title: Dietary catechins and procyanidins modulate zinc homeostasis in human HepG2 cells.
abstract: Catechins and their polymers procyanidins are health-promoting flavonoids found in edible vegetables and fruits. They act as antioxidants by scavenging reactive oxygen species and by chelating the redox-active metals iron and copper. They also behave as signaling molecules, modulating multiple cell signalling pathways and gene expression, including that of antioxidant enzymes. This study aimed at determining whether catechins and procyanidins interact with the redox-inactive metal zinc and at assessing their effect on cellular zinc homeostasis. We found that a grape-seed procyanidin extract (GSPE) and the green tea flavonoid (-)-epigallocatechin-3-gallate (EGCG) bind zinc cations in solution with higher affinity than the zinc-specific chelator Zinquin, and dose-dependently prevent zinc-induced toxicity in the human hepatocarcinoma cell line HepG2, evaluated by the lactate dehydrogenase test. GSPE and EGCG hinder intracellular accumulation of total zinc, measured by atomic flame absorption spectrometry, concomitantly increasing the level of cytoplasmic labile zinc detectable by Zinquin fluorescence. Concurrently, GSPE and EGCG inhibit the expression, evaluated at the mRNA level by quantitative reverse transcriptase-polymerase chain reaction, of zinc-binding metallothioneins and of plasma membrane zinc exporter ZnT1 (SLC30A1), while enhancing the expression of cellular zinc importers ZIP1 (SLC39A1) and ZIP4 (SLC39A4). GSPE and EGCG also produce all these effects when HepG2 cells are stimulated to import zinc by treatment with supplemental zinc or the proinflammatory cytokine interleukin-6. We suggest that extracellular complexation of zinc cations and the elevation of cytoplasmic labile zinc may be relevant mechanisms underlying the modulation of diverse cell signaling and metabolic pathways by catechins and procyanidins.
authors.affiliation: Department of Biochemistry and Biotechnology, Nutrigenomics Research Group, Universitat Rovira i Virgili, Tarragona, Spain.
authors.forename: Isabel M
authors.initials: IM
authors.lastname: Quesada
authors.forename: Mario
authors.initials: M
authors.lastname: Bustos
authors.forename: Mayte
authors.initials: M
authors.lastname: Blay
authors.forename: Gerard
authors.initials: G
authors.lastname: Pujadas
authors.forename: Anna
authors.initials: A
authors.lastname: Ardèvol
authors.forename: M Josepa
authors.initials: MJ
authors.lastname: Salvadó
authors.forename: Cinta
authors.initials: C
authors.lastname: Bladé
authors.forename: Lluís
authors.initials: L
authors.lastname: Arola
authors.forename: Juan
authors.initials: J
authors.lastname: Fernández-Larrea
mesh_terms: D044946:Biflavonoids / Q000008:administration & dosage*; D006528:Carcinoma, Hepatocellular / Q000378:metabolism; D002392:Catechin / Q000008:administration & dosage* / Q000031:analogs & derivatives / Q000737:chemistry / Q000494:pharmacology; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D004032:Diet; D005786:Gene Expression Regulation; D056604:Grape Seed Extract / Q000737:chemistry / Q000494:pharmacology; D056945:Hep G2 Cells; D006706:Homeostasis; D006801:Humans; D015850:Interleukin-6 / Q000032:analysis / Q000378:metabolism; D008113:Liver Neoplasms / Q000378:metabolism; D008668:Metallothionein / Q000032:analysis / Q000378:metabolism; D044945:Proanthocyanidins / Q000008:administration & dosage*; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013662:Tea / Q000737:chemistry; D015032:Zinc / Q000032:analysis / Q000378:metabolism*
chemical_list: D044946:Biflavonoids; D027682:Cation Transport Proteins; D056604:Grape Seed Extract; D015850:Interleukin-6; D044945:Proanthocyanidins; D012333:RNA, Messenger; C498299:SLC30A1 protein, human; C403517:SLC39A1 protein, human; C486791:SLC39A4 protein, human; D013662:Tea; C017674:procyanidin; D002392:Catechin; D008668:Metallothionein; C045651:epigallocatechin gallate; D015032:Zinc