6-cyano-7-nitroquinoxaline-2-3-dione and Alzheimer-Disease

We have recently developed aged cortical neuron cultures from autopsied human brains with Alzheimer's disease (AD). During the culturing process, we found that glutamatergic cortical neurons from the AD brain lacked a response to glial cell line-derived neurotrophic factor (GDNF), including no axonal regrowth, and were starting to undergo apoptosis. Here we showed that, in cortical neurons from age- and gender-matched cognitively normal control (NC) subjects (NC neurons), GDNF enhanced the expression of GDNF family receptor subtype α1 (GFRα1), but not the other three subtypes (GFRα2, GFRα3, and GFRα4), whereas GDNF failed to induce GFRα1 expression in cortical neurons from the AD brain (AD neurons). The exogenous introduction of GFRα1, but not of its binding partner α1-neural cell adhesion molecule, or RET into AD neurons restored the effect of GDNF on neuronal survival. Moreover, between NC and AD neurons, the AMPA receptor blocker CNQX and the NMDA receptor blocker AP-5 had opposite effects on the GFRα1 expression induced by GDNF. In NC neurons, the presence of glutamate receptors was necessary for GDNF-linked GFRα1 expression, while in AD neurons the absence of glutamate receptors was required for GFRα1 expression by GDNF stimulation. These results suggest that, in AD neurons, specific impairments of GFRα1, which may be linked to glutamatergic neurotransmission, shed light on developing potential therapeutic strategies for AD by upregulation of GFRα1 expression.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Aged; Aged, 80 and over; Alzheimer Disease; Apoptosis; Case-Control Studies; Cells, Cultured; Female; Glial Cell Line-Derived Neurotrophic Factor; Glial Cell Line-Derived Neurotrophic Factor Receptors; Humans; Male; Neural Cell Adhesion Molecules; Neurons; Proto-Oncogene Proteins c-ret; Receptors, AMPA; Receptors, Glutamate; Receptors, N-Methyl-D-Aspartate

Several drugs are in clinical use for symptomatic treatment of Alzheimer's disease patients. Since Alzheimer's disease is known to be associated with down-regulation of the cholinergic and N-methyl-D-aspartate (NMDA) systems, most of these drugs inhibit acetylcholinesterase, potentiate the activity of nicotinic acetylcholine receptors (nAChRs), or modulate NMDA receptors. Galantamine is an anticholinesterase and allosterically potentiates the activity of the nicotinic receptors. We have recently found that galantamine potentiates the activity of NMDA receptors as well. Memantine is unique in that it inhibits the NMDA receptors. We have developed a hypothesis that combining galantamine and memantine will be more effective for improving the patient's conditions than monotherapy with either drug. Patch clamp and intracellular Ca(2+) imaging experiments using rat cortical and hippocampal neurons clearly provided the in vitro bases for our hypothesis. Memantine blocked the extrasynaptic NMDA receptor 100 times more potently than the synaptic NMDA receptor at negative membrane potentials and the block of both types of NMDA receptors was attenuated with depolarization. However, galantamine potentiation of the NMDA receptors was not voltage dependent. Thus, co-application of memantine with galantamine prevented the galantamine potentiation and the activation of extrasynaptic NMDA receptors, but membrane depolarization revealed the galantamine potentiation. Therefore, cell death is expected to be prevented by memantine near the resting potential while the NMDA-mediated synaptic transmission, which is down-regulated in the patients, is maintained and potentiated by galantamine. These results provide in vitro bases for the beneficial actions of galantamine and memantine combinations.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Alzheimer Disease; Animals; Bicuculline; Calcium Signaling; Cells, Cultured; Cerebral Cortex; Cholinesterase Inhibitors; Corpus Striatum; Drug Evaluation, Preclinical; Drug Synergism; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Galantamine; Glycine; In Vitro Techniques; Inhibitory Concentration 50; Memantine; Nerve Tissue Proteins; Neuroprotective Agents; Nicotinic Agonists; Patch-Clamp Techniques; Perfusion; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Receptors, Nicotinic; Strychnine; Synaptic Transmission; Therapeutic Irrigation

This study reveals mechanisms in the mouse hippocampus that may underlie nicotinic influences on attention, memory, and cognition. Induction of synaptic plasticity, arising via generally accepted mechanisms, is modulated by nicotinic acetylcholine receptors. Properly timed nicotinic activity at pyramidal neurons boosted the induction of long-term potentiation via presynaptic and postsynaptic pathways. On the other hand, nicotinic activity on interneurons inhibited nearby pyramidal neurons and thereby prevented or diminished the induction of synaptic potentiation. The synaptic modulation was dependent on the location and timing of the nicotinic activity. Loss of these synaptic mechanisms may contribute to the cognitive deficits experienced during Alzheimer's diseases, which is associated with a loss of cholinergic projections and with a decrease in the number of nicotinic receptors.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Acetylcholine; alpha7 Nicotinic Acetylcholine Receptor; Alzheimer Disease; Amino Acid Substitution; Animals; Bicuculline; Heterozygote; Hippocampus; Humans; In Vitro Techniques; Interneurons; Long-Term Potentiation; Mecamylamine; Membrane Potentials; Mice; Mice, Inbred C57BL; Mice, Mutant Strains; Models, Animal; Neuronal Plasticity; Nicotinic Antagonists; Patch-Clamp Techniques; Point Mutation; Pyramidal Cells; Receptors, Nicotinic; Synapses

In Alzheimer's disease, neurotoxic beta-amyloid peptides cause a deleterious influx of calcium ions into neurons. This increase in [Ca2+]int is expected to trigger intracellular events that eventually cause cell dysfunction and cell death. We find that the aggregated beta-amyloid peptide beta AP25-35 opens irreversibly a Ca(2+)-carrying channel, as does aggregated beta AP1-42. The opening of this channel is unaffected by DL-AP5, but it is blocked by Mg2+, CNQX and DNQX, suggesting a non-NMDA channel. External calcium enters and cytosolic calcium levels rise several-fold, as measured by fura-2 ratiometric analysis. Our findings illustrate a very early molecular event in the neurotoxicity of Alzheimer's disease. To combat the neurotoxic effect of aggregated beta-amyloid peptides, we have devised a series of very short antagonistic peptides. Using a combinatorial library of hexapeptides made from D-amino acids, we have selected peptides by their ability to complex with the tagged beta-amyloid peptide beta AP25-35. Certain of these so-called 'decoy peptides', as well as some modified decoy peptides, are able to abolish the calcium influx caused by aggregated, probably fibrillar, beta-amyloid peptides beta AP25-35 and beta AP1-42.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Alzheimer Disease; Amino Acid Sequence; Amyloid beta-Peptides; Calcium; Calcium Channels; Cells, Cultured; Excitatory Amino Acid Antagonists; Humans; Ion Channel Gating; Ligands; Magnesium; Molecular Sequence Data; Neurofibrillary Tangles; Neurons; Peptide Fragments; Protein Structure, Secondary; Receptors, N-Methyl-D-Aspartate