Proteomic-Based Detection of Urine Proteins Associated with Acute Renal Allograft Rejection

Abstract

Abstract. At present, the diagnosis of renal allograft rejection requires a renal biopsy. Clinical management of renal transplant patients would be improved by the development of noninvasive markers of rejection that can be measured frequently. This study sought to determine whether such candidate proteins can be detected in urine using mass spectrometry. Four patient groups were rigidly defined on the basis of allograft function, clinical course, and allograft biopsy result: acute clinical rejection group (n ϭ 18), stable transplant group (n ϭ 22), acute tubular necrosis group (n ϭ 5), and recurrent (or de novo) glomerulopathy group (n ϭ 5). Urines collected the day of the allograft biopsy were analyzed by mass spectrometry. As a normal control group, 28 urines from healthy individuals were analyzed the identical manner, as well as 5 urines from non-transplanted patients with lower urinary tract infection. Furthermore, sequential urine analysis was performed in patients in the acute clinical rejection and the stable transplant group. Three prominent peak clusters were found in 17 of 18 patients (94%) with acute rejection episodes, but only in 4 of 22 patients (18%) without clinical and histologic evidence for rejection and in 0 of 28 normal controls (P Ͻ 0.001). In addition, the presence or absence of these peak clusters correlated with the clinicopathologic course in most patients. Acute tubular necrosis, glomerulopathies, lower urinary tract infection, and cytomegalovirus viremia were not confounding variables. In conclusion, proteomic technology together with stringent definition of patient groups can detect urine proteins associated with acute renal allograft rejection. Identification of these proteins may prove useful as non-invasive diagnostic markers for rejection and the development of novel therapeutic agents.

How Can We Measure Immunologic Tolerance in Humans?

“…As an alternative approach, mass spectrometry has been used to quantify the amount of protein that is present in the urine after renal transplantation (74). Individual proteins are identified by their mass-to-charge ratio.…”

Protocol Transplant Biopsies

“…The tests that are needed for this assessment ideally would be noninvasive, allowing for frequent sampling, and be capable of detecting subclinical inflammation with satisfactory sensitivity and specificity. The urine may be the ideal medium to look for candidate tests that may include the products of alloactivated or cytotoxic cells (46), chemokines and cytokines (47,48), the patterns of proteins detected by proteomic techniques (49), or those of low molecular weight metabolites detected by magnetic resonance (50). Detection of subclinical inflammation by these means may allow for the tailoring of the intensity of immunosuppression to the inflammatory status of the graft and result in the reduction of both the incidence of late allograft losses and the unwanted side effects of immunosuppressive therapy.…”

Urine proteomics for the early diagnosis of acute glomerulonephritis: Has the time come?

“…Given the heterogeneity of autoimmune diseases that affect the kidneys, classic renal histology coupled with microarray and proteomic analysis of the blood and the kidneys, and probably more importantly, urine proteomics may allow further classification of the disease and improve prognostication and selection of appropriate therapy (10). Initial studies involving application of urine proteomic analysis in distinguishing patients with acute rejection from patients with stable disease have identified common biomarkers (␤ 2 -microglobulin) with promising performance characteristics (sensitivity, specificity, and positive and negative predictive values) (15,16). Other studies in patients with IgA nephropathy suggest that urine protein patterns allow discrimination of patients with IgA nephropathy from healthy controls and patients with membranous nephropathy; importantly, treatment changes the patterns of protein excretion (17).…”