Urine proteomic analysis: use of two-dimensional gel electrophoresis, isotope coded affinity tags, and capillary electrophoresis.

The identities and abundance levels of proteins excreted in urine are not only key indicators of diseases associated with renal function but are also indicators of the overall health of individuals. Urine specimens are readily available and provide a noninvasive means to assess and diagnose many disease states. Proteins in urine originate from two sources: the ultrafiltrate of plasma, and those that are shed from the urinary tract. The protein concentration in urine excreted from a normal adult is approximately 150 mg/day, and is typically not greater than 10 mg/100 mL in any single specimen. Following precipitation, concentration, and fractionation methods, proteins of interest from urine samples can be separated, identified, and quantified. One of the most commonly used techniques in the field of urine proteomics is gel electrophoresis followed by identification with mass spectrometry and protein database search algorithms. In this chapter, two-dimensional gel electrophoresis (2-DE) will be discussed, along with less frequently applied techniques, such as isotope coded affinity tags (ICAT) and capillary electrophoresis (CE). Publications discussing the application of these techniques to urine proteomic analyses of healthy individuals and urinary disease biomarker discovery will also be summarized.