[Effects of ursolic acid on c-Cbl-associated protein expression in 3T3-L1 adipocytes with insulin resistance].

Objective: To observe the effects of ursolic acid (UA) on insulin resistance and cell differentiation in 3T3-L1 adipocytes and to explore the mechanisms.

Methods: 3T3-L1 adipocytes were cultured in Dulbecco's modified Eagle's medium (DMEM) supplemented with glucose (25 mmol/L) and insulin (10(-6) mol/L) to induce insulin resistance. After culture, glucose consumption of the adipocytes was detected by glucose oxidase method and glucose uptake was detected by using tritium-marked glucose. Drug concentration for following test was determined through detecting the effects of different concentrations of UA on the activity of 3T3-L1 adipocytes with insulin resistance by methyl thiazolyl tetrazolium (MTT) staining. 3T3-L1 adipocytes with insulin resistance were cultured with DMEM, rosiglitazone, and low- and high-dose UA, and then, glucose uptake and differentiation of 3T3-L1 adipocytes were detected. Finally, real-time fluorescence quantitative polymerase chain reaction and Western blot methods were used to detect the effects of UA on expressions of adipocyte lipid binding protein (aP2), c-Cbl-associated protein (CAP) and matrix metalloproteinase-1 (MMP-1) in 3T3-L1 cells with insulin resistance.

Results: After dealing with high glucose/hyperinsulin for 24 h, insulin resistance was induced successfully in the 3T3-L1 adipocytes. The concentrations of UA were defined to be 4 to 20 μmol/L. Compared with the model group, the glucose uptake was significantly increased in the rosiglitazone group and groups treated with low- and high-dose UA (P<0.01). The differentiation levels of 3T3-L1 adipocytes in the UA groups were lower than those in the control group and the rosiglitazone group. Effects of UA on the expressions of aP2 and MMP-1 were not obvious, but UA could up-regulate expression of CAP both in mRNA and protein levels (P<0.01).

Conclusion: Low- and high-dose UA can improve the glycometabolism and differentiation of 3T3-L1 adipocytes with insulin resistance by up-regulating the expression of CAP.