The prevailing amyloid hypothesis for Alzheimer's disease (AD) holds that amyloid beta-protein (Abeta) causes neuronal degeneration by forming neurotoxic fibrillar structures. Yet, many aspects of AD pathology and symptoms are not well explained by this hypothesis. Here, we present evidence that neurotoxicity of soluble oligomeric Abeta closely corresponds to the selective neurodegeneration so distinctly manifest in AD. Selectivity was first observed in vitro, where only the human central nervous system neuronal cells were susceptible to soluble oligomeric Abeta. Furthermore, in mouse cerebral slice treated with soluble oligomeric Abeta, selective regiospecific toxicity was evident in the hippocampal CA1, a division important for memory, but not in the CA3 subfield. The fibrillar Abeta, however, killed neurons in all regions of the cerebral slice cultures and also in cerebellar slices. Remarkably, even at the highest soluble oligomeric Abeta concentrations, cerebellar neurons were completely spared, consistent with one of the hallmark features of AD pathology. Our observation of the selective neurodegeneration of soluble oligomeric Abeta to neurons involved in cognitive function may provide a new opportunity for the development of an effective AD therapy as well as elucidating the pathological mechanism of AD.

: Pharmacological studies and clinical practices have indicated that Radix Astragali, a dried root of Astragalus membranaceus possesses a lot of biological activities, including antioxidant, hepatoprotective, anti-diabetic, tonic, diuretic, antimicrobial, antiviral, and immunological activities. These biological activities approved by the modern pharmacological studies are mainly due to the constituents of Astragalus membranaceus including polysaccharides, saponins, flavonoids, amino acids, and trace elements. In resent, the main constituents in the root part showing a lot of biological activities has been isolated also from the aboveground parts such as leaves and sprouts in our laboratory. However, the safety evaluation for the aboveground parts of Astragalus membranaceus should be checked before expanding their application as one of food. In the study, a 90-day rat oral gavage study has been conducted with the extracts from Astragalus membranaceus-aboveground parts at doses of 1000, 3000, and 5000 ㎎/㎏/day. The following endpoints were evaluated: clinical observations, body weight, gross and microscopic pathology, clinical chemistry, and hematology. Based on the analysis of these endpoints, it was estimated that NOEL (no observed effect level) for male rats and NOAEL (no observed adverse effect level) for female rats are 5000 ㎎/㎏/day of the water-extracts from Astragalus membranaceus-aboveground parts.

: The six polysaccharide fractions were prepared by chromatographic procedure from the hot water extracts of the aboveground parts of Astragalus membranaceus. These six polysaccharides from aboveground parts of Astragalus membranaceus Bunge were tested for gut-mucosal immune activity and acute toxicity. In a view of molecular weight, the six fractions were estimated to be 75000, 88000, 129000 and 345000 Da, respectively. Component sugar analysis indicated that these fractions were mainly consisted of galactose (46.3~11.8%) and arabinose (35.4~9.9%) in addition to glucose, rhamnose, fucose, arabinose, xylose, mannose, glucuronic acid and galacturonic acid. Among the six major purified polysaccharides, AMA-1-b-PS2 showed highest bone merrow cell proliferation and lymphocyte of Peyer's patch stimulating activity. It may be concluded that intestinal immune system modulating activity of aboveground parts from Astragalus membranaceus Bunge is caused by polysaccharides having a polygalacturonan moiety with neutral sugars such as arabinose and galactose. In single oral dose toxicity study, no differences were observed between control and treated groups in clinical signs. The results indicated that lethal dose 50 (LD 50 ) of water extracts from Astragalus membranaceus-aboveground parts was found to be higher than 5000 ㎎/㎏/day in this experiment. From the above results, we may suggest that Astragalus membranaceus-aboveground parts might have useful as a safe material for functional food and pharmaceutics.

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-The object of this study was to obtain single oral dose toxicity of Arisaema Rhizome (Arisaema amurense f. serratum (Nakai) Kitag) aqueous extracts. Arisaema Rhizome (Chunnamsong in Korean) is one of the most important folk remedy plants used in Asia. In the study, a 28-day rat oral gavage study has been conducted with the extracts from Arisaema Rhizome at dose of 1,250, 2,500 and 5,000 ㎎/㎏/day. The following endpoints were evaluated: clinical observations, body weight, gross and microscopic pathology, clinical chemistry, and hematology. Based on the analysis of these endpoints, it was estimated that NOEL (no observed effect level) for male rats and NOAEL (no observed adverse effect level) for female rats are 5000 ㎎/㎏/day of the water-extracts from Arisaema Rhizome.