title: A novel retinoic acid analogue, 7-hydroxy retinoic acid, isolated from cyanobacteria.
abstract: BACKGROUND
  All-trans retinoic acid (RA) is a low-molecular compound derived from vitamin A. It induces events in various ways by binding with the retinoic acid receptor (RAR), a nuclear receptor, in animal cells. RA and its metabolites have been found in animal tissues. In this paper, we report a novel RA analogue found in cyanobacterial cells, describe the method for its isolation, and compare its photo-stability with that of all-trans RA.
  
  
  METHODS
  The new A analogue was extracted from cells of Microcystis aeruginosa and Spirulina sp. and fractionated by high-performance liquid chromatography. The analogue was analysed using a yeast two-hybrid assay method to measure in vitro RAR-agonistic activity. Liquid chromatography-mass spectrometry/mass spectrometry analyses was performed to elucidate the chemical structure of this RA analogue.
  
  
  RESULTS
  The results of the analysis of the fragments revealed that the novel RA analogue was 7-hydroxy RA. The yields from 3.5 μg (4.5% of the total RAR-agonistic activity of Spirulina sp. cells) of 7-hydroxy RA was a mixture of 4 isomers due to cis-trans isomerisation coupled with keto-enol tautomerism; its relative RAR agonistic activity was 0.49 ± 0.01 (n=3) when the activity of all trans RA was set up to 1.00. Under fluorescent light, the mixture of 7-hydroxy RA isomers was more stable than all- trans RA.
  
  
  CONCLUSIONS
  We isolated a novel RAR-activating compound, 7-hydroxy RA, from cyanobacteria.
  
  
  CONCLUSIONS
  7-hydroxy RA is more stable than all-trans RA under UV-A.
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1, Ten-nodai, Tsukuba, 305-8572 Japan. kaya@sakura.cc.tsukuba.ac.jp
authors.forename: Kunimitsu
authors.initials: K
authors.lastname: Kaya
authors.forename: Fujio
authors.initials: F
authors.lastname: Shiraishi
authors.forename: Hideaki
authors.initials: H
authors.lastname: Uchida
authors.forename: Tomoharu
authors.initials: T
authors.lastname: Sano
mesh_terms: D006801:Humans; D046931:Microcystis / Q000737:chemistry*; D018168:Receptors, Retinoic Acid / Q000819:agonists* / Q000378:metabolism; D053545:Spirulina / Q000737:chemistry*; D014212:Tretinoin / Q000031:analogs & derivatives* / Q000302:isolation & purification / Q000494:pharmacology; D020798:Two-Hybrid System Techniques
chemical_list: C558316:7-hydroxyretinoic acid; D018168:Receptors, Retinoic Acid; D014212:Tretinoin