Urinary vitamin D-binding protein as a marker of ovarian reserve

Ovarian reserve reflects the quality and quantity of available oocytes and has become an indispensable measure for the better understanding of reproductive potential. Proteomic approaches are especially helpful in discerning differential protein expression patterns associated with normal and diseased states and, thus, proteomic analyses are increasingly used to identify clinically useful biomarkers. The aim of this study was to investigate proteins secreted in the urine of patients with different ovarian reserve by proteomic techniques to identify potential markers for assessing ovarian reserve.

Urine samples were obtained from patients with polycystic ovary syndrome (PCOS) and diminished ovarian reserve (DOR), and from normal control (NC)participants. We used isobaric tags for relative and absolute quantification (iTRAQ) technology combined with mass spectrometry analysis to identify candidate urinary proteins in the three groups. The selected proteins were confirmed using western blot analysis and enzyme-linked immunosorbent assay (ELISA). Diagnostic performance of the selected proteins was assessed using receiver operating characteristic analysis.

When Compared with NC samples, 285 differentially expressed proteins (DEPs) were identified in the DOR samples and 372 in the PCOS samples. By analyzing the intersection of the two groups of DEPs, we found 26 proteins with different expression trends in the DOR and PCOS groups. Vitamin D-binding protein (VDBP) was the key protein for the protein-protein interaction network. ELISA quantification of urinary VDBP revealed the highest levels in the PCOS group, followed by the NC group and the lowest levels in the DOR group (115.90 ± 26.02, 81.86 ± 23.92 and 52.84 ± 21.37 ng/ml, respectively; P < 0.05). As a diagnostic marker, VDBP had a sensitivity of 67.4% and a specificity of 91.8% for DOR, and a sensitivity of 93.8% and a specificity of 77.6% for PCOS.

Urinary VDBP is closely associated with ovarian reserve and can be considered as a novel noninvasive biomarker of ovarian reserve. However, studies including large sample sizes are needed to validate these results.