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Current Opinion in Nephrology and... Jan 2013Endogenous cardiotonic steroids (CTS) exert long-term effects on salt and blood pressure homeostasis. Here we discuss recent observations on mechanisms of salt... (Review)
Review
PURPOSE OF REVIEW
Endogenous cardiotonic steroids (CTS) exert long-term effects on salt and blood pressure homeostasis. Here we discuss recent observations on mechanisms of salt sensitivity that involve endogenous ouabain and novel pathways in the brain and discuss their possible relationship to arterial and renal function in hypertension.
RECENT FINDINGS
Chronic elevation of brain sodium promotes sustained hypertension mediated by central endogenous ouabain and the Na(+) pump α-2 catalytic subunit. The intermediary pressor mechanism in the brain involves aldosterone biosynthesis, activation of mineralocorticoid receptors and increased epithelial sodium channel activity. In the periphery, elevated plasma CTS raise contractility and blood pressure by augmentation of sympathetic nerve responses, increasing arterial Ca(2+) signaling and blunting nitric oxide production in the renal medulla and collecting ducts.
SUMMARY
Endogenous ouabain in the brain appears to play a critical role in salt sensitivity and hypertension. In the periphery, the J-shaped relationship of plasma endogenous ouabain in response to short-term changes in salt balance in humans raises the possibility that endogenous ouabain contributes to the increased risk of adverse cardiovascular events associated with both low and high salt intakes.
Topics: Animals; Blood Pressure; Brain; Homeostasis; Humans; Hypertension; Ouabain; Sodium Chloride
PubMed: 23207724
DOI: 10.1097/MNH.0b013e32835b36ec -
The Journal of Physiology Mar 2014'Classic' cardiotonic steroids (CTSs) such as digoxin and ouabain selectively inhibit Na+, K+ -ATPase (the Na+ pump) and, via Na+ / Ca2+ exchange (NCX), exert...
'Classic' cardiotonic steroids (CTSs) such as digoxin and ouabain selectively inhibit Na+, K+ -ATPase (the Na+ pump) and, via Na+ / Ca2+ exchange (NCX), exert cardiotonic and vasotonic effects. CTS action is more complex than previously thought: prolonged subcutaneous administration of ouabain, but not digoxin, induces hypertension, and digoxin antagonizes ouabain's hypertensinogenic effect. We studied the acute interactions between CTSs in two indirect assays of Na+ pump function: myogenic tone (MT) in isolated, pressurized rat mesenteric small arteries, and Ca2+ signalling in primary cultured rat hippocampal neurones. The 'classic' CTSs (0.3-10 nm) behaved as 'agonists': all increased MT70 (MT at 70 mmHg) and augmented glutamate-evoked Ca2+ (Fura-2) signals. We then tested one CTS in the presence of another. Most CTSs could be divided into ouabain-like (ouabagenin, dihydroouabain (DHO), strophanthidin) or digoxin-like CTS (digoxigenin, digitoxin, bufalin). Within each group, the CTSs were synergistic, but ouabain-like and digoxin-like CTSs antagonized one another in both assays: For example, the ouabain-evoked (3 nm) increases in MT70 and neuronal Ca2+ signals were both greatly attenuated by the addition of 10 nm digoxin or 10 nm bufalin, and vice versa. Rostafuroxin (PST2238), a digoxigenin derivative that displaces 3H-ouabain from Na+, K+ -ATPase, and attenuates some forms of hypertension, antagonized the effects of ouabain, but not digoxin. SEA0400, a Na+ / Ca2+ exchanger (NCX) blocker, antagonized the effects of both ouabain and digoxin. CTSs bind to the α subunit of pump αβ protomers. Analysis of potential models suggests that, in vivo, Na+ pumps function as tetraprotomers ((αβ)4) in which the binding of a single CTS to one protomer blocks all pumping activity. The paradoxical ability of digoxin-like CTSs to reactivate the ouabain-inhibited complex can be explained by de-oligomerization of the tetrameric state. The interactions between these common CTSs may be of considerable therapeutic relevance.
Topics: Animals; Blood Flow Velocity; Calcium Signaling; Cardiotonic Agents; Cells, Cultured; Digoxin; Dose-Response Relationship, Drug; Drug Interactions; Hippocampus; In Vitro Techniques; Male; Mesenteric Arteries; Neurons; Ouabain; Rats; Rats, Sprague-Dawley; Vascular Resistance; Vasoconstriction
PubMed: 24344167
DOI: 10.1113/jphysiol.2013.266866 -
European Journal of Biochemistry May 2002The search for endogenous digitalis has led to the isolation of ouabain as well as several additional cardiotonic steroids of the cardenolide and bufadienolide type from... (Review)
Review
The search for endogenous digitalis has led to the isolation of ouabain as well as several additional cardiotonic steroids of the cardenolide and bufadienolide type from blood, adrenals, and hypothalamus. The concentration of endogenous ouabain is elevated in blood upon increased Na(+) uptake, hypoxia, and physical exercise. Changes in blood levels of ouabain upon physical exercise occur rapidly. Adrenal cortical cells in tissue culture release ouabain upon addition of angiotensin II and epinephrine, and it is thought that ouabain is released from adrenal cortex in vivo. Ouabain levels in blood are elevated in 50% of Caucasians with low-renin hypertension. Infusion over several weeks of low concentrations of ouabain, but not of digoxin, induces hypertension in rats. A digoxin-like compound, which has been isolated from human urine and adrenals, as well various other endogenous cardiac glycosides may counterbalance their actions within a regulatory framework of water and salt metabolism. Marinobufagenin, for instance, whose concentration is increased after cardiac infarction, may show natriuretic properties because it inhibits the alpha1 isoform of Na(+)/K(+)-ATPase, the main sodium pump isoform of the kidney, much better than other sodium pump isoforms. In analogy to other steroid hormones, cardiotonic steroid hormones in blood are bound to a specific cardiac glycoside binding globulin. The discovery of ouabain as a new adrenal hormone affecting Na(+) metabolism and the development of the new ouabain antagonist PST 2238 allows for new possibilities for the therapy of hypertension and congestive heart failure. This will lead in turn to a better understanding of the disease on a physiological and endocrinological level and of the action of ouabain on the cellular level as a signal that is transduced to the plasma membrane as well as to the cell nucleus.
Topics: Animals; Blood Proteins; Cardiac Glycosides; Cardiotonic Agents; Hormones; Humans; Ouabain; Protein Binding; Sodium-Potassium-Exchanging ATPase; Steroids
PubMed: 12027881
DOI: 10.1046/j.1432-1033.2002.02911.x -
American Journal of Physiology. Cell... Jan 2012The endogenous cardiac steroid-like compounds, endogenous ouabain (EO) in particular, are present in the human circulation and are considered putative ligands of the...
The endogenous cardiac steroid-like compounds, endogenous ouabain (EO) in particular, are present in the human circulation and are considered putative ligands of the inhibitory binding site of the plasma membrane Na(+)-K(+)-ATPase. A vast amount of data shows that, when added to cell cultures, these steroids promote the growth of cardiac, vascular, and epithelial cells. However, the involvement of the endogenous compounds in the regulation of cell viability and proliferation has never been addressed experimentally. In this study, we show that EO is present in mammalian sera and cerebral spinal fluid, as well as in commercial bovine and horse sera. The lowering of serum EO concentration by the addition of specific anti-ouabain antibodies caused a decrease in the viability of several cultured cell lines. Among these, neuronal NT2 cells were mostly affected, whereas no reduction in viability was seen in rat neuroendocrine PC12 and monkey kidney COS-7 cells. The anti-ouabain antibody-induced reduction in NT2 cell viability was significantly attenuated by the addition of ouabain and was not observed in cells growing in serum-free media. Furthermore, the addition to the medium of low concentrations (nM) of the cardenolide ouabain, but not of the bufadienolide bufalin, increased NT2 and PC12 cell viability and proliferation. In addition, at these concentrations both ouabain and bufalin caused the activation of ERK1/2 in the NT2 cells. The specific ERK1/2 inhibitor U0126 inhibited both the ouabain-induced activation of the enzyme and the increase in cell viability. Furthermore, anti-ouabain antibodies attenuated serum-stimulated ERK1/2 activity in NT2 but not in PC12 cells. Cumulatively, our results suggest that EO plays a significant role in the regulation of cell viability. In addition, our findings support the notion that activation of the ERK1/2 signaling pathway is obligatory but not sufficient for the induction of cell viability by EO.
Topics: Animals; Antibodies; Bufanolides; Butadienes; COS Cells; Cattle; Cell Proliferation; Cell Survival; Chlorocebus aethiops; Dose-Response Relationship, Drug; Enzyme Activation; Enzyme Inhibitors; Extracellular Signal-Regulated MAP Kinases; Horses; Humans; Nitriles; Ouabain; PC12 Cells; Rats
PubMed: 22031604
DOI: 10.1152/ajpcell.00336.2011 -
International Journal of Molecular... Jul 2020The ability of exogenous low ouabain concentrations to affect claudin expression and therefore epithelial barrier properties was demonstrated previously in cultured cell...
The ability of exogenous low ouabain concentrations to affect claudin expression and therefore epithelial barrier properties was demonstrated previously in cultured cell studies. We hypothesized that chronic elevation of circulating ouabain in vivo can affect the expression of claudins and tight junction permeability in different tissues. We tested this hypothesis in rats intraperitoneally injected with ouabain (1 μg/kg) for 4 days. Rat jejunum, colon and brain frontal lobes, which are variable in the expressed claudins and tight junction permeability, were examined. Moreover, the porcine jejunum cell line IPEC-J2 was studied. In IPEC-J2-cells, ouabain (10 nM, 19 days of incubation) stimulated epithelial barrier formation, increased transepithelial resistance and the level of cSrc-kinase activation by phosphorylation, accompanied with an increased expression of claudin-1, -5 and down-regulation of claudin-12; the expression of claudin-3, -4, -8 and tricellulin was not changed. In the jejunum, chronic ouabain increased the expression of claudin-1, -3 and -5 without an effect on claudin-2 and -4 expression. In the colon, only down-regulation of claudin-3 was observed. Chronic ouabain protected the intestine transepithelial resistance against functional injury induced by lipopolysaccharide treatment or by modeled acute microgravity; this regulation was most pronounced in the jejunum. Claudin-1 was also up-regulated in cerebral blood vessels. This was associated with reduction of claudin-3 expression while the expression of claudin-5 and occludin was not affected. Altogether, our results confirm that circulating ouabain can functionally and tissue-specifically affect barrier properties of epithelial and endothelial tissues via Na,K-ATPase-mediated modulation of claudins expression.
Topics: Animals; Brain; Capillary Permeability; Cell Line; Claudins; Intestinal Mucosa; Intestines; Male; Ouabain; Permeability; Rats; Rats, Wistar; Swine; Tight Junctions
PubMed: 32709081
DOI: 10.3390/ijms21145067 -
In Vivo (Athens, Greece) 2021Ouabain, isolated from natural plants, exhibits anticancer activities; however, no report has presented its mechanism of DNA damage induction in human osteosarcoma...
BACKGROUND/AIM
Ouabain, isolated from natural plants, exhibits anticancer activities; however, no report has presented its mechanism of DNA damage induction in human osteosarcoma cancer cells in vitro. The aim of this study was to investigate whether ouabain induces DNA damage and repair, accompanied with molecular pathways in human osteosarcoma cancer U-2 OS cells in vitro.
MATERIALS AND METHODS
The percentage of viable cell number was measured by flow cytometric assay; DNA damage was assayed by DAPI staining, comet assay, and agarose gel electrophoresis. DNA damage and repair associated protein expressions were assayed by western blotting assays.
RESULTS
Ouabain reduced total cell viability, induced chromatin condensation, DNA fragmentation, and DNA damage in U-2 OS cells. Ouabain increased p-ATM, p-ATR, and p53 at 2.5-10 μM, increased p-p53 at 10 μM; however, it decreased p-MDM2 at 2.5-10 μM. Ouabain increased p-H2A.X, MDC-1, and PARP at 2.5-10 μM and BRCA1 at 5-10 μM; however, it decreased DNA-PK and MGMT at 2.5-10 μM in U-2 OS cells at 48 h treatment. Ouabain promoted expression and nuclear translocation of p-H2A.X in U-2 OS cells and this was confirmed by confocal laser microscopy.
CONCLUSION
Ouabain reduced total viable cell number through triggering DNA damage and altering the protein expression of DNA damage and repair system in U-2 OS cells in vitro.
Topics: Apoptosis; Bone Neoplasms; Cell Line, Tumor; DNA Damage; DNA Repair; Humans; Osteosarcoma; Ouabain
PubMed: 34410957
DOI: 10.21873/invivo.12552 -
British Journal of Pharmacology Apr 2022Na /K -ATPase, a transmembrane protein essential for maintaining the electrochemical gradient across the plasma membrane, acts as a receptor for cardiotonic steroids... (Review)
Review
Na /K -ATPase, a transmembrane protein essential for maintaining the electrochemical gradient across the plasma membrane, acts as a receptor for cardiotonic steroids such as ouabain. Cardiotonic steroids binding to Na /K -ATPase triggers signalling pathways or inhibits Na /K -ATPas activity in a concentration-dependent manner, resulting in a modulation of Ca levels, which are essential for homeostasis in neurons. However, most of the pharmacological strategies for avoiding neuronal death do not target Na /K -ATPase activity due to its complexity and the poor understanding of the mechanisms involved in Na /K -ATPase modulation. The present review aims to discuss two points regarding the interplay between Na /K -ATPase and Ca signalling in the brain. One, Na /K -ATPase impairment causing illness and neuronal death due to Ca signalling and two, benefits to the brain by modulating Na /K -ATPase activity. These interactions play an essential role in neuronal cell fate determination and are relevant to find new targets for the treatment of neurodegenerative diseases. LINKED ARTICLES: This article is part of a themed issue on Building Bridges in Neuropharmacology. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.8/issuetoc.
Topics: Calcium; Calcium Signaling; Cardiac Glycosides; Ions; Neurons; Ouabain; Sodium; Sodium-Potassium-Exchanging ATPase
PubMed: 33644859
DOI: 10.1111/bph.15419 -
Pharmacological Reviews Mar 2009Endogenous cardiotonic steroids (CTS), also called digitalis-like factors, have been postulated to play important roles in health and disease for nearly half a century.... (Review)
Review
Endogenous cardiotonic steroids (CTS), also called digitalis-like factors, have been postulated to play important roles in health and disease for nearly half a century. Recent discoveries, which include the specific identification of endogenous cardenolide (endogenous ouabain) and bufadienolide (marinobufagenin) CTS in humans along with the delineation of an alternative mechanism by which CTS can signal through the Na(+)/K(+)-ATPase, have increased the interest in this field substantially. Although CTS were first considered important in the regulation of renal sodium transport and arterial pressure, more recent work implicates these hormones in the regulation of cell growth, differentiation, apoptosis, and fibrosis, the modulation of immunity and of carbohydrate metabolism, and the control of various central nervous functions and even behavior. This review focuses on the physiological interactions between CTS and other regulatory systems that may be important in the pathophysiology of essential hypertension, preeclampsia, end-stage renal disease, congestive heart failure, and diabetes mellitus. Based on our increasing understanding of the regulation of CTS as well as the molecular mechanisms of these hormone increases, we also discuss potential therapeutic strategies.
Topics: Animals; Blood Pressure; Bufanolides; Cardiac Glycosides; Cardiotonic Agents; Diabetes Mellitus; Enzyme Inhibitors; Female; Heart Failure; Humans; Hypertension; Ouabain; Pre-Eclampsia; Pregnancy; Signal Transduction; Sodium-Potassium-Exchanging ATPase
PubMed: 19325075
DOI: 10.1124/pr.108.000711 -
BioMed Research International 2013Ouabain is a common tool to explore the pathophysiological changes in adult mammalian cochlea in vivo. In prior studies, locally administering ouabain via round window...
Ouabain is a common tool to explore the pathophysiological changes in adult mammalian cochlea in vivo. In prior studies, locally administering ouabain via round window membrane demonstrated that the ototoxic effects of ouabain in vivo varied among mammalian species. Little is known about the ototoxic effects in vitro. Thus, we prepared cochlear organotypic cultures from postnatal day-3 rats and treated these cultures with ouabain at 50, 500, and 1000 μM for different time to elucidate the ototoxic effects of ouabain in vitro and to provide insights that could explain the comparative ototoxic effects of ouabain in vivo. Degeneration of cochlear hair cells and spiral ganglion neurons was evaluated by hair-cell staining and neurofilament labeling, respectively. Annexin V staining was used to detect apoptotic cells. A quantitative RT-PCR apoptosis-focused gene array determined changes in apoptosis-related genes. The results showed that ouabain-induced damage in vitro was dose and time dependent. 500 μM ouabain and 1000 μM ouabain were destructively traumatic to both spiral ganglion neurons and cochlear hair cells in an apoptotic signal-dependent pathway. The major apoptotic pathways in ouabain-induced spiral ganglion neuron apoptosis culminated in the stimulation of the p53 pathway and triggering of apoptosis by a network of proapoptotic signaling pathways.
Topics: Animals; Apoptosis; Cells, Cultured; Enzyme Inhibitors; Gene Expression Profiling; Gene Expression Regulation; Hair Cells, Auditory; Neurons; Ouabain; Rats; Rats, Sprague-Dawley; Reverse Transcriptase Polymerase Chain Reaction; Signal Transduction; Spiral Ganglion
PubMed: 24228256
DOI: 10.1155/2013/628064 -
International Journal of Molecular... Dec 2023Ionizing radiation (IR) causes disturbances in the functions of the gastrointestinal tract. Given the therapeutic potential of ouabain, a specific ligand of the...
Ionizing radiation (IR) causes disturbances in the functions of the gastrointestinal tract. Given the therapeutic potential of ouabain, a specific ligand of the Na,K-ATPase, we tested its ability to protect against IR-induced disturbances in the barrier and transport properties of the jejunum and colon of rats. Male Wistar rats were subjected to 6-day intraperitoneal injections of vehicle or ouabain (1 µg/kg/day). On the fourth day of injections, rats were exposed to total-body X-ray irradiation (10 Gy) or a sham irradiation. Isolated tissues were examined 72 h post-irradiation. Electrophysiological characteristics and paracellular permeability for sodium fluorescein were measured in an Ussing chamber. Histological analysis and Western blotting were also performed. In the jejunum tissue, ouabain exposure did not prevent disturbances in transepithelial resistance, paracellular permeability, histological characteristics, as well as changes in the expression of claudin-1, -3, -4, tricellulin, and caspase-3 induced by IR. However, ouabain prevented overexpression of occludin and the pore-forming claudin-2. In the colon tissue, ouabain prevented electrophysiological disturbances and claudin-2 overexpression. These observations may reveal a mechanism by which circulating ouabain maintains tight junction integrity under IR-induced intestinal dysfunction.
Topics: Male; Rats; Animals; Claudin-2; Ouabain; Rats, Wistar; Sodium-Potassium-Exchanging ATPase; Intestines
PubMed: 38203449
DOI: 10.3390/ijms25010278