Emodin Mediates Reduction Of Inflammatory Responses And Enhancement Of Glucose Uptake Via The Pi3K/Akt Pathway In3T3-L1Adipocytes

Objectives:To investigate the potential effects of emodin on the inflammation and glucose uptake; and to understand the underlying molecular mechanisms of the actions of emodin.Methods (1) Differentiated3T3-L1adipocytes were incubated with emodin at various concentrations for24h in the presence of10ng/mL LPS. IL-6levels in cell culture medium were measured using a mouse IL-6ELISA kit; Western blot analysis was performed to measure the expression of NF-κB p50, NF-κB p65, PTEN, PKB, p-PKB.(2) Differentiated3T3-L1adipocytes were incubated with emodin at various concentrations for24h in the presence of10ng/mL LPS. Glucose uptake assays were performed by6-NBDG; The mRNA level of GluT-4in3T3-L1adipocytes wasquantified using Real Time-PCR; Western blot analysis was performed to measure the expression of GluT-4.(3) After inhibiting the activity of PI3K by the PI3K/Akt pathway inhibitor wortmannin, the levels of PKB and p-PKB were measured; IL-6levels were measured and glucose uptake assays were performed.Results (1) Emodin significantly inhibited LPS-induced secretion of IL-6in3T3-L1adipocytes(lβM p<0.05;10βM,50βM p<0.01); significantly reduced the levels of NF-κB p65andNF-KB p50in the nuclear fraction analysed of3T3-L1adipocytes; significantly reduced the levels of PTEN(p<0.01); significantly increased the ratio of p-PKB/PKB(10μM,50μM p<0.01).(2) Emodin significantly improved the glucose uptake of differentiated3T3-L1adipocytes (1μM,10μM p<0.05;50μM p<0.01). Moreover, it significantly increased the mRNA level of GluT-4(1μM,50μM p<0.05;10μM p<0.01) and cell surface GluT-4in3T3-L1adipocytes (1μM p<0.05;10μM,50μM p<0.01).(3) Wortmannin, a PI3K inhibitor, reduced the ratio of p-PKB/PKB in3T3-L1adipocytes (p<0.05) and that was revesed by emodin; markedly induced IL-6production from3T3-L1adipocytes (p<0.05), which was abrogated by emodin. In addition, Wortmannin decreaed glucose uptake (p<0.05)and that was reversed by emodin.Conclusion Emodin inhibited PTEN expression, leading to activation of PI3K/Akt signaling pathway, resulting in suppression of the nuclear translation of NF-κB p65and p50subunits and inhibition of IL-6production. Emdoin-madiated activation of the PI3K/Akt signaling pathway also led to increase glucose uptake, possibly through up-regualtion of GluT-4mRNA expression and thereby increase of cell surface GluT-4in3T3-L1adipocytes.The experimental results suggest that emodin increased insulin sensitivity maybe by inhibiting inflammation, and then improved the glucose uptake of differentiated3T3-L1adipocytes.