FOXO4-DRI: The Clever Mirror-Image Peptide for Zombie Cells

Some of your cells turn into zombies as you age. They stop dividing, but they do not die. They hang around and leak signals that bother the healthy cells nearby.

In 2017, a team in the Netherlands built a clever peptide to clear them out. In old mice, the results turned heads: thicker fur, livelier mice and better kidney blood tests. The peptide is called FOXO4-DRI.

What it is

A peptide is a short chain of amino acids. Think of amino acids as beads and a peptide as a short bead bracelet. New to this? Start with what a peptide is.

FOXO4-DRI is made in a lab. It copies a small piece of a natural protein called FOXO4, with a clever twist.

In nature, the amino acids in proteins come almost always in one shape. Most also have a mirror-image twin, like your left hand and your right hand. FOXO4-DRI uses the mirror-image beads. Then it strings them in reverse order.

That is what "DRI" means. Done right, the flipped version can still fit where the natural piece fits. Better yet, the body's cutting enzymes, which chop up peptides, have a hard time chewing beads that are built backwards.

What it does in the body

Every cell has a self-destruct guard called p53. When a cell is badly damaged, p53 can tell it to shut down for good. That keeps broken cells from causing trouble.

Zombie cells, which scientists call senescent cells, are damaged. So why don't they self-destruct?

The 2017 study found the answer. Zombie cells made extra FOXO4. In the control room of the cell, where the genes live, FOXO4 held on to p53. That grip kept the self-destruct order from going out.

This is where the design shines. FOXO4-DRI slips in and breaks that grip. Freed p53 moves out of the control room. Then the zombie cell shuts itself down.

Drugs that clear out zombie cells are called senolytics. FOXO4-DRI is a peptide senolytic.

What scientists have found

In cells: In the 2017 study, scientists turned human lung cells into zombie cells in a dish. FOXO4-DRI made the zombie cells self-destruct. Healthy cells were mostly left alone.

In a 2021 study, cartilage cells from healthy donors were grown in a dish for a long time. Many turned into zombie cells. FOXO4-DRI removed more than half of the cells in that long-grown batch, while barely touching a fresh batch. It did not boost cartilage building in that test.

In animals: The 2017 mouse results are the heart of the story. The team used two kinds of mice. One kind was bred to age fast and lose fur early. The other was simply old.

In the fast-aging mice, FOXO4-DRI led to thicker fur. The mice ran more on their wheels. Blood tests of kidney function improved too.

In the naturally old mice, fur thickened and the mice were more lively. Their kidney blood tests also got better.

In a 2020 study, old male mice made less testosterone than young ones. Signs of zombie cells showed up in their testes. After FOXO4-DRI, those signs dropped. Testosterone in the old mice rose.

In people: Studies in people are the exciting next step. No clinical trials of FOXO4-DRI in people have been published yet. One early clue comes from the 2020 team, who looked at testes tissue from men. In older men, FOXO4 sat more often inside the control room of the testosterone-making cells.

Where it stands

FOXO4-DRI is not approved by the FDA. For now, it is an early research tool.

The next big step is testing in people. Scientists also want to know how long the effects last and which tissues gain the most.

Zombie-cell clearing is one to watch. For another peptide aging researchers love, read about Humanin.

The bottom line

• Zombie cells stop dividing but don't die. FOXO4 helps keep them alive by holding on to p53, the cell's self-destruct guard.
• FOXO4-DRI is a clever mirror-image peptide that breaks that grip. In cells, the zombie cells self-destruct.
• In old mice, it thickened fur and improved kidney tests. Studies in people are the exciting next step.