Podocyturia as an early diagnostic marker of preeclampsia: a literature review

Potential urinary biomarkers in preeclampsia: a narrative review

INTRODUCTION

Preeclampsia (PE) is a highly relevant pregnancy-related disorder. An early and accurate diagnosis is crucial to prevent major maternal and neonatal complications and mortality. Due to the association of kidney dysfunction with the pathophysiology of the disease, urine samples have the potential to provide biomarkers for PE prediction, being minimally invasive and easy to perform. Therefore, searching for novel biomarkers may improve outcomes. This narrative review aimed to summarize the scientific literature about the traditional and potential urinary biomarkers in PE and to investigate their applicability to screen and diagnose the disorder.

METHODS

A non-systematic search was performed in PubMed/MEDLINE, Scopus, and SciELO databases.

RESULTS

There is significant divergence in the literature regarding traditionally used serum markers creatinine, cystatin C, and albuminuria, accuracy in PE prediction. As for the potential renal biomarkers investigated, including vascular epithelial growth factor (VEGF), placental growth factor (PlGF), and soluble fms-like tyrosine kinase (sFlt-1), urinary levels of PlGF and sFtl-1/PlGF ratio in urine seem to be the most promising as screening tests. The assessment of the global load of misfolded proteins through urinary congophilia, podocyturia, and nephrinuria has also shown potential for screening and diagnosis. Studies regarding the use of proteomics and metabolomics have shown good accuracy, sensitivity, and specificity for predicting the development and severity of PE.

CONCLUSION

However, there are still many divergences in the literature, which requires future and more conclusive research to confirm the predictive role of urinary biomarkers in pregnant women with PE.

Peptide Charge Derivatization as a Tool for Early Detection of Preeclampsia by Mass Spectrometry-A Comparison with the ELISA Test

Early detection of any preeclampsia biomarkers may lower the risk of mortality, both for a mother and a child. Our study focuses on techniques for preeclampsia biomarker identification by comparing the results of a method using liquid chromatography mass spectrometry in multiple reaction monitoring mode (LC-MS/MS) with those by the enzyme-linked immunosorbent assay (ELISA) test, as well as by comparing the obtained results with clinical data. In the proposed LC-MS/MS method a tryptic digest peptide charge derivatization strategy was used as a tool for sensitive detection of podocin, i.e., a previously discovered preeclampsia biomarker present in urine samples from pregnant women. Urine samples from pregnant women with diagnosed preeclampsia were collected at different stages of pregnancy and from healthy subjects, and then were analyzed by ELISA test and the proposed method with LC-MS/MS. Charge derivatization of the ε amino group of C-terminal lysine residues in tryptic digests by 2,4,6-triphenylpyrylium salt was performed to increase the ionization efficiency in the LC-MS/MS mode. Podocin was identified at the early stage of pregnancy, while its detection using an ELISA test was not possible. The protocol for urine sample preparation was optimized. Our results show that the proposed method by LC-MS/MS in combination with peptide charge derivatization, provides an ultrasensitive tool for diagnosis of preeclampsia, and provides earlier detection than a clinical diagnosis or ELISA test. The proposed solution may revolutionize medical diagnostics.

Detection of Podocin in Human Urine Sediment Samples by Charge Derivatization and LC-MS-MRM Method

Detection of podocytes in urine might serve as a useful diagnostic tool in both primary and secondary glomerular diseases. The utility of podocyturia has been confirmed for both pre-eclampsia and glomerulonephritis. Here, we present a new and sensitive method for qualitative LC-MS-multiple-reaction-monitoring (MRM) analysis of podocin, serving as a podocyturia biomarker in urine sediments. The following podocin tryptic peptides with the ¹⁶⁹LQTLEIPFHEIVTK¹⁸², ²¹³AVQFLVQTTMK²²³, ²⁴⁰SIAQDAK²⁴⁶, and ²⁹²MIAAEAEK²⁹⁹ sequences were applied as a model. The selective chemical derivatization of the ε amino group of C-terminal lysine residue in tryptic peptides, by 2,4,6-triphenylpyrylium salt (TPP) as a fixed charge tag, was employed to increase the ionization efficiency, in routine ESI-MS analysis. Additionally, the generation of a reporter ion, in the form of a protonated 2,4,6-triphenylpyridinium cation, makes the derivatized peptide analysis in the MRM mode unambiguous. Identification of derivatized and non-derivatized peptides were performed, and the obtained results suggest that the peptide with the ²⁹²MIAAEAEK²⁹⁹ sequence may serve as a marker of podocyturia.

Enrichment of Cysteine-Containing Peptide by On-Resin Capturing and Fixed Charge Tag Derivatization for Sensitive ESI-MS Detection

High complexity of cell and tissue proteomes limits the investigation of proteomic biomarkers. Therefore, the methods of enrichment of some chemical groups of peptides including thiopeptides are important tools that may facilitate the proteomic analysis by reducing sample complexity and increasing proteome coverage. Here, we present a new method of cysteine-containing tryptic peptide enrichment using commercially available TentaGel R RAM resin modified by the linker containing the maleimide group, allowing thiol conjugation. The captured tryptic peptides containing lysine residue were then tagged by 2,4,6-triphenylpyrylium salt to form 2,4,6-triphenylpyridinium derivatives, which increases the ionization efficiency during mass spectrometry analysis. This makes it possible to conduct an ultrasensitive analysis of the trace amount of compounds. The proposed strategy was successfully applied in the enrichment of model tryptic podocin peptide and podocin tryptic digest.

Early Detection of Active Glomerular Lesions in Dogs and Cats Using Podocin

In veterinary medicine, sensitive and specific markers of the early stages of renal failure still remain to be established. Podocytes could be a promising diagnostic tool in veterinary nephrology, especially in the differentiation of active pathological disease and glomerulopathies. Podocin is one of the robust proteins exploitable in detection of podocyturia. This article presents podocyte detection in urine for diagnostic purposes in veterinary medicine using a variety of methods. We describe the advantages and disadvantages of the immunohistochemical technique currently used, and of scanning microscopy, chromatography, and immunostaining. The identification of podocin-positive cells is a promising diagnostic tool in the detection of the early stages of glomerular basement membrane damage. The detection of renal failure prior to the occurrence of azotaemia is of high clinical importance from the clinical and scientific points of view.

Evaluation of Tryptic Podocin Peptide in Urine Sediment Using LC-MS-MRM Method as a Potential Biomarker of Glomerular Injury in Dogs with Clinical Signs of Renal and Cardiac Disorders

The early asymptomatic stage of glomerular injury is a diagnostic challenge in the course of renal and extra-renal disease, e.g., heart insufficiency. It was found that podocin, a podocyte-specific protein present in the urine, may serve as a biomarker in the diagnosis of glomerular disease in humans and animals including glomerulonephritis, glomerulosclerosis, amyloidosis, or nephropathy. Therefore, there is a need of development of the sensitive and straightforward method of urinary podocin identification. In this work, we report our extended research under the glomerular injury investigation in dogs by application of clinical examination and LC-MS-MRM method in the identification of canine podocin in urine samples. The LC-MS-MRM method is based on the identification of podocin tryptic peptide with the ²¹⁸H-AAEILAATPAAVQLR-OH²³² sequence. The model peptide was characterized by the highest ionization efficiency of all the proposed model podocin tryptic peptides in a canine urine sediment according to the LC-MS/MS analysis. The obtained results revealed the presence of the model peptide in 40.9% of dogs with MMVD (active glomerular injury secondary to heart disease = cardiorenal syndrome-CRS) and 33.3% dogs with chronic kidney disease. The potential applicability of the developed methodology in the analysis of podocin in canine urine sediments was confirmed.

Association of vascular endothelial growth factor and renal thrombotic microangiopathy-like lesions in patients with Castleman's disease

AIM

Renal thrombotic microangiopathy (TMA) is a common pathological manifestation of Castleman's disease (CD)-associated renal lesions. Increased level of plasma vascular endothelial growth factor (VEGF) has been shown in single-case reports. We aimed to investigate the dysregulation of VEGF in the pathogenesis of CD-associated TMA-like lesions (CD-TMA) in a larger cohort.

METHODS

Nineteen patients with clinico-pathologically diagnosed CD with renal involvement were enrolled. Ten patients with pregnancy TMA or TMA of unknown reasons were enrolled as TMA control group. The plasma levels of VEGF, soluble Flt-1 and interleukin-6 (IL-6) were detected using enzyme-linked immunosorbent assay kits. The expression of VEGF in the kidney biopsied tissue sections and the lymph node specimens were detected by immunostaining.

RESULTS

The plasma levels of VEGF and IL-6 levels were the highest in CD-TMA group compared to TMA control group and healthy controls. The levels of plasma VEGF was positively correlated with that of IL-6, and increased expression of VEGF and IL-6 was also observed in the lymph nodes from CD-TMA patients. However, the expression of VEGF in the glomerular podocytes was significantly decreased in CD-TMA group as well as in the TMA control.

CONCLUSION

Our findings suggest that renal VEGF expression might be important in the pathogenetic mechanism of CD-associated TMA-like lesions.