Horseshoe Crab – The Blue Blood that Saves Millions Of Lives
Limulus Polyphemus, the Atlantic horseshoe crab which origin 450 million years ago, also known as the “living fossil”. For sure the horseshoe crab doesn’t survive millions of years without learning a trick or two. In this case, the horseshow crab developed blood with remarkable antibacterial properties which have been used in pharmaceutical manufacturing for the past 40 years.
Image by Kristine Paulus via Flickr
What Makes It So Special?
Unlike human red blood, the blood of the horseshoe crab is in milky blue. This is because as oxygen is transported by hemocyanin instead of haemoglobin in vertebrate. That is the reason which makes it valuable.
In the United State, all drugs approved by the Food and Drug Administration (FDA) have to be tested for bacterial contaminants. Endotoxin is a common bacterial contaminant in drugs which might lead to toxic shock or life-threatening fever if it is injected into our body.
From the 1940s to 1970s, all pharmaceutical industries in the US used rabbits to detect the endotoxin. However, this technique was time-consuming and results in thousands of rabbits killed annually. In the 1970s, researchers found out that the blood of horseshoe crab contains amebocytes, which is highly sensitive to endotoxin contamination. The presence of endotoxin will react with the amebocytes, which results in a thick solution. On the other hand, the absence of endotoxin will result normal flow solution in the drug. For the past 40 years till today, all injectable medications and some other drugs are screened for endotoxin using the horseshoe crab blood.
The Pricey Blue Blood
Image by Nizza via ELITE READERS
In order to retrieve a cell critical to medical research, the blood of the horseshoe crab is harvested in massive scale for the past 40 years.
The calls for the blood is increasing years by years, and the population of the horseshoe crab is decreasing. As results, a quart of the horseshoe blood could be sold for US$15,000. To cash in, companies are harvesting up to 600,000 crabs per year. Approximately 13% of the crabs are sold to fisheries as bait, and the rest are released. However, the bleeding and the time out of water results in potential mortality and injury to the horseshoe crabs which consequence 130,000 crabs killed annually.
Time To Stop Horseshoe Crab Harvesting
In 1997, a group of researchers from National University of Singapore found out the potential of using cloned, laboratory-synthesised DNA recombinant Factor C (rFC) to replace the blood of the horseshoe crab for endotoxin screening. However, due to the concern of rFC efficiency and the cautious to adopt a new detection technique, most of the pharmaceutical companies were hesitant to use the alternative rFC.
After 20 years of improvement of rFC, the efficiency of endotoxin detection is better than the horseshoe crab nowadays, and pharmaceutical industries are slowly shifting to the rFC.
For more information please refer to:
1) Saving the horseshoe crab: A synthetic alternative to horseshoe crab blood for endotoxin detection
2) Horseshoe crabs are drained for their blue blood. That practice will soon be over.