Involvement of NO/cGMP signaling in the apoptotic and anti-angiogenic effects of beta-lapachone on endothelial cells in vitro

Neovascularization is an essential process in tumor development, it is conceivable that anti-angiogenic treatment may block tumor growth. In angiogenesis, nitric oxide (NO) is an important factor which mediates vascular endothelial cell growth and migration. beta-Lapachone (3,4-dihydro-2,2-dimethyl-2H-naphtho-1,2-b]pyran-5,6-dione), a natural product extracted from the lapacho tree (Tabebuia avellanedae), has been demonstrated to possess anti-cancer and anti-viral effects. Whether beta-lapachone can induce endothelial cell death or has an anti-angiogenic effect is still an enigma. We investigated the in vitro effect of beta-lapachone on endothelial cells, including human vascular endothelial cell line, EAhy926, and human umbilical vascular endothelial cells (HUVEC). Our results revealed that (1) the intracellular cGMP levels and the mitochondria membrane potential (MMP) decreased, and calpain and caspases were activated, during beta-lapachone-induced endothelial cell death; (2) co-treatment with calpain inhibitors (ALLM or ALLN) or the intracellular calcium chelator, BAPTA, but not the general caspase inhibitor, zVAD-fmk, provided significant protection against apoptosis by preventing the beta-lapachone-induced MMP decrease and cytoplasmic calcium increase; (3) addition of NO downregulated the beta-lapachone-induced cGMP depletion and protected the cells from apoptosis by blocking the MMP decrease and the calcium increase; and (4) exogenous NO protects endothelial cells against the cell death induced by beta-lapachone, but not the anti-angiogenic effect. From all the data above, we demonstrated that NO can attenuate the apoptotic effect of beta-lapachone on human endothelial cells and suggest that beta-lapachone may have potential as an anti-angiogenic drug.