Brazilian Propolis Suppresses Angiogenesis by Inducing Apoptosis in Tube-Forming Endothelial Cells through Inactivation of Survival Signal ERK1/2.

We recently reported that propolis suppresses tumor-induced angiogenesis through tube formation inhibition and apoptosis induction in endothelial cells. However, molecular mechanisms underlying such angiogenesis suppression by propolis have not been fully elucidated. The aim of this study was to investigate the effects of ethanol extract of Brazilian propolis (EEBP) on two major survival signals, extracellular signal-regulated kinase 1/2 (ERK1/2) and Akt, and to elucidate whether changes in these signals were actually involved in antiangiogenic effects of the propolis. Detection by western blotting revealed that EEBP suppressed phosphorylation of ERK1/2, but not that of Akt. Pharmacological inhibition by U0126 demonstrated that ERK1/2 inactivation alone was enough to inhibit tube formation and induce apoptosis. It was also shown that EEBP and U0126 similarly induced activation of caspase-3 and cleavage of poly ADP-ribose polymerase (PARP) and lamin A/C, all of which are molecular markers of apoptosis. These results indicate that inhibition of survival signal ERK1/2, and subsequent induction of apoptosis, is a critical mechanism of angiogenesis suppression by EEBP.

Artepillin C (ARC) in Brazilian green propolis selectively blocks oncogenic PAK1 signaling and suppresses the growth of NF tumors in mice.

There are mainly three types of propolis whose major anticancer ingredients are entirely different: (1) CAPE (caffeic acid phenethyl ester)-based propolis in Europe, Far East and New Zealand, (2) artepillin C (ARC)-based Brazilian green propolis and (3) Brazilian red propolis. It was shown previously that NF (neurofibromatosis)-associated tumors require the kinase PAK1 for their growth, and CAPE-based propolis extracts such as Bio 30 suppress completely the growth of NF tumors in vivo by blocking PAK1 signaling. Also it was demonstrated that ARC suppresses angiogenesis, suggesting the possibility that ARC also blocks oncogenic PAK1 signaling. Here it is shown for the first time that both ARC and green propolis extract (GPE) indeed block the PAK1 signaling selectively, without affecting another kinase known as AKT. Furthermore, it was confirmed that ARC as well as GPE suppress almost completely the growth of human NF tumor xenografts in mice, as does Bio 30. These results suggest that both CAPE-based and ARC-based propolis extracts are natural anti-PAK1 remedies and could be among the first effective NF therapeutics available on the market. Since more than 70% of human cancers such as breast and prostate cancers require the kinase PAK1 for their growth, it is quite possible that GPE could be potentially useful for the treatment of these cancers, as is Bio 30.

Suppression of tumor-induced angiogenesis by Brazilian propolis: major component artepillin C inhibits in vitro tube formation and endothelial cell proliferation.

Propolis, a resinous substance collected by honeybees from various plant sources, possesses various physiological activities such as antitumor effects. We have previously shown that propolis of Brazilian origin was composed mainly of artepillin C and that its constituents were quite different from those of propolis of European origin. In this report, we examined an antiangiogenic effects of Brazilian propolis and investigated whether artepillin C was responsible for such effects. In an in vivo angiogenesis assay using ICR mice, we found that the ethanol extract of Brazilian propolis (EEBP) significantly reduced the number of newly formed vessels. EEBP also showed antiangiogenic effects in an in vitro tube formation assay. When compared with other constituents of EEBP, only artepillin C was found to significantly inhibit the tube formation of HUVECs in a concentration-dependent manner (3.13-50microg/ml). In addition, artepillin C significantly suppressed the proliferation of HUVECs in a concentration-dependent manner (3.13-50microg/ml). Furthermore, artepillin C significantly reduced the number of newly formed vessels in an in vivo angiogenesis assay. Judging from its antiangiogenic activity in vitro and in vivo, we concluded that artepillin C at least in part is responsible for the antiangiogenic activity of EEBP in vivo. Artepillin C may prove useful in the development of agents and foods with therapeutic or preventive activity against tumor angiogenesis.