A synthetic tetrapeptide that crosses the inner mitochondrial membrane, binds cardiolipin, and stabilizes the electron transport chain — with Phase 2 clinical trial data behind it.
SS-31 — also known as Elamipretide, MTP-131, or Bendavia — is a synthetic tetrapeptide designed to selectively target the inner mitochondrial membrane. Unlike most peptides that act on cell surface receptors, SS-31 works inside the cell at the organelle level, making it structurally and mechanistically unlike anything else in the research peptide space.
The compound was developed by Hazel Szeto and Peter Schiller at Weill Cornell Medicine, which is where the "SS" in the name comes from. Its four-amino-acid sequence — D-Arg-Dmt-Lys-Phe-NH₂ — was specifically engineered to penetrate cell membranes, accumulate in mitochondria, and interact with cardiolipin, a phospholipid critical to mitochondrial function.
Most peptides bind receptors on the outside of cells. SS-31 crosses the cell membrane, crosses the inner mitochondrial membrane, and binds directly to cardiolipin inside the organelle. It's one of the few research compounds acting at this level of cellular infrastructure.
The inner mitochondrial membrane (IMM) is where ATP production happens. Cardiolipin is a unique phospholipid found almost exclusively on this membrane, and it plays a structural role in organizing the electron transport chain (ETC) complexes — the molecular machinery that generates ATP through oxidative phosphorylation.
As cells age or come under oxidative stress, cardiolipin oxidizes and the ETC complexes lose their structural organization. This leads to inefficient electron transfer, increased reactive oxygen species (ROS) production, and declining ATP output — the cellular energy crisis underlying many age-related conditions.
SS-31 binds directly to cardiolipin via electrostatic and hydrophobic interactions. This binding does three things simultaneously:
More organized ETC → less electron leak → less ROS → more ATP per unit of substrate consumed. This is why SS-31 research shows benefits across such a wide range of tissues: heart, kidney, skeletal muscle, brain — anywhere mitochondrial dysfunction is a factor.
Because mitochondrial dysfunction underlies a remarkably broad range of conditions, SS-31 has been studied across multiple disease areas — a scope that is unusual even by peptide research standards.
SS-31 (as Elamipretide) has completed Phase 2 clinical trials — a level of human safety data rarely seen in research peptides. Stealth BioTherapeutics ran the PROGRESS-HF and EMBRACE-HF trials before the company folded in 2020. The compound itself remains active in research.
| Factor | SS-31 | MOTS-c | Humanin |
|---|---|---|---|
| Origin | Synthetic (engineered) | Mitochondrial genome | Mitochondrial genome |
| Primary target | Cardiolipin / IMM | AMPK / metabolic signaling | IGFBP-3 / cell survival |
| Key mechanism | ETC stabilization, ROS reduction | Exercise mimicry, fat metabolism | Anti-apoptotic, neuroprotective |
| Clinical data | Phase 2 trials (HF, AKI) | Phase 1 only | Preclinical mostly |
| Muscle aging data | Strong preclinical | Strong preclinical | Limited |
| Half-life | ~2 hours | ~20 minutes | ~3–5 minutes |
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