Expression of clinically relevant drug‐metabolizing enzymes along the human intestine and their correlation to drug transporters and nuclear receptors: An intra‐subject analysis

Abstract

The oral bioavailability of many drugs is highly influenced not only by hepatic but also by intestinal biotransformation. To estimate the impact of intestinal phase I and II metabolism on oral drug absorption, knowledge on the expression levels of the respective enzymes is an essential prerequisite. In addition, the potential interplay of metabolism and transport contributes to drug disposition. Both mechanisms may be subjected to coordinative regulation by nuclear receptors, leading to unwanted drug‐drug interactions due to induction of intestinal metabolism and transport. Thus, it was the aim of this study to comprehensively analyse the regional expression of clinically relevant phase I and II enzymes along the entire human intestine and to correlate these data to expression data of drug transporters and nuclear receptors of pharmacokinetic relevance. Gene expression of 11 drug‐metabolizing enzymes (CYP2B6, 2C8, 2C9, 2C19, 2D6, 3A4, 3A5, SULT1A, UGT1A, UGT2B7, UGT2B15) was studied in duodenum, jejunum, ileum and colon from six organ donors by real‐time RT‐PCR. Enzyme expression was correlated with expression data of the nuclear receptors PXR, CAR and FXR as well as drug transporters observed in the same cohort. Intestinal expression of all studied metabolizing enzymes was significantly higher in the small intestine compared to colonic tissue. CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP3A4/5, SULT1A, UGT1A and UGT2B7 expression increased from the duodenum to jejunum but was markedly lower in the ileum. In the small intestine, that is, the predominant site of drug absorption, the highest expression has been observed for CYP3A4, CYP2C9, SULT1A and UGT1A. In addition, significant correlations were found between several enzymes and PXR as well as ABC transporters in the small intestine. In conclusion, the observed substantial site‐dependent intestinal expression of several enzymes may explain regional differences in intestinal drug absorption. The detected correlations between intestinal enzymes, transporters and nuclear receptors provide indirect evidence for their coordinative expression, regulation and function in the human small intestine.

Quantitative Proteomics of Clinically Relevant Drug-Metabolizing Enzymes and Drug Transporters and Their Intercorrelations in the Human Small Intestine

“…Intercorrelations were found between P450, between UGTs, between P450 and UGTs, and between DMEs and transporters, in line with that previously established in studies using mRNA expression levels at the mRNA level; strong intercorrelations have been reported between CYP3A4-ABCB1 (P-gp) and UGT1A1-ABCC2 (MRP2) (Drozdzik et al, 2014;Bruckmueller et al, 2017;Fritz et al, 2019). In the present study, similar strong intercorrelation was observed at the protein level between these protein pairs.…”

“…Challenges associated with obtaining intestinal tissue samples increase the value of studies reporting the actual protein abundances as opposed to mRNA levels. There are a number of reports on mRNA expression data of genes encoding DMEs and drug transporters in the human small intestine (Thörn et al, 2005;Clermont et al, 2019;Fritz et al, 2019). However, caution should be exercised in using these values because the relationship between mRNA and protein abundance appears inconsistent (Berggren et al, 2007;Hayeshi et al, 2008), suggesting that mRNA data in a high-turnover tissue such as intestine may have limited utility for PBPK modeling.…”

Activity and mRNA expression levels of selected cytochromes P450 in various sections of the human small intestine

“…However, the design of our study allowed us to investigate interindividual differences and regional distribution of cytochrome P450 isoforms. Our work complements and supports results from previous studies as it reports data on several subjects, as well as multiple sections from the same donors …”

“…and Fritz et al . reported similar data in their study measuring protein expression, with a ranking of CYP3A4 > CYP2C9 > CYP2C19 . Since they did not quantify CYP2J2, it is not possible to compare the protein expression of that isoform with our mRNA data …”

“…Comprehensive studies conducted in non‐human primates have characterized the regional distribution of cytochrome P450 mRNAs and activities in the small intestine of cynomolgus monkeys . Similarly, in human, evidence suggests that cytochromes P450 have a regional distribution and a higher concentration in the villus tips . This regional expression, from the duodenum to the ileum, appears to be isoform‐dependent .…”