Apolipoprotein C-I Levels Are Associated with the Urinary Protein/Urinary Creatinine Ratio in Pediatric Idiopathic Steroid-Sensitive Nephrotic Syndrome: A Case Control Study

Humoral factors may cause idiopathic steroid-sensitive nephrotic syndrome (ISSNS). In the present study, we analyzed serum proteins using mass spectrometry (MS) to identify proteins associated with the pathophysiology of pediatric ISSNS. We collected serial serum samples from 33 children during each ISSNS phase; Phase A1 is the acute phase prior to steroid treatment (STx), Phase A2 represents the remission period with STx, and Phase A3 represents the remission period after completion of STx. Children with normal urinalyses (Group B) and children with a nephrotic syndrome other than ISSNS (Group C) served as controls. No significant differences in urinary protein/urinary creatinine (UP/UCr) ratios were observed between the children with phase A1 ISSNS and Group C. We used surface-enhanced laser desorption/ionization time of flight MS for sample analysis. Four ion peaks with a mass-to-charge ratio (m/z) of 6,444, 6,626, 8,695, and 8,915 were significantly elevated during ISSNS Phase A1 compared to Phase A2, Phase A3, and Group C. The intensity of an m/z of 6,626 significantly correlated with the UP/UCr ratio and an m/z of 6,626 was identified as apolipoprotein C-I (Apo C-I). Apo C-I levels correlate with the UP/UCr ratio in pediatric ISSNS. Our findings provide new insights into the pathophysiology of ISSNS.