Background & aims: Alcoholic liver disease (ALD) remains a major cause of morbidity and mortality, with no Food and Drug Administration-approved therapy. Chronic alcohol consumption causes a pro-oxidant environment and increases hepatic lipid peroxidation, with acrolein being the most reactive/toxic by-product. This study investigated the pathogenic role of acrolein in hepatic endoplasmic reticulum (ER) stress, steatosis, and injury in experimental ALD, and tested acrolein elimination/scavenging (using hydralazine) as a potential therapy in ALD.
Methods: In vitro (rat hepatoma H4IIEC cells) and in vivo (chronic+binge alcohol feeding in C57Bl/6 mice) models were used to examine alcohol-induced acrolein accumulation and consequent hepatic ER stress, apoptosis, and injury. In addition, the potential protective effects of the acrolein scavenger, hydralazine, were examined both in vitro and in vivo.
Results: Alcohol consumption/metabolism resulted in hepatic accumulation of acrolein-protein adducts, by up-regulation of cytochrome P4502E1 and alcohol dehydrogenase, and down-regulation of glutathione-s-transferase-P, which metabolizes/detoxifies acrolein. Alcohol-induced acrolein adduct accumulation led to hepatic ER stress, proapoptotic signaling, steatosis, apoptosis, and liver injury; however, ER-protective/adaptive responses were not induced. Notably, direct exposure to acrolein in vitro mimicked the in vivo effects of alcohol, indicating that acrolein mediates the adverse effects of alcohol. Importantly, hydralazine, a known acrolein scavenger, protected against alcohol-induced ER stress and liver injury, both in vitro and in mice.
Conclusions: Our study shows the following: (1) alcohol consumption triggers pathologic ER stress without ER adaptation/protection; (2) alcohol-induced acrolein is a potential therapeutic target and pathogenic mediator of hepatic ER stress, cell death, and injury; and (3) removal/clearance of acrolein by scavengers may have therapeutic potential in ALD.
Keywords: ADH, alcohol dehydrogenase; ALD, alcoholic liver disease; ALDH, aldehyde dehydrogenase; ALT, alanine aminotransferase; AST, aspartate aminotransferase; ATF, activating transcription factor; Apoptosis; CHOP; CHOP, CCAAT/enhancer-binding protein homologous protein; CYP2E1, cytochrome P4502E1; ER, endoplasmic reticulum; FDP-lysine, Nε-(3-formyl-3,4-dehydropiperidino)lysine; GRP, glucose regulated protein; GSTP, glutathione-s-transferase-Pi; IRE1, inositol-requiring enzyme 1; JNK, cJun N-terminal kinase; LPO, lipid peroxidation; Lipid Peroxidation; NIAAA, National Institute on Alcohol Abuse and Alcoholism; PERK, protein kinase RNA-like endoplasmic reticulum kinase; PUFA, polyunsaturated fatty acids; TRAF, TNF receptor-associated factor; TUNEL, terminal deoxynucleotidyl transferase–mediated deoxyuridine triphosphate nick-end labeling; Therapeutic; UPR, unfolded protein response; XBP1, X-box binding protein-1; mRNA, messenger RNA; siRNA, small interfering RNA.