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

The distinction between healthy and harmful heart enlargement sits at the center of the work. Cardiac hypertrophy, the thickening of heart muscle, comes in two physiologically opposite flavors. Physiological hypertrophy, triggered by exercise or pregnancy, enlarges the heart while preserving or improving its contractile function, and it is accompanied by efficient energy metabolism, robust blood vessel growth, and molecular profiles dominated by fatty acid oxidation. Pathological hypertrophy, driven by chronic hypertension, valve disease, or heart attack, produces similar gross enlargement but with stiffening walls, impaired pumping, fibrosis, metabolic inflexibility, and a march toward heart failure. Decades of research have sought the molecular switch that separates these two trajectories, and the new findings place cytosolic NADPH firmly on the protective side of that divide.

Technically, the study hinged on the ability to see and manipulate NADPH in living systems, a long-standing challenge because NADPH and its oxidized counterpart NADP+ are structurally almost identical and interconvert rapidly. Wu and colleagues combined genetic models targeting glucose-6-phosphate dehydrogenase, or G6PD, the rate-limiting enzyme of the oxidative pentose phosphate pathway and the principal cytosolic source of NADPH, with readouts of cardiac structure, function, and metabolism. When exercise-induced increases in G6PD activity were blunted, the beneficial cardiac remodeling that normally follows training was lost, demonstrating that the pathway is not merely a byproduct of exercise but a necessary component of its cardiac benefits.

The protective payoff became most apparent in models of ischemia/reperfusion injury, the cellular catastrophe that occurs when blood supply to the heart is briefly cut off and then restored, as happens during a heart attack. Animals with elevated cytosolic NADPH, whether achieved through exercise or through the spermidine-derived compound, showed improved cardiac function and reduced injury after the insult. The team traced this protection to NADPH’s established biochemical roles: the molecule is the electron donor for thioredoxin and glutathione antioxidant systems that neutralize reactive oxygen species, the corrosive byproducts of reoxygenation that kill cardiomyocytes in the minutes and hours after blood flow returns. By keeping antioxidant capacity high, elevated NADPH effectively raises the heart’s threshold for reperfusion damage.

What makes the result especially compelling is the pharmacological angle. Spermidine itself has been linked in prior studies to cardioprotection and extended healthspan, prompting interest in its derivatives as drug candidates. Wu and colleagues identified a candidate spermidine derivative that raises cytosolic NADPH and reproduces key features of the exercise phenotype: physiological growth of the heart, enhanced antioxidant buffering, and resilience to ischemic injury, without the maladaptive gene expression patterns that characterize pathological hypertrophy. In effect, the compound simulates a metabolic signature of the trained heart in sedentary animals.

The concept of an exercise-mimicking pill has long hovered at the edge of cardiovascular research, often disappointing in translation because broad interventions that mimic one aspect of exercise tend to disrupt others. The NADPH-centered approach is narrower and, its proponents argue, more principled. Rather than attempting to replicate the whole-body storm of hormones, neural signals, and mechanical loading that exercise produces, the strategy targets a single downstream metabolite that sits at a convergence point for the cardiac benefits of training. NADPH is consumed in the synthesis of reduced glutathione, regenerated by G6PD and by malic enzyme and isocitrate dehydrogenase reactions, and shuttled across compartments by dedicated transporters, making its cytosolic pool a well-positioned control point for redox homeostasis.

The study also builds on a growing appreciation that NADPH metabolism is not uniform across cellular compartments. Mitochondrial NADPH, generated by transhydrogenase and other enzymes, has distinct roles in antioxidant defense and biosynthesis, while nuclear and cytosolic pools feed separate redox circuits. By focusing specifically on the cytosolic compartment and linking it to G6PD flux, the work offers a more precise target than earlier, cruder attempts to boost cellular reduction potential. Fluorescent biosensors that distinguish NADPH from NADH, developed in recent years, made the compartment-specific measurements feasible and are likely to accelerate follow-up studies in other tissues where NADPH balance governs immune function, fat metabolism, and aging.

Important caveats remain before the findings can inform human medicine. The work was conducted in animal models, and the dose, safety, and long-term consequences of chronically elevating cytosolic NADPH are unknown. Excessive NADPH generation has been implicated in other contexts in fueling proliferative signaling and in providing reducing equivalents to NADPH oxidases, which produce the very reactive oxygen species the heart must defend against. The authors and commentators, including Bryce J. Carpenter and Pieterjan Dierickx of the Max Planck Institute for Heart and Lung Research, who wrote an accompanying News and Views analysis, emphasize that the therapeutic window will need careful definition: the goal is the physiological range achieved by exercise, not an unbounded increase. Questions also remain about whether NADPH elevation alone can recapitulate the vascular and neuronal adaptations of exercise or whether it must be paired with other signals.

Even with those qualifications, the study reframes a central question in cardiovascular medicine. If the protective effects of exercise on the heart converge on a measurable metabolite, then patients confined to hospital beds, older adults with frailty, and the vast population that fails to meet physical activity guidelines may one day have access to a therapy that borrows the heart’s own training program. A candidate spermidine derivative that lifts cytosolic NADPH is an early but concrete step along that path, and it signals that the metabolic underpinnings of exercise’s benefits are finally becoming druggable.

Subject of Research: The role of cytosolic NADPH produced by the pentose phosphate pathway in mediating exercise-induced physiological cardiac hypertrophy and protection against ischemia/reperfusion injury.

Article Title: Increasing cytosolic NADPH to mimic exercise

Article References: Increasing cytosolic NADPH to mimic exercise. (n.d.). https://doi.org/10.1038/s42255-026-01580-2

Image Credits: AI Generated

DOI: 10.1038/s42255-026-01580-2

Keywords: NADPH, cardiac hypertrophy, exercise mimicry, pentose phosphate pathway, G6PD, spermidine, ischemia/reperfusion injury, heart failure, cardiac metabolism, antioxidant defense, Nature Metabolism, cardioprotection