SS-31, also known as elamipretide, is a synthetic mitochondria-targeted tetrapeptide that selectively binds cardiolipin on the inner mitochondrial membrane. It is the first in its class of cardiolipin-directed therapeutics, and in 2025 it received accelerated FDA approval for Barth syndrome in patients above 30 kilograms of body weight. All other uses are off-label.

The molecule carries a net charge of plus three at physiologic pH. Its alternating cationic and aromatic residues make it cell permeable, water soluble, and resistant to peptidase degradation, which helps it reach the cytoplasm and concentrate in the mitochondria. It accumulates several hundred-fold at the inner membrane and does not enter the matrix.

How it works

By binding cardiolipin, SS-31 stabilizes cristae membrane integrity and inhibits cytochrome C peroxidase activity, which limits cardiolipin peroxidation under oxidative stress. It optimizes electron transport across complexes I through IV by stabilizing supercomplex assemblies, with a noted effect on complex IV. It interacts with the adenine nucleotide translocator (ANT) and ATP synthase, improving ADP sensitivity in aged mitochondria and supporting ATP and NAD production.

Reduced electron leak lowers reactive oxygen species at the source. SS-31 has been described as activating the NRF2 antioxidant response and inhibiting NF-kB, the master inflammatory transcription pathway. Notably, it acts selectively on dysfunctional mitochondria, with no significant effect on healthy mitochondria. The mechanism appears to involve functional remodeling of cardiolipin rather than a change in its absolute amount.

Clinical evidence

In the TAZPOWER Barth syndrome trial, the placebo-controlled phase showed no significant change in primary endpoints at 12 weeks, while the open-label extension over 168 weeks showed improved stroke volume, knee extensor strength, and six-minute walk distance. Heart-failure trials in reduced ejection fraction did not meet primary endpoints, though evaluation continues. A single subcutaneous dose in older adults rapidly and reversibly raised mitochondrial capacity in aging muscle. Preclinical work spans cardiac, renal, and neuroprotection models.

Clinical application

SS-31 is given subcutaneously, commonly on a twice-weekly or three-times-weekly schedule, with dosing described in the 25 to 50 milligram range. Adverse effects are mostly mild and centered on injection-site reactions and pruritus, with no serious adverse events noted in reviewed data. Because it is renally excreted, baseline and ongoing renal function should be followed. Monitoring may include lactate-to-pyruvate and beta-hydroxybutyrate-to-acetoacetate ratios, fatigue indexes, functional strength, and cardiac parameters over time.

Key clinical points

• First-in-class, FDA-approved mitochondria-targeted peptide; approved for Barth syndrome, all other uses off-label.
• Binds cardiolipin to stabilize cristae and supercomplexes, acting selectively on dysfunctional mitochondria.
• Works by functional remodeling of cardiolipin rather than increasing its quantity.
• Cardiac effects build gradually over weeks to months, with durable residual effects beyond the drug half-life.
• Subcutaneous dosing with renal monitoring; track functional and metabolic biomarkers to gauge response.