Ken-Ichi Nakashima1, Tohru Murakami1, Hiroki Tanabe1, Makoto Inoue2. 1. Laboratory of Natural Resources, School of Pharmacy, Aichi Gakuin University, 1-100 Kusumoto-cho, Chikusa-ku, Nagoya 464-8650, Japan. 2. Laboratory of Natural Resources, School of Pharmacy, Aichi Gakuin University, 1-100 Kusumoto-cho, Chikusa-ku, Nagoya 464-8650, Japan. Electronic address: minoue@aichi-gakuin.ac.jp.
Abstract
BACKGROUND: Brazilian green propolis (BGP), a resinous substance produced from Baccharis dracunculifolia by Africanized honey bees (Apis mellifera), is used as a folk medicine. Our present study explores the retinoid X receptor (RXR) agonistic activity of BGP and the identification of an RXR agonist in its extract. METHODS: RXRα agonistic activity was evaluated using a luciferase reporter gene assay. Isolation of the RXRα agonist from the ethanolic extract of BGP was performed using successive silica gel and a reversed phase column chromatography. The interaction between the isolated RXRα agonist and RXRα protein was predicted by a receptor-ligand docking simulation. The nuclear receptor (NR) cofactor assay was used to estimate whether the isolated RXRα agonist bound to various NRs, including RXRs and peroxisome proliferator-activated receptors (PPARs). We further examined its effect on adipogenesis in 3T3-L1 fibroblasts. RESULTS: We identified drupanin as an RXRα agonist with an EC50 value of 4.8 ± 1.0 μM. Drupanin activated three RXR subtypes by a similar amount and activated PPARγ moderately. Additionally, drupanin induced adipogenesis and elevated aP2 mRNA levels in 3T3-L1 fibroblasts. CONCLUSIONS: Drupanin, a component of BGP, is a novel RXR agonist with slight PPARγ agonistic activity. GENERAL SIGNIFICANCE: This study revealed for the first time that BGP activates RXR and drupanin is an RXR agonist in its extract.
BACKGROUND: Brazilian green propolis (BGP), a resinous substance produced from Baccharis dracunculifolia by Africanized honey bees (Apis mellifera), is used as a folk medicine. Our present study explores the retinoid X receptor (RXR) agonistic activity of BGP and the identification of an RXR agonist in its extract. METHODS: RXRα agonistic activity was evaluated using a luciferase reporter gene assay. Isolation of the RXRα agonist from the ethanolic extract of BGP was performed using successive silica gel and a reversed phase column chromatography. The interaction between the isolated RXRα agonist and RXRα protein was predicted by a receptor-ligand docking simulation. The nuclear receptor (NR) cofactor assay was used to estimate whether the isolated RXRα agonist bound to various NRs, including RXRs and peroxisome proliferator-activated receptors (PPARs). We further examined its effect on adipogenesis in 3T3-L1 fibroblasts. RESULTS: We identified drupanin as an RXRα agonist with an EC50 value of 4.8 ± 1.0 μM. Drupanin activated three RXR subtypes by a similar amount and activated PPARγ moderately. Additionally, drupanin induced adipogenesis and elevated aP2 mRNA levels in 3T3-L1 fibroblasts. CONCLUSIONS:Drupanin, a component of BGP, is a novel RXR agonist with slight PPARγ agonistic activity. GENERAL SIGNIFICANCE: This study revealed for the first time that BGP activates RXR and drupanin is an RXR agonist in its extract.