Agnes Simonyi

Resveratrol protects against global cerebral ischemic injury in gerbils

Increased oxidative stress has been implicated in the mechanisms of delayed neuronal cell death (DND) following cerebral ischemic insult. In this study, we investigated whether resveratrol, a polyphenolic antioxidant enriched in grape, may ameliorate ischemia-induced neuron cell death. Mongolian gerbils were divided into three groups, namely, sham control, ischemia and ischemia treated with resveratrol. Transient global cerebral ischemia was induced by occlusion of both common carotid arteries (CCA) for 5 min. Resveratrol was injected i.p. (30 mg/kg body weight), either during or shortly after CCA occlusion, and again at 24 h after ischemia. Cerebral blood flow was monitored before and during CCA occlusion using a laser Doppler flowmeter. Brain sections were immuno-stained for neurons, astrocytes and microglial cells. A time course study was also carried out to assess the bioavailability of resveratrol in serum, liver and brain using high performance liquid chromatography (HPLC). Morphometric measurements indicated extensive DND in the hippocampal CA1 region 4 days after ischemia and that neuron cell death was marked by the increase in reactive astrocytes and microglial cells. Administration of resveratrol, either during or after CCA occlusion, significantly (P<0.05) decreased DND as well as glial cell activation. Analysis of resveratrol after i.p. injection indicated its presence in serum, liver and brain with peak activity at 1, 4 and 4 h, respectively. This study demonstrated for the first time that resveratrol, a polyphenolic antioxidant, can cross the blood-brain barrier and exert protective effects against cerebral ischemic injury.

Phospholipase A2 in the central nervous system: implications for neurodegenerative diseases.

Phospholipase A2 (PLA2) belongs to a family of enzymes that catalyze the cleavage of fatty acids from the sn-2 position of phospholipids. There are more than 19 different isoforms of PLA2 in the mammalian system, but recent studies have focused on three major groups, namely, the group IV cytosolic PLA2, the group II secretory PLA2 (sPLA2), and the group VI Ca2+-independent PLA2. These PLA2s are involved in a complex network of signaling pathways that link receptor agonists, oxidative agents, and proinflammatory cytokines to the release of arachidonic acid (AA) and the synthesis of eicosanoids. PLA2s acting on membrane phospholipids have been implicated in intracellular membrane trafficking, differentiation, proliferation, and apoptotic processes. All major groups of PLA2 are present in the central nervous system (CNS). Therefore, this review is focused on PLA2 and AA release in neural cells, especially in astrocytes and neurons. In addition, because many neurodegenerative diseases are associated with increased oxidative and inflammatory responses, an attempt was made to include studies on PLA2 in cerebral ischemia, Alzheimers disease, and neuronal injury due to excitotoxic agents. Information from these studies has provided clear evidence for the important role of PLA2 in regulating physiological and pathological functions in the CNS.

The "French Paradox" and beyond: neuroprotective effects of polyphenols.

Chronic ethanol ingestion is known to cause oxidative damage to a number of organs including the brain. This is partly due to the ability of ethanol to enhance oxygen free radical production and lipid peroxidation. Increase in oxidative stress has been regarded as an important underlying factor for a number of human health problems including cardiovascular diseases, aging, as well as many age-related neurodegenerative diseases. The strikingly low incidences of coronary heart diseases (CHD) in France, despite intake of a high-fat diet, have been attributed to the consumption of red wine containing high levels of polyphenolic compounds. In recent years, understanding the “French Paradox” has stimulated new research interest to investigate whether polyphenolic antioxidants may offer protective effects beyond the cardiovascular system, and whether polyphenols from other botanical sources may similarly offer beneficial effects to human health. Our studies with animal models have provided information clearly indicating the ability of grape polyphenols to ameliorate neuronal damages due to chronic ethanol consumption. Studies with resveratrol, an important component of grape polyphenols, also show protective effects on neuron cell death induced by ethanol and other oxidative agents. These studies demonstrate an urgent need to extend research beyond the “French Paradox” towards better understanding molecular mechanisms of action of polyphenolic compounds and their application to human health.

Kainic acid-mediated excitotoxicity as a model for neurodegeneration

Neuronal excitation involving the excitatory glutamate receptors is recognized as an important underlying mechanism in neurodegenerative disorders. Excitation resulting from stimulation of the ionotropic glutamate receptors is known to cause the increase in intracellular calcium and trigger calcium-dependent pathways that lead to neuronal apoptosis. Kainic acid (KA) is an agonist for a subtype of ionotropic glutamate receptor, and administration of KA has been shown to increase production of reactive oxygen species, mitochondrial dysfunction, and apoptosis in neurons in many regions of the brain, particularly in the hippocampal subregions of CA1 and CA3, and in the hilus of dentate gyrus (DG). Systemic injection of KA to rats also results in activation of glial cells and inflammatory responses typically found in neurodegenerative diseases. KA-induced selective vulnerability in the hippocampal neurons is related to the distribution and selective susceptibility of the AMPA/kainate receptors in the brain. Recent studies have demonstrated ability of KA to alter a number of intracellular activities, including accumulation of lipofuscin-like substances, induction of complement proteins, processing of amyloid precursor protein, and alteration of tau protein expression. These studies suggest that KA-induced excitotoxicity can be used as a model for elucidating mechanisms underlying oxidative stress and inflammation in neurodegenerative diseases. The focus of this review is to summarize studies demonstrating KA-induced excitotoxicity in the central nervous system and possible intervention by anti-oxidants.

Apocynin protects against global cerebral ischemia-reperfusion-induced oxidative stress and injury in the gerbil hippocampus

Increased production of reactive oxygen species (ROS) following cerebral ischemia-reperfusion (I/R) is an important underlying cause for neuronal injury leading to delayed neuronal death (DND). In this study, apocynin, a specific inhibitor for NADPH oxidase, was used to test whether suppression of ROS by the NADPH oxidase inhibitor can protect against ischemia-induced ROS generation and decrease DND. Global cerebral ischemia was induced in gerbils by a 5-min occlusion of bilateral common carotid arteries (CCA). Using measurement of 4-hydroxy-2-nonenal (HNE) as a marker for lipid peroxidation, apocynin (5 mg/kg body weight) injected i.p. 30 min prior to ischemia significantly attenuated the early increase in HNE in hippocampus measured at 3 h after I/R. Apocynin also protected against I/R-induced neuronal degeneration and DND, oxidative DNA damage, and glial cell activation. Taken together, the neuroprotective effects of apocynin against ROS production during early phase of I/R and subsequent I/R-induced neuronal damage provide strong evidence that inhibition of NADPH oxidase could be a promising therapeutic mechanism to protect against stroke damage in the brain.

Resveratrol as a Therapeutic Agent for Neurodegenerative Diseases

Excess production of reactive oxygen species in the brain has been implicated as a common underlying risk factor for the pathogenesis of a number of neurodegenerative disorders, including Alzheimers disease (AD), Parkinsons disease (PD), and stroke. In recent years, there is considerable interest concerning investigation of antioxidative and anti-inflammatory effects of phenolic compounds from different botanical sources. In this review, we first describe oxidative mechanisms associated with stroke, AD, and PD, and subsequently, we place emphasis on recent studies implicating neuroprotective effects of resveratrol, a polyphenolic compound derived from grapes and red wine. These studies show that the beneficial effects of resveratrol are not only limited to its antioxidant and anti-inflammatory action but also include activation of sirtuin 1 (SIRT1) and vitagenes, which can prevent the deleterious effects triggered by oxidative stress. In fact, SIRT1 activation by resveratrol is gaining importance in the development of innovative treatment strategies for stroke and other neurodegenerative disorders. The goal here is to provide a better understanding of the mode of action of resveratrol and its possible use as a potential therapeutic agent to ameliorate stroke damage as well as other age-related neurodegenerative disorders.

Serial review: alcohol, oxidative stress and cell injuryThe “French paradox” and beyond: neuroprotective effects of polyphenols1,2

Chronic ethanol ingestion is known to cause oxidative damage to a number of organs including the brain. This is partly due to the ability of ethanol to enhance oxygen free radical production and lipid peroxidation. Increase in oxidative stress has been regarded as an important underlying factor for a number of human health problems including cardiovascular diseases, aging, as well as many age-related neurodegenerative diseases. The strikingly low incidences of coronary heart diseases (CHD) in France, despite intake of a high-fat diet, have been attributed to the consumption of red wine containing high levels of polyphenolic compounds. In recent years, understanding the “French Paradox” has stimulated new research interest to investigate whether polyphenolic antioxidants may offer protective effects beyond the cardiovascular system, and whether polyphenols from other botanical sources may similarly offer beneficial effects to human health. Our studies with animal models have provided information clearly indicating the ability of grape polyphenols to ameliorate neuronal damages due to chronic ethanol consumption. Studies with resveratrol, an important component of grape polyphenols, also show protective effects on neuron cell death induced by ethanol and other oxidative agents. These studies demonstrate an urgent need to extend research beyond the “French Paradox” towards better understanding molecular mechanisms of action of polyphenolic compounds and their application to human health.

Cyclooxygenase-2 inhibition improves amyloid-β-mediated suppression of memory and synaptic plasticity

Non-steroidal anti-inflammatory agents (NSAIDs) are associated with a marked reduction in the risk of developing Alzheimers disease, a form of dementia characterized by the accumulation of amyloid plaques containing the amyloid-beta protein (Abeta). Studies of the effects of NSAIDs upon the inflammatory response surrounding amyloid plaques and upon the generation of Abeta from the amyloid precursor protein (APP) have led to two proposed mechanisms by which NSAIDs may protect against Alzheimers disease: one, the selective lowering of Abeta42 by a subset of NSAIDs; and two, the reduction of inflammation. Although Alzheimers disease is a disorder of brain and synaptic function, the effects of NSAIDs on Abeta-mediated suppression of synaptic plasticity and memory function have never been reported. We therefore investigated how three different NSAIDs, chosen for their distinct effects on Abeta42 production and the inhibition of the cyclooxygenase (COX) isoenzymes, COX-1 and COX-2, affect memory function and synaptic plasticity. By focusing upon brain and synapse function, we made novel observations about the effects of NSAIDs on Abeta-mediated neural processes. Here we report that the selective inhibition of COX-2, but not COX-1, acutely prevented the suppression of hippocampal long-term plasticity (LTP) by Abeta. The non-selective NSAIDs, ibuprofen and naproxen, and a selective COX-2 inhibitor, MF-tricyclic, each restored memory function in Tg2576 mice over-expressing APP, and also blocked Abeta-mediated inhibition of LTP. There was no advantage of ibuprofen, a selective Abeta42-lowering agent (SALA), over the non-SALAs, naproxen and MF-tricyclic. The beneficial effects on memory did not depend upon lowered levels of Abeta42 or the inflammatory cytokines, tumour necrosis factor alpha (TNF-alpha) and interleukin 1beta (IL-1beta). Intriguingly, improved memory function was inversely related to prostaglandin E2 (PGE2) levels. Conversely, exogenous PGE2 prevented the restorative effects of COX-2 inhibitors on LTP. The data indicate that the inhibition of COX-2 blocks Abeta-mediated suppression of LTP and memory function, and that this block occurs independently of reductions in Abeta42 or decreases in inflammation. The results lead us to propose a third possible mechanism by which NSAIDs may protect against Alzheimers disease, involving the blockade of a COX-2-mediated PGE2 response at synapses.

Amyloid beta peptide and NMDA induce ROS from NADPH oxidase and AA release from cytosolic phospholipase A2 in cortical neurons.

Increase in oxidative stress has been postulated to play an important role in the pathogenesis of a number of neurodegenerative diseases including Alzheimer’s disease. There is evidence for involvement of amyloid‐β peptide (Aβ) in mediating the oxidative damage to neurons. Despite yet unknown mechanism, Aβ appears to exert action on the ionotropic glutamate receptors, especially the N‐methyl‐D‐aspartic acid (NMDA) receptor subtypes. In this study, we showed that NMDA and oligomeric Aβ1–42 could induce reactive oxygen species (ROS) production from cortical neurons through activation of NADPH oxidase. ROS derived from NADPH oxidase led to activation of extracellular signal‐regulated kinase 1/2, phosphorylation of cytosolic phospholipase A2α (cPLA2α), and arachidonic acid (AA) release. In addition, Aβ1–42‐induced AA release was inhibited by d(−)‐2‐amino‐5‐phosphonopentanoic acid and memantine, two different NMDA receptor antagonists, suggesting action of Aβ through the NMDA receptor. Besides serving as a precursor for eicosanoids, AA is also regarded as a retrograde messenger and plays a role in modulating synaptic plasticity. Other phospholipase A2 products such as lysophospholipids can perturb membrane phospholipids. These results suggest an oxidative‐degradative mechanism for oligomeric Aβ1–42 to induce ROS production and stimulate AA release through the NMDA receptors. This novel mechanism may contribute to the oxidative stress hypothesis and synaptic failure that underline the pathogenesis of Alzheimer’s disease.

Neuroprotective mechanisms of curcumin against cerebral ischemia-induced neuronal apoptosis and behavioral deficits.

Increased oxidative stress has been regarded as an important underlying cause for neuronal damage induced by cerebral ischemia/reperfusion (I/R) injury. In recent years, there has been increasing interest in investigating polyphenols from botanical source for possible neuroprotective effects against neurodegenerative diseases. In this study, we investigated the mechanisms underlying the neuroprotective effects of curcumin, a potent polyphenol antioxidant enriched in tumeric. Global cerebral ischemia was induced in Mongolian gerbils by transient occlusion of the common carotid arteries. Histochemical analysis indicated extensive neuronal death together with increased reactive astrocytes and microglial cells in the hippocampal CA1 area at 4 days after I/R. These ischemic changes were preceded by a rapid increase in lipid peroxidation and followed by decrease in mitochondrial membrane potential, increased cytochrome c release, and subsequently caspase‐3 activation and apoptosis. Administration of curcumin by i.p. injections (30 mg/kg body wt) or by supplementation to the AIN76 diet (2.0 g/kg diet) for 2 months significantly attenuated ischemia‐induced neuronal death as well as glial activation. Curcumin administration also decreased lipid peroxidation, mitochondrial dysfunction, and the apoptotic indices. The biochemical changes resulting from curcumin also correlated well with its ability to ameliorate the changes in locomotor activity induced by I/R. Bioavailability study indicated a rapid increase in curcumin in plasma and brain within 1 hr after treatment. Together, these findings attribute the neuroprotective effect of curcumin against I/R‐induced neuronal damage to its antioxidant capacity in reducing oxidative stress and the signaling cascade leading to apoptotic cell death.