DKK3 as a Biomarker of Peritoneal Fibrosis in Peritoneal Dialysis Patients

Background: Peritoneal fibrosis is the main limiting factor for long-term peritoneal dialysis. The underlying mechanism is mesothelial-to-mesenchymal transition (MMT), driven by TGF-β1 and the Wnt/β-catenin pathway. DKK3 is a profibrotically active glycoprotein acting as an amplifier in this network. The only published study of DKK3 in PD dialysate (Ehleiter et al., BMC Nephrology 2024, n=29) demonstrated measurable DKK3 levels and called for longitudinal follow-up studies. No prospective 12-month longitudinal study exists.

Study Design: Prospective, monocentric, non-interventional, exploratory cohort study with biobanking. No randomization, no blinding, no intervention. All treatment decisions remain with the treating physician.

Time Points:

T0 (Day 0): PD catheter insertion. Baseline blood and urine sampling. Initial peritoneal lavage sample for dialysate DKK3 baseline.

T1 (12 weeks / ~90 days): First Modified PET. Blood, urine and dialysate sampling. Combined with catheter quality control assessment.

T2 (6 months): Second Modified PET. Blood, urine and dialysate sampling. T3 (12 months): Third Modified PET. Blood, urine and dialysate sampling. Primary endpoint time point.

T30 (30 days): Telephone interview for catheter complication assessment only.

Modified PET Method: Performed according to La Milia et al. (Kidney Int 2006; DOI: 10.1038/sj.ki.5000183) using 2L of 3.86% glucose solution. Key parameters: sodium dip (ΔDNa at 60 min, reference value 8.4 ± 3.8 mmol/L) as aquaporin-1 marker, D/P creatinine at 240 min for transporter classification, and net ultrafiltration by weighing.

Biobanking: Dialysate samples are centrifuged at 400×g, 4°C, 10 minutes. Supernatant is stored at -80°C for DKK3 ELISA and future biomarker analyses. Cell pellets are cryopreserved in CryoStor CS10 at -196°C for possible future single-nucleus RNA sequencing or proteomics. Serum and urine aliquots are stored at -80°C.

DKK3 Measurement: Human DKK3 ELISA ReFine (by DiaRen). Dialysate samples diluted 1:50 in kit sample buffer prior to measurement (validated by spike-recovery: ~102% at 1:50 dilution). Creatinine in dialysate measured by enzymatic method (Jaffé method excluded due to glucose interference validated internally). Sodium measured by indirect ISE (COBAS); no correction formula required as validated internally.

Statistical Analysis: Exploratory study, no confirmatory hypothesis testing. Wilcoxon signed-rank test for paired comparisons, Spearman correlation for association analyses. No correction for multiple testing. Separate analysis of intention-to-treat and per-protocol populations. Urinary DKK3 evaluated only in patients with residual renal function >0 ml/24h.

Inclusion criteria

• Age ≥18 years
• End-stage renal disease with decision for peritoneal dialysis
• PD catheter insertion at Department of Internal Medicine IV, Saarland University Medical Center
• Written informed consent obtained at least 24 hours before the first study procedure

Exclusion criteria

• Age <18 years
• Lack of capacity to give informed consent
• Pregnancy or breastfeeding
• Active malignancy (except basal cell carcinoma of the skin)
• Active peritonitis at time of inclusion
• Life expectancy <12 months as assessed by the treating physician
• Severe peritoneal adhesions precluding PD catheter insertion (intraoperative assessment)