DKK3 as a Biomarker of Peritoneal Fibrosis in Peritoneal Dialysis Patients

Overview

Peritoneal dialysis (PD) uses the peritoneal membrane as a natural filter to remove waste products from the blood in patients with kidney failure. Over time, the peritoneal membrane can become scarred and less functional - a process called peritoneal fibrosis - which eventually leads to ultrafiltration failure and loss of the PD technique. Currently, there is no reliable early biomarker to detect this process before it causes clinical problems. PERIMARK is a prospective, single-center, observational study investigating whether DKK3 (Dickkopf-3), a protein involved in fibrosis signaling, can serve as an early biomarker of peritoneal membrane deterioration. DKK3 will be measured in urine, peritoneal dialysate and serum at four time points over 12 months (T0: catheter insertion; T1: 12 weeks; T2: 6 months; T3: 12 months). At each follow-up visit, peritoneal membrane function will be assessed by the Modified Peritoneal Equilibration Test (Modified PET) with 3.86% glucose, measuring the sodium dip (ΔDNa) as a marker of aquaporin-1-mediated water transport and D/P creatinine as a marker of small solute transport. The primary endpoint is the intraindividual change in DKK3/creatinine ratio in urine, dialysate and serum from baseline to 12 months. Secondary endpoints include the correlation of DKK3 with the sodium dip, longitudinal changes in peritoneal transport parameters, and the exploratory question of whether an early DKK3 rise predicts a later decline in aquaporin-1 function. The study also includes a biobank of serum, urine, dialysate supernatant and cell pellets for possible future analyses. Target enrollment is 25-30 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.