Physiologic changes of urinary proteome by caffeine and excessive water intake

Background: Diurnal variations and physiologic changes of urinary proteome have been suggested in the urinary proteomics field. However, no clear evidence has been demonstrated. The present study thus aimed to define changes in urinary proteome by physiological stimuli, i.e. caffeine intake and excessive water drinking, both of which cause physiologic diuresis. Methods: Urine samples were collected from 30 healthy individuals under three different conditions: (i) morning void as the control; (ii) after drinking a cup of coffee; and (iii) after drinking 1 L of water within 20 min. Thereafter, differentially excreted proteins were analyzed by 2-DE proteomics approach and validated by Western blotting and ELISA. Results: Spot matching, quantitative intensity analysis, and ANOVA followed by Tukey's post-hoc multiple comparisons and the Bonferroni correction revealed significant differences in levels of five protein spots among three different conditions. These proteins were identified by quadrupole time-of-flight mass spectrometry (Q-TOF MS) and/or MS/MS analyses as kininogen 1 isoform 3, beta-actin, prostaglandin D synthase (PGDS), fibrinogen alpha-chain and immunoglobulin light chain. Among these, the decreased level of immunoglobulin was successfully validated by Western blotting and ELISA. Conclusions: These data indicated that caffeine intake and excessive water drinking could affect urinary excretion of some proteins and may affect urinary proteome analysis.