Experimental approaches to evaluate activities of cytochromes P450 3A

Effect of eugenol on cytochrome P450 1A2, 2C9, 2D6, and 3A4 activity in human liver microsomes

This study aimed to provide an understanding of the influence of eugenol on CYP1A2, 2C9, 2D6, and 3A4 in human liver microsomes (HLM). Specific substrate for CYP1A2, 2C9, 2D6, and 3A4 were incubated in HLM with or without eugenol. The formation of their respective metabolites was assessed with HPLC analytical methods. Eugenol at 1, 10 and 100 µM levels inhibited the activity of CYP1A2 and CYP2C9 by 23.38 %, 23.57 %, 39.80 % and 62.82 %, 63.27 %, 67.70 % respectively. While, CYP2D6 and CYP3A4 activity was decreased by 40.70 %, 45.88 %, 62.68 % and 37.41 %, 42.58 % and 67.86 % at 1, 10 and 100 µM eugenol level respectively. The IC50 value of eugenol for CYP2D6 and CYP3A4 was calculated as 11.09 ± 3.49 µM and 13.48 ± 3.86 µM respectively. Potential herb-drug interactions was noted when eugenol is administered simultaneously with medications metabolized by these enzymes, most notably CYP2C9, CYP2D6 and CYP3A4.

Effect of Naltrexone Hydrochloride on Cytochrome P450 1A2, 2C9, 2D6, and 3A4 Activity in Human Liver Microsomes

BACKGROUND AND OBJECTIVE

Cytochrome P450 (CYP) 1A2, 2C9, 2D6, and 3A4 are the most important phase I drug-metabolizing enzymes in the liver, but there is a dearth of literature available on the effects of naltrexone hydrochloride on these major enzymes present in the human liver. Thus, in the present study, the effect of naltrexone hydrochloride on the activity of CYP1A2, 2C9, 2D6, and 3A4 using human liver microsomes (HLM) was investigated.

METHODS

A selective probe for CYP1A2, 2C9, 2D6, and 3A4 was incubated with HLM with or without naltrexone hydrochloride. Phenacetin O-deethylation, tolbutamide 4-hydroxylation, dextromethorphan O-demethylation, and testosterone 6β-hydroxylation reactions were monitored for enzyme activity.

RESULTS

The activity of all the studied CYP enzymes except 1A2 was significantly inhibited by naltrexone hydrochloride 1 µM. Furthermore, 1 µM naltrexone hydrochloride inhibited CYP3A4 enzyme activity, the most by 37.9% followed by CYP2C9 (36.5%) and CYP2D6 (31.8%). The CYP2C9 and CYP2D6 metabolic activities were greatly affected by naltrexone hydrochloride, which even at the lowest concentration of naltrexone hydrochloride (0.01 µM) significantly decreased the metabolic activity by 34.9 and 16.0%, respectively. The half maximal inhibition concentration (IC₅₀) values for CYP2C9 and CYP2D6 inhibition were 3.40 ± 1.78 and 5.92 ± 1.58 µM, respectively.

CONCLUSION

These outcomes advocate that there is a great possibility of drug interactions resulting from the concurrent administration of naltrexone hydrochloride with actives that are metabolized by these CYP enzymes, particularly CYP2C9 and CYP2D6. Nevertheless, further clarification is needed through detailed in vivo pharmacokinetic studies.

Inhibition of cytochrome P450 enzymes by thymoquinone in human liver microsomes

The aim of the present study was to investigate the potential effect of thymoquinone (TQ) on the metabolic activity of four major drug metabolizing enzymes in human liver microsomes, namely cytochrome P450 (CYP) 1A2, CYP2C9, CYP2D6 and CYP3A4. The inhibition of CYP enzymatic activities by TQ was evaluated by incubating typical substrates (phenacetin for CYP1A2, tolbutamide for CYP2C9, dextromethorphan for CYP2D6, and testosterone for CYP3A4) with human liver microsomes and NADPH in the absence or presence of TQ (1, 10 and 100 µM). The respective metabolite of the substrate that was formed was measured by HPLC. Results of the presented study presented that the metabolic activities of all the investigated CYP enzymes, viz. CYP1A2, CYP2C9, CYP2D6 and CYP3A4, were inhibited by TQ. At 1 µM TQ, CYP2C9 enzyme activity was maximally inhibited by 46.35%, followed by CYP2D6 (20.26%) > CYP1A2 (13.52%) > CYP3A4 (12.82%). However, at 10 µM TQ, CYP2C9 enzyme activity was maximally inhibited by 69.69%, followed by CYP3A4 (23.59%) > CYP1A2 (23.51%) > CYP2D6 (11.42%). At 100 µM TQ, CYP1A2 enzyme activity was maximally inhibited by 81.92%, followed by CYP3A4 (79.24%) > CYP2C9 (69.22%) > CYP2D6 (28.18%). The IC₅₀ (mean ± SE) values for CYP1A2, CYP2C9, CYP2D6 and CYP3A4 inhibition were 26.5 ± 2.9 µM, 0.5 ± 0.4 µM, >500 µM and 25.2 ± 3.1 µM, respectively. These findings suggest that there is a high probability of drug interactions resulting from the co-administration of TQ or herbs containing TQ with drugs that are metabolized by the CYP enzymes, particularly CYP2C9.