Urinary vitamin D-binding protein levels are increased in patients with endometriosis

Abstract

Endometriosis, defined as the proliferation of endometrial tissue outside the uterine cavity, is one of the most common benign gynecologic disorders. However, diagnosis of endometriosis can be often confusing since no definite diagnostic biomarker is available, yet. Therefore, at present, direct visualization of the lesion and histologic confirmation through surgical procedures are essential for the definitive diagnosis of endometriosis. The purpose of this study was to investigate the clinical value of proteins secreted in urine in the diagnosis of endometriosis using proteomic analysis. Patients included in the study all underwent laparoscopy for different indications including pelvic masses, pelvic pain, suspicious endometriosis, infertility, and diagnostic evaluation, and only after pathologic confirmation were patients assigned to the endometriosis group. Urine samples were collected into sterile plastic tubes when the bladder was catheterized after induction of anesthesia. Proteomic techniques and mass spectrometry were used to identify proteins secreted in the urine of the patients with and without endometriosis and quantification of identified protein was performed using Western blot and specific commercial sandwich enzyme-linked immunosorbent assays (ELISA). Among 22 protein spots with significantly different expressions in urine of patients with and without endometriosis, vitamin D-binding protein (VDBP) was identified. Western blot analysis showed that the relative density of urinary VDBP was significantly higher in patients with endometriosis than the controls. Quantification of urinary vitamin D-binding protein corrected for creatinine (VDBP-Cr, nanogram per milligram) using ELISA revealed that urinary VDBP-Cr was significantly higher in patients with endometriosis than those without (111.96 ± 74.59 ng/mg Cr vs. 69.90 ± 43.76 ng/mg Cr, P=0.001). When urinary VDBP-Cr was combined with serum CA-125 levels, the diagnostic performance of detecting endometriosis showed sensitivity and specificity of 73.2% and 97.3% with cutoff value of 2755.71. Urinary vitamin D-binding protein levels are increased in patients with endometriosis and may be used as a simple and easily obtained diagnostic biomarker for endometriosis.