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- Abu-Bakar, A'edah, et al.
(författare)
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Metabolism of bilirubin by human cytochrome P450 2A6
- 2012
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Ingår i: Toxicology and Applied Pharmacology. - : Elsevier BV. - 0041-008X .- 1096-0333. ; 261:1, s. 50-58
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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.
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| 2. |
- Hanhineva, Kati, et al.
(författare)
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Discovery of urinary biomarkers of whole grain rye intake in free-living subjects using non-targeted LC-MS metabolite profiling
- 2015
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Ingår i: Molecular Nutrition & Food Research. - : Wiley. - 1613-4125 .- 1613-4133. ; 59:11, s. 2315-2325
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Tidskriftsartikel (refereegranskat)abstract
- SCOPE: Whole grain (WG) intake is associated with decreased risk of developing colorectal cancer, type 2 diabetes and cardiovascular disease and its comorbidities. However, the role of specific grains is unclear. Moreover, intake of specific WG is challenging to measure accurately with traditional dietary assessment methods. Our aim was to use non-targeted metabolite profiling to discover specific urinary biomarkers for WG rye to objectively reflect intake under free-living conditions.METHODS AND RESULTS: WG rye intake was estimated by weighed food records, and 24 h urine collections were analyzed by LC-MS. Multivariate modelling was undertaken by repeated double cross-validated partial least squares regression against reported WG rye intake, which correlated well with multivariate prediction estimates (r = 0.67-0.80, p<0.001), but not with intakes of WG wheat or oats. Hydroxyhydroxyphenyl acetamide (HHPA) sulfate, 3,5-dihydroxyphenylpropionic acid (DHPPA) sulfate, caffeic acid sulfate and hydroxyphenyl acetamide (HPAA) sulfate were among the 20 features which had the greatest potential as intake biomarkers of WG. In addition, three compounds exhibited MS/MS fragmentation of carnitine structures.CONCLUSION: With this non-targeted approach, we confirmed the specificity of alkylresorcinol metabolites as biomarkers for WG rye intake, but also discovered other compounds that should be evaluated as putative biomarkers in future studies.
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