Marinobufagenin Stimulates Fibroblast Collagen Production and Causes Fibrosis in Experimental Uremic Cardiomyopathy

Abstract

Abstract-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. (Hypertension. 2007;49:215-224.)

Selective association of endogenous ouabain with subclinical organ damage in treated hypertensive patients

“…[32][33][34] EDLF increases the calcium influx in vascular smooth muscle cells by blocking Na þ /K þ -ATPase and longterm ouabain administration and MBG stimulates fibroblast, which in turn leads to collagen accumulation in the wall of artery and in rats it causes stiffness of artery. 14,35 We found an inverse relationship between plasma EO and the augmentation index of carotid artery as well as positive correlations between levels of urinary EO and b-stiffness index and pulse wave velocity of carotid artery (Figure 1), which suggests that EO have a role in development of artery stiffness. Some studies have shown that the arterial stiffness relates with age, body mass index, systolic blood pressure, diabetes and hypertension and independently associates decreased glomerular filtration rate.…”

“…EO take part in the development of hypertension through increased sympathetic tone, and in direct prohypertrophic effects on myocytes of heart and arteries, as well as causing collagen overproduction and cardiomyopathy in uraemic rat heart. 13,14 These processes can lead to cardiac hypertrophy in vivo. 17 In our study, we have found association between left ventricular diastolic dysfunction (E/A) and level of plasma EO in HT þ DM þ CKD group.…”

“…[11][12][13] The digitalis-like factors also stimulate fibroblast causing collagen overproduction and fibrosis in rats, which is perhaps important in the development of cardiomyopathy. 14 Some human studies have shown that the elevated plasma EO positively correlates with systolic and diastolic blood pressure in untreated hypertensive individuals and further studies have found positive correlation with left ventricular mass index, and left ventricular end-diastolic volume and cardiac dysfunction. 15,16 Elevated EO plasma level also correlated with total peripheral resistance in humans emphasizing possible role of EO in the development of arterial stiffness, which is a strong predictor of the early atherosclerosis, subclinical organ damage and cardiovascular diseases.…”

Endogenous digitalis: pathophysiologic roles and therapeutic applications

“…Active immunization against marinobufagenin attenuates most of the biochemical, physiological and morphological features of uremic cardiomyopathy in animals subjected to partial nephrectomy. 135,136 Exposure to very small amounts of marinobufagenin (and of other cardiotonic steroids) virtually identical to the circulating plasma concentrations seen in experimental and clinical renal failure directly stimulated the production of collagen in primary cultures of cardiac fibroblasts. 134,135 Again, this effect required signaling through the Na + /K + -ATPase-Src-EGFR cascade.…”

Changes in Sodium Pump Expression Dictate the Effects of Ouabain on Cell Growth

“…Ultimately, this chain of signaling events would alter cellular functions and cell growth in a cell-specific manner (5, 9 -12). For instance, we and others have demonstrated that ouabain-induced activation of ERK and PI3K/Akt/mTOR pathways are responsible for cell growth stimulation in transformed cell lines, in primary cultures, as well as in vivo (13)(14)(15)(16)(17)(18).…”