MO1004IMBALANCE IN URINARY PROTEOGLYCANS AND THE INSULIN GROWTH FACTOR (IGF) AXIS IN CHILDREN WITH NEPHROLITHIASIS*

Abstract

Abstract Background and Aims In vitro experiments have shown that exposure of renal epithelial cells to calcium oxalate crystals leads to synthesis of proteins involved in extracellular matrix (ECM) production. Cell proliferation and accumulation of ECM proteins have been reported in animal models and kidney biopsies from patients with stones. Based on the role of ECM in the Randall plaque formation, we aimed to identify and quantify ECM proteins in the urine of children with nephrolithiasis (RS) using a proteomic approach. Method 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 healthy controls (HC), using liquid chromatography-mass spectrometry (LC-MS/MS). Patient inclusion criteria consisted of age 5-18 years, history of clinically (typical renal colic) and radiographically (ultrasound or CT) proven renal stone, at least two 24-hour satisfactory urine collections (urinary creatinine more than 15 mg/kg/day), absence of hematuria or pyuria, and normal renal function. Children who were not toilet trained, or those with bladder stones, nephrocalcinosis, neuropathic bladder, major congenital bladder abnormality, active urinary tract infection, presence of blood in urine, chronic kidney disease, previous major reconstructive bladder surgery requiring catheterization, and significant cardiac, pulmonary, gastro-intestinal, and neurological problems were excluded. Relative protein abundance was estimated using spectral counting. The criteria for protein selection were: 1) patient/control abundance ratios of >5 or <0.2 as a threshold to be well above observed technical variations in MS experiments; and 2) ≤0.05 p-value for the Fisher’s Exact Test. Results were confirmed by ELISA testing. Statistical analyses were conducted with IBM SPSS® version 20. Results We found 36 (15.7%) ECM proteins out of 229 proteins that met the above criteria. Significant differences between RS and HC were found among two proteoglycans and four insulin growth factor (IGF) proteins (Table). Significant increase in the urinary excretion of IGFBP4 in RS (37.00 ± 37.68 ng/mg creatinine ) versus HC (19.04 ± 20.32 ng/mg creatinine) was confirmed by ELISA (p=0.049). Statistically significant correlation was found between urinary IGFBP4 concentration and 24-hour urinary calcium excretion (p<0.001). Conclusion Alteration in proteoglycans and the IGF axis appears to have a significant role in the mechanism of nephrolithiasis, likely by modulating ECM biosynthesis. Further understanding of their roles in nephrolithiasis may aid in generation of novel therapeutic approaches.