. The broad, long-term objectives of this research are to understand the properties of glutathione transferase Z1 (GSTZ1) and its role in the elimination of the investigational drug dichloroacetic acid (DCA) across the human lifespan. This is important because while DCA, an inhibitor of mitochondrial pyruvate dehydrogenase kinase, has therapeutic benefits as a metabolic regulator in treating lactic acidosis, certain solid tumors and pulmonary arterial hypertension, it exhibits marked age- and genetics- related individual variability in pharmacokinetics that are linked to DCA's side effects. The first step in DCA metabolism is dechlorination to glyoxylate, catalyzed by GSTZ1. Also known as maleylacetoacetate isomerase, GSTZ1 plays an important physiological role in isomerizing endogenous reactive metabolites of the tyrosine catabolism pathway, maleylacetoacetate and maleylacetone. GSTZ1 is expressed chiefly in the liver, but also in kidney, intestine, brain and heart. It is the only enzyme known to catalyze the dehalogenation of DCA to its primary metabolite, glyoxylate. Although it is well recognized that DCA inhibits its own metabolism as well as that of its endogenous substrates, through inactivation of GSTZ1, the reasons for the marked individual variability in pharmacokinetics of DCA after repeated doses are only partially understood. Most adults clear repeated doses of DCA more slowly than children, and clearance is GSTZ1 haplotype dependent in children and adults. There is preliminary evidence that extrahepatic sites of DCA metabolism become of greater importance relative to liver following DCA treatment, and that this is age-dependent. Finally, chloride (Cl-) concentration affects the rate of inactivation of GSTZ1 by DCA in a haplotype-dependent manner; the much lower [Cl-] in mitochondria compared with cytosol is thought to be a factor in the more rapid inactivation of the mitochondrial matrix enzyme, and could be a factor in the observed age-dependent differences, as intracellular [Cl-] varies with age. The mechanism of how Cl- protects GSTZ1 from DCA-dependent inactivation is not known. This application seeks to examine reasons for age- and genetics- related changes in expression and activity of GSTZ1 in people.
Three specific aims are proposed. The first specific aim will study the role of microRNA (miR) in regulating the documented age-related changes in hepatic GSTZ1 expression.
This aim will use banked human liver of different aged donors to identify miRs, and cell-based systems to verify involvement. The second specific aim will investigate the mechanism of protection of GSTZ1 from inactivation by DCA in the presence of Cl- and certain other anions, and the influence of haplotype. Expressed recombinant GSTZ1A and 1B will be crystallized and the binding sites of DCA and anions studied. The third specific aim will use juvenile and adult rats as models of children and adults to examine the roles of extrahepatic tissues relative to liver in the expression and activity of GSTZ1 following multiple DCA doses, to mimic the clinical use.

Public Health Relevance

. This application will investigate the age-related developmental changes in amount, activity and properties of an enzyme, glutathione transferase Z1 (GSTZ1), known to determine the duration of action of dichloroacetate, and implicated in the side effects of this drug, which vary with age and genetic make-up. Dichloroacetate is a metabolic regulator and anticancer investigational drug in clinical trials for use in children and adults; while GSTZ1 converts dichloroacetate to an inactive metabolite, this drug also inactivates GSTZ1, resulting in slower elimination of dichloroacetate, and build-up of toxic endogenous substrates of GSTZ1. This research will help us better understand these variations, and tailor treatment to the individual patient.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM099871-06
Application #
9338247
Study Section
Xenobiotic and Nutrient Disposition and Action Study Section (XNDA)
Program Officer
Okita, Richard T
Project Start
2012-09-01
Project End
2020-08-31
Budget Start
2017-09-01
Budget End
2018-08-31
Support Year
6
Fiscal Year
2017
Total Cost
Indirect Cost
Name
University of Florida
Department
Pharmacology
Type
Schools of Pharmacy
DUNS #
969663814
City
Gainesville
State
FL
Country
United States
Zip Code
32611
Mangal, Naveen; James, Margaret O; Stacpoole, Peter W et al. (2018) Model Informed Dose Optimization of Dichloroacetate for the Treatment of Congenital Lactic Acidosis in Children. J Clin Pharmacol 58:212-220
Jahn, Stephan C; Smeltz, Marci G; Hu, Zhiwei et al. (2018) Regulation of dichloroacetate biotransformation in rat liver and extrahepatic tissues by GSTZ1 expression and chloride concentration. Biochem Pharmacol 152:236-243
Zhong, Guo; James, Margaret O; Smeltz, Marci G et al. (2018) Age-Related Changes in Expression and Activity of Human Hepatic Mitochondrial Glutathione Transferase Zeta1. Drug Metab Dispos 46:1118-1128
James, Margaret O; Jahn, Stephan C; Zhong, Guo et al. (2017) Therapeutic applications of dichloroacetate and the role of glutathione transferase zeta-1. Pharmacol Ther 170:166-180
Jiang, Yu; Milavetz, Gary; James, Margaret O et al. (2017) A Mechanism-Based Pharmacokinetic Enzyme Turnover Model for Dichloroacetic Acid Autoinhibition in Rats. J Pharm Sci 106:1396-1404
James, Margaret O; Stacpoole, Peter W (2016) Pharmacogenetic considerations with dichloroacetate dosing. Pharmacogenomics 17:743-53
Jahn, Stephan C; Solayman, Mohamed Hassan M; Lorenzo, Ryan J et al. (2016) GSTZ1 expression and chloride concentrations modulate sensitivity of cancer cells to dichloroacetate. Biochim Biophys Acta 1860:1202-10
Jahn, Stephan C; Rowland-Faux, Laura; Stacpoole, Peter W et al. (2015) Chloride concentrations in human hepatic cytosol and mitochondria are a function of age. Biochem Biophys Res Commun 459:463-8
Langaee, Taimour Y; Zhong, Guo; Li, Wenjun et al. (2015) The influence of human GSTZ1 gene haplotype variations on GSTZ1 expression. Pharmacogenet Genomics 25:239-45
Boone, Christopher D; Zhong, Guo; Smeltz, Marci et al. (2014) Preliminary X-ray crystallographic analysis of glutathione transferase zeta 1 (GSTZ1a-1a). Acta Crystallogr F Struct Biol Commun 70:187-9

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