GSPE attenuates aggregation of Aβ peptides into soluble oligomeric forms in vitro. A, B, Dose-dependent inhibition by GSPE of synthetic Aβ_1–42 or Aβ_1–40 peptide aggregation into HMW oligomeric Aβ forms. Aβ_1–42 (final concentration 50 µg/ml) or Aβ_1–40 (final concentration 50 µg/ml) peptide was incubated with various concentrations of GSPE [lanes1–6, 0, 0.2, 1, 5, 25, and 100 µm; CTR (control) are samples without incubation] at 37°C for 24 h. Bands were visualized by Western blot analysis probed with 6E10 antibody. C, D, SDS-PAGE of Aβ_1–42 and Aβ_1–40 in the presence or absence of GSPE after PICUP (see Materials and Methods). Aβ_1–42 or Aβ_1–40 was cross-linked in the presence or absence of 50 µm GSPE, and the bands were visualized using silver staining. CTR, Non-cross-linked Aβ_1–42 (C) or Aβ_1–40 (D); lanes 1 and 2, Aβ peptide with 1× Ru(Bpy) and APS in the absence and presence of GSPE; lanes 3 and 4, Aβ peptide with 2× Ru(Bpy) and APS in the absence and presence of GSPE. The data are representative of results obtained in each of three independent experiments. The ~13.5 kDa (trimer) bands are an SDS-induced artifact (Bitan et al., 2003).

Chronic treatment of Tg2576 mice with GSPE prevents amyloid neuropathology by prevention of Aβ oligomerization. A, B, GSPE has no effect on body weight (A) or liquid consumption (B) in Tg2576 mice after 5 months of treatment. C, Assessments of PBS-soluble, extracellular HMW Aβ peptide content in the brain using an antibody (A11) specific for HMW oligomeric Aβ peptides in a dot blot analysis. C, Inset, Representative dot blot analysis of HMW soluble Aβ contents. D, Western blot analysis of soluble extracellular HMW oligomeric Aβ peptide (antibody A11) and monomeric Aβ peptide (antibody 6E10) in the brain of Tg2576 mice. E, Assessment of Aβ_1–42 and Aβ_1–40 peptide concentrations in the brain of GSPE-treated or control mice. F, Stereological assessment of cerebral cortex and hippocampal formation Aβ amyloid plaque burden in GSPE-treated or control mice expressed as thioflavin-S-positive volume as a percentage of regional volume. F, Inset, Representative photographs of thioflavin-S-positive Aβ amyloid plaque neuropathology in neocortex (CTX) and hippocampal formation (Hippo) in untreated control (top) and GSPE-treated (bottom) Tg2576 mice. Values represent group mean ± SEM. n = 5–8 mice per group. *p < 0.05, **p < 0.01 by two-tailed Student’s t test analysis. CTL, Control.

Treatment with GSPE attenuates cognitive deterioration in Tg2576 mice coincidentally with decreased extracellular HMW oligomeric Aβ. A–D, The influence of GSPE on Aβ-related spatial memory in Tg2576 mice versus the untreated control mice by Morris water maze test. A, Hidden platform acquisition. Latency score represents time taken to escape to the platform from the water. B, Motor function of the GSPE-treated animals and the control animals as reflected by their swim speeds. C, D, Probe trial. Percentage of time in quadrant is calculated as the ratio of time spent in the target quadrant area relative to the time spent in the rest of the pool. Platform crossing is calculated as the number of crosses over the exact location of the hidden platform. E, Assessments of soluble, extracellular HMW Aβ peptide contents in the brain of Tg2576 mice using an antibody specific for HMW oligomeric Aβ peptides in a dot blot analysis. E, Inset, Representative dot blot analysis of HMW soluble Aβ contents. Values represent group mean ± SEM. n = 6–7 mice per group. C–E, *p < 0.05 by two-tailed Student’s t test analysis. CTL, Control.