In Vivo Inhibition of CYP3A-Mediated Midazolam Metabolism by Anchusan in Rats

Inhibition of CYP3A-mediated Midazolam Metabolism by <i>Kaempferia Parviflora</i>

Kaempferia parviflora (KP) extract has recently attracted attention in Japan as a dietary supplement; however, there is little information regarding food-drug interactions (FDIs). The current study was conducted to clarify the FDI of KP extract via inhibition of cytochrome P450 3A (CYP3A), a typical drug-metabolizing enzyme. The inhibitory effects of KP extract and its main ingredients, 5,7-dimethoxyflavone (5,7-DMF) and 3,5,7,3’,4’-pentamethoxyflavone (3,5,7,3’,4’-PMF), on CYP3A-mediated midazolam 1’-hydroxylation (MDZ 1’-OH) activity were investigated in human liver microsomes. In addition, the effect of a single oral treatment with KP extract (135 mg/kg) on oral MDZ (15 mg/kg) metabolism was investigated in rats. Serum MDZ concentration was analyzed and pharmacokinetic parameters were compared with the control group. KP extract competitively inhibited MDZ 1’-OH activity with an inhibition constant value of 78.14 µg/ml, which was lower than the estimated concentration in the small intestine after ingestion. Furthermore, KP extract, 5,7-DMF, and 3,5,7,3’,4’-PMF inhibited the activity in a time-, NADPH-, and concentration-dependent manner. In vivo study showed that administration of KP extract to rats 2 h before MDZ significantly increased the area under the serum concentration-time curve and the maximum concentration of MDZ significantly by 2.3- and 1.9- fold, respectively (p < 0.05). Conversely, administration of MDZ 18 h after KP extract treatment displayed a weaker effect. These results suggest that KP extract competitively inhibits CYP3A-mediated MDZ metabolism, and that this inhibition may be time-dependent but not irreversible. This work suggests an FDI through CYP3A inhibition by KP extract.

Effect of Benifuuki Tea on Cytochrome P450-mediated Metabolic Activity in Rats

BACKGROUND/AIM

Benifuuki tea has recently been used as an alternative therapy for pollinosis, and it may be consumed with pharmaceutical drugs. This study aimed to examine cytochrome P450 (CYP)-mediated food-drug interactions with Benifuuki tea in rats.

MATERIALS AND METHODS

The inhibitory effects of Benifuuki tea and (-)-epigallocatechin-3-O-(3-O-methyl) gallate (EGCG3"Me) on CYP activities were evaluated in vitro. Midazolam pharmacokinetics was investigated after two treatments with Benifuuki tea. In an ex vivo study, CYP activities were determined after 1-week-treatment with the tea.

RESULTS

Benifuuki tea and EGCG3"Me inhibited CYP2D and CYP3A activities in a concentration-dependent manner in vitro. However, MDZ metabolism did not change by Benifuuki treatment in vivo and ex vivo. In contrast, CYP2D activity was decreased ex vivo.

CONCLUSION

Normal intake of Benifuuki tea is not likely to cause food-drug interactions by CYP3A inhibition or induction. In contrast, Benifuuki tea consumption may lead to food-drug interactions through the inhibition of CYP2D.

Inhibitory Effect of Oxethazaine on Midazolam Metabolism in Rats

There have been few reports concerning to the drug-drug interactions (DDIs) with OTC drugs although an increase in the use of OTC drugs in recent years. This current study was conducted to clarify the DDIs through CYP3A inhibition by oxethazaine (OXZ), an antacid available as an OTC drug. Midazolam (MDZ) was used as a probe drug for CYP3A activity. In an in vivo study, a single oral dose of OXZ (50 mg/kg) was administered to rats 30, 60, or 120 min before oral MDZ administration (15 mg/kg). Serum concentrations of MDZ were analyzed by HPLC, and its pharmacokinetic parameters were compared with a water-treated control group. The inhibitory effect of OXZ on MDZ 1'-hydroxylation (MDZ 1'-OH) activity was investigated in vitro using rat liver and intestinal microsomes. Pretreatment of OXZ 120 min before MDZ administration significantly increased the area under the serum concentration-time curve (AUC_0-∞) of MDZ six-fold compared to the control group without a change in elimination half-life (t_1/2). In contrast, OXZ pretreatment 30 or 60 min before MDZ administration did not show any remarkable change in MDZ pharmacokinetic parameters. The in vitro study showed that OXZ inhibited MDZ 1'-OH activity in a concentration-dependent manner both in liver and intestinal microsomes. These results suggested that OXZ increases serum MDZ concentration presumably by the inhibition of liver and/or intestinal CYP3A activity. OXZ was predicted to cause the DDIs mediated by CYP3A inhibition, although this effect depended on the dose interval.

Induction of CYP3A by morroniside in rats

Morroniside is one of the most important iridoid glycosides in the herbal drug Cornus officinalis Sieb. et Zucc. The current study was designed to investigate the ex vivo and in vivo effects of morroniside on CYP3A activity in rats after treatment with morroniside for 7 days (at 10, 30, 90 mg/kg, i.g.). Morroniside was found to induce CYP3A. According to the ex vivo experiment, the activity of CYP3A was measured by the quantification of 1-hydroxymidazolam, which was the metabolite from CYP3A probe substrate, midazolam. The concentration of 1-hydroxymidazolam was determined by using a validated liquid chromatography coupled with tandem mass spectrometry detection (LC-MS/MS) method. The levels of messenger RNA (mRNA) and protein of CYP3A were determined by reverse transcriptase-polymerase chain reaction (RT-PCR) and western blotting analysis, respectively. The pharmacokinetics of midazolam in rats after treatment with morroniside for 7 days (at 10, 30, 90 mg/kg, i.g.) were investigated in vivo. After treatment with morroniside, the activity, mRNA and protein expression of CYP3A were significantly induced and the absorbance and bioavailability of midazolam in rats were reduced. The results indicated that morroniside could induce the activity of CYP3A.

Pharmacokinetic changes of unbound theophylline are due to plasma protein binding displacement and CYP1A2 activity inhibition by baicalin in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Baicalin is one of the major bioactive constituents of Scutellariae Radix, the root of Scutellariae baicalensis Georgi and possesses a wide variety of pharmacological properties.

AIM OF THE STUDY

To elucidate the effect of baicalin on the pharmacokinetics of theophylline in rats, focusing on plasma protein binding displacement and inhibition effect on CYP1A2 in vivo and in vitro.

MATERIALS AND METHODS

The study was a randomized, three-period crossover design. Nine rats were given saline (control) or 450 mg/kg baicalin (dosage regimen A or B). Dosage regimen A was administered once at 0 h. Dosage regimen B was divided into three dosages (225,112.5, 112.5 mg/kg) and was given at 0, 2 and 4 h, respectively. Then theophylline (5 mg/kg, i.v.) was administered immediately. The effect of baicalin on CYP1A2 activity was determined by metabolism of phenacetin in vitro and plasma protein binding of theophylline was determined by ultrafiltration.

RESULTS

C(max) decreased from (12.4 ± 1.6) to (8.7 ± 0.9) and (8.6 ± 2.0) mg/L, T(1/2) increased by 116 and 96%, V(d) increased by 51 and 49% for total theophylline in rats treated with dosage regimen A and B of baicalin, respectively. Cmax was significantly increased, V(d) decreased by 43 and 29% for unbound theophylline in rats treated with dosage regimen A and B of baicalin, respectively (P < 0.01). T(1/2) of unbound theophylline increased by 104% only in rats treated with dosage regimen B. No significant effects on the CL and AUC of both total and unbound theophylline were observed in the rats treated with dosage regimen A, but the CL decreased and AUC increased for total theophylline and CL decreased for unbound theophylline in the group treated with dosage regimen B (P < 0.05). Correlation analysis showed that the mean unbound theophylline (%) and mean baicalin concentration was in good correlation (P < 0.01). Baicalin decreased metabolism of phenacetin and exhibited a mixed-type inhibition in rat liver microsomes, with a K(i) value of 88.1 μM in vitro. Moreover baicalin was a competitive displacer of theophylline from plasma protein in vitro.

CONCLUSIONS

The changes in Cmax, T(1/2), CL and AUC of theophylline due to baicalin may be attributed to two mechanisms, plasma protein binding displacement and CYP1A2 activity inhibition.

Study on intestinal absorption and pharmacokinetic characterization of diester diterpenoid alkaloids in precipitation derived from fuzi-gancao herb-pair decoction for its potential interaction mechanism investigation

ETHNOPHARMACOLOGICAL RELEVANCE

Aconitum carmichaelii Debx. (Fuzi in Chinese) has been widely clinically used to treat heart failure and rheumatism. Whereas its serious toxicity, Radix et Rhizoma Glycyrrhizae (Gancao in Chinese) was combined with it as traditional Chinese medicine (TCM) herb-pair for toxicity reduction and pharmacological effect improvement. Though some previous viewpoints about that has been reported, the underlying interaction mechanism of two herbs remain unknown and definitely worthy of investigating.

AIM OF STUDY

In present study, we focus on Fuzi-Gancao herb-pair precipitation (FGP), considering it related to the compatibility mechanism of Fuzi-Gancao herb-pair. The intestinal absorption and pharmacokinetic characters of 3 diester diterpenoid alkaloids in the precipitation were investigated.

MATERIALS AND METHODS

Both everted gut sac model and in situ single-pass intestinal perfusion model were used to investigate rat small intestinal permeability and transport mechanism of aconitine, hypaconitine and mesaconitine. Moreover, by means of determination of the plasma concentration, the pharmacokinetic characters of 3 alkaloid compounds in rats have been developed.

RESULTS

In everted gut sac permeability experiment, the permeability of hypaconitine appeared best in ileum. Furthermore, their uptakes were increased in the presence of P-glycoprotein (P-gp) inhibitors. In situ single-pass intestinal perfusion uptake experiment, results revealed that the transport mechanism may fit the active transport mechanism. And 3 alkaloids in FPG could be absorbed well in rats, fitting 2-compartment model with 1(st) order absorption and lag time.

CONCLUSIONS

Our results in present study indicated that 3 diester diterpenoid alkaloids in FGP could be dissolved out in gastrointestinal tract firstly and then absorbed in blood after oral administration, which could result in prolonging their mean residence time and adding their absorbed doses, avoiding dose dumping. The current study has significant enlightenments for further investigation on the interaction mechanisms of other acid-base herb-pairs as well as Fuzi-Gancao herb-pair.

Concentration-dependent inhibitory effects of baicalin on the metabolism of dextromethorphan, a dual probe of CYP2D and CYP3A, in rats

Baicalin has been shown to possess many pharmacological effects, including antiviral, antioxidant, anti-cancer and anti-inflammatory properties. In the current study, we reveal the inhibitory effects of baicalin on the metabolism of dextromethorphan (DXM), a dual probe substrate of CYP2D and CYP3A, in rats. Lineweaver-Burk plots demonstrated that baicalin inhibited the activities of CYP2D and CYP3A in a non-competitive manner in rat liver microsomes (RLMs). Concomitant administration of baicalin (0.90 g/kg, i.v.) and DXM (10 mg/kg, i.v.) increased the maximum drug concentration (C(max)) (37%) and the area under concentration-time curve (AUC) (42%) and decreased the clearance (CL) (27%) of DXM in a randomised, crossover study in rats (P < 0.01). The change in the AUC of DXM was significantly correlated with the C(max) and AUC of baicalin (P < 0.05). The inhibitory effects of multiple doses of baicalin (0.90 g/kg, i.v., 12 days) on the metabolism of DXM were similar to those observed following a single dose in rats. The activity of CYP3A in excised liver samples from rats following multiple baicalin treatment was significantly decreased compared to that of the control group (P < 0.05), whereas multiple doses of baicalin had no obvious effect on the activity of CYP2D. Taken together, these data demonstrate that baicalin inhibits the metabolism of DXM in a concentration-dependent manner in rats, possibly through inhibiting hepatic CYP2D and CYP3A activities.