Comprehensive analysis of short peptides in sera from patients with IgA nephropathy

We analyzed serum short peptides comprehensively to know whether they were useful to characterize IgA nephropathy (IgAN). Serum samples from 26 patients with untreated IgAN and 25 healthy donors were tested. Short peptides with molecular weights of approximately 7 kDa, purified from the serum samples by magnetic-beads-based weak cation exchange, were detected by mass spectrometry. Then the peptide peaks detected were subjected to the multivariate data analysis by SIMCA-P+ containing principal component analysis (PCA) and orthogonal partial-least-squares-discriminate analysis (OPLS-DA). A total of 92 peptide peaks were detected in the tested serum samples. The OPLS-DA analysis revealed that the profile of all the peptide peak intensities discriminated the IgAN group and the healthy group completely with a high R2 value (0.919) and a high Q2 value (0.861). Further, the profile of only five peptide peaks was found to discriminate the two groups. By tandem mass spectrometry and database searching, three of the five peptides which increased in the IgAN group were identified as fragments of fibrinogen alpha chain, and the two peptides which increased in the healthy group were identified as fragments of complement C3f and kininogen-1 light chain. Taken together, the profile of the serum short peptides would be useful to discriminate IgAN and healthy conditions. Further, the five peptides may be candidate serum markers for IgAN and may be related to pathogenesis of IgA.