An In-Depth Glycosylation Assay for Urinary Prostate-Specific Antigen

Abstract

The concentration of prostate-specific antigen (PSA) in serum is used as an early detection method of prostate cancer (PCa); however, it shows low sensitivity, specificity, and a poor predictive value. Initial studies suggested the glycosylation of PSA to be a promising marker for a more specific yet noninvasive PCa diagnosis. Recent studies on the molecular features of PSA glycosylation (such as antenna modification and core fucosylation) were not successful in demonstrating its potential for an improved PCa diagnosis, probably due to the lack of analytical sensitivity and specificity of the applied assays. In this study, we established for the first time a high-performance PSA Glycomics Assay (PGA), allowing differentiation of α2,6- and α2,3-sialylated isomers, the latter one being suggested to be a hallmark of aggressive types of cancer. After affinity purification from urine and tryptic digestion, PSA samples were analyzed by CE-ESI-MS (capillary electrophoresis–electrospray ionization coupled to mass spectrometry). Based on positive controls, an average interday relative standard deviation of 14% for 41 N-glycopeptides was found. The assay was further verified by analyzing PSA captured from patients’ urine samples. A total of 67 N-glycopeptides were identified from the PSA pooled from the patients. In summary, the first PGA successfully established in this study allows an in-depth relative quantitation of PSA glycoforms from urine. The PGA is a promising tool for the determination of potential glycomic biomarkers for the differentiation between aggressive PCa, indolent PCa, and benign prostate hyperplasia in larger cohort studies.

Towards structure-focused glycoproteomics

“…Furthermore, isomeric α2,3- and α2,6-sialoglycopeptides possess different electrophoretic mobilities facilitating their separation using capillary electrophoresis (CE)-ESI-MS [ 185 , 186 ]. Recent improvements in the CE hyphenation methods have increased the sensitivity and reproducibility of glycopeptide analysis by CE-MS [ 187 , 188 ] and opened interesting avenues for CE-based glycoproteomics [ 189 ].…”

Recent advances in capillary electrophoresis‐mass spectrometry: Instrumentation, methodology and applications

“…. Later, a glycosylation assay for PSA analysis in urine was developed by the same group, based on a similar CE method in combination with dopant (ACN) enriched nitrogen gas to enhance sensitivity . In addition, the Dovichi group observed an improved resolution of different N ‐glycopeptide species with the same peptide sequence, especially if differentially sialylated, compared to RPLC .…”

Proteoform Analysis to Fulfill Unmet Clinical Needs and Reach Global Standardization of Protein Measurands in Clinical Chemistry Proteomics

“…Aiming for an improved PSA test, glycosylation of PSA has recently been described based on glycopeptide analysis, in which a total of 67 N-glycopeptides (proteoforms!) were identified [56]. Here it was concluded that PSA proteoform profiling might be a promising tool for the determination of potential glycomic biomarkers for the differentiation between aggressive PCa, indolent PCa and benign prostate hyperplasia in larger cohort studies.…”