesis. It differs in chemical structure from GABA and its half-life is much longer (McLean, 1994). One MRS study in humans has found that the administration of gabapentin increased brain GABA levels by 55.7% (Cai et al., 2012). Nonetheless, a study exploring the effects of gabapentin in both rat and human neocortical slice preparations suggests that there might be a considerable difference between rodents and humans in the effects on GABA levels: gabapentin was found to increase GABA concentrations by 13% in human neocortical slices, while having no significant effect in rat neocortical slices (Errante et al., 2002).

    Patients with Huntington’s disease also have reduced GABA levels in the brain (Perry et al., 1973), but administration of GABA to remedy this deficiency has shown mixed results with regards to the reduction of symptoms (Barbeau, 1973 Fisher et al., 1974 Shoulson et al., 1976). Of course, that the administration of GABA does not consistently alter the symptoms in complex and multifaceted disorders such as epilepsy and Huntington’s disease, does not necessarily mean that GABA is unable to affect the brain.

    GABA as a Food Supplement

    In recent years researchers have reported a number of placebo-controlled studies in which GABA was administered as a food supplement to healthy participants and participants with a history of acrophobia. One study found an increase in alpha waves in healthy participants and reduced levels of immunoglobulin A (IgA an indicator of immune system functioning) in participants with a history of acrophobia when they were exposed to heights (Abdou et al., 2006). However, the sample size for the second finding was very small (four participants per group). Another study reported reduced heart rate variability and salivary chromogranin A (CgA) during an arithmetic task compared to a control group after the administration of GABA-enriched chocolate (Nakamura et al., 2009). A third study reported less salivary cortisol and CgA than a control group during a psychological stress-inducing arithmetic task. Additionally, participants who received 50 mg of GABA dissolved in a beverage reported less psychological fatigue after completion of the task (Kanehira et al., 2011). Finally, in a fourth study, participants were found to show a decrease in alpha waves over time while performing an arithmetic task. This decrease was smaller in the group that orally received GABA (100 mg) compared to a control group (Yoto et al., 2012). By way of comparison, one would have to eat 2.34 kg of uncooked spinach in order to consume a similar amount of GABA, and spinach is relatively rich in GABA compared to other foods (Oh et al., 2003).

    The results of these studies support the claims made by hundreds of consumers of GABA food supplement products and fit with a growing trend in which GABA is administered through everyday (natural) foods (Diana et al., 2014). However, there are some caveats to consider. First, at least one of the authors in each of these four studies was affiliated with the company that produces the GABA supplement in question. However, a declaration of conflicting interests is lacking in three out of four of these studies. Second, the reported studies used “pharma-GABA,” which is produced for the Asian market through a fermentation process using a strain of lactic acid bacteria, Lactobacillus hilgardii K-3 (Kanehira et al., 2011). Pharma-GABA has been approved by the FDA as a food ingredient (Food and Drug Administration, 2008). While the manufacturer of pharma-GABA suggests that there are important differences with the synthetic GABA supplement sold online in Western countries (http://www.natural-pharmagaba.com/q-and-a.html), these differences refer to the production process and the occurrence of potentially harmful byproducts in synthetically produced GABA, and not to the chemical structure of the active compound GABA.

    A recent study by Steenbergen et al. (2015a) with human subjects has shown that the ingestion of synthetic GABA (800 mg) enhanced the ability of prioritized planned actions and inhibitory control (as indexed by the stop-change task Verbruggen and Logan, 2008 Steenbergen et al., 2015a). However, in view of the lack of evidence with regards to GABA’s BBB permeability in humans, the mechanism through which GABA might have exerted these effects remains unclear. The same holds for the pharma-GABA studies that were discussed above: none of these effects exclude an indirect of GABA on the brain. The oral intake of these supplements may have exerted these effects through indirect pathways, for example through the enteric nervous system (ENS).

    Enteric Nervous System Effects of GABA

    The bidirectional signaling between the brain and the ENS is vital in maintaining homeostasis (Cryan and O’Mahony, 2011). Even though most research thus far has focused on the signaling from the brain to the gut, an increasing number of studies has explored the influence of the gut’s microbiota on the brain. For example, gut microbiota have been shown to improve mood and reduce anxiety in patients with chronic fatigue (Logan and Katzman, 2005 Rao et al., 2009). Similarly, oral intake of probiotics resulted in reduced urinary cortisol and perceived psychological stress (Messaoudi et al., 2011) and reduced reactivity to sad mood (Steenbergen et al., 2015b) in healthy subjects.

    It has been found that certain probiotic strains are able to produce GABA in vivo. Specifically, bacteria from the strains Lactobacillus and Bifidobacterium were effective at increasing GABA concentrations in the ENS (Barrett et al., 2012). Indeed, both GABA and its receptors are widely distributed through the ENS (Auteri et al., 2015). Additionally, there is considerable communication between the gut and the brain through the vagal nerve (Cryan and O’Mahony, 2011 Cryan and Dinan, 2012). This nerve consists, for the most part, of sensory nerve fibers that relay information about the state of bodily organs to the central nervous system (Thayer and Sternberg, 2009).

    A study in mice showed that the administration of Lactobacillus rhamnosus (JB-1) consistently modulated the mRNA expression of GABAA㬒, GABAA㬑, and GABAB1b receptor subunits (Bravo et al., 2011), receptors commonly associated with anxiety-like behavior. Indeed, on a behavioral level the L. rhamnosus (JB-1)-fed mice were less anxious and displayed antidepressant-like behaviors in comparison with controls. Furthermore, the administration of these bacteria reduced the stress-induced elevation of corticosterone compared to the control mice. Importantly, none of these effects were present in mice that underwent vagotomy (Bravo et al., 2011).

    In humans, the stimulation of the vagus nerve through transcutaneous vagus nerve stimulation (tVNS) has been used to treat refractory epilepsy (Vonck et al., 2014). This technique has been shown to affect norepinephrine, acetylcholine and GABA concentrations (Van Leusden et al., 2015). With regards to GABA, VNS seems to increase the level of free GABA in the cerebrospinal fluid (Ben-Menachem et al., 1995). Similarly to the administration of synthetic GABA (Steenbergen et al., 2015a), active tVNS was found to enhance the ability of prioritizing and cascading different actions when performing a stop-change paradigm (Steenbergen et al., 2015c).

    To summarize, bacteria from the Lactobacillus spp. strain contribute to the formation of GABA in the ENS. The oral administration of bacteria from this strain can influence GABAergic firing in the mice brain through the vagus nerve. Furthermore, stimulation of the vagal nerve through tVNS has been shown to affect processes thought to be GABAergic in humans. Finally, a similar behavioral effect has been found both for the administration of synthetic GABA and tVNS with regards to action cascading. Even if GABA is unable to cross the BBB at all in humans, an indirect effect through the ENS might be a viable route for an effect of GABA food supplements. The link between the oral administration of GABA, the vagal nerve and GABA levels in the brain has not been established yet, but in view of the available evidence it is a promising candidate for future research.


    Break on through to the other side: How HIV penetrates the blood-brain barrier

    Although it is known that HIV can enter the brain early during infection, causing inflammation and memory/cognitive problems, exactly how this occurs has been largely unknown. A new research report appearing in the February 2015 issue of the Journal of Leukocyte Biology solves this mystery by showing that HIV relies on proteins expressed by a type of immune cell, called "mature monocytes," to enter the brain. These proteins are a likely drug target for preventing HIV from reaching brain cells. Although not a direct focus of this research, these proteins might also shed light on novel mechanisms for helping drugs penetrate the blood-brain barrier.

    "I hope this study brings awareness to the need for adjunctive therapies targeting monocyte influx into the brain as a means to decrease HIV entry into the brain and HIV-associated neurocognitive disorder," said Dionna W. Williams, Ph.D., a researcher involved in the work from the Department of Pathology at the Albert Einstein College of Medicine in Bronx, New York.

    To make their discovery, scientists received blood from two groups of people--people infected by HIV and people who were not infected. Mature monocytes were obtained from the blood of people from both groups and researchers determined how many of these cells were present, what proteins the cells expressed and also characterized how they entered into the brain. The researchers found that the mature monocytes had an increased ability to enter into the brain due to the unique proteins they expressed, which could lead to HIV infecting the brain.


    Masters of disguise

    Sure enough, the breast cancer cells taken from the brain expressed a receptor for GABA, plus a transporter protein that brings GABA into the cell, and a host of other compounds that convert GABA into energy. In this way, the metastatic tumour cells had in effect disguised themselves as neurons. No such machinery was seen in the non-metastatic breast cancer cells.

    “The idea that metastasising cells can adopt a new identity, shielding them from intrinsic defence mechanisms, is very exciting and suggests that cancer cells are likely more plastic than previously suspected,” says Ellen Carpenter, a neuroscientist at the University of California, Los Angeles, who was not involved in the work. “I think this is likely a tremendous advance in breast cancer research.”

    But understanding the neuronal disguise – a mechanism that other cancers may be using to spread in the brain, says Jandial – requires further work. For example, it’s not clear whether breast cancer cells evolved the GABA machinery by chance over time, or somehow acquired it from their environment.

    Still, Jandial hopes the results will lead to new chemotherapies based on existing drugs for brain cancers or neurodegenerative disease, or help us discover novel drugs to treat tumours that spread to the brain.


    What are the consequences of leaky brain?

    “A dysfunction of the blood brain barrier leading to a ‘leaky brain’ can be linked to various neurological diseases, including autistic spectrum disorder (ASD), dementia, Alzheimer’s disease, depression, and schizophrenia”

    It can also be linked to stroke and Parkinson’s disease. Other signs and symptoms include “foggy” brain, poor concentration, chronic fatigue, headaches, memory loss, and cognitive decline.