10 (4) Systolic blood pressure, mm Hg 134 AE 17 136 AE 16 137 AE 19 0.18 Diastolic blood pressure, mm Hg 83 AE 11 83 AE 11 82 AE 11 0.60 Use of antihypertensive medication 187 (84) 197 (89) 208 (92) 0.02 Dietary intake Total energy intake, kcal/d 2259 AE 633 2088 AE 634 2152 AE 587 0.45 Cereals, g/d 187 (147-231) 176 (146-211) 178 (138-212) 0.21 Potatoes, g/d 111 (70-146) 118 (73-166) 122 (76-173) 0.29 Vegetables, g/d 80 (56-116) 80 (48-124) 75 (53-107) 0.54 Fruits, g/d 100 (48-189) 110 (53-197) 104 (39-186) 0.22 Legumes, g/d 29 (14-48) 30 (18-45) 31 (17-43) 0.88 Nuts, g/d 5.

The pathophysiology of late kidney-allograft failure remains complex and poorly understood. Activation of filtered or locally produced complement may contribute to the progression of renal failure through tubular C5b-9 formation. This study aimed to determine urinary properdin and sC5b-9 excretion and assess their association with long-term outcome in renal transplant recipients (RTR).Methods: We measured urinary properdin and soluble C5b-9 in a well-defined cross-sectional cohort of RTR. Urinary specimens were taken from a morning urine portion, and properdin and sC5b-9 were measured using an enzyme-linked-immunosorbent assay (ELISA). Cox proportional hazard regression analyses were used to investigate prospective associations with death-censored graft failure.Results: We included 639 stable RTR at a median [interquartile range] 5.3 (1.8–12.2) years after transplantation. Urinary properdin and sC5b-9 excretion were detectable in 161 (27%) and 102 (17%) RTR, respectively, with a median properdin level of 27.6 (8.6–68.1) ng/mL and a median sC5b-9 level of 5.1 (2.8–12.8) ng/mL. In multivariable-adjusted Cox regression analyses, including adjustment for proteinuria, urinary properdin (HR, 1.12; 95% CI 1.02–1.28; P = 0.008) and sC5b-9 excretion (HR, 1.34; 95% CI 1.10–1.63; P = 0.003) were associated with an increased risk of graft failure. If both urinary properdin and sC5b-9 were detectable, the risk of graft failure was further increased (HR, 3.12; 95% CI 1.69–5.77; P < 0.001).Conclusions: Our findings point toward a potential role for urinary complement activation in the pathogenesis of chronic allograft failure. Urinary properdin and sC5b-9 might be useful biomarkers for complement activation and chronic kidney allograft deterioration, suggesting a potential role for an alternative pathway blockade in RTR.

Introduction: Proteinuria contributes to progression of renal damage, partly by complement activation on proximal tubular epithelial cells. By pattern recognition, properdin has shown to bind to heparan sulfate proteoglycans on tubular epithelium and can initiate the alternative complement pathway (AP). Properdin however, also binds to C3b(Bb) and properdin binding to tubular cells might be influenced by the presence of C3b(Bb) on tubular cells and/or by variability in properdin proteins in vitro. In this study we carefully evaluated the specificity of the properdin-heparan sulfate interaction and whether this interaction could be exploited in order to block alternative complement activation. Methods: Binding of various properdin preparations to proximal tubular epithelial cells (PTEC) and subsequent AP activation was determined in the presence or absence of C3 inhibitor Compstatin and properdin inhibitor Salp20. Heparan sulfate proteoglycan dependency of the pattern recognition of properdin was evaluated on PTEC knocked down for syndecan-1 by shRNA technology. Solid phase binding assays were used to evaluate the effectivity of heparin(oids) and recombinant Salp20 to block the pattern recognition of properdin. Results: Binding of serum-derived and recombinant properdin preparations to PTECs could be dose-dependently inhibited (P < 0.01) and competed off (P < 0.01) by recombinant Salp20 (IC50: ∼125 ng/ml) but not by Compstatin. Subsequent properdin-mediated AP activation on PTECs could be inhibited by Compstatin (P < 0.01) and blocked by recombinant Salp20 (P < 0.05). Syndecan-1 deficiency in PTECs resulted in a ∼75% reduction of properdin binding (P = 0.057). In solid-phase binding assays, properdin binding to C3b could be dose-dependently inhibited by recombinant Salp20> heparin(oid) > C3b. Discussion: In this study we showed that all properdin preparations recognize heparan sulfate/syndecan-1 on PTECs with and without Compstatin C3 blocking Lammerts et al. C3b-Independent Properdin Binding to PTECs conditions. In contrast to Compstatin, recombinant Salp20 prevents heparan sulfate pattern recognition by properdin on PTECs. Both complement inhibitors prevented properdin-mediated C3 activation. Binding of properdin to C3b could also be blocked by heparin(oids) and recombinant Salp20. This work indicates that properdin serves as a docking station for AP activation on PTECs and a Salp20 analog or heparinoids may be viable inhibitors in properdin mediated AP activation.