Horseshoe Crabs

I need to suck your blood….

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OK. Today is the day for the WayBack Machine. And, that will be true for a whole bunch of reasons.

Mr. Peabody's WayBack Machine

Medical products (devices, drugs, components) that may come in contact with human cells (or extracorpreal blood circulation) have to be free of microbes and pyrogens. Microbes, I’m sure you understand. Bacteria could produce infections in humans, so their presence in drugs or devices would prove to be a grave danger. Pyrogens, you might never heard about. A pyrogen is a portion of a DEAD or destroyed gram-negative bacteria. The cell walls of these cells have components that, when in contact with human cells, cause a reaction- a temperature rise (hence the word PYROgen), or an inflammatory response.

Way back (here’s the first instance) when I began my involvement with dialysis, neurosurgery, and respiratory care, the testing for microbes was straight-forward. Various petri dishes containing different kinds of agar (which would promote the growth of the microbes about which we were petrified could come in contact with humans) were inoculated with samples of our drug, swabs from our devices, etc. After 1,2, or 3 days (called the inoculation period), we’d check to see if any bacteria grew. If they did, we generally had a failed batch. If not, the product could be used (sold or shipped).

To check for pyrogens,  a more elaborate approach was required. We had to use rabbits to discern if our product was at risk. While the test procedures were nailed down in 1920, it wasn’t until 1942 that the USP (United States Pharmacopeia) adopted the test as part of a standard demonstrating the safety of a product. An intravenous injection into a group of 3 rabbits (with internal temperatures between 38 and 39.8 C- and none of the temperature span sexceeding 1 C) is effected and then we wait for a (hoping that there is no) rise in temperature of the rabbit. Rabbits were chosen because they were “cheap” animals and provided reproducible results.

(This has nothing to do with the subject. But, I bet you didn’t know that rabbit fur was a critical component for the first Xerox machines. The fur “cleaned off” the copy drum- and precluded the buildup of static electricity. My dad’s company supplied those pelts to Xerox!)

In 1977, the FDA first considered the use of a different test, the Limulus Amoebocyte Lysate (LAL) testing. By 1983, the LAL test was considered acceptable for final product testing.

LAL Test Kit

But, what the heck is LAL? We recover it from the blood (loosely defined) of horseshoe crabs. It’s based on copper and it gleams blue when in contact with oxygen- as opposed to our blood that gleams red when oxygenated and blue when it’s deprived. But, it’s the immune cells in their blood that we want- these amoebocytes clump and form a gel when in contact with a bacterium- or a portion of said microbe.

Horseshoe crabs, which look like German combat helmets, with a 15 cm spine (a bony Davy Crockett appendage), and ten eyes, produce this stuff. And, horseshoe carbs have been around a very long time. (Here comes the next WayBack machine.) These living fossils (I kid you not) have been around for 450 million years. Yes, million! One of the few dinosaur-era organisms that survived nature’s desire to render extinct their cousins. (And, here you thought the cockroach was the most likely creature to survive millennia! Well, these creatures predate them.)

Horseshoe Crabs

They really aren’t crabs, either. They predate spiders and scorpions (and trilobites). But, crabs is the name we gave them. They are found in the Delaware Bay and the New England coastlines. Every May and June, when there is a new Jewish month (i.e., no moon) and during high tide, the crabs have an orgy on the beaches. (The original “sex on the beach”!) And, then bury their eggs.

Remember, when these suckers first came about, there were no land animals. So, burying their eggs guaranteed their survival. Because there were no creatures to dig the eggs up from the sand.

After the crabs are hatched, they molt 18 times over their first decade. Then, they are “old” enough to spawn. Not surprisingly, they don’t spawn in captivity- they are very particular where their orgies are to be held! As far as we can tell, there are at least 4 million (but less than 12 million) of them living in the Atlantic (and it’s only one species). In the Pacific, three species obtain- and the counts of them are even more “squishy”.

Nowadays, crabbers collect the animals and send them to a few labs. The labs suck about 1/3 of the blood from the crabs, recover the immune cells, process them into LAL, and then the crabs are dropped back into the same waters from which they were robbed. (That’s why there are two big processors of LAL- one in New England, the other off the Chesapeake.) We’re talking about $ 50 million of LAL assays sold a year, by the way.

So, it’s not surprising that the Atlantic Horseshoe Crab is now considered “vulnerable”. And, it’s not just the LAL business (which only vampires 500K crabs a year)- because it doesn’t kill them per se- but it seems that 20 to 30% may not survive our catch and release programs. It’s our using them for eel and conch fishing (this is primarily in the Pacific)- and due to climate change (with rising sea levels, acidification of the oceans) may be cutting down the census.

Won’t it be sad if the crabs that survived four extinction periods – including an asteroid strike- will be taken down by own politicians refusal to recognize the facts of global warming?

Roy A. Ackerman, Ph.D., E.A.

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