Curcumin is a direct inhibitor of glucose transport in adipocytes

Curcumin has been reported to inhibit insulin signaling and translocation of GLUT4 to the cell surface in 3T3-L1 adipocytes. We have investigated the effect of curcumin on insulin signaling in primary rat adipocytes. Curcumin (20 mu M) inhibited both basal and insulin-stimulated glucose transport (2-deoxyglucose uptake), but had no effect on insulin inhibition of lipolysis. Dose-response experiments demonstrated that curcumin (0-100 mu M) inhibited basal and insulin-stimulated glucose transport, but even at the highest concentration tested did not affect lipolysis. Inhibition was equal in cells that had been pre-incubated with curcumin and in cells to which curcumin was added immediately before the glucose transport assay. Similarly, time-course experiments revealed that the inhibitory effect of curcumin was evident at the earliest time point tested (30 s). Thus it is unlikely that inhibition of insulin signaling or of translocation of GLUT4 to the cell surface is involved in the inhibitory effect of curcumin. Curcumin did not affect the stimulatory action of insulin on phosphorylation of Ala at serine 473. We conclude that curcumin is a direct inhibitor of glucose transporters in rat adipocytes. (C) 2013 Elsevier GmbH. All rights reserved.