Investigations Of Neurotransmitters Interacting With Amyloid β-peptide

A(3is the major constitute of senile plaque, a hallmark in the brain of AD victims. It is well-known that Aβ is crucial for the development of AD. The interactions of Aβ with neurotransmitters (Cu DA and NE) may affect the neuron. And the interactions of A(3with Cu2+DA and NE are very important for the neurobiological processes and pathogenesis of AD, therefore, the mechanisms of A(3interacting with Cu2+, DA and NE are investigated to get the kinetic constants, and the roles of A(3interacting with Cu2+, DA and NE in the pathogenesis of AD are discussed preliminarily. Base on the above considerations, the following studies were carried out.(1) Interactions of Aβ with Cu2+are known to be pH-dependent and believed to play a crucial role in the neurotoxicity of AD. However, there is no reports about the affinity of Aβ-Cu2+under acidic pH. In this study, SPR sensor with immobilized Aβ was used to investigate the formation of Aβ-Cu2+complexes under acidic pH conditions. Dissociation constants (Kd) were calculated and shown to be pH-dependent, ranging from8.7×10-3to3.5×10-8mol·L-1under pH4.0-7.0. The physiological significance of Kd was preliminarily investigated by monitoring the generation of·OH in aerobic solutions containing Aβ-Cu2+and Cu2+. The results imply that acidic conditions could aggravate the oxidative stress in the presence of Cu2+, and the weak affinities of Aβ-Cu2+under acidic pH could further enhance the oxidative damage. However, under mildly acidic pH conditions, the formation of Ap-Cu2+reduced free Cu2+, inhibited the generation of·OH. In biological milieu, Aβ could protect neuron from oxidative stress.(2) Numerous studies in the recent ten years show a large variation on the dissociation constant of Aβ-Cu2+under different solvent conditions. Among the common buffers, Tris is considered to be the most reliable. However, Tris is rich of nucleophilic groups, so it may have a more diversified role in the interaction of Aβ with Cu2+. Under acidic conditions, a Tris-Aβ-Cu2+ternary complex was identified using ESI-MS and TEM. The results of surface plasmon resonance reveal that the formation of a ternary complex increases the dissociation constant by almost one order of magnitude. Consequently, toxicity assessment indicates that the generation of-OH induced by the Aβ-Cu2+complex is enhanced in the presence of Tris. Increased pH condition disfavors the formation of Tris-Ap-Cu2+complex.(3) Due to the controversial effects of DA on the toxicity of Aβ and the development of AD, it is necessary to understand the interaction of Aβ with DA. In this study, the stoichiometric ratio (1:1), binding site (Tyr10) and dissociation constant (KA=0.30μmol·L-1) of DA interacting with Aβ1-16were revealed. The physiological significance of Kd was investigated by monitoring the generation of·OH in aerobic solutions containing Cu2+. The results demonstrat that DA inhibits the interaction of Aβ with Cu2+, enhances the generation of-OH. The CD results preliminarily imply that DA may improve the formation of Aβ oligomer, and then enhance the neurotoxicity.(4) The stoichiometric ratio (1:1), binding site (Tyr10) and dissociation constant (Kd=0.25μmol·-L-1) of NE interacting with Aβwere revealed by electrochemistry and SPR techniques. The physiological significance of Kd was investigated by monitoring the generation of·OH in aerobic solutions containing Cu2+. The results demonstrate that NE inhibits the interaction of Aβ with Cu2+, enhances the generation of-OH. The CD results preliminarily imply that NE may improve the formation of Aβ oligomer.