Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Direct and indirect mechanisms for aryl hydrocarbon receptor activation mediated by 6-formylindolo[3,2-b]carbazole
Stockholm University, Faculty of Science, Department of Genetics, Microbiology and Toxicology. (Ulf Rannug)
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The aryl hydrocarbon receptor (AhR) is mostly recognized for mediating the adverse effects of dioxins. In addition, endogenous activation of the AhR seems to have important biological functions.

 Several studies have demonstrated an activation of the receptor when no exogenous ligand was added. Furthermore, different physical stimuli such as UV irradiation, fluid shear stress, and hyperoxia have been shown to induce AhR-dependent transcriptional activity. Together these reports indicate either the presence of endogenous ligands or a non-ligand dependent activation. While the mechanisms behind such responses are still elusive, formation of tryptophan photoproducts with high AhR-affinity has been suggested to explain the activation observed after UVB irradiation. The photoproduct 6-formylindolo[3,2-b]carbazole (FICZ) has been proposed to be an endogenous signal substance, and is the focus of the present thesis.

 The objective of the work presented in this thesis was to further characterize the formation and metabolism of FICZ, to identify the biotransforming enzymes required for its metabolism, and subsequently to isolate FICZ-derived metabolites in human urine.

 The studies reveal that FICZ is an excellent substrate for CYP1 enzymes resulting in an efficient metabolism and rapid clearance of FICZ, and a reduced or abolished affinity for the AhR. The hydroxylated metabolites are in turn very good substrates for sulfo-conjugation, and monosulfated derivatives of FICZ were identified in human urine, proving the existence of FICZ in vivo. Furthermore, disturbing the CYP1-dependent metabolic clearance of FICZ efficiently attenuated the rapid depletion of intracellular levels of FICZ, and resulted in a delayed and prolonged AhR-activation. These results suggest that inhibition of degradation of FICZ provides a potent mechanism for indirect regulation of the AhR response.

 The high affinity and AhR activating capacity, together with its rapid clearance by AhR regulated biotransforming enzymes and presence in humans in vivo, all strengthen the hypothesis that FICZ is an endogenous ligand for the AhR and an important biological signaling molecule.

 

Place, publisher, year, edition, pages
Stockholm: Department of Genetics, Microbiology and Toxicology, Stockholm University , 2009. , 49 p.
National Category
Pharmacology and Toxicology
Research subject
Genetic Toxicology
Identifiers
URN: urn:nbn:se:su:diva-29266ISBN: 978-91-7155-926-5 (print)OAI: oai:DiVA.org:su-29266DiVA: diva2:232056
Public defence
2009-09-18, G-salen, Svante Arrhenius väg 20 C, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: In progress.Available from: 2009-08-27 Created: 2009-08-19 Last updated: 2009-08-20Bibliographically approved
List of papers
1. Metabolic fate of the Ah receptor ligand 6-formylindolo[3,2-b]carbazole
Open this publication in new window or tab >>Metabolic fate of the Ah receptor ligand 6-formylindolo[3,2-b]carbazole
Show others...
2004 (English)In: Chemico-Biological Interactions, ISSN 0009-2797, Vol. 149, no 2-3, 151-164 p.Article in journal (Refereed) Published
Abstract [en]

The physiological role of the aryl hydrocarbon receptor (AhR), a member of the basic helix-loop-helix PER-ARNT-SIM (PAS) transcription factor family is not known. We have suggested that the AhR is involved in light signaling through binding of photoproducts with high AhR affinity. This suggestion is based on (i) the high AhR affinity of the tryptophan photoproduct formylindolo[3,2-b]carbazole (FICZ), (ii) the induction of rapid and transient expression of AhR-regulated genes by FICZ and by extracts of UV-irradiated tryptophan as well as (iii) the fact that light induces the AhR-regulated cytochrome P450s CYP1A1, CYP1B1 and CYP2S1. The transient mRNA expression caused by light and tryptophan photoproducts suggests that the biotransformation enzymes induced by AhR activation take part in a metabolic degradation of the natural AhR ligand. This study aimed at identifying the involvement of phase I and phase II enzymes in the metabolic degradation of FICZ. A cytochrome P450-dependent metabolism of FICZ giving rise to preferentially mono- and di-hydroxylated derivatives has earlier been reported. In the present study, rat and human hepatic S9 mixes were employed together with specific enzyme inhibitors and cofactors. Compared to the Aroclor-induced rat liver S9, the non-induced rat liver S9 and the human liver S9 caused a more complex metabolite profile of FICZ. The CYP1A1 enzyme was confirmed to be the most important enzyme for the first step in the metabolism. CYP1A2 was found to have overlapping specificity with CYP1A1 being able to form the same major metabolites although with different kinetics. CYP1B1 turned out to be preferentially involved in the further metabolism of dihydroxylated metabolites. Microsomal epoxide hydrolase, and as yet not identified forms of sulphotransferases and glucuronosyltransferases were also found to take part in the metabolic degradation of FICZ. Thus, tryptophan photoproducts fit into a model in which the ligand-activated AhR signaling is autoregulated by the induced metabolic enzymes.

Keyword
Animals, Aroclor 1254/metabolism, Carbazoles/*metabolism/toxicity, Chromatography; High Pressure Liquid, Cytochrome P-450 Enzyme System/antagonists & inhibitors/*metabolism, Enzyme Inhibitors/pharmacology, Humans, Indoles/*metabolism/toxicity, Male, Microsomes; Liver/enzymology/*metabolism, Rats, Rats; Sprague-Dawley, Receptors; Aryl Hydrocarbon/*metabolism, Tryptophan/metabolism
Identifiers
urn:nbn:se:su:diva-16046 (URN)10.1016/j.cbi.2004.08.005 (DOI)15501436 (PubMedID)
Available from: 2008-12-12 Created: 2008-12-12 Last updated: 2010-01-11Bibliographically approved
2. The suggested physiologic aryl hydrocarbon receptor activator and cytochrome P4501 substrate 6-formylindolo[3,2-b]carbazole is present in humans
Open this publication in new window or tab >>The suggested physiologic aryl hydrocarbon receptor activator and cytochrome P4501 substrate 6-formylindolo[3,2-b]carbazole is present in humans
Show others...
2009 (English)In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 284, no 5, 2690-2696 p.Article in journal (Refereed) Published
Abstract [en]

Dioxins and other polycyclic aromatic compounds formed during the combustion of waste and fossil fuels represent a risk to human health, as well as to the well being of our environment. Compounds of this nature exert carcinogenic and endocrine-disrupting effects in experimental animals by binding to the orphan aryl hydrocarbon receptor (AhR). Understanding the mechanism of action of these pollutants, as well as the physiological role(s) of the AhR, requires identification of the endogenous ligand(s) of this receptor. We reported earlier that activation of AhR by ultraviolet radiation is mediated by the chromophoric amino acid tryptophan (Trp), and we suggested that a new class of compounds derived from Trp, in particular 6-formylindolo[3,2-b]carbazole (FICZ), acts as natural high affinity ligands for this receptor. Here we describe seven new FICZ-derived indolo[3,2-b]carbazole-6-carboxylic acid metabolites and two sulfoconjugates, and we demonstrate the following. (i) FICZ is formed efficiently by photolysis of Trp upon exposure to visible light. (ii) FICZ is an exceptionally good substrate for cytochromes P450 (CYP) 1A1, 1A2, and 1B1, and its hydroxylated metabolites are remarkably good substrates for the sulfotransferases (SULTs) 1A1, 1A2, 1B1, and 1E1. Finally, (iii) sulfoconjugates of phenolic metabolites of FICZ are present in human urine. Our findings indicate that formylindolo[3,2-b]carbazols are the most potent naturally occurring activators of the AhR signaling pathway and may be the key substrates of the CYP1 and SULT1 families of enzymes. These conclusions contradict the widespread view that xenobiotic compounds are the major AhR ligands and CYP1 substrates.

Identifiers
urn:nbn:se:su:diva-17533 (URN)10.1074/jbc.M808321200 (DOI)
Available from: 2009-01-16 Created: 2009-01-16 Last updated: 2010-04-22Bibliographically approved
3. Indirect activation of aryl hydrocarbon receptor signaling caused by inhibitors of the metabolic degradation of the natural ligand 6-formylindolo[3,2-b]carbazole
Open this publication in new window or tab >>Indirect activation of aryl hydrocarbon receptor signaling caused by inhibitors of the metabolic degradation of the natural ligand 6-formylindolo[3,2-b]carbazole
(English)Manuscript (preprint) (Other academic)
Identifiers
urn:nbn:se:su:diva-29265 (URN)
Available from: 2009-08-19 Created: 2009-08-19 Last updated: 2010-01-11Bibliographically approved
4. Synthesis and biological evaluation of fused thio- and selenopyrans as new indolocarbazole analogues with aryl hydrocarbon receptor affinity
Open this publication in new window or tab >>Synthesis and biological evaluation of fused thio- and selenopyrans as new indolocarbazole analogues with aryl hydrocarbon receptor affinity
2009 (English)In: Bioorganic & Medicinal Chemistry, ISSN 0968-0896, Vol. 17, no 4, 1648-1653 p.Article in journal (Refereed) Published
Abstract [en]

A series of thio- and selenopyrans having two fused indole units, structurally related to indolocarbazoles, have been prepared and evaluated for aryl hydrocarbon receptor (AhR) affinity, leading to the identification of several new significant AhR ligands. In particular, the parent thiopyrano[2,3-b:6,5-b′]diindole and its derivative having a methyl group in the central ring, as well as the two corresponding selenopyrans, displayed the highest potencies of the compounds tested.

Place, publisher, year, edition, pages
Elsevier, 2009
Identifiers
urn:nbn:se:su:diva-29264 (URN)10.1016/j.bmc.2008.12.072 (DOI)000263502300028 ()
Available from: 2009-08-19 Created: 2009-08-19 Last updated: 2010-01-11Bibliographically approved

Open Access in DiVA

No full text

Search in DiVA

By author/editor
Wincent, Emma
By organisation
Department of Genetics, Microbiology and Toxicology
Pharmacology and Toxicology

Search outside of DiVA

GoogleGoogle Scholar

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 380 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf