Adenosine signaling contributes to ethanol-induced fatty liver in mice

Fatty liver is commonly associated with alcohol ingestion and abuse. While the molecular pathogenesis of these fatty changes is well understood, the biochemical and pharmacological mechanisms by which ethanol stimulates these molecular changes remain unknown. During ethanol metabolism, adenosine is generated by the enzyme ecto-S'-nucleotidase, and adenosine production and adenosine receptor activation are known to play critical roles in the development of hepatic fibrosis. We therefore investigated whether adenosine and its receptors play a role in the development of alcohol-induced fatty liver. WT mice fed ethanol on the Lieber-DeCarli diet developed hepatic steatosis, including increased hepatic triglyceride content, while mice lacking ecto-5'-nucleotidase or adenosine A(1) or A(2)B receptors were protected from developing fatty liver. Similar protection was also seen in WT mice treated with either an adenosine A(1) or A(2B) receptor antagonist. Steatotic livers demonstrated increased expression of genes involved in fatty acid synthesis, which was prevented by blockade of adenosine A(1) receptors, and decreased expression of genes involved in fatty acid metabolism, which was prevented by blockade of adenosine A(2B) receptors. In vitro studies supported roles for adenosine A, receptors in promoting fatty acid synthesis and for A(2B) receptors in decreasing fatty acid metabolism. These results indicate that adenosine generated by ethanol metabolism plays an important role in ethanol-induced hepatic steatosis via both A(1) and A(2B) receptors and suggest that targeting adenosine receptors may be effective in the prevention of alcohol-induced fatty liver.