Background In patients with renal transplant albuminuria is associated with salt-sensitive hypertension. Aberrantly filtered serine proteases e.g. plasmin has shown to activate ENaC through proteolytic cleavage of the γ-subunit with subsequent increased sodium reabsorption and expansion of ECV.This study was designed to address the hypothesis that albuminuria in kidney graft recipients correlated with increased urine serine protease activity, with the ability to activate ENaC, and with expansion of extracellular fluid volume and higher blood pressure.Methods Kidney transplant patients with normoalbuminuria(n=19) and albuminuria(n=18) were included.Blood pressure,spot urine and plasma samples were obtained.Using a bioimpedance device, overhydration(OH) was estimated.Urine samples were analyzed by western blotting for serine proteases.Total u-plasminogen was measured by ELISA. Urine protease activity was confirmed by serine protease assay. Urine exosome protein was immunblotted for AQP2, γENaC and exosomal markers(ALIX). Results Urinary albumin was 1722mg/g creatinine and 8mg/g in the albuminuric and normoalbuminuric patients,respectively.This was associated with a significant difference in systolic blood pressure(146vs128mmHg) diastolic blood pressure(82±2vs75±1mmHg)and numbers of antihypertensive drugs(2,4±0,3vs1,3±0,3) when compared to the normoalbuminuric patients.Densitometry of immunoblots (n=8 in both groups) demonstrated a significantly higher urinary plasmin(ogen),active uPA and prostasin excretion in patients with albuminuria.No significant difference was observed in OH between the groups but OH correlated directly with systolic blood pressure, urinary albumin/creatinine ratio and u-plasminogen/creatinine.Urine-plasminogen correlated with u-albumin.The urine exosome markers ALIX and AQP2 exhibited similar abundance between groups(n=8 in both groups) and γENaC displayed bands at 75 and 50kDa with difference between groups.No intact γENaC was observed in either group compared to human kidney homogenate.Conclusion Albuminuria in kidney transplant patients is associated with increased urinary protease activity,with activated ENaC in exosomes and with increased systolic blood pressure and OH. Data are consistent with a role for proteolytic activation of ENaC by proteases in sodium retention, expansion of ECV and hypertension in kidney transplant patients with albuminuria.

CITATION INFORMATION: Hinrichs G, Bistrup C, Birn H, Jensen B. Albuminuria in Kidney Transplant Patients Is Associated with Increased Urine Serine Proteases with the Ability to Activate ENaC. Am J Transplant. 2017;17 (suppl 3).

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