| 1. |
- Abu-Bakar, A'edah, et al.
(författare)
-
Metabolism of bilirubin by human cytochrome P450 2A6
- 2012
-
Ingår i: Toxicology and Applied Pharmacology. - : Elsevier BV. - 0041-008X .- 1096-0333. ; 261:1, s. 50-58
-
Tidskriftsartikel (refereegranskat)abstract
- The mouse cytochrome P450 (CYP) 2A5 has recently been shown to function as hepatic "Bilirubin Oxidase" (Abu-Bakar, A., et al., 2011. Toxicol. Appl. Pharmacol. 257, 14-22). To date, no information is available on human CYP isoforms involvement in bilirubin metabolism. In this paper we provide novel evidence for human CYP2A6 metabolising the tetrapyrrole bilirubin. Incubation of bilirubin with recombinant yeast microsomes expressing the CYP2A6 showed that bilirubin inhibited CYP2A6-dependent coumarin 7-hydroxylase activity to almost 100% with an estimated K-i of 2.231 mu M. Metabolite screening by a high-performance liquid chromatography/electrospray ionisation mass spectrometry indicated that CYP2A6 oxidised bilirubin to biliverdin and to three other smaller products with m/z values of 301,315 and 333. Molecular docking analyses indicated that bilirubin and its positively charged intermediate interacted with key amino acid residues at the enzyme's active site. They were stabilised at the site in a conformation favouring biliverdin formation. By contrast, the end product, biliverdin was less fitting to the active site with the critical central methylene bridge distanced from the CYP2A6 haem iron facilitating its release. Furthermore, bilirubin treatment of HepG2 cells increased the CYP2A6 protein and activity levels with no effect on the corresponding mRNA. Co-treatment with cycloheximide (CHX), a protein synthesis inhibitor, resulted in increased half-life of the CYP2A6 compared to cells treated only with CHX. Collectively, the observations indicate that the CYP2A6 may function as human "Bilirubin Oxidase" where bilirubin is potentially a substrate and a regulator of the enzyme.
|
|
| 2. |
- Hakkola, Jukka, et al.
(författare)
-
Expression of CYP1B1 in human adult and fetal tissues and differential inducibility of CYP1B1 and CYP1A1 by Ah-receptor ligands in human placenta and cultured cells
- 1997
-
Ingår i: Carcinogenesis. - 0143-3334 .- 1460-2180. ; 18:2, s. 391-7
-
Tidskriftsartikel (refereegranskat)abstract
- Expression of the Ah receptor-regulated cytochrome P4501B1 (CYP1B1) gene was studied in human adult and fetal tissues and cells in culture by reverse transcriptase-coupled polymerase chain reaction (RT-PCR). In adults, CYP1B1 mRNA was detected in liver, lymphocytes, cells of bronchoalveolar lavage samples and uterine endometrium, but not in lung. The level of expression was very low in adult liver and only three out of six fetal livers expressed CYP1B1. Extrahepatic fetal tissues, especially brains and kidneys, expressed high levels of CYP1B1. CYP1B1 mRNA was constitutively detected at a low level in first trimester and full-term placental samples. A competitive RT-PCR assay was developed to assess the regulation of CYP1B1. CYP1B1 mRNA was not induced in placenta by maternal cigarette smoking. Inducibility of CYP1B1 in cells in culture by the Ah receptor ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin was studied in primary fibroblasts and chorion carcinoma cell line JEG-3 having different CYP1A1 induction properties. Inducibility of CYP1B1 was found to be regulated independently from CYP1A1. In JEG-3 cells CYP1A1 mRNA was induced up to 9000-fold, while the expression of CYP1B1 was not affected. Expression of Ah receptor and Ah receptor nuclear translocator (regulators of the CYP1 family) was determined in human placenta and in the JEG-3 cell line. Expression of these transcription factors was found neither to be co-regulated nor affected by Ah receptor ligands. This study provides evidence that in addition to the Ah receptor complex, other cell-specific factors modulate the response of CYP1B1 and CYP1A1 to Ah receptor ligands.
|
|
| 3. |
- Nyman, Madeleine, et al.
(författare)
-
Contaminant exposure and effects in Baltic ringed and grey seals as assessed by biomarkers
- 2003
-
Ingår i: Marine Environmental Research. ; 55:1, s. 73-99
-
Tidskriftsartikel (refereegranskat)abstract
- The Baltic Sea ecosystem has suffered from a heavy pollutant load for more than three decades. Persistent organic pollutants (POPs) and heavy metals have been of most concern due to their persistence and toxic properties. Ringed seals (Phoca hispida baltica) and grey seals (Halichoerus grypus) living in the Baltic Sea have been suffering from pathological impairments, including reproductive disturbances, which have resulted in a depressed reproductive capacity. We investigated several biochemical parameters as potential biomarkers for exposure to and effects of the contaminant load in the Baltic seals. Seals from less polluted areas were used as reference material in terms of the pollution load. In both Baltic seal populations, the levels of some biochemical parameters diverged from those in the reference seals, and some of these showed a clear correlation with the individual contaminant load. Of the potential bioindicators, we propose cytochrome P4501A activity and vitamin E levels, in blubber or plasma, as exposure biomarkers for polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDT) in both species. The arylhydrocarbon receptor-mediated chemical-activated luciferase gene expression (CALUX) response reflects the whole PCB and DDT burden in ringed seals. Retinyl palmitate (vitamin A) levels showed a negative correlation with the individual POP load, and is proposed as potential effect biomarkers for the depletion of the vitamin A stores. As the nutritional levels of both vitamin A and E have an impact on the vitamin levels in the seals, more information on the dietary vitamin levels is needed before any conclusions can be drawn. As the relationship between biochemical parameters and contaminants varied between the two species, species-specific characteristics has to be considered when monitoring the health status and possible toxic effects of the contaminant load in ringed and grey seals.
|
|
| 4. |
- Oscarsson, Mikael, et al.
(författare)
-
Genotyping of human cytochrome P450 2A6 (CYP2A6), a nicotine C-oxidase
- 1998
-
Ingår i: FEBS Letters. - 0014-5793 .- 1873-3468. ; 438:3, s. 201-205
-
Tidskriftsartikel (refereegranskat)abstract
- Cytochrome P450 2A6 (CYP2A6) is a polymorphic enzyme responsible for the oxidation of certain precarcinogens and drugs and is the major nicotine C-oxidase. The role of CYP2A6 for nicotine elimination was emphasised recently by the finding that smokers carrying defective CYP2A6 alleles consumed fewer cigarettes [Pianezza et al. (1998) Nature 393, 750]. The method used for CYP2A6 genotyping has, however, been found to give erroneous results with respect to the coumarin hydroxylase phenotype, a probe reaction for the CYP2A6 enzyme. The present study describes an allele-specific PCR genotyping method that identifies the major defective CYP2A6 allele and accurately predicts the phenotype. An allele frequency of 1-3% was observed in Finnish, Spanish, and Swedish populations, much lower than described previously.
|
|
| 5. |
|
|
