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PubMed1986

Studies on the optimization of parameters of preparative liquid chromatographic columns for production of cardiac glycosides.

Investigations aimed at maximization of the output of the production of cardiac glycosides from their mixtures using liquid chromatography are reported. The dependences of the yield of the process on column length, particle size and surface area of the packing and linear velocity of the mobile phase were examined. It has been established that a simultaneous decrease in the particle size and an increase in the column length and mobile phase flow-rate results in an improvement in the yield. However, such a procedure is limited by technological considerations. Optimum production conditions have been characterized.

Cardiac Glycosides↗
PubMed2001

Cardiac glycosides from Cryptostegia grandiflora.

From the leaves of Cryptostegia grandiflora, four new cardiac glycosides oleandrigenin 3-O-beta-glucopyranosyl-(1-->4)-beta-cymaropyranosyl-(1-->4)-beta-digitoxopyranoside, cryptostigmin I, oleandrigenin 3-O-beta-glucopyranosyl-(1-->4)-alpha-rhamnopyranoside, cryptostigmin II, 16-propionylgitoxigenin 3-O-beta-glucopyranosyl-(1-->4)-alpha-rhamnopyranoside, cryptostigmin III and oleandrigenin 3-O-beta-glucopyranosyl-(1-->6)-beta-glucopyranosyl-(1-->4)-beta-cymaropyranosyl-(1-->4)-beta-digitoxopyranoside, cryptostigmin IV have been isolated together with two known cardenolides subalpinosid and 16-O-acetyl-digitalinum verum. The structures of the isolated compounds were verified by means of MS and NMR spectral analyses.

Apocynaceae↗
PubMed2002

Do cardiac glycosides affect platelet function? A flow cytometric study in healthy volunteers.

OBJECTIVE: Cardiac glycosides exert their inotropic effect by increasing intracellular calcium. Increased intracellular calcium is a key event in platelet aggregation. In aggregometer studies, digitalis has been found to augment platelet agonist responses. A prothrombotic effect of digitalis might be concealed since heart failure and atrial fibrillation per se predispose to thromboembolism. The present study investigates the effects of digitoxin on platelet function in healthy volunteers. METHODS: Twenty healthy, non-smoking volunteers were randomised to receive digitoxin ( n = 10, 0.6 mg day 1, 0.4 mg day 2, then 0.1 mg daily) or placebo ( n = 10) for 10 days. Platelet function was then analysed ex vivo using three-colour whole-blood-flow cytometry, both in non-stimulated mode and after agonist stimulation with 0.1 micromol/l adenosine diphosphate (ADP), 10 micromol/l ADP and 5.0 micromol/l epinephrine (final concentrations). Expression of activated fibrinogen receptor, von Willebrand's factor receptor and P-selectin, formation of platelet-platelet and platelet-leukocyte aggregates and particle size were examined. RESULTS: No significant difference between the placebo and the digitoxin group (digitoxin levels 17-42 nmol/l) was found, neither on a global level nor for any isolated parameter. CONCLUSIONS: Theory and in vitro data suggest that digitoxin treatment could activate platelets. No evidence for this was found in healthy volunteers. This observation is strengthened by the unequivocal results for all parameters measured. However, thrombosis-prone patients with heart failure and/or atrial fibrillation may respond differently to digitalis therapy.

Adult↗
PubMed1992

Cardiac glycoside poisoning involved in deaths from traditional medicines.

Autopsy cases (from all areas of South Africa except the Cape Province) are referred for chemical investigation to the Johannesburg Forensic Chemistry Laboratory of the State Health Department. Over a 1-year period in 41 autopsies where death was presumed to have been caused by a herbal medicine, the presence of cardiac glycosides was sought and was found in 44%. Most of the cases were from the Transvaal, followed by Natal. Clinical histories of the patients revealed that gastrointestinal irritation was the most common syndrome experienced after traditional medicine administration (54%). It is concluded that in patients presenting with gastro-intestinal symptoms, presumably due to poisoning by traditional medicines, cardiac glycoside poisoning should be suspected.

Adolescent↗
PubMed1990

Age-dependent change in myocardial cardiac glycoside receptor (Na,K-pump) concentration in children.

Myocardial Na,K-ATPase concentration was quantified in 18 0-8-year-old human subjects by vanadate-facilitated 3H-ouabain binding to intact samples of the left ventricle of the heart obtained at autopsy. Within the first 6 months of life, the Na,K-ATPase concentration showed a rapid decrease. The mean value in the age range from birth to 6 months was 1.6 times the mean value obtained in the age range 6 months to 8 years. The mean values +/- SEM were 1,076 +/- 57 (n = 10) and 671 +/- 28 (n = 8) (p less than 0.001) pmol/g wet weight, respectively. The highest value [1,433 +/- 56 pmol/g wet weight (n = 5)] was found in a 3-month-old child and the lowest value [545 +/- 22 pmol/g wet weight (n = 5)] in an 8-year-old. Evaluation of 3H-ouabain-binding kinetics showed no age-dependent variations. The total amount of Na,K-ATPase found in the heart was approximately 30 and 80 nmol within the first 3 years of life and at 8 years, respectively. The age-dependent change in myocardial Na,K-ATPase concentration can be ascribed to variation in the ratio between the amount of Na,K-ATPase and muscle mass during development. Since myocardial Na,K-ATPase is the receptor for cardiac glycosides, the present results may in part explain the clinical observation that cardiac glycoside sensitivity and toxicity change in young age.

Aging↗
PubMed2000

Selective inhibition of human erythrocyte Na+/K+ ATPase by cardiac glycosides and by a mammalian digitalis like factor.

Na+/K+ATPase is a transport membrane protein which contains the functional receptor for digitalis compounds. In this work we compare the inhibition curves of Na+/K+ATPase measured by the inhibition of 86Rb uptake in human red blood cells by cardiac glycosides and by an endogenous digitalis like factor (EDLF) extracted from human newborn cord blood. The curves of Na+/K+TPase inhibition show a monophasic shape for ouabain, strophantidin, digitoxin, proscillaridin and EDLF whereas a biphasic shape for ouabagenin, digoxin, digoxigenin and digitoxigenin. All the drugs are potent inhibitors of erythrocyte Na+/K+ATPase with an IC50 ranging from 1.8 x 10(-9) M to 1.4 x 10(-11) M for the higher affinity binding site and from 1.8 x 10(-6) M to 5.5 x 10(-9) M for the lower affinity site. Digitoxigenin is the most active showing the higher active site at 1.4 x 10(-11) M. Ouabain and digoxin have higher affinity compared with their corresponding genins, while digitoxigenin shows a binding site with higher affinity than the respective cardiac glycosides. The increased affinity of the drugs to Na+/K+ATPase may be related to a lipophilic region in correspondence of the carbons 10, 9, 11, 12, 13 of the steroid nucleus, situated in the opposite side with respect of the C-OH-14. The comparison of the inhibition curves and the HPLC profile of newborn EDLF and of the investigated cardenolides suggest that EDLF may be a compound identical or very similar to ouabain.

Cardiac Glycosides↗
PubMed1991

Investigation of electrophysiologic mechanisms for the antiarrhythmic actions of R 56865 in cardiac glycoside toxicity.

R 56865 is an experimental compound that has been shown to ameliorate the effects of cardiac glycoside toxicity and myocardial ischemia. We evaluated the direct electrophysiological effects of R 56865 and its effects on the electrophysiological sequelae of ouabain toxicity in vivo and in vitro. In normal anesthetized dogs, R 56865 alone at doses of 0.04 to 0.16 mg/kg i.v. had no effect on atrial, AV nodal, or ventricular conduction times and refractoriness, but at doses of 0.64 to 2.5 mg/kg it tended to increase these parameters. In ouabain-pretreated dogs, R 56865 (0.08 to 0.32 mg/kg i.v.) dose-relatedly reduced ouabain-induced ventricular arrhythmias. In normal isolated canine Purkinje fibers, R 56865 (1-10 microM) reduced Vmax at short pacing cycle lengths and decreased the action potential duration at concentrations of 0.1 to 10 microM. R 56865 at concentrations through 10 microM had no significant effect on normal action potentials of canine ventricular muscle and slow response action potentials in guinea pig papillary muscles. In Purkinje fibers exposed to toxic concentrations of ouabain, R 56865 (1 microM) reduced the delayed after depolarization (DAD) amplitude and inhibited triggered activity. R 56865 had no effect on normal automaticity in canine Purkinje fibers at 1 microM, but 10 microM significantly slowed it. R 56865 at 10 microM did not affect isoproterenol-enhanced automaticity and only slightly reduced barium-induced abnormal automaticity that occurred at reduced membrane potentials. These results demonstrate that R 56865 reverses cardiac glycoside-induced arrhythmias in anesthetized dogs at doses that do not significantly affect conduction or refractoriness. Suppression of ouabain-induced DAD and triggered activity in isolated Purkinje fibers, at concentrations not affecting normal or abnormal automaticity, may be the mechanism of R 56865's antiarrhythmic actions in vivo. Suppression of DAD does not appear to be associated with blockade of voltage-dependent calcium channels, but R 56865 may prevent intracellular sodium overload by limiting excessive sodium entry during ouabain intoxication.

Action Potentials↗
PubMed1981

Changes in cellular Na+, K+, and Ca2+ contents, monovalent cation transport rate, and contractile state during washout of cardiac glycosides from cultured chick heart cells.

To delineate more clearly the importance of altered monovalent cation transport rate in the mediation of the positive inotropic effects of cardiac glycosides, we studied changes in the contractile state and rate of uptake of K+ and Rb+ by monolayer cultures of chick embryo ventricular cells during exposure to and washout of ouabain and dihydro-ouabain. These cardiac glycosides produced a positive inotropic effect in this system, accompanied by a significant reduction in monovalent cation transport rate, by increases in cellular contents of Na+ and Ca2+, and by a decrease in cellular content of K+ as judged by radioisotopic tracer studies. Following removal of glycosides from media bathing the cultures, monovalent cation transport rate returned to normal within 1 minute, followed by a loss of inotropy which was complete by 7 minutes, a time at which cellular [Ca2+] had returned to normal. The bulk cellular concentration of Na+ remained increased, however, and that of K+ depressed for longer periods. Veratrine (1 microgram/ml) induced a positive inotropic effect, but caused a less marked increase in cellular [Na+] than did equipotent concentrations of ouabain and dihydroouabain. These results indicate that there is not a simple relationship between bulk cellular [Na+] and magnitude of inotropic effect in these cells, and are consistent with the proposal that there is a subsarcolemmal space in which [Na+] regulates Ca2+ fluxes and contractility, and in which [Na+] is regulated primarily by the balance between transsarcolemmal influx and Na+ pump rate and, to a lesser degree, by bulk [Na+].

Animals↗
PubMed2002

Subcellular and molecular mechanisms of the effects of cardiac glycosides and angiotensin-converting enzyme inhibitors on contractile function and energy conversion in myocardial myofibrils under normal conditions and during acute cardiac insufficiency.

Experiments on skinned and hybrid myocardial fibers isolated from normal dogs and animals subjected to 120-min occlusion of the anterior interventricular branch of the coronary artery showed that in contrast to cardiac glycosides, angiotensin-converting enzyme inhibitors suppress contractile ability of myocardial myofibrils in a dose-independent manner within the concentration range of 10(-12)-10(-4)M. This effect is accompanied by a decrease in fiber relaxation rate most pronounced in the presence of captopril. Actin, the major protein of fine filaments is the target for b-acetyldigoxin, K-strophanthin, captopril, enalapril, and trandolapril in myocardial myofibrils. During coronary occlusion, the inhibitors of angiotensin-converting enzyme induce structural and conformational changes in actin that decrease efficiency of contraction. The data obtained cast doubt on advisability of therapeutic use of angiotensin-converting enzyme inhibitors in the therapy of myocardial infarction, especially in its early period.

Actins↗
PubMed1994

[Inhibitory effects of 6 cardiac glycosides on sodium pump in sheep Purkinje fibers].

The inhibitory effects of 6 cardiac glycosides (digoxin, meproscillarin, acrihellin, deslanoside, ouabain, K-strophanthin) on sodium pump in sheep Purkinje fibers were studied. Isolated Purkinje fibers were used and stimulated at 0.4 Hz regularly. Intracellular sodium activity (aiNa), potassium activity (aiK) and membrane potential (Em) were monitored with single barrel normal and ion-selective micro-electrodes. It was shown that aiNa rose definitely from the concentration of 30 nmol.L-1, and became more significant until the dose of 0.4 mumol.L-1. aiNa rose very much faster within the range of toxic doses (from 1-20 mumol.L-1 to 1 mmol.L-1). The occurrence time of delay afterdepolarization (DAD) after adding drugs varied with various drugs used, or with different experiments, hence the time points of DAD and delta aiNa-time, concentration relation curves were quite scattered. But when basing on the appearance of DAD as a common time point we calculated the temporal variation of aiNa before and after toxic effect, the relation curves in a same sort of glycoside were kept uniform. When the toxic effects of glycosides appeared, the inhibition degree of sodium pump activity was quite close (between 52.8% and 65.5%), suggesting that there existed close relationship between sodium pump inhibition and toxic effects of glycosides. Intracellular potassium ions lost progressly within the scope of subtoxic doses (10-30 nmol.L-1) and lost more significantly within the scope of toxic doses (1-20 mumol.L-1). Based on the results of calculation, the inward current induced by the sodium pump inhibition might be responsible for the abnormal automaticity.

Animals↗
PubMed1996

Transport and epithelial secretion of the cardiac glycoside, digoxin, by human intestinal epithelial (Caco-2) cells.

1. Human intestinal epithelial Caco-2 cells have been used to investigate the transepithelial permeation of the cardiac glycoside, digoxin. 2. Transepithelial basal to apical [3H]-digoxin flux exceeds apical to basal flux, a net secretion of [3H]-digoxin being observed. At 200 microM digoxin, net secretory flux (Jnet) was 10.8 +/- 0.6 nmol cm-2 h-1. Maximal secretory flux (Jmax) of vinblastine was 1.3 +/- 0.1 nmol cm-2 h-1. Cellular uptake of digoxin was different across apical and basal cell boundaries. It was greatest across the basal surface at 1 microM, whereas at 200 microM, apical uptake exceeded basal uptake. 3. Net secretion of [3H]-digoxin was subject to inhibition by digitoxin and bufalin but was not inhibited by ouabain, convallatoxin, and strophanthidin (all 100 microM). Inhibition was due to both a decrease in Jb-a and an increase in Ja-b. Uptake of [3H]-digoxin at the apical surface was increased by digitoxin and bufalin. All cardiac glycosides decreased [3H]-digoxin uptake at the basal cell surface (except for 100 microM digitoxin). 4. The competitive P-glycoprotein inhibitors, verapamil (100 microM), nifedipine (50 microM) and vinblastine (50 microM) all abolished net secretion of [3H]-digoxin due to both a decrease in Jb-a and an increase in Ja-b. Cellular accumulation of [3H]-digoxin was also increased across both the apical and basal cell surfaces. I-Chloro-2,4,-dinitrobenzene (10 microM), a substrate for glutathione-S-transferase and subsequent ATP-dependent glutathione-S-conjugate secretion, failed to inhibit net secretion of [3H]-digoxin. The increase in absorptive permeability Pa-b (= Ja-b/Ca) and cellular [3H]-digoxin uptake upon P-glycoprotein inhibition, showed that the intestinal epithelium was rendered effectively impermeable by ATP-dependent extrusion at the apical surface. 5. A model for [3H]-digoxin secretion by the intestinal epithelium is likely to involve both diffusional uptake and Na(+)-K+ pump-mediated endocytosis, followed by active extrusion at the apical membrane.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1976

Cardiac glycosides: relationship among active 86Rb uptake, (Na+,K+)-ATPase activity, and inotropy in guinea pig heart.

Relationships among positive inotropic responses, (Na+,K+)-ATPase inhibition, and sodium pump activities were studied using paced Langendorff preparations of guinea pig heart. (Na+,K+)-ATPase activity was estimated from the initial velocity of [3H] ouabain binding in ventricular homogenates, and sodium pump activity from ouabain-sensitive 86Rb uptake of ventricular slices. These parameters were measured in control, or in ouabain-or digitoxin-treated hearts either at the time of inotropic response or during the course of drug washout and compared with inotropy in the same heart. Perfusion of ouabain or digitoxin caused an increase in contractile force and a decrease in the initial velocity of ATP-dependent [3H] ouabain binding. The levels of [3H] ouabain binding in homogenates observed after a long incubation period were not different in ouabain-perfused and control homogenates, indicating that the nonlabeled ouabain bound to (Na+,K+)-ATPase during Langendorff perfusion was exchangeable with [3H] ouabain. Perfusion of drug-free solution after a 20-min perfusion of the isolated heart with either ouabain or digitoxin resulted in a loss of inotropic response and a recovery of the inhibition of the initial velocity of ATP-dependent [3H] ouabain binding. Inotropic responses to digitoxin during perfusion and subsequent loss during washout were accompanied by a reduction and subsequent recovery of ouabain-sensitive 86Rb uptake. Thus, it would appear that with cardiac glycosides, a relationship exists among cardiac contractile force, the inhibition of cardiac (Na+,K+)-ATPase, and the inhibition of the sodium pump activity. The inhibition of (Na+,K+)-ATPase and sodium pump because of cardiac glycoside perfusion of the isolated beating heart was reversible.

Adenosine Triphosphatases↗
PubMed1984

Involvement of the sugar moiety in the inhibitory action of the cardiac glycosides on the palytoxin-induced responses in vascular smooth muscles.

The effects of ouabain and other cardiotonic steroids were examined to investigate whether changes in Na,K-adenosine triphosphatase (ATPase) activity modified the actions of palytoxin (PTX) in rabbit aortic vascular smooth muscle. The effects of these agents on rabbit aorta were compared with those on rat aorta, as it is known that the concentration of cardiac glycosides required to inhibit Na,K-ATPase of rat aorta is markedly higher than that of other species. PTX induced contraction in rabbit and rat aortas in a similar concentration range (10(-11) to 10(-8) M). PTX rapidly decreased tissue K content of these preparations. Ouabain (2 X 10(-5) M) inhibited both the contraction and the loss of tissue K in rabbit aorta but not in rat aorta. In rabbit aorta, convallatoxin (2 X 10(-5) M), which has one rhamnose as a sugar moiety like ouabain, and cymarin (2 X 10(-5) M), which has one cymarose, inhibited the PTX-induced contraction and the loss of tissue K, although ouabagenin, convallatoxigenin and cymarigenin (strophanthidin) (2 X 10(-5) M) did not. Other cardiotonic steroids, digoxin and digitoxin, which have 3 U of digitoxose as a sugar component, or the corresponding aglycones failed to inhibit the PTX-responses. On the other hand, all the cardiotonic steroids at concentration of 2 X 10(-5) M equally inhibited the reuptake of K and relaxation of norepinephrine-induced contractions induced by the readdition of K. Inhibition of Na-K pump by K-free solution potentiated rather than inhibited the PTX-induced contraction. These results suggest that the specific sugar moiety of cardiac glycosides is important for the inhibitory effect exerted by these compounds on the PTX-induced responses and that the inhibition is not related to the activity of the Na,K-ATPase.

Acrylamides↗
PubMed1985

Effects of K+ on the interaction between cardiac glycosides and Na,K-ATPase.

Inhibition of Na,K-ATPase by cardiac glycosides is at least partially antagonized by K+. The kinetics of the antagonism, however, appear complicated because K+ is capable of reducing both association and dissociation rate constants for the glycoside-enzyme interaction. In order to better understand the effect of K+, inhibition of partially purified Na,K-ATPase obtained from rat brain, guinea-pig heart and rat heart by ouabain, digoxin, digoxigenin, dihydrodigoxin and cassaine were compared in the presence of 1, 3 or 10 mM K+. Higher concentrations of K+ caused a parallel shift to the right in the concentration-inhibition curves for these compounds. For ouabain or digoxin, the extent of the shift was minimal with rat brain enzyme, intermediate with guinea-pig heart enzyme and more substantial with rat heart enzyme. For digoxigenin, dihydrodigoxin or cassaine, the extent of the shift was substantial in all enzyme preparations. These results could not be explained from either the affinity of the enzyme for the compound or its lipid solubility alone. The concentrations of these compounds required to cause a 50 percent inhibition of enzyme activity were markedly different with rat brain enzyme, but relatively similar with rat heart enzyme. The effects of K+, which depend on the source of the enzyme and chemical structures of the compounds, have to be considered in studies on comparative effects of various compounds on Na,K-ATPase, [3H]ouabain binding, sodium pumping and the force of myocardial contraction.

Abietanes↗
PubMed2005

Molecular modeling of cardiac glycoside binding by the human sequence monoclonal antibody 1B3.

The amino acid sequences of the heavy- and light-chain variable regions of the high-affinity human sequence antidigoxin monoclonal antibody 1B3 (mAb 1B3) were determined, and a structural model for the mAb's variable region was developed by homology modeling techniques. The structural model provided the basis for computationally docking digoxin and eight related cardiac glycosides into the putative binding site of mAb 1B3. Analysis of the consensus binding mode obtained for digoxin showed that the cardenolide moiety of digoxin is deeply embedded in a predominantly hydrophobic, narrow cavity, whereas the terminal, gamma-carbohydrate group is solvent-exposed. The docking results indicated that the primary driving forces for digoxin binding by mAb 1B3 are hydrophobic interactions with the digoxin steroid ring system and hydrogen bonds with the digitoxose groups. The binding model accounts for the experimentally observed variations in mAb 1B3 binding affinity for various structural analogs of digoxin used previously to develop a 3D structure-activity relationship model of drug binding (Farr CD, Tabet MR, Ball WJ Jr, Fishwild DM, Wang X, Nair AC, Welsh WJ. Three-dimensional quantitative structure-activity relationship analysis of ligand binding to human sequence antidigoxin monoclonal antibodies using comparative molecular field analysis. J Med Chem 2002;45:3257-3270). In particular, the hydrogen bond pattern is consistent with the unique sensitivity of mAb 1B3's binding affinity to the number of sugar residues present in a cardiac glycoside. The hydrophobic environment about the steroid moiety of digoxin is compatible with the mAb's reduced affinity for ligands that possess hydrophilic hydroxyl and acetyl group modifications in this region. The model also indicated that most of the amino acid residues in contact with the ligand reside in or about the three complementarity determining regions (CDRs) of the heavy chain and the third CDR of the light chain. A comparison of the 1B3 binding model with the crystal structures of two murine antidigoxin mAbs revealed similar binding patterns used by the three mAbs, such as a high frequency of occurrence of aromatic, hydrophobic residues in the CDRs and a dominant role of the heavy chain CDR3 in antigen binding.

Amino Acid Sequence↗
PubMed1990

Effectiveness of cardiac glycosides in human myocardium with and without "downregulated" beta-adrenoceptors.

We investigated the "receptor-effector-coupling" in the beta-adrenoceptor- and the Na+, K(+)-ATPase-mediated systems in nonfailing hearts and terminally failing human myocardium from patients with cardiomyopathy. The density of beta-adrenoceptors in the failing human myocardium was significantly (p less than 0.01) lower as compared with nonfailing hearts, whereas the receptor density and affinity measured by [3H]ouabain binding (cardiac glycoside receptor) was not different in either group. The maximal inotropic response to isoprenaline was significantly reduced in papillary muscle strips from failing human hearts (2.1 +/- 0.5 mN) as compared with control hearts (8.0 +/- 1.0 mN; p less than 0.05). Ouabain remained effective in both groups (6.8 +/- 1.0 vs. 5.5 +/- 0.6 mN; NS). The positive inotropic response due to extracellular Ca2+ elevation (1.8-15 mM) was studied for comparison. Maximal Ca2+ effects were reduced by 30% in failing human myocardium (7.2 +/- 0.5 mN vs. 5.1 +/- 0.8 mN, p less than 0.05). Ouabain had effectiveness (95%) similar to that of Ca2+ in nonfailing and failing human cardiac muscle. It is concluded that treatment with cardiac glycosides may still be effective in end-stage heart failure with "downregulated" beta-adrenoceptors, as judged from these in vitro studies.

Adult↗