The role of AMP-activated protein kinase in quercetin-induced apoptosis of HL-60 cells

Quercetin induces autophagy-associated death in HL-60 cells through CaMKKβ/AMPK/mTOR signal pathway

Acute myeloid leukemia (AML) is one of the most common malignancies of the hematopoietic progenitor cell in adults. Quercetin has gained recognition over the years because of its anti-cancer effect with minimal toxicity. Herein, we aim to investigate the anti-leukemia mechanism of quercetin and to decipher the signaling pathway of quercetin in HL-60 leukemic cells. We observed that quercetin induces apoptosis and autophagic cell death, in which both pathways play an important role in suppressing the viability of leukemia cells. Phosphorylated AMPK (p-AMPK) protein expressions are lower in primary AML cells, HL-60 cells, KG-1 and THP-1 cells than in peripheral blood monocular cells. After quercetin treatment, the expression of p-AMPK is increased while the expression of p-mTOR is decreased in a dose-dependent manner. Mechanistically, compound C, an AMPK phosphorylation inhibitor, upregulates the phosphorylation of mTOR and inhibits autophagy and apoptosis in quercetin-induced HL-60 cells, while silencing of CaMKKβ inhibits the quercetin-induced phosphorylation of AMPK, resulting in increased mTOR phosphorylation. Furthermore, silencing of CaMKKβ inhibits the autophagy in HL-60 cells. Taken together, our data delineate that quercetin plays its anti-leukemia role by inhibiting cell viability and inducing apoptosis and autophagy in leukemia cells. Quercetin inhibits the phosphorylation of mTOR by regulating the activity of AMPK, thus playing a role in the regulation of autophagy and apoptosis. CaMKKβ is a potential upstream molecule for AMPK/mTOR signaling pathway, through which quercetin induces autophagy in HL-60 cells.

LKB1 alleviates high glucose‑ and high fat‑induced inflammation and the expression of GnRH and sexual precocity‑related genes, in mouse hypothalamic cells by activating the AMPK/FOXO1 signaling pathway

Precocious puberty (PP) is a developmental disorder. Hypothalamic cells can produce gonadotropin-releasing hormone (GnRH), the final output of neuroendocrine regulation that occurs during puberty. The aim of the present study was to investigate the role of live kinase B1 (LKB1), also known as serine/threonine kinase, in the progression of PP and identify the underlying mechanisms. First, the levels of LKB1 in peripheral blood and peripheral blood mononuclear cells of children with PP were detected by reverse transcription-quantitative (RT-q) PCR or western blotting. After the GT1-7 mouse hypothalamus cell line was treated with high glucose (HG) and high fat (HF), the expression of LKB1 and GnRH was tested. LKB1 was overexpressed by transfection with a pcDNA3.1 plasmid and the levels of inflammatory factors, GnRH, PP-related factors and proteins in the AMP-activated protein kinase (AMPK)/forkhead box protein O1 (FOXO1) pathway were determined using RT-qPCR or western blot analysis. Subsequently, Compound C, an inhibitor of AMPK/FOXO1 signaling, was used to clarify whether the effects of LKB1 on PP were mediated by the regulation of this pathway. Results indicated that children with PP exhibited a lower LKB1 expression. In addition, HG and HF culture resulted in an enhanced GnRH expression and a reduced LKB1 expression in GT1-7 cells. LKB1 overexpression inhibited the contents of TNF-α, IL-6 and GnRH in in GT1-7 cells exposed to HG and HF and reduced the expression of PP-related proteins, including estrogen receptor-β, cluster of differentiation 36 and G-protein-coupled receptor. In addition, the expression of phosphorylated (p)-AMPK and p-FOXO1 was markedly downregulated following LKBI overexpression. Furthermore, compound C intervention partially diminished the inhibitory effects of LKB1-mediated upregulation on the levels of inflammation and PP-related factors. In conclusion, these results demonstrated that LKB1 alleviated HG- and HF-induced inflammation, as well as the expression of GnRH and sexual precocity-related genes, in GT1-7 cells by activating the AMPK/FOXO1 signaling pathway.

Quercetin restores corticosteroid sensitivity in cells from patients with chronic obstructive pulmonary disease

Corticosteroid resistance is a major barrier to the effective treatment of chronic obstructive pulmonary disease (COPD). Oxidative stress from cigarette smoke and chronic inflammation is likely to induce this corticosteroid insensitivity. Quercetin is a polyphenol that has been reported to be an active oxygen scavenger as well as a functional adenosine monophosphate-activated protein kinase (AMPK) activator.

The aim of this study was to investigate the effect of quercetin on corticosteroid responsiveness in COPD cells. Corticosteroid sensitivity was examined in human monocytic U937 cells exposed to cigarette smoke extract (CSE) and peripheral blood mononuclear cells (PBMC) collected from patients with COPD. Corticosteroid sensitivity was determined as the dexamethasone concentration causing 40% inhibition of tumor necrosis factor alpha-induced CXCL8 production (Dex-IC₄₀) in the presence or absence of quercetin. In U937 cells, treatment with quercetin activated AMPK and induced expression of nuclear factor erythroid 2-related factor 2, and consequently reversed CSE-induced corticosteroid insensitivity. PBMC from patients with COPD showed corticosteroid insensitivity compared with those from healthy volunteers, and treatment with quercetin restored corticosteroid sensitivity.

In conclusion, quercetin restores corticosteroid sensitivity, and has the potential to be a novel treatment in combination with corticosteroids in COPD.

Quercetin-Induced AMP-Activated Protein Kinase Activation Attenuates Vasoconstriction Through LKB1-AMPK Signaling Pathway

The vascular tone plays an important role in blood pressure and flow. It is influenced by the contraction of vascular smooth muscle cells (VSMCs), which in turn is regulated by the balance between the myosin light chain kinase (MLCK) and the phosphorylated myosin light chain (p-MLC). Quercetin is a common flavonoid which is found in many fruits and red wine. Although quercetin has been widely reported to be involved in cell proliferation, migration, and apoptosis in VSMCs, it has not yet been demonstrated whether quercetin is related to vasocontraction, a function regulated by the AMP-activated protein kinase (AMPK) signaling pathway. Accordingly, the aim of this study is to investigate the molecular mechanism through which the quercetin-activated LKB1-AMPK signaling pathway regulates the contraction of VSMCs. In cultured VSMCs, quercetin activated AMPK in a dose- and time-dependent manner. Quercetin inhibited the phenylephrine (PE)-induced expression of MLCK and p-MLC through the LKB1-AMPK signaling pathway and decreased the mRNA level of MLCK. Adenovirus-AMPK DN α1 and AMPK DN α2-transduced VSMCs displayed higher p-MLC expression. Moreover, quercetin inhibited the PE-mediated contraction in rat aorta. These data suggest that the quercetin-activated LKB1-AMPK signaling pathway regulates VSMC contraction by inhibiting MLCK and p-MLC; hence, it may be a therapeutic intervention for the treatment of cardiovascular disorders such as atherosclerosis and hypertension.

Established Human Cell Lines as Models to Study Anti-leukemic Effects of Flavonoids

Despite the extensive work on pathological mechanisms and some recent advances in the treatment of different hematological malignancies, leukemia continues to present a significant challenge being frequently considered as incurable disease. Therefore, the development of novel therapeutic agents with high efficacy and low toxicity is urgently needed to improve the overall survival rate of patients. In this comprehensive review article, the current knowledge about the anticancer activities of flavonoids as plant secondary polyphenolic metabolites in the most commonly used human established leukemia cell lines (HL-60, NB4, KG1a, U937, THP-1, K562, Jurkat, CCRF- CEM, MOLT-3, and MOLT-4) is compiled, revealing clear anti-proliferative, pro-apoptotic, cell cycle arresting, and differentiation inducing effects for certain compounds. Considering the low toxicity of these substances in normal blood cells, the presented data show a great potential of flavonoids to be developed into novel anti-leukemia agents applicable also in the malignant cells resistant to the current conventional chemotherapeutic drugs.

Quercetin is a potent anti-atherosclerotic compound by activation of SIRT1 signaling under oxLDL stimulation

SCOPE

Atherosclerosis is believed to be an independent predictor of cardiovascular diseases. A growing body of evidence suggests that quercetin is a potent antioxidant and anti-inflammatory compound. The molecular mechanisms underlying its protective effects against oxidative stress in human endothelial cells remain unclear. This study was designed to confirm the hypothesis that quercetin inhibits oxidized LDL (oxLDL) induced endothelial oxidative damage by activating sirtuin 1 (SIRT1) and to explore the role of adenosine monophosphate activated protein kinase (AMPK), which is a negative regulator of Nicotinamide adenine dinucleotide phosphate-oxidase (NADPH oxidase) and free radicals.

METHODS AND RESULTS

Human umbilical vein endothelial cells were treated with oxLDL with or without quercetin pretreatment. We found that quercetin pretreatment increased SIRT1 mRNA expression. In fact, quercetin protected against oxLDL-impaired SIRT1 and AMPK activities and reduced oxLDL-activated NOX2 and NOX4. However, silencing SIRT1 and AMPK diminished the protective function of quercetin against oxidative injuries. The results also indicated that oxLDL suppressed AKT/endothelial NO synthase, impaired mitochondrial dysfunction, and enhanced reactive oxygen species formation, activating the Nuclear Factor Kappa B (NF-κB) pathway.

CONCLUSION

These results provide new insight regarding the possible molecular mechanisms of quercetin. Quercetin suppresses oxLDL-induced endothelial oxidative injuries by activating SIRT1 and modulating the AMPK/NADPH oxidase/AKT/endothelial NO synthase signaling pathway.

The role of glycyrrhetinic acid modification on preparation and evaluation of quercetin-loaded chitosan-based self-aggregates

Quercetin (QC), a type of plant-based chemical, has been reported to own anticancer activity in vivo. However, the poor water solubility limits its pharmaceutical application. In this study, two kinds of QC-loaded self-aggregates based on O-carboxymethyl chitosan-cholic acid conjugates (CMCA) were developed to improve the drug bioavailability in which glycyrrhetinic acid (GA) modification was utilized in the nanocarrier fabrication (QC-GA-CMCA) or not (QC-CMCA). These self-aggregates were prepared by a modified ultrasound-dialysis method and the role of GA modification on the evaluation of QC-loaded self-aggregates was investigated. Transmission Electron Microscopy (TEM) images revealed the formation of spherical particles of both self-aggregates. Dynamic Light Scattering (DLS) analysis and UV-VIS spectroscopy showed that the QC-GA-CMCA had smaller size, narrower size distribution, higher drug loading and entrapment efficiency than corresponding QC-CMCA aggregates. QC-GA-CMCA showed more obvious sensitivity to acidic pH condition based on the zeta potential measurements at various pHs, and fastest drug release was observed at pH 5.7 for QC-CMCA while at pH 6.5 for QC-GA-CMCA. In addition, QC-GA-CMCA demonstrated enhanced cell cytotoxicity and higher cell apoptosis rate in vitro, and also higher AUC value and a prolonged residence time of drug in vivo.

Multi-Target Cytotoxic Actions of Flavonoids in Blood Cancer Cells

To date, cytotoxic effects of flavonoids in various cancer cells are well accepted. However, the intracellular signaling cascades triggered by these natural compounds remain largely unknown and elusive. In this mini- review, the multiplicity of molecular targets of flavonoids in blood cancer cells is discussed by demonstrating the involvement of various signaling pathways in induction of apoptotic responses. Although these data reveal a great potential of flavonoids for the development of novel agents against different types of hematological malignancies, the pleiotropic nature of these compounds in modulation of cellular processes and their interactions certainly need unraveling and further investigation.