Comparison of the Biotransformation of the 14 C‐Labelled Insecticide Carbaryl by Non‐Transformed and Human CYP1A1‐, CYP1A2‐, and CYP3A4‐Transgenic Cell Cultures of Nicotiana tabacum

Transgenic tobacco‐cell‐suspension cultures expressing separately the human cytochrome P450 monooxygenases CYP1A1, CYP1A2, and CYP3A4 were utilized to study the biotransformation of the 14 C‐labelled insecticide carbaryl (=naphthalen‐1‐yl methylcarbamate). The resulting data were compared to similar data from the corresponding non‐transformed (NT) tobacco‐cell culture and commercially available membrane preparations ( Bactosomes ® ) of genetically modified bacteria separately containing the same human P450s. A rapid conversion rate of carbaryl was observed with the CYP1A1 and CYP1A2 cells, where only 49.7 and 0.2% of applied carbaryl (1 mg/l), respectively, remained after 24 h, as compared to 77.7% in the non‐transformed culture. Unexpectedly, the corresponding results obtained from the CYP3A4 cultures were not definite. With 25 mg/l of carbaryl and 96 h of incubation, it was proven that the insecticide is also substrate of CYP3A4. This finding was supported by GC/EI‐MS analysis of the primary metabolite pattern produced by the isozyme. This consisted of naphthalene‐1‐ol, N ‐(hydroxymethyl)carbaryl, 4‐hydroxycarbaryl, and 5‐hydroxycarbaryl, whereas the main product in non‐transformed cells was N ‐(hydroxymethyl)carbaryl. Data obtained from the CYP1A1, CYP1A2, or CYP3A4 Bactosomes ® agreed with those of the P450‐transgenic tobacco cells. Problems with GC/EI‐MS analysis of carbaryl and its metabolites are discussed.