SS-31 research: what the published studies show

Identity, and Three Names for One Compound

SS-31 is an aromatic-cationic tetrapeptide with the sequence D-Arg-dimethylTyr-Lys-Phe-NH2, which reference 1 states in its own abstract.^[1] The compound is also called elamipretide, its international non-proprietary name, and by the development names Bendavia and MTP-131. Every clinical trial cited below used elamipretide, and the mechanism work used SS-31.^{[1][2][3][4][5][6][7]} Each sentence on this page names which.

What It Binds, and What That Does in Isolated Systems

Liposome and bicelle work put the interaction at about one molecule of SS-31 to one of cardiolipin, and only where cardiolipin was present.^[1] Nuclear magnetic resonance showed the aromatic residues penetrating deep into cardiolipin-containing bilayers, and SS-31 restored cytochrome c reduction and mitochondrial oxygen consumption when cardiolipin was added.^[1] In fresh mitochondria it increased state 3 respiration and the efficiency of ATP synthesis.^[1]

A polarity-sensitive fluorescent analogue showed SS-31 binding with high affinity to cardiolipin, the anionic phospholipid of the inner mitochondrial membrane that cristae formation requires.^[2] The complex inhibited cytochrome c peroxidase activity, which drives cardiolipin peroxidation, and in rat kidney ischemia SS-31 protected cristae membranes and prevented mitochondrial swelling.^[2] Prompt recovery of ATP on reperfusion followed, along with restored actin cytoskeleton and cell polarity, inhibited apoptosis and protected tubular barrier function.^[2]Both of these are isolated-system and animal work.^[1][2] Neither is evidence about a person.

Heart Failure, Where Two Trials Disagree

An ascending-dose trial gave a single four-hour infusion of elamipretide to people with reduced ejection fraction, eight per dose cohort against twelve on placebo.^[3] Against placebo, the highest cohort showed left ventricular end-diastolic volume down 18 mL at P = 0.009.^[3] End-systolic volume was down 14 mL at P = 0.005, both measured at end of infusion.^[3] The authors describe a temporal association and a dose-effect relationship and call for further study.^[3]

PROGRESS-HF then randomized 71 people with reduced ejection fraction to placebo or one of two elamipretide doses daily for 28 days, with cardiac magnetic resonance as the measure.^[4] Change in end-systolic volume did not differ from placebo at either dose, at P = 0.90 and P = 0.28.^[4] No significant difference appeared in ejection fraction either, and the authors conclude the compound was well tolerated but did not improve end-systolic volume.^[4]

Nothing reconciles these two results.^[3][4] One measured an acute change during a single infusion and found it; the other measured a sustained change after four weeks of daily dosing and did not. Both are randomized and placebo-controlled, and this page reports the disagreement rather than resolving it.

Barth Syndrome, Where the Two Halves of One Trial Disagree

Twelve people with Barth syndrome entered a randomized double-blind placebo-controlled crossover trial, twelve weeks per arm with a four-week washout.^[5] Neither primary endpoint was met.^[5] The endpoints were the six-minute walk test and a symptom assessment scale.^[5]

Ten participants continued into an open-label extension.^[5] At 36 weeks that extension reported the six-minute walk distance up 95.9 meters at P = 0.024 and the symptom score down 2.1 points at P = 0.031.^[5] Knee extensor strength, patient global impression and some cardiac measures also improved.^[5] The authors conclude that daily administration led to improvement in symptoms.^[5]

The controlled comparison found nothing and the uncontrolled follow-on found a great deal. That ordering is worth stating plainly because the extension result is the one that gets quoted.

Primary Mitochondrial Myopathy, the Largest Trial

MMPOWER-3 randomized 218 people with genetically confirmed primary mitochondrial myopathy, half to elamipretide and half to placebo for 24 weeks.^[6] Mean age was 45.6 years, 64 per cent were women, and 74 per cent carried a mitochondrial DNA alteration.^[6] The study did not meet its primary endpoints.^[6]

Six-minute walk distance differed from placebo by minus 3.2 meters, with a confidence interval from minus 18.7 to 12.3 and P = 0.69.^[6] The symptom-assessment total fatigue score differed by minus 0.07, confidence interval minus 0.10 to 0.26, P = 0.37.^[6] This is the largest and most decisive trial of the compound and it is null on both measures.

Healthy Older Adults, and a Result Worth Reading Closely

Thirty-nine healthy older adults were randomized to a single dose or placebo, with magnetic resonance and optical spectroscopy measuring mitochondrial capacity in the first dorsal interosseous muscle.^[7] Enrolment was based on the presence of poorly functioning mitochondria.^[7]

A single dose raised mitochondrial energetic capacity against placebo immediately after a two-hour infusion.^[7] The two expressions of that result were P = 0.055 for the absolute change and P = 0.045 for the percentage change.^[7] One of the pair sits above the conventional threshold and one below, and no difference remained on day 7, consistent with the compound's half-life in human blood.^[7] Resting mitochondrial coupling did not change, and despite the rise in capacity there was no significant effect on fatigue resistance.^[7]

State of the Evidence

Roughly 523 records are indexed across the names SS-31, elamipretide and Bendavia. Seven are cited here.

The pattern across the trials is consistent and it is not flattering.^{[3][4][5][6][7]} Acute and mechanistic measurements move. Sustained, controlled, clinically meaningful endpoints have not. The single-infusion cardiac result was not reproduced over four weeks. The randomized Barth phase missed both endpoints and the phase 3 myopathy trial missed both endpoints. The healthy-adult study raised a capacity measure without changing fatigue.

The compound is also the active ingredient of a licensed medicine.^[5] That medicine's regulatory record is not described on this page, and it is not evidence about the material supplied here.

Authorship is concentrated in the mechanism work.^[1][2] Hazel Szeto, Alexander Birk and J David Warren are authors of both references 1 and 2, which are the two sources for everything this page says about cardiolipin binding. The trials come from different groups.

Nothing here is extrapolated from a neighbor. No result from any other product on this site appears above, and no result from this page should travel to one.