Influence of Protein Glycosylation on the Measurement of Soluble Urokinase Plasminogen Activator Receptor.

Background: Elevated concentrations of the glycoprotein soluble urokinase plasminogen activator receptor (suPAR) predict worse cardiovascular disease (CVD) outcomes. However, glycosylation effects on its measurement are unknown.

Methods: Plasma samples were obtained from healthy volunteers (n = 70), patients with and without myocardial infarction (MI) from an acute chest pain cohort (n = 65), and patients with and without acute decompensated heart failure (ADHF) from an acute breathlessness cohort (n = 103). After the addition of either deglycosylation enzymes or a diluent to paired samples from each patient, subsequent measurements for suPAR were undertaken with the suPARnostic assay. Percentage change in concentrations between enzyme-treated and matched nontreated samples was calculated. MI and ADHF discrimination by receiver operating characteristic area under the curve was used to compare performances of nontreated suPAR vs deglycosylated suPAR.

Results: Following deglycosylation, measured suPAR concentrations are increased by a median of 52.8% (from 1.9 to 3.0 ng/mL, P < 0.0001) in healthy subjects. Similar increases for deglycosylated suPAR were observed in MI (53.6%) and non-MI acute chest pain patients (53.3%). Although acutely breathless patients obtained smaller increases in deglycosylated suPAR values than healthy individuals (P < 0.0001), the percentage increase was higher in ADHF (38.6%) compared to non-HF (24.4%, P = 0.002) patients. ADHF discrimination was superior for deglycosylated suPAR than non-treated suPAR (0.850 vs 0.765, P = 0.003), but no differences were observed for MI discrimination (0.485 vs 0.501, P = 0.508).

Conclusions: Glycosylation underestimates suPAR measurement using the suPARnostic assay. Although glycosylation effects varied across patient groups, removal of suPAR glycosylation appears to enhance heart failure discrimination.