Supplementary Material for: Uromodulin and α1-Antitrypsin Urinary Peptide Analysis to Differentiate Glomerular Kidney Diseases

Background/Aims: Glomerular kidney disease (GKD) is suspected in patients based on proteinuria, but its diagnosis relies primarily on renal biopsy. We used urine peptide profiling as a noninvasive means to link GKD-associated changes to each glomerular entity. Methods: Urinary peptide profiles of 60 biopsy-proven glomerular patients and 14 controls were analyzed by combining magnetic bead peptide enrichment, MALDI-TOF MS analysis, and ClinProTools v2.0 to select differential peptides. Tentative identification of the differential peptides was carried out by HPLC-MS/MS. Results: The HPLC-MS/MS results suggest that uromodulin (UMOD; m/z: 1682, 1898 and 1913) and α₁-antitrypsin (A1AT; m/z: 1945, 2392 and 2505) are differentially expressed urinary peptides that distinguish between GKD patients and healthy subjects. Low UMOD and high A1AT peptide abundance was observed in 80–92% of patients with GKD. Proliferative forms of GKD were distinguished from nonproliferative forms, based on a combination of UMOD and A1AT peptides. Nonproliferative forms correlated with higher A1AT peptide levels – focal segmental glomerulosclerosis was linked more closely to high levels of the m/z 1945 peptide than minimal change disease. Conclusion: We describe a workflow – urinary peptide profiling coupled with histological findings – that can be used to distinguish GKD accurately and noninvasively, particularly its nonproliferative forms.