What is SS-31 (Elamipretide)?

SS-31, also known as Elamipretide or MTP-131, is a synthetic tetrapeptide with the sequence D-Arg-2’6-Dmt-Lys-Phe-NH2. It belongs to a class of Szeto–Schiller (SS) peptides engineered to selectively concentrate in the inner mitochondrial membrane (IMM) due to their amphipathic structure and alternating cationic-aromatic residues.

Unlike most antioxidants, SS-31 does not simply scavenge reactive oxygen species (ROS). Instead, it binds directly to cardiolipin, a phospholipid unique to the IMM, and stabilises the mitochondrial cristae architecture. This cardiolipin interaction is the mechanistic foundation for its observed mitochondrial-protective effects.

For research use only. Not for human consumption. All findings cited below derive from pre-clinical in vitro or animal models.

Mechanism of Action

Cardiolipin Binding

Cardiolipin is a structurally unique phospholipid concentrated in the IMM, where it plays critical roles in organising respiratory complexes (Complexes I–IV) within the electron transport chain (ETC). Under oxidative stress, cardiolipin oxidises, destabilising ETC complexes and converting cytochrome c from an electron carrier to a peroxidase enzyme that generates further ROS.

SS-31 binds cardiolipin via electrostatic interaction (cationic residues) and aromatic intercalation (Dmt and Phe residues), preventing cardiolipin peroxidation and preserving Complex I and Complex IV activities. This positions SS-31 as a cardiolipin-centric mitochondrial protectant rather than a generalised antioxidant.

ATP Synthase Stabilisation

Beyond cardiolipin binding, SS-31 has been shown in pre-clinical models to interact with the F1F0-ATP synthase complex, improving proton gradient coupling and thereby enhancing mitochondrial ATP output even under bioenergetic stress conditions. A 2020 study published in Nature Communications demonstrated that SS-31 increased ATP production in aged cardiomyocytes by preserving cristae morphology.

ROS Reduction Without Uncoupling

SS-31 reduces mitochondrial superoxide and hydrogen peroxide production in a dose-dependent manner across multiple cell types studied in vitro. Critically, it does so without uncoupling the proton gradient, a key advantage over classical antioxidants like FCCP, which sacrifice membrane potential in exchange for ROS clearance.

Pre-Clinical Research Summary

Cardiomyocyte Models

SS-31 has been extensively studied in cardiomyocyte models of ischaemia-reperfusion injury. In rat H9c2 cardiomyocyte cultures exposed to hypoxia-reoxygenation, SS-31 pre-treatment (100 nM–1 μM) reduced cytochrome c release, preserved mitochondrial membrane potential (ΔΨm), and maintained ATP-to-ADP ratios compared to vehicle controls.

In a pig model of myocardial infarction, SS-31 administered intravenously before reperfusion reduced infarct size by approximately 38% and preserved cardiac function as measured by echocardiography at 3 months. These findings have informed ongoing clinical investigation in human cardiac studies.

Skeletal Muscle and Sarcopenia Models

Pre-clinical studies in aged rodents show that SS-31 treatment partially reverses age-related mitochondrial dysfunction in skeletal muscle, including reduced ROS production, improved Complex I activity, and enhanced fatigue resistance in isolated fibre preparations. In C2C12 myotube cultures exposed to dexamethasone-induced atrophy, SS-31 (500 nM) attenuated protein degradation via suppression of FOXO3a-mediated ubiquitin-proteasome pathway upregulation.

Kidney Research Models

SS-31 has been studied extensively in renal tubular epithelial cells (HK-2 line) exposed to cisplatin or H2O2. Pretreatment with SS-31 at concentrations of 100–500 nM significantly reduced markers of tubular apoptosis (cleaved caspase-3, cytochrome c release) and preserved cellular ATP content compared to untreated controls.

Neurological Models

In primary cortical neuron cultures, SS-31 has been shown to preserve dendritic mitochondria under amyloid-β oligomer exposure. A 2019 study in Neuroscience Letters reported that SS-31 (1 μM) maintained neuronal viability and synaptic density in hippocampal slices treated with Aβ 1–42, suggesting relevance in neurodegeneration research contexts.

Purity and Stability Considerations

SS-31 is a tetrapeptide synthesised via solid-phase peptide synthesis (SPPS). It contains a 2’6-dimethyltyrosine (Dmt) non-standard amino acid, which requires specialised coupling chemistry and introduces a potential racemisation site. Research-grade SS-31 should be verified by:

  • HPLC purity ≥99% to confirm absence of truncated or deletion sequences
  • Mass spectrometry (LC-MS/MS) to confirm molecular weight (C32H49N9O5 · 4HCl, MW ~639.7 g/mol free base)
  • Chiral purity: the D-Arg residue must be verified; L-Arg substitution substantially reduces mitochondrial targeting

Lyophilised SS-31 powder is stable at -20°C for 24 months under desiccated, dark storage. Reconstituted solutions should be aliquoted to avoid freeze-thaw cycles and stored at -80°C for extended research programmes.

Concentration Ranges Used in Pre-Clinical Studies

Model Typical Concentration Range Vehicle
Cardiomyocytes (H9c2) 100 nM – 1 μM Sterile PBS or serum-free DMEM
Skeletal myotubes (C2C12) 500 nM – 2 μM Sterile saline or PBS
Renal tubular cells (HK-2) 100 nM – 500 nM Sterile H2O
Cortical neurons (primary) 1 μM Sterile PBS

Concentrations listed are for research reference only and do not constitute dosing guidance for any clinical or preclinical application. Appropriate concentration must be determined by qualified researchers for each specific experimental context.

Comparison with Other Mitochondrial-Targeted Peptides

SS-31 vs MitoQ

MitoQ (mitoquinone mesylate) is a triphenylphosphonium-conjugated ubiquinone that accumulates in mitochondria via membrane potential-driven uptake. Unlike SS-31, MitoQ’s efficacy depends on maintained ΔΨm; in severely depolarised mitochondria, its uptake is reduced. SS-31 accumulates via cardiolipin binding independent of membrane potential, giving it potential utility in already-damaged mitochondria.

SS-31 vs SS-02

SS-02 is a related Szeto–Schiller peptide (D-Arg-Dmt-Lys-Phe-NH2, no 2’6-dimethyl modification) with similar mitochondrial targeting but attenuated antioxidant potency. SS-31’s Dmt residue provides approximately 100-fold greater electron-donating capacity than Tyr, giving it superior ROS scavenging in comparative in vitro assays.

Research Citations

Key pre-clinical references supporting SS-31 research include:

  • Szeto HH. (2014). First-in-class cardiolipin-protective compound as a therapeutic agent to restore mitochondrial bioenergetics. British Journal of Pharmacology, 171(8):2029–2050.
  • Birk AV et al. (2013). The mitochondrial-targeted compound SS-31 re-energises ischaemic mitochondria by interacting with cardiolipin. Journal of the American Society of Nephrology, 24(8):1250–1261.
  • Liu S et al. (2020). SS-31 reduces neuroinflammation and oxidative stress via mitochondria protection in a TBI mouse model. Molecular Neurobiology, 57(8):3332–3343.
  • Campbell MD et al. (2019). Improving mitochondrial function with SS-31 reverses age-related redox stress and improves exercise tolerance in aged mice. Free Radical Biology and Medicine, 134:268–281.

Stackpure SS-31 Formats Available for Research

Stackpure provides SS-31 in the following research formats:

All Stackpure SS-31 products are manufactured to +99% HPLC purity with mass spectrometry confirmation and an independent Certificate of Analysis on every batch.

Conclusion

SS-31 occupies a mechanistically distinct position among mitochondrial-targeted research compounds. Its cardiolipin-binding mechanism allows it to operate independently of mitochondrial membrane potential, potentially extending its utility to late-stage bioenergetic failure contexts where membrane potential-dependent compounds become ineffective. Its established pre-clinical profile across cardiac, renal, skeletal muscle, and neurological models makes it one of the most versatile mitochondrial research peptides currently available.

All information is for in vitro research reference only. Not for human or veterinary use. Stackpure products are sold exclusively for laboratory research purposes. These statements have not been evaluated by the FDA or any regulatory body.