Identification of flavone glucuronide isomers by metal complexation and tandem mass spectrometry: regioselectivity of uridine 5'-diphosphate-glucuronosyltransferase isozymes in the biotransformation of flavones.
Flavone glucuronide isomers of five flavones (chrysin, apigenin, luteolin, baicalein, and scutellarein) were differentiated by collision-induced dissociation of [Co(II) (flavone-H) (4,7-diphenyl-1,10-phenanthroline)(2)](+) complexes. The complexes were generated via postcolumn addition of a metal-ligand solution after separation of the glucuronide products generated upon incubation of each flavone with an array of uridine 5'-diphosphate (UDP)-glucuronosyltransferase (UGT) isozymes. Elucidation of the glucuronide isomers allowed a systematic investigation of the regioselectivity of 12 human UGT isozymes, including 8 UGT1A and 4 UGT2B isozymes. Glucuronidation of the 7-OH position was the preferred site for all the flavones except for luteolin, which possessed adjacent hydroxyl groups on the B ring. For all flavones and UGT isozymes, glucuronidation of the 5-OH position was never observed. As confirmed by the metal complexation/MS/MS strategy, glucuronidation of the 6-OH position only occurred for baicalein and scutellarein when incubated with three of the UGT isozymes.
Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas 78712, United States.
Scott A
SA
Robotham
Jennifer S
JS
Brodbelt
D047310:Apigenin / Q000032:analysis* / Q000737:chemistry; D001711:Biotransformation; D002851:Chromatography, High Pressure Liquid; D056831:Coordination Complexes / Q000032:analysis / Q000737:chemistry; D044950:Flavanones / Q000032:analysis* / Q000737:chemistry; D005419:Flavonoids / Q000032:analysis* / Q000737:chemistry; D020719:Glucuronides / Q000737:chemistry / Q000302:isolation & purification*; D014453:Glucuronosyltransferase / Q000032:analysis / Q000737:chemistry; D007527:Isoenzymes / Q000032:analysis / Q000737:chemistry; D007536:Isomerism; D047311:Luteolin / Q000032:analysis* / Q000737:chemistry; D053719:Tandem Mass Spectrometry
D056831:Coordination Complexes; D044950:Flavanones; D005419:Flavonoids; D020719:Glucuronides; D007527:Isoenzymes; C043561:chrysin; C006680:baicalein; D047310:Apigenin; D014453:Glucuronosyltransferase; D047311:Luteolin; C458179:scutellarein