SS-31

What SS-31 is

SS-31 is a synthetic tetrapeptide belonging to the Szeto-Schiller (SS) peptide family, a series of aromatic-cationic peptides designed to accumulate selectively within mitochondria ^[1]. The compound was co-discovered in the early 2000s by pharmacologist Dr. Hazel Szeto at Weill Cornell Medicine and peptide chemist Dr. Peter W. Schiller at the Montreal Clinical Research Institute (IRCM), who were originally studying synthetic opioid peptides for pain signalling research ^[2]. Its formal sequence is D-Arg–2′,6′-dimethyltyrosine (Dmt)–Lys–Phe–NH₂, giving it alternating cationic and aromatic side chains that drive its selective uptake into the inner mitochondrial membrane ^[3].

The compound's development name 'SS-31' refers to its position in the Szeto-Schiller series, while 'elamipretide' is the International Nonproprietary Name used in clinical and regulatory contexts, and 'Bendavia' or 'MTP-131' are earlier trade/development names ^[4]. Commercialised by Stealth BioTherapeutics, it earned FDA Orphan Drug and Fast Track designations before receiving accelerated approval on September 19, 2025 under the brand name Forzinity—making it the first mitochondria-targeted therapeutic to receive FDA approval, specifically for Barth syndrome ^[5]. It has also been studied in Phase II/III trials for heart failure, primary mitochondrial myopathy, dry age-related macular degeneration, and renal ischaemia-reperfusion injury ^[6].

What it is being researched for

1. Mitochondrial disease & Barth syndrome

Barth syndrome is an X-linked genetic disorder caused by mutations in the TAFAZZIN gene that impair cardiolipin remodelling, resulting in dysfunctional mitochondria, cardiac failure, and muscle weakness ^[5]. Because elamipretide directly interacts with cardiolipin to stabilise its functional interactions with mitochondrial proteins, it represents a mechanistically targeted approach to treating the downstream consequences of tafazzin deficiency ^[7]. The TAZPOWER clinical trial evaluated elamipretide in patients with Barth syndrome; while the randomised crossover phase missed its primary endpoints, improvements in six-minute walk distance and symptoms emerged in the open-label extension ^[4]. In a tafazzin knockdown mouse model, SS-31 restored mitochondrial morphology, improved defective mitophagy, and enhanced mitochondrial respiratory efficiency through improved stabilisation of cardiolipin–protein interactions ^[8]. Patient-derived fibroblast studies also showed that SS-31 reversed mitochondrial fragmentation and reduced elevated reactive oxygen species (ROS) production associated with the dilated cardiomyopathy with ataxia (DCMA) syndrome, a related mitochondrial cardiomyopathy ^[9].

2. Cardiac protection & heart failure

The heart is one of the most mitochondria-dense organs, making it particularly sensitive to impairments in oxidative phosphorylation ^[4]. Preclinical models have shown that SS-31 protects cardiac tissue from ischaemia-reperfusion injury by interacting with cardiolipin, re-energising ischaemic mitochondria and limiting infarct development ^[1]. A proteomic study published in PNAS mapped SS-31's interactions across 12 key mitochondrial inner-membrane proteins involved in ATP generation, providing molecular context for its cardiac effects ^[3]. In aged mouse hearts, SS-31 was shown to restore late-life cardiac function by reversing mitochondrial dysfunction, improving diastolic performance ^[6]. However, the EMBRACE clinical trial in 71 patients with heart failure with reduced ejection fraction did not achieve statistical significance on its primary endpoint of change in left ventricular end-systolic volume at day 28 ^[6], illustrating that promising preclinical findings have not fully translated to human trials in this indication.

3. Cognitive function & neuroprotection

Mitochondrial oxidative stress in the brain vasculature has been identified as a contributor to age-related cognitive decline, and SS-31 has been studied as a way to interrupt this pathway ^[10]. In aged mouse models, treatment with SS-31 significantly improved neurovascular coupling responses by increasing nitric-oxide-mediated cerebromicrovascular dilation, and these changes were associated with improved spatial working memory, motor skill learning, and gait coordination ^[10]. In a traumatic brain injury (TBI) mouse model, SS-31 reversed mitochondrial dysfunction and ameliorated secondary brain injury by decreasing ROS content, restoring superoxide dismutase (SOD) activity, and reducing neural apoptosis ^[11]. Separately, SS-31 improved functional connectivity in the hippocampus and related regions in aged rats following neuroinflammation induced by lipopolysaccharide (LPS) ^[12]. It is important to note that, as of available research, these cognitive and neuroprotective effects have been observed exclusively in animal models; no controlled human trials have confirmed these outcomes ^[13].

4. Skeletal muscle & age-related exercise intolerance

Sarcopenia—the age-related loss of muscle mass and function—is closely linked to mitochondrial oxidative stress and declining ATP production. Research in aged mice showed that sustained SS-31 treatment reversed age-related decline in maximal mitochondrial ATP production and coupling of oxidative phosphorylation, restored redox homeostasis, and increased treadmill endurance capacity without increasing mitochondrial content ^[14]. A follow-up study confirmed that elamipretide improves ADP sensitivity in aged skeletal and cardiac mitochondria by increasing nucleotide uptake through the adenine nucleotide translocator (ANT), providing a molecular mechanism for its functional effects ^[15]. Intermittent treatment protocols also preserved exercise tolerance and left ventricular mass in aged female mice, although the kidney benefits previously observed with continuous delivery were not replicated, suggesting that administration context matters ^[16]. These findings are currently informing translational research, as elamipretide is in clinical trials for primary mitochondrial myopathy ^[6].

5. Renal protection & kidney injury

SS-31 was among the earliest investigated applications of this peptide family and provided much of the foundational cardiolipin-mechanism evidence ^[6]. In rodent models of ischaemia-reperfusion injury, SS-31 reduced mitochondrial ROS generation, preserved ATP synthesis, and attenuated histological markers of tubular damage including necrosis and cast formation ^[17]. A review of SS-31 in kidney disease concluded that its antioxidative stress effect has been demonstrated across multiple models including ischaemia-reperfusion injury, unilateral ureteral obstruction, and diabetic nephropathy, where it alleviates apoptosis, epithelial–mesenchymal transition, and fibrosis ^[17]. In aged mice, SS-31 improved age-related glomerulosclerosis and mitochondrial morphology within glomerular cells, reduced markers of podocyte injury, and improved cytoskeletal integrity even when therapy was initiated late in life ^[18]. More recent work has explored modified SS-31 derivatives with enhanced renal accumulation to overcome its rapid elimination, suggesting active interest in improving its pharmacokinetics for renal indications ^[19].

6. Neurodegeneration & Parkinson's / Alzheimer's disease models

Mitochondrial dysfunction is an early and prominent feature of both Parkinson's disease (PD) and Alzheimer's disease (AD), making SS-31 of mechanistic interest in these fields ^[20]. Preclinical studies have indicated that SS-31 protects dopaminergic neurons against parkinsonian damage in mouse models, reduces amyloid-beta accumulation in cell models of Alzheimer's disease, and enhances neural mitochondrial function in mouse models of cognitive deficits ^[20]. A dedicated biophysical study investigated SS-31's ability to modulate the membrane binding and aggregation of alpha-synuclein—a protein central to Parkinson's pathology—finding that the peptide can compete with alpha-synuclein for membrane binding sites and potentially inhibit its toxic aggregation ^[20]. Novel SS-31 derivatives synthesised in 2024 showed significantly greater anti-inflammatory activity than the parent peptide in LPS-stimulated cells, reducing TNF-α levels and increasing ATP synthesis in rotenone-injured neuronal cells, suggesting potential for next-generation neurodegenerative disease research ^[21].

How it is thought to work

SS-31's primary mechanism centres on its selective accumulation within the inner mitochondrial membrane (IMM), where it binds to cardiolipin (CL)—a unique phospholipid found almost exclusively in this location ^[1]. Cardiolipin plays a critical structural role in organising the cristae folds of the IMM and in stabilising the respiratory complexes (Complexes I–IV) of the oxidative phosphorylation (OXPHOS) system ^[3]. By binding cardiolipin, SS-31 stabilises cristae architecture, optimises electron transfer efficiency across the respiratory chain, and supports ATP synthesis ^[7]. Critically, this stabilisation also limits the electron 'leak' that generates superoxide and other reactive oxygen species (ROS), meaning SS-31 acts as a source-targeted antioxidant rather than a non-specific free-radical scavenger ^[1]. A 2020 proteomic study published in PNAS identified SS-31's interactions with 12 IMM-associated proteins, including components directly involved in ATP generation, providing a broader molecular map of its effects beyond just cardiolipin binding ^[3].

Downstream of these membrane-level interactions, SS-31 reduces mitochondrial ROS production, preserves membrane potential, and inhibits opening of the mitochondrial permeability transition pore (mPTP)—a channel whose uncontrolled opening leads to cytochrome c release and apoptotic cell death ^[6]. In ischaemia-reperfusion models, preventing mPTP opening has been shown to correspond with substantial reductions in infarct size ^[6]. SS-31 also modulates mitochondrial dynamics: in disease models it has been associated with restoration of normal mitochondrial morphology, reduction of excessive fragmentation, and promotion of mitophagy (the selective removal of damaged mitochondria) ^[8]. In aged tissues specifically, it improves ADP sensitivity within mitochondria by enhancing nucleotide uptake through the adenine nucleotide translocator (ANT), directly linking the molecular interaction with cardiolipin to improved bioenergetic capacity in tissues where age-related ADP insensitivity is a key deficit ^[15].

Where the evidence stands

The bulk of published SS-31 research consists of well-replicated in vitro (cell) and in vivo (rodent and larger animal) studies demonstrating improvements in mitochondrial morphology, ATP output, oxidative stress markers, and tissue function across cardiac, renal, neurological, and skeletal muscle models ^{[8][11][14][17]}. These preclinical findings are internally consistent and mechanistically coherent, underpinned by detailed proteomic and biophysical characterisation of how the compound interacts with cardiolipin and the IMM ^[3]. However, translation to human benefit has proven more difficult to establish. In the TAZPOWER Phase II/III randomised crossover trial in Barth syndrome patients, the primary endpoints were missed, though open-label extension data showed functional improvements ^[4]. The EMBRACE trial in heart failure with reduced ejection fraction also failed to meet its primary endpoint ^[6], and the MMPOWER-3 Phase III trial in 218 adults with primary mitochondrial myopathy similarly missed both primary endpoints ^[4].

Despite these mixed clinical results, SS-31 (elamipretide) received FDA accelerated approval on September 19, 2025 under the brand name Forzinity for Barth syndrome—the first approval of a mitochondria-targeted therapeutic—based on muscle strength as an intermediate clinical endpoint, with confirmatory trials required ^[5]. In clinical trials across multiple mitochondrial disorders it has been reported as generally well tolerated ^[7]. For all indications outside Barth syndrome, the compound remains investigational, and the gap between strong preclinical data and confirmed human efficacy is an acknowledged limitation of the current evidence base ^[13]. Notably, no controlled human trial data currently supports the cognitive, neuroprotective, or longevity-related uses that have generated popular interest ^[13].

Frequently asked questions

What is SS-31 and what is it used for in research?

SS-31 (elamipretide) is a synthetic four-amino-acid peptide that targets the inner mitochondrial membrane by binding a lipid called cardiolipin. In research, it is studied for its ability to stabilise mitochondrial structure, improve ATP production, and reduce oxidative stress across conditions ranging from mitochondrial genetic diseases to cardiac dysfunction, kidney injury, and age-related cognitive and muscle decline. It received FDA accelerated approval in September 2025 specifically for Barth syndrome; all other applications remain investigational.

Is SS-31 the same as elamipretide?

Yes. SS-31 is the original research designation within the Szeto-Schiller (SS) peptide series, while elamipretide is the International Nonproprietary Name used in clinical and regulatory contexts. The compound has also been referred to as MTP-131, Bendavia, and most recently marketed under the brand name Forzinity. All of these names refer to the same tetrapeptide molecule.

How does SS-31 work inside cells?

SS-31 is cell-permeable and selectively accumulates in the inner mitochondrial membrane, where it binds cardiolipin—a phospholipid that is critical for organising cristae folds and stabilising the respiratory complexes that produce ATP. By doing so, it limits the electron 'leak' that generates harmful reactive oxygen species and prevents the opening of the mitochondrial permeability transition pore, which would otherwise trigger cell death. These actions collectively help restore bioenergetics in cells under metabolic or oxidative stress.

Has SS-31 been tested in human clinical trials?

Yes. SS-31 (elamipretide) has been evaluated in multiple human trials including TAZPOWER (Barth syndrome), EMBRACE (heart failure with reduced ejection fraction), and MMPOWER-3 (primary mitochondrial myopathy). The compound received FDA accelerated approval for Barth syndrome in September 2025. However, the randomised controlled phases of several trials failed to meet their primary endpoints, and confirmatory data is still required to validate the Barth syndrome approval. All other indications remain investigational.

What does the research show about SS-31 and cognitive function?

Animal studies have shown that SS-31 improves neurovascular coupling, cerebral blood flow responses, spatial working memory, and gait coordination in aged mice by reducing mitochondrial oxidative stress in cerebral blood-vessel cells. It has also been shown to reduce neuroinflammation-associated cognitive impairment in aged rat models. Critically, none of these cognitive effects have been confirmed in controlled human trials; the Alzheimer's Drug Discovery Foundation notes that no human research currently supports cognitive benefits.

What is cardiolipin and why does SS-31 target it?

Cardiolipin is a unique phospholipid found almost exclusively in the inner mitochondrial membrane, where it plays a structural role in organising the cristae folds and stabilising the respiratory protein complexes that generate ATP. In many disease states and during ageing, cardiolipin becomes oxidised or remodelled abnormally, destabilising these complexes and increasing ROS production. SS-31's alternating cationic-aromatic structure gives it strong, selective affinity for cardiolipin, allowing it to protect this critical lipid and restore mitochondrial function at the source.

Is SS-31 approved for use in Canada?

As of the time of writing, SS-31 (elamipretide / Forzinity) has received FDA accelerated approval in the United States for Barth syndrome only. Health Canada has not granted market authorisation for elamipretide for any indication. Outside of approved research contexts, the compound is considered a research chemical in Canada. Researchers should consult current Health Canada guidelines for applicable regulations.

What are the known limitations of SS-31 research?

The primary limitation is that many of the most compelling findings—spanning cognition, ageing, cardiac protection, and renal injury—come from rodent and cell-based studies that have not yet been replicated in adequately powered human randomised controlled trials. Several Phase III human trials have missed their primary endpoints. Additionally, elamipretide is not orally bioavailable, which constrains delivery options and may affect real-world applicability beyond specialist clinical settings.

What other names is SS-31 known by?

SS-31 is the original research code within the Szeto-Schiller peptide series. It is also known as elamipretide (INN), MTP-131, Bendavia (an earlier development trade name), and Forzinity (the FDA-approved brand name for the Barth syndrome indication). All names refer to the same tetrapeptide compound with the sequence D-Arg–Dmt–Lys–Phe–NH₂.

Who discovered SS-31 and when?

SS-31 was co-discovered by Dr. Hazel Szeto at Weill Cornell Medicine and Dr. Peter W. Schiller at the Montreal Clinical Research Institute (IRCM) in the early 2000s, originally in the course of synthetic opioid peptide research. The 'SS' in the compound's name stands for Szeto-Schiller. Dr. Szeto founded Stealth Peptides (later Stealth BioTherapeutics) in 2006 to advance the compound's clinical development.

Glossary

Cardiolipin (CL)

A unique phospholipid found almost exclusively in the inner mitochondrial membrane that is essential for organising cristae structure and stabilising the respiratory protein complexes responsible for ATP production.

Cristae

The inward folds of the inner mitochondrial membrane that dramatically increase surface area and serve as the structural platform on which the oxidative phosphorylation complexes are assembled.

Oxidative phosphorylation (OXPHOS)

The mitochondrial process by which electrons are passed through a series of protein complexes (the electron transport chain) to generate ATP, the primary energy currency of the cell.

Reactive oxygen species (ROS)

Chemically reactive molecules derived from oxygen—such as superoxide and hydrogen peroxide—that are byproducts of mitochondrial electron transfer and can damage cellular components when produced in excess.

Mitochondrial permeability transition pore (mPTP)

A large, non-selective channel in the inner mitochondrial membrane whose prolonged opening releases cytochrome c into the cytoplasm and triggers programmed cell death (apoptosis).

Barth syndrome

A rare X-linked genetic disorder caused by mutations in the TAFAZZIN gene that impair cardiolipin remodelling, leading to mitochondrial dysfunction, dilated cardiomyopathy, skeletal muscle weakness, and fatigue.

Szeto-Schiller (SS) peptides

A class of synthetic aromatic-cationic tetrapeptides, developed by Drs. Hazel Szeto and Peter Schiller, that are cell-permeable and selectively accumulate within mitochondria due to their affinity for cardiolipin.

Neurovascular coupling

The physiological mechanism by which local increases in neuronal activity trigger proportional increases in cerebral blood flow, ensuring adequate oxygen and glucose delivery to active brain regions.

References

1. The mitochondrial-targeted compound SS-31 re-energizes ischemic mitochondria by interacting with cardiolipin — Journal of the American Society of Nephrology (PubMed)
2. An Exceptional Event: Treatment for a Rare Genetic Disorder Co-Discovered at the IRCM Approved by the FDA — Montreal Clinical Research Institute (IRCM)
3. Mitochondrial protein interaction landscape of SS-31 — Proceedings of the National Academy of Sciences (PNAS)
4. Elamipretide: A Review of Its Structure, Mechanism of Action, and Therapeutic Potential — PMC / International Journal of Molecular Sciences
5. FRDA Investigator Initiated Study (IIS) With Elamipretide — Protocol and SAP — ClinicalTrials.gov
6. Late-life restoration of mitochondrial function reverses cardiac dysfunction in old mice — eLife
7. Beneficial effects of SS-31 peptide on cardiac mitochondrial dysfunction in tafazzin knockdown mice — Scientific Reports
8. SS-31 treatment ameliorates cardiac mitochondrial morphology and defective mitophagy in a murine model of Barth syndrome — Scientific Reports
9. SS-31 Peptide Reverses the Mitochondrial Fragmentation Present in Fibroblasts From Patients With DCMA, a Mitochondrial Cardiomyopathy — Frontiers in Cardiovascular Medicine (PubMed)
10. Treatment with the mitochondrial-targeted antioxidant peptide SS-31 rescues neurovascular coupling responses and cerebrovascular endothelial function and improves cognition in aged mice — Aging Cell
11. SS-31 Provides Neuroprotection by Reversing Mitochondrial Dysfunction after Traumatic Brain Injury — PMC / Oxidative Medicine and Cellular Longevity
12. Elamipretide (SS-31) Improves Functional Connectivity in Hippocampus and Other Related Regions Following Prolonged Neuroinflammation Induced by Lipopolysaccharide in Aged Rats — PMC / Frontiers in Aging Neuroscience
13. SS-31 (Elamipretide) — Cognitive Vitality for Researchers — Alzheimer's Drug Discovery Foundation
14. Improving mitochondrial function with SS-31 reverses age-related redox stress and improves exercise tolerance in aged mice — Free Radical Biology and Medicine
15. The mitochondrially targeted peptide elamipretide (SS-31) improves ADP sensitivity in aged mitochondria by increasing uptake through the adenine nucleotide translocator (ANT) — GeroScience