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The deposition of amyloid beta-protein in the brain is a fundamental process in the development of Alzheimeris disease; however, the mechanism underlying aggregation of amyloid beta-protein remains to be determined. Here, we report that a membrane-mimicking environment, generated in the presence of detergents or a ganglioside, is sufficient per se for amyloid fibril formation from soluble amyloid beta-protein. Furthermore, hereditary variants of amyloid beta-protein, which are caused by amyloid precursor protein gene mutations, including the Dutch (E693Q), Flemish (A692G) and Arctic (E693G) types, show mutually different aggregation behavior in these environments. Notably, the Arctic-type amyloid beta-protein, in contrast to the wild-type and other variant forms, shows a markedly rapid and higher level of amyloid fibril formation in the presence of sodium dodecyl sulfate or GM1 ganglioside. These results suggest that there are favorable local environments for fibrillogenesis of amyloid beta-protein.

Cerebral deposition of amyloid beta-peptide (Abeta) in the brain is an invariant feature of Alzheimer's disease (AD). A consistent protective effect of wine consumption on AD has been documented by epidemiological studies. In the present study, we used fluorescence spectroscopy with thioflavin T and electron microscopy to examine the effects of wine-related polyphenols (myricetin, morin, quercetin, kaempferol (+)-catechin and (-)-epicatechin) on the formation, extension, and destabilization of beta-amyloid fibrils (fAbeta) at pH 7.5 at 37 degrees C in vitro. All examined polyphenols dose-dependently inhibited formation of fAbeta from fresh Abeta(1-40) and Abeta(1-42), as well as their extension. Moreover, these polyphenols dose-dependently destabilized preformed fAbetas. The overall activity of the molecules examined was in the order of: myricetin = morin = quercetin > kaempferol > (+)-catechin = (-)-epicatechin. The effective concentrations (EC50) of myricetin, morin and quercetin for the formation, extension and destabilization of fAbetas were in the order of 0.1-1 micro m. In cell culture experiments, myricetin-treated fAbeta were suggested to be less toxic than intact fAbeta, as demonstrated by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay. Although the mechanisms by which these polyphenols inhibit fAbeta formation from Abeta, and destabilize pre-formed fAbetain vitro are still unclear, polyphenols could be a key molecule for the development of preventives and therapeutics for AD.

Inhibition of the accumulation of amyloid β-peptide (Aβ) and the formation of β-amyloid fibrils (fAβ) from Aβ, as well as the degradation of pre-formed fAβ in the CNS would be attractive therapeutic objectives for the treatment of Alzheimer's disease (AD). We previously reported that nordihydroguaiaretic acid (NDGA) inhibited fAβ formation from Aβ(1–40) and Aβ(1–42) dose-dependently in the range of 10–30 µmin vitro. Utilizing fluorescence spectroscopic analysis with thioflavin T and electron microscopic study, we show here that NDGA dose-dependently breaks down fAβ(1–40) and fAβ(1–42) within a few hours at pH 7.5 at 37°C. At 4 h, the fluorescence of fAβ(1–40) and fAβ(1–42) incubated with 50 µm NDGA was 5% and 10% of the initial fluorescence, respectively. The activity of NDGA to break down these fAβs was observed even at a low concentration of 0.1 µm. At 1 h, many short, sheared fibrils were observed in the mixture incubated with 50 µm NDGA, and at 4 h, the number of fibrils reduced markedly, and small amorphous aggregates were observed. We next compared the activity of NDGA to break down fAβ(1–40) and fAβ(1–42), with other molecules reported to inhibit fAβ formation from Aβ and/or to degrade pre-formed fAβ both in vivo and in vitro. At a concentration of 50 µm, the overall activity of the molecules examined in this study was in the order of: NDGA >> rifampicin = tetracycline > poly(vinylsulfonic acid, sodium salt) = 1,3-propanedisulfonic acid, disodium salt > β-sheet breaker peptide (iAβ5). In cell culture experiments, fAβ disrupted by NDGA were less toxic than intact fAβ, as demonstrated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Although the mechanisms by which NDGA inhibits fAβ formation from Aβ, as well as breaking down pre-formed fAβin vitro, are still unclear, NDGA could be a key molecule for the development of therapeutics for AD.

The deposition of amyloid beta-protein in the brain is a fundamental process in the development of Alzheimerís disease; however, the mechanism underlying aggregation of amyloid beta-protein remains to be determined. Here, we report that a membrane-mimicking environment, generated in the presence of detergents or a ganglioside, is sufficient per se for amyloid fibril formation from soluble amyloid beta-protein. Furthermore, hereditary variants of amyloid beta-protein, which are caused by amyloid precursor protein gene mutations, including the Dutch (E693Q), Flemish (A692G) and Arctic (E693G) types, show mutually different aggregation behavior in these environments. Notably, the Arctic-type amyloid beta-protein, in contrast to the wild-type and other variant forms, shows a markedly rapid and higher level of amyloid fibril formation in the presence of sodium dodecyl sulfate or GM1 ganglioside. These results suggest that there are favorable local environments for fibrillogenesis of amyloid beta-protein.

Cerebral deposition of amyloid beta-peptide (Abeta) in the brain is an invariant feature of Alzheimer's disease (AD). A consistent protective effect of wine consumption on AD has been documented by epidemiological studies. In the present study, we used fluorescence spectroscopy with thioflavin T and electron microscopy to examine the effects of wine-related polyphenols (myricetin, morin, quercetin, kaempferol (+)-catechin and (-)-epicatechin) on the formation, extension, and destabilization of beta-amyloid fibrils (fAbeta) at pH 7.5 at 37 degrees C in vitro. All examined polyphenols dose-dependently inhibited formation of fAbeta from fresh Abeta(1-40) and Abeta(1-42), as well as their extension. Moreover, these polyphenols dose-dependently destabilized preformed fAbetas. The overall activity of the molecules examined was in the order of: myricetin = morin = quercetinkaempferol(+)-catechin = (-)-epicatechin. The effective concentrations (EC50) of myricetin, morin and quercetin for the formation, extension and destabilization of fAbetas were in the order of 0.1-1 micro m. In cell culture experiments, myricetin-treated fAbeta were suggested to be less toxic than intact fAbeta, as demonstrated by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay. Although the mechanisms by which these polyphenols inhibit fAbeta formation from Abeta, and destabilize pre-formed fAbetain vitro are still unclear, polyphenols could be a key molecule for the development of preventives and therapeutics for AD.

Iron as well as aluminum is reported to accumulate in neurons with neurofibrillary tangles (NFTs) of Alzheimer's disease (AD) brain. Previously we demonstrated that aluminum (III) shows phosphate-dependent binding with hyperphosphorylated tau (PHFtau), the major constituent of NFTs, thereby inducing aggregation of PHFtau. Herein we report that iron (III) can also induce aggregation of soluble PHFtau. Importantly, for the aggregation of PHFtau to occur, iron in the oxidized state (III) is essential since iron in the reduced state (II) lacks such ability. Furthermore, iron (III)-induced aggregation is reversed by reducing iron (III) to iron (II). Thus the iron-participating aggregation is mediated not only by tau phosphorylation but also by the transition of iron between reduced (II) and oxidized (III) states. Further incubation of insoluble PHFtau aggregates isolated from AD brain with reducing agents produced liberation of solubilized PHFtau and iron (II), indicating that PHFtau in association with iron (III) constitutes the insoluble pool of PHFtau. These results indicate that iron might play a role in the aggregation of PHFtau leading to the formation of NFTs in AD brain.

Inhibition of the accumulation of amyloid beta-peptide (Abeta) and the formation of beta-amyloid fibrils (fAbeta) from Abeta, as well as the degradation of pre-formed fAbeta in the CNS would be attractive therapeutic objectives for the treatment of Alzheimer's disease (AD). We previously reported that nordihydroguaiaretic acid (NDGA) inhibited fAbeta formation from Abeta(1-40) and Abeta(1-42) dose-dependently in the range of 10-30 micromin vitro. Utilizing fluorescence spectroscopic analysis with thioflavin T and electron microscopic study, we show here that NDGA dose-dependently breaks down fAbeta(1-40) and fAbeta(1-42) within a few hours at pH 7.5 at 37 degrees C. At 4 h, the fluorescence of fAbeta(1-40) and fAbeta(1-42) incubated with 50 microm NDGA was 5% and 10% of the initial fluorescence, respectively. The activity of NDGA to break down these fAbetas was observed even at a low concentration of 0.1 microm. At 1 h, many short, sheared fibrils were observed in the mixture incubated with 50 microm NDGA, and at 4 h, the number of fibrils reduced markedly, and small amorphous aggregates were observed. We next compared the activity of NDGA to break down fAbeta(1-40) and fAbeta(1-42), with other molecules reported to inhibit fAbeta formation from Abeta and/or to degrade pre-formed fAbeta both in vivo and in vitro. At a concentration of 50 microm, the overall activity of the molecules examined in this study was in the order of: NDGArifampicin = tetracyclinepoly(vinylsulfonic acid, sodium salt) = 1,3-propanedisulfonic acid, disodium saltbeta-sheet breaker peptide (iAbeta5). In cell culture experiments, fAbeta disrupted by NDGA were less toxic than intact fAbeta, as demonstrated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Although the mechanisms by which NDGA inhibits fAbeta formation from Abeta, as well as breaking down pre-formed fAbetain vitro, are still unclear, NDGA could be a key molecule for the development of therapeutics for AD.

Iron as well as aluminum is reported to accumulate in neurons with neurofibrillary tangles (NFTs) of Alzheimer's disease (AD) brain. Previously we demonstrated that aluminum (III) shows phosphate-dependent binding with hyperphosphorylated τ (PHFτ), the major constituent of NFTs, thereby inducing aggregation of PHFτ. Herein we report that iron (III) can also induce aggregation of soluble PHFτ. Importantly, for the aggregation of PHFτ to occur, iron in the oxidized state (III) is essential since iron in the reduced state (II) lacks such ability. Furthermore, iron (III)-induced aggregation is reversed by reducing iron (III) to iron (II). Thus the iron-participating aggregation is mediated not only by τ phosphorylation but also by the transition of iron between reduced (II) and oxidized (III) states. Further incubation of insoluble PHFτ aggregates isolated from AD brain with reducing agents produced liberation of solubilized PHFτ and iron (II), indicating that PHFτ in association with iron (III) constitutes the insoluble pool of PHFτ. These results indicate that iron might play a role in the aggregation of PHFτ leading to the formation of NFTs in AD brain.