Paraoxonase 1 (PON1) expression in hepatocytes is upregulated by pomegranate polyphenols: a role for PPAR-gamma pathway.
OBJECTIVE
Serum paraoxonase-1 (PON1) expression is regulated by polyphenols, shown to activate the peroxisome proliferator-activated receptor gamma (PPARgamma). Pomegranate juice (PJ) is a polyphenol-rich fruit. Because promoter sequence of PON1 gene indicates that it could be regulated by nuclear receptors, we investigated the effect of PJ polyphenols on PON1 gene expression in HuH7 hepatocytes.


RESULTS
PON1 protein or mRNA expression, determined by immunocytochemistry, or quantitative PCR, respectively, as well as PON1 gene promoter activation, was significantly increased in hepatocytes incubated with PJ or with its major polyphenols punicalagin, or gallic acid (GA). Ellagic acid (EA) elicited only modest stimulatory effect. Accordingly, PJ, punicalagin, GA, and less so EA, dose-dependently increased cell-associated and hepatocyte-secreted PON1 arylesterase activity. Functionally, the secreted PON1 exhibited biological activity by protecting LDL and HDL from oxidation. Finally, PJ polyphenols upregulated the hepatocyte PON1 expression, at least in part, via the intracellular signaling cascade PPARgamma-PKA-cAMP.


CONCLUSIONS
This study shows for the first time that PJ polyphenols have a specific transcriptional role in hepatocyte PON1 expression upregulation, and its secretion to the medium. We conclude that the anti-atherogenic characteristics of PJ polyphenols are modulated, at least in part, via hepatocyte PON1 upregulation and its subsequent release to the medium.
The Lipid Research Laboratory, Technion Faculty of Medicine, The Rappaport Family Institute for Research in the Medical Sciences, and Rambam Medical Center, Haifa, Israel.
Jasmin
J
Khateeb
Anna
A
Gantman
Adam J
AJ
Kreitenberg
Michael
M
Aviram
Bianca
B
Fuhrman
D043303:Aryldialkylphosphatase / Q000096:biosynthesis*; D002478:Cells, Cultured; D004610:Ellagic Acid / Q000494:pharmacology*; D005707:Gallic Acid / Q000494:pharmacology*; D022781:Hepatocytes / Q000201:enzymology*; D006801:Humans; D047348:Hydrolyzable Tannins / Q000494:pharmacology*; D029561:Lythraceae; D047495:PPAR gamma / Q000502:physiology*; D015854:Up-Regulation
D047348:Hydrolyzable Tannins; D047495:PPAR gamma; D004610:Ellagic Acid; D005707:Gallic Acid; C115642:punicalagin; D043303:Aryldialkylphosphatase