Mass spectrometry as a novel method for detection of podocyturia in pre-eclampsia

Podocyturia, i.e. urinary loss of viable podocytes, may serve as a diagnostic tool for pre-eclampsia and as a marker of active renal disease. The current method to detect podocyturia is technically complex, lengthy and requires a high level of expertise for interpretation. The aim of this study was to develop a new technique for the identification of urinary podocytes, based on the detection of podocyte-specific tryptic peptides by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS), which will provide an operator-independent and highly reproducible method. The diagnosis of pre-eclampsia was confirmed in the presence of hypertension (>140/90 mmHg) and proteinuria >0.3 g/24 h urine. The diagnosis of HELLP was confirmed based on the accepted clinical criteria of hemolysis, elevated liver enzymes and low platelet count. Random urine samples within 24 h prior to delivery were collected and centrifuged. One half of the sediment was cultured for 24 h to select for viable cells and then stained with a podocin antibody, followed by a secondary fluorescein isothiocyanate-labeled antibody to identify podocytes. The second half of the pellet was solubilized, digested and analyzed by LC-MS/MS using an internal standard. We have recruited 13 patients with pre-eclampsia and 6 patients with pre-eclampsia/HELLP syndrome. The presence of podocytes was confirmed in all patients by the podocyte culture method. In the respective samples, the presence of a podocin-specific tryptic peptide was confirmed with LC-MS/MS technology. The LC-MS/MS method is a reliable technology for the identification of urinary podocytes, based on the presence of podocyte-specific proteins in the urine.