Role of mitochondrial GSH on the hepatotoxicity induced by Bile Acids

Abstract

Cholestatic liver diseases can be induced by diverse reasons including genetic defects, drug toxicity, hepatobiliary malignancy, or bile duct obstruction. Acute and chronic cholestasis promotes hepatocellular injury, bile duct proliferation, fibrosis, cirrhosis, and eventually liver failure. Diminished bile flow during cholestasis provokes the hepatic accumulation of products normally excreted into bile, such as cholesterol and bile acids (BAs). Some BAs, especially hydrophobic ones, can induce cell injury in hepatocytes. Cholesterol, a highly regulated molecule found in the lipid bilayer of cells, is the precursor of BAs mainly in the classical pathway, which is modulated by CYP7A1 and CYP8B1. Besides, cholesterol can be transported to the mitochondria by StARD1 protein, functioning as an additional source of BAs in the alternative pathway, which is controlled by CYP27A1 and CYP7B1. Moreover, StARD1 overexpression in cholestatic liver diseases have been described. The upregulated protein leads to the overload of cholesterol in the mitochondrial inner membrane, changing its physicochemical properties and losing its plasticity and permeability. Membrane rigidity can affect the transport of glutathione (GSH) to the mitochondrial matrix, where serves as a cofactor for several antioxidant and detoxifying enzymes. In addition, impaired bile flow promotes the accumulation of toxic BAs in hepatocytes, causing oxidative stress, mitochondrial damage, and hepatic impairment. Given the high production of reactive oxygen species in this process and the inability to transport glutathione into mitochondria due to membrane stiffness, liver damage occurs leading to the pathophysiology of the disease. Although it has long been believed that cholestatic liver damage was due to a direct effect of BAs toxicity, recent studies have shown that an inflammatory response might be the leading cause of injury. This master’s thesis aims to clarify the effect of BAs on primary hepatocytes and to elucidate the role of glutathione in cholestatic pathologies, such as primary biliary cholangitis and primary sclerosing cholangitis. After exposing primary mouse hepatocytes to high concentrations of BAs in vitro, as cholestasis-like conditions, it has been shown that BAs do not induce cell death directly. The depletion of mitochondrial GSH sensitizes the hepatocytes to a second hit and predisposes them to cellular damage via oxidative stress and the release of pro-inflammatory cytokines involved in the inflammatory response