Regional Expression Levels of Drug Transporters and Metabolizing Enzymes along the Pig and Human Intestinal Tract and Comparison with Caco-2 Cells

Abstract

Intestinal transporter proteins and metabolizing enzymes play a crucial role in the oral absorption of a wide variety of drugs. The aim of the current study was to characterize better available intestinal in vitro models by comparing expression levels of these proteins and enzymes between porcine intestine, human intestine, and Caco-2 cells. We therefore determined the absolute protein expression of 19 drug transporters and the mRNA expression of 12 metabolic enzymes along the pig intestinal tract (duodenum, jejunum, ileum; = 4), in human intestine (jejunum; = 9), and Caco-2 cells. Expression of the included transporters and enzymes was in general well comparable between porcine and human intestinal tissue, although breast cancer resistance protein, monocarboxylate transporter 5, multidrug resistance protein (MRP) 1, MRP1, MRP3 (∼2-fold), and organic anion-transporting polypeptide (OATP) 4A1 (∼6-fold) was higher expressed in pig compared with human jejunum. Alternatively, expression level of relevant transporter proteins (glucose transporter 1, OATP4A1, MRP2, MRP1, and OATP2B1) was significantly higher (3- to 130-fold) in Caco-2 cells compared with human jejunum. Moreover, all examined CYPs showed at least a fivefold lower gene expression in Caco-2 cells compared with human jejunum, with the smallest differences for CYP1A1 and CYP3A5 and the largest difference for CYP3A4 (871-fold higher expression in human jejunum compared with Caco-2 cells). In conclusion, a comprehensive overview is provided of the expression levels of clinically relevant transporter proteins and metabolic enzymes in porcine and human intestinal tissue and Caco-2 cells, which may assist in deciding upon the most suitable model to further improve our understanding of processes that determine intestinal absorption of compounds.

Protein Abundance of Clinically Relevant Drug Transporters in the Human Liver and Intestine: A Comparative Analysis in Paired Tissue Specimens

“…In line with our previous analysis, OATP1A2 could not be detected in any intestinal segment (data not shown), which argues against its involvement in interaction studies with juices or drugs, as frequently discussed . Our results also corroborate observations of other authors …”

“…Furthermore, we could verify the distinct increase in P‐gp, BCRP, and PEPT1 proteins from proximal to distal small intestine, which is expected to significantly affect oral drug absorption, as discussed elsewhere . However, the obtained quantitative data cannot be directly compared to currently available studies, as those studies analyzed enriched membrane fractions but not whole‐tissue lysates . However, correlation analysis of the present data with our previous study demonstrated significant correlation ( R > 0.7) of transporter protein abundance in the duodenum, ileum, and colon (data not shown).…”

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

“…Our data confirmed that CYP3A4 and CYP2C9 are the major CYP enzymes in the human small intestine, whereas the expression of CYP2C19, CYP2B6, CYP3A5 and CYP2D6 is substantially lower . In a very recent study, we could confirm these findings also on small intestinal protein levels in a different cohort of nine donors in which we characterized the intestinal and hepatic abundance of clinically relevant metabolizing enzymes (CYP3A4 > CYP2C9 > CYP2C19 > CYP2D6 ~ CYP2B6 > CYP3A5) …”

“…Our data confirmed that CYP3A4 and CYP2C9 are the major CYP enzymes in the human small intestine, whereas the expression of CYP2C19, CYP2B6, CYP3A5 and CYP2D6 is substantially lower. 18,20,33,44,45 In a very recent study, we could confirm these findings also on small intestinal protein levels in a different cohort of nine donors in which we characterized the intestinal and hepatic abundance of clinically relevant metabolizing enzymes (CYP3A4 > CYP2C9 > CYP2C19 > CYP2D6C YP2B6 > CYP3A5). 46 In line with this observation, CYP3A4 and CYP2C9 substrates (eg, for CYP3A4: midazolam, nifedipine, simvastatin, cyclosporine, tacrolimus, sirolimus, lopinavir, ritonavir; for CYP2C9: tolbutamide, diclofenac, warfarin) were shown to undergo substantial first-pass metabolism.…”

“…With reference to phase II enzymes, our study could confirm the high expression of UGT1A, UGT2B7 and SULT1A enzymes in the human intestine. 20,21,25,34,44,45,50,51 As already mentioned for CYP enzymes, extensive intestinal phase II metabolism may also bear the risk of DDIs for drugs that undergo extensive intestinal glucuronidation such as morphine, ezetimibe, mycophenolic acid or estrogens. [52][53][54] However, convincing clinical evidence for this hypothesis…”