A step towards solving the ALS mystery

A step towards solving the ALS mystery

Who can forget the sight of Professor Stephen Hawking hunched in his wheel chair with hands on his lap and speaking through a speech-generating device? Professor Hawking suffered from a type of Motor Neuron Disease (MND) called the Amyotrophic Lateral Sclerosis (ALS), also known as the Lou Gehrig’s disease. It is a progressive disease resulting from the loss of neurons controlling voluntary muscles that produce movement such as talking, moving, and eating. Currently, there is no cure for ALS or treatment for halting the progression of the disease. The patient has 3–4 years at most from the time of diagnosis (Stephen Hawking was an exception). Approximately, fifteen thousand Americans die each year from the disease. There are more men afflicted than women and the incidence of ALS increases after the age of 55.

Prof. Stephen Hawking. Image credit: Getty Images

What we know about ALS? Unfortunately, not much

There are a number of studies, clinical and non-clinical, on ALS to find a cure and to help the patients have a better quality of life. Most of these efforts are hampered because the pathways leading to development of ALS are still unclear. Few genes have been shown to be associated with the disease-C9ORF72, SOD1, FUS, etc. However, 90% of the cases are sporadic with no known cases of the disease in the family. There is no cure for the disease and the drugs approved by the FDA, riluzole and edaravone, only prolong life by few months.

Effect of ALS on nerve cells and muscles

Mechanism of ALS and current study

Cells maintain a fine balance of various cations and anions such as Na+, Cl- and Ca2+through involvement of various organelles, ion pumps, and channels on the cell membrane as well as organelle membranes. Evidence for involvement of Ca2+dysregulation and organelle dysfunction in various neurological and neuro-degenerative diseases is increasing. However, exact mechanisms leading to the death of motor neurons in ALS and other neuro-degenerative diseases remain elusive.

A recent study published in the Frontiers in Cellular Neuroscience(https://doi.org/10.3389/fncel.2016.00295), focuses on involvement of Ca2+ in motor neurons degeneration and how riluzole, but not melatonin, ameliorates MN degeneration in the model systems studied.

Riluzole, a FDA approved neuro-protective drug for ALS, is known to preferentially block sodium channels and also, accelerate glutamate clearance from synapse and prevent glutamate release from presynaptic terminals. Another molecule that has gained recent fame is Melatonin; it’s an antioxidant known to scavenge free radicals and reactive oxygen species (ROS). Melatonin has been shown to be neuro-protective in Alzheimer’s disease, another neuro-degenerative disease with no known cures.

This research, conducted on human cell lines and mice, elegantly shows how the drugs alleviate Ca2+-induced toxicity in the cells and in mitochondria, in particular. Moreover, it establishes a method to screen drug targets individually or together (like in a multi-drug therapy regime) and fast track drug screening at the pre-clinical level.

Years of research discovered a mutation in a key gene SOD1is involved in the pathogenicity of ALS. The current research study investigated how two drugs, riluzole and melatonin, might prevent the mitochondrial SOD1mediated cell death. They used the chemical, sodium azide, a known inhibitor of mitochondria electron transport chain IV, to induce excitotoxicity and eventual cell death in control and SOD1 mutant cells. They then observe how this toxicity is reduced when riluzole and melatonin are used. Intracellular calcium levels were measured using fluorescence-based assays. They go on to show how the function of mitochondria is affected in SOD1 mutant human cells and mice leading to motor neurons degeneration and that riluzole, but not melatonin, moderately ameliorates MN degeneration by inhibiting calcium toxicity.

Mechanism of action of Riluzole on SOD-1

The project leader and lead author of the paper, Dr. Manoj Kumar Jaiswal, when asked how this work is significant, answered, “Many ALS clinical trials investigating the efficacy of a new drug have failed due to the vast heterogeneity of the ALS patient population, resulting in drugs benefitting a small patient subgroup. We have done the groundwork and tested the efficacy of these two drugs (riluzole and melatonin) on mutant SOD1neuronal cell lines and control cells. Different patient cell types react differently to the same antioxidant drugs and therefore our study can be extended in the future to either motor neurons co-cultured with astrocytes, microglia, oligo dendrocytes and several other cell types or cell types specific iPSC (induced Pluripotent Stem Cells) derived from ALS patients”.

“Molecules targeting the protection of mitochondrial function and Ca2+ homeostasis could be useful in both sporadic and familial ALS and most likely prolong survival of ALS patients”

This work has shown the importance of gaining exact knowledge of mechanism of drug action and goes on to show how riluzole can prevent cell death by restoring Ca2+homeostasis. Dr. Jaiswal concludes, “Molecules targeting the protection of mitochondrial function and Ca2+ homeostasis could be useful in both sporadic and familial ALS and most likely prolong survival of ALS patients”. His experiments promise a potential effective and methodological way to test the multiple drugs and their targets using different drug cocktails to check the efficacy of multi-drug therapy.