Bioactivity guided fractionation of methanolic extract of Terminalia arjuna for its CYP3A and CYP2D inhibition in rat liver microsomes.

Terminalia arjuna (T. arjuna) is an Indian medicinal plant belonging to the family Combretaceae and possesses numerous therapeutic activities including its immense cardioprotective activity. In the present work, a methanolic bark extract of T. arjuna was evaluated for CYP3A and CYP2D inhibition potential in rat liver microsomes (RLM). Further, the methanolic bark extract was fractionated successively using increasing polarity solvents starting with petroleum ether, chloroform, ethyl acetate and n-butanol. The fractions so obtained were also evaluated for their CYP3A and CYP2D inhibition potential. Probe substrates testosterone and dextromethorphan were used for CYP3A and CYP2D respectively. The IC50 values for the methanolic extract and the fractions were found to be less than 50 µg/ml in RLM for both CYP3A and CYP2D isoenzymes. The most potent n-butanol fraction was further fractionated with column chromatography to isolate the highest active constituent responsible for the activity. Fraction 4 of the n-butanol extract was the most potent fraction with IC50 values of 5.64 ± 0.735 µg/ml and 16.63 ± 0.879 µg/ml for CYP3A and CYP2D in RLM, respectively. Therefore, in vitro data indicated that the Terminalia arjuna extract contains constituents that can potentially inhibit the CYP3A and CYP2D isoenzymes which may in turn lead to pharmacokinetic drug-herb interaction.

In Vitro CYP2D Inhibitory Effect and Influence on Pharmacokinetics and Pharmacodynamic Parameters of Metoprolol Succinate by Terminalia arjuna in Rats.

BACKGROUND: Terminalia arjuna Wight & Arn. (Combretaceae) is a tree having an extensive medicinal potential in cardiovascular disorders. T. arjuna bark extract has been reported to play a significant role as a cardiac stimulant for its beneficial effects in angina. Herb - drug interactions (HDI) are one of the most important clinical concerns in the concomitant consumption of herbs and prescription drugs. Our study was to investigate the in vitro CYP2D inhibition potential of Terminalia arjuna (T. arjuna) extracts in rat liver microsomes and to study the influence of aqueous bark extract of T. arjuna on the oral pharmacokinetics and pharmacodynamics of metoprolol succinate in rats. METHODS: The CYP2D inhibition potential of herbal extracts of T. arjuna was investigated in rat liver microsomes. Pharmacokinetic-pharmacodynamic interaction of aqueous extract of T. arjuna with metoprolol succinate was investigated in rats. RESULTS: The ethyl acetate, alcoholic & aqueous bark extracts of T. arjuna showed potent reversible non-competitive inhibition CYP2D enzyme in rat liver microsomes with IC50 values less than 40 µg/mL. Arjunic acid, arjunetin and arjungenin did not show significant inhibition of CYP2D enzyme in rat liver microsomes. Pharmacokinetic studies showed that aqueous bark extract of T. arjuna led to a significant reduction (P < 0.05) in AUC0-24h and Cmax of metoprolol succinate in rats, when co-administered. Pharmacodynamic studies reveal a significant reduction in therapeutic activity of metoprolol succinate on co-administration with aqueous bark extract of T. arjuna. CONCLUSION: Based on our in vitro and in vivo findings and until further clinical drug interaction experiments are conducted, the co-administration of drugs, especially those primarily cleared via CYP2D catalyzed metabolism, with T. arjuna extracts should be done with caution.

In vitro assessment of CYP1A2 and 2C9 inhibition potential of Withania somnifera and Centella asiatica in human liver microsomes.

BACKGROUND: Several herbal drugs and allopathic medicines when co-administered can lead to severe herb-drug interactions. Hence, this study was undertaken in order to assess the in vitro inhibition potential of Withania somnifera and Centella asiatica with cytochrome P450 (CYP) 1A2 and 2C9 enzyme using human liver microsomes. METHODS: Inhibitory potential of crude extracts of both the medicinal plants along with their principal phytoconstituents were investigated using selective probe substrate technique. IC50, Ki values and mode of inhibition were determined. RESULTS: The results of the study revealed that W. somnifera showed no significant interaction with both the isoforms of CYP. However, ethanolic extract of C. asiatica significantly inhibited both CYP1A2 (IC50 value - 42.23±3.65 µg/mL/Ki value - 14.93±4.59 µg/mL) and 2C9 enzyme (IC50 value - 48.41±4.64 µg/mL/Ki value - 23.89±3.14 µg/mL) in a competitive manner. The flavonoids, quercetin and kaempferol showed potent (IC50 values less than 10 µM) inhibition of CYP1A2 activity with no significant inhibition of CYP2C9 enzyme. CONCLUSIONS: Thus, these findings of the study might be helpful for safe and effective use of C. asiatica in clinical practice. However, its in vivo interaction study in humans is still warranted.

Investigation of CYP3A4 and CYP2D6 Interactions of Withania somnifera and Centella asiatica in Human Liver Microsomes.

Withania somnifera is commonly used as a rejuvenator, whereas Centella asiatica is well known for its anxiolytic and nootropic effects. The present study aims at investigating the effect of crude extracts and principal phytoconstituents of both the medicinal plants with CYP3A4 and CYP2D6 enzyme activity in human liver microsomes (HLM). Phytoconstituents were quantified in the crude extracts of both the medicinal plants using reverse phase HPLC. Crude extracts and phytoconstituents of W. somnifera showed no significant interaction with both CYP3A4 and CYP2D6 enzymes in HLM. Of the crude extracts of C. asiatica screened in vitro, methanolic extract showed potent noncompetitive inhibition of only CYP3A4 enzyme (Ki-64.36 ± 1.82 µg/mL), whereas ethanol solution extract showed potent noncompetitive inhibition of only CYP2D6 enzyme (Ki-36.3 ± 0.44 µg/mL). The flavonoids, quercetin, and kaempferol showed potent (IC50 values less than 100 µM) inhibition of CYP3A4 activity, whereas quercetin alone showed potent inhibition of CYP2D6 activity in HLM. Because methanolic extract of C. asiatica showed a relatively high percentage content of quercetin and kaempferol than ethanol solution extract, the inhibitory effect of methanolic extract on CYP3A4 enzyme activity could be attributed to the flavonoids. Thus, co-administration of the alcoholic extracts of C. asiatica with drugs that are substrates of CYP3A4 and CYP2D6 enzymes may lead to undesirable herb-drug interactions in humans.

In vitro modulatory effects of Terminalia arjuna, arjunic acid, arjunetin and arjungenin on CYP3A4, CYP2D6 and CYP2C9 enzyme activity in human liver microsomes.

Terminalia arjuna is a tree having an extensive medicinal potential in cardiovascular disorders. Triterpenoids are mainly responsible for cardiovascular properties. Alcoholic and aqueous bark extracts of T. arjuna, arjunic acid, arjunetin and arjungenin were evaluated for their potential to inhibit CYP3A4, CYP2D6 and CYP2C9 enzymes in human liver microsomes. We have demonstrated that alcoholic and aqueous bark extract of T. arjuna showed potent inhibition of all three enzymes in human liver microsomes with IC50 values less than 50 µg/mL. Arjunic acid, arjunetin and arjungenin did not show significant inhibition of CYP enzymes in human liver microsomes. Enzyme kinetics studies suggested that the extracts of arjuna showed reversible non-competitive inhibition of all the three enzymes in human liver microsomes. Our findings suggest strongly that arjuna extracts significantly inhibit the activity of CYP3A4, CYP2D6 and CYP2C9 enzymes, which is likely to cause clinically significant drug-drug interactions mediated via inhibition of the major CYP isozymes.

In vitro and in vivo Evaluation of CYP1A Interaction Potential of Terminalia Arjuna Bark.

Terminalia arjuna Wight and Arn. (Combretaceae) is a tree having an extensive medicinal potential in cardiovascular disorders. Triterpenoids are mainly responsible for cardiovascular properties. Aqueous, hydroalcoholic and alcoholic extract of T. arjuna, arjunic acid and arjungenin were examined for their potential to inhibit CYP1A enzyme in rat and human liver microsomes. IC50 values of aqueous, hydroalcoholic and alcoholic extract of T. arjuna was found to be 11.4, 28.9 and 44.6 µg/ml in rat liver microsomes while 30.0, 29.7 and 39.0 µg/ml in human liver microsomes, respectively for CYP1A. However IC50 values of arjunic acid and arjungenin for both rat liver microsomes and human liver microsomes were found to be >50 µM. Arjunic acid and arjungenin did not show inhibition of CYP1A enzyme up to concentrations of 50 µM. These in vitro data indicate that Terminalia arjuna extracts contain constituents that can potently inhibit the activity of CYP1A, which could in turn lead to undesirable pharmacokinetic drug-herb interactions in vivo. Based on the in vitro data, interaction potential of the aqueous extract of Terminalia arjuna orally in rats was investigated. A probe substrate, phenacetin, was used to index the activity of CYP1A. In vivo pharmacokinetic study of coadministration of aqueous extract of Terminalia arjuna and phenacetin, revealed that the aqueous extract did not lead to any significant change in the pharmacokinetic parameters of phenacetin as compared with control group. Though there was no in vivo-in vitro correlation, drug interactions could arise with drugs having a narrow therapeutic range and extensively cleared by CYP1A enzyme, which could lead to undesirable side effects.

In vitro evaluation of hepatic and extra-hepatic metabolism of coumarins using rat subcellular fractions: correlation of in vitro clearance with in vivo data.

7-Ethoxycoumarin (7-EC) and 7-hydroxycoumarin (7-HC) were chosen as model compounds to study hepatic and extra-hepatic metabolism in rat tissue subcellular (microsomal and S9) fractions and to scale the observed in vitro clearance to in vivo plasma clearance. 7-EC and 7-HC showed significant metabolic degradation in liver subcellular fractions as compared to subcellular fractions obtained from intestine, kidney, lung and brain. The total in vitro metabolic clearance for 7-EC and 7-HC was determined by adding the individual in vitro organ clearance values obtained in hepatic and extra-hepatic microsomes or S9 fractions. The predicted in vivo clearance for 7-HC was 63.6 and 81.6 ml/min/kg by in vitro scaling from microsomes and S9 fractions, respectively. For 7-EC, the values were 78.5 and 76.8 ml/min/kg, respectively. The predicted clearance was found to be reasonably accurate with slight over- and underprediction. Interestingly, the relative contribution of hepatic and extra-hepatic metabolism to the total clearance of 7-EC and 7-HC was remarkably high, ranging from 62-77% and 22-38%, respectively, of the total metabolic clearance. It is concluded that the model of multi-organ subcellular fractions is a useful in vitro tool for the prediction of in vivo metabolic clearance, as it can provide information about the relative contribution of extra-hepatic and hepatic metabolism to total metabolic clearance.