Henri Brugère

Electroanalytical characterization of Alzheimer's disease and ovine spongiform encephalopathy by repeated cyclic voltammetry at a capillary graphite paste electrode

Abstract Linear sweep voltammetry (sweep rate, 1–10 mV/s) of biological fluids impregnating electrodes made of electrochemically inert compressed graphite powder allows all electrochemically oxidizable compounds which are present in these fluids to be characterized rapidly and cheaply, without preliminary separation, by peaks occurring at specific potentials, and their concentrations to be quantified by the corresponding peak areas or heights. The main components normally present in biological fluids which can be characterized at specific potentials by this electroanalytical technique are ascorbate, urate, xanthin, oxalate, tyrosine, tryptophan, 5-HIAA, VMA, HVA, and some other minor catabolites of catecholamines and serotonin. The oxidation peaks of these components frequently correspond to irreversible oxidations, sometimes generating reversibly oxidizable products which are detected on the first return sweep and in further backward and forward sweeps by a reduction peak which usually occurs at a lower potential than the primary oxidation. The voltammetric profiles obtained for urine samples are remarkably constant when these samples come from healthy patients, but they may undergo substantial quantitative or qualitative alterations with specific features when various types of drugs are administered or pathologies are present. Characteristic features are observed in the urine of patients e.g. after administration of paracetamol, benzodiazepins, opiates and folinic acid. The perfusion of cisplatinum or carboplatinum derivatives results in the formation of a peak which has been attributed to 2, 8-dihydroxyadenine. Strong reductions in the amplitudes of most peaks relating to catabolites which are normally present are observed in urine samples from newborn children. Very strong and sensitive increases in the amplitudes of several peaks appear in urine samples from patients with a variety of inflammatory reactions. Qualitative variations resulting in the formation of peaks which are not normally detected in urine are observed in patients suffering from Alzheimers disease. An epidemiological survey of the correlation between the amplitude of the reduction at 850 mV (vs. the standard hydrogen electrode) on the first return sweep and the clinical indexes in use for the identification of senile dementia have shown that the presence of these electrochemical characteristics is specific for degenerative dementia. Urine samples from sheep affected by spongiform encephalopathy, identified by post-mortem histology of brain tissues, have demonstrated the presence of the same electrochemical characteristics. The catabolite responsible for the electrochemical features described above, which has not yet been structurally identified, is not extracted by the organic solvents used for performing chromatographic analysis of catecholamines or indolic catabolites. In conclusion, in view of the relatively low cost of the equipment and execution, this method could be systematically used for rapid and cheap control of the effects of many drugs and for prediagnosis screening of several pathological conditions.

Méthodes de diagnostic des « maladies à prions » chez l'homme et chez l'animal

The potential existence of clinically silent cases of bovine spongiform encephalopathy (BSE) among cattle, and of humans incubating the new variant Creutzfeldt-Jakob disease (nvCJD) is still a major public health concern. Therefore, the development of screening tests for transmissible subacute spongiform encephalopathies (TSSE) in man and animals remains a priority. In the first part of this paper, we review the main methods used to diagnose generally clinical TSSE, such as brain imaging, electroencephalogram (EEG) analysis, and cerebrospinal fluid (CSF) analysis. In the second part, we present the post-mortem tests used to confirm a TSSE diagnosis, such as inoculation to laboratory animals, histological examination, and identification of abnormal prion protein (PrPres) using biochemical methods. Finally, the third part presents so-called rapid tests (Prionics, Bio-rad, Enfer), validated by the European Commission (EC) for post-slaughter BSE diagnosis in cattle. Now used on a large scale in Europe, these tests have helped assess the extent of the epizooty and eliminate from the food chain animals presenting a risk for human consumption. Since 2002, they have been used for the post-slaughter diagnosis of scrapie in small ruminants. New tests have recently been evaluated by the EC, but it is too soon to predict their role in the field.