Stereoselective Formation and Metabolism of 20(S)‐Protopanaxadiol Ocotillol Type Epimers in Vivo and in Vitro

Abstract

(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.

Molecular Insight into Stereoselective ADME Characteristics of C20-24 Epimeric Epoxides of Protopanaxadiol by Docking Analysis

“…In contrast to the 24R-epimer, 24S-PDQ displayed a higher apparent formation rate from PPD along with a lower elimination rate by phase I metabolism enzymes [14]. Based on assay of in vivo biliary excretion, it was found that 24S-PDQ was more preferential to be metabolized into glucuronide conjugates than the 24R-epimer, whereas CYP3A4 was confirmed as the predominant isoform responsible for rapid oxygenation metabolism of 24R-epimer in human liver microsomes [14,15]. However, to the best of our knowledge, the molecular mechanisms underlying such stereoselective ADME fate of PDQ epimers are still unclear yet.…”

“…More concretely, 24R-epimer was found to be equipotent with PPD in terms of attenuating myocardial ischemic injury induced by isoproterenol and hence contribute to overall therapeutic effect of PPD, while 24S-PDQ orally administered at an equal dosage had no such effect [13]. In contrast to the 24R-epimer, 24S-PDQ displayed a higher apparent formation rate from PPD along with a lower elimination rate by phase I metabolism enzymes [14]. Based on assay of in vivo biliary excretion, it was found that 24S-PDQ was more preferential to be metabolized into glucuronide conjugates than the 24R-epimer, whereas CYP3A4 was confirmed as the predominant isoform responsible for rapid oxygenation metabolism of 24R-epimer in human liver microsomes [14,15].…”

“…Three types of enzymes were selected as target proteins for molecular docking analysis of stereoselective ADME properties, which included P-glycoprotein (P-gp, PDB ID: 5KOY), the cytochrome P450 (CYP) isoform 3A4 (PDB ID: 1W0F) and UDP-glucuronosyltransferase (UGT) isoform 1A8 (accession ID: Q9HAW9). According to the available results from both in vitro and in vivo experiments [14,17,18], the three target proteins are mainly involved in disposition of PDQ The different stereochemistry of PDQ epimers leads to significant stereoselectivities in both pharmacological effects and ADME properties. More concretely, 24R-epimer was found to be equipotent with PPD in terms of attenuating myocardial ischemic injury induced by isoproterenol and hence contribute to overall therapeutic effect of PPD, while 24S-PDQ orally administered at an equal dosage had no such effect [13].…”

“…Three types of enzymes were selected as target proteins for molecular docking analysis of stereoselective ADME properties, which included P-glycoprotein (P-gp, PDB ID: 5KOY), the cytochrome P450 (CYP) isoform 3A4 (PDB ID: 1W0F) and UDP-glucuronosyltransferase (UGT) isoform 1A8 (accession ID: Q9HAW9). According to the available results from both in vitro and in vivo experiments [14,17,18], the three target proteins are mainly involved in disposition of PDQ epimers and other ginsenosides such as absorption, phase I redox metabolism and phase II conjugation.…”

Discovery, semisynthesis, biological activities, and metabolism of ocotillol-type saponins

“…Wang et al [82] observed the in vitro and in vivo formation and metabolism of 20 and 23 . Stereoselective metabolism isoforms of CYP450 enzymes contributed to the HLMs were elucidated.…”