We report here a novel in vitro enteric experimental system, cryopreserved human intestinal mucosa (CHIM), for the evaluation of enteric drug metabolism, drug-drug interaction, drug toxicity, and pharmacology. CHIM was isolated from the small intestines of four human donors. The small intestines were first dissected into the duodenum, jejunum, and ileum, followed by collagenase digestion of the intestinal lumen. The isolated mucosa was gently homogenized to yield multiple cellular fragments, which were then cryopreserved in a programmable liquid cell freezer and stored in liquid nitrogen. After thawing and recovery, CHIM retained robust cytochrome P450 (P450) and non-P450 drug-metabolizing enzyme activities and demonstrated dose-dependent induction of transcription of CYP24A1 (approximately 300-fold) and CYP3A4 (approximately 3-fold) by vitamin D as well as induction of CYP3A4 (approximately 3-fold) by rifampin after 24 hours of treatment. Dose-dependent decreases in cell viability quantified by cellular ATP content were observed for naproxen and acetaminophen, with higher enterotoxicity observed for naproxen, consistent with that observed in humans in vivo. These results suggest that CHIM may be a useful in vitro experimental model for the evaluation of enteric drug properties, including drug metabolism, drug-drug interactions, and drug toxicity.

1. Ritonavir and cobicistat are pharmacokinetic boosting agents used to increase systemic exposure to other antiretroviral therapies. The manufacturer's data suggests that cobicistat is a more selective CYP3A4 inhibitor than ritonavir. However, the inhibitory effect of ritonavir and cobicistat on human UDP glucuronosyltransferase (UGT) enzymes in Phase II metabolism is not established. This study evaluated the inhibition of human UGT isoforms by ritonavir versus cobicistat. 2. Acetaminophen and ibuprofen were used as substrates to evaluate the metabolic activity of the principal human UGTs. Metabolite formation rates were determined by HPLC analysis of incubates following in vitro incubation of index substrates with human liver microsomes (HLMs) at different concentrations of ritonavir or cobicistat. Probenecid and estradiol served as positive control inhibitors. 3. The 50% inhibitory concentrations (IC) of cobicistat and ritonavir were at least 50 µM, which substantially exceeds usual clinical plasma concentrations. Probenecid inhibited the glucuronidation of acetaminophen (IC 0.7 mM), but not glucuronidation of ibuprofen. At relatively high concentrations, estradiol inhibited ibuprofen glucuronidation (IC 17 µM). 4. Ritonavir and cobicistat are unlikely to produce clinically important drug interactions involving drugs metabolized to glucuronide conjugates by UGT1A1, 1A3, 1A6, 1A9, 2B4 and 2B7.

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Commercial formulations of 29 commonly used herbal supplements (HS) and grapefruit juice were evaluated for drug interaction potential via quantification of their CYP3A inhibitory potential in two in vitro experimental models of human small intestine, cryopreserved human intestinal mucosa (CHIM) and cryopreserved human enterocytes (CHE). Two CYP3A substrates were used-in the studies with CHIM, CYP3A activity was quantified via LC/MS-MS quantification of midazolam 1'-hydroxylation while in CHE, luciferin IPA metabolism to luciferin was quantified by luminescence. Upon treatment of CHIM with the estimated lumen concentration of the HS upon each oral administration (manufacturers' recommended dosage dissolved in 200 mL of culture medium), >80% CYP3A inhibition was observed for green tea extract, St. John's wort, valerian root, horehound and grapefruit juice. Less than 50% inhibition was observed for fenugreek, aloe vera, guarana, soy isoflavone, maca, echinacea, spirulina, evening primrose, milk thistle, cranberry, red yeast rice, rhodiola, ginkgo biloba, turmeric, curcumin, white kidney bean,, garlic, cinnamon, saw palmetto berries, panax ginseng, black elderberry, wheat grass juice, flaxseed oil, black cohosh, and ginger root. The results were confirmed in a a dose-response study with HS obtained from three suppliers for the four inhibitory HS (green tea extract, horehound, St. John's wort, valerian root), and three representative non-inhibitory HS (black cohosh, black elderberry, echinacea). Similar results were obtained with the inhibitory HS in CHE. The results illustrate that CHIM and CHE represent physiologically relevant in vitro experimental models for the evaluation of drug interaction potential of herbal supplements. Based on the results, green tea extract, horehound, St. John's wort, and valerian root may cause drug interactions with orally administered drugs that are CYP3A substrates as observed for grapefruit juice. Significance Statement In vitro evaluation of 29 popular herbal supplements in cryopreserved human intestinal mucosa identified green tea extract, horehound, St. John's wort, valerian root to have CYP3A inhibitory potential similar to that for grapefruit juice, suggesting their potential to have clinically-significant pharmacokinetic interaction with orally administered drugs that are CYP3A substrates. The results suggest that CHIM can be used for in vitro evaluation of drug interactions involving enteric drug metabolism.