Mitochondrial-targeted therapy with elamipretide preserves cardiac function and prevents late mortality in murine sepsis-induced cardiac dysfunction.

Technical Summary: Mitochondrial-Targeted Therapy with Elamipretide in Sepsis-Induced Cardiac Dysfunction

Problem Statement
Sepsis-induced cardiac dysfunction (SICD) affects nearly half of septic patients, is associated with increased mortality, and lacks targeted therapies. While clinical and experimental evidence suggests that myocardial bioenergetic failure and impaired oxygen utilization (rather than supply) drive SICD, the upstream mechanisms linking septic stress to mitochondrial dysfunction and contractile failure remain poorly defined. Specifically, the role of cardiolipin (CL), a mitochondria-specific phospholipid critical for cristae architecture and electron transport chain (ETC) stability, in the pathogenesis of SICD has not been fully elucidated. Furthermore, the potential of mitochondrial-targeted therapies to reverse these defects and improve outcomes in sepsis remains unexplored.

Methodology
The study utilized a murine model of polymicrobial sepsis induced by intraperitoneal injection of cecal slurry (CS) in C57BL/6N mice.

• Intervention: Mice received a single early dose of elamipretide (Ela; 10 mg/kg) or PBS vehicle at 1 hour post-inoculation.
• Functional Assessment: Cardiac performance was evaluated via echocardiography (strain, ejection fraction), pressure-volume (PV) loop analysis (load-independent contractility, efficiency, ventriculo-arterial coupling), and isolated working heart perfusion (substrate oxidation rates).
• Molecular & Metabolic Profiling:
  • Lipidomics: Untargeted profiling of cardiac tissue to assess cardiolipin and other phospholipid species.
  • Proteomics & Metabolomics: Data-independent acquisition shotgun proteomics and targeted LC-MS/MS metabolomics to map metabolic flux, enzyme abundance, and substrate accumulation.
  • Respirometry: High-resolution respirometry of cardiac homogenates to measure oxygen flux across specific ETC complexes (Complex I, II, and IV).
  • Structural Analysis: Transmission electron microscopy (TEM) for mitochondrial ultrastructure.
  • Long-term Outcomes: Survival was monitored for 30 days, with cardiovascular and metabolic assessments performed at day 10 (T10d) to characterize post-sepsis recovery.

Key Contributions and Results

1. Elamipretide Preserves Cardiac Function and Prevents Late Mortality:

   • Sepsis induced severe biventricular systolic and diastolic dysfunction, reduced cardiac efficiency, and increased mortality.
   • Early administration of Ela attenuated illness severity and completely prevented late sepsis-related mortality (days 10–20).
   • Ela restored intrinsic myocardial contractility (end-systolic elastance, preload-recruitable stroke work), improved ventriculo-arterial coupling, and normalized diastolic function. These benefits occurred despite persistent systemic inflammation, indicating that Ela's effects are independent of immunomodulation.

2. Sepsis Induces Cardiolipin Depletion and Complex I Dysfunction:

   • Lipidomic analysis revealed a broad depletion of cardiac cardiolipin species in septic hearts, particularly the dominant species CL 18:2-18:2-18:2-18:2.
   • This depletion correlated with mitochondrial ultrastructural abnormalities, including cristae loss and membrane disruption.
   • Functional assays identified a specific defect in Complex I (NADH-linked) respiratory capacity and enzymatic activity, while Complex II (succinate-linked) function remained preserved. This led to a bottleneck in electron transfer, reduced ATP production, and increased oxidative stress (elevated MDA, NADP+/NADPH ratio).

3. Metabolic Reprogramming and the Pyruvate Oxidation Bottleneck:

   • Sepsis caused a metabolic inflexibility characterized by a "glycolytic congestion" where glycolytic intermediates (glucose-6-phosphate, pyruvate) and CoA esters (acetyl-CoA, succinyl-CoA) accumulated, while downstream oxidative flux was impaired.
   • This was driven by the upregulation of Pyruvate Dehydrogenase Kinase 4 (PDK4), which inhibited Pyruvate Dehydrogenase (PDH). The study found this PDK4 induction was post-translational (protein stabilization via fatty acid availability) rather than transcriptional.
   • Consequently, glucose oxidation was blunted, and the heart relied inefficiently on fatty acid oxidation, which was also partially impaired (evidenced by ethylmalonate accumulation).

4. Mechanism of Elamipretide Action:

   • Ela treatment restored cardiolipin content and normalized the cardiac lipidome, specifically reversing the depletion of CL species and restoring mitochondrial membrane integrity.
   • By stabilizing cardiolipin, Ela restored Complex I function, improved electron transport, and normalized metabolic flux. This led to the resolution of the pyruvate/acetyl-CoA bottleneck, reduced oxidative stress, and improved ATP levels.
   • Ela partially restored insulin responsiveness and glucose oxidation, though some upstream glycolytic congestion persisted.

5. Long-term Recovery:

   • At day 10 post-sepsis, untreated mice exhibited residual cardiac dysfunction (reduced strain, impaired efficiency) and persistent downregulation of ETS proteins, particularly Complex I subunits.
   • Ela treatment mitigated these residual deficits, preserving mitochondrial protein abundance and respiratory capacity, thereby preventing the transition to persistent post-sepsis cardiomyopathy.

Significance
The paper identifies cardiolipin-dependent mitochondrial dysfunction, specifically centered on Complex I impairment, as a central pathogenic mechanism underlying SICD. The findings demonstrate that sepsis disrupts the integration of substrate oxidation with mitochondrial energy transduction, creating a metabolic bottleneck that leads to bioenergetic failure and oxidative stress.

The study positions mitochondrial-targeted therapy with elamipretide as a promising strategy for SICD. By stabilizing cardiolipin, Ela restores mitochondrial membrane architecture, rescues Complex I function, and normalizes metabolic flux. Crucially, the study shows that this approach improves both acute cardiac performance and long-term survival, even in the presence of ongoing systemic inflammation. The authors conclude that metabolic modulation represents a viable therapeutic avenue for addressing the cardiovascular burden of sepsis, with potential implications for other disorders characterized by similar mitochondrial energy transduction defects.