Curcumin inhibits the formation of capillary-like tubes by rat lymphatic endothelial cells

The natural pigments curcumin and berberine have been shown to exhibit a variety of pharmacologic effects including anti-inflammatory, anti-cancer, and anti-metastatic properties. Here, we investigated the anti-lymphangiogenic effect with an in vitro tube-forming model using conditionally immortalized lymphatic endothelial TR-LE cells, a newly established cell line originating from the thoracic duct of a transgenic rat expressing the temperature-sensitive SV40 large T-antigen. Curcumin, but not berberine, exhibited a dose-dependent inhibition of the formation of capillary-like tubes by TR-LE cells without affecting cell viability and adhesion to Matrigel. To address the molecular mechanisms involved, we performed experiments with specific inhibitors against putative targets of curcumin, including 1 kappa B kinase (IKK), epidermal growth factor receptor (EGFR), phosphatidylinositol-3 kinase (PI3K)/Akt, and matix metalloproteinases (MMPs). While the IKK-2 inhibitor VI and EGFR tyrosine kinase inhibitors gefitinib and PD153035 had no effect, both the PI3K inhibitor LY294002 and the MMP inhibitor GM6001 shortened the tubes by approximately 50%. Western blot analysis and gelatin zymography revealed that curcumin, but not berberine, has an inhibitory effect on the phosphorylation of Akt and enzymatic activity of MMP-2 in TR-LE cells. These results suggest that curcumin exerts its inhibitory effect on lymphangiogenesis partly through Akt and MMP-2. (C) 2006 Elsevier Ireland Ltd. All rights reserved.