Abstract
BackgroundNADPH oxidase is implicated in neurotoxic microglial activation and the progressive nature of Alzheimer's Disease (AD). Here, we test the ability of two NADPH oxidase inhibitors, apocynin and dextromethorphan (DM), to reduce learning deficits and neuropathology in transgenic mice overexpressing human amyloid precursor protein with the Swedish and London mutations (hAPP(751)SL).MethodsFour month old hAPP(751)SL mice were treated daily with saline, 15 mg/kg DM, 7.5 mg/kg DM, or 10 mg/kg apocynin by gavage for four months.ResultsOnly hAPP(751)SL mice treated with apocynin showed reduced plaque size and a reduction in the number of cortical microglia, when compared to the saline treated group. Analysis of whole brain homogenates from all treatments tested (saline, DM, and apocynin) demonstrated low levels of TNFα, protein nitration, lipid peroxidation, and NADPH oxidase activation, indicating a low level of neuroinflammation and oxidative stress in hAPP(751)SL mice at 8 months of age that was not significantly affected by any drug treatment. Despite in vitro analyses demonstrating that apocynin and DM ameliorate Aβ-induced extracellular superoxide production and neurotoxicity, both DM and apocynin failed to significantly affect learning and memory tasks or synaptic density in hAPP(751)SL mice. To discern how apocynin was affecting plaque levels (plaque load) and microglial number in vivo, in vitro analysis of microglia was performed, revealing no apocynin effects on beta-amyloid (Aβ) phagocytosis, microglial proliferation, or microglial survival.ConclusionsTogether, this study suggests that while hAPP(751)SL mice show increases in microglial number and plaque load, they fail to exhibit elevated markers of neuroinflammation consistent with AD at 8 months of age, which may be a limitation of this animal model. Despite absence of clear neuroinflammation, apocynin was still able to reduce both plaque size and microglial number, suggesting that apocynin may have additional therapeutic effects independent of anti-inflammatory characteristics.
Highlights
Alzheimer’s disease (AD) is a devastating and progressive neurodegenerative disease that culminates in dementia, affecting over 5 million people in the United States alone
We propose that targeting NADPH oxidase and neurotoxic microglial activation may be of significant therapeutic relevance for Alzheimer’s Disease (AD)
We addressed whether chronic administration of known NADPH oxidase inhibitors, beginning at the time plaque deposition began to occur in hAPP(751)SL mice, could prevent neuroinflammation, neuron damage, and behavioral learning and memory deficits
Summary
Alzheimer’s disease (AD) is a devastating and progressive neurodegenerative disease that culminates in dementia, affecting over 5 million people in the United States alone. The hallmark neuropathology of AD consists of insoluble extracellular plaques containing b -amyloid (Ab) and intraneuronal neurofibrillary tangles in the cortical region of the brain. The resident immune cells in the brain, have been implicated in the progressive nature of numerous neurodegenerative diseases, AD [1]. We propose that targeting NADPH oxidase and neurotoxic microglial activation may be of significant therapeutic relevance for AD. NADPH oxidase is implicated in neurotoxic microglial activation and the progressive nature of Alzheimer’s Disease (AD). We test the ability of two NADPH oxidase inhibitors, apocynin and dextromethorphan (DM), to reduce learning deficits and neuropathology in transgenic mice overexpressing human amyloid precursor protein with the Swedish and London mutations (hAPP(751)SL)
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