TOWARDS A PHARMACOLOGICAL APPROACH OF ALZHEIMERS-DISEASE BASED ON THE MOLECULAR-BIOLOGY OF THE AMYLOID PRECURSOR PROTEIN (APP)

After heart disease, cancer and stroke, Alzheimer's disease (AD) is the fourth major cause of death in the developed countries. Due to demographic changes, this situation will further worsen in the future. With the use of molecular biology techniques, important progress has recently been made in the understanding of the molecular changes leading to some forms of this disabling illness. The first step was the partial sequencing of the amyloid protein accumulating in the senile plaques and vascular deposits characteristic of AD. This allowed the cloning of a cDNA coding for a long amyloid precursor protein (APP). During the last few years, independent reports have described the presence of several reproducible point mutations in specific codons of APP in early onset familial Alzheimer patients. These mutations are responsible for an abnormal processing of APP, leading to the formation of pathological beta/A4 amyloid deposits. beta/A4 has been shown to possess neurotrophic properties in embryonic neurones and to be a potent neurotoxic agent in differentiated hippocampal neurones. More recently, modifications of intracellular calcium, activation of kinases, free radical generation and anomalies in potassium channels have been described as possible mechanisms of beta/A4 toxicity. Some forms of Apo-E lipoprotein may be an additional risk factor. Hence, it now seems possible to elaborate a coherent theory to explain the cascade of events leading to the development of AD. Genetically induced point mutations or environmental factors may produce a modification of the APP metabolism and processing. As a consequence, abnormal deposits of beta/A4 are formed. They may exert direct or indirect neurotoxic actions. A degeneration of cholinergic, catecholaminergic and other neurones follows, leading to the well known cognitive and behavioural changes of AD. On the basis of this theory, research projects and experimental tools aimed at screening drugs potentially active on different steps of the APP pathological cascade may be proposed. They will be presented in the next pages, taking into account the technical possibilities and limitations of our laboratory, in the fields of cellular and molecular biology as well as electrophysiology. 1) The potential protective action of drugs against the neuronotoxic effect of beta/A4 fragments and other neurotoxins will be studied in hippocampal cell cultures. 2) The effect of beta/A4 on the electrophysiological activity of rat brain neurones and the antagonistic action of the tested drug will be studied in hippocampal slices. Other pathological conditions such as hypoxia, free radical formation and lipid peroxidation will also be used. 3) When appropriate, the action of the drug on cholinergic neurones of the septum medialis and CA1 hippocampal pyramidal cells will be studied by means of extra- or intracellular recording techniques. 4) Potential protective drugs acting on neuronal potassium channels may also be studied by these electrophysiological techniques.