Date of Award

2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Pharmaceutical Sciences

Department

Biomedical and Pharmaceutical Sciences

First Advisor

Roberta King

Abstract

The role of conjugation of chemicals and endogenous compounds is an important mechanism in detoxification and metabolic signaling. Specifically, amidation, sulfonation, and glucuronidation are necessary functions of the human body. Exposure to environmental toxins such as bisphenols must be conjugated in order to be excreted from the body. Bisphenol A was originally developed as a synthetic estrogen, however later found use as a monomer within the plastics industry allowing for wide-spread exposure to BPA through food and drink containers. While most healthy individuals are capable of metabolizing and excreting bisphenol A, this metabolism can be impacted by diet and disease. Herein, the effects of obesity and fasting are shown to reduce the capacity of BPA glucuronidation in wild-type and ob/ob mice. In addition to environmental toxins, endogenous compounds such as bile acids can undergo sulfonation, amidation, and glucuronidation. Occasionally, drugs can cause drug-induced liver injury, often leading to cholestasis that can cause permanent liver injury if the drug is not stopped. The buildup of bile acids within the liver can then lead to liver damage because bile acids are amphiphilic compounds that act as strong detergents, capable of breaking down the hepatocellular membrane. In order to combat this build up toxic bile acids, conjugation occurs to increase the polarity and water solubility of the bile acids, thus leading to increased excretion. I proposed that drugs may inhibit the sulfonation of lithocholic acid (LCA), the most toxic bile acid, or inhibiting the amidation of other bile acids (the predominate form of bile acids) leading to drug induced liver injury. LCA sulfonation is catalyzed by human cytosolic sulfotransferase (SULT) 2A1. Bile acid amidation is catalyzed by human bile acid coenzyme A synthetase/bile acid coenzyme A: amino acid N-acyltransferase (BACS/BAAT). In this study, 125 drugs were screened for inhibition of SULT2A1 and the BACS/BAAT enzymes. I successfully identified several compounds as potent SULT2A1 inhibitors. While only a single inhibitor of amidation was discovered, I developed a novel one step enzymatic assay to test for the inhibition of BACS and BAAT. While drugs can cause cholestasis as an unwanted effect, a class of drugs called fibrates are being studied for use in treatment of primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC). Fibrates are known peroxisome proliferator-activated receptor (PPAR) activators, and in this study, I proposed the use of fenofibrate in patients with PBC and PSC will reduce serum liver enzymes and bile acids. In both patient cohorts, we observed large decreases in serum bile acids, particularly conjugated bile acids, and the bile acid precursor 7α-hydroxy-4-cholesten-3-one (C4). In addition, we observed a shift from the classic synthesis pathway of bile acids towards an alternative pathway of chenodeoxycholic acid (CDCA) synthesis. These results suggest the downregulation of bile acid synthesis and the BACS/BAAT amidation system indicating a potential alternative treatment for cholestasis.

Available for download on Thursday, December 10, 2020

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