Chemistry in the News: Redefining our Understanding of Brown Recluse Venom

              Most of us who grew up in North Carolina have heard of the brown recluse.  Though the spiders are more common in the southern part of the central US, we still encounter the brown recluse in NC.  As the name recluse implies, the spider is not aggressive and rarely attacks.  Studies have shown that most people who are bitten by the brown recluse were bitten because the spider was inside of their clothing or shoes, to which the victim wasn't aware.  In fact, the fangs of the brown recluse are so small that they cannot penetrate fabric.  The venom of the brown recluse is a hemotoxin, and can produce tissue damage near the site of the wound or in more severe cases the victim can have a systemic reaction and the person can experience heart failure or death.  In one study, "Clinical presentation and outcome of brown recluse spider bite." showed that in 37% of bites that the person suffered necrotizing skin wounds.  Many of these wounds resulted in later skin grafts by plastic surgery.  Though the bites by these spiders can be very dangerous, until recently we had little idea about how the venom of the black widow works.
                Researchers at the UA BIO5 institute recently isolated and identified the protein that causes the tissue damage when a brown recluse bites an animal.  When introduced into tissue, the protein cleaves off the head of the lipids in the cell membrane.  Up until now, scientists thought that the reaction ended with the headless lipid being vulnerable to break down from the venom. Instead, we know that the protein actually causes the lipids to form cyclical structures.  Many other insect bites create the same headless lipid structure, which very rarely in other insect bites causes systemic reactions.  This discrepancy between other insect bites and brown recluse bites and their respective effects was one of the sources of inspiration for this study.  When the ring structure forms, it initiates an immune response.  This immune response is "basically our tissues committing suicide".  The cells in the tissues begin to lose blood flow and begin to die, which stops the blood containing the venomous toxin from entering healthy tissues.  If we have better understanding of the function of the cyclical structure that forms in the lipid tissue after a brown recluse bite, we could potentially develop an anti-venom to inhibit the protein and stop tissue damage or systemic reaction.  

Resources:

1. Daniel M. Lajoie, Pamela A. Zobel-Thropp, Vlad K. Kumirov, Vahe Bandarian, Greta J. Binford, Matthew H. J. Cordes.Phospholipase D Toxins of Brown Spider Venom Convert Lysophosphatidylcholine and Sphingomyelin to Cyclic Phosphates. PLoS ONE, 2013; 8 (8): e72372 DOI:10.1371/journal.pone.0072372
2.  Wright SW, Wrenn KD, Murray L, Seger D. Clinical presentation and outcome of brown recluse spider bite. Ann Emerg Med 1997;30: 28–3