title: Cyanidin, a natural flavonoid, is an agonistic ligand for liver X receptor alpha and beta and reduces cellular lipid accumulation in macrophages and hepatocytes.
abstract: Cyanidin, a natural flavonoid abundant in fruits and vegetables, is known to regulate cellular lipid metabolism; however, its underlying mechanism of action and protein targets remain unknown. Here, the ligand binding activity of cyanidin on liver X receptors (LXRs) was investigated utilizing surface plasmon resonance and time-resolved fluorescence energy transfer (TR-FRET) analyses. LXRs are nuclear receptors which function as critical transcription factors in the regulation of cellular lipid and glucose metabolism. This includes the stimulation of high-density-lipoprotein synthesis and activation of reverse cholesterol transport. The present findings show that cyanidin induces the transactivation of LXRs and binds directly to the ligand-binding domain of both LXRα and LXRβ with dissociation constants of 2.2 and 73.2μM, respectively. Cell-free FRET analysis demonstrated that cyanidin induces the recruitment of co-activator peptide for LXRα and LXRβ with EC50 of 3.5μM and 125.2μM, respectively. In addition, intracellular cholesterol and triglyceride (TG) concentrations were reduced in macrophages following cyanidin stimulation. In cultured hepatocytes, cyanidin mildly induced SREBP1c gene expression but marginally affected cellular TG concentrations as well as reduced cellular cholesterol accumulations which activated the expression of genes for reverse cholesterol transport. Two cyanidin metabolites, procatechic acid and phloroglucinaldehyde, did not directly bind or activate LXRs. These results demonstrate that cyanidin is a direct ligand for both LXRα and LXRβ, suggesting that cyanidin may operate, at least in part, through modulation of cellular LXR activity.
authors.affiliation: Department of Biotechnology, The Graduate School of Life Sciences & Biotechnology, Korea University, 5-ga, Anam, Seongbuk, Seoul 136-713, Republic of Korea.
authors.forename: Yaoyao
authors.initials: Y
authors.lastname: Jia
authors.forename: Minh Hien
authors.initials: MH
authors.lastname: Hoang
authors.forename: Hee-Jin
authors.initials: HJ
authors.lastname: Jun
authors.forename: Ji Hae
authors.initials: JH
authors.lastname: Lee
authors.forename: Sung-Joon
authors.initials: SJ
authors.lastname: Lee
mesh_terms: D000872:Anthocyanins / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism*; D005419:Flavonoids / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D031541:Fluorescence Resonance Energy Transfer; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D008024:Ligands; D000071518:Liver X Receptors; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism; D057093:Orphan Nuclear Receptors / Q000819:agonists* / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D020033:Protein Isoforms / Q000819:agonists / Q000378:metabolism; D014280:Triglycerides / Q000378:metabolism*
chemical_list: D000872:Anthocyanins; D005419:Flavonoids; D008024:Ligands; D000071518:Liver X Receptors; C000605213:NR1H3 protein, human; D057093:Orphan Nuclear Receptors; D020033:Protein Isoforms; D014280:Triglycerides; C017154:cyanidin; D002784:Cholesterol