Tamar Amit

Neuroprotection and neurorescue against Aβ toxicity and PKC-dependent release of nonamyloidogenic soluble precursor protein by green tea polyphenol (-)-epigallocatechin-3-gallate

Green tea extract and its main polyphenol constituent (‐)‐epigallocatechin‐3‐gallate (EGCG) possess potent neuroprotective activity in cell culture and mice model of Parkinsons disease. The central hypothesis guiding this study is that EGCG may play an important role in amyloid precursor protein (APP) secretion and protection against toxicity induced by β‐amyloid (Aβ). The present study shows that EGCG enhances (~6‐fold) the release of the non‐amyloidogenic soluble form of the amyloid precursor protein (sAPPα) into the conditioned media of human SH‐SY5Y neuroblastoma and rat pheochromocytoma PC12 cells. sAPPα release was blocked by the hydroxamic acid‐based metalloprotease inhibitor Ro31–9790, which indicated mediation via α‐secretase activity. Inhibition of protein kinase C (PKC) with the inhibitor GF109203X, or by down‐regulation of PKC, blocked the EGCG‐induced sAPPα secretion, suggesting the involvement of PKC. Indeed, EGCG induced the phosphorylation of PKC, thus identifying a novel PKC‐dependent mechanism of EGCG action by activation of the non‐amyloidogenic pathway. EGCG is not only able to protect, but it can rescue PC12 cells against the β‐amyloid (Aβ) toxicity in a dose‐dependent manner. In addition, administration of EGCG (2 mg/kg) to mice for 7 or 14 days significantly decreased membrane‐bound holoprotein APP levels, with a concomitant increase in sAPPα levels in the hippocampus. Consistently, EGCG markedly increased PKCα and PKCε in the membrane and the cytosolic fractions of mice hippocampus. Thus, EGCG has protective effects against Aβ‐induced neurotoxicity and regulates secretory processing of non‐amyloidogenic APP via PKC pathway.

Cell signaling pathways in the neuroprotective actions of the green tea polyphenol (‐)‐epigallocatechin‐3‐gallate: implications for neurodegenerative diseases

Accumulating evidence supports the hypothesis that brain iron misregulation and oxidative stress (OS), resulting in reactive oxygen species (ROS) generation from H2O2 and inflammatory processes, trigger a cascade of events leading to apoptotic/necrotic cell death in neurodegenerative disorders, such as Parkinsons (PD), Alzheimers (AD) and Huntingtons diseases, and amyotrophic lateral sclerosis (ALS). Thus, novel therapeutic approaches aimed at neutralization of OS-induced neurotoxicity, support the application of ROS scavengers, transition metals (e.g. iron and copper) chelators and non-vitamin natural antioxidant polyphenols, in monotherapy, or as part of antioxidant cocktail formulation for these diseases. Both experimental and epidemiological evidence demonstrate that flavonoid polyphenols, particularly from green tea and blueberries, improve age-related cognitive decline and are neuroprotective in models of PD, AD and cerebral ischemia/reperfusion injuries. However, recent studies indicate that the radical scavenger property of green tea polyphenols is unlikely to be the sole explanation for their neuroprotective capacity and in fact, a wide spectrum of cellular signaling events may well account for their biological actions. In this article, the currently established mechanisms involved in the beneficial health action and emerging studies concerning the putative novel molecular neuroprotective activity of green tea and its major polyphenol (-)-epigallocatechin-3-gallate (EGCG), will be reviewed and discussed.

Multifunctional activities of green tea catechins in neuroprotection. Modulation of cell survival genes, iron-dependent oxidative stress and PKC signaling pathway.

Many lines of evidence suggest that oxidative stress resulting in reactive oxygen species (ROS) generation and inflammation play a pivotal role in the age-associated cognitive decline and neuronal loss in neurodegenerative diseases including Alzheimer’s (AD), Parkinson’s (PD) and Huntington’s diseases. One cardinal chemical pathology observed in these disorders is the accumulation of iron at sites where the neurons die. The buildup of an iron gradient in conjunction with ROS (superoxide, hydroxyl radical and nitric oxide) are thought to constitute a major trigger in neuronal toxicity and demise in all these diseases. Thus, promising future treatment of neurodegenerative diseases and aging depends on availability of effective brain permeable, iron-chelatable/radical scavenger neuroprotective drugs that would prevent the progression of neurodegeneration. Tea flavonoids (catechins) have been reported to possess potent iron- chelating, radical-scavenging and anti-inflammatory activities and to protect neuronal death in a wide array of cellular and animal models of neurological diseases. Recent studies have indicated that in addition to the known antioxidant activity of catechins, other mechanisms such as modulation of signal transduction pathways, cell survival/death genes and mitochondrial function, contribute significantly to the induction of cell viability. This review will focus on the multifunctional properties of green tea and its major component (–)-epigallocatechin-3-gallate (EGCG) and their ability to induce neuroprotection and neurorescue in vitro and in vivo. In particular, their transitional metal (iron and copper) chelating property and inhibition of oxidative stress.

Cell signaling pathways in the neuroprotective actions of the green tea polyphenol (-)-epigallocatechin-3-gallate: implications for neurodegenerative diseases: Signaling pathways in EGCG neuroprotection

Accumulating evidence supports the hypothesis that brain iron misregulation and oxidative stress (OS), resulting in reactive oxygen species (ROS) generation from H2O2 and inflammatory processes, trigger a cascade of events leading to apoptotic/necrotic cell death in neurodegenerative disorders, such as Parkinsons (PD), Alzheimers (AD) and Huntingtons diseases, and amyotrophic lateral sclerosis (ALS). Thus, novel therapeutic approaches aimed at neutralization of OS‐induced neurotoxicity, support the application of ROS scavengers, transition metals (e.g. iron and copper) chelators and non‐vitamin natural antioxidant polyphenols, in monotherapy, or as part of antioxidant cocktail formulation for these diseases. Both experimental and epidemiological evidence demonstrate that flavonoid polyphenols, particularly from green tea and blueberries, improve age‐related cognitive decline and are neuroprotective in models of PD, AD and cerebral ischemia/reperfusion injuries. However, recent studies indicate that the radical scavenger property of green tea polyphenols is unlikely to be the sole explanation for their neuroprotective capacity and in fact, a wide spectrum of cellular signaling events may well account for their biological actions. In this article, the currently established mechanisms involved in the beneficial health action and emerging studies concerning the putative novel molecular neuroprotective activity of green tea and its major polyphenol (‐)‐epigallocatechin‐3‐gallate (EGCG), will be reviewed and discussed.

The distal axis of growth hormone (GH) in nutritional disorders: GH-binding protein, insulin-like growth factor-I (IGF-I), and IGF-I receptors in obesity and anorexia nervosa.

The endocrine abnormalities along the growth hormone (GH) axis in anorexia nervosa (AN) and in obesity include hypothalamic, pituitary, and peripheral elements. The present study was undertaken to evaluate the effects of these nutritional extremes on GH-binding protein (BP) levels and on Insulin-like growth factor-I (IGF-I) receptors on red blood cells (RBC). Nine patients with AN and 20 obese subjects were compared with normal control children, adolescents, and adults. GH-BP was measured by a binding assay with dextran-coated charcoal separation. IGF-I binding was measured on enriched RBC. Serum GH-BP levels were markedly reduced in the AN patients, and highly increased in the obese. Scatchard analyses showed linear plots with unaltered binding affinities (Ka). The binding capacity (Bmax) was significantly lower than normal control in the AN patients and higher in the obese. GH-BP levels correlated positively with the body mass index (BMI). RBC [125I]IGF-I binding was significantly elevated in the AN patients and low in the obese. Scatchard analyses showed curvilinear plots. The high-affinity constants (Ka1) were slightly, but significantly, higher in the AN patients and in the obese compared with control. The binding capacity of the first binder (Bmax1) was lower in obesity than in AN or control. The low-affinity constants (Ka2) were similar in the three groups, and its binding capacity (Bmax2) was similar in the AN patients and the controls, but significantly lower in the obese. [125I]IGF-I binding correlated negatively and significantly with the BMI and with the GH-BP.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuroprotection via pro-survival protein kinase C isoforms associated with Bcl-2 family members

This study provides new insights into neuroprotection involving interaction of protein kinase C (PKC) pathway with Bcl‐2 family proteins. Using a model of serum deprivation, we investigated the mechanism by which the anti‐Parkinson/monoamine oxidase (MAO)‐B inhibitor drug, rasagiline, exerts its neuroprotective effect in rat pheochromocytoma PC12 cells. Here, we report that rasagiline (0.1–10 µM) decreased apoptosis via multiple protection mechanisms, including the stimulation of PKC phosphorylation; up‐regulation of PKCα and PKCε mRNAs, induction of Bcl‐xL, Bcl‐w, and brain‐derived neurotrophic factor (BDNF) mRNAs; and down‐regulation of Bad and Bax mRNAs. Moreover, rasagiline inhibited the cleavage and activation of procaspase‐3 and poly (ADP‐ribose) polymerase (PARP), whereas the PKC inhibitor, GF109203X, reversed these actions. Similarly, rasagiline decreased serum‐free‐induced levels of the important regulator of cell death, Bad, which was also blocked by GF109203X, indicating the involvement of PKC in rasagiline‐induced cell survival. Furthermore, these studies have established that PKC‐ and Bcl‐2‐dependent neuroprotective activity of rasagiline is dependent on its propargyl moiety, because propargylamine had similar effects with the same potency.

Neuroprotective molecular mechanisms of (−)-epigallocatechin-3-gallate: a reflective outcome of its antioxidant, iron chelating and neuritogenic properties

Tea, the major source of dietary flavonoids, particularly the epicatechins, signifies the second most frequently consumed beverage worldwide, which varies its status from a simple ancient cultural drink to a nutrient component, endowed possible beneficial neuro-pharmacological actions. Accumulating evidence suggests that oxidative stress, resulting in reactive oxygen species generation, plays a pivotal role in neurodegenerative diseases, supporting the implementation of radical scavengers and metal chelating agents, such as natural tea polyphenols, for therapy. Vast epidemiology data indicate a correlation between occurrence of neurodegenerative disorders, such as Parkinson’s and Alzheimer’s diseases, and green tea consumption. In particular, recent literature strengthens the perception that diverse molecular signaling pathways, participating in the neuroprotective activity of the major green tea polyphenol, (−)-epigallocatechin-3-gallate (EGCG), renders this natural compound as potential agent to reduce the risk of various neurodegenerative diseases. In the current review, we discuss the studies concerning the mechanisms of action implicated in EGCG-induced neuroprotection and discuss the vision to translate these findings into a lifestyle arena.

Simultaneous Manipulation of Multiple Brain Targets by Green Tea Catechins: A Potential Neuroprotective Strategy for Alzheimer and Parkinson Diseases

Current therapeutic approaches for Alzheimer and Parkinson disease (AD and PD, respectively) are merely symptomatic, intended for the treatment of symptoms, but offer only partial benefit, without any disease‐modifying activity. Novel promising strategies suggest the use of antiinflammatory drugs, antioxidants, iron‐complexing molecules, neurotrophic factor delivery, inhibitors of the amyloid precursor protein (APP)‐processing secretases, gamma and beta (that generate the amyloid‐beta peptides, Aβ), anti‐Aβ aggregation molecules, the interference with lipid cholesterol metabolism and naturally occurring plant flavonoids to potentially reverse the course of the diseases. Human epidemiological and new animal data suggest that tea drinking may decrease the incidence of dementia, AD, and PD. In particular, its main catechin polyphenol constituent (‐)‐epigallocatechin‐3‐gallate (EGCG) has been shown to exert neuroprotective/neurorescue activities in a wide array of cellular and animal models of neurological disorders. In the current article, we review the literature on the impact of the multimodal activities of green tea polyphenols and their neuroprotective effect on AD and PD.

Contrasting neuroprotective and neurotoxic actions of respective metabolites of anti-Parkinson drugs rasagiline and selegiline.

The anti-Parkinson selective irreversible monoamine oxidase B inhibitor drugs, rasagiline and selegiline, have been shown to possess neuroprotective activities in cell culture and in vivo models. While rasagiline is metabolized to its major metabolite aminoindan, selegiline gives rise to L-methamphetamine. Cultured PC-12 cells in absence of serum and nerve growth factor (NGF) die by an apoptotic process. Pretreatment of PC12 cells in absence of serum and NGF for 24 h with either rasagiline (1 microM) or selegiline (1 microM) is neuroprotective and anti-apoptotic as determined by ELISA and MTT tests. However, while aminoindan (1 microM), the major metabolite of rasagiline does not interfere with the neuroprotective activities of rasagiline or selegiline in PC-12 cells deprived of serum and NGF, the major metabolite of selegiline, L-methamphetamine (1 microM), inhibits them. In contrast to L-methamphetamine, aminoindan is itself is neuroprotective in this system. Recently it has been demonstrated that rasagiline directly activates PKC-MAP kinase pathway by a concentration and time dependent phosphorylation of p42 and p44 MAP kinase. In the present studies the neuroprotective activity of rasagiline is blocked by ERK inhibitor, PD98059 (20 microM), suggesting the involvement of PKC-MAP kinase pathway in the neuroprotection. These findings may have implication for the possible disease modifying action of rasagiline in treatment of Parkinsons disease.

Regulation of Bcl-2 family proteins, neurotrophic factors, and APP processing in the neurorescue activity of propargylamine

The anti‐Parkinson drug, rasagiline (N‐propargyl‐(1R)‐aminoindan) promotes neuronal survival, via neuroprotective activity related to its propargyl moiety (propargylamine). We have investigated the neurorescue effects of propargylamine, in a progressive neuronal death model, induced by long‐term serum deprivation in human SH‐SY5Y neuroblastoma cells. Propargylamine (0.1–10 µM) dose‐dependently reduced the levels of the early apoptosis‐associated phosphorylated protein, H2A‐X (ser 139), as well as decreased the cleavage of caspase‐3 and its substrate poly‐ADP ribose polymerase (PARP). In addition, the compound markedly reversed the apoptotic effects induced by long‐term serum withdrawal, including down‐regulation of the antiapoptotic protein, Bcl‐2, as well as up‐regulation of the proapoptotic proteins, Bax, Bad, and Bim. Real‐time RT‐PCR demonstrated that propargylamine elevated gene expression levels of Bcl‐2, and the neurotrophic factors glial cell line‐derived neurotrophic factor (GDNF) and brain‐derived neurotrophic factor (BDNF) and reduced Bax gene expression. Serum deprivation increased mRNA and protein levels of holo‐amyloid precursor protein (APP), which was markedly decreased by propargylamine. This was accompanied by inducing the release of the nonamyloidogenic α‐secretase form of soluble APP (sAPPα) into the medium. Similar effects on cell survival and APP regulation/processing were demonstrated for rasagiline. These results indicate that both rasagiline and propargylamine possess neurorescue activity, associated with regulation of Bcl‐2 family proteins, neurotrophic factors, and APP metabolism.