7 cytochrome P450s (CYPs) under mechanism-based inactivation condi- tions was evaluated to understand the broader applications of hydralazine as a selective AO inhibitor in hepatocytes when used for reaction pheno- typing. The results showed that hydralazine inhibited CYP1A2 (56%-74%), 2B6 (22%-36%), 2D6 (31%-65%) and 3A (25%-37%) at concentrations that chemically knocked out most of the AO activities (50 mM) in human hepatocytes. Furthermore, hydralazine is a time-dependent inhibitor of CYP1A2 with kobs values of 0.0072 min-1 in hepatocytes and 0.012 min-1 in liver microsomes at 50 mM respectively The results helped to define the limitations of using hydralazine for AO reaction phenotyping, Fm,AO determination, and AO substrate identification. Based on these findings, precautions need to be taken when using hydralazine as an AO inhibitor for in vitro studies because fraction metabolized by AO is likely to be over- estimated and the likelihood of false positives in identifying AO substrates increases. This study also highlighted the importance of using relevant substrate concentration for selectivity studies. When substrate concen- tration is too high, inhibitors may appear to be more selective than they are. P105 - BDE-99 REPROGRAMS THE LIVER EPIGENOME PERSISTNENTLY ALTERING THE TRANSCRIPTOME Joseph Dempsey , Joe Lim, James MacDonald, Theo Bammler, Terrance Kavanagh, Julia Yue Cui. University of Washington, USA Background: Growing evidence in the literature suggests that early life exposure to environmental chemicals may lead to delayed onset of dis- eases later in life. Polybrominated diphenyl ethers (PBDEs) are a class of recently banned flame retardants found in consumer products and in the environment. Concentrations in human specimens, such as blood, breast milk, and adipose tissue, have increased exponentially over the past 30 years. Infants and toddlers are particularly vulnerable to PBDE-induced adverse effects due to ingestion of PBDE-contaminated breast milk and household dust. During liver development, profound changes occur in the chromatin epigenetic architecture that regulates the ontogenic expression of many genes involved in xenobiotic biotransformation. The goal of this study was to test our hypothesis that neonatal exposure to PBDEs repro- grams the liver epigenome and persistently alter alters transcription of xenobiotic biotransformation genes. Methods: Two-day-old male and female C57BL/6J mice were exposed to corn oil or 57 mg/kg BDE-99 (an enriched PBDE congener in humans), supralingually once daily for three days. At 60-days adult age, whole transcriptome sequencing was performed (n¼3 per exposure per gender), and data were analyzed using HISAT2 and Cufflinks. In parallel, ChIP-Seq of histone 3 lysine 27 acetylation (H3K27ac), which is a permissive epigenetic mark for enhancers and promoters, was performed in these samples, and data were analyzed using bowtie 2 and MACS2. Results: Neonatal exposure to BDE-99 persistently altered the RNA expression of distinct xenobiotic biotransformation enzymes, and this was associated with altered H3K27ac. In adult mice, there were 10,843 H3K27ac peaks in control livers and 12,374 peaks in livers of early life BDE- 99 exposed groups. These peaks were associated with 4378 and 3747 unique protein-coding genes (PCGs), respectively, and the expression of 218 of the PCGs were persistently altered by early-life exposure to BDE-99. Pathway analyses of these PCGs (STRING) identified metabolism of xeno- biotics by cytochrome P450s (Cyp), drug metabolism (other enzymes), and glutathione metabolism as significantly enriched KEGG pathways for the differentially regulated PCGs that carry the H3K27ac mark. Interestingly, Cyp2c29, 2c38, and 2c50 gained an enriched acetylation peak in the BDE- 99 exposed male mice but had decreased RNA expression; whereas Cyp3a16 gained an H3K27ac peak and had increased RNA expression, indicating that site specificity of H3K27ac has dual functions in gene transcription. Similarly glutathione-s-transferase alpha 3 (Gsta3), which had decreased expression following BDE-99 exposure, had no H3K27ac peaks in control conditions, but gained 3 peaks (one significantly enriched) following BDE-99 exposure. Conclusion: Our results demonstrate that neonatal exposure to BDE-99 reprograms the epigenetic mark H3K27ac in liver, corresponding to persistently altered expression of certain xenobiotic biotransformation genes in adult age. P106 - APPLICATION OF CRYOPRESERVED HUMAN INTESTINAL MUCOSA (CHIM) IN THE EVALUATION OF REGIONAL DIFFERENCE IN INTESTINAL DRUG METABOLISM Albert P. Li , Novera Alam, David Ho, Kirsten Amaral, Walter Mitchell. In Vitro ADMET Laboratories Inc., USA Oral ingestion represents the most desirable route of drug administration. An orally administered drug is firstly subjected to first pass metabolism by the small intestines before absorption into the portal vein followed by hepatic metabolism. Understanding potential regional differences in drug metabolism in the small intestine may aid our understanding of oral bioavailability, enteric drug toxicity, and enteric drug-drug interaction during the transit of an ingested drug in the small intestine. This is espe- cially important for controlled-release capsules with prolonged retention durations in the small intestine. We recently reported the establishment of a novel in vitro experimental model of the human small intestine, namely the cryopreserved human intestinal mucosa (CHIM) which retained high viability and drug metabolizing enzyme activities upon recovery from cryopreservation. To investigate potential regional differences in intestinal drug metabolism, CHIM were isolated from 10 12-inch segment of the small intestines. Drug metabolizing enzyme activities evaluated were: CYP1A1 (resorufin 7-deethylation), CYP1A2 (phenacetin hydroxylation), CYP2A6 (coumarin hydroxylation), CYP2B6 (buproprion hydroxylation), CYP2C8 (paclitaxel 6a-hydroxylation), CYP2C9 (diclofenac 4-hydroxyl- ation), CYP2C19 (s-mephenytoin 4-hydroxylation), CYP2D6 (dextrome- thorphan hydroxylation), CYP2E1 (chlorzoxazone 6-hydroxylation), CYP3A4 (midazolam 1-hydroxylation and testosterone 6b-hydroxylation), UGT (7-OH-coumarin glucuronidation), SULT (7-hydroxycoumarin sulfa- tion), GST (NAPQI-GSH conjugation), FMO (benzydamine N-oxidation), MAO (kynuramine 4-hydroxylation), AO (carbazeran 4-hydroxylation), and NAT-1 (4-aminobenzoic acid N-acetylation). Regional difference in activity was observed, with the regions proximal to the stomach in general having the higher activities. The manifestation of regional difference, however, differ among individuals. Our observation of regional differences in intestinal metabolism suggest that drugs may be metabolized during transit upon ingestion. The individual differences suggest environmental factors may play a role in the regional differences in intestinal drug metabolism activity in the small intestine. P107 - A COMPARISON OF ENTERIC AND HEPATIC METABOLISM USING IN VITRO ENTERIC AND HEPATIC EXPERIMENTAL SYSTEMS: CRYOPRESERVED HUMAN ENTEROCYTES, METMAX CRYOPRESERVED ENTEROCYTES, CRYOPRESERVED HUMAN INTESTINAL MUCOSA, CRYOPRESERVED HUMAN HEPATOCYTES, AND METMAX CRYOPRESERVED HUMAN HEPATOCYTES Albert P. Li , Novera Alam, David Ho, Kirsten Amaral, Walter Mitchell. In Vitro ADMET Laboratories Inc., USA An ingested drug is firstly subjected to intestinal metabolism by the enterocytes in the intestinal mucosa and then hepatic metabolism upon absorption into the portal circulation. It is important to understand the difference between enteric and hepatic metabolism for an accurate pre- diction of the in vivo metabolic fates of an ingested drug. In our laboratory, we have developed in vitro experimental systems for the liver (cry- opreserved human hepatocytes and MetMax™ (permeabilized, cofactor supplemented) cryopreserved human hepatocytes for the liver), and the small intestine (cryopreserved enterocytes, MetMax™ cryopreserved enterocytes, and cryopreserved human intestinal mucosa (CHIM)). We report here the drug metabolizing enzyme activities of these experimental systems to define the similarities and differences between hepatic and enteric drug metabolism. The drug metabolizing enzyme activities eval- uated were: CYP1A1 (resorufin 7-deethylation), CYP1A2 (phenacetin hy- droxylation), CYP2A6 (coumarin hydroxylation), CYP2B6 (buproprion hydroxylation), CYP2C8 (paclitaxel 6a-hydroxylation), CYP2C9 (diclofenac 4-hydroxylation), CYP2C19 (s-mephenytoin 4-hydroxylation), CYP2D6 (dextromethorphan hydroxylation), CYP2E1 (chlorzoxazone 6-hydroxyl- ation), CYP3A4 (midazolam 1-hydroxylation and testosterone 6b- Drug Metabolism and Pharmacokinetics 35 (2020) S23eS99 / Abstracts S54