Date of Award

2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Pharmaceutical Sciences

Specialization

Pharmacology and Toxicology

Department

Biomedical and Pharmaceutical Sciences

First Advisor

Nisanne Ghonem

Abstract

Cholestatic liver diseases, i.e. primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC), result from a disruption of bile flow. While bile acids are crucial to maintain hemostasis, retention of bile acids becomes inherently cytotoxic and can lead to hepatocellular inflammation. Currently, the treatment options for these diseases are Ursodeoxycholic acid (Ursodiol) and Obeticholic acid. However, ~40% of patients do not respond to Ursodiol and pruritus is a limiting side effect of Obeticholic acid. Without proper treatment these diseases can progress to fibrosis, cirrhosis, and eventually liver failure. Recently, fenofibrate, a peroxisome proliferator-activated receptor alpha (PPARa) agonist has become an off-label therapeutic option for patients with refractory cholestasis. Clinically, it has been shown that combination treatment with fenofibrate and Ursodiol have led to reduced serum liver enzymes and reduced total serum bile acids; however, the mechanism of how fenofibrate contributes to mediating bile acid toxicity and inflammation during cholestasis remains unknown. Glucuronidation, a phase II metabolism pathway responsible for BA detoxification, is regulated by PPARα. In the first study, we proposed that adult patients with PBC and PSC who were subtherapeutic to Ursodiol monotherapy would have decreased total serum bile acids and increased serum bile acid-glucuronides upon receiving combination therapy with fenofibrate. Combination therapy with fenofibrate significantly decreased elevated serum alkaline phosphatase, total serum bile acids and increased serum bile acid-glucuronides versus Ursodiol monotherapy. Fenofibrate also upregulated the expression of uridine 5’-diphosphoglucuronosyltransferases and multidrug resistance-associated protein 3 messenger RNA in primary human hepatocytes. Lastly, we found that certain serum bile acid-glucuronides can serve as strong indicators of response to treatment. Cholestatic liver diseases are also negatively impacted by hepatic inflammation. In the second study, we proposed that fenofibrate could help reduce pro-inflammatory cytokine secretion by inhibiting NF-κB signaling. We found in adult patients with PBC and an incomplete biochemical response to Ursodiol, the addition of fenofibrate reduced serum levels of TNF-α, IL-17A, IL-1b, IL-6, IL-8, and MCP-1 and increased IL-10. Additionally, in THP-1 cells stimulated with LPS for inflammation, NF-κB binding and nuclear protein expression were decreased. In the last study, we observed if fenofibrate transcriptionally regulates multidrug resistance protein 3 (MRP3)/ATP-dependent transporter of the ATP-binding cassette family 3 (ABCC3), which is a basolateral transporter, that has primarily been identified to transport glucuronide metabolites such as bile acid-glucuronides. In silico analysis of the MRP3 promoter identified multiple PPARα response elements. Electrophoretic mobility shift (EMSA) assays confirmed binding of PPARα to the MRP3 promoter. Together, this data suggests that fenofibrate treatment could be beneficial for reducing bile acid toxicity and inflammation in cholestatic patients who are subtherapeutic to Ursodiol monotherapy.

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