Amyotrophic lateral sclerosis research

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Research on amyotrophic lateral sclerosis (ALS) has focused on animal models of the disease, its mechanisms, ways to diagnose and track it, and treatments. [1]

Contents

Disease models

Many models have been used by researchers in labs to study the disease pathways, mechanisms, and symptoms on simple organisms. [2] [1]

In vitro

In this strategy the disease is introduced to cell cultures in petri dishes. [2] In this case, motor cells can be grown, and the gene expression is controlled. CRISPR/Cas9 technique can be used to knock-out/in genes that are related to ALS, and it is very beneficial in increasing the expression of the genes to mimic the human model of ALS for a faster onset of the disease. [2] This type of model can be beneficial in high-throughput screening for drug candidates for ALS. [2]

Familial ALS is the most studied; however, a new technique that was recently introduced is the use of induced pluripotent stem cells (iPSC). [2] In this study the researcher can isolate skin fibroblast from a patient with familial or sporadic ALS and reprogram them into motor neuron to study ALS. [2] The main advantage of iPSC is that it allowed researchers to study and understand sALS, and it shows a remarkable contribution in cell-based therapy and drug screening. [2] A recent example had used iPSC of patient with SOD1 dominant mutation and they studied the motor neurons derived from the patient, and they found that the functional genes and the ER stress regulating genes of the mitochondria were reduced in SOD1 patients, similar to the effect of C9orf72 mutation on the patients. [3] In addition, some studies showed that iPSC is better than other types of stem cells due to its ability in differentiating into a mature neuron cell, and many other cells too. These iPSC derived cells can be used in transplant cell therapy, in which they can introduce the differentiated cells into the ALS patient to reduce the symptoms without harming the patient. [3]

In vivo

Many animals have been used over the years to study ALS and to search for a potential therapy. [1] The animal models can be C. elegans which has only 959 cells with simple structure, and known gene code. [4] Also, some studied have introduced the transgenic strain of C. elegans, which has a mutation in a gene related to ALS for example, and crossed them with the transgenic nlp-29 GFP reporter strain, resulting in fluorescent markers to the cells that are expressing these mutated genes, which can be used to monitor the disease development and effects. [5] Similar, but more complex nervous system from the C. elegans is the Drosophila . Fruit fly ALS models can be used to study the locomotion and eye changes that can be related to human symptoms. [6] Thus, drugs can be tested on these transgenic fruit flies to discovery new target molecules. [4] [6] On the other hand, zebrafish models have been used widely due to their similarity in the development and anatomy characteristics as a vertebrate to the human body. [4] A study introduced the SOD1/GFP transgenic zebra-fish to study that specific gene on the development and occurrence of ALS in the fish, and how can that be used in testing potential therapeutic molecules. [7] All the previous models are considered simple, and save time and money due to their short lifespan and small and simple body structure. [4]

The most studied model for ALS is the rodent, mouse model, which provide the most complex representation of nervous system that is considered the closest in mimicking human nervous system. [4] In this model, the phenotype, and genotype characteristics can be studied and controlled. Many researchers have used transgenic mouse models to study ALS, and one example is the expressing of C9orf72 mutation that can be introduced in mouse using the BAC C9orf72 gene with the multiple repeats of GGGGCC. [8] In that study they chose the bacterial artificial chromosome that has the human length of C9orf72 gene, and they introduced multiple repeats for faster onset of ALS. [8] Also, they have selected for the most stable clone using different conditions, and concluded that the 40 and 500 repeats in the low temperature condition was the most efficient in retaining expansion mutations. [8] Using different BAC C9orf72 transgenic mouse model, they were able to study the symptoms of ALS, such as gait abnormalities, anxiety-like behavior, reduced grip strength, and even death rates. [8] Also, the denervation of motor neurons and dysfunction of neurons can be visualized using fluorescent markers to study the neurodegenerative disorder progression in ALS. [8] Another study also used the SOD1 mutation transgenic mice where they have showed similar signs of ALS that included the axonal and mitochondrial dysfunction and denervation of motor neurons and the reduction of the overall number of neurons in the limbs of the mouse. [9] The TDP-43 transgenic mouse model was also used for ALS studies and it shows similar results to the SOD1 expression, which includes the axon denervation phenotype. [9] For this model which depends on the promoters, they have made many other transgenic mouse models that uses different promoter to compare their phenotype and progression of TDP-43 ALS. [9] Rat models, on the other hand is not very widely used, but their large size can be beneficial in intrathecal injection or mini pump insertion is needed in pharmacological trials. In fact, studied showed that using SOD1 transgenic rat models showed similar development of the genetic and phenotypic traits of the ALS disease. [9]

In silico

Since the early 2000s, computational approaches involving the application of computational statistics and machine learning techniques to data of patients diagnosed with ALS have been employed by researchers worldwide. For example, crowd-sourcing DREAM challenge about computational approaches for ALS electronic health records' data has been carried out in 2017. [10]

Potential treatments

Past clinical trials

From the 1960s until 2014, about 50 drugs for ALS were tested in randomized controlled trials (RCTs); of these, riluzole was the only one that showed a slight benefit in improving survival[ citation needed ]. Drugs not shown to be effective in clinical trials in humans include antiviral drugs (transfer factor, tilorone, indinavir, [11] and amantadine); [12] anti-excitotoxic drugs (branched-chain amino acids, threonine, lamotrigine, gabapentin, nimodipine, dextromethorphan, topiramate, memantine, talampanel, and ceftriaxone), growth factors (acetylcholinesterase inhibitors, octacosanol, gangliosides, thyrotropin-releasing hormone, growth hormone, and erythropoietin); neurotrophic factors (ciliary neurotrophic factor, insulin-like growth factor 1, brain-derived neurotrophic factor, glial cell line-derived neurotrophic factor, xaliproden, and granulocyte colony-stimulating factor), anti-inflammatory drugs (plasma exchange, cyclosporine, [11] cyclophosphamide, [12] total lymphoid irradiation, glatiramer acetate, celecoxib, minocycline, and NP001); antioxidants (acetylcysteine, glutathione, selegiline, vitamin E, and coenzyme Q); anti-apoptotic drugs (pentoxyfilline, omigapil, and minocycline); and drugs to improve mitochondria function (creatine, acetyl-L-carnitine, dexpramipexole, and olesoxime). Other drugs with a variety of mechanisms were tested in clinical trials and not shown to be effective, including phenylbutyrate, valproic acid, lithium carbonate, pioglitazone, Ono-2506 (arundic acid), and arimoclomol. [11]

Repetitive transcranial magnetic stimulation had been studied in amyotrophic lateral sclerosis in small and poorly designed clinical trials; as of 2013, there was insufficient evidence to know whether rTMS is safe or effective for ALS. [13]

One 2016 review of stem cell therapy trials found tentative evidence that intraspinal stem cell implantation was relatively safe and possibly effective. [14] A 2019 Cochrane review of cell based therapies found that there was insufficient evidence to speculate about efficacy. [15] Stem cell therapy can provide additional proteins and enzymes that have shown to help prolong survival and control the symptoms associated with ALS. [16] [17] Those proteins include neurotrophic factors and insulin-like growth factor 1. Both those proteins are still under clinical trials and need to be further studied to evaluate their efficiency and associated side effects. [16] [17]

Masitinib has been approved as an orphan medication in Europe and the United States with studies ongoing as of 2016. [18] Medications tested but without evidence for efficacy include lamotrigine, dextromethorphan, gabapentin, BCAAs, Vitamin E, acetylcysteine, selegiline, amantadine, cyclophosphamide, various neurotrophic factors, which has shown promise in both in-vitro and in-vivo models of ALS but is yet to be effective in human models of ALS [12] [16] [17] and creatine. [19] Beta-adrenergic agonist drugs have been proposed as a treatment for their effects on muscle growth and neuroprotection, but there is insufficient research in humans to determine their efficacy. [20]

Techniques to deliver drugs and medications in a better manner are also being investigated and those include altering and developing drugs with specific characteristics, such as size and charge, to allow for their passage through the blood-brain barrier. [17] [21] Furthermore, specific antisense oligonucleotides are being developed that may slow down the progression of ALS and reduce toxicity. [21] Antisense oligonucleotides target specific sequences associated with the C9ORF72 gene that has been identified as a cause for ALS. [21] Another delivery technique being investigated is through adeno-associated viruses that have the ability to deliver drugs and other proteins and genetic components to the central nervous system and aid in protecting neurons from damage caused by ALS. [17] [21]

Related Research Articles

<span class="mw-page-title-main">Motor neuron diseases</span> Group of neurological disorders affecting motor neurons

Motor neuron diseases or motor neurone diseases (MNDs) are a group of rare neurodegenerative disorders that selectively affect motor neurons, the cells which control voluntary muscles of the body. They include amyotrophic lateral sclerosis (ALS), progressive bulbar palsy (PBP), pseudobulbar palsy, progressive muscular atrophy (PMA), primary lateral sclerosis (PLS), spinal muscular atrophy (SMA) and monomelic amyotrophy (MMA), as well as some rarer variants resembling ALS.

Gene silencing is the regulation of gene expression in a cell to prevent the expression of a certain gene. Gene silencing can occur during either transcription or translation and is often used in research. In particular, methods used to silence genes are being increasingly used to produce therapeutics to combat cancer and other diseases, such as infectious diseases and neurodegenerative disorders.

Antisense therapy is a form of treatment that uses antisense oligonucleotides (ASOs) to target messenger RNA (mRNA). ASOs are capable of altering mRNA expression through a variety of mechanisms, including ribonuclease H mediated decay of the pre-mRNA, direct steric blockage, and exon content modulation through splicing site binding on pre-mRNA. Several ASOs have been approved in the United States, the European Union, and elsewhere.

<span class="mw-page-title-main">Peripherin</span> Protein-coding gene in the species Homo sapiens

Peripherin is a type III intermediate filament protein expressed mainly in neurons of the peripheral nervous system. It is also found in neurons of the central nervous system that have projections toward peripheral structures, such as spinal motor neurons. Its size, structure, and sequence/location of protein motifs is similar to other type III intermediate filament proteins such as desmin, vimentin and glial fibrillary acidic protein. Like these proteins, peripherin can self-assemble to form homopolymeric filamentous networks, but it can also heteropolymerize with neurofilaments in several neuronal types. This protein in humans is encoded by the PRPH gene. Peripherin is thought to play a role in neurite elongation during development and axonal regeneration after injury, but its exact function is unknown. It is also associated with some of the major neuropathologies that characterize amyotropic lateral sclerosis (ALS), but despite extensive research into how neurofilaments and peripherin contribute to ALS, their role in this disease is still unidentified.

Primary lateral sclerosis (PLS) is a very rare neuromuscular disease characterized by progressive muscle weakness in the voluntary muscles. PLS belongs to a group of disorders known as motor neuron diseases. Motor neuron diseases develop when the nerve cells that control voluntary muscle movement degenerate and die, causing weakness in the muscles they control.

<span class="mw-page-title-main">Neurodegenerative disease</span> Central nervous system disease

A neurodegenerative disease is caused by the progressive loss of structure or function of neurons, in the process known as neurodegeneration. Such neuronal damage may ultimately involve cell death. Neurodegenerative diseases include amyotrophic lateral sclerosis, multiple sclerosis, Parkinson's disease, Alzheimer's disease, Huntington's disease, multiple system atrophy, tauopathies, and prion diseases. Neurodegeneration can be found in the brain at many different levels of neuronal circuitry, ranging from molecular to systemic. Because there is no known way to reverse the progressive degeneration of neurons, these diseases are considered to be incurable; however research has shown that the two major contributing factors to neurodegeneration are oxidative stress and inflammation. Biomedical research has revealed many similarities between these diseases at the subcellular level, including atypical protein assemblies and induced cell death. These similarities suggest that therapeutic advances against one neurodegenerative disease might ameliorate other diseases as well.

Progressive bulbar palsy (PBP) is a medical condition. It belongs to a group of disorders known as motor neuron diseases. PBP is a disease that attacks the nerves supplying the bulbar muscles. These disorders are characterized by the degeneration of motor neurons in the cerebral cortex, spinal cord, brain stem, and pyramidal tracts. This specifically involves the glossopharyngeal nerve (IX), vagus nerve (X), and hypoglossal nerve (XII).

Mecasermin rinfabate, also known as rhIGF-1/rhIGFBP-3, is a drug consisting of recombinant human insulin-like growth factor 1 (IGF-1) and recombinant human insulin-like growth factor binding protein-3 (IGFBP-3) which is used for the treatment of amyotrophic lateral sclerosis.

<span class="mw-page-title-main">Xaliproden</span> Chemical compound

Xaliproden is a drug which acts as a 5HT1A agonist. It has neurotrophic and neuroprotective effects in vitro, and has been proposed for use in the treatment of several neurodegenerative conditions including amyotrophic lateral sclerosis (ALS) and Alzheimer's disease.

<span class="mw-page-title-main">SOD1</span> Protein-coding gene in the species Homo sapiens

Superoxide dismutase [Cu-Zn] also known as superoxide dismutase 1 or hSod1 is an enzyme that in humans is encoded by the SOD1 gene, located on chromosome 21. SOD1 is one of three human superoxide dismutases. It is implicated in apoptosis, familial amyotrophic lateral sclerosis and Parkinson's disease.

<span class="mw-page-title-main">ALS</span> Rare neurodegenerative disease

Amyotrophic lateral sclerosis (ALS), also known as motor neurone disease (MND) or Lou Gehrig's disease, is a rare and terminal neurodegenerative disease that results in the progressive loss of motor neurons that control voluntary muscles. ALS is the most common form of the motor neuron diseases. Early symptoms of ALS include stiff muscles, muscle twitches, gradual increasing weakness, and muscle wasting. Limb-onset ALS begins with weakness in the arms or legs, while bulbar-onset ALS begins with difficulty in speaking or swallowing. Around half of people with ALS develop at least mild difficulties with thinking and behavior, and about 15% develop frontotemporal dementia. Motor neuron loss continues until the abilities to eat, speak, move, or, lastly, breathe are lost.

Pridopidine is an orally administrated small molecule investigational drug. Pridopidine is a selective and potent Sigma-1 Receptor agonist. It is being developed by Prilenia Therapeutics and is currently in late-stage clinical development for Huntington’s disease (HD) and Amyotrophic Lateral Sclerosis (ALS).

Ozanezumab is a monoclonal antibody designed for the treatment of ALS and multiple sclerosis.

<span class="mw-page-title-main">C9orf72</span> Protein-coding gene in the species Homo sapiens

C9orf72 is a protein which in humans is encoded by the gene C9orf72.

Project MinE is an independent large scale whole genome research project that was initiated by 2 patients with amyotrophic lateral sclerosis and started on World ALS Day, June 21, 2013.

Neuroinflammation is inflammation of the nervous tissue. It may be initiated in response to a variety of cues, including infection, traumatic brain injury, toxic metabolites, or autoimmunity. In the central nervous system (CNS), including the brain and spinal cord, microglia are the resident innate immune cells that are activated in response to these cues. The CNS is typically an immunologically privileged site because peripheral immune cells are generally blocked by the blood–brain barrier (BBB), a specialized structure composed of astrocytes and endothelial cells. However, circulating peripheral immune cells may surpass a compromised BBB and encounter neurons and glial cells expressing major histocompatibility complex molecules, perpetuating the immune response. Although the response is initiated to protect the central nervous system from the infectious agent, the effect may be toxic and widespread inflammation as well as further migration of leukocytes through the blood–brain barrier may occur.

<span class="mw-page-title-main">Epigenetics of neurodegenerative diseases</span> Field of study

Neurodegenerative diseases are a heterogeneous group of complex disorders linked by the degeneration of neurons in either the peripheral nervous system or the central nervous system. Their underlying causes are extremely variable and complicated by various genetic and/or environmental factors. These diseases cause progressive deterioration of the neuron resulting in decreased signal transduction and in some cases even neuronal death. Peripheral nervous system diseases may be further categorized by the type of nerve cell affected by the disorder. Effective treatment of these diseases is often prevented by lack of understanding of the underlying molecular and genetic pathology. Epigenetic therapy is being investigated as a method of correcting the expression levels of misregulated genes in neurodegenerative diseases.

There are more than 25 genes known to be associated with amyotrophic lateral sclerosis (ALS) as of June 2018, which collectively account for about 70% of cases of familial ALS (fALS) and 10% of cases of sporadic ALS (sALS). About 5–10% of cases of ALS are directly inherited. Overall, first-degree relatives of an individual with ALS have a 1% risk of developing ALS. ALS has an oligogenic mode of inheritance, meaning that mutations in two or more genes are required to cause disease.

Bryan J. Traynor is a neurologist and a senior investigator at the National Institute on Aging, and an adjunct professor at Johns Hopkins University. Dr. Traynor studies the genetics of human neurological conditions such as amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). He led the international consortium that identified pathogenic repeat expansions in the C9orf72 gene as a common cause of ALS and FTD. Dr. Traynor also led efforts that identified other Mendelian genes responsible for familial ALS and dementia, including VCP, MATR3, KIF5A, HTT, and SPTLC1.

Merit Cudkowicz is an American neurologist and neuroscientist who studies amyotrophic lateral sclerosis (ALS). Cudkowicz is Julieanne Dorn Professor of Neurology at Harvard Medical School, director of the ALS clinic and the Neurological Clinical Research Institute at Massachusetts General Hospital (MGH), and chair of the Department of Neurology at MGH. Cudkowicz has led several large-scale collaborations and clinical trials to test novel treatments for ALS and as of 2020, researching ways to detect early biomarkers of ALS to improve diagnosis.

References

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  18. ↑ "Public summary of opinion on orphan designation Masitinib mesilate for treatment of amyotrophic lateral sclerosis" (PDF). EMA. European Medicines Agency, Committee for Orphan Medicinal Products. 22 September 2016. Archived (PDF) from the original on 6 November 2016. Retrieved 6 November 2016.
  19. ↑ Pastula, Daniel M.; Moore, Dan H.; Bedlack, Richard S. (12 December 2012). "Creatine for amyotrophic lateral sclerosis/motor neuron disease". The Cochrane Database of Systematic Reviews. 12: CD005225. doi:10.1002/14651858.CD005225.pub3. ISSN   1469-493X. PMID   23235621.
  20. ↑ Bartus, Raymond T.; Bétourné, Alexandre; Basile, Anthony; Peterson, Bethany L.; Glass, Jonathan; Boulis, Nicholas M. (1 January 2016). "β2-Adrenoceptor agonists as novel, safe and potentially effective therapies for Amyotrophic lateral sclerosis (ALS)". Neurobiology of Disease. 85: 11–24. doi: 10.1016/j.nbd.2015.10.006 . ISSN   1095-953X. PMID   26459114.
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