The premature occurrence of Alzheimer-like beta-amyloid senile plaques in non-demented subjects with coronary artery disease prompted neuropathologic investigations of rabbits fed high cholesterol diet compared to animals fed control diet. Initial studies in this accepted animal model of coronary artery disease suggest a relationship between the length of rime on the cholesterol diet and increasing widespread accumulation of neuronal beta-amyloid(1-16) immunoreactivity in the brain on a regional basis; extracellular deposition was rarely observed In the current studies, regional levels of cholesterol were established in fresh brains from rabbits fed 2% cholesterol or control diet 8 weeks. In the same animals, activity of the free radical scavenger enzymes superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) was determined in blood and brain. Adjacent sections of 4% paraformaldehyde perfused brain from rabbits fed 2% cholesterol 4, 6 and 8 weeks and control diet 8 weeks were immunohistochemically investigated using probes for SOD, beta-amyloid(1-12), beta-amyloid precursor protein (beta-APP; N-terminal specific), and the lysosomal enzyme cathepsin D. Cholesterol concentration increased on a regional basis in the brain after 8 weeks of experimental diet compared to controls. Dietary cholesterol induced alterations in the activity of SOD and GSH-Px in brain paralleled changes in the blood The activity of SOD was increased and GSH-Px was decreased There was an identifiable relationship between regional cholesterol levels and SOD activity in both experimental and control rabbits. This relationship did not occur SOY brain cholesterol levels and GSH-Px activity. Accumulation of beta-amyloid inzmunoreactivity induced by dietary cholesterol was confirmed using another specific beta-amyloid antibody (beta-amyloid(1-12)). In Contrast to studies utilizing beta-amyloid(1-16) antibody the incidence of extracellular beta-amyloid(1-12) immunoreactive deposits increased with longer duration of cholesterol diet. There was no beta-APP immunoreactivity demonstrable in the brain of any rabbit, and therefore, accumulation of this peptide did not contribute to the enhanced beta-amyloid immunoreactivity produced by dietary cholesterol. Increased neuronal SOD immunoreactivity occurred early in the time-course of cholesterol administration and enhanced cathepsin D immunoreactivity occurred well after neuronal accumulation of beta-amyloid immrmoreactivity. As a result, increased cathepsin D enzymatic activity probably does not initiate beta-amyloid production in the cholesterol fed rabbit, but may potentiate the process. These studies suggest that elevated circulating levels of cholesterol causes increased levels in the brain which seems to be correlated to the level of neuronal beta-amyloid accumulation on a regional basis. By direct and/or indirect mechanisms increased brain cholesterol likely leads to enhanced free mrtical activity and the observed neuronal oxidative stress. Via unknown mechanism(s), this oxidative stress may initiate the pathologic and neuronal accumulation of Alzheimer-like beta-amyloid peptides, which thereafter may be deposited in the neuropil. Because many of the neurophatologic alterations induced in the brains of these animals are similar to those found in AD brain, the data support the hypothesis that the cholesterol Sed rabbit may be an animal model to investigate this dementing human disorder. (C) 1997, Medikal Press.
