Non-invasive Testing : Mining the Urine Proteome for Biomarker Discovery

Management of human diseases calls for the discovery of improved markers for diagnosis, prognosis, and responsiveness to treatment. The development of proteomic technologies for high-throughput analyses of proteins from bodily fluids has provided means for discovering non-invasive biomarkers to replace invasive tissue biopsies for the diagnosis and follow-up on many diseases. Considering that urine is an easily accessible biofluid rich with proteins derived from the plasma and kidneys, the urine proteome is a useful resource for discovering novel biomarkers to advance non-invasive testing for several diseases. Moreover, urine is stable in its composition when handled properly and is enriched in low molecular weight proteins and peptides that can be directly analysed by mass spectrometry bypassing initial protease digestion steps.¹

Urologic cancers are a major epidemic worldwide and urinary microparticles provide a source for discovering biomarkers for non-invasive testing in bladder cancer patients. Chen et al., used isotopic dimethylation labeling followed by liquid chromatography coupled to a LTQ orbitrap analyzer to discover biomarkers in the urine proteome specific for bladder cancer.² Using this approach they reported significant changes in the concentrations of 24 proteins in the urinary microparticles of bladder cancer patients versus control hernia patients using quantitative MRM (multiple reaction monitoring) analysis. They went on to verify that tumor-associated calcium-signal transducer 2 (TACSTD2) is a potential diagnostic marker for bladder cancer. The study highlights the significance of urinary microparticles in noninvasive testing of urologic cancer.

In a study led by Loftheim et al., a shotgun proteomics approach was used to identify urinary biomarkers for acute rejection (AR) following renal transplantation.³ State-of-the-art LTQ-Orbitrap analyzers were used to compare the urine proteome from a cohort of renal transplant recipients diagnosed with biopsy-proven acute rejection with that from age-matched controls without clinical manifestation of rejection. A total of 11 proteins, categorized as growth-factor proteins or immune-response proteins, were reported to be upregulated in AR patients several days prior to the appearance of clinical symptoms, whereas no regulation was observed in the control group. The clinical relevance of this discovery requires additional validation with regards to its application in clinical AR diagnosis but is a fine example to demonstrate that the urine proteome is a valuable matrix for developing noninvasive testing tools.

Contemporary technologies have made urinary proteomics a promising tool for discovering noninvasive biomarkers for cancer and other diseases. Future clinical validation of newly discovered urine biomarkers will bring scientists closer to replacing invasive tests with noninvasive biomarkers.

References

1. Pejcic, M., et al. (2010) ‘Urinary proteomics-a tool for biomarker discovery‘, Renal Failure, 32 (2), (pp. 259-268)

2. Chen, C.-L., et al. (2012) ‘Comparative and targeted proteomic analyses of urinary microparticles from bladder cancer and hernia patients‘, Journal of Proteome Research, 11 (12), (pp. 5611-5629)

3. Loftheim, H., et al. (2012) ‘Urinary proteomic shotgun approach for identification of potential acute rejection biomarkers in renal transplant recipients‘, Transplantation Research, 1 (1), (pp. 1-9)