There really is a lot in this post. I had to read it twice.
As is often the case, this post started at the end with the therapy (a trial of Afobazole) and then I just looked at why it might be effective.
Today's post is all about sigma-1 receptors and the many clever things that happen when they are activated.
Even the above diagram showing the effect of Sigma-1R is incomplete!
In the mouse study below, the Russian researchers looked at the effect of Afobazole treatment just over a few days; I think other effects might have developed if they had looked at an extended time period. They focus on Sigma1-R receptors modulating NMDA-based neurotransmission, but there seem to many possible further effects within the Endoplasmic Reticulum that relate specifically to autism. These researchers have published other studies using Afobazole, including recently one on Parkinson's disease.
The multifactorial nature of ASD precludes the use of its modern genetic models in the study of pharmacologic effects exerted on entire symptomatic complex of autism although they could relate functional correction of ASD with a certain gene. In experiments, the models of idiopathic ASD are based on inbred mice selected by behavioral phenotype. BALB/c mice demonstrate pronounced autism-relevant behavioral phenotype characterized by low level of social relations, high levels of anxiety and aggression, increased brain weight, undeveloped corpus callosum, and lower serotonin concentration in the brain [7,12]. The emotional stress reaction (ESR) in these animals is associated with weaker binding capacity of the benzodiazepine site in GABAA receptor [6]. Transformation of ESR into the cell stress augments reception in the domain responsible for binding the endo- and exogenous ligands of sigma 1 receptor chaperon protein (Sigma1R) [1] responsible for adaptive reactions [8]. In addition, Sigma1R stimulate BDNF and NGF synthesis, promote the growth and arborization of nerve terminals, and control functional activity of potassium, calcium, and chloride ion channels and a variety of neuroreceptors [5,8,13]. Thus, this chaperon protein can be an important player in physiological and pharmacological regulation of ASD features.
Afobazole is a non-benzodiazepine anxiolytic drug that acts via activation of Sigma1R and interaction with MT1 and MT3 melatonin receptors and a regulatory site of MAO-A [4]. Clinical observations showed that Afobazole optimizes psychophysiological parameters in emotionally unstable persons without impairing attention, psychomotor responsiveness, and decision-making alertness in the model of operator work. The drug is characterized by mild activation effect and reduces anxiety, thus promoting adaptation to novel environment [2]. This work was designed to examine the effects of Afobazole on cognitive rigidity in BALB/c mice.
Evidently, enhanced motor activity of Afobazole treated BALB/c mice reflected the anxiolytic effect of this drug, which stimulated exploratory behavior aimed at solving the novel task. Thus, Afobazole improved adaptation to changing environment
The present study revealed the potency of Afobazole to promote retraining and reversal learning of BALB/c mice, which manifested in increased rate of adaptation to novel environment and more effective solution of the modified task. Afobazole interacts with Sigma1R receptors and induces their activation [1]. It cannot be excluded that the anxiolytic effect of Afobazole is accompanied by up-regulation of Sigma1R chaperone functions, because this drug normalizes the stress-induced down-regulation of reception in benzodiazepine site of GABAA receptor [6]. A large cluster of Sigma1R receptor was revealed in the hippocampus that plays a key role in adaptive behavior related to building of spatial cognitive maps, learning, and memory. Sigma1R receptors modulate NMDA-based neurotransmission; they can enhance spontaneous release of glutamate in the hippocampus, potentiate glutamate-induced release of neurotrophic factor, and participate in synaptic plasticity [8]. However, Sigma1R receptors regulate cognitive processes under disturbed neurotransmitter balance only. All these data agree with our previous findings and with the current views on the mechanism of Afobazole action [1,4,5]. Thus, the mode of action and pharmacological effects of Afobazole are promising features, which justify the hopes to use it as an effective remedy to treat cognitive rigidity in ASD patients
More on sigma-1 and NMDA receptors:-
NMDA Receptors Are Upregulated and Trafficked to the Plasma Membrane after Sigma-1 Receptor Activation in the Rat Hippocampus
Sigma-1 receptors (σ-1Rs) are endoplasmic reticulum resident chaperone proteins implicated in many physiological and pathological processes in the CNS. A striking feature of σ-1Rs is their ability to interact and modulate a large number of voltage- and ligand-gated ion channels at the plasma membrane. We have reported previously that agonists for σ-1Rs potentiate NMDA receptor (NMDAR) currents, although the mechanism by which this occurs is still unclear. In this study, we show that in vivo administration of the selective σ-1R agonists (+)-SKF 10,047 [2S-(2α,6α,11R*]-1,2,3,4,5,6-hexahydro-6,11-dimethyl-3-(2-propenyl)-2,6-methano-3-benzazocin-8-ol hydrochloride (N-allylnormetazocine) hydrochloride], PRE-084 (2-morpholin-4-ylethyl 1-phenylcyclohexane-1-carboxylate hydrochloride), and (+)-pentazocine increases the expression of GluN2A and GluN2B subunits, as well as postsynaptic density protein 95 in the rat hippocampus. We also demonstrate that σ-1R activation leads to an increased interaction between GluN2 subunits and σ-1Rs and mediates trafficking of NMDARs to the cell surface. These results suggest that σ-1R may play an important role in NMDAR-mediated functions, such as learning and memory. It also opens new avenues for additional studies into a multitude of pathological conditions in which NMDARs are involved, including schizophrenia, dementia, and stroke.
Afobazole is primarily used to treat mild anxiety. Indeed it appears that sigma-1 receptor activation ameliorates anxiety through NR2A-CREB-BDNF signalling. NR2A is a sub-unit of NMDA receptors.
Sigma-1 receptor activation ameliorates anxiety-like behavior through NR2A-CREB-BDNF signaling pathway in a rat model submitted to single-prolonged stress.
It does seem that activating the sigma-1 receptor might be another of those nexuses in treatment, where different dysfunctions in autism might well respond to the same therapy. Recall how many functions of the Endoplasmic Reticulum are impaired in autism, such as the all important calcium homeostasis.
It also might account for some of the people with autism that respond to Memantine/Nameda and Donepezil. My old post on IP3R and the endoplasmic reticulum, looked at the interesting hypothesis proposed by Gargus.
Is dysregulated IP3R calcium signaling a nexus where genes altered in ASD converge to exert their deleterious effect?
Components of a typical animal cell:
Endoplasmic Reticulum (ER) and ER Stress
The endoplasmic reticulum (ER) is the cellular organelle in which protein folding, calcium homeostasis, and lipid biosynthesis occur. Stimuli such as oxidative stress, ischemic insult, disturbances in calcium homeostasis, and enhanced expression of normal and/or folding-defective proteins lead to the accumulation of unfolded proteins, a condition referred to as ER stress.
Prolonged ER stress typically results in cell death by apoptosis; an answer to “where did all the Purkinje cells go?”, in people with severe autism, perhaps.
ER stress is known to affect "neurite outgrowth", which is all the bits like dendrites. Purkinje cells have the most dendrites. Loss of Purkinje cells affects your motor skills and the Pukinje cell layer is found to be severely depleted in people with autism. Many people with autism, even some Aspies, have poor motor skills.
Research shows that exercise suppresses Purkinje cell losss and that the ones remaining in autistic brains are likley dysfunctional. When synaptic pruning works correctly each Purkinje cell in an adult receives only one climbing fiber input, in ASD models there is an abundance of climbing fibers. It does seem that with enough practice you may overcome poor motor skills in autism.
Interestingly, in the research we see that both Atorvastatin and Rosuvastatin enhance neurite outgrowth. Atorvastatin has long been part of my PolyPill for severe autism.
For effective synaptic pruning you need microglia that are not activated, so shift them back to M0. This is another part of my PolyPill.
ER stress is known to affect "neurite outgrowth", which is all the bits like dendrites. Purkinje cells have the most dendrites. Loss of Purkinje cells affects your motor skills and the Pukinje cell layer is found to be severely depleted in people with autism. Many people with autism, even some Aspies, have poor motor skills.
Research shows that exercise suppresses Purkinje cell losss and that the ones remaining in autistic brains are likley dysfunctional. When synaptic pruning works correctly each Purkinje cell in an adult receives only one climbing fiber input, in ASD models there is an abundance of climbing fibers. It does seem that with enough practice you may overcome poor motor skills in autism.
Interestingly, in the research we see that both Atorvastatin and Rosuvastatin enhance neurite outgrowth. Atorvastatin has long been part of my PolyPill for severe autism.
For effective synaptic pruning you need microglia that are not activated, so shift them back to M0. This is another part of my PolyPill.
Protein folding is the physical process by which a protein chain acquires its native 3-dimensional structure, a conformation that is usually biologically functional.
Molecular chaperones are a class of proteins that aid in the correct folding of other proteins, sigma-1 is one example.
A protein is considered to be misfolded if it cannot achieve its normal native state and function.
Incorrect protein folding is a common feature of neurodegenerative disease.
An emerging approach is to use pharmaceutical chaperones to fold mutated proteins to render them functional.
As will be seen in the research, ER stress is a feature of severe autism and indeed schizophrenia.
The result is that perfect genes do not produce perfect functional proteins. They produce misfolded perfect proteins that cannot function.
Misfolded proteins can interact with one another and form structured aggregates and gain toxicity through intermolecular interactions, but that would lead to a degenerative brain disease (Alzheimer’s, Huntington’s, Parkinson’s etc). So, the misfolding in autism, if present, it not catastrophic (except perhaps for those Purkinje cells); but a nice folded shirt does give a better result than a crumpled one. Better keep your proteins neatly folded.
Is there ER Stress in Autism?
The short answer is yes, at least in the kind of autism that leads to young human brains being donated to medical research.
Autism research based on human brain tissue is biased towards severe autism (they can die in childhood), whereas many/most clinical trials are now biased towards mild autism (having participants who are fully verbal and cooperative makes life easier for researchers, but their young brains do not get donated to medical research).
Autism research based on human brain tissue is biased towards severe autism (they can die in childhood), whereas many/most clinical trials are now biased towards mild autism (having participants who are fully verbal and cooperative makes life easier for researchers, but their young brains do not get donated to medical research).
Altered Expression of Endoplasmic Reticulum Stress-Related Genes in the Middle Frontal Cortex of Subjects with Autism Spectrum Disorder |
The endoplasmic reticulum (ER) is an important organelle responsible for the folding and sorting of proteins. Disturbances in ER homeostasis can trigger a cellular response known as the unfolded protein response, leading to accumulation of unfolded or misfolded proteins in the ER lumen called ER stress. A number of recent studies suggest that mutations in autism spectrum disorder (ASD)-susceptible synaptic genes induce ER stress. However, it is not known whether ER stress-related genes are altered in the brain of ASD subjects. In the present study, we investigated the mRNA expression of ER stress-related genes (ATF4, ATF6, PERK, XBP1, sXBP1, CHOP, and IRE1) in the postmortem middle frontal gyrus of ASD and control subjects. RT-PCR analysis showed significant increases in the mRNA levels of ATF4, ATF6, PERK, XBP1, CHOP, and IRE1 in the middle frontal gyrus of ASD subjects. In addition, we found a significant positive association of mRNA levels of ER stress genes with the diagnostic score for stereotyped behavior in ASD subjects. These results, for the first time, provide the evidence of the dysregulation of ER stress genes in the brain of subjects with ASD.
Increase in mRNA levels of endoplasmic reticulum stress genes in the middle frontal gyrus of autism spectrum disorder (ASD) subjects. mRNA levels of endoplasmic reticulum stress genes were determined by qRT-PCR in the middle frontal gyrus of ASD (n = 13) and control (n = 12) subjects. The Ct values were normalized to the mean of 18S and β-actin. a Activating transcription factor 4 (ATF4). b Activating transcription factor 6 (ATF6). c Protein kinase-like endoplasmic reticulum kinase (PERK). d X-box protein 1 (XBP1). e Spliced X-box protein 1 (sXBP1). f CCAAT-enhancer-binding protein homologous protein (CHOP). g Inositol-requiring enzyme 1 (IRE1). * p < 0.05, ** p < 0.01, and *** p < 0.0001 vs. controls.
We found significant increases in ATF4, ATF6, PERK, XBP1, CHOP, and IRE1 mRNA levels in the middle frontal gyrus of ASD subjects. Among these molecules, CHOP is known to interact with the heterodimeric receptors GABAB1aR/GABAB2R and inhibits the formation of heterodimeric complexes resulting in the intracellular accumulation and reduced cell surface expression of receptors [34]. Interestingly, decreased levels of GABAB1R and GABAB2R have been found in the brain of ASD subjects [35]. What are the downstream mechanism mediating ER stress-induced changes in central nervous system function? One potential mechanism is inflammation. Accumulating evidence suggest that pathways activated by the ER stress response induce inflammation. When activated, all three sensors of the UPR, PERK, IRE1, and ATF6, participate in upregulating inflammatory processes. It is known that PERK and IRE1 activation can interfere with NFκB inhibitory signals, thereby promoting a proinflammatory response [36]. In addition, CHOP has been shown to induce the expression of proinflammatory cytokines such as IL-23 [37]. Moreover, ER stress activates NLRP3 inflammasomes via thioredoxin-interacting protein (TXNIP), leading to increases in proinflammatory cytokine levels [38,39]. In this regard, our earlier studies using the same tissue samples of the present study found increased levels of proinflammatory cytokines IL-1β and IFN-γ in the middle frontal gyrus of ASD subjects [30].
Also, chronic ER stress is known to induce cellular apoptosis through a number of pathways including CHOP, calcium signaling, and microRNAs [40]. Activation of PERK triggers a series of transcriptional responses mediated by ATF4 and CHOP, which in turn inhibit the expression of anti-apoptotic protein Bcl2 and induce pro-apoptotic proteins such as Bcl2-interacting mediator of cell death (BIM) and p53 upregulated modulator of apoptosis (PUMA) [40]. The induction of pro-apoptotic signaling pathway results in the activation of BAX- and BAK-dependent apoptosis at the mitochondria and the activation of the caspase cascade [41]. Interestingly, decrease in Bcl2, but increase in p53 protein levels have been reported in the frontal cortex of ASD subjects [42].
We found that mRNA levels of ER stress genes are positively associated with the stereotyped behavior domain of the ADI-R. It has been shown that autism-associated mutations in NLGN3, which is known to induce ER stress, also increase stereotyped behavior in mice [43]. Similarly, mice lacking CNTNAP2 showed increased repetitive behaviors such as grooming and digging [44], further suggesting that abnormalities in ASD candidate genes implicated in ER stress induce stereotyped behavior in rodents. The present data was collected in a relatively small number of study subjects, which needs further investigation using larger samples before a conclusion can be drawn. Also, the change in gene expression as part of ER stress axis in ASD could be associated with other priming factors functional on different coordinates of this complex neurodevelopmental disorder. Additional studies are warranted to analyze the ER stress-inducing factors with direct relationship to the pathophysiological changes associated with ASD. To further establish a definitive role of ER stress in ASD pathophysiology, the following questions still need to be addressed: (1) Is ER stress in ASD of neurodevelopmental origin? (2) Are there factors other than mutant synaptic proteins that can trigger ER stress leading to ASD phenotype? (3) Is inflammation triggering ER stress or is ER stress triggering inflammation leading to ASD phenotype? (4) Does ER stress induce changes in neural connectivity between key brain regions implicated in ASD pathophysiology? Future studies addressing the above questions might lead to a better understanding of the pathophysiology and provide new avenues of treatment of this disorder.
Cellular stress and apoptosis contribute to the pathogenesis ofautism spectrum disorder
Lay Summary
Autism results in significant morbidity and mortality in children. The functional and molecular changes in the autistic brains are unclear. The present study utilized autistic brain tissues from the National Institute of Child Health and Human Development's Brain Tissue Bank for the analysis of cellular and molecular changes in autistic brains. Three key brain regions, the hippocampus, the cerebellum, and the frontal cortex, in six cases of autistic brains and six cases of non‐autistic brains from 6 to 16 years old deceased children, were analyzed. The current study investigated the possible roles of endoplasmic reticulum (ER) stress, oxidative stress, and apoptosis as molecular mechanisms underlying autism. The activation of three signals of ER stress (protein kinase R‐like endoplasmic reticulum kinase, activating transcription factor 6, inositol‐requiring enzyme 1 alpha) varies in different regions. The occurrence of ER stress leads to apoptosis in autistic brains. ER stress may result from oxidative stress because of elevated levels of the oxidative stress markers: 4‐Hydroxynonenal and nitrotyrosine‐modified proteins in autistic brains. These findings suggest that cellular stress and apoptosis may contribute to the autistic phenotype. Pharmaceuticals and/or dietary supplements, which can alleviate ER stress, oxidative stress and apoptosis, may be effective in ameliorating adverse phenotypes associated with autism.
Figure 1. Immunoblot analysis of endoplasmic reticulum (ER) stress signals in the autistic cerebellum. Immunoblot analysis of the cerebellum homogenate was performed using p-IRE1a, p-PERK, and total ATF6 antibodies.
In summary, we showed the elevation of ER stress signals, oxidative stress, and apoptosis in three regions of autistic brains. Based on these findings, we reason that increased cellular stress and apoptosis in the autistic brain may be associated with the pathogenesis of autism. Because autism is affected by multiple genetic and environmental factors that are case-specific and there are inherent limitations in the postmortem brain, the present observations will need further confirmation in future studies. Further research with larger sample sizes is needed to investigate the association of cellular stress and apoptotic events with the severity and clinical phenotypes of autism.
Chaperone Sigma1R mediates the neuroprotective action of afobazole in the 6-OHDA model of Parkinson’s disease
Abstract
Parkinson’s disease (PD) is a progressive neurodegenerative disease with limited treatment options. Therefore, the identification of therapeutic targets is urgently needed. Previous studies have shown that the ligand activation of the sigma-1 chaperone (Sigma1R) promotes neuroprotection. The multitarget drug afobazole (5-ethoxy-2-[2-(morpholino)-ethylthio]benzimidazole dihydrochloride) was shown to interact with Sigma1Rs and prevent decreases in striatal dopamine in the 6-hydroxydopamine (6-OHDA)-induced parkinsonism model. The aim of the present study was to elucidate the role of Sigma1Rs in afobazole pharmacological activity. Using ICR mice we found that administration of afobazole (2.5 mg/kg, i.p.) or selective agonist of Sigma1R PRE-084 (1.0 mg/kg, i.p.) over 14 days normalizes motor disfunction and prevents decreases in dopamine in the 6-OHDA-lesioned striatum. Afobazole administration also prevents the loss of TH + neurons in the substantia nigra. The pre-administration of selective Sigma1R antagonist BD-1047 (3.0 mg/kg, i.p.) abolishes the activity of either afobazole or PRE-084, as determined using the rotarod test and the analysis of striatal dopamine content. The current study demonstrates the contribution of Sigma1Rs in the neuroprotective effect of afobazole in the 6-OHDA model of Parkinson’s disease and defines the therapeutic perspective of Sigma1R agonists in the clinic.
Sigma-1 (σ1) Receptor in Memory and Neurodegenerative Diseases
The sigma-1 (σ1) receptor has been associated with regulation of intracellular Ca2+ homeostasis, several cellular signaling pathways, and inter-organelle communication, in part through its chaperone activity. In vivo, agonists of the σ1 receptor enhance brain plasticity, with particularly well-described impact on learning and memory. Under pathological conditions, σ1 receptor agonists can induce cytoprotective responses. These protective responses comprise various complementary pathways that appear to be differentially engaged according to pathological mechanism. Recent studies have highlighted the efficacy of drugs that act through the σ1 receptor to mitigate symptoms associated with neurodegenerative disorders with distinct mechanisms of pathogenesis. Here, we will review genetic and pharmacological evidence of σ1 receptor engagement in learning and memory disorders, cognitive impairment, and neurodegenerative diseases, including Alzheimer’s disease, Parkinson’s disease, amyotrophic lateral sclerosis, multiple sclerosis, and Huntington’s disease.
Crosstalk between endoplasmic reticulum stress and oxidative stress in schizophrenia: The dawn of new therapeutic approaches
Highlights
The complete understanding of the pathways and the point of convergence of ER and oxidative stress in schizophrenia is still quite fragmentary.
Neuronal migration along with altered secretion of neurotrophins modulates neuronal circuits and synaptic function during schizophrenia.
Chemical chaperones including Sigma-1 receptor agonists may prevent stress-induced protein misfolding associated with schizophrenia.
ER-stress inhibitors, sigma-1 receptor agonists and gene therapies holds a strong therapeutic potential against schizophrenia.
Disruption of oxidant/anti-oxidant ratio as well as endoplasmic reticulum (ER) stress are thought to be involved in the pathophysiology of schizophrenia. These stresses can lead to impairments in brain functions progressively leading to neuronal inflammation followed by neuronal cell death. Moreover, the cellular stresses are interlinked leading us to the conclusion that protein misfolding, oxidative stress and apoptosis are intricately intertwined events requiring further research into their mechanistic and physiological pathways. These pathways can be targeted by using different therapeutic interventions like anti-oxidants, sigma-1 receptor agonists and gene therapy to treat the neurodegenerative course of schizophrenia. We have also put empahsis on use of synthetic and natural ER stress inhibitors like 4-phenylbutyrate or salubrinal for the treatment of this disorder. This would provide an opportunity to create new therapeutic benchmarks in the field of neuropsychiatric disorders like schizophrenia, dissociative identity disorder and obsessive compulsive disorder.
Targeting ligand-operated chaperone sigma-1 receptors in the treatment of neuropsychiatric disorders
Current conventional therapeutic drugs for the treatment of psychiatric or neurodegenerative disorders have certain limitations of use. Psychotherapeutic drugs such as typical and atypical antipsychotics, tricyclic antidepressants, and selective monoamine reuptake inhibitors, aim to normalize the hyper- or hypo-neurotransmission of monoaminergic systems. Despite their great contribution to the outcomes of psychiatric patients, these agents often exert severe side effects and require chronic treatments to promote amelioration of symptoms. Furthermore, drugs available for the treatment of neurodegenerative disorders are severely limited.
Areas covered
This review discusses recent evidence that has shed light on sigma-1 receptor ligands, which may serve as a new class of antidepressants or neuroprotective agents. Sigma-1 receptors are novel ligand-operated molecular chaperones regulating a variety of signal transduction, ER stress, cellular redox, cellular survival, and synaptogenesis. Selective sigma-1 receptor ligands exert rapid antidepressant-like, anxiolytic, antinociceptive and robust neuroprotective actions in preclinical studies. The review also looks at recent studies which suggest that reactive oxygen species might play a crucial role as signal integrators at the downstream of Sig-1Rs
Expert opinion
The significant advances in sigma receptor research in the last decade have begun to elucidate the intracellular signal cascades upstream and downstream of sigma-1 receptors. The novel ligand-operated properties of the sigma-1 receptor chaperone may enable a variety of interventions by which stress-related cellular systems are pharmacologically controlled.
Sigma-1 receptor ligands
Clinically used drugs:
· Afobazole (5-ethoxy-2-[2-(morpholino)-ethylthio]benzimidazole dihydrochloride): Anxiolytic drug
· Carbetapentane: Cough suppressant
· Dextromethorphan (DM): Antitussive drug; DM-quinidine (Q) therapy is effective in reducing pseudobulbar affect in ALS and multiple sclerosis
· Donepezil: Sigma-1 agonist; acetylcholine esterase inhibitor used in Alzheimer’s disease
· Fluvoxamine: Clinically used SSRI; Sig-1R agonist
· Sertraline: Clinically used SSRI with a putative Sig-1R antagonist property
· Haloperidol: Clinically used antipsychotic; potent, but non selective sigma antagonist
· Haloperidol-metabolite II (reduced HP, 4-(4-chlorophenyl)-alpha-(4-fluorophenyl)-4-hydroxy-1-piperidinebutanol): In contrast to haloperidol, having higher selectivity to Sig-1Rs
· Memantine: A novel Alzheimer’s disease medication blocking NMDA glutamate receptors
· Zonisamide: Anti-Parkinson drug approved in Japan
Involvement of endoplasmic reticulum stress and neurite outgrowth in the model mice of autism spectrum disorder
Implication of Endoplasmic Reticulum Stress in Autism Spectrum Disorder
Autism spectrum disorder (ASD) is categorized as a neurodevelopmental disorder according to the Diagnostic and Statistical Manual of Disorders, Fifth Edition and is defined as a congenital impairment of the central nervous system. ASD may be caused by a chromosomal abnormality or gene mutation. However, these etiologies are insufficient to account for the pathogenesis of ASD. Therefore, we propose that the etiology and pathogenesis of ASD are related to the stress of the endoplasmic reticulum (ER). ER stress, induced by valproic acid, increased in ASD mouse model, characterized by an unfolded protein response that is activated by this stress. The inhibition of neurite outgrowth and expression of synaptic factors are observed in ASD. Similarly, ER stress suppresses the neurite outgrowth and expression of synaptic factors. Additionally, hyperplasia of the brain is observed in patients with ASD. ER stress also enhances neuronal differentiation. Synaptic factors, such as cell adhesion molecule and shank, play important roles in the formation of neural circuits. Thus, ER stress is associated with the abnormalities of neuronal differentiation, neurite outgrowth, and synaptic protein expression. ER stress elevates the expression of the ubiquitin-protein ligase HRD1 for the degradation of unfolded proteins. HRD1 expression significantly increased in the middle frontal cortex in the postmortem of patients with ASD. Moreover, HRD1 silencing improved the abnormalities induced by ER stress. Because other ubiquitin ligases are related with neurite outgrowth, ER stress may be related to the pathogenesis of neuronal developmental diseases via abnormalities of neuronal differentiation or maturation.
Sigma-1 receptor: The novel intracellular target of neuropsychotherapeutic drugs
The sigma-1 receptor localized at the ER modulates via its chaperone activity inter-organelle communications. Sigma-1 receptors thus regulate a variety of cellular events, such as neuronal differentiation, cellular survival, and bioenergetics. By numerous animal studies, these actions of the sigma-1 receptors have been linked to the pathophysiology of certain human diseases such as depression, ischemia, drug abuse, pain, and cancer. Considering the current pharmacotherapy of neuropsychiatric diseases that largely depends on drugs developed based on the monoamine theory, the sigma-1 receptor is expected to serve as a molecule, which provides a novel target of “post-monoamine” drugs, thus bringing a new approach for treatment of patients suffering from neuropsychiatric diseases.
Fig. 1. Molecular functions of the sigma-1 receptor. The sigma-1 receptor possesses two transmembrane domains and mainly localize at the ER membrane. Sigma-1 receptors are clustered at the mitochondria-associated ER membrane (MAM) and ER membranes juxtaposing postsynaptic density of specific types of neurons. The ER lumenal domain of the sigma-1 receptor exerts chaperone activities by which ER membrane proteins are stabilized. The figure depicts the recently reported actions of the sigma-1 receptors including: 1) Sigma-1 receptors associating with BiP stabilizes IP3 receptors type-3 (IP3R) at the MAM, leading to regulation of Ca2+ influx into mitochondria and following ATP production; 2) Sigma-1 receptors stabilize the ER stress sensor IRE1 at the MAM in an ROS-dependent manner, leading to prolongation of the IRE1-XBP1 cell survival signal; 3) Sigma-1 receptors suppress generation of reactive oxygen species (ROS) and following activation of the NFkB signaling (How the sigma-1 receptor regulates ROS generation is unknown); 4) Sterols such as 25-hydroxycholesterol promote the association of sigma-1 receptors with Insig-1 [Collaborating with Insig-1, sigma-1 receptors regulate ER-associated degradation (ERAD) of HMG-CoA reductase and galactosylceramide synthase at the ER]; 5) Sigma-1 receptors regulate the trafficking of potassium channel subunits from the ER to the plasma membrane or processing/secretion of brain-derived trophic factor (BDNF). Sigma-1 receptors likely associate with potassium channel subunits or pro-BDNF at the ER. In spinal neurons, sigma-1 receptors, which colocalize with a K channel subunit are clustered at the ER membrane apposing postsynaptic densities (PSD). How the sigma-1 receptor regulates processing/secretion of BDNF is unknown. (in the earlier part of this post the mechanism that increases BDNF is explained, if you activate sigma-1R you inevitably will increase BDNF)
Conclusion
In our simplified view of autism, aimed at actually treating it, we should have a list of stresses and what to do about them:-
· Oxidative stress
· Nitrosative stress
· Endoplasmic Reticulum (ER) stress
Reducing oxidative stress has multiple biological and behavioral effects; the overall effect is generally positive.
Reducing endoplasmic reticulum (ER) stress, if present, does look a good idea. It will have numerous effects; it should even reduce oxidative stress. The sigma-1 chaperone looks like it will have many effects that, on balance, should be positive, but undoubtedly may upset something and produce an overall negative effect in some people – it is inevitable. I hope the effect on NMDA receptors does not cause a problem where an E/I (excitatory/inhibitory) imbalance is already being treated.
A highly selective sigma-1R agonist, one that does not affect any other receptors, does not exist.
Many psychiatric drugs like antidepressants do affect sigma-1R, but they are not suitable for long term use because of side effects, tolerance, addiction etc.
Afobazole is interesting because clinical trials have shown it to be well tolerated, non-addictive and reasonably effective for the treatment of anxiety. Afobazole also affects the melatonin receptor MT1, it is not directly sedating but might affect some types of sleep abnormality.
Afobazole is only researched in Russia, but findings are shared internationally, for example at this conference
The drug was developed, and is currently researched, by the “Research Zakusov Institute of Pharmacology” in Moscow. They recently also published a paper on the use of Afobazole in Parkinson’s disease. In the Parkinson’s paper (https://www.nature.com/articles/s41598-019-53413-w) the researchers argue the role of the drug is in targeting ER stress, protein misfolding, IP3R etc. The very things I am suggesting may be relevant to autism in today’s post.
Another interesting drug from the former USSR, though actually from Latvia (now in the European Union) is Mildronate. I did suggest a long time ago, based on the research studies, that this might be effective to treat people with a lack of the Mitochondrial Complex 1.
I think mitochondrial disease is likely over diagnosed by MAPS-type doctors, but it is a genuine cause/contributing factor to some people’s autism.
So many people are using Mildronate to boost sporting performance and some for academic performance, it is now widely available from the same vendors /platforms selling Afobazole. (eBay, Amazon etc)
The underlying message is that when considering repurposing safe old drugs to treat neurological conditions, consider all of them, including Japanese, Russian and indeed Latvian.
Many interesting novel substances are mentioned in this blog, like Basmisanil a highly selective negative allosteric modulator of α5 subunit-containing GABAA receptors for the treatment of cognitive impairment specifically associated with Down syndrome. The problem with such novel substances is that they will be ultra expensive and often they fail in their clinical trials and are never commercialized. Roche cancelled Basmisanil because it failed in the Down Syndrome trial. Tuning down the response from GABAa receptors containing the α5 subunit may very well be an effective way to improve cognitive function in some people, but the failure of this trial likely means no new substances will be developed.
While it is okay to write about new drugs in development, the real interest is in applying what can be used today. All four of the following need to be satisfied:
1. Safe (no/minimal side effects, no tolerance, no addiction, interactions)
2. Affordable
3. Available
4. Effective
Some drugs, not commonly used in Western countries, likely do tick the first 3 points, whether effective in autism depends on the individual sub-type. Many do look interesting - from Ibudilast (Japan), to Mildronate (Latvia) for Complex 1 mitochondrial disease and perhaps Afobazole (Russia) for some schizophrenia/autism.
Afobazole is a cheap over-the-counter anxiety treatment in Russia. It is apparently “effective” in the BALB/c mouse model, that may be relevant to autism. BALB/c mice show low sociability, relatively high levels of anxiety and aggressive behaviors, large brain size, underdevelopment of the corpus callosum, and low levels of brain serotonin.
Is Afobazole the answer to ER stress in autism? If not, then what might be? The schizophrenia research suggests 4-phenylbutyrate, salubrinal, cordycepin, taurosodeoxycholic acid. Cordycepin comes from a mushroom that I recall one of our Aspie readers favours.
This post could go on forever; I think I have made my point, but a little more:-
The lipophilic 4-phenylbutyric acid derivative prevents aggregation and retention of misfolded proteins
Chemical chaperones prevent protein aggregation. However, the use of chemical chaperones as drugs against diseases due to protein aggregation is limited by the very high active concentrations (mM range) required for mediating their effect. One of the most common chemical chaperones is 4-phenylbutyric acid (4-PBA). Despite its non-favorable pharmacokinetic properties, 4-PBA was approved as a drug to treat ornithine cycle diseases. Here we report that 2-isopropyl-4-phenylbutanoic acid (compound 5) was (2-10 fold) more effective than 4- PBA in several in vitro models of protein aggregation. Importantly, compound 5 reduced the secretion rate of autism-linked Arg451Cys Neuroligin3 (R451C NLGN3).
Protein misfolding, detectable in blood samples, predicts Alzheimer's Disease up to 14 years before onset, perhaps in time to start effective therapy? perhaps targeting sigma-1R, or perhaps with betanin, that pigment in beetroot, that seems to disrupt plaque formation.
This post could go on forever; I think I have made my point, but a little more:-
The lipophilic 4-phenylbutyric acid derivative prevents aggregation and retention of misfolded proteins
Chemical chaperones prevent protein aggregation. However, the use of chemical chaperones as drugs against diseases due to protein aggregation is limited by the very high active concentrations (mM range) required for mediating their effect. One of the most common chemical chaperones is 4-phenylbutyric acid (4-PBA). Despite its non-favorable pharmacokinetic properties, 4-PBA was approved as a drug to treat ornithine cycle diseases. Here we report that 2-isopropyl-4-phenylbutanoic acid (compound 5) was (2-10 fold) more effective than 4- PBA in several in vitro models of protein aggregation. Importantly, compound 5 reduced the secretion rate of autism-linked Arg451Cys Neuroligin3 (R451C NLGN3).
Protein misfolding, detectable in blood samples, predicts Alzheimer's Disease up to 14 years before onset, perhaps in time to start effective therapy? perhaps targeting sigma-1R, or perhaps with betanin, that pigment in beetroot, that seems to disrupt plaque formation.
Protein misfolding as a risk marker for Alzheimer's disease
In symptom-free individuals, the detection of misfolded amyloid-beta protein in the blood indicated a considerably higher risk of Alzheimer's disease -- up to 14 years before a clinical diagnosis was made. Amyloid-beta folding proved to be superior to other risk markers evaluated.
