Biomarker is the measurable change associated with a physiological or pathophysiological process. Unlike blood which has mechanisms to keep the internal environment homeostatic, urine is more likely to reflect changes of the body. As a result, urine is likely to be a better biomarker source than blood. However, since the urinary proteome is affected by many factors, including diuretics, careful evaluation of those effects is necessary if urinary proteomics is used for biomarker discovery. Here, we evaluated the effects of three commonly-used diuretics （furosemide, F; hydrochlorothiazide, H; and spirolactone, S） on the urinary proteome in rats. Urine samples were collected before and after intragastric administration of diuretics at therapeutic doses and the proteomes were analyzed using label-free liquid chromatography-tandem mass spectrometry （LC-MS/MS）. Based on the criteria of P ≤ 0.05, a fold change ≥2, a spectral count ≥ 5, and false positive rate （FDR） ≤1%, 14 proteins （seven for F, five for H, and two for S） were identified by Progenesis LC-MS. The human orthologs of most of these 14 proteins are stable in the healthy human urinary proteome, and ten of them are reported as disease biomarkers. Thus, our results suggest that the effects of diuretics deserve more attention in future urinary protein biomarker studies. Moreover, the distinct effects of diuretics on the urinary proteome may provide clues to the mechanisms of diuretics.
The most fundamental property of biomarkers is change.But changes are hard to maintain in plasma since it is strictly controlled by homeostatic mechanisms of the body.There is no homeostatic mechanism for urine.Besides,urine is partly a filtration of blood,and systematic information can be reflected in urine.We hypothesize that change of blood can be reflected in urine more sensitively.Here we introduce the interference into the blood by two anticoagulants heparin or argatroban.Plasma and urine proteins were profiled by LC-MS/MS and then validated by Western blot in totally six SD female rats before and after the drug treatments.In argatroban treated group,with exactly the same experimental procedure and the same cutoff value for both plasma and urine proteins,62 proteins changed in urine,only one of which changed in plasma.In heparin treated group,27 proteins changed in urine but only three other proteins changed in plasma.Both LC-MS/MS and Western blot analyses demonstrated drug-induced increases in transferrin and hemopexin levels in urine but not in plasma.Our data indicates that urine may serve as a source for more sensitive detection of protein biomarkers than plasma.
