SS-31 (Elamipretide)

1. Overview

SS-31 (elamipretide; also known as Bendavia and MTP-131) is a synthetic mitochondria-targeted tetrapeptide with the sequence D-Arg-2',6'-dimethyltyrosine(Dmt)-Lys-Phe-NH2 and a molecular weight of 640.8 Da. It is the lead compound of the Szeto-Schiller (SS) peptide family, a class of aromatic-cationic peptides discovered by Hazel H. Szeto and Peter W. Schiller at Weill Cornell Medical College in the early 2000s [1][2]. The defining structural feature of SS peptides is an alternating motif of aromatic and basic amino acid residues, which enables them to concentrate more than 1,000-fold in the inner mitochondrial membrane (IMM) independently of membrane potential [1][2].

Unlike conventional antioxidants, which must accumulate in large concentrations to be effective, SS-31 works at the nanomolar level by selectively binding cardiolipin, an anionic phospholipid uniquely expressed on the IMM that is essential for cristae formation, electron transport chain (ETC) supercomplex assembly, and ATP synthase function [5][13]. This targeted mechanism distinguishes SS-31 from untargeted antioxidant therapies and has led to its development for a wide range of mitochondrial dysfunction disorders.

Elamipretide received FDA accelerated approval in September 2025 under the brand name Forzinity as the first disease-specific treatment for Barth syndrome, a rare X-linked genetic disorder caused by tafazzin mutations that impair cardiolipin remodeling [24]. It has also been investigated in clinical trials for heart failure with reduced ejection fraction (HFrEF), primary mitochondrial myopathy, dry age-related macular degeneration (AMD), and renal ischemia-reperfusion injury.

Molecular Weight

640.8 Da

Sequence

D-Arg-Dmt-Lys-Phe-NH2 (Dmt = 2',6'-dimethyltyrosine)

Half-life

~4 hours (subcutaneous)

Routes Studied

Subcutaneous (SC), intravenous (IV)

FDA Status

Approved (accelerated) for Barth syndrome (2025, as Forzinity); investigational for other indications

Developer

Stealth BioTherapeutics

Target

Cardiolipin on the inner mitochondrial membrane

2. Mechanism of Action

2.1 Cardiolipin Binding

The primary mechanism of SS-31 involves selective, high-affinity binding to cardiolipin (CL) on the inner mitochondrial membrane [5][13]. Cardiolipin is a unique diphosphatidylglycerol lipid found almost exclusively in the IMM, where it constitutes approximately 20% of total lipid content. It plays essential structural and functional roles in maintaining cristae curvature, anchoring ETC complexes, facilitating supercomplex assembly, and supporting ATP synthase oligomerization [5][12][23].

Biophysical studies by Mitchell et al. (2020) demonstrated that SS-31 partitions into the membrane interfacial region with an affinity directly proportional to surface charge, showing preferential interaction with CL-containing bilayers [13]. The peptide stabilizes rather than disrupts lamellar membrane architecture, while causing saturable alterations in lipid packing that optimize the biophysical environment for protein-lipid interactions [13]. Crucially, SS-31 modulates the surface electrostatics of mitochondrial membranes, reducing surface potential through its polybasic character and altering divalent cation (calcium) distribution within the interfacial region [13]. This electrostatic modulation reduces the energetic burden of calcium stress on mitochondria [13].

2.2 Cristae Stabilization and ETC Optimization

By binding cardiolipin, SS-31 stabilizes the cristae membrane architecture that is essential for efficient oxidative phosphorylation [5]. Birk et al. (2013) demonstrated that SS-31 preserves cristae membranes during renal ischemia and prevents the mitochondrial swelling that typically accompanies ischemia-reperfusion injury [5]. This structural protection enables prompt recovery of ATP on reperfusion.

The cardiolipin-SS-31 interaction also has direct consequences for electron transport chain function. SS-31 facilitates the assembly of CL-dependent protein complexes, including ETC supercomplexes (respirasomes) and ATP synthase oligomers, which increases the efficiency of electron transfer and reduces electron leak [6][23]. In the canine heart failure model, Sabbah et al. (2016) showed that elamipretide restored Complex I and Complex IV enzymatic activity and normalized the ATP/ADP ratio from 0.38 to 1.16 [6]. The 2025 review by Sabbah confirmed that the mechanism extends beyond simple ROS scavenging to involve sophisticated modulation of membrane properties and facilitation of mitochondrial protein complex assembly [23].

2.3 ROS Reduction and Cytochrome c Protection

The original discovery of SS-31 highlighted its potent antioxidant properties. The dimethyltyrosine (Dmt) residue is essential for ROS scavenging activity, as analogs lacking Dmt (such as SS-20) do not inhibit mitochondrial ROS generation [1]. SS-31 scavenges hydrogen peroxide and peroxynitrite and inhibits lipid peroxidation with nanomolar potency [1][2].

A critical mechanistic finding by Birk et al. (2013) was that the SS-31/cardiolipin interaction inhibits cytochrome c peroxidase activity [5]. During ischemia, cytochrome c can catalyze the peroxidation of cardiolipin, creating a vicious cycle of membrane damage. SS-31 protects the heme iron of cytochrome c from oxidative damage, preventing this pathological peroxidase function and thereby maintaining both CL integrity and cytochrome c's normal electron carrier role [5].

2.4 Structure-Activity Relationships

Mitchell et al. (2022) performed comprehensive structure-activity analysis of the SS peptide family [19]. They found that SS-31 adopts an extended conformation without intramolecular hydrogen bonds when bound to membranes, distinguishing it from other analogs that form compact reverse-turn structures [19]. While all tested tetrapeptide analogs bound CL-containing membranes, they exhibited significant differences in equilibrium binding behavior and membrane electrostatic modulation, indicating that subtle structural variations dramatically influence biological activity [19].

3. Researched Applications

Heart Failure

Evidence level: Moderate (Phase 1/2 positive signals; Phase 2 primary endpoint not met)

The rationale for SS-31 in heart failure rests on the well-established role of mitochondrial dysfunction in HFrEF. Failing cardiomyocytes exhibit impaired oxidative phosphorylation, depleted cardiolipin, disorganized cristae, and excessive ROS production [6][23].

Sabbah et al. (2016) provided proof-of-concept in dogs with microembolization-induced heart failure, demonstrating that 3 months of elamipretide treatment significantly improved LVEF from 30% to 36% (P<0.05), decreased NT-proBNP by 774 pg/mL, and restored the ATP/ADP ratio to near-normal levels [6].

The EMBRACE trial (Daubert et al. 2017) was the first-in-human HF study, showing that a single 4-hour IV infusion at the highest dose (0.25 mg/kg/h) reduced LVEDV by 18 mL (P=0.009) and LVESV by 14 mL (P=0.005) in 36 patients with LVEF <35% [10]. However, the larger PROGRESS-HF trial (Butler et al. 2020), which tested 28 days of subcutaneous elamipretide (4 mg or 40 mg daily) in 71 patients, failed to demonstrate significant improvements in LVESV or LVEF compared to placebo [14]. This neutral result raised questions about whether the subcutaneous route, treatment duration, or dose selection were sufficient for cardiac remodeling.

Barth Syndrome

Evidence level: High (FDA-approved indication)

Barth syndrome is an ultra-rare X-linked recessive disorder caused by mutations in the tafazzin (TAZ) gene, which encodes a phospholipid transacylase essential for cardiolipin remodeling. Patients exhibit abnormal cardiolipin profiles, mitochondrial dysfunction, cardiomyopathy, skeletal myopathy, neutropenia, and exercise intolerance [18][22]. The disease directly disrupts the molecular target of elamipretide, making Barth syndrome a rational indication.

The TAZPOWER trial (NCT03098797) evaluated elamipretide 40 mg SC daily in a double-blind, placebo-controlled crossover design followed by an open-label extension (OLE). The natural history comparison study by Hornby et al. (2022) demonstrated a 79.7-meter advantage in 6MWT at week 64 (P=0.0004) and 91.0-meter advantage at week 76 (P=0.0005) compared to untreated controls [18]. Muscle strength, measured by handheld dynamometry, improved by 40.8 Newtons at week 64 (P=0.0002) [18]. Long-term OLE data through 168 weeks (Thompson et al. 2024) showed cumulative 6MWT improvement of 96.1 meters (P=0.003), sustained reductions in BTHS-SA fatigue scores, and significant trends for improvement in LV volumes [22].

Based on these data, elamipretide (Forzinity) received FDA accelerated approval in September 2025 to improve muscle strength in patients with Barth syndrome weighing 30 kg or more, becoming the first disease-specific therapy for this condition [24].

Primary Mitochondrial Myopathy

Evidence level: Moderate (Phase 1/2 positive signal; Phase 3 primary endpoint not met)

Primary mitochondrial myopathy (PMM) encompasses a genetically heterogeneous group of disorders with impaired mitochondrial oxidative phosphorylation affecting skeletal muscle function. The MMPOWER-1 dose-escalation trial (Karaa et al. 2018) demonstrated a dose-dependent improvement in 6MWT distance, with the highest IV dose achieving 64.5 meters improvement versus 20.4 meters for placebo [11]. After covariate adjustment, the treatment effect was 51.2 meters versus 3.0 meters (P=0.03) [11].

However, the pivotal MMPOWER-3 Phase 3 trial (Karaa et al. 2023) did not meet its primary endpoint in the genotypically diverse study population [20]. Post-hoc genotype-specific analysis suggested differential responses across genetic subtypes, indicating that a subset of patients may benefit more than others [20]. This has prompted consideration of genotype-enrichment strategies for future PMM trials.

Age-Related Macular Degeneration

Evidence level: Moderate (Phase 2 secondary endpoints positive; primary endpoints not met)

The retinal pigment epithelium (RPE) is among the most metabolically active tissues in the body, with high mitochondrial density and oxidative phosphorylation demands. Mitochondrial dysfunction in the RPE is implicated in the pathogenesis of dry AMD and geographic atrophy [15][16].

Phase 1 ReCLAIM studies established safety and tolerability of subcutaneous elamipretide in patients with dry AMD and intermediate AMD [15][16]. The ReCLAIM-2 Phase 2 trial (Ehlers et al. 2024) enrolled 176 patients randomized 2:1 to elamipretide 40 mg SC daily or placebo for 48 weeks [21]. While primary endpoints (change in low-luminance BCVA and GA growth rate) were not met, elamipretide demonstrated significant preservation of ellipsoid zone (EZ) integrity: 43% reduction in total EZ attenuation/loss (P=0.0034) and 47% reduction in partial EZ attenuation (P=0.004) [21]. Significantly more elamipretide-treated patients achieved clinically meaningful visual gains of 10 or more letters in LL BCVA (14.6% vs 2.1%, P=0.04) [21]. The EZ endpoint, which measures photoreceptor integrity that precedes and predicts progressive vision loss, has been selected as the primary endpoint for planned Phase 3 trials.

Renal Ischemia-Reperfusion Injury

Evidence level: Moderate (strong preclinical; early clinical)

Renal protection was among the earliest studied applications of SS-31 and provided much of the foundational mechanistic understanding. Szeto et al. (2011) demonstrated in rats that SS-31 accelerated ATP recovery, protected mitochondrial structure, reduced tubular apoptosis and necrosis, completely prevented macrophage infiltration, and accelerated tubular cell proliferation [4]. Birk et al. (2013) used renal ischemia models to elucidate the cardiolipin-binding mechanism [5]. Long-term studies showed that SS-31 given only during the acute ischemia-reperfusion period suppressed inflammasome activation (IL-1beta, IL-18) and prevented progression to chronic kidney disease at 9 months [8].

Saad et al. (2017) conducted a Phase 2a trial of elamipretide during renal stent revascularization in patients with atherosclerotic renal artery stenosis, providing early clinical evidence of renal cortical perfusion preservation [9]. SS-31 has also shown protection against obesity-related nephropathy in high-fat diet models [7].

Aging and Skeletal Muscle

Evidence level: Preliminary to Moderate (preclinical; early clinical)

Mitochondrial dysfunction is a hallmark of biological aging. Szeto and Liu (2018) reviewed evidence that cardiolipin-targeted peptides rejuvenate mitochondrial function and promote tissue regeneration in aging models [12]. Roshanravan et al. (2021) demonstrated that a single dose of elamipretide improved in vivo mitochondrial ATP production in older adult skeletal muscle, measured by phosphorus-31 magnetic resonance spectroscopy, providing the first direct evidence of bioenergetic enhancement in aging humans [17]. Mitchell et al. (2025) showed that elamipretide improved both cardiac and skeletal muscle function in aging animal models [25].

4. Clinical Evidence Summary

5. Dosing in Research

The following table summarizes doses used in published research and the approved clinical dose. In all clinical trials, elamipretide was administered either intravenously (IV) or subcutaneously (SC). The approved dose for Barth syndrome is 40 mg SC once daily.

6. Safety and Side Effects

Across all clinical trials, elamipretide has demonstrated a generally favorable safety profile [10][14][22][24].

Injection site reactions are the most commonly reported adverse events with subcutaneous administration, including injection site pain, pruritus, bruising, erythema, and induration. In the ReCLAIM-2 trial, 86% of elamipretide recipients reported adverse events compared to 71% on placebo, predominantly driven by injection site reactions [21].

Cardiovascular safety: In the EMBRACE trial, blood pressure and heart rate remained stable across all dose cohorts [10]. No serious adverse events were reported. In PROGRESS-HF, rates of study drug-related adverse events were similar across all three groups (placebo, 4 mg, 40 mg) [14].

Long-term safety: The TAZPOWER OLE provided the longest safety follow-up at 168 weeks, with injection site reactions remaining the predominant adverse event and no new safety signals emerging during extended treatment [22].

Key areas of uncertainty include:

• Immunogenicity: Long-term immunogenicity data in broader populations beyond Barth syndrome remains limited.
• Off-target effects: While SS-31 is highly selective for cardiolipin on the IMM, the consequences of chronic cardiolipin modulation across all tissues over many years have not been fully characterized.
• Drug interactions: Systematic evaluation of interactions with standard heart failure, neurological, or ophthalmic medications has not been comprehensively published.
• Pregnancy and development: No human reproductive safety data exists. Elamipretide should be considered investigational for any use outside the approved Barth syndrome indication.

7. Regulatory Status

United States (FDA): Elamipretide received accelerated approval in September 2025 under the brand name Forzinity, indicated to improve muscle strength in adult and pediatric patients with Barth syndrome weighing 30 kg or more [24]. The accelerated approval was based on the surrogate endpoint of muscle strength improvement; confirmatory trials may be required. The drug is also in Phase 3 development for dry AMD (based on the EZ preservation endpoint from ReCLAIM-2) and remains investigational for heart failure and mitochondrial myopathy.

Orphan drug designation: Elamipretide received orphan drug designation from the FDA for Barth syndrome, reflecting the ultra-rare prevalence of the condition (estimated at 1 in 300,000-400,000 live births).

Developer: Stealth BioTherapeutics (now operating under updated corporate structure following the Barth syndrome approval).

8. Pharmacokinetics

SS-31 (elamipretide) has a distinctive pharmacokinetic profile shaped by its small size (640.8 Da), cationic character, and extraordinary mitochondrial targeting properties.

Subcutaneous Administration: Following subcutaneous injection of 40 mg (the approved clinical dose), elamipretide is rapidly absorbed with a Tmax of approximately 1 hour. The absolute bioavailability after SC injection has not been publicly disclosed but is sufficient to support once-daily dosing at the approved 40 mg dose [4][24].

Elimination Half-Life: The plasma elimination half-life is approximately 4 hours following subcutaneous administration [24]. This relatively short systemic half-life contrasts with the peptide's prolonged pharmacodynamic effects, which are attributable to its rapid and extensive mitochondrial accumulation and retention.

Intravenous Pharmacokinetics: In the EMBRACE trial, elamipretide was administered as a 4-hour continuous IV infusion at doses of 0.005, 0.05, or 0.25 mg/kg/h. Dose-proportional increases in plasma concentrations were observed, with hemodynamic effects (reduced LV volumes) apparent at the highest dose level [10].

Mitochondrial Targeting Efficiency: The defining pharmacokinetic feature of SS-31 is its greater than 1,000-fold concentration in the inner mitochondrial membrane (IMM), driven by the alternating aromatic-cationic structural motif (D-Arg-Dmt-Lys-Phe) rather than by mitochondrial membrane potential [1][2]. This distinguishes SS-31 from triphenylphosphonium (TPP)-based mitochondrial targeting agents such as MitoQ, which rely on the mitochondrial membrane potential (approximately -180 mV) to drive accumulation. Because SS-31's targeting is potential-independent, it can access and protect dysfunctional mitochondria that have lost their membrane potential -- precisely the mitochondria most in need of therapeutic intervention [2][12].

Tissue Distribution: SS-31 distributes broadly to metabolically active tissues including heart, kidney, skeletal muscle, retina, and brain. Preclinical radiolabeling studies demonstrated rapid uptake into renal cortex and cardiac tissue within minutes of administration [4][5]. The small molecular weight and amphipathic character enable SS-31 to cross cell membranes without requiring active transport, contributing to its favorable tissue penetration [1][2].

Metabolism and Elimination: As a small tetrapeptide, elamipretide is expected to undergo peptidase-mediated degradation. Detailed human metabolic pathway data have not been publicly disclosed. Renal excretion of intact peptide and metabolites is presumed to contribute to elimination [24].

Steady-State Considerations: With daily dosing at the 40 mg SC dose, steady-state pharmacodynamic effects (as measured by functional endpoints such as 6MWT and muscle strength) develop over weeks to months, reflecting the time required for mitochondrial structural remodeling and bioenergetic recovery rather than drug accumulation per se [22].

9. Dose-Response Relationships

Elamipretide demonstrates dose-dependent effects across multiple clinical and preclinical endpoints, with the 40 mg SC daily dose emerging as the optimal clinical regimen.

Preclinical Dose-Response: In the rat renal ischemia-reperfusion model, Szeto et al. (2011) tested SS-31 at 0.5 to 5 mg/kg SC and observed dose-dependent protection of mitochondrial structure, ATP recovery, and tubular cell preservation [4].

MMPOWER-1 (Mitochondrial Myopathy) Dose-Ranging: Karaa et al. (2018) conducted a formal dose-escalation in 36 adults with primary mitochondrial myopathy, testing IV doses of 0.01, 0.1, and 0.25 mg/kg/h [11]:

• 0.01 mg/kg/h: Minimal improvement in 6MWT distance
• 0.1 mg/kg/h: Moderate improvement
• 0.25 mg/kg/h: 64.5 m improvement vs 20.4 m placebo; after covariate adjustment, 51.2 m vs 3.0 m (P=0.03)

This established a clear dose-dependent functional improvement in skeletal muscle performance.

EMBRACE (Heart Failure) IV Dose-Ranging: Daubert et al. (2017) tested three IV dose tiers (0.005, 0.05, 0.25 mg/kg/h) in 36 HFrEF patients [10]:

• Only the highest dose (0.25 mg/kg/h) produced statistically significant reductions in LVEDV (-18 mL, P=0.009) and LVESV (-14 mL, P=0.005)
• Lower doses showed no significant effect, establishing a clear dose threshold for acute cardiac remodeling effects

PROGRESS-HF SC Dose Comparison: Butler et al. (2020) compared 4 mg vs 40 mg SC daily in 71 HFrEF patients over 28 days [14]. Neither dose achieved the primary endpoint, but the 40 mg dose showed a numerically greater trend toward LVESV reduction (P=0.28 vs P=0.90 for 4 mg), suggesting that higher SC doses may be needed for cardiac effects.

Barth Syndrome Dose Selection: The 40 mg SC daily dose was selected for the TAZPOWER trial based on prior PK/PD modeling and the dose-response signals from MMPOWER-1 and EMBRACE. At this dose, Barth syndrome patients achieved [18][22]:

• 79.7 m advantage in 6MWT at week 64 (P=0.0004)
• 91.0 m advantage at week 76 (P=0.0005)
• 96.1 m cumulative improvement at week 168 (P=0.003)
• 40.8 N improvement in muscle strength at week 64 (P=0.0002)

The sustained and progressive improvement over 168 weeks suggests that the 40 mg dose achieves sufficient mitochondrial exposure for ongoing cristae remodeling and bioenergetic restoration in the Barth syndrome population.

Preclinical Nanomolar Potency: In vitro, SS-31 scavenges ROS and inhibits mitochondrial permeability transition at nanomolar concentrations (EC50 in the low nanomolar range), consistent with its high-affinity cardiolipin binding [1][5]. This nanomolar potency distinguishes it from conventional antioxidants that require micromolar to millimolar concentrations.

10. Comparative Effectiveness

SS-31 vs CoQ10 (Ubiquinone/Ubiquinol)

Mechanism: CoQ10 is an endogenous lipid-soluble quinone that functions as an electron carrier between Complexes I/II and Complex III of the ETC. It also has antioxidant properties within lipid membranes. Unlike SS-31, CoQ10 does not specifically target cardiolipin and does not modulate mitochondrial membrane electrostatics [12][23].

Targeting: Oral CoQ10 has poor bioavailability (approximately 2-3% absorption) and distributes broadly without preferential mitochondrial accumulation. SS-31 concentrates more than 1,000-fold in the IMM [1][2]. This targeting difference is fundamental -- CoQ10 must reach effective concentrations throughout the cell and all membranes, whereas SS-31 acts specifically at the cardiolipin-rich IMM where ETC complexes reside.

Clinical Evidence: CoQ10 supplementation (100-300 mg/day) has shown modest benefits in heart failure (Q-SYMBIO trial: 42% reduction in major adverse cardiovascular events over 2 years) and mitochondrial myopathies. However, the effect sizes are generally smaller than those observed with elamipretide in Barth syndrome, where the disease directly involves cardiolipin pathology [18][22].

SS-31 vs MitoQ (Mitoquinone)

Mechanism: MitoQ consists of ubiquinone covalently linked to a triphenylphosphonium (TPP+) cation, which drives accumulation in the mitochondrial matrix driven by the mitochondrial membrane potential [12].

Critical Limitation: MitoQ's accumulation is entirely dependent on an intact mitochondrial membrane potential. In diseased or ischemic mitochondria where the membrane potential is dissipated -- the very mitochondria most in need of protection -- MitoQ cannot accumulate effectively. SS-31's potential-independent targeting via cardiolipin binding means it retains access to depolarized, dysfunctional mitochondria [2][12]. This represents a fundamental pharmacological advantage for conditions involving mitochondrial depolarization, including ischemia-reperfusion injury, Barth syndrome, and aging.

Site of Action: MitoQ accumulates in the matrix compartment and acts primarily as a matrix antioxidant. SS-31 acts at the IMM surface, where it modulates cardiolipin interactions with ETC supercomplexes and ATP synthase oligomers [13][23]. This surface-localized mechanism allows SS-31 to influence membrane architecture and protein complex assembly, effects not achievable by matrix-targeted antioxidants.

SS-31 vs Idebenone

Mechanism: Idebenone is a synthetic short-chain benzoquinone analog of CoQ10 with improved oral bioavailability. It has been approved in the EU for Leber hereditary optic neuropathy (LHON) and studied in Friedreich ataxia and Duchenne muscular dystrophy.

Comparison: Like CoQ10, idebenone lacks specific mitochondrial targeting. It can shuttle electrons directly to Complex III, partially bypassing Complex I deficiency. SS-31 operates by a fundamentally different mechanism: stabilizing cardiolipin-dependent protein complex assembly rather than providing alternative electron transfer. For conditions involving cardiolipin pathology (Barth syndrome) or cristae disorganization, SS-31's mechanism is more directly targeted.

SS-31 vs N-Acetylcysteine (NAC) and Other General Antioxidants

Fundamental Limitation of Untargeted Antioxidants: Clinical trials of general antioxidants (vitamin E, vitamin C, NAC, alpha-lipoic acid) for mitochondrial diseases have been largely disappointing. The 2025 review by Sabbah highlighted that the contemporary understanding of SS-31's mechanism extends well beyond simple ROS scavenging [23]. SS-31 modulates mitochondrial membrane surface potential, facilitates ETC supercomplex and ATP synthase oligomer assembly, and stabilizes cristae architecture -- none of which are achievable by untargeted antioxidants operating in the cytoplasm or at non-specific membrane locations.

11. Enhanced Safety Profile

Quantitative Adverse Event Data

Injection Site Reactions (Most Common AE):

• TAZPOWER OLE (168 weeks, n=10): Injection site reactions were the most common adverse event, reported in the majority of patients. No patients discontinued due to injection site reactions [22]
• ReCLAIM-2 (48 weeks, n=118 elamipretide, n=58 placebo): Overall AE rate 86% elamipretide vs 71% placebo, driven predominantly by injection site reactions. Injection site pain, pruritus, erythema, bruising, and induration were the most frequent specific events [21]

Cardiovascular Safety:

• EMBRACE (n=36): Blood pressure and heart rate remained stable across all three dose cohorts (0.005, 0.05, 0.25 mg/kg/h IV). No serious cardiovascular adverse events occurred [10]
• PROGRESS-HF (n=71): Rates of study drug-related AEs were comparable across placebo (18%), 4 mg (22%), and 40 mg (17%) groups. No significant hemodynamic perturbation was observed [14]
• TAZPOWER OLE (168 weeks): LV volumes showed trends toward improvement rather than deterioration, and no new cardiovascular safety signals emerged during extended chronic therapy [22]

Serious Adverse Events:

• Across all clinical trials, no pattern of drug-related serious adverse events has been identified. In the pooled analysis of the Barth syndrome program, serious AEs were infrequent and not attributed to elamipretide [22][24]
• MMPOWER-3 (Phase 3, n=218): Elamipretide was well tolerated with no significant safety imbalance between treatment arms, despite the primary efficacy endpoint not being met [20]

Immunogenicity:

• Anti-drug antibody formation has not been reported as a significant clinical issue in published elamipretide trials. However, long-term immunogenicity data in broader populations beyond Barth syndrome remains limited. The small size of elamipretide (640.8 Da) may reduce its immunogenic potential compared to larger peptide or protein therapeutics [24]

Glucose Metabolism:

• Unlike growth hormone secretagogues and many metabolic peptides, elamipretide has not demonstrated significant effects on glucose metabolism or insulin sensitivity in published clinical trials [10][14][22]

Reproductive Safety:

• No human reproductive safety data exists. In the absence of pregnancy and developmental toxicology data, elamipretide should be considered investigational for any use during pregnancy or in women of reproductive potential without appropriate contraception [24]

Long-Term Safety (168 Weeks):

• The TAZPOWER open-label extension provides the most extensive safety dataset, with 8 of 10 patients completing 168 weeks of continuous daily therapy [22]. No dose-limiting toxicities, organ toxicities, or cumulative adverse effects were identified. The safety profile at 168 weeks was consistent with that observed during the initial treatment period, supporting the tolerability of chronic elamipretide administration.

Drug Interactions:

• Systematic evaluation of drug-drug interactions has not been comprehensively published. Given elamipretide's mechanism of action (cardiolipin binding in the IMM) and small peptide structure, significant cytochrome P450-mediated interactions are not anticipated. However, formal interaction studies with common cardiovascular, neurological, and ophthalmic medications have not been reported [24].

12. Related Peptides

See also: MOTS-c (Mitochondrial-Derived Peptide), AOD-9604, Epithalon (Epitalon)

13. References

1. [1] Zhao K, Zhao GM, Wu D, Soong Y, Birk AV, Schiller PW, Szeto HH. (2004). Cell-permeable peptide antioxidants targeted to inner mitochondrial membrane inhibit mitochondrial swelling, oxidative cell death, and reperfusion injury. Journal of Biological Chemistry. DOI PubMed
2. [2] Szeto HH. (2006). Cell-permeable, mitochondrial-targeted, peptide antioxidants. AAPS Journal. DOI PubMed
3. [3] Szeto HH. (2006). Mitochondria-targeted peptide antioxidants: novel neuroprotective agents. AAPS Journal. DOI PubMed
4. [4] Szeto HH, Liu S, Soong Y, Wu D, Darrah SF, Cheng FY, Zhao Z, Ganger M, Tow CY, Seshan SV. (2011). Mitochondria-targeted peptide accelerates ATP recovery and reduces ischemic kidney injury. Journal of the American Society of Nephrology. DOI PubMed
5. [5] Birk AV, Liu S, Soong Y, Mills W, Singh P, Warren JD, Seshan SV, Pardee JD, Szeto HH. (2013). The mitochondrial-targeted compound SS-31 re-energizes ischemic mitochondria by interacting with cardiolipin. Journal of the American Society of Nephrology. DOI PubMed
6. [6] Sabbah HN, Gupta RC, Kohli S, Wang M, Hachem S, Zhang K. (2016). Chronic therapy with elamipretide (MTP-131), a novel mitochondria-targeting peptide, improves left ventricular and mitochondrial function in dogs with advanced heart failure. Circulation: Heart Failure. DOI PubMed
7. [7] Szeto HH, Liu S, Soong Y, Alam N, Prusky GT, Seshan SV. (2016). Protection of mitochondria prevents high-fat diet-induced glomerulopathy and proximal tubular injury. Kidney International. DOI PubMed
8. [8] Szeto HH, Liu S, Soong Y, Seshan SV, Cohen-Gould L, Manber V, Bhardwaj ML, Bhatt K. (2017). Mitochondria protection after acute ischemia prevents prolonged upregulation of IL-1beta and IL-18 and arrests CKD. Journal of the American Society of Nephrology. DOI PubMed
9. [9] Saad A, Herrmann SMS, Eirin A, Woollard JR, Lerman A, Textor SC. (2017). Phase 2a clinical trial of mitochondrial protection (elamipretide) during stent revascularization in patients with atherosclerotic renal artery stenosis. Circulation: Cardiovascular Interventions. DOI PubMed
10. [10] Daubert MA, Yow E, Dunn G, Marchev S, Barnhart H, Douglas PS, O'Connor C, Goldstein S, Udelson JE, Sabbah HN. (2017). Novel mitochondria-targeting peptide in heart failure treatment: a randomized, placebo-controlled trial of elamipretide. Circulation: Heart Failure. DOI PubMed
11. [11] Karaa A, Haas R, Goldstein A, Vockley J, Weaver WD, Cohen BH. (2018). Randomized dose-escalation trial of elamipretide in adults with primary mitochondrial myopathy. Neurology. DOI PubMed
12. [12] Szeto HH, Liu S. (2018). Cardiolipin-targeted peptides rejuvenate mitochondrial function, remodel mitochondria, and promote tissue regeneration during aging. Archives of Biochemistry and Biophysics. DOI PubMed
13. [13] Mitchell W, Ng EA, Tamucci JD, Boyd KJ, Sathappa M, Coscia A, Pan M, Han X, Eddy NA, May ER, Szeto HH, Alder NN. (2020). The mitochondria-targeted peptide SS-31 binds lipid bilayers and modulates surface electrostatics as a key component of its mechanism of action. Journal of Biological Chemistry. DOI PubMed
14. [14] Butler J, Khan MS, Anker SD, Fonarow GC, Kim RJ, et al. (2020). Effects of elamipretide on left ventricular function in patients with heart failure with reduced ejection fraction: the PROGRESS-HF phase 2 trial. Journal of Cardiac Failure. DOI PubMed
15. [15] Mettu PS, Allingham MJ, Cousins SW. (2021). Phase 1 clinical trial of elamipretide in dry age-related macular degeneration and noncentral geographic atrophy. Ophthalmology Science. PubMed
16. [16] Allingham MJ, Mettu PS, Cousins SW. (2021). Phase 1 clinical trial of elamipretide in intermediate age-related macular degeneration and high-risk drusen. Ophthalmology Science. PubMed
17. [17] Roshanravan B, Liu SZ, Ali AS, et al. (2021). In vivo mitochondrial ATP production is improved in older adult skeletal muscle after a single dose of elamipretide. PLoS One. PubMed
18. [18] Hornby B, Thompson WR, Almuqbil M, Manuel R, Abbruscato A, Carr J, Vernon HJ. (2022). Natural history comparison study to assess the efficacy of elamipretide in patients with Barth syndrome. Orphanet Journal of Rare Diseases. PubMed
19. [19] Mitchell W, Tamucci JD, Ng EL, Liu S, Birk AV, Szeto HH, May ER, Alexandrescu AT, Alder NN. (2022). Structure-activity relationships of mitochondria-targeted tetrapeptide pharmacological compounds. eLife. DOI PubMed
20. [20] Karaa A, Bertini E, Carelli V, Cohen BH, Enns GM, Falk MJ, et al. (2023). Efficacy and safety of elamipretide in individuals with primary mitochondrial myopathy: the MMPOWER-3 randomized clinical trial. Neurology. PubMed
21. [21] Ehlers JP, Hu A, Boyer D, Cousins SW, Waheed NK, Rosenfeld PJ, Brown D, Kaiser PK, Abbruscato A, Gao G, Heier J. (2024). ReCLAIM-2: a randomized phase II clinical trial evaluating elamipretide in age-related macular degeneration, geographic atrophy growth, visual function, and ellipsoid zone preservation. Ophthalmology Science. PubMed
22. [22] Thompson WR, Manuel R, Abbruscato A, Carr J, Campbell J, Hornby B, Vaz FM, Vernon HJ. (2024). Long-term efficacy and safety of elamipretide in patients with Barth syndrome: 168-week open-label extension results of TAZPOWER. Genetics in Medicine. PubMed
23. [23] Sabbah HN. (2025). Contemporary insights into elamipretide's mitochondrial mechanism of action and therapeutic effects. Biomedicine & Pharmacotherapy. PubMed
24. [24] Shirley M. (2025). Elamipretide: First Approval. Drugs. PubMed
25. [25] Mitchell W, et al. (2025). The mitochondria-targeted peptide therapeutic elamipretide improves cardiac and skeletal muscle function during aging. Aging Cell. PubMed