Punicalagin Induces Serum Low‐Density Lipoprotein Influx to Macrophages

Abstract

High levels of circulating low-density lipoprotein (LDL) are a primary initiating event in the development of atherosclerosis. Recently, the antiatherogenic effect of polyphenols has been shown to be exerted via a mechanism unrelated to their antioxidant capacity and to stem from their interaction with specific intracellular or plasma proteins. In this study, we investigated the interaction of the main polyphenol in pomegranate, punicalagin, with apolipoprotein B-100 (ApoB100) that surrounds LDL. Punicalagin bound to ApoB100 at low concentrations (0.25–4 μM). Upon binding, it induced LDL influx to macrophages in a concentration-dependent manner, up to 2.5-fold. In contrast, another polyphenol which binds to ApoB100, glabridin, did not affect LDL influx. We further showed that LDL influx occurs specifically through the LDL receptor, with LDL then accumulating in the cell cytoplasm. Taken together with the findings of Aviram et al., 2000, that pomegranate juice and punicalagin induce plasma LDL removal and inhibit macrophage cholesterol synthesis and accumulation, our results suggest that, upon binding, punicalagin stimulates LDL influx to macrophages, thus reducing circulating cholesterol levels.

Punicalagin Decreases Serum Glucose Levels and Increases PON1 Activity and HDL Anti‐Inflammatory Values in Balb/c Mice Fed a High‐Fat Diet

“…We have recently shown that punicalagin binds specifically to LDL and induces its influx into macrophage cells without foam cell formation. Such a mechanism may remove excess cholesterol from these cells to the liver, thereby lowering cholesterol levels in the circulation [ 39 ]. In this study, the antiatherogenic and anti-inflammatory properties of punicalagin and its ability to affect serum lipid and glucose levels were explored in vivo.…”

“…Moreover, punicalagin, but not quercetin or other polyphenols, binds to LDL and induces its influx into macrophages without foam cell formation. This could be proposed as a mechanism that lowers cholesterol blood concentration and attenuates the development of atherosclerosis [ 39 ]. The present study is aimed at supporting this latter finding and to examine the biological functions of punicalagin and quercetin in relation to glucose and lipid levels, PON1 activity, and inflammation in the sera of hyperlipidemic mice.…”

“…Similarly, punicalagin binds to apolipoprotein B-100 and induces LDL influx into macrophages to a level that prevents their transformation into foam cells. Such an effect might provide an alternative mechanism for lowering blood cholesterol concentration and attenuating the development of atherosclerosis [ 39 ].…”

“…To validate our recent in vitro results showing antiatherogenic effects on punicalagin and quercetin upon specific binding to a protein located on HDL or LDL particles [ 39 ], we aimed to characterize those polyphenols' effects in vivo. In this study, the effects of punicalagin and quercetin, administered subcutaneously (sc) via osmotic minipumps, were investigated in mice fed a high-fat diet (HFD).…”

LDL Cholesterol Uptake Assay Using Live Cell Imaging Analysis with Cell Health Monitoring

“…This was then replaced by the use of fluorescently labelled LDL proteins such as DiI-LDL, and subsequent immunostaining or extraction of protein for fluorescent readings using a spectrophotometer or plate reader 15,16 . Fluorescently labelled LDL has also been used in Fluorescence-activated cell sorting (FACS) for analysis of internalization of LDL and cell surface LDL binding 17 . While these methods allow for collection of data after treatment, monitoring the viability of the cells during treatment is not possible.…”