| 1. |
- Bainy, Afonso C.D., et al.
(författare)
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Functional characterization of a full length pregnane X receptor, expression in vivo, and identification of PXR alleles, in Zebrafish (Danio rerio)
- 2013
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Ingår i: Aquatic Toxicology. - : Elsevier BV. - 0166-445X. ; 142-143, s. 447-457
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Tidskriftsartikel (refereegranskat)abstract
- The pregnane X receptor (PXR) (nuclear receptor NR1I2) is a ligand activated transcription factor, mediating responses to diverse xenobiotic and endogenous chemicals. The properties of PXR in fish are not fully understood. Here we report on cloning and characterization of full-length PXR of zebrafish, Danio rerio, and pxr expression in vivo. Initial efforts gave a cDNA encoding a 430 amino acid protein identified as zebrafish pxr by phylogenetic and synteny analysis. The sequence of the cloned Pxr DNA binding domain (DBD) was highly conserved, with 74% identity to human PXR-DBD, while the ligand-binding domain (LBD) of the cloned sequence was only 44% identical to human PXR-LBD. Sequence variation among clones in the initial effort prompted sequencing of multiple clones from a single fish. There were two prominent variants, one sequence with S183, Y218 and H383 and the other with I183, C218 and N383, which we designate as alleles pxr*1 (nr1i2*1) and pxr*2 (nr1i2*2), respectively. In COS-7 cells co-transfected with a PXR-responsive reporter gene, the full-length Pxr*1 (the more common variant) was activated by known PXR agonists clotrimazole and pregnenolone 16α-carbonitrile but to a lesser extent than the full-length human PXR. Activation of full-length Pxr*1 was only 10% of that with the Pxr*1 LBD. Quantitative real time PCR analysis showed prominent expression of pxr in liver and eye, as well as brain and intestine of adult zebrafish. The pxr was expressed in heart and kidney at levels similar to that in intestine. The expression of pxr in liver was weakly induced by ligands for mammalian PXR or constitutive androstane receptor (NR1I3). The results establish a foundation for PXR studies in this vertebrate model. PXR allelic variation and the differences between the full-length PXR and the LBD in reporter assays have implications for assessing the action of PXR ligands in zebrafish.
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| 2. |
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| 3. |
- Bignert, Anders, et al.
(författare)
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Fiskar lever i en kemisk cocktail
- 2013
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Ingår i: Formas Fokuserar: Havsbruk som håller i längden. - : Forskningsrådet Formas, T1:2013. - 9789154060740 ; , s. 131-142
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 4. |
- Celander, Malin C., 1962
(författare)
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Cocktail-effects on biomarker responses in fish
- 2011
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Ingår i: Aquatic Toxicology. ; 105S, s. 72-77
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Forskningsöversikt (refereegranskat)abstract
- One of today’s greatest challenges in environmental toxicology is to understand effects of mixture toxicity, commonly referred to as cocktail effects, in humans and in wildlife. Biomarker responses in fish are routinely used to assess exposure of anthropogenic chemicals in the aquatic environment. However, little is known about how cocktail effects affect these biomarker responses. For this reason, there is an obvious risk for misinterpretation of biomarker-data and this can have profound negative effects on stakeholder’s decisions and actions, as well as on legislations and remediation-plans initiated in order to reduce exposure to certain chemicals. Besides, chemical safety-levels are traditionally based on experiences from lab-studies with single chemicals, which is unfortunate as a chemical can be more toxic when it is mixed with other chemicals, because of the cocktail effect. This review focuses on pharmacokinetic interactions between different classes of pollutants on detoxification mechanisms and how that affects two commonly used biomarkers in the aquatic environment: 1) induction of cytochrome P450 1A (CYP1A) that is mediated via activation of the arylhydrocarbon receptor (AhR), used to assess exposure to aromatic hydrocarbons; 2) induction of vitellogenin (VTG) that is mediated via activation of the estrogen receptor (ER), used to assess exposure to estrogenic chemicals. These responses can be either directly or indirectly affected by the presence of other classes of pollutants as a result of cocktail effects. For example, chemicals that inhibit the function of key metabolic enzymes and transporter pumps that are involved in elimination of AhR- and ER agonists, can result in bioaccumulation of aromatic hydrocarbons and estrogenic chemicals resulting in increased biomarker responses. This cocktail effect can lead to overestimation of the actual exposure pressure. On the contrary, induction of expression of key metabolic enzymes and transporter activities can result in increased elimination of AhR- and ER agonists that can lead to possible underestimation of the exposure. Another type of cocktail effect is inhibiting receptor cross-talk that may cause decreased biomarker responses that can also lead to underestimation of the actual exposure. To address the possible involvement of pharmacokinetic interactions including receptor cross-talks, we need to combine analyses on receptor signaling with studies on function of key biotransformation enzymes such as major catabolic CYP enzymes (e.g. CYP1-4) as well as efflux pumps (e.g. ATP-binding cassette transporter proteins). Besides, studies of inhibition of these enzymes and pumps activities pose a great potential to be used as future biomarkers as they are more clearly liked to adverse outcomes, compared to for example induction of CYP1A and VTG expression.
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| 5. |
- Celander, Malin C., 1962
(författare)
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Cocktail effects on fish biomarkers
- 2012
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Ingår i: 4th Norwegian Environmental Toxicology Symposium, October 16-18, Tromso, Norway.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Chemicals with different modes-of-action can share common routes for their metabolism and excretion. A chemical’s toxicity and biological half-life can be altered in mixtures as a result of toxicokinetic interactions and these interactions can also interfere with biomarker responses. Two common biomarkers; induction of CYP1A, via AhR activation, and induction of vitellogenin, via ER activation, can be affected by exposures to mixtures. There are different types of cocktail effects that can affect these biomarker responses and hence can result in either overestimation or underestimation of the exposure. For example, exposure to chemicals that can act as inhibitors of catabolic CYP enzymes (CYP1-4) and efflux pumps (ABC-transporters) can result in decreased elimination of other chemicals. Reduced elimination of AhR agonists results in increased induction of CYP1A and leads to overestimation of the exposure to AhR agonists. Inhibition receptor cross-talk can also interfere with biomarker responses. For example, exposure to AhR agonists that activate AhR signaling can result in decreased ER signaling. This results in decreased induction of vitellogenin and leads to underestimation of the actual exposure. To address the possible involvement of toxicokinetic interactions and receptor cross-talks, we need to combine analyses on receptor signaling with studies on functions of key detoxification mechanisms.
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| 6. |
- Celander, Malin C., 1962, et al.
(författare)
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DEVELOPMENT OF ALTERNATIVE MATHEMATICAL TOOLS TO ASSESS SYNERGISTIC MIXTURE EFFECTS
- 2015
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Ingår i: 18th International symposium on Pollutant Responses in Marine Organisms (PRIMO18).
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Mixture effects are well known problems but chemical legislations are typically based on single chemical toxicity, which is unfortunate as chemicals occur as mixtures in the environment. There are mathematical models to assess additive mixture effects that are based on linear mixture effects such as toxicodynamic interactions. Chemicals with same or different mode-of-actions can also interfere with each other’s elimination pathways that can result in toxicokinetic interactions and cause indirect mixture effects. Therefore, chemicals that inhibit CYP enzymes in the elimination pathways of different classes of environmental pollutants can cause non-linear mixture effects that are more-than-additive. More-than-additive mixture effects have been observed between azoles and other classes of environmental pollutants such as estrogenic chemicals and aromatic hydrocarbons, as a result of toxicokinetic interactions via CYP1A/CYP3A inhibitions. There is need for new mathematical models to assess non-linear mixture effects. We have initiated the development of alternative mathematical tools to forecast non-linear mixture effects that are based on toxicokinetic interactions from earlier lab-studies in fish and fish cells. Time-dynamic is a key factor in toxicokinetic interactions and therefore we will combine multiple differential equations in the models. These equations describe how one chemical’s concentration changes over time in relationship to changes of another chemical’s concentration over time and how that affect biomarker responses such as CYP1A and vitellogenin. We will use statistical tools to quantitatively fit the suggested models with data from lab-studies. Non-linear models can be used to describe synergistic mixture effects. Those could be bottom-up-models, where we start from the different chemicals involved, or they could be top-down-models, where we fit a multi-dimension function to a given dataset using an auxiliary non-linear model. Our preliminary non-linear mathematical top-down model describes how the vitellogenin and the CYP1A biomarker responses can vary with concentrations of a synthetic estrogen and an antimycotic azole.
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| 8. |
- Celander, Malin C., 1962, et al.
(författare)
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Effects of pharmaceuticals on pregnane X receptor (PXR) and cytochrome P450 3A (CYP3A) signaling in rainbow trout liver
- 2009
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Ingår i: SETAC Europe 19th Annual Meeting Abstract Book, Göteborg 31 May - 4 June, 2009, s. 58.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The PXR has been described as a pharmacophore, as it can be activated by a wide array of structurally diverse pharmaceuticals. The PXR regulate various responses such as the expression of CYP3A genes. In mammals, CYP3A enzymes have been shown to metabolize over 50% of all pharmaceuticals. The promiscuity of the PXR and the unusually wide substrate specificities of the CYP3A enzymes assure an efficient metabolic clearance of numerous pharmaceuticals. Compared to human and traditional laboratory animals, less is known about the PXR-CYP3A signaling in wildlife. Yet, a great number of pharmaceutical that can activate human PXR and/or affect CYP3A metabolism have been detected in the aquatic environment. We have cloned the PXR from rainbow trout liver and are using a reporter system to screen different pharmaceuticals for PXR activation in vitro. In addition, we treated rainbow trout hepatocytes with prototypical mammalian PXR agonists. Preliminary results from the reporter assay studies show that the rainbow trout PXR is less responsive compared to the mammalian counterparts. This is also conformed in the exposure studies of hepatocytes. Thus, neither dexamethasone nor rifampicin had any effect on CYP3A mRNA levels in the trout hepatocytes. However, rifampicin is a potent inhibitor of the CYP3A enzyme activity in rainbow trout liver. Interestingly, exposure to dexamethasone appeared to downregulate expression of the PXR mRNA levels without affecting the CYP3A mRNA levels. Exposure to other mammalian PXR agonist such as lithocholic acid and pregnenolone 16alpha-carbonitrile resulted in a weak upregulation CYP3A mRNA levels in trout hepatocytes. Together these data suggest complex interactions between pharmaceuticals and PXR-CYP3A signaling in rainbow trout.
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