| Objective:Alzheimer's disease(AD) is a neurodegenerative disease of the nervous system which is characterized by irreversible memory impairment, continuous cognitive decline,and behavioral disturbances.Amyloid-βpeptide (Aβ)is the main component of blood-vessel and core part of neuritic plaques,which is regarded as one of the most important disease-causing material.The etiology and pathogensis of AD are still unknown to date, but a growing body of evidence suggests that neuroinflammation may play a significant role in etiology and pathogenesis of AD and it is also the main case in animal paradigms of the disease. Glucagon-like peptide 1 (GLP-1)is a 30-amino acid peptide hormone produced in the intestinal epithelial endocrine L-cells, in response to meal intake.It has been documented that GLP-1 can induce neurite outgrow, neurotropic properties, and can protect cells against excessive glutamate and other toxic insults.GLP-1 is probably a promising agent in the therapy of AD.Compared with traditional fluorescent dye, Quantum Dots(QDs)is a new fluorescence probe which has significant advantages in fluorescent intensity and ray stability.Thus, molecular imaging of A 0 in Vivo by Quantum Dot can provide not only highly sensitive monitoring of the course of AD at the early stage, which will be of great help in early diagnosis, and also evaluation of the curative effect of GLP-1 used in early treatment.This study was designed to evaluate the biocompatibility and get the preliminary data of A in Vivo labeled by Quantum Dots-probe for real-time subsurface imaging in APP transgenic mice in Vivo, then to discuss the neuroprotective effect of intracerebroventricular injection of GLP-1 in APP transgenic mice, and revealed its probable mechanism.Methods:1.Normal C57BL mice were randomly divided into control-, QDs-Aβ-Ab-and QDs-group.Observing the response of injecting with respectively 5μL QDs, QDs-Aβ-Ab probe and saline in each group with behavioral comparison,HE staining, nissl staining, electron micrograph. Urine and blood cadmium levels were measured by HPLC.Hepatic and renal functions were detected by using automatic chemistry analyzer.2.10-and 16-month old APP transgenic mice and normal C57BL mice were randomly divided into T10,GLP-1A,GLP-1+ExA,normal groups and T16,GLP-IB,GLP-1+ExB,normal groups, After intracerebroventricular injection of respectively 5μL GLP-1,GLP-1 and Exendin Fragment 9-39, saline,do the Morris water maze tests and use behavioral comparison on each group.The histomorphology of hippocampus were tested by micrograph. TNF-a and IL-1βlevels were measured by enzyme-linked immunosorbent assay (ELISA). The expression of GFAP,Aβand GLP-1R were tested by immuno-stochemistry. The distribution of Aβand GLP-1R were observed by Quantum Dots immunofluorescence double-labeling part.The variable expression of GLP-1 mRNA was detected by Real-time PCR. p-p38MAPK protein levels were investigated by western blot.3.Monitoring the variation of Aβin T10,T16,GLP-1A and normal groups by using bio-imaging system and binocular stereomicroscope.After 3 days, using fluorescence microscope to detect the changes of the Aβin the frozen sections of the brain.Results:1. QDs-Aβ-Ab probe showed only one band as NH2-QDs-605 on the agarose gel electrophoresis.Cell morphology, ultrastructureand and nissl bodies in hippocampal CA1 of probe and QDs group mice are probably normal as control.After intracerebroventricular injecting with QDs and probes, t the urine cadmium levels were apparently higher than that in controls in 12 hours and down to normal as control in 1～7days. But there was little change in the blood cadmium level.The movements of all groups were normal.There was no significant difference in the content of serum ALT,AST,BUN and CRE among the three groups. 2.The learning and memory ability of APP transgenic mice was greatly declined, the ultrastructure in hippocampal CA1 shows neurons damage and is very vague. A part of distribution of Aβand GLP-1R were overlapped. The expression of IL-1β,TNFα, GFAP, Aβ,GLP-1R and p-p 38 are largely increased in APP transgenic mice, but the expressions are obviously decreased after GLP-1 treatment. GLP-1 had improved the spatial learning-memory in mices on a certain extent. GLP-1+ExA group had no significant change after treatment.3.There were some non-specific deposits after NH2-QDs-605 injection in brain, but the optical properties of QDs and the probe remain stable. By using QDs-Aβ-Ab probe to bio-image the Aβ, the spatial width of fluorescence in T16 group were wider than T10.The spatial width of fluorescence in T10 group becomes less after GLP-1 treatment. The frozen section showed the same change as bio-imaging.Conclusion:1.The QDs-Aβ-Ab probe is successfully constructed, which had no toxic effects and good biocompatibility in brain.2.GLP-1R are largely increased in APP transgenic mice. GLP-1 can improve the learning and memory ability combined with GLP-1R.3.GLP-1 can play a part as an inhibitor of p38 MAPK phosphorylation, which might be a mechanism for the inhibition of neuroinflammation4.The QDs-Aβ-Ab probe can be used in the investigation of the animal brain, and can effectively identify Aβ.5.Bio-imaging with QDs can evaluate the curative effect of drugs in AD animal model.
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