What is SS-31? The Mitochondria-Targeted Peptide Explained
A research guide to SS-31 (elamipretide) — the cardiolipin-binding tetrapeptide studied for its role in mitochondrial membrane stabilisation and cellular energy research.
SS-31 — also known as elamipretide, Bendavia, or MTP-131 — is a synthetic aromatic-cationic tetrapeptide (D-Arg-2′,6′-Dmt-Lys-Phe-NH2) developed as part of the Szeto-Schiller (SS) peptide series. Unlike most compounds studied in mitochondrial research, SS-31 does not rely on the mitochondrial membrane potential to accumulate at its site of action, which allows it to remain active even in depolarised or metabolically compromised mitochondria — a property that has made it a widely referenced tool compound in mitochondrial biology research.
What Makes SS-31 Unique?
SS-31 selectively concentrates in the inner mitochondrial membrane, where it binds reversibly and with high affinity to cardiolipin — a phospholipid found almost exclusively in this membrane and essential for organising the electron transport chain into efficient “supercomplexes.” This targeted, voltage-independent accumulation distinguishes SS-31 from many other mitochondria-associated research compounds.
By stabilising cardiolipin’s structural interactions with cristae membranes, SS-31 is studied for its capacity to preserve mitochondrial architecture under metabolic and oxidative stress, rather than acting as a conventional antioxidant or metabolic stimulant.
Mechanism of Action
SS-31’s primary mechanism centres on cardiolipin binding and cristae stabilisation, with downstream effects on electron transport efficiency and reactive oxygen species (ROS) output.
- Cardiolipin Stabilisation: SS-31 binds cardiolipin on the inner mitochondrial membrane, helping preserve cristae folding and the structural scaffolding required for efficient oxidative phosphorylation.
- Electron Transport Chain Support: By maintaining cardiolipin-dependent supercomplex assembly, SS-31 is studied for its effects on electron transfer efficiency between Complexes I, III and IV.
- Reduced Electron Leak: Research models suggest that more efficient electron transport correlates with reduced electron leakage and lower superoxide/ROS generation at the membrane.
- ATP Synthesis Efficiency: These combined effects are studied for their influence on ATP output per unit of oxygen consumed, particularly in high-energy-demand tissue models such as cardiac and skeletal muscle.
Key Research Areas
Cardiac Ischaemia-Reperfusion Research: SS-31 is one of the most extensively studied compounds in models of cardiac ischaemia-reperfusion injury, where mitochondrial dysfunction is a central driver of tissue damage on reperfusion.
Age-Related Mitochondrial Decline: Because cardiolipin content and cristae integrity decline with age, SS-31 is a frequently referenced tool in ageing and longevity research examining mitochondrial quality control and bioenergetic decline.
Musculoskeletal and Renal Research: Studies have examined SS-31 in models of sarcopenia and age-related muscle fatigue, as well as in renal mitochondrial dysfunction models, given the high mitochondrial density of kidney tissue.
Ocular and Neurodegeneration Models: SS-31 has also been investigated in models of mitochondrial dysfunction relevant to retinal and neurodegenerative research, reflecting the broad applicability of cardiolipin-targeted approaches across high-energy-demand tissues.
Compound Profile
| Property | Detail |
|---|---|
| Sequence | D-Arg-Dmt-Lys-Phe-NH2 (Dmt = 2′,6′-dimethyltyrosine) |
| Molecular formula | C32H49N9O5 |
| Molecular weight | 639.8 g/mol |
| CAS number | 736992-21-5 |
| Other names | Elamipretide, MTP-131, Bendavia; marketed in the US as Forzinity (elamipretide HCl) |
| Target | Cardiolipin on the inner mitochondrial membrane |
| Regulatory status | US FDA accelerated approval (September 2025) for Barth syndrome in patients weighing at least 30 kg; not approved in the UK |
Key Published Research
- Discovery (2004): Szeto–Schiller peptides were shown to concentrate in the inner mitochondrial membrane and to inhibit mitochondrial swelling, oxidative cell death and reperfusion injury in isolated hearts.1
- Cardiolipin mechanism (2014): A review set out how SS-31 binds cardiolipin to protect cristae structure and electron transport, rather than acting as a simple antioxidant.2
- Ageing muscle (2019): Eight weeks of SS-31 reversed age-related redox stress and improved exercise tolerance in aged mice.3
- Barth syndrome — TAZPOWER (2021, 2024): In 12 patients, the placebo-controlled crossover phase did not meet its primary endpoints, but the open-label extension showed functional improvements that were sustained through 168 weeks.4,5
- Primary mitochondrial myopathy — MMPOWER-3 (2023): In 218 adults, elamipretide did not improve the primary endpoints of six-minute walk distance or fatigue compared with placebo.6
Regulatory & Research Status (2026)
- September 2025 — FDA accelerated approval: Elamipretide became the first approved treatment for Barth syndrome, a rare genetic disorder of cardiolipin metabolism. The approval rests on improved knee-extensor muscle strength, an intermediate endpoint, so confirmatory evidence is required.
- Beyond Barth syndrome: Results in broader mitochondrial disease have been mixed (MMPOWER-3), and research into ageing, kidney and eye applications remains largely preclinical.
Evidence Quality & Limitations
SS-31 has one of the stronger translational records of any mitochondria-targeted peptide, reaching an approved indication. Even so, its pivotal Barth syndrome data come from 12 patients and an intermediate endpoint, and the largest randomised trial to date (MMPOWER-3) was negative. Findings from ageing and organ-injury models should not be assumed to carry over to humans.
References
- Zhao K, et al. Cell-permeable peptide antioxidants targeted to inner mitochondrial membrane inhibit mitochondrial swelling, oxidative cell death, and reperfusion injury. J Biol Chem. 2004;279:34682–90. PubMed
- Szeto HH. First-in-class cardiolipin-protective compound as a therapeutic agent to restore mitochondrial bioenergetics. Br J Pharmacol. 2014;171:2029–50. PubMed
- Campbell MD, et al. Improving mitochondrial function with SS-31 reverses age-related redox stress and improves exercise tolerance in aged mice. Free Radic Biol Med. 2019;134:268–81. PubMed
- Reid Thompson W, et al. A phase 2/3 randomized clinical trial followed by an open-label extension to evaluate the effectiveness of elamipretide in Barth syndrome. Genet Med. 2021;23:471–8. PubMed
- Thompson WR, et al. Long-term efficacy and safety of elamipretide in patients with Barth syndrome: 168-week open-label extension results of TAZPOWER. Genet Med. 2024;26:101138. PubMed
- Karaa A, et al. Efficacy and safety of elamipretide in individuals with primary mitochondrial myopathy: the MMPOWER-3 randomized clinical trial. Neurology. 2023;101:e238–52. PubMed
