Induction of Hepatic Cytochrome P450 2e1 in Alcoholic and Non-Alcoholic Fatty Liver as a Driving Force for Hepatic Fibrosis and Carcinogenesis

Abstract

Introduction: As the childhood obesity epidemic grows, an increasing number of children are diagnosed with non-alcoholic fatty liver disease (NAFLD) and type 2 non-alcoholic steatohepatitis (NASH). One common finding in NASH patients is increased levels of free fatty acids (FFA). Peroxidation of FFA by reactive oxygen species (ROS) has been shown to cause damage to cellular membranes and organelles such as mitochondria. Studies in humans and animals have demonstrated that oxidative stress, which produces ROS, is a critical player in the pathogenesis of NASH. PON1 is an enzyme exclusively synthesized in the liver and functions as an antioxidant preventing the oxidation of High Density Lipoproteins (HDL). Studies in adults have shown comparable activity of PON1 in both liver and serum, thus making it a potential biomarker for evaluating liver disease. Adult human and animal studies have demonstrated decreased or depleted PON1 activity with diseased liver architecture and changes in plasma lipoprotein subclass distribution. This can lead to increased production of oxidative stress and subsequent atherosclerotic risk. Currently the relationships between PON1 and pediatric (type 2) NASH, is unknown. This study focuses on the gene expression of PON1 in type 2 NASH. Methods and Results: NASH was diagnosed according to Kleiner's criteria. Data mining on NASH microarray database [1] showed a difference in the relative expression of PON1 among insulin resistant (1.77x) and non insulin resistant (2.24x) pediatric NASH patients compared to normal controls (NC). Additional quantitative analysis of the PON1 expression in liver tissue of NASH (n=18) and NC (n= 4) with GAPDH as the housekeeping gene was performed with real time PCR. PON1 mRNA expression level was found to be 8.18 times that of the NC (p< 0.005). Conclusion: The increase in the expression of PON1 in pediatric NASH livers suggests a shift in the balance between antioxidants and oxidative stress. This finding is in contrast to adult NASH studies where a decreased level of PON1 activity in serum was reported with NASH type I. Our findings suggest that the hepatic damage involved in type 2 NASH is not as extensive compared to the hepatic damage noted in type 1 NASH. In addition this data suggests that serum levels of PON1 are likely inadequate surrogate for liver biopsy when assessing pediatric liver disease, additional studies are necessary.