Urinary EGF Receptor Ligand Excretion in Patients with Autosomal Dominant Polycystic Kidney Disease and Response to Tolvaptan

Background and objectives Recent animal experiments suggest that dysregulation of the EGF receptor pathway plays a role in the pathophysiology of autosomal dominant polycystic kidney disease (ADPKD). Research on EGF receptor ligands in humans with ADPKD is lacking. EGF receptor figands were measured in patients with ADPKD at baseline and after treatment with a vasopressin V2 receptor antagonist (V2RA) because this information might provide a rationale for future V2RA combination therapy. Design, setting, participants, & measurements Blood and urine concentrations of the EGF receptor ligands heparin-binding (HB)-EGF, EGF, and TGF-alpha were measured by ELISAs in 27 patients with ADPKD who participated in a single-center study investigating a V2RA in 2011-2013 and in 27 controls who were selected from a general population based observational study. Cyst fluid concentrations were also measured. In patients with ADPKD, ligands were measured at baseline, after 3-week treatment with a V2RA, arid 3 weeks after drug withdrawal. The measured GFR (mGFR) was determined by iothalamate infusion, and total kidney volume was.measured by magnetic resonance imaging. Results Urinary HB-EGF excretion and plasma concentration were higher in patients with ADPKD than in controls (median, 1.4 [interquartile range, 1.2-1.9] versus 0.6 [0.4-0.8] mu g/24 hours [P<0.001] and 157.9 [83.1 225.9] versus 77.2 [37.2-174.3] pg/ml [P=0.04]). In contrast, urinary EGF excretion and plasma EGF concentration were lower in patients with ADPKD, whereas TGF-alpha did not differ between patients and controls. Higher HB-EGF excretion was correlated with more severe disease, assessed as lower mGFR (r=0.39; P=0.05), higher total kidney volume (r=0.39; P=0.05), and higher urinary excretion of albumin and heart-type fatty acid binding protein, whereas higher EGF excretion and TGF-alpha excretion were negatively correlated with disease severity. During V2RA treatment, HB-EGF excretion increased (from 1.4 [1.2-1.9] to 2.4 [2.1-3.1] mu g/24 hours; P<0.001). Conclusion In patients with ADPKD, higher urinary HB-EGF excretion is correlated with more severe disease. Whether this association is causal needs to be investigated in intervention studies.