The technical centerpiece of the work is a family of fluorescent biosensors called iNap, which fluoresce in proportion to NADPH concentration and can be targeted to specific cellular compartments. When the researchers expressed these sensors in adult mouse cardiomyocytes, they observed that swimming and running exercise elevated the NADPH signal in the cytosol while leaving the mitochondrial pool untouched. This compartmental specificity matters, because cytosolic and mitochondrial NADPH fluxes are known to be independently regulated, and it points the finger away from mitochondrial transhydrogenase and toward cytosolic sources. Among those sources, the pentose phosphate pathway, or PPP, stood out: a glucose-shunting branch of metabolism whose rate-limiting enzyme, glucose-6-phosphate dehydrogenase (G6PD), strips electrons from glucose-6-phosphate and deposits them onto NADP+ to make NADPH.

The causal chain was established through a series of loss-of-function experiments. When the team inhibited PPP activity or depleted cytosolic NADPH in mice, the heart’s response to exercise was blunted: the characteristic enlargement of cardiomyocytes that normally accompanies training failed to materialize. Conversely, the study showed that NADPH itself is a driver of cardiomyocyte growth, acting by inhibiting the HDAC3/C/EBPβ pathway—a signaling axis previously implicated in the control of exercise-induced cardiac growth. In other words, the reducing equivalents manufactured by the PPP do more than keep reactive oxygen species in check; they directly tune an epigenetic and transcriptional program that tells heart cells to grow in a coordinated, physiological manner rather than in the maladaptive fashion seen in disease.

The protective side of the story emerged from mouse models of acute ischemia–reperfusion injury, a scenario that unfolds in millions of patients each year when a blocked coronary artery is reopened and the sudden return of oxygen floods the tissue with reactive oxygen species. Mice with an exercise-activated PPP/NADPH pathway suffered measurably less injury from a subsequent ischemia–reperfusion challenge, and this protection persisted: four weeks after the insult, heart function remained significantly preserved compared with sedentary controls. The mechanism appears to be twofold. First, abundant NADPH sustains the glutathione and thioredoxin antioxidant systems that neutralize the oxidative burst of reperfusion. Second, by suppressing HDAC3 activity, NADPH restrains the transcriptional changes that push stressed cardiomyocytes toward death and maladaptive remodeling.

What makes the study more than an elegant piece of mechanistic cardiology is its drug-discovery angle. The researchers screened 310 Tibetan medicinal compounds for the ability to raise intracellular NADPH, and one molecule rose to the top: lyciumspermidine-0527, a spermidine derivative derived from a plant used in traditional Tibetan medicine. Biochemical and structural analyses showed that this compound directly activates G6PD, the rate-limiting enzyme of the pentose phosphate pathway, stabilizing the enzyme’s active dimeric form. In cultured cardiomyocytes and in living mice, lyciumspermidine-0527 elevated cytosolic NADPH, promoted cardiomyocyte growth, and—most strikingly—alleviated ischemia–reperfusion injury to a degree that rivaled exercise itself.

Safety data accompanying the compound were encouraging. Across a range of doses in vitro and in vivo, lyciumspermidine-0527 did not significantly induce cell death in the heart, and histological examination of heart, liver, lung, kidney, and brain tissue showed no overt toxicity. The compound also maintained redox homeostasis in cardiomyocytes, consistent with its proposed mechanism of boosting, rather than overwhelming, the cell’s antioxidant buffering capacity. Genetic confirmation followed: when G6PD was knocked down, the protective effects of the compound vanished, placing G6PD squarely upstream of the observed benefit and ruling out major off-target explanations for the phenotype.

Conceptually, the findings reframe physiological cardiac hypertrophy as a metabolic checkpoint phenomenon. The healthy heart’s enlargement in response to exercise has long been distinguished from the pathological hypertrophy of hypertension or heart failure by its reversibility and preserved function, but the molecular gatekeepers separating the two states have been only partially mapped. By demonstrating that PPP-derived NADPH is required for exercise-induced growth and simultaneously protective against injury, the study positions a single metabolite as a checkpoint that integrates the demand for biosynthesis (NADPH feeds fatty acid and nucleotide production), antioxidant defense (NADPH powers glutathione reductase), and epigenetic regulation (NADPH inhibits the HDAC3–Ncor complex). Exercise, in this view, is a metabolic intervention, and its cardiac benefits can be recapitulated—at least in mice—by pharmacologically opening a single metabolic valve.

The translational horizon is tantalizing but cautious. Lyciumspermidine-0527 is not yet a drug, and the leap from mouse models of surgically induced ischemia–reperfusion to human myocardial infarction is considerable. G6PD activity is a double-edged sword: the same pathway that supports antioxidant defense in cardiomyocytes also supports nucleotide synthesis and growth in cancer cells, raising questions about systemic effects that would need careful evaluation in longer-term studies. Nonetheless, the identification of a small molecule that directly activates G6PD offers a starting point for medicinal chemistry, and the iNap biosensor toolkit the team deployed provides a template for screening compounds by their ability to raise NADPH in specific subcellular compartments rather than by crude proxies.

For now, the study’s most immediate contribution is conceptual clarity. It explains, in mechanistic terms, why the exercising heart grows well and withstands injury better, connecting the dots from a transcription factor (SP1-driven G6PD expression), through a metabolic flux (the pentose phosphate pathway), to a redox cofactor (cytosolic NADPH), and finally to an epigenetic effector (HDAC3/C/EBPβ) and a clinical phenotype (preserved function after reperfusion). It also validates a natural-product-inspired approach to finding exercise mimetics for the heart. If the PPP/NADPH axis holds up in larger preclinical models, the prospect of a pill that trains the heart’s metabolism—conferring some of exercise’s cardioprotection on patients who cannot exercise—moves from metaphor to plausible pipeline.

Subject of Research: Pentose phosphate pathway-derived NADPH as a metabolic checkpoint regulating exercise-induced physiological cardiac hypertrophy and protection against ischemia–reperfusion injury

Article Title: Pentose phosphate pathway-derived NADPH facilitates physiological hypertrophy and alleviates ischemia–reperfusion injury in the heart

Article References: Wu, D., Chen, T., Dong, X., Li, H., Cheng, Z., Li, H., Chao, Y., Li, F., Yin, Y., Guo, F., Xu, X., Zhang, Y., Ning, K., Fu, X., Bian, Y., Ma, F., Ritterhoff, J., Wang, W., & Hu, Q. (2026). Pentose phosphate pathway-derived NADPH facilitates physiological hypertrophy and alleviates ischemia–reperfusion injury in the heart. Nature Metabolism. https://doi.org/10.1038/s42255-026-01587-9

Image Credits: AI Generated

DOI: 10.1038/s42255-026-01587-9

Keywords: NADPH, pentose phosphate pathway, cardiac hypertrophy, exercise, ischemia-reperfusion injury, glucose-6-phosphate dehydrogenase, cardiomyocytes, HDAC3, lyciumspermidine-0527, redox homeostasis, cardiac metabolism, Nature Metabolism

Normothermic machine perfusion departs fundamentally from traditional cold storage methods by maintaining the kidney in a warm, oxygenated, and metabolically active state outside the body. This approach preserves the organ’s cellular and vascular integrity far better than simple hypothermic preservation, potentially mitigating ischemia-reperfusion injury that often compromises graft function once transplanted. By providing continuous oxygen supply and nutrients, NMP keeps the kidney “alive” in a near-physiological environment, allowing not only preservation but also real-time functional assessment and therapeutic intervention.

The clinical introduction of NMP technology marks a paradigm shift in how transplant teams assess organ viability. Unlike static cold storage, NMP enables dynamic monitoring of key parameters such as renal blood flow, urine output, and metabolic activity. These physiological markers provide invaluable information about graft quality, helping clinicians decide whether to proceed with transplantation or discard marginal organs that might otherwise have been rejected without adequate evaluation. This capability could profoundly increase the donor pool by revitalizing kidneys previously deemed unsuitable.

Despite these advantages, the authors emphasize several technical and logistical challenges inherent in widespread NMP implementation. For instance, the machinery required for normothermic perfusion is complex and costly, necessitating specialized training and infrastructure in transplant centers. This increases the resource burden and limits accessibility, especially in low- and middle-income settings where the need for improving organ utilization is arguably greatest. Additionally, standardization of perfusion protocols remains an unmet need, with variability in pressure settings, perfusate composition, and duration potentially influencing outcomes.

The biological mechanisms by which NMP confers protective effects warrant further exploration. The study outlines emerging evidence that NMP not only reduces ischemic injury but may also modulate immune activation and mitigate inflammatory cascades triggered by transplantation. The ability to “recondition” kidneys during ex vivo perfusion might open avenues for targeted drug delivery to the organ, providing localized anti-inflammatory or regenerative therapies prior to implantation. Such possibilities underscore the versatility of NMP beyond mere preservation.

From a clinical trials perspective, the authors report promising but still early-stage data supporting the safety and efficacy of NMP. Several pilot studies indicate improved early graft function and reduced delayed graft function incidence. However, larger multicenter randomized controlled trials with long-term follow-up are essential to establish definitive benefits in survival and quality of life. Regulatory approvals and harmonized guidelines will also depend on accumulating robust evidence of reproducibility and cost-effectiveness.

Ethical considerations arise as well, especially surrounding consent, allocation, and equitable access to this advanced technology. Transplant programs must ensure that the introduction of NMP does not exacerbate existing disparities in transplant opportunities. Moreover, organ allocation policies may need re-evaluation to incorporate viability assessments made possible through perfusion parameters, balancing fairness and utility.

In addition to kidney transplantation, the potential applications of normothermic machine perfusion extend to other solid organs such as the liver, lung, and heart. While each organ presents unique perfusion demands and vulnerabilities, the foundational principle of maintaining physiological conditions ex vivo offers transformative potential across the transplantation landscape. Cross-disciplinary collaboration will be pivotal to adapting and optimizing NMP protocols for diverse organ types.

Technological innovation is driving rapid improvements in perfusion systems, including miniaturization, automation, and integration with biosensors and artificial intelligence. Machine learning algorithms could analyze real-time perfusion data to predict graft viability with unprecedented precision, guiding clinical decisions and further personalizing organ therapy. These innovations embody a convergence of biotechnology, data science, and transplantation medicine.

The environmental impact of increased use of disposable components in machine perfusion systems also merits consideration. Sustainable design and waste reduction strategies are necessary to ensure that this cutting-edge technology’s ecological footprint is minimized, aligning with broader healthcare goals of environmental responsibility.

Training surgeons, perfusionists, and healthcare teams to expertly operate and interpret NMP data is a critical component being addressed through specialized courses and simulation-based education. Capacity building will enable the safe and effective scaling of NMP, with professional societies playing a key role in establishing competency standards.

Patient perspectives and psychosocial factors tied to NMP transplantation remain underexplored. Understanding how recipients perceive this evolving technology and its impact on their transplant experience will inform counseling and consent processes, ultimately fostering shared decision-making.

Finally, the economic implications of adopting normothermic machine perfusion must be weighed against potential cost savings from improved graft longevity and reduced complications. Health economic modeling and real-world cost-effectiveness studies will provide vital insights for policymakers and healthcare payers.

In conclusion, normothermic machine perfusion stands at the forefront of a new era in kidney transplantation. The study by Rabelink and colleagues articulates a comprehensive vision of this technology’s transformative promise alongside the pragmatic considerations for its integration into clinical practice. As ongoing research addresses outstanding questions and technological refinements continue apace, NMP is poised to reshape the transplant landscape, offering hope for enhanced graft survival and improved quality of life for patients worldwide.

Subject of Research: Normothermic machine perfusion in kidney transplantation

Article Title: Opportunities and challenges with the implementation of normothermic machine perfusion in kidney transplantation

Article References:
Rabelink, T.J., Hosgood, S., Minor, T. et al. Opportunities and challenges with the implementation of normothermic machine perfusion in kidney transplantation. Nat Commun 16, 6883 (2025). https://doi.org/10.1038/s41467-025-60410-3