Urine proteomics for prediction of disease progression in patients with IgA nephropathy

Abstract

Background: Risk of kidney function decline in immunoglobulin A (IgA) nephropathy (IgAN) is significant and may not be predicted by available clinical and histological tools. To serve this unmet need, we aimed at developing a urinary biomarker-based algorithm that predicts rapid disease progression in IgAN, thus enabling a personalized risk stratification.

Methods: In this multicentre study, urine samples were collected in 209 patients with biopsy-proven IgAN. Progression was defined by tertiles of the annual change of estimated glomerular filtration rate (eGFR) during follow-up. Urine samples were analysed using capillary electrophoresis coupled mass spectrometry. The area under the receiver operating characteristic curve (AUC) was used to evaluate the risk prediction models.

Results: Of the 209 patients, 64% were male. Mean age was 42 years, mean eGFR was 63 mL/min/1.73 m2 and median proteinuria was 1.2 g/day. We identified 237 urine peptides showing significant difference in abundance according to the tertile of eGFR change. These included fragments of apolipoprotein C-III, alpha-1 antitrypsin, different collagens, fibrinogen alpha and beta, titin, haemoglobin subunits, sodium/potassium-transporting ATPase subunit gamma, uromodulin, mucin-2, fractalkine, polymeric Ig receptor and insulin. An algorithm based on these protein fragments (IgAN237) showed a significant added value for the prediction of IgAN progression [AUC 0.89; 95% confidence interval (CI) 0.83-0.95], as compared with the clinical parameters (age, gender, proteinuria, eGFR and mean arterial pressure) alone (0.72; 95% CI 0.64-0.81).

Conclusions: A urinary peptide classifier predicts progressive loss of kidney function in patients with IgAN significantly better than clinical parameters alone.

Keywords: IgAN; biomarker; glomerulonephritis; progression; urine proteomics.

Graphical Abstract

FIGURE 1

Study design of the PERSTIGAN project. (A) We collected urine samples and clinical data from n = 209 patients with biopsy-proven IgAN. Patients were stratified by eGFR slope tertiles based on annual eGFR slope during follow-up. Patients in the highest eGFR slope tertile were defined as non-progressors, and patients in the lowest eGFR slope tertile were defined as progressors (patients in the middle tertile were excluded for biomarker definition and validation). N = 140 patients were randomized into a training set and into a test set in a 2:1 ratio. (B) For the biomarker definition all detected urinary peptides of the training cohort were compared between progressors and non-progressors (left compiled 3D depiction of all peptide signals in the training cohort), resulting in definition of 237 discriminating peptides (right compiled 3D depiction of 237 significant peptide signals in the training cohort). Protein names of the identified significant peptides are shown in the lower right corner.

FIGURE 2

ROC for prediction of IgAN progression by the IgAN237 biomarker panel. (A) n-1 cross-validated training set (n = 94). (B) Test set (n = 46). Light lines: 95% CI.

FIGURE 3

Association of IgAN237 scores with clinical parameters at baseline and during follow-up. (A) Scatter diagram for correlation between IgAN237 score and baseline proteinuria and IgAN237 score and eGFR, respectively. (B) Scatter diagram for correlation of IgAN237 score with eGFR slope and IgAN237 score and last eGFR value, respectively. (C) IgAN237 scores in form of box-and-whisker plot (median, 25–75 percentile) in patients who progressed to ESKD and who did not, *P < 0.05.

FIGURE 4

IgAN237 classification score. IgAN237 score in the progressor (n = 70), intermediate (n = 69) and non-progressor (n = 70) groups, *P < 0.05, **P < 0.001.

FIGURE 5

ROC for prediction of IgAN progression based on clinical characteristics or a combination of clinical characteristics and the IgAN237 biomarker panel in all progressor and non-progressor patients (n = 140). Clinical characteristics were age, gender, eGFR, proteinuria and MAP. Dashed lines: 95% CI.