SS-31: Research, Mechanism of Action & Scientific Overview

What Is SS-31?

SS-31, also known as Elamipretide, Bendavia, or MTP-131, is a synthetic tetrapeptide composed of four modified amino acids: D-Arg-Dmt-Lys-Phe-amide (where Dmt is 2',6'-dimethyltyrosine). Originally developed by researchers at Cornell University and later clinically advanced by Stealth BioTherapeutics, SS-31 was designed as a mitochondria-targeted compound. It belongs to a class of Szeto-Schiller (SS) peptides engineered to accumulate within mitochondria and interact specifically with the inner mitochondrial membrane.

Unlike most peptides that act on cell-surface receptors, SS-31 does not appear to have a traditional receptor interaction. Instead, research indicates that it selectively binds to cardiolipin, a phospholipid found almost exclusively in the inner mitochondrial membrane, where it plays a role in maintaining the structural integrity of electron transport chain complexes and supporting ATP synthesis.

Key Identifier

Peptide Profile

Full Name: Elamipretide (SS-31, MTP-131, Bendavia)
Sequence: D-Arg-Dmt-Lys-Phe-NH2
Molecular Weight: 639.79 g/mol
CAS Number: 736992-21-5
Classification: Mitochondrial-targeted tetrapeptide

Mechanism of Action

SS-31's mechanism of action is distinct from most peptides studied in the research literature. Its primary molecular target is cardiolipin, and its downstream effects center on stabilizing mitochondrial bioenergetics and attenuating mitochondrial reactive oxygen species (ROS) production.

Cardiolipin Binding

Cardiolipin is a phospholipid concentrated in the inner mitochondrial membrane, where it supports the organization of cytochrome c and the respiratory chain supercomplexes. Research indicates that SS-31 selectively binds to cardiolipin through electrostatic and hydrophobic interactions, without disrupting membrane potential. This binding has been associated with preservation of cristae architecture and electron transport chain efficiency under stress conditions.

Reduction of Reactive Oxygen Species

Preclinical studies have consistently reported that SS-31 reduces mitochondrial production of reactive oxygen species, particularly under conditions of ischemia-reperfusion injury, heart failure, or age-related decline. Rather than acting as a direct antioxidant, SS-31 appears to reduce ROS generation at its source by stabilizing the electron transport chain and preventing electron leakage.

Preservation of ATP Synthesis

By supporting cardiolipin-dependent organization of respiratory complexes, SS-31 has been shown in preclinical research to preserve oxidative phosphorylation efficiency and ATP production in stressed or aged mitochondria. This has been observed across cardiac, skeletal muscle, renal, and neuronal tissue models.

Mitochondrial Permeability Transition Pore Modulation

Research has also examined SS-31's effect on the mitochondrial permeability transition pore (mPTP), a key mediator of cell death during ischemic injury. Studies suggest SS-31 may delay or reduce mPTP opening in models of reperfusion injury, contributing to observed cytoprotective effects.

Research Overview

SS-31 has been studied across a broad range of preclinical and clinical settings. It is among the relatively few peptides in its class to have progressed into advanced-stage human clinical trials.

Research Area	Key Findings	Study Type
Cardiac Ischemia-Reperfusion	Preclinical models have shown reduced infarct size, preserved contractile function, and improved mitochondrial ATP output following ischemic injury	In vivo (rodent, porcine)
Heart Failure	Phase 2 clinical trials (EMBRACE-HF, PROGRESS-HF) have investigated elamipretide in patients with heart failure with preserved or reduced ejection fraction	Human clinical (Phase 2)
Primary Mitochondrial Myopathy	MMPOWER trials investigated elamipretide in primary mitochondrial myopathy; Phase 3 trials have been conducted	Human clinical (Phase 2/3)
Leber Hereditary Optic Neuropathy	Elamipretide has been examined for effects on visual function in this mitochondrial optic neuropathy	Human clinical
Age-Related Decline	Rodent studies have reported restoration of skeletal muscle function, exercise tolerance, and mitochondrial respiration in aged animals	In vivo (rodent)
Renal Ischemia	Preclinical kidney injury models have shown preservation of tubular function and reduced oxidative damage	In vivo (rodent, porcine)

Research Context

SS-31 is among the more clinically advanced peptides in mitochondrial research, with multiple Phase 2 and Phase 3 human trials conducted by its clinical developer. However, results across indications have been mixed, and regulatory approval has not been secured to date. Preclinical findings remain robust, while translation to human clinical endpoints continues to be investigated.

Common Areas of Research Interest

The scientific focus on SS-31 centers on conditions characterized by mitochondrial dysfunction. The following domains have seen the most published investigation.

Cardiovascular research, Ischemia-reperfusion injury, heart failure, and cardiac fibrosis have been extensively studied in animal models and human trials
Mitochondrial myopathies, Primary and secondary mitochondrial disease models, including muscle biopsy studies in human patients
Age-related sarcopenia, Aged rodent models have demonstrated improvements in muscle function and fatigue resistance with SS-31 administration
Neurodegenerative research, Parkinson's, Alzheimer's, and optic neuropathy models have been examined for mitochondrial-protective effects
Renal protection, Acute kidney injury and ischemic nephropathy preclinical models
Metabolic research, Studies have investigated effects on insulin sensitivity and mitochondrial capacity in metabolic dysfunction

Pharmacokinetics

SS-31 pharmacokinetic data is relatively well characterized compared to many research peptides, owing to its clinical-stage development. It is typically administered via subcutaneous or intravenous routes in research settings.

~3-4h

Plasma Half-Life

Mitochondria

Accumulation Site

640

Molecular Weight (Da)

Amino Acid Residues

A defining pharmacokinetic feature of SS-31 is its preferential accumulation within mitochondria at concentrations reported to be 1,000 to 5,000 times higher than extracellular levels. This is driven by its net positive charge and affinity for cardiolipin, rather than the membrane potential-dependent accumulation seen with other mitochondria-targeted compounds. This selectivity is a central part of its research interest.

Comparison to Similar Peptides

SS-31 is frequently discussed alongside other compounds investigated for mitochondrial function, particularly those with overlapping cardiovascular or age-related research applications.

Feature	SS-31 (Elamipretide)	MOTS-c	Humanin
Origin	Synthetic tetrapeptide (Szeto-Schiller class)	Encoded within mitochondrial 12S rRNA	Encoded within mitochondrial 16S rRNA
Primary Target	Cardiolipin (inner mitochondrial membrane)	AMPK, folate cycle	BAX, IGFBP-3
Research Focus	Cardiac, mitochondrial disease, aging	Metabolism, exercise, insulin sensitivity	Neuroprotection, apoptosis modulation
Clinical Stage	Phase 2/3 human trials conducted	Preclinical	Preclinical

Frequently Asked Questions

What does SS-31 stand for?

The "SS" in SS-31 refers to Szeto-Schiller, named after Dr. Hazel Szeto and Dr. Peter Schiller, the researchers at Cornell University who developed the SS peptide class. SS-31 is the 31st compound in that research series.

Is SS-31 the same as Elamipretide and Bendavia?

Yes. SS-31, Elamipretide, Bendavia, and MTP-131 all refer to the same tetrapeptide. Elamipretide is the international nonproprietary name (INN), Bendavia was an earlier clinical-development name, and MTP-131 is another designation used in Stealth BioTherapeutics' pipeline.

How is SS-31 different from a typical antioxidant?

Conventional antioxidants neutralize reactive oxygen species after they are generated. SS-31 does not directly scavenge ROS. Instead, research suggests it reduces ROS production at the source by stabilizing cardiolipin-dependent respiratory complexes, improving electron transport efficiency and reducing electron leakage.

What types of research has SS-31 progressed furthest in?

SS-31 has advanced into Phase 2 and Phase 3 clinical trials in heart failure, primary mitochondrial myopathy, and Leber hereditary optic neuropathy. These are among the most clinically developed applications of any peptide in the mitochondrial-targeted class.

Does SS-31 depend on membrane potential to enter mitochondria?

No. Unlike many mitochondrial-targeted compounds that rely on the electrochemical gradient across the inner mitochondrial membrane, SS-31's accumulation is driven by its cationic charge and cardiolipin affinity. This is considered advantageous in pathological states where mitochondrial membrane potential is compromised.

What is the typical research administration route?

In preclinical research, SS-31 has been administered most commonly by subcutaneous injection or intravenous infusion. In human clinical trials, it has also been delivered by subcutaneous daily dosing.

Sources & References

Zhao K, et al. "Cell-permeable peptide antioxidants targeted to inner mitochondrial membrane inhibit mitochondrial swelling, oxidative cell death, and reperfusion injury." Journal of Biological Chemistry. 2004;279(33):34682-34690. PubMed
Szeto HH. "First-in-class cardiolipin-protective compound as a therapeutic agent to restore mitochondrial bioenergetics." British Journal of Pharmacology. 2014;171(8):2029-2050. PubMed
Siegel MP, et al. "Mitochondrial-targeted peptide rapidly improves mitochondrial energetics and skeletal muscle performance in aged mice." Aging Cell. 2013;12(5):763-771. PubMed
Karaa A, et al. "Randomized dose-escalation trial of elamipretide in adults with primary mitochondrial myopathy." Neurology. 2018;90(14):e1212-e1221. PubMed
Daubert MA, et al. "Novel mitochondria-targeting peptide in heart failure treatment: A randomized, placebo-controlled trial of elamipretide." Circulation: Heart Failure. 2017;10(12):e004389. PubMed
Birk AV, et al. "The mitochondrial-targeted compound SS-31 re-energizes ischemic mitochondria by interacting with cardiolipin." Journal of the American Society of Nephrology. 2013;24(8):1250-1261. PubMed

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SS-31: Mitochondrial-Targeted Peptide