Many major tissues secrete proteins that can induce longevity.

“one of the things David Sabatini and I talked a lot about I'm actually gonna see David for dinner tonight I'm sure this will come up is if you could wave a magic wand and make rapamycin for example tissue-specific let alone complex specific but you get into this and the same thing with metformin it probably does have some tissue specificity probably working more on the liver than it is working in other cells it seems unlikely that a molecule would have uniform and ubiquitous take up of all cells”