Apigenin: a promising molecule for cancer prevention

Inhibitory effect of liquiritigenin on migration via downregulation proMMP-2 and PI3K/Akt signaling pathway in human lung adenocarcinoma A549 cells

Liquiritigenin (LQ) is a flavanone extracted from Glycyrrhizae, which has multiple biological effects, such as antiinflammation and anticancer. This study is the first to investigate the effect of LQ on the migration of human lung adenocarcinoma A549 cells in vitro. First, LQ exhibited inhibitory effects on the adhesion and migration of A549 cells in the absence of cytotoxicity. Gelatin zymography and Western blot analysis showed that LQ significantly reduced the expression of promatrix metalloproteinase-2 (proMMP-2) in A549 cells in terms of both activity and protein level. Second, LQ inhibited the phosphorylation of Akt and activated the phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1/2). Furthermore, the treatment of inhibitors specific for Akt (LY294002) and ERK1/2 (U0126) to A549 cells resulted in reduced activity of proMMP-2. These results suggested that the inhibition on proMMP-2 expression by LQ may be through suppression on PI3K/Akt signaling pathway, which in turn led to the inhibition of lung adenocarcinoma A549 cells migration. However, activation of ERK might not be involved in the regulation of proMMP-2. Taken together, LQ may be considered as a potential interfering agent of cancer progression.

Enhancement of pentobarbital-induced sleep by apigenin through chloride ion channel activation

This experiment was performed to investigate whether apigenin has hypnotic effects and/or enhances pentobarbital-induced sleep behaviors through the GABAergic systems. Apigenin prolonged sleep time induced by pentobarbital similar to muscimol, a GABA(A) receptors agonist. Apigenin also increased sleep rate and sleep time in the combined administration with pentobarbital at the sub-hypnotic dosage, and showed synergic effects with muscimol in potentiating sleep onset and enhancing sleep time induced by pentobarbital. In addition, both of apigeinin and pentobarbital increased chloride influx in primary cultured cerebellar granule cells. Apigenin increased glutamate decarboxylase (GAD) and had no effect on the expression of GABA(A) receptor α-, β-, γ-subunits in n hippocampus of mouse brain, showing different expression of subunits from pentobarbital treatment group. In conclusion, it is suggested that apigenin augments pentobarbital-induced sleep behaviors through chloride ion channel activation.

Identification and analysis of the active phytochemicals from the anti-cancer botanical extract Bezielle

Bezielle is a botanical extract that has selective anti-tumor activity, and has shown a promising efficacy in the early phases of clinical testing. Bezielle inhibits mitochondrial respiration and induces reactive oxygen species (ROS) in mitochondria of tumor cells but not in non-transformed cells. The generation of high ROS in tumor cells leads to heavy DNA damage and hyper-activation of PARP, followed by the inhibition of glycolysis. Bezielle therefore belongs to a group of drugs that target tumor cell mitochondria, but its cytotoxicity involves inhibition of both cellular energy producing pathways. We found that the cytotoxic activity of the Bezielle extract in vitro co-purified with a defined fraction containing multiple flavonoids. We have isolated several of these Bezielle flavonoids, and examined their possible roles in the selective anti-tumor cytotoxicity of Bezielle. Our results support the hypothesis that a major Scutellaria flavonoid, scutellarein, possesses many if not all of the biologically relevant properties of the total extract. Like Bezielle, scutellarein induced increasing levels of ROS of mitochondrial origin, progressive DNA damage, protein oxidation, depletion of reduced glutathione and ATP, and suppression of both OXPHOS and glycolysis. Like Bezielle, scutellarein was selectively cytotoxic towards cancer cells. Carthamidin, a flavonone found in Bezielle, also induced DNA damage and oxidative cell death. Two well known plant flavonoids, apigenin and luteolin, had limited and not selective cytotoxicity that did not depend on their pro-oxidant activities. We also provide evidence that the cytotoxicity of scutellarein was increased when other Bezielle flavonoids, not necessarily highly cytotoxic or selective on their own, were present. This indicates that the activity of total Bezielle extract might depend on a combination of several different compounds present within it.

Apigenin-induced suicidal erythrocyte death

Apigenin, a flavone in fruits and vegetables, stimulates apoptosis and thus counteracts cancerogenesis. Erythrocytes may similarly undergo suicidal cell death or eryptosis, characterized by cell shrinkage and phosphatidylserine exposure at the cell surface. Triggers of eryptosis include increase of cytosolic Ca(2+) activity ([Ca(2+)](i)), ceramide formation and ATP depletion. The present study explored the effect of apigenin on eryptosis. [Ca(2+)](i) was estimated from Fluo3-fluorescence, cell volume from forward scatter, phosphatidylserine exposure from annexin V binding, hemolysis from hemoglobin release, ceramide utilizing antibodies, and cytosolic ATP with luciferin-luciferase. A 48 h exposure to apigenin significantly increased [Ca(2+)](i) (≥ 1 μM), increased ceramide formation (15 μM), decreased ATP concentration (15 μM), decreased forward scatter (≥ 1 μM), and increased annexin V binding (≥ 5 μM) but did not significantly modify hemolysis. The effect of 15 μM apigenin on annexin V binding was blunted by Ca(2+) removal. The present observations reveal novel effects of apigenin, i.e. stimulation of Ca(2+) entry, ceramide formation and ATP depletion in erythrocytes with subsequent triggering of suicidal erythrocyte death, paralleled by cell shrinkage and phosphatidylserine exposure.

Proteomic study of granulocytic differentiation induced by apigenin 7-glucoside in human promyelocytic leukemia HL-60 cells

BACKGROUND

Nutritional factors is one of the most important regulators in the progression of cancer. Some dietary elements promote the growth of cancer but others, such as plant-derived compounds, may reverse this process.

PURPOSE

We tried to investigate yet another approach of cancer prevention through cancer cell differentiation, using a common non-mutagenic flavonoid apigenin 7-glucoside.

METHODS

HL-60 cells were treated with or without apigenin 7-glucoside. Cell proliferation was measured by MTT assay, and the cell cycle distribution was estimated by propidium iodide staining of DNA. To determine cellular differentiation, cell surface differentiation markers CD11b and CD14 were used. Two-dimensional gel electrophoresis was then performed to identify proteins that may be important in HL-60 cell differentiation following apigenin 7-glucoside treatment.

RESULTS

Apigenin 7-glucoside inhibited HL-60 cell growth, dose- and time-dependently, but did not cause apoptosis. The distribution of cells at different stages in the cell cycle indicated an accumulation of treated cells in G(2)/M phase. Moreover, apigenin 7-glucoside induced granulocytic differentiation of HL-60 cells. Ten proteins that might play essential role in granulocytic differentiation were identified by proteomics.

CONCLUSIONS

A complete understanding of the preventive effects of plant-based diet on cancer depends on the mechanisms of action of different plant components on processes. We hope these findings may contribute to the understandings of the different approaches for chemoprevention of cancer.

Involvement of catalase in the apoptotic mechanism induced by apigenin in HepG2 human hepatoma cells

Apigenin has been reported to inhibit proliferation of cancer cells; however, the mechanism underlying its action is not completely understood. Here, we evaluated the effects of apigenin on the levels of expression and activity of antioxidant enzymes, and the involvement of ROS in the mechanism of cell death induced by apigenin in HepG2 human hepatoma cells. Upon treatment with apigenin, HepG2 cells displayed a reduction in cell viability in a dose- and time-dependent manner, and some morphological changes. In addition, apigenin treatment induced ROS generation and significantly decreased the mRNA levels and activity of catalase and levels of intracellular GSH. On the other hand, apigenin treatment did not alter the expression or activity levels of other antioxidant enzymes. Addition of exogenous catalase significantly reduced the effects of apigenin on HepG2 cell death. We also demonstrated that HepG2 cells are more sensitive to apigenin-mediated cell death than are primary cultures of mouse hepatocytes, suggesting a differential toxic effect of this agent in tumor cells. Our results suggest that apigenin-induced apoptosis in HepG2 cells may be mediated by a H(2)O(2)-dependent pathway via reduction of the antioxidant defenses.

Apigenin affects leptin/leptin receptor pathway and induces cell apoptosis in lung adenocarcinoma cell line

BACKGROUND

Apigenin, a common edible plant flavonoid, is a well characterised antioxidant. The adipokine leptin exerts proliferative and anti-apoptotic activities in a variety of cell types. In cancer cells, apigenin may induce a pro-apoptotic pathway whereas leptin has an anti-apoptotic role. The purpose of the study is to investigate the role of apigenin and of leptin/leptin receptor pathway on proliferation and on apoptosis in lung adenocarcinoma.

METHODS

Immunocytochemistry, flow cytometry and RT-q-RT PCR, were used to investigate the expression and modulation of leptin receptors on the lung adenocarcinoma cell line A549 in presence or absence of apigenin and of leptin, alone or combined. Clonogenic test to evaluate cell proliferation was assessed. Exogenous leptin binding to its receptors by flow cytometry, reactive oxygen species (ROS) by dichlorofluorescein diacetate analysis, cell death by ethidium bromide and apoptosis by annexin V analysis were assessed. Apoptosis was assessed also in presence of lung adenocarcinoma pleural fluids (PF) (n=6).

RESULTS

A549 express leptin/leptin receptor pathway and its expression is upregulated by apigenin. Apigenin alone or combined with leptin significantly decreases cell proliferation and significantly increases the spontaneous release of ROS, with augmented cell death and apoptosis, this latter also in the presence of lung adenocarcinoma PF. Leptin alone significantly increases cell proliferation and significantly decreases cell death.

CONCLUSIONS

These results strongly suggest the potential utility of the flavonoid apigenin in the complementary therapeutic approach of patients with lung adenocarcinoma.

Mucin 1 C-terminal subunit oncoprotein is a target for small-molecule inhibitors

Mucin 1 (MUC1) is a heterodimeric protein that is overexpressed in diverse human carcinomas. The oncogenic function of the MUC1 C-terminal subunit (MUC1-C) subunit is dependent on the formation of dimers through its cytoplasmic domain; however, it is not known whether MUC1-C can be targeted with small-molecule inhibitors. In the present work, an assay using the MUC1-C cytoplasmic domain (MUC1-CD) was established to screen small-molecule libraries for compounds that block its dimerization. Using this approach, the flavone apigenin was identified as an inhibitor of MUC1-CD dimerization in vitro and in cells. By contrast, the structurally related flavone baicalein was ineffective in blocking the formation of MUC1-CD dimers. In concert with these results, apigenin, and not baicalein, blocked the localization of MUC1-C to the nucleus. MUC1-C activates MUC1 gene expression in an autoinductive loop, and apigenin, but not baicalein, treatment was associated with down-regulation of MUC1 mRNA levels and MUC1-C protein. The results also demonstrate that apigenin-induced suppression of MUC1-C expression is associated with apoptotic cell death and loss of clonogenic survival. These findings represent the first demonstration that the MUC1-C cytoplasmic domain is a target for the development of small-molecule inhibitors.

Calcium- and phosphatidylinositol 3-kinase/Akt-dependent activation of endothelial nitric oxide synthase by apigenin

AIMS

The generation of NO by endothelial nitric oxide synthase (eNOS) plays a major role in maintaining cardiovascular homeostasis. The objective of our present study was to investigate the effects of the flavone compound, apigenin, on eNOS activity and elucidate the molecular mechanisms underlying these effects in endothelial cells (ECs).

MAIN METHODS

Bovine artery endothelial cells (BAECs) were exposed in a serum-free medium to apigenin. Cell viability was measured using an Alamar blue assay. The production of intracellular NO was determined using DAF-2/DA. The level of protein was examined by Western blotting. The intracellular Ca(2+) was measured using a fluorescent dye, Fura 2-AM.

KEY FINDINGS

Apigenin significantly induced NO production after 6h of treatment. This production was inhibited by pretreatment with the eNOS inhibitor, N(ω)-nitro l-arginine methyl ester (L-NAME). However, treatment with apigenin did not alter the eNOS protein levels but induced a sustained activation of eNOS Ser(1179) phosphorylation. Apigenin was further found to activate ERK1/2, JNK and Akt over various time courses in ECs. Treatment with specific PI3-kinase inhibitors significantly inhibited the increases in NO production and phosphorylation. In contrast, the inhibition of (ERK)1/2, JNK and p38 had no influence on NO production. In addition, apigenin stimulates an increase in the cytosolic Ca(2+) concentration. Apigenin-induced eNOS Ser(1179) phosphorylation and NO production are calcium-dependent, as pretreatment with extracellular or intracellular Ca(2+) chelators inhibits these processes.

SIGNIFICANCE

Apigenin-induced calcium-dependent activation of eNOS is primarily mediated via phosphatidylinositol 3-kinase- and Akt pathways, and occurs independently of the eNOS protein content.