More about the toxin, Domoic acid..

Domoic acid is a potent neurotoxin produced by a naturally occuring Harmful Algal Bloom. Specifically, it is made by a microscopic, red-brown, salt-water plant, or diatom calledNitzchia pungens. The toxin produced by these diatoms is concentrated in shellfish such as mussels and causes Amnesic Shellfish Poisoning when the contaminated shellfish are eaten. What makes this toxin more dangerous is the fact that it is not destroyed after cooking, which can cause many unsuspecting consumers to fall ill with Amnesic Shellfish Poisoning..

How dangerous is Domoic Acid?
Domoic acid is a toxin that affects the brain, specifically the  hippocampus, and affects both animals and humans. It may cause severe health implications.

Fig 1- Left: normal California sea lion brain section. Right: a not so normal one that has been affected by domoic acid exposure; notice the shrunken hippocampus in the center of the brain section

In humans..
Domoic Acid causes Amnesic Shellfish Poisoning(ASP).  ASP can be a life-threatening syndrome, and is characterized by both gastrointestinal and neurological disorders.
After consumption of the contaminated shellfish, Gastroenteritis usually develops.

Symptoms include:
-Nausea
-Vomiting
-Abdominal cramps
-Diarrhea.

In severe cases, neurological symptoms also appear, usually within 48 hours of toxic shellfish consumption.

Symptoms include:
-Dizziness
-Headache
-Seizures
-Disorientation
-Short-term memory loss
-Respiratory difficulty
-Coma


How does Domoic Acid work?

To understand this, we first have to introduce a new molecule- Glutamic acid.

Fig 2: Glutamic Acid structure

So what’s so important about this molecule?
Glutamate (the ionized form of glutamic acid) is a neurotransmitter, a molecule used to send a message from one nerve cell to another, and plays an important role in thought, learning, and memory. Binding of glutamate to a glutamate receptor causes the opening of channels allowing embedded on the membrane of the receiving nerve cell, the receptor opens channels in the membrane that allow calcium ions to flow into the cell. The influx of charge causes a voltage to build up across the cell membrane, and the nerve cell fires, passing the signal on to the next nerve cell.

However, too much glutamate acts as an excitotoxin- which kills cells by exciting them too much. This will eventually lead to an excitotoxic cascade, which plays an important role in brain injury and neurodegenerative diseases.

Now, back to Domoic Acid and how it causes damage to the brain.

Domoic acid’s structure is similar to glutamic acid.As a result, nerve cells mistakenly recognize domoic acid as glutamic acid- a fatal error.  Its five-sided ring makes it less flexible than glutamate, which causes it to bind very tightly to glutamate receptors. As a result, the excitatory effect of domoate is 30 to 100 times more powerful than that of glutamate, resulting in an excitotoxic cascade.

What is being done now to prevent another outbreak of Amnesic Shellfish Poisoning?
Luckily for us, commercial shellfish and seafood are now monitored regularly for domoic acid, using HPLC(High-Performance Liquid Chromatography) to identify the toxin. The screening and testing procedures have so far been successful- not a single instance of domoic acid poisoning in humans has been reported since the 1987 outbreak.

Read on to our next post to find out how we can carry out Quantitative Analysis on Domoic Acid!

Citations

1. Egglilng, S. (n.d.). Common names of amino acids. Retrieved from http://dl.clackamas.cc.or.us/ch106-05/common.htm

2. Foley, S. (2009, July 01). Domoic acid-toxipedia. Retrieved from http://toxipedia.org/display/toxipedia/Domoic Acid

3. Senese, F. (2010, February 15). General chemistry online: The poisoned needle. Retrieved from http://antoine.frostburg.edu/chem/senese/101/features/domoic.shtml

4. Human illness associated with hab. (n.d.). Retrieved from http://www.whoi.edu/science/B/redtide/illness/illness.html

5. Potera, C. (2009). Harmful algal blooms: An unexpected deep-sea diver. Environ Health Perspect, 117(6), Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2702427/

 6. The marine mammal centre: Domoic acid toxicity. (n.d.). Retrieved from http://www.marinemammalcenter.org/science/top-research-projects/domoic-acid-toxicity.html