Alcoholic liver disease - Ursus maritimus (polar bear)

Alcoholic liver disease (ALD) refers to the damages to the liver and its functions due to alcohol overconsumption. It ranges from simple steatosis to steatohepatitis, cirrhosis, and even hepatocellular carcinoma. Alcohol consumption promotes liver inflammation by increasing the translocation of gut-derived endotoxins to the portal circulation and activating Kupffer cells to produce TNF-alpha through the LPS/Toll like receptor (TLR) 4 pathways. TNF-alpha induces hepatocellular damage. When alcohol intake is chronic and heavy, steatosis is caused via generation of acetaldehyde, reactive oxygen species (ROS) and ER stress. ROS inhibits key hepatic transcriptional regulators such as AMP-activated kinase (AMPK) and peroxisome proliferator-activated receptor alpha (PPAR-alpha), which are responsible for fatty acid oxidation and export via ACC and CPT-1. The blockade of AMPK also leads to overexpression of SREBP-1, resulting in an increase of de novo lipogenesis. Moreover, excessive intracellular ROS production induced by ethanol and its metabolite have a critical role in ethanol-induced apoptosis, which may be the critical process in the exacerbation of ALD. It is inferred that the apoptotic signal derived from ROS that was produced by NOX, is mainly transduced through the JNK and p38 MAPK pathways.