Introduction: Ureteropelvic junction obstruction (UPJO) particularly represents a challenge in regard to management, as not all hydronephrosis (HN) represent a kidney-damaging state. Urinary biomarkers have been proposed as noninvasive tools. Extracellular matrix (ECM) proteins are associated with tissue fibrosis in the setting of UPJO and is poorly explored.

Objective: To investigate whether urinary ECM proteins are useful to discriminate the severity of urinary obstruction on unilateral UPJO.

Study design: Children with unilateral UPJO were prospective enrolled. Urinary (u) matrix metalloproteinases (MMP-1,-2,-9 and TIMP-1,-2) as well as clinical characteristics were measured in the following groups: 26 children with obstructive HN at initial diagnosis and after six months of dismembered pyeloplasty; 22 children with non-obstructive HN at diagnosis and after six months of observation; 26 children without any urinary tract condition, as the control group. Results were assessed statistically using for homogenous groups, a one-way analysis of variances (ANOVA) and for nonparametric groups, Mann-Whitney test or Kruskal-Wallis test was performed. ROC curves were performed.

Results: Baseline samples demonstrated a higher concentration of uMMP-1/Cr, uMMP-2/Cr, u-TIMP-1/Cr and u-TIMP-2/Cr in obstructive HN group; uMMP-9/Cr levels were higher in non-obstructive HN group and all studied biomarkers had lower concentrations for the control group. On follow-up, for the obstructive HN group, urinary concentration of uTIMP-1/Cr and uTIMP-2/Cr decreased, and uMMP-1/Cr, uMMP-2/Cr and uMMP-9/Cr increased when comparing preoperative to postoperative values. In the non-obstructive HN group, all proteins analyzed were stable after six months of observation. ROC curves analysis showed a promising diagnostic profile for the detection of obstructive HN for uTIMP-1/Cr (area under the curve -AUC-; of 0.692), uTIMP-2/Cr (AUC of 0.678) and for uMMP-2/Cr (AUC of 0.655).

Discussion: The severity of kidney obstruction could correlate with the urinary ECM proteins concentration in this study. This is concordant with prior studies demonstrating that a disruption of the balance of accumulation/degradation of the ECM proteins occur on obstructive uropathy. Limitations of our study include the older age of our patients and that these markers had no influence at all on the surgical decision.

Conclusion: We demonstrate that obstructive HN have significantly higher uMMP-2, uTIMP-1 and uTIMP-2 concentrations. Particularly, uTIMP-2 levels were correlated to severity of obstruction and therefore, it might be a useful urinary biomarker to correctly allocate children with HN between surgical management vs follow-up. After pyeloplasty, uTIMP-1 and uTIMP-2 presented a progressive decrease postoperatively, which is also highly desirable for urinary markers.