AhR Assays
Background of AhR
Aryl hydrocarbon receptor (AhR) acts as a transcription factor, modulating the gene expression. The ligands of AhR include natural ligands, derivatives of tryptophan, tetrapyrroles, the arachidonic acid metabolites lipoxin A4 and prostaglandin G, modified low-density lipoprotein, and dietary carotenoids, as well as synthetic ligands, the halogenated and polycyclic aromatic hydrocarbons. Synthetic ligands are under development as the treatment of breast cancer.
Fig.1 Pathway of activation of the aryl hydrocarbon receptor and the responses triggered by this pathway. (Denison, 2003)
Distribution and Function of AhR
The AhRs are mainly distributed in the liver and barrier organs. They play an essential role in the transcription of particular genes, such as PER1, CYP1A1, and THP-1. The AhR also participates in non-genomic signaling. The AhR is also involved in the development of the liver, immune system, and nervous system, hematopoiesis, promotion of aging, cell proliferation and differentiation, and inhibition of inflammatory reactions. In addition, AhR can elicit aversion in response to toxic substances.
Mechanism of AhR
AhR is the only subtype of the family of aryl hydrocarbon receptors. Non-ligand bound AhR is resident in the cytoplasm, which couples to chaperone heat shock protein 90 (HSP90), AhR interacting protein (AIP), p23, XAP2, and AhR-activated 9 (ARA9) to form a protein complex. When AhR is bound and activated by ligands, the complex will migrate to the nucleus and bind the AhR nuclear translocator (ARNT). The AhR/ARNT complex is capable of regulating the transcription of specific genes via the combination with xenobiotic response elements (XRE).
Published Data
| Paper Title | Novel cell‐based assay reveals associations of circulating serum AhR‐ligands with metabolic syndrome and mitochondrial dysfunction |
| Journal | Biofactors |
| Published | 2013 |
| Abstract | Serum concentrations of environmental pollutants have been proven to be positively correlated with diabetes, metabolic syndrome, and abnormal mitochondrial function. Based on the cell-based measurement of AhR ligand mixtures, which is called chemically activated luciferase gene expression (CALUX) assay, researchers have developed a novel cell-based aryl hydrocarbon receptor (AhR) agonist bioassay system without a solvent extraction process. They analyzed the association between low-dose circulating AhR ligands in human serum and parameters of metabolic syndrome and mitochondrial function, such as obesity, blood pressure, serum triglyceride, and fasting glucose. The study has established a rapid cell-based assay using the minute volume of human serum, which may provide one of the best monitoring systems for circulating AhR ligands. The monitoring of AhR ligands provided good clinical biomarkers for the progress of disease and therapeutic efficacy. |
| Result |
They modified the CALUX assay to create the cell-based AhR ligand activity (CALA) assay, which allowed them to determine the cumulative levels of circulating AhR ligands by directly incubating the pDRE-luc-transfected reporter cells with 10 lL human serum samples without solvent extraction. They measured serum levels of total AhR ligands from 97 Korean subjects (47 with glucose intolerance and 50 matched controls, average age of 46.6 ± 9.9 years, 53 male and 45 female). The results of serum 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalent (sTCDDeq) were higher in participants with glucose intolerance than normal controls and were positively associated (P < 0.01) with obesity, blood pressure, serum triglyceride, and fasting glucose, while sTCDDeq was not related to HDL-cholesterol. In addition, body mass index demonstrated a positive linear relationship with serum AhR ligands in healthy participants. The result indicated that circulating AhR ligands may directly reduce mitochondrial function in tissues, leading to weight gain, glucose intolerance, and metabolic syndrome.
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Fig.2 Reliability of CALA AhR ligand activity assay. (Park, 2013)
References
- Denison M.S.; Nagy S.R. Activation of the aryl hydrocarbon receptor by structurally diverse exogenous and endogenous chemicals. Annual Review of Pharmacology and Toxicology. 2003, 43: 309–34.
- Park, W. H.; et al. Novel cell‐based assay reveals associations of circulating serum AhR‐ligands with metabolic syndrome and mitochondrial dysfunction. Biofactors. 2013, 39(4): 494-504.
