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Showing posts with label Glutamate. Show all posts
Showing posts with label Glutamate. Show all posts

Friday 21 April 2017

The Excitatory/Inhibitory Imbalance – GABAA stabilization via IP3R


This blog aims to synthesize the relevant parts of the research and make connections that point towards some potential therapeutic avenues.  Most researchers work in splendid isolation and concentrate on one extremely narrow area of interest.

The GABAA reset, not functional in some autism

On the one hand things are very simple, if the GABAA receptors function correctly and are inhibitory and the glutamate receptors (particularly NMDA and mGluRx) function correctly, there is harmony and a  perfect excitatory/inhibitory balance.

Unfortunately numerous different things can go wrong and you could write a book about each one.

As you dig deeper you see that the sub-unit make-up of GABAA receptors is not only critical but changes.  The plus side is that you can influence this.

Today we see that the receptors themselves are physically movable and sometimes get stuck in the “wrong place”. When the receptors cluster close together they produce a strong inhibitory effect, but continual activation of NMDA receptors by the neurotransmitter glutamate - as occurs naturally during learning and memory, or in epilepsy - leads to an excess of incoming calcium, which ultimately causes the receptors to become more spread out, reducing how much the neuron can be inhibited by GABA. There needs to be a mechanism to move the GABAA receptors back into their original clusters.

Very clever Japanese researchers have figured out the mechanism and to my surprise it involves one of those hubs, where strange things in autism seem to connect to, this time IP3R.





I guess the Japanese answer to my question above is simple. YES,


A very recent science-light article by Gargus on IP3:-






Now to the Japanese.






I wonder if Gargus has read the Japanese research, because both the cause and cure for the GABAA receptors dispersing and clustering is an increase in calcium and both mediated by glutamate.  

The excitatory neurotransmitter glutamate binds to the mGluR receptor and activates IP3 receptor-dependent calcium release and protein kinase C to promote clustering of GABAA receptors at the postsynaptic membrane - the place on a neuron that receives incoming neurotransmitters from connecting neurons.

If Professor Gargus is correct, and IPR3 does not work properly in autism, the GABAA receptors are likely not sitting there in nice neat clusters. As a result their inhibitory effect is reduced and neurons fire when they should not.

Gargus has found that in the types of autism he has investigated IP3 receptor open as they should, but close too fast and so do not release enough calcium from the cell’s internal calcium store (the endoplasmic reticulum).

In particular the Japanese researchers found that:-

“Stabilization of GABA synapses by mGluR-dependent Ca2+ release from IP3R via PKC”
If the IP3 receptor does not stay open as long as it should, not enough Ca2+ will be released and GABA synapses will not be stabilized. Then GABAA receptors will be diffused rather than being in neat clusters.

The science-light version of the Japanese study:-




Just as a thermostat is used to maintain a balanced temperature in a home, different biological processes maintain the balance of almost everything in our bodies, from temperature and oxygen to hormone and blood sugar levels. In our brains, maintaining the balance -- or homeostasis -- between excitation and inhibition within neural circuits is important throughout our lives, and now, researchers at the RIKEN Brain Science Institute and Nagoya University in Japan, and École Normale Supérieure in France have discovered how disturbed inhibitory connections are restored. Published in Cell Reports, the work shows how inhibitory synapses are stabilized when the neurotransmitter glutamate triggers stored calcium to be released from the endoplasmic reticulum in neurons.

"Imbalances in excitation and inhibition in the brain has been linked to several disorders," explains lead author Hiroko Bannai. "In particular, forms of epilepsy and even autism appear to be related to dysfunction in inhibitory connections."

One of the key molecules that regulates excitation/inhibition balance in the brain is the inhibitory neurotransmitter GABA. When GABA binds to GABAA receptors on the outside of a neuron, it prevents that neuron from sending signals to other neurons. The strength of the inhibition can change depending on how these receptors are spaced in the neuron's membrane.

While GABAA receptors are normally clustered together, continual neural activation of NMDA receptors by the neurotransmitter glutamate -- as occurs naturally during learning and memory, or in epilepsy -- leads to an excess of incoming calcium, which ultimately causes the receptors to become more spread out, reducing how much the neuron can be inhibited by GABA.

To combat this effect, the receptors are somehow continually re-clustered, which maintains the proper excitatory/inhibitory balance in the brain. To understand how this is accomplished, the team focused on another signaling pathway that also begins with glutamate, and is known to be important for brain development and the control of neuronal growth.

In this pathway glutamate binds to the mGluR receptor and leads to the release of calcium from internal storage into the neuron's internal environment. Using quantum dot-single particle tracking, the team was able to show that after release, this calcium interacts with protein kinase C to promote clustering of GABAA receptors at the postsynaptic membrane--the place on a neuron that receives incoming neurotransmitters from connecting neurons.

These findings show that glutamate activates distinct receptors and patterns of calcium signaling for opposing control of inhibitory GABA synapses.

Notes Bannai, "it was surprising that the same neurotransmitter that triggers GABAA receptor dispersion from the synapse, also plays a completely opposite role in stabilizing GABAA receptors, and that the processes use different calcium signaling pathways. This shows how complex our bodies are, achieving multiple functions by maximizing a limited number of biological molecules.

Pre-activation of the cluster-forming pathway completely prevented the dispersion of GABAA receptors that normally results from massive excitatory input, as occurs in status epilepticus -- a condition in which epileptic seizures follow one another without recover of consciousness. Bannai explains, "further study of the molecular mechanisms underlying the process we have uncovered could help develop treatments or preventative medication for pathological excitation-inhibition imbalances in the brain.

"The next step in understanding how balance is maintained in the brain is to investigate what controls which pathway is activated by glutamate. Most types of cells use calcium signals to achieve biological functions. On a more basic level, we believe that decoding these signals will help us understand a fundamental biological question: why and how are calcium signals involved in such a variety of biological phenomena?"


The full Japanese study:-





·        Bidirectional synaptic control system by glutamate and Ca2+ signaling

·        Stabilization of GABA synapses by mGluR-dependent Ca2+ release from IP3R via PKC

·        Synaptic GABAAR clusters stabilized through regulation of GABAAR lateral diffusion

·        Competition with an NMDAR-dependent Ca2+ pathway driving synaptic destabilization

GABAergic synaptic transmission regulates brain function by establishing the appropriate excitation-inhibition (E/I) balance in neural circuits. The structure and function of GABAergic synapses are sensitive to destabilization by impinging neurotransmitters. However, signaling mechanisms that promote the restorative homeostatic stabilization of GABAergic synapses remain unknown. Here, by quantum dot single-particle tracking, we characterize a signaling pathway that promotes the stability of GABAA receptor (GABAAR) postsynaptic organization. Slow metabotropic glutamate receptor signaling activates IP3 receptor-dependent calcium release and protein kinase C to promote GABAAR clustering and GABAergic transmission. This GABAAR stabilization pathway counteracts the rapid cluster dispersion caused by glutamate-driven NMDA receptor-dependent calcium influx and calcineurin dephosphorylation, including in conditions of pathological glutamate toxicity. These findings show that glutamate activates distinct receptors and spatiotemporal patterns of calcium signaling for opposing control of GABAergic synapses.



In this study, we demonstrate that the mGluR/IICR/PKC pathway stabilizes GABAergic synapses by constraining lateral diffusion and increasing clustering of GABAARs, without affecting the total number of GABAAR on the cell surface. This pathway defines a unique form of homeostatic regulation of GABAergic transmission under conditions of basal synaptic activity and during recovery from E/I imbalances. The study also highlights the ability of neurons to convert a single neurotransmitter (glutamate) into an asymmetric control system for synaptic efficacy using different calcium-signaling pathways.

The most striking conceptual finding in this study is that two distinct intracellular signaling pathways, NMDAR-driven Ca2+ influx and mGluR-driven Ca2+ release from the ER, effectively driven by the same neurotransmitter, glutamate, have an opposing impact on the stability and function of GABAergic synapses. Sustained Ca2+ influx through ionotropic glutamate receptor-dependent calcium signaling increases GABAAR lateral diffusion, thereby causing the dispersal of synaptic GABAAR, while tonic mGluR-mediated IICR restrains the diffusion of GABAAR, thus increasing its synaptic density. How can Ca2+ influx and IICR exert opposing effects on GABA synaptic structure? Our research indicates that each Ca2+ source activates a different Ca2+-dependent phosphatase/kinase: NMDAR-dependent Ca2+ influx activates calcineurin, while ER Ca2+ release activates PKC.


Taken together, these results lead us to propose the following model for bidirectional competitive regulation of GABAergic synapses by glutamate signaling. Phasic Ca2+ influx through NMDARs following sustained neuronal excitation or injury leads to the activation of calcineurin, overcoming PKC activity and relieving GABAAR diffusion constraints. In contrast, during the maintenance of GABAergic synaptic structures or the recovery from GABAAR dispersal, the ambient tonic mGluR/IICR pathway constrains GABAAR diffusion by PKC activity, overcoming basal calcineurin activity. One possible mechanism of dual regulation of GABAAR by Ca2+ is that each Ca2+-dependent enzyme has a unique sensitivity to the frequency and number of external glutamate release events and can act to decode neuronal inputs (Fujii et al., 2013xNonlinear decoding and asymmetric representation of neuronal input information by CaMKIIα and calcineurin. Fujii, H., Inoue, M., Okuno, H., Sano, Y., Takemoto-Kimura, S., Kitamura, K., Kano, M., and Bito, H. Cell Rep. 2013; 3: 978–987

Abstract | Full Text | Full Text PDF | PubMed | Scopus (24)See all References, Li et al., 2012xCalcium input frequency, duration and amplitude differentially modulate the relative activation of calcineurin and CaMKII. Li, L., Stefan, M.I., and Le Novère, N. PLoS ONE. 2012; 7: e43810

Crossref | PubMed | Scopus (29)See all References, Stefan et al., 2008xAn allosteric model of calmodulin explains differential activation of PP2B and CaMKII. Stefan, M.I., Edelstein, S.J., and Le Novère, N. Proc. Natl. Acad. Sci. USA. 2008; 105: 10768–10773

Crossref | PubMed | Scopus (44)See all References) in inhibitory synapses.

Tight control of E/I balance, the loss of which results in epilepsy and other brain and nervous system diseases/disorders, is dependent on GABAergic synaptic transmission (Mann and Paulsen, 2007xRole of GABAergic inhibition in hippocampal network oscillations. Mann, E.O. and Paulsen, O. Trends Neurosci. 2007; 30: 343–349

Abstract | Full Text | Full Text PDF | PubMed | Scopus (194)See all ReferencesMann and Paulsen, 2007). A recent study showed that the excitation-induced acceleration of GABAAR diffusion and subsequent dispersal of GABAARs from synapses is the cause of generalized epilepsy febrile seizure plus (GEFS+) syndrome (Bouthour et al., 2012xA human mutation in Gabrg2 associated with generalized epilepsy alters the membrane dynamics of GABAA receptors. Bouthour, W., Leroy, F., Emmanuelli, C., Carnaud, M., Dahan, M., Poncer, J.C., and Lévi, S. Cereb. Cortex. 2012; 22: 1542–1553

Crossref | PubMed | Scopus (14)See all ReferencesBouthour et al., 2012). Our results indicate that pre-activation of the mGluR/IICR pathway by DHPG could completely prevent the dispersion of synaptic GABAARs induced by massive excitatory input similar to status epilepticus. Thus, further study of the molecular mechanisms underlying the mGluR/IICR-dependent stabilization of GABAergic synapses via regulation of GABAAR lateral diffusion and synaptic transmission could be helpful in the prevention or treatment of pathological E/I imbalances, for example, in the recovery of GABAergic synapses from epileptic states


DHPG = group I mGluR agonist dihydroxyphenylglycine.

On a practical level you want to inhibit GABAA  dispersion and promote GABAA stabilization. How you might do this would depend on exactly what was the underlying problem.

If the problem is IP3R not releasing enough calcium, you might activate PKC in a different way or just increase the signal from Group 1 mGluR. If the problem is too much calcium influx through NMDA receptors due to excess glutamate, you could increase the re-uptake of glutamate, via GLT-1, using Riluzole.  You could block the flow of Ca2+ through NMDA receptors using an antagonist.

The Japanese used dihydroxyphenylglycine (DHPG) as their Group 1 mGluR agonist.  DHPG is an agonist of mGluR1 and mGluR5.  We have come across mGluR5 many times before in this blog.  Mavoglurant is an experimental drug candidate for the treatment of fragile X syndrome.  It is an antagonist of mGluR5.

We have seen many times before that there is both hypo and hyper function possible and indeed that fragile X is not necessarily a good model for autism.

The selective mGluR5 agonist CHPG protects against traumatic brain injury, which would indeed make sense. Although, that research suggests an entirely different mechanism.



The calcium released by IP3 works in complex way together with DAG (diacylglycerol ) to activate PKC (protein kinase C).





Ideally you would have enough calcium released from IP3, but you could also increase DAG. It depends which part of the process is rate-limiting.

Diacylglycerol (DAG) has been investigated extensively as a fat substitute due to its ability to suppress the accumulation of body fat.  Diglycerides, generally in a mix with monoglycerides are common food additives largely used as emulsifiers. In Europe, when used in food the mix is called E471.


Conclusion

On the one hand things are getting very complicated, but on the other we keep coming back to the same variables (IP3R, mGlur5, GABAA etc.).

It is pretty clear that some very personalized therapy will be needed.  Is it an mGlur5 agonist or antagonist? Or quite possibly neither, because in different parts of the brain it will have a good/bad effect.

It does look like Riluzole should work well in some people.

A safe IP3R agonist looks a possibility. As shown in the diagram earlier in this post,IP3 is usually made in situ, but agonists exist.

In effect autism could be the opposite of Huntington’s disease. In Huntington’s,  type 1 IP3 receptors are  more sensitive to IP3, which leads to the release of too much Ca2+ from the ER. The release of Ca2+ from the ER causes an increase in concentrations of Ca2+inside cells and in mitochondria.

According to Gargus we should have reduced concentrations of Ca2+inside cells in autism.

I suspect it is much more complicated in reality, because it is not just the absolute  level of Ca2+ but rather the flow of Ca2+; so it matters where it is coming from. I think we likely have impaired calcium channel activity of multiple types in autism and the actual level of intracellular calcium will not tell you much at all.

As the Japanese commented, it is surprising that glutamate is the neurotransmitter that controls the clustering, or not, of GABAA receptors.  This suggests that you cannot ignore glutamate and just “fix” GABA.





Monday 3 April 2017

Different Types of Excitatory/Inhibitory Imbalance in Autism, Fragile-X & Schizophrenia


There is much written in the complex scientific literature about the Excitatory/Inhibitory (E/I) imbalance between neurotransmitters in autism. 

Many clinical trials have already been carried out, particularly in Fragile-X.  These trials were generally ruled as failures, in spite of a significant minority who responded quite well in some of these trials.

As we saw in the recent post on the stage II trial of bumetanide in severe autism, there is so much “background noise” in the results from these trials and it is easy to ignore a small group who are responders.  I think if you have less than 40%, or so, of positive responders they likely will get lost in the data. 

You inevitably get a significant minority who appear to respond to the placebo, because people with autism usually have good and bad days and testing is very subjective.

There are numerous positive anecdotes from people who participated in these “failed” trials.  If you have a child who only ever speaks single words, but while on the trial drug starts speaking full sentences and then reverts to single words after the trial, you do have to take note. I doubt this is a coincidence.

Here are some of the trialed drugs, just in Fragile-X, that were supposed to target the E/I imbalance:-

Metabotropic glutamate receptor 5 (mGluR5) antagonist

·        Mavoglurant

·        Lithium

mGluR5 negative allosteric modulator

·        Fenobam

N-methyl-D-aspartic acid (NMDA) antagonist

·        Memantine

Glutamate re-uptake promoter

·        Riluzole

Suggested to have effects on NMDA & mGluR5 & GABAA

·        Acamprosate

GABAB agonist

·        Arbaclofen

Positive allosteric modulator (PAM) of GABAA receptor

·        Ganaxolone


Best not to be too clever

Some things you might use to modify the E/I imbalance can appear to have the opposite effect, as was highlighted in the comments in the post below:-



So whilst it is always a good idea to try and figure things out, you may end up getting things the wrong way around, mixing up hypo and hyper.

The MIT people who work on Fragile-X are really clever and they have not figured it all out.


Fragile-X and Idiopathic Autism

Fragile-X gets a great deal of attention, because its biological basis is understood.  It results in a failure to express the fragile X mental retardation protein (FMRP), which is required for normal neural development.

We saw in the recent post about eIF4E, that this could lead to an E/I imbalance and then autism.




Our reader AJ started looking at elF4E and moved on to EIF4E- binding protein number 1.

In the green and orange boxes below you can find elF4E and elF4E-BP2.

This has likely sent some readers to sleep, but for those whose child has Fragile-X, I suggest they read on, because it is exactly here that the lack of fragile X mental retardation protein (FMRP) causes a big problem.  The interaction between FMRP on the binding proteins of elF4E, cause the problem with neuroligins (NLGNs), which causes the E/I imbalance.  Look at the red oval shape labeled FMRP and green egg-shaped NLGNs.

In which case, while AJ might naturally think Ribavirin is a bit risky for idiopathic autism, it might indeed be very effective in some Fragile-X.  You would hope some researcher would investigate this.




Can you have more than one type of E/I imbalance?

Readers whose child responds well to bumetanide probably wonder if they have solved their E/I imbalance.

I think they have most likely improved just one dysfunction that fits under the umbrella term E/I imbalance.  There are likely other dysfunctions that if treated could further improve cognition and behavior.

On the side of GABA, it looks like turning up the volume on α3 sub-unit and turning down the volume on α5 may help. We await the (expensive) Down syndrome drug Basmisanil for the latter, given that the cheap 80 year old drug Cardiazol is no longer widely available. Turning up the volume on α3 sub-unit can be achieved extremely cheaply, and safely, using a tiny dose of Clonazepam.

It does appear that targeting glutamate is going to be rewarding for at least some of those who respond to bumetanide.

One agonist of NMDA receptors is aspartic acid. Our reader Tyler is a fan of L-Aspartic Acid, that is sold as a supplement that may boost athletic performance.  

Others include D-Cycloserine, already used in autism trials; also D-Serine and L-Serine.

D-Serine is synthesized in the brain from L-serine, its enantiomer, it serves as a neuromodulator by co-activating NMDA receptors, making them able to open if they then also bind glutamate. D-serine is a potent agonist at the glycine site of NMDA receptors. For the receptor to open, glutamate and either glycine or D-serine must bind to it; in addition a pore blocker must not be bound (e.g. Mg2+ or Pb2+).

D-Serine is being studied as a potential treatment for schizophrenia and L-serine is in FDA-approved human clinical trials as a possible treatment for ALS/Motor neuron disease.  

You may be thinking, my kid has autism, what has this got to do with ALS/Motor neuron disease (from the ice bucket challenge)? Well one of the Fragile-X trial drugs at the beginning of this post is Riluzole, a drug developed for specially for ALS.  Although it does not help that much in ALS, it does something potentially very useful for some autism, ADHD and schizophrenia; it clears away excess glutamate.


Fragile-X is likely quite different to many other types of autism

I suspect that within Fragile-X there are many variations in the downstream biological dysfunctions and so that even within this definable group, there may be no universal therapies.  So for some people an mGluR5 antagonist may be appropriate, but not for others.

Even within this discrete group, we come back to the need for personalized medicine.

I do not think Fragile-X is a good model for broader autism.


Glutamate Therapies

There are not so many glutamate therapies, so while the guys at MIT might disapprove, it would not be hard to apply some thoughtful trial and error.

You have:

mGluR5

     ·        mGluR5 agonists (only research compounds)

·        mGluR5 positive allosteric modulators (only research compounds)

·        mGluR5 antagonists (Mavoglurant, Lithium)

·        mGluR5 negative allosteric modulators (Fenobam, Pu-erh tea decreases mGluR5 expression )

Today you can only really treat too much mGluR5 activity.  It there is too little activity, the required drugs are not yet available.  I wonder how many people with Fragile-X are drinking Pu-erh tea, it is widely available.


NMDA agonists

D-Cycloserine an antibiotic with similar structure to D-Alanine (D-Cycloserine was trialed in autism and schizophrenia)

ɑ-amino acids:

·         Aspartic acid (trialed and used  by Tyler, suggested for schizophrenia)

·         D-Serine (trialed in schizophrenia)




NMDA antagonists


·        Memantine (widely used off-label in autism, but failed in clinical trials)


·        Ketamine (trialed intra-nasal in autism)


Glutamate re-uptake promoters via GLT-1


·        Riluzole


·        Bromocriptine


·        Beta-lactam antibiotics









Friday 31 March 2017

The Glutamate Side of Things

Some readers have suggested that since we have discovered so many ways to treat the GABAA dysfunctions common in autism, it is time to look at the glutamate side of things. Glutamate is the main excitatory neurotransmitter and has to be in balance with the opposing influence of GABA.

The chart below is really a summary of what has already been covered in this blog.  To newcomers it will look complicated, to regular readers it is just bringing together everything we have already covered, even those tauopathies appear. Tau protein tangles appear in Alzheimer’s and some autism.
Glutamate excitoxicity is what happens when things go really wrong, for example in a severe autistic regression.  I doubt you could be in a permanent state like this.



I am beginning to wonder is my son’s summer time raging, though triggered by allergy, develops to a so-called glutamatergic storm.  It fades to nothing  by using a Cav1.2 channel blocker, which does indeed stop those allergy mast cells de-granulating, but it stops the calcium influx in the above chart.  Existing dysfunction in Cav1.2 and Cav1.4 puts you at risk of excitotoxicity.
The oxidative damage to mitochondria causes lipid peroxidation and in particular the 4-HNE produced will cause tau protein, from a recent post and Alzheimer’s, to produce tau tangles, a damaging feature of so-called tauopathies.
The nitrosative stress in particular damages the production of the Complex 1 enzyme leading to mitochondrial disease/dysfunction. The damaging peroxynitrates can be quenched using high doses of calcium folinate. Oxidative stress and the reduced level of GSH can be treated with antioxidants like NAC and ALA.  

Reduced reuptake of glutamate, known to be caused by elevated TNF-α and immune dysfunction, is treatable via upregulating the GLT-1 transporter (beta-lactam antibiotics, riluzole and bromocriptine).
Elevated BDNF is a biomarker of autism and unfortunately this increases the chances of glutamate excitotoxicity.
An inactivated GABA switch that leaves neurons immature, will result in GABA acting excitatory rather than inhibitory, this itself can trigger of glutamate excitotoxicity. Use bumetanide.
Some types of autism feature NMDA hyper-function, this is treatable.  A deviation of NMDA function in either direction (hypo or hyper) leads to autism, but you need to know which way it is, to treat it.

It is also possible to have over/under expression of NMDA receptors.




Friday 9 December 2016

Glutamate Inhibitors to Treat Some Autism and ADHD




 A festive queue at the pharmacy for Glutamate Inhibitors


We have now established that much autism and indeed other disorders, from Down Syndrome to Schizophrenia, features a degree of excitatory/inhibitory (E/I) imbalance.

It is very likely that there are multiple underlying causes for this and so there may be multiple treatments.  We can even potentially use a treatment for one cause (ALS) to improve outcomes in others.  So we can (partially) solve a problem without fully understanding its origin, as frequently is the case in biology.

An E/I imbalance might cause anxiety in the adult with Asperger (treatable with Baclofen), contribute to MR/ID in the child with Down Syndrome and contribute to seizures and cognitive loss in someone with severe autism.

Very interestingly in the comments to a previous post, Agnieszka has pointed out why common penicillin type antibiotics (beta-lactams) improve many people’s autism.  This is very common observation and our other guest blogger Seth Bittker found the same in his son. Nat’s guest speaker at her autism conference also found this in his son.

The Glutamate Transporter 1 (GLT-1) is a protein that in humans is encoded by the SLC1A2 gene.   It is the principal transporter that clears the excitatory neurotransmitter glutamate from the extracellular space at synapses in the central nervous system. Glutamate clearance is necessary for proper synaptic activation and to prevent neuronal damage from excessive activation of glutamate receptors. Glutamate is an excitatory neurotransmitter, so it encourages neurons to fire.

By upregulating the GLT1 transporter you increase the inactivation of glutamate and so shift the Excitatory/Inhibitory balance towards inhibitory.

Agnieszka highlighted this paper from Johns Hopkins:-




Glutamate is the principal excitatory neurotransmitter in the nervous system. Inactivation of synaptic glutamate is handled by the glutamate transporter GLT1 (also known as EAAT2; refs 1, 2), the physiologically dominant astroglial protein. In spite of its critical importance in normal and abnormal synaptic activity, no practical pharmaceutical can positively modulate this protein. Animal studies show that the protein is important for normal excitatory synaptic transmission, while its dysfunction is implicated in acute and chronic neurological disorders, including amyotrophic lateral sclerosis (ALS), stroke, brain tumours and epilepsy. Using a blinded screen of 1,040 FDA-approved drugs and nutritionals, we discovered that many beta-lactam antibiotics are potent stimulators of GLT1 expression. Furthermore, this action appears to be mediated through increased transcription of the GLT1 gene. beta-Lactams and various semi-synthetic derivatives are potent antibiotics that act to inhibit bacterial synthetic pathways. When delivered to animals, the beta-lactam ceftriaxone increased both brain expression of GLT1 and its biochemical and functional activity. Glutamate transporters are important in preventing glutamate neurotoxicity. Ceftriaxone was neuroprotective in vitro when used in models of ischaemic injury and motor neuron degeneration, both based in part on glutamate toxicity. When used in an animal model of the fatal disease ALS, the drug delayed loss of neurons and muscle strength, and increased mouse survival. Thus these studies provide a class of potential neurotherapeutics that act to modulate the expression of glutamate neurotransmitter transporters via gene activation.



It actually gets more interesting and relevant to treatment.

Mutations in SLC1A2 which decrease expression of the GLT-1 protein are associated with amyotrophic lateral sclerosis (ALS). 

The drug riluzole approved for the treatment of ALS upregulates GLT-1.

This would suggest that Agnieszka, Seth and John Rodakis might want to pay a visit to the pharmacy and pick up some riluzole.  It is certainly worth investigating.

I did check and there is even a trial on Riluzole in autism and evidence of existing off-label use.  They have not of course made Agnieszka’s connection; they seem to be just trying it because nothing else seems to help. That really is trial and error and makes this blog look positively scientific by comparison.
Drug: Riluzole

50mg once daily (QD) for 12 weeks for participants 6-11 years old; 50mg twice daily (BID) for 12 weeks for participants 12-17 years old





A reformulation of riluzole that originated at Yale University and is known by the code name BHV-0223 is under development for the treatment of generalized anxiety disorder and mood disorders  by Biohaven Pharmaceuticals.

  
Anyway, are there any other ways to inhibit Glutamate?

Yes, our reader Valentine just stumbled on one, tizanidine, but there are at least two others. 


α2 adrenergic agonists

Three other known inhibitors of glutamate happen to be α2 adrenergic agonists

·        Clonidine

·        Guanfacine

·        Tizanidine


All three of the above are already used in ADHD and sometimes in autism, but not to reduce glutamate.

I wrote a post about Clonidine use in autism a long time ago.



Guanfacine is an ADHD drug known to inhibit glutamate release.



At five sites, children with ASD and moderate to severe hyperactivity were either given guanfacine or a placebo tablet for eight weeks, in a randomized and double-blind clinical trial. The research team collected information from parents and measured each child’s overall response. After eight weeks of treatment, extended release guanfacine was superior to placebo for decreasing hyperactivity and impulsiveness.


Our reader Valentina seems to have stumbled upon tizanidine, but finds it helpful for her son. Tizanidine is a α2 adrenergic agonists but also inhibits glutamate.  It is one of the drugs used off-label by Dr Chez in ADHD and autism




CONCLUSION:


The overall safety of tizanidine in the pediatric group appeared good; however, the adverse event profile differed from that in adults. This difference most likely reflects the off-label use of tizanidine as adjunctive treatment for attention disorders and autism. The frequency and nature of adverse events in adults were consistent with the tizanidine prescribing information as reported for its approved indication, i.e. management of spasticity.



Conclusion

Ideally you would have a comparison of the four drugs:


·        Riluzole

·        Tizanidine

·        Clonidine

·        Guanfacine


We know clonidine is not an autism wonder drug, but then what is?

I think Riluzole is likely to be a good one, but very likely what works best will vary from person to person.

Perhaps a positive response to beta-lactam (penicillin) antibiotics is a biomarker for people who will respond to Riluzole? It should be.