#57 Tubular biomarkers in proteinuric kidney diseases

Abstract Background and Aims Proteinuria is not only a biomarker of chronic kidney disease (CKD) and a risk predictor of adverse outcomes but also a driver of kidney disease progression. The excessive filtration of plasma proteins through the glomerular filtration barrier exerts a toxic effect on tubular cells which ultimately leads to fibrosis and end-stage kidney disease (ESKD. The aim of this study was to assess the levels of various tubular biomarkers in both serum and urine in patients with biopsied glomerular and proteinuric kidney diseases, and correlate them with renal histology and kidney outcomes. Method A retrospective study and observational study was conducted at a single center from January 2016 to December 2021. Serum and urine samples were collected on the same day of renal biopsy and were correlated with histological data from a cohort of 156 patients with proteinuric kidney diseases. Kidney outcomes were registered during a median follow-up period of 26 months and defined as a decrease in eGFR ≥ 40% from baseline or the development of end-stage kidney disease. The following urinary markers, adjusted to urine creatinine, were analyzed: β2-mcg (beta 2 microglobulin), α1-mcg (alpha 1 microglobulin), NGAL (Neutrophil Gelatinase-Associated Lipocalin), uKIM-1 (Kidney Injury Molecule-1), MCP-1 (Monocyte Chemoattractant Protein-1), uDKK-3 (urinary Dickkopf-3), and uUMOD (uromodulin). Serum markers sKIM-1 and uUMOD were also collected.  Results Regarding the etiology of proteinuric kidney disease, the majority corresponded to glomerular disease (68.6%) followed by diabetic kidney disease (12.8%). Higher levels of proteinuria were associated with increased values of β2-mcg and α1-mcg levels and low levels of uUMOD and sUMOD. A significant correlation between the extent of interstitial fibrosis and specific biomarkers was observed: uDKK3 (rho = 0.804, p < 0.001), sKIM-1 (rho = 0.472, p < 0.001), sUMOD (rho = −0.370, p < 0.001), uUMOD (rho = −0.317, p < 0.001), MCP-1 (rho = 0.374, p < 0.001), uKIM-1 (rho = 0.368, p < 0.001), and β2-mcg (rho = 0.392, p < 0.001). Multivariate regression analysis identified uDKK3 as an independent predictor of interstitial fibrosis (Beta 0.728, p < 0.001) adjusted for age, serum creatinine and proteinuria. Elevated levels of MCP-1 and uKIM-1 were associated with a higher risk of significant cortical interstitial inflammation >10% in the logistic regression analysis adjusted for eGFR, proteinuria, and microhematuria: MCP-1 OR = 5.14, 95% CI (2.27−11.62), p < 0.001 and uKIM-1 OR = 1.64, 95% CI (1.05−2.58), p = 0.031. Patients with higher tertiles of β2mcg, MCP1, uDKK3, and KIM1s, and lower tertiles of uUMOD and sUMOD experienced a significantly reduced renal event-free survival in the analysis of Kaplan-Meier model (Fig.). Moreover, of all the evaluated markers, uDKK3 was identified as the best predictor of renal events [HR = 1.03, 95% CI (1.01−1.06), p = 0.008], independently of age, baseline eGFR, proteinuria, and the extent of interstitial fibrosis at the time of renal biopsy. Conclusion Tubular biomarkers may offer prognostic value in proteinuric kidney diseases, particularly uDKK3, exhibiting a notable correlation with interstitial fibrosis and serving as a potential predictor of CKD progression.