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Alzheimer's disease is a neurodegenerative disorder, for which no curative treatment has been developed yet. In 2007 the global prevalence was 29 million (Brookmeyer et al. 2007). The major contributors in the pathogenesis of the disease are the formation of Aβ plaques and neurofibrillary tangles. In addition neuroinflammation plays a significant role (Krause und Muller 2010). Kynurenic acid is produced in the kynurenine pathway, which has a central position in tryptophan catabolism. Kynurenic acid is an endogenous antagonist of the α7nAChR. In the literature a neuroprotective role for kynurenic acid has been described (Gulaj et al. 2010).
Objective of this thesis was to investigate the effect of kynurenic acid and Aβ on microglial cells using various in vitro experiments.
At first the modulation of α7nACh receptor expression by kynurenic acid was examined with Western blot. Furthermore the range of methods included MTT-assays and flow cytometry to study cell viability and apoptosis. For the detection of proinflammatory cytokines and NO in cell culture supernatants, cytokine-ELISAs and NO-assays were performed. In addition, the microglial phagocytosis of Aβ was examined using FITC-labeled Aβ and flow cytometry and verified using Western blots. The concentration of kynurenic acid in serum samples from patients with AD and healthy controls was determined with an ELISA.
Neither Aβ nor kynurenic acid showed an effect on the expression of α7nACh receptor. In terms of toxicity no change in cell viability was detected. However, a significant reduction in the rate of apoptosis after co-incubation with kynurenic acid could be achieved. Moreover it could be shown that kynurenic acid reduces Aβ-induced release of TNF-α significantly and of IL-6 and NO by trend. Microglial phagocytosis of Aβ could be reduced significantly by co-stimulation with kynurenic acid. In the ELISA no differences of kynurenic acid concentration in the sera of AD patients compared with healthy controls could be seen.
Taken together a protective effect of the endogenous α7nAChR antagonist kynurenic acid on Aβ-treated microglial cells could be detected in vitro and should be subjected to in vivo experiments using AD transgenic mice.