Alzheimer's disease (AD) and several other neurological disorders have been linked to the overactivation of glutamatergic transmission and excitotoxicity as a common pathway of neuronal injury. The beta-amyloid peptide (Abeta) is centrally related to the pathogenesis of AD, and previous reports have demonstrated that the blockade of glutamate receptors prevents Abeta-induced neuronal death. We show that taurine, a beta-amino acid found at high concentrations in the brain, protects chick retinal neurons in culture against the neurotoxicity of Abeta and glutamate receptor agonists. The protective effect of taurine is not mediated by interaction with glutamate receptors, as demonstrated by binding studies using radiolabeled glutamate receptor ligands. The neuroprotective action of taurine is blocked by picrotoxin, an antagonist of GABA(A) receptors. GABA and the GABA(A) receptor agonists phenobarbital and melatonin also protect neurons against Abeta-induced neurotoxicity. These results suggest that activation of GABA receptors decreases neuronal vulnerability to excitotoxic damage and that pharmacological manipulation of the excitatory and inhibitory neurotransmitter tonus may protect neurons against a variety of insults. GABAergic transmission may represent a promising target for the treatment of AD and other neurological disorders in which excitotoxicity plays a relevant role.

Alzheimer's disease (AD) is a major public health problem, and there is currently no clinically accepted treatment to cure it or to stop its progression. Fibrillar aggregates of the β–amyloid peptide (Aβ) are major constituents of the senile plaques found in the brains of AD patients and have been related to AD neurotoxicity. Here it is shown that nitrophenols prevent aggregation and cause disaggregation of Aβ fibrils and that they strongly prevent the neurotoxicity of Aβ to rat hippocampal neurons in culture. Furthermore, by using an in vivo model system of cerebral amyloid deposition, it is shown that nitrophenols cause a marked reduction in the volume occupied by amyloid deposits in the hippocampi of rats. These results raise the possibility that nitrophenols or their derivatives may be useful lead compounds for the development of drugs to prevent the neurotoxicity and deposition of Aβ in AD.

Once surgical tissue is available, the current protocol is easy to perform and produces functional slices from adult human brain. These slice cultures may represent a preferred model for translational studies of neurodegenerative disorders when long term culturing in not required, as in investigations on AβO neurotoxicity.

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The beta-amyloid peptide (Abeta) is centrally related to the pathogenesis of Alzheimer's disease (AD). Previous studies have suggested that the neurotoxicity of Abeta may be related to the overactivation of glutamatergic transmission and excitotoxicity, and that blockade of glutamate receptors prevents Abeta-induced cell death. Here, we show that melatonin, a pineal hormone, protects chick retinal neurons in culture against the neurotoxicity of Abeta and glutamate. Right-angle light scattering and thioflavin T fluorescence measurements, as well as light microscopy analysis, indicated that, under our experimental conditions, melatonin had no effect on the aggregation of Abeta. Interestingly, the neuroprotective action of melatonin against the toxicity of Abeta was significantly decreased in the presence of picrotoxin, an antagonist of GABA(A)-like receptors. By itself, picrotoxin had no effect. These results suggest that the neuroprotective effects of melatonin against Abeta neurotoxicity could be at least in part related to a decrease in the excitatory tonus, mediated by activation of GABA receptors and the resulting hyper-polarization of the neurons. Thus, selective pharmacological manipulation of neuronal excitatory/inhibitory tonus could be a potentially interesting new approach in the treatment of AD.

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The neurotoxicity of the amyloid-β peptide (Aβ) appears to be, at least in part, related to pathological activation of glutamate receptors by Aβ aggregates. However, the downstream signaling pathways leading to neurodegeneration are still incompletely understood. Hyperactivation of nitric oxide synthase (NOS) and increased nitric oxide (NO) production have been implicated in excitotoxic neuronal damage caused by overactivation of glutamate receptors, and it has been suggested that increased NO levels might also play a role in neurotoxicity in Alzheimer's disease. We have examined the effect of blockade of NO production on the neurotoxicity instigated by Aβ₄₂ and by elevated concentrations of glutamate in chick embryo retinal neurons in culture. Results showed that L-nitroarginine methyl ester, a potent inhibitor of all NOS isoforms, had no protective effect against neuronal death induced by either Aβ₄₂ (20 μM) or glutamate (1 mM). Surprisingly, at short incubation times both Aβ and glutamate decreased NO production in retinal neuronal cultures in the absence of neuronal death. Thus, excitotoxic insults induced by Aβ and glutamate cause inhibition rather than activation of NO synthase in retinal neurons, suggesting that cell death induced by Aβ or glutamate is not related to increased NO production. On the other hand, considering the role of NO in long term potentiation and synaptic plasticity, the decrease in NO levels instigated by Aβ and glutamate suggests a possible mechanism leading to synaptic failure in AD.

The equilibrium unfolding of dimeric yeast glutathione reductase (GR) by guanidine hydrochloride (GdnHCl) was investigated. Unfolding was monitored by a variety of techniques, including intrinsic fluorescence emission, anisotropy and iodide quenching measurements, far-ultraviolet circular dichroism and thiol reactivity measurements. At 1 M GdnHCl, one thiol group of GR became accessible to modification with 5,5'-dithiobis-(2-nitrobenzoic) acid (DTNB), whereas no changes could be detected in the spectroscopic properties (fluorescence, circular dichroism) of the protein. Between 2 and 3 M GdnHCl, two partially folded intermediate states possessing flexible tertiary structures (revealed by fluorescence data) but compact secondary structures (as indicated by circular dichroism measurements) were identified. The quaternary structure of GR in the presence of GdnHCl was also investigated by size-exclusion liquid chromatography. These results indicated the presence of an expanded predissociated dimer at 2.5 M GdnHCl and partially folded monomers at 3 M GdnHCl. Taken together, these results suggest the existence of two molten-globule-like intermediate species (one dimeric and one monomeric) in the unfolding of GR. The results are discussed in terms of the mechanism of GR folding and dimerization.