Pomegranate Juice Polyphenols Induce Macrophage Death via Apoptosis as Opposed to Necrosis Induced by Free Radical Generation: A Central Role for Oxidative Stress

Pomegranate Peel Extract Decreases Plaque Necrosis and Advanced Atherosclerosis Progression in Apoe -/- Mice

Atherosclerosis is a chronic lipid-driven inflammatory condition of the arteries and is a leading cause of stroke, myocardial infarction, and other peripheral arterial diseases. Plant products rich in polyphenols such as pomegranate juice and peel extract are known to have beneficial effects in suppressing atherogenesis. However, the mechanism of action and its effect on advanced atherosclerosis progression which results in adverse clinical outcomes are not well understood. Herein, we use a standardized hydroethanolic extract of Punica granatum (pomegranate) peel in the Apoe^-/- a murine model of advanced atherosclerosis. It was observed that the pomegranate peel extract fed mice have decreased plaque necrosis and elevated lesional collagen content which was associated with a favorable metabolic profile including lowering of blood glucose, cholesterol, and triglyceride. The decrease in plaque necrosis was linked with increased lesional macrophage efferocytosis efficiency which was associated with enhanced expression of the efferocytosis receptor Mertk. Using in vitro studies, we show that pomegranate peel extract blocks the shedding of Mertk and preserves macrophage efferocytosis efficiency. These data identify a novel mechanism by which pomegranate peel extract promotes the resolution of inflammation in atherosclerosis.

Pu-erh Tea Ameliorates Atherosclerosis Associated with Promoting Macrophage Apoptosis by Reducing NF-κB Activation in ApoE Knockout Mice

We explored whether pu-erh tea consumption ameliorates atherosclerosis and the possible mechanism for its effects in apolipoprotein E-deficient (ApoE^−/−) mice. Our data showed that pu-erh tea consumption markedly reduced early fatty streak formation and the advanced fibrofatty plaque sizes. Additionally, the mean proportion of inflammatory macrophages in the plaque decreased, and the number of apoptotic macrophages increased significantly. NF-κB activity in peritoneal macrophages decreased by 75.6% compared to the controls, similar with the levels of IL-6, IL-12, and TNF-α expression. The tea extract increased the apoptosis of RAW264.7 cells by decreasing NF-κB activation and reducing the inflammatory cytokine expression. In conclusion, pu-erh tea ameliorates atherosclerosis progress by alleviating the chronic inflammatory state by reducing NF-κB activation and promoting macrophage apoptosis in atherosclerotic plaques.

Pro-atherogenic and pro-oxidant crosstalk between adipocytes and macrophages

PURPOSE

Obesity, which is characterized by triglyceride accumulation mainly in adipocytes but also in arterial wall cells such as macrophages, is a major risk factor for developing atherosclerosis. We aimed to identify the crosstalk related to lipid metabolism and oxidation status between adipocytes and macrophages.

METHODS

We used a co-culture model system with J477A.1 cultured macrophages and 3T3L1 cultured adipocytes. For an in-vivo co-culture system, we used C57BL/6 mouse peritoneal macrophages and visceral or subcutaneous adipose tissue.

RESULTS

Adipocytes significantly increased reactive oxygen species generation, up to twofold, and decreased cholesterol content by 22% in the co-cultured macrophages. Macrophages significantly increased triglyceride-biosynthesis rate by twofold and decreased triglyceride-degradation rate by 30%, resulting in increased triglyceride accumulation in the co-cultured adipocytes by up to 72%. In the in-vivo mouse model, visceral adipose tissue crosstalk with macrophages resulted in a significant pro-atherogenic phenotype with respect to cellular cholesterol metabolism. In contrast, the interaction between subcutaneous adipose tissue and macrophages mostly affected cellular triglyceride metabolism. There were no significant effects on mitochondrial respiration capacity in the macrophages. Upon oxidative-stress reduction in the co-cultured cells using the polyphenol-rich antioxidant, pomegranate juice, the expression of genes related to cellular lipid accumulation was significantly reduced.

CONCLUSIONS

We reveal, for the first time, that paracrine interactions between adipocytes and macrophages result in oxidative stress and lipids metabolic alterations in both cells, toward increased atherogenicity which can be reversed by phenolic antioxidants.

Leucine supplementation attenuates macrophage foam-cell formation: Studies in humans, mice, and cultured macrophages

Whereas atherogenicity of dietary lipids has been largely studied, relatively little is known about the possible contribution of dietary amino acids to macrophage foam-cell formation, a hallmark of early atherogenesis. Recently, we showed that leucine has antiatherogenic properties in the macrophage model system. In this study, an in-depth investigation of the role of leucine in macrophage lipid metabolism was conducted by supplementing humans, mice, or cultured macrophages with leucine. Macrophage incubation with serum obtained from healthy adults supplemented with leucine (5 g/d, 3 weeks) significantly decreased cellular cholesterol mass by inhibiting the rate of cholesterol biosynthesis and increasing cholesterol efflux from macrophages. Similarly, leucine supplementation to C57BL/6 mice (8 weeks) resulted in decreased cholesterol content in their harvested peritoneal macrophages (MPM) in relation with reduced cholesterol biosynthesis rate. Studies in J774A.1 murine macrophages revealed that leucine dose-dependently decreased cellular cholesterol and triglyceride mass. Macrophages treated with leucine (0.2 mM) showed attenuated uptake of very low-density lipoproteins and triglyceride biosynthesis rate, with a concurrent down-regulation of diacylglycerol acyltransferase-1, a key enzyme catalyzing triglyceride biosynthesis in macrophages. Similar effects were observed when macrophages were treated with α-ketoisocaproate, a key leucine metabolite. Finally, both in vivo and in vitro leucine supplementation significantly improved macrophage mitochondrial respiration and ATP production. The above studies, conducted in human, mice, and cultured macrophages, highlight a protective role for leucine attenuating macrophage foam-cell formation by mechanisms related to the metabolism of cholesterol, triglycerides, and energy production. © 2018 BioFactors, 44(3):245-262, 2018.

Connexin43 and AMPK Have Essential Role in Resistance to Oxidative Stress Induced Necrosis

Reactive oxygen species (ROS) induced oxidative stress leads to cell damage and neurological disorders in astrocytes. The gap junction protein connexin43 (Cx43) could form intercellular channels in astrocytes and the expression of Cx43 plays an important role in protecting the cells from damage. In the present study, we investigated the contribution of Cx43 to astrocytic necrosis induced by the ROS hydrogen peroxide (H₂O₂) and the mechanism by which AMPK was involved in this process. Fluorescence microscopy, flow cytometry, and western blot were used quantitatively and qualitatively to determine the cell apoptosis, necrosis, and protein expression. Lack of Cx43 expression or blockage of Cx43 channels resulted in increased H₂O₂-induced astrocytic necrosis, supporting a cell protective effect of functional Cx43 channels. Our data suggest that AMPK is important for Cx43-mediated ROS resistance. Inhibition of AMPK activation results in reduction of necrosis and ROS production. Taken together, our findings suggest that the role of Cx43 in response to H₂O₂ stress is dependent on the activation of AMPK signaling pathways and regulates ROS production and cell necrosis.

Effects of Pomegranate (Punica Granatum L.) Seed and Peel Methanolic Extracts on Oxidative Stress and Lipid Profile Changes Induced by Methotrexate in Rats

Purpose: Methotrexate (MTX) is prescribed in many diseases and can result in oxidative stress (OS) followed by injuries in some tissues. Antioxidants administration are effective in reducing OS. Pomegranate exhibits high anti-oxidant capacities. This study investigated whether pomegranate seed and peel methanolic extracts (PSE and PPE) could protect against MTX-induced OS and lipid profile changes in rats.

Methods: Forty-eight rats were randomly divided into 6 groups: control group (normal salin), PSE group (500 mg/kg, orally), PPE group (500 mg/kg, orally), MTX group (10 mg/kg, IM), MTX and PSE group, and MTX and PPE group. Blood samples were taken for analysis in the end of the procedure.

Results: The findings showed a significant reduction in Glutathione peroxidase (GPx) and Superoxide dismutase (SOD), and an enhancement in malondialdehyde (MDA) values after MTX treatment (p < 0.05). SOD and GPx levels reached the levels of the control group in MTX+SPE and MTX+PPE groups. No significant differences were observed in catalase (CAT) and total antioxidant capacity (TAC) levels between groups. The results showed a significant decrease in total cholesterol (TC), low density lipoprotein (LDL), and high density lipoprotein (HDL) in the MTX treated group (p < 0.01). The values of TC, HDL, and LDL became elevated to the normal control levels in the MTX+PSE and MTX+PPE treated groups.

Conclusion: The results showed the OS induced by MTX and the protective effects of PSE and PPE against MTX-induced serum oxidative stress and lipid profile changes in rats.

Supplementation with linoleic acid-rich soybean oil stimulates macrophage foam cell formation via increased oxidative stress and diacylglycerol acyltransferase1-mediated triglyceride biosynthesis

During the last decades there has been a staggering rise in human consumption of soybean oil (SO) and its major polyunsaturated fatty acid linoleic acid (LA). The role of SO or LA in cardiovascular diseases is highly controversial, and their impact on macrophage foam cell formation, the hallmark of early atherogenesis, is unclear. To investigate the effects of high SO or LA intake on macrophage lipid metabolism and the related mechanisms of action, C57BL/6 mice were orally supplemented with increasing levels of SO-based emulsion or equivalent levels of purified LA for 1 month, followed by analyses of lipid accumulation and peroxidation in aortas, serum and in peritoneal macrophages (MPM) of the mice. Lipid peroxidation and triglyceride mass in aortas from SO or LA supplemented mice were dose-dependently and significantly increased. In MPM from SO or LA supplemented mice, lipid peroxides were significantly increased and a marked accumulation of cellular triglycerides was found in accordance with enhanced triglyceride biosynthesis rate and overexpression of diacylglycerol acyltransferase1 (DGAT1), the key enzyme in triglyceride biosynthesis. In cultured J774A.1 macrophages treated with SO or LA, triglyceride accumulated via increased oxidative stress and a p38 mitogen-activated protein kinase (MAPK)-mediated overexpression of DGAT1. Accordingly, anti-oxidants (pomegranate polyphenols), inhibition of p38 MAPK (by SB202190) or DGAT1 (by oleanolic acid), all significantly attenuated SO or LA-induced macrophage triglyceride accumulation. These findings reveal novel mechanisms by which supplementation with SO or LA stimulate macrophage foam cell formation, suggesting a pro-atherogenic role for overconsumption of SO or LA. © 2016 BioFactors, 43(1):100-116, 2017.