Pinellic Acid Isolated from Quercetin-rich Onions has a Peroxisome Proliferator-Activated Receptor-Alpha/Gamma (PPAR-α/γ) Transactivation Activity

Quercetin, a flavonol, is a functional compound that is abundant in onions and is known to have antioxidant and anti-inflammatory effects. Quercetin and its glucoside are known to function as peroxisome proliferator-activated receptor (PPAR) ligands and showed high PPAR-<i>α</i> transactivation activity but little PPAR-<i>γ</i> transactivation activity in some reports. In this study, we demonstrated that an aqueous extract of a quercetin-rich onion cultivar increased transactivation activities not only of PPAR-<i>α</i> but also of PPAR-<i>γ</i>. We isolated (9<i>S</i>,12<i>S</i>,13<i>S</i>)-(10<i>E</i>)-9,12,13-trihydroxyoctadec-10-enoic acid (pinellic acid) obtained from the aqueous extract using PPAR-<i>γ</i> transactivation as an index. Furthermore, it was revealed that pinellic acid could transactivate PPAR-<i>α</i>. Our findings are the first report mentioned showing that trihydroxyoctadec-10-enoic acids showed PPAR-<i>α</i>/<i>γ</i> transactivation activities.