Renal Tubular Dysfunction in Pediatric Urolithiasis: Proteomic Evidence

Abstract

To investigate whether inflammation, oxidation, and tubular injury are present in children with stones (RS) compared with healthy controls (HC) by measuring urinary proteins involved in these processes. Quantitative proteomic comparison of pooled urine from RS (N = 30, 24 females, mean age 12.95 ± 4.03 years) versus age- and gender-matched HC (N = 30), using liquid chromatography-mass spectrometry. Relative protein abundance was estimated using spectral counting. Proteins of interest were selected using the following criteria: (1) ≥5 spectral counts; (2) ≥2-fold difference in spectral counts; and (3) P-value ≤.05 for Fisher's exact test. Of the 1813 proteins identified, 230 met the above criteria, with 163 proteins upregulated in the RS group and 67 upregulated in HC. Functional analysis revealed 19 inflammatory proteins, 5 proteins involved in oxidative stress, and 5 involved in tubular injury. Of those proteins, NADPH-oxidase, a major source of reactive oxygen species, was only found in the RS group, whereas glutathione S-transferase A2, an important antioxidant enzyme, was more abundant in controls. ELISA analysis confirmed statistically significant differences in the urinary excretion of retinol-binding protein 4, a marker of proximal tubular dysfunction, between stone patients with hypercalciuria and controls. We provide proteomic evidence of oxidative stress, inflammation, and tubular injury in children with renal stones. We speculate that inflammation and changes in the oxidant-antioxidant balance may cause tubular damage in these patients. Targeting these proteins may have therapeutic benefits.