Influence of Dichloroacetate Treatment on the Contributions of Rodent Brain, Heart, Liver and Kidney in the Expression of GSTZ1

Abstract

Glutathione transferase zeta 1 (GSTZ1)/maleylacetoacetate isomerase (MAAI) is a critical enzyme in tyrosine catabolism via its trans‐isomerization of maleylacetoacetate (MAA) and maleylacetone (MA). GSTZ1 also catalyzes the metabolism of dichloroacetate (DCA), an investigational drug utilized in the treatment of cancer and mitochondrial diseases. The pharmacology and toxicity of DCA are influenced, in part, by subject age. DCA is a mechanism‐based inactivator of GSTZ1, and repetitive DCA dosing results in the auto‐inhibition of DCA metabolism. Consequently, the chronic use of DCA in adults can lead to development of reversible peripheral neuropathy. However this effect is seldom observed in children, who metabolize DCA more quickly than adults. The tissue accumulation of DCA, MAA, and MA, due to GSTZ1 degradation, may be a mechanism responsible for DCA toxicity. Although liver is the main site of GSTZ1 expression and activity, extrahepatic tissues also express GSTZ1. Following a single dose of DCA to female rats, GSTZ1 expression and activity were reduced in liver to a greater extent than in kidney, brain and heart. However, the role of extrahepatic tissues in metabolism of DCA, MAA, and MA following repeated doses of DCA that mimic therapy has not been studied. Therefore, we examined the relative tissue expression of GSTZ1 following multiple doses of DCA. Adult female Sprague Dawley rats, 8 per group, and juvenile female Sprague Dawley rats, 4 per group, were treated with sodium DCA (100 mg/kg) or sodium acetate (100 mg/kg) by oral gavage daily for 8 consecutive days. On the 9th day the tissues were removed and used to prepare cytosolic and mitochondrial subcellular fractions. GSTZ1 expression was then assessed via Western blot using a polyclonal antibody to rat GSTZ1. In comparison to the same tissue in acetate‐treated adults, the expression of cytosolic GSTZ1 remaining in the liver, kidney, heart and brain of DCA‐treated adults was 2.8%, 9.8%, 8.6% and 5.7%, respectively, with liver retaining the highest expression at 0.030 ± 0.009 ng GSTZ1/μg protein (mean ± S.E.). Similarly, the expression of cytosolic GSTZ1 in DCA‐treated juveniles was greatest in liver (0.044 ± 0.014), whereas extrahepatic tissues were 20‐fold lower. Expression of mitochondrial GSTZ1 in DCA‐treated animals was highest in juvenile liver (0.016 ± 0.005) and adult kidney (0.048 ± 0.007). Considering the higher protein yield and larger size of the liver, compared with extrahepatic tissues, most DCA metabolism is expected to occur in the liver, even after repeated dosing. Given the greater proportion of liver to body weight in young rats, the hepatic metabolism of DCA is predicted to be augmented within this age group. This is consistent with the higher clearance of DCA in young populations, as children may retain a higher capacity for the GSTZ1‐catalyzed metabolism of DCA due to relative liver size.Support or Funding InformationSupported in part by the US Public Health Service GM 099871This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.