Abstract

The liver and small intestine restrict oral bioavailability of drugs and constitute the main sites of pharmacokinetic drug-drug interactions. Hence, detailed data on hepatic and intestinal activities of drug metabolizing enzymes is important for modelling drug disposition and optimizing pharmacotherapy in different patient populations. The aim of this study was to determine the activities of seven cytochrome P450 (CYP) enzymes in paired liver and small intestinal samples from patients with obesity. Biopsies were obtained from twenty patients who underwent Roux-en-Y gastric bypass surgery following a three-week low energy diet. Individual hepatic and intestinal microsomes were prepared and specific probe substrates in combined incubations were used for determination of CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6 and CYP3A activities. Activities of CYP2C8, CYP2C9, CYP2D6 and CYP3A were quantified in both human liver microsomes (HLM) and human intestinal microsomes (HIM), while activities of CYP1A2, CYP2B6 and CYP2C19 were only quantifiable in HLM. Considerable interindividual variability was present in both HLM (9 to 23-fold) and HIM (5 to 55-fold). The median metabolic HLM/HIM ratios varied from 1.5 for CYP3A to 252 for CYP2C8. Activities of CYP2C9 in paired HLM and HIM were positively correlated (r=0.74, p<0.001), while no interorgan correlations were found for activities of CYP2C8, CYP2D6 and CYP3A (p>0.05). Small intestinal CYP3A activities were higher in females compared with males (p<0.05). Hepatic CYP2B6 activity correlated negatively with body mass index (r=-0.72, p<0.001). These data may be useful for further in vitro-in vivo predictions of drug disposition in patients with obesity.