For the millions living with heart failure with preserved or mildly reduced ejection fraction — a condition notoriously resistant to effective treatment — the neutrophil-MPO inflammatory axis had emerged as a promising therapeutic target. This Phase 2b trial delivers a sobering but scientifically instructive verdict on that hypothesis.
The randomized controlled trial, published in Nature Medicine, evaluated mitiperstat, a selective inhibitor of myeloperoxidase (MPO), in patients with HFpEF or HFmrEF. MPO is a heme enzyme released by activated neutrophils during oxidative inflammatory cascades, and elevated circulating MPO has been associated with cardiac fibrosis, endothelial dysfunction, and worse clinical outcomes in heart failure. Despite this mechanistic rationale, mitiperstat treatment failed to produce statistically meaningful improvements in either symptom burden or exercise capacity compared to placebo across the trial cohort.
This null result carries considerable weight for the field. HFpEF and HFmrEF account for roughly half of all heart failure cases and remain poorly served by the pharmacological toolkit developed for reduced ejection fraction phenotypes. The MPO pathway was attractive precisely because it offered a mechanistically distinct target from neurohormonal blockade — yet the failure here mirrors a broader pattern of promising inflammatory and oxidative targets not translating to clinical benefit in this heterogeneous syndrome. The trial's Phase 2b design and randomized structure lend credibility to the finding, though key questions remain: whether specific subpopulations with confirmed MPO elevation might still respond, whether duration of treatment was sufficient to reverse structural remodeling, and whether endpoint selection fully captured relevant patient-centered outcomes. This result is unlikely to be paradigm-shifting in isolation, but it meaningfully narrows the field of viable anti-inflammatory strategies for HFpEF, redirecting investigative attention toward better patient stratification rather than population-wide enzyme inhibition.