Optimizing Urine Processing Protocols for Protein and Metabolite Detection

There is significant interest in studying urine proteins and metabolites as potential biomarkers for clinical diseases. Urine serves as an easily accessible biologic fluid that can be accessed usingnoninvasive methods. Urine is proximate to the bladder wall, and also contains renally-cleared systemic compounds and metabolites. Thus urinary biomarkers may be helpful in distinguishing pathologic versus normal biologic processes for renal, genitourinary, and other medical conditions.

In clinically obtained urine samples, multiple factors may introduce variability and affect the predictive value of urine protein and metabolite data. In general, normal (non-proteinuric) urine has low quantities of protein. Some would argue that 1st morning voids, containing the highest protein concentrations, are helpful for proteomic studies. However, logistically there is an obligate time delay when study participants collect their 1st morning void, and factors such as time at room temperature, ongoing protease activity, or bacterial contamination from urethral microbes may affect data quality. Thus prior studies have suggestedcollecting the 2nd morning or other random “spot” urine. However, it remains unclear if the addition of protease inhibitors or bacteriostatic agents may preserve proteins and metabolites in 1st morning samples and facilitate their use. This is relevant since urinary proteomic studies require maximal concentrations of protein from urine with minimal loss.