Ginsenoside Rb1 inhibits tube‐like structure formation of endothelial cells by regulating pigment epithelium‐derived factor through the oestrogen β receptor

Abstract

Background and purpose: Angiogenesis is a crucial step in tumour growth and metastasis. Ginsenoside-Rb1 (Rb1), the major active constituent of ginseng, potently inhibits angiogenesis in vivo and in vitro. However, the underlying mechanism remains unknown. We hypothesized that the potent anti-angiogenic protein, pigment epithelium-derived factor (PEDF), is involved in regulating the anti-angiogenic effects of Rb1. Experimental approaches: Rb1-induced PEDF was determined by real-time PCR and western blot analysis. The antiangiogenic effects of Rb1 were demonstrated using endothelial cell tube formation assay. Competitive ligand-binding and reporter gene assays were employed to indicate the interaction between Rb1 and the oestrogen receptor (ER). Key results: Rb1 significantly increased the transcription, protein expression and secretion of PEDF. Targeted inhibition of PEDF completely prevented Rb1-induced inhibition of endothelial tube formation, suggesting that the anti-angiogenic effect of Rb1 was PEDF specific. Interestingly, the activation of PEDF occurred via a genomic pathway of ERb. Competitive ligandbinding assays indicated that Rb1 is a specific agonist of ERb, but not ERa. Rb1 effectively recruited transcriptional activators and activated an oestrogen-responsive reporter gene. Furthermore, Rb1-mediated PEDF activation and the subsequent inhibition of tube formation were blocked by the ER antagonist ICI 182,780 or transfection of ERb siRNA, indicating ERb dependence. Conclusions and implications:Here we show for the first time that the Rb1 suppressed the formation of endothelial tube-like structures through modulation of PEDF via ERb. These findings demonstrate a novel mechanism of the action of this ginsenoside that may have value in anti-cancer and anti-angiogenesis therapy.

Intranasal Ginsenoside Rb1 Targets the Brain and Ameliorates Cerebral Ischemia/Reperfusion Injury in Rats

“…31) GRb1 has been proven to activate estrogen receptor (ER)-a and -b. 32) This activation serves as a bias for the effects of GRb1 in some situations, such as attenuating capillary morphogenesis 33) and protecting specific neurons against oxidative stress. 34) Estrogen can protect the brain from cerebral ischemia through anti-apoptosis, interacting with neurotrophic factors and inducing neurogenesis.…”

A ginseng‐derived oestrogen receptor β (ERβ) agonist, Rb1 ginsenoside, attenuates capillary morphogenesis

“…In the present issue of the British Journal of Pharmacology, Leung et al (2007) report on the ability of ginsenoside Rb1 to inhibit tube-like network formation on Matrigel. It should be pointed out that Sengupta et al (2004), using similar concentrations of Rb1, showed an increase in FGF-2 þ TNFa and VEGF þ TNF-a-stimulated tubulogenesis in fibrin gels and matrix-driven network formation on the Matrigel.…”

“…In their publication, Leung et al (2007) propose that Rb1 exerts its effects on PEDF expression by activating the ERb (Figure 1). It has been previously proposed that Rb1 stimulates ER without physically interacting with them (Cho et al, 2004).…”

“…It should, however, be kept in mind that the cells used by Cho et al (2004), MCF-7, express high levels of the ERa. In the article by Leung et al (2007) Figure 1 Schematic representation of the proposed mechanism of action for ginsenoside Rb1. R1 is -Glc 2 -1 Glc, R2 is -H and R3 -Glc 6 -1 Glc.…”

Ginseng (Panax quinquefolius) Attenuates Leptin-Induced Cardiac Hypertrophy through Inhibition of p115Rho Guanine Nucleotide Exchange Factor-RhoA/Rho-Associated, Coiled-Coil Containing Protein Kinase-Dependent Mitogen-Activated Protein Kinase Pathway Activation

“…The chemical structures of ginsenosides, which are triterpene saponins and are considered the primary active constituents contributing to the medicinal effects of ginseng (Attele et al, 1999), have been compared with steroidal structures such as estrogen. Leung et al (2007) alluded to the competitive binding of the specific ginsenoside Rb1 (the predominant ginsenoside of North American ginseng), selective to the estrogen receptor ␤, where it was theorized to be engulfed with the bound ginsenoside through endocytosis into the cytoplasm in which it translocates into the nucleus to bind to transcription factors eliciting its effects as an antiangiogenic factor. Indeed, we previously have shown that estrogen (as 17␤-estradiol) exerts a pro-hypertrophic effect on cultured ventricular myocytes at very low (1 pM) concentrations but has antihypertrophic actions at nanomolar concentrations (Kilić et al, 2009).…”