gms | German Medical Science

Background: The pharmacokinetics of most drugs on the market is markedly influenced by intestinal and hepatic biotransformation enzymes such as cytochrome P450 (CYP450) enzymes and UDP-glucuronosyltransferases (UGT). In order to predict their impact on drug disposition as well as drug-drug interactions, data on their absolute intestinal and hepatic abundance are required. In contrast to the liver, few respective protein data has been published for the intestine. Hence, the aim of the current study was the absolute quantification of clinically relevant metabolizing enzymes along the human intestine.

Methods: 8 jejunal, 8 ileum and 8 colon samples were obtained from patients undergoing intestinal surgery. The tissues had no macroscopic signs of inflammation or necrosis. After a tryptic digest of the isolated microsomal fraction, the previously developed and validated LC-MS/MS method [1] has been applied for the simultaneous detection of nine CYP (CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4 and CYP3A5) and four UGT enzymes (UGT1A1, UGT1A3, UGT2B7 and UGT2B15) which are considered to be of clinical relevance in human drug metabolism [2]. Protein quantification has been conducted by targeted proteomics using enzyme specific tryptic peptides and stable isotope-labelled peptides as internal standard. The MS/MS detection of all peptides was performed simultaneously with a scheduled multiple reaction monitoring method in the positive mode by monitoring in each case three mass transitions per enzyme specific peptides and the corresponding isotope-labelled internal standards. In addition, the respective gene expression was determined using quantitative real-time PCR.

Results: Generally, four CYP (CYP2C9, CYP2C19, CYP2D6, CYP3A4) as well as three UGT (UGT1A1, UGT1A3, UGT2B7) enzymes of the monitored 13 proteins could be found along the human intestine. Almost all of these enzymes showed the highest abundance in the jejunum, lesser amounts in the ileum and the lowest extent in the colon. Table 1 [Tab. 1] shows the detailed values for each section. The gene expression data was mostly in accordance with these findings.

Conclusion: Our study reports a comprehensive overview about the absolute protein abundance of clinical relevant enzymes along the human intestine. The enzyme distribution was markedly different between the investigated intestinal sections which may affect the intestinal drug absorption.