Another Potential Autism Therapy - novel compound E100 from Krakow, a combined histamine H3 receptor blocker (H3R antagonist) and an acetylcholine esterase inhibitor (AChEI)

 

Source:  Sukiennice and Main Square as seen from St. Mary's Basilica

Krakow’s old town is well worth a visit and is notable in Poland for not having been destroyed by the Germans, Russians or the US/UK during World War 2

 

Brain histamine and acetylcholine are implicated in cognitive disorders such as Alzheimer’s, schizophrenia, anxiety, and narcolepsy, all of which are found to be comorbid with autism.  This led a group in the United Arab Emirates (UAE) to test a new compound developed in Krakow, Poland, to see if this new Alzheimer’s compound is effective in two different models of autism. 

The Valproic Acid induced model of autism and the BTBR models were chosen.  The BTBR model is seen as a proxy for idiopathic autism; in this model there is no corpus callosum, which joins the left are right sides of the brain (red part in the graphic below). In an earlier post we looked at agenesis of the corpus callosum, which can be full or partial and is a feature of many types of disabling autism.

 

Source: https://en.wikipedia.org/wiki/Corpus_callosum#/media/File:Corpus_callosum.gif

  

The results of the mouse research were positive and it was concluded that E-100 is a potential drug candidate for future therapeutic management of autistic-like behaviours.

  

Simultaneous Blockade of Histamine H₃ Receptors and Inhibition of Acetylcholine Esterase Alleviate Autistic-Like Behaviors in BTBR T+ tf/J Mouse Model of Autism

Autism spectrum disorder (ASD) is a heterogenous neurodevelopmental disorder defined by persistent deficits in social interaction and the presence of patterns of repetitive and restricted behaviors. The central neurotransmitters histamine (HA) and acetylcholine (ACh) play pleiotropic roles in physiological brain functions that include the maintenance of wakefulness, depression, schizophrenia, epilepsy, anxiety and narcolepsy, all of which are found to be comorbid with ASD. Therefore, the palliative effects of subchronic systemic treatment using the multiple-active test compound E100 with high H₃R antagonist affinity and AChE inhibitory effect on ASD-like behaviors in male BTBR T+tf/J (BTBR) mice as an idiopathic ASD model were assessed. E100 (5, 10 and 15 mg/kg, i.p.) dose-dependently palliated social deficits of BTBR mice and significantly alleviated the repetitive/compulsive behaviors of tested animals. Moreover, E100 modulated disturbed anxiety levels, but failed to modulate hyperactivity parameters, whereas the reference AChE inhibitor donepezil (DOZ, one milligram per kilogram) significantly obliterated the increased hyperactivity measures of tested mice. Furthermore, E100 mitigated the increased levels of AChE activity in BTBR mice with observed effects comparable to that of DOZ and significantly reduced the number of activated microglial cells compared to the saline-treated BTBR mice. In addition, the E100-provided effects on ASD-like parameters, AChE activity, and activated microglial cells were entirely reversed by co-administration of the H₃R agonist (R)-α-methylhistamine (RAM). These initial overall results observed in an idiopathic ASD mice model show that E100 (5 mg/kg) alleviated the assessed behavioral deficits and demonstrate that simultaneous targeting of brain histaminergic and cholinergic neurotransmissions is crucial for palliation of ASD-like features, albeit further in vivo assessments on its effects on brain levels of ACh as well as HA are still needed. 

The observed results in an idiopathic ASD mice model comprehend our previously obtained palliative effects of E100 in VPA-induced ASD in mice. Also, the current observations demonstrate that simultaneous targeting of the CNS histaminergic and cholinergic neurotransmissions is crucial for palliation of several ASD-like features, namely ASD-like social deficits and repetitive/compulsive behaviors and mitigated the levels of cerebellar microglial cells and AChE activity of tested BTBR mice used as idiopathic ASD model. Whether the alleviation of autistic-like behaviors in BTBR mice is obtained after administration of H₃R antagonist or co-administration of an H₃R antagonist and an AChEI was beyond the scope of this project and will require dose-finding experiments for several ratios of the combination of AChEIs and H₃R antagonist. Further in vivo assessments on brain levels of ACh as well as HA in BTBR mice following different systemic treatments of test compound as well as reference drugs including a standard H₃R antagonist (e.g., pitolisant) are still needed to evaluate whether multiple-active compounds, e.g., E100, is superior to AChEIs or H₃R antagonists when administered alone.

The design and synthesis of E100, namely 1-(7-(4-chlorophenoxy)heptyl)azepane, was carried out in the Department of Technology and Biotechnology of Drugs, Jagiellonian University Medical College, Krakow, Poland and as described in in previous reports.

  

The Dual-Active Histamine H₃ Receptor Antagonist and Acetylcholine Esterase Inhibitor E100 Alleviates Autistic-Like Behaviors and Oxidative Stress in Valproic Acid Induced Autism in Mice

The histamine H3 receptor (H3R) functions as auto- and hetero-receptors, regulating the release of brain histamine (HA) and acetylcholine (ACh), respectively. The enzyme acetylcholine esterase (AChE) is involved in the metabolism of brain ACh. Both brain HA and ACh are implicated in several cognitive disorders like Alzheimer’s disease, schizophrenia, anxiety, and narcolepsy, all of which are comorbid with autistic spectrum disorder (ASD). Therefore, the novel dual-active ligand E100 with high H3R antagonist affinity (hH3R: K_i = 203 nM) and balanced AChE inhibitory effect (EeAChE: IC₅₀ = 2 µM and EqBuChE: IC₅₀ = 2 µM) was investigated on autistic-like sociability, repetitive/compulsive behaviour, anxiety, and oxidative stress in male C57BL/6 mice model of ASD induced by prenatal exposure to valproic acid (VPA, 500 mg/kg, intraperitoneal (i.p.)). Subchronic systemic administration with E100 (5, 10, and 15 mg/kg, i.p.) significantly and dose-dependently attenuated sociability deficits of autistic (VPA) mice in three-chamber behaviour (TCB) test (all p < 0.05). Moreover, E100 significantly improved repetitive and compulsive behaviors by reducing the increased percentage of marbles buried in marble-burying behaviour (MBB) (all p < 0.05). Furthermore, pre-treatment with E100 (10 and 15 mg/kg, i.p.) corrected decreased anxiety levels (p < 0.05), however, failed to restore hyperactivity observed in elevated plus maze (EPM) test. In addition, E100 (10 mg/kg, i.p.) mitigated oxidative stress status by increasing the levels of decreased glutathione (GSH), superoxide dismutase (SOD), and catalase (CAT), and decreasing the elevated levels of malondialdehyde (MDA) in the cerebellar tissues (all p < 0.05). Additionally, E100 (10 mg/kg, i.p.) significantly reduced the elevated levels of AChE activity in VPA mice (p < 0.05). These results demonstrate the promising effects of E100 on in-vivo VPA-induced ASD-like features in mice, and provide evidence that a potent dual-active H3R antagonist and AChE inhibitor (AChEI) is a potential drug candidate for future therapeutic management of autistic-like behaviours.

 

Acetylcholinesterase inhibitor (AChEI)

An acetylcholinesterase inhibitor (AChEI) inhibits the enzyme acetylcholinesterase from breaking down the neurotransmitter acetylcholine, thereby increasing both its level and duration of action.

We know that a surge in acetylcholine improves learning.

Examples of acetylcholinesterase inhibitors include: -

·        Alzheimer’s drugs Donepezil and Galantamine (both used off-label in autism)

·        Caffeine

·        Rosmarinic acid

  

Histamine H3 antagonists

Histamine H3 antagonists bind to H3 receptors in the brain so that histamine cannot activate them, examples include: -

Betahistine

Betahistine/Ciproxifan produces wakefulness and attentiveness in animal studies, and produced cognitive enhancing effects without prominent stimulant effects at relatively low levels of receptor occupancy, and pronounced wakefulness at higher doses. It has therefore been proposed as a potential treatment for sleep disorders such as narcolepsy and to improve vigilance in old age, particularly in the treatment of conditions such as Alzheimer's disease 

Pitolisant 

Pitolisant/ Wakix, is a medication for the treatment of excessive daytime sleepiness (EDS) in adults with narcolepsy. It is a histamine 3 (H₃) receptor antagonist/inverse agonist. It represents the first commercially available medication in its class. Pitolisant enhances the activity of histaminergic neurons in the brain that function to improve a person's wakefulness.

The most common side effects include difficulty sleeping, nausea, and feeling worried

  

There is a lot in this blog about histamine, mainly in relation to mast cells and allergic responses. You do have mast cells in your brain. Science has not fully established the role of histamine in humans, particularly in the brain. 

A quick recap on histamine:- 

H1 receptor

The H1 receptor is what mediates things like pollen allergies, but it plays a role in the brain that affects sleep, appetite, body temperature and cognition.

 

H2 receptor

The H2 receptor in the gut is the target of acid lowering drugs. These receptors do exist in the brain, but nobody has figured out their function.

 

H3 receptor

The H3 receptor is mainly in the central nervous system where it regulates the release of brain histamine (HA) and acetylcholine (ACh); it also affects the release of serotonin and norepinephrine. Elsewhere in the body H3 receptors play a role in the release of gastric acids. 

H4 receptor

The H4 receptor is not well understood. It plays a role in mast cells, but its role in cognition, allergy and inflammation is not fully understood.

 

Histamine-gated Chloride Channels

It does not seem to have a cute name like H5, but there appears to be another target for histamine, that is a histamine gated chloride channel, which seems to be present in the brain 

 

Histamine is produced from the amino acid histidine.  Some food contains histamine.

Somewhat bizarrely, it seems that if you supplement the amino acid histidine you get an anti-allergy effect; it is like more histidine makes/releases less histamine.  One of nature’s feedback loops at work, I suppose.

Histamine is mainly stored in mast cells (the target of mast cell stabilizer drugs), some is stored in basophils. Within the brain histamine functions as a neurotransmitter and you have so-called histaminergic neurons.

Once released, histamine is supposed to be deactivated by the enzymes HNMT or DAO (histamine-N-methyltransferase or diamine oxidase).  If you lack HNMT or DAO you will have problems with histamine.

  

Is there a synergistic benefit from blocking the H3 receptors in the brain and increasing the level of acetylcholine? 

The researchers from the UAE seem to believe that the new Polish drug E-100 has the unique benefit of doing two clever things at once that together might be helpful in human autism, as well as in the original target, Alzheimer’s.

 

 

Conclusion 

I did write in length in this blog about histamine; there are 18 posts tagged with Histamine. 

https://epiphanyasd.blogspot.com/search/label/Histamine

This did take me to the world of mast cell stabilizers and then L-type calcium channel blockers, so it was productive; but there were clearly huge gaps in the science that still remain.

The interesting substances from my original investigation include: -

·        H1 anti-histamines that also stabilize mast cells (Azelastine, Rupatadine, Ketotifen).

·        Pure mast cell stabilizers like Cromolyn Sodium

·        L-type calcium channel blockers such as Verapamil

 

It seemed highly likely that H3 and H4 receptors might also be useful targets, let alone the even less understood histamine gated chloride channels.

Is the new Polish drug E-100 going to be effective in human autism? and in which people?  Are the people with mast cell problems likely to be among the responders?