SS-31 (Elamipretide)

Elamipretide (SS-31) is a synthetic aromatic-cationic tetrapeptide with the sequence D-Arg-Dmt-Lys-Phe-NH2, where Dmt denotes 2',6'-dimethyltyrosine. The alternating arrangement of positively charged and aromatic residues enables the molecule to traverse cellular membranes in an energy-independent, voltage-independent manner and accumulate selectively on the inner mitochondrial membrane.

The principal molecular target is cardiolipin, a dianionic phospholipid found almost exclusively on the inner leaflet of the inner mitochondrial membrane. Elamipretide binds cardiolipin through electrostatic and hydrophobic interactions, producing a controlled down-tuning of membrane surface electrostatics without charge reversal. Binding affinity scales with surface charge density rather than strict cardiolipin identity, and each peptide molecule interacts with approximately one anionic lipid binding site in a saturable manner.

• Stabilizes cristae curvature and supports assembly of electron transport chain (ETC) supercomplexes involving complexes I, III, and IV. • Prevents cardiolipin peroxidation, reducing electron leakage and reactive oxygen species (ROS) generation. • Inhibits opening of the mitochondrial permeability transition pore (mPTP), limiting cytochrome c release and downstream apoptotic signaling. • Reduces local calcium accumulation at the membrane interface, attenuating calcium-driven mitochondrial stress. • Restores mitochondrial membrane potential and improves ATP synthesis efficiency through complex V.

These effects are most pronounced in dysfunctional or aging mitochondria; preclinical data indicate limited impact on healthy, baseline mitochondrial function.

Elamipretide has been evaluated in more than 17 completed parenteral clinical studies across approximately 200 healthy subjects and multiple disease populations, making it the most extensively studied mitochondria-targeted therapeutic peptide to date.

The pivotal program is TAZPOWER (NCT03098797), a Phase 2/3 randomized, double-blind, placebo-controlled crossover trial in Barth syndrome (BTHS), a rare X-linked mitochondrial cardiomyopathy caused by tafazzin mutations leading to abnormal cardiolipin composition. Twelve subjects received 40 mg subcutaneous elamipretide daily. Primary endpoints of six-minute walk test (6MWT) improvement and the Barth Syndrome Symptom Assessment score were not met in the randomized phase. A 168-week open-label extension showed cumulative 6MWT gains of 96.1 m, reduced fatigue scores, and improved cardiac stroke volume and left ventricular volumes. Based on improvement in knee extensor muscle strength as an intermediate clinical endpoint, the FDA granted accelerated approval to elamipretide (brand name FORZINITY) on September 19, 2025, for BTHS patients weighing at least 30 kg—the first approved therapy for the condition. Continued approval is contingent on confirmatory trial verification.

In heart failure, a Phase 2 randomized ascending-dose study (n=36; PMID 29217757) showed that a single IV infusion at 0.25 mg/kg/h significantly reduced left ventricular end-systolic volume by 14 mL (P=0.005) compared to placebo. The PROGRESS-HF trial did not meet its primary endpoint of LVESV reduction over four weeks. The EMBRACE-STEMI trial found no infarct size reduction in anterior STEMI patients undergoing PCI, though 24-hour heart failure incidence was reduced.

MMPOWER-3 (Phase 3, primary mitochondrial myopathy) did not meet its 6MWT or fatigue primary endpoints in the full population; a subgroup with nuclear DNA defects showed fatigue reduction. The Phase 2 ReCLAIM trial in dry age-related macular degeneration missed primary visual function endpoints but observed slowing of ellipsoid zone degradation as a secondary finding.

In animal models, a 10-month SC treatment study in aged C57BL/6 mice (PMID 36250163; Aging Pathobiology and Therapeutics, 2022) showed improved diastolic function in both sexes, grip strength gains in males, and cognitive improvement in females. A separate mouse aging study (PMID 32779818; Aging Cell, 2020) demonstrated that SS-31 partially reversed age-related diastolic decline, with additive improvements when combined with NMN.

Typical dosage: Clinical trials ongoing (research).

The FDA-approved dosage for FORZINITY (elamipretide) in patients with Barth syndrome weighing at least 30 kg is 40 mg administered subcutaneously once daily, at the same time each day. In adults with severe renal impairment (eGFR less than 30 mL/min not on dialysis), the approved dose is halved to 20 mg once daily; no adjustment is required for mild or moderate renal impairment. No pediatric weight-based titration below 30 kg is established. The drug is supplied as a sterile, clear solution at 80 mg/mL in single-patient-use vials; once opened, vials may be stored refrigerated (2-8 degrees C) or at room temperature (20-25 degrees C) for up to 8 days before discard.

In clinical trials beyond BTHS, the same 40 mg SC once-daily regimen was employed in MMPOWER-3 and ReCLAIM. Acute intravenous dosing in cardiac studies ranged from 0.005 to 0.25 mg/kg/hour over 4-hour infusions (PMID 29217757) and 0.05 mg/kg/hour over 1 hour in EMBRACE-STEMI; these IV protocols are investigational only and not approved.

Elamipretide is not approved for antiaging or longevity indications. In preclinical aging studies, the standard protocol was 3 mg/kg SC administered five days per week. Some practitioners in the research-peptide community report using 40 mg SC daily or on a five-days-on/two-days-off schedule, mirroring the clinical trial dose, but no human data establish safety or efficacy for these off-label uses.

This information is provided for educational reference purposes only and does not constitute medical advice. Dosing decisions and any off-label use should occur only under the supervision of a qualified healthcare provider.

No compound-specific stability data has been identified for this peptide. The general lyophilized-peptide handling framework applies — see Storage & handling for temperature, reconstitution diluent, and beyond-use dating principles.

The best-studied combination is SS-31 with NMN (nicotinamide mononucleotide), evaluated in aged male C57BL/6 mice (Whitson et al., Aging Cell, 2020; PMID 32779818). SS-31 alone partially reversed age-related diastolic dysfunction; NMN alone restored systolic function at high workload; combined treatment achieved both effects simultaneously and produced significantly higher steady-state myocardial NAD(H) levels than either agent alone. The proposed rationale is mechanistic complementarity: SS-31 stabilizes cardiolipin structure and ETC supercomplex assembly, while NMN replenishes the NAD+ cofactor availability required by those same ETC enzymes. This remains a preclinical finding with no human trial replication.

Preclinical work has also explored elamipretide combined with sacubitril/valsartan in a doxorubicin-induced cardiomyopathy model, reporting attenuation of inflammatory markers, oxidative stress, mitochondrial damage, and BNP levels.

In the research-peptide community, SS-31 is anecdotally stacked with CoQ10, MitoQ, or other mitochondria-targeted antioxidants on the premise of complementary ROS scavenging across different membrane compartments. No clinical trials support any such combination in humans, and this use is wholly anecdotal.

SS-31 (Elamipretide) is not currently FDA-approved for any indication. It is generally classified as a research compound. Regulatory status varies by country.

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Reported side effects: Clinical trials. Side effects under study

Elamipretide has a well-characterized safety profile from the TAZPOWER program and multiple phase 1/2 studies spanning up to 168 weeks of continuous exposure. Injection site reactions are the dominant adverse event class. In TAZPOWER (n=12 per arm), erythema occurred in 100% of treated subjects versus 25% on placebo; injection site pain in 75% versus 42%; induration in 67% versus 17%; pruritus in 67% versus 17%; bruising in 25% versus 0%; urticaria in 25% versus 0%. Reactions were characterized as mild to moderate. Across broader phase 1 SC dosing studies, headache was the only systemic adverse event occurring in more than 5% of healthy subjects (8.8%); nausea, hyponatremia, and dizziness each occurred in under 3%.

A notable laboratory finding is transient eosinophilia: absolute eosinophil counts increased by a mean of approximately 0.5-0.6 x 10 cubed per microliter, peaking near day 90 and resolving within 6-12 months. The clinical significance of this finding is uncertain; no eosinophilic organ toxicity has been attributed to the drug in trial records.

The FDA prescribing label (FORZINITY, 2025) identifies two formal warnings. First, the formulation contains benzyl alcohol (20 mg/mL) as a preservative and is not approved for use in neonates due to risk of gasping syndrome and metabolic acidosis in low-birth-weight or preterm infants. Second, serious hypersensitivity reactions—including rash and respiratory symptoms—may occur within minutes to months of initiation; the drug should be discontinued and not rechallenged.

The single contraindication is known serious hypersensitivity to elamipretide or any excipient. No clinically significant effects on vital signs, ECG parameters, or standard laboratory values have been identified in studies of up to 168 weeks. No deaths have been attributed to elamipretide in the clinical trial program. In vitro and in vivo drug interaction studies identified no clinically meaningful interactions with aspirin, clopidogrel, or unfractionated heparin.