Alcoholic Liver Disease: Alcohol Metabolism, Cascade of Molecular Mechanisms, Cellular Targets, and Clinical Aspects

Alcoholic liver disease is the result of cascade events, which clinically first lead to alcoholic fatty liver, and then mostly via alcoholic steatohepatitis or alcoholic hepatitis potentially to cirrhosis and hepatocellular carcinoma. Pathogenetic events are linked to the metabolism of ethanol and acetaldehyde as its first oxidation product generated via hepatic alcohol dehydrogenase (ADH) and the microsomal ethanol-oxidizing system (MEOS), which depends on cytochrome P450 2E1 (CYP 2E1), and is inducible by chronic alcohol use. MEOS induction accelerates the metabolism of ethanol to acetaldehyde that facilitates organ injury including the liver, and it produces via CYP 2E1 many reactive oxygen species (ROS) such as ethoxy radical, hydroxyethyl radical, acetyl radical, singlet radical, superoxide radical, hydrogen peroxide, hydroxyl radical, alkoxyl radical, and peroxyl radical. These attack hepatocytes, Kupffer cells, stellate cells, and liver sinusoidal endothelial cells, and their signaling mediators such as interleukins, interferons, and growth factors, help to initiate liver injury including fibrosis and cirrhosis in susceptible individuals with specific risk factors. Through CYP 2E1-dependent ROS, more evidence is emerging that alcohol generates lipid peroxides and modifies the intestinal microbiome, thereby stimulating actions of endotoxins produced by intestinal bacteria; lipid peroxides and endotoxins are potential causes that are involved in alcoholic liver injury. Alcohol modifies SIRT1 (Sirtuin-1; derived from Silent mating type Information Regulation) and SIRT2, and most importantly, the innate and adapted immune systems, which may explain the individual differences of injury susceptibility. Metabolic pathways are also influenced by circadian rhythms, specific conditions known from living organisms including plants. Open for discussion is a 5-hit working hypothesis, attempting to define key elements involved in injury progression. In essence, although abundant biochemical mechanisms are proposed for the initiation and perpetuation of liver injury, patients with an alcohol problem benefit from permanent alcohol abstinence alone.

Alcoholic steatohepatitis (ASH) and alcoholic hepatitis (AH): cascade of events, clinical aspects, and pharmacotherapy options

INTRODUCTION

Clinicians caring for patients with alcoholic hepatitis (AH) are often confronted with the question of the best pharmacotherapy to be used.

AREAS COVERED

This article covers metabolic aspects of alcohol as the basis of understanding pharmacotherapy and to facilitate choosing the drug therapeutic options for patients with severe AH.

EXPERT OPINION

Alcoholic steatohepatitis (ASH) and alcoholic hepatitis (AH) as terms are often used interchangeably in scientific literature but a stringent differentiation is recommended for proper clarity. As opposed to ASH, the clinical course of AH is often severe and requires an effective drug treatment strategy, in addition to absolute alcohol abstinence and nutritional support. Drug options include corticosteroids as a first choice and pentoxifylline, an inhibitor of phosphodiesterase, as a second line therapy, especially in patients with contraindications for a corticosteroid therapy such as infections or sepsis. At seven days under corticosteroids, treatment should be terminated in non-responders, and patients must then be evaluated for liver transplantation. Pentoxifylline is not effective as a rescue therapy for these patients. Other treatments such as infliximab, propylthiouracil, N-acetylcysteine, silymarin, colchicine, insulin and glucagon, oxandrolone, testosterone, and polyunsaturated lecithin are not effective in severe AH. For liver transplantation, few patients will be eligible.