β-Apocarotenoids do not significantly activate retinoic acid receptors α or β

beta-Carotene oxygenase 2 cleaves beta-carotene asymmetrically at non-central double bonds of the polyene chain, yielding apocarotenal molecules. The hypothesis tested was that apocarotenoids are able to stimulate transcription by activating retinoic acid receptors (RARs). The effects of long- and short-chain apocarotenals and apocarotenoic acids on the activation of RAR alpha and RAR beta transfected into monkey kidney fibroblast cells (CV-1) were investigated. We synthesized or purified beta-apo-beta'-carotenoic acid (apo-8'-CA), beta-apo-14'-carotenoic acid (apo-14'-CA), beta-cyclocitral (BCL), beta-cyclogernanic acid (BCA), beta-ionone (BI), beta-ionylideneacetaldehyde (BIA) beta-ionylideneacetic acid (BIAA) and a C13 ketone, beta-apo-13-carotenone (C13). None of the apocarotenoids tested showed significant transactivation activity for the RARs when compared with all-trans retinoic acid (RA). The results suggest that biological effects of these apocarotenoids are through mechanisms other than activation of RAR alpha and beta.