About the worst thing that can happen to a human being is venomous snake bite. Whatever the venom’s primary mode of action, incredible tissue destruction always follows a venomous bite (only a half to two thirds of bites by poisonous snakes actually inject venom. The rest are “dry” bites that are not dangerous and have no symptoms other than a little bleeding).
Evolutionary drivers for the conversion of otherwise ordinary and harmless saliva glands to venom factories vary among different varieties of snake. In the mambas and boomslang, African arboreal species, the venom is evolved to act rapidly—probably an adaptation for eating birds, which need to be put down swiftly before they can fly away.
Black mamba in action
One of the first things that happens in a mamba bite is blood thinning. With the blood morphed so it slides through the vessels like a NASCAR machine on steroids, the venom quickly reaches heart, lungs and muscles where other modes-of-action—tissue degradation or respiratory suppression—drop the bird in place before its fight-or-flight hormones can carry it away.
Black mamba fangs on display
In contrast, venoms of viper snakes tend to cause rapid and massive destruction of circulatory system, muscles, and organs. In this is the clue to the evolutionary origins of venom. Of necessity—lacking limbs to hold prey and cutting or tearing teeth to rip it into bite-size pieces—snakes swallow their food whole. And often they swallow food items of enormous size relative to the size of the snake.
Viper eating food bigger than its head
This engenders some physiological problems in an ectothermic (“cold-blooded”) animal. Specifically, digesting a huge meal takes time. So much so that the food item can begin to rot before it is broken down into absorbable (is that a word? Spell checker seems to like it…) molecular fragments. Having a vat of rotting flesh in the gut is problematic. Decomposition microbes can pour out of the food, killing the snake by rotting its gastrointestinal tract. Indeed, in captivity, maintaining digestive health of snakes is a technical issue of importance.
Anyway. Evolutionarily, it seems that venom is primarily an adaptation for feeding, not self-defense. Injecting a fat dose of tissue-destroying toxin into a prey item begins digestion processes even before the food is ingested. Eating is safer and more efficient when venom is involved.
This also means that snake venom is chemically complex. A variety of physiologically active substances, almost all of them proteins, are present in snake venoms. The composition varies from species to species, and even among individuals of the same species. But in general, snake venom is a complicated soup of bioactive chemicals, many acting as enzymes. Some of them tear tissues apart and destroy cells, some control blood clotting and circulation, some affect respiration, muscle tension, and nerve functions.
Why a lecture on snake physiology here at this cancer-themed weblog? Because the chemical complexity of venom gives it enormous pharmacologic potential. That potential is being explored for medicinal purposes—including cancer treatment.
An excellent (although grammatically weak—could’ve used a good technical edit) review of snake venoms in cancer treatment is titled Therapeutic Potential of Snake Venom in Cancer Therapy: Current Perspectives [1]. Chemicals purified from venoms have been shown to bind specifically to tumor cells. Such chemicals may be applied to tag and identify tumors or to carry other, anti-tumor substances to the diseased tissue. Other venom chemicals can re-program cell death into tumor cells that refuse to die as they would normally. Some venom components inhibit tumor cell reproduction, destroy tumor cell membranes, or constrain cell metabolism. Tumor cell adhesion and migration can be inhibited by venom chemicals, preventing tumors from finding susceptible places to settle. In addition, venom compounds provide indirect but useful functions including pain inhibition, inflammation reduction, or enhancement of blood and lymph flow.
So snake venoms may prove to be a valuable pharmacy of cancer-fighting chemicals. Identifying, testing, and applying these chemicals of course takes time, money, and technical expertise. In other words, it’s going to be a long time before the therapeutic potential of venom is realized. Of course, it would be less time if the U.S. government could function without shutdowns interrupting research programs periodically.
In any case, I’m not going to be around long enough to benefit from snake venom pharmaceuticals. But I may be around for a longer time than it seemed just a few months ago. I still have issues with mucous production, throat inflammation, weakness and discomfort, and of course my diet is limited to weird milky medical foods dumped directly to my gut via polyvinyl tubing. But once that whining is out of the way, I’m getting better. This week we drove up to Amherst, Massachusetts where I was (oddly) a guest-of-honor at an awards dinner provided by the Association for Environmental Health and Sciences, the not-for-profit for whom I write a weekly column on environmental sustainability (www.aehsfoundation.org, go to the lower left of the home page to click through to the PeopleSystems column). I had a great time driving the 6 hours each way, listening to music and enjoying being functional. At the conference, I was pretty much exhausted, but had a wonderful evening at the dinner. Many old friends were there, some of whom had made long trips to get there to share the event.
To those friends and to all of you reading this, you have my eternal gratitude and love. I could not have fought me way through the past few years without you. Knowing you are pulling for me, and that only by surviving could I hope to see you again, are powerful motivators. Thank you. Talk to you next week!
Notes
[1] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3627178/
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