amyloid-beta-peptides and 6-7-dihydroxyflavone

Interest in brain-derived neurotrophic factor (BDNF) was greatly enhanced when it was recognized that its expression is reduced in neurodegenerative disorders, especially in Alzheimer's disease (AD). BDNF signaling through the TrkB receptor has a central role in promoting synaptic transmission, synaptogenesis, and facilitating synaptic plasticity making the BDNF-TrkB signaling pathway an attractive candidate for targeted therapies. Here we investigated the early effect of the small molecule TrkB agonist, 7,8 dihydroxyflavone (7,8-DHF), on AD-related pathology, dendritic arborization, synaptic density, and neurochemical changes in the 5xFAD mouse model of AD. We treated 5xFAD mice with 7,8-DHF for 2 months beginning at 1 month of age. We found that, in this model of AD, 7,8-DHF treatment decreased cortical Aβ plaque deposition and protected cortical neurons against reduced dendritic arbor complexity but had no significant impact on the density of dendritic spines. In addition 7,8-DHF treatment protected against hippocampal increase in the level of choline-containing compounds and glutamate loss, but had no significant impact on hippocampal neurogenesis.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Animals; Dendritic Spines; Disease Models, Animal; Flavones; Hippocampus; Mice; Neuroprotective Agents; Peptide Fragments

It is reported that 7,8-dihydroxyflavone (DHF), a TrkB agonist, has beneficial effects on neuronal excitotoxicity, stroke, and Parkinson disease in animal models by enhancing axon regeneration, muscle reinnervation and neuromuscular transmission. The effect of DHF on AD neuropathology remains not well defined. In this study we examined whether DHF affects APP processing and cognitive functions in vitro and in vivo. We found that DHF had no significant effect on amyloid β precursor protein (APP), BACE1 and amyloid β protein (Aβ). DHF had little effect on APP processing in cell cultures. DHF treatment did not reduce the deposition of Aβ to form neuritic plaques in the brain of AD model mice APP23/PS45. Furthermore, DHF did not alleviate learning and memory impairments in the AD model mice. Our study suggest that further extensive and careful studies are warranted for considering DHF as a new therapeutic agent for reducing amyloid pathology and alleviating cognitive deficits for AD treatment.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Amyloid beta-Protein Precursor; Animals; Antipsychotic Agents; Cells, Cultured; Disease Models, Animal; Dose-Response Relationship, Drug; Enzyme-Linked Immunosorbent Assay; Flavones; HEK293 Cells; Humans; Maze Learning; Mice; Mice, Transgenic; Mutation; Peptide Fragments; Presenilin-1; RNA, Messenger; Time Factors; Transfection

Increasing evidence suggests that reductions in brain-derived neurotrophic factor (BDNF) and its receptor tyrosine receptor kinase B (TrkB) may have a role in the pathogenesis of Alzheimer's disease (AD). However, the efficacy and safety profile of BDNF therapy (eg, gene delivery) remains to be established toward clinical trials. Here, we evaluated the effects of 7,8-dihydroxyflavone (7,8-DHF), a recently identified small-molecule TrkB agonist that can pass the blood-brain barrier, in the 5XFAD transgenic mouse model of AD. 5XFAD mice at 12-15 months of age and non-transgenic littermate controls received systemic administration of 7,8-DHF (5 mg/kg, i.p.) once daily for 10 consecutive days. We found that 7,8-DHF rescued memory deficits of 5XFAD mice in the spontaneous alternation Y-maze task. 5XFAD mice showed impairments in the hippocampal BDNF-TrkB pathway, as evidenced by significant reductions in BDNF, TrkB receptors, and phosphorylated TrkB. 7,8-DHF restored deficient TrkB signaling in 5XFAD mice without affecting endogenous BDNF levels. Meanwhile, 5XFAD mice exhibited elevations in the β-secretase enzyme (BACE1) that initiates amyloid-β (Aβ) generation, as observed in sporadic AD. Interestingly, 7,8-DHF blocked BACE1 elevations and lowered levels of the β-secretase-cleaved C-terminal fragment of amyloid precursor protein (C99), Aβ40, and Aβ42 in 5XFAD mouse brains. Furthermore, BACE1 expression was decreased by 7,8-DHF in wild-type mice, suggesting that BDNF-TrkB signaling is also important for downregulating baseline levels of BACE1. Together, our findings indicate that TrkB activation with systemic 7,8-DHF can ameliorate AD-associated memory deficits, which may be, at least in part, attributable to reductions in BACE1 expression and β-amyloidogenesis.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Amyloid Precursor Protein Secretases; Animals; Aspartic Acid Endopeptidases; Brain; Brain-Derived Neurotrophic Factor; Disease Models, Animal; Female; Flavones; Humans; Male; Maze Learning; Memory Disorders; Mice; Mice, Inbred Strains; Mice, Transgenic; Peptide Fragments; Phosphorylation; Receptor, trkB; Signal Transduction