SS-31 / Elamipretide

Mitochondria-Targeting Aromatic-Cationic Tetrapeptide

Mitochondrial Signaling

AMR Research Evidence Profile

Synthetic Peptide

Evidence Profile: Human Clinical + Preclinical; Support Varies by Indication

Structural Map

Core ID Code

SS-31

Scientific Nomenclature ID

Chain ID

Elamipretide; MTP-131; Bendavia

H-D-Arg-Dmt-Lys-Phe-NH2

Peptide Family

Cationic-aromatic Szeto–Schiller tetrapeptide

N-Terminal Type

Unblocked N-terminus

Registry #

736992-21-5 (elamipretide active moiety)

C-Terminal Type

Modified

Empirical Formula (Active State)

C32H49N9O5

Chiral Residues

D-Arg = D-arginine; Dmt = 2,6-dimethyl-L-tyrosine

Molecular Weight (Active Moiety)

639.79 g/mol

Intracellular Focal Pt

Inner mitochondrial membrane / cardiolipin-responsive interfaces

Research Sphere

Mitochondrial & Metabolic Signaling

Mechanistic Context

SS-31 (elamipretide) is a synthetic Szeto–Schiller tetrapeptide designed to associate with cardiolipin-rich regions of the inner mitochondrial membrane. Experimental work supports high-affinity interaction with cardiolipin and localization to the inner mitochondrial membrane in preclinical models.

The molecular architecture is distinct from conventional antioxidants or electron-transport inhibitors. SS-31 is characterized as an aromatic-cationic peptide that concentrates in mitochondria and interacts with cardiolipin; downstream effects on respiratory-chain organization, reactive oxygen species (ROS), and bioenergetics are investigated in preclinical and human biomarker studies, but are not uniformly established as disease-modifying across indications.

D-Arg → Dmt → Lys → Phe-NH2

Mitochondrial Membrane Association

SS-31 has been studied as a mitochondria-associating peptide that preferentially localizes to cardiolipin-containing inner mitochondrial membranes. Preclinical and translational studies report effects on mitochondrial structure and function, including changes in cristae morphology, respiratory-chain organization, and indices of mitochondrial membrane potential and ATP production. These findings are context- and model-dependent and do not, by themselves, establish clinical efficacy.

Downstream Bioenergetic and Signaling Effects Under Investigation

SS-31 is not best described as a classical GPCR agonist or ion-channel modulator. Instead, it is investigated as a mitochondria-targeting peptide whose primary interaction is with cardiolipin in the inner mitochondrial membrane. Proposed downstream effects include modulation of electron-transport-chain organization, mitochondrial membrane potential, ROS generation, and bioenergetic efficiency, but the strength of evidence varies by model and endpoint.

Experimental and translational studies have examined relationships among cardiolipin association, respiratory-chain organization, electron transfer, ATP production, ROS generation, and mitochondrial membrane potential. Increases in ATP or reductions in ROS reported in isolated mitochondria, cells, or animal models should not be interpreted as established clinical benefit without indication-specific human outcome data.

Mechanistic distinction: SS-31 is primarily studied as a cardiolipin-interacting peptide that may influence mitochondrial structure and signaling. Its role is mechanistic and context-dependent; any proposed protective, "restorative," or "repair" effects on mitochondria remain subject to indication-specific clinical evaluation and should not be generalized across diseases.

Research Areas

Mitochondrial Bioenergetics

Research involving ATP production, respiratory-chain function, and mitochondrial bioenergetics in isolated mitochondria, cells, animal models, and selected human biomarker studies. These findings are indication- and model-specific and do not, by themselves, establish clinical efficacy.

Cardiolipin Biology

Research involving cardiolipin-rich inner mitochondrial membranes, including preclinical and translational studies of SS-31 association with cardiolipin and related structural and signaling effects. These mechanistic observations require separate clinical outcome data for each indication.

Oxidative Stress

Experimental work examining reactive oxygen species (ROS) and oxidative stress markers in mitochondrial and cellular models, with some translational biomarker data. Reductions in ROS or oxidative markers in these settings should not be interpreted as established therapeutic antioxidant efficacy without indication-specific human outcome evidence.

Skeletal-Muscle Energetics

Research examining mitochondrial performance in muscle and other tissues, including bioenergetic measurements and exercise-physiology endpoints. Changes in mitochondrial physiology or exercise parameters in specific studies do not, by themselves, demonstrate long-term clinical benefit or anti-aging efficacy.

Mitochondrial Disease Models

Translational investigation involving mitochondrial disease models across multiple indications. Evidence from one disease population (e.g., Barth syndrome) should not be generalized to other conditions such as primary mitochondrial myopathy, heart failure, renal disease, or ophthalmic disorders without indication-specific human trial data.

Aging Biology

Experimental research examining age-associated mitochondrial changes and skeletal-muscle energetics. Observed changes in mitochondrial physiology or performance metrics in aging models are classified as Preliminary or Mechanistic and do not establish broad anti-aging efficacy.

Translational Chain

SS-31

Cardiolipin-Rich Inner Mitochondrial Membrane

Membrane/Respiratory Organization

Cellular Bioenergetics

Tissue Energetics

Biomarkers

Functional Outcomes

Each downstream step requires independent evidence: cardiolipin interaction, mitochondrial structural changes, bioenergetic effects, biomarker shifts, and functional or clinical outcomes must be evaluated separately for each indication. Positive findings in one domain or disease area do not automatically translate into established clinical benefit in another.

Human Clinical Evidence Overview

Human exposure and clinical research involving elamipretide (SS-31) include randomized and open-label studies across several indications. Evidence must be interpreted separately for each disease area, with particular attention to Barth syndrome, primary mitochondrial myopathy, and other mitochondrial or cardiometabolic conditions. In primary mitochondrial myopathy, early trials such as MMPOWER-2 (randomized, double-blind, placebo-controlled crossover, N≈30) did not meet the primary 6-minute walk endpoint but showed signals in some patient-reported secondary outcomes, while the larger Phase 3 MMPOWER-3 trial (randomized, double-blind, placebo-controlled, N≈218) did not meet either primary endpoint (6-minute walk distance and PMMSA total fatigue), indicating Preliminary / mixed human evidence rather than established efficacy.

In Barth syndrome, elamipretide (Forzinity) received FDA accelerated approval in 2025 to improve muscle strength in patients weighing at least 30 kg, based on improvement in knee-extensor muscle strength as a surrogate endpoint reasonably likely to predict clinical benefit. Confirmatory evidence is still required, and approval does not by itself establish broad disease modification or universal functional improvement across all clinical outcomes.

Randomized and open-label studies in Barth syndrome and other indications have evaluated endpoints such as muscle strength, exercise capacity, cardiac function, biomarkers, and patient-reported outcomes. Some trials have shown favorable changes in selected endpoints, while others have not met primary endpoints or have produced mixed or nonsignificant results. These findings should not be generalized across diseases or interpreted as uniform efficacy.

For each indication, interpretation of elamipretide’s clinical evidence depends on trial design (randomized vs uncontrolled, blinded vs open-label, crossover vs parallel), sample size, duration, and the distinction between primary, secondary, exploratory, and surrogate endpoints. Failed primary endpoints, nonsignificant findings, and limitations such as small cohorts or open-label extensions must be preserved in any evidence summary.

Alford Molecular Research classifies human clinical evidence for elamipretide by indication: for Barth syndrome, the muscle-strength surrogate endpoint supporting FDA accelerated approval is treated as Supported human evidence, with Regulatory Status: FDA Accelerated Approval for improving muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg; broader Barth syndrome clinical benefit remains Supported / Preliminary pending confirmatory data; primary mitochondrial myopathy and other indications are classified as Preliminary or mixed human evidence depending on trial outcomes; systemic disease-modifying effects outside approved indications are treated as an Evidence Gap.

Analytical & Quality-Control Considerations

Analytical Identity Requirements

Mass Spectrometry – Provide mass-spectrometric data that are consistent with the expected molecular identity and mass of the active peptide moiety; MS alone does not establish absolute purity, peptide content, sterility, endotoxin, biological activity, solution stability, or clinical quality.

Stereochemistry – Confirm D-arginine rather than L-arginine and verify the presence of the noncanonical Dmt residue; stereochemical confirmation supports identity but is not a substitute for full stability testing.

Terminal Amidation – Confirm C-terminal amide; this is an identity feature and does not determine formulation stability or clinical performance.

Counterion / Salt State – Differentiate neutral peptide from acetate, TFA, or other counterion-associated forms. Salt form and hydration state affect total mass and may influence solubility and stability; properties of one salt or formulation should not be assumed for another without supporting data.

Residual Solvents – Assess independently from peptide identity; solvent content may be relevant for quality and regulatory assessment but does not define peptide stability or efficacy.

Sterility – Where relevant, evaluate sterility using microbiological methods. Sterility is distinct from HPLC purity, mass-spectrometric identity, filtration, or vendor labeling and cannot be assumed without appropriate testing.

Example Analytical Documentation

Alford Molecular Research has reviewed third-party analytical documentation for selected SS-31 lots, including identity and purity data generated by external laboratories or suppliers. These records are used for research documentation and evidence classification and do not imply that AMR performed the underlying laboratory testing.

Analytical documentation for one lot does not establish stability, sterility, or quality for other lots, formulations, or suppliers. Vendor- or manufacturer-reported data are treated as source-dependent. Lot-specific analytical identity/purity is classified as Established where supported by sufficiently documented, method-appropriate analytical data from a reliable source; otherwise it is treated as Supported or Preliminary depending on provenance, method documentation, and traceability.

Molecular State, Clinical Parameters & Regulatory Status

Reported SS-31 molecular weight can vary depending on whether values refer to the active peptide moiety or to a specific salt, counterion, or hydration state. Pharmacokinetic parameters such as Cmax, AUC, and half-life are route- and study-specific and should be interpreted in the context of the administered formulation and trial design.

Exact PK interpretation requires clear identification of route (e.g., intravenous vs subcutaneous), dosing regimen (single vs repeated administration), and whether parameters are measured in humans or derived from animal or modeled data. Modeled PK estimates should not be treated as experimentally measured values.

Mass specification, salt state, hydration state, and analytical documentation must be considered when comparing PK or exposure data across studies. Human PK data provide Established evidence for measured parameters within the studied populations and conditions, but do not by themselves establish clinical efficacy.

Stability & Handling (Scientific Context)

Lyophilized SS-31 research material is generally characterized using analytical methods such as HPLC and mass spectrometry to assess identity and purity at the time of testing. These data describe the state of a specific lot under defined storage conditions and do not, by themselves, establish in-use solution stability, compounded-product stability, or long-term shelf life across all formulations.

Regulatory Status: FDA Accelerated Approval — Barth Syndrome

SS-31 / elamipretide has been investigated in human clinical trials with safety and tolerability profiles that vary by indication, route, and duration. Clinical studies and the current Forzinity label identify local injection-site reactions as common adverse events and describe serious hypersensitivity reactions as an important labeled risk. In studies with administration lasting 30 days or longer, increases in absolute eosinophil counts were also observed frequently; these generally peaked after initial exposure and may normalize with longer follow-up. Short-term tolerability in specific trial populations does not establish long-term safety across all indications or patient groups.

The presence of human clinical research and an FDA-approved indication for Barth syndrome does not imply that elamipretide or SS-31 is approved or established as effective for primary mitochondrial myopathy, heart failure, renal disease, ophthalmic disorders, aging-related conditions, or other uses. Clinical development has occurred in several indications, but those uses remain indication-specific and may be investigational or have produced mixed or negative efficacy results.

Forzinity received FDA accelerated approval for its labeled Barth syndrome indication. Continued approval is contingent on verification of clinical benefit through a required postmarketing confirmatory trial: a randomized, double-blind, placebo-controlled study in patients with Barth syndrome age 5 years and older, designed to verify and describe clinical benefit predicted by improvement in knee-extensor muscle strength. Outside the approved indication, long-term safety and efficacy remain indication-specific and are treated as an Evidence Gap unless supported by robust human data.

Alford Molecular Research evaluates molecular and clinical evidence for elamipretide (SS-31) within a research and documentation framework. Forzinity, the FDA-approved drug product containing elamipretide, received FDA accelerated approval on September 19, 2025, to improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg. This regulatory status is indication-specific and does not extend to other mitochondrial or cardiometabolic conditions. Research-grade SS-31 materials and alternative elamipretide formulations are not automatically equivalent to the approved Forzinity product.

Evidence Classification: Molecular identity Established; cardiolipin/mitochondrial mechanism Supported / Mechanistic; human PK Established within studied conditions; Barth syndrome muscle-strength surrogate Supported human evidence with FDA Accelerated Approval; broader Barth clinical benefit Supported / Preliminary; primary mitochondrial myopathy and other indications Preliminary / mixed; formulation-specific stability and some analytical parameters include Evidence Gaps.

RP-HPLC / UPLC – Evaluate chromatographic purity and detect major impurities or degradation products; a single purity value (e.g., 95–99% area by HPLC) does not establish net peptide content, long-term stability, sterility, endotoxin status, or absence of future degradation.

Dmt Identity – Characterize the presence and identity of the noncanonical 2,6-dimethyl-L-tyrosine residue using appropriate orthogonal structural or analytical methods; intact mass alone may be consistent with, but does not fully establish, side-chain identity or stereochemistry.

Quantitative Peptide Content – Where available, use a validated or appropriately qualified assay (e.g., quantitative HPLC with reference standard) to determine net peptide content. Area-percent HPLC purity alone is not sufficient to quantify peptide content by mass. In the absence of a quantitative assay, peptide content is treated as an Evidence Gap.

Water Content – Assess moisture or hydrate state using methods appropriate for water determination (e.g., Karl Fischer titration). Water content is distinct from peptide purity, counterion content, and net peptide mass and cannot be inferred from HPLC or intact-mass data alone.

Endotoxin – Evaluate endotoxin levels using appropriate endotoxin assays. Endotoxin status is independent of HPLC purity, mass-spectrometric identity, and visual appearance and must not be inferred from those measures.

Research & Evidence Context

AMR provides research analysis and evidence classification of elamipretide/SS-31. This page is not clinical guidance. Forzinity is an FDA-approved elamipretide drug product for a specific Barth syndrome indication under accelerated approval; research-grade or alternative elamipretide materials are not automatically equivalent to the approved product. Human clinical evidence exists, but strength and outcome support vary substantially by indication. Mechanistic studies support cardiolipin-associated mitochondrial effects; downstream clinical significance is indication-specific.