SS-31: What Researchers Should Know About Elamipretide

SS-31 (also known as Elamipretide, MTP-131, or Bendavia) is a mitochondria-targeted tetrapeptide that has gained increasing attention in biomedical research over recent years. Since September 2025, the pharmaceutical formulation has been approved in the US under the trade name FORZINITY for Barth syndrome - the first FDA-approved mitochondria-targeted therapy ever. For researchers, the question is: what distinguishes research-grade SS-31 from the approved drug, and what matters when sourcing it?

SS-31longevity

Mitochondria-targeted tetrapeptide (Elamipretide) that stabilizes cardiolipin and prevents ROS formation at the source.

Structure and Biochemical Properties

SS-31 is a synthetic tetrapeptide with the sequence:

D-Arg-dimethylTyr-Lys-Phe-NH2

The structure was specifically designed for mitochondrial uptake. Two properties are central:

Positive charge: The amino acids D-arginine and lysine carry positive charges that direct the peptide towards the negatively charged inner mitochondrial membrane. The mitochondrial membrane potential amplifies this accumulation.

Amphipathic character: The aromatic residues (phenylalanine and 2',6'-dimethyltyrosine) partially shield the positive charge, enabling passage through cell membranes. The amphipathic structure - hydrophobic and hydrophilic regions - allows both membrane interaction and solubility in aqueous environments.

Why D-Arginine?

The use of D-arginine (rather than L-arginine) increases resistance to peptidases and extends the biological half-life. This is a typical design principle for synthetic peptides that need to be enzymatically stable.

Mechanism of Action: Cardiolipin Binding

The central mechanism of action of SS-31 is based on selective binding to cardiolipin, a phospholipid found almost exclusively in the inner mitochondrial membrane. Cardiolipin plays a structural and functional role in organising respiratory chain complexes and maintaining cristae structure.

What SS-31 does at cardiolipin:

Stabilisation of cristae architecture: The binding protects cardiolipin from oxidative damage, thereby maintaining the spatial organisation of the respiratory chain.
Reduction of ROS production: By stabilising the electron transport chain, electron leakage is reduced, which decreases the formation of reactive oxygen species.
Preservation of ATP synthesis: The intact cristae structure and stabilised membrane potential support oxidative phosphorylation.
Modulation of membrane electrostatics: Recent work (2025, ScienceDirect) shows that SS-31 influences electrostatic surface potentials of the mitochondrial membrane, thereby promoting the assembly of cardiolipin-dependent protein complexes.

No effect on healthy mitochondria

A notable finding: SS-31 accumulates in the inner mitochondrial membrane but is not transported into the mitochondrial matrix. In preclinical models, no effects on normally functioning mitochondria were observed. The effect appears primarily in dysfunctional mitochondria.

FDA Approval: FORZINITY for Barth Syndrome

On 19 September 2025, the FDA granted accelerated approval to FORZINITY (elamipretide injection) to improve muscle strength in adult and paediatric patients with Barth syndrome weighing at least 30 kg.

What is Barth syndrome?

Barth syndrome (BTHS) is a rare, X-linked mitochondrial disorder affecting approximately 150 individuals in the United States. It is caused by mutations in the TAFAZZIN gene, which is responsible for cardiolipin remodelling. The result: abnormal cardiolipin, impaired mitochondrial function, cardiomyopathy, skeletal muscle weakness, and neutropenia.

Why is the approval significant?

First FDA-approved therapy for Barth syndrome
First FDA-approved mitochondria-targeted therapy ever
Validation of cardiolipin stabilisation as a therapeutic principle

Important limitation: The approval was granted under the Accelerated Approval pathway based on a surrogate endpoint (muscle strength). Stealth BioTherapeutics must conduct a post-marketing study to confirm clinical benefit. The start of this study is planned for the first half of 2026.

TAZPOWER Study: The Basis for Approval

The approval of FORZINITY is based on the TAZPOWER study, a randomised, double-blind, placebo-controlled trial with a subsequent open-label extension.

Study design:

Phase 2 study with cross-over design
40 mg elamipretide subcutaneously daily
168-week open-label extension (OLE)

Results of the 168-week OLE:

6-minute walk test: Cumulative improvement of 96.1 metres from OLE baseline (p = 0.003)
Muscle strength: Improvement in knee extensor strength (primary endpoint for approval)
Cardiac parameters: Clinically meaningful improvements in left ventricular end-diastolic and end-systolic volumes as well as stroke volume
Biomarker: Significant decrease in the MLCL:CL ratio (an elevated ratio is pathognomonic for BTHS)
Fatigue: Improvements in clinical and fatigue survey scores

Safety in TAZPOWER: Ten patients entered the OLE; eight reached the 168-week visit. Elamipretide was well tolerated. The most common adverse events were injection site reactions.

Further Clinical Trials

SS-31/Elamipretide is being investigated in several indications beyond Barth syndrome.

MMPOWER-3: Primary Mitochondrial Myopathy

The pivotal phase 3 study MMPOWER-3 evaluated elamipretide in 218 patients with genetically confirmed primary mitochondrial myopathy (PMM). Result: the primary endpoints (6-minute walk test and fatigue score) were not met. The difference between elamipretide and placebo was -3.2 metres on the 6MWT (p = 0.69).

A post-hoc analysis showed, however, that patients with nuclear DNA variants (nDNA) showed improvement on the 6MWT, while patients with mitochondrial DNA variants (mtDNA) showed no difference from placebo. This finding is relevant for hypothesis generation but should be interpreted with caution as a post-hoc analysis.

ReCLAIM and ReNEW: Dry Age-Related Macular Degeneration (AMD)

The phase 1 ReCLAIM study demonstrated the safety of subcutaneous elamipretide injections in intermediate AMD and geographic atrophy. The phase 3 ReNEW study (NCT06373731) reached the 50% mark of the planned 360 participants in March 2025. The primary endpoint is the rate of change in macular photoreceptor loss, measured by SD-OCT and ellipsoid zone mapping. Results are expected in 2026.

A second phase 3 study (ReGAIN) in dry AMD is planned to start in the coming months.

PROGRESS-HF: Heart Failure

The phase 2 PROGRESS-HF study evaluated elamipretide in patients with heart failure with reduced ejection fraction (HFrEF). Elamipretide was well tolerated but did not significantly improve left ventricular end-systolic volume at four weeks compared to placebo.

Safety Profile

The safety profile of SS-31/Elamipretide has been consistently documented across multiple clinical trials.

Most common adverse effects (subcutaneous administration):

Erythema at the injection site (57%)
Pruritus at the injection site (47%)
Pain at the injection site (20%)
Urticaria at the injection site (20%)
Irritation at the injection site (10%)
Headache and dizziness (occasional)

Most injection site reactions were mild and self-limiting. In the TAZPOWER study, they could be managed with oral antihistamines or topical corticosteroids.

Intravenous administration: SS-31 was also well tolerated intravenously over a wide dose range (0.01 - 0.25 mg/kg/h over 4 hours) in early studies.

No serious drug-related adverse events or deaths were reported in clinical trials.

Research-Grade SS-31 vs. FORZINITY: Key Differences

For researchers, the distinction between the approved drug and research-grade peptide is essential.

Feature	FORZINITY (approved)	Research-Grade SS-31
Regulatory status	FDA-approved for BTHS	For research use only (RUO)
Manufacturing	GMP production, pharmaceutical quality	Research-grade, not for clinical use
Target group	Patients with Barth syndrome (30 kg+)	Researchers (in vitro, preclinical)
Access	Prescription only, via specialty pharmacy	Available for research purposes

Regulatory clarification

Research-grade SS-31 is not an approved medicinal product and is not intended for human use. The FDA approval of FORZINITY applies exclusively to the pharmaceutical preparation in the approved indication.

Quality Criteria When Purchasing

When sourcing SS-31 for research, analytical transparency is key.

Purity testing

A meaningful COA should contain HPLC purity analysis, mass spectrometry for identity confirmation, peptide content, and residual moisture data. Independent testing by recognised laboratories such as Janoshik Analytical increases reliability.

Storage: SS-31 is supplied as lyophilised powder. Store at -20 degrees C in this form. After reconstitution, keep refrigerated (2-8 degrees C) and use promptly.

EU shipping: For researchers in Europe, shipping within the EU offers the advantage of no customs duties and short delivery times. PeptidesDirect ships from the EU with tracking.

Combination with Other Longevity Peptides

SS-31 targets the inner mitochondrial membrane and thus conceptually complements peptides that affect other aspects of mitochondrial or cellular function.

SS-31 and NAD+: complementary targets

While SS-31 addresses cardiolipin stability and thus the structural integrity of mitochondria, NAD+ acts as a coenzyme in redox and signalling processes. The two molecules act at different points in the mitochondrial functional chain.

SS-31 and MOTS-c: MOTS-c is a mitochondrially encoded peptide linked in research to AMPK activation and metabolic adaptation. In combination with SS-31, structural and metabolic aspects of mitochondrial function can be investigated.

SS-31 and Epitalon: Epitalon is discussed in ageing research in connection with telomere-related hypotheses. In combination with SS-31, an experimental framework emerges that covers both mitochondrial and telomeric ageing mechanisms.

SS-31longevity

Mitochondria-targeted tetrapeptide (Elamipretide) that stabilizes cardiolipin and prevents ROS formation at the source.

Frequently Asked Questions

Order SS-31

When sourcing SS-31 for research, look for independent purity analyses, EU shipping without customs risks, and transparent quality documentation. The clear distinction between research-grade peptide and the approved drug FORZINITY is a sign of a serious supplier.

SS-31longevity

Mitochondria-targeted tetrapeptide (Elamipretide) that stabilizes cardiolipin and prevents ROS formation at the source.