The purpose of the study is to measure regional brain concentrations of N-Acetyl-L-Aspartic acid(NAA) in Alzheimer's disease(AD), in order to explore the use of quantitative determination of NAA as a method of studying neuronal degeneration. The proposed research will characterize the regional concentrations of NAA in post-mortem brain tissue of patients with AD. NAA is a normal constituent of neurons but not of other brain cells. It is readily quantified by nuclear magnetic resonance(NMR) spectroscopy. Because of well-described neuronal degeneration which is seen in AD, we expect regional NAA concentrations to reflect the extent of neuronal degeneration and, in turn, the severity of dementia.
Our specific aims are 1) to measure the regional concentrations of NAA in post-mortem brains of patients with AD and in non-demented controls; 2) to study the association between regional brain NAA concentrations and indices of neuronal degeneration in AD and; 3) to investigate the association between regional brain NAA concentrations and the severity of dementia in AD. Cortical and white matter tissue samples will be from age-matched patients with pathologically verified AD (n=30) and non-demented controls (n=30) of comparable age group. The AD sample will consist of patients who have been clinically diagnosed and followed-up yearly until death. Brain tissue samples for NAA determination will be excised at autopsy and the remaining brain will be fixed in formalin for 1) subsequent pathological verification and; 2) quantitative morphometric analyses of the areas immediately adjacent to where the samples for NAA analyses were obtained. The areas chosen will consist of the amygdala, the parahippocampal gyrus, the association areas of the temporal, parietal and frontal lobes and the motor cortex, representing areas of clinico-pathological significance in Alzheimer's disease. NAA will be quantitatively determined using high-resolution proton NMR spectroscopy of excised tissues, after perchloric acid extraction. NMR-derived values will be validated with HPLC on the same tissue samples and quantitative neuropathology will be performed using standard protocols. While limited results of proton NMR spectra have been published on young subjects such data on older individuals are currently lacking. In addition, the study of NAA and its relationship to age, to the presence of dementia, and to the severity of dementia has not been performed. We seek to demonstrate that the proton spectra from cortical tissue of patients with AD will be different from controls. We hypothesize that 1) significantly reduced NAA concentrations will be observed from areas of maximal predilection in AD; 2) these reductions will correlate with the degree of neuronal degeneration and; 3) these reductions will parallel the clinical severity of the disease during life. The experimental results will provide validated in vitro data to further the development of in vivo proton spectroscopic images of NAA, as a means of quantifying neuronal degeneration in AD that can be extended to other degenerative diseases.
