Elamipretide Restores Mitochondrial Energy in Rare Fatty Acid Disorder
A cardiolipin-binding peptide improves exercise endurance and mitochondrial bioenergetics in a mouse model and patient fibroblasts with TFP deficiency.
Summary
Mitochondrial trifunctional protein (TFP) deficiency impairs long-chain fatty acid oxidation, causing cardiomyopathy, neuropathy, and retinopathy. Researchers tested elamipretide—a synthetic cardiolipin-binding peptide already FDA-approved for Barth syndrome—in a βTFP-mutant mouse model and patient-derived fibroblasts. Treated mice showed improved treadmill exercise endurance and enhanced liver mitochondrial fatty acid oxidation and electron transport chain enzyme activities. In patient fibroblasts, elamipretide increased mitochondrial bioenergetics and reduced reactive oxygen species in a genotype-dependent manner. Notably, cardiolipin content and composition were unchanged, suggesting elamipretide acts by stabilizing interactions between fatty acid oxidation enzymes and ETC complexes rather than by restoring cardiolipin levels.
Detailed Summary
Mitochondrial trifunctional protein (TFP) deficiency is a rare inherited disorder of long-chain fatty acid β-oxidation (FAO) caused by mutations in HADHA (α-subunit, encoding ECH and LCHAD activities) or HADHB (β-subunit, encoding KAT activity). Despite newborn screening and dietary interventions such as triheptanoin, patients continue to develop hypoglycemia, rhabdomyolysis, cardiomyopathy, peripheral neuropathy, and retinopathy. A recently discovered fourth enzymatic function of the HADHA subunit—monolysocardiolipin acyltransferase-1 (MLCLAT-1) activity—catalyzes cardiolipin (CL) remodeling in the inner mitochondrial membrane. The authors had previously shown reduced CL levels in TFP/LCHAD-deficient patient fibroblasts and a βTFP-mutant mouse model, motivating investigation of elamipretide, a synthetic cardiolipin-binding tetrapeptide with FDA accelerated approval for Barth syndrome.
Using a C57BL/6J-Hadhb-m1Ytc mouse model carrying a missense mutation (p.M404K) that recapitulates the human disease phenotype, the team delivered elamipretide via subcutaneous osmotic minipumps (3 μg/g/day for 28 days) after dose-finding experiments revealed toxicity at higher doses. Functional endpoints included treadmill exercise endurance and cold-stress tolerance after fasting. Biochemical endpoints included liver and skeletal muscle mitochondrial FAO-ETC enzyme activities assessed by blue-native PAGE (BN-PAGE), in-gel activity staining, and western blotting, as well as cardiolipin quantification by mass spectrometry. Patient-derived fibroblasts from four TFP/LCHAD-deficient individuals were evaluated using Seahorse XF analysis for mitochondrial bioenergetics and fluorescent probes for reactive oxygen species (ROS).
Key results showed that elamipretide-treated βTFP-deficient male mice ran significantly farther and longer on the treadmill compared to PBS controls, demonstrating improved exercise capacity. Liver mitochondria from treated male mice exhibited enhanced FAO and ETC complex activities. However, cold tolerance after fasting was not improved, and female mice showed less pronounced responses, suggesting sex-specific effects. Importantly, cardiolipin content and acyl-chain composition remained unchanged in treated animals, indicating that elamipretide's mechanism in this model is independent of CL restoration. In patient fibroblasts, elamipretide produced a genotype-dependent increase in mitochondrial oxygen consumption rate and ATP production alongside reduced ROS levels, with patients harboring different HADHA/HADHB variants showing variable magnitudes of response.
The authors propose that elamipretide acts by physically stabilizing the interaction between FAO enzyme complexes and ETC supercomplexes at the inner mitochondrial membrane—effectively improving substrate channeling and OXPHOS efficiency without altering CL abundance. This mechanism is consistent with emerging evidence that elamipretide improves mitochondrial supercomplex organization in other disease contexts.
These findings position elamipretide as a promising candidate therapeutic for TFP/LCHAD deficiency, particularly for complications like peripheral neuropathy and retinopathy that are not addressed by current dietary treatments. However, the study is preclinical, with small group sizes, sex-limited efficacy signals, and no direct assessment of neuropathy or retinal outcomes. Further studies with larger cohorts, longer treatment durations, and disease-relevant endpoints are warranted before clinical translation.
Key Findings
- Elamipretide via osmotic minipump improved treadmill exercise endurance in male βTFP-deficient mice.
- Liver mitochondrial FAO and ETC complex enzyme activities were enhanced in treated male mice.
- Cardiolipin content and acyl-chain composition were unchanged, ruling out CL restoration as the mechanism.
- Patient fibroblasts showed genotype-dependent increases in mitochondrial bioenergetics and reduced ROS.
- Cold-stress tolerance after fasting was not improved, and female mice showed weaker responses.
Methodology
In vivo studies used a βTFP-mutant (Hadhb p.M404K) mouse model receiving elamipretide or PBS via subcutaneous osmotic minipumps for 28 days, assessed by treadmill exercise, cold-stress tests, BN-PAGE, and cardiolipin mass spectrometry. In vitro studies used Seahorse XF bioenergetics analysis and ROS fluorescent assays in patient-derived skin fibroblasts from four TFP/LCHAD-deficient individuals and two healthy controls.
Study Limitations
Group sizes were small (3–4 animals per group), limiting statistical power, and efficacy was primarily observed in male mice with unclear sex-specific mechanisms. Cold tolerance was not improved and no direct assessments of peripheral neuropathy, retinopathy, or cardiac outcomes were performed, leaving key clinical endpoints unaddressed.
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