CATALYTIC ACTIVITIES, PROTEIN-EXPRESSION AND MESSENGER-RNA-EXPRESSIONOF CYTOCHROME-P450 ISOENZYMES IN INTESTINAL-CELL LINES

1. Certain chemicals and drugs in addition to metabolically activated carcinogens are substrates for intestinal cytochrome P450s (CYPs) and a number of cell lines are available which could be used in metabolism studies. These include the rat duodenal cell line IEC 6, rat ileal IE C 18, foetal human HuTu 80, foetal human small intestinal FHS 74, huma n duodenal HCT 8 and human colon CaCo-2 cells, but they lack thorough biochemical characterization. 2. The aim of the present study was ther efore to investigate the mRNA and protein expression of CYP1A1, CYP1A2 , CYP2C9/10, CYP2E1 and CYP3A. In addition, the metabolism of the immu nosuppressant drug tacrolimus and of the procarcinogen 7,12-dimethyl-b enz[a]anthracene (DMBA) was studied to obtain information on the funct ional activity on these cell lines. 3. Of all the cell lines tested on ly CaCo-2 cells expressed CYP1A1 at the protein and mRNA level, but th e CYP2E1 and CYP3A protein was also detected in CaCo-2 and FHS 74 cell s. It is of considerable interest that none of the other cell lines ex pressed CYP1A1, CYP1A2, CYP2C9/10 or CYP3A4 at the protein and mRNA le vel. 4. When the metabolism of DMBA (a model carcinogen) was studied, CaCo-2 cells produced the following metabolites: 7,12-dihydroxymethylb enz[a]anthracene, 7,12-dimethylbenz-[a]anthracene-di-hydrodiol, 7-meth yl-12-hydroxymethylbenz[a]anthracene, 7-hydroxy-methyl-12-benz[a]anthr acene and possibly the dihydrated product of the latter two derivative s. 5. CaCo-2 cells also catalysed the metabolism of the immunosuppress ant drug tacrolimus resulting in the formation of 13-O-demethyl-tacrol imus bisdemethyl-hydroxy-tacrolimus and demethyl-dihydroxy-tacrolimus. Neither the foetal human small intestinal FHS 74 cell line nor any of the other cell lines were able to catalyse the biotransformation of t acrolimus. 6. In conclusion, only CaCo-2 cells were able to produce me tabolites similar to those observed in in vivo metabolism studies, whe reas all other cell lines were metabolically incompetent. Therefore, t his cell line may be used in studies of intestinal biotransformation.