5-Aminoimidazole-4-carboxyamide-ribonucleoside (AICAR)-Stimulated Hepatic Expression of Cyp4a10, Cyp4a14, Cyp4a31, and Other Peroxisome Proliferator-Activated Receptor α-Responsive Mouse Genes Is AICAR 5′-Monophosphate-Dependent and AMP-Activated Protein Kinase-Independent

5-Aminoimidazole-4-carboxyamide-ribonucleoside (AICAR), a prodrug activator of AMP-activated protein kinase (AMPK), increased hepatic expression of cytochrome P450 4a10, 4a14, and 4a31 mRNAs 2-, 3-, and 4-fold, respectively, and liver microsomal lauric acid omega-hydroxylation increased 2.8-fold. Likewise, mRNA levels of the peroxisome proliferator-activated receptor alpha (PPAR alpha)-responsive genes, Acox1, Acadm, Cpt1a, and Fabp1, were also increased by AICAR treatment. AICAR did not elicit these changes in PPAR alpha null mice. In isolated murine hepatocytes, AICAR and adenosine produced similar effects, and these responses were blocked by the PPAR alpha antagonist [(2S)-2-[[(1Z)-1-methyl-3-oxo-3-[4-(trifluoromethyl)phenyl]-1-propenyl]amino]-3-[4-[2-(5-methyl-2-phenyl-4-oxazolyl)ethoxy]phenyl]propyl]-carbamic acid ethyl ester (GW6471). Inhibition of AMPK using compound C (dorsomorphin or 6-[4-(2-piperidin-1-ylethoxy)phenyl]-3-pyridin-4-ylpyrazolo[1,5-a]pyrimidine) did not block the induction of the PPAR alpha-responsive genes by AICAR or adenosine, and 6,7-dihydro-4-hydroxy-3-(2'-hydroxy[1,1'-biphenyl]-4-yl)-6-oxo-thieno[2,3-b]pyridine-5-carbonitrile (A-769662), a non-nucleoside, direct activator of AMPK, did not increase expression of PPAR alpha-responsive genes. An inhibitor of adenosine kinase, 5-iodotubercidin, blocked these responses, suggesting that the phosphorylation of AICAR and adenosine to AICAR 5'-monophosphate (ZMP) or AMP, respectively, was required. Concentrations of ZMP and AMP were elevated and ATP levels diminished at 24 h. The PPAR alpha-dependent responses were associated with increased concentrations of oleic acid, a potent PPAR alpha agonist, and diminished levels of oleoyl-CoA. Oleoyl-CoA synthase activity was inhibited by ZMP and AMP with IC50 values of 0.28 and 0.41 mM, respectively. These results suggest that PPAR alpha is activated by increased concentrations of free fatty acids that may arise from impaired fatty acid metabolism caused by altered levels of ATP, AMP, and ZMP after AICAR or adenosine treatment.