Top-Down Proteomics in the Assessment of Kidney Donor Quality: a novel approach to increased organ utilization

Kidney transplantation faces a critical paradox: while thousands await organs, approximately 30% of potential deceased donor kidneys are discarded for various reasons, including subjective assessments due to the lack of an objective molecular biomarker of preservation quality. Here, we applied novel "top-down" proteoform imaging mass spectrometry across living donor (LD), deceased donor (brain death or cardiac death), and discarded human kidneys to quantify proteoforms correlating with post-transplant kidney function. This approach preserves post-translational modifications and splice variants, revealing molecular tissue variability beyond protein presence. LD kidneys displayed robust metabolic signatures, including L-xylulose reductase and cytochrome oxidase subunits, whereas deceased donor and discarded organs showed elevated cellular stress markers such as alpha-B-crystallin and peroxiredoxin 1. Post-transplant blood proteoform analysis validated tissue findings, demonstrating persistent cellular stress and immune activation in deceased donor recipients compared with physiologic wound healing in LD recipients. Consistent with these molecular predictions, serum creatinine levels were highest in DCD, intermediate in DBD, and lowest in LD recipients. The intersection of tissue proteoform signatures across all marginal tissues identified four proteoforms consistently elevated in deceased and discarded kidneys: ACTG1, acetylated CRYAB, PARK7, and S100A4. Collectively, these proteoforms capture key molecular indicators of graft quality, reflecting oxidative stress, cellular injury, and immune activation pathways. As such, they represent promising point-of-care (POC) biomarker candidates for objective kidney classification, potentially improving donor kidney utilization.