Anti-angiogenic activity and mechanism of kaurane diterpenoids from Wedelia chinensis

Abstract

Background: Wedelia chinensis is a traditional medicinal herb used in Asia and it has been reported to possess various bioactivities including anti-inflammatory and anticancer effects. However, its anti-angiogenic activity has never been reported.

Purpose: To determine the most potent anti-angiogenic component in W. chinensis and its molecular mechanism of action.

Study design: Initially, the active fraction of the plant was studied. Then, we determined the active components of the fraction and explored the mechanism of the most active compound.

Methods: The ethanol extract of W. chinensis and its four fractions with different polarities were evaluated for their anti-angiogenic activity in the Zebrafish model using quantitative endogenous alkaline phosphatase (EAP) assay. The molecular mechanism of the most active compound from the active fraction was studied using the real-time polymerase chain reaction (PCR) assay on Zebrafish embryos. The inhibitory effect of the most active compound on the proliferation, invasion and tube formation steps of angiogenesis was evaluated using the vascular endothelial growth factor (VEGF)-induced human umbilical vein endothelial cells (HUVECs) model, and the influences of the active compound on tyrosine phosphorylation of VEGF receptor (VEGFR-2) and its downstream signal pathway were evaluated by western blotting assay. Moreover, its anti-angiogenic effect was further evaluated by the VEGF-induced sprouts formation on aortic ring assay and the VEGF-induced vessel formation of mice on matrigel plug assay, respectively.

Results: Petroleum ether (PE) fraction of the plant displayed potent anti-angiogenic activity. Twelve kaurane diterpenoids (1-12) isolated from this fraction showed quite different effects. Compounds 9-12 could dose-dependently inhibit vessel formation in the Zebrafish embryos while the others showed little inhibitory effect. Among the active diterpenoids, compound 10, 3α-cinnamoyloxy-9ß-hydroxy-ent-kaura-16-en-19-oic acid (CHKA), possessed the strongest effect, and it affected multiple molecular targets related to angiogenesis including VEGF and angiopoietin in Zerbrafish. Moreover, CHKA significantly inhibited a series of VEGF-induced angiogenesis processes including proliferation, invasion, and tube formation of endothelial cells. Besides, it directly inhibited VEGFR-2 tyrosine kinase activity and its downstream signaling pathways in HUVECs. CHKA also obviously inhibited sprouts formation of aortic ring, and block vessel formation in mice.

Conclusion: Our findings demonstrate that kaurane diterpenoids is one of anti-angiogenic components in W. chinensis, and CHKA may become a promising candidate for the development of anti-angiogenic agent.

Keywords: Anti-angiogenesis; Kaurane diterpenoid; Mechanism; Wedelia chinensis; Zerbrafish.