Isolation and identification of potential urinary microparticle biomarkers of bladder cancer

Bladder cancer leads to approximately 13 000 deaths annually in the United States. Early disease is often treated with minimal morbidity and has good prognosis, while the opposite is true for advanced disease. Currently, no tools exist for early detection of this cancer. Microparticles are small, subcellular particles released by essentially all cells upon activation and are known to be produced constitutively by cancer cells. Since most bladder cancers originate in the urothelial cells lining the lumen of the organ, we hypothesize that these cells will release microparticles into the urine. The goal of this study was to identify potential biomarkers in the urinary microparticles of individuals with bladder cancer. Urine microparticles from five healthy individuals and four individuals with bladder cancer were isolated. Samples were delipidated by PAGE and trypsin-digested, peptides were extracted, and the proteome was examined by LC-MS/MS using a Thermo Finnigan LTQ and LTQ-FT ion trap mass spectrometer. Protein identification was determined by SEQUEST and relative quantitation was assessed by comparing spectral counts. Eight proteins were elevated in the microparticles from individuals with bladder cancer. They include five proteins associated with the epidermal growth factor receptor pathway, the alpha subunit of GsGTP binding protein, resistin, and retinoic acid-induced protein 3. Further studies will be needed to validate these potential biomarkers.