SS-31 — known by its generic name elamipretide, and previously studied under the code MTP-131 and the name Bendavia — is a synthetic tetrapeptide designed to target mitochondria directly. Unlike most research peptides that act on cell-surface receptors, SS-31 works inside the cell, binding a specific lipid in the inner mitochondrial membrane.
This article covers what SS-31 is, the mechanism behind its mitochondrial targeting, what the published trial data actually shows — including a major trial that did not meet its primary endpoints — and what researchers working with it need to know.
Prefer a quick-reference summary? See the SS-31 Research Brief — mechanism, dosing data, and evidence tiers at a glance.
01 — What Is SS-31?
SS-31 is a synthetic tetrapeptide with the sequence D-Arg-Dmt-Lys-Phe-NH₂, where "Dmt" refers to 2′,6′-dimethyltyrosine, a modified aromatic amino acid. Its molecular formula is C₃₂H₄₉N₉O₅, with a molecular weight of 639.8 Da as the free base.
The peptide's structure — alternating cationic residues (D-arginine, lysine) with aromatic residues (dimethyltyrosine, phenylalanine) — is what gives it its defining property: selective concentration in the inner mitochondrial membrane, achieved through electrostatic binding to cardiolipin, a phospholipid found almost exclusively in that membrane. This targeting mechanism is why SS-31 is classified as a mitochondria-targeted peptide rather than a conventional receptor-agonist peptide.
02 — Proposed Mechanisms
Cardiolipin Binding and Cristae Stabilisation
SS-31's primary and best-characterised mechanism is direct binding to cardiolipin via electrostatic interaction. Cardiolipin is essential to the structural integrity of the inner mitochondrial membrane's folds (cristae) and to the proper assembly of the electron transport chain complexes embedded within it. By binding cardiolipin, SS-31 is proposed to stabilise cristae structure, particularly under conditions where cardiolipin is damaged or depleted.
Electron Transport Chain Support
Research indicates SS-31 promotes more efficient electron transfer through the respiratory chain and inhibits cytochrome c peroxidase activity — an aberrant enzymatic activity that cytochrome c can acquire when cardiolipin is oxidatively damaged. Reducing this activity is proposed to limit electron leakage and, by extension, reduce production of reactive oxygen species (ROS) at the source rather than scavenging them after the fact.
Direct Antioxidant Activity
The dimethyltyrosine residue in SS-31's structure has intrinsic free-radical scavenging activity, reacting with reactive oxygen species to form comparatively unreactive tyrosine radicals. This gives SS-31 a secondary, direct antioxidant mechanism in addition to its structural cardiolipin-stabilising effect.
The combination of these mechanisms — structural stabilisation, electron transport support, and direct radical scavenging — is why SS-31 research spans a wide range of conditions involving mitochondrial dysfunction, rather than a single organ system.
03 — What the Published Studies Show
Barth Syndrome — the TAZPOWER Trial
The most clinically advanced research on SS-31 concerns Barth syndrome, a rare genetic disorder of mitochondrial cardiolipin metabolism. The TAZPOWER trial was a randomised, double-blind, placebo-controlled crossover study: 12 subjects received 40 mg/day of subcutaneous elamipretide or placebo for 12 weeks, followed by a 4-week washout, then crossed over to the opposite arm.
In this initial crossover phase, neither primary endpoint — improvement on the 6-minute walk test (6MWT) or on a Barth Syndrome Symptom Assessment scale — reached statistical significance.
The picture changed substantially with longer exposure. Ten of the original subjects entered a 168-week open-label extension; 8 reached the final visit. By week 168, the cumulative improvement on the 6MWT was 96.1 metres (P = .003), alongside improvements in cardiac performance measures. The compound was reported as well tolerated, with injection-site reactions the most common adverse event.
Based on this body of evidence, the FDA granted accelerated approval to elamipretide (brand name FORZINITY) for Barth syndrome in patients weighing at least 30 kg, effective September 2025. This approval is specific to Barth syndrome and to the approved pharmaceutical product — it does not extend to other indications or to research-grade SS-31 supplied for laboratory use.
Primary Mitochondrial Myopathy — the MMPOWER-3 Trial
MMPOWER-3 was a considerably larger Phase 3 trial: 218 participants with genetically confirmed primary mitochondrial myopathy (74% with mtDNA mutations, the remainder with nuclear DNA defects), randomised to elamipretide or placebo.
This trial did not meet its primary endpoints. Neither the 6-minute walk test nor the Total Fatigue Score on the Primary Mitochondrial Myopathy Symptom Assessment showed significant improvement over placebo in the overall study population.
A post hoc subgroup analysis found a different picture in participants with nuclear DNA (nDNA) pathogenic variants — specifically those with mtDNA replisome disorders — who showed a measurable 6MWT benefit versus placebo. Subgroup findings identified after the fact are hypothesis-generating, not confirmatory, and this result would need a dedicated prospective trial in that specific genetic subgroup to be considered established.
Kidney and Cardiac Ischaemia-Reperfusion Research
Separate from the myopathy programme, preclinical research has examined SS-31 in models of acute kidney injury and cardiac ischaemia-reperfusion injury — situations where mitochondrial dysfunction from oxidative stress is a central driver of tissue damage. This body of work remains preclinical (animal and cell-model research) and has not progressed to the same clinical stage as the Barth syndrome or myopathy programmes.
04 — What Is Not Yet Established
The MMPOWER-3 primary endpoint failure is a real negative result, not a footnote — the largest trial of SS-31 to date did not show benefit in its overall study population
The nDNA subgroup signal from MMPOWER-3 is unconfirmed — a post hoc finding, not evidence from a trial designed to test that specific population
FDA approval is condition-specific — it applies to elamipretide as FORZINITY for Barth syndrome in patients ≥30 kg, not to SS-31 generally or to other proposed applications
Kidney and cardiac ischaemia-reperfusion research remains preclinical — no human trial data has been published in these areas at the time of writing
Optimal research parameters for laboratory applications outside the studied clinical contexts are not established in standardised published protocols
05 — Research Formats
SS-31 is available as a lyophilised powder for research applications. It requires reconstitution with bacteriostatic water before use in any research protocol. Full reconstitution guide →
Unreconstituted vials should be stored refrigerated. Reconstituted solutions should be kept refrigerated and used within 28–30 days.
