| 1. |
- Bergander, Linda, 1972-
(författare)
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Formation and metabolism of the tryptophan-derived 6-formylindolo[3,2-b]carbazole - a light-induced Ah-receptor ligand
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aryl hydrocarbon receptor (AhR) is a ligand dependent transcription factor ubiquitously expressed in mammalian cells. It is a genetically ancient protein mostly known for binding the extremely toxic contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Binding to the AhR explains the variety of toxic responses of TCDD as well as the induction of several drug metabolizing enzymes. Induction of cytochrome P4501A1 (CYP1A1) is the most well characterized of the AhR regulated responses. The physiological functions of AhR and the endogenous ligand(s) for the receptor are under investigation but are not yet unraveled. Several tryptophan (TRP) derived indol-containing compounds have been reported to possess AhR affinity/CYP1A1 inducing capacity and TRP mediates CYP1A1 induction by UV light. The TRP photoproduct, 6-formylindolo[3,2-b]carbazole (FICZ) has the highest AhR affinity described so far and it causes a rapid and transient induction of the CYP1A1 gene in human cells. A number of reports on constitutive CYP1A1 activity in cultured cells is therefore most likely explained by the presence of TRP-derived AhR ligands in cell culture media. The aims of the studies were to investigate the impact of FICZ and FICZ metabolism on CYP1A1 gene regulation, to explore the metabolic fate of FICZ and to identify whether normal laboratory light could lead to formation of FICZ and thereby contribute to earlier observed CYP1A1 inducing effects by cell culture media. Metabolic studies using fractions of Aroclor-induced and non-induced rat liver and human liver as well as heterologously expressed enzymes revealed that FICZ can be efficiently metabolized by the CYP enzymes 1A1 and 1A2 and by an unknown cytosolic enzyme, to a number of hydroxylated and other oxidized metabolites. All of the hitherto identified 11 hydroxylated metabolites of FICZ are prone to conjugation reactions by glucuronosyltranferases and sulfotransferases. The metabolites formed by human enzymes are primarily sulfated. Thus, the sulfated metabolites of FICZ will be crucial in the future analyzes of FICZ formation in vivo. FICZ was identified to be formed, not only by UV illumination, but also by normal laboratory light. The constitutive CYP1A1 activity was significantly induced through the formation of several TRP related photoproducts in light-exposed medium. One of these photoproducts was identified as FICZ. Thus, the TRP photoproduct, FICZ, fits into a model in which FICZ auto-regulates the expression of induced enzymes. It is hypothesized that FICZ might function as a chemical messenger that activates AhR in response to light and might be one of several possible endogenous AhR ligands.
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| 2. |
- Bergander, Linda, et al.
(författare)
-
Metabolic fate of the Ah receptor ligand 6-formylindolo[3,2-b]carbazole
- 2004
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Ingår i: Chemico-Biological Interactions. - : Elsevier BV. - 0009-2797. ; 149:2-3, s. 151-164
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Janosik, Tomasz, et al.
(författare)
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Chemistry and Properties of Indolocarbazoles
- 2018
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Ingår i: Chemical Reviews. - : American Chemical Society (ACS). - 0009-2665 .- 1520-6890. ; 118:18, s. 9058-9128
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Tidskriftsartikel (refereegranskat)abstract
- The indolocarbazoles are an important class of nitrogen heterocycles which has evolved significantly in recent years, with numerous studies focusing on their diverse biological effects, or targeting new materials with potential applications in organic electronics. This review aims at providing a broad survey of the chemistry and properties of indolocarbazoles from an interdisciplinary point of view, with particular emphasis on practical synthetic aspects, as well as certain topics which have not been previously accounted for in detail, such as the occurrence, formation, biological activities, and metabolism of indolo[3,2-b]carbazoles. The literature of the past decade forms the basis of the text, which is further supplemented with older key references.
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| 4. |
- Mohammadi-Bardbori, Afshin, et al.
(författare)
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NADPH Oxidase-Dependent Mechanism Explains How Arsenic and Other Oxidants Can Activate Aryl Hydrocarbon Receptor Signaling
- 2015
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Ingår i: Chemical Research in Toxicology. - : American Chemical Society (ACS). - 0893-228X .- 1520-5010. ; 28:12, s. 2278-2286
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Tidskriftsartikel (refereegranskat)abstract
- The mechanisms explaining arsenic toxicity are not well understood, but physiological consequences of stimulated aryl hydrocarbon receptor (AHR) signaling both directly and through cross-talk with other pathways have been indicated. The aim of this study was to establish how arsenic interacts with AHR-mediated transcription. The human hepatoma cell line (HepG2-XRE-Luc) carrying a luciferase reporter under the control of two AHR response elements (AHREs) and immortalized human keratinocytes (HaCaT) were exposed to sodium arsenite (NaAsO2; As3+), alone or in combination with the endogenous high affinity AHR ligand 6-formylindolo[3,2-b]carbazole (FICZ). Luciferase activity, cytochrome P4501A1 (CYP1A1) activity, oxidative stress-related responses, metabolic clearance of FICZ, and NADPH:oxidase (NOX) activity as well as nuclear factor (erythroid-derived 2)-like 2 (Nrf2)-dependent gene expression were measured. Arsenic inhibited,CYP1A1 enzyme activity and reduced the metabolic clearance of FICZ. Arsenic also led to activated CYP1A1 transcription but only in cells grown in medium containing trace amounts of the endogenous ligand FICZ, pointing to an indirect mechanism of activation. Initially, arsenic caused dose-dependent inhibition of FICZ-activated AHR signaling, disturbed intracellular GSH status, and increased expression of oxidative stress-related genes. Silencing of NOX4, addition of N-acetylcystein, or pretreatment with arsenic itself attenuated the initial dose-dependent inhibition of AHR signaling. Arsenic pretreatment led to elevated GSH levels and sensitized the cells to ligaild-dependent AHR signaling, while silencing of Nrf2 significantly reduced arsenic-mediated, activation of the AHR. In addition, influence of NOX on AHR activation was also observed in cells treated with the SH-reactive metals cadmium, mercury, and nickel. Together, the results suggest that SH-reactive agents via a new and possibly general NOX/H2O2-dependent mechanism can interfere with the endogenous regulation of the AHR.
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| 5. |
- Mohammadi-Bardbori, Afshin, et al.
(författare)
-
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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| 6. |
- Oberg, Mattias, et al.
(författare)
-
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.
- 2005
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Ingår i: Toxicol Sci. - : Oxford University Press (OUP). - 1096-6080 .- 1096-0929. ; 85:2, s. 935-43
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Rannug, Agneta, et al.
(författare)
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The tryptophan derivative 6-formylindolo[3,2-b]carbazole, FICZ, a dynamic mediator of endogenous aryl hydrocarbon receptor signaling, balances cell growth and differentiation
- 2018
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Ingår i: Critical reviews in toxicology. - : Informa UK Limited. - 1040-8444 .- 1547-6898. ; 48:7, s. 555-574
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Forskningsöversikt (refereegranskat)abstract
- The aryl hydrocarbon receptor (AHR) is not essential to survival, but does act as a key regulator of many normal physiological events. The role of this receptor in toxicological processes has been studied extensively, primarily employing the high-affinity ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). However, regulation of physiological responses by endogenous AHR ligands remains to be elucidated. Here, we review developments in this field, with a focus on 6-formylindolo[3,2-b]carbazole (FICZ), the endogenous ligand with the highest affinity to the receptor reported to date. The binding of FICZ to different isoforms of the AHR seems to be evolutionarily well conserved and there is a feedback loop that controls AHR activity through metabolic degradation of FICZ via the highly inducible cytochrome P450 1A1. Several investigations provide strong evidence that FICZ plays a critical role in normal physiological processes and can ameliorate immune diseases with remarkable efficiency. Low levels of FICZ are pro-inflammatory, providing resistance to pathogenic bacteria, stimulating the anti-tumor functions, and promoting the differentiation of cancer cells by repressing genes in cancer stem cells. In contrast, at high concentrations FICZ behaves in a manner similar to TCDD, exhibiting toxicity toward fish and bird embryos, immune suppression, and activation of cancer progression. The findings are indicative of a dual role for endogenously activated AHR in barrier tissues, aiding clearance of infections and suppressing immunity to terminate a vicious cycle that might otherwise lead to disease. There is not much support for the AHR ligand-specific immune responses proposed, the differences between FICZ and TCDD in this context appear to be explained by the rapid metabolism of FICZ.
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| 8. |
- Sadiktsis, Ioannis, 1982-, et al.
(författare)
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Removal of polycyclic aromatic hydrocarbons and genotoxic compounds in urban air using air filter materials for mechanical ventilation in buildings
- 2016
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Ingår i: Science and Technology for the Built Environment. - : Informa UK Limited. - 2374-474X .- 2374-4731. ; 22:3, s. 346-355
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Tidskriftsartikel (refereegranskat)abstract
- Humans spend most of their lives in indoor environments; hence, indoor exposure to air pollution may constitute a large part of the total exposure to air pollution. Polycyclic aromatic hydrocarbons are well known for their mutagenicity and carcinogenicity and are ubiquitous in urban environments as a result of combustion from e.g. vehicular traffic. Polycyclic aromatic hydrocarbons associated to air particulate matter in indoor environments originates from several sources including: cooking and heating, outdoor sources, smoking, candle and incense burning. Infiltration has been suspected to be one major source of indoor polycyclic aromatic hydrocarbons. In this study, four different air filter materials intended for mechanical ventilation were tested for their capability to remove particle bound polycyclic aromatic hydrocarbons and other genotoxic compounds from a real urban aerosol. Particles were sampled at two highly trafficked locations in Stockholm using a sampling system capable of sample particles in parallel, thus allowing sampling of filtered and un-filtered air simultaneously. The sampled particles were extracted and analysed for polycyclic aromatic hydrocarbons and the genotoxicity of the organic extract was determined using Ames mutagenicity tests. Each air filters capability of removing polycyclic aromatic hydrocarbons and reducing genotoxic effects was determined by comparing the filtered and un-filtered air samples. The results showed that all air filter materials had the capability of removing polycyclic aromatic hydrocarbons and reduce genotoxic effects downstream the air filter, and that the magnitude of the reduction was correlated with the standardized particulate collection efficiencies of a 0.4 μm particles for the tested air filter materials. However, the filter with the lowest performance did not significantly reduce direct acting mutagens.
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| 9. |
- Smirnova, Anna, et al.
(författare)
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Evidence for New Light-Independent Pathways for Generation of the Endogenous Aryl Hydrocarbon Receptor Agonist FICZ
- 2016
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Ingår i: Chemical Research in Toxicology. - : American Chemical Society (ACS). - 0893-228X .- 1520-5010. ; 29:1, s. 75-86
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Tidskriftsartikel (refereegranskat)abstract
- Activation of the aryl hydrocarbon receptor (AhR), a conserved transcription factor best known as a target for highly toxic halogenated substances such as dioxin, under normal xenobiotic-free conditions is of considerable scientific interest. We have demonstrated previously that a photoproduct of tryptophan, 6-formylindolo[3,2-b]carbazole (FICZ), fulfills the criteria for an endogenous ligand for this receptor and proposed that this compound is the enigmatic mediator of the physiological functions of AhR. Here, we describe novel light-independent pathways by which FICZ can be formed. The oxidant H2O2 was shown to convert tryptophan to FICZ on its own in the absence of light. The enzymatic deamination of tryptamine yielded indole-3-acetaldehyde (I3A), which then rearranged to FICZ and its oxidation product, indolo[3,2-b]carbazole-6-carboxylic acid (CICZ). Indole-3-pyruvate (I3P) also produced I3A, FICZ, and CICZ. Malassezia yeast species, which constitute a part of the normal skin microbiota, produce a number of AhR activators from tryptophan. We identified both FICZ and CICZ among those products. Formation of FICZ from tryptophan or I3P produces a complex mixture of indole derivatives, some of which are CYP1A1 inhibitors. These can hinder the cellular clearance of FICZ and thereby increase its power as an AhR agonist. We present a general molecular mechanism involving dehydrogenations and oxidative coupling for the formation of FICZ in which I3A is the important precursor. In conclusion, our results suggest that FICZ is likely to be formed systemically.
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| 10. |
- Wincent, Emma, 1978-
(författare)
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Direct and indirect mechanisms for aryl hydrocarbon receptor activation mediated by 6-formylindolo[3,2-b]carbazole
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 11. |
- 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
-
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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| 12. |
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| 13. |
- Wincent, Emma, et al.
(författare)
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The suggested physiologic aryl hydrocarbon receptor activator and cytochrome P4501 substrate 6-formylindolo[3,2-b]carbazole is present in humans
- 2009
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 284:5, s. 2690-2696
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 14. |
- Bengtsson, Johanna, 1985-
(författare)
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The impact of cytochrome P4501-inhibitors on aryl hydrocarbon receptor signaling
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aryl hydrocarbon receptor (AHR) best known as a ligand-activated transcription factor that mediates toxic responses to xenobiotics such as dioxins, is also activated by certain endogenous compounds. Activation of the AHR up-regulates transcription of a large number of genes, including those encoding members of the cytochrome P450 1 family of enzymes (CYP1s). Although the AHR has been shown to be involved in several normal processes, its physiological role remains elusive. The endogenous ligand 6-formylindolo[3,2-b]carbazole (FICZ), formed from tryptophan, is present in cell culture media and biological specimens. FICZ is an excellent substrate for CYP1 enzymes and together FICZ/AHR/CYP1A1 interactions constitute an auto regulatory feedback loop that controls AHR signaling. A vast number of compounds that inhibit CYP1 enzymes have been reported to be AHR activators, even though they have little or no affinity for the receptor. We hypothesized, that their agonistic effects are dependent on the presence of background levels of FICZ. To test this, AHR signaling in different cell systems exposed to FICZ and/or inhibitors was assessed by measuring EROD activity and CYP1A1 transcription. In addition to a commercial culture medium, a medium free of background levels of FICZ was used. Activation of AHR by of a diverse set of CYP1A1 inhibitors did require FICZ in the culture medium. Furthermore, the compounds tested both prolonged and potentiated FICZ-induced receptor signaling. On the basis of these observations we propose that a compound may activate AHR signaling indirectly by inhibiting CYP1A1 and thereby attenuating the metabolism of FICZ. This mechanism was confirmed for certain polyphenols and pharmaceuticals. Surprisingly, the activating capacity and potentiating effect of two pharmaceuticals on AHR signaling could not be explained by the mechanism proposed, and we speculated that in these cases the agonistic effect might involve interactions of the cellular antioxidant response with the basic transcription machinery. Together, our observations provide a mechanistic explanation as to how compounds that inhibit CYP1A1 can activate AHR signaling. They also indicate that the general perception of the binding pocket of AHR as promiscuous, is probably wrong. The fact that indirect activation of AHR may cause sustained signaling requires further studies in vivo not least, in order to prevent toxicity.
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| 15. |
- Berg, Ingrid, et al.
(författare)
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Two modes of germline instability at human minisatellite MS1 (locus D1S7) : complex rearrangements and paradoxical hyperdeletion.
- 2003
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Ingår i: Am J Hum Genet. - 0002-9297. ; 72:6, s. 1436-47
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Tidskriftsartikel (refereegranskat)abstract
- Minisatellite MS1 (locus D1S7) is one of the most unstable minisatellites identified in humans. It is unusual in having a short repeat unit of 9 bp and in showing somatic instability in colorectal carcinomas, suggesting that mitotic replication or repair errors may contribute to repeat-DNA mutation. We have therefore used single-molecule polymerase chain reaction to characterize mutation events in sperm and somatic DNA. As with other minisatellites, high levels of instability are seen only in the germline and generate two distinct classes of structural change. The first involves large and frequently complex rearrangements that most likely arise by recombinational processes, as is seen at other minisatellites. The second pathway generates primarily, if not exclusively, single-repeat changes restricted to sequence-homogeneous regions of alleles. Their frequency is dependent on the length of uninterrupted repeats, with evidence of a hyperinstability threshold similar in length to that observed at triplet-repeat loci showing expansions driven by dynamic mutation. In contrast to triplet loci, however, the single-repeat changes at MS1 exclusively involve repeat deletion, and can be so frequent--as many as 0.7-1.3 mutation events per sperm cell for the longest homogeneous arrays--that alleles harboring these long arrays must be extremely ephemeral in human populations. The apparently impossible existence of alleles with deletion-prone uninterrupted repeats therefore presents a paradox with no obvious explanation.
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| 16. |
- Bergknut, Magnus, et al.
(författare)
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Identification of potentially toxic compounds in complex extracts of environmental samples using gas chromatography-mass spectrometry and multivariate data analysis
- 2007
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Ingår i: Environmental Toxicology and Chemistry. - New York : Pergamon. - 0730-7268 .- 1552-8618. ; 26:2, s. 208-217
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we examined 31 samples of varying chemical composition, including samples of soils from gasworks, coke production sites, and sites where wood preservatives were heavily used; ash and soot from municipal solid waste incinerators; antiskid sand; and dust from areas with heavy road traffic. The samples were comprehensively chemically characterized, especially their polycyclic aromatic compound contents, using gas chromatography-time-of-flight mass spectrometry, whereas their biological effects were assessed using dehydrogenase activity, root growth (Hordeum vulgare), reproduction of springtails (Folsomia candida), algal growth (Desmodesmus subspicatus), germinability (Sinapis alba), Vibrio fischeri, DR-CALUX, and Ames Salmonella assays. The number of compounds detected in the samples ranged from 123 to 527. Using the multivariate regression technique of partial-least-squares projections to latent structures, it was possible to find individual compounds that exhibited strong correlations with the different biological responses. Some of the results, however, indicate that a broader chemical characterization may be needed to identify all the compounds that may cause the measured biological responses.
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| 17. |
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| 18. |
- Hansson, Tomas, 1970-
(författare)
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Biomarkers in perch (Perca fluviatilis) used in environmental monitoring of the Stockholm recipient and background areas in the Baltic Sea
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis reports the results of biomarker measurements in three environmental monitoring projects. In the first project, which was part of the Swedish national environmental monitoring, biomarkers were measured annually in female perch (Perca fluviatilis) in two background areas in the Baltic Sea during 1988–2000, resulting in a unique 13-year series of measurements. The most important results were a strong decreasing temporal trend in the gonadosomatic index (GSI) and a strong increasing temporal trend in the hepatic ethoxyresorufin O-deethylase (EROD) activity in the Baltic Proper. In the second project, biomarkers and concentrations of classic pollutants were measured in female perch in the Stockholm recipient 1999–2001. This was the first time a large city was investigated as a point source of pollution, and the gradient was longer and included more stations than customary. Severe pollution conditions in central Stockholm were indicated by the poor health status of the perch: retarded growth, decreased frequency of sexually mature females, low GSI, disturbed visceral fat metabolism, increased hepatic EROD activity, decreased muscle acetylcholinesterase activity, increased frequency of hepatic DNA adducts, and a high concentration of biliary 1-pyrenol. Muscle ΣDDT and ΣPCB were measured as pollution indicators and were 10–28 respectively 12–35 times higher than the background levels in perch from the Baltic Proper. In the Stockholm archipelago two superimposed gradients were found. Whereas the response of several biomarkers consistently decreased with increasing distance from central Stockholm, the response of others first decreased from Stockholm to the middle archipelago and then increased to the open Baltic Sea. The latter biomarkers included the frequency of sexually mature females, GSI, hepatic EROD activity, and hepatic DNA adducts. In the third project, potential toxicity from munitions on the seafloor, at a dumpsite in the Stockholm archipelago, was analysed by the nanoinjection of sediment extracts into newly fertilised rainbow trout (Oncorhynchus mykiss) eggs, followed by the measurement of biomarkers in the developing larvae. No biological effects of the dumped munitions were found. The same stations in the Stockholm archipelago as in the second project were investigated as a positive control. The results of the three projects agreed well, which demonstrated the continuous pollution of the Baltic Sea and the severe pollution conditions and adverse biological effects in central Stockholm. Further investigations are urgently needed to identify which pollutants or other factors are causing the observed biological effects, both in the background areas in the Baltic Sea and in the Stockholm recipient.
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| 19. |
- Kamat, Nasir, et al.
(författare)
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Chemotherapy induced microsatellite instability and loss of heterozygosity in chromosomes 2, 5, 10, and 17 in solid tumor patients
- 2014
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Ingår i: Cancer Cell International. - : Springer Science and Business Media LLC. - 1475-2867. ; 14, s. 118-
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Tidskriftsartikel (refereegranskat)abstract
- Background: The inevitable side effects of the currently used chemotherapy are associated with serious syndromes. Genotoxic effects and consequent genetic instability may play an important role in these syndromes. The aim of the study was to evaluate chemotherapy-related microsatellite instability (MSI), loss of heterozygosity (LOH), and loss of mismatch repair (MMR) expression in solid tumor patients. Methods: Samples were collected from 117 de novo patients with solid tumors of different origins. Specimens, taken pre- and post-treatment, were screened for MSI and LOH in 10 microsatellite sequences in blood, and expression of five MMR proteins were analyzed in cancer tissues using immunohistochemistry. Statistical analysis included the use of; Fisher's exact test, Chi Square, and an inter-rater reliability test using Cohen's kappa coefficient. Results: Microsatellite analysis showed that 66.7% of the patients had MSI, including 23.1% high-positive MSI and 43.6% low-positive MSI. A large portion (41%) of the patients exhibited LOH in addition to MSI. MSI and LOH were detected in seven loci in which incidence rates ranged from 3.8% positive for Bat-26 to 34.6% positive for Tp53-Alu. Immunohistochemistry revealed that human mutL homolog 1 (hMLH1) expression was deficient in 29.1% of the patients, whereas 18.8%, 23.9%, 13.4%, and 9.7% were deficient for human mutS homolog 2 (hMSH2), P53, human mutS homolog 6 (hMSH6) and human post-meiotic segregation increased 2 (hPMS2), respectively. There was a significant correlation between MSI and LOH incidence in Tp53-Alu, Mfd41, and APC with low or deficient expression of hMLH1, hMSH2, and P53. A significant association between MSI and LOH, and incidence of secondary tumors was also evident. Conclusions: The negative correlation between MMR expression, MSI, and LOH and increased resistance to anti-cancer drugs and development of secondary cancers demonstrates a useful aid in early detection of potential chemotherapy-related side-effects. The diagnostic value demonstrated in our earlier study on breast cancer patients was confirmed for other solid tumors.
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| 20. |
- Kamat, Nasir, 1970-, et al.
(författare)
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Chemotherapy induced microsatellite instability and loss of heterozygosity in chromosomes 2, 5, 10, and 17 in solid tumor patients
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Objectives: The aim of the studywas to evaluate chemotherapy-related microsatellite instability (MSI), loss of heterozygosity (LOH), and loss of mismatch repair (MMR) expression in solid tumor patients. Methods: Samples were collected from 117 de novo patients with solid tumors of different origins. Specimens, taken pre- and post-treatment, were screened for MSI and LOH in 10 microsatellite sequences in blood, and expression of five MMR proteins were analyzed in cancer tissues using immunohistochemistry. Results: Microsatellite analysis showed that 66.7% of the patients had MSI, including 23.1% high-positive MSI and 43.6% low-positive MSI. A large portion (41%) of the patients exhibited LOH in addition to MSI. MSI and LOH were detected in seven loci in which incidence rates ranged from 3.8% positive for Bat-26 to 34.6% positive for Tp53-Alu. Immunohistochemistry revealed that human mutL homolog 1 (hMLH1) expression was deficient in 29.1% of the patients, whereas18.8%, 23.9%, 13.4%, and 9.7% were deficient for human mutS homolog 2(hMSH2), P53, human mutS homolog 6 (hMSH6) and human post-meiotic segregation increased 2 (hPMS2), respectively. There was a significant correlation between MSI and LOH incidence in Tp53-Alu, Mfd41, and APC with low or deficient expression of hMLH1, hMSH2, and P53. A significant association between MSI and LOH, and incidence of secondary tumors was also evident. Conclusions: The negative correlation between MMR expression, MSI, and LOH and increased resistance to anti-cancer drugs and development of secondary cancers demonstrates a useful aid in early detection of potential chemotherapy-related side-effects. The diagnostic value demonstrated in our earlier study on breast cancer patients was confirmed for other solid tumors.
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| 21. |
- Kamat, Nasir, et al.
(författare)
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High incidence of microsatellite instability and loss of heterozygosity in three loci in breast cancer patients receiving chemotherapy : a prospective study
- 2012
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Ingår i: BMC Cancer. - : Springer Science and Business Media LLC. - 1471-2407. ; 12, s. 373-
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Tidskriftsartikel (refereegranskat)abstract
- Background: The aim of the study was to evaluate potential chemotherapy-induced microsatellite instability, loss of heterozygosity, loss of expression in mismatch repair proteins and associations with clinical findings in breast cancer patients, especially resistance to chemotherapy and/or development of other tumors in the four years following chemotherapy treatment. Methods: A comprehensive study of chemotherapy-related effects with a follow-up period of 48 months post treatment was conducted. A total of 369 peripheral blood samples were collected from 123 de novo breast cancer patients. Microsatellite instability and loss of heterozygosity in five commonly used marker loci (including Tp53-Alu of the tumor suppressor gene TP53) were analyzed in blood samples. Sampling was conducted on three occasions; 4-5 weeks prior to the first chemotherapy session (pre-treatment), to serve as a baseline, followed by two consecutive draws at 12 weeks intervals from the first collection. Mismatch repair protein expression was evaluated in cancer tissues using immunohistochemistry for three mismatch-repair related proteins. Results: A total of 70.7% of the patients showed microsatellite instability for at least one locus, including 18.6% marked as high-positive and 52.1% as low-positive; 35.8% showed loss of heterozygosity in addition to microsatellite instability, while 29.3% exhibited microsatellite stability. The following incidence rates for microsatellite instability and loss of heterozygosity were detected: 39.1% positive for Tp53-Alu, 31.1% for locus Mfd41, and 25.3% for locus Mfd28. A higher occurrence of loss of heterozygosity was noted with alleles 399 and 404 of Tp53-Alu. The mismatch repair protein expression analysis showed that the chemotherapy caused a loss of 29.3% in hMLH1 expression, and 18.7% and 25.2% loss in hMSH2 and P53 expression, respectively. A strong correlation between low or deficient hMSH2 protein expression and occurrence of mismatch repair/loss of heterozygosity events in Mfd41, Tp53-Alu, and Mfd28 was evident. A significant association between mismatch repair/loss of heterozygosity and incidence of secondary tumors was also established. Conclusion: Our results suggest that microsatellite instability, loss of heterozygosity, and deficiency in mismatch repair may serve as early prognostic factors for potential chemotherapy-related side effects in breast cancer patients.
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| 22. |
- Kamat, Nasir K., 1970-
(författare)
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Genotoxic effects of systemic chemotherapy in cancer patients, with special focus on the relation between MSI, LOH and development of secondary cancers
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Systemic chemotherapy results in both phenotypic and genotypic side effects. Genotoxicity posed by chemotherapy is a major concern since it induces DNA damage and instability in the patients’ genome. Chemotherapy-related genetic instability is thought to be the cause of some secondary tumors especially the acute myeloid leukemia and/or myelodysplasia, which affect 2-15% of patients receiving chemotherapy. Microsatellites are polymorphic repetitive DNA sequences that undergo changes in their length due to instability. Microsatellite instability (MSI) and loss of heterozygosity (LOH) are the main features of chemotherapy-related genotoxicity.Using a panel of five and ten microsatellite markers, MSI and LOH were evident in blood specimens collected from patients with breast cancer or other solid tumors, respectively. In addition, the expression of mismatch repair (MMR) proteins was analyzed in tumor tissues using immunohistochemistry. The results showed a decreased expression of the following proteins, human mutL homolog 1 (hMLH1), human mutS homolog 2 (hMSH2), human mutS homolog 6 (hMSH6), human post-meiotic segregation increased 2 (hPMS2), and p53 tumor suppressor protein (p53) after completion of chemotherapy. The clinical complications resistance to chemotherapy, recurrence of primary tumor, and development of secondary tumors were also studied. Incidence of MSI and LOH detected in Tp53-Alu, the marker related to the TP53 tumor suppressor gene, was noticeable compared to the other studied microsatellites. Statistical analysis showed a significant correlation between alterations in microsatellites in blood specimens (MSI and LOH) and MMR expression in tumor tissues. Another strong correlation observed was between MSI, LOH and MMR and the recurrence of primary tumor and/or development of secondary cancers.The findings support the hypothesis that MSI and LOH play an important role in tumorigenesis of primary and secondary tumors, and that MSI and LOH may be used as screening tools for early prediction of chemotherapy-related side effects, especially resistance to treatment, recurrence of primary cancer and generation of secondary tumors.
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| 23. |
- Kamat, Nasir, et al.
(författare)
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Microsatellite instability and loss of heterozygosity detected in middle-aged patients with sporadic colon cancer : A retrospective study
- 2013
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Ingår i: Oncology Letters. - : Spandidos Publications. - 1792-1074 .- 1792-1082. ; 6:5, s. 1413-1420
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Tidskriftsartikel (refereegranskat)abstract
- Microsatellite instability (MSI) is a mutator phenotype that results from a defective mismatch repair (MMR) pathway. The present study examined the incidence of MSI and loss of heterozygosity (LOH) according to five markers from the panel of the National Cancer Institute (NCI) in 38 colorectal cancer (CRC) patients from the United Arab Emirates (UAE). MSI and LOH were analyzed using fragment analyses in a multiplex PCR setting on a capillary array electrophoresis platform. The expression of the MMR proteins, hMLH1 and hMSH2, was analyzed using immunohistochemistry. The cohort consisted of 17 females (44.7%) and 21 males (55.3%) with mean ages of 59.9 and 63.3 years, respectively. The overall MSI incidence was 31.3% (95% CI, 16.1-50.0), and included three patients with high MSI (MSI-H; 9.4%; 95% CI, 2.0-25.0) and seven patients with low MSI (MSI-L; 21.9%; 95% CI, 10.7-39). LOH was detected in three patients, while the remaining 25 patients (65.8%) showed no instability and were therefore classified as microsatellite stable (MSS). MSI was detected in the following screened markers: Bat25 in seven patients, Bat26 in three patients, adenomatous polyposis coli (APC; D5S346) in five patients, AFM093xh3 (D2S123) in two patients and Mfd15 (D17S250) in three patients. Of the five MSI-positive patients, four (80%) were evidently younger, aged 38, 48, 49 and 59 years, respectively. The MSI-H incidence (9.4%) was lower compared with that of other ethnic groups. In terms of the MMR proteins, hMLH1 expression was deficient in seven patients, of whom three were MSI-H patients, and hMSH2 was deficient in three patients. Fisher's exact test showed significant associations between hMLH1 and MSI when classified as MSS, MSI-L or MSI-H (P=0.0003). No such association was observed with abnormal MMR protein expression, age, cancer stage or gender.
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| 24. |
- Linderoth, Maria, 1975-
(författare)
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Biochemical characterisation of landfill leachate toxicity in fish
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Deposition remains the most common form of waste disposal in many parts of the world. As a terminus of the products consumed in our society a landfill may contain virtually all sorts of man-made chemicals. Despite this, the harmfulness of landfill leachate has not been extensively evaluated in feral organisms in the environment. In a leachate-contaminated lake, Molnbyggen, in Sweden, our studies reported a low percent of sexually mature (SM) female perch (Perca fluviatilis) that had decreased plasma androgen levels, decreased brain aromatase activity, distinctive sores and fin erosion. The impairments were attributed to unidentified compound(s) present in the leachate. In one out of four other investigated leachate-contaminated lakes, the low percent of SM female perch had reduced plasma sex steroid levels and similar sores as perch in Molnbyggen. The biochemical mechanism causing the disorders was investigated in order to establish a connection between the impairments and possible causative compound(s). Plasma levels of progesterone and 17α-hydroxyprogesterone were unaffected. Ovarian 17,20-lyase activity was decreased while levels of biliary steroid conjugates and hepatic testosterone UDP-glucuronosyltransferase activity did not differ between exposed and reference SM fish. Furthermore, the decreased brain aromatase activity seems to be a secondary effect; possibly a result of low substrate availability. Altogether, this suggests a possible disruption in the synthesis of androgens, knowledge that could be used as a tool in biomarker-directed fractionation studies to pinpoint compound(s). Molnbyggen sediment extracts decreased the testosterone and estradiol concentrations in whole-body homogenates of zebrafish (Danio rerio) after a three week exposure period. This suggests that compound(s) with the potency to alter endocrine function are present in the sediment. Although the first steps have been taken towards identifying compound(s) responsible for this kind of reproductive impairments, they still remain unidentified. Measures have to be taken to identify harmful chemicals in our society, to reduce their number, and to minimise their uncontrolled dispersal.
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| 25. |
- Magnusson, Roger, et al.
(författare)
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Effect of Gasoline and Lubricant on Emissions and Mutagenicity of Particles and Semivolatiles in Chain Saw Exhaust
- 2000
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Ingår i: Environmental Science & Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 34:14, s. 2918-24
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Tidskriftsartikel (refereegranskat)abstract
- The exhaust from a two-stroke chain saw engine was characterized using two different types of gasoline, aliphatic gasoline and conventional lead-free gasoline, in combination with four lubricants differing in mineral oil, polyolester, and polyisobutylene (PIB) content. This characterization was focused on emissions of polycyclic aromatic hydrocarbons (PAH) and mutagenicity testing using Ames Salmonella assay. In addition, exhaust emissions of carbon monoxide (CO), nitrogen oxides (NOx), aldehydes, and hydrocarbons (HC) were measured. The two-stroke engine was tested in a test bench, and particulate, semivolatile, and gaseous exhaust components were sampled using a dilution tunnel. Much less PAH were emitted when using aliphatic gasoline due to a much lower gasoline content of PAH and aromatics than the conventional gasoline. Also about half the NOx emissions, up to 50% higher formaldehyde and acetaldehyde emissions, and 10% higher total HC emissions were observed for the aliphatic gasoline. The influence of lubricant on the studied exhaust emissions was found to be of minor importance. In terms of mutagenicity, significant effects were seen for six of the eight gasoline/lubricant combinations, and the highest effects were observed without a metabolizing system. Generally, the conventional gasoline gave higher effects than did the aliphatic gasoline. A difference between lubricants was also seen, especially in combination with gasoline A; however, the interpretation of mutagenic effects of the lubricants was not straightforward. Overall, one synthetic ester-based lubricant and one mineral oil-based lubricant gave the highest mutagenicity.
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| 26. |
- Masala, Silvia, et al.
(författare)
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Pressurized liquid extraction as an alternative to the Soxhlet extraction procedure stated in the US EPA method TO-13A for the recovery of polycyclic aromatic hydrocarbons adsorbed on polyurethane foam plugs
- 2014
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Ingår i: Analytical Methods. - : Royal Society of Chemistry (RSC). - 1759-9660 .- 1759-9679. ; 6:20, s. 8420-8425
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the present study was to develop a pressurized liquid extraction (PLE) method as an alternative to the relatively time consuming Soxhlet extraction procedure described in the United States Environmental Protection Agency (US EPA) method TO-13A for the extraction of PAHs adsorbed onto polyurethane foam plugs (PUFs). For this purpose PUF air samples were collected and split into two parts: one part extracted using PLE and the other one using Soxhlet extraction. Comparable PAH concentrations were obtained upon analysis of the extracts showing that the PLE method developed in this work is a more convenient choice than the commonly used Soxhlet extraction technique proposed by US EPA for the determination of PAHs in air samples. In fact, the developed PLE method required shorter assay times (minutes versus hours), less solvent consumption and simpler operational methods. The exhaustiveness of the developed PLE method was evaluated using repeat static extraction cycles, demonstrating an extraction efficiency for the PAHs of greater than 99%. The PLE method was then applied to diesel exhaust and wood smoke PUF samples showing an extraction efficiency for the PAHs of greater than 93% and 96%, respectively. Furthermore, a PLE method for PUF cleaning was developed as well and employed as an alternative to Soxhlet extraction. The PLE methods developed for cleaning and extracting PUFs presented in this work are suitable to be used in mutagenicity studies using the Ames Salmonella assay as no mutagenicity was found in the PLE generated blanks
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| 27. |
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