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Background Cardiotonic steroids (CTS) are implicated in pathophysiology of uremic cardiomyopathy. In the present study, we tested whether a monoclonal antibody (mAb) against the bufadienolide CTS, marinobufagenin (MBG), alleviates cardiac hypertrophy and fibrosis in partially nephrectomized (PNx) rats. Methods In PNx rats, we compared the effects of 3E9 anti-MBG mAb and of Digibind, an affinity-purified digoxin antibody, on blood pressure and cardiac hypertrophy and fibrosis following 4 weeks after the surgery. Results In PNx rats, a four-fold elevation in plasma MBG levels was associated with hypertension, increased cardiac levels of carbonylated protein, cardiac hypertrophy, a reduction in cardiac expression of a nuclear transcription factor which is a negative regulator of collagen synthesis, Fli-1, and an increase in the levels of collagen-1. A single intraperitoneal administration of 3E9 mAb to PNx rats reduced blood pressure by 59 mmHg for 7 days and produced a significant reduction in cardiac weight and cardiac levels of oxidative stress, an increase in the expression of Fli-1, and a reduction in cardiac fibrosis. The effects of Digibind were similar to those of 3E9 mAb, but were less pronounced. Conclusions In experimental chronic renal failure, elevated levels of MBG contribute to hypertension and induce cardiac fibrosis via suppression of Fli-1, representing a potential target for therapy.

We have previously reported that the sodium potassium adenosine triphosphatase (Na/K-ATPase) can effect the amplification of reactive oxygen species. In this study, we examined whether attenuation of oxidant stress by antagonism of Na/K-ATPase oxidant amplification might ameliorate experimental uremic cardiomyopathy induced by partial nephrectomy (PNx). PNx induced the development of cardiac morphological and biochemical changes consistent with human uremic cardiomyopathy. Both inhibition of Na/K-ATPase oxidant amplification with pNaKtide and induction of heme oxygenase-1 (HO-1) with cobalt protoporphyrin (CoPP) markedly attenuated the development of phenotypical features of uremic cardiomyopathy. In a reversal study, administration of pNaKtide after the induction of uremic cardiomyopathy reversed many of the phenotypical features. Attenuation of Na/K-ATPase oxidant amplification may be a potential strategy for clinical therapy of this disorder.

Abstract-Spironolactone has been noted to attenuate cardiac fibrosis. We have observed that the cardiotonic steroid marinobufagenin plays an important role in the diastolic dysfunction and cardiac fibrosis seen with experimental renal failure. We performed the following studies to determine whether and how spironolactone might ameliorate these changes. First, we studied rats subjected to partial nephrectomy or administration of exogenous marinobufagenin. We found that spironolactone (20 mg/kg per day) attenuated the diastolic dysfunction as assessed by ventricular pressure-volume loops and essentially eliminated cardiac fibrosis as assessed by trichrome staining and Western blot. Next, we examined the effects of spironolactone and its major metabolite, canrenone (both 100 nM), on marinobufagenin stimulation of rat cardiac fibroblasts. Both spironolactone and canrenone prevented the stimulation of collagen production by 1 nM marinobufagenin but not 100 nM marinobufagenin, as assessed by proline incorporation and procollagen 1 expression, as well as signaling through the sodium-potassium-ATPase, as evidenced by protein kinase C isoform ␦ translocation and extracellular signal regulated kinase 1/2 activation. Both spironolactone and canrenone also altered ouabain binding to cultured porcine cells in a manner consistent with competitive inhibition. Our data suggest that some of the antifibrotic effects of spironolactone may be attributed to antagonism of marinobufagenin signaling through the sodium-potassium-ATPase. Key Words: cardiomyopathy Ⅲ renal failure Ⅲ cardiotonic steroids Ⅲ collagen Ⅲ fibrosis C ardiac fibrosis oftentimes complicates congestive cardiomyopathies, and it has been suggested that aldosterone may directly cause cardiac fibrosis. 1 Spironolactone is a synthetic steroid molecule that has been characterized as a mineralocorticoid receptor antagonist. 2,3 In recent years, it has been found that spironolactone can reduce the artery stiffness and left ventricular mass index in cardiomyopathic conditions. 4 -6 Mechanistically, spironolactone treatment inhibits angiotensin II and aldosterone-induced activation of epidermal growth factor receptor/extracellular signal regulated kinase (ERK), NAD(P)H oxidase/lectin-like oxidized low-density lipoprotein receptor 1, and -kinase pathways. 7 In addition to a well-defined ability to prevent the binding of aldosterone to the mineralocorticoid receptor, spironolactone and its major metabolite, canrenone, 8,9 also interact with the plasmalemmal sodium-potassium-ATPase (Na/K-ATPase). 10 Both have been shown to competitively inhibit ouabain and digoxin binding, and the latter has even been used clinically with the aim of combating digitalis toxicity. 11 Depending on the experimental conditions, spironolactone or canrenone has been characterized as either a pure competitive antagonist of ouabain or a "partial inhibitor" of Na/K-ATPase enzymatic (ion pumping) function. We have observed previously that spironolactone functions as an inotrope in vitro. 12 Moreover,...