Early branched-chain amino acid reduction delays the onset of cognitive decline in a mouse model of Alzheimer's disease

Background Many Alzheimer's disease (AD) treatments focus on a single variable of AD that have yet demonstrated clinically meaningful and perceived benefits by the patients. We recently showed that lowering plasma branched-chain amino acids (BCAAs) can deliver multiple pro-neuronal effects in APP/PS1 and 5xFAD mouse models. Objective The main aim was to determine the optimal point in time for the disease-modifying effects of BCAA reduction during AD development. Methods 12-month-old, cognitively impaired male WT and APP/PS1 mice were injected with either vehicle or BCAA-lowering compound BT2 (40 mg/kg/day ip) for 30 days. To test if early BT2 during AD progression would have long-lasting beneficial effects, 2-month-old, cognitively intact male 5xFAD mice were treated with BT2 after which they were left alone for a month. Results Plasma BCAAs were reduced in BT2-treated APP/PS1 mice. Despite Aβ 42 reduction, BT2 did not modify proteins or genes related to AD-related pathology, dendritic density and neurotransmitters in the cortex and hippocampus, or alleviate cognitive deficit. In another experiment, BT2-treated 5xFAD mice had lower plasma BCAAs. Importantly, early BT2, even after treatment cessation for a month, was able to effectively delay cognitive impairment which was associated with a complete restoration of cortical neurotransmitters. These results were observed without any changes in pathology markers in the brain. Conclusions Our findings suggest that BT2-induced BCAA reduction is a novel strategy to delay AD progression possibly through enhanced neurotransmission. The efficacy is time-dependent such that treating with BT2 before the onset of AD can successfully rescue cognitive function.