Myelination in the Central Nervous System (CNS) Oligodendrocyte myelinating multiple axons
The previous post on myelin was this one.
In that post we saw that you can activate P2X7 receptors with an antihistamine called Clemastine and you can block P2X7 with another cheap antihistamine called Oxatomide. The P2X7 receptor plays a role in both inflammation and myelination and this receptor appears to be linked to neurological disorders including schizophrenia and even depression.
In that post I also compared experimental MS therapies with experimental autism therapies.
The yellow box means, we know it works, at least for some people, based on trial results.
The widely available PDE4 inhibitor, Roflumilast, has been patented as a cognitive enhancer, but even at that lower dose it can make people vomit. Ibudilast seems to have fewer side effects and is under investigation in the US to treat MS, but is currently only approved in Japan and as an asthma therapy.
The logical next step is to investigate the two P2X7 modifying antihistamines, which should have opposing effects.
Oxatomide is widely used in Italy. Clemastine is OTC in the US and the UK.
I did some more investigation of Clemastine and came across some encouraging reports of off-label use in psychiatry at modest doses. Off label use to treat MS at high doses was associated with quite negative reports, due to the sedating effect, which is inevitable with antihistamines that can cross the blood brain barrier.
Today’s post goes into more detail about myelination and concludes with the open question of who might actually benefit from a half dose of clemastine, (Dayhist in the US, Tavegil in the UK); clearly some people do already benefit.
At least one US child psychiatrist is a fan and the research suggests many conditions might benefit, ranging from severe to more trivial. At 15-20 times higher dosage, clemastine is proposed as a therapy for Multiple Sclerosis (MS), but at that dosage clemastine is highly sedating. High dose clemastine might be a potential immediate response to the onset of regression in autism and CDD (Childhood Disintegrative Disorder).
Clemastine and Ibudilast have different modes of action. Clemastine works by activating P2X7 receptors in oligodendrocytes (in the CNS) and schwann cells (in the PNS) to make more myelin.
PDE4 inhibitors cause enhanced differentiation of OPCs (oligodendrocyte progenitor cells). OPC are precursors to oligodendrocytes.
So Roflumilast and Ibudilast should make more oligodendrocytes, while clemastine just kicks the ones you already have to work harder. So in any one person the effect of these two types of drug may very well differ.
Also, note that myelin needs to be constantly repaired in a process naturally called remyelination. So really we are just trying to benefit from improving this already existing repair service.
Some relevant background information:
“Myelination is only prevalent in a few brain regions at birth and continues into adulthood. The entire process is not complete until about 25–30 years of age. Myelination is an important component of intelligence. Neuroscientist Vincent J. Schmithorst proposes that there is a correlation with white matter and intelligence. People with greater white matter had higher IQs. A study done with rats by Janice M. Juraska showed that rats that were raised in an enriched environment had more myelination in their corpus callosum.
The role of myelin
Myelin has been compared to the insulation on electrical cables. If only it was that simple, there would not be so many genes involved in the process.
Nodes of Ranvier do matter
If you look at the above graphic of a neuron you will see gaps in the myelin, that are called Nodes of Ranvier.
The electrical signal does not pass along the axon like a piece of copper wire, rather it jumps from one Node of Ranvier to the next, in a process called saltatory conduction.
Also each subsequent piece of myelin along the length of an axon is connected to a different oligodendrocyte. Otherwise there would be no electrical conduction possible; there has to be a “potential difference” for a current to flow.
Each oligodendrocyte can be connected to 50 different pieces of myelin, many on different axons. Just imagine what that looks like; forget the spaghetti of cables connected to your TV, this is something really jumbled up.
If the electrical signal jumps to an adjacent axon rather than jumping along the same axon, there will be a problem.
If there is too much myelin produced you might squeeze out the node of Ranvier and then the signal cannot pass along to the next neuron.
Myelination Defects in Autism
We have already seen in previous posts that myelination is often found to be abnormal in autism.
A very thorough recent study looked at myelination in a number of single gene autisms. The conclusion was that in these very different types of autism there was a common theme of defective myelination.
This adds further weight to the idea of considering impaired myelination a key feature of much autism.
Loss of myelination has been suggested to be a core feature of regressive autism and I propose a very likely driver of Childhood Disintegrative Disorder (CDD).
“Improving myelination” rather than simply “more myelination” might well be very helpful to many types of severe autism. It seems that even in much milder neurological conditions improving myelination can be therapeutic.
The usual target of experimental myelination therapies is Multiple Sclerosis (MS), it may also be the hardest to treat.
Some researchers and clinicians are repurposing MS therapies for other neurological disorders, either in mouse models or in humans. This seems like a very good idea to me.
One Sentence Summary: RNA sequencing of seven syndromic autism mouse models identify myelination genes disrupted in human ASD.
Autism Spectrum Disorder (ASD) is genetically heterogeneous in nature with convergent symptomatology, suggesting dysregulation of common molecular pathways. We analyzed transcriptional changes in the brains of five independent mouse models of Pitt-Hopkins Syndrome (PTHS), a syndromic ASD caused by autosomal dominant mutation in TCF4, and identified considerable overlap in differentially expressed genes (DEGs). Gene and cell-type enrichment analyses of these DEGs identified oligodendrocyte dysregulation that was subsequently validated by decreased protein levels. We further showed significant enrichment of myelination genes was prevalent in two additional mouse models of ASD (Ptenm3m4/m3m4, Mecp2KO). Moreover, we integrated syndromic ASD mouse model DEGs with ASD risk-gene sets (SFARI) and human idiopathic ASD postmortem brain RNA-seq and found significant enrichment of overlapping DEGs and common biological pathways associated with myelination and oligodendrocyte differentiation. These results from seven independent mouse models are validated in human brain, implicating disruptions in myelination is a common ASD pathophysiology.
To address these questions, we performed integrative transcriptomic analyses of seven independent mouse models of three syndromic forms of ASD generated across five laboratories, and assessed dysregulated genes and their pathways in human postmortem brain from patients with ASD and unaffected controls. These cross-species analyses converged on shared disruptions in myelination and axon development across both syndromic and idiopathic ASD, highlighting both the face validity of mouse models for these disorders and identifying novel convergent molecular phenotypes amendable to rescue with therapeutics.
Shared myelination gene regulation between mouse models of syndromic ASD. Venn diagram of DEGs (differentially expressed genes) in each mouse model of ASD
Top GO (Gene ontology) terms of the CAGs (convergent ASD genes) enrich for myelination processes
P2X purinoceptor 7 is a protein that in humans is encoded by the P2RX7 gene.
The product of this gene belongs to the family of purinoceptors for ATP. Multiple alternatively spliced variants which would encode different isoforms have been identified although some fit nonsense-mediated decay criteria.
The receptor is found in the central and peripheral nervous systems, in microglia, in macrophages, in uterine endometrium, and in the retina. The P2X7 receptor also serves as a pattern recognition receptor for extracellular ATP-mediated apoptotic cell death, regulation of receptor trafficking, mast cell degranulation, and inflammation.
Our findings point to P2X7R as a potential therapeutic target in schizophrenia.
The P2X7 purinergic receptor: An emerging therapeutic target in cardiovascular diseases
The P2X7 purinergic receptor, a calcium permeable cationic channel, is activated by extracellular ATP. Most studies show that P2X7 receptor plays an important role in the nervous system diseases, immune response, osteoporosis and cancer. Mounting evidence indicates that P2X7 receptor is also associated with cardiovascular disease. For example, the P2X7 receptor activated by ATP can attenuate myocardial ischemia-reperfusion injury. By contrast, inhibition of P2X7 receptor decreases arrhythmia after myocardial infarction, prolongs cardiac survival after a long term heart transplant, alleviates the dilated cardiomyopathy and the autoimmune myocarditis process. The P2X7 receptor also mitigates vascular diseases including atherosclerosis, hypertension, thrombosis and diabetic retinopathy. This review focuses on the latest research on the role and therapeutic potential of P2X7 receptor in cardiovascular diseases.
Clemastine is an extracellularly binding allosteric P2X7 receptor modulator.
Clemastine can potentiate the sensitivity of P2X7 to lower ATP concentrations. Additionally, clemastine increases the release of IL-1β from macrophages. Thus, clemastine may be a potential P2X7 activator.
Brain ischemia leading to stroke is a major cause of disability in developed countries. Therapeutic strategies have most commonly focused on protecting neurons from ischemic damage. However, ischemic damage to white matter causes oligodendrocyte death, myelin disruption, and axon dysfunction, and it is partially mediated by glutamate excitotoxicity. We have previously demonstrated that oligodendrocytes express ionotropic purinergic receptors. The objective of this study was to investigate the role of purinergic signaling in white matter ischemia. We show that, in addition to glutamate, enhanced ATP signaling during ischemia is also deleterious to oligodendrocytes and myelin, and impairs white matter function. Thus, ischemic oligodendrocytes in culture display an inward current and cytosolic Ca(2+) overload, which is partially mediated by P2X7 receptors. Indeed, oligodendrocytes release ATP after oxygen and glucose deprivation through the opening of pannexin hemichannels. Consistently, ischemia-induced mitochondrial depolarization as well as oxidative stress culminating in cell death are partially reversed by P2X7 receptor antagonists, by the ATP degrading enzyme apyrase and by blockers of pannexin hemichannels. In turn, ischemic damage in isolated optic nerves, which share the properties of brain white matter, is greatly attenuated by all these drugs. Ultrastructural analysis and electrophysiological recordings demonstrated that P2X7 antagonists prevent ischemic damage to oligodendrocytes and myelin, and improved action potential recovery after ischemia. These data indicate that ATP released during ischemia and the subsequent activation of P2X7 receptor is critical to white matter demise during stroke and point to this receptor type as a therapeutic target to limit tissue damage in cerebrovascular diseases.
Clemastine as a practical intervention
I came across a discussion among MS sufferers and a specific comment from a US child psychiatrist that drew my attention.
Daniel Kerlinsky says: september 1 1, 2018 at 123 AM
Clemastine is a highly effective medication for re-myelination of white matter fiber bundles that connect neurons everywhere in the brain.
High doses aren't needed. One quarter of a 2.68 mg tablet is enough to start recruiting new oligodendrocytes to start making and applying myelin.
It does not have to be taken every day; it can be taken twice a week and still have a positive effect by recruiting the worker cells that repair the brain.
Remember normal myelination starts at the top of the brain and works downward during childhood development. At first the baby can't hold its head up, then it can sit up, then crawl, then stand.
Many MS lesions are located further down inside the brain and spinal cord so it takes time to get there.
The anti-inflammatory Minocycline taken once or twice a week is needed to stop the inflammatory part of the disease.
And it takes cranio-sacral therapy to take full advantage of the new myelin which plumps the brain and even lubricates stiff joints like the sphenoid-occipital junction.
Don't give up on clemastine.
Its first and most obvious effect is improved emotional self regulation. Because myelination increases the speed of information processing ten-fold you will notice that thinking better comes next.
I can't tell you how long it will take to notice a difference. But the MS patient who told me about Clemastine got up out of her electric wheel chair and walked down the hall and back without a walker or her canes for the first time in two years.
It works great for kids with tantrums and developmental problems in about a month. It helps people with chronic depression and PTSD in about three months.
Back your dose down to 1.34 mg or 0.67 mg and give it two years. It takes a toddler that long.„
Increasing evidence suggests that white matter disorders based on myelin sheath impairment may underlie the neuropathological changes in schizophrenia. But it is unknown whether enhancing remyelination is a beneficial approach to schizophrenia. To investigate this hypothesis, we used clemastine, an FDA-approved drug with high potency in promoting oligodendroglial differentiation and myelination, on a cuprizone-induced mouse model of demyelination. The mice exposed to cuprizone (0.2% in chow) for 6 weeks displayed schizophrenia-like behavioral changes, including decreased exploration of the center in the open field test and increased entries into the arms of the Y-maze, as well as evident demyelination in the cortex and corpus callosum. Clemastine treatment was initiated upon cuprizone withdrawal at 10 mg/kg per day for 3 weeks. As expected, myelin repair was greatly enhanced in the demyelinated regions with increased mature oligodendrocytes (APC-positive) and myelin basic protein. More importantly, the clemastine treatment rescued the schizophrenia-like behavioral changes in the open field test and the Y-maze compared to vehicle, suggesting a beneficial effect via promoting myelin repair. Our findings indicate that enhancing remyelination may be a potential therapy for schizophrenia.
Altered myelin structure and oligodendrocyte function have been shown to correlate with cognitive and motor dysfunction and deficits in social behavior. We and others have previously demonstrated that social isolation in mice induced behavioral, transcriptional, and ultrastructural changes in oligodendrocytes of the prefrontal cortex (PFC). However, whether enhancing myelination and oligodendrocyte differentiation could be beneficial in reversing such changes remains unexplored. To test this hypothesis, we orally administered clemastine, an antimuscarinic compound that has been shown to enhance oligodendrocyte differentiation and myelination in vitro, for 2 weeks in adult mice following social isolation. Clemastine successfully reversed social avoidance behavior in mice undergoing prolonged social isolation. Impaired myelination was rescued by oral clemastine treatment, and was associated with enhanced oligodendrocyte progenitor differentiation and epigenetic changes. Clemastine induced higher levels of repressive histone methylation (H3K9me3), a marker for heterochromatin, in oligodendrocytes, but not neurons, of the PFC. This was consistent with the capability of clemastine in elevating H3K9 histone methyltransferases activity in cultured primary mouse oligodendrocytes, an effect that could be antagonized by cotreatment with muscarine. Our data suggest that promoting adult myelination is a potential strategy for reversing depressive-like social behavior.
SIGNIFICANCE STATEMENT Oligodendrocyte development and myelination are highly dynamic processes influenced by experience and neuronal activity. However, whether enhancing myelination and oligodendrocyte differentiation is beneficial to treat depressive-like behavior has been unexplored. Mice undergoing prolonged social isolation display impaired myelination in the prefrontal cortex. Clemastine, a Food and Drug Administration-approved antimuscarinic compound that has been shown to enhance myelination under demyelinating conditions, successfully reversed social avoidance behavior in adult socially isolated mice. This was associated with enhanced myelination and oligodendrocyte differentiation in the prefrontal cortex through epigenetic regulation. Thus, enhancing myelination may be a potential means of reversing depressive-like social behavior.
BACKGROUND:
Multiple sclerosis is a degenerative inflammatory disease of the CNS characterised by immune-mediated destruction of myelin and progressive neuroaxonal loss. Myelin in the CNS is a specialised extension of the oligodendrocyte plasma membrane and clemastine fumarate can stimulate differentiation of oligodendrocyte precursor cells in vitro, in animal models, and in human cells. We aimed to analyse the efficacy and safety of clemastine fumarate as a treatment for patients with multiple sclerosis.
METHODS:
We did this single-centre, 150-day, double-blind, randomised, placebo-controlled, crossover trial (ReBUILD) in patients with relapsing multiple sclerosis with chronic demyelinating optic neuropathy on stable immunomodulatory therapy. Patients who fulfilled international panel criteria for diagnosis with disease duration of less than 15 years were eligible. Patients were randomly assigned (1:1) via block randomisation using a random number generator to receive either clemastine fumarate (5·36 mg orally twice daily) for 90 days followed by placebo for 60 days (group 1), or placebo for 90 days followed by clemastine fumarate (5·36 mg orally twice daily) for 60 days (group 2). The primary outcome was shortening of P100 latency delay on full-field, pattern-reversal, visual-evoked potentials. We analysed by intention to treat. The trial is registered with ClinicalTrials.gov, number NCT02040298.
FINDINGS:
Between Jan 1, 2014, and April 11, 2015, we randomly assigned 50 patients to group 1 (n=25) or group 2 (n=25). All patients completed the study. The primary efficacy endpoint was met with clemastine fumarate treatment, which reduced the latency delay by 1·7 ms/eye (95% CI 0·5-2·9; p=0·0048) when analysing the trial as a crossover. Clemastine fumarate treatment was associated with fatigue, but no serious adverse events were reported.
INTERPRETATION:
To our knowledge, this is the first randomised controlled trial to document efficacy of a remyelinating drug for the treatment of chronic demyelinating injury in multiple sclerosis. Our findings suggest that myelin repair can be achieved even following prolonged damage.
Drug: Clemastine
12mg (4mg 3x/day) clemastine for 7 days followed by 8mg clemastine (4mg 2x/day) until 3 months. Patients will be off treatment from 3-9 months and will be reevaluated at 9 months.
Hopefully this post takes us one step closer to finding safe, side effect free, inexpensive ways to improve myelination in those with impaired myelination.
In the case of treating Multiple Sclerosis (MS), side effects clearly remain an issue. The suggestion of the psychiatrist in today’s post is to just lower the clemastine dosage and give it some time (2 years). That sounds like smart advice to me.
Fortunately, it appears that in less severe cases of impaired myelination you may not need to wait 2 years.
Who exactly is going to benefit remains an open question, but for people already using H1 antihistamines to treat allergy, or other mast cell activation, switching to a different OTC antihistamine drug does not look like such a big step to take.
People with schizophrenia and allergy also might want to consider switching their antihistamine.
Undoubtedly some people will have the opposite issue with P2X7 receptors and for them there is another old antihistamine drug called Oxatomide.
