Urine proteins from calcium oxalate stone patients actively promote crystal formation in vitro, while healthy urine proteins inhibit it — with ~2.5x more oxidized proteins driving the difference.
Journal: Journal of Advanced Research | Published: 2025-05-23 | Type: Journal Article (in vitro proteomics) | PMID: 40414344 Authors: Hadpech S, Peerapen P, Chaiyarit S, Sritippayawan S, Thongboonkerd V — Medical Proteomics Unit and Division of Nephrology, Siriraj Hospital, Mahidol University, Bangkok Funding/COI: Funding not disclosed. Authors declare no competing interests.
Urine proteins from CaOx kidney stone patients don't just fail to prevent crystal formation — they actively accelerate it. This in vitro proteomics study found that the urinary proteome of stone formers promoted calcium oxalate crystallization, growth, and aggregation, while healthy urine proteome inhibited all three. The key difference: stone formers' urine contained roughly 2.5 times more oxidatively modified proteins, with methionine oxidation as the dominant modification.
This is a well-executed mechanistic proteomics study with clear in vitro methodology. Proteomic identification used high-sensitivity mass spectrometry (Orbitrap), and findings were independently validated by ELISA on individual samples rather than relying solely on pooled proteomics. Crystal assays measured size, number, and mass across three conditions with triplicate independent experiments, which is appropriate for this type of work.
However, there is a significant confound baked into the design: healthy controls averaged 26.1 ± 2.9 years old, while stone formers averaged 44.9 ± 11.2 years — an 18-year age gap. Oxidative protein modifications accumulate with age. The paper does not address or adjust for this, which means age could explain some or all of the difference in oxidized protein burden. The study also uses pooled urine for proteomics, which obscures individual variability, and sample sizes are small (40 healthy, 37 patients).
The core finding is biologically interesting — that the urinary proteome isn't just a passive bystander in stone formation but may actively modulate crystallization — and the proteomics methodology is solid. The problem is the glaring age confound: you cannot conclude that stone disease causes elevated oxidized proteins when your patient group is 19 years older on average. A matched-cohort design would substantially strengthen this. For now, this is useful as a mechanistic hypothesis-generator, not evidence that oxidized proteins are a clinical risk factor for kidney stones.