A Radical Proposal

You can drop cigarettes. Avoid alcohol. But there’s one toxin you just can’t dodge: oxygen. With every gulp of air, oxygen gives you life. Some of it, however, gets converted inside your cells into a radical molecule that can wreak havoc, degrading those same cells and others. A growing number of scientists say this damage is what causes aging. They also think they may one day be able to fend off oxygen’s ill effects and help us live a lot longer. Scientists have long known that oxygen is capricious. As molecules go, it gets around, reacting with all kinds of things. Mostly, that’s good. Oxygen combines with fats and carbohydrates, in a part of cells known as the mitochondrion, to churn out the energy that gets you through the day.

But the conversion isn’t perfect. A small amount of oxygen is regenerated in a nasty form called a free radical, or oxidant—the very critter that causes metal to rust. The oxidants careen about, binding to and disrupting the membranes, proteins, DNA and other cell structures that make your body work. Over time, this damage adds up, and the result just might be an older, frailer you. According to one estimate, oxidants bombard the DNA inside every one of our cells roughly 10,000 times a day. Thankfully, most of the assailants are intercepted by a small army of antioxidant chemicals. Proteins also patch up the damage caused by the radicals that do get through. “The house is always getting dirty, and we’re always trying to clean it up,” remarks John Carney, chief technical officer at Centaur Pharmaceuticals in Sunnyvale, Calif., which is developing drugs to fight various diseases of aging. But eventually, the theory goes, our tired cells get less efficient at repelling free radicals and mopping up oxidative messes, and the damage accumulates.

We begin to rust from the inside out. If oxidants do send us crumbling into old age, then ramping up our biochemical defenses should extend life. That’s what scientists are finding, at least in the flies, rats, worms and other animals they have under scrutiny in the laboratory. Whether the techniques they are pursuing will ever lengthen life in humans remains an open question. But some researchers think they’re getting close to an answer. “The key is to really understand how oxidative damage works, and we’re learning that,” says biochemist Bruce N. Ames of the University of California at Berkeley. “I’m convinced life expectancy will get longer a lot faster than anybody thinks.”