ABSTRACT
This study investigated the effects of a silk peptide fraction obtained by incubating silk proteins with Protease N and Neutrase (SP-NN) on cognitive dysfunction of Alzheimer disease model rats. In order to elucidate underlying mechanisms, the effect of SP-NN on the expression of choline acetyltransferase (ChAT) mRNA was assessed in F3.ChAT neural stem cells and Neuro2a neuroblastoma cells; active amino acid sequence was identified using HPLC-MS. The expression of ChAT mRNA in F3.ChAT cells increased by 3.79-fold of the control level by treatment with SP-NN fraction. The active peptide in SP-NN was identified as tyrosine-glycine with 238.1 of molecular weight. Male rats were orally administered with SP-NN (50 or 300mg/kg) and challenged with a cholinotoxin AF64A. As a result of brain injury and decreased brain acetylcholine level, AF64A induced astrocytic activation, resulting in impairment of learning and memory function. Treatment with SP-NN exerted recovering activities on acetylcholine depletion and brain injury, as well as cognitive deficit induced by AF64A. The results indicate that, in addition to a neuroprotective activity, the SP-NN preparation restores cognitive function of Alzheimer disease model rats by increasing the release of acetylcholine.
Subject(s)
Alzheimer Disease/psychology , Aziridines/toxicity , Choline O-Acetyltransferase/genetics , Choline/analogs & derivatives , Cognition/drug effects , Disease Models, Animal , Insect Proteins/chemistry , Peptide Fragments/pharmacology , Silk/chemistry , Alzheimer Disease/chemically induced , Animals , Avoidance Learning/drug effects , Cell Line, Tumor , Choline/toxicity , Gene Expression Regulation, Enzymologic , Male , Maze Learning/drug effects , Rats , Rats, Sprague-DawleyABSTRACT
PURPOSE: The objective was to confirm the anti-obesity activity of a silk peptide (SP) and a silkworm pupa peptide (SPP) in rats fed a high-fat diet (HFD) and to elucidate their action mechanism(s) in a preadipocyte culture system. METHODS: In an in vitro mechanistic study, the differentiation and maturation of 3T3-L1 preadipocytes were stimulated with insulin (5 µg/mL), and effects of SP and SPP on the adipogenesis of mature adipocytes were assessed. In an in vivo anti-obesity study, male C57BL/6 mice were fed an HFD containing SP or SPP (0.3, 1.0, or 3.0%) for 8 weeks, and blood and tissue parameters of obesity were analyzed. RESULTS: Hormonal stimulation of preadipocytes led to a 50-70% increase in adipogenesis. Polymerase chain reaction and Western blot analyses revealed increases in adipogenesis-specific genes (leptin and Acrp30) and proteins (peroxisome proliferator-activated receptor-γ and Acrp30). The hormone-induced adipogenesis and activated gene expression was substantially inhibited by treatment with SP and SPP (1-50 µg/mL). The HFD markedly increased body weight gain by increasing the weight of epididymal and mesenteric fat. Body and fat weights were significantly reduced by SP and SPP, in which decreases in the area of abdominal adipose tissue and the size of epididymal adipocytes were confirmed by magnetic resonance imaging and microscopic examination, respectively. Long-term HFD caused hepatic lipid accumulation and increased blood triglycerides and cholesterol, in addition to their regulatory factors Acrp30 and leptin. However, SP and SPP recovered the concentrations of Acrp30 and leptin, and attenuated steatosis. CONCLUSIONS: SP and SPP inhibit the differentiation of preadipocytes and adipogenesis by modulating signal transduction pathways and improve HFD-induced obesity by reducing lipid accumulation and the size of adipocytes.
