Potential Relationship between Hepatobiliary Osteopontin and Peroxisome Proliferator–Activated Receptor α Expression following Ethanol-Associated Hepatic Injury In Vivo and In Vitro

• Published in: Toxicological sciences 2008-11, Vol.106 (1), p.290-299
• Main Authors: Lee, Jin-Hyung, Banerjee, Atrayee, Ueno, Yoshi, Ramaiah, Shashi K.
• Format: Article
• Language: English
• Subjects: Acetaldehyde; Animals; bezafibrate; Bezafibrate - pharmacology; Bile Ducts - drug effects; Bile Ducts - metabolism; Bile Ducts - pathology; Cell Line, Tumor; Disease Models, Animal; Epithelial Cells - metabolism; Ethanol; Hepatocytes - metabolism; Humans; Lipopolysaccharides; Liver - drug effects; Liver - metabolism; Liver - pathology; Liver Diseases, Alcoholic - etiology; Liver Diseases, Alcoholic - metabolism; Liver Diseases, Alcoholic - pathology; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; osteopontin; Osteopontin - deficiency; Osteopontin - genetics; Osteopontin - metabolism; peroxisome proliferator–activated receptor-α; PPAR alpha - agonists; PPAR alpha - genetics; PPAR alpha - metabolism; Rats; Rats, Sprague-Dawley; RNA, Messenger - metabolism; Systems Toxicology; Transcription, Genetic; Transfection
• ISSN: 1096-6080; 1096-0929
• DOI: 10.1093/toxsci/kfn165

Osteopontin (OPN) up-regulation is known to mediate hepatic inflammation in a rodent model of alcoholic liver disease (ALD) and alcohol ingestion is reported to inhibit hepatic peroxisome proliferator–activated receptor-α (PPAR-α) activity leading to hepatic steatosis and inflammation. Therefore, the objective of this study was to investigate the potential relationship between the anti-inflammatory PPAR-α and proinflammatory OPN in rats and mice livers, and cell cultures of hepatocytes and biliary epithelium. Experiments were designed to evaluate the influence of ethanol (EtOH), lipopolysaccharide (LPS), and acetaldehyde (ACA) on OPN and PPAR-α expression levels in vivo (rats and mice) and in vitro (hepatocytes and biliary epithelium). Adult Sprague-Dawley rats and C57BL6 mice were fed EtOH-containing Lieber-DeCarli liquid diet for 6 weeks and injected with a single dose of LPS. A combination of EtOH and LPS treated rats and mice showed significant induction of hepatic OPN expression compared with the controls. Similarly, cells exposed to physiological doses of EtOH, LPS, a combination of EtOH and LPS, and ACA resulted in increased OPN protein and mRNA expression. Rats and mice in ALD model and cells treated with EtOH and ACA showed downregulation of PPAR-α mRNA. Also, DNA binding activity of PPAR-α to PPAR response element was significantly reduced following treatment. Overexpression of PPAR-α rescued the reduced PPAR-α activity and PPAR-α agonist, bezafibrate, elevated PPAR-α activity after treatment of EtOH, LPS, and ACA when cells were exposed by bezafibrate. To further delineate the potential relationship between OPN and PPAR-α, OPN−/− mice showed no change of PPAR-α mRNA level although wild-type mice showed downregulation of PPAR-α mRNA after EtOH treatment. In conclusion, the current study suggests that OPN is induced by EtOH and its metabolite ACA and opposite relationship likely exist between PPAR-α and OPN expression within the liver during ALD.