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

ABSTRACT

AIMS: To characterize mRNA expression levels (17 cytochromes P450) and activity (9 isoforms) of major cytochromes P450 expressed throughout the human small intestine. METHODS: Tissue samples were obtained from 9 deceased subjects and intestinal sections (n = 10) were isolated for each subject. Relative mRNA expression levels were determined using quantitative real-time PCR. Intestinal microsomes were prepared from 5 subsections duodenum, jejunum (proximal and mid-jejunum) and ileum (proximal and mid-ileum) regions. In vitro incubations were performed with various cytochrome P450 probe substrates bupropion (CYP2B6), repaglinide (CYP2C8), tolbutamide (CYP2C9), S-mephenytoin (CYP2C19), bufuralol (CYP2D6), chlorzoxazone (CYP2E1), ebastine (CYP2J2), midazolam (CYP3A4/5) and lauric acid (CYP4A11). Metabolite formation was assessed using validated liquid chromatography-tandem mass spectrometry assays. RESULTS: Cytochrome P450 mRNA levels ranked as follows CYP3A4 > CYP2C9 > CYP2C19 > CYP2J2 > CYP4F2. Cytochrome P450 mRNA transcripts showed different patterns in their relative expression from 1 region to the other but CYP3A4, CYP2C9, CYP2C19 and CYP2J2 displayed the highest levels of mRNA expression (>5%) in all intestinal sections. Cytochrome P450 activities were greater in proximal part of the small intestine with the jejunum showing the greatest drug-metabolism activity. Spearman's correlation analyses indicated that cytochrome P450 mRNA expressions and corresponding cytochrome P450 activities in the human intestine were moderately associated for CYP2C19, CYP2D6 and CYP4A11 (rs  = 0.44-0.56). CONCLUSIONS: Our study provides new and additional information on the expression and activities of selected cytochromes P450 in various sections of the human small intestine.