Modulation of Ca2+ Signals by Epigallocatechin-3-gallate(EGCG) in Cultured Rat Hippocampal Neurons

Green tea has been receiving considerable attention as a possible neuroprotective agent against neurodegenerative disease. Epigallocatechin-3-gallate (EGCG) is the major compound of green tea. Calcium signaling has profound effects on almost all aspects of neuronal function. Using digital calcium imaging and patch-clamp technique, we determined the effects of EGCG on Ca2+ signals in hippocampal neurons. The results indicated that EGCG caused a dose-dependent increase in intracellular Ca2+ ([Ca2+]i). This [Ca2+]i increase was blocked by depleting intracellular Ca2+ stores with the endoplasmic reticulum Ca2+ pump inhibitor thapsigargin and cyclopiazonic acid. Furthermore, EGCG-stimulated increase in [Ca2+]i was abolished following treatment with a PLC inhibitor. However, EGCG inhibited high-voltage activated Ca2+ currents (IHVA) and NMDA-induced inward currents (INMDA). These data suggest that EGCG triggers a cascade of events: it activates phospholipase C (PLC), mobilizes intracellular Ca2+ stores, raises the cytosolic Ca2+ levels, and inhibits the VGCC and NMDA receptors-mediated Ca2+ influx through a process that remains to be determined

Sustained proliferation in cancer: mechanisms and novel therapeutic targets

Proliferation is an important part of cancer development and progression. This is manifest by altered expression and/or activity of cell cycle related proteins. Constitutive activation of many signal transduction pathways also stimulates cell growth. Early steps in tumor development are associated with a fibrogenic response and the development of a hypoxic environment which favors the survival and proliferation of cancer stem cells. Part of the survival strategy of cancer stem cells may manifested by alterations in cell metabolism. Once tumors appear, growth and metastasis may be supported by overproduction of appropriate hormones (in hormonally dependent cancers), by promoting angiogenesis, by undergoing epithelial to mesenchymal transition, by triggering autophagy, and by taking cues from surrounding stromal cells. A number of natural compounds (e.g., curcumin, resveratrol, indole-3-carbinol, brassinin, sulforaphane, epigallocatechin-3-gallate, genistein, ellagitannins, lycopene and quercetin) have been found to inhibit one or more pathways that contribute to proliferation (e.g., hypoxia inducible factor 1, nuclear factor kappa B, phosphoinositide 3 kinase/Akt, insulin-like growth factor receptor 1, Wnt, cell cycle associated proteins, as well as androgen and estrogen receptor signaling). These data, in combination with bioinformatics analyses, will be very important for identifying signaling pathways and molecular targets that may provide early diagnostic markers and/or critical targets for the development of new drugs or drug combinations that block tumor formation and progression

Phytochemicals in Cancer Prevention and Therapy: Truth or Dare?

A voluminous literature suggests that an increase in consumption of fruit and vegetables is a relatively easy and practical strategy to reduce significantly the incidence of cancer. The beneficial effect is mostly associated with the presence of phytochemicals in the diet. This review focuses on a group of them, namely isothiocyanate, curcumin, genistein, epigallocatechin gallate, lycopene and resveratrol, largely studied as chemopreventive agents and with potential clinical applications. Cellular and animal studies suggest that these molecules induce apoptosis and arrest cell growth by pleiotropic mechanisms. The anticancer efficacy of these compounds may result from their use in monotherapy or in association with chemotherapeutic drugs. This latter approach may represent a new pharmacological strategy against several types of cancers. However, despite the promising results from experimental studies, only a limited number of clinical trials are ongoing to assess the therapeutic efficacy of these molecules. Nevertheless, the preliminary results are promising and raise solid foundations for future investigations

Redox Properties and Cytotoxicity of Synthetic Isomeric Mitochondriotropic Derivatives of the Natural Polyphenol Quercetin

Mitochondria-targeted redox-active polyphenol derivatives are being developed to affect redox processes in the organelles and as tools either to protect cells from oxidative damage or to precipitate their death. The properties of such compounds may be altered by substituents introduced to enhance mitochondrial delivery. Accordingly, we have characterized the redox behaviour of two isomeric mitochondriotropic quercetin-based compounds, 3O- and 7O-[4-triphenylphosphonio)butyl]quercetin iodide. In both cyclic voltammetric determinations of the oxidation potential and in 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assays, the 7-substituted isomer behaved much like quercetin itself, whereas the 3-substituted isomer was less reactive. Low \u3bcM concentrations of either compound increased superoxide radical anion formation in cultured cells; both compounds were also cytotoxic. The 7-substituted derivative proved to be more active in both types of assays, thus emerging as the isomer of choice for further bioactivity studies and in efforts to understand the link between redox properties, pro-oxidant behaviour and cytotoxicity

A mitochondriotropic derivative of quercetin: a strategy to increase the effectiveness of polyphenols

Mitochondria-targeted compounds are needed to act on a variety of processes that take place in these subcellular organelles and that have great pathophysiological relevance. In particular, redox-active molecules that are capable of homing in on mitochondria provide a tool to intervene on a major cellular source of reactive oxygen species and on the processes they induce, notably the mitochondrial permeability transition and cell death. We have linked the 3-OH of quercetin (3,3',4',5,7-pentahydroxy flavone), a model polyphenol, and the triphenylphosphonium moiety, a membrane-permeant cationic group, to produce proof-of-principle mitochondriotropic quercetin derivatives. The remaining hydroxyls were sometimes acetylated to hinder metabolism and improve solubility. The new compounds accumulate in mitochondria in a transmembrane potential-driven process and are only slowly metabolised by cultured human colon cells. They inhibit mitochondrial ATPase activity much as quercetin does, and are toxic for fast-growing cells