Stimulation of the amyloidogenic pathway by cytoplasmic superoxide radicals in an Alzheimer's disease mouse model.

Oxidative stress is involved in the pathogenesis of neurodegeneration. Amyloid ß (Aß) oligomer as an intermediate of aggregates causes memory loss in Alzheimer's disease (AD). We have suggested that oxidative stress plays an important role in Aß oligomerization and cognitive impairment using a human amyloid precursor protein (hAPP) transgenic AD mice lacking cytoplasmic superoxide dismutase (hAPP/Sod1-/-). Recently, clinical trials revealed inhibitors of Aß production from hAPP as promising therapeutics, but the relationship between oxidative stress and Aß metabolism remains unclear. Here we found that Sod1 deficiency enhanced ß-cleavage of hAPP, suggesting that it increased Aß production in hAPP/Sod1-/- mice. In contrast, Aß degradation did not decrease in hAPP/Sod1-/- as compared with hAPP/Sod1+/+ mice. Furthermore, we successfully detected in situ superoxide radicals associated with increased protein carbonylation in hAPP/Sod1-/-. These results suggest that cytoplasmic oxidative stress is involved in Aß production as well as aggregation during AD progression.

SOD1 (copper/zinc superoxide dismutase) deficiency drives amyloid ß protein oligomerization and memory loss in mouse model of Alzheimer disease.

Oxidative stress is closely linked to the pathogenesis of neurodegeneration. Soluble amyloid ß (Aß) oligomers cause cognitive impairment and synaptic dysfunction in Alzheimer disease (AD). However, the relationship between oligomers, oxidative stress, and their localization during disease progression is uncertain. Our previous study demonstrated that mice deficient in cytoplasmic copper/zinc superoxide dismutase (CuZn-SOD, SOD1) have features of drusen formation, a hallmark of age-related macular degeneration (Imamura, Y., Noda, S., Hashizume, K., Shinoda, K., Yamaguchi, M., Uchiyama, S., Shimizu, T., Mizushima, Y., Shirasawa, T., and Tsubota, K. (2006) Proc. Natl. Acad. Sci. U.S.A. 103, 11282-11287). Amyloid assembly has been implicated as a common mechanism of plaque and drusen formation. Here, we show that Sod1 deficiency in an amyloid precursor protein-overexpressing mouse model (AD mouse, Tg2576) accelerated Aß oligomerization and memory impairment as compared with control AD mouse and that these phenomena were basically mediated by oxidative damage. The increased plaque and neuronal inflammation were accompanied by the generation of N(ε)-carboxymethyl lysine in advanced glycation end products, a rapid marker of oxidative damage, induced by Sod1 gene-dependent reduction. The Sod1 deletion also caused Tau phosphorylation and the lower levels of synaptophysin. Furthermore, the levels of SOD1 were significantly decreased in human AD patients rather than non-AD age-matched individuals, but mitochondrial SOD (Mn-SOD, SOD2) and extracellular SOD (CuZn-SOD, SOD3) were not. These findings suggest that cytoplasmic superoxide radical plays a critical role in the pathogenesis of AD. Activation of Sod1 may be a therapeutic strategy for the inhibition of AD progression.

Vitamin C restores behavioral deficits and amyloid-ß oligomerization without affecting plaque formation in a mouse model of Alzheimer's disease.

Oxidative stress is related to the pathogenesis of Alzheimer's disease (AD) characterized by progressive memory impairment. Soluble amyloid-ß (Aß) oligomers cause cognitive loss and synaptic dysfunction rather than senile plaques in AD. The decline of the antioxidant status is associated with dementia in AD patients, especially low levels of vitamin C. Our group previously reported a relationship between anti-aging and supplementation of vitamin C derivatives. Here we report that vitamin C mitigated Aß oligomer formation and behavioral decline in an AD mouse model treated with a vitamin C solution for 6 months. The attenuation of Aß oligomerization was accompanied with a marked decrease in brain oxidative damage and in the ratio of soluble Aß42 to Aß40, a typical indicator of AD progression. Furthermore, the intake of vitamin C restored the declined synaptophysin and the phosphorylation of tau at Ser396. On the other hand, brain plaque deposition was not altered by the dietary intake of vitamin C. These results support that vitamin C is a useful functional nutrient for the prevention of AD.

Insulin receptor mutation results in insulin resistance and hyperinsulinemia but does not exacerbate Alzheimer's-like phenotypes in mice.

Obesity is a risk factor for Alzheimer's disease (AD), which is characterized by amyloid ß depositions and cognitive dysfunction. Although insulin resistance is one of the phenotypes of obesity, its deleterious effects on AD progression remain to be fully elucidated. We previously reported that the suppression of insulin signaling in a mouse with a heterozygous mutation (P1195L) in the gene for the insulin receptor showed insulin resistance and hyperinsulinemia but did not develop diabetes mellitus [15]. Here, we generated a novel AD mouse model carrying the same insulin receptor mutation and showed that the combination of insulin resistance and hyperinsulinemia did not accelerate plaque formation or memory abnormalities in these mice. Interestingly, the insulin receptor mutation reduced oxidative damage in the brains of the AD mice. These findings suggest that insulin resistance is not always involved in the pathogenesis of AD.

Silymarin attenuated the amyloid ß plaque burden and improved behavioral abnormalities in an Alzheimer's disease mouse model.

Alzheimer's disease (AD) is characterized by progressive cognitive impairment and the formation of senile plaques. Silymarin, an extract of milk thistle, has long been used as a medicinal herb for liver diseases. Here we report marked suppression of amyloid ß-protein (Aß) fibril formation and neurotoxicity in PC12 cells after silymarin treatment in vitro. In vivo studies had indicated a significant reduction in brain Aß deposition and improvement in behavioral abnormalities in amyloid precursor protein (APP) transgenic mice that had been preventively treated with a powdered diet containing 0.1% silymarin for 6 months. The silymarin-treated APP mice also showed less anxiety than the vehicle-treated APP mice. These behavioral changes were associated with a decline in Aß oligomer production induced by silymarin intake. These results suggest that silymarin is a promising agent for the prevention of AD.

Monoclonal antibody against the turn of the 42-residue amyloid ß-protein at positions 22 and 23.

Aggregation of the 42-mer amyloid ß-protein (Aß42) plays a critical role in the pathogenesis of Alzheimer's disease (AD). We have proposed a toxic conformer with a turn at positions 22 and 23, as well as a nontoxic conformer with a turn at positions 25 and 26, in Aß42 aggregates from systematic proline scanning and solid-state NMR studies. Although recent clinical trials of immunization targeting Aß42 aggregates have proved useful, some adverse effects were reported. One of the reasons was hypothesized to be excessive immunoreactions derived from the unintended removal of nontoxic Aß42, which plays an important role in the physiological function. To develop a monoclonal antibody for toxic Aß42, E22P-Aß10-35, a minimum moiety for neurotoxicity containing the turn at positions 22 and 23, was used for the generation of antibodies, following the selection of clones using Aß42 mutants of E22P (turn-inducing) and E22V (turn-preventing). The obtained clone (11A1) showed a high binding affinity (K(D) = 10.3 nM) for Aß42 using surface plasmon resonance. 11A1 also inhibited the neurotoxicity of Aß42 in PC12 cells. Immunohistochemical studies showed that not only extracellular but intracellular amyloid was stained in human AD brains. In Western blotting analyses using human brains, low-molecular weight-oligomers rather than the monomer of Aß were readily recognized by 11A1. These results imply that 11A1 could detect toxic Aß42 oligomers with the turn at positions 22 and 23 and that 11A1 could be applicable for the therapeutic targeting of toxic Aß42 in AD.