Much of this
blog to date has been connected with aspects related to the neurotransmitter
GABA. It did get rather complicated, but
at least for me, it has been highly rewarding. I have identified treatable
dysfunctions in Monty, aged 10 with ASD, using Bumetanide and now Clonazepam.
It is also
clear that a group of people with autism also benefit from treatment with
R-baclofen, a potent GABAB receptor agonist.
R-baclofen/Arbaclofen and Arbaclofen Placarbil are not commercially available. The commercially available drug Baclofen
contains R-Baclofen and another substance that, in-effect, works to oppose it and so may be much less effective.
Based on the
successful results of this investigation into GABA-related interventions, it
would therefore make sense to look in detail at Glutamate, the other
neurotransmitter that appears to be dysfunctional in many types of autism.
As with GABA
dysfunctions, there are already are some existing treatments for glutamate
dysfunctions.
While many
researchers have concluded that glutamate is implicated in autism, some think,
in effect, there is too much and some think there is too little. Since we have learnt that in fact within “autism”
are many discrete diseases, both groups of researchers might be right.
In other
types of neurological disorders glutamatergic modulators
are an emerging therapy and there are many ongoing clinical trials. Off-label, some of these therapies have been
used for decades. In autism there have
been some trials over the years, but as seems to be often the case, they are
not followed up to a final undisputed conclusion. This may be about to change.
Yet again, the
mineral Magnesium appears and there is yet another possible explanation for its
apparent positive impact, in some cases of autism.
I imagine
that under the umbrella diagnosis of autism, there are those who have a GABA
dysfunction and there are those that have a Glutamate dysfunction. Just to complicate matters, if there is Serotonin
dysfunction, this will affect both GABA and Glutamate. So everything is inter-related and nothing is
simple. Fortunately,
in medicine, trial and error is a long trusted technique and “stumbled upon” is still
a satisfactory explanation; we do not need to understand things 100%.
First we
have to look at the terminology and in doing so we stumble upon a novel
hypothesis as to what caused autism in the first place, which occurred to me
today, but back in 2007 at the University of Mississippi.
Glutamate
Glutamate is the most abundant excitatory neurotransmitter.
Glutamate is involved in cognitive functions like learning and memory in the
brain. Too much glutamate can be
extremely bad for you and research shows it leads to neuronal death, mental
retardation and indeed autism.
So called Glutamate transporters remove
glutamate from the extracellular space. In brain injury or disease, they can
work in reverse, and excess glutamate can accumulate outside cells. This
process causes calcium ions to enter cells via NMDA receptor channels, leading
to neuronal damage and eventual cell death;
this is called excitotoxicity.
So it is plausible that the root cause of the autism is actually a
dysfunction of one of the glumate transporters.
The calcium ions are just the messenger.
There are 4 types of glutamate transporter. When there is a dysfunction the
following is known to happen:-
·
Over activity of glutamate transporters may
result in inadequate synaptic glutamate and may be involved in schizophrenia
and other mental illnesses
·
During injury processes such as ischemia and traumatic brain injury, the action
of glutamate transporters may fail, leading to toxic buildup of glutamate.
·
Loss of the Na+-dependent
glutamate transporter EAAT2 is suspected to be associated with
neurodegenerative diseases such as Alzheimer's disease
Excessive glumate release
Excitotoxicity due to excessive glutamate release and impaired uptake
occurs as part of the ischemic
cascade and is associated with stroke, autism, some forms of intellectual
disability, and diseases like Alzheimer's disease.
Epilepsy and Calcium Channels
Glutamic acid has been implicated in epileptic seizures.
Microinjection of glutamic acid into neurons produces spontaneous depolarisations
around one second apart, and this firing pattern is similar to what is known as
paroxysmal depolarizing shift in epileptic attacks. This change in the resting membrane potential at
seizure foci could cause spontaneous opening of voltage-activated calcium channels, leading to glutamic acid release and further
depolarization
Too much or too little Glutamate
Activity?
Studies propose both hyper-and hypoglutamatergic ideologies for autism.
You may be
thinking that somebody is clearly wrong here, but it is not so simple. We will see later, when we get to the clever
people at MIT, that in fact both views may be correct; in some people their
autism is improved by inhibiting the specific receptor (mGluR5) and in other
people by exciting the same receptor.
GABA & GAD
Glutamate also serves as the precursor for the synthesis of the inhibitory gamma-aminobutyric
acid (GABA) in GABA-ergic neurons. This reaction is catalyzed by glutamate decarboxylase (GAD),
which is most abundant in the cerebellum and pancreas.
GAD is interesting in itself. There
are two types, GAD67 and GAD65
It appears that anti-GAD antibodies are the trigger that leads to
diabetes. Since the pancreas has
abundant GAD, a direct immunological destruction occurs in the pancreas and the
patients will have developed diabetes.
Diabetes
Both GAD67 and GAD65
are targets of autoantibodies in people who later develop type 1 diabetes
or latent autoimmune diabetes. Injections
with GAD65 has been shown to preserve some insulin production for 30
months in humans with type 1 diabetes
Schizophrenia and bipolar disorder
Substantial dysregulation of GAD mRNA
expression, coupled with down regulation of reelin, is observed in schizophrenia
and bipolar disorder. The most pronounced down regulation of GAD67 was found in
hippocampal stratum oriens layer in both disorders.
Parkinson disease
The bilateral delivery of GAD by an adeno-associated viral vector into the
subthalamic nucleus of patients between 30 and 75 years of age with advanced,
progressive, levodopa-responsive Parkinson disease resulted in significant
improvement over baseline during the course of a six-month study
Cerebellar disorders
Intracerebellar administration of GAD
autoantibodies to animals increase the excitability of motoneurons and impairs
the production of nitric oxide (NO), a molecule involved in learning. Epitope
recognition contributes to cerebellar involvement
Stiff Person Syndrome
Anti-GAD antibodies are associated with Stiff-person syndrome but their
causal role is not yet established.
We have seen before that comorbidities of autism can point us in the right
direction and also that many mental health / neurological disorders are overlapping.
So is not a surprise that a GAD dysfunction also exists in autism:-
“This suggests a disturbance in
the intrinsic cerebellar circuitry in the autism group potentially interfering
with the synchronous firing of inferior olivary neurons, and the timing of
Purkinje cell firing and inputs to the dentate nuclei. Disturbances in critical
neural substrates within these key circuits could disrupt afferents to motor
and/or cognitive cerebral association areas in the autistic brain likely
contributing to the marked behavioral consequences characteristic of autism.
Both GAD isoforms have been shown
to be affected in a variety of psychiatric and developmental disorders. GAD67
has been implicated in schizophrenia, bipolar disorder, major depression
disorder, and autism.
In animal studies, GAD65 is
strongly implicated in anxiety.
Clinical research indicates that
discrete cerebellar lesions, in otherwise healthy children, cause behavioral
and/or cognitive impairments. In autism, however, cerebellar pathology is
likely acquired during critical developmental period(s) when the brain is
capable of constructing alternate innervation patterns. It is thus possible that there is a “miswiring” of
key circuits in the autistic cerebellum with a developmental basis persisting
into adulthood”
We see again
a form of self-destruction. With
arthritis the body destroys its joints and with diabetes, the pancreas is
(partially) destroyed.
From the
research it would appear that low levels of GAD67 and GAD65 played a critical
role in the process that initiated the brain damage that led to autism. Perhaps the low levels are the result of GAD
antibodies.
GAD antibodies test as a predictor
There is a
widely available of a GAD antibodies test.
Because diabetes is so common, it is also well researched.
So now back
to autism. Now, I am thinking that maybe
pregnant mothers might have high levels of GAD antibodies and this might be
passed on to the developing fetus, potentially causing brain damage (autism) or
perhaps diabetes later in life. Well,
somebody has already come to the same conclusion.
“Conclusions
Studies of serum GAD-Abs in autism are warranted but
have not been done so far. Positive findings would stimulate the development of
specific prenatal diagnostic markers and therapeutics that may involve maternal
administration of immunosuppressants to prevent the development
of
autism or intravenous immunoglobulins therapy in
children with emerging autistic symptoms.”
This again
points towards immunomodulation as a therapy, this time for the mother. Such treatment, in mothers with high GAD-Abs
(GAB antibodies) might lead to a reduction is in cases of autism and indeed diabetes
(type 1).
In the case of children and adults with autism,
treatment with GAD65 or GAD67 might be effective, or it might just be too late
to do any good. This would be worthy of
study.
Glutamate receptors
Glutamate receptors are responsible for the glutamate-mediated excitation
of neural cells, and are important for neural communication, memory formation, learning,
and regulation.
Glutamate receptors are implicated in a number of neurological conditions.
Their central role in excitotoxicity and prevalence in the central nervous
system has been linked or speculated to be linked to many neurodegenerative
diseases, and several other conditions have been further linked to glutamate
receptor gene mutations.
There are
four types of glumate receptors.
The first
three types are Ionotropic,
and by definition, are ligand-gated nonselective cation channels that allow the flow of K+, Na+ and sometimes
Ca2+ in response to glutamate binding. Upon binding, the agonist will stimulate
direct action of the central pore of the receptor, an ion channel, allowing ion
flow and causing excitatory postsynaptic current (EPSC). This current is
depolarizing and, if enough glutamate receptors are activated, may trigger an
action potential in the postsynaptic neuron
These receptors are involved in Ca2+ and K+ ion channels and varying the
concentration of Ca2+ and K+
Glutamate binding to the
extracellular region of an mGluR causes G proteins bound to the intracellular
region to be phosphorylated, affecting multiple biochemical pathways and ion
channels in the cell. Because of this, mGluRs can both increase or decrease the
exitability of the postsynaptic cell, thereby causing a wide range of
physiological effects.
Selected Conditions associated with
Glumate Receptors (source Wikipedia)
Attention
deficit hyperactivity disorder (ADHD)
In 2006 the glutamate receptor subunit gene GRIN2B
(responsible for key functions in memory and learning) was associated with
ADHD. This followed earlier studies
showing a link between glutamate modulation and hyperactivity.
Further mutations to four different metabotropic glutamate receptor genes
were identified in a study of 1013 paediatric ADHD patients compared to 4105
non-ADHD controls, replicated in a subsequent study of 2500 more patients.
Deletions and duplications affected GRM1, GRM5, GRM7 and GRM8. The study
concluded that "CNVs affecting
metabotropic glutamate receptor genes were enriched across all cohorts (P = 2.1
× 10−9)", "over 200 genes interacting with glutamate receptors were
collectively affected by CNVs", "major hubs of the (affected genes')
network include TNIK50, GNAQ51, and CALM", and "the fact that
children with ADHD are more likely to have alterations in these genes
reinforces previous evidence that the GRM pathway is important in ADHD".
In 2012 UPenn and MIT
teams have independently converged on mGluRs as players in ADHD and autism. The
findings suggest agonizing mGluRs in patients with ADHD or certain forms of
autism and antagonizing the targets in other forms of autism
Although the precise molecular basis of the interaction remains to be
determined, the data show unambiguously that mGluR5 and FMRP act as an opponent
pair in several functional contexts, and support the theory that many CNS
symptoms in fragile X are accounted for by unbalanced activation of Gp1 mGluRs.
These findings have major therapeutic implications for fragile X syndrome and
autism.
Autism
The etiology of autism may include excessive glutaminergic mechanisms.
A link between glutamate receptors and autism was also identified via the structural
protein ProSAP1/SHANK2 and
potentially ProSAP2/SHANK3. The study
authors concluded that the study "illustrates the significant role
glutamatergic systems play in autism" and "By comparing the data on
ProSAP1/Shank2−/− mutants with ProSAP2/Shank3αβ−/− mice,
we show that different abnormalities in synaptic glutamate receptor expression
can cause alterations in social interactions and communication. Accordingly, we
propose that appropriate therapies for autism spectrum disorders are to be
carefully matched to the underlying synaptopathic phenotype.
Seizures
Glutamate receptors have been discovered to have a role in the onset of
epilepsy. NMDA and metabotropic types have been found to induce epileptic
convulsions. Using rodent models, labs have found that the introduction of
antagonists to these glutamate receptors helps counteract the epileptic
symptoms. Since glutamate is a ligand
for ligand-gated ion channels, the binding of this neurotransmitter will open
gates and increase sodium and calcium conductance. These ions play an integral
part in the causes of seizures. Group 1 metabotropic glutamate receptors (mGlu1
and mGlu5) are the primary cause of seizing, so applying an antagonist to these
receptors helps in preventing convulsions.
Current
and Future interventions
The possible
interventions that follow from what we have learnt would appear to be:-
1. Targeting NMDA glutamate receptor
function
2. Targeting mGluRs (metabotropic
glutamate receptors)
3. Targeting glutamate transporters
4. GAD therapy
There would
seem to be four possible areas of intervention.
The first one is to target the NMDA glutamate receptors using existing
drugs and other three are cleverer, but only possible using experimental drugs.
Very few pharmacological
tools are currently available to investigate glumate transporter (EAAT)
function and to then consider these transporters as therapeutic targets, but even that is
beginning to change. Here is a Glutamate Transporter Inhibitor:-
"Neurologix's gene therapy
approach to PD aims to reset the overactive brain cells to inhibit electrical
activity and return brain network activity to more normal levels. The strategy
involves restoring GABA and thus improving the patient's motor control by using
an AAV vector (a disabled, non-pathogenic virus) to deliver the GAD gene back
into the STN (subthalamic nucleus). Increasing GAD causes more GABA to be
synthesized, thus helping to calm the STN over-activity."
They are
calling it gene therapy for PD; I would call it GAD therapy. I think GAD therapy might well be effective
in some types of autism.
mGluRs
Targeting mGluRs is very much associated with a
researcher called Mark Bear at MIT. We
came across him earlier in this blog, since he is also the man behind
Arbaclofen, at Seaside Therapeutics.
This research is very recent and is linked to Fragile
X. Here is a PhD thesis written in 2013
by one of Mark Bear’s students, which seems to sum things up.
If you can follow my blog, you
can definitely follow his thesis. In
effect, what he is saying is that errors in synaptic protein synthesis are
behind several types of autism and that these errors can be corrected using
either positive or negative stimulators of the receptor mGluR5. It is clear that at Bear Lab, they view all
autisms as part of a family, rather than discrete disorders.
This would imply that positive
allosteric modulators and negative allosteric modulators of MGluR5 are
potentially effective autism treatments.
Another name would be MGluR5 agonist/antagonist. Such drugs are already under study in both
autism and other conditions. Here are
two examples.
Seaside Therapeutics, Roche and
Novartis have each developed therapeutic compounds targeting the mGluR5 pathway.
Roche is developing RG7090, an
inhibitor of mGluR5 that is currently in clinical trials. CTEP is a mouse
version of RG7090. One dose of CTEP,
which can be taken orally, deactivates most mGLuR5 receptors in the brain for
about 48 hours.
A single dose
of CTEP is enough to reverse the same features of fragile X syndrome — such as
an overproduction of proteins in the brain and susceptibility to seizures — as
those treated by previous mGLuR5 inhibitors. It also corrects a process that
allows neurons to change the strength of their connections in response to
learning.
It took four weeks of continued
treatment to see improvements in the behavioral features of the syndrome,
including sensory sensitivities and problems with learning and memory.
Fenobam is an existing inhibitor of mGluR5, developed in the
1970s. It was trialed in Fragile X in
2009 with good results using just a single dose.
“In summary, this trial did not
find major safety concerns to a single administration of fenobam in FXS, and
suggested that clinical improvements in behaviour and PPI may be seen even
after a single dose. This would indicate that placebo controlled trials of
fenobam and other mGluR5 antagonists involving longer term treatment of
individuals with FXS should be considered to investigate whether rescue of the
FXS phenotype observed in animal models can be extended to humans.”
The current
interventions are mainly NDMA receptor antagonists and are based on that
trusted medical approach called trial and error, rather than the Bear Lab
approach . The drugs are:-
·
Ketamine
·
Memantine,
·
D-Cycloserine
·
Magnesium
·
Fenobam (mGluR5 inhibitor – see above, not FDA
approved)
Chemicals that deactivate the NMDA receptor are called
antagonists. NMDAR antagonists fall into four categories:
-
noncompetitive
antagonists, which inhibit NMDARs by binding to allosteric sites
Uncompetitive
antagonists, which block the ion channel by binding to a site within it
glycine
antagonists, which bind to and block the glycine site
Ketamine is
a non-competitive antagonist. It has recently been in the headlines for
having a remarkable effect in some cases of depression.
In large
doses it is used as an anaesthetic particularly in children and pet
animals. It is also used as a
recreational drug “Special K”, which is why it is a controlled substance.
In small
doses the intra-nasal route is favoured.
In effect the vial of ketamine normally administered by injection is
diluted with a saline solution and put in a standard metered dose nasal
spray. It is also possible to make eye
drops the same way. The nasal/eye route
is effective since the drug can enter the bloodstream without the need for an
injection or a very ineffective oral tablet.
A study is
underway in Cincinnati to test intranasal ketamine on adults with autism.
Dr. Logan Wink, Cincinnati
Children's Hospital
Start Date: 11/2013
In
a human clinical trial with 24 adults with Autism, researchers at the
Cincinnati Children’s Hospital will conduct a pilot double-blind placebo
controlled study of intranasal ketamine in adults with ASD using novel
quantitative outcome measures of social and communication impairment.
Ketamine
has a unique drug profile clearly differentiated from other glutamatergic
modulators (drugs that support the glutamate receptors) studied in ASD to date.
This profile, coupled with ketamine’s long safety track record and novel
intranasal (IN) delivery system, make ketamine worthy of drug investigation for
treatment of the core features of ASD. As a generically available inexpensive
drug, ketamine holds significant promise to widely treat the core social and
communication impairments that are the hallmark of ASD. The results of this
study, if positive, would support the use of a drug with a demonstrated safety
profile that is cost-effective to use.
If
this pilot project demonstrates efficacy and tolerability of IN ketamine, the
next steps will include the following. 1) Design and obtain funding for a large
phase II placebo controlled trial of ketamine in adults with ASD. 2) Design a
pilot study of ketamine in children with ASD. 3) Publish the data on the pilot
study for other researchers and clinicians to use to support patients with ASD.
Memantine is
an uncompetitive agonist. It has a modest effect in
moderate-to-severe Alzheimer's disease.
It has been around for a long time, having been first synthesized in
1968.
There are two other Alzheimer’s drugs that seem to be
helpful in some types of autism. They
are Donepezil (Aricept) and
Galantamine They are both
centrally acting reversible acetylcholinesterase inhibitors. So they work in an entirely different way to Memantine.
There have
been several trials of Memantine in autism over the years. Recently the producer, Forest Laboratories
have been intensive trials to show its effectiveness and safety in childhood
autism.
In 2007
Michael Chez carried out a study:-
Open-label add-on therapy was
offered to 151 patients with prior diagnoses of autism or Pervasive
Developmental Disorder Not Otherwise Specified over a 21-month period. To
generate a clinician-derived Clinical Global Impression Improvement score for
language, behavior, and self-stimulatory behaviors, the primary author observed
the subjects and questioned their caretakers within 4 to 8 weeks of the
initiation of therapy. Chronic maintenance therapy with the drug was continued
if there were no negative side effects. Results showed significant improvements
in open-label use for language function, social behavior, and self-stimulatory
behaviors, although self-stimulatory behaviors comparatively improved to a
lesser degree. Chronic use so far appears to have no serious side effects.
Autism
speaks have funded studies:-
Even the
Iranians have been trialing it, but as usual as an adjunct therapy.
Forest
Laboratories have a series of trials underway of Memantine in autism
D-Cycloserine is a glycine antagonist.
Its main use is as an antibiotic for treating drug resistant TB. It is also used to treat drug addiction and
social anxiety disorder.
It has been investigated in both mouse models of autism
and in humans.
Abstract
OBJECTIVE: The authors assessed the effects of d-cycloserine on the core symptom of social impairment in
subjects with autism. METHOD: Following a 2-week, single-blind placebo
lead-in phase, drug-free subjects with autistic disorder were administered three
different doses of d-cycloserine
during each of three 2-week periods. Measures used for subject ratings included
the Clinical Global Impression (CGI) scale and Aberrant Behavior Checklist. RESULTS:
Significant improvement was found on the CGI and social withdrawal subscale
of the Aberrant Behavior Checklist. d-Cycloserine
was well tolerated at most of the doses used in this study. CONCLUSIONS: In this pilot study, d-cycloserine treatment resulted in
significant improvement in social withdrawal. Further controlled studies of d-cycloserine in autism appear
warranted.
Direct stimulation
of NMDARs with D-cycloserine, a
partial agonist of NMDARs, normalizes NMDAR function and improves social
interaction in Shank22/2 mice.
These results
suggest that reduced NMDAR function may contribute to the development of
ASD-like phenotypes in Shank22/2 mice, and mGluR modulation of NMDARs offers a
potential strategy to treat ASD.
Magnesium
Magnesium is
an uncompetitive NMDA channel blocker. As you can see below on the diagram of the NMDA receptor site (source Wikipedia)
1. Cell membrane
2. Channel blocked by Mg2+ at the block site (3)
3. Block site by Mg2+
4. Hallucinogen compounds binding site
5. Binding site for Zn2+
6. Binding site for agonists(glutamate) and/or antagonist ligands(APV)
7. Glycosilation sites
8. Proton biding sites
9. Glycine binding sites
10. Polyamines binding site
11. Extracellular space
12. Intracellular space
Magnesium seems to have a therapeutic
effect in some types of autism. There
are several possible reasons why this might be and these have been covered in
earlier posts. The idea of using
magnesium to block dysfunctional NMDA receptors is intriguing. It is clear from the graphic that the
receptor has evolved with this specifically in mind.
There are two simple ways to raise the
concentration of magnesium, one is orally and the other is trans-dermally. A problem with the oral route is that magnesium
tends to upset the stomach and that is why it is used as laxative.
The clever transdermal route is take a
bath in Epsom salts (MgSO4) this will raise the level of magnesium
(also sulphate).
Many people take such baths to feel
better and look better, but be aware they also will reduce your blood
pressure. Some celebrities claim to take
a daily bath in Epsom salts.
While some parents report that their
child with ASD has behavioral improvements after an Epsom salt bath, in Monty,
aged 10 with ASD, the reverse is true.
It does not make him calm, it agitates him.
Since it is cheap and widely available,
an Epsom salt bath is not a bad thing to try.
Maybe it helps and maybe it will not; you will only know by trying.
Conclusion
Most likely in some subtypes of autism
there is too much (hyper-function) glutamate activity, in some subtypes there
is too little (hypo-function) and in other sub-types glutamate function is not
impaired at all. This is again saying
that sub-types are different diseases.
For the time being, the only therapy would
be one of trial and error with existing drugs.
Intranasal ketamine therapy is
intriguing, but this might be hard to get hold of unless you are in a clinical
trial, or your neighbour is a vet.
“I have had very good success using ketamine eye drops in
varying dilutions from 1:100 down to 1:5. Some of the responses have been quite
remarkable. I also make ketamine nasal spray 1:25 and 1:10 and monitor its use
because of a slight potential for abuse.”
Dr Jay Goldstein, treating various neurological disorders
Memantine has now been trialed in over 1,000 children. If it was highly effective in a large percentage of people, I think we would have heard about it. It looks to be the "wrong" Alzheimer's drug , the other two, Donepezil and Galantamine seem more beneficial for ASD.
One long-existing mGluR5 inhibitor, Fenebam, has
already been trialed on people with Fragile X.
Until other drugs are developed, I wonder why this drug has been
forgotten.
In the
medium term, the new mGluR5 positive and negative modulators look like they may
be able to address core defects in some sub-types of autism. This would be a case where hard science and
medicine really did work as they should (i.e. together).
I would put my money on this being the most effective Glutamate-related
therapy.
I personally like to look for the route
cause, as far back up the chain of events as possible, to where the trouble
began, and that might point to GAD therapy, but that is far in the future.
