Proteomic analysis of inhibitory protein profiles in the urine of children with nephrolithiasis: implication for disease prevention

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International urology and nephrology


PURPOSE: In this study we aimed to screen for the presence of biomarkers that are downregulated in children with nephrolithiasis (RS) compared to healthy controls (HC) using a proteomic approach. We hypothesized that RS and HC would display unique inhibitory protein profiles that could be used for comparative pathway analysis.

METHODS: This is a prospective, controlled, pilot study of pooled urine from RS (N = 30, 24 females, mean age 12.95 ± 4.03 years) versus age- and gender-matched HC, using liquid chromatography-mass spectrometry. The criteria for protein selection were: (1) patient/control abundance ratio of < 0.5; and (2) ≤ 0.05 p-value for the Fisher's Exact Test. Results were confirmed by ELISA testing in individual samples.

RESULTS: 67 proteins were downregulated in RS group, and 17 of those were significantly different compared to controls. Of those seventeen proteins, five (two actins, annexin A5, keratin 6B, and serpin B4) were completely absent in the urine of stone patients but were found in controls. The remaining twelve proteins were significantly less abundant in the patient's urine compared to healthy controls. Protein-protein interaction modeling of significant proteins identified syndecan-1 as the key node, a protein associated with adhesion pathways. ELISA analysis by subgroups showed statistically significant difference in the urinary excretion of osteopontin (5.1 ± 3.22 ng/mg creatinine vs 14.1 ± 9.5 ng/mg creatinine, p = 0.046) between stone patients with hypocitraturia and controls. Urinary osteopontin concentration was positively correlated with urinary citrate excretion (r = 0.417, p = 0.03).

CONCLUSIONS: Children with RS have a different urinary inhibitory polypeptide profile compared to HC. Decreased urinary excretion of these proteins indicates their potential inhibitory role in renal stone formation, especially of the adhesion phase. Lower concentration of urinary osteopontin in children with nephrolithiasis and hypocitraturia suggests its potential involvement in the pathogenesis of this disease. Further characterization of these proteins in a larger sample is imperative.

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ePub ahead of print