Epigallocatechin-3-gallate has dual, independent effects on the cardiac sarcoplasmic reticulum/endoplasmic reticulum Ca2+ ATPase

Natural Polyphenols as SERCA Activators: Role in the Endoplasmic Reticulum Stress-Related Diseases

Sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) is a key protein responsible for transporting Ca²⁺ ions from the cytosol into the lumen of the sarco/endoplasmic reticulum (SR/ER), thus maintaining Ca²⁺ homeostasis within cells. Accumulating evidence suggests that impaired SERCA function is associated with disruption of intracellular Ca²⁺ homeostasis and induction of ER stress, leading to different chronic pathological conditions. Therefore, appropriate strategies to control Ca²⁺ homeostasis via modulation of either SERCA pump activity/expression or relevant signaling pathways may represent a useful approach to combat pathological states associated with ER stress. Natural dietary polyphenolic compounds, such as resveratrol, gingerol, ellagic acid, luteolin, or green tea polyphenols, with a number of health-promoting properties, have been described either to increase SERCA activity/expression directly or to affect Ca²⁺ signaling pathways. In this review, potential Ca²⁺-mediated effects of the most studied polyphenols on SERCA pumps or related Ca²⁺ signaling pathways are summarized, and relevant mechanisms of their action on Ca²⁺ regulation with respect to various ER stress-related states are depicted. All data were collected using scientific search tools (i.e., Science Direct, PubMed, Scopus, and Google Scholar).

Effects of Standardized Green Tea Extract and Its Main Component, EGCG, on Mitochondrial Function and Contractile Performance of Healthy Rat Cardiomyocytes

We recently showed that the long-term in vivo administration of green tea catechin extract (GTE) resulted in hyperdynamic cardiomyocyte contractility. The present study investigates the mechanisms underlying GTE action in comparison to its major component, epigallocatechin-3-gallate (EGCG), given at the equivalent amount that would be in the entirety of GTE. Twenty-six male Wistar rats were given 40 mL/day of a tap water solution with either standardized GTE or pure EGCG for 4 weeks. Cardiomyocytes were then isolated for the study. Cellular bioenergetics was found to be significantly improved in both GTE- and EGCG-fed rats compared to that in controls as shown by measuring the maximal mitochondrial respiration rate and the cellular ATP level. Notably, the improvement of mitochondrial function was associated with increased levels of oxidative phosphorylation complexes, whereas the cellular mitochondrial mass was unchanged. However, only the GTE supplement improved cardiomyocyte mechanics and intracellular calcium dynamics, by lowering the expression of total phospholamban (PLB), which led to an increase of both the phosphorylated-PLB/PLB and the sarco-endoplasmic reticulum calcium ATPase/PLB ratios. Our findings suggest that GTE might be a valuable adjuvant tool for counteracting the occurrence and/or the progression of cardiomyopathies in which mitochondrial dysfunction and alteration of intracellular calcium dynamics constitute early pathogenic factors.

Evaluation of the neuroprotective effect of EGCG: a potential mechanism of mitochondrial dysfunction and mitochondrial dynamics after subarachnoid hemorrhage

(-)-Epigallocatechin-3-gallate (EGCG), the main bioactive component of tea catechins, exhibits broad-spectrum health efficacy against mitochondrial damage after subarachnoid hemorrhage (SAH). The mechanisms, however, are largely unknown. Here, the ability of EGCG to rescue mitochondrial dysfunction and mitochondrial dynamics following the inhibition of cell death was investigated by using in vitro and in vivo SAH models. EGCG blocked the cytosolic channel ([Ca2+])i influx via voltage-gated calcium channels (VGCCs), which induced mitochondrial dysfunction, including mitochondrial membrane potential depolarization and reactive oxygen species (ROS) release. As expected, EGCG ameliorated oxyhemoglobin (OxyHb)-induced impairment of mitochondrial dynamics by regulating the expression of Drp1, Fis1, OPA1, Mfn1, and Mfn2. As a result, EGCG restored the increases in fragmented mitochondria and the mtDNA copy number in the OxyHb group to almost the normal level after SAH. In addition, the normal autophagic flux induced by EGCG at both the initiation and formation stages regulated Atg5 and Beclin-1 after SAH for the timely elimination of damaged mitochondria. In the end, EGCG increased the neurological score by decreasing cell death through the cyt c-mediated intrinsic apoptotic pathway. The results revealed the mechanisms behind the neuroprotective effects of EGCG via inhibition of the overloaded [Ca2+]i-induced mitochondrial dysfunction and the imbalanced mitochondrial fusion and fission cycle. Therefore, the simultaneous inhibition and timely elimination of damaged mitochondria could determine the therapeutic effect of EGCG.

Epigallocatechin-3-Gallate Accelerates Relaxation and Ca2+ Transient Decay and Desensitizes Myofilaments in Healthy and Mybpc3-Targeted Knock-in Cardiomyopathic Mice

Background: Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiac muscle disease with left ventricular hypertrophy, interstitial fibrosis and diastolic dysfunction. Increased myofilament Ca²⁺ sensitivity could be the underlying cause of diastolic dysfunction. Epigallocatechin-3-gallate (EGCg), a catechin found in green tea, has been reported to decrease myofilament Ca²⁺ sensitivity in HCM models with troponin mutations. However, whether this is also the case for HCM-associated thick filament mutations is not known. Therefore, we evaluated whether EGCg affects the behavior of cardiomyocytes and myofilaments of an HCM mouse model carrying a gene mutation in cardiac myosin-binding protein C and exhibiting both increased myofilament Ca²⁺ sensitivity and diastolic dysfunction. Methods and Results: Acute effects of EGCg were tested on fractional sarcomere shortening and Ca²⁺ transients in intact ventricular myocytes and on force-Ca²⁺ relationship of skinned ventricular muscle strips isolated from Mybpc3-targeted knock-in (KI) and wild-type (WT) mice. Fractional sarcomere shortening and Ca²⁺ transients were analyzed at 37°C under 1-Hz pacing in the absence or presence of EGCg (1.8 μM). At baseline and in the absence of Fura-2, KI cardiomyocytes displayed lower diastolic sarcomere length, higher fractional sarcomere shortening, longer time to peak shortening and time to 50% relengthening than WT cardiomyocytes. In WT and KI neither diastolic sarcomere length nor fractional sarcomere shortening were influenced by EGCg treatment, but relaxation time was reduced, to a greater extent in KI cells. EGCg shortened time to peak Ca²⁺ and Ca²⁺ transient decay in Fura-2-loaded WT and KI cardiomyocytes. EGCg did not influence phosphorylation of phospholamban. In skinned cardiac muscle strips, EGCg (30 μM) decreased Ca²⁺ sensitivity in both groups. Conclusion: EGCg hastened relaxation and Ca²⁺ transient decay to a larger extent in KI than in WT cardiomyocytes. This effect could be partially explained by myofilament Ca²⁺ desensitization.

Global Analysis of Type Three Secretion System and Quorum Sensing Inhibition of Pseudomonas savastanoi by Polyphenols Extracts from Vegetable Residues

Protection of plants against bacterial diseases still mainly relies on the use of chemical pesticides, which in Europe correspond essentially to copper-based compounds. However, recently plant diseases control is oriented towards a rational use of molecules and extracts, generally with natural origin, with lower intrinsic toxicity and a reduced negative environmental impact. In this work, polyphenolic extracts from vegetable no food/feed residues of typical Mediterranean crops, as Olea europaea, Cynara scolymus, and Vitis vinifera were obtained and their inhibitory activity on the Type Three Secretion System (TTSS) and the Quorum Sensing (QS) of the Gram-negative phytopathogenic bacterium Pseudomonas savastanoi pv. nerii strain Psn23 was assessed. Extract from green tea (Camellia sinensis) was used as a positive control. Collectively, the data obtained through gfp-promoter fusion system and real-time PCR show that all the polyphenolic extracts here studied have a high inhibitory activity on both the TTSS and QS of Psn23, without any depressing effect on bacterial viability. Extracts from green tea and grape seeds were shown to be the most active. Such activity was confirmed in planta by a strong reduction in the ability of Psn23 to develop hyperplastic galls on explants from adult oleander plants, as well as to elicit hypersensitive response on tobacco. By using a newly developed Congo red assay and an ELISA test, we demonstrated that the TTSS-targeted activity of these polyphenolic extracts also affects the TTSS pilus assembly. In consideration of the potential application of polyphenolic extracts in plant protection, the absence of any toxicity of these polyphenolic compounds was also assessed. A widely and evolutionary conserved molecular target such as Ca²⁺-ATPase, essential for the survival of any living organism, was used for the toxicity assessment.

Reduction in Autophagy by (-)-Epigallocatechin-3-Gallate (EGCG): a Potential Mechanism of Prevention of Mitochondrial Dysfunction After Subarachnoid Hemorrhage

Mitochondrial dysfunction and subsequent autophagy, which are common features in central nervous system (CNS) disorders, were found to contribute to neuronal cell injury after subarachnoid hemorrhage (SAH). (-)-Epigallocatechin-3-gallate (EGCG), the main biological active of tea catechin, is well known for its beneficial effects in the treatment of CNS diseases. Here, the ability of EGCG to rescue cellular injury and mitochondrial function following the improvement of autophagic flux after SAH was investigated. As expected, EGCG-protected mitochondrial function depended on the inhibition of cytosolic Ca²⁺ concentration ([Ca²⁺]_i) influx via voltage-gated calcium channels (VGCCs) and, consequently, mitochondrial Ca²⁺ concentration ([Ca²⁺]_m) overload via mitochondrial Ca²⁺ uniporter (MCU). The attenuated [Ca²⁺]_i and [Ca²⁺]_m levels observed in the EGCG-treated group likely lessened oxyhemoglobin (OxyHb)-induced mitochondrial dysfunction, including mitochondrial membrane potential depolarization, mitochondrial membrane permeability transition pore (mPTP) opening, reactive oxygen species (ROS), and cytochrosome c (cyt c) releasing. Subsequently, EGCG can restore the disrupted autophagy flux after SAH both at the initiation and formation stages by regulating Atg5, LC3B, and Becn-1 (Beclin-1) mRNA expressions. Thus, precondition EGCG resulted in autophagosomes and more autolysosomes compared with SAH group. As a result, EGCG pre-treatment increased the neurological score and decreased cell death. This study suggested that the mitochondrial dysfunction and abnormal autophagy flux synergistically contribute to SAH pathogenesis. Thus, EGCG can be regarded as a new pharmacological agent that targets both mitochondria and altered autophagy in SAH therapy.

New insights into the mechanisms of polyphenols beyond antioxidant properties; lessons from the green tea polyphenol, epigallocatechin 3-gallate

Green tea is rich in polyphenol flavonoids including catechins. Epigallocatechin 3-gallate (EGCG) is the most abundant and potent green tea catechin. EGCG has been extensively studied for its beneficial health effects as a nutriceutical agent. Based upon its chemical structure, EGCG is often classified as an antioxidant. However, treatment of cells with EGCG results in production of hydrogen peroxide and hydroxyl radicals in the presence of Fe (III). Thus, EGCG functions as a pro-oxidant in some cellular contexts. Recent investigations have revealed many other direct actions of EGCG that are independent from anti-oxidative mechanisms. In this review, we discuss these novel molecular mechanisms of action for EGCG. In particular, EGCG directly interacts with proteins and phospholipids in the plasma membrane and regulates signal transduction pathways, transcription factors, DNA methylation, mitochondrial function, and autophagy to exert many of its beneficial biological actions.

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Many biological actions of EGCG are mediated by specific mechanisms other than its well-known anti-oxidant properties.

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EGCG is a pro-oxidant per se in some biological contexts.

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EGCG directly interacts with cell surface membrane proteins and specific known receptors.

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Treatment of cells with EGCG regulates specific intracellular signaling pathways and transcription.

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Specific biological actions of EGCG are regulated in a concentration-dependent manner.

Coordinated regulation of murine cardiomyocyte contractility by nanomolar (-)-epigallocatechin-3-gallate, the major green tea catechin

Green tea polyphenolic catechins exhibit biological activity in a wide variety of cell types. Although reports in the lay and scientific literature suggest therapeutic potential for improving cardiovascular health, the underlying molecular mechanisms of action remain unclear. Previous studies have implicated a wide range of molecular targets in cardiac muscle for the major green tea catechin, (-)-epigallocatechin-3-gallate (EGCG), but effects were observed only at micromolar concentrations of unclear clinical relevance. Here, we report that nanomolar concentrations of EGCG significantly enhance contractility of intact murine myocytes by increasing electrically evoked Ca(2+) transients, sarcoplasmic reticulum (SR) Ca(2+) content, and ryanodine receptor type 2 (RyR2) channel open probability. Voltage-clamp experiments demonstrate that 10 nM EGCG significantly inhibits the Na(+)-Ca(2+) exchanger. Of importance, other Na(+) and Ca(2+) handling proteins such as Ca(2+)-ATPase, Na(+)-H(+) exchanger, and Na(+)-K(+)-ATPase were not affected by EGCG ≤ 1 μM. Thus, nanomolar EGCG increases contractility in intact myocytes by coordinately modulating SR Ca(2+) loading, RyR2-mediated Ca(2+) release, and Na(+)-Ca(2+) exchange. Inhibition of Na(+)-K(+)-ATPase activity probably contributes to the positive inotropic effects observed at EGCG concentrations >1 μM. These newly recognized actions of nanomolar and micromolar EGCG should be considered when the therapeutic and toxicological potential of green tea supplementation is evaluated and may provide a novel therapeutic strategy for improving contractile function in heart failure.