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

This work revises and complements existing findings on the distribution of drug‐metabolizing enzymes in the first‐pass effect organs. We explored gene expression (quantitative polymerase chain reaction) and protein abundance (liquid chromatography/ tandem mass spectrometry) of CYP1A2, CYP2B6, CYP2C8/9/19, CYP2D6, CYP2E1, CYP3A4/5, UGT1A1/3, UGT2B7/15 in the liver, duodenum, jejunum, ileum, and colon in paired tissues from nine organ donors. All proteins were detected in the liver, but in the intestine CYP2C9/19, CYP2D6, CYP3A4/5, UGT1A1/3, and UGT2B7 were found. CYP3A4 showed comparable abundance in the liver and jejunum, whereas other enzymes were markedly higher in the hepatic tissue. Nearly all detected enzymes showed their highest abundance in the jejunum. Significant correlations between mRNA and protein levels in liver or intestine were found for most enzymes. CYP3A4 and CYP3A5 protein abundance, but not other enzymes, were significantly correlated in the liver and the small intestine. Our data may contribute to an improved understanding of hepatic and intestinal drug metabolism.