Resveratrol increases glutamate uptake, glutathione content, and S100B secretion in cortical astrocyte cultures

Resveratrol commonly displays hormesis: occurrence and biomedical significance

Resveratrol induces hormetic dose responses in a wide range of biological models, affecting numerous endpoints of biomedical and therapeutic significance. These responses were reported for numerous human tumor cell lines affecting breast, prostate, colon, lung, uterine and leukemia. In such cases, low concentrations of resveratrol enhanced tumor cell proliferation whereas higher concentrations were inhibitory. Similar resveratrol-induced biphasic dose responses were seen with several parasitic diseases, including Leishmaniasis and trichinella. Hormetic effects were also reported in animal models for cardiovascular induced injury, gastric lesions, ischemic stroke, Alzheimer's disease and osteoporosis. In these cases, there was often a protective effect at low doses but an adverse effect at higher doses, exacerbating the disease process/incidence. This analysis indicates that many effects induced by resveratrol are dependent on dose and that opposite effects occur at low and high doses, being indicative of a hormetic dose response. Despite consistent occurrence of hormetic dose responses of resveratrol in a wide range of biomedical models, epidemiologic and clinical trials are needed to assess the nature of its dose-response in humans.

Resveratrol modulates astroglial functions: neuroprotective hypothesis

Resveratrol, a redox active compound present in grapes and wine, has a wide range of biological effects, including cardioprotective, chemopreventive, and anti-inflammatory activities. The central nervous system is a target of resveratrol, which can pass the blood-brain barrier and induce neuroprotective effects. Astrocytes are one of the most functionally diverse groups of cells in the nervous system, intimately associated with glutamatergic metabolism, transmission, synaptic plasticity, and neuroprotection. In this review, we focus on the resveratrol properties and response to oxidative insult on important astroglial parameters involved in brain plasticity, such as glutamate uptake, glutamine synthetase activity, glutathione content, and secretion of the trophic factor S100B.

ERK activation by the polyphenols fisetin and resveratrol provides neuroprotection in multiple models of Huntington's disease

Huntington's disease (HD) is an inherited, progressive and ultimately fatal neurodegenerative disorder that is characterized by psychiatric, cognitive and motor symptoms. Among the pathways implicated in HD are those involving mitogen-activated protein kinase signaling and particularly the Ras-extracellular signal-regulated kinase (ERK) cascade. Studies in both cells and animal models suggest that ERK activation might provide a novel therapeutic target for the treatment of HD but compounds that specifically activate ERK are few. To test the hypothesis that pharmaceutical activation of ERK might be protective for HD, a polyphenol, fisetin, which was previously shown to activate the Ras-ERK cascade, was tested in three different models of HD: PC12 cells expressing mutant Httex1 under the control of an inducible promoter, Drosophila expressing mutant Httex1 and the R6/2 mouse model of HD. The results indicate that fisetin can reduce the impact of mutant huntingtin in each of these disease models. Prompted by this observation, we determined that the related polyphenol, resveratrol, also activates ERK and is protective in HD models. Notably, although more than a dozen small molecule inhibitors of ERK activation are in clinical trials, very few small molecule activators of ERK signaling are reported. Thus, fisetin, resveratrol and related compounds might be useful for the treatment of HD by virtue of their unique ability to activate ERK.

Effect of resveratrol on gliotransmitter levels and p38 activities in cultured astrocytes

Accumulating evidence suggests that resveratrol may have beneficial effects against traumatic brain injury. However, its effect on the regulation of extracellular levels of gliotransmitter and on the activation of p38 MAPK in astrocytes is still unknown. We have examined whether resveratrol regulates extracellular levels of gliotransmitter as well as the activation of p38 MAPK in cultured astrocytes before and after stretch injury. The extracellular levels of glutamate, D-/L-serine and D-serine were apparently reduced by 100 μM resveratrol in control astrocyte cultures. The dramatic increase of glutamate and D-serine release induced by stretch injury was also clearly inhibited by resveratrol. Resveratrol mediates this response by reduction of release through inhibition of extracellular calcium influx and increment of gliotransmitter uptake through enhancement of amino acid transporter expressed in the membrane of astrocyte. In addition, resveratrol definitely reduced the activation of p38 MAPK in cultured astrocytes following stretch injury. AMPA receptor is involved in the activation of p38 following injury. Conversely, the levels of glutamine and glycine were not obviously affected by resveratrol before and after injury. Intracellular levels of glutamate and D-serine are not apparently changed by stretch injury. Collectively, our data suggest that resveratrol might play an important role in protection of the nervous system after injury by decreasing the extracellular levels of gliotransmitter and inhibiting activation of p38 MAPK following injury.

The S100B/RAGE Axis in Alzheimer's Disease

Increasing evidence suggests that the small EF-hand calcium-binding protein S100B plays an important role in Alzheimer's disease. Among other evidences are the increased levels of both S100B and its receptor, the Receptor for Advanced Glycation Endproducts (RAGEs) in the AD diseased brain. The regulation of RAGE signaling by S100B is complex and probably involves other ligands including the amyloid beta peptide (Aβ), the Advanced Glycation Endproducts (AGEs), or transtheyretin. In this paper we discuss the current literature regarding the role of S100B/RAGE activation in Alzheimer's disease.

Neurones express glutamine synthetase when deprived of glutamine or interaction with astrocytes

Glutamine synthetase (GS) forms glutamine by catalyzing the ATP-dependent amidation of glutamate. In healthy brains, GS is restricted to astrocytes but in Alzheimer's disease and cell culture, GS has been detected in neurones. The present study demonstrates the expression of functional GS in cultured cerebellar granule cells and investigates conditions required to reduce this expression. Cerebellar granule cells from neonatal rats were grown in the absence of glutamine. Immunostaining revealed that the majority of neurones contained GS in their somata and dendrites. Treatment of neuronal cultures with glutamine greatly reduced the enzymatic activity of GS and also reduced the intensity of GS immunolabelling in dendrites. GS activity was reduced by 32% in neurones that had been transiently co-cultured with astrocytes, whereas GS immunoreactivity was largely abolished from neurones that had been directly seeded onto astrocytic monolayers. These results imply that GS expression in neurones occurs in response to a reduced availability of glutamine from astrocytes, and that neuronal GS expression represents a default phenotype which is normally suppressed via direct contacts with astrocytes. The aberrant expression of GS in sporadic neurones in Alzheimer's disease may indicate an impairment of such interactions.

Exacerbation of tobacco smoke mediated apoptosis by resveratrol: an unexpected consequence of its antioxidant action

Resveratrol, a polyphenolic compound rich in grapes and red wine, has been reported to protect cells against oxidative damage and cell death by increasing cellular antioxidant/detoxification capacity. Cigarette smoking is a major risk factor for respiratory diseases and oxidative damage is implicated in its pathogenesis. Here we investigated the enhancement of antioxidant capacity by resveratrol and its potential protection against cell death caused by cigarette smoke in human bronchial epithelial cells (HBE1). At concentrations that did not affect cell growth, resveratrol activated Nrf2 signaling and increased the expression of NAD(P)H:quinone reductase-1, heme oxygenase-1, and the catalytic subunit of glutamate cysteine ligase. Surprisingly, instead of protecting against cell death, resveratrol significantly enhanced cigarette smoke extract-induced apoptosis. To define the underlying mechanism, the effect of resveratrol on caspase activity was examined and it was found that resveratrol significantly enhanced cigarette smoke-stimulated caspase activity. In conclusion, results from this study suggest that although resveratrol increased antioxidant and detoxification capacity, it increased rather than protected against cigarette smoke-induced apoptosis.

Sensory neurons and schwann cells respond to oxidative stress by increasing antioxidant defense mechanisms

Elevated blood glucose is a key initiator of mechanisms leading to diabetic neuropathy. Increases in glucose induce acute mitochondrial oxidative stress in dorsal root ganglion (DRG) neurons, the sensory neurons normally affected in diabetic neuropathy, whereas Schwann cells are largely unaffected. We propose that activation of an antioxidant response in DRG neurons would prevent glucose-induced injury. In this study, mild oxidative stress (1 microM H2O2) leads to the activation of the transcription factor Nrf2 and expression of antioxidant (phase II) enzymes. DRG neurons are thus protected from subsequent hyperglycemia-induced injury, as determined by activation of caspase 3 and the TUNEL assay. Schwann cells display high basal antioxidant enzyme expression and respond to hyperglycemia and mild oxidative stress via further increases in these enzymes. The botanical compounds resveratrol and sulforaphane activate the antioxidant response in DRG neurons. Other drugs that protect DRG neurons and block mitochondrial superoxide, identified in a compound screen, have differential ability to activate the antioxidant response. Multiple cellular targets exist for the prevention of hyperglycemic oxidative stress in DRG neurons, and these form the basis for new therapeutic strategies against diabetic neuropathy.

Atypical neuroleptic risperidone modulates glial functions in C6 astroglial cells

Risperidone has demonstrated therapeutic advantages over conventional neuroleptics and offers a valuable emerging option for the treatment of social behavior associated with autistic disorder. Considering the putative involvement of astroglial cells in neuropsychiatric disorders, we investigated the effect of risperidone on parameters of astrocyte activity - glutamate uptake, glutamine synthetase (GS) activity and glutathione (GSH) levels. Risperidone was able to induce a significantly increase on glutamate uptake (32%); GS activity (15%); GSH levels (58%). These findings imply the perspectives for further investigations directed on astrocytes from different brain areas. Our present results suggest that risperidone might exert its neuroprotective effects against brain illness at least partially via modulation of astrocyte functions.

Resveratrol and 4-hydroxynonenal act in concert to increase glutamate cysteine ligase expression and glutathione in human bronchial epithelial cells

Resveratrol has been shown to protect against oxidative stress through modulating antioxidant capacity. In this study, we investigated resveratrol-mediated induction of glutathione (GSH) and glutamate cysteine ligase (GCL), and the combined effect of resveratrol and 4-hydroxynonenal (HNE) on GSH synthesis in cultured HBE1 human bronchial epithelial cells. Resveratrol increased GSH and the mRNA contents of both the catalytic (GCLC) and modulatory subunit (GCLM) of GCL. Combined HNE and resveratrol treatment increased GSH content and GCL mRNAs to a greater extent than either compound did alone. Compared to individual agent, combining exposure to HNE and resveratrol also showed more protection against cell death caused by oxidative stress. These effects of combined exposure were additive rather than synergistic. In addition, Nrf2 silencing significantly decreased the combined effect of HNE and resveratrol on GCL induction. Our data suggest that resveratrol increases GSH and GCL gene expression and that there is an additive effect on GSH synthesis between resveratrol and HNE. The results also reveal that Nrf2-EpRE signaling was involved in the combined effects.

S100B's double life: intracellular regulator and extracellular signal

The Ca2+-binding protein of the EF-hand type, S100B, exerts both intracellular and extracellular functions. Recent studies have provided more detailed information concerning the mechanism(s) of action of S100B as an intracellular regulator and an extracellular signal. Indeed, intracellular S100B acts as a stimulator of cell proliferation and migration and an inhibitor of apoptosis and differentiation, which might have important implications during brain, cartilage and skeletal muscle development and repair, activation of astrocytes in the course of brain damage and neurodegenerative processes, and of cardiomyocyte remodeling after infarction, as well as in melanomagenesis and gliomagenesis. As an extracellular factor, S100B engages RAGE (receptor for advanced glycation end products) in a variety of cell types with different outcomes (i.e. beneficial or detrimental, pro-proliferative or pro-differentiative) depending on the concentration attained by the protein, the cell type and the microenvironment. Yet, RAGE might not be the sole S100B receptor, and S100B's ability to engage RAGE might be regulated by its interaction with other extracellular factors. Future studies using S100B transgenic and S100B null mice might shed more light on the functional role(s) of the protein.

Resveratrol prevents the expression of glaucoma markers induced by chronic oxidative stress in trabecular meshwork cells

Elevated intraocular pressure (IOP) constitutes the best characterized risk for primary open-angle glaucoma (POAG). Elevated IOP is believed to result from an increase in aqueous humor outflow resistance at the level of the trabecular meshwork (TM)/Schlemm's canal. Malfunction of the TM in POAG is associated with the expression of markers for inflammation, cellular senescence, oxidative damage, and decreased cellularity. Current POAG treatments rely on lowering IOP, but there is no therapeutic approach available to delay the loss of function of the TM in POAG patients. We evaluated the effects of chronic administration of the dietary supplement resveratrol on the expression of markers for inflammation, oxidative damage, and cellular senescence in primary TM cells subjected to chronic oxidative stress (40% O2). Resveratrol treatment effectively prevented increased production of intracellular reactive oxygen species (iROS) and inflammatory markers (IL1alpha, IL6, IL8, and ELAM-1), and reduced expression of the senescence markers sa-beta-gal, lipofuscin, and accumulation of carbonylated proteins. Furthermore, resveratrol exerted antiapoptotic effects that were not associated with a decrease in cell proliferation. These results suggest that resveratrol could potentially have a role in preventing the TM tissue abnormalities observed in POAG.

Resveratrol, a unique phytoalexin present in red wine, delivers either survival signal or death signal to the ischemic myocardium depending on dose

Recent studies have demonstrated the cardioprotective abilities of resveratrol, a polyphenolic antioxidant present in red wine. Resveratrol can also kill cancer cells at relatively higher doses by exerting a death signal. We reasoned that resveratrol might possess the ability to protect the cells at lower doses as observed during pharmacological preconditioning of the heart, while at higher doses cause cell death as found for cancer cells. To test this hypothesis, rats were randomly fed for 14 days by gavaging any of the four doses of resveratrol - 2.5, 5.0, 25 or 50 mg/kg - while vehicle-fed animals served as placebo control. After 14 days, isolated working hearts were prepared from both experimental and control animals, and the hearts were subjected to 30-min global ischemia followed by 2 h of reperfusion. The rats fed either 2.5 or 5 mg/kg dose of resveratrol for 14 days provided cardioprotection as evidenced by improved post-ischemic ventricular recovery and reduction of myocardial infarct size and cardiomyocyte apoptosis compared to control. In contrast, the hearts fed either 25 or 50 mg/kg dose of resveratrol depressed cardiac function and increased myocardial infarct size and number of apoptotic cells. The results for Western blots and RT-PCR demonstrated an increase of protein and RNA transcripts of redox proteins including thioredoxin (Trx)-1, Trx-2, glutaredoxin (Grx)-1, Grx-2, redox factor Ref-1 as well as redox-sensitive transcription factor NFkappaB, and survival factors such as phosphorylated-Akt (p-Akt), and Bcl-2 in the animals fed lower doses (2.5 and 5 mg/kg) of resveratrol, while the reverse was true for the animals fed higher doses (25 and 50 mg/kg) of resveratrol. The results thus indicate that at lower doses (2.5 or 5 mg/kg), resveratrol exerts survival signal by up-regulating anti-apoptotic and redox proteins Akt and Bcl-2, while at higher doses (>25 mg/kg), it potentiates a death signal by down-regulating redox proteins and up-regulating pro-apoptotic proteins.

Resveratrol: a natural compound with pharmacological potential in neurodegenerative diseases

Resveratrol is a phytoalexin structurally related to stilbenes, which is synthesized in considerable amounts in the skin of grapes, raspberries, mulberries, pistachios and peanuts, and by at least 72 medicinal and edible plant species in response to stress conditions. It was isolated in 1940 and did not maintain much interest for around five decades until its role in treatment of cardiovascular diseases was suggested. To date, resveratrol has been identified as an agent that may be useful to treat cancer, pain, inflammation, tissue injury, and other diseases. However, currently the attention is being focused in analyzing its properties against neurodegenerative diseases and as antiaging compound. It has been reported that resveratrol shows effects in in vitro models of epilepsy, Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, and nerve injury. However, evidences in vivo as well as in human beings are still lacking. Thus, further investigations on the pharmacological effects of resveratrol in vivo are necessary before any conclusions on its effects on neurodegenerative diseases can be obtained.

S100B is expressed in, and released from, OLN-93 oligodendrocytes: Influence of serum and glucose deprivation

S100B (member of a family of proteins that are 100% soluble in ammonium sulfate at neutral pH) has been widely used as astrocyte marker in animal models and in human brain diseases. Recent studies revealed S100B-immunopositivity in oligodendrocytes and O2A oligodendroglial progenitor cells. It is unknown, however, if oligodendrocytes produce S100B themselves, or if the S100B-immunolabeling is caused by binding or absorption of the protein. To address this question, S100B expression and protein release were analyzed in a highly pure oligodendrocytic OLN-93 cell line (from rat), in the astrocytic C6 cell line (from rat) and primary astrocytes. S100B was gene expressed in all cultures, as revealed by reverse transcriptase polymerase chain reaction (RT-PCR) analysis. OLN-93 cells and glial fibrillary acidic protein (GFAP)-negative astrocytes expressed the multiligand receptor for advanced glycation end products (RAGE). S100B protein levels were determined in supernatants and cell homogenates by immunoluminometry under normal conditions and after serum and glucose deprivation (SGD). SGD led to a several-fold increased release of S100B (after 6 and 24 h), which was particularly pronounced in primary astrocytes. Increased S100B in cell homogenates was most notable in OLN-93 cells under SGD, indicating activated S100B synthesis. These cells also showed the highest percentage of dead cells, as determined by propidium iodide-positivity, after SGD. Incubation with 0.5, 2 and 5 microg/l exogenous S100B was not toxic to OLN-93 cells. In conclusion, OLN-93 cells produce more S100B under SGD than astrocytes and are more susceptible to cell death upon SGD, which provokes leakage of S100B. Our data indicate active S100B secretion from astrocytes under SGD since highly elevated levels of S100B were detected in the supernatant despite a low percentage of dead cells. The experimental results provide further evidence for a production/release of S100B in/from oligodendrocytes, e.g. in metabolic stress conditions like cerebral ischemia. Studies on S100B in bodily fluids should be carefully interpreted in order to avoid misleading hypotheses concerning the specific involvement of astrocytes, due to the various cellular sources of S100B.

Chronic treatment with red wine polyphenol compounds mediates neuroprotection in a rat model of ischemic cerebral stroke

In this study, we investigated the in vivo effects of red wine polyphenol compounds (RWPC) in rats that were submitted to middle cerebral occlusion as an experimental model of stroke. Male Wistar rats were given RWPC [30 mg/(kg x d) dissolved in drinking water] or water for 1 wk before being subjected to transient middle cerebral artery occlusion followed by reperfusion. Sham-operated rats were subjected to transient occlusion in which the filament was not completely introduced. The release of amino acids and energy metabolites were monitored by intracerebral microdialysis. The volume of the ischemic lesion was assessed 24 h after reperfusion. Proteomic analysis of brain tissue was performed to study the effects of ischemia and RWPC on specific protein expression. Treatment with RWPC completely prevented the burst of excitatory amino acids that occurred in response to ischemia in untreated rats and significantly reduced brain infarct volumes. Rats chronically treated with RWPC, however, had lower basal concentrations of energy metabolites, including glucose and lactate in the brain parenchyma, compared with untreated rats. Chronic RWPC treatment significantly enhanced the residual cerebral blood flow during occlusion and reperfusion in rats subjected to transient occlusion compared with untreated rats. This effect resulted from arterial vasodilatation, as the internal diameters of several arteries were significantly enlarged after RWPC treatment. Proteomic studies revealed the modulation by RWPC of the expression of proteins involved in the maintenance of neuronal caliber and axon formation, in the protection against oxidative stress, and in energy metabolism. These findings provide an experimental basis for the beneficial effects of RWPC on the neurovascular unit during stroke.

Protective effects of resveratrol on hydrogen peroxide induced toxicity in primary cortical astrocyte cultures

It is well established that the brain is particularly susceptible to oxidative damage due to its high consumption of oxygen and that astrocytes are involved in a variety of important activities for the nervous system, including a protective role against damage induced by reactive oxygen species (ROS). The use of antioxidant compounds, such as polyphenol resveratrol found in red wine, to improve endogenous antioxidant defenses has been proposed for neural protection. The aim of this study is to evaluate the putative protective effect of resveratrol against acute H2O2-induced oxidative stress in astrocyte cultures, evaluating ROS production, glutamate uptake activity, glutathione content and S100B secretion. Our results confirm the ability of resveratrol to counteract oxidative damage caused by H2O2, not only by its antioxidant properties, but also through the modulation of important glial functions, particularly improving glutamate uptake activity, increasing glutathione content and stimulating S100B secretion, which all contribute to the functional recovery after brain injury.