Introduction: As the use of dietary supplements increases, botanical-drug interaction (BDI) potentials should be evaluated. Boswellia serrata extract (BSE) is traditionally used as an anti-inflammatory supplement. In the scientific literature, BSE has been shown to reduce the activity (55% to ‡65%) across major CYP450 enzymes, including CYP3A4/5 and CYP2C9, using baculovirus-infected insect cells. These reported results, contrasted with a seemingly history of safe use of BSE, led us to question the relevance of the results using pooled human liver microsomes (PHLM), when compared to a more physiologically relevant model such as primary human hepatocytes. Methods: This study compared PHLM and sandwich-cultured human hepatocytes (SCHH) by evaluating BSE potential inhibitory effects on CYP3A4/5 and CYP2C9 enzymatic activity. Results: In SCHH, inhibition of CYP3A4/5 by BSE was observed resulting in an IC 50 = 17.4 lg/mL with maximum inhibition effect of >70% at 75 lg/mL versus IC 50 = 1.4 lg/mL with a maximum inhibition effect of 98% at 50 lg/mL in PHLM. IC 50 values for CYP2C9 inhibition by BSE were >75 lg/mL with a maximum inhibition effect of <30% versus 11 lg/mL with a maximum inhibition effect of 84% at 50 lg/mL using SCHH and PHLM, respectively. Discussion and Conclusions: Potent CYP3A4/5 and CYP2C9 inhibition observed for BSE in microsomal systems was not observed in SCHH. SCHH are particularly useful for studying complex mixtures such as botanicals. Although our data would suggest that BDI with BSE is low for most drugs, narrow therapeutic drugs such as warfarin should still be used with caution when combined with BSE.

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