Eicosapentaenoic acid and docosahexaenoic acid selectively attenuate U46619-induced smooth muscle cell proliferation

Endogenously generated omega-3 fatty acids attenuate vascular inflammation and neointimal hyperplasia by interaction with free fatty acid receptor 4 in mice

Background

Omega‐3 polyunsaturated fatty acids (ω3 PUFAs) suppress inflammation through activation of free fatty acid receptor 4 (FFAR4), but this pathway has not been explored in the context of cardiovascular disease. We aimed to elucidate the involvement of FFAR4 activation by ω3 PUFAs in the process of vascular inflammation and neointimal hyperplasia in mice.

Methods and Results

We used mice with disruption of FFAR4 (Ffar4^−/−), along with a strain that synthesizes high levels of ω3 PUFAs (fat‐1) and a group of crossed mice (Ffar4^−/−/fat‐1), to elucidate the role of FFAR4 in vascular dysfunction using acute and chronic thrombosis/vascular remodeling models. The presence of FFAR4 in vascular‐associated cells including perivascular adipocytes and macrophages, but not platelets, was demonstrated. ω3 PUFAs endogenously generated in fat‐1 mice (n=9), but not in compound Ffar4^−/−/fat‐1 mice (n=9), attenuated femoral arterial thrombosis induced by FeCl₃. Neointimal hyperplasia and vascular inflammation in the common carotid artery were significantly curtailed 4 weeks after FeCl₃ injury in fat‐1 mice (n=6). This included greater luminal diameter and enhanced blood flow, reduced intima:media ratio, and diminished macrophage infiltration in the vasculature and perivascular adipose tissue compared with control mice. These effects were attenuated in the Ffar4^−/−/fat‐1 mice.

Conclusions

These results indicate that ω3 PUFAs mitigate vascular inflammation, arterial thrombus formation, and neointimal hyperplasia by interaction with FFAR4 in mice. Moreover, the ω3 PUFA–FFAR4 pathway decreases inflammatory responses with dampened macrophage transmigration and infiltration.

Aspirin enhances protective effect of fish oil against thrombosis and injury-induced vascular remodelling

BACKGROUND AND PURPOSE

Although aspirin (acetylsalicylic acid) is commonly used to prevent ischaemic events in patients with coronary artery disease, many patients fail to respond to aspirin treatment. Dietary fish oil (FO), containing ω3 polyunsaturated fatty acids (PUFAs), has anti-inflammatory and cardio-protective properties, such as lowering cholesterol and modulating platelet activity. The objective of the present study was to investigate the potential additional effects of aspirin and FO on platelet activity and vascular response to injury.

EXPERIMENTAL APPROACH

Femoral arterial remodelling was induced by wire injury in mice. Platelet aggregation, and photochemical- and ferric chloride-induced carotid artery thrombosis were employed to evaluate platelet function.

KEY RESULTS

FO treatment increased membrane ω3 PUFA incorporation, lowered plasma triglyceride and cholesterol levels, and reduced systolic BP in mice. FO or aspirin alone inhibited platelet aggregation; however, when combined, they exhibited synergistic suppression of platelet activity in mice, independent of COX-1 inhibition. FO alone, but not aspirin, attenuated arterial neointimal growth in response to injury. Strikingly, a combination of FO and aspirin synergistically inhibited injury-induced neointimal hyperplasia and reduced perivascular inflammatory reactions. Moreover, co-administration of FO and aspirin decreased the expression of pro-inflammatory cytokines and adhesion molecules in inflammatory cells. Consistently, a pro-resolution lipid mediator-Resolvin E1, was significantly elevated in plasma in FO/aspirin-treated mice.

CONCLUSIONS AND IMPLICATIONS

Co-administration of FO and low-dose aspirin may act synergistically to protect against thrombosis and injury-induced vascular remodelling in mice. Our results support further investigation of adjuvant FO supplementation for patients with stable coronary artery disease.

The role of perivascular adipose tissue in vascular smooth muscle cell growth

Adipose tissue is the largest endocrine organ, producing various adipokines and many other substances. Almost all blood vessels are surrounded by perivascular adipose tissue (PVAT), which has not received research attention until recently. This review will discuss the paracrine actions of PVAT on the growth of underlying vascular smooth muscle cells (VSMCs). PVAT can release growth factors and inhibitors. Visfatin is the first identified growth factor derived from PVAT. Decreased adiponectin and increased tumour necrosis factor-α in PVAT play a pathological role for neointimal hyperplasia after endovascular injury. PVAT-derived angiotensin II, angiotensin 1-7, reactive oxygen species, complement component 3, NO and H(2) S have a paracrine action on VSMC contraction, endothelial or fibroblast function; however, their paracrine actions on VSMC growth remain to be directly verified. Factors such as monocyte chemoattractant protein-1, interleukin-6, interleukin-8, leptin, resistin, plasminogen activator inhibitor type-1, adrenomedullin, free fatty acids, glucocorticoids and sex hormones can be released from adipose tissue and can regulate VSMC growth. Most of them have been verified for their secretion by PVAT; however, their paracrine functions are unknown. Obesity, vascular injury, aging and infection may affect PVAT, causing adipocyte abnormality and inflammatory cell infiltration, inducing imbalance of PVAT-derived growth factors and inhibitors, leading to VSMC growth and finally resulting in development of proliferative vascular disease, including atherosclerosis, restenosis and hypertension. In the future, using cell-specific gene interventions and local treatments may provide definitive evidence for identification of key factor(s) involved in PVAT dysfunction-induced vascular disease and thus may help to develop new therapies.

LINKED ARTICLES

This article is part of a themed section on Fat and Vascular Responsiveness. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-3.

n-3 Fatty acids and cardiovascular disease: actions and molecular mechanisms

Cardiovascular disease and atherosclerosis are a leading cause of morbidity and mortality worldwide. Epidemiological studies and randomized control intervention trials have reported that n-3 fatty acids reduce cardiovascular events. A variety of biologic and molecular effects of n-3 fatty acids can modulate the mechanisms of development and progression of atherosclerosis. These include n-3 fatty acid effects on inflammation, cardiac excitability, platelet function, triglyceride blood levels, blood pressure and the stability of atheroma plaques. The molecular mechanisms are still not fully defined; but might involve changes in membrane fluidity, receptor responses and binding to intracellular receptors regulating gene transcription. Understanding and elucidating these mechanisms is important to development of future strategies for prevention and treatment of cardiovascular disease.

Comparison of the inhibitory effects of docosahexaenoic acid (DHA) on U46619- and phenylephrine-induced contractions in guinea-pig aorta

Inhibitory effects of docosahexaenoic acid (DHA) on the muscle contractions induced by U46619, a thromboxane A2 (TXA2) mimetic, and phenylephrine were compared in guinea-pig aorta. In de-endothelialized guinea-pig aortic ring preparations, DHA at 10 microM strongly inhibited a sustained contraction produced by U46619 (3-100 nM) whereas it did not exhibit an appreciable effect on phenylephrine (3-10 microM)-induced contraction. The present findings indicate that DHA inhibits more selectively TXA2 receptor (TP receptor)-mediated vascular contraction than alpha-adrenoceptor-mediated response. Selective inhibition by DHA of TP receptor-mediated contraction of blood vessels seems underlie in part the mechanisms by which this polyunsaturated fatty acid exerts its circulatory-protective effects.

Acute and chronic effects of eicosapentaenoic acid on voltage-gated sodium channel expressed in cultured human bronchial smooth muscle cells

This study investigated acute and chronic effects of eicosapentaenoic acid (EPA) on voltage-gated Na+ current (I(Na)) expressed in cultured human bronchial smooth muscle cells (hBSMCs). The whole-cell voltage clamp technique and quantitative real-time RT-PCR analysis were applied. The alterations in the fatty acid composition of phospholipids after treatment with EPA were also examined. Extracellular application of EPA produced a rapid and concentration-dependent suppression of tetrodotoxin-sensitive I(Na) with the half-maximal inhibitory concentration of 2 microM. After washing out EPA with albumin, I(Na) returned to the control level. Similar inhibitory effects were observed regarding other fatty acids (docosahexaenoic, arachidonic, stearic, and oleic acids), but EPA was the most potent inhibitor. The effect of EPA on I(Na) was not blocked by nordihydroguaiaretic acid and indometacin, and was accompanied by a significant shift of the steady-state inactivation curve to more negative potentials. In cells chronically treated with EPA, the EPA content of the cell lipid fraction (mol%) increased time-dependently, while arachidonic acid (AA) decreased, resulting in an increase of EPA to AA ratio. Then, the level of mRNA (SCN9A) encoding I(Na) decreased significantly. These results provide novel evidence that EPA not only rapidly inhibits I(Na), but also reduces the mRNA levels of the Na+ channel after cellular incorporation of EPA in cultured hBSMCs.

Serotonin and thromboxane A2 stimulate platelet-derived microparticle-induced smooth muscle cell proliferation

INTRODUCTION

At the sites of vascular injury, activated and aggregating platelets release small vesiculated structures called platelet microparticles (PMPs). Apart from PMPs they also release several vasoactive mediators including serotonin and thromboxane A2 (TXA2). PMPs, serotonin, and TXA2 have been shown to stimulate vascular smooth muscle cell (VSMC) proliferation. Thus, this study is designed to examine the interaction between PMPs and serotonin or TXA2 in inducing rabbit VSMC proliferation.

METHODS

Growth-arrested rabbit SMCs were incubated in serum-free medium with different concentrations of PMPs with or without serotonin or TXA2. VSMC proliferation was examined by increase in incorporation of [3H]thymidine into DNA and by increase in cell number.

RESULTS

PMPs stimulated DNA synthesis in a dose-dependent manner; up to an added concentration of 30 microg/ml (1489 +/- 90%) they stimulated SMC proliferation in a logarithmic fashion. Serotonin at 50 microM (345 +/- 21%) and TXA2 at 7.5 microM (900 +/- 36%) had their maximal effect. When added together, PMPs (10 microg/ml) and serotonin (5 microM), synergistically induced DNA synthesis (581 +/- 36% and 211 +/- 11% when added alone and 1201 +/- 95% when added together), whereas PMPs (10 microg/ml) and TXA2 (5 microM) additively induced DNA synthesis (581 +/- 36% and 781 +/- 56% when added alone and 1262 +/- 115% when added together). These increases in DNA synthesis were paralleled by increase in cell number.

CONCLUSION

PMPs, serotonin, and TXA2 are mitogenic to SMC, and function as amplification factors to each other, suggesting that inhibition of neointimal proliferation after vascular injury may require the combined use of multiple growth factor inhibitors to simultaneously block several critical cellular activation pathways.

Docosahexaenoic acid induces apoptosis in proliferating human endothelial cells

n-3 polyunsaturated fatty acids (PUFAs) have been shown to exert beneficial effects in the prevention of cardiovascular disease, inflammation, and on tumor growth. To investigate effects of PUFAs on proliferation and apoptosis in endothelial cells, we tested the n-3 PUFA docosahexaenoic acid (DHA) and the n-6 PUFA arachidonic acid (AA) in human umbilical vein endothelial cells (HUVEC). The mitochondrial membrane potential (MMP) and the production of reactive oxygen species were examined by flow cytometry. Phosphorylation of p53 or p38 MAP kinase, and total levels of p53 were measured by Western blot. DNA binding activity of p53 was analyzed with a TransAM transcription factor assay kit. Tube formation was assessed on Matrigel. In proliferating HUVEC, but not in confluent cells, DHA reduced cell viability and induced apoptosis, as demonstrated by increases in membrane leakage (propidium iodide (PI) staining), Annexin-V binding, sub G(1) phase in the cell cycle, and TUNEL-positive cells. AA had no effect on these parameters. In addition to a reduced MMP and increased reactive oxygen species, phosphorylation of p38 and p53 (serine 15) and impaired DNA binding of p53 were observed. There was no change in total levels of p53. The p38 inhibitor SB203580 had no effect on Annexin V binding. DHA also attenuated HUVEC tube formation. Taken together, DHA induces apoptosis in proliferating, but not in resting HUVEC, potentially via the phosphorylation of p53, resulting in decreased p53 DNA binding. The results suggest that anti-angiogenic effects of DHA may be due to induction of apoptosis in proliferating endothelial cells.

Modulation of cyclin D1 and early growth response factor-1 gene expression in interleukin-1beta-treated rat smooth muscle cells by n-6 and n-3 polyunsaturated fatty acids

The proliferation of smooth muscle cells (SMC) is a key event in the development of atherosclerosis. In addition to growth factors or cytokines, we have shown previously that n-3 polyunsaturated fatty acids (PUFAs) act in opposition to n-6 PUFAs by modulating various steps of the inflammatory process. We have investigated the molecular mechanisms by which the incorporation of the n-6 PUFA, arachidonic acid, increases the proliferation of rat SMC treated with interleukin-1beta, while the n-3 PUFAs eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), elicit no mitogenic response. Incorporation of EPA or DHA into SMC, which are then activated by interleukin-1beta to mimic inflammation, decreases promoter activity of the cyclin D1 gene and phosphorylation of the retinoblastoma protein. Together, our data demonstrate that n-3 effects are dependent on the Ras/Raf-1/extracellular signal regulated kinase (ERK)/mitogen-activated protein kinase pathway, and that down-regulation of the cyclin D1 promoter activity is mediated by the specific binding of the early growth response factor-1. Finally, we have shown that the incorporation of EPA and DHA also increased the concentration of caveolin-1 and caveolin-3 in caveolae, which correlated with n-3 PUFA inhibition of SMC proliferation through the mitogen-activated protein kinase pathway. We provide evidence indicating that, in contrast to n-6 PUFAs, n-3 PUFAs exert antiproliferative effects on SMC through the mitogen-activated protein kinase/ERK pathway.

The role of fish oil/omega-3 fatty acids in the treatment of IgA nephropathy

Beneficial effects of omega-3 polyunsaturated fatty acids (n-3 PUFA) have been reported in recent epidemiologic studies and randomized clinical trials in a variety of cardiovascular and autoimmune diseases. Fish and marine oils are the most abundant and convenient sources of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), the two major n-3 fatty acids that serve as substrates for cyclooxygenase and lipoxygenase pathways leading to less potent inflammatory mediators than those produced through the n-6 PUFA substrate, arachidonic acid. N-3 PUFA can also suppress inflammatory and/or immunologic responses through eicosanoid-independent mechanisms. Although the pathophysiology of IgA nephropathy is incompletely understood, it is likely that n-3 PUFA prevents renal disease progression by interfering with a number of effector pathways triggered by mesangial immune-complex deposition. In addition, potential targets of n-3 PUFA relevant to renal disease progression could be similar to those involved in preventing the development and progression of cardiovascular disease by lowering blood pressure, reducing serum lipid levels, decreasing vascular resistance, or preventing thrombosis. In IgA nephropathy, efficacy of n-3 PUFA contained in fish oil supplements has been tested with varying results. The largest randomized clinical trial performed by our collaborative group provided strong evidence that treatment for 2 years with a daily dose of 1.8 g of EPA and 1.2 g of DHA slowed the progression of renal disease in high-risk patients. These benefits persisted after 6.4 years of follow up. With safety, composition, and dosing convenience in mind, we can recommend two products that are available as pharmaceutical-grade fish-oil concentrates, Omacor (Pronova Biocare, Oslo, Norway) and Coromega (European Reference Botanical Laboratories, Carlsbad, CA).

Long-chain omega 3 fatty acids, blood lipids and cardiovascular risk reduction

Increasing evidence suggests that omega 3 fatty acids derived from fish and fish oils may play a protective role in coronary heart disease and its many complications, through a variety of actions, including effects on lipids, blood pressure, cardiac and vascular function, prostanoids, coagulation and immunological responses. Interesting differences between the effects of highly purified eicosapentaenoic acid and docosahexaenoic acid are emerging, which may be relevant in the choice of omega 3 fatty acid for incorporation into food products. On the basis of our current knowledge, we believe it is justified to recommend, particularly to high-risk populations, an increased dietary intake of omega 3 fatty acids through the consumption of fish.