LINK: Blood from youth keeps you young

Okay, I actually went and looked at the papers and followed a chain of citations back until I found where they are actually getting the protein.

Looks like my assessment was unnecessarily pessimistic. Those that I could find the source of their proteins who studied this protein in isolation seem to have bought a recombinant product from Peprotech, a biotech company that sells huge numbers of proteins. Their website (http://www.peprotech.com/en-US/Pages/Product/Recombinant_Human_GDF-11/120-11) seems to indicate that it is being produced in E. coli. I suspect they have altered the gene a bit to only produce the part cut by the protease that is active and may be doing some post-processing to get it folded right since they indicate that it comes as a dimer held together by disulfide bonds which have a hard time forming in bacterial cytosol. I suspect there's a bunch of industrial techniques and optimization going on in there that we in the research labs don't bother with in favor of doing things faster with more complicated or versatile small scale systems.

EDIT: and now I found this http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0085890 in which just this year someone managed to screw up the redox metabolism of bacteria such that you can more easily express proteins that form disulfide bonds in the cytosol of bacteria without the need for expensive post-processing to get the bonds right. One of a class of recent modded bacterial strains that are more amenable to expressing eukaryotic proteins at the expense of some metabolic upset. Cool stuff.

EDIT 2: Additionally, someone in my lab is in the process of trying to make large amounts of a couple of novel weird fungal proteins in order to study their activity in vitro. She can't express them in a fungus (the context in which they fold normally) since they will alter the cell division cycle of the fungi and probably kill them, so she's expressing them in bacteria. Had a very hard time getting them to both fold correctly and stay stable without degradation. Over the course of more than six months she's had to rebuild the system she is using to express it several times, and the final successful version involves expressing the protein alongside a binding partner that is required to make it not aggregate into mush immediately upon translation, fused to a tag that makes it more soluble, and using slightly nonstandard extraction chemicals to keep it from denaturing. You probably need to apply a similarly tailored approach to many novel proteins when you yank them across contexts, which you can justify more readily if you stand to make money off it.

On the other hand, I also looked at a number of recent papers studying the effects of this growth factor. All the studies used daily intraperitoneal injections (injections through the abdominal wall into the space around the intestines) for about a month, of 0.1 mg per kilogram of body weight. That might just be because it can be difficult to get lots of needles into a mouse blood vessel in a short period of time though, but it still suggests that maintaining levels needs lots of injection. Also, according to Peprotech, their cheapest cost is $3900 per milligram (at their current levels of production, which is limited and for research purposes). Of course, insulin is probably a better model of a protein product that makes it big time, though not a perfect one since that prevents rather severe issues immediately rather than slowing chronic ones.

As for stuff brought up in this post, I think that it is probably should indeed possible to muck around with yeast until you can get it to process secreted proteins how you want - just taking a lot longer.

Given how much people spend on drugs that only pretend to reverse aging or treat one small symptom of it, I'm pretty sure a pill that actually does reverse it would be of major interest to billions of people.