What is SS-31 (Elamipretide)?

SS-31 (also known as Elamipretide and MTP-131) is a synthetic aromatic-cationic tetrapeptide: D-Arg-dimethylTyr-Lys-Phe-NH2. It was developed by Hazel Szeto and Peter Schiller and belongs to the Szeto-Schiller (SS) peptide family. SS-31 selectively concentrates in the inner mitochondrial membrane where it binds cardiolipin, a unique phospholipid essential for electron transport chain efficiency. By stabilizing cardiolipin, SS-31 optimizes ATP synthesis and reduces mitochondrial ROS production. It is For Research Use Only.

What is cardiolipin and why does SS-31 target it?

Cardiolipin is a unique dimeric phospholipid found almost exclusively in the inner mitochondrial membrane. It plays essential structural roles: anchoring the electron transport chain complexes (I, III, IV) in the membrane, maintaining their conformation, and facilitating proton gradient generation for ATP synthesis. In aging and disease states, cardiolipin becomes oxidized and loses its interaction with cytochrome c, causing electron leakage and increased ROS. SS-31 binds cardiolipin with high affinity, protecting it from oxidative damage and restoring optimal ETC function.

Has SS-31 been studied in clinical trials?

Yes. Elamipretide (SS-31) has been studied in Phase II clinical trials for heart failure with preserved ejection fraction (HFpEF), the INDIE-HFpEF trial, and for Barth syndrome (a rare mitochondrial cardiopathy). The INDIE-HFpEF trial did not meet its primary endpoint, though biomarker and functional subgroup data have prompted continued investigation. Barth syndrome studies showed positive safety and some functional improvement signals. As of 2026, no FDA approval has been granted. Rainbow Peptide supplies SS-31 For Research Use Only.

What aging research has been published on SS-31?

SS-31 is one of the most studied mitochondria-targeted peptides in aging biology research. Key preclinical findings include: restoration of cardiac mitochondrial function in aged rodent models to near-young levels; improvement in skeletal muscle mitochondrial bioenergetics and physical performance in aged mice; attenuation of age-related kidney decline in rodent models; and reversal of age-related reductions in endothelial mitochondrial function. SS-31 is considered a benchmark compound in the 'mitochondrial medicine' research field.

SS-31 (Elamipretide) Research Guide

What Is SS-31?

SS-31 is a synthetic aromatic-cationic tetrapeptide with the sequence D-Arg-dimethylTyr-Lys-Phe-NH2. It belongs to the Szeto-Schiller (SS) family of mitochondria-targeted peptides, developed by pharmacologist Hazel Szeto at Cornell University and chemist Peter Schiller.

The peptide is also known by the pharmaceutical development name Elamipretide and the code MTP-131 (mitochondria-targeted peptide 131). It is unique among research peptides in its specific subcellular targeting: SS-31 selectively accumulates in the inner mitochondrial membrane (IMM) at concentrations hundreds to thousands of times higher than in the cytoplasm, driven by the large negative electrochemical potential across the IMM (~180 mV).

Once concentrated in the IMM, SS-31 binds cardiolipin, a phospholipid found almost exclusively in this membrane, through electrostatic and hydrophobic interactions mediated by its alternating cationic and aromatic residues.

Cardiolipin: The Target

Cardiolipin (bis(monoacylglycero)phosphate) is a dimeric phospholipid unique to the inner mitochondrial membrane in eukaryotes (and bacterial plasma membranes, an evolutionary remnant of mitochondria's bacterial ancestry). Its key biological roles:

ETC complex stabilization: Cardiolipin physically anchors respiratory chain complexes I, III, and IV within the IMM, maintaining their quaternary structure and enabling the formation of "respirasomes" (supercomplexes of ETC components)
Cytochrome c interaction: Cardiolipin tightly binds cytochrome c, the mobile electron carrier between complex III and IV, keeping it associated with the IMM for efficient electron transfer. When cardiolipin is oxidized, this interaction is disrupted, releasing cytochrome c into the cytoplasm where it triggers apoptosis.
Proton gradient maintenance: The conical geometry of cardiolipin contributes to the high curvature of the IMM cristae, which concentrates protons for F0F1-ATPase (ATP synthase) activity

In aging and oxidative stress conditions, cardiolipin is preferentially oxidized, its polyunsaturated fatty acid side chains are highly susceptible to ROS attack. This cardiolipin oxidation is now recognized as a key mechanism of age-related mitochondrial dysfunction.

Mechanism of Action

SS-31's proposed mechanism is deceptively simple: by binding and protecting cardiolipin from oxidation, it restores optimal ETC function. The downstream effects documented in research:

Restored cytochrome c binding: Prevents cytochrome c release from IMM, maintaining electron flux through complex IV and reducing electron leak to oxygen (→ less superoxide generation)
Improved ATP synthesis efficiency: Restored ETC supercomplex formation and proton gradient integrity → higher ATP:ADP ratio
Reduced mitochondrial ROS: By keeping electrons moving efficiently through the chain rather than leaking to form superoxide, SS-31 reduces net ROS production, measured as decreased H₂O₂ flux in isolated mitochondria
Preserved mitochondrial membrane potential (ΔΨm): Measured by JC-1 or TMRE staining in cell culture studies
Reduced apoptotic signalling: By retaining cytochrome c at the IMM, SS-31 reduces caspase-9/3 activation in stress conditions

Aging Research Data

SS-31 is one of the benchmark compounds in the emerging field of "mitochondrial medicine" targeting age-related bioenergetic decline. Key published findings:

Cardiac Aging

Aged mouse heart mitochondria show hallmark deficits: reduced complex I/III activity, increased ROS, reduced ATP output. In multiple published studies, acute SS-31 infusion in aged mice (24+ months) restored mitochondrial function measured ex vivo to levels comparable to young mice, described in one study as "reversing 20 years of aging" in murine cardiac bioenergetics.

Skeletal Muscle & Physical Performance

Aging is associated with reduced skeletal muscle mitochondrial capacity and decreased physical performance (VO2 max, grip strength, walking speed). Published rodent studies show SS-31 administration improved maximal mitochondrial respiration in aged skeletal muscle and increased treadmill performance in aged mice, without changes in muscle mass.

Vascular Aging

Age-related endothelial dysfunction involves mitochondrial ROS-mediated reduction of nitric oxide bioavailability. SS-31 treatment in aged mouse aortas restored endothelium-dependent vasodilation and reduced mitochondrial oxidative stress in endothelial cells, effects attributed to cardiolipin protection in vascular mitochondria.

Cardiac Protection Studies

SS-31 has been extensively studied in cardiac ischemia-reperfusion (I/R) injury models:

I/R injury: SS-31 administered before or at reperfusion consistently reduces myocardial infarct size in rodent and pig models, one of the most replicated findings in the SS peptide literature
Heart failure models: In pressure overload (TAC) and diabetic cardiomyopathy models, SS-31 attenuated mitochondrial dysfunction and preserved cardiac function over multi-week treatment periods
Barth syndrome: This rare X-linked cardiomyopathy is caused by mutations in tafazzin, the enzyme that remodels cardiolipin to its mature form. It is mechanistically the most direct application for SS-31, and clinical trial data in Barth syndrome patients has shown functional improvements

Renal Protection Research

The kidney's proximal tubule cells are among the most mitochondria-rich cells in the body, making them highly susceptible to mitochondrial dysfunction. SS-31 has been studied in several renal models:

Acute kidney injury (cisplatin-induced, I/R-induced), attenuated tubular cell death and functional decline
Chronic kidney disease models, slowed fibrotic progression and preserved GFR in aged rodents
Contrast-induced nephropathy models, protective effect in animal studies

Clinical Trial History

Trial	Indication	Phase	Result
INDIE-HFpEF	Heart failure with preserved EF	Phase II	Primary endpoint (exercise capacity) not met; positive biomarker signals
Barth Syndrome (TAZPOWER)	Barth syndrome cardiomyopathy	Phase II/III	Positive safety; functional improvement signals in subgroups
EMBRACE STEMI	Acute MI / cardiac surgery	Phase II	Completed; mixed results; ongoing analysis

No FDA approval as of 2026. Development rights held by Stealth BioTherapeutics (various corporate history); ongoing investigation by academic and pharmaceutical groups. Rainbow Peptide supplies SS-31 For Research Use Only.

SS-31 vs MOTS-c: Mitochondrial Peptide Comparison

SS-31 and MOTS-c are the two most studied mitochondria-focused research peptides, but they work through completely different mechanisms:

SS-31 is a synthetic peptide that physically enters the IMM and binds cardiolipin to protect ETC function. It acts directly on mitochondrial structure.
MOTS-c is an endogenous peptide encoded in mitochondrial DNA that translocates to the nucleus under stress conditions and activates AMPK signalling, a metabolic sensor pathway. Its effects are more systemic and involve gene expression changes.

Both are available from Rainbow Peptide. Researchers studying mitochondrial bioenergetics may find SS-31 more directly mechanistic; those studying metabolic signalling and aging physiology may prefer MOTS-c or combination designs.

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