A Limonoid Kihadanin B from Immature <i>Citrus unshiu</i> Peels Suppresses Adipogenesis through Repression of the Akt-FOXO1-PPARγ Axis in Adipocytes

<i>Citrus</i> limonoids are secondary metabolites and exhibit a variety of biological activities. In this study, we elucidated the suppression of adipogenesis by a <i>Citrus</i> limonoid kihadanin B and determined its molecular mechanism in mouse 3T3-L1 adipocytes. Kihadanin B was purified from the peels of immature <i>Citrus unshiu</i> by HPLC, and its chemical structure was determined by NMR and mass spectrometry. Kihadanin B reduced the lipid accumulation with the reduction of the expression levels of the adipogenic and lipogenic genes, but did not affect lipolysis in adipocytes. Phosphorylation levels of Akt and a forkhead transcriptional factor, FOXO1, a repressor of PPARγ, were lowered by kihadanin B. Furthermore, kihadanin B increased the binding level of FOXO1 to the PPARγ gene promoter in adipocytes. These results indicate that a <i>Citrus</i> limonoid kihadanin B repressed the adipogenesis by decreasing lipid accumulation through the suppression of the Akt-FOXO1-PPARγ axis in 3T3-L1 adipocytes