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Depression is one of the most frequent psychiatric disorders of Alzheimer's disease (AD). Depression and anxiety are associated with increased risk of developing AD. Silibinin, a flavonoid derived from milk thistle (Silybum marianum), has been used as a hepato-protectant in the clinical treatment of liver diseases. In this study, the effect of silibinin on Aβ-induced anxiety/depression-like behaviors in rats was investigated. Silibinin significantly attenuated anxiety/depression-like behaviors caused by Aβ1-42-treatment as shown in tail suspension test (TST), elevated plus maze (EPM) and forced swimming tests (FST). Moreover, silibinin was able to attenuate the neuronal damage in the hippocampus of Aβ1-42-injected rats. Silibinin-treatment up-regulated the function through BDNF/TrkB pathway and attenuated autophagy in the hippocampus. Our study provides a new insight into the protective effects of silibinin in the treatment of anxiety/depression.

Alzheimer's disease (AD) is a progressive, neurodegenerative disease. Accumulating evidence suggests that inflammatory response, oxidative stress and autophagy are involved in amyloid β (Aβ)-induced memory deficits. Silibinin (silybin), a flavonoid derived from the herb milk thistle, is well known for its hepatoprotective activities. In this study, we investigated the neuroprotective effect of silibinin on Aβ25-35-injected rats. Results demonstrated that silibinin significantly attenuated Aβ25-35-induced memory deficits in Morris water maze and novel object-recognition tests. Silibinin exerted anxiolytic effect in Aβ25-35-injected rats as determined in elevated plus maze test. Silibinin attenuated the inflammatory responses, increased glutathione (GSH) levels and decreased malondialdehyde (MDA) levels, and upregulated autophagy levels in the Aβ25-35-injected rats. In conclusion, silibinin is a potential candidate for AD treatment because of its anti-inflammatory, antioxidant and autophagy regulating activities.

To examine the sensitivity of a commercially available bovine spongiform encephalopathy (BSE) kit (NippIBL) for the detection of ovine scrapie, 50 scrapie-positive ovine samples from the UK, and 54 scrapie-negative ovine samples from Japan were obtain and tested using this kit. The sensitivity and specificity of NippIBL for ovine samples were 96% and 100%, respectively. The detection limit of the abnormal isoform of prion protein (PrP(Sc) ) of NippIBL was examined using diluted scrapie-positive samples. The sensitivity of NippIBL to ovine scrapie was 3-10 times superior to that of another commercial BSE diagnosis kit. Thus, the NippIBL kit proved more effective for the detection of ovine scrapie.

Prion diseases are fatal neurodegenerative disorders, and the conformational conversion of normal cellular prion protein (PrP(C)) into its pathogenic, amyloidogenic isoform (PrP(Sc)) is the essential event in the pathogenesis of these diseases. Lactoferrin (LF) is a cationic iron-binding glycoprotein belonging to the transferrin (TF) family, which accumulates in the amyloid deposits in the brain in neurodegenerative disorders, such as Alzheimer's disease and Pick's disease. In the present study, we have examined the effects of LF on PrP(Sc) formation by using cell culture models. Bovine LF inhibited PrP(Sc) accumulation in scrapie-infected cells in a time- and dose-dependent manner, whereas TF was not inhibitory. Bioassays of LF-treated cells demonstrated prolonged incubation periods compared with non-treated cells indicating a reduction of prion infectivity. LF mediated the cell surface retention of PrP(C) by diminishing its internalization and was capable of interacting with PrP(C) in addition to PrP(Sc). Furthermore, LF partially inhibited the formation of protease-resistant PrP as determined by the protein misfolding cyclic amplification assay. Our results suggest that LF has multifunctional antiprion activities.

In our previous study, we demonstrated the propagation of mouse-passaged scrapie isolates with long incubation periods (L-type) derived from natural Japanese sheep scrapie cases in murine hypothalamic GT1-7 cells, along with disease-associated prion protein (PrPSc) accumulation. We here analyzed the susceptibility of GT1-7 cells to scrapie prions by exposure to infected mouse brains at different passages, following interspecies transmission. Wild-type mice challenged with a natural sheep scrapie case (Kanagawa) exhibited heterogeneity of transmitted scrapie prions in early passages, and this mixed population converged upon one with a short incubation period (S-type) following subsequent passages. However, when GT1-7 cells were challenged with these heterologous samples, L-type prions became dominant. This study demonstrated that the susceptibility of GT1-7 cells to L-type prions was at least 105 times higher than that to S-type prions and that L-type prion-specific biological characteristics remained unchanged after serial passages in GT1-7 cells. This suggests that a GT1-7 cell culture model would be more useful for the economical and stable amplification of L-type prions at the laboratory level. Furthermore, this cell culture model might be used to selectively propagate L-type scrapie prions from a mixed prion population.

Conformational differences in abnormal prion proteins (PrP(Sc)) have been postulated to produce different prion phenotypes. During the interspecies transmission of prions, the conformation of PrP(Sc) may change with passage; however, little is known about the mechanism of PrP(Sc) transition. In this study, novel PrP(Sc)-specific monoclonal antibodies (mAbs) were developed that could detect the PrP(Sc) of mouse but not that of sheep. By using these mAbs, we attempted to examine PrP(Sc) accumulated in mice inoculated with sheep scrapie serially up to five passages. The presence of PrP(Sc) in the mice was confirmed at all passages; however, mAb-bound PrP(Sc) conformer was detected only from the third passage onward. The generated mAb enabled tracing of a particular conformer during adaptation in sheep-to-mice transmission of prion, suggesting that the conformational transition of PrP(Sc) was caused by propagation of this conformer. Such mAbs capable of discriminating conformational differences may allow us to address questions concerning PrP(Sc) conformation and strain diversity.

Several lines of evidence suggest that microglia have important roles in the pathogenesis of prion diseases. Here, we establish a novel microglial cell line (MG20) from neonatal tga20 mice that overexpress murine prion protein. After exposure to Chandler scrapie, we observed the replication and accumulation of disease-associated forms of the prion protein in MG20 cells up to the 15th passage. Furthermore, MG20 cells were susceptible to ME7, Obihiro scrapie, and bovine spongiform encephalopathy agents. Thus, MG20 cell lines persistently infected with various murine prion strains provide a useful model for the study of the pathogenesis of prion diseases.