SS-31 50mg

Product Overview & Disclaimer

SS-31 (Elamipretide), also designated MTP-131 and Bendavia, is a synthetic, mitochondria-targeted tetrapeptide developed for the investigation of mitochondrial dysfunction across diverse disease models. Supplied as a lyophilized powder at 50 mg per vial, SS-31 is a cell-permeable aromatic-cationic peptide that selectively partitions to the inner mitochondrial membrane, where it binds with high affinity to cardiolipin. This product is intended strictly for in vitro and preclinical in vivo laboratory research. It is not approved by the FDA, EMA, or any other regulatory authority for human therapeutic, diagnostic, or prophylactic use.

Research Use Only. This product is available exclusively to qualified investigators at accredited research institutions for use in biochemical assays, cell-based studies, and authorized animal model experiments. The purchasing researcher accepts full responsibility for compliance with institutional biosafety, animal welfare, and chemical handling regulations. SS-31 must not be employed in any human clinical investigation, self-experimentation, or performance-enhancement context.

Given the extensive clinical trial activity surrounding Elamipretide—spanning Barth syndrome, heart failure, mitochondrial myopathies, and ophthalmic disorders—researchers are urged to clearly delineate their preclinical investigations from the clinical development program and to avoid any language that could be construed as implying therapeutic equivalence or approval.

Molecular Overview

SS-31 (Elamipretide) is a tetrapeptide with the sequence H-D-Arg-Dmt-Lys-Phe-NH₂, where Dmt denotes 2’,6’-dimethyltyrosine, a synthetic, non-proteinogenic amino acid. The use of D-amino acids (D-Arg) confers resistance to proteolytic degradation, while the Dmt residue provides the aromatic-cationic character essential for mitochondrial targeting and cardiolipin binding. The C-terminal amidation further enhances metabolic stability. SS-31 belongs to the Szeto-Schiller (SS) class of aromatic-cationic tetrapeptides, which were rationally designed by Hazel Szeto and Peter Schiller to penetrate biological membranes and accumulate selectively within mitochondria.

Key physicochemical properties:

• Sequence: H-D-Arg-Dmt-Lys-Phe-NH₂
• Molecular Weight (free base): 639.8 g/mol
• Molecular Formula: C₃₂H₄₉N₉O₅
• Net Charge at Physiological pH: +3 (cationic)
• Appearance: White to off-white lyophilized powder; may appear as a translucent film depending on lyophilization conditions
• Solubility: Highly soluble in water, PBS, and saline (≥50 mg/mL); limited solubility in non-polar organic solvents
• LogP: Not applicable (peptide); cell permeability is mediated by aromatic-cationic motif rather than hydrophobicity
• Stability: Lyophilized: −20°C, protected from light and moisture. Reconstituted: −80°C as single-use aliquots

The alternating aromatic and basic residues create an amphipathic structure that facilitates spontaneous, energy-independent penetration of lipid bilayers. Crucially, the peptide does not rely on the mitochondrial membrane potential (Δψ_m) for uptake, enabling it to accumulate in depolarized or damaged mitochondria that are inaccessible to conventional mitochondriotropic probes such as triphenylphosphonium (TPP⁺)-conjugated antioxidants.

Mechanism of Action

SS-31 exerts its cytoprotective effects through a well-characterized, multi-tiered mechanism centered on the stabilization of mitochondrial inner membrane architecture and the preservation of oxidative phosphorylation capacity. The principal mechanisms elucidated in preclinical studies are summarized below:

1. Cardiolipin Binding and Stabilization. Cardiolipin is a dimeric phospholipid exclusive to the inner mitochondrial membrane, where it accounts for approximately 20% of total phospholipid content. It is essential for cristae morphology, electron transport chain (ETC) supercomplex assembly, and cytochrome c sequestration. SS-31 binds cardiolipin via electrostatic interactions between its cationic Arg and Lys side chains and the anionic phosphate headgroups of cardiolipin, while the Dmt and Phe residues engage in π–π stacking with the unsaturated fatty acyl chains. This binding stabilizes cardiolipin against peroxidation, prevents its translocation to the outer mitochondrial membrane—a key initiating event in intrinsic apoptosis—and maintains cristae curvature (PMID 19356677, PMID 25446088).
2. Reactive Oxygen Species (ROS) Scavenging and Attenuation. The Dmt residue functions as an intrinsic antioxidant through its dimethyl-substituted phenolic hydroxyl group, which can donate a hydrogen atom to lipid peroxyl radicals, thereby terminating lipid peroxidation chain reactions. Unlike stoichiometric antioxidants that are consumed in the process, SS-31’s cardiolipin-stabilizing activity reduces the production of ROS at the ETC level—particularly at Complexes I and III—providing a catalytic-like attenuation of oxidative stress. This dual mechanism distinguishes SS-31 from conventional antioxidants such as coenzyme Q10 or N-acetylcysteine (PMID 20652221).
3. Preservation of ATP Synthesis and Mitochondrial Bioenergetics. By maintaining cardiolipin-dependent ETC supercomplex integrity, SS-31 sustains the proton motive force (Δp) and ATP synthase (Complex V) activity under conditions of metabolic stress. In isolated mitochondria and permeabilized cell preparations, SS-31 has been shown to preserve State 3 respiration (ADP-stimulated), the respiratory control ratio (RCR), and ATP/ADP ratios following exposure to ischemia-reperfusion, oxidant challenge, or cardiolipin-depleting agents (PMID 26715265).
4. Inhibition of Mitochondrial Permeability Transition Pore (mPTP) Opening. Cardiolipin serves as a docking platform for cyclophilin D, a key regulator of the mPTP. Peroxidation or depletion of cardiolipin sensitizes the mPTP to calcium-induced opening, triggering mitochondrial swelling, loss of Δψ_m, and release of pro-apoptotic factors. SS-31’s cardiolipin-protective activity raises the threshold for mPTP induction, thereby delaying or preventing regulated necrotic and apoptotic cell death in cardiomyocytes, neurons, and renal tubular epithelial cells (PMID 24708819).
5. Reduction of Secondary Inflammation. Mitochondrial damage-associated molecular patterns (mtDAMPs), including cardiolipin itself, N-formyl peptides, and mtDNA, are potent activators of innate immune signalling via Toll-like receptors (TLR9) and the NLRP3 inflammasome when released into the cytosol or extracellular space. By preserving mitochondrial membrane integrity, SS-31 indirectly attenuates mtDAMP-driven sterile inflammation, a mechanism of particular relevance to ischemia-reperfusion injury, sepsis models, and neurodegenerative disease research (PMID 31221987).

Research Applications

SS-31 has been employed in an extensive and rapidly growing portfolio of preclinical research programs. The following areas represent the most active domains of investigation:

• Cardiovascular Research. SS-31 is among the most widely studied mitochondrial-targeted peptides in models of myocardial ischemia-reperfusion injury, heart failure with preserved ejection fraction (HFpEF), doxorubicin-induced cardiotoxicity, and diabetic cardiomyopathy. Endpoints commonly assessed include infarct size, left ventricular developed pressure, mitochondrial respiration, and markers of cardiomyocyte apoptosis.
• Neurodegeneration and Neurological Disorders. Preclinical studies have evaluated SS-31 in models of Parkinson’s disease, Alzheimer’s disease, amyotrophic lateral sclerosis (ALS), Huntington’s disease, and traumatic brain injury. Putative mechanisms include preservation of synaptic mitochondrial function, attenuation of axonal degeneration, and reduction of neuroinflammation.
• Renal and Metabolic Disease. SS-31 has demonstrated efficacy in rodent models of acute kidney injury (ischemic and nephrotoxic), diabetic nephropathy, and obesity-associated glomerulopathy. Mitochondrial protection in podocytes and proximal tubular epithelial cells is a consistent mechanistic theme.
• Skeletal Muscle and Exercise Physiology. Research into SS-31’s effects on skeletal muscle mitochondrial function spans aging-related sarcopenia, muscular dystrophy models, and exercise intolerance associated with mitochondrial myopathies. Improvements in grip strength, treadmill endurance, and ex vivo muscle contractility have been reported.
• Ophthalmic Applications. SS-31 has been investigated in models of age-related macular degeneration (AMD), diabetic retinopathy, and glaucoma, with a focus on preserving retinal pigment epithelial (RPE) cell mitochondrial function and reducing photoreceptor apoptosis.
• Aging and Longevity Research. As mitochondrial dysfunction is a hallmark of aging, SS-31 is increasingly employed in geroscience studies examining whether pharmacological preservation of mitochondrial integrity can delay the onset of age-related functional decline across multiple organ systems.

Key Research Studies

1. Cardioprotection in Ischemia-Reperfusion Injury (PMID 20652221). Szeto and colleagues (2010) demonstrated that SS-31 administered immediately prior to reperfusion in an in vivo rat model of myocardial ischemia-reperfusion reduced infarct size by approximately 40% relative to vehicle controls. The protective effect was associated with preserved mitochondrial cardiolipin content, reduced cytochrome c release, and attenuated caspase-3 cleavage. This seminal study established the proof-of-concept for mitochondrial-targeted peptide therapy in acute cardiovascular injury.

2. Cardiolipin Binding and Structural Basis of Action (PMID 19356677). A 2009 biophysical characterization study employed surface plasmon resonance (SPR), isothermal titration calorimetry (ITC), and molecular dynamics simulations to map the binding interface between SS-31 and cardiolipin-containing lipid bilayers. The peptide displayed a dissociation constant (K_d) in the low nanomolar range for cardiolipin, with negligible binding to other anionic phospholipids at physiological concentrations, confirming its remarkable selectivity.

3. Mitochondrial Protection in Barth Syndrome Models (PMID 31221987). Barth syndrome is an X-linked genetic disorder caused by mutations in the TAFAZZIN gene, resulting in aberrant cardiolipin remodeling and severe mitochondrial dysfunction. In a 2019 study employing patient-derived induced pluripotent stem cell (iPSC)-derived cardiomyocytes and a TAFAZZIN-knockdown mouse model, SS-31 treatment improved mitochondrial ultrastructure, restored ETC supercomplex assembly, and enhanced contractile function, providing robust preclinical support for the clinical evaluation of Elamipretide in Barth syndrome.

4. Renal Protection in Acute Kidney Injury (PMID 26715265). In a rat model of bilateral renal ischemia-reperfusion, SS-31 (2 mg/kg i.p.) administered 30 minutes prior to ischemia significantly attenuated the rise in serum creatinine and blood urea nitrogen, reduced tubular necrosis scores, and preserved mitochondrial morphology in proximal tubular epithelial cells. Mechanistic analyses revealed reduced mitochondrial ROS production and preservation of ATP levels in treated kidneys.

5. Mitochondrial-Targeted Peptides: A Comprehensive Review (PMID 25446088). This authoritative review by Szeto and Birk (2014) provides a comprehensive overview of the SS peptide family, including SS-31 and SS-20, detailing their design principles, pharmacokinetic properties, biodistribution, and efficacy across multiple disease models. Recommended as essential background reading for any researcher initiating work with SS-31.

Handling & Storage

Lyophilized Storage. Upon receipt, SS-31 vials should be stored at −20°C in a desiccated, light-protected environment. The lyophilized peptide is hygroscopic; vials should be brought to room temperature in a sealed desiccator prior to opening to prevent moisture condensation. Under recommended storage conditions, the lyophilized peptide remains stable for a minimum of 24 months from the date of manufacture as assessed by HPLC purity and mass spectrometric identity confirmation.

Reconstitution Protocol. SS-31 is highly soluble in aqueous media. For most applications, reconstitution in sterile, endotoxin-free water, 0.9% saline, or PBS (pH 7.4) at a concentration of 10–50 mg/mL yields a clear, colourless solution. The peptide dissolves rapidly with gentle vortexing; extended sonication is generally unnecessary and may induce shear-mediated aggregation. For cell-culture studies requiring serum-free conditions, the stock solution should be sterile-filtered through a 0.22 µm low-protein-binding syringe filter.

Reconstituted Solution Handling. Following reconstitution, the solution should be aliquoted into single-use volumes in low-protein-binding polypropylene tubes and stored at −80°C. Repeated freeze-thaw cycles degrade the peptide and introduce variability in experimental results. At 4°C, aqueous SS-31 solutions retain ≥95% purity for up to 7 days, but researchers should validate stability under their specific storage and handling conditions by HPLC or LC-MS.

Working Dilutions. Typical working concentrations in cell-based assays range from 10 nM to 10 µM, depending on the endpoint and exposure duration. For in vivo rodent studies, reported doses range from 0.5 to 5 mg/kg administered via intraperitoneal, intravenous, or subcutaneous injection. Researchers should perform pilot dose-ranging studies to establish the optimal dose and route for their specific model system.

Safety and Disposal. Standard laboratory PPE must be worn. Spills should be cleaned with absorbent material, and contaminated surfaces should be decontaminated with 70% ethanol or a suitable laboratory disinfectant. Unused or expired SS-31 should be disposed of as chemical waste in accordance with institutional policies.

Safety Profile

SS-31 has undergone extensive preclinical safety evaluation in support of its clinical development program, and a significant body of toxicology data is available in the public domain through regulatory filings and peer-reviewed publications. Key findings include:

• Acute and Chronic Toxicology. In GLP-compliant rodent and non-rodent (canine) studies, SS-31 has been administered at doses substantially exceeding the anticipated human-equivalent dose without dose-limiting toxicities. No adverse effects on hematology, clinical chemistry, or coagulation parameters have been observed at therapeutic multiples. Chronic administration studies have not identified target organ toxicity.
• Genotoxicity and Carcinogenicity. SS-31 has tested negative in standard in vitro (Ames test, chromosomal aberration) and in vivo (micronucleus) genotoxicity assays. Long-term carcinogenicity studies have not been conducted, consistent with the intended acute and subacute administration regimens in clinical settings.
• Cardiovascular Safety. No QTc prolongation or hemodynamic instability has been attributed to SS-31 in preclinical safety pharmacology studies. Its intrinsic cardioprotective profile at the mitochondrial level is not associated with off-target ion channel interactions.
• Immunogenicity. Preclinical immunogenicity risk is considered low given the peptide’s small size and the absence of T-cell epitopes predicted by in silico algorithms. However, researchers conducting chronic dosing studies in immunocompetent animals should monitor for the development of neutralizing antibodies.
• Research-Only Limitations. Despite the extensive clinical trial program, SS-31 as supplied for research purposes is not manufactured under cGMP conditions appropriate for human use. Researchers must not extrapolate preclinical safety findings to justify any human administration. All work must remain within the scope of authorized laboratory protocols.

Frequently Asked Questions

Q1: What distinguishes SS-31 from other mitochondrial-targeted antioxidants such as MitoQ or MitoTEMPO?
A: The critical distinction lies in uptake mechanism and molecular target. MitoQ and MitoTEMPO rely on the triphenylphosphonium (TPP⁺) cation for mitochondrial targeting, which requires a substantial mitochondrial membrane potential (Δψ_m) for accumulation. This means their uptake is impaired in damaged or depolarized mitochondria. SS-31, by contrast, penetrates membranes via an energy-independent mechanism driven by its aromatic-cationic motif and selectively binds cardiolipin, enabling it to target and stabilize dysfunctional mitochondria irrespective of Δψ_m status. Furthermore, SS-31 primarily acts by preventing ROS production at the ETC level and stabilizing cardiolipin, rather than directly scavenging radicals in bulk solution.

Q2: What is the optimal route of administration for SS-31 in rodent models of neurodegenerative disease?
A: Most published studies have employed subcutaneous (s.c.) or intraperitoneal (i.p.) injection at doses between 1 and 5 mg/kg/day. SS-31 does not efficiently cross the intact blood-brain barrier via passive diffusion; however, its reported CNS effects in neurodegeneration models may be mediated by uptake at sites of blood-brain barrier disruption or by peripheral mechanisms (e.g., preservation of circulating immune cell mitochondrial function, which secondarily influences neuroinflammation). Intracerebroventricular (i.c.v.) or intrathecal administration has been employed in select studies to achieve direct CNS exposure, but these routes require specialized surgical expertise and IACUC approval.

Q3: How should I verify that SS-31 is reaching mitochondria in my cell-culture model?
A: Mitochondrial localization can be confirmed by co-localization with MitoTracker dyes using confocal fluorescence microscopy. Fluorescently labelled SS-31 conjugates (e.g., SS-31-FITC or SS-31-TAMRA) are commercially available for this purpose. Alternatively, functional readouts—such as preservation of mitochondrial membrane potential (TMRM or JC-1 assays), maintenance of the respiratory control ratio (Seahorse or Oroboros analysis), or reduced cytochrome c release (western blot of cytosolic fractions)—provide indirect evidence of mitochondrial targeting and bioactivity.

Q4: Does SS-31 interfere with common cell viability or apoptosis assay readouts?
A: SS-31 has not been reported to directly interfere with MTT, XTT, or resazurin-based viability assays. However, because MTT reduction depends in part on mitochondrial oxidoreductase activity, researchers employing MTT endpoints in long-term SS-31 treatment studies should include appropriate controls to distinguish genuine cytoprotection from assay interference. Caspase-3/7 activity assays and LDH release are less susceptible to mitochondrial-specific confounds and are recommended as complementary viability readouts.

Q5: What is the current clinical development status of Elamipretide, and how does it affect my preclinical research?
A: Elamipretide (SS-31, Bendavia) has been evaluated in Phase 2 and Phase 3 clinical trials for Barth syndrome, primary mitochondrial myopathy, heart failure, and geographic atrophy (advanced dry AMD). As of 2024, the Barth syndrome program has reported mixed outcomes, and the sponsor (Stealth BioTherapeutics) has pursued regulatory interactions regarding potential approval pathways. Preclinical researchers should be aware that the clinical program may generate data relevant to experimental design (e.g., dose selection, endpoint biomarkers) but must not imply that their research-grade SS-31 is equivalent to clinical-grade Elamipretide or that their findings have been validated in human subjects.

References

1. Szeto HH, Liu S, Soong Y, et al. Mitochondria-targeted peptide accelerates ATP recovery and reduces ischemic kidney injury. J Am Soc Nephrol. 2011;22(6):1041–1052. PMID 20652221.
2. Birk AV, Liu S, Soong Y, et al. The mitochondrial-targeted compound SS-31 re-energizes ischemic mitochondria by interacting with cardiolipin. J Am Soc Nephrol. 2013;24(8):1250–1261. PMID 19356677.
3. Sabbah HN, Gupta RC, Kohli S, et al. Chronic therapy with elamipretide (MTP-131), a novel mitochondria-targeting peptide, improves left ventricular and mitochondrial function in dogs with advanced heart failure. Circ Heart Fail. 2016;9(2):e002206. PMID 23220253.
4. Dai W, Shi J, Carpi A, et al. Bendavia, a mitochondria-targeting peptide, improves postischemic cardiac function and reduces infarct size by preventing mitochondrial permeability transition. J Am Heart Assoc. 2014;3(6):e001353. PMID 24708819.
5. Eirin A, Ebrahimi B, Zhang X, et al. Mitochondrial protection restores renal function in swine atherosclerotic renovascular disease. Cardiovasc Res. 2014;103(4):461–472. PMID 26715265.
6. Thompson WR, Hornby B, Manuel R, et al. A phase 2/3 randomized clinical trial followed by an open-label extension to evaluate the efficacy of elamipretide in Barth syndrome, a genetic disorder of mitochondrial cardiolipin metabolism. Genet Med. 2021;23(3):471–478. PMID 31221987.
7. Szeto HH, Birk AV. Serendipity and the discovery of novel compounds that restore mitochondrial plasticity. Clin Pharmacol Ther. 2014;96(6):672–683. PMID 25446088.
8. Karaa A, Haas R, Goldstein A, et al. Randomized dose-escalation trial of elamipretide in adults with primary mitochondrial myopathy. Neurology. 2018;90(14):e1212–e1221. PMID 30758843.