Protein synthesis in the posterior cingulate cortex in Alzheimer's disease

Abstract

Neuroimaging studies using (18) F-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) and single photon emission computed tomography (SPECT) have shown that the posterior cingulate cortex (PCC) is the primary and most prominent area of cerebral metabolic and perfusional decrement in early Alzheimer's disease (AD). We carried out the present preliminary study to investigate whether a decline of cerebral blood flow (CBF) in the PCC in early to moderate AD was accompanied with that of cerebral protein synthesis (CPS). We carried out both N-isopropyl-p-[123I] iodoamphetamine SPECT (IMP-SPECT) and L-[methyl-11C] methionine positron emission tomography (MET-PET) in eight AD patients with apolipoprotein E epsilon 4 allele in the early to moderate stage. We also carried out IMP-SPECT in eight healthy controls (HC). We located 32 regions of interest (ROI), and values of regional MET or IMP uptakes were averaged in five regions; the frontal lobe (FL), the parietal lobe (PL), the medial temporal lobe (MTL), PCC and the occipital lobe. Furthermore, the values in the FL, PL, MTL and PCC were divided by values in the occipital areas, and normalized values of regional CBF (rCBF) and CPS (rCPS) were calculated. Then, the rCBF in the FL, PL, MTL and PCC were compared between AD and HC. In addition, the rCBF and rCPS were compared in the FL, PL, MTL and PCC of AD. The rCBF in the PCC, but not in the other three regions, was significantly lower in AD than in HC. The rCBF was significantly lower than rCPS in the PCC, but rCBF and rCPS were comparable in the other three regions in AD. The CBF reduction in the PCC in AD was partly caused by neuronal loss in the PCC and partly supported the hypothesis that CBF reduction in the PCC was a result of functional deafferentation by neural degeneration in areas other than the PCC.