Inhibitory effects of baicalin in the early stage of 3T3-L1 preadipocytes differentiation by down-regulation of PDK1/Akt phosphorylation

Baicalin is a flavonoid derived from the root of Scutellaria baicalensis and exhibits a broad spectrum of biological activities including anti-adipogenesis. However, the inhibitory role of baicalin in the early stage of 3T3-L1 adipocyte differentiation relevant to the signaling up-stream of peroxisome proliferator-activated receptor-γ (PPAR-γ) and CCAAT/enhancer binding proteins (C/EBPs) expression is unclear, and is the subject of the present investigation. We used 3T3-L1 preadipocytes for adipocyte differentiation, Oil Red-O staining for the intracellular lipid accumulation assay, and real-time polymerase chain reaction (RT-PCR) for assaying the expression of major adipocyte transcription factors. We found that baicalin markedly suppressed the Akt phosphorylation in early stage of adipocytes differentiation. In addition, we observed that baicalin and LY294002 (as an inhibitor of Akt phosphorylation) significantly inhibited adipocyte differentiation by down-regulating several adipocyte-specific transcription factors, including PPAR-γ and C/EBPs in 3T3-L1 preadipocytes. Furthermore, we observed that baicalin significantly suppressed the Akt phosphorylation by inhibiting phosphoinositide-dependent kinase 1 (PDK1). These results indicate that the anti-adipogenesis effect of baicalin involves down-regulation of major transcription factors in 3T3-L1 adipocyte differentiation including PPAR-γ, C/EBP-β, and C/EBP-α through the down-regulation of PDK1/Akt phosphorylation.