SS-31

Origin and Structure

SS-31 — known generically as elamipretide and by the trade names Bendavia and FORZINITY — is a synthetic tetrapeptide with the sequence D-Arg-Dmt-Lys-Phe-NH₂ (where Dmt is 2,6-dimethyltyrosine). The unusual alternating aromatic-cationic structure and the D-amino-acid at the N-terminus give SS-31 both protease resistance and an unusual affinity for a specific intracellular target: the inner mitochondrial membrane phospholipid cardiolipin.

The peptide was developed by Hazel Szeto and Peter Schiller, originally in the context of opioid-receptor pharmacology where they were exploring Dmt-containing peptides. The cardiolipin-targeting and mitochondrial-protective activities were an unexpected discovery. SS-31 has been developed commercially by Stealth BioTherapeutics since the mid-2000s.

Mechanism of Action

SS-31 accumulates selectively on the inner mitochondrial membrane by binding cardiolipin — an anionic phospholipid essentially unique to mitochondria and central to the organization of the electron transport chain. By interacting with cardiolipin, SS-31:

• Stabilizes cristae architecture and preserves the structural organization of the electron transport chain supercomplexes.
• Reduces mitochondrial reactive oxygen species production by improving electron-transfer efficiency rather than by scavenging free radicals directly.
• Preserves ATP synthesis under stress conditions (ischemia, aging, mitochondrial disease).
• Inhibits mitochondrial permeability transition pore opening, a key early event in cellular injury.

This mechanism is distinct from that of any other commercially developed peptide and represents one of the clearest examples of a subcellular-targeted peptide therapeutic.

Clinical Development

Stealth BioTherapeutics has run an unusually broad clinical program. Key trials include:

• MMPOWER-3, a Phase 3 trial in primary mitochondrial myopathy, which missed its primary endpoint on the initial readout but generated extensive data on exercise capacity and quality of life that supported subsequent regulatory engagement.
• ReCLAIM-2 in geographic atrophy secondary to age-related macular degeneration, and ReSIGHT and related programs in Leber's hereditary optic neuropathy (LHON), both reflecting the extraordinary mitochondrial density and vulnerability of retinal tissue.
• Barth syndrome programs, leading to FDA approval of elamipretide under the brand name FORZINITY in late 2025 — the first approved therapy for this rare X-linked cardiolipin-remodeling disorder.
• Heart failure trials (EMBRACE and related), which produced mixed results in HFpEF and HFrEF but established the peptide's cardiovascular safety profile.

The Barth syndrome approval is a particularly clean proof-of-concept: Barth syndrome is caused by mutations in TAFAZZIN, a gene required for normal cardiolipin remodeling, which makes cardiolipin-targeted therapy an unusually rational match of mechanism to disease.

Practical Considerations

In its approved indication, elamipretide is administered subcutaneously. Research-chemical use of SS-31 outside approved indications draws on the long elamipretide clinical program for its dose and safety context, but this is off-label extrapolation and not a substitute for trial data in the specific use case. Primary mitochondrial disease is the best-supported indication; applications in general anti-aging or athletic performance are speculative.

Safety Profile

The elamipretide program has generated an unusually large human safety dataset for a peptide in this category. The most common adverse events are injection-site reactions — erythema, pruritus, induration — which are frequent but generally mild to moderate. Systemic tolerability has been acceptable across multiple indications, with no signals of hepatic, renal, or hematologic toxicity. Long-term exposure data continues to accumulate through post-approval surveillance of the Barth syndrome population.

Regulatory Status

Elamipretide is FDA-approved for Barth syndrome (FORZINITY, 2025). Additional indications remain in development. Non-elamipretide SS-31 research material is available through research-chemical suppliers, with the usual quality caveats — given the existence of an approved medicinal form, patients and clinicians pursuing clinical applications should work with the approved product rather than research-grade material. For broader context on the FDA peptide regulatory landscape, see our 2026 FDA peptide reclassification overview.

The Bottom Line

SS-31 / elamipretide is the most clinically developed mitochondria-targeted peptide ever to reach the market — a first-in-class cardiolipin-binding tetrapeptide with a validated rare-disease indication and an active pipeline across mitochondrial myopathy and retinal disease. It is also the best contemporary example of peptide drug development that ties a precise subcellular mechanism to a specific disease biology. For the aging-biology context, see MOTS-c and our biological age primer.