ocotillol and protopanaxadiol

(20S,24S)-epoxy-dammarane-3,12,25-triol (24S-epimer) and (20S,24R)-epoxy- dammarane-3,12,25-triol (24R-epimer), a pair of ocotillol type epimers, were identified as the main metabolites of 20(S)-protopanaxadiol (PPD). The aim of this study was to systematically investigate the formation and metabolism of this pair of epimers in vivo and in vitro and to elucidate the isoforms of cytochrome P450 enzymes responsible for the stereoselective metabolism of both epimers. The result showed that 24S-epimer was a more predominant ingredient in rat plasma after oral administration of PPD with higher area under the curve (AUC) values. Both the enzyme kinetic evaluations of the formation and elimination of 24S-epimer and 24R-epimer in rat liver microsomes (RLM) and human liver microsomes (HLM) indicated that 24S-epimer had a higher formation rate and a lower oxygenation metabolism rate than 24R-epimer, and the stereoselective differences were more obvious in HLM than in RLM. The chemical inhibition and recombinant human P450 isoforms assay showed that CYP3A4 was the predominant isoform responsible for the further metabolism of 24R-epimer in HLM. The biliary excretion ratio of the 24S-epimer glucuronide was more than 28-fold higher than that of 24R-epimer glucuronide after intravenous administration to rats, which also indicated 24S-epimer was more preferential to be metabolized as the glucuronide conjugate than 24R-epimer.

Topics: Administration, Oral; Animals; Bile; Cytochrome P-450 Enzyme System; Ginsenosides; Humans; Male; Microsomes, Liver; Rats, Sprague-Dawley; Sapogenins; Saponins; Species Specificity; Stereoisomerism

Chemical and pharmacological studies of Panax vietnamensis (Vietnamese ginseng; VG) have been reported since its discovery in 1973. However, the content of each saponin in different parts of VG has not been reported. In this study, 17 ginsenosides in the different underground parts of P. vietnamensis were analyzed by HPLC/evaporative light scattering detector (ELSD). Their contents in the dried rhizome, radix, and fine roots were 195, 156, and 139 mg/g, respectively, which were extremely high compared to other Panax species. The content of protopanaxatriol (PPT)-type saponins were not much different among underground parts; however, the content of protopanaxadiol (PPD)- and ocotillol (OCT)-type saponins were greatly different. It is noteworthy that the ginsenoside pattern in the fine roots is different from other underground parts. In particular, despite the content of PPD-type saponins being the highest in the fine roots, which is similar to other Panax species, the total content of saponins was the lowest in the fine roots, which is different from other Panax species. The ratios of PPT : PPD : OCT-type saponins were 1 : 1.7 : 7.8, 1 : 1.6 : 5.5, and 1 : 4.8 : 3.3 for the rhizome, radix, and fine roots, respectively. OCT-type saponins accounted for 36-75% of total saponins and contributed mostly to the difference in the total saponin content of each part.

Topics: Chromatography, High Pressure Liquid; Ginsenosides; Panax; Plant Roots; Sapogenins; Saponins

To study stereoselectivity in the pharmacokinetics of each epimer, a rapid, specific and reliable liquid chromatography tandem mass spectrometry method has been established for simultaneous quantitation of both epimers in rat plasma. Plasma samples were pretreated by liquid-liquid extraction. Chromatographic separations were performed on a Shim-pack XR-ODS C18 column (50 mm × 2.1mm, i.d., 2.2 μm) with an isocratic elution. Both epimers and the internal standard tanshinone II A were ionized with an ESI source operated in positive ion mode and measured by selective reactions monitoring mode. Calibration curve was linear over the concentration range of 1-1000 ng/mL with the lower limit of quantitation of 1 ng/mL for both epimers. Intra and inter-day precisions were less than 6.7% and 9.5%, and the accuracy was within ±5.8% for both epimers. The validated method has been successfully applied to a pharmacokinetic study of the two epimers in rats after oral administration.

Topics: Administration, Oral; Animals; Chromatography, Liquid; Drug Stability; Ginsenosides; Limit of Detection; Liquid-Liquid Extraction; Male; Rats; Rats, Sprague-Dawley; Reproducibility of Results; Sapogenins; Sensitivity and Specificity; Stereoisomerism; Tandem Mass Spectrometry