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.
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.
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:
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.