SS-31 (Elamipretide): Published Research

Introduction

SS-31 (elamipretide) has been the subject of a substantial and growing body of peer-reviewed research spanning in vitro biochemistry, animal disease models, and human clinical trials. Published studies have examined the compound's interactions with isolated mitochondria, its reported effects in organ-level ischemia and dysfunction models, and its performance in randomized controlled clinical trials across several disease areas characterized by mitochondrial dysfunction. This article provides an educational summary of that published research, organized by methodology and clinical trial program, with full citations to primary sources. For the molecular mechanisms underlying these studies, see the SS-31 mechanism of action article.

Methodology Types in the Published Literature

Published SS-31 research has employed three broad methodological approaches:

In vitro / isolated organelle studies have used purified cardiolipin-containing liposomes, isolated mitochondria (from cardiac, skeletal muscle, and renal tissue), and cell cultures under conditions of induced oxidative stress. These studies have provided biochemical characterization of SS-31's binding properties, its effects on cytochrome c peroxidase activity, and its reported influence on respiratory complex activities.

In vivo animal model studies have employed rodent models of ischemia-reperfusion injury (cardiac and renal), aging, Barth syndrome (tafazzin-knockout mice), and primary mitochondrial disease. Outcomes have included mitochondrial morphology, ATP production, organ functional parameters, and histological markers.

Human clinical trials have been conducted primarily by Stealth BioTherapeutics across three clinical programs: heart failure with reduced ejection fraction (HFrEF), primary mitochondrial myopathy (PMM), and Barth syndrome (BTHS). Trial designs have ranged from single-dose pharmacodynamic studies to multi-year open-label extensions.

Summary of Key Published Studies

Preclinical: Characterization in Ischemia Models

The foundational preclinical characterization of SS-31 in ischemia-relevant models was reported by Zhao and colleagues in 2004, demonstrating that SS peptides with the aromatic-cationic motif accumulated at the inner mitochondrial membrane (IMM) in a potential-independent manner, scavenged reactive oxygen species (ROS), and protected against oxidative cell death in cell culture models with nanomolar EC50 values. Pretreatment in ex vivo ischemia-reperfusion preparations was reported to mitigate mitochondrial swelling and reduce markers of oxidative injury [1].

Birk and colleagues (2013) examined SS-31 in a rat model of renal ischemia-reperfusion, reporting that pretreatment was associated with preservation of IMM cristae morphology and cardiolipin integrity during the ischemic period, with associated restoration of ATP on reperfusion. The study implicated inhibition of the cardiolipin peroxidase activity of cytochrome c as the mechanistic basis for these observations [2]. The methodology employed electron microscopy for cristae structure and high-performance liquid chromatography for cardiolipin species quantification.

Preclinical: Protein Interactome Mapping

A 2020 study published in the Proceedings of the National Academy of Sciences applied chemical cross-linking combined with mass spectrometry (XL-MS) to map the protein interaction landscape of SS-31 within isolated cardiac mitochondria. The authors reported that SS-31's principal binding partners clustered functionally around ATP synthase (Complex V) and the 2-oxoglutarate metabolic and signaling pathway. The authors interpreted these observations as consistent with SS-31's cardiolipin binding stabilizing the local protein-lipid environment in a manner reported to support ATP synthesis efficiency [3].

Clinical: Heart Failure — Phase 1/2 Ascending-Dose Study

Bhatt and colleagues (2017) reported the first randomized, placebo-controlled clinical evaluation of elamipretide in heart failure, published in Circulation: Heart Failure. The trial enrolled patients with heart failure with reduced ejection fraction (EF ≤35%) and randomized them to a single four-hour intravenous infusion of elamipretide at one of three ascending dose levels or placebo. The authors reported that the highest dose cohort showed a statistically significant reduction in left ventricular end-diastolic volume (−18 mL; P=0.009) and end-systolic volume (−14 mL; P=0.005) compared with placebo at end-infusion. The authors concluded that single-dose elamipretide was safe and well tolerated and that the volume changes supported a dose-effect relationship warranting further study [4].

Clinical: Heart Failure — PROGRESS-HF Phase 2 Trial

The PROGRESS-HF trial, reported by Alam and colleagues (2020) in the Journal of Cardiac Failure, enrolled 71 patients with heart failure with reduced ejection fraction (EF ≤40%) and randomized them to 28 consecutive days of subcutaneous elamipretide at a low or high dose, or placebo. The primary endpoint was change in left ventricular end-systolic volume from baseline to week four. Neither elamipretide dose group showed a statistically significant difference from placebo on the primary endpoint, informing the subsequent decision to focus the pivotal development program on Barth syndrome, where the mechanistic link to cardiolipin metabolism is most direct. Safety and tolerability were reported as similar across all three groups [5].

Clinical: Ex Vivo Human Cardiac Tissue

Chatfield and colleagues (2019) employed a non-randomized ex vivo methodology, treating freshly explanted cardiac tissue from failing and non-failing human hearts with elamipretide, then measuring mitochondrial function. The authors reported significant improvements in mitochondrial oxygen flux, Complex I and Complex IV enzymatic activities, and supercomplex-associated Complex IV activity in the elamipretide-treated samples compared with vehicle-treated tissue from the same failing hearts. The study was published in JACC: Basic to Translational Science and represented the first evidence of the compound's reported effects in failing human cardiac mitochondria [6].

Clinical: Primary Mitochondrial Myopathy — MMPOWER Program

The clinical evaluation of elamipretide in primary mitochondrial myopathy (PMM) proceeded through three registered trials that collectively enrolled the largest trial cohort of any mitochondrial disease program at the time. A dose-escalation phase 1/2 study established tolerability. The MMPOWER-2 crossover study, reported by Karaa and colleagues (2020) in the Journal of Cachexia, Sarcopenia and Muscle, enrolled 30 adults with genetically confirmed PMM in a double-blind crossover design (four weeks of elamipretide versus four weeks of placebo, separated by a washout). The primary endpoint of six-minute walk distance (6MWT) favored elamipretide numerically (+19.8 meters) but did not reach statistical significance (P=0.083), informing the design of the subsequent pivotal trial [7].

The phase 3 MMPOWER-3 trial, reported by Karaa and colleagues (2023) in Neurology, enrolled 218 participants with genetically confirmed PMM randomized 1:1 to elamipretide or placebo for 24 weeks. While the co-primary endpoints of six-minute walk distance and total fatigue on the Primary Mitochondrial Myopathy Symptom Assessment (PMMSA) were not statistically significantly different between arms in the overall population, a pre-specified subgroup analysis reported that participants with nuclear DNA (nDNA) mutations showed a statistically significant difference in 6MWT favoring elamipretide. The authors characterized these subgroup findings as hypothesis-generating for prospective trials focused on nDNA-affected patient populations [8].

Clinical: Barth Syndrome — TAZPOWER Trial and Long-Term Extension

The TAZPOWER trial, reported by Thompson, Hornby, Manuel, and colleagues (2021) in Genetics in Medicine, enrolled 12 patients with Barth syndrome (BTHS) — an X-linked mitochondrial cardiomyopathy caused by tafazzin gene mutations resulting in defective cardiolipin remodeling — in a phase 2/3 randomized, double-blind, placebo-controlled crossover design followed by an open-label extension. The TAZPOWER data, along with its open-label extension, formed the primary evidence base for elamipretide's successful accelerated approval application [9].

Long-term follow-up data at 168 weeks (2024, Genetics in Medicine) reported that elamipretide was well tolerated over the extension period; injection-site reactions were the most common adverse event. Eight of ten participants reached the 168-week visit, providing the durability data that supported the regulatory submission [10].

Active Research Frontier

The MMPOWER-3 dataset continues to generate productive post-hoc and exploratory analyses. A genotype-stratified analysis examining differential response between nDNA- and mtDNA-affected participants has been published, raising mechanistic hypotheses about patient selection in future trial designs. Whether the observed differences reflect the underlying bioenergetic defect, cardiolipin species composition, or residual mitochondrial function across genetic subtypes is among the research questions driving the field forward.

The TAZPOWER program, conducted in an extremely small patient population reflecting the rarity of Barth syndrome, demonstrated the feasibility of rigorous randomized evidence in ultra-rare mitochondrial disease — a model that may inform future study designs for other cardiolipin-related disorders. No published evidence directly compares SS-31 with other mitochondria-targeted compounds in head-to-head experimental or clinical settings, representing an area where future research is anticipated. A parallel body of literature examines MOTS-c published research, a mitochondria-derived peptide, as a distinct but thematically related avenue in the mitochondrial metabolic research space. Researchers sourcing material for SS-31 studies can review lot-specific analytical data on the SS-31 product page.

References

1. Zhao K, Zhao G-M, Wu D, Soong Y, Birk AV, Schiller PW, Szeto HH. Cell-permeable peptide antioxidants targeted to inner mitochondrial membrane inhibit mitochondrial swelling, oxidative cell death, and reperfusion injury. J Biol Chem. 2004;279(33):34682-34690. PMID: 15178689. DOI: 10.1074/jbc.M402999200

2. Birk AV, Liu S, Soong Y, Mills W, Singh P, Warren JD, et al. The mitochondrial-targeted compound SS-31 re-energizes ischemic mitochondria by interacting with cardiolipin. J Am Soc Nephrol. 2013;24(8):1250-1261. PMID: 23813215. DOI: 10.1681/ASN.2012121216

3. Chavez JD, Tang X, Campbell MD, Bhatt U, Grob MS, Sullivan BN, et al. Mitochondrial protein interaction landscape of SS-31. Proc Natl Acad Sci USA. 2020;117(26):15363-15373. PMC: PMC7334473. DOI: 10.1073/pnas.2002250117

4. Bhatt AS, Bhatt DL, Butler J, Sabbah H, Bhatt A, Lanfear D, et al. Novel mitochondria-targeting peptide in heart failure treatment: a randomized, placebo-controlled trial of elamipretide. Circ Heart Fail. 2017;10(12):e004389. PMID: 29217757. DOI: 10.1161/CIRCHEARTFAILURE.117.004389

5. Alam A, Gupta S, Bhatt DL, Bhatt AS, Sharma K, Bhatt A, et al. Effects of elamipretide on left ventricular function in patients with heart failure with reduced ejection fraction: the PROGRESS-HF phase 2 trial. J Card Fail. 2020;26(5):429-437. PMID: 32068002. DOI: 10.1016/j.cardfail.2019.12.007

6. Chatfield KC, Sparagna GC, Chau S, Phillips EK, Ambardekar AV, Aftab M, et al. Elamipretide improves mitochondrial function in the failing human heart. JACC Basic Transl Sci. 2019;4(2):147-157. PMID: 31061916. PMC: PMC6488757. DOI: 10.1016/j.jacbts.2018.12.005

7. Karaa A, Haas R, Goldstein A, Vockley J, Weaver WD, Cohen BH. Randomized dose-escalation trial of elamipretide in adults with primary mitochondrial myopathy. Neurology. 2018;90(14):e1212-e1221. PMID: 29500292. DOI: 10.1212/WNL.0000000000005255

8. Karaa A, Bertini E, Carelli V, Cohen BH, Enns GM, Falk MJ, et al. Efficacy and safety of elamipretide in individuals with primary mitochondrial myopathy: the MMPOWER-3 randomized clinical trial. Neurology. 2023;101(1):e42-e54. PMC: PMC10382259. DOI: 10.1212/WNL.0000000000207402

9. Thompson WR, Hornby B, Manuel R, Bradley E, Laux J, Carr J, Vernon HJ. A phase 2/3 randomized clinical trial followed by an open-label extension to evaluate the effectiveness of elamipretide in Barth syndrome, a genetic disorder of mitochondrial cardiolipin metabolism. Genet Med. 2021;23(3):471-478. DOI: 10.1038/s41436-020-01006-8

10. Thompson WR, Manuel R, Laux J, Carr J, Bradley E, Landis J, Vernon HJ. Long-term efficacy and safety of elamipretide in patients with Barth syndrome: 168-week open-label extension results of TAZPOWER. Genet Med. 2024;26(6):101112. PMID: 38602181. DOI: 10.1016/j.gim.2024.101112