Analysis of urinary kidney-specific cell-free DNA in preeclampsia

To assess the feasibility of a novel methodology for quantifying kidney-specific cell-free DNA (ks-cfDNA) and explore whether levels differed between individuals with preeclampsia (PE) and normotensive pregnant controls (NP).

Cell-free DNA (cfDNA) is released during cell death and circulates in bodily fluids, including urine. cfDNA quantities reflect the degree of organ injury. As PE is associated with hypertension and kidney injury, we hypothesised that urinary ks-cfDNA would be elevated in PE.

In this single-centre prospective case-control study urine samples were collected from 20 women with PE and 20 NP controls. Digital PCR was used to quantify three kidney-specific epigenetic targets (ks-et): ks-et1 (pan-kidney marker), ks-et2 (renal proximal tubular epithelial cell (RPTEC) and podocyte marker) and ks-et3 (RPTEC marker). The beta-actin gene (ACTB) represented total cfDNA (t-cfDNA).

ks-et2 and ks-et3 were higher in the PE group. Median ks-et2 was 231 copies/mL (IQR 65-383) versus 62 copies/mL (IQR 29-215) in NP controls (P = 0.028). Median ks-et3 was 81 copies/mL (IQR 28-199) in PE versus 20 copies/mL (IQR 9-81) for NP participants (P = 0.047). ks-et1 and t-cfDNA showed non-significant increases in PE. Fractional ks-et quantities normalised to t-cfDNA did not differ between groups. Urinary creatinine levels were higher in the PE group (10.9 mmol/L (IQR 4.1-15.3) versus 3.9 mmol/L (IQR 2.3-5.6), P = 0.005). Urine creatinine demonstrated the highest AUC (0.76, 95% CI 0.59-0.92).

This exploratory study found that quantification of urinary ks-cfDNA was feasible and that absolute quantities of ks-cfDNA markers ks-et2 and ks-et3 were elevated in PE. Consistent with previous studies, urinary creatinine was a good predictor of PE and outperformed ks-cfDNA in discriminating between preeclamptic and normotensive pregnancies. Further studies are needed to determine the clinical utility and predictive ability of ks-cfDNA in PE.