RESUMO
PURPOSE: While marked reductions in neural activity and mitochondrial function have been reported in Alzheimer's disease (AD), the degree of mitochondrial activity in mild cognitive impairment (MCI) or early-stage AD remains unexplored. Here, we used positron emission tomography (PET) to examine the direct relationship between mitochondrial activity (18F-BCPP-EF) and ß-amyloid (Aß) deposition (11C-PiB) in the same brains of senescence-accelerated mouse prone 10 (SAMP10) mice, an Aß-developing neuroinflammatory animal model showing accelerated senescence with deterioration in cognitive functioning similar to that in MCI. METHODS: Five- to 25-week-old SAMP10 and control SAMR1 mice, were used in the experiments. PET was used to measure the binding levels (standard uptake value ratios; SUVRs) of [18F]2-tert-butyl-4-chloro-5-2H-pyridazin-3-one (18F-BCPP-EF) for mitochondrial complex 1 availability, and 11C-PiB for Aß deposition, in the same animals, and immunohistochemistry for ATPB (an ATP synthase on the mitochondrial inner membrane) was also performed, to determine changes in mitochondrial activity in relation to amyloid burden during the early stage of cognitive impairment. RESULTS: The SUVR of 18F-BCPP-EF was significantly lower and that of 11C-PiB was higher in the 15-week-old SAMP10 mice than in the control and 5-week-old SAMP10 mice. The two parameters were found to negatively correlate with each other. The immunohistochemical analysis demonstrated temporal upregulation of ATPB levels at 15-week-old, but decreased at 25 week-old SAMP10 mice. CONCLUSION: The present results provide in vivo evidence of a decrease in mitochondrial energy production and elevated amyloidosis at an early stage in SAMP10 mice. The inverse correlation between these two phenomena suggests a concurrent change in neuronal energy failure by Aß-induced elevation of neuroinflammatory responses. Comparison of PET data with histological findings suggests that temporal increase of ATPB level may not be neurofunctionally implicated during neuropathological processes, including Aß pathology, in an animal model of early-phase AD spectrum disorder.
