digitoxin and digitoxigenin-bis(digitoxoside)

The crystal structures and conformations of bisdigitoxosides of digitoxigenin (I), gitoxigenin (II) and digoxigenin (III and IV) have been determined using single-crystal X-ray crystallographic techniques. Crystals of (I), (II) and (IV) were grown from ethyl acetate solutions of the glycosides while (III) was grown from a solution of the digitoxoside in ethanol. As in other cardiac glycosides the ring junctions A-B and C-D are cis. The D ring in these structures shows different conformations while the A, B and C rings remain conformationally similar. Although digitoxigenin bisdigitoxoside and gitoxigenin bisdigitoxoside differ from each other in the absence and presence of a hydroxyl group at C(16) of the D ring, these two biosides crystallize in the space group P2(1)2(1)2 [corrected] and are isomorphous. The presence of the hydroxyl group at C(16) does not affect the orientation of the lactone ring and the conformation of the molecule. Digoxigenin bisdigitoxoside crystallizes in two different crystal systems with four molecules of water in the orthorhombic form and one molecule of ethyl acetate in the triclinic form. In both forms the hydroxyl at C(3') of the first sugar forms a hydrogen bond with the ring oxygen of the second sugar. This has also been observed in the trioside digoxin. The torsion angle C(13)-C(17)-C(20)-C(22) in the two forms differs by 7 degrees.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Cardenolides; Cardiac Glycosides; Digitalis; Digitoxigenin; Digoxigenin; Molecular Conformation; Molecular Structure; Plants, Medicinal; Plants, Toxic; Structure-Activity Relationship; X-Ray Diffraction

Liver microsomes of male Beagle dogs contain a form of UDP-glucuronyltransferase which is capable of conjugating digitoxin and its cleavage products digitoxigenin-bisdigitoxoside and digitoxigenin-monodigitoxoside. The highest reaction rates (Vmax 236 pmoles/mg microsomal protein min) were found for digitoxin and digitoxigenin-monodigitoxoside whereas the lowest Km was obtained for digitoxigenin-bisdigitoxoside (29 microM). Digoxin cannot be glucuronidated and digitoxigenin is glucuronidated only in traces. The result may explain the fast digitoxin elimination in dogs. Mutual induction experiments utilizing cardenolides and model substrates of UDP-glucuronyltransferase result in the conclusion that a specific form of UDP-glucuronyltransferase is responsible for glucuronidating digitoxigenin glycosides.

Topics: Animals; Biphenyl Compounds; Digitoxigenin; Digitoxin; Dogs; Glucuronates; Glucuronosyltransferase; In Vitro Techniques; Kinetics; Male; Microsomes, Liver; Nitrophenols; Pregnanediol; Substrate Specificity; Testosterone

A specific assay for determining the urinary excretion of unchanged digitoxin and its metabolites is described. The procedure includes solvent extraction of urine at pH 8.5, reversed-phase high-performance liquid chromatography (HPLC) and radioimmunoassay (RIA) of equivalent fractions. Confidence limits showed good linearity and precision of recovery and high sensitivity, accuracy and specificity. Cross-reactivities were high for digitoxigenin (DGTN) and digitoxigenin bisdigitoxoside (Bis-DGTN), they were low for digitoxigenin monodigitoxoside (Mono-DGTN) or digoxin when [125I]digitoxin RIA was used. The interference of endogenous compounds in urine in the RIA was overcome by using HPLC. Compared with results reported in the literature, the urinary recovery of unchanged digitoxin was lower, being only 8.11 +/- 1.51% of the dose administered. Amounts of 6.52 +/- 1.31% were excreted hydrolysed as Bis-DGTN, Mono-DGTN, DGTN or C12-hydroxylated as digoxin.

Topics: Adult; Biotransformation; Chromatography, High Pressure Liquid; Digitoxigenin; Digitoxin; Digoxin; Humans; Radioimmunoassay

The kinetics of digitoxin and two of its metabolites, the bis- and monodigitoxosides of digitoxigenin, were determined in six normal subjects. Mean t 1/2s and total body clearances were 134.4, 15.4, and 0.59 hr and 2.66, 27.3, and 1071 ml/min. Mean renal clearance of the monodigitoxoside was more rapid (7.24 ml/min) than those of digitoxin (0.81 ml/min) or the bisdigitoxoside (0.94 ml/min). The volumes of distribution were of the same order, 0.45 l/kg for digitoxin, 0.57 l/kg for the bisdigitoxoside, and 0.83 l/kg for the monodigitoxoside. The short t 1/2 of monodigitoxoside would make it unsuitable for clinical use, but the bisdigitoxoside of digitoxigenin has a t 1/2 of an intermediate length and may have significant therapeutic advantages.

Topics: Adult; Aged; Digitoxigenin; Digitoxin; Drug Evaluation; Female; Half-Life; Humans; Injections, Intravenous; Kinetics; Male; Middle Aged; Radioimmunoassay

The kinetics of digitoxin and two of its major metabolites, the bis- and monodigitoxosides of digitoxigenin, were determined in six subjects with renal insufficiency and compared to those in six age- and sex-matched normal control subjects. No significant differences between the two groups were found in elimination t 1/2, total body clearance, or volume of distribution. Average renal clearances of all three drugs were reduced in subjects with renal failure, but the differences were significant only in the case of digitoxin. The bis-digitoxoside of digitoxigenin has kinetic properties that offer clinical advantages.

Topics: Acute Kidney Injury; Adult; Aged; Creatinine; Digitoxigenin; Digitoxin; Drug Evaluation; Female; Half-Life; Humans; Injections, Intravenous; Kinetics; Male; Middle Aged; Radioimmunoassay; Random Allocation

The metabolism of digitoxin (Dt3) in isolated hepatocyte preparations was studied in young (3-mth-old) male and female rats, young castrated (3-mth-old) male rats and old (22- to 28-mth-old) male rats. When hepatocytes were incubated with [3H]Dt3, the predominant metabolite of Dt3 was digitoxigenin-bis-digitoxoside (Dt2) which was 70-90% of the total metabolites in the three male rat groups. Only in the young female rat group was the proportion of Dt2 (40%) slightly exceeded by that of digoxigenin-bis-digitoxoside (Dg2) (50%). A kinetic analysis for Dt3 degradation velocity obtained from studies using different Dt3 concentrations in old male rats yielded a Vmax of only 21% of the young value. In young castrated males, the Vmax also decreased to 13% of the young non-castrated males, which is approaching the young female value. The changes were primarily due to the decline of Dt2 formation velocity in these groups. Apparent Km values also decreased with both castration and aging. The plasma testosterone levels which were much higher in young male rats than in female rats became significantly lower in young castrated rats as well as in old male rats. The results suggest that apparent decreases in Vmax and Km values observed in old male rats for Dt3 metabolic degradation may be at least partly through the steroidal hormone control, presumably, the decline of androgenic induction during aging.

Topics: Aging; Animals; Castration; Chromatography, Thin Layer; Digitoxigenin; Digitoxin; Estradiol; Female; Kinetics; Liver; Male; Rats; Rats, Inbred Strains; Testosterone

A specific assay is described for measuring the concentration of digitoxin and the bis- and monoglycosides of digitoxigenin in serum. The procedure includes: (1) addition of a tracer amount of tritium labeled parent compound to the serum in order to measure percentage recovery; (2) solvent extraction to separate polar and non-polar metabolites; (3) reversed-phase thin-layer chromatography of the non-polar fraction to separate digoxigenins from digitoxigenins; (4) thin-layer chromatography to isolate digitoxin, and the bis- and monoglycosides of digitoxigenin; and (5) use of an 125I-radioimmunoassay to determine the concentration of the glycosides. Each of these three glycosides was administered intravenously to a normal subject, and the concentration of parent compound was measured in the serum at various times.

Topics: Adult; Digitoxigenin; Digitoxin; Humans; Male; Radioimmunoassay; Stereoisomerism; Time Factors

The biliary excretion of digitoxin (Dt3) and its metabolites were compared between young (3-month-old) and old (25-month-old) male Wistar rats after an iv injection of [3H]Dt3 (0.03 mg/100g body weight) for 2 hrs. The 2-hr. total biliary recovery of iv injected radioactivity (percent of the dose) was two times lower in old rats (7.40 +/- 1.36% mean +/- SD) compared with young rats (14.74 +/- 4.10%). This difference was primarily due to the decrease in the excretion of Dt3 metabolites in the bile, while the excretion of the parent drug, Dt3 was 1.3 times higher in old rats. Among various Dt3 metabolites in the bile, digitoxigenin bis-digitoxoside (Dt2), digoxigen bis-digitoxoside (Dg2), and polar (conjugated) metabolites were major components, which all decreased with age. In accord with the decreased excretion of the radioactivity in the bile of old rats, the plasma disappearance of radioactivity was generally slower in old animals compared with young ones, yielding significantly higher plasma levels at different times of observation. Despite the increase in plasma radioactivity, the radioactivity concentration in the liver 2 hrs. after the injection was almost equal between the two age groups. It is suggested that at least in this rat strain and sex the biliary excretion of Dt3 metabolites was markedly age-dependent, presumably due to the decreased capacity of the liver to biotransform Dt3 with age. Furthermore, the lower liver plasma radioactivity ratio in old animals suggested the possibility that the distribution of Dt3 in the liver may also decrease with age.

Topics: Aging; Animals; Bile; Digitoxigenin; Digitoxin; Digoxigenin; Injections, Intravenous; Kidney; Liver; Male; Myocardium; Rats; Rats, Inbred Strains