The original Specific Aim 1 of this grant was to conduct a 2-day exposure of oral DCA covering the environmental (2.5 ?g/kg/d)-clinical (25 mg/kg/d) dose range in adult patients just prior to them undergoing open surgical removal of a benign liver lesion (e.g., cyst, adenoma). Adjacent healthy tissue excised with the lesion would be taken for analysis of the zeta-1 family isoform of glutathione transferase (GSTz1), which biotransforms DCA to glyoxylate. GSTz1 is identical to the penultimate enzyme in tyrosine catabolism, maleylacetoacetate isomerase (MAAI). Because DCA inhibits this enzyme in animal livers, we postulated it would also do so in human livers, leading to the plasma accumulation of potentially toxic tyrosine metabolites. However, last year the standard-of-care approach applied by UF surgeons to these patients changed from open incisions to percutaneous drainage of cysts and percutaneous removal of most adenomas, thereby essentially eliminating our recruitment of subjects for this Aim. Accordingly, the purpose of this Competitive Revision of ES014617 is to redress this deficiency by applying state-of-the-art stable isotope kinetics and kinetic modeling techniques developed by the PI and his colleagues prior to and since the awarding of this R01 to accomplish the following aim:
Specific Aim 4 : Quantify the effects of DCA on human tyrosine metabolism and on its own biotransformation in relation to dose and genotype.
This aim tests the postulate that inhibition of GSTz1/MAAI by DCA alters 13C-tyrosine kinetics in healthy adults at both environmental and clinical exposure levels, resulting in accumulation of potentially toxic tyrosine metabolites. We further postulate that inhibition of tyrosine metabolism will be greatest in subjects who harbor the KRT variant for GSTz1/MAAI for which DCA exhibits a high Km. Whole body protein turnover will also be determined to aid in the interpretation of the tyrosine kinetic data.
Dichloroacetate (DCA) occupies a unique place in biomedicine because of its significance as both a potential environmental toxin and a therapeutic agent. DCA is believed to inhibit human tyrosine metabolism and this it thought to be genetically influenced and related to its potential environmental and clinical toxicology. This application seeks to determine the quantitative impact of DCA, administered at both environmentally and clinically relevant doses, on tyrosine metabolism in human in relation to genotype, thereby elucidating the relevant risk of human populations to different DCA exposure levels.
