NEUROTOXICOLOGY OF TRIALKYL-TIN AND LEAD COMPOUNDS

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The objective of this work is to elucidate the molecular mechanisms for the neurophysiological and neurotoxicological effects of certain organotin and organo-lead compounds that demonstrate selective structure-related neurotoxicity. It aims to determine the cellular signal transduction mechanism(s) that are triggered by such compounds and to relate them to the specific biochemical and physiological response in nervous tissue. A specific aim 1), is to test the hypothesis that the selective neurotoxicological effects of triethyltin (TET), trimethyltin (TMT), triethyllead (TEL and trimethyllead (TML) are produced by alterations in the states of phosphorylation, and thus, of the function, of target proteins in specific regions of the brain. Sub-cellular fractions from various sections of rat brain will be exposed to these compounds, in the presence of (Gamma-32P)ATP, to analyze their effects on the rates and extent of phosphorylation of endogenous proteins by means of sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) and autoradiography. Proteins that demonstrate organometal-induced altered states of phosphorylation will be isolated in order to determine the mechanisms by which these changes are produced. The effects of the organometals on the states of phosphorylation of these proteins in brain slices, cultured brain cells and in the intact animal will be analyzed to determine whether they could be physiologically relevant. Another aim 2), is to ascertain, in particular, the significance of observations made in preliminary experiments, that the phosphorylation of brain mitochondrial pyruvate dehydrogenase is selectively stimulated by TET. The enzyme will be isolated to determine the molecular mechanism of stimulation. Furthermore, the significance of this TET-induced modification, in vivo, will be examined by investigating the effects of PDH phosphorylation on cellular Ca2+ flux and neurotransmitter (acetylcholine) release in tissue slices and cell cultures. The work will also seek 3), to identify two other proteins, (Mr=50,000 and 80,000), whose states of phosphorylation are affected specifically by TET and TEL. The mechanisms of phosphorylation as well as the physiological relevance of these modifications will likewise be investigated. An additional aim 4), is to determine whether the organometals act as signals that influence brain membrane phosphatidylinositol turnover. This will be assessed by measuring the release of inositolphosphates from brain cells that are pre-labeled with phosphatidylinositol.