The most complete urine metabolome to date

Scientists in Canada have constructed the most complete metabolome of human urine to date, specifying more than 3000 metabolites from a combination of experimental and literature studies. The resulting Urine Metabolome Database is freely available, listing not only the metaboilites and their concentration values, but linking them to diseases and clinical data as well as information in other databases.

The methodology behind this project is described in PLoS ONE. In the first instance, the team carried out a comprehensive literature review which identified 2206 compounds and was used to decide the subsequent experimental methods. A combination of six methods led to a broader set of identified urinary metabolites than any one method alone.

So, NMR spectroscopy identified and measured 208 compounds (108 unique to this method), GC/MS gave 179 (89 unique), direct flow injection-LC/MS/MS gave 127 (98 unique), ICPMS gave 40 (40 unique), HPLC-UV gave 6 compounds (6 unique) and HPLC with fluorescence detection gave 4 compounds (3 unique). This led to a further 445 compounds identified, of which 378 were measured and 53 were reported for the first time as normal urinary components.

The overall total number of metabolites in the database is 2651, which corresponds to 3079 metabolites with precisely defined structures. This is by far the largest metabolome definition so far but it is by no means complete. "This is certainly not the final word on the chemical composition of urine. As new techniques are developed and as more sensitive instruments are produced, I am sure that hundreds more urinary compounds will be identified. In fact, new compounds are being added to the UMDB almost every day," said David Wishart who was involved in the study and supports the database.