Association of Urinary Plasminogen-Plasmin with Edema and Epithelial Sodium Channel Activation in Patients with Nephrotic Syndrome

<b><i>Background:</i></b> Previous animal experiments and small human studies suggest that urinary plasmin can activate the epithelial sodium channel (ENaC) and contribute to sodium retention in nephrotic syndrome (NS), but this however is not well studied in clinical settings, and its relevance to edema formation is not well characterized in humans. We have investigated the association between urinary plasmin and clinical phenotypes in a large group of patients with NS from multiple etiologies, aiming to assess the role of urinary plasmin in sodium handling and edema formation. <b><i>Methods:</i></b> Two hundred and three NS patients with urine and blood samples were divided into mild and severe symptom groups based on their edema severity. Twenty six of them had serial samples collected during the course of immunosuppressive therapy. The plasminogen-plasmin level and other key parameters were assayed, and their association with clinical manifestations were analyzed. <b><i>Results:</i></b> One hundred and one of the 203 patients had renal biopsies performed, the results of which had included all the common types of primary NS and various types of secondary NS. Quantitative comparison and multivariate logistic regression analysis identified urinary plasminogen-plasmin to creatinine ratio (uPLG-PL/C), serum albumin, D-Dimer, and cardiac dysfunction history, but not albuminuria or 24-h urine protein, as independent risk factors for edema (<i>p</i> &#x3c; 0.01). In patients who were treated and had serial samples, a decrease in uPLG-PL/C was identified as an independent influencing factor of edema remission (<i>p</i> &#x3c; 0.01). Finally, the urinary fractional excretion of sodium (FENa) in patients was inversely correlated with the fractional excretion of potassium (FEK; <i>p</i>&#x3c; 0.001), and FEK/FENa ratio was positively correlated with uPLG-PL/C (<i>p</i> &#x3c; 0.001), suggesting a close association between uPLG-PL and ENaC activation. <b><i>Conclusions:</i></b> Our study identifies uPLG-PL abundance as an independent influencing factor of edema in adult NS patients, and supports the conclusion that plasmin-dependent ENaC activation is an important pathophysiological mechanism of sodium retention and edema formation in humans with NS.