No abstract

Introduction: In vitro bile salt export pump (BSEP) inhibition alone does not accurately predict in vivo drug-induced liver injury in humans, suggesting that other mechanisms may be involved. Inhibition of BSEP has been shown to increase the hepatocellular concentrations of bile acids (BAs), and hepatobiliary disposition of BAs is tightly regulated by the farnesoid X receptor (FXR). Activation of FXR leads to decreased synthesis of BAs and increased expression of BA efflux transporters, BSEP, and organic solute and steroid transporter (OSTa/b). The link between BSEP inhibition and activation of the BA compensatory mechanism has not been clearly demonstrated. Materials and Methods: Therefore, we utilized BSEP inhibitors, cyclosporine A (CsA) and troglitazone (Trog), to explore this ''triggering'' event using Transporter CertifiedÔ sandwich-cultured human hepatocytes (SCHH). Results: Biliary excretion of glycine-cholic acid (GCA) as a percentage of total GCA accumulation was reduced in SCHH treated with either CsA or Trog. Within 12 hours, CsA treatment concomitantly increased intracellular concentrations (ICCs) of GCA and FGF19 mRNA content, an FXR-target gene. Separately, a synergistic 76.6fold increase of OSTb mRNA was observed following CsA and chenodeoxycholic acid co-exposure. In contrast, Trog exposure prevented the synergistic increase of OSTb, a component of the basolateral BA efflux transporter, under the same conditions. Finally, BA toxicity potency was increased in SCHH exposed to Trog but not CsA. Discussion and Conclusions: Overall, these results suggested that BSEP inhibition activates the BA compensatory mechanism reducing ICCs of BAs. However, Trog possesses both BSEP inhibition and FXR antagonist properties blocking the activation of the compensatory mechanism resulting in BA-induced hepatotoxicity.

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.