The generation of carcinogenic etheno-DNA adducts in the liver of patients with nonalcoholic fatty liver disease

Abstract

Background: Nonalcoholic fatty liver disease (NAFLD), in particular its more aggressive form nonalcoholic steatohepatitis (NASH) is increasingly observed as a cause of end stage liver disease and hepatocellular carcinoma (HCC). Reactive oxygen species (ROS) are an important factor in the pathogenesis of HCC. ROS can react with polyunsaturated fatty acids derived from membrane phospholipids resulting in the production of reactive aldehydes as lipid oxidation (LPO) byproducts, such as 4-hydroxynonenal (4 HNE). 4 HNE can react with DNA to form mutagenic exocyclic etheno-DNA adducts. ROS is induced by inflammatory processes, but also by induction of cytochrome P450 2E1 (CYP2E1), as seen with chronic alcohol consumption.

Methods: Immunohistochemical detection of CYP2E1, 4 HNE and hepatic exocyclic etheno-DNA adducts was performed on liver sections from 39 patients with NFLD. Spearman rank correlation was calculated to examine possible correlations.

Results: Exocyclic etheno-DNA adducts were detected and correlated significantly with 4 HNE, but not with CYP2E1.

Conclusions: This is the first description of highly carcinogenic exocyclic etheno-DNA adducts in NAFLD patients. We could show that exocyclic etheno-DNA adducts significantly correlated with lipid peroxidation product 4 HNE, but not with CYP2E1, implying that in NAFLD ROS generation with consecutive DNA damage is rather inflammation driven through various cytokines than by induction of CYP2E1.

Keywords: Nonalcoholic fatty liver disease (NAFLD); etheno-DNA adducts; hepatocellular carcinoma (HCC).

Figure 1

Immunohistology of εdA in one liver biopsy from a patients with NASH, magnification 40×. εdA, etheno-2'-deoxyadenosine; NASH, nonalcoholic steatohepatitis.

Figure 2

Simplified pathophysiology of ROS and etheno-DNA adduct formation. In NASH, inflammation driven cytokine secretion results in ROS generation, which leads to lipidperoxidation with the occurrence of lipidperoxidation products such as 4 HNE. These adducts react with DNA bases to form exocyclic etheno-DNA adducts. Chronic alcohol consumption results in the induction of CYP2E1, which is involved in ethanol oxidation through the microsomal ethanol oxidizing pathway. During this reaction ROS is generated without inflammation. ROS, reactive oxygen species; NASH, nonalcoholic steatohepatitis; 4 HNE, 4-hydroxynonenal; CYP2E1, cytochrome P450 2E1.