In vitro stereoselective inhibition of ginsenosides toward UDP-glucuronosyltransferase (UGT) isoforms.

We evaluated in vitro, the potential of the six pairs of ginsenoside isomers, stereoisomers at the chiral carbon on position 20, to inhibit the enzymatic activity of several UDP-glucuronosyltransferase (UGT) isoenzymes, major players in the human phase II drug metabolism. The results show that the tested six pairs of ginsenoside isomers exhibited stereoselective inhibitory effects of varying degrees on the ten UGT isoenzymes explored. Of the tested twelve stereoselective ginsenosides, 20(R)-Rg3 had the strongest inhibitory effect on the UGT1A8 isoform with the lowest IC50 value of 5.66±1.04µM. On the other hand, the (S)-isomers of Rg3 and Rh2 also exerted remarkable inhibition on UGT1A8, with IC50 values of 6.89±0.812µM and 5.85±0.821µM, respectively. Although the inhibitory effect was low, both 20(R)-PPT and 20(S)-PPT also inhibited UGT1A8 activity. Considering 1) that the relative contents of 20(R)-Rg3 in processed ginseng are high, 2) that higher exposure to (R)-isomers of ginsenosides occur in the intestine compared to that in the liver, and 3) the inhibitory effects of other ginsenosides on enzymatic activity [20(S)-Rg3, 20(S)-Rh2, 20(R)- and 20(S)-PPT], there may be a potential for herb-drug interactions between processed ginseng and UGT1A8 substrates when concomitantly administered.

Pharmacokinetic properties of trifolirhizin, (-)-maackiain, (-)-sophoranone and 2-(2,4-dihydroxyphenyl)-5,6-methylenedioxybenzofuran after intravenous and oral administration of Sophora tonkinensis extract in rats.

1. SKI3301, a standardized dried 50% ethanolic extracts of Sophora tonkinensis, contains four marker compounds (trifolirhizin, TF; (-)-maackiain, Maack; (-)-sophoranone, SPN, and (2-(2,4-dihydroxyphenyl)-5,6-methylenedioxybenzofuran, ABF), is being developed as an herbal medicine for the treatment of asthma in Korea. This study investigates the pharmacokinetic properties of SKI3301 extract in rats. 2. The dose-proportional AUCs suggest linear pharmacokinetics of TF, Maack, SPN and ABF in the SKI3301 extract intravenous dose range of 5-20 mg/kg. After the oral administration of 200-1000 mg/kg of the extract, TF and Maack exhibited non-linearity due to the saturation of gastrointestinal absorption. However, linear pharmacokinetics of SPN and ABF were observed. 3. The absorptions of TF, Maack, SPN and ABF in the extract were increased relative to those of the respective pure forms due to the increased solubility and/or the decreased metabolism by other components in the SKI3301 extract. 4. No accumulation was observed after multiple dosing, and the steady-state pharmacokinetics of TF, Maack, SPN and ABF were not significantly different from those after a single oral administration of the extract. 5. The pharmacokinetics of TF, SPN and ABF were not significantly different between male and female rats after oral administration of the extract, but a significant gender difference in the pharmacokinetics of Maack in rats was observed. 6. Our findings may help to comprehensively elucidate the pharmacokinetic characteristics of TF, Maack, SPN and ABF and provide useful information for the clinical application of SKI3301 extract.

Acute interstitial nephritis induced by Dioscorea quinqueloba.

BACKGROUND: The use of herbal medicine may be a risk factor for the development of kidney injury, as it has been reported to cause various renal syndromes. Dioscorea quinqueloba is a medicinal herb that is used as an alternative therapy for cardiovascular disease and various medical conditions. CASE PRESENTATION: A 52-year-old man was admitted with complaints of skin rash and burning sensation. He had ingested a raw extract of D. quinqueloba as a traditional remedy. Laboratory tests revealed the following values: absolute eosinophil count, 900/mm(3); serum creatinine level, 2.7 mg/dL; and blood urea nitrogen, 33.0 mg/dL. The immunoglobulin E level was markedly increased at 1320.0 IU/mL. Urinalysis revealed a fractional excretion of sodium of 3.77%, protein 1+, and blood 3+. Histological examination of the renal biopsy specimen showed a diffusely edematous interstitium with infiltrates composed of eosinophils, lymphocytes, and neutrophils. CONCLUSION: Here, we present the first reported case of biopsy-proven acute interstitial nephritis following ingestion of D. quinqueloba associated with skin rash, eosinophilia, and increased plasma immunoglobulin E level.

Pharmacokinetics and tissue distribution of ginsenoside Rh2 and Rg3 epimers after oral administration of BST204, a purified ginseng dry extract, in rats.

1. BST204, a purified ginseng dry extract containing a high concentration of racemic Rh2 and Rg3 mixtures, is being developed for supportive care use in cancer patients in Korea. This study investigates the pharmacokinetics and tissue distribution of BST204 in rats. 2. After oral administration of BST204, only the S epimers, S-Rh2 and S-Rg3, could be determined in rat plasma. The poor absorption of the R-epimers, R-Rh2 and R-Rg3, may be attributed to lower membrane permeability and extensive intestinal oxygenation and/or deglycosylation into metabolites. The AUC and Cmax values of both S-Rh2 and S-Rg3 after BST204 oral administration were proportional to the administered BST204 doses ranged from 400 mg/kg to 2000 mg/kg, which suggested linear pharmacokinetic properties. 3. There were no statistically significant differences in the pharmacokinetics of S-Rh2 and S-Rg3 after oral administration of pure S-Rh2 (31.5 mg/kg) and S-Rg3 (68 mg/kg) compared with oral administration of BST204, 1000 mg/kg. These indicated that the presence of other components of BST204 extract did not influence the pharmacokinetic behavior of S-Rh2 and S-Rg3. 4. After oral dosing of BST204, S-Rh2 and S-Rg3 were distributed mainly to the liver and gastrointestinal tract in rats. 5. Our finding may help to understand pharmacokinetic characteristics of S-Rh2, R-Rh2, S-Rg3, and R-Rg3, comprehensively, and provide useful information in clinical application of BST204.

Evaluation of the in vitro/in vivo drug interaction potential of BST204, a purified dry extract of ginseng, and its four bioactive ginsenosides through cytochrome P450 inhibition/induction and UDP-glucuronosyltransferase inhibition.

We evaluated the potential of BST204, a purified dry extract of ginseng, to inhibit or induce human liver cytochrome P450 enzymes (CYPs) and UDP-glucuronosyltransferases (UGTs) in vitro to assess its safety. In vitro drug interactions of four bioactive ginsenosides of BST204, S-Rg3, R-Rg3, S-Rh2, and R-Rh2, were also evaluated. We demonstrated that BST204 slightly inhibited CYP2C8, CYP2D6, CYP2C9, and CYP2B6 activities with IC50 values of 17.4, 26.8, 31.5, and 49.7µg/mL, respectively. BST204 also weakly inhibited UGT1A1, UGT1A9, and UGT2B7 activities with IC50 values of 14.5, 26.6, and 31.5µg/mL, respectively. The potential inhibition by BST204 of the three UGT activities might be attributable to S-Rg3, at least in part, as its inhibitory pattern was similar to that of BST204. However, BST204 showed no time-dependent inactivation of the nine CYPs studied. In addition, BST204 did not induce CYP1A2, 2B6, or 3A4/5. On the basis of an in vivo interaction studies, our data strongly suggest that BST204 is unlikely to cause clinically significant drug-drug interactions mediated via inhibition or induction of most CYPs or UGTs involved in drug metabolism in vivo. Our findings offer a clearer understanding and possibility to predict drug-drug interactions for the safe use of BST204 in clinical practice.

Potent inhibition of cytochrome P450 2B6 by sibutramine in human liver microsomes.

The present study was performed to evaluate the potency and specificity of sibutramine as an inhibitor of the activities of nine human CYP isoforms in liver microsomes. Using a cocktail assay, the effects of sibutramine on specific marker reactions of the nine CYP isoforms were measured in human liver microsomes. Sibutramine showed potent inhibition of CYP2B6-mediated bupropion 6-hydroxylation with an IC50 value of 1.61µM and Ki value of 0.466µM in a competitive manner at microsomal protein concentrations of 0.25mg/ml; this was 3.49-fold more potent than the typical CYP2B6 inhibitor thio-TEPA (Ki=1.59µM). In addition, sibutramine slightly inhibited CYP2C19 activity (Ki=16.6µM, noncompetitive inhibition) and CYP2D6 activity (Ki=15.7µM, noncompetitive inhibition). These observations indicated 35.6- and 33.7-fold decreases in inhibition potency, respectively, compared with that of CYP2B6 by sibutramine. However, no inhibition of CYP1A2, CYP2A6, CYP2C8, CYP2C9, CYP2D6, or CYP2E1 activities was observed. In addition, the CYP2B6 inhibitory potential of sibutramine was enhanced at a lower microsomal protein concentration of 0.05mg/ml. After 30min preincubation of human liver microsomes with sibutramine in the presence of NADPH, no shift in IC50 was observed in terms of inhibition of the activities of the nine CYPs, suggesting that sibutramine is not a time-dependent inactivator. These observations suggest that sibutramine is a selective and potent inhibitor of CYP2B6 in vitro, whereas inhibition of other CYPs is substantially lower. These in vitro data support the use of sibutramine as a well-known inhibitor of CYP2B6 for routine screening of P450 reversible inhibition when human liver microsomes are used as the enzyme source.

Inhibitory effects of astaxanthin, ß-cryptoxanthin, canthaxanthin, lutein, and zeaxanthin on cytochrome P450 enzyme activities.

Astaxanthin, ß-cryptoxanthin, canthaxanthin, lutein and zeaxanthin, the major xanthophylls, are widely used in food, medicine, and health care products. To date, no studies regarding the inhibitory effects of these xanthophylls on the nine CYPs isozymes have been reported. This study investigated the reversible and time-dependent inhibitory potentials of five xanthophylls on CYPs activities in vitro. The reversible inhibition results showed that the five compounds had only a weak inhibitory effect on the nine CYPs. Lutein did not inhibit the nine CYPs activities. Astaxanthin weakly inhibited CYP2C19, with an IC50 of 16.2 µM; and ß-cryptoxanthin weakly inhibited CYP2C8, with an IC50 of 13.8 µM. In addition, canthaxanthin weakly inhibited CYP2C19 and CYP3A4/5, with IC50 values of 10.9 and 13.9 µM, respectively. Zeaxanthin weakly inhibited CYP3A4/5, with an IC50 of 15.5 µM. However, these IC50 values were markedly greater than the Cmax values reported in humans. No significant IC50 shift was observed in the time-dependent inhibition screening. Based on these observations, it is unlikely that these five xanthophylls from the diet or nutritional supplements alter the pharmacokinetics of drugs metabolized by CYPs. These findings provide some useful information for the safe use of these five xanthophylls in clinical practice.