Urine—an untapped goldmine for biomarker discovery?

The past decade witnessed a few biomarkers discovered and validated;however,biomarker research as a whole has not been fruitful as expected.A majority of our efforts has been focused on blood,the dynamic tissue directly connecting every part of the body.Nevertheless,despite all the interest and endeavor spent on it,the blood has failed to deliver sufficient number of clinically valuable biomarkers.Is it possible that we have been barking up the wrong tree?

Changes of proteins induced by anticoagulants can be more sensitively detected in urine than in plasma

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.

Urimem,a membrane that can store urinary proteins simply and economically,makes the large-scale storage of clinical samples possible

By nature,biomarker is the measurable change associated with a physiological or pathophysiological process.Unlike blood which has mechanisms to minimize changes and to keep the internal environment homeostatic,urine is more likely to reflect changes of the body and is a better biomarker source.Because of its potential in biomarker discovery,urinary proteins should be preserved comprehensively as the duration of the patients’corresponding medical records.Here,we propose a method to adsorb urinary proteins onto a membrane we named Urimem.This simple and inexpensive method requires minimal sample handling,uses no organic solvents,and is environmentally friendly.Urine samples were filtered through the membrane,and urinary proteins were adsorbed onto the membrane.The proteins on the membrane were dried and stored in a vacuum bag,which keeps the protein pattern faithfully preserved.The membrane may even permit storage at room temperature for weeks.Using this simple and inexpensive method,it is possible to begin preserving urine samples from all consenting people.Thus,medical research especially biomarker research can be conducted more economically.Even more objective large-scale prospective studies will be possible.This method has the potential to change the landscape of medical research and medical practice.

Applications of urinary proteomics in biomarker discovery

Urine is an important source of biomarkers. This article reviews current advances, major challenges, and future prospects in the field of urinary proteorrfics. Because the practical clinical problem is to distinguish diseases with similar symptoms, merely comparing samples from patients of a particular disease to those of healthy individuals is inadequate for finding biomarkers with sufficient diagnostic power. In addition, the variation of expression levels of urinary proteins among healthy individuals and individuals under different physiological conditions adds to the difficulty in identifying biomarkers. We propose that es- tablishing the natural variation in urinary protein expression among a healthy population can serve as a reference to help iden- tify protein abundance changes that are caused by disease, not by individual variations or physiological changes. We also dis- cuss that comparing protein expression levels between urine and plasma may reveal the physiological function of the kidney and that may facilitate biomarker discovery. Finally, we propose that establishing a data-sharing platform for data collection and integrating results from all urinary biomarker studies will help promote the development of urinary proteomics.