Vitamin D-Binding Protein Is a Potential Urinary Biomarker of Irbesartan Treatment Response in Patients with IgA Nephropathy

Aims: The purpose of this study was to identify predictive markers of irbesartan (an angiotensin receptor blocker) treatment response in immunoglobulin A nephropathy (IgAN) patients. Methods: Urine samples were collected both before and after irbesartan treatment in IgAN patients and compared with urine from healthy volunteers. The total urinary protein produced in 24 h was measured to determine therapeutic response. The urinary proteome was evaluated by two-dimensional gel electrophoresis coupled with MALDI-TOF-MS/MS analysis. Western blotting was used to verify protein expression. A receiver operating characteristic curve was used to evaluate the sensitivity and specificity of candidate biomarkers. Results: Four differentially expressed proteins were identified as vitamin D-binding proteins (VDPs). Western blot showed that urinary VDPs were significantly elevated in nonresponsive versus responsive IgAN patients. The sensitivity, specificity, and accuracy of urinary VDP as a predictive biomarker of irbesartan nonresponsiveness in IgAN were 65%, 85%, and 75%, respectively. Conclusion: Our results revealed that urinary VDP might be a useful biomarker for predicting irbesartan treatment response.