Highlights
In a female rat model of heart failure with preserved ejection fraction (HFpEF), skeletal muscle showed evidence of mitochondrial dysfunction, reduced cardiolipin content, contractile impairment, titin abnormalities, and muscle atrophy.
Elamipretide (SS-31), a mitochondria-targeted peptide that stabilizes cardiolipin, improved whole-muscle force, enhanced single-fiber performance, and prevented further muscle wasting.
The study supports a mechanistic link between cardiolipin dysregulation, impaired oxidative phosphorylation, and skeletal muscle dysfunction in HFpEF.
These findings are preclinical and do not establish clinical efficacy, but they strengthen the rationale for mitochondrial therapies in exercise intolerance associated with HFpEF.
Study Background and Clinical Context
Heart failure with preserved ejection fraction (HFpEF) is a common and clinically challenging syndrome characterized by heart failure symptoms despite a preserved left ventricular ejection fraction. One of its most burdensome features is exercise intolerance, which often persists even when congestion is controlled and resting cardiac function appears relatively stable. In recent years, HFpEF has increasingly been recognized as a multisystem disorder rather than a purely cardiac one, with skeletal muscle abnormalities contributing substantially to reduced functional capacity.
Mitochondrial dysfunction is a plausible driver of this limitation. Skeletal muscle from patients and experimental models of HFpEF may exhibit reduced oxidative capacity, impaired bioenergetics, oxidative stress, and structural derangements that interfere with contraction. Cardiolipin, a phospholipid located in the inner mitochondrial membrane, is essential for maintaining mitochondrial architecture and supporting the activity of respiratory-chain complexes. When cardiolipin is altered or depleted, mitochondrial energy production may become less efficient, potentially worsening muscle performance.
Elamipretide (SS-31) is a mitochondria-targeted tetrapeptide designed to bind cardiolipin and stabilize the inner mitochondrial membrane. It has been investigated in other conditions linked to bioenergetic failure, making it a biologically plausible candidate for HFpEF-related skeletal muscle dysfunction. This study asked whether cardiolipin abnormalities are present in the skeletal muscle of HFpEF rats and whether elamipretide can reverse the resulting functional deficits.
Study Design
This preclinical study used female zucker fatty spontaneously hypertensive heart failure F1 hybrid lean rats as controls (n=10) and obese rats as the HFpEF model (n=24). At 20 weeks of age, the HFpEF rats were randomized to receive either NaCl (n=12) or elamipretide (n=12) for 12 weeks.
The investigators examined skeletal muscle using multiple complementary approaches, including whole-muscle force testing, single-fiber mechanics, mitochondrial respiration analyses, histology, and molecular assays. They also assessed cardiolipin content and maturation, titin phosphorylation, oxidative stress markers, and muscle fiber size.
The study was designed to connect a mechanistic abnormality at the mitochondrial membrane level with measurable contractile and structural outcomes in skeletal muscle. Because this was an animal study, the results are hypothesis-generating rather than directly practice-changing.
Key Findings
HFpEF was associated with mitochondrial and structural muscle abnormalities
Compared with lean controls, HFpEF rats showed lower cardiolipin levels, reported as a 6.8% reduction (P=0.007). The investigators also found evidence of impaired cardiolipin maturation, reflected by altered tafazzin expression. Tafazzin is a cardiolipin-remodeling enzyme, and abnormalities in this pathway suggest disrupted mitochondrial membrane maintenance.
Beyond the mitochondrial phenotype, HFpEF rats had clear skeletal muscle abnormalities. These included reduced contractile function, titin hyperphosphorylation, fiber atrophy, and increased oxidative stress markers. Titin is a large sarcomeric protein that influences passive tension, elasticity, and mechanical stability of muscle fibers; hyperphosphorylation may alter muscle mechanics and contribute to functional impairment.
Elamipretide improved muscle force and fiber mechanics
After 12 weeks of treatment, elamipretide improved whole-muscle contractile performance. In soleus muscle, force increased by 8.2% (P=0.041), and in extensor digitorum longus (EDL), force increased by 10.9% (P=0.016). These are modest but statistically significant improvements at the whole-muscle level.
More strikingly, elamipretide improved single-fiber contractile function. In soleus muscle, single-fiber performance increased by 173.2% (P<0.001), while in EDL the increase was 66.0% and did not reach statistical significance. The large effect in soleus fibers suggests a meaningful restoration of intrinsic contractile properties, although the magnitude should be interpreted cautiously in the setting of a small animal study and a complex endpoint set.
Elamipretide influenced titin phosphorylation and muscle size
The treatment also normalized titin phosphorylation, with reductions of 35.4% in soleus (P<0.001) and 40.2% in EDL (P<0.001). Because titin phosphorylation affects passive stiffness and force transmission, this finding provides a plausible structural explanation for improved muscle mechanics.
Elamipretide also prevented the development of muscle atrophy. Soleus fiber size increased by 49% (P=0.001), and EDL fiber size increased by 54.8% (P<0.001) relative to the untreated HFpEF group. This suggests that mitochondrial stabilization may not only improve function but also preserve muscle mass, which is clinically relevant because muscle wasting is closely linked to frailty and reduced exercise capacity.
Mitochondrial function appeared to improve in parallel
The authors reported improved mitochondrial function after elamipretide, presumably through cardiolipin-mediated enhancement of oxidative phosphorylation. Although the abstract does not provide the detailed respiratory parameters, the interpretation is biologically coherent: cardiolipin supports the organization and activity of electron transport chain complexes, and stabilizing it could improve ATP production, reduce reactive oxygen species generation, and help preserve muscle integrity.
Overall, the data suggest that mitochondrial dysfunction in HFpEF skeletal muscle is not merely an epiphenomenon but may contribute directly to impaired force generation and atrophy. Elamipretide appears to have acted upstream at the membrane level, with downstream benefits on muscle mechanics and structure.
Expert Commentary
This study is noteworthy for several reasons. First, it broadens the focus of HFpEF biology beyond the heart and vasculature to include skeletal muscle mitochondrial health. This is clinically important because many patients with HFpEF experience exertional limitation that appears disproportionate to resting cardiac findings. Second, it identifies cardiolipin dysregulation as a potentially actionable mechanism in peripheral muscle, not just myocardium. Third, it provides mechanistic support for a therapy designed to target mitochondrial membranes rather than conventional neurohormonal pathways.
At the same time, several limitations must temper interpretation. The work was performed in an animal model, and rodent skeletal muscle biology does not fully reproduce human HFpEF. The model used was female, which is relevant because HFpEF is more prevalent in women, but it also limits generalizability to male patients. The sample size was relatively small, and the abstract does not provide confidence intervals, full respiratory data, or prespecified clinical correlates such as exercise capacity in vivo. In addition, multiple endpoints were tested, increasing the possibility that some findings could be influenced by multiplicity despite the strong mechanistic coherence of the results.
From a translational standpoint, the key unanswered question is whether improving mitochondrial membrane integrity in human HFpEF will translate into meaningful gains in peak oxygen uptake, walking distance, fatigue, or quality of life. Prior human studies of mitochondrial-directed therapies have produced mixed results across diseases, so rigorous clinical testing will be essential. Nonetheless, the biological plausibility is strong, and the present findings justify further exploration of elamipretide or related compounds in HFpEF patients with demonstrable skeletal muscle dysfunction.
Clinical and Research Implications
If the preclinical signal proves reproducible in humans, cardiolipin stabilization could represent a new therapeutic axis for HFpEF, particularly for patients whose dominant limitation is exercise intolerance rather than congestion. Such an approach would be complementary to standard HFpEF care, which currently focuses on diuretics, blood pressure control, comorbidity management, and selected guideline-directed therapies.
Future studies should clarify whether benefits are driven primarily by improved oxidative phosphorylation, reduced oxidative stress, altered sarcomeric signaling, or a combination of these effects. It will also be important to determine which HFpEF phenotypes are most likely to respond, whether response differs by sex or metabolic status, and whether skeletal muscle biomarkers can identify patients with mitochondrial impairment.
Conclusion
In this HFpEF rat model, elamipretide improved skeletal muscle performance, reduced atrophy, and corrected abnormalities linked to cardiolipin dysfunction and titin phosphorylation. The findings strengthen the concept that skeletal muscle mitochondrial dysfunction is a meaningful therapeutic target in HFpEF. While the results are promising, they remain preclinical and require careful validation in human studies before clinical application.
Funding and clinicaltrials.gov
The abstract provided does not specify funding sources or a clinicaltrials.gov identifier. Because this was a preclinical animal study, clinical trial registration is not applicable.
References
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