Bio-Transformation of (G-3H)-Digitoxin and (G-3H)-Digoxin by Digitalis purpurea.

The biotransformation of (G- (3)H) digitoxin and (G- (3)H) digoxin has been studied in a strain of DIGITALIS PURPUREA in which cardenolides of the B series were predominant. A direct method of introducing the tritiated glycosides into the plant is described and the conversions monitored at intervals during the subsequent 6 weeks. Conversion of labelled digitoxin to purpurea glycosides A and B, gitoxin and gitaloxin occurred. Of particular interest was the conversion of digitoxin to the digitalose - containing glycosides, strospeside and verodoxin. Digoxin, an exogenous glycoside to D. PURPUREA, was glycosylated to desacetyl lanatoside C; there was some conversion to B and E series glycosides but only minimal formation of A series cardenolides.     

Influence of quinidine on the binding of [3H]-ouabain and [3H]-digoxin by human lymphocytes

Summary To explore the molecular basis of the glycoside-quinidine interaction, the in vitro effect of quinidine on the binding of [³H]-ouabain and [³H]-digoxin to Na⁺ K⁺ ATPase receptors on human mononuclear cells was investigated. The maximum [³H]-ouabain binding capacity was 45.7±9.4×10³ molecules/cell in pure lymphocyte preparations (n=8) and 75.5±7.3×10³ molecules/cell in mixtures of mononuclear cells (n=8). These parameters were not influenced by 10⁻⁵ M quinidine. In eight equilibrium experiments with pure lymphocytes, the dissociation constant of [³H]-ouabain increased from 0.79±0.26×10⁻⁸ M in the absence of 10⁻⁵ M quinidine to 1.56±0.74×10⁻⁸ M in its presence (p<0.01), indicating that the affinity of the drug was decreased. Similar findings were observed using mixed mononuclear cells. In five uptake and release experiments, quinidine decreased the association rate constant of [³H]-ouabain from 3.15±0.36×10⁴ M⁻¹×s⁻¹ to 2.01±0.37×10⁴ M⁻¹ s⁻¹ (p<0.01), whereas the dissociation rate constant was not affected. A therapeutic concentration of quinidine does not affect the number of glycoside receptors on lymphocytes, but it does appear to reduce fractional receptor occupancy by both [³H]-ouabain and [³H]-digoxin at lower tracer concentrations. This finding is compatible with the clinical observation that quinidine reduces the distribution volume of digoxin.     

Screening of new chemopreventive compounds from Digitalis purpurea

Chemopreventive agents induce a battery of genes whose protein products can protect cells from chemical-induced carcinogenesis. In this study, we isolated four different glycosides (1 acteoside; 2 purpureaside A; 3 calceolarioside B; and 4, plantainoside D) from the leaves of Digitalis purpurea and studied their abilities to induce glutathione S-transferase (GST) and their protective efficiencies against aflatoxin B1-induced cytotoxicity in H4IIE cells. Of these four glycosides, acteoside significantly inhibited the cytotoxicity induced by aflatoxin B1 (AFB1) and also selectively increased GSTalpha protein levels. Reporter gene analysis using an antioxidant response element (ARE) containing construct and subcellular fractionation assays, revealed that GSTalpha induction by acteoside might be associated with Nrf2/ARE activation. The results suggest that acteoside possesses a potent hepatoprotective effect against AFB1 and that it can be applied as a potential chemopreventive agent.     

Steryl esters of Digitalis purpurea L. herb

The non-polar fraction sterols of Digitalis purpurea flowering plants were separated into a steryl ester and free sterol fraction. The ester fraction consisted of cycloeucalenol, obtusifoliol, 24-methylenelophenol, 24-ethylenelophenol, cholesterol, campesterol, stigmasterol, sitosterol, isofucosterol and 24-methylenecholesterol. These compounds were esterified with an αβ-unsaturated C10 fatty acid, whereas the glycerides from the same plant consisted of a complex of acids predominated by C18 and C16 types. The free sterols consisted of cycloartenol, 24-methylenecycloartenol, cholesterol, campesterol, stigmasterol, sitosterol, fucosterol and 24-methylenecholesterol. The relative proportions of each of these steroids in the two fractions were recorded.     

Rapid identification of Digitalis purpurea using near-infrared reflectance spectroscopy

Glycosides from Digitalis are widely used for the treatment of various cardiac conditions. The potential for near-infrared (NIR) spectroscopy as a technique for the rapid identification of Digitalis purpurea was studied. If successful, this method would be advantageous over traditional methods which are destructive and time-consuming. It was possible to identify D. purpurea from other plants using a Maximum Distance in Wavelength Space statistical comparison method on standard normal variate-corrected, second-derivative spectra. Match values ranged from 1.65 to 2.26 for correct identification and were greater than 11.2 [corrected] for other plants. It was also possible to discriminate between different plant parts of D. purpurea, with match values ranging from 1.52 to 2-26 for leaves and greater than 29 for other parts of the same plant. The use of correlation coefficients and the Correlation in Wavelength Space methods proved less conclusive, with resulting values for leaves from different plants being very high, and in all but one case, above 0.9. A two-wavelength, nearest neighbours analysis was carried out for de-trended (baseline corrected), standard normal variate-corrected spectra at 1150 and 2160 nm. This resulted in the successful identification of unknown samples. NIR spectroscopy has the potential for the rapid identification of D. purpurea, and possibly for other natural products of pharmaceutical interest.