| 1. |
- Mohammadi-Bardbori, Afshin, et al.
(författare)
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Quercetin, Resveratrol, and Curcumin Are Indirect Activators of the Aryl Hydrocarbon Receptor (AHR)
- 2012
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Ingår i: Chemical Research in Toxicology. - : American Chemical Society (ACS). - 0893-228X .- 1520-5010. ; 25:9, s. 1878-1884
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Tidskriftsartikel (refereegranskat)abstract
- Several polyphenols have been shown to activate the aryl hydrocarbon receptor (AHR) in spite of the fact that they bind to the receptor with low affinity. The aim of this study was to investigate whether quercetin (QUE), resveratrol (RES), and curcumin (CUR) interfere with the metabolic degradation of the suggested endogenous AHR ligand 6-formylindolo[3,2-b]carbazole (FICZ) and thereby indirectly activate the AHR. Using recombinant human enzyme, we confirmed earlier reported inhibitory effects of the polyphenols on cytochrome P4501A1 (CYP1A1) activity, and inhibition of metabolic clearance of FICZ was documented in FICZ-treated immortalized human keratinocytes (HaCaT). CYP1A1 activity was induced in HaCaT cells by all three compounds, and when they were added together with FICZ, a prolonged activation was observed after a dose-dependent inhibition period. The same pattern of responses was seen at the transcriptional level as determined with a CYP1A1 reporter assay in human liver hepatoma (HepG2) cells. To test the ability of the polyphenols to activate the AHR in the absence of FICZ, the cells were treated in medium, which in contrast to commercial batches of medium did not contain background levels of FICZ. Importantly, AHR activation was only observed in the commercial medium. Taken together, these findings suggest that QUE, RES, and CUR induce CYP1A1 in an indirect manner by inhibiting the metabolic turnover of FICZ. Humans are exposed to these compounds through the diet and nutritional supplements, and we propose that altered systemic levels of FICZ caused by such compounds may have physiological consequences.
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| 2. |
- Svensson, Johan, 1983-
(författare)
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Androgenic Effects of the Progestin Levonorgestrel in Three-spined Stickleback (Gasterosteus aculatus)
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The extensive use of pharmaceuticals and their poor removal by wastewater treatment plants has led to the emergence of pharmaceutical compounds as global aquatic contaminants. Progestins, the synthetic analogues to progesterone, are receiving increasing attention as contaminants and have been shown to impair reproduction in fish and amphibians at low ng L-1 concentrations. Certain progestins, like levonorgestrel (LNG), have androgenic properties and are several orders of magnitude more potent in terms of reproductive impairment in fish than non-androgenic progestins. We exposed three-spined stickleback (Gasterosteus aculeatus) to LNG to investigate its androgenic effects in fish. Male stickleback kidneys produce spiggin, a glue-like glycoprotein used in nest building. Spiggin production is directly and specifically governed by androgens and its induction in females serves as the best known biomarker for androgen exposure in fish. In the present project females were exposed to LNG for 21 days after which effects on spiggin biomarkers and vitellogenesis were evaluated. Male sticklebacks that were in the final stage of a breeding period were exposed to various concentrations of LNG for six weeks under winter conditions, after which reproductive status was evaluated from gross morphology, histology and key gene transcript levels. In female sticklebacks, LNG induced spiggin production in the kidneys and suppressed vitellogenesis in the liver. In males, LNG inhibited the post-breeding regression of secondary sex characters and spiggin production, as well as the resumption of spermatogenesis; thus LNG functionally inhibits the natural transition from breeding into non-breeding condition. Suppression of vitellogenesis in females and disruption of the male reproductive cycle as shown in this thesis could entail severe fitness costs and severely affect natural stickleback populations. Some of the present effects occurred at 6.5 ng L-1, well within the range of environmental LNG levels, and may therefore occur in progestin-contaminated waters. In conclusion, the present results establish LNG as a highly potent androgenic pollutant of environmental concern, and support the contention that the reproductive impairment in fish caused by progestins could to a significant degree be mediated by their androgenic properties.
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| 3. |
- Wincent, Emma, et al.
(författare)
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Inhibition of cytochrome P4501-dependent clearance of the endogenous agonist FICZ as a mechanism for activation of the aryl hydrocarbon receptor
- 2012
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 109:12, s. 4479-4484
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Tidskriftsartikel (refereegranskat)abstract
- Altered systemic levels of 6-formylindolo[3,2-b]carbazole (FICZ), an enigmatic endogenous ligand for the aryl hydrocarbon receptor (AHR), may explain adverse physiological responses evoked by small natural and anthropogenic molecules as well as by oxidative stress and light. We demonstrate here that several different chemical compounds can inhibit the metabolism of FICZ, thereby disrupting the autoregulatory feedback control of cytochrome P4501 systems and other proteins whose expression is regulated by AHR. FICZ is both the most tightly bound endogenous agonist for the AHR and an ideal substrate for cytochrome CYP1A1/1A2 and 1B1, thereby also participating in an autoregulatory loop that keeps its own steady-state concentration low. At very low concentrations FICZ influences circadian rhythms, responses to UV light, homeostasis associated with pro-and anti-inflammatory processes, and genomic stability. Here, we demonstrate that, if its metabolic clearance is compromised, femtomolar background levels of this compound in cell-culture medium are sufficient to up-regulate CYP1A1 mRNA and enzyme activity. The oxidants UVB irradiation and hydrogen peroxide and the model AHR antagonist 3'-methoxy-4'-nitroflavone all inhibited induction of CYP1A1 enzyme activity by FICZ or 2,3,7,8-tetrachlorodibenzo-p-dioxin, thereby subsequently elevating intracellular levels of FICZ and activating AHR. Taken together, these findings support an indirect mechanism of AHR activation, indicating that AHR activation by molecules with low affinity actually may reflect inhibition of FICZ metabolism and raising questions about the reported promiscuity of the AHR. Accordingly, we propose that prolonged induction of AHR activity through inhibition of CYP1 disturbs feedback regulation of FICZ levels, with potential detrimental consequences.
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