Mechanism of the vasodilator effect of Euxanthone in rat small mesenteric arteries

Nitric-Oxide-Mediated Vasodilation of Bioactive Compounds Isolated from Hypericum revolutum in Rat Aorta

Simple Summary

Hypericum revolutum (HR) is reported to produce vasodilating activity in phenylephrine-precontracted aortae, where the chloroform fraction is the most potent. Chemical investigation of this fraction yielded two new compounds, revolutin (1) and hyperevolutin C (2), along with three known metabolites, β-sitosterol (3), euxanthone (4), and 2,3,4-tirmethoxy xanthone (5). Isolated compounds 1, 2, 3, and 5 produce vasodilation activities that are dependent on endothelial nitric oxide release.

Abstract

Vasodilators are an important class in the management of hypertension and related cardiovascular disorders. In this regard, the chloroform fraction of Hypericum revolutum (HR) has been reported to produce vasodilating activity in phenylephrine-precontracted aortae. The current work aims to identify the active metabolites in the chloroform fraction of HR and illustrate the possible mechanism of action. The vasodilation activities were investigated using the isolated artery technique. NO vascular release was assessed by utilizing the NO-sensitive fluorescent probe DAF-FM. Free radical scavenging capacity was assessed utilizing DPPH. Chemical investigation of this fraction yielded two new compounds, revolutin (1) and hyperevolutin C (2), along with three known metabolites, β-sitosterol (3), euxanthone (4), and 2,3,4-tirmethoxy xanthone (5). Compounds 1, 2, 3, and 5 showed significant vasodilation activities that were blocked by either endothelial denudation or L-NAME (nitric oxide synthase inhibitor), pointing towards a role of endothelial nitric oxide in their activities. In confirmation of this role, compounds 1–3 showed a significant release of NO from isolated vessels, as indicated by DAF-FM. On the other hand, only compound 5 showed free radical scavenging activities, as indicated by DPPH. In conclusion, isolated compounds 1, 2, 3, and 5 produce vasodilation activities that are dependent on endothelial nitric oxide release.

Euxanthone represses the proliferation, migration, and invasion of glioblastoma cells by modulating STAT3/SHP-1 signaling

Glioblastoma is one of the most prevalent primary malignant brain tumors. Glioblastoma often develops resistance to conventional chemoradiotherapy, and thus, new ways to treat glioblastoma are urgently required. The aim of this study was to investigate the effect of euxanthone on the anticancer activities of glioblastoma and its potential mechanism. The U87 and U251 glioblastoma cell lines were cultured in media containing different concentrations of euxanthone. CCK-8 and colony formation assay were used to evaluate the cell proliferation. Cell migration and invasion were evaluated by wound healing and Transwell assays. Flow cytometry was used to assess the cell cycle and apoptosis rate. TUNEL assay was also employed to evaluate the apoptosis rate. Gene and protein expressions were determined by RT-qPCR and western blotting, respectively. A xenograft model was established to evaluate the efficacy of euxanthone in vivo. Euxanthone significantly repressed cell viability, migration, invasion, and epithelial-to-mesenchymal transition of U87 and U251 cells; and increased the rate of apoptosis. Western blotting results revealed that the levels of p21, p27, cleaved caspase-3, Bax, TIMP-3, and E-cadherin were upregulated while, the levels of CDK4, CDK6, pro-caspase-3, Bcl-2, MMP-2, MMP-9, N-cadherin, and Vimentin were downregulated by euxanthone. In addition, the expression of p-STAT3 was decreased, while the expression of SHP-1 was upregulated by euxanthone. We proposed that euxanthone could repress the malignant behavior of glioblastoma cells through suppression of STAT3 phosphorylation and activation of SHP-1. Further, in vivo data demonstrated that euxanthone repressed tumor growth and promoted apoptosis.

Cytoprotective effects of euxanthone against ox-LDL-induced endothelial cell injury is mediated via Nrf2

AIM

Atherosclerosis (AS) is a chronic condition of the arterial vessels and a risk factor for myocardial infarction and stroke. Euxanthone is a xanthone compound extracted from Polygala caudata, and shows vasodilatory action. The aim of this study was to determine the potential pharmacological effects of euxanthone against oxidized low-density lipoprotein (ox-LDL)-induced endothelial cell injury.

MATERIAL AND METHODS

Human umbilical vein endothelial cells (HUVECs) were exposed to ox-LDL, following pre-treatment with different concentrations of euxanthone. Viability, apoptosis and DNA fragmentation were respectively assessed by CCK-8 assay, Annexin-V/PI staining and TdT-mediated dUTP Nick-End Labeling (TUNEL) assay. The cellular levels of malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) were analyzed by enzyme linked immune-sorbent assays (ELISA), and reactive oxygen species (ROS) levels using dichlorodihydrofluorescin diacetate (DCFH) staining. Quantitative RT-PCR and Western blotting were respectively used to analyze the expression levels of specific mRNAs and proteins. HUVECs were transfected with Nrf2 siRNA to induce knockdown of the latter.

KEY FINDINGS

Euxanthone pre-treatment rescued the HUVECs from ox-LDL-induced cytotoxicity, apoptosis and DNA fragmentation in a dose-dependent manner. In addition, euxanthone also significantly reversed ox-LDL-triggered loss of mitochondrial membrane potential (MMP), cytochrome C release from mitochondria to cytosol, cleavage of caspase-3 and PARP, and increase in Bax/Bcl-2 ratio. Pre-treatment with euxanthone markedly suppressed ox-LDL-induced ROS generation and inhibition of antioxidant enzymes, as well as the up-regulation of pro-inflammatory factors like MCP-1, IL-1β and TNF-α in the HUVECs. Euxanthone up-regulated and activated Nrf2 by repressing Keap1, and increased the expression of its downstream genes HO-1 and NQO-1. Nrf2 knockdown abrogated the cyto-protective, anti-apoptotic, anti-oxidant and anti-inflammatory effects of euxanthone in ox-LDL-treated HUVECs. Finally, euxanthone activated Nrf2 via the MAPK pathway and blocking the latter likewise negated the protective effects of euxanthone against cell ox-LDL.

SIGNIFICANCE

Euxanthone protected HUVECs against the oxidative and inflammatory damage induced by ox-LDL, indicating its potential as a novel therapeutic agent for AS.

Euxanthone suppresses tumor growth and metastasis in colorectal cancer via targeting CIP2A/PP2A pathway

AIM

Colorectal cancer (CRC) accounts for over 600,000 deaths annually worldwide. Euxanthone is a flavonoid compound extracted from Polygala caudata, with documented anti-neoplastic actions. The current study aimed to determine the therapeutic potential of euxanthone in CRC.

METHODS AND MATERIALS

Cell Counting Kit-8 (CCK-8) assay was used to analyze the effect of euxanthone on the cell viability, and apoptosis was detected by the TUNEL assay. The in vitro migratory capacity was determined by wound healing and the invasiveness was assessed by Transwell assay. Western blotting was used to determine the level of relevant proteins. Furthermore, a CRC xenograft murine model was used to analyze the therapeutic efficacy of euxanthone in vivo. Isobaric tags for relative and absolute quantification (iTRAQ) was then performed to identify the potential targets of euxanthone. To validate the role of cancerous inhibitor of PP2A (CIP2A) in the anti-cancer effects of euxanthone, plasmid overexpressing CIP2A and shRNA targeting CIP2A were used in in vitro assays.

KEY FINDINGS

Euxanthone decreased cell viability and increased apoptosis in CRC cells, in addition to restraining migration, invasion and EMT. Similarly, euxanthone also effectively suppressed tumor growth and pulmonary metastasis in vivo. iTRAQ analysis identified CIP2A as the primary target responsible for the anticancer effects of euxanthone. The mediatory role of CIP2A was validated when the anticancer activity of euxanthone was significantly blocked by CIP2A overexpression, while CIP2A knockdown sensitized the CRC cells to euxanthone.

SIGNIFICANCE

Euxanthone exerts anti-cancer effects in vitro and in vivo in CRC by targeting CIP2A/PP2A signaling.

Euxanthone inhibits glycolysis and triggers mitochondria-mediated apoptosis by targeting hexokinase 2 in epithelial ovarian cancer

Epithelial ovarian cancer (EOC) is one of the most prevalent gynaecological cancers. Euxanthone, an active ingredient of the medicinal plant Polygala caudata, exhibits a selective cytotoxic effect in tumour cells. The present study was aimed to determine whether euxanthone could suppress ovarian tumour growth, and to study the relevant mechanism. Two EOC cell lines, SKOV3 and A2780, were used as the in vitro model and treated with euxanthone. Cell viability and apoptosis were assayed using Cell Counting Kit-8 (CCK-8) and Annexin-V FITC/PI staining, respectively. Commercially available kits were used to measure the glucose consumption, lactate production, and intracellular ATP levels. Western blots assay was conducted to examine the level of apoptotic markers. To examine the roles of HK2 and STAT3 in the anti-tumour effect of euxanthone, cells were transfected with vectors overexpressing HK2 or STAT3, and assayed as above. Finally, SKOV3 cells were injected to mice models to appreciate the anti-neoplastic effect of euxanthone in vivo. We found that euxanthone impaired the cell viability and induced apoptosis via the intrinsic pathway in a concentration-dependent fashion in both SKOV3 and A2780 cells. Euxanthone also caused inhibition of glycolysis. Apoptosis and glycolysis inhibition was mediated by the downregulation of HK2, which in turn was a result of STAT3 inactivation. In vivo experiments also supported that euxanthone could exert anti-cancer activities without general toxicity. In conclusion, euxanthone triggered mitochondrial apoptosis and inhibited glycolysis in EOC cells.

SIGNIFICANCE OF THE STUDY

Euxanthone triggered mitochondrial apoptosis and inhibited glycolysis in EOC cells. Our findings provide preliminary experimental data that support further studies on the potential therapeutic role of euxanthone in ovarian cancer.

Autophagy is a pro-survival mechanism in ovarian cancer against the apoptotic effects of euxanthone

BACKGROUND

Ovarian cancer is one of the most prevalent gynecological malignancies and thus the development of novel therapeutic agents for managing ovarian cancer is imperative. Euxanthone, a xanthone derived from Polygala caudata, has been found to exert cytotoxic effects on cancerous cells. This study was designed to assess the role of euxanthone in ovarian cancer.

METHODS AND MATERIALS

Cell Counting Kit-8 (CCK-8) assay was utilized to assess the viability of human ovarian cancer SKOV3 and OVCAR3 cell lines. The population of apoptotic cells was measured by flow cytometry and TUNEL assay. Cell cycle analysis was carried out by flow cytometry. Autophagy was determined by western blotting to detect LC3-II, p62 degradation, and Beclin1 expression, by transfection with GFP-LC3B expressing plasmid and by flow cytometry. To examine the role of STAT3 in the induction of autophagy and apoptosis by euxanthone, STAT3 expression was suppressed using siRNA. Moreover, xenograft model was established to evaluate the therapeutic effect of euxanthone in vivo.

RESULTS

Euxanthone decreased cell viability and blocked cell cycle progression at G2/M phase. Euxanthone induced apoptotic cell death in a caspase-dependent manner in ovarian cancer cells. Euxanthone treatment also led to the accumulation of autophagosomes. We also found that inhibition of autophagy by 3-MA or Beclin1 siRNA enhanced the pro-apoptotic effect of euxanthonein ovarian cancer cells. Furthermore, our results revealed that euxanthone induced apoptosis and autophagy by modulating pSTAT3/Bcl-2 signaling. In vivo data also demonstrated that euxanthone exerted anti-tumor activities without harming healthy tissues.

CONCLUSION

Euxanthone induced cytoprotective autophagy in ovarian cancer cells, which negatively contributed to its anti-tumor activities. Our findings provide preliminary experimental data that support further investigation on the therapeutic efficacy of euxanthone in ovarian cancer.