Berberine acutely activates the glucose transport activity of GLUT1

Berberine, which has a long history of use in Chinese medicine, has recently been shown to have efficacy in the treatment of diabetes. While the hypoglycemic effect of berberine has been clearly documented in animal and cell line models, such as 3T3-L1 adipocytes and L6 myotube cells, the mechanism of action appears complex with data implicating activation of the insulin signaling pathway as well as activation of the exercise or AMP kinase-mediated pathway. There have been no reports of the acute affects of berberine on the transport activity of the insulin-insensitive glucose transporter, GLUT1. Therefore, we examined the acute effects of berberine on glucose uptake in L929 fibroblast cells, a cell line that express only GLUT1. Berberine- activated glucose uptake reaching maximum stimulation of five-fold at >40 μM. Significant activation (P < 0.05) was measured within 5 min reaching a maximum by 30 min. The berberine effect was not additive to the maximal stimulation by other known stimulants, azide, methylene blue or glucose deprivation, suggesting shared steps between berberine and these stimulants. Berberine significantly reduced the K_m of glucose uptake from 6.7 ± 1.9 mM to 0.55 ± 0.08 mM, but had no effect on the V_max of uptake. Compound C, an inhibitor of AMP kinase, did not affect berberine-stimulated glucose uptake, but inhibitors of downstream kinases partially blocked berberine stimulation. SB203580 (inhibitor of p38 MAP kinase) did not affect submaximal berberine activation, but did lower maximal berberine stimulation by 26%, while PD98059 (inhibitor of ERK kinase) completely blocked submaximal berberine activation and decreased the maximal stimulation by 55%. It appears from this study that a portion of the hypoglycemic effects of berberine can be attributed to its acute activation of the transport activity of GLUT1.