Effects of Fish Oil Combined with Selenium and Zinc on Learning and Memory Impairment in Aging Mice and Amyloid Precursor Protein Processing.

Alzheimer's disease is characterized by the aggregation of amyloid-beta (Aß) peptide into plaques and neurofibrillary tangles. Aß peptide is generated by the cleavage of the ß-amyloid precursor protein (APP) by ß- and γ-secretase. The present study was conducted to investigate the effects of fish oil (or eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)), selenium, and zinc on learning and memory impairment in an aging mouse model and on APP. We performed the Morris water maze and platform recorder tests on male Kunming mice (10/group) grouped as control and D-galactose-induced aging model mice treated with vehicle, fish oil, fish oil + selenium, fish oil + selenium + zinc, and positive control (red ginseng extract). Fish oil + zinc + selenium for 7 weeks significantly improved learning and memory impairments in aging model animals in the Morris water maze and platform recorder tests, as evidenced by shortened incubation periods and number of errors. In vitro analysis of Aß1-40 content in APP695-transfected CHO cells revealed a decrease after treatment with EPA, DHA, and their combinations with selenium or selenium and zinc. Assaying ß- and γ-secretase activities revealed a decrease in PC12 cells and mouse serum as well as a decrease in ß-site APP-cleaving enzyme 1 and presenilin 1 protein levels in the PC12 cells and mouse serum. Taken together, our results show that fish oil combined with selenium and zinc inhibited APP processing and alleviated learning and memory impairment in a mouse model of aging.

C-terminal fragments of amyloid precursor proteins increase cofilin phosphorylation by LIM kinase in cultured rat primary neurons.

Amyloid precursor proteins (APPs) are processed by ß-, γ-, and ε-secretases and caspase-3 to generate C-terminal fragments of APP (APP-CTFs), which may contribute to the pathology of Alzheimer's disease (AD). In addition to amyloid plaques and neurofibrillary tangles, AD brains contain Hirano bodies, which are rod-like structures mostly composed of actin and the actin-binding protein, cofilin. However, the mechanisms underlying the formation of cofilin-actin rods are still unknown. In this study, we aim to elucidate the effects of APP-CTFs on the actin-depolymerizing factor [(ADF)/cofilin]. Our data indicate that transfection with APP-CT99 and APP-CT57 may increase the phosphorylation level of Ser3 of ADF/cofilin and Thr508 of LIM-kinase 1 in rat primary cortical neuronal cultures. S3 peptide, a synthetic peptide competitor of LIM-kinase 1 for ADF/cofilin phosphorylation and an inhibitor of APP-CTFs, induced ADF/cofilin phosphorylation. In comparison with the wild-type mouse, the APP-CT transgenic mouse showed increased immunoreactivity of phosphorylated cofilin (p-cofilin) in the brain. Treatment with DAPT, an inhibitor of γ-secretase, resulted in a decrease in p-cofilin protein level in the group transfected with full-length APP-695. Transfection with the mutant APP-CTF with a deleted YENPTY domain resulted in no significant increase in p-cofilin level. Thus, APP-CTFs induced cofilin phosphorylation to facilitate nuclear translocation. These results suggest a relationship between APP-CTFs and ADF/cofilin that may be suggestive of a new toxic pathway in the pathology of AD.

Selenium and Zinc against Aß25-35-Induced Cytotoxicity and Tau Phosphorylation in PC12 Cells and Inhibits γ-cleavage of APP.

Amyloid beta (Aß) is the main component of the amyloid plaques that accumulate in the brains of Alzheimer patients. The present study was conducted to investigate whether the combined treatment with selenium (Se) and zinc (Zn) offers more beneficial effects than that provided by either of them alone in reversing Aß25-35-induced neurotoxicity in PC12 cells. Cells were pretreated with 0.1 µmol/L of Se and Zn for 4 h, after treated with 10 mmol/L Aß25-35 for 24 h. Cells were divided into control and five treated groups, and received either 10 mmol/L Aß25-35,10 mmol/L Aß25-35 + 0.1 µmol/L Se, 10 mmol/L Aß25-35 + 0.1 µmol/L Zn, 10 mmol/LAß25-35 + 0.1 µmol/L Se + 0.1 µmol/L Zn, or 0.1 µmol/L Se + 0.1 µmol/L Zn. The result showed that cell viability was decreased in MTT metabolic rate; LDH release and MDA, H2O2, and NO levels were increased and the GSK-3ß and phosphorylated tau protein level were increased in Aß25-35-treated group (P < 0.05 or P < 0.01), which whole changes were attenuated by Se and Zn and Se combined Zn. In order to evaluate whether the Se and Zn have an effect on processing pathway of amyloid precursor protein (APP), we examined the activity of γ-secretase in primary cultured cortical neuron cells. ELISA analysis showed that Se and Zn could inhibit the activity of γ-secretase. Then we also investigated the effect of Se and Zn on the Aß1-40 concentration and APP-N-terminal fragment expression from APP695 stably transfected Chinese hamster ovary (CHO) cells. APP695 stably transfected CHO cells were treated with 0.1 µmol/L Se and Zn; cells were divided into control and four treated groups, which received either 0.5 M DAPT, 0.1 µmol/L Se, 0.1 µmol/L Zn, or 0.1 µmol/L Se + 0.1 µmol/L Zn. Se and Zn could decrease Aß1-40 production and increase the APP-N-terminal fragment protein expression. These experiments indicate that Se and Zn have a protective effect on AD pathology that a possible mechanism is inhibiting the activity of γ-secretase to decreasing Aß1-40 production further influencing the APP processing. Altogether, our findings may provide a novel therapeutic target to treat AD sufferers.