Betulinic Acid Inhibits Growth Factor‐induced in vitro Angiogenesis via the Modulation of Mitochondrial Function in Endothelial Cells

Betulinic acid (BetA), a pentacyclic triterpene, is a selective apoptosis‐inducing agent that works directly in mitochondria. Recent study has revealed that BetA inhibits in vitro enzymatic activity of aminopeptidase N (APN, EC 3.4.11.2), which is known to play an important role in angiogenesis, but the anti‐angiogenic activity of BetA has not been reported yet. Data presented here show that BetA potently inhibited basic fibroblast growth factor (bFGF)‐induced invasion and tube formation of bovine aortic endothelial cells (BAECs) at a concentration which had no effect on the cell viability. To access whether the anti‐angiogenic nature of BetA originates from its inhibitory action against aminopeptidase N (APN) activity, the effect of BetA on APN was investigated. Surprisingly, BetA did not inhibit in vivo APN activity in endothelial cells or APN‐positive tumor cells. On the other hand, BetA significantly decreased the mitochondrial reducing potential, and treatment with mitochondrial permeability transition (MPT) inhibitors attenuated BetA‐induced inhibition of endothelial cell invasion. These results imply that anti‐angiogenic activity of BetA occurs through a modulation of mitochondrial function rather than APN activity in endothelial cells.