Plasma Levels Of Endogenous Ouabain Research Articles

#1954 Effects of lanosterol synthase (LSS) gene on the development of acute kidney injury after cardiac surgery

Abstract Background and Aims Acute kidney injury (AKI) is a common post-cardiac surgery complication, significantly affecting morbidity and mortality. Recent studies reported that high plasma levels of endogenous ouabain (EO), a stress hormone secreted by the adrenal glands, are associated to worse kidney outcomes after cardiac surgery. Our group demonstrated that EO activity is affected by a missense variant (rs2254524, C -> A, Val642Leu) in Lanosterol Synthase (LSS) gene, an enzyme implicated in EO synthesis. The aim of this work is to analyze the relationship between this LSS polymorphism and the development of AKI after cardiac surgery. Method 1237 patients undergoing elective cardiac surgery were enrolled in the study. Preoperative biological samples were collected (Table 1). LSS genotypes were determined for each patient. The primary outcome was AKI development, according to KDIGO 2012 guidelines. Results 21.4% of patients developed AKI. Different preoperative clinical variables were analyzed, identifying five independent risk factors significantly correlated to AKI development in multivariate logistic regression analysis: age (p < 0.001), FE (p = 0.005), NYHA class (p < 0.001), reoperation (p = 0.002) and complex surgical intervention (p < 0.001), Table 2. No significant differences were observed between preoperative EO plasma levels and allelic variants of LSS gene and patients with the less common A allele were not associated to a more severe preoperative clinical presentation, expressed as EuroScore II value (AA 2.54 ± 3.86 vs AC 2.15 ± 2.52 vs CC 2.04 ± 2.73; p = ns). LSS minor variants turned out significantly associated with the incidence of AKI (AA = 29.3%; AC = 25.3%; CC = 17.2%; X2 p < 0.001—Fig. 1). This evidence remains significant after correction for covariates associated to AKI previously reported (Log regression p = 0.002; RR for AA variant: 2.09 (IC95% 1.15-3.78)) Conclusion Patients with at least one mutated allele of LSS variant have a higher probability of developing AKI after cardiac surgery. We think these results could be of interest to further understand cellular mechanisms underlying AKI development, especially in the cardiac surgery field.

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

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. 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. 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." 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. Preoperative plasma endogenous ouabain levels are powerful biomarkers of acute kidney injury and postoperative complications and may be a direct cause of podocyte damage.

Increased arterial smooth muscle Ca2+ signaling, vasoconstriction, and myogenic reactivity in Milan hypertensive rats

The Milan hypertensive strain (MHS) rats are a genetic model of hypertension with adducin gene polymorphisms linked to enhanced renal tubular Na(+) reabsorption. Recently we demonstrated that Ca(2+) signaling is augmented in freshly isolated mesenteric artery myocytes from MHS rats. This is associated with greatly enhanced expression of Na(+)/Ca(2+) exchanger-1 (NCX1), C-type transient receptor potential (TRPC6) protein, and sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA2) compared with arteries from Milan normotensive strain (MNS) rats. Here, we test the hypothesis that the enhanced Ca(2+) signaling in MHS arterial smooth muscle is directly reflected in augmented vasoconstriction [myogenic and phenylephrine (PE)-evoked responses] in isolated mesenteric small arteries. Systolic blood pressure was higher in MHS (145 ± 1 mmHg) than in MNS (112 ± 1 mmHg; P < 0.001; n = 16 each) rats. Pressurized mesenteric resistance arteries from MHS rats had significantly augmented myogenic tone and reactivity and enhanced constriction to low-dose (1-100 nM) PE. Isolated MHS arterial myocytes exhibited approximately twofold increased peak Ca(2+) signals in response to 5 μM PE or ATP in the absence and presence of extracellular Ca(2+). These augmented responses are consistent with increased vasoconstrictor-evoked sarcoplasmic reticulum (SR) Ca(2+) release and increased Ca(2+) entry, respectively. The increased SR Ca(2+) release correlates with a doubling of inositol 1,4,5-trisphosphate receptor type 1 and tripling of SERCA2 expression. Pressurized MHS arteries also exhibited a ∼70% increase in 100 nM ouabain-induced vasoconstriction compared with MNS arteries. These functional alterations reveal that, in a genetic model of hypertension linked to renal dysfunction, multiple mechanisms within the arterial myocytes contribute to enhanced Ca(2+) signaling and myogenic and vasoconstrictor-induced arterial constriction. MHS rats have elevated plasma levels of endogenous ouabain, which may initiate the protein upregulation and enhanced Ca(2+) signaling. These molecular and functional changes provide a mechanism for the increased peripheral vascular resistance (whole body autoregulation) that underlies the sustained hypertension.

How NaCl raises blood pressure: a new paradigm for the pathogenesis of salt-dependent hypertension

Excess dietary salt is a major cause of hypertension. Nevertheless, the specific mechanisms by which salt increases arterial constriction and peripheral vascular resistance, and thereby raises blood pressure (BP), are poorly understood. Here we summarize recent evidence that defines specific molecular links between Na(+) and the elevated vascular resistance that directly produces high BP. In this new paradigm, high dietary salt raises cerebrospinal fluid [Na(+)]. This leads, via the Na(+)-sensing circumventricular organs of the brain, to increased sympathetic nerve activity (SNA), a major trigger of vasoconstriction. Plasma levels of endogenous ouabain (EO), the Na(+) pump ligand, also become elevated. Remarkably, high cerebrospinal fluid [Na(+)]-evoked, locally secreted (hypothalamic) EO participates in a pathway that mediates the sustained increase in SNA. This hypothalamic signaling chain includes aldosterone, epithelial Na(+) channels, EO, ouabain-sensitive α(2) Na(+) pumps, and angiotensin II (ANG II). The EO increases (e.g.) hypothalamic ANG-II type-1 receptor and NADPH oxidase and decreases neuronal nitric oxide synthase protein expression. The aldosterone-epithelial Na(+) channel-EO-α(2) Na(+) pump-ANG-II pathway modulates the activity of brain cardiovascular control centers that regulate the BP set point and induce sustained changes in SNA. In the periphery, the EO secreted by the adrenal cortex directly enhances vasoconstriction via an EO-α(2) Na(+) pump-Na(+)/Ca(2+) exchanger-Ca(2+) signaling pathway. Circulating EO also activates an EO-α(2) Na(+) pump-Src kinase signaling cascade. This increases the expression of the Na(+)/Ca(2+) exchanger-transient receptor potential cation channel Ca(2+) signaling pathway in arterial smooth muscle but decreases the expression of endothelial vasodilator mechanisms. Additionally, EO is a growth factor and may directly participate in the arterial structural remodeling and lumen narrowing that is frequently observed in established hypertension. These several central and peripheral mechanisms are coordinated, in part by EO, to effect and maintain the salt-induced elevation of BP.

Independent and incremental prognostic value of endogenous ouabain in idiopathic dilated cardiomyopathy

Increased circulating levels of endogenous ouabain (EO) have been observed in some heart failure patients, but their long term clinical significance is unknown. This study investigated the prognostic value of EO for worsening heart failure among 140 optimally treated patients (age 50+/-14 years; 104 male; NYHA class 1.9+/-0.7) with idiopathic dilated cardiomyopathy. Plasma EO was determined by RIA and by liquid chromatography mass spectrometry, values were linearly correlated (r = 0.89) in regression analysis. During follow-up (13+/-5 months), heart failure progression was defined as worsening clinical condition leading to one or more of the following: sustained increase in conventional therapies, hospitalization, cardiac transplant, or death. NYHA functional class, age, LVEF, peak VO2 and plasma levels of EO were predictive for heart failure progression. Heart failure worsened 1.5 fold (HR: 1.005; 95% CI: 1.001-1.007; p<0.01) for each 100 pmol/L increase in plasma EO. Moreover, those patients with higher plasma EO values had an odds ratio of 5.417 (95% CI: 2.044-14.355; p<0.001) for heart failure progression. Following multivariate analysis, LVEF, NYHA class and plasma EO remained significantly linked with clinical events. This study provides the first evidence that circulating EO is a novel, independent and incremental marker that predicts the progression of heart failure.

Endogenous digitalis-like ligands and Na/K-ATPase inhibition in experimental diabetes mellitus

Dysregulation of the Na/K-ATPase (NKA) in the kidney, cardiovascular system, and peripheral nervous system is believed to contribute to pathogenesis of diabetes mellitus (DM) and its complications. Recently we demonstrated that, in addition to endogenous ouabain (EO), mammalian tissues contain another NKA inhibitor, a bufadienolide marinobufagenin (MBG). In vitro MBG, a natriuretic and a vasoconstrictor, acts as a selective inhibitor of alpha-1 NKA, the main isoform of the sodium pump in renal tubules and vascular smooth muscle. To determine whether digitalis-like NKA inhibitors are linked to NKA dysregulation in DM, we studied changes in renal excretion and plasma levels of MBG and EO and the activity of erythrocyte NKA in male Wistar rats with type 1 DM and type 2 DM. Rats with type 1 DM were studied four weeks following a single intraperitoneal injection of 65 mg/kg streptozotocin (STZ)(n = 12), and rats with type 2 DM were studied 10 weeks after intraperitoneal injection of STZ during the neonatal period (n = 12). Renal excretion and plasma levels of EO did not change in rats with both types of DM as compared to that in the control groups. Renal excretion (57.5 +/- 9.4 pmol/kg/ 3 hours vs. 12.6 +/- 2.1 pmol/kg/ 3 hours; P less than 0.01) and plasma levels (2.23 +/- 0.82 nmol/L vs. 0.29 +/- 0.07 nmol/L; P less than 0.01) of MBG increased, and NKA activity in erythrocytes was inhibited by 50% in rats with type 1 DM as compared to controls. In rats with type 2 DM, plasma levels (1.48 +/- 0.09 nmol/L vs. 0.46 +/- 0.02 nmol/L; P less than 0.01) and renal excretion (21.3 +/- 3.2 pmol/kg/ 3 hours vs. 13.1 +/- 2.1 pmol/kg/ 3 hours) of MBG also became elevated, but less than in the animals with type 1 DM. Accordingly, activity of NKA in erythrocytes from rats with type 2 DM was inhibited by 35%. In vitro treatment of erythrocytes from rats with type 1 and type 2 DM with anti-MBG antibody reversed the DM induced inhibition of the NKA. These results suggest that digitalis-like factors are involved in the pathogenesis of DM and that MBG, rather than EO, is responsible for DM-induced NKA inhibition.

Coordinated shifts in Na/K-ATPase isoforms and their endogenous ligands during cardiac hypertrophy and failure in NaCl-sensitive hypertension.

NaCl loading of Dahl salt-sensitive rats (DS) stimulates marinobufagenin (MBG), an alpha1 Na/K-ATPase (NKA) isoform ligand. Cardiac function depends on NKA, which is regulated in part by endogenous digitalis-like ligands. Our goal was to study whether changes occur in MBG and endogenous ouabain (EO) production during cardiac remodelling in hypertensive DS, and whether these are associated with changes in myocardial NKA isoforms and sensitivity to MBG and ouabain. Changes in MBG and EO levels, changes in myocardial NKA isoform composition, and sensitivity to endogenous ligands during development of cardiac hypertrophy and the transition to heart failure were studied in DS rats with an 8% NaCl intake. The animals developed compensated left ventricular hypertrophy after 4 weeks, which progressed to heart failure at 9-12 weeks. The hypertrophic stage was associated with increased plasma MBG levels (mean +/- SEM of 1.22 +/- 0.22 versus 0.31 +/- 0.03 nmol/l; P < 0.01), increased sensitivity of NKA to MBG, and an increased abundance of alpha1 NKA. Plasma levels of EO did not change, and the sensitivity of NKA to ouabain decreased. The transition to heart failure was accompanied by a decrease in alpha1 NKA, a reduction in plasma MBG, and decreased sensitivity of NKA to MBG. In addition, an increased abundance of ouabain-sensitive alpha3 NKA, a three-fold rise in plasma EO (1.01 +/- 0.13 versus 0.27 +/- 0.06 nmol/l), and a seven-fold increase in the ouabain sensitivity of NKA compared with controls were observed. During cardiac hypertrophy and the transition to heart failure, a shift in endogenous NKA ligands production is linked to a shift in myocardial NKA isoforms.

Antihypertensive compounds that modulate the Na-K pump.

A primary impairment of the kidney sodium excretion has been documented both in hypertensive patients (EH) and genetic animal models (Milan hypertensive rat [MHS]) carrying mutations of the cytoskeletal protein adducin and/or increased plasma levels of endogenous ouabain (EO). Ouabain (OU) itself induces hypertension in rats and both OU and mutated adducin activate the renal Na/K-ATPase function both in vivo and in cultured renal cells (NRK). A new antihypertensive agent, PST 2238, able to selectively interact with these alterations has been developed. PST lowers blood pressure (BP) by normalizing the expression and activity of the renal Na-K pump selectively in those rat models carrying the adducin mutation (MHS) and/or increased EO levels (OS) at oral doses of 0.1-10 micro g/kg. In NRK cells either transfected with mutated adducin or incubated with 10(-9) M OU, PST normalizes the Na-K pump activity. Recently, an association between EO and cardiac complications has been observed in both EH and rat models consistent with a prohypertrophic activity of OU. OS rats showed a 10% increase of left ventricle and kidney weights as compared with controls, and PST 2238 (1 micro g/kg OS) prevented both ventricle and renal hypertrophy. This effect was associated with the ability of PST to antagonize the OU-dependent activation of growth-related genes, in the membrane subdomains of caveolae. In conclusion, PST is a new antihypertensive agent that may prevent cardiovascular complications associated with hypertension through the selective modulation of the Na-K pump function.

Immunoreactive endogenous ouabain in primary aldosteronism and essential hypertension: relationship with plasma renin, aldosterone and blood pressure levels.

To investigate the role of ouabain in human hypertension and to establish whether immunoreactive endogenous ouabain is secreted by the adrenal gland under the influence of dopaminergic regulation. We measured plasma levels of endogenous ouabain by immunoassay, together with other variables, including plasma renin activity and aldosterone levels, in 91 clinically selected hypertensives and 19 healthy volunteers. We also measured endogenous ouabain in adrenal venous blood and the effect of DA2 dopaminergic receptor blockade and stimulation. After a thorough clinical evaluation, 64 patients were diagnosed with essential hypertension and 24 with primary aldosteronism. Plasma levels of endogenous ouabain were higher in essential hypertensives than in controls. Multiple regression analysis showed a significant relationship of mean blood pressure with plasma endogenous ouabain, age and body mass index, but not with other measured parameters. The plasma levels of endogenous ouabain were more than two standard deviations above the mean value for normotensives in 45% of patients with essential hypertension in whom plasma renin activity was normal. Higher plasma levels of endogenous ouabain were found in patients with aldosterone excess, specifically affecting 56% of 17 patients with surgically confirmed adrenal cortical adenoma and one (14%) of seven patients with idiopathic causes. Removal of adenomas lowered blood pressure in half of the patients in whom plasma levels of endogenous ouabain normalized after surgery. Plasma endogenous ouabain levels were similar in venous blood from the adrenal and inferior vena cava, and plasma levels were not influenced by DA2 dopaminergic blockade and stimulation. Approximately half of Caucasian patients with essential hypertension and with hyperaldosteronism exhibit elevated circulating levels of endogenous ouabain. The latter do not appear to be secondary to hypertension, are unrelated to plasma renin activity, and may not involve adrenal type-2 dopaminergic receptors.