Nordihydroguaiaretic acid potently breaks down pre-formed Alzheimer's β-amyloid fibrils in vitro

Abstract

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(1-42) and Aβ(1-42) dose-dependently in the range of 10-30 μM in 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 vivoand 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 preformed fAβ in vitro, are still unclear, NDGA could be a key molecule for the development of therapeutics for AD.