Biological indicators of neurotoxicity in central and peripheral toxic neuropathies

This article reviews the biological indicators available for monitoring human neurotoxicity by exogenous chemicals with reference to the phases in which the neurotoxic process takes place, namely delivery, receptor-linkage, and toxicodynamic phase. Among the delivery phase tests, indicators are available for metals (lead, mercury) and some organic substances (CS2, n-hexane, DDT, etc.), but a correlation between neurotoxic effects and these indices is rather loose or not yet proved. The receptor-phase tests comprise well known enzymes, such as cholinesterase, less known but promising indicators, such as neuropathy target esterase (NTE), and new tools under study, such as acrylamide-hemoglobin adducts or 2,5-hexanedione-protein adducts. The toxicodynamic phase tests, which mainly consist of measuring substances released from the nervous system, have provided so far rather poor results, but more specific techniques of measurement (monoclonal antibodies) could offer new possibilities in the future.