Background: A recent advancement in isolation and cryopreservation has resulted in
commercially available primary human enterocytes that express various drug metabolizing enzymes
(DMEs) and transporters. The main objective of this study was to further evaluate the utility of pooled
cryopreserved enterocytes, specifically MetMax™ cryopreserved human enterocytes (In vitro ADMET
Laboratories), as an in vitro model for assessing intestinal clearance in comparison to hepatocytes.
Methods: It was found that, for CYP3A4/5 substrates such as midazolam, amprenavir and loperamide,
in vitro metabolic clearance is generally lower in enterocytes compared to that of hepatocytes, which is
consistent with the relative abundance of the enzyme between the intestine and liver. In contrast,
raloxifene, a surrogate UGT activity substrate, showed 3-fold greater turnover in enterocytes than
hepatocytes, which is likely attributed to the differential expression of individual UGTs in human liver
and intestine. For procaine, a known CES2 substrate, the measured apparent clearance was higher in
hepatocytes, but formation of 4-aminobenzoic acid, a CE2-specific metabolite, was more pronounced
in enterocytes, suggesting that CE2 is more active in enterocytes. Salbutamol, a SULT1A3 substrate,
showed little turnover in both enterocytes and hepatocytes, and more abundant sulfate conjugate was
detected in enterocytes, indicating higher SULT activity in enterocytes than hepatocytes. As expected,
ketoconazole inhibited CYP3A4/5-mediated metabolite formation in enterocytes for midazolam,
amprenavir and loperamide, suggesting that cryopreserved enterocytes may be useful in determining
intestinal CYP3A inhibition parameters. Interestingly, elacridar, a P-gp inhibitor, suppressed metabolite
formation in enterocytes for loperamide, a substrate of CYP3A4 and P-gp, suggesting that enterocytes
in suspension do not have active P-gp efflux functions, and the suppression of metabolism in
enterocytes is probably caused by inhibition of CYP3A4/5 by elacridar.
Results: Our results suggest that pooled cryopreserved human enterocytes, specifically the MetMax™
cryopreserved human enterocytes, represent a valuable in vitro model for assessing first-pass clearance
and potential drug interactions in human intestine.