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Identification of the tryptophan photoproduct 6-formylindolo[3,2-b]carbazole, in cell culture medium, as a factor that controls the background aryl hydrocarbon receptor activity.
Stockholm University, Faculty of Science, Department of Genetics, Microbiology and Toxicology.
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2005 (English)In: Toxicol Sci, ISSN 1096-6080, Vol. 85, no 2, 935-43 p.Article in journal (Refereed) Published
Abstract [en]

The presence of high affinity ligands for the aryl hydrocarbon receptor (AhR) in cell culture medium has generally been overlooked. Such compounds may confound mechanistic studies of the important AhR regulatory network. Numerous reports have described that light exposed cell culture medium induces AhR-dependent activity. In this study, we aimed at identifying the causative substance(s). A three-dimensional factorial design was used to study how the background activity of CYP1A1 in a rat hepatoma cell line (MH1C1) was controlled by photoproducts formed in the medium exposed to normal laboratory light. The light induced activity was found to be tryptophan dependent, but independent of riboflavin and other components in the medium. The light exposed medium showed the same transient enzyme inducing activity in vitro as the AhR ligand 6-formylindolo[3,2-b]carbazole (FICZ). This substance, which we have previously identified as being formed in UV-exposed tryptophan solutions, is a substrate for CYP1A1 and it has a higher AhR binding affinity than TCDD. Several tryptophan related photoproducts were detected in the light-exposed medium. For the first time one of the formed photoproducts was identified as FICZ with bioassay driven fractionation coupled with HPLC/MS. These results clearly show that tryptophan derived AhR ligands, which have been suggested to be endogenous AhR ligands, influence the background levels of CYP1A1 activity in cells in culture.

Place, publisher, year, edition, pages
2005. Vol. 85, no 2, 935-43 p.
Keyword [en]
Animals, Carbazoles/chemistry/*pharmacology/radiation effects, Cell Line; Tumor, Culture Media, Cytochrome P-450 CYP1A1/biosynthesis/metabolism/radiation effects, Enzyme Induction/drug effects, Enzyme Inhibitors/chemistry/*pharmacology/radiation effects, Indoles/chemistry/*pharmacology/radiation effects, Light, Liver Neoplasms; Experimental/metabolism, Photochemistry, Photosensitizing Agents/pharmacology, Rats, Receptors; Aryl Hydrocarbon/drug effects/*metabolism/radiation effects, Riboflavin/pharmacology, Spectrometry; Mass; Electrospray Ionization, Teratogens, Tryptophan/*chemistry/metabolism
National Category
Biochemistry and Molecular Biology Analytical Chemistry
URN: urn:nbn:se:su:diva-16030PubMedID: 15788723OAI: diva2:182550
Available from: 2008-12-12 Created: 2008-12-12 Last updated: 2011-01-12Bibliographically approved

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