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NEW SCIENTIST (UK) 06 June 06 New antivenom could save more snakebite victims (Debora MacKenzie)
A snakebite antivenom has been developed that is more powerful than conventional antidotes and works even when it is unclear exactly what species of snake has bitten the victim.
Snakebites kill tens of thousands of people each year, yet supplies of traditional antivenom are drying up. The inventors of the new antidote hope it will be taken up in the poor countries where it is most needed.
Snake venom contains a complex cocktail of tissue-destroying enzymes. The only antidote till now has been the antibody-rich serum extracted from the blood of horses after they have been injected with venom milked from snakes.
In recent years, big drug companies have stopped making antivenom as it is increasingly unprofitable: the serum needs to be purified to meet stringent safety standards, animal rights activists object because the horses suffer, and most of the people who need the product can't afford it. Serum against African snakes is now especially scarce.
Snake-free venom
Simon Wagstaff and colleagues at the Liverpool School of Tropical Medicine in the UK have now made a serum without using snake venom. Instead, they started with the DNA of the carpet viper, which is responsible for the majority of snakebite deaths in west Africa, and looked for the genes that are active when the snake is refilling its venom sacs.
A dozen of these genes code for metalloprotease enzymes that destroy blood vessels and cause haemorrhaging. From these genes they created a “consensus” sequence that resembles as closely as possible all the different genes.
From this generic gene they took seven DNA stretches that code for parts of the outside of the protein molecules and should therefore elicit antibody responses in the body, and joined these together to make a single strand.
Sure enough, when they injected this synthetic DNA into mice, the animals made antibodies to these parts of the protein. When serum extracted from these animals was tested on other mice it was more powerful than classic serum against carpet viper venom, but also against other west African vipers, and even a viper from north Africa.
This generic action is important, as classic antivenom works best against the species from whose venom it is prepared, yet victims may not know which snake has bitten them. Also, because the serum produces specific antibodies, rather than the much larger range of antibodies in classic serum, it is less likely to provoke an allergic reaction.
Western companies are unlikely to snap up Wagstaff's technique, however, as it still requires the use of large animals such as horses to produce viable amounts of serum.
But Wagstaff told New Scientist that he hopes producers in developing countries will try making serum using the team’s technique.
Journal reference: PLoS Medicine, DOI: 10.1371/journal.pmed.0030184

http://www.newscientist.com/article/dn9277-new-antivenom-could-save-more-snakebite-victims.html

If this does not require pints of antivenin to treat a bite & cost a couple of years' wages for treatment, it will be better than what is available presently.

~~Greg~~

I'm not a genetecist, nor do I play one on TV, but I'm guessing the big question here is how expensive is it to synthesize large quantities of this DNA. If that can be done cheaply, it opens the possibility of bypassing the antibody production entirely and just making a vaccine. If it's as expensive as I'm GUESSING it is, they've found a more expensive may to make almost the same thing...

Dr. Fry?

If you're just worried about making more dna, that is incredibly easy. Assuming the DNA is small enough (ie, the strands are not too long) there's a commonly used technique called PCR. It simply starts with a small amount of DNA and makes more. We use this in our research lab to genotype the knockout mice that we use in experiments.

Now, I can't imagine that you would need a whole lot of this DNA if it is just used to get antibodies from supply animals.

As for price, consider this... Essentially (and so simple it might not be 100% accurate), antivenin is obtained by injecting venom into a horse or other animal with venom (dried, purified, what ever) and the serum is obtained. It sounds like from this article that this combined strand of synthesized DNA is injected and serum is obtained. So, essentially it's the same process as far as the outcome is concerned. Right, we'll need less in the case of a bite, which will save some money. However, I fail to see how vial costs are going to be any less than they are now.

Here's my logic simplified. Take animal species A. Inject with something from snake (venom, dna, what ever). Let animal species A produce antibodies. Purify serum, dry, bottle and sell.

So, we may save on longer shelf life (didn't actually notice that in the article since I skimmed, but someone mentioned it) and fewer doses. Both of these are great, but again, vial for vial, I can't see how it would be much cheaper (and maybe more like the new crotalid AV).

Dave

>>If you're just worried about making more dna, that is incredibly easy. Assuming the DNA is small enough (ie, the strands are not too long) there's a commonly used technique called PCR. It simply starts with a small amount of DNA and makes more. We use this in our research lab to genotype the knockout mice that we use in experiments.

Sounds easy enough, and cheap in small quantities, but aren't you working in nanogram to maybe microgram quantities? How well does it scale, what would the costs be in multi-gram quantities? Is it THAT cheap? Most snake venoms sell for a few hundred dollars per gram or less.

The article suggests you would need a smaller quantity because it eliminates the unnecessary componets of the venom, but it doesn't say much about how much less... I guess it could be a really tiny amount if it's specific enough.

I wonder. If the DNA sample they use is specific enough that it induces production of antibodies but doesn't produce any toxic effects, then maybe it could be used in higher concentrations yielding more antibodies per unit of blood (I have no idea whether it works that way). Then you could reduce the number of animals used which would probably make more of a difference than just cutting out the actual venom.

Recall that DNA is a blueprint for making protein. The injected animals' cells use the injected DNA as a set of instructions to make proteins resembling important pieces of snake-venom proteins. The animals' immune systems recognize the proteins as foreign and mount an immunologic response which results in production of antibodies. One piece of injected DNA can be used over and over to make a protein so you don’t need as much DNA as you might think to get an appreciable protein amount.

That's how it should work, theoretically, but I'm sure there will be kinks to iron out before this sort of AV becomes a commercial reality. Still, it's an interesting idea that sounds like it could work.

Cheers,
WK

I have only a rudimentary understanding of DNA replication from first semester biology, but my reccolection is that the "machinery" to support replication exists inside cells, and even a small strand of DNA is too large to cross cell walls, isn't it? So my understanding is that free DNA in the blood stream would not be replicated.

What you describe sounds like the PCR method mentioned above, but it sounds like they've only fairly recently found an exotic bacterium that will actually do this, and it requires extreme temperatures to do it efficiently...

I could easily be completely confused though.

You're right - DNA is too large to passively cross cell membranes. The cells actively take it up. The cells then make protein based upon the DNA code. PCR is just repetitive amplification of a DNA sequence. DNA to protein is a different and more complex process.