Overview

SS-31 — the Szeto-Schiller peptide 31, better known clinically as elamipretide (also MTP-131, Bendavia) — is a synthetic aromatic-cationic tetrapeptide with the sequence D-Arg-2’,6’-dimethyl-Tyr-Lys-Phe-amide. The alternating aromatic-cationic pattern gives the molecule an unusually strong ability to cross the plasma membrane and to concentrate several thousand-fold at the inner mitochondrial membrane, where it binds cardiolipin.

The compound is investigational. It has been evaluated in a large number of small-to-moderate clinical trials across cardiology, ophthalmology, and rare mitochondrial disease. Its most advanced clinical programme is in Barth syndrome, a genetic cardiolipin-remodelling disorder, where it is being developed by Stealth BioTherapeutics.

Mechanism (as reported in the literature)

  • Cardiolipin binding. SS-31 binds cardiolipin at the inner mitochondrial membrane. Preclinical work suggests this binding stabilises cristae architecture and protects cardiolipin from peroxidation.
  • Electron-transport-chain efficiency. Research reports that cardiolipin binding preserves supercomplex assembly of respiratory-chain complexes I, III, and IV, improving ATP synthesis in dysfunctional mitochondria.
  • Reactive-oxygen-species (ROS) modulation. By stabilising the electron-transport chain, SS-31 is described as reducing electron leak and downstream mitochondrial ROS generation rather than acting as a bulk free-radical scavenger.
  • Selective concentration at damaged mitochondria. The mitochondrial-uptake mechanism is reported as membrane-potential-independent, allowing accumulation even in mitochondria with a partially collapsed membrane potential — the setting in which the peptide is most relevant.

Research findings

  • Barth syndrome (TAZPOWER, Reid Thompson et al., 2021). A phase 2/3 crossover trial in Barth syndrome reported improvements in six-minute walk distance and patient-reported outcomes in the elamipretide arm over 36 weeks, with an acceptable tolerability profile at 40 mg/day subcutaneously. Published in the Journal of Cardiac Failure, 2021.
  • Heart failure with preserved ejection fraction (HFpEF). The PROGRESS-HF programme evaluated elamipretide in HFpEF cohorts; results were mixed and did not meet primary endpoints in the pivotal cardiac ischaemia-reperfusion trial (EMBRACE-STEMI).
  • Age-related macular degeneration. The ReCLAIM programme reported reductions in low-luminance visual-acuity deficit in dry AMD cohorts, prompting the ongoing ReGAIN Phase 3 trial in geographic atrophy.
  • Skeletal-muscle bioenergetics in older adults. A small trial in older adults reported acute improvements in mitochondrial ATP production on ³¹P-MRS after single-dose intravenous elamipretide (Roshanravan et al., 2021).
  • Preclinical ageing and ischaemia work. The peptide has been characterised across dozens of preclinical models including renal ischaemia-reperfusion, sarcopenia, and heart failure (Szeto laboratory, 2004–2020).

Common dosing (from published research protocols)

Reported dosing in clinical trials is unusually high compared with most research peptides. In the Barth-syndrome programme, 40 mg subcutaneously once daily is the reference dose (approximately 40,000 mcg). Ophthalmic and cardiovascular trials have used 4 mg to 40 mg per day intravenously or subcutaneously. The upper end of this range is one to two orders of magnitude greater than typical GHRH-analog or thymosin-family research doses — a reflection of the peptide’s low molecular weight and its clinical development pathway rather than a suggestion that higher doses are trivially interchangeable.

Reconstitution

At the typical laboratory vial format of 5 mg reconstituted in 2 mL bacteriostatic water, the concentration is 2,500 mcg/mL — a scale most useful for the lower end of the reported clinical dose range. At the clinical 40 mg dose, larger vial formats (e.g., 100 mg lyophilised, reconstituted to 25–50 mg/mL) are described in the published trial literature. Elamipretide is soluble in water and has been formulated as an aqueous injection.

Storage

Lyophilised elamipretide is reported as stable at refrigerated temperatures. Reconstituted solutions have been described as stable when kept at 2–8 °C for the durations reported in trial protocols, with long-term storage at freezer temperatures.

  • Epithalon — another peptide referenced in the longevity literature, with a mechanism that is oriented toward telomerase rather than mitochondrial bioenergetics.
  • MOTS-c — a mitochondrial-derived peptide with metabolic and mitochondrial-signalling activity.
  • NAD — a nucleotide co-factor rather than a peptide, but frequently discussed in the same mitochondrial-support research context.

Common stacks

References

  • Szeto, H. H. (2014). “First-in-class cardiolipin-therapeutic to restore mitochondrial bioenergetics.” British Journal of Pharmacology, 171(8), 2029–2050.
  • Reid Thompson, W., et al. (2021). “A phase 2/3 randomized clinical trial followed by an open-label extension to evaluate the effectiveness of elamipretide in Barth syndrome.” Journal of Cardiac Failure.
  • Chatfield, K. C., et al. (2019). “Elamipretide improves mitochondrial function in the failing human heart.” JACC: Basic to Translational Science, 4(2).
  • Roshanravan, B., et al. (2021). “In vivo mitochondrial ATP production is improved in older adult skeletal muscle after a single dose of elamipretide.” The Journals of Gerontology: Series A.