Pathways of liver injury in alcoholic liver disease

Abstract

The development of ethanol-induced liver injury including liver cirrhosis and severe alcoholic steatohepatitis (ASH) is a complex process involving various liver cell types and mainly factors released under the control of the innate immune system. Chronic ethanol consumption induces oxidative stress and production of reactive oxygen species (ROS), cytokine release, mitochondrial dysfunction, endoplasmic reticulum stress, and others. ROS initiate lipid peroxidation that directly damages plasma and intracellular membranes and leads to the production of reactive aldehydes with potent pro-inflammatory and pro-fibrotic properties. Oxidative stress and ROS are predominantly generated through the induction of cytochrome P450-2E1 (CYP2E1). A key role for this enzyme in ethanol-induced liver injury has been demonstrated by its inhibition through chlormethiazole and by the finding that CYP2E1 knock-out (KO) mice do not show evidence of ethanol-induced liver disease [1]. Furthermore, transgenic overexpression of human CYP2E1 in a mouse model results in more severe liver disease. Both the hydroxyethyl radical and acetaldehyde, the first products of ethanol metabolism, can bind glutathione (GSH), a tripeptide that acts as a direct free radical scavenger. The transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2) protects cells against xenobiotic and oxidative stress. Nrf2 KO mice exhibit a dramatically increased mortality after ethanol feeding, highlighting the important role of oxidative stress in ethanol-induced injury [1] (Fig. 1).