Temporal stability of the urinary proteome after kidney transplant: More sensitive than protein composition?

The temporal urinary proteome was examined in 4 groups of individuals in order to determine the temporal stability of diverse individuals with apparently good kidney health. The groups consisted of (1) healthy volunteers at zero time, 1 and 6 months, (2) kidney donors before and after surgery, (3) recipients immediately after surgery, and (4) successful kidney transplant recipients from 1 month to 4 years after transplant. Proteins were detected by reverse phase extraction of urine followed by MALDI- TOF profile and by iTRAQ analysis. Unusual components of the MALDI-TOF profiles found only in transplant subjects occurred at mlz = 3370, 3441 and 3385 (human neutrophil defensins), 4303,10350, and 11732 (β-2 microglobulin, B2M). The peaks at mlz = 4303 and 11732 were also quite intense among kidney donors following surgery. The peaks at mlz = 4303 and 10350 in transplant recipients were associated with higher serum creatinine. Several additional proteins detected by iTRAQ were up-regulated in a manner that correlated closely with B2M. Overall, despite large differences between protein composition in different transplant recipients, there was remarkable stability for each individual as detected by either MALDI-TOF or iTRAQ analyses. These results suggested that, within limits, stability of profile components may be as important as protein content for definition of kidney health. Longitudinal study of urinary proteins from kidney recipients may demonstrate instability as a sensitive biomarker of adverse kidney health.