RESUMEN
Digitalis-like compounds (DLCs), such as digoxin and digitoxin that are derived from digitalis species, are currently used to treat heart failure and atrial fibrillation, but have a narrow therapeutic index. Drug-drug interactions at the transporter level are frequent causes of DLCs toxicity. P-glycoprotein (P-gp, ABCB1) is the primary transporter of digoxin and its inhibitors influence pharmacokinetics and disposition of digoxin in the human body; however, the involvement of P-gp in the disposition of other DLCs is currently unknown. In present study, the transport of fourteen DLCs by human P-gp was studied using membrane vesicles originating from human embryonic kidney (HEK293) cells overexpressing P-gp. DLCs were quantified by liquid chromatography-mass spectrometry (LC-MS). The Lily of the Valley toxin, convallatoxin, was identified as a P-gp substrate (Km: 1.1±0.2 mM) in the vesicular assay. Transport of convallatoxin by P-gp was confirmed in rat in vivo, in which co-administration with the P-gp inhibitor elacridar, resulted in increased concentrations in brain and kidney cortex. To address the interaction of convallatoxin with P-gp on a molecular level, the effect of nine alanine mutations was compared with the substrate N-methyl quinidine (NMQ). Phe343 appeared to be more important for transport of NMQ than convallatoxin, while Val982 was particularly relevant for convallatoxin transport. We identified convallatoxin as a new P-gp substrate and recognized Val982 as an important amino acid involved in its transport. These results contribute to a better understanding of the interaction of DLCs with P-gp.
Asunto(s)
Subfamilia B de Transportador de Casetes de Unión a ATP/metabolismo , Estrofantinas/metabolismo , Animales , Transporte Biológico/fisiología , Encéfalo/metabolismo , Línea Celular , Digoxina/metabolismo , Células HEK293 , Humanos , Corteza Renal/metabolismo , Masculino , Proteínas de Transporte de Membrana/metabolismo , Ratas , Ratas WistarRESUMEN
CONTEXT: Cardiac glycosides of plant origin are implicated in toxic ingestions that may result in hospitalization and are potentially lethal. The utility of commonly available digoxin serum assays for detecting foxglove and oleander ingestion has been demonstrated, but no studies have evaluated the structurally similar convallatoxin found in Convallaria majalis (lily of the valley) for rapid laboratory screening, nor has digoxin immune Fab been tested as an antidote for this ingestion. OBJECTIVE: We aimed to (1) evaluate multiple digoxin assays for cross-reactivity to convallatoxin, (2) identify whether convallatoxin could be detected in vivo at clinically significant doses, and (3) determine whether digoxin immune Fab could be an effective antidote to convallatoxin. MATERIALS AND METHODS: Cross-reactivities of purified convallatoxin and oleandrin with five common digoxin immunoassays were determined. Serum from mice challenged with convallatoxin was tested for apparent digoxin levels. Binding of convallatoxin to digoxin immune Fab was determined in vitro. RESULTS: Both convallatoxin and oleandrin were detectable by a panel of commonly used digoxin immunoassays, but cross-reactivity was variable between individual assays. We observed measurable apparent digoxin levels in serum of convallatoxin intoxicated mice at sublethal doses. Convallatoxin demonstrated no binding by digoxin immune Fab. CONCLUSION: Multiple digoxin immunoassays detect botanical cardiac glycosides including convallatoxin and thus may be useful for rapid determination of severe exposures, but neutralization of convallatoxin by digoxin immune Fab is unlikely to provide therapeutic benefit.
Asunto(s)
Estrofantinas/análisis , Vasodilatadores/análisis , Animales , Animales no Consanguíneos , Cardenólidos/análisis , Cardenólidos/metabolismo , Cardiotónicos/análisis , Cardiotónicos/antagonistas & inhibidores , Cardiotónicos/metabolismo , Convallaria/envenenamiento , Reacciones Cruzadas , Digoxina/análisis , Digoxina/antagonistas & inhibidores , Digoxina/metabolismo , Relación Dosis-Respuesta a Droga , Femenino , Inmunoensayo , Fragmentos Fab de Inmunoglobulinas/metabolismo , Dosificación Letal Mediana , Ratones , Intoxicación por Plantas/sangre , Intoxicación por Plantas/diagnóstico , Intoxicación/sangre , Intoxicación/diagnóstico , Estrofantinas/administración & dosificación , Estrofantinas/metabolismo , Estrofantinas/toxicidad , Vasodilatadores/administración & dosificación , Vasodilatadores/metabolismo , Vasodilatadores/toxicidadRESUMEN
Steady-state kinetics of thioproperazine, triftazine, aminazine, and o-dianisidine oxidation with hydrogen peroxide catalyzed by horseradish peroxidase were studied in the presence of strophanthin G. Values of the inhibition and activation constants (Ki, Ka) were determined in the pH range 5.0-7.5. At acidic pH, strophanthin G activated peroxidase during the oxidation of thioproperazine by the uncompetitive mechanism, and when triftazine was oxidized, the inhibition was noncompetitive. At pH > 6.0, the patterns of activation and inhibition changed to mixed-type during the peroxidase oxidation of thioproperazine and triftazine and to competitive inhibition of peroxidase with strophanthin G during the oxidation of aminazine. These effects are suggested to be due to an ionizable enzyme group of pK approximately 6.0. Strophanthin G inhibited free-radical oxidation of o-dianisidine via binding to the enzyme-substrate complex, preventing the generation of a stable semi-oxidized product of o-dianisidine, and thus inhibiting the enzyme by the anticompetitive mechanism. Mechanisms of oxidation of slowly and rapidly oxidizable substrates of peroxidase in the presence of strophanthin G are suggested.
Asunto(s)
Peroxidasas/metabolismo , Estrofantinas/farmacología , Ácido Ascórbico/metabolismo , Concentración de Iones de Hidrógeno , Cinética , NAD/metabolismo , Oxidación-Reducción , Estrofantinas/metabolismo , Especificidad por SustratoRESUMEN
Interactions of three horseradish peroxidase (HRP)-strophanthin conjugates containing one, two, or three glycoside molecules (HRP-Str1, 2, or 3, respectively) with polyclonal anti-HRP antibodies were studied by homogeneous enzyme immunoassay. The total peroxidase activity of free conjugates and their immune complexes was estimated from the oxidation of o-phenylenediamine. The dissociation constants of the immune complexes and the rate constants of their dissociation and formation were determined. The equilibrium and kinetic parameters were determined for the interactions of the HRP-Str2 immune complex with anti-strophanthin and anti-HRP antibodies. The determined equilibrium and kinetic parameters of the HRP-Str interactions with anti-HRP antibodies depended on the molecular weights, sizes, and structures of the antigens studied.
Asunto(s)
Anticuerpos/metabolismo , Peroxidasa de Rábano Silvestre/inmunología , Estrofantinas/metabolismo , Peroxidasa de Rábano Silvestre/metabolismo , Técnicas para Inmunoenzimas , Cinética , Especificidad por SustratoRESUMEN
Two models of heart failure were used in rat experiments to study the effect of isoptin on tolerance to the toxic effect of k-strophanthin. Calcium antagonist-induced changes in the cardiotonic and chronotropic effects of the cardiac glycoside and myocardial oxygen consumption were examined in isolated frog atria with a movable-electrode electron tube and polarography. Isoptin was shown to substantially enhance tolerance to the toxic effect of k-strophanthin and slightly decrease positive inotropic effects of the cardiotonic, by slowing down its development rate. The agent potentiated the negative chronotropic action and lowered myocardial oxygen consumption.
Asunto(s)
Gasto Cardíaco Bajo/metabolismo , Atrios Cardíacos/metabolismo , Miocardio/metabolismo , Estrofantinas/metabolismo , Verapamilo/metabolismo , Animales , Gasto Cardíaco Bajo/tratamiento farmacológico , Gasto Cardíaco Bajo/fisiopatología , Interacciones Farmacológicas , Electrodos Implantados , Frecuencia Cardíaca/efectos de los fármacos , Modelos Biológicos , Consumo de Oxígeno/efectos de los fármacos , Ranidae , Ratas , Ratas Wistar , Estrofantinas/farmacología , Estrofantinas/uso terapéutico , Verapamilo/farmacología , Verapamilo/uso terapéuticoAsunto(s)
Azidas/metabolismo , Citratos/farmacología , Cimarina/metabolismo , Isoenzimas/biosíntesis , Retina/enzimología , ATPasa Intercambiadora de Sodio-Potasio/biosíntesis , Estrofantinas/metabolismo , Animales , Cimarina/análogos & derivados , Inducción Enzimática , Masculino , Metionina/metabolismo , Ratas , Ratas Endogámicas , Valores de ReferenciaRESUMEN
In 33 healthy male volunteers, given a single oral and intravenous dose of cymarin (k-strophanthin-alpha), k-strophanthoside (k-strophanthin-gamma) and ouabain (g-strophanthin), enteral absorption and renal excretion of these glycosides and their metabolites were investigated by radioimmunoassay and HPLC. Cymarin was absorbed at 47% of the given dose. After intravenous injection 46% and after oral administration 21% of the given dose, i.e. the total amount as detected by radioimmunoassay which consisted of the unchanged glycoside and its metabolites, were excreted by the kidneys mainly as conjugated metabolites. The half-life of elimination, calculated from the total excreted amount was 13 h (i.v.) and 23 h (p.o.), respectively. k-Strophanthoside was absorbed at 16% of the given dose. After i.v.-injection 73% of the given dose was excreted by the kidneys with a half-life of elimination of 99 h. From this total amount about 70% was excreted as the unchanged drug, the remaining 30% as various metabolites. After oral administration 11% of the given dose were excreted with a half-life of elimination of 22 h. 80% of this amount consisted mainly of conjugated k-strophanthoside and conjugated metabolites as k-strophanthin-beta, cymarin, k-strophanthidin, cymarol and k-strophanthidol. Only 6% was excreted as the unchanged drug. Ouabain was absorbed after oral administration to a minimum of 1.4%. Given intravenously a total renal excretion of 33% of the given dose with a half-life of elimination of 23 h was measured. Of this 80% was unchanged ouabain.(ABSTRACT TRUNCATED AT 250 WORDS)
Asunto(s)
Estrofantinas/metabolismo , Administración Oral , Adulto , Biotransformación , Cimarina/metabolismo , Humanos , Inyecciones Intravenosas , Absorción Intestinal , Masculino , Ouabaína/metabolismo , Estrofantinas/orinaRESUMEN
The gluconic fragment of strophantin K oxidation by sodium metaperiodate yields a dialdehyde derivate conjugated with catalase. The conjugate obtained contains 11 molecules of cardiac glucoside. Adsorption and circular dichroism spectra of the native enzyme and its conjugate were compared and structural differences between both samples were revealed. The kinetics of ethanol oxidation into acetaldehyde by cumene hydroperoxide was studied at 30 degrees C in the phosphate buffer pH 6.6; this reaction was shown to proceed with the participation of catalase and its cat-str conjugate. The catalytic constants for catalase are 1.2-1.5 times as high as those for cat-str, whereas the Km values for both substrates for the conjugate as 1.5-2 times as high as those for catalase. Catalase modification by strophantin K increases the enzyme thermostability up to the isokinetic point of 40 degrees C; above this threshold the cat-str thermostability decreases as compared with the native enzyme. The thermodynamical activation parameters for catalase and cat-str inactivation were determined.
Asunto(s)
Derivados del Benceno , Catalasa/metabolismo , Etanol/metabolismo , Estrofantinas/metabolismo , Animales , Bovinos , Técnicas In Vitro , Cinética , Hígado/enzimología , Oxidación-ReducciónRESUMEN
Specific binding of cardiac glycosides to their receptors precedes their actions on the myocardium. Thus changes in the number and affinity of these membrane bound receptors will vary the response to cardiac glycoside therapy and the incidence of side-effects. Several studies have reported an age-dependent decrease in the number of cardiac glycoside receptors in animals as well as in human erythrocytes. These results may explain the increase in cardiac glycoside sensitivity with age which is not accounted for by the reduction in kidney function. Furthermore, changes in both binding affinity and capacity are known to occur in several diseases which are more common in older patients. Therefore, we have measured the number and affinity of cardiac glycoside receptors in atrial samples from 209 patients and in papillary muscle samples from 59 patients taken during coronary bypass graft surgery or mitral valve replacement. Further, the maximal increase in force of contraction was measured using papillary muscle strips from some of these patients. Our results show no significant age-dependent alteration in the characteristics of the cardiac glycoside receptors but a reduced myocardial receptor density in males (3.47 +/- 0.14 X 10(14)/g protein) compared with females (4.44 +/- 0.21 X 10(14)/g protein) (p less than 0.001) which is more pronounced in older patients. About 30% fewer cardiac receptors either per g protein or per g wet weight are present in patients with coronary heart disease or dilative cardiomyopathy. The maximal inotropic effect of ouabain in human papillary muscle strips is correlated with the number of cardiac glycoside receptors present.(ABSTRACT TRUNCATED AT 250 WORDS)
Asunto(s)
Envejecimiento , Glicósidos Cardíacos/metabolismo , Atrios Cardíacos/enzimología , Receptores de Droga/metabolismo , Adolescente , Adulto , Anciano , Glicósidos Cardíacos/farmacología , Niño , Preescolar , Enfermedad Coronaria/enzimología , Femenino , Enfermedades de las Válvulas Cardíacas/enzimología , Humanos , Lactante , Masculino , Persona de Mediana Edad , Contracción Miocárdica/efectos de los fármacos , Músculos Papilares/enzimología , Receptores de Droga/efectos de los fármacos , ATPasa Intercambiadora de Sodio-Potasio/metabolismo , Estrofantinas/metabolismoAsunto(s)
Glicósidos Cardíacos/metabolismo , Estrofantinas/metabolismo , Animales , Biofarmacia , Glicósidos Cardíacos/administración & dosificación , Enfermedades Cardiovasculares/tratamiento farmacológico , Evaluación Preclínica de Medicamentos , Electrocardiografía , Inyecciones , Conejos , Ratas , Ramnosa/análogos & derivados , Ramnosa/metabolismo , SupositoriosRESUMEN
In 10 patients, 5 having received 3H-cymarol i.v., 5 orally, the radioactivity in plasma, urine and in the feces of some patients also was determined. After oral administration the plasma levels rose rapidly reaching maximum levels 1--2 h after administration. After i.v. injection about 30% of the given radioactivity were excreted in the urine. The remaining radioactivity was found in the feces suggesting a high biliary excretion. Only 10% of the radioactivity excreted in the first 24 h were chloroform-extractable. The radioactivity found in the urine after oral administration of the drug amounted to 17.6%. Between 51.1 and 58.5% of the drug were bound to serum proteins.
Asunto(s)
Cimarina/metabolismo , Estrofantinas/metabolismo , Anciano , Proteínas Sanguíneas/metabolismo , Cimarina/análogos & derivados , Cimarina/sangre , Cimarina/orina , Heces/análisis , Humanos , Absorción Intestinal , Masculino , Persona de Mediana Edad , Unión ProteicaAsunto(s)
Adenosina Trifosfatasas/antagonistas & inhibidores , Glicósidos Cardíacos/farmacología , Miocardio/metabolismo , Receptores de Droga/metabolismo , Glicósidos Cardíacos/metabolismo , Membrana Celular/metabolismo , Digitoxina/metabolismo , Digitoxina/farmacología , Digoxina/análogos & derivados , Digoxina/metabolismo , Digoxina/farmacología , Humanos , Técnicas In Vitro , Proscilaridina/metabolismo , Proscilaridina/farmacología , Estrofantinas/metabolismo , Estrofantinas/farmacologíaAsunto(s)
Glicósidos Cardíacos/farmacología , Enfermedad Coronaria/tratamiento farmacológico , Corazón/efectos de los fármacos , Adenosina Trifosfatasas/antagonistas & inhibidores , Adenosina Trifosfatasas/metabolismo , Animales , Calcio/metabolismo , Digitoxina/metabolismo , Digitoxina/farmacología , Digitoxina/uso terapéutico , Digoxina/metabolismo , Digoxina/farmacología , Digoxina/uso terapéutico , Perros , Cobayas , Humanos , Miocardio/metabolismo , Potasio/metabolismo , Sodio/metabolismo , Estrofantinas/metabolismo , Estrofantinas/farmacología , Estrofantinas/uso terapéuticoRESUMEN
Recent findings from our laboratory as well as those of other laboratories do not support the postulation that the mechanism of the positive inotropic action of digitalis is due to inhibition of NA,K-ATPase. Using short-acting digitalis steroids and drug washout experiments, in isolated myocardial preparations, it has been demonstrated that Na,K-ATPase isolated from such preparations is still significantly inhibited, whereas the positive inotropic effect is no longer present. Also, based on kinetic measurements the two exponential rate constants observed for drug half-life, a rapid and slow phase, were found to be associated, respectively, with the very short inotropic half-life and the very long enzyme inhibition half-life. In addition, a dissociation of the transient inotropic effects of digitalis was observed from the long lasting cardiotoxic effects of digitalis during drug washout. Moreover, a temporal correlation was noted between the persistent inhibitory effects of digitalis on Na,K-ATPase and the persistent cardiotoxic effects of digitalis. Therefore, it is concluded that inhibition of Na,K-ATPase is not responsible for the positive inotropic action of digitalis, but may be the mechanism, at least in part, for certain cardiotoxic effects of digitalis.
Asunto(s)
Adenosina Trifosfatasas/antagonistas & inhibidores , Glicósidos Digitálicos/farmacología , Contracción Miocárdica/efectos de los fármacos , Miocardio/enzimología , Adenosina Trifosfatasas/metabolismo , Animales , Glicósidos Digitálicos/toxicidad , Relación Dosis-Respuesta a Droga , Corazón/efectos de los fármacos , Cinética , Potenciales de la Membrana/efectos de los fármacos , Ouabaína/metabolismo , Unión Proteica , Sodio/metabolismo , Estrofantinas/metabolismoRESUMEN
1. Diacetylcymarol is an acetylated glycoside which is better absorbed than the parent glycoside, cymarol. 2. Diacetyl[19-3H]cymarol was rapidly metabolized and excreted by the rat following intraperitoneal administration. 3. The drug was metabolized extensively to polar compounds with the principal pathway involving loss of the C-19 acetyl group and probable demethylation of the sugar. 4. The bulk of the radioactive material was excreted in the bile and there was little reabsorption. 5. The results show that acetylation was successful in converting the poorly absorbed glycoside, cymarol, into a derivative that was rapidly absorbed from the peritoneal cavity. 6. Following or during absorption, the biologically inactive diacetylcymarol was converted to polar derivatives with potential therapeutic activity. However, subsequent elimination was so rapid that little therapeutic benefit could be expected.
Asunto(s)
Cimarina/metabolismo , Estrofantinas/metabolismo , Animales , Bilis/metabolismo , Cinamatos , Cimarina/análogos & derivados , Cimarina/orina , Heces/metabolismo , Intestino Delgado/metabolismo , Hígado/metabolismo , Ratas , Factores de TiempoRESUMEN
The various cardiac glycosides differ significantly in their retention as a result of renal failure. In the case of digoxin, digitoxin, and strophanthin the retention is directly related to the normal renal clearance of these cardiac glycosides: Strophanthin has the highest clearance and the most marked prolongation of pharmacological action in renal failure, whereas digitoxin shows the lowest renal clearance and even in uremic patients a total elimination comparable to normal subjects as a result of increased hepatic clearance; digoxin takes an intermediate position. The quantity of a cardiac glycoside and its metabolites excreted by the kidneys depends, besides the renal clearance, on the plasma concentration which increases considerably during the first days after onset of treatment. From the daily dose approximately 90% of strophanthin, 70% of digoxin, 50% of digitoxin plus metabolites are excreted by normal kidneys under steady-state conditions. The efficiency of hemodialysis in the elimination of cardiac glycosides is low (3-5%) if estimated in relation to a single dose injected before dialysis and high (30-50%) if estimated in relation to the excretory capacity of normal kidneys during a period corresponding to the duration of a dialysis. During hemodialysis the plasma concentration of digoxin decreases as rapidly as in patients with normal renal function. Beside the efficiency of dialysis this finding may be explained by the decrease in the apparent volume of distribution of cardiac glycosides in patients with advanced renal failure; a reduced tissue protein binding seems likely to be the main reason for these changes in chronic renal insufficiency. A reduced volume of distribution and a reduced myocardial sensitivity are the main reasons for a very low predictability of the necessary individual maintenance dose of cardiac glycosides from the creatinine clearance. In patients with advanced renal insufficiency the tolerance to cardiac glycosides is reduced with respect to the daily dose, but it is rather increased in relation to the plasma concentration required to maintain the positive inotropic effect. The combination of hyperkalemia, hypermagnesemia, bypocalcemia and acidosis which is found almost exclusively with chronic renal failure, may explain the reduced myocardial sensitivity. Dosage regimens based on the measurement of creatinine-clearance are of little help in "effective digitalisation". Serial measurements of steady-state plasma concentration of cardiac glycosides may be the only way to reduce the risk of under- and overtreatment in patients with impaired renal function.