Evaluation of PPARa activation by known blueberry constituents

Authors: Rimando, Agnes; KHAN, SHABANA - University Of Mississippi; MIZUNO, CASSIA - University Of New England; REN, GUANG - Auburn University; MATHEWS, SURESH - Auburn University; KIM, HYUNSOOK - Konkuk University; Yokoyama, Wallace - Wally

Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/18/2015
Publication Date: 5/21/2015
Citation: Rimando, A.M., Khan, S.I., Mizuno, C., Ren, G., Mathews, S.T., Kim, H., Yokoyama, W.H. 2015. Evaluation of PPARa activation by known blueberry constituents. Journal of the Science of Food and Agriculture. 96(5):1666-1671. doi: 10.1002/jsfa.7269.

Interpretive Summary: In a follow-up study, we demonstrate that pterostilbene activates the protein PPAR-alpha, which is involved in fatty acid metabolism, at concentrations lower than those used in our earlier study. We also show that in the presence of a specific inhibitor activation was decreased. We further show that pterostilbene significantly and dose-dependently (at 10, 20 and 50 µM) increased PPARa gene expression, and exhibited greater induction than 100 and 200 µM of fenofibrate, a prescription medication used for the treatment dyslipidemia. We investigated whether (+)-catechin and (-)-epicatechin, compounds found in tea, would activate PPARa, and performed molecular docking studies of the stilbenes and catechins into the PPARa binding site. Pterostilbene and resveratrol docked in a similar manner and exhibited interactions with amino acids considered essential for PPARa activation. The catechins did not dock in the active pocket, which explains the lack of a dose-dependent response in the cell experiments. In hamsters fed diet mixed with extract of blueberry fruit pomace (BBX), PPARa expression in the liver was up-regulated. Pterostilbene was found in the extract at low concentrations. The concentration of pterostilbene in the BBX may not be at efficacious level but it may contribute to the up-regulation of PPARa expression in the liver.

Technical Abstract: We previously showed that pterostilbene, a stilbene found in some Vaccinium berries, is an agonist for the nuclear transcription factor peroxisome proliferator activated receptor alpha isoform (PPARa). In the present study, we demonstrate a dose-dependent activation of PPARa by pterostilbene in a rat hepatoma cell line (H4IIEC3), similar to those of the fibrate drugs ciprofibrate and fenofibrate, at concentrations ranging from 3.12 to 50.00 µM. In the presence of chenodeoxycholic acid, a specific inhibitor of PPARa, pterostilbene showed dose-dependent decreases in luciferase response paralleling those of Wy-1463, a synthetic PPARa ligand. Real-time gene expression analysis in H4IIEC3 cells revealed pterostilbene significantly and dose-dependently (at 10, 20 and 50 µM) increased PPARa gene expression, and exhibited greater induction than 100 and 200 µM of fenofibrate. We also investigated the PPARa activation by (+)-catechin and (-)-epicatechin, and performed molecular docking studies of the stilbenes and catechins into the PPARa ligand binding domain. Pterostilbene and resveratrol docked in a similar manner in the benzophenone pocket and exhibited H-bond interaction with amino acids considered essential for PPARa activation. The catechins did not dock in the active pocket, which explains the lack of a dose-dependent response obtained in vitro. In hamsters fed diet supplemented with an ethanolic extract (at 2%) of blueberry fruit pomace (BBX), up-regulation of hepatic PPARa mRNA expression was observed. A significant negative correlation between liver LDL-cholesterol levels and PPARa expression was also observed. Catechin, epicatechin, pterostilbene and resveratrol were quantitated in the BBX. The concentration of pterostilbene in the BBX may not be at efficacious level but it may contribute to the up-regulation of hepatic PPARa expression in hamsters in response to BBX.