Eicosapentaenoic acid abolishes the proatherogenic effects of cholesterol: effects on migration of bovine smooth muscle and endothelial cells in vitro

Docosapentaenoic acid-rich oil lowers plasma glucose and lipids in a mouse model of diabetes and mild obesity

Many studies have investigated the beneficial effects of n-3 polyunsaturated fatty acids, such as their potential for lowering lipid levels and reducing diabetes risk. However, few studies have specifically examined docosapentaenoic acid (DPA), an n-3 polyunsaturated fatty acid with limited availability in its pure form. We hypothesized that DPA would have lipid-lowering effects and improve insulin resistance in KK/Ta mice. To test our hypothesis, 7-week-old KK/Ta mice were fed a high-fat diet for 12 weeks to induce obesity before being divided into 3 groups and fed an experimental diet for 10 weeks. The experimental diets were: LSO, using lard and safflower oil as fat sources; SO, in which lard in the LSO diet was replaced with safflower oil; and DPA, in which lard in the LSO diet was replaced with DPA oil. After 10 weeks, plasma triglyceride and total cholesterol concentrations were significantly decreased in the DPA group, but not in the SO group. Sterol regulatory element-binding protein-1 and stearoyl-CoA desaturase-1 gene expressions involved in fatty acid synthesis in the liver were significantly lower in the DPA group compared with the LSO group. Plasma glucose concentrations were significantly decreased in both the SO group and the DPA group compared with the LSO group, whereas plasma insulin concentrations were significantly decreased in the DPA group alone. These results indicate that DPA has plasma lipid-lowering and hypoglycemic effects, possibly from suppression of fatty acid synthesis in the liver.

Does nutrition have a role in peripheral vascular disease?

Peripheral vascular disease (PVD) is a manifestation of systemic atherosclerosis in the lower limbs, and PVD patients have a 3- to 5-fold increased risk of cardiovascular mortality compared with age-matched controls. Nevertheless, recent reports show how PVD patients are undertreated with regard to CVD risk-factor reduction and the use of lipid-lowering or antiplatelet drugs. There is appreciable evidence that demonstrates the beneficial effects of certain nutrients and dietary habits in the prevention of CVD, but there has been little attention paid to the role of nutrients in PVD. The purpose of the present review is to provide an overview of our understanding of how foods could possibly benefit PVD. In the last few decades, several nutrients have arisen as potentially health-promoting in PVD. While nutritional interventions in PVD show positive clinical effects for fish oil, carnitine or vitamin E, others such as olive oil or vitamin C seem to interact only at a biochemical level by decreasing risk factors. Moreover, only epidemiological associations exist for the potential role of fibre, folates or vitamin B6 in this disease. In all cases, the limited data available provide no clear-cut evidence in favour of the clinical benefit of nutritional interventions aimed at reducing risk factors and ameliorating symptoms in PVD patients. No practical recommendations can be given at this stage, and further studies are clearly needed.

Polarization of Plasma Membrane Microviscosity during Endothelial Cell Migration

Cell movement is characterized by anterior-posterior polarization of multiple cell structures. We show here that the plasma membrane is polarized in moving endothelial cells (EC); in particular, plasma membrane microviscosity (PMM) is increased at the cell leading edge. Our studies indicate that cholesterol has an important role in generation of this microviscosity gradient. In vitro studies using synthetic lipid vesicles show that membrane microviscosity has a substantial and biphasic influence on actin dynamics; a small amount of cholesterol increases actin-mediated vesicle deformation, whereas a large amount completely inhibits deformation. Experiments in migrating ECs confirm the important role of PMM on actin dynamics. Angiogenic growth factor-stimulated cells exhibit substantially increased membrane microviscosity at the cell front but, unexpectedly, show decreased rates of actin polymerization. Our results suggest that increased PMM in lamellipodia may permit more productive actin filament and meshwork formation, resulting in enhanced rates of cell movement.

Simvastatin enhanced sodium nitroprusside-induced apoptosis of smooth muscle cells. An involvement of geranylgeraniol

A decrease in serum cholesterol is one of the most beneficial effects in anti-atherogenesis. Nitric oxide is also an anti-atherogenic substance, inducing vasodilation and inhibits proliferation of smooth muscle cells (SMC). Therefore, we examined sodium nitroprusside (SNP)-induced apoptosis of vascular SMC with respect to cholesterol metabolism. Cultured vascular SMC from bovine carotid arteries and rat aorta were used. Apoptosis was determined by propidium iodide assay. Treatment of the SMC with SNP(100 micromol/l-1 mmol/l ) for 6 h induced a little nuclear fragmentation. SNP (1 mmol/l ) elicited apoptosis in 4.4+/-2.2% of cells. Pretreatment of SMC with simvastatin (1 microg/ml, 2 days), a hydroxymethylglutaryl Coenzyme A (HMG CoA) reductase inhibitor, synergistically enhanced SNP-induced apoptosis (% apoptosis =15. 9+/-3.3%). Either mevalonate (100 micromol/l) or geranylgeraniol (30 micromol/l) recovered the simvastatin (1 microg/ml)-enhanced SMC apoptosis induced by SNP. Neither squalene (10 mmol/l) nor farnesol (30 micromol/l) had a recovery effect on the simvastatin-enhanced SMC apoptosis induced by SNP. Pretreatment with simvastatin (1 microg/ml) reduced total cholesterol content in SMC. Mevalonate (100 micromol/l) restored a decrease in total cholesterol content. However, incubation with LDL deficient serum did not enhance SNP-induced apoptosis of SMC, although treatment with LDL deficient serum decreased the total cholesterol content in SMC. These data suggested that decrease in HMG CoA reductase metabolites, especially geranylgeraniol might enhance the SNP-induced apoptosis of SMC, and that, apoptosis was not involved in a decrease in cholesterol of SMC.

Arachidonic acid pretreatment enhances smooth muscle cell migration via increased Ca2+ influx

It is well known that vascular smooth muscle cell (SMC) migration is an initial step in atheromatous plaque formation. In the present study, we investigated the effects of arachidonic acid (AA, 20:4 n-6) on bovine carotid artery SMC migration using the modified Boyden chamber technique. SMCs pretreated with 2.5 microg/ml of AA for 2 days, showed an enhanced migration response to fetal bovine serum. AA pretreatment (0.5-5.0 microg/ml) increased fetal bovine serum-induced SMC migration dose-dependently, and maximum stimulation was observed at a concentration of 2.5 microg/ml. However, AA pretreatment did not enhance fetal bovine serum-induced endothelial cell migration. Using lipid analysis, we found that AA was substantially incorporated into cellular phospholipids. When SMC migration was induced by platelet derived growth factor (PDGF)-BB, instead of serum, the stimulative effect of AA pretreatment was retained. SMCs pretreated with AA showed greater mobilization of intracellular Ca2+ in response to PDGF-BB than SMCs without AA pretreatment (controls). Nifedipine, a Ca2+ channel blocker, and glycoletherdiamine-tetraacetic acid (EGTA) had no effect on PDGF-induced migration of controls but both drugs reduced the enhanced PDGE-induced migration of AA-pretreated SMCs to the control level. Baicalein, an inhibitor of 12-lipoxygenase, reduced PDGF-BB-induced migration of both control and AA pretreated SMCs, however the AA-pretreated cells still showed enhanced migration compared to control cells. These findings suggest that AA accelerates SMC migration in the thickening of the intima during atheroma formation, via stimulation of extracellular Ca2+ influx.

Effects of ethyl-all-cis-5,8,11,14,17-icosapentaenoate (EPA-E), pravastatin and their combination on serum lipids and intimal thickening of cuff-sheathed carotid artery in rabbits

The anti-arteriosclerotic effects of ethyl all-cis-5, 8, 11, 14, 17-icosapentaenoate (EPA-E), pravastatin and their combination in cuff-treated rabbits were investigated. EPA-E at 600 mg/kg, pravastatin at 50 mg/kg or their combination was orally administered once daily for 5 weeks, and each of the animals was sheathed with a cuff on the carotid artery 2 weeks after the beginning of drug administration. EPA-E, pravastatin and their combination significantly reduced serum total cholesterol compared to the control group. EPA-E also potently reduced serum triglyceride, while pravastatin only slightly reduced it. The combination of these two agents had the most potent effect on the level of serum triglyceride. Serum phospholipids were also reduced by these treatments in a similar fashion. At the end of treatment, diffuse intimal thickening was observed in the cuff-covered region in all animals in the control group, and the intima/media area ratio in this group was 0.293 +/- 0.038. Treatment with EPA-E alone tended to prevent the intimal thickening, and the intima/media area ratio was 0.209 +/- 0.058 (p = 0.094). This ratio was 0.287 +/- 0.048 (p = 0.902) when pravastatin was administered alone, indicating that it had no significant effect on intimal thickening. The ratio was 0.175 +/- 0.041 (p = 0.042) when both EPA-E and pravastatin were administered, indicating that this combination had a significant inhibitory effect on intimal thickening in the cuff-sheathed region. These findings suggest that combined treatment with EPA-E and pravastatin is more effective than respective monotherapies in lowering serum lipids and/or preventing an intimal thickening as events of atherogenesis.

Omega-3 polyunsaturated fatty acids inhibit migration of human vascular smooth muscle cells in vitro

Arterial smooth muscle cell migration from the media to the intima is a crucial process in the pathogenesis of atherosclerosis. Platelet-derived growth factor (PDGF) has been proposed to play a key role in the development of advanced atherosclerotic lesions by stimulating the migration and proliferation of vascular smooth muscle cells. Polyunsaturated fatty acids (PUFA) of the omega-3 series, extracted from fish oil has been shown to have beneficial effects on atherosclerosis. In this study, we evaluated the effects of omega-3 PUFA on the migration of human aortic smooth muscle cell (hASMC) in vitro. The migration assay was performed according to the Capsoni's method using transwell culture plates. PDGF, fibrinogen or 10% FCS significantly stimulated hASMC migration, however, omega-3 PUFA significantly inhibited PDGF-induced migration of hASMC. These results suggest that the inhibitory effect of omega-3 PUFA on cell migration may be an important aspect by which omega-3 PUFA exerts its antiatherosclerotic influence.

Enhancement of membrane fluidity in cholesterol-poor endothelial cells pre-treated with simvastatin

We examined the membrane fluidity of the cholesterol-poor bovine carotid artery endothelial cells (BAEC). Cholesterol-poor BAEC were obtained by treating the cells with 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors under 10% low density lipoprotein (LDL)-deficient serum condition for 2 days. Simvastatin reduced the intracellular cholesterol content significantly at a concentration of 0.1 microgram/ml. The reduction in the cholesterol content was accompanied by the enhancement of the cell membrane fluidity which was measured by a photobleaching technique. Additional data suggested that the reduction in cholesterol content referred to the reduction in the proliferation of BAEC.

Docosapentaenoic acid (22:5, n-3), an elongation metabolite of eicosapentaenoic acid (20:5, n-3), is a potent stimulator of endothelial cell migration on pretreatment in vitro

Endothelial cell (EC) migration plays an important role in wound repair of blood vessels. We have previously reported that eicosapentaenoic acid (EPA; 20:5, n-3) pretreatment stimulates migration of ECs but not smooth muscle cells. In the present study, we used the modified Boyden chamber technique to investigate whether the stimulative effect of EPA pretreatment on EC migration is caused by EPA itself or by some metabolites of EPA. When ECs were treated with EPA (5 micrograms/ml) for 2 days, EPA was predominantly elongated to docosapentaenoic acid (DPA; 22:5, n-3), with little docosahexaenoic acid (DHA; 22:6, n-3) being formed. Direct pretreatment of ECs with DPA (0.01-1.0 microgram/ml) resulted in a dose-dependent increase in migration in response to fetal bovine serum. Moreover, maximum stimulation of EC migration by DPA pretreatment (0.5 microgram/ml) was achieved at a concentration one-tenth of that required for maximal stimulation by EPA pretreatment (5.0 micrograms/ml), indicating that DPA is a potent stimulator of EC migration. We have demonstrated by lipid analysis that direct DPA pretreatment (0.5 microgram/ml) sufficiently increased the absolute quantity of phospholipids of ECs. Cyclooxygenase inhibitor and lipoxygenase inhibitor did not abolish the stimulative effect of DPA pretreatment on EC migration. In contrast to EC migration, DPA pretreatment had no effect on smooth muscle cell migration. Together these data suggest that the stimulative effect of EPA on EC migration occurs via DPA, and that DPA may act as a powerful anti-atherogenic factor.

Dietary gamma-linolenic acid modulates macrophage-vascular smooth muscle cell interactions. Evidence for a macrophage-derived soluble factor that downregulates DNA synthesis in smooth muscle cells

Macrophages and smooth muscle cells (SMCs) are two of the major reactive cell types in atherosclerosis, a disease characterized by uncontrolled proliferation of SMCs. The present study was designed to determine how dietary oils containing gamma-linolenic acid (GLA) (primrose oil [PO]) and long-chain n-3 fatty acids (fish oil) influence the ability of macrophages to modulate SMC DNA synthesis in vitro. Mice were fed one of four diets containing 10% (wt/wt) corn oil (CO), PO, fish oil-CO mix (FC; 9:1, wt/wt), or fish oil-PO mix (FP; 1:3, wt/wt) for 2 weeks. Resident peritoneal macrophages were isolated from these mice and seeded on a semipermeable membrane with a 30-kDa cutoff. Macrophages were preincubated with or without 50 mumol/L indomethacin (a cyclooxygenase inhibitor) or 50 mumol/L L655,238 (a 5-lipoxygenase inhibitor) for 30 minutes and subsequently cocultured with naive murine aortic SMCs grown on culture dishes. DNA synthesis in SMCs and prostaglandin formation in coculture supernatants were measured at the end of a 39-hour incubation period. SMC DNA synthesis was inhibited by 28% and 60% in PO and FP diets containing 10.1% and 8.2% GLA, respectively, relative to the control CO diet containing no GLA or long-chain n-3 fatty acid. A fourfold increase in the levels of PGE1, a potent antiproliferative eicosanoid derived from GLA, was observed in the PO and FP groups relative to the control CO group.(ABSTRACT TRUNCATED AT 250 WORDS)