[Comparison of methods for enriching urine proteins]

The abundance of proteins in human urine is low and easily to be masked by high-abundance proteins during mass spectrometry analysis. Development of efficient and highly selective enrichment methods is therefore a prerequisite for achieving deep coverage of urine protein markers. Notably, different experimental methods would affect the urine protein enrichment efficacy and the coverage of urine proteome. In this study, ultrafiltration, nitrocellulose membrane enrichment and saturated ammonium sulfate precipitation were used to process 10 mL urine samples from five healthy volunteers and five bladder cancer patients. The urine proteins were enriched and separate by SDS-PAGE to compare the purification efficiency of different methods. Moreover, the peptide identification effects of different purification methods were analyzed by mass spectrometry to determine the best method for enriching urine protein histones. Saturated ammonium sulfate precipitation method outperformed the ultrafiltration and the nitrocellulose membrane enrichment methods in terms of the protein enrichment efficacy and quality. The interference of highly abundant albumin was reduced, whereas the amount of low-abundance protein was increased, and the sensitivity of mass spectrometry identification was increased. The saturated ammonium sulfate precipitation method may be applied for large-scale urine processing for screening clinical diagnostic markers through proteomics.