ALS - Mutation, Protein Misfolding and a Possible Treatment
Amyotrophic Lateral Sclerosis or ALS
Amyotrophic lateral sclerosis can be a devastating disease, as I unfortunately know from experience. My mother died from the illness. The condition is also known as ALS, motor neuron or motor neurone disease, and Lou Gherig's disease. Gherig was a famous New York Yankees player who suffered from the illness. ALS is proving to be a very difficult condition to understand and to treat. A recent and exciting discovery at Oregon State University may lead to an effective treatment for at least some cases of the disease, however.
ALS is a neurodegenerative condition in which motor neurons are harmed and stop functioning. These neurons, or nerve cells, control movement, swallowing, speaking and breathing. The patient develops problems with all these abilities, but in many patients the cognitive abilities of the brain are unaffected. Death is generally a consequence of breathing problems. Most ALS patients die within two to five years of diagnosis.
Technically, the term "motor neuron disease" refers to a group of diseases involving the degeneration of motor neurons. In North America, though, the term is nearly always synonymous with amyotrophic lateral sclerosis. In the UK, the term "motor neurone disease" is used for ALS.
Stephen Hawking and ALS
Stephen Hawking is often mentioned with respect to ALS, or motor neurone disease as it's called in Britain. His case offers hope to other patients and also illustrates our lack of understanding of the disease. Hawking is a famous physicist who has lived with amyotrophic lateral sclerosis since he was diagnosed in 1963 at the age of twenty-one. He has a very slowly progressing form of the disease that appeared at a relatively early age. In most ALS sufferers, the disease appears in middle age or later and progresses rapidly.
Hawking's condition is gradually worsening. He's confined to a wheelchair and needs special equipment in order to communicate. He is still exploring theoretical physics, however, and is making some interesting proposals about the nature of the universe.
The Nervous System
Finding a Cure for ALS
It's very hard to create a treatment for a disease when we don't understand its cause. There are still many unanswered questions about the development of ALS. Researchers continue to make discoveries, but the problem as I see it is that the separate discoveries can't yet be related to each other in order to make a unified whole. There are different subtypes of ALS, so there may well be multiple causes of the disease and different processes that lead to similar symptoms.
The only drug that extends life for ALS patients at the moment is riluzole (brand name Rilutek). This drug only works in some people and only lengthens life for a few months. It's thought to lower the high level of glutamate in the central nervous system. Toxicity to nerves from excess glutamate is one of the proposed causes of ALS. Glutamate may be a factor in the disease, but we need to find the primary cause in order to create a truly effective treatment.
An Overview of Amyotrophic Lateral Sclerosis
The video above refers to the Ice Bucket Challenge for ALS. In this event, volunteers agree to have icy water thrown over them and to be filmed while this happens in order to raise awareness for ALS. Another goal of the event is to raise money for ALS research.
Familial and Sporadic ALS
Amyotrophic lateral sclerosis is most commonly classified as either familial or sporadic. As its name suggests, familial ALS runs in families and is believed to be caused by a mutated gene. Sporadic ALS appears for no known reason, although it's thought to be due to a combination of a genetic problem and an environmental trigger. About ninety percent of ALS cases are sporadic.
DNA, or deoxyribonucleic acid, is located in the nucleus of a cell. The order of nitrogenous bases on one strand of a DNA molecule provides instructions for making proteins.
A protein-coding gene is a section of a DNA molecule that contains the instructions for making one protein. The instructions are encoded in a series of chemicals known as nitrogenous bases. When a gene mutates, the order or identity of the nitogenous bases is altered. As a result, the code is changed and an altered protein is made (if it can be made at all). Like the gene, the altered protein is often said to be mutated.
The SOD1 Protein and ALS
Familial ALS has frequently been linked to a mutation in the gene that codes for a protein called copper, zinc superoxide dismutasase. This protein is also known as SOD1. SOD1 acts as an enzyme (a protein that controls chemical reactions) and serves a very important function. It breaks down superoxide radicals. These radicals are by-products of cellular processes involving oxygen. They are dangerous because they damage cells. Cells normally remove the superoxide radicals once they form, however, so they remain safe.
In many people with familial ALS, the mutated gene for SOD1 causes an abnormal protein to be made. The mutated SOD1 protein is misfolded. Proteins are long chains of amino acids that must be folded into a specific shape in order to do their job.
Misfolded SOD1 is unable to perform its usual function. Research in mice suggests that this is not the main reason why the mutant protein is harmful, however. The mutated SOD1 protein appears to be toxic to neurons.
A protein is made of a chain of amino acids. The chain is known as a polypeptide, since peptide bonds join the amino acids together. Many proteins consist of more than one polypeptide.
The Oregon State University Research
The researchers at Oregon State University performed their experiment with a "mouse model" of ALS. The mice were genetically programmed to develop the disease and had a mutated gene for SOD1. The scientists were able to stop the progression of ALS in the mice by treating them with a chemical called Cu-ATSM. The mice went on to live an almost normal lifespan.
When the researchers stopped the treatment in one group of mice, the symptoms of ALS began to worsen within two months. If treatment wasn't resumed, the mice died. If the scientists resumed the Cu-ATSM treatment in the mice, the progression of the disease stopped and the mice survived.
The results of the experiment were clear-cut and impressive. Clinical trials must be performed to see if the same results occur in humans, however.
The Blood-Brain Barrier or BBB
Cu-ATSM is a chemical compound that is already used in medicine in low doses. It's a significant chemical because it's able to cross the blood-brain barrier. This barrier consists of a network of tiny blood vessels, or capillaries, in the brain and spinal cord. Capillaries exist throughout the body, but the ones in the central nervous system have a special feature. The endothelial cells that line the capillaries in the CNS lie much closer together than those in other capillaries. The cells form a barrier that prevents substances from leaving the bloodstream and entering the CNS.
Essential substances such as oxygen and nutrients can still pass through the blood-brain barrier using specific transport methods, but many chemicals are blocked. The barrier is important because it keeps harmful substances out of the central nervous system. However, it makes it hard for doctors to deliver medicines to the CNS. Fortunately, Cu-ATSM can cross the blood-brain barrier.
Copper-ATSM and the SOD1 Protein
At the moment, Cu-ATSM is mainly used for imaging studies. It's useful for detecting tissues that contain a low oxygen level. The new research indicates that Cu-ATSM has another useful function. It's able to deliver copper to cells in the brain and spinal cord, including the motor neurons.
Copper is an essential part of SOD1's structure. A mutated, copper-deficient form of the protein is believed to be involved in some cases of familial ALS. Without copper, the protein is unable to fold correctly.
It's thought that copper supplied by Cu-ATSM prevents the misfolding of SOD1 in a nerve cell. A protein called copper chaperone for SOD transfers the copper from the Cu-ATSM to the SOD1.
The copper from Cu-ATSM may have additional benefits within the cell. For example, it seems to improve the condition of mitochondria. Mitochondria are the organelles that produce energy for cells.
The researchers caution that ALS sufferers mustn't take large doses of a copper supplement as a self-treatment. Supplemental copper doesn't behave the same way inside the body as Cu-ATSM. In addition, ingesting copper supplements at high or even moderate doses is dangerous.
Interpreting the Results of the Mouse Experiment
The new discovery is very exciting, but we need to interpret it with some caution. First, the research was performed in genetically-altered mice, not humans. Mouse results often apply to humans, but not always. The researchers hope to start clinical trials in humans as soon as possible.
Secondly, the discovery most obviously applies to certain cases of familial ALS. There is evidence that SOD1 problems are involved in at least some people with sporadic ALS, however, so the new discovery may be useful for this type of ALS as well. Another point to note is that although the treatment stopped ALS from getting worse and killing the mice, it didn't repair neuron damage that had already occurred.
On the plus side, this is not the first time that scientists have found a possible benefit of Cu-ATSM for ALS symptoms. The discovery could be excellent news for at least some ALS patients if its safety and effectiveness are confirmed.
If the treatment becomes a reality, therapeutical techniques and special equipment might be able to help patients deal with the symptoms that have already developed. In the future, researchers may find a way to improve the condition of damaged neurons. The researchers may even find a way to generate new motor neurons from stem cells and then implant them into the body of ALS patients. This strategy is already bring explored.
ALS and Protein Misfolding
Dr. Cashman has made an observation that has also been made by other scientists. Once a protein is misfolded in ALS, it appears to trigger another one to misfold. This process repeats in a chain reaction like a row of dominoes collapsing.
Significance of the Discovery for Neurodegenerative Diseases
The new discovery is very interesting with respect to ALS treatment. It could also be indirectly significant for some other neurodegenerative diseases. Protein misfolding is involved in Alzheimer's disease and Parkinson's disease as well as in ALS. An understanding of why and how proteins misfold could help more than one health problem.
The Oregon State University researchers must demonstrate that the higher doses of Cu-ATSM needed to (potentially) treat ALS are safe before they can start clinical trials. If the clinical trials are successful, the copper compound will probably be offered to the general ALS population. The researchers say that they are moving as quickly as possible. Time is of the essence when treating ALS.
The research results have attracted a great deal of attention. One of the researchers has posted an online letter to ALS patients. People concerned about the disease have waited a very long time for an effective treatment. I hope the recent discovery is helpful for many people.
© 2016 Linda Crampton
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