SS-31, also known as elamipretide, is unusual. It is a small peptide that selectively reaches the inside of mitochondria, the part of the cell where ATP is made. Most drugs cannot get there efficiently.
What SS-31 Is
SS-31 has several names in the literature: elamipretide, MTP-131, and Bendavia. The sequence is short — D-Arg-Dmt-Lys-Phe-NH2 — only four amino acids, with modifications that make it stable.
The peptide carries a positive charge. Mitochondria, by contrast, maintain a strong negative charge across their inner membrane. Opposites attract. SS-31 is pulled toward and into that membrane simply because of physics (Szeto, 2014).
This natural targeting is what makes the compound interesting. Researchers do not need a complicated delivery system to get it where it needs to go.
Binding Cardiolipin
Once inside, SS-31 binds cardiolipin. Cardiolipin is a phospholipid found almost exclusively in the mitochondrial inner membrane. It anchors the proteins of the electron transport chain — the machinery that produces ATP.
Cardiolipin is fragile. Reactive oxygen species, the natural byproducts of energy production, can oxidize it. Once damaged, cardiolipin no longer holds the ATP-making machinery in place. Energy production drops, and signals for cell death can be triggered (Birk et al., 2013).
SS-31 binds cardiolipin and shields it from this peroxidation. That is the proposed mechanism behind its protective effects in injury and disease models.
Research Areas
SS-31 has been studied in several conditions where mitochondrial dysfunction is central. Heart failure is a major area, since the heart is one of the most energy-hungry tissues in the body. Ischemia-reperfusion injury — damage that occurs when blood flow returns after being cut off — is another.
Kidney disease and age-related muscle weakness have also been studied. So have primary mitochondrial diseases, which are inherited disorders where the mitochondria themselves are defective.
Each of these conditions shares a thread: damaged or stressed mitochondria. SS-31 is one of the few tools available to test what happens when those mitochondria are protected.
Clinical Trial Results
SS-31 has reached human trials, with mixed results. A Phase III study in primary mitochondrial myopathies failed its primary endpoint, meaning the headline measure did not reach statistical significance (Karaa et al., 2020).
Phase II work in heart failure has been more nuanced. Some endpoints showed signal, others did not. These outcomes have prompted ongoing analysis of which patient subgroups, doses, and durations might be most informative for future trials.
Mixed results are not the same as no results. They tell researchers something about which questions to ask next and how to design better studies.
Open questions remain. Which conditions, if any, show consistent benefit? What dose and duration matter most? Can biomarkers predict who responds? These compounds are sold strictly for in vitro laboratory research and are not approved for human consumption.