The University of Texas at Austin
  • The dangers of cannibalism

    By Andy Ellington
    Published: July 14, 2011

    Andy Ellington studies RNA, the origins of life, synthetic biology and develops therapeutics. He is a research professor in the Department of Chemistry and Biochemistry and the Institute for Cellular and Molecular Biology. This story originally appeared on Ellington’s blog and can also be read on the Texas Science Web site.

    Illustration of cannibalism
    Image: Elia Violante on Flickr/CC

    Cannibalism. One of the last, great taboos. And for good biological reasons. In the Eastern Highlands of Papua New Guinea the locals, known as the Fore, practiced what was politely called “transumption,” which led during the late 1950s to the person-to-person transmission of a debilitating disease, kuru, in epidemic proportions. The “laughing disease” led to massive neural degeneration, eventually resulting in death (although sometimes with long latency periods), and was the result of the transmission of prions.

    Prions are interesting because they’re sort of the exception that proves the rule of DNA. That is, while DNA replicates sequence, prions replicate conformation. Prions are peptides or proteins that assume a particular conformation. When a prion comes in contact with a similar protein that is not shaped the same the prion forces the protein to assume its conformation, and they aggregate together in a tight knit architecture known as an amyloid. This is the same sort of amyloid that occurs in the very similar prion disease Creutzfeld-Jakob disease (CJD) and in Alzheimer’s. So, you can sort of think of prions as the first domino that initiates a cascade of conformational events that leads to a big, tangled mess in your brain. Not good.

    Here’s what’s been making me think. There is a variant of CJD (vCJD) that arose a few years ago in England and that could be traced, roughly, to the widespread distribution of what Denny Crane would call “the mad cow disease,” but which is more commonly known as Bovine Spongiform Encephelapathy. Here’s what I find fascinating: you feed cows the remains or waste of other cows, BSE can spread like wildfire (and who can forget the giant bonfires of cows in England circa the late 1980s). But while there were upwards of 180,000 cases of BSE amongst cows, there were only about 153 cases of vCJD (Beghi et al. (2004), Neurol Sci 25:122). The causal link between BSE and vCJD is sort of like the causal link between human activity and global warming: pretty convincing evidence, but hard to definitively prove (and in both cases the appropriate experiments that might directly test the hypotheses are understandably hard to run).

    abnormal prion protein
    These round, packed deposits of abnormal prion protein are known as florid plaque. They often form in the brains of people suffering from variant Creutzfeld-Jakob disease (vCJD).

    Some folks think that the low transmission rates from cows to humans just hide an epidemic-to-come in which those of us who consume multiple hamburgers per day (what?) will eventually twitch out. But it is more likely that there are huge species barriers in prion replication. This is because at the molecular level a cow prion may only partially recognize and bind to the amino acid sequence in the corresponding normal human protein, inhibiting the kicking over of that first domino (Priola (1999), Biomed Pharmacother 53:27).

    This presumed species barrier is confirmed by experiments with prion transmission in test tubes, cells, and transgenic mice. Thus, cow-on-cow or human-on-human chomping is a much more likely route to disease than humans eating cows (or whatever happens in the future on the Gary Larson-esque “Planet of the Cows“).

    So, what are the implications of this understanding? Clearly, don’t eat people, soylent or not. Indeed, the depth of the taboo suggests that our species may have discovered this edict several times over in our past (and there is even a serious-but-unlikely hypothesis that cannibalistic Neanderthals succumbed to spongiform encephalopathies). Keep your factory farms clean. Amusingly, many of the bans on beef that accompanied the outbreak of BSE in England (and more minor outbreaks in the US) were more political than practical.

    But I think there’s also a more fundamental issue. While spongiform encephalopathies seem to focus on a relatively small number of neurologically important proteins, a surprisingly huge number of proteins can form amyloids. Indeed, work from the Marcotte lab down the hall (with a small assist from our own lab) has revealed that a surprisingly large number of yeast proteins (like, 30 percent, of all proteins) seem to self-aggregate. To the extent that those aggregates are amyloids this would mean that there are many dominoes waiting to fall. Why don’t they? Well, most proteins inside of cells are disentangled by energy-burning so-called chaperones (and, indeed, the prion protein that falls down is on the *outside* of cells in the brain).

    Indeed, the fact that we’re not cannibals means we don’t know much about these other dominos. Or, to put it another way, prions are a growth industry from a biodefense point of view. How many different human peptides, available orally, just like kuru was, would inevitably take down large fractions of a population after a suitably long and stealthy incubation period? And given the concerns I’ve previously noted about the quality controls in our supply chains (see “On Pepcid,” which incidentally is back on the shelves, woo hoo!), would such prions be relatively easy to introduce (think melamine)? And unlike viral or microbial diseases, where we at least have a basal understanding of how to construct a biodefense, there really is no defense against prions (just as, sadly, there is no real cure for Alzheimer’s). The suggested procedures for prion researchers to decontaminate their workspaces and tools involve essentially treating everything with the most caustic agents you can imagine. That’s not going to work for your brain. And so I am left once again with a conclusion that is an unsatisfying bummer: we’re hosed. Unless the same cultural prohibitions that keep us from eating one another kick in with respect to infecting one another. The thin, nice line. Quaint.

    • Quote 2
      Jaye said on July 5, 2012 at 11:01 a.m.
      Andy, I came on this article in search for some 'possible answers' to another article about the use of human genetic material for new varieties of rice. My first thought was the threat of neural degeneration that seems to follow an animal consuming other animals of the same species ('mad cow', 'laughing disease'). Could you see a scenario whereby these prions could be in our food crops just as casually as transfats presently exist in processed foods?
    • Quote 2
      EwanNJ said on July 25, 2011 at 4:33 p.m.
      Geez, mention "climate change" and it's all over! Poor Mike H. spends his days obsessively googling "climate change" to see what those money-grubbing scientists are up to. Mike, was that you in the 80s spinning rock'n'roll records backwards trying to hear Iron Maiden say something satanic?
    • Quote 2
      Suzy said on July 25, 2011 at 9:17 a.m.
      "...the causal link between human activity and global warming: pretty convincing evidence..." Yeah, that stopped me too. It calls the researcher's objectivity and therefore credibility into question.
    • Quote 2
      Regina Zeyzus said on July 22, 2011 at 12:19 p.m.
      Mike Haseler,in his zeal to grind his axe about money grabbing, missed the authors' point about global warming and BSE. As the author clearly stated, scientifically proving the link between BSE and vCJD is as difficult as scientifically proving the link between global warming and CO2. No comparison at all was made or meant between the links themselves. Miscomprehension of the written word apparently isn't limited to politicians and the uneducated.
    • Quote 2
      Shannon said on July 21, 2011 at 12:52 p.m.
      Those poor cows! First they eat of cow and then are killed for being mad. I'm mad for them!
    • Quote 2
      John Turner said on July 21, 2011 at 9:29 a.m.
      If the Fore cannibals from New Guinea ate BSE infected beef from England, would the resulting flatuance produce greenhouse inducing methane that could also cause Alzheimers in patients as far away as North America?
    • Quote 2
      Notmike Either said on July 20, 2011 at 5:26 p.m.
      >Well, I guess Mike said it all! Yes, but "it all" was the digestive waste product of a mature male cow.
    • Quote 2
      Will Bargmann said on July 19, 2011 at 2:53 p.m.
      Amazing the first comment is from rabid right excoriating the notion of global warming which was used as an example of a hard to prove causal set of events leading to climate change. Gee, I would hate to think it might be possible we could have something to do with the problem and, by the way, we are suffering through extreme drought and running neck and neck for the hottest summer in Austin, TX history. One of my favorite tongue in cheek stories ever told was by Swift entitled "A Modest Proposal" wherein the poor street children of the recently industrialized cities of England should be rounded up, fattened up and used as a new meat source. Me thinks Mr. Haseler might approve.
    • Quote 2
      Kevin said on July 18, 2011 at 7:21 p.m.
      Why harp on a detail and miss the bigger picture? The comparison to global warming was merely made to illustrate a point. Whatever inadequacies that analogy might have do not in any way undermine the integrity of the article as whole.
    • Quote 2
      Andrew said on July 18, 2011 at 5:31 p.m.
      "they were nor even aware they had a raised temperature" Mike, You obviously haven't been back to Texas in awhile.
    • Quote 2
      Brian B said on July 17, 2011 at 11:29 p.m.
      There is pretty much a step-for-step correlation between CO2 levels and rising global average temperatures, not to mention widely accepted science about CO2/O2 levels related to climate change and past ice ages (see: snowball earth).
    • Quote 2
      Not Mike said on July 17, 2011 at 11:24 p.m.
      Oh those darned scientists and their darn powerful lobby destroying everything our honest oil extracting bosses worked so hard for. National Academy of Sciences: YOU ARE WHAT'S WRONG WITH AMERICA! You are denying Mr. Haseler his right to pick his favorite side of the argument. Your silly pictures of melted icecaps and records of migration patterns, smog, extinctions, and holes in the ozone are ruining the very fabric, nay, the very DNA SEQUENCE of our dear state.
    • Quote 2
      BillW said on July 15, 2011 at 6:48 p.m.
      Well, I guess Mike said it all! So much for all that research and scholarly examination. Humm, seems a bit hotter to me lately. LOL
    • Quote 2
      Mike Haseler said on July 15, 2011 at 1:11 a.m.
      What a ridiculous comparison. The link between global warming and CO2 is nothing like BSE a vCJD. Unless I am very much mistaken, vCJD is a single disease with a single cause. In contrast global temperature is not a disease and there are multiple (millions) of causes. A more accurate comparison would be to take human body temperature. The "patient" has a temperature a fraction of a degree higher than what the "doctor" considers normal. The doctor has diagnosed a terminal disease requiring an immense course of treatment at high cost all overseen by the doctor. At no time has the patient seen anything which they feel is abnormal, they were nor even aware they had a raised temperature until the doctor told them. Although how you could compare their previous measurement with a tin pot thermometer with the modern one is very difficult to believe. AND EVER SINCE THE DOCTOR SAID THE PATIENT WAS GOING INTO A TERMINAL AND EXPONENTIAL TEMPERATURE RISE ... THE PATIENT'S TEMPERATURE HAS BEEN STABLE. As everyone ought to know, just as the body temperature varies, so the planet's temperature varies, and just as a fraction of a degree rise in body temperature is not something worth worrying about, nor is a fraction of a degree rise in the temperature of the planet. And just as there are money grabbing doctors and drug companies who will fleece us dry if they had the chance, so there are money grabbing "scientists" and renewables companies who will fleece us dry if they have the chance.
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