Prolonged cold ischemia remains a major determinant of early graft dysfunction and survival after heart transplantation. In the setting of persistent donor organ shortages and increasingly adverse donor risk profiles, extended ischemic times increasingly contribute to primary graft dysfunction and early mortality.1,2 Although hypothermic preservation reduces metabolic demand, it does not prevent the molecular injury cascades that culminate in irreversible myocardial damage. Accordingly, there is growing interest in active preservation strategies that directly address the biological mechanisms underlying ischemia/reperfusion injury. Mitochondrial dysfunction is central to cold ischemia/reperfusion injury. Hypothermia impairs oxidative phosphorylation, promotes reactive oxygen species generation, and destabilizes mitochondrial membranes, leaving cardiomyocytes particularly vulnerable upon reperfusion.3,4 Among regulated cell death pathways, ferroptosis—an iron-dependent, lipid peroxidation–driven process—has emerged as an important contributor to myocardial injury during prolonged cold storage.5,6 Because ferroptosis is tightly linked to mitochondrial redox imbalance, interventions targeting mitochondrial metabolism represent a rational therapeutic approach. In this issue of Transplantation, Yang et al7 describe a novel strategy based on cardiomyocyte-targeted mitochondrial transfer carrying dihydroorotate dehydrogenase (DHODH). DHODH, an inner mitochondrial membrane enzyme involved in de novo pyrimidine biosynthesis, has recently been recognized as a key suppressor of ferroptosis through maintenance of coenzyme Q redox cycling.8,9 Although exogenous single-dose DHODH supplementation confers transient protection, its limited tissue specificity and short functional persistence restrict its translational applicability. To address these limitations, the authors overexpress DHODH in bioengineered mitochondria modified with an ischemic cardiomyocyte-targeting peptide. This approach directly confronts a longstanding challenge in mitochondrial transplantation—namely rapid clearance by the reticuloendothelial system and limited myocardial uptake.10 Notably, mitochondrial transfer is performed ex vivo at the time of donor heart procurement, reframing the intervention as metabolic preconditioning rather than postreperfusion rescue. This timing is biologically relevant, as it allows reinforcement of mitochondrial redox capacity before the oxidative stress of reperfusion ensues. A particular strength of this study is its assessment of longer-term outcomes. Using a 2-mo allogeneic rat heart transplant model, Yang et al demonstrate that DHODH-loaded mitochondrial transfer delays graft failure, attenuates fibrosis and apoptosis, and preserves mitochondrial membrane potential compared with repeated DHODH administration during ischemia or in control conditions, while maintaining a low immunogenic risk. These findings address a frequent limitation of metabolic therapies, which often demonstrate benefit only during early reperfusion. Equally noteworthy is the observation that graft protection persists despite mitochondrial degradation of the transplanted tissue. Although engineered mitochondria exhibit a finite half-life of approximately 2 wk, DHODH activity and mitochondrial redox homeostasis remain enhanced beyond their physical persistence. These data support a model of metabolic priming, in which early restoration of mitochondrial function enables endogenous protective mechanisms to sustain graft resilience. This concept mitigates concerns regarding permanent mitochondrial engraftment or uncontrolled mitochondrial propagation. Given the immunogenic potential of mitochondria, safety considerations are paramount. Mitochondrial components can act as damage-associated molecular patterns, activating innate immune pathways.11 The authors report only modest, transient cytokine elevations resolving by day 7, balanced macrophage polarization, and minimal off-target biodistribution, providing preliminary reassurance regarding immunologic safety. Nonetheless, validation in large-animal models will be essential before clinical translation. CLINICAL IMPLICATIONS If confirmed in large-animal studies and clinical trials, DHODH-targeted mitochondrial transfer could meaningfully extend acceptable cold ischemic times, facilitating safer long-distance organ sharing and improved utilization of marginal donor hearts. By intervening at the level of donor organ metabolism rather than recipient rescue, this strategy may reduce the incidence of primary graft dysfunction and attenuate early allograft injury. More broadly, metabolic priming during cold storage may represent a generalizable preservation strategy for other organs in which mitochondrial dysfunction and ferroptosis contribute to ischemic injury. In summary, Yang et al advance a compelling organ-directed approach that shifts the focus of graft protection mechanisms upstream to the donor heart itself. By targeting mitochondrial vulnerability during cold ischemia, this work aligns mechanistic insight with a clinically relevant unmet need. If successfully translated, mitochondrial-based preservation strategies may reshape how donor hearts are prepared for the metabolic demands of reperfusion.
Knosalla et al. (Mon,) studied this question.