Soluble Urokinase Plasminogen Activator Receptor and Sirtuin 1 as Biomarkers of Disease Severity and Progression in Children with Chronic Kidney Disease​

Technical Summary: Soluble Urokinase Plasminogen Activator Receptor and Sirtuin 1 as Biomarkers in Pediatric CKD

Problem Statement
Cardiovascular (CV) disease is the leading cause of morbidity and mortality in children with chronic kidney disease (CKD), driven by systemic inflammation, endothelial dysfunction, and premature vascular aging. While Soluble Urokinase Plasminogen Activator Receptor (suPAR) and Sirtuin 1 (SIRT1) are recognized as promising biomarkers for renal and CV pathophysiology in adult populations, their utility in pediatric CKD remains unexplored. Specifically, there is a lack of systematic evaluation regarding whether these biomarkers can distinguish pediatric CKD patients from healthy controls, correlate with CV involvement (arterial stiffness, left ventricular hypertrophy), or indicate disease severity and progression in children.

Methodology
This cross-sectional study was conducted at Ege University Faculty of Medicine involving 49 children with CKD and 20 healthy controls.

• Participants: CKD patients were defined by KDIGO criteria, with staging based on the updated "Bedside" Schwartz equation for estimated GFR (eGFR). Inclusion required at least six months of follow-up and recent completion of hemogram, biochemical analysis, echocardiography, pulse wave velocity (PWV), and augmentation index (AIx) evaluations.
• Biomarker Measurement: Serum levels of suPAR and SIRT1 were quantified using specific Human ELISA kits (Elabscience).
• Clinical Assessments: CV risk factors (hypertension, anemia, hyperparathyroidism, etc.) and CV involvement (arterial stiffness via PWV/AIx and left ventricular mass index [LVMI] via echocardiography) were recorded.
• Statistical Analysis: Data were analyzed using IBM SPSS Statistics 25.0. Comparisons between groups utilized t-tests, Mann-Whitney U, ANOVA, or Kruskal-Wallis tests as appropriate. Correlations were assessed via Spearman rank correlation. Receiver Operating Characteristic (ROC) curve analysis was performed to evaluate diagnostic accuracy (AUC).

Key Results

1. Diagnostic Value: Neither suPAR nor SIRT1 levels differed significantly between the CKD group and healthy controls (suPAR: 2.51 vs. 2.30 ng/mL, p=0.754; SIRT1: 8.01 vs. 9.06 ng/mL, p=0.463). ROC analysis confirmed limited diagnostic utility for distinguishing CKD from health (AUC 0.475 for suPAR; 0.443 for SIRT1).
2. Association with Disease Severity (suPAR): Contrary to the lack of difference between groups, suPAR levels varied significantly across CKD stages (p=0.004). A paradoxical trend was observed where suPAR levels were highest in Stage 2 (3.84 ng/mL) and markedly declined in Stage 5 (0.03 ng/mL). suPAR showed a strong positive correlation with eGFR (r=0.531, p<0.001) and a negative correlation with creatinine (r=-0.390, p=0.014).
3. Association with Disease Progression (SIRT1): SIRT1 levels remained stable across CKD stages and showed no correlation with kidney function parameters. However, in the analysis of disease progression phenotypes, patients with stable kidney function (eGFR ≥ 0) exhibited numerically higher SIRT1 levels (10.06 ng/mL) compared to those with rapid decline (7.47 ng/mL), though this did not reach statistical significance in the three-category analysis (p=0.326).
4. Cardiovascular Correlations: Neither biomarker correlated significantly with arterial stiffness parameters (PWV, AIx) or hypertension status. No significant differences in biomarker levels were found between patients with and without CV risk factors or between early and advanced CKD stages regarding CV involvement, except that patients requiring Kidney Replacement Therapy (KRT) had higher LVMI.

Key Contributions

• First Pediatric Evaluation: This study provides the first comprehensive simultaneous evaluation of suPAR and SIRT1 in a pediatric CKD cohort.
• Reframing suPAR Utility: The study challenges the notion of suPAR as a simple diagnostic marker for CKD presence, instead identifying it as a marker of current disease severity that inversely correlates with disease progression in this specific pediatric cohort (declining as CKD advances).
• SIRT1 as a Potential Adaptive Marker: The findings suggest SIRT1 may function as an indicator of an adaptive cellular response, where higher levels are associated with stable kidney function, potentially offering a protective mechanism against CKD progression.
• Phenotypic Stratification: The lack of correlation between the two biomarkers suggests they reflect distinct pathophysiological pathways (inflammation/endothelial dysfunction vs. cellular adaptation), allowing for potential stratification of patients into distinct phenotypes based on inflammatory burden and adaptive capacity.

Significance and Claims
The authors conclude that while suPAR and SIRT1 lack diagnostic value for distinguishing pediatric CKD from healthy controls, they serve as complementary indicators of disease characteristics. suPAR appears to reflect the current burden of kidney impairment and inflammatory status, while SIRT1 may indicate the capacity for cellular adaptation and stability of kidney function. The study posits that these biomarkers warrant further prospective evaluation to determine their prognostic value. The authors emphasize that the cross-sectional nature of the study and the small sample size are limitations, and that future multicenter studies with serial measurements are necessary to confirm these findings and establish clinical utility in pediatric nephrology.