I recently came across this rather interesting article (ominously titled The Blood Harvest) by Alexis C. Madrigal in The Atlantic from February of this year about horseshoe crabs and the use of their startlingly blue blood for biomedical purposes. While I had read a bit about the horseshoe crab and its particularly interesting evolutionary history before, I had not heard of the rather indispensable role it plays in modern medicine.
It seems that a chemical named coagulogen found only in the amoebocytes (similar functionally to white blood cells in vertebrates) of this amazing blue blood can detect traces of bacterial presence at concentrations as low as of one part per trillion and trap them in inescapable clots. Pharmaceutical companies have made use of this property of coagulogen by adding it to test samples of any products which might end up in the human bloodstream;
If there is no bacterial contamination, then the coagulation does not occur, and the solution can be considered free of bacteria. It’s a simple, nearly instantaneous test that goes by the name of the LAL, or Limulus amebocyte lysate, test (after the species name of the crab, Limulus polyphemus).
This procedure has allowed pharmaceutical companies move away from the previous standard procedure, which was more expensive, difficult and inexact, as well as PR-nightmare, involving the testing on large populations of rabbits. The process of actually harvesting large amounts of horseshoe crab, draining up to 30% of their blood, and releasing them back into the wild miles from where they were collected, can of course lead to concerns for the safety of the creatures, as a number of them die during the process and others seem to remain lethargic after release, especially regarding mating (which no one wants to inflict on our poor blue-blooded infection-fighting friends).
Because they have remained largely genetically unchanged for about 450 million years ago, horseshoe crabs are often considered living fossils, and, as the article points out, have been sadly had their populations seriously endangered by various human uses for them over the last couple of hundred years. Now, any of you who know my views on animal rights and graduated levels of consciousness, know that I do not lament this because I believe creatures as comparatively simple as horseshoe crabs have comparable feelings, consciousness or rights, but rather that, from a conservation point of view, and a basic good rule of minimising interference with the lives of otherwise unproblematic animals, a synthetic solution to replace this large scale harvesting is in everyone’s best interests (not least so that the horseshoe crabs can get back to their uninterrupted love-making).
Strictly speaking it might be a bit misleading to mention cloning in the title of this post, as what is being done to replicate the beneficial properties of horseshoe crab blood isn’t exactly cloning, but rather genetic engineering with the goal of isolating some of the genes responsible for the beneficial characteristics of super-powered blue crab blood and replicating them synthetically – much in the way we do now for producing insulin through genetically modified yeast, rather than animal hosts.
As Madrigal points out, there are a number of companies fortunately undertaking, with some heartening degrees of success, the process of replacing the need for horseshoe crab blood with synthetically produced versions of Recombinant Factor C (rFC), the endotoxin-inducible coagulation enzyme in LAL, or alternative tests which don’t require this strangely vampiric sci-fi production method;
In particular, biologist Ding Jeak Ling from the National University of Singapore succeeded in producing the key bacterial detection enzyme, known as Factor C, in yeast. She licensed the process to Lonza, which has brought it to market as aproduct called PyroGene. A German company named Hyglos has been working on another synthetic endotoxin detector, too. Other, even more advanced technologies are on the way, too.
The article also makes mention to a brilliant Vanity Fair cartoon from 1861 on whales celebrating the discovery of oil wells in Pennsylvania (one has to keep in mind that we did in fact rather barbarically use whale oil for most of our oily needs before the large scale discovery and adoption of alternatives like kerosene and crude oil);
Source: The British Library
The author ends with the fine point, “Let’s hope we don’t wipe horseshoe crabs out after we finish cloning their ancient chemical wisdom.” Bioengineering ancient chemical wisdom from the blue blood of half a billion year old crab species – isn’t science grand.