A four-amino-acid peptide that already has an FDA approval for a rare heart disease did something unexpected in a new animal study. In aging female mice, it raised litter size and restored the quality of eggs that had degraded with age. In leftover human eggs from a fertility clinic, it pushed more of them through the steps that a healthy egg has to complete.
The peptide is elamipretide ↗, known in the lab as SS-31 and sold as Forzinity. The work was published in Aging Cell ↗ in early October by researchers at Nanjing Agricultural University. It is a preclinical study, mice and lab dishes, not a treatment anyone can get for fertility today. But it points the peptide at a problem that no drug currently touches: the decline in egg quality that drives age-related infertility.
What the peptide is, and why eggs
Elamipretide is a synthetic string of just four amino acids that homes to the inner membrane of mitochondria, the compartments inside every cell that turn food and oxygen into usable energy. There it binds cardiolipin, a distinctive fat that lines that inner membrane and holds its folds in shape. When cardiolipin is intact, the mitochondria run cleanly. Late in 2025 the drug became the first mitochondria-targeted medicine to win FDA approval, under accelerated approval for Barth syndrome, a rare inherited disorder that weakens the heart and skeletal muscle.
The egg is the most mitochondria-dependent cell in the body. A mature egg carries hundreds of thousands of mitochondria, far more than an ordinary cell, because the energy they supply has to power fertilization and the first several cell divisions before the embryo can make its own. As a woman ages, those mitochondria accumulate damage, and the egg's ability to finish maturation and divide correctly falls off. That is a large part of why fertility drops with age and why miscarriage and chromosomal errors rise. The study's premise was simple: if a drug can stabilize mitochondria in a failing heart, can it do the same in an aging egg.
What happened in the mice
The team worked with aged female mice at 8, 10, and 12 months old, well past the mouse reproductive prime, and gave them elamipretide by daily injection. A dose of 5 milligrams per kilogram over a seven-day course was the most effective combination. Treated aged mice produced larger litters and better-quality eggs than untreated aged mice.
The most specific result was about a developmental roadblock. Eggs from old mice tend to stall after fertilization, getting stuck between the two-cell and four-cell stage instead of continuing to divide. Elamipretide reversed that block, and more embryos progressed past it. When the researchers traced the mechanism, two things stood out: the drug shifted vitamin B6 metabolism inside the egg, and it switched on VEGF-A signaling, a pathway better known for growing blood vessels. Blocking that pathway undid much of the benefit, which is the kind of evidence that argues the pathway is doing real work rather than riding along.
The human and pig experiments
The researchers went further than mice. In pig eggs stressed with hydrogen peroxide to mimic oxidative damage, elamipretide at 1 millimolar rescued maturation and restored the normal distribution of mitochondria inside the cell. And in a small human experiment, they used leftover immature eggs donated by patients going through intracytoplasmic sperm injection, or ICSI, the IVF technique where a single sperm is injected into an egg. From 39 patients, 54 immature eggs from three women aged 35 and older were treated with 500 micromolar elamipretide. Treated eggs showed better maturation, fertilization, and early division at both 24 and 48 hours.
Three women and 54 eggs is a tiny sample, and leftover immature eggs are not the same as the eggs a clinic would actually use. No one has tested elamipretide as a fertility treatment in a living person, and the approved use remains Barth syndrome. The result is a signal, not a therapy.
What makes it worth watching is the through-line. This site has already covered the same peptide slowing radiation aging in lab heart cells ↗ and defending mitochondrial structure in the fatty livers of aged mice ↗. Heart, liver, and now egg are different tissues with the same failure mode, mitochondria that stop holding their shape with age, and the same small peptide clamping onto cardiolipin ↗ to slow it down. A drug approved for one rare disease keeps producing the same kind of result wherever aging mitochondria are the problem. The reproductive data is the earliest and least proven of the three, but it is aimed at the largest patient group by far.