SS-31

Research Use Only: This page is for research and educational purposes only. It does not provide medical advice, treatment instructions, or guaranteed outcome claims.

What Is SS-31 (Elamipretide)?

SS-31 is a water-soluble, cell-permeable tetrapeptide with the sequence D-Arg–2′,6′-dimethyltyrosine (Dmt)–Lys–Phe–NH₂. It belongs to the Szeto-Schiller peptide family — a series of aromatic-cationic peptides designed to accumulate selectively within mitochondria. The alternating aromatic and cationic residues in its structure enable rapid, energy-independent uptake across cell membranes, concentrating the peptide over 1,000-fold within mitochondria within minutes of exposure.

Unlike triphenylphosphonium (TPP⁺)-conjugated molecules that rely on mitochondrial membrane potential for uptake, SS-31 accumulates in the inner mitochondrial membrane independently of membrane potential. This makes it effective even in dysfunctional mitochondria where the electrochemical gradient is compromised — a critical advantage in disease states and ageing.

The compound was originally designated as a mitochondrial-targeted antioxidant, but subsequent research has revealed that its primary mechanism involves direct interaction with cardiolipin rather than free radical scavenging. This distinction is significant: while general antioxidants reduce oxidative stress broadly, SS-31 specifically modulates the lipid microenvironment necessary for electron transport chain complex assembly and function.

Compound Profile

Mechanism of Action

The elamipretide mechanism centres on its selective binding to cardiolipin, a tetra-acyl phospholipid found almost exclusively in the inner mitochondrial membrane. Cardiolipin plays indispensable roles in mitochondrial biology: it anchors and organises electron transport chain (ETC) supercomplexes, maintains cristae curvature, facilitates cytochrome c interactions, and supports ATP synthase dimerisation.

Research by Szeto and colleagues has demonstrated that SS-31 binds to cardiolipin through electrostatic and hydrophobic interactions, stabilising the cardiolipin-cytochrome c interaction and preventing cytochrome c from converting to a peroxidase. Under normal conditions, cytochrome c shuttles electrons between Complex III and Complex IV. However, when cardiolipin becomes oxidised — as occurs during ischaemia, ageing, and metabolic disease — cytochrome c binds more tightly to damaged cardiolipin and gains peroxidase activity, further oxidising cardiolipin in a destructive positive feedback loop.

By stabilising the cardiolipin–cytochrome c electron transfer relationship, this cardiolipin peptide restores several downstream functions:

• Electron transport chain efficiency — improved supercomplex assembly reduces electron leak and ROS generation at Complexes I and III
• ATP synthesis — enhanced proton motive force coupling increases ATP output per oxygen consumed
• Cristae architecture — cardiolipin stabilisation preserves the membrane curvature necessary for efficient oxidative phosphorylation
• Mitochondrial dynamics — improved membrane integrity supports balanced fission and fusion

This mechanism is distinct from peptides like MOTS-c, which acts as a mitochondrial-derived peptide signalling molecule through AMPK activation. Whereas MOTS-c modulates cellular metabolism at the transcriptional level, SS-31 acts directly at the biophysical level of mitochondrial membrane organisation.

Barth Syndrome Research

Barth syndrome is a rare X-linked genetic disorder caused by mutations in the TAFAZZIN gene, which encodes an enzyme responsible for cardiolipin remodelling. Patients with Barth syndrome have abnormal cardiolipin species — predominantly monolysocardiolipin — leading to severe mitochondrial dysfunction, cardiomyopathy, skeletal myopathy, neutropenia, and exercise intolerance.

Because elamipretide Barth syndrome research directly targets the downstream consequences of tafazzin deficiency — specifically the disrupted cardiolipin–protein interactions — it represents a mechanistically rational therapeutic approach. Preclinical and clinical evidence supports this rationale:

• In a Phase II trial (TAZPOWER), elamipretide treatment was associated with improvements in the six-minute walk test (6MWT) distance and participant-reported measures of fatigue and muscle weakness in adolescents and adults with Barth syndrome
• A 2025 case report documented expanded-access use of elamipretide in a newborn with severe Barth syndrome-related cardiomyopathy, reporting stabilisation of cardiac function during the treatment period
• Psychometric evaluation of the Barth Syndrome Symptom Assessment (BTHS-SA) instrument from the Phase II study demonstrated that patient-reported outcomes captured meaningful changes during elamipretide treatment

Elamipretide received FDA Fast Track designation for Barth syndrome, reflecting the unmet medical need and the biological plausibility of its mechanism in this condition. However, regulatory review has been complex, and the compound has not yet received marketing approval for this indication.

Cardiac Research

Heart failure is characterised by progressive mitochondrial dysfunction, with declining cardiolipin content and composition documented in failing myocardium. SS-31 has been investigated in both preclinical models and clinical trials for heart failure with reduced ejection fraction (HFrEF).

A 2017 Phase I/II randomised, placebo-controlled trial (Daubert et al.) demonstrated that a single infusion of elamipretide produced a statistically significant reduction in left ventricular end-diastolic volume in patients with HFrEF, suggesting acute improvement in cardiac function. The peptide was well tolerated at all tested concentrations.

The larger Phase II PROGRESS-HF trial (Butler et al., 2020) evaluated 28 days of elamipretide treatment in patients with stable HFrEF. While the primary endpoint of change in left ventricular end-systolic volume did not reach statistical significance, secondary analyses showed trends toward improvement in cardiac biomarkers. The trial provided important pharmacokinetic and safety data that informed subsequent trial design.

A 2025 comprehensive review by Sabbah and colleagues integrates the cardiac research evidence and discusses how elamipretide’s mechanism — restoring cardiolipin-dependent supercomplex organisation — may explain its effects on myocardial energetics. This review contextualises SS-31 alongside other mitochondrial-targeted therapies under investigation for cardiovascular disease, including compounds that target other aspects of mitochondrial dysfunction such as BPC-157, which has been studied for its cardioprotective properties through different pathways.

Age-Related Mitochondrial Dysfunction

Mitochondrial decline is one of the hallmarks of biological ageing. With age, cardiolipin content decreases, its acyl chain composition shifts toward more saturated species, and ETC supercomplex stability deteriorates. These changes result in reduced ATP production, increased mitochondrial ROS emission, and impaired cellular quality control through mitophagy.

SS-31 has shown notable effects in preclinical models of age-related mitochondrial dysfunction:

• Skeletal muscle — Siegel et al. (2013) demonstrated that even a single treatment with this mitochondrial-targeted peptide rapidly reversed age-related declines in mitochondrial energetics and improved skeletal muscle performance in aged mice, with effects apparent within one hour
• Kidney ageing — Szeto and colleagues showed that SS-31 prevented glomerulopathy and proximal tubular injury in high-fat diet models, and protected mitochondria after acute ischaemia to prevent progression to chronic kidney disease
• Cardiac ageing — age-related cardiac hypertrophy and diastolic dysfunction were attenuated by SS-31 treatment in aged mouse models, with restoration of mitochondrial proteome homeostasis
• Tissue regeneration — a 2018 review by Szeto and Liu documented that cardiolipin-targeted peptides promoted tissue regeneration during ageing across multiple organ systems

These findings have positioned SS-31 as a compound of interest in the broader field of longevity research, alongside other peptides investigated for age-related decline such as Epithalon, which targets telomere biology through a distinct mechanism, and FOXO4-DRI, which addresses cellular senescence.

Neuroprotection Research

The brain’s high metabolic demand makes neuronal mitochondria particularly vulnerable to dysfunction. SS-31 has been investigated across several preclinical models of neurological disease and injury, with emerging evidence for neuroprotective effects:

• Spinal cord injury — a 2025 study by Ravenscraft et al. demonstrated that the mitochondrial cardiolipin-targeted tetrapeptide SS-31 exerted neuroprotective effects in both in vitro and in vivo models of spinal cord injury, reducing neuronal apoptosis and preserving mitochondrial function in injured tissue
• Diabetic retinopathy — Alam et al. (2015) showed that SS-31 reversed visual decline in mouse models of diabetes, with improvements in retinal function attributed to restored mitochondrial integrity in retinal neurons
• Glaucoma — preclinical evidence suggests mitochondria-targeted antioxidant SS-31 may offer neuroprotection for retinal ganglion cells, with potential relevance to optic neuropathies
• Neurodegenerative disease models — SS-31 has shown effects in preclinical models of Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis, though clinical translation in these areas remains early-stage

The neuroprotective profile of SS-31 complements other peptides under investigation for neurological applications, such as Cerebrolysin, which provides neurotrophic support through a different mechanism, and Thymosin Alpha-1, which modulates neuroinflammation through immune pathways.

Side Effects and Safety Profile

The elamipretide side effects profile has been characterised across multiple clinical trials. In general, the compound has demonstrated a favourable safety profile:

• Injection site reactions — the most commonly reported adverse event in subcutaneous administration trials, typically mild and self-limiting
• Cardiovascular monitoring — no clinically significant changes in blood pressure, heart rate, or ECG parameters were observed in Phase I and II studies
• Renal and hepatic function — laboratory parameters remained within normal limits across clinical trials
• Immunogenicity — as a small tetrapeptide, elamipretide has a low immunogenic potential, and no significant anti-drug antibody responses have been reported

Long-term safety data beyond the duration of completed clinical trials remain limited. The compound’s specificity for the mitochondrial inner membrane — rather than broad cytoplasmic activity — may contribute to its tolerability, though this hypothesis requires further validation through extended exposure studies.

All current safety information derives from controlled clinical trial settings. Researchers should note that safety profiles may differ in different populations or with prolonged use. This information is provided for research reference purposes only.

Pharmacokinetics

SS-31 exhibits several pharmacokinetic properties that distinguish it from larger peptide therapeutics:

• Absorption — rapid absorption following subcutaneous injection, with peak plasma concentrations typically reached within 30–60 minutes
• Distribution — the peptide achieves over 1,000-fold concentration within mitochondria relative to the cytoplasm, driven by its aromatic-cationic structure rather than mitochondrial membrane potential
• Metabolism — the inclusion of D-arginine and the unnatural amino acid 2′,6′-dimethyltyrosine (Dmt) confers resistance to enzymatic degradation, extending the peptide’s effective half-life compared to naturally occurring tetrapeptides
• Elimination — the plasma half-life supports once-daily subcutaneous administration in clinical trial protocols
• Cell permeability — SS-31 crosses cell membranes rapidly and in an energy-independent manner, distinguishing it from peptides that require active transport or receptor-mediated endocytosis

The compound’s small size (639.78 g/mol) places it well below the typical molecular weight threshold for cell membrane penetration. Its alternating aromatic-cationic motif — a shared structural feature across the Szeto-Schiller peptide family — appears to be the critical determinant of its membrane-penetrating behaviour.

FAQ

What is SS-31?

SS-31 is a synthetic tetrapeptide from the Szeto-Schiller peptide family that selectively targets cardiolipin in the inner mitochondrial membrane. Also known as elamipretide, it is under clinical investigation for mitochondrial diseases including Barth syndrome and heart failure. It is classified as a mitochondrial-targeted peptide and is distinct from conventional antioxidant peptides.

How does the SS-31 peptide mechanism differ from conventional antioxidants?

Conventional antioxidants work by scavenging reactive oxygen species (ROS) throughout the cell. SS-31, by contrast, concentrates specifically in the inner mitochondrial membrane where it binds to cardiolipin. This interaction stabilises electron transport chain supercomplexes, reduces electron leak at the source, and preserves mitochondrial cristae architecture — addressing the root cause of excessive mitochondrial ROS rather than neutralising ROS after they are produced.

What is the connection between elamipretide and Barth syndrome?

Barth syndrome is caused by mutations in the TAFAZZIN gene, which impairs cardiolipin remodelling. Because elamipretide directly interacts with cardiolipin to stabilise its functional interactions with mitochondrial proteins, it represents a mechanistically targeted approach to treating the downstream consequences of tafazzin deficiency. The compound has received FDA Fast Track designation for this indication.

Has SS-31 been tested in clinical trials for heart failure?

Yes. SS-31 (elamipretide) has been evaluated in multiple clinical trials for heart failure with reduced ejection fraction (HFrEF). The Phase I/II trial demonstrated acute improvements in cardiac volumes, and the Phase II PROGRESS-HF trial provided further safety and exploratory efficacy data. The compound’s mechanism of restoring mitochondrial energetics is considered relevant to heart failure pathophysiology.

What makes SS-31 a mitochondrial-targeted peptide?

SS-31’s alternating aromatic-cationic residue structure (D-Arg–Dmt–Lys–Phe–NH₂) enables it to cross cell membranes rapidly and concentrate over 1,000-fold within mitochondria. Critically, this uptake is independent of mitochondrial membrane potential — unlike TPP⁺-conjugated compounds — meaning it can still reach dysfunctional mitochondria. Once inside, it binds specifically to cardiolipin in the inner mitochondrial membrane.

What are the reported elamipretide side effects?

In clinical trials, the most commonly reported side effect has been mild injection site reactions following subcutaneous administration. No clinically significant cardiovascular, renal, or hepatic adverse effects were observed across Phase I and II studies. The compound’s small size and specificity for the mitochondrial inner membrane may contribute to its favourable tolerability profile. Long-term safety data beyond trial durations remain limited.

How does SS-31 relate to ageing research?

Mitochondrial dysfunction is a recognised hallmark of biological ageing. Preclinical studies have shown that SS-31 rapidly reverses age-related declines in mitochondrial energetics, improves skeletal muscle performance in aged mice, protects against age-related kidney and cardiac changes, and promotes tissue regeneration. These findings have made it a compound of interest in longevity research, though human ageing trials have not yet been completed.

Is SS-31 the same as elamipretide?

Yes. SS-31 is the original research designation for the compound, named as part of the Szeto-Schiller (SS) peptide series. Elamipretide is the international nonproprietary name (INN) adopted for clinical development. The compound has also been referred to as MTP-131 and Bendavia in earlier development stages. All names refer to the same D-Arg–Dmt–Lys–Phe–NH₂ tetrapeptide.

What is cardiolipin and why does it matter?

Cardiolipin is a unique phospholipid found almost exclusively in the inner mitochondrial membrane. It is essential for the organisation and stability of electron transport chain supercomplexes, ATP synthase function, cristae formation, and cytochrome c electron transfer. Cardiolipin dysfunction — whether from genetic mutations (as in Barth syndrome), ageing, or metabolic disease — leads to impaired energy production and increased oxidative stress. SS-31’s ability to stabilise cardiolipin interactions is the basis for its therapeutic mechanism.

Is SS-31 approved by the FDA?

As of early 2026, SS-31 (elamipretide) is not approved for any indication. It has received FDA Fast Track designation for Barth syndrome, and clinical trials are ongoing or have been completed for several conditions. The compound remains under investigation, and all current uses are limited to clinical trials or expanded-access programmes. This information is provided for research reference purposes only.

References

1. Siegel MP, Kruse SE, Percival JM, et al. Mitochondrial-targeted peptide rapidly improves mitochondrial energetics and skeletal muscle performance in aged mice. Aging Cell. 2013;12(5):763-771. doi:10.1111/acel.12102. PMID: 23692570
2. Dai DF, Chiao YA, Marcinek DJ, Szeto HH, Rabinovitch PS. Mitochondrial oxidative stress in aging and healthspan. Longev Healthspan. 2014;3:6. doi:10.1186/2046-2395-3-6. PMID: 24860647
3. Alam NM, Mills WC 4th, Wong AA, Douglas RM, Szeto HH, Prusky GT. A mitochondrial therapeutic reverses visual decline in mouse models of diabetes. Dis Model Mech. 2015;8(7):701-710. doi:10.1242/dmm.020248. PMID: 26035391
4. Daubert MA, Yow E, Dunn G, et al. Novel Mitochondria-Targeting Peptide in Heart Failure Treatment: A Randomized, Placebo-Controlled Trial of Elamipretide. Circ Heart Fail. 2017;10(12):e004389. doi:10.1161/CIRCHEARTFAILURE.117.004389. PMID: 29217757
5. Szeto HH, Liu S. Cardiolipin-targeted peptides rejuvenate mitochondrial function, remodel mitochondria, and promote tissue regeneration during aging. Arch Biochem Biophys. 2018;660:137-148. doi:10.1016/j.abb.2018.10.013. PMID: 30359579
6. Szeto HH. Stealth Peptides Target Cellular Powerhouses to Fight Rare and Common Age-Related Diseases. Protein Pept Lett. 2018;25(12):1108-1123. doi:10.2174/0929866525666181101105209. PMID: 30381054
7. Butler J, Khan MS, Anker SD, et al. Effects of Elamipretide on Left Ventricular Function in Patients With Heart Failure With Reduced Ejection Fraction: The PROGRESS-HF Phase 2 Trial. J Card Fail. 2020;26(5):429-437. doi:10.1016/j.cardfail.2020.02.001. PMID: 32068002
8. Ortmann L, Velasco D, Cole J. Expanded-access use of elamipretide in a newborn with Barth syndrome: a case report. Eur Heart J Case Rep. 2025;9(2):ytaf030. doi:10.1093/ehjcr/ytaf030. PMID: 39917770
9. Ravenscraft B, Lee DH, Dai H, et al. Mitochondrial Cardiolipin-Targeted Tetrapeptide, SS-31, Exerts Neuroprotective Effects Within In Vitro and In Vivo Models of Spinal Cord Injury. Int J Mol Sci. 2025;26(7):3327. doi:10.3390/ijms26073327. PMID: 40244206
10. Sabbah HN, Alder NN, Sparagna GC, et al. Contemporary insights into elamipretide’s mitochondrial mechanism of action and therapeutic effects. Biomed Pharmacother. 2025;187:118056. doi:10.1016/j.biopha.2025.118056. PMID: 40294492