title: Effects of curcumin and demethoxycurcumin on amyloid-β precursor and tau proteins through the internal ribosome entry sites: a potential therapeutic for Alzheimer's disease.
abstract: OBJECTIVE
  This study aims to determine the effects of curcumin and demethoxycurcumin on the internal ribosome entry site of the amyloid-β precursor protein (APP) and tau protein through a bi-cistronic reporter assay for screening of anti-Alzheimer's disease agents.
  
  
  METHODS
  A bi-cistronic assay was performed wherein the expression of the first cistron, a β-galactosidase gene under the control of a cytomegalovirus promoter, represents the canonical cap-dependent mechanism of translation initiation; while the second cistron involves the utilization of the APP or the tau IRES elements to drive the expression of secreted alkaline phosphatase (SEAP) under a cap-independent mechanism. Bioactive natural products reported to have therapeutic potential for AD such as curcumin and demethoxycurcumin were screened in an murine neuroblastoma (N2A) cell model. Western blot analyses for the expression of APP C-terminal protein, human tau-1, and phosphorylated tau at Serine 262 (p(262)) and Serine 396 (pS(396)) were done after treatment of N2A cells with the test compounds.
  
  
  RESULTS
  The bi-cistronic reporter assay revealed that curcumin was more effective than demethoxycurcumin, a structural analog of curcumin, in inhibiting both APP and tau IRES-dependent translation initiation. This result was further confirmed by Western blot analysis for the expression of APP C-terminal protein, human tau-1, pS(262) and pS(396) suggesting that curcumin may play a role in AD pathology alleviation through the inhibition of the APP and tau IRES-mediated translation mechanism. On the other hand, demethoxycurcumin was observed to inhibit the phosphorylation of both tau pS(262) and pS(396).
  
  
  CONCLUSIONS
  A novel assay system using the bi-cistronic reporter constructs for the identification of compounds with activity against the translation directed by APP and tau IRES was developed. The results provide novel suggestive insights for the potential use of the mentioned compounds as prophylactic and therapeutic anti-AD agents.
authors.affiliation: Department of Chemistry, Chung Yuan Christian University, Chung Li, Taiwan.
authors.forename: Oliver B
authors.initials: OB
authors.lastname: Villaflores
authors.forename: Ying-Ju
authors.initials: YJ
authors.lastname: Chen
authors.forename: Chih-Ping
authors.initials: CP
authors.lastname: Chen
authors.forename: Jui-Ming
authors.initials: JM
authors.lastname: Yeh
authors.forename: Tzong-Yuan
authors.initials: TY
authors.lastname: Wu
mesh_terms: D000469:Alkaline Phosphatase / Q000235:genetics; D000544:Alzheimer Disease / Q000188:drug therapy / Q000378:metabolism*; D016564:Amyloid beta-Protein Precursor / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology*; D045744:Cell Line, Tumor; D003474:Curcumin / Q000031:analogs & derivatives* / Q000494:pharmacology*; D036381:Diarylheptanoids; D015870:Gene Expression / Q000187:drug effects; D017930:Genes, Reporter / Q000187:drug effects; D051379:Mice; D010442:Peptide Chain Initiation, Translational / Q000187:drug effects*; D010766:Phosphorylation / Q000187:drug effects; D012270:Ribosomes / Q000187:drug effects; D001616:beta-Galactosidase / Q000235:genetics; D016875:tau Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D016564:Amyloid beta-Protein Precursor; D000975:Antioxidants; D036381:Diarylheptanoids; D016875:tau Proteins; D000469:Alkaline Phosphatase; D001616:beta-Galactosidase; D003474:Curcumin; C050229:demethoxycurcumin