METHODS: Diabetic rats were randomly assigned to four groups, with six rats in each group. Group 1 was administered distilled water. Group 2 was administered V. amygdalina aqueous leaf extract alone. Group 3 was administered metformin alone. Group 4 was co-administered V. amygdalina extract plus metformin. Blood was collected at predetermined intervals, and plasma metformin levels were measured with liquid chromatography. The area under the curve (AUC0-t), maximum plasma concentration (Cmax), time to reach Cmax (Tmax), half-life (t1/2), and clearance (CL), were calculated based on noncompartment analysis. The effect of the extract on CYP2C9, CYP3A4, and UGT activities was determined using a Fluorometric Screening Kit.
RESULTS: The combined treatment altered the pharmacokinetic parameters of metformin. The Tmax increased from 90±0.18 min to 180±0.13 min and the Cmax, increased from 0.91±0.32 μg/mL to 2.153±0.28 μg/mL. Additionally, the AUC(0-t) increased from 118.25±1.37 μg min mL-1 to 301.006±1.96 μg min mL-1 and the t1/2 increased from 34.69±0.61 min to 101.321±0.55 min. However, the CL rate was decreased. The extract inhibited CYP3A4 and CYP2C9 enzyme activities.
CONCLUSIONS: The alteration of pharmacokinetic parameters by the extract suggests potential herb-drug interactions.
METHODS: The quantification of the bioactive compounds was conducted using ultra-high-performance liquid chromatography multiple reactions monitoring tandem mass spectrometry (UHPLC-MS/MS-MRM) technique. The effect of the extract on CYP2C9 and CYP3A4 activities was determined using a fluorometric screening kit according to the manufacturer's instructions.
RESULTS: The three bioactive compounds were detected and quantified in the aqueous leaf extract. Results showed that the content of luteolin-7-O-glucuronide (47 μg/mg) was the highest followed by luteolin-7-O-glucoside (3.5 μg/mg) and 1,5-O-dicaffeoylquinic acid (1.07 μg/mg). The extract showed an inhibitory effect on CYP3A4 and CYP2C9 enzyme activities in control and diabetic rats.
CONCLUSIONS: The UHPLC-MS/MS-MRM method is sensitive and reliable for the quality control of V. amygdalina leaf extract. The inhibitory effect of the extract suggests that concomitant use of V. amygdalina leaf preparations with conventional drugs metabolized and eliminated from the body by CYP3A4 and CYP2C9 enzymes may lead to possible interaction.
AIM OF THE STUDY: The present study was carried out to examine the potential modulatory effects of three commercially available active components (asiaticoside, asiatic acid and madecassic acid) and four extracts (aqueous, ethanol, dichloromethane and hexane) of CA on three major cDNA-expressed human cytochrome P450 (CYP) isoforms.
MATERIALS AND METHODS: High-performance liquid chromatography (HPLC)-based enzyme assays, namely tolbutamide 4-methyhydroxylase, dextromethorphan O-demethylase and testosterone 6beta-hydroxylase assays were developed to probe activities of CYP2C9, CYP2D6 and CYP3A4, respectively. Probe substrates were incubated with or without each active component and extract for each isoform, followed by examination of the kinetics parameters, IC(50) and K(i), to characterize modulatory effects.
RESULTS: CYP2C9 was more susceptible to inhibitory effects by CA extracts compared to CYP2D6 and CYP3A4. Moderate degree of inhibition was observed in ethanol (K(i)=39.1 microg/ml) and dichloromethane (K(i)=26.6 microg/ml) extracts implying potential risk of interaction when CYP2C9 substrates are consumed with CA products. The two extracts however showed negligible inhibition towards CYP2D6 and CYP3A4 (IC(50)'s of 123.3 microg/ml and above). Similarly CA aqueous and hexane extracts did not significantly inhibit all three isoforms investigated (IC(50)'s of 117.9 microg/ml and above). Among the active constituents investigated, asiatic acid and madecassic acid appeared to selectively inhibit CYP2C9 and CYP2D6 more than CYP3A4. Of particular interest is the potent inhibitory effect of asiatic acid on CYP2C9 (K(i)=9.1 microg/ml). This signifies potential risk of interaction when substrates for this isoform are taken together with CA products with high asiatic acid content. Inhibitions of asiatic acid with the other isoforms and that of madecassic acid with all isoforms were only moderate (K(i)'s ranged from 17.2 to 84.4 microg/ml). On the other hand, the IC(50) values for asiaticoside were high (1070.2 microg/ml or above) for all three isoforms, indicating negligible or low potential of this compound to modulate CYP enzymatic activity.
CONCLUSION: Centella asiatica extracts and active constituents inhibited CYP2C9, CYP2D6 and CYP3A4 activities with varying potency with CYP2C9 being the most susceptible isoform to inhibition. Significant inhibition was observed for asiatic acid and CA ethanol and dichloromethane extracts, implying involvement of semipolar constituents from CA in the effect. This study suggested that CA could cause drug-herb interactions through CYP2C9 inhibition.