Why Are People Injecting Themselves with Peptides? | The New Yorker

The human body produces thousands of peptides. Many are portions of proteins which send messages or regulate systems in the body, often in ways that scientists don’t fully understand. Researchers have known about some peptides for decades, and dozens have been turned into safe and effective drugs. The hormone insulin is a peptide that moves sugar from the bloodstream into cells; GLP-1, or glucagon-like peptide-1, spurs the pancreas to release insulin and slows the passage of food through the gut. (Peptides are usually defined as having about fifty amino acids or fewer; more than that and they’re proteins.) But the science underpinning the current peptide craze dates to the turn of the century, when Pinchas Cohen, a respected pediatric endocrinologist at the University of California, Los Angeles, started to focus on age-related diseases. For one project, Cohen tried to disrupt a protein associated with insulin resistance and diabetes. By injecting human DNA into yeast cells, he was able to produce several chains of amino acids that clung to his target. Cohen told me that the first two chains were known proteins, but the third was “this ridiculous little thing” made up of only twenty-four amino acids. Strangely, he couldn’t figure out where it had come from. According to the conventional wisdom of the day, the DNA he’d injected shouldn’t have coded for it. The peptide, humanin, was ultimately traced to a tiny snippet of mitochondrial DNA—part of the ninety-eight per cent of the human genome that had long been dismissed as “junk DNA.” Cohen’s work helped reveal that, in the three-billion-letter book that is our genome, even obscure one-liners can be an important part of the story. Junk DNA, it turned out, wasn’t junk: it contains instructions for numerous peptides and proteins that had never been studied. “The public conception of peptides doesn’t grasp what’s going on from a scientific perspective,” Cohen told me. “This is not a dozen or so things you can buy at the gym. This is a revolution in science. It’s going to start a new era of drug discovery.”