| Abstract: |
Activation of the aryl hydrocarbon receptor (AHR) by 2,3,7,8- tetrachlorodibenzo-p-dioxin (TCDD) is required for AHR dependent transcriptional activation and TCDD toxicity. We previously reported that aqueous tryptophan exposed to sunlight through window glass (aTRP) contains multiple photoproducts, including the well characterized 6-formylindolo[3,2-b]carbazole (FICZ), capable of activating the AHR and inducing CYP1A and CYP1A-mediated enzyme activities. We report here the isolation from aTRP and chemical characterization and synthesis of 1-(1H-indol-3-yl)-9H-pyrido[3,4-b]indole (IPI), a compound previously identified as a natural product of marine ascidia and now shown to be a TRP photoproduct with AHR-inducing properties. IPI, FICZ and TCDD produced equieffective induction of CYP1A-mediated 7-ethoxyresorufin deethylase (EROD) activity in chick embryo primary hepatocytes and mammalian Hepa1c1c7 cells. EROD induction by IPI was markedly curtailed in AHR-defective c35 cells, supporting the AHR dependence of the IPI response. Although IPI had a higher EC 50 for EROD induction than FICZ, the much larger amount of IPI than FICZ in aTRP makes IPI a prominent contributor to EROD induction in aTRP. IPI was detected in TRP-containing culture medium under ambient laboratory conditions but not in TRP-free medium, consistent with its production from TRP. Cotreatment of hepatocytes with submaximal EROD-inducing doses of IPI and FICZ or TCDD produced additive increases in EROD without synergistic or inhibitory interactions. IPI and FICZ were readily metabolized by cultured hepatocytes. In addition to increasing CYP1A4 mRNA and EROD, IPI and FICZ decreased hepatocyte phosphoenolpyruvate carboxykinase mRNA expression and glucose output, biological effects associated with TCDD metabolic dysregulation. The findings underscore a role for sunlight in generating AHR-activating bioactive molecules. © 2011 Elsevier Ireland Ltd. All rights reserved. |
| Keywords: |
controlled study; unclassified drug; nonhuman; chemical analysis; mass spectrometry; animal cell; mammalia; animal tissue; gene; enzyme inhibition; embryo; enzyme activity; gene expression regulation; biological activity; messenger rna; laboratory test; chemical structure; indole derivative; cell metabolism; glucose transport; sunlight; enzyme synthesis; aromatic hydrocarbon receptor; tryptophan; photoactivation; chick embryo; chemical interaction; 1-(1h-indol-3-yl)-9h-pyrido[3,4-b]indole (ipi); 6-formylindolo[3,2- b]carbazole (ficz); aryl hydrocarbon receptor; cytochrome p4501a; tryptophan photoproduct; 1 (1h indol 3 yl) 9h pyrido[3,4 b]indole; 2,3,7,8 tetrachlorodibenzo para dioxin; 6 formylindolo[3,2 b]carbazole; chemical compound; cytochrome p450 1a; ethoxyresorufin deethylase; ascidiacea; cytochrome p450 1a gene; gluconeogenesis; liver cell culture; phosphoenolpyruvate carboxykinase gene; ascidia
|
