title: Carlinoside reduces hepatic bilirubin accumulation by stimulating bilirubin-UGT activity through Nrf2 gene expression.
abstract: Accumulation of bilirubin, primarily because of its insolubility, has been found to be associated with liver diseases including jaundice. Free bilirubin is insoluble; its glucuronidation by bilirubin-UGT enzyme (UGT1A1) makes it soluble and eliminates it through urine and faeces. Taking CCl(4) induced rat liver dysfunction model, we demonstrated that suppression of UGT1A1 activity in rat liver increased serum bilirubin level which could be reversed by carlinoside (Cln), a flavone glycoside. Although Cln is a flavone compound, it escaped self-glucuronidation in the intestine and readily absorbed. Kinetic study of microsomal UGT1A1 from HepG2 cells suggested that Cln enhanced enzyme activity by increasing V(max) without altering K(m). This altered V(max) was found to be due to UGT1A1 overexpression by Cln which was observed in both HepG2 and rat primary hepatocytes. Since Nrf2 is the transcription factor of UGT1A1, we examined whether Cln effect on UGT1A1 overexpression is mediated through Nrf2. In Nrf2 knock-out cells, Cln could not elevate UGT1A1 activity indicating Nrf2 to be its target. Cln significantly increased Nrf2 gene expression in HepG2 cells which was subsequently localized in nuclear region. Results from ChIP assay showed that Cln markedly augmented Nrf2 binding to UGT1A1 promoter that consequently enhanced reporter activity. Our findings therefore show that Cln upregulated Nrf2 gene expression, increased its nuclear translocation and stimulated UGT1A1 promoter activity. Total outcome of these events brought about a significant increase of bilirubin glucuronidation. Cln therefore could be a worthy choice to intervene hyperbilirubinemia due to liver dysfunction.
authors.affiliation: Cellular and Molecular Endocrinology Laboratory, School of Life Science, Visva-Bharati University, Santiniketan 731 235, India.
authors.forename: Rakesh
authors.initials: R
authors.lastname: Kundu
authors.forename: Suman
authors.initials: S
authors.lastname: Dasgupta
authors.forename: Anindita
authors.initials: A
authors.lastname: Biswas
authors.forename: Sushmita
authors.initials: S
authors.lastname: Bhattacharya
authors.forename: Bikas C
authors.initials: BC
authors.lastname: Pal
authors.forename: Shelley
authors.initials: S
authors.lastname: Bhattacharya
authors.forename: P G
authors.initials: PG
authors.lastname: Rao
authors.forename: N C
authors.initials: NC
authors.lastname: Barua
authors.forename: Manobjyoti
authors.initials: M
authors.lastname: Bordoloi
authors.forename: Samir
authors.initials: S
authors.lastname: Bhattacharya
mesh_terms: D000818:Animals; D001663:Bilirubin / Q000378:metabolism*; D002251:Carbon Tetrachloride / Q000633:toxicity; D056486:Chemical and Drug Induced Liver Injury / Q000378:metabolism; D047309:Flavones / Q000737:chemistry / Q000494:pharmacology*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D014453:Glucuronosyltransferase / Q000235:genetics / Q000378:metabolism*; D006027:Glycosides / Q000737:chemistry / Q000494:pharmacology*; D056945:Hep G2 Cells; D006801:Humans; D015394:Molecular Structure; D051267:NF-E2-Related Factor 2 / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D051381:Rats; D000099148:UGT1A1 Enzyme
chemical_list: D001663:Bilirubin; D002251:Carbon Tetrachloride; D047309:Flavones; D014453:Glucuronosyltransferase; D006027:Glycosides; D051267:NF-E2-Related Factor 2; D000099148:UGT1A1 Enzyme; C495635:NFE2L2 protein, human; C495637:Nfe2l2 protein, rat; C499946:Ugt1a1 protein, rat; C568398:carlinoside