Implications of Synthetic Modifications of the Cardiotonic Steroid Lactone Ring on Cytotoxicity.

Na,K-ATPase (NKA) and cardiotonic steroids (CTS) have shown potent cytotoxic and anticancer effects. Here, we have synthesized a series of CTS digoxin derivatives (γ-benzylidene) with substitutions in the lactone ring and evaluated the cytotoxicity caused by digoxin derivatives in tumor and non-tumor cells lines, as well as their effects on NKA. The cytotoxicity assay was determined in HeLa, A549, and WI-26 VA4 after they were treated for 48 h with increased concentrations of CTS. The effects of CTS on NKA activity and immunoblotting of α1 and ß1 isoforms were evaluated at IC50 concentrations in A549 cell membrane. NKA activity from mouse brain cortex was also measured. The majority of CTS exhibited low cytotoxicity in tumor and non-tumor cells, presenting IC50 values at micromolar concentrations, while digoxin showed cytotoxicity at nanomolar concentrations. BD-15 presented the lowest IC50 value (8 µM) in A549 and reduced its NKA activity in 28%. In contrast, BD-7 was the compound that most inhibited NKA (56% inhibition) and presented high IC50 value for A549. In mouse cortex, only BD-15 modulated the enzyme activity in a concentration-dependent inhibition curve. These results demonstrate that the cytotoxicity of these compounds is not related to NKA inhibition. The substitutions in the lactone ring of digoxin led to an increase in the cytotoxic concentration in tumor cells, which may not be interesting for cancer, but it has the advantage of increasing the therapeutic margin of these molecules when compared to classic CTS, and can be used safely in research for other diseases.

Antagonistic anticancer effect of paclitaxel and digoxin combination.

Despite the growing interest in the antitumor effect of cardiotonic steroids, combination treatments with well-established chemotherapy drugs like paclitaxel have been rarely investigated. Moreover, paclitaxel has been suggested as a Na+ /K+ -ATPase inhibitor. Here we investigated the effect of paclitaxel and digoxin alone or in combination on the viability of human lung (A549) and cervical cancer (HeLa) cell lines and the inhibitory effect of paclitaxel on several mammalian Na+ /K+ -ATPases. Although the viability of both tumor cell lines was concentration-dependently affected by digoxin treatment after 48 hours (A549 IC50 = 31 nM and HeLa IC50 = 151 nM), a partial effect was observed for paclitaxel, with a maximal inhibitory effect of 45% at 1000 nM with A549 and around 70% with HeLa cells (IC50 = 1 nM). Although the two drugs were cytotoxic, their combined effect in HeLa cells was revealed to be antagonistic, as estimated by the combination index. No direct inhibitory effect of paclitaxel was detected in human, pig, rat, and mouse Na+ /K+ -ATPase enzymes, but high concentrations of paclitaxel decreased the Na+ /K+ -ATPase activity in HeLa cells after 48 hours without affecting protein expression. Our findings demonstrate that, under our conditions, paclitaxel and digoxin cotreatment produce antagonistic cytotoxic effects in HeLa cells, and the mechanism of action of paclitaxel does not involve a direct inhibition of Na+ /K+ -ATPase. More studies shall be designed to evaluate the consequences of the interaction of cardiotonic steroids and chemotherapy drugs.

Isoproterenol induces an increase in muscle fiber size by the proliferation of Pax7-positive cells and in a mTOR-independent mechanism.

ß-Adrenergic signaling regulates many physiological processes in skeletal muscles. A wealth of evidence has shown that ß-agonists can increase skeletal muscle mass in vertebrates. Nevertheless, to date, the specific role of ß-adrenergic receptors in different cell phenotypes (myoblasts, fibroblasts, and myotubes) and during the different steps of embryonic skeletal muscle differentiation has not been studied. Therefore, here we address this question through the analysis of embryonic chick primary cultures of skeletal muscle cells during the formation of multinucleated myotubes. We used isoproterenol (ISO), a ß-adrenergic receptor agonist, to activate the ß-adrenergic signaling and quantified several aspects of muscle differentiation. ISO induced an increase in myoblast proliferation, in the percentage of Pax7-positive myoblasts and in the size of skeletal muscle fibers, suggesting that ISO activates a hyperplasic and hypertrophic muscle response. Interestingly, treatment with ISO did not alter the number of fibroblast cells, suggesting that ISO effects are specific to muscle cells in the case of chick myogenic cell culture. We also show that rapamycin, an inhibitor of the mammalian target of rapamycin signaling pathway, did not prevent the effects of ISO on chick muscle fiber size. The collection of these results provides new insights into the role of ß-adrenergic signaling during skeletal muscle proliferation and differentiation and specifically in the regulation of skeletal muscle hyperplasia and hypertrophy.

Telocinobufagin and Marinobufagin Produce Different Effects in LLC-PK1 Cells: A Case of Functional Selectivity of Bufadienolides.

Bufadienolides are cardiotonic steroids (CTS) identified in mammals. Besides Na⁺/K⁺-ATPase inhibition, they activate signal transduction via protein⁻protein interactions. Diversity of endogenous bufadienolides and mechanisms of action may indicate the presence of functional selectivity and unique cellular outcomes. We evaluated whether the bufadienolides telocinobufagin and marinobufagin induce changes in proliferation or viability of pig kidney (LLC-PK1) cells and the mechanisms involved in these changes. In some experiments, ouabain was used as a positive control. CTS exhibited an inhibitory IC50 of 0.20 (telocinobufagin), 0.14 (ouabain), and 3.40 µM (marinobufagin) for pig kidney Na⁺/K⁺-ATPase activity and concentrations that barely inhibited it were tested in LLC-PK1 cells. CTS induced rapid ERK1/2 phosphorylation, but corresponding proliferative response was observed for marinobufagin and ouabain instead of telocinobufagin. Telocinobufagin increased Bax:Bcl-2 expression ratio, sub-G0 cell cycle phase and pyknotic nuclei, indicating apoptosis. Src and MEK1/2 inhibitors blunted marinobufagin but not telocinobufagin effect, which was also not mediated by p38, JNK1/2, and PI3K. However, BIO, a GSK-3ß inhibitor, reduced proliferation and, as telocinobufagin, phosphorylated GSK-3ß at inhibitory Ser9. Combination of both drugs resulted in synergistic antiproliferative effect. Wnt reporter activity assay showed that telocinobufagin impaired Wnt/ß-catenin pathway by acting upstream to ß-catenin stabilization. Our findings support that mammalian endogenous bufadienolides may exhibit functional selectivity.

Effects of cardiotonic steroids on isolated perfused kidney and NHE3 activity in renal proximal tubules.

Cardiotonic steroids (CS) are known as modulators of sodium and water homeostasis. These compounds contribute to the excretion of sodium under overload conditions due to its natriuretic property related to the inhibition of the renal Na+/K+-ATPase (NKA) pump α1 isoform. NHE3, the main route for Na+ reabsorption in the proximal tubule, depends on the Na+ gradient generated by the NKA pump. In the present study we aimed to investigate the effects of marinobufagin (MBG) and telocinobufagin (TBG) on the renal function of isolated perfused rat kidney and on the inhibition of NKA activity. Furthermore, we investigated the mechanisms for the cardiotonic steroid-mediated natriuretic effect, by evaluating and comparing the effects of bufalin (BUF), ouabain (OUA), MBG and TBG on NHE3 activity in the renal proximal tubule in vivo. TBG significantly increased GFR, UF, natriuresis and kaliuresis in isolated perfused rat kidney, and inhibits the activity of NKA at a much higher rate than MBG. By stationary microperfusion technique, the perfusion with BUF, OUA, TBG or MBG promoted an inhibitory effect on NHE3 activity, whereas BUF was the most effective agent, and demonstrated a dose-dependent response, with maximal inhibition at 50nM. Furthermore, our data showed the role of NKA-Src kinase pathway in the inhibition of NHE3 by CS. Finally, a downstream step, MEK1/2-ERK1/2 was also investigated, and, similar to Src inhibition, the MEK1/2 inhibitor (U0126) suppressed the BUF effect. Our findings indicate the involvement of NKA-SRc-Kinase-Ras-Raf-ERK1/2 pathway in the downregulation of NHE3 by cardiotonic steroids in the renal proximal tubule, promoting a reduction of proximal sodium reabsorption and natriuresis.

γ-Benzylidene digoxin derivatives synthesis and molecular modeling: Evaluation of anticancer and the Na,K-ATPase activity effect.

Cardiotonic steroids (CS), natural compounds with traditional use in cardiology, have been recently suggested to exert potent anticancer effects. However, the repertoire of molecules with Na,K-ATPase activity and anticancer properties is limited. This paper describes the synthesis of 6 new digoxin derivatives substituted (on the C17-butenolide) with γ-benzylidene group and their cytotoxic effect on human fibroblast (WI-26 VA4) and cancer (HeLa and RKO) cell lines as well as their effect on Na,K-ATPase activity and expression. As digoxin, compound BD-4 was almost 100-fold more potent than the other derivatives for cytotoxicity with the three types of cells used and was also the only one able to fully inhibit the Na,K-ATPase of HeLa cells after 24h treatment. No change in the Na,K-ATPase α1 isoform protein expression was detected. On the other hand it was 30-40 fold less potent for direct Na,K-ATPase inhibition, when compared to the most potent derivatives, BD-1 and BD-3, and digoxin. The data presented here demonstrated that the anticancer effect of digoxin derivatives substituted with γ-benzylidene were not related with their inhibition of Na,K-ATPase activity or alteration of its expression, suggesting that this classical molecular mechanism of CS is not involved in the cytotoxic effect of our derivatives.

Heparin prevents the cytotoxic activity of Bothrops jararacussu and Apis mellifera venoms in renal cells.

Envenomation by Bothrops snakes and Apis mellifera bee may imply systemic disorders which affect well-perfused organs such as kidneys, a process that can lead to acute renal failure. Nevertheless, there is scarce information regarding a direct renal cell effect and the putative antagonism by antivenoms. Here the cytotoxic effect of B. jararacussu and A. mellifera venoms was evaluated in the renal proximal tubule cell line LLC-PK1, as well as the antagonism of this effect by heparin. B. jararacussu venom showed significant cytotoxicity as assessed by LDH release and MTT reduction, with a sharp decline of the cell number after 180 min (>90% at 50 µg/mL). A. mellifera venom produced a much faster and potent cytotoxic activity, conferring almost no viable cells after 15 min at 25 µg/mL. Phase contrast microscopy revealed that while B. jararacussu venom induced a progressive loss of cell adhesion and detachment, A. mellifera venom promoted a rapid plasma membrane disruption and nuclear condensation suggestive of necrotic cell death. Pre-incubation of both venoms with heparin for 30 min significantly reduced cytotoxicity. Our results demonstrate direct toxicity of B. jararacussu and A. mellifera venoms toward renal cells but with distinct kinetics and cell pattern, suggesting different mechanisms of action. In addition, the antagonistic, cytoprotective effect of heparin ascribes such compound as a promising drug for preventing renal failure from envenomation.

Effect of Fe3+ on Na,K-ATPase: Unexpected activation of ATP hydrolysis.

Iron is a key element in cell function; however, its excess in iron overload conditions can be harmful through the generation of reactive oxygen species (ROS) and cell oxidative stress. Activity of Na,K-ATPase has been shown to be implicated in cellular iron uptake and iron modulates the Na,K-ATPase function from different tissues. In this study, we determined the effect of iron overload on Na,K-ATPase activity and established the role that isoforms and conformational states of this enzyme has on this effect. Total blood and membrane preparations from erythrocytes (ghost cells), as well as pig kidney and rat brain cortex, and enterocytes cells (Caco-2) were used. In E1-related subconformations, an enzyme activation effect by iron was observed, and in the E2-related subconformations enzyme inhibition was observed. The enzyme's kinetic parameters were significantly changed only in the Na+ curve in ghost cells. In contrast to Na,K-ATPase α2 and α3 isoforms, activation was not observed for the α1 isoform. In Caco-2 cells, which only contain Na,K-ATPase α1 isoform, the FeCl3 increased the intracellular storage of iron, catalase activity, the production of H2O2 and the expression levels of the α1 isoform. In contrast, iron did not affect lipid peroxidation, GSH content, superoxide dismutase and Na,K-ATPase activities. These results suggest that iron itself modulates Na,K-ATPase and that one or more E1-related subconformations seems to be determinant for the sensitivity of iron modulation through a mechanism in which the involvement of the Na, K-ATPase α3 isoform needs to be further investigated.

Effect of ouabain on calcium signaling in rodent brain: A systematic review of in vitro studies.

The Na+/K+-ATPase is an integral membrane ion pump, essential to maintaining osmotic balance in cells in the presence of cardiotonic steroids; more specifically, ouabain can be an endogenous modulator of the Na+/K+-ATPase. Here, we conducted a systematic review of the in vitro effects of cardiotonic steroids on Ca2+ in the brain of rats and mice. Methods: The review was carried out using the PubMed, Virtual Health Library, and EMBASE databases (between 12 June 2020 and 30 June 2020) and followed the guidelines described in the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA). Results: in total, 829 references were identified in the electronic databases; however, only 20 articles were considered, on the basis of the inclusion criteria. The studies demonstrated the effects of ouabain on Ca2+ signaling in synaptosomes, brain slices, and cultures of rat and mouse cells. In addition to the well-known cytotoxic effects of high doses of ouabain, resulting from indirect stimulation of the reverse mode of the Na+/Ca2+ exchanger and increased intracellular Ca2+, other effects have been reported. Ouabain-mediated Ca2+ signaling was able to act increasing cholinergic, noradrenergic and glutamatergic neurotransmission. Furthermore, ouabain significantly increased intracellular signaling molecules such as InsPs, IP3 and cAMP. Moreover treatment with low doses of ouabain stimulated myelin basic protein synthesis. Ouabain-induced intracellular Ca2+ increase may promote the activation of important cell signaling pathways involved in cellular homeostasis and function. Thus, the study of the application of ouabain in low doses being promising for application in neurological diseases. Systematic Review Registration: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020204498, identifier CRD42020204498.

In vitro effect of valepotriates isolated from Valeriana glechomifolia on rat P-type ATPases.

Valepotriates are iridoids found in variable amounts in Valerianaceae and might be among the bioactive compounds which confer anxiolytic properties to the Valeriana species. On the other hand, unspecific cytotoxicity has also been described. Presently, however, no particular molecular target has been defined for these compounds. Here we studied the effect of valtrate, acevaltrate, and 1- ß-acevaltrate isolated from Valeriana glechomifolia on the enzymatic activity of rat P-type ATPases. Valepotriates did not affect rat skeletal muscle sarco/endoplasmic reticulum Ca²âº-ATPase (SERCA) activity at the highest concentration used (100 µM). In contrast, the same concentration inhibited roughly half of the total H⁺/K⁺-ATPase activity from rat gastric epithelium (valtrate 54.6 ± 3.2 %, acevaltrate 60.7 ± 7.3 %, 1- ß-acevaltrate 50.2 ± 3.1 %; mean ± SEM, n = 3-5). Finally, these substances showed the highest inhibitory potency toward Na⁺/K⁺-ATPase, and the inhibition curves obtained provided a similar IC50 (in µM) for rat kidney α1 isoform (valtrate 21.2, acevaltrate 22.8, 1- ß-acevaltrate 24.4) and brain hemispheres α2/ α3 isoforms (valtrate 19.4, acevaltrate 42.3, 1- ß-acevaltrate 38.3). Our results suggest that P-type ATPases are differentially inhibited by valepotriates and that Na⁺/K⁺-ATPase might be one of their molecular targets in vivo.

A Novel Apilic Antivenom to Treat Massive, Africanized Honeybee Attacks: A Preclinical Study from the Lethality to Some Biochemical and Pharmacological Activities Neutralization.

Massive, Africanized honeybee attacks have increased in Brazil over the years. Humans and animals present local and systemic effects after envenomation, and there is no specific treatment for this potentially lethal event. This study evaluated the ability of a new Apilic antivenom, which is composed of F(ab')2 fraction of specific immunoglobulins in heterologous and hyperimmune equine serum, to neutralize A. mellifera venom and melittin, in vitro and in vivo, in mice. Animal experiments were performed in according with local ethics committee license (UFRJ protocol no. DFBCICB072-04/16). Venom dose-dependent lethality was diminished with 0.25-0.5 µL of intravenous Apilic antivenom/µg honeybee venom. In vivo injection of 0.1-1 µg/g bee venom induced myotoxicity, hemoconcentration, paw edema, and increase of vascular permeability which were antagonized by Apilic antivenom. Cytotoxicity, assessed in renal LLC-PK1 cells and challenged with 10 µg/mL honeybee venom or melittin, was neutralized by preincubation with Apilic antivenom, as well the hemolytic activity. Apilic antivenom inhibited phospholipase and hyaluronidase enzymatic activities. In flow cytometry experiments, Apilic antivenom neutralized reduction of cell viability due to necrosis by honeybee venom or melittin. These results showed that this antivenom is effective inhibitor of honeybee venom actions. Thus, this next generation of Apilic antivenom emerges as a new promising immunobiological product for the treatment of massive, Africanized honeybee attacks.

Conformational states of the pig kidney Na+/K+-ATPase differently affect bufadienolides and cardenolides: A directed structure-activity and structure-kinetics study.

There is a renewed interest in the Na+/K+-ATPase (NKA, EC 3.6.3.9) either as a target for new therapeutic uses or for understanding the putative pathophysiological role of its mammalian endogenous ligands. Recent data indicate that bufalin binds to the pig kidney NKA in a way different from ouabain and digoxin, raising the question of a putative class difference between bufadienolides and cardenolides. The purpose of this work was to perform a study of the relationship between structure and both activity and kinetics, focusing mainly on the influence of the lactone ring in C17 (5 vs. 6 membered), the effect of C14-15 cyclization and the carbohydrate moiety in C3. We compared the potency of fourteen related cardiotonic steroids (CTS) for inhibition of the cycling pig kidney NKA in two different concentrations of K+, as well as the affinity for binding to the E2P conformation of the enzyme (Mg-Pi medium) and the potency for inhibiting the E2[2K] conformation of the NKA (K+-pNPPase activity). Cardenolides were clearly sensitive to the antagonistic effect of high K+ concentrations whereas bufadienolides were not or less sensitive. The C14-15 cyclization observed in some bufadienolides, such as resibufogenin and marinobufagin, caused a drastic fall in the affinity for binding to the NKA in the E2P conformation and increased the velocity of K+-pNPPase inhibition. The absence of a carbohydrate moiety in C3 increased the velocity of inhibition. Cardenolides were much more dependent on the E2P conformation for binding than bufadienolides since their ratios of E2[2K] IC50 to E2P Ki were higher than for bufadienolides. Therefore, the present data established the remarkable influence of C14-15 cyclization and of the carbohydrate moiety in C3 on both affinity and kinetics of CTS and indicate that, as a class, bufadienolides would harbor qualitative differences from cardenolides with respect to the NKA conformations to which they can bind.

Revisiting the binding kinetics and inhibitory potency of cardiac glycosides on Na+,K+-ATPase (α1ß1): Methodological considerations.

INTRODUCTION: Ouabain and digoxin are classical inhibitors of the Na+,K+-ATPase. In addition to their conventional uses as therapeutic agents or experimental tools there is renewed interest due to evidence suggesting they could be endogenous hormones. Somewhat surprisingly, different publications show large discrepancies in potency for inhibiting Na+,K+-ATPase activity (IC50), particularly for the slow binding inhibitors, ouabain and digoxin. METHODS: Using purified pig kidney Na+,K+-ATPase (α1ß1FXYD2) and purified detergent-soluble recombinant human Na+,K+-ATPase (α1ß1FXYD1) we have re-evaluated binding and inhibition kinetics and effects of K+ concentration for ouabain, digoxin, ouabagenin and digoxigenin. RESULTS: We demonstrate unequivocally that for slow binding inhibitors, ouabain and digoxin, long incubation times (≥60 min at 37 °C) are required to avoid under-estimation of potency and correctly determine inhibition (IC50 around 100-200 nM at 5 mM K+) contrary to what occurs when pre-incubation of the drugs without ATP is followed by a short incubation time. By contrast, for the rapidly bound inhibitors, ouabagenin and digoxigenin, short incubation times suffice (<10 min). The strong reduction of inhibitory potency observed at high un-physiological K+ concentrations (≥5 mM) also explained the low potency reported by some authors. DISCUSSION: The data resolve discrepancies in the literature attributable to sub-optimal assay conditions. Similar IC50 values are obtained for pig kidney and recombinant human Na+,K+-ATPase, showing that inhibitory potencies are not determined by the species difference (pig versus human) or environment (membrane-bound versus detergent-soluble) of the Na+,K+-ATPase. The present methodological considerations are especially relevant for drug development of slow binding inhibitors.

Na+/K+-ATPase alpha isoforms expression in stroke-prone spontaneously hypertensive rat heart ventricles: effect of salt loading and lacidipine treatment.

Changes in myocardial expression of Na+/K+-ATPase alpha-subunit isoforms have been demonstrated in different models of cardiac hypertrophy and hypertension. Here we studied the expression of these isozymes in stroke-prone spontaneously hypertensive rats (SHRSP) and the influence of high salt diet and treatment with the dihydropyridine lacidipine. Adult SHRSP were offered either 1% NaCl or water as drinking solution for 6 weeks. Salt-loaded SHRSP were treated or not with 1 mg/kg/day lacidipine. Compared to Wistar Kyoto (WKY) rats, non-salt-loaded SHRSP presented significant hypertension and cardiac hypertrophy. Salt intake markedly enhanced cardiac hypertrophy, an effect blunted by lacidipine. [3H]Ouabain binding assays on total particulate fractions from heart ventricles revealed the existence of two high-affinity sites with Kd approximately 25 and approximately 200 nM, ascribed to the alpha3 and alpha2 isoforms, respectively. Bmax of alpha3 was unexpectedly high (40% of total high-affinity binding) in ventricles from WKY rats but very low in all groups of SHRSP. On the other hand, Bmax of alpha2 was similar in WKY and non-salt-loaded SHRSP; however, salt loading of SHRSP resulted in a Bmax reduction of 20% (P<0.05), an effect blocked by lacidipine. These effects were largely confirmed by immunoblotting analysis, which, in addition, demonstrated that the density of the ubiquitous alpha1 isoform was comparable among the experimental groups. In conclusion, WKY rats showed a high myocardial expression of the Na+/K+-ATPase alpha3 subunit, which was not found in SHRSP; the level of the alpha2 isoform was similar in untreated SHRSP and WKY; salt-loading of SHRSP promoted reduction of the alpha2 isoform, and this effect was completely hampered by lacidipine.

[Similia Similibus Curentur: revisiting historical aspects of homeopathy nine years later]. / Similia Similibus Curentur: revisitando aspectos históricos da homeopatia nove anos depois.

Revising earlier conceptual misconstructions and delving deeper into the historical debate on the origins of homeopathy, this text returns to discussions initiated in the article "Simila Similibus Curentur: historical notes on homeopathic medicine" (1997). Research has been based on two main sources: ancient texts--Corpus Hippocraticum and works by Galen, Paracelsus, and Hahnemann--and the studies of commentators. In the nine years since original publication, previously explored content has undergone gradual revision, some points have been corrected, and discussions have developed further, lending substantially greater maturity to earlier positions. 'Born' in the eighteenth century yet rooted in the very origins of Western medicine, homeopathy is endeavoring to blossom in the twenty-first century as a specialty that wants to be autonomous but that needs the legitimacy of 'traditional' medical science.

Bufadienolides from parotoid gland secretions of Cuban toad Peltophryne fustiger (Bufonidae): Inhibition of human kidney Na(+)/K(+)-ATPase activity.

Parotoid gland secretions of toad species are a vast reservoir of bioactive molecules with a wide range of biological properties. Herein, for the first time, it is described the isolation by preparative reversed-phase HPLC and the structure elucidation by NMR spectroscopy and/or mass spectrometry of nine major bufadienolides from parotoid gland secretions of the Cuban endemic toad Peltophryne fustiger: ψ-bufarenogin, gamabufotalin, bufarenogin, arenobufagin, 3-(N-suberoylargininyl) marinobufagin, bufotalinin, telocinobufagin, marinobufagin and bufalin. In addition, the secretion was analyzed by UPLC-MS/MS which also allowed the identification of azelayl arginine. The effect of arenobufagin, bufalin and ψ-bufarenogin on Na(+)/K(+)-ATPase activity in a human kidney preparation was evaluated. These bufadienolides fully inhibited the Na(+)/K(+)-ATPase in a concentration-dependent manner, although arenobufagin (IC50 = 28.3 nM) and bufalin (IC50 = 28.7 nM) were 100 times more potent than ψ-bufarenogin (IC50 = 3020 nM). These results provided evidence about the importance of the hydroxylation at position C-14 in the bufadienolide skeleton for the inhibitory activity on the Na(+)/K(+)-ATPase.

Adaptive expression pattern of different proteins involved in cellular calcium homeostasis in denervated rat vas deferens.

The activity and protein expression of plasma membrane and sarco(endo)plasmic reticulum (Ca2+-Mg2+)ATPases and ryanodine receptors were investigated in surgically denervated rat vas deferens. The function of thapsigargin-sensitive but not thapsigargin-resistant (Ca2+-Mg2+)ATPase (from sarco(endo)plasmic reticulum and plasma membrane, respectively), evidenced by enzyme activity and Ca2+ uptake experiments, was significantly depressed by 30-50% when compared to innervated vas. Western blots showed that such reduction in sarco(endo)plasmic reticulum (Ca2+-Mg2+)ATPase performance was accompanied by a decrement of similar magnitude in sarco(endo)plasmic reticulum (Ca2+-Mg2+)ATPase type 2 protein expression, without any significant change in plasma membrane (Ca2+-Mg2+)ATPase expression. Finally, [3H]ryanodine binding revealed that the density of ryanodine binding sites was reduced by 45% after denervation without modification in affinity. The present findings demonstrate that sarco(endo)plasmic reticulum proteins involved in intracellular calcium homeostasis are clearly down-regulated and brings further evidence of a modified calcium translocation in denervated rat vas deferens.

Different effects of myotoxins bothropstoxin-I and II from Bothrops snake venom on cation transport ATPases from murine fast twitch skeletal muscle.

Bothrops jararacussu venom drastically decreases sarcoplasmic Ca(2+)-ATPase (SERCA) protein expression in vivo and inhibits its activity in vitro, in contrast to a slight increase of Na(+)/K(+)-ATPase expression in murine EDL. We investigated the effect of myotoxins bothropstoxin-I and/or -II (BthTX-I, BthTX-II and BthTX-I+II) on this model. No changes were seen in SERCA1, SERCA2 and Na(+)/K(+)-ATPase α1 protein expression as well as (2+)Ca-ATPase activity, but BthTX-II (1 µg/g) reduced Na(+)/K(+)-ATPase α2 expression by 50% one day after perimuscular injection. Interestingly, BthTX-II inhibited Ca(2+)-ATPase activity (IC50 around 6 nM). Our findings suggest that only BthTX-II affects ion transport ATPases, being a potent SERCA inhibitor and a putative target for antivenom drug development.

Role of noradrenaline on the expression of the Na+/K+-ATPase alpha2 isoform and the contractility of cultured rat vas deferens.

Rat vasa deferentia were cultured for 3 days in Dulbecco's modified Eagle's medium in the absence or presence of 1 microM noradrenaline (NA) to investigate if the lack of NA release is the key factor to explain the selective reduction of the Na(+)/K(+)-ATPase alpha(2) isoform previously observed after in vivo denervation of this organ (Quintas et al., Biochem Pharmacol 2000;60:741-7). The lack of effects of the indirect sympathomimetic tyramine and the neuronal amine uptake blocker cocaine on NA curves indicated that cultured organs were denervated completely. Organ culture induced supersensitivity, expressed as a 6.3-fold increase of pD(2) and a 42% elevation of maximal contraction for NA but not for Ba(2+). Western blotting indicated that the level of the alpha(1) isoform of Na(+)/K(+)-ATPase was unchanged after organ culture, but the alpha(2) isoform was down-regulated drastically to levels that were barely detectable. The addition of NA to the culture medium did not prevent the reduction of alpha(2) expression although it did impede NA supersensitivity (in fact a 4-fold decrease of pD(2) and a 32% reduction of maximal response were observed after incubation in the presence of NA). A striking reduction of L-type Ca(2+) channel expression also was observed, indicated by an 85% decrease of [3H]isradipine binding sites. These data suggest that NA is a trophic factor relevant to the control of muscle contraction, mediated by alpha(1)-adrenoceptors, but not to the expression of either Na(+)/K(+)-ATPase or the L-type Ca(2+) channel.

Inhibitory effect of combinations of digoxin and endogenous cardiotonic steroids on Na+/K+-ATPase activity in human kidney membrane preparation.

AIMS: Cardiac glycosides have been extensively used in the treatment of congestive heart failure for more than 200 years. Recently, cardenolides and bufadienolides were isolated from mammalian tissue and are considered as a new class of steroidal hormones. The aim of the present work was to characterize the interaction between the most clinical used cardiac glycoside digoxin and the cardiac glycosides known to exist endogenously, i.e., ouabain, marinobufagin and telocinobufagin, on human kidney Na(+)/K(+)-ATPase. MAIN METHODS: Inhibition of Na(+)/K(+)-ATPase activity from crude membrane preparations of human kidney was performed using increasing concentrations of the drugs alone or mixtures of ouabain:digoxin, telocinobufagin:digoxin and marinobufagin:digoxin in a fixed ratio 1:4, 2:3 and 3:2, respectively. The colorimetric method of Fiske and Subbarow was used to measure the inorganic phosphate released. KEY FINDINGS: Analyses of inhibition curves showed that the experimental curves for all combinations were superimposed on the theoretical additive curves indicating that an additive effect occurs among distinct cardenolides and bufadienolides combinations on the human α1ß1 Na(+)/K(+)-ATPase protomer. SIGNIFICANCE: Considering the extensive use of digoxin in the treatment of heart failure and the recent findings that endogenous cardiac glycosides may have altered levels in many diseases, including heart failure, the demonstration of additive effect between cardiac glycosides can help in the understanding of recent clinical observations, including that lower than usual doses of cardiac glycosides are necessary for decreasing mortality in these patients.