Alzheimer disease and familial British dementia are neurodegenerative diseases that are characterized by the presence of numerous amyloid plaques in the brain. These lesions contain fibrillar deposits of the ␤-amyloid peptide (A␤) and the British dementia peptide (ABri), respectively. Both peptides are toxic to cells in culture, and there is increasing evidence that early "soluble oligomers" are the toxic entity rather than mature amyloid fibrils. The molecular mechanisms responsible for this toxicity are not clear, but in the case of A␤, one prominent hypothesis is that the peptide can induce oxidative damage via the formation of hydrogen peroxide. We have developed a reliable method, employing electron spin resonance spectroscopy in conjunction with the spin-trapping technique, to detect any hydrogen peroxide generated during the incubation of A␤ and other amyloidogenic peptides. Here, we monitored levels of hydrogen peroxide accumulation during different stages of aggregation of A␤-(1-40) and ABri and found that in both cases it was generated as a short "burst" early on in the aggregation process. Ultrastructural studies with both peptides revealed that structures resembling "soluble oligomers" or "protofibrils" were present during this early phase of hydrogen peroxide formation. Mature amyloid fibrils derived from A␤-(1-40) did not generate hydrogen peroxide. We conclude that hydrogen peroxide formation during the early stages of protein aggregation may be a common mechanism of cell death in these (and possibly other) neurodegenerative diseases.There is mounting evidence for the importance of oxidative damage to the brain in a wide range of neurodegenerative diseases based on detection of markers such as elevated levels of redox-active transition metal ions, lipid peroxidation, DNA and protein oxidation, and the introduction of carbonyl groups into proteins (reviewed, for example, in Refs. 1-6). These are hallmarks of attack by reactive oxygen species (ROS), 3 including superoxide, hydrogen peroxide, and the hydroxyl radical. The ␤-amyloid peptide (A␤), which is responsible for senile plaque formation in Alzheimer disease (AD), has been reported to generate hydrogen peroxide from molecular oxygen through electron transfer interactions involving bound redox-active metal ions (7-10). Hydrogen peroxide is readily converted into the aggressive hydroxyl radical by Fenton chemistry and these two ROS could be responsible for some of the oxidative damage seen in the brain in AD. Familial British dementia (FBD) is an inherited neurodegenerative disorder that is strikingly similar in neuropathology to AD, including the presence of extracellular amyloid plaques and intracellular neurofibrillary tangles. FBD is due to a stop codon mutation in the BRI gene, the protein product of which undergoes proteolytic cleavage to release an abnormally long peptide fragment (ABri) that rapidly aggregates in vitro into toxic oligomers (11,12). Only ABri with an intact intramolecular disulfide bond can do this, whereas the correspondi...

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The relaxation dynamics of water-rich glycerol-water mixtures is studied by broadband dielectric spectroscopy (BDS) at 173-323 K and differential scanning calorimetry (DSC) at 138-313 K. These data indicate the existence of the critical concentration of 40 mol % glycerol. In the studied temperature range for water-rich glycerol mixtures, the two states of water (ice and interfacial water) are observed in addition to water in the mesoscopic 40 mol % glycerol-water domains. The possible kinetics of water exchange between different water states is discussed in order to explain the mechanism of the broad melting behavior observed by DSC.

We discuss the relaxation dynamics of glycerol-water mixtures, as studied by dielectric spectroscopy in the frequency range from 1 Hz to 250 MHz and at temperatures between 173 and 323 K. The experimental results obtained for the glycerol-rich mixtures suggest that the main dielectric relaxation process, as well as the so-called high-frequency "excess wing" (EW) and dc conductivity, follow the same temperature dependence. This result indicates that all of these processes are induced by the same molecular origin. A new phenomenological function is proposed to describe the whole dielectric spectrum in the covered frequency range, and some possible mechanisms of dielectric behaviors through the dc conductivity, the main relaxation process, and the EW are discussed.

Zinc, iron and copper are concentrated in senile plaques of Alzheimer disease. Copper and iron catalyze the Fenton-Haber-Weiss reaction, which likely contributes to oxidative stress in neuronal cells. In this study, we found that ascorbate oxidase activity and the intensity of ascorbate radicals measured using ESR spectroscopy, generated by free Cu(II), was decreased in the presence of amyloid-beta (Abeta), the major component of senile plaques. Specifically, the ascorbate oxidase activity was strongly inhibited (85% decrease) in the presence of Abeta1-16 or Abeta1-42, whereas it was only slightly inhibited in the presence of Abeta1-12 or Abeta25-35 (<20% inhibition). Ascorbate-dependent hydroxyl radical generation by free Cu(II) decreased in the presence of Abeta in the identical order of Abeta1-42, Abeta1-16 > Abeta1-12 and was abolished in the presence of 2-fold molar excess glycylhystidyllysine (GHK). Ascorbate oxidase activity and ascorbate-dependent hydroxyl radical generation by free Fe(III) were inhibited by Abeta1-42, Abeta1-16, and Abeta1-12. Although Cu(II)-Abeta shows a significant SOD-like activity, the rate constant for the reaction of superoxide with Cu(II)-Abeta was much slower than that with SOD. Overall, our results suggest that His6, His13, and His14 residues of Abeta1-42 control the redox activity of transition metals present in senile plaques.

Dielectric spectroscopy measurements for aqueous urea solutions were performed at 298 K through a concentration range from 0.5 to 9.0 M with frequencies between 200 MHz and 40 GHz. Observed dielectric spectra were well represented by the superposition of two Debye type relaxation processes attributable to the bulk-water clusters and the urea-water coclusters. Our quantitative analysis of the spectra shows that the number of hydration water molecules is approximately two per urea molecule for the lower concentration region below 5.0 M, while the previous molecular dynamics studies predicted approximately six water molecules. It was also indicated by those studies, however, that there are two types of hydration water molecule in urea solution, which are strongly and weakly associated to the urea molecule, respectively. Only the strongly associated water was distinguishable in our analysis, while the weakly associated water exhibited the same dynamic feature as bulk water. This implies that urea retains the weakly associated water in the tetrahedral structure and, thus, is not a strong structure breaker of water. We also verified the model of liquid water where water consists of two states: the icelike-ordered and dense-disordered phases. Our dielectric data did not agree with the theoretical prediction based on the two-phase model. The present work supports the argument that urea molecules can easily replace near-neighbor water in the hydrogen-bonding network and do not require the presence of the disordered phase of water to dissolve into water.

Time domain dielectric spectroscopy has been used to study spherical erythrocytes, suspended in diluted phosphate buffered saline (PBS) buffers at varying concentrations of D-and L-glucose at 25˚C. The osmolarity for each glucose solution was adapted, equalling that of a 63% PBS (183 mOsm). The strong effect of the electrode polarization was corrected using the fractal approach in time domain. For analysis of the dielectric properties of suspensions of erythrocytes, the Maxwell-Wagner model is used for small volume fractions. Values of the permittivity and conductivity of the cell membrane were obtained from a fitting procedure according to the one-shell model. The non-monotonic and specific response of membrane electric properties on D-glucose concentrations were observed, with a dramatic decrease around 12 mM. No changes of membrane properties have been observed in the presence of increasing concentrations of L-glucose, the biologically inactive enantiomer of D-glucose. The effect is thus specific to D-glucose. The possible mechanism of specific cell reaction to D-glucose is discussed in this paper.

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