Regiospecificity of Human UDP-glucuronosyltransferase Isoforms in Chalcone and Flavanone Glucuronidation Determined by Metal Complexation and Tandem Mass Spectrometry

Abstract

The glucuronidation of a series of chalcones (2'-hydroxychalcone, 2',4'-dihydroxychalcone, 3,2'-dihydroxychalcone, 4,2'-dihydroxychalcone, and cardamonin) and their corresponding cyclized flavanones (7-hydroxyflavanone, 3'-hydroxyflavanone, 4'-hydroxyflavanone, and alpinetin) by nine human UDP-glucuronosyltransferase (UGT) 1A enzymes was evaluated. A post-column metal complexation LC-MS/MS strategy was used successfully to produce characteristic mass spectrometric product ions that were utilized in combination with elution order trends to identify chalcone and flavanone monoglucuronides unambiguously, thus allowing determination of the regioselectivities of the UGT1A isoforms. The presence of hydroxy groups on the A or B-ring had a significant effect on the glucuronide product yield and the site where glucuronidation occurred. For example, for reaction with UGT1A9, formation of the 2'-O-glucuronide was increased for dihydroxychalcones with A-ring hydroxy substituents. In contrast, although UGT1A8 reacted with 3,2'-dihydroxychalcone and 4,2'-dihydroxychalcone to yield 2'-O-glucuronide products, the presence of a B-ring hydroxy group at the 4' position on cardamonin and 2',4'-dihydroxychalcone quenched the reaction at the OH-2' position. Moreover, the A-ring OH-4 group promoted glucuronidation at the 2' position for the reaction of 4,2'-dihydroxychalcone with UGT1A1 and 1A3. For UGT1A7, hydroxy group substituents on the chalcone A-ring also promoted cyclization and formation of the corresponding flavanone glucuronide.

UGT1A polymorphisms as genetic biomarkers for hepatocellular carcinoma risk in Caucasian population

“…39 The UGT1A7 isoform is not expressed in the liver but in several extrahepatic tissues (ie lung, upper gastrointestinal tract), 11,12 mostly devoted to the front-line glucuronidation of numerous xenobiotics, including some molecules (ie dietary components) that display anticancer, anti-inflammation and anti-oxidative proprieties as flavones. [45][46][47] From the present findings, the low-activity UGT1A7*3 allele appeared to protect towards HCC development, independent of viral status. It could be therefore hypothesized that the UGT1A7*3 marker impact HCC risk by a differential metabolism at "entry sites" of environmental health-beneficial molecules similar to that previously described for the UGT1A1/A9 isoforms.…”

“…The UGT1A7 isoform is not expressed in the liver but in several extrahepatic tissues (ie lung, upper gastrointestinal tract), mostly devoted to the front‐line glucuronidation of numerous xenobiotics, including some molecules (ie dietary components) that display anticancer, anti‐inflammation and anti‐oxidative proprieties as flavones . From the present findings, the low‐activity UGT1A7*3 allele appeared to protect towards HCC development, independent of viral status.…”

In vitro selective cytotoxicity of the dietary chalcone cardamonin (CD) on melanoma compared to healthy cells is mediated by apoptosis

“…These data suggest that melanoma cells are either metabolizing CD or extruding it faster than NHDF or NHEM. As a spontaneous cyclization of the chalcone CD to the flavanone alpinetin has been described [58,59], we checked the occurrence of alpinetin in the medium (Fig 7B) and in the cell extract after 24 h post incubation (Fig 7C). A high amount of alpinetin was detected in the cell culture medium (cell culture supernatant) of the three cell lines at 24 h after treatment the cells with CD indicating cyclization of CD to alpinetin (Fig 7B).…”

The UDP-Glycosyltransferase (UGT) Superfamily: New Members, New Functions, and Novel Paradigms

“…This extrahepatic UGT is expressed mainly in stomach and is involved in conjugation with a large number of structurally diverse exogenous compounds including dietary constituents and carcinogens. The former include flavonols (518,767), isoflavone calycosin (609), ferulic acid (405), and flavanone hesperetin (69); the latter include tobacco carcinogens benzo(␣)pyrene and NNAL (377,798) as discussed further in section IV. An unusual substrate for UGT1A7 is NF1586, a cytokinin-derived neutrophil growth factor (649), which may have utility as an antiinflammatory molecule.…”