Oxytocin. Model via Wikipedia
Oxytocin. Model via Wikipedia

The Secret Ingredient in Young Blood: Oxytocin?

Last month, I wrote in the New York Times about a creepy yet potent way to reverse aging. All you have to do is join an old mouse to a young mouse. As the young mouse’s blood flows through the old mouse’s body, it rejuvenates the heart, skeletal muscle, and even the brain.

When scientists saw just how dramatic this reversal could be, they started investigating how it happens. They suspected that it wasn’t blood as a whole that was responsible for the transformation. Blood is a finely blended consommé of cells and free-floating molecules. It was possible that only certain compounds in young blood are required to counter aging. That would be excellent if true, since it would put a damper on any vampire-like strategies for applying this discovery to people. All old people would need to do was take a pill containing the compounds that bring about the change.

As I wrote in my article last month, scientists identified one protein, called GDF11, may help reverse aging in the young blood experiments. But they suspected that more than one molecule would be involved. And today, a team of scientists at the University of California at Berkeley are publishing evidence in favor of a new molecule. What makes this result especially surprising is that this molecule is already fairly famous for other effects on the body. It’s oxytocin.

You may have heard of oxytocin as a love drug, or as a moral molecule. It is certainly true that this hormone, which is produced in the brain, plays some important roles in the social life of mammals. Monogamous voles, for example, appear to depend on oxytocin to strengthen their bonds with their mates. When scientists prevent their cells from taking up oxytocin, the voles become more promiscuous. Likewise, oxytocin plays a part in the mother-child bond. Its concentration rises in women during pregnancy and nursing. If ewes are blocked from taking up oxytocin, they neglect their newborn lambs.

But, as fellow Phenom Ed Yong explained in this 2012 Slate piece, at this point oxytocin should really be called the “hype hormone.” People are way too eager to leap from the existing evidence about oxytocin’s effects to calls for its use as a therapy for children with depression or autism. And as Ed wrote in April in The Scientist, oxytocin also seems to be involved in negative emotions and even lying. Reckless use of oxytocin could have some unwanted effects.

It may seem strange for one little molecule to influence us in so many ways. But that’s true for many hormones. They are signals, but the message they deliver depends on their context. In that respect, hormones are like the words we use to relay messages to each other. Think of the wildly different messages, depending on the context, that just five words can have: “What are you doing here?”

In fact, the effects of oxytocin range far beyond emotions and behaviors. In recent years, for example, scientists have found evidence that oxytocin can reduce osteoporosis and obesity. Oxytocin can relay important signals to cells throughout the body, not just in the brain.

Recently Irina Conboy and her colleagues became intrigued by a few of these experiments. When scientists remove the ovaries from female mice, for example, their levels of oxytocin drop dramatically. The mice also start to age rapidly. Could there be a cause and effect there?

Another clue came from the receptors on the surfaces of cells that can grab oxytocin. The cells with these receptors include stem cells that can produce new muscle. Was it possible that oxytocin sent these cells a signal to develop and renew old muscle?

Clues like these fostered a hunch in the minds of the scientists. Maybe oxytocin was one of the molecules in young blood that could rejuvenate old animals.

As the scientists report in Natural Communications, they ran a series of experiments that strongly suggest that this is indeed the case. They wondered, for example, if naturally aging mice lost oxytocin, in the same way as mice that have their ovaries removed. They found that as mice get old, their oxytocin level drops to a third of the level in young mice. They also found muscle stem cells produce fewer receptors for oxytocin as mice get older.

The scientists then gave oxytocin to old mice. They found that the mice were able to regenerate more new muscle fibers. And when they blocked oxytocin in young mice, the mice couldn’t renew their muscles. In this respect, they became old.

Conboy and her colleagues got a similar result when they engineered mice that could not produce oxytocin. The mice developed normal muscles, but as adults they lost muscle mass much faster than normal mice.

To get a closer look at what oxytocin was doing, the scientists reared muscle stem cells in a dish and added oxytocin to them. Once the cells grabbed onto the hormone, they multiplied quickly. In other words, oxytocin appears to be directly altering the behavior of stem cells, just as the scientists had suspected.

The new study provides a new hypothesis for how we get old. When people are young, they produce lots of oxytocin. On top of whatever psychological effects it may have, that extra oxytocin also tells stem cells to turn into muscle cells, keeping people strong. Young people might also produce GDF11 and other molecules at high levels, and in combination, they may keep all the organs young. And once those signals start to fade in old age, the body starts to fall apart.

Theoretically, giving old people compounds like oxytocin or GDF11 may cause their cells to act young again. The compounds could be the basis for an all-purpose treatment for the diseases of old age, from osteoporosis to heart disease to Alzheimer’s.

Theoretically.

It’s worth bearing in mind that all the studies I’m writing about have only been carried out in mice or rats. We can’t say for sure that the effects would carry over into human trials. We don’t even know if oxytocin is high in children and low in old people–not to mention what the “right” level of oxytocin would be to reverse aging.

It’s also worth bearing in mind that there may very well be a good reason that youth-generating signals fade as we get older. If the signals don’t deliver exactly the right message, in exactly the right context, our cells might misinterpret them in a disastrous way. Instead of just multiplying to restore weakened muscles, for example, stem cells might grow uncontrollably, leading to cancer.

But Conboy and her colleagues respond to that concern by pointing out that we already know a lot about oxytocin as a drug in people. Because its other effects have gained so much attention, it’s already been extensively tested. In its synthetic form, pitocin, it’s approved for use in pregnant women who are past term, in order to speed up their labor. Human clinical trials are already underway to try out oxytocin as treatment for psychological disorders. While it’s not free of side-effects, oxytocin has never been linked to cancer in all the testing that it’s undergone.

Of the many messages oxytocin delivers around our bodies, it’s possible that the message to stay youthful is relatively clear. On the other hand, if there’s one thing oxytocin has taught us so far, it’s that hype can’t replace real research.