Mariko Tani

Apolipoprotein CIII Links Hyperlipidemia With Vascular Endothelial Cell Dysfunction

Background— Apolipoprotein CIII (apoCIII) is a component of some triglyceride-rich very-low-density and low-density lipoprotein and is elevated in dyslipidemia with insulin resistance and the metabolic syndrome. We previously reported that apoCIII directly activates proinflammatory and atherogenic signaling in vascular endothelial cells through protein kinase C-&bgr; (PKC&bgr;). Because PKC&bgr; impairs the response of vascular endothelial cells to insulin, we tested the hypothesis that apoCIII affects insulin signaling in vascular endothelial cells and its function in vitro and in vivo. Methods and Results— ApoCIII inhibited insulin-induced tyrosine phosphorylation of insulin receptor substrate 1 (IRS-1), decreasing phosphatidylinositol 3-kinase (PI3K)/Akt activation in human umbilical vein endothelial cells. These effects of apoCIII led to reduced endothelial nitric oxide synthase (eNOS) activation and NO release into the media. ApoCIII activated PKC&bgr; in human umbilical vein endothelial cells, resulting in IRS-1 dysfunction via serine phosphorylation. ApoCIII also activated mitogen-activated protein kinase through PKC&bgr;. The impaired insulin signaling was restored by PKC&bgr; inhibitor or MEK1 inhibitor. ApoCIII-rich very-low-density lipoprotein and apoCIII impaired insulin signaling in the aorta of C57BL/6J mice and in human umbilical vein endothelial cells, which was recovered by PKC&bgr; inhibitor. They also inhibited endothelium-dependent relaxation of the aortas of C57BL/6J mice. In summary, apoCIII in very-low-density lipoprotein impaired insulin stimulation of NO production by vascular endothelium and induced endothelial dysfunction in vivo. This adverse effect of apoCIII was mediated by its activation of PKC&bgr;, which inhibits the IRS-1/PI3K/Akt/eNOS pathway. Conclusion— Our results suggest that apoCIII is a crucial link between dyslipidemia and insulin resistance in vascular endothelial cells with consequential deleterious effects on their atheroprotective functions.

Pitavastatin Inhibits Remnant Lipoprotein-Induced Macrophage Foam Cell Formation Through ApoB48 Receptor–Dependent Mechanism

Objective— Atherogenic remnant lipoproteins (RLPs) are known to induce foam cell formation in macrophages in vitro and in vivo. We examined the involvement of apoB48 receptor (apoB48R), a novel receptor for RLPs, in that process in vitro and its potential regulation by pitavastatin. Methods and Results— THP-1 macrophages were incubated in the presence of RLPs (20 mg cholesterol/dL, 24 hours) isolated from hypertriglyceridemic subjects. RLPs significantly increased intracellular cholesterol ester (CE) and triglyceride (TG) contents (4.8-fold and 5.8-fold, respectively) in the macrophages. Transfection of THP-1 macrophages with short interfering RNA (siRNA) against apoB48R significantly inhibited RLP-induced TG accumulation by 44%. When THP-1 macrophages were pretreated with pitavastatin (5 &mgr;mol/L, 24 hours), the expression of apoB48R was significantly decreased and RLP-induced TG accumulation was reduced by 56%. ApoB48R siRNA also inhibited TG accumulation in THP-1 macrophage induced by &bgr;–very-low-density lipoprotein derived from apoE−/− mice by 58%, supporting the notion that apoB48R recognizes and takes-up RLPs in an apoE-independent manner. Conclusions— RLPs induce macrophage foam cell formation via apoB48R. Pitavastatin inhibits RLP-induced macrophage foam cell formation. The underlying mechanism involves, at least in part, inhibition of apoB48R-dependent mechanism. Our findings indicate a potential role of apoB48R in atherosclerosis.

Pleiotropic preventive effects of dietary polyphenols in cardiovascular diseases.

Polyphenols are common constituents of the diet, and research on their health benefits has developed quickly over the past few years. Our purpose is to review recent findings highlighting daily dietary polyphenol intake and the diverse function of polyphenols and their possible relationships to cardiovascular disease (CVD). Several cohort studies have reported an inverse relationship between the daily consumption of polyphenols and CVD risk. Many studies showed that beverages could be a large source of polyphenols. Our previous findings provide that Japanese people intake polyphenols mainly from beverages, especially coffee and green tea (in descending order of polyphenol content). Many kinds of polyphenols act as an antioxidant against low-density lipoprotein oxidation, which is known to promote atherosclerosis. Recent accumulating evidence suggests that dietary polyphenols could exert their cardioprotective actions through their potential to improve metabolic disorder and vascular inflammation. These findings raise the possibility that polyphenols have a wide variety of roles in the intestine, liver and vascular tissue. In addition to identifying mechanisms of polyphenol bioactivity by basic research, much more epidemiological and clinical evidence linking reduced cardiovascular risk with dietary polyphenols intake are needed.

Sweet potato (Ipomoea batatas L.) leaves suppressed oxidation of low density lipoprotein (LDL) in vitro and in human subjects

Sweet potato (Ipomoea batatas L.) leaves are consumed as vegetables around the world, especially in Southeast Asia. The aim of this study was to investigate the inhibitory effect of sweet potato leaves on low-density lipoprotein oxidation in vitro and in human subjects. We compared the antioxidant activity of 8 kinds of sweet potato leaves. Every sweet potato leaf had high radical scavenging activity and prolonged a lag time for starting low-density lipoprotein oxidation in vitro. We found that sweet potato leaves contained abundant polyphenol compounds and the radical scavenging activity and prolongation rate of lag time were highly correlated with total polyphenol content. We also confirmed that thiobarbituric acid reactive substances production was increased in endothelial cell-mediated low-density lipoprotein oxidation, which was decreased by treatment with sweet potato leaves. We further measured the low-density lipoprotein oxidizability in 13 healthy volunteers after their intake of 18 g of “Suioh”, raw sweet potato leaves. “Suioh” prolonged a lag time for starting low-density lipoprotein oxidation and decreased low-density lipoprotein mobility. These results suggest that sweet potato leaves have antioxidant activity leading to the suppression of low-density lipoprotein oxidation.

Effects of magnesium on postprandial serum lipid responses in healthy human subjects

Postprandial hyperlipidaemia has been recognised to be a risk factor for atherosclerosis development. Epidemiological and animal studies have shown that Mg intake is inversely associated with some risk factors of atherosclerosis, including lipid metabolism. The present study was performed to determine the effects of Mg supplementation on postprandial responses in serum lipid levels. We used bittern (Nigari, in Japanese), a natural MgCl(2) solution from sea or salt lake water, for Mg supplementation. In a two-way, randomised, crossover study, sixteen healthy male volunteers consumed 30 g butter with or without 5 ml bittern containing 500 mg of Mg. Fasting and postprandial blood samples were taken 2, 3, 4 and 6 h after ingestion. Postprandial lipid responses were evaluated by serum TAG, chylomicron TAG, apo-B48, remnant-like particle cholesterol (RLP-C) and NEFA concentrations. We found that the serum and the chylomicron TAG responses after the fat load were reduced and delayed by Mg supplementation. The concentrations of apo-B48 (P < 0.05), RLP-C (P < 0.05) and NEFA (P < 0.05) were significantly lower at 2 h after the fat-with-Mg meal compared with the fat-only meal. The present study indicated that Mg supplementation could inhibit fat absorption and improve postprandial hyperlipidaemia in healthy subjects.

Coffee and beverages are the major contributors to polyphenol consumption from food and beverages in Japanese middle-aged women.

Food and beverages rich in polyphenols have been shown to reduce the risk of non-communicable diseases. The present study estimated polyphenol levels and consumption from food and beverages in Japanese women. Randomly recruited housewives living in the area around Tokyo (n 109; aged 21–56 years; Group 1) recorded all beverages and foods they ingested for 7 d, and the total polyphenol (TP) consumption was estimated based on the TP content of each item measured with a modified Folin–Ciocalteu method. For Group 1, TP was consumed at 841 (sd 403) mg/d (range 113–1759 mg/d), and beverages were a larger source of TP (79 %) than food (21 %). The largest single source of TP was coffee at 47 %, followed by green tea, black tea, chocolate, beer and soya sauce, at 16, 5·7, 3·3, 3·2 and 3·1 %, respectively. In terms of food groups, cereals/noodles, vegetables, fruits, beans and seeds, and seasonings (except for soya sauce) contributed 5·0, 4·0, 1·4, 1·8 and 2·4 %, respectively. Another group of housewives who consumed at least one cup of coffee per d were separately recruited (n 100; Group 2) in the same area. Their consumption of TP was higher at 1187 (sd 371) mg/d (range 440–2435 mg/d) than Group 1 (P < 0·001), and the difference mostly came from the coffee consumption. We conclude that not food but beverages, especially coffee, may be the major contributor to TP consumption in Japanese women.

Skin photoprotection and consumption of coffee and polyphenols in healthy middle-aged Japanese females.

Reactive oxygen species are known to mediate skin photoaging, which results in the formation of pigmented spots and wrinkles. Coffee is the largest source of polyphenols, which supplies a large number of antioxidants in ones daily life. However, little is known about how much coffee and polyphenol consumption influences skin health. In this study, a cross‐sectional survey of the diet, environmental factors, and skin conditions was conducted in healthy Japanese females to explore the influence of coffee and polyphenol consumption on skin conditions.

Sphingosine 1‐phosphate (S1P) inhibits monocyte–endothelial cell interaction by regulating of RhoA activity

Recent studies suggest that sphingosine 1‐phosphate (S1P) protects against atherosclerosis. We assessed the effects of S1P on monocyte–endothelial interaction in the presence of inflammatory mediators. Pretreatment of THP‐1 cells with S1P abolished Phorbol 12 myristate 13‐acetate (PMA)‐induced THP‐1 cell adhesion to human umbilical vein endothelial cells (HUVECs). S1P inhibited PMA‐induced activation of RhoA, but not PKCs. S1P activated p190Rho GTPase activation protein (GAP) only in the presence of PMA, suggesting an inhibitory effect of S1P and PMA to suppress RhoA. In conclusion, S1P inhibited monocyte–endothelial interactions by inhibiting RhoA activity which may explain its anti‐atherogenic effects.

Pine bark extract prevents low-density lipoprotein oxidation and regulates monocytic expression of antioxidant enzymes.

Polyphenols are widely distributed in leaves, seeds, bark, and flowers and considered to have beneficial effects on cardiovascular health. We hypothesized that the potent antioxidant properties of pine bark extract (PBE) are exerted by its ability to scavenge free radicals and induce antioxidant enzymes. Therefore, we investigated the effects of PBE on low-density lipoprotein (LDL) oxidation and the antioxidant defense system in monocytes. Oxidative susceptibility of LDL was determined by lag time assay in vitro and by using a human umbilical vein endothelial cell-mediated oxidation model. THP-1 monocytic cells were treated with PBE, and the expression of antioxidant enzymes was measured by real-time polymerase chain reaction and Western blot. Pine bark extract showed radical scavenging ability and significantly inhibited free radical-induced and endothelial cell-mediated LDL oxidation in vitro. Pine bark extract treatment resulted in increases in the expressions of antioxidant enzymes, glutathione peroxidase-1, catalase, and heme oxygenase-1 in THP-1 cells. In addition, PBE induced nuclear factor-erythroid-2-related factor 2 activation, which was accompanied by the activation of extracellular signal-regulated kinase and Akt despite a down-regulation of reactive oxygen species. After the monocyte investigations, we further examined the antioxidant effect after the intake of PBE by 10 healthy male volunteers. Pine bark extract significantly prolonged the lag time of LDL oxidation. Based on our findings, it appears that PBE enhances the antioxidant defense capacity of LDL and monocytes and may play a preventive role in atherosclerosis progression.

7-Ketocholesterol enhances leukocyte adhesion to endothelial cells via p38MAPK pathway

7-Ketocholesterol is a major dietary cholesterol oxidation product found in high concentrations in atherosclerotic plaques, which contribute to the development of atherosclerosis. This study aimed to investigate the effects of 7-ketocholesterol on endothelial inflammation, as well as the underlying mechanisms. Pretreatment of human umbilical vein endothelial cells (HUVEC) with 7-ketocholesterol significantly enhanced the total interactions between human monocytic cells (THP-1 cell line) and TNFα-activated HUVECs under physiological flow conditions, compared to pretreatment with cholesterol (TNFα+50 μM cholesterol: 13.1 ± 0.54 cells/CPF, TNFα+50 μM 7-ketocholesterol: 18.9 ± 0.35 cells/CPF, p < 0.01). 7-Ketocholesterol enhanced the expression of E-selectin, ICAM-1, and VCAM-1 proteins. It also activated p38 mitogen-activated protein kinase (MAPK), and treatment with a p38 MAPK inhibitor inhibited both E-selectin expression via ATF-2 activation and 7-ketocholesterol-induced THP-1 adhesion to HUVECs. These findings suggest that 7-ketocholesterol enhances leukocyte–endothelial interactions by upregulating the expression of adhesion molecules, presumably via the p38 MAPK-dependent pathway.