Quercetin up-regulates paraoxonase 1 gene expression via sterol regulatory element binding protein 2 that translocates from the endoplasmic reticulum to the nucleus where it specifically interacts with sterol responsive element–like sequence in paraoxonase 1 promoter in HuH7 liver cells

We previously showed that quercetin expresses its antiatherogenic effects by up-regulating paraoxonase 1 (PON1) gene and high-density lipoprotein\u27s protective capacity against low-density lipoprotein oxidation. In an attempt to elucidate the mechanism of action of quercetin, we have now determined the effects of quercetin on PON1 gene expression, activity, protein level, nuclear mature sterol regulatory element binding protein 2 (SREBP2) level, and its translocation from the endoplasmic reticulum to nucleus and its interaction with PON1 promoter in human HuH7 liver cells using real-time reverse transcriptase polymerase chain reaction, spectrophotometry, immunoblot, confocal microscopy, and electrophoretic mobility shift assay techniques, respectively. Quercetin (20 μmol/L) treatment increased PON1 messenger RNA by 75% (P \u3c .02), with a concomitant 2-fold (P \u3c .05) increase in PON1 activity accompanied by 60% (P \u3c .01) increase in PON1 protein level. There was parallel to the 1.5- to 2.0-fold increase (P \u3c .05) in mature SREBP2 in the cell nuclei that was verified by increased immunolocalization of the mature SREBP2 (65-kd species) in the nuclei of quercetin-treated cells by confocal microscopy. Evaluation of the binding of biotin-labeled sterol responsive element (SRE)–like element of the PON1 promoter to the nuclear extract from the 24-hour quercetin (20 μmol/L)–treated HuH7 cells by electrophoretic mobility shift assay revealed that the SREBP2 specifically binds to the SRElike element that was abolished by prior incubation with anti-SREBP2 or significantly decreased by 200-fold molar excess of unlabeled SRElike sequence. Based on these results, we conclude that quercetin exhibits its antiatherogenic property by eliciting the translocation of the mature SREBP2 from endoplasmic reticulum to the nucleus, where it binds to SRE-like sequence in the PON1 promoter and up-regulates PON1 gene transcription and PON1 activity

Is alcohol beneficial or harmful for cardioprotection?

While the effects of chronic ethanol consumption on liver have been well studied and documented, its effect on the cardiovascular system is bimodal. Thus, moderate drinking in many population studies is related to lower prevalence of coronary artery disease (CAD). In contrast, heavy drinking correlates with higher prevalence of CAD. In several other studies of cardiovascular mortalities, abstainers and heavy drinkers are at higher risk than light or moderate drinkers. The composite of this disparate relation in several population studies of cardiovascular mortality has been a “U-” or “J-”shaped curve. Apart from its ability to eliminate cholesterol from the intima of the arteries by reverse cholesterol transport, another major mechanism by which HDL may have this cardioprotective property is by virtue of the ability of its component enzyme paraoxonase1 (PON1) to inhibit LDL oxidation and/or inactivate OxLDL. Therefore, PON1 plays a central role in the disposal of OxLDL and thus is antiatherogenic. Furthermore, PON1 is a multifunctional antioxidant enzyme that can also detoxify the homocysteine metabolite, homocysteine thiolactone (HTL), which can pathologically cause protein damage by homocysteinylation of the lysine residues, thereby leading to atherosclerosis. We demonstrated that moderate alcohol up regulates liver PON1 gene expression and serum activity, whereas heavy alcohol consumption had the opposite effects in both animal models and in humans. The increase in PON1 activity in light drinkers was not due to preferential distribution of high PON1 genotype in this group. It is well known that wine consumption in several countries shows a remarkable inverse correlation to local rates of CAD mortality. Significantly, apart from its alcohol content, red wine also has polyphenols such as quercetin and resveratrol that are also known to have cardioprotective effects. We have shown that quercetin also up regulates PON1 gene in rats and in human liver cells. The action of quercetin seems to be mediated via the active form of the nuclear lipogenic transcription factor, sterol-regulatory element-binding protein 2 (SREBP2) that is translocated from endoplasmic reticulum to the nucleus. However, the mechanism of action of ethanol-mediated up-regulation of PON1 gene remains to be elucidated. We conclude that both moderate ethanol and quercetin, the two major components of red wine, exhibit cardioprotective properties via the up-regulation of the antiatherogenic gene PON1