Calcium oxalate nephrolithiasis: urinary "medium size peptides"analysis using MALDI-TOF mass spectrometry.

OBJECTIVE: Urinary lithiasis is one of the most common benign urological diseases. The pathogenic mechanisms of renal stone formation are complex and not clearly defined. We have studied the urinary protein composition of patients affected by calcium oxalate (CaOx) nephrolithiasis in a range of molecular weight between 1 and 5 kDa (medium size peptides). These molecules seem to have a double role in limiting the crystal adhesion to renal cells and at the same time in facilitating the degradation of crystals once internalised in cells. Their daily excretion is high, approximately 2-7 mg/die, even if studies have reported higher values. Our aim in surveying the urinary peptides was to look for qualitative difference in the medium size range, possible indication of the presence of a biomarker or any predisposing factors in patients affected by calcium oxalate nephrolithiasis. MATERIALS AND METHODS: The urinary protein composition of 17 patients (11 male, 6 female; mean age 45 yrs +/- 14SD) affected by CaOx nephrolithiasis was assessed in comparison with 17 healthy subjects. It was performed a qualitative assay using MALDI-TOF mass spectrometry (MS) in a range of molecular weight between 1 and 5kDa (medium size peptides). RESULTS: No differences were detected in the mass spectrums between patients and control subjects: all peaks overlapped. In addition, the values of peak intensity were comparable in both patient and control subject mass spectrums. CONCLUSIONS: In the range of molecular weight between 1 and 5 kDa, we have not detected significant differences in the urinary composition between stone former patients and healthy subjects. Our results warrant further research in different molecular size peptides.