Mitochondria-targeted compounds: SS-31, MOTS-c and Humanin

Three chemically unrelated compounds, one address in the cell: what the research shows, and where the evidence is strong versus still preclinical.

Peptalis: for laboratory research use only. Not for human use.

Michel van der Veen · Registered Nurse · Science Editor, Peptalis · Deep Dive

Three compounds in our database share a single address: the mitochondrion. That is the part of the cell that supplies energy: the place where nutrients and oxygen are converted into ATP, the molecule a cell uses to pay for almost all of its work. SS-31 acts on the inner membrane of the mitochondrion. MOTS-c and Humanin come from a more surprising direction: they are encoded by the mitochondrial genome itself, the small piece of DNA the mitochondrion carries separately from the cell nucleus.

The three are chemically unrelated and work through different routes. Yet the research around them keeps asking the same question. What happens if the cell's energy household is engaged not indirectly, through hormones or receptors on the outside, but directly inside the mitochondrion itself? This article sets the three mechanisms side by side. It also shows where that research stands: for SS-31 as far as an approved medicine in one rare condition, for MOTS-c and Humanin still largely in preclinical and early-human work.

Part A · The foundation

Three ways into one organelle.

Part 1

SS-31: binding to cardiolipin

Objective: understand how SS-31 acts on the inner membrane

SS-31 is a synthetic tetrapeptide (a chain of four amino acids) that accumulates in the mitochondrion and binds there to cardiolipin. Cardiolipin is a distinctive fat-like molecule (a phospholipid) found almost exclusively in the inner mitochondrial membrane. That inner membrane is folded into pleats, the cristae, and it is on those pleats that the protein complexes producing ATP are arranged. Cardiolipin holds that architecture together.

The point of action has been mapped fairly precisely. Birk and colleagues showed in 2013 that SS-31 binds cardiolipin with high affinity, and that the complex inhibits cardiolipin peroxidation, a damage process that breaks down the mitochondrial cristae during oxygen shortage (Birk et al., J Am Soc Nephrol 2013). In a follow-up, Chavez and colleagues used mass spectrometry to map the proteins SS-31 contacts inside the mitochondrion; nearly all were cardiolipin binders from the ATP-producing chain (Chavez et al., PNAS 2020).

Fig. 1Schematic: SS-31 accumulates in the inner membrane and binds cardiolipin (accent); two protective routes support recovery of ATP production. Mechanism from in-vitro and animal models.

A concrete, verifiable third-party fact makes SS-31 especially current this year. The US FDA granted accelerated approval on 19 September 2025 to FORZINITY™ (elamipretide HCl, the hydrochloride form of SS-31, from Stealth BioTherapeutics) for Barth syndrome, a rare genetic mitochondrial disorder. This is a fact about the FDA and the manufacturer, not a statement that SS-31 as a research compound “treats” anything. It is, however, the first time a mitochondria-targeted peptide has made the step from laboratory to approved medicine in a specific indication.

Takeaway. SS-31 protects the structure in which energy is made; the mechanism is consistent across groups, with the strongest data from animal and tissue models.

Part 2

MOTS-c: the peptide the mitochondrion sends to the rest of the cell

Objective: grasp that the mitochondrion itself encodes signals

MOTS-c is of an entirely different order. It is a small sixteen-amino-acid peptide encoded in the mitochondrion itself rather than in the cell nucleus, within a short reading frame inside the 12S rRNA gene of mitochondrial DNA. Lee and colleagues described it in 2015 as the first of its kind within that specific gene, and showed that it inhibits the folate cycle and thereby activates the energy-sensing enzyme AMPK (Lee et al., Cell Metab 2015). AMPK is the enzyme that pushes a cell to burn fuel when its energy reserves fall.

In mice, that activation was accompanied by improved insulin sensitivity and protection against diet-induced weight gain (Lee et al., 2015). Skeletal muscle appears to be the main target organ. Later reviews placed MOTS-c in a broader category: the “mitochondrial-derived peptides”, signals that act from the mitochondrion at the cellular and organismal level (Lee, Kim & Cohen, Free Radic Biol Med 2016).

Fig. 2Schematic: MOTS-c is encoded in the mitochondrial genome and acts along a metabolic and a nuclear route. The dashed pill marks that the human evidence is still early.

Takeaway. strong animal evidence and a growing but still early human trail.

Part 3

Humanin: a survival signal from the same genome

Objective: cytoprotection as a research question

Humanin was the first mitochondrially encoded peptide to be described, and it comes from another gene on that same small genome: the 16S rRNA gene (MT-RNR2). It is known above all as a cytoprotective signal: a molecule that protects cells against conditions that would otherwise lead to cell death. Reviews describe Humanin as an inhibitor of apoptosis, programmed cell death, in part through an interaction with proteins of the BCL-2 family and through a receptor complex that engages the JAK2/STAT3 route (Zuccato et al., Expert Opin Ther Targets 2019; Hazafa et al., Life Sci 2020).

What makes Humanin interesting as a research question is that it is measurable in the blood, and that the circulating amount tracks with age and with various disease states. It is therefore studied as a point of action and also as a possible biomarker.

Fig. 3Schematic: Humanin blocks cell death and activates a receptor route toward survival. The dashed pill marks that controlled human studies are largely absent.

Takeaway. mechanistically rich, but controlled human intervention studies are largely absent.

Part B · The comparison

What the three share, and where the evidence diverges.

Part 4

What the three share, and where the evidence diverges

Objective: weigh the three mechanisms side by side and distinguish the evidence level per compound

Set the three side by side and a pattern emerges. SS-31 acts on the mitochondrion from the outside and protects the structure in which energy is made. MOTS-c and Humanin are made inside the mitochondrion and carry a message outward, to the rest of the cell and even to other tissues. The first is a structural protector; the other two are messengers. Together they illustrate a shift in thinking: the mitochondrion as a power plant and as a source of signals.

Just as important is where the evidence diverges, and that is exactly the kind of distinction a researcher wants to be able to make. SS-31 has travelled the full path to an approved medicine in one rare, genetically defined condition. That says nothing about other applications, but it does show the mechanism was solid enough to pass a registration route. MOTS-c rests on strong animal evidence and a growing but still early human trail. Humanin is mechanistically rich, but controlled human intervention studies are scarce.

That scarcity is itself an invitation. For laboratories doing mechanistic work on mitochondrial biology, clear follow-up questions lie here: how do the metabolic effects of MOTS-c from animal models translate to humans, and does the cytoprotective action of Humanin reproduce in a controlled setting? These are not promises about outcomes. They are open questions that can move the field forward.

Scientific references

All references are PubMed-indexed and verified (as of August 2026). According to PubMed.

  1. 01Birk AV, et al. The mitochondrial-targeted compound SS-31 re-energizes ischemic mitochondria by interacting with cardiolipin. J Am Soc Nephrol. Preclinical mechanism PMID 23813215 · DOI
  2. 02Chavez JD, et al. Mitochondrial protein interaction landscape of SS-31. Proc Natl Acad Sci USA. Preclinical mechanism PMID 32554501 · DOI
  3. 03Lee C, et al. The mitochondrial-derived peptide MOTS-c promotes metabolic homeostasis and reduces obesity and insulin resistance. Cell Metab. Preclinical (in vitro + animal) PMID 25738459 · DOI
  4. 04Lee C, Kim KH, Cohen P. MOTS-c: A novel mitochondrial-derived peptide regulating muscle and fat metabolism. Free Radic Biol Med. Review PMID 27216708 · DOI
  5. 05Zuccato CF, et al. Mitochondrial-derived peptide humanin as therapeutic target in cancer and degenerative diseases. Expert Opin Ther Targets. Review PMID 30582721 · DOI
  6. 06Hazafa A, et al. Humanin: A mitochondrial-derived peptide in the treatment of apoptosis-related diseases. Life Sci. Review PMID 33130077 · DOI

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Michel van der Veen · Registered Nurse · Science Editor, Peptalis · Sources checked via PubMed · 6 references · educational use only, within the RUO framework · chemistry and references verified, reference date August 2026.

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