Preoperative Endogenous Ouabain Predicts Acute Kidney Injury in Cardiac Surgery Patients*

Abstract

Objectives Acute kidney injury is a frequent complication of cardiac surgery and increases morbidity and mortality. As preoperative biomarkers predicting the development of acute kidney injury are not available, we have tested the hypothesis that preoperative plasma levels of endogenous ouabain may function as this type of biomarker. Rationale and Design Endogenous ouabain is an adrenal stress hormone associated with adverse cardiovascular outcomes. Its involvement in acute kidney injury is unknown. With studies in patients and animal settings, including isolated podocytes, we tested the above mentioned hypothesis. Patients Preoperative endogenous ouabain was measured in 407 patients admitted for elective cardiac surgery and in a validation population of 219 other patients. We also studied the effect of prolonged elevations of circulating exogenous ouabain on renal parameters in rats and the influence of ouabain on podocyte proteins both “in vivo” and “in vitro.” Main Results In the first group of patients, acute kidney injury (2.8%, 8.3%, 20.3%, p < 0.001) and ICU stay (1.4 ± 0.38, 1.7 ± 0.41, 2.4 ± 0.59 days, p = 0.014) increased with each incremental preoperative endogenous ouabain tertile. In a linear regression analysis, the circulating endogenous ouabain value before surgery was the strongest predictor of acute kidney injury. In the validation cohort, acute kidney injury (0%, 5.9%, 8.2%, p < 0.0001) and ICU stay (1.2 ± 0.09, 1.4 ± 0.23, 2.2 ± 0.77 days, p = 0.003) increased with the preoperative endogenous ouabain tertile. Values for preoperative endogenous ouabain significantly improved (area under curve: 0.85) risk prediction over the clinical score alone as measured by integrate discrimination improvement and net reclassification improvement. Finally, in the rat model, elevated circulating ouabain reduced creatinine clearance (–18%, p < 0.05), increased urinary protein excretion (+ 54%, p < 0.05), and reduced expression of podocyte nephrin (–29%, p < 0.01). This last finding was replicated ex vivo by incubating podocyte primary cell cultures with low-dose ouabain. Conclusions Preoperative plasma endogenous ouabain levels are powerful biomarkers of acute kidney injury and postoperative complications and may be a direct cause of podocyte damage.

Rostafuroxin Protects from Podocyte Injury and Proteinuria Induced by Adducin Genetic Variants and Ouabain

“…Conversely, conditions that protect from podocyte injury, such as those observed in the presence of mutant a-adducin genetic variant in MHS and NA rats, restore proteinuria and nephrin expression to normal levels. Similar alterations of podocyte protein expression have been reproduced by culturing podocytes from NB congenic rats (Ferrandi et al, 2010b) or by incubating podocytes in the presence of nanomolar concentrations of ouabain (Bignami et al, 2013). These data imply that b-adducin mutation and ouabain induce direct changes in podocyte architecture and activity.…”

“…3F) (Bignami et al, 2013), but did not affect synaptopodin (Fig. 3G), as documented by a Western blot analysis.…”

“…Ouabain and rostafuroxin did not induce variations of creatinine excretion (control, 31.8 6 1.16, n 5 15; OHR, 30.63 6 0.95, n 5 15; OHR 1 rostafuroxin, 30.98 6 1.14 mg/24 hours, n 5 15). Conversely, ouabain infusion in rats induced a significant increase of urinary protein excretion (milligrams per 24 hours) (Bignami et al, 2013), which was normalized by the prolonged treatment with rostafuroxin (Fig. 3B).…”

“…3, C and E) but not synaptopodin (Fig. 3, D and E) (Bignami et al, 2013), as measured by Western blot in renal microsomes and immunofluorescence analysis. Prolonged treatment of OHR rats with rostafuroxin restored nephrin protein expression (Fig.…”

“…Recently, we produced data indicating that mutant b-adducin and EO/ouabain affect the expression of nephrin (Ferrandi et al, 2010b;Bignami et al, 2013), a selective podocyte marker protein (Verma et al, 2006), both in animal models and in patients.…”