030 - Potential Role for Plasmin Mediated Proteolytic Activation of ENaC in Diuretic Resistance in Heart Failure

Abstract

Background: The amiloride sensitive Epithelial Na + channel (ENaC) plays a major role in regulation of sodium transport in the collecting duct of the kidney. Recent studies have shown that proteolytic cleavage of α and γ subunits by urinary proteases like plasmin play a major role in ENaC activation. Activation of ENaC in collecting tubules is thought to be an important mechanism driving renal Na + retention in several edematous disease states. Our aim was to probe if plasmin mediated ENaC activation is a potential mechanism of diuretic resistance in heart failure. Hypothesis: Increased urinary levels of plasminogen/plasmin will predict poor diuretic response in HF patients receiving loop diuretics. Methods: Heart failure outpatients in the Yale Transition Care Center treated with loop diuretics were prospectively studied (N = 131). Blood and urine chemistries were collected at baseline and at 1 to 1.5 hours post diuretic administration. Diuretic efficiency (DE) was defined as total sodium excreted per doubling of the diuretic dose. Total plasminogen was measured using the ELISA kit from Molecular Innovations (Novi, MI, USA). This assay kit measures both plasminogen and plasmin in biological fluids. Plasmin/plasminogen was indexed to urinary creatinine to correct for changes in urinary dilution. Results: The median dose of diuretic administered was 160 mg (40–280 mg) of furosemide equivalents, which resulted in an average of 987 ± 575 ml of urine and 97.4 ± 71.4 mmol of sodium output. There was good correlation between urinary plasminogen levels prior to and after administration of the loop diuretic (r = 0.74, P < .001), but interestingly plasmin levels increased by 190% ± 307% (P < .0001) with diuretic administration. Higher urinary plasminogen (indexed to urinary creatinine) levels at baseline were correlated with lower DE (r = −0.32, P = .001), as was the increase following administration of diuretics (r = −0.30, P = .004). In line with activation of ENaC, the fractional excretion of potassium at baseline (r = 0.26, P = .014) and post diuretic (r = 0.24, P = .012) was correlated with the corresponding urinary plasminogen concentration. Furthermore, the change in plasminogen was correlated with the post diuretic potassium to sodium ratio (a marker of distal tubular sodium/potassium exchange activity, r = 0.31, P = .002). Conclusion: In patients with heart failure receiving loop diuretics, urinary levels of plasmin/plasminogen were correlated with the degree of diuretic responsiveness and metrics of distal tubular potassium wasting. These hypothesis generating results suggest that ENaC activation via luminal plasmin may be a relevant and therapeutically modifiable target in HF. Additional research is warranted.