marinobufagenin and Renal-Insufficiency

To integrate recent studies showing that abnormal Na transport in the central nervous system plays a pivotal role in genetic models of salt-sensitive hypertension.. Na transport-regulating mechanisms classically considered to reflect renal control of the blood pressure, i.e. aldosterone-mineralocorticoid receptors-epithelial sodium channels-Na/K-ATPase, have now been demonstrated to be present in the central nervous system contributing to regulation of cerebrospinal fluid [Na] by the choroid plexus and to neuronal responsiveness to cerebrospinal fluid/brain [Na]. Dysfunction of either or both can activate central nervous system pathways involving 'ouabain' and angiotensin type 1 receptor stimulation. The latter causes sympathetic hyperactivity and adrenal release of marinobufagenin - a digitalis-like inhibitor of the alpha1 Na/K-ATPase isoform - both contributing to hypertension on high salt intake. Conversely, specific central nervous system blockade of mineralocorticoid receptors or epithelial sodium channels prevents the development of hypertension on high salt intake, irrespective of the presence of a 'salt-sensitive kidney'. Variants in the coding regions of some of the genes involved in Na transport have been identified, but sodium sensitivity may be mainly determined by abnormal regulation of expression, pointing to primary abnormalities in regulation of transcription.. Looking beyond the kidney is providing new insights into mechanisms contributing to salt-sensitive hypertension, which will help to dissect the genetic factors involved and to discover novel strategies to prevent and treat salt-sensitive hypertension.

Topics: Blood Pressure; Brain; Bufanolides; Calmodulin-Binding Proteins; Cerebrospinal Fluid; Cytochrome P-450 Enzyme System; Endosomal Sorting Complexes Required for Transport; Enzyme Inhibitors; Epithelial Sodium Channels; Humans; Hypertension; Immediate-Early Proteins; Nedd4 Ubiquitin Protein Ligases; Ouabain; Protein Serine-Threonine Kinases; Receptor, Angiotensin, Type 1; Receptors, Angiotensin; Receptors, Mineralocorticoid; Receptors, Vasopressin; Renal Insufficiency; Renin-Angiotensin System; Sodium-Potassium-Exchanging ATPase; Sodium, Dietary; Transcription, Genetic; Ubiquitin-Protein Ligases; Vasoconstrictor Agents

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 delta 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.

Topics: Animals; Bufanolides; Canrenone; Cardiomyopathies; Cardiotonic Agents; Cells, Cultured; Disease Models, Animal; Drug Interactions; Endomyocardial Fibrosis; Fibroblasts; Mineralocorticoid Receptor Antagonists; Myocardium; Nephrectomy; Ouabain; Procollagen; Proline; Rats; Renal Insufficiency; Spironolactone; Tritium; Uremia

Because of the plethora of genetic manipulations available in the mouse, we performed a partial nephrectomy in the mouse and examined whether the phenotypical features of uremic cardiomyopathy described in humans and rats were also present in the murine model. A 5/6 nephrectomy was performed using a combination of electrocautory to decrease renal mass on the left kidney and right surgical nephrectomy. This procedure produced substantial and persistent hypertension as well as increases in circulating concentrations of marinobufagenin. Invasive physiological measurements of cardiac function demonstrated that the 5/6 nephrectomy resulted in impairment of both active and passive left ventricular relaxation at 4 wk whereas tissue Doppler imaging detected changes in diastolic function after 6 wk. Morphologically, hearts demonstrated enlargement and progressive fibrosis, and biochemical measurements demonstrated downregulation of the sarcoplasmic reticulum calcium ATPase as well as increases in collagen-1, fibronectin, and vimentin expression. Our results suggest that partial nephrectomy in the mouse establishes a model of uremic cardiomyopathy which shares phenotypical features with the rat model as well as patients with chronic renal failure.

Topics: Animals; Antihypertensive Agents; Blood Pressure; Bufanolides; Cardiomegaly; Cardiomyopathies; Disease Models, Animal; Echocardiography, Doppler; Extracellular Signal-Regulated MAP Kinases; Fibrosis; Heart; Male; Mice; Mice, Inbred Strains; Myocardium; Myocytes, Cardiac; Nephrectomy; Renal Insufficiency; Sarcoplasmic Reticulum Calcium-Transporting ATPases; Sodium-Potassium-Exchanging ATPase; src-Family Kinases; Stroke Volume; Ventricular Function, Left

We have observed recently that experimental renal failure in the rat is accompanied by increases in circulating concentrations of the cardiotonic steroid, marinobufagenin (MBG), and substantial cardiac fibrosis. We performed the following studies to examine whether MBG might directly stimulate cardiac fibroblast collagen production. In vivo studies were performed using the 5/6th nephrectomy model of experimental renal failure (PNx), MBG infusion (MBG), PNx after immunization against MBG, and concomitant PNx and adrenalectomy. Physiological measurements with a Millar catheter and immunohistochemistry were performed. In vitro studies were then pursued with cultured isolated cardiac fibroblasts. We observed that PNx and MBG increased MBG levels, blood pressure, heart size, impaired diastolic function, and caused cardiac fibrosis. PNx after immunization against MBG and concomitant PNx and adrenalectomy had similar blood pressure as PNx but less cardiac hypertrophy, diastolic dysfunction, and cardiac fibrosis. MBG induced increases in procollagen-1 expression by cultured cardiac fibroblasts at 1 nM concentration. These increases in procollagen expression were accompanied by increases in collagen translation and increases in procollagen-1 mRNA without any demonstrable increase in procollagen-1 protein stability. The stimulation of fibroblasts with MBG could be prevented by administration of inhibitors of tyrosine phosphorylation, Src activation, epidermal growth factor receptor transactivation, and N-acetyl cysteine. Based on these findings, we propose that MBG directly induces increases in collagen expression by fibroblasts, and we suggest that this may be important in the cardiac fibrosis seen with experimental renal failure.

Topics: Animals; Blood Pressure; Bufanolides; Cardiomyopathies; Cells, Cultured; Collagen; Fibroblasts; Fibrosis; Heart; Male; Myocardium; Rats; Rats, Sprague-Dawley; Renal Insufficiency; Signal Transduction; Sodium-Potassium-Exchanging ATPase; Transforming Growth Factor beta; Uremia