Last updated: March 2026
SS-31 (Elamipretide, MTP-131) is a synthetic tetrapeptide that binds directly to cardiolipin — a phospholipid found only in the mitochondrial inner membrane — stabilizing the electron transport chain and protecting mitochondrial architecture. It is one of the most clinically advanced mitochondria-targeted therapeutics, with active Phase 2/3 trials for primary mitochondrial myopathy and heart failure.
SS-31's mechanism is unusually specific — it targets a single molecular target found exclusively in one cellular organelle. This selectivity is what makes it different from general antioxidants or mitochondrial support supplements.
Cardiolipin is a unique anionic phospholipid found only in the mitochondrial inner membrane. It constitutes ~20% of the inner membrane's lipid composition. SS-31's alternating aromatic and basic residues (D-Arg-dimethylTyr-Lys-Phe-NH₂) give it high affinity for cardiolipin's negatively charged head groups.
By binding cardiolipin, SS-31 stabilizes the cristae architecture and electron transport chain supercomplexes (Complexes I, III, IV). This is critical — ETC complex instability is the root cause of reduced ATP production and increased ROS in mitochondrial disease states.
Cardiolipin normally anchors cytochrome c to the inner membrane as an electron carrier. When cardiolipin is oxidized (peroxidized), cytochrome c detaches, releases into cytoplasm, and triggers apoptosis. SS-31 prevents cardiolipin peroxidation, keeping cytochrome c in its functional role.
Dysfunctional ETC complexes "leak" electrons to molecular oxygen, producing superoxide and downstream reactive oxygen species. By stabilizing Complex I and III, SS-31 reduces electron leak and decreases mitochondrial ROS production — without simply scavenging free radicals.
Healthy cristae (the inner folds of the mitochondrial inner membrane) are essential for efficient ATP synthesis. Cardiolipin maintains cristae curvature. In mitochondrial disease and heart failure, cristae collapse and become disorganized. SS-31 restores cristae architecture even in aged or diseased mitochondria.
SS-31 is administered subcutaneously or intravenously in clinical trials. Its alternating charge pattern facilitates rapid cell penetration independent of membrane potential — meaning it works even in cells with collapsed mitochondrial membrane potential (i.e., the sickest mitochondria).
Mitochondrial dysfunction is implicated in an enormous range of diseases — from rare genetic disorders to common age-related conditions like heart failure, Parkinson's, and Type 2 diabetes.
SS-31/Elamipretide has one of the deepest clinical development programs of any mitochondria-targeted peptide. Key trials across multiple indications.
The TAZPOWER trial enrolled 12 patients with Barth syndrome — a rare X-linked cardiomyopathy caused by TAZ gene mutations resulting in defective cardiolipin remodeling. This is the most direct indication for SS-31 given the direct cardiolipin pathology.
Primary mitochondrial myopathy (PMM) is a rare inherited disease causing progressive muscle weakness and exercise intolerance due to ETC dysfunction. The MMPOWER-3 trial is a pivotal Phase 3 study targeting functional improvement.
Heart failure with preserved ejection fraction (HFpEF) is highly associated with mitochondrial dysfunction in cardiomyocytes. Multiple studies have examined elamipretide's effect on cardiac function and exercise capacity.
Retinal pigment epithelial cells are among the most metabolically demanding cells in the body and are highly dependent on mitochondrial function. Geographic atrophy (dry AMD) involves significant mitochondrial damage in these cells.
Quantified outcomes from published Phase 2/3 trials. All data from peer-reviewed sources; cross-trial comparisons carry inherent limitations.
SS-31 has one of the most turbulent but also most advanced development stories of any peptide in the mitochondrial space — a cautionary tale and a case study in peptide pharmaceutical development.
Dr. Hazel Szeto at Weill Cornell Medical College synthesizes a series of Szeto-Schiller (SS) peptides targeting mitochondrial membranes. SS-31 (D-Arg-dimethylTyr-Lys-Phe-NH₂) shows the strongest cardiolipin-binding affinity and mitochondrial protection in preclinical models.
Patent rights licensed to Stealth BioTherapeutics (Boston). The compound is renamed Elamipretide (INN) / MTP-131 internally. Stealth raises substantial venture capital and begins IND submissions. Initial human Phase 1 data shows favorable safety.
Stealth runs parallel Phase 2 trials — MMPOWER (mitochondrial myopathy), PROGRESS-HF (heart failure), RACE (AMD), and the Barth syndrome program. FDA grants Orphan Drug Designation for Barth syndrome and PMM. Positive Phase 2 signals emerge across indications.
TAZPOWER completes with statistically significant results for Barth syndrome. However, Stealth's MMPOWER-3 pivotal trial in PMM misses its primary endpoint in the original analysis (large placebo effect), and the company undergoes significant financial restructuring. Plans for a US IPO are shelved.
The elamipretide program continues after corporate restructuring. Academic and industry researchers continue publishing on the compound's mechanisms. The Barth syndrome data remains compelling; discussions about regulatory filing continue. Academic labs use SS-31 extensively in aging, heart failure, and neuroscience research.
The Barth syndrome indication remains the most likely path to FDA approval given the statistically significant Phase 3 data, the Orphan Drug status, and the severity/unmet need of the disease. A successful NDA/BLA filing would represent the first FDA-approved cardiolipin-targeting therapeutic.
SS-31 is not a general wellness compound — it is a disease-state intervention aimed at pathological mitochondrial dysfunction. Understanding who benefits most is critical to interpreting the data.
Across 7+ clinical trials and hundreds of patients, elamipretide has demonstrated a consistent safety profile. Here's what the trials show.
SS-31 belongs to a broader class of mitochondria-targeting peptides. While Humanin and MOTS-c are endogenous peptides encoded by mitochondrial DNA, SS-31 is a synthetic peptide that mimics cardiolipin's binding partners.
Target: Cardiolipin (inner membrane)
Mechanism: ETC complex stabilization, ROS reduction, cristae preservation
Status: Phase 2/3 trials — most advanced
Origin: Synthetic tetrapeptide (not endogenous)
Target: IGFBP3, BAX, tBID (anti-apoptotic)
Mechanism: Cytoprotection, insulin sensitization, neuroprotection
Status: Preclinical only — no human trials
Origin: Endogenous 24-AA peptide from mitochondrial 16S rRNA
Target: AMPK pathway, nuclear gene regulation
Mechanism: Metabolic reprogramming, glucose utilization, anti-aging
Status: Phase 1 trials initiated
Origin: Endogenous 16-AA peptide from mitochondrial 12S rRNA
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This page is for educational and informational purposes only. SS-31 (Elamipretide) is an investigational drug that has not received FDA approval. All clinical data presented comes from published peer-reviewed trials in specific patient populations with mitochondrial diseases. Cross-trial comparisons carry inherent limitations. Nothing on this page constitutes medical advice. Always consult a qualified physician before starting any new substance. SS-31 is not approved for self-administration or general wellness use.