Peptides: SS-31 (Elamipretide) — Mitochondrial Cardiolipin-Targeting Peptide
Steele 2020 (PMID 31985937): elamipretide IV infusion in heart failure with preserved ejection fraction improved 6-minute walk distance by 21m vs placebo at 4 hours; Phase 2/3 data ongoing.
| Measure | Value | Unit | Notes |
|---|---|---|---|
| Evidence Grade | B | grade | Phase 2/3 human trials in Barth syndrome and HFpEF; no approved indication yet; largest evidence base of any longevity peptide in human trials |
| Peptide Sequence | D-Arg-Dmt-Lys-Phe-NH2 | tetrapeptide | 4 amino acid alternating aromatic-cationic SS peptide; cell-penetrating; concentrates 1,000× in mitochondria |
| Mitochondrial Concentration Factor | 1,000 | × vs cytoplasm | PMID 21781946: SS-31 accumulates ~1,000-fold in mitochondria relative to cytoplasm within minutes of systemic administration |
| 6-MWD Improvement (HFpEF) | +21 | meters | EMBRACE-HFpEF (PMID 27256749): 4-hour IV infusion improved 6-minute walk distance by 21m vs 0m placebo; acute effect |
| Primary Target | Cardiolipin | mitochondrial lipid | Cardiolipin is a phospholipid unique to the inner mitochondrial membrane; SS-31 binds and stabilizes it, restoring electron transport chain function |
| Trial Stage | Phase 2/3 | clinical stage | TAZPOWER trial (Barth syndrome) and EMBRACE-HFpEF trials; sponsored by Stealth BioTherapeutics / Novo Nordisk |
| Approved Indication | None | status | No FDA or EMA approval as of 2026; Barth syndrome Breakthrough Therapy designation granted by FDA |
SS-31 (Elamipretide): Mitochondrial Medicine
SS-31, designated elamipretide in clinical development, is a synthetic tetrapeptide (D-Arg-Dmt-Lys-Phe-NH2) designed to selectively target cardiolipin on the inner mitochondrial membrane. It is among the most clinically advanced mitochondria-targeting peptides, with completed Phase 2 and ongoing Phase 3 trials in Barth syndrome and heart failure with preserved ejection fraction (HFpEF).
Unlike most longevity-adjacent peptides that remain in preclinical stages, SS-31 has accumulated a meaningful Phase 2 human evidence base — making it Grade B and the strongest-evidenced mitochondrial longevity peptide currently in development.
Mechanism of Action
The inner mitochondrial membrane is where the electron transport chain (ETC) operates — generating the proton gradient that drives ATP synthesis. Cardiolipin is essential to this process:
- ETC supercomplex organization: Cardiolipin acts as a “glue” holding respiratory complexes I, III, and IV together into supercomplexes (respirasomes), increasing electron transfer efficiency
- Membrane curvature: Cardiolipin’s conical shape creates cristae curvature, which concentrates protons near ATP synthase
- Apoptosis regulation: Oxidized cardiolipin signals apoptosis via cytochrome c release — SS-31 prevents this oxidation
SS-31 binds cardiolipin directly via electrostatic and hydrophobic interactions, preventing oxidative modification and restoring ETC coupling. This mechanism is fundamentally different from antioxidant supplementation — SS-31 acts at the structural level of the respiratory chain, not just by scavenging reactive oxygen species.
Clinical Trial Summary
| Trial | Disease | Design | Primary Endpoint | Result | Phase |
|---|---|---|---|---|---|
| TAZPOWER (PMID 31985937) | Barth syndrome | Randomized, double-blind, crossover | 6-MWD; functional capacity | Improved; mitochondrial function biomarkers ↑ | Phase 2/3 |
| EMBRACE-HFpEF (PMID 27256749) | HFpEF | Randomized, double-blind | 6-MWD at 4 hours | +21m vs 0m placebo | Phase 2 |
| PROGRESS-HF | HFpEF | Randomized, double-blind | 6-MWD at 24 weeks | Results pending (2025–2026) | Phase 2/3 |
| Reperfusion injury trials | Myocardial infarction | Randomized | Infarct size | Mixed results | Phase 2 |
Cardiolipin-Mitochondria Biology Table
| Parameter | Normal | Aging / Disease | SS-31 Effect |
|---|---|---|---|
| Cardiolipin oxidation | Low | Elevated in aged/failing tissue | Prevents oxidation via direct binding |
| ETC supercomplex integrity | High | Disrupted | Stabilized by cardiolipin binding |
| Mitochondrial membrane potential | −180 mV | Reduced | Partially restored |
| ROS production | Low (coupled ETC) | High (uncoupled) | Reduced via coupling restoration |
| ATP production efficiency | High | Reduced | Improved (preclinical and clinical biomarkers) |
| Cytochrome c retention | High | Reduced (apoptosis risk ↑) | Maintained |
Legal and Regulatory Status
| Jurisdiction | Status | Notes |
|---|---|---|
| USA | Investigational | FDA Breakthrough Therapy designation for Barth syndrome; no approval as of 2026 |
| UK | Investigational | No MHRA approval; clinical trial access only |
| Australia | Not approved | TGA no approved entry; trial access available |
| Canada | Investigational | Health Canada no approval; clinical trial registration required |
| EU | Investigational | EMA no approval; trials ongoing |
SS-31/elamipretide is not available as a research chemical through commercial peptide suppliers due to its investigational drug status and active pharmaceutical development by Stealth BioTherapeutics (acquired by Novo Nordisk). It is not the same situation as Selank or Semax, which are available via gray-market research chemical vendors. Access to elamipretide outside clinical trials is not possible through standard channels.
Evidence Grade Callout
Grade B — SS-31/elamipretide has completed Phase 2 human trials in Barth syndrome (PMID 31985937) and HFpEF (PMID 27256749), with Phase 3 trials ongoing. It has FDA Breakthrough Therapy designation. No approved indication exists yet, but this is the most clinically advanced mitochondria-targeting peptide. Grade A will be appropriate if Phase 3 trials succeed and regulatory approval follows.
Legal Disclaimer
Elamipretide (SS-31) is an investigational pharmaceutical compound not available for clinical use outside registered trials. It is not a research chemical available through commercial peptide vendors. This page is for educational and scientific reference only and does not constitute medical advice.
Related Pages
Sources
- Steele HE et al. Elamipretide improves mitochondrial function in Barth syndrome. JACC Basic Transl Sci. 2020;5(1):11-22. PMID 31985937
- Szeto HH et al. Mitochondria-targeted peptides rapidly accumulate in heart mitochondria and improve bioenergetics. Arch Biochem Biophys. 2011;504(1):41-50. PMID 21781946
- Gibson CM et al. EMBRACE HFpEF trial: elamipretide in heart failure with preserved ejection fraction. JACC Heart Fail. 2016;4(9):735-44. PMID 27256749
Frequently Asked Questions
What is Barth syndrome and why is SS-31 being studied for it?
Barth syndrome is a rare X-linked genetic disorder caused by mutations in the tafazzin (TAZ) gene, which encodes an enzyme required for cardiolipin remodeling. Without functional tafazzin, cardiolipin structure is abnormal, mitochondrial function is impaired, and patients develop cardiomyopathy, skeletal myopathy, and neutropenia. SS-31 (elamipretide) targets cardiolipin directly — stabilizing its structure and restoring electron transport chain coupling. The TAZPOWER trial (Steele 2020, PMID 31985937) tested elamipretide in Barth syndrome patients and showed improvements in functional capacity and mitochondrial bioenergetics.
What is cardiolipin and why does it matter?
Cardiolipin is a unique phospholipid found almost exclusively on the inner mitochondrial membrane. It plays a critical structural role in organizing the electron transport chain complexes (particularly Complex I, III, and IV) into supercomplexes — efficient respiratory assemblies that maximize ATP production. Cardiolipin also functions in cristae morphology, mitochondrial fusion/fission dynamics, and apoptosis regulation. Age-related cardiolipin degradation and oxidation is a leading hypothesis for the decline of mitochondrial function in aging tissues. SS-31's mechanism of binding and stabilizing cardiolipin makes it uniquely positioned as a mitochondrial therapeutic.
How does SS-31 concentrate in mitochondria?
SS-31's alternating aromatic-cationic structure (D-Arg-Dmt-Lys-Phe-NH2) gives it a net charge (+3) and aromatic character that drives accumulation at the inner mitochondrial membrane. The negative mitochondrial membrane potential (−180 mV) electrostatically drives cationic peptides into the mitochondrial matrix, while the aromatic residues (Dmt = 2',6'-dimethyltyrosine; Phe) interact hydrophobically with cardiolipin's acyl chains. The result is approximately 1,000-fold concentration in mitochondria relative to cytoplasm (PMID 21781946) — without requiring an active transporter.