Mechanisms of vasorelaxation induced by eicosapentaenoic acid (20:5n-3) in WKY rat aorta

The Influence of n-3PUFA Supplementation on Muscle Strength, Mass, and Function: A Systematic Review and Meta-Analysis

The effects of omega 3 polyunsaturated fatty acids (n-3PUFA) supplementation on skeletal muscle are currently unclear. The purpose of this systematic review was to synthesize all available evidence regarding the influence of n-3PUFA supplementation on muscle mass, strength, and function in healthy young and older adults. Four databases were searched (Medline, Embase, Cochrane CENTRAL, and SportDiscus). Predefined eligibility criteria were determined according to Population, Intervention, Comparator, Outcomes, and Study Design. Only peer-reviewed studies were included. The Cochrane RoB2 Tool and the NutriGrade approach were used to access risk of bias and certainty in evidence. Effect sizes were calculated using pre-post scores and analyzed using a three-level, random-effects meta-analysis. When sufficient studies were available, subanalyses were performed in the muscle mass, strength, and function outcomes according to participant's age (<60 or ≥60 years), supplementation dosage (<2 or ≥2 g/day), and training intervention ("resistance training" vs. "none or other"). Overall, 14 individual studies were included, total 1443 participants (913 females; 520 males) and 52 outcomes measures. Studies had high overall risk of bias and consideration of all NutriGrade elements resulted in a certainty assessment of moderate meta-evidence for all outcomes. n-3PUFA supplementation had no significant effect on muscle mass (standard mean difference [SMD] = 0.07 [95% CI: -0.02, 0.17], P = 0.11) and muscle function (SMD = 0.03 [95% CI: -0.09, 0.15], P = 0.58), but it showed a very small albeit significant positive effect on muscle strength (SMD = 0.12 [95% CI: 0.006, 0.24], P = 0.04) in participants when compared with placebo. Subgroup analyses showed that age, supplementation dose, or cosupplementation alongside resistance training did not influence these responses. In conclusion, our analyses indicated that n-3PUFA supplementation may lead to very small increases in muscle strength but did not impact muscle mass and function in healthy young and older adults. To our knowledge, this is the first review and meta-analysis investigating whether n-3PUFA supplementation can lead to increases in muscle strength, mass, and function in healthy adults. Registered protocol: doi.org/10.17605/OSF.IO/2FWQT.

Omega-3 polyunsaturated fatty acid-induced vasodilation in mouse aorta and mesenteric arteries is not mediated by ATP-sensitive potassium channels

There is strong evidence that the omega-3 polyunsaturated fatty acids (n-3 PUFAs) docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) have cardioprotective effects. n-3 PUFAs cause vasodilation in hypertensive patients, in part controlled by increased membrane conductance to potassium. As KATP channels play a major role in vascular tone regulation and are involved in hypertension, we aimed to verify whether n-3 PUFA-mediated vasodilation involved the opening of KATP channels. We used a murine model in which the KATP channel pore subunit, Kir6.1, is deleted in vascular smooth muscle. The vasomotor response of preconstricted arteries to physiologically relevant concentrations of DHA and EPA was measured using wire myography, using the channel blocker PNU-37883A. The effect of n-3 PUFAs on potassium currents in wild-type native smooth muscle cells was investigated using whole-cell patch clamping. DHA and EPA induced vasodilation in mouse aorta and mesenteric arteries; relaxations in the aorta were sensitive to KATP blockade with PNU-37883A. Endothelium removal didn't affect relaxation to EPA and caused a small but significant inhibition of relaxation to DHA. In the knock-out model, relaxations to DHA and EPA were unaffected by channel knockdown but were still inhibited by PNU-37883A, indicating that the action of PNU-37883A on relaxation may not reflect inhibition of KATP. In native aortic smooth muscle cells DHA failed to activate KATP currents. We conclude that DHA and EPA cause vasodilation in mouse aorta and mesenteric arteries. Relaxations in blocker-treated arteries from knock-out mice demonstrate that KATP channels are not involved in the n-3 PUFA-induced relaxation.

Clinical significance of polyunsaturated fatty acids in the prevention of cardiovascular diseases

Cardiovascular diseases are one of the most important problems of modern medicine. They are associated with a large number of health care visits, hospitalizations and mortality. Prevention of atherosclerosis is one of the most effective strategies and should start as early as possible. Correction of lipid metabolism disorders is associated with definite clinical successes, both in primary prevention and in the prevention of complications of many cardiovascular diseases. A growing body of evidence suggests a multifaceted role for polyunsaturated fatty acids. They demonstrate a variety of functions in inflammation, both participating directly in a number of cellular processes and acting as a precursor for subsequent biosynthesis of lipid mediators. Extensive clinical data also support the importance of polyunsaturated fatty acids, but all questions have not been answered to date, indicating the need for further research.

Subtype-specific responses of hKv7.4 and hKv7.5 channels to polyunsaturated fatty acids reveal an unconventional modulatory site and mechanism

The K_V7.4 and K_V7.5 subtypes of voltage-gated potassium channels play a role in important physiological processes such as sound amplification in the cochlea and adjusting vascular smooth muscle tone. Therefore, the mechanisms that regulate K_V7.4 and K_V7.5 channel function are of interest. Here, we study the effect of polyunsaturated fatty acids (PUFAs) on human K_V7.4 and K_V7.5 channels expressed in Xenopus oocytes. We report that PUFAs facilitate activation of hK_V7.5 by shifting the V₅₀ of the conductance versus voltage (G(V)) curve toward more negative voltages. This response depends on the head group charge, as an uncharged PUFA analogue has no effect and a positively charged PUFA analogue induces positive V₅₀ shifts. In contrast, PUFAs inhibit activation of hK_V7.4 by shifting V₅₀ toward more positive voltages. No effect on V₅₀ of hK_V7.4 is observed by an uncharged or a positively charged PUFA analogue. Thus, the hK_V7.5 channel's response to PUFAs is analogous to the one previously observed in hK_V7.1-7.3 channels, whereas the hK_V7.4 channel response is opposite, revealing subtype-specific responses to PUFAs. We identify a unique inner PUFA interaction site in the voltage-sensing domain of hK_V7.4 underlying the PUFA response, revealing an unconventional mechanism of modulation of hK_V7.4 by PUFAs.

Omega-3 polyunsaturated fatty acids and hypertension: a review of vasodilatory mechanisms of docosahexaenoic acid and eicosapentaenoic acid

Hypertension is often characterised by impaired vasodilation involving dysfunction of multiple vasodilatory mechanisms. ω-3 polyunsaturated fatty acids (PUFAs), docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) can reduce blood pressure and vasodilation. In the endothelium, DHA and EPA improve function including increased NO bioavailability. However, animal studies show that DHA- and EPA-mediated vasodilation persists after endothelial removal, indicating a role for vascular smooth muscle cells (VSMCs). The vasodilatory effects of ω-3 PUFAs on VSMCs are mediated via opening of large conductance calcium-activated potassium channels (BK_Ca ), ATP-sensitive potassium channels (K_ATP ) and possibly members of the K_v 7 family of voltage-activated potassium channels, resulting in hyperpolarisation and relaxation. ω-3 PUFA actions on BK_Ca and voltage-gated ion channels involve electrostatic interactions that are dependent on the polyunsaturated acyl tail, cis-geometry of these double bonds and negative charge of the carboxyl headgroup. This suggests structural manipulation of ω-3 PUFA could generate novel, targeted, therapeutic leads.

Effect of omega-3 polyunsaturated fatty acids in modulation of vascular tone under physiological and pathological conditions

Omega-3 polyunsaturated fatty acids (n-3 PUFAs), including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are mainly found in marine fish oils and commercially available fish oil supplements. Several studies have documented that n-3 PUFAs can reduce the risk of cardiovascular diseases through anti-inflammatory, anti-thrombotic, and anti-atherosclerotic properties. Notably, regulation of vascular tone is one of the most important bases of cardiovascular health and especially for maintaining blood pressure within optimal physiological ranges. Recent clinical and animal studies indicate an association between n-3 PUFAs and vascular functions. In this regard, many clinical trials and basic experimental studies have been conducted so far to investigate the influence of n-3 PUFAs on vascular tone. In this review, we have summarized the results obtained from both clinical and basic studies that evaluated the effect of n-3 PUFAs under physiological and pathological conditions. Moreover, we also focus on verifying the underlying basic molecular mechanism of n-3 PUFAs on the vascular system.

Effect of the double bond conjugation on the vascular physiology and nitric oxide production of isomers of eicosapentaenoic and docosahexaenoic acids prepared from shark oil

A collection of evidence suggests that conjugation of double bonds of eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids, omega-3 polyunsaturated fatty acids (n-3 PUFAs), increases their anticarcinogenic activity; however, the effect of such conjugation on vascular tone activity remains unknown. We propose that the mixture of conjugated PUFAs exerts higher vasorelaxation activity than the corresponding mixture of nonconjugated PUFAs. The vascular response to different concentrations of conjugated and nonconjugated isomers of EPA and DHA, among other fatty acids (FAs) naturally present in shark oil, and the role of nitric oxide (NO) as a vasorelaxant agent were investigated. Both conjugated EPA (CEPA) and conjugated DHA (CDHA) were prepared by alkaline isomerization of all PUFAs contained in shark oil. Different concentrations of conjugated and nonconjugated PUFAs were placed in contact with precontracted aortic rings of Wistar rats to assess their effect on vascular tone. All tested samples exerted a vasorelaxant effect. Compared to nonconjugated PUFAs, conjugated isomers exhibited an increase in the dilatation of the aortic rings (P<0.001) in a dose-dependent manner (P<0.001). In addition, nonconjugated PUFAs produced nitric oxide (NO) in a dose-dependent manner, while conjugated PUFAs did not, suggesting that their dilatation mechanism is not totally dependent on NO.

In Vitro Effects of Eicosapentaenoic and Docosahexaenoic Acid on the Vascular Tone of a Human Saphenous Vein: Influence of Precontractile Agents

BACKGROUND

Cardiovascular effects of omega-3 polyunsaturated fatty acids including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have been widely reported. However, there are limited studies concerning their effects on human blood vessels. Therefore, the aim of this study was to investigate the direct vascular effects of EPA and DHA on the human saphenous vein (SV) precontracted with either prostaglandin F2α (PGF2α), or thromboxane A2 analogue (U46619), or norepinephrine (NE). Moreover, we aimed to investigate the protein expression of free fatty acid receptor 4 (FFAR4) in human SV.

METHODS

Pretreatment of human SV rings with EPA and DHA (100 μM, 30 min) was tested on vascular reactivity induced by PGF2α (10 nM to 5 μM), NE (10 nM to 100 μM), and U46619 (1 nM to 100 nM). In addition, direct relaxant effects of EPA/DHA (1-100 μM) were tested in human SV rings precontracted by PGF2α, NE, and U46619. Furthermore, the involvement of potassium channels on their vascular effects was investigated in the presence of the nonselective K⁺ channel inhibitor tetraethylammonium chloride.

RESULTS

Pretreatment with EPA and DHA resulted in a significant decrease in vascular reactivity induced by U46619 and PGF2α compared to NE. In the presence of TEA, the relaxant effects of EPA and DHA were significantly decreased in SV preparations precontracted by U46619 and PGF2α for DHA. Furthermore, FFAR-4 protein was expressed in tissue extracts of human SV.

CONCLUSIONS

Our study demonstrates that both EPA and DHA reduce the increased vascular tone elicited by contractile agents on the human SV and that the direct vasorelaxant effect is likely to involve potassium channels.

Altered Potassium Ion Channel Function as a Possible Mechanism of Increased Blood Pressure in Rats Fed Thermally Oxidized Palm Oil Diets

Intake of thermally oxidized palm oil leads to cytotoxicity and alteration of the potassium ion channel function. This study investigated the effects of fresh and thermally oxidized palm oil diets on blood pressure and potassium ion channel function in blood pressure regulation. Male Wistar rats were randomly divided into three groups of eight rats. Control group received normal feed; fresh palm oil (FPO) and thermally oxidized palm oil (TPO) groups were fed a diet mixed with 15% (weight/weight) fresh palm oil and five times heated palm oil, respectively, for 16 weeks. Blood pressure was measured; blood samples, hearts, and aortas were collected for biochemical and histological analyses. Thermally oxidized palm oil significantly elevated basal mean arterial pressure (MAP). Glibenclamide (10^-5 mmol/L) and tetraethylammonium (TEA; 10^-3 mmol/L) significantly raised blood pressure in TPO compared with FPO and control groups. Levcromakalim (10^-6 mmol/L) significantly (p < .01) reduced MAP by 32.0% in FPO and by 5.4% in TPO. NS1619 (10 mmol/L) significantly (p < .01) decreased MAP by 19.5% in FPO and by 8% in TPO. The TPO significantly (p < 0.01) increased the tissue levels of peroxide, total cholesterol, triglyceride, and low-density lipoprotein cholesterol while catalase and superoxide dismutase activities were significantly (p < .01) decreased compared with control and FPO groups. Histological alterations were prominent in aortas and hearts of rats in the TPO group. These results suggest that prolonged consumption of repeatedly heated palm oil increases MAP probably due to the attenuation of adenosine triphosphate-sensitive potassium (K_ATP) and large-conductance calcium-dependent potassium (BK_Ca) channels, tissue peroxidation, and altered histological structures of the heart and blood vessels.

Eicosapentaenoic acid ethyl ester improves endothelial dysfunction in type 2 diabetic mice

Background

Eicosapentaenoic acid (EPA) is thought to have many beneficial effects, such as anti-atherosclerogenic and anti-inflammatory properties. However, few studies have reported its effects of endothelial dysfunction in diabetes and its direct effects on the aorta. Here, we investigated the effects of EPA treatment on impaired endothelium-dependent relaxation of the aorta in KKAy mice, a model of type 2 diabetes.

Methods

Male KKAy mice were fed a high-fat (HF) diet for 8 weeks to induce diabetes, after which they were divided into two groups. One group was fed a HF diet, and the other group was fed a HF diet containing EPA ethyl ester (EPA-E, 10 mg/day) for 4 weeks. Then, the vascular reactivities of prepared aortic rings were measured in an organ bath to determine if EPA-E administration changed vascular function in these diabetic mice. In addition, we examined effect of EPA-E and its metabolites to vascular action using aorta separated from C57BL/6 J mice.

Results

Although EPA-E administration did not change the plasma glucose and insulin levels in diabetic mice, total cholesterol levels were significantly decreased. The aorta extracted from EPA-E untreated diabetic mice showed impaired endothelium-dependent relaxation in response to acetylcholine (ACh). However, EPA-E administration improved the relaxation response to ACh to the control levels observed in non-diabetic C57BL/6 J mice. On the other hand, endothelium-independent relaxation in response to sodium nitroprusside did not significantly differ among these three groups. The enhanced contractile response by phenylephrine in diabetic mice was not altered by the administration of EPA-E. In addition, the direct administration of EPA-E metabolites such as EPA, docosahexaenoic acid, and docosapentaenoic acid led to vasodilation in the aortic rings of C57BL/6 J mice.

Conclusion

These results showed that chronic EPA-E administration prevented the development of endothelial dysfunction in KKAy mice, partly via the direct action of EPA-E metabolites on the aorta.

Characterisation of the vasodilation effects of DHA and EPA, n-3 PUFAs (fish oils), in rat aorta and mesenteric resistance arteries

Background and purpose

Increasing evidence suggests that the omega-3 polyunsaturated acids (n-3 PUFA), docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), are beneficial to cardiovascular health, promoting relaxation of vascular smooth muscle cells and vasodilation. Numerous studies have attempted to study these responses, but to date there has not been a systematic characterisation of both DHA and EPA mediated vasodilation in conduit and resistance arteries. Therefore, we aimed to fully characterise the n-3 PUFA-induced vasodilation pathways in rat aorta and mesenteric artery.

Methods

Wire myography was used to measure the vasomotor responses of freshly dissected rat mesenteric artery and aorta. Arteries were pre-constricted with U46619 and cumulative concentrations of either DHA or EPA (10 nM-30 μM) were added. The mechanisms by which n-3 PUFA relaxed arteries were investigated using inhibitors of vasodilator pathways, which include: nitric oxide synthase (NOS; L-NAME), cycloxygenase (COX; indomethacin), cytochrome P450 epoxygenase (CYP450; clotrimazole); and calcium-activated potassium channels (K_Ca), SK_Ca (apamin), IK_Ca (TRAM-34) and BK_Ca (paxilline).

Results

Both DHA- and EPA-induced relaxations were partially inhibited following endothelium removal in rat mesenteric arteries. Similarly, in aorta EPA-induced relaxation was partially suppressed due to endothelium removal. CYP450 also contributed to EPA-induced relaxation in mesenteric artery. Inhibition of IK_Ca partially attenuated DHA-induced relaxation in aorta and mesenteric artery along with EPA-induced relaxation in mesenteric artery. Furthermore, this inhibition of DHA- and EPA-induced relaxation was increased following the additional blockade of BK_Ca in these arteries.

Conclusions

This study provides evidence of heterogeneity in the vasodilation mechanisms of DHA and EPA in different vascular beds. Our data also demonstrates that endothelium removal has little effect on relaxations produced by either PUFA. We demonstrate IK_Ca and BK_Ca are involved in DHA-induced relaxation in rat aorta and mesenteric artery; and EPA-induced relaxation in rat mesenteric artery only. CYP450 derived metabolites of EPA may also be involved in BK_Ca dependent relaxation. To our knowledge this is the first study indicating the involvement of IK_Ca in n-3 PUFA mediated relaxation.

Omega-3 polyunsaturated fatty acids reduce vascular tone and inflammation in human saphenous vein

Dietary intake of omega-3 polyunsaturated fatty acids, including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), has been reported to have beneficial cardiovascular effects. However, little is known about the effect of EPA and DHA on human vascular tone. Therefore, the aim of this study is to evaluate the effect of EPA and DHA on vascular tone of the human saphenous vein (SV) obtained from patients undergoing coronary bypass operation under normal and inflammatory conditions. Moreover, we aimed to investigate the effect of EPA and DHA on the release of inflammatory mediators from SV. Pretreatment of SV with EPA and DHA (100μM, 18h) decreased the contractile response of SV to norepinephrine (NE) under normal and inflammatory conditions. Moreover, EPA and DHA pretreatment diminished increased Monocyte Chemoattractant Protein-1 (MCP-1) and Tumor Necrosis Factor-alpha (TNF-α) release from SV under inflammatory conditions. In conclusion, our results suggest that EPA and DHA pretreatment may be beneficial to counteract graft vasospasm and vascular inflammation in SV which are important factors in graft failure development. Therefore, dietary intake of EPA and DHA may have potential clinical applications in improving coronary bypass graft patency.

Modulation of Systemic and Aortic Nitric Oxide by Melatonin and n-3 Polyunsaturated Fatty Acids in Isoproterenol Affected Spontaneously Hypertensive and Normotensive Wistar Rats

We aimed to explore the effects of melatonin and n-3 polyunsaturated fatty acids (PUFA) supplementation on plasma and aortic nitric oxide (NO) levels in isoproterenol (Iso) affected spontaneously hypertensive (SHR) and Wistar rats. Untreated control rats were compared with Iso injected (118 mg/kg, s.c.) rats, and Iso injected plus supplemented with melatonin (10 mg/kg, p.o.) or PUFA (1.68 g/kg, p.o.) for two months. Plasma and aortic basal, L-NAME inhibited, adrenaline and acetylcholine stimulated NO were determined using Griess method. Plasma NO levels were lower in SHR versus Wistar rats. Iso decreased NO in Wistar while not in SHR. PUFA but not melatonin intake of Iso treated SHR increased plasma NO along with a decrease in systolic blood pressure. Basal aortic NO level was higher in SHR than Wistar rats and not altered by Iso. Intake of melatonin increased but PUFA decreased basal NO levels in Wistar+Iso and did not affect in SHR+Iso rats. Acetylcholine and adrenaline induced aortic NO release was significantly increased in Wistar+Iso but not SHR+Iso group. Melatonin intake increased Ach induced aortic NO in Wistar+Iso and SHR+Iso groups, whereas there was no effect of PUFA intake. Findings suggest that PUFA modulates plasma and melatonin aortic NO levels of isoproterenol affected rats in a strain-dependent manner.

The prolactin family hormones regulate vascular tone through NO and prostacyclin production in isolated rat aortic rings

AIM

Prolactin family hormones include growth hormone, placental lactogen and prolactin, which are able to regulate angiogenesis via NO and prostaglandins. However, their effects on vascular tone are not fully understood. The aim of this study was to evaluate the effects of prolactin family hormones on rat vascular tone in vitro.

METHODS

Aortic rings were prepared from adult male rats and precontracted with phenylephrine, then treated with the hormones and drugs. The tension was measured with isometric force displacement transducer connected to a polygraph. NO production and prostacyclin release in physiological solution was determined. Cultured rat aortic endothelial cells (RAECs) were treated with the hormones and drugs, and the phosphorylation of eNOS at serine 1177 was assessed using Western bolt analysis.

RESULTS

Administration of growth hormone or placental lactogen (0.01-100 nmol/L) induced endothelium-dependent vasodilation. Both the hormones significantly increased the phosphorylation of eNOS in RAECs and NO level in physiological solution. Preincubation with L-NAME blocked growth hormone- or placental lactogen-induced vasodilation and NO production. Preincubation with an antibody against growth hormone receptors blocked growth hormone- and placental lactogen-induced vasodilation. Addition of a single dose of prolactin (0.01 nmol/L) induced sustained vessel relaxation, whereas multiple doses of prolactin induced a biphasic contraction-relaxation effect. The vascular effects of prolactin depended on endothelium. Prolactin significantly increased the level of prostacyclin I2 in physiological solution. Preincubation with indomethacin or an antibody against prolactin receptors blocked prolactin-induced vasodilation.

CONCLUSION

The prolactin family hormones regulate rat vascular tone, selectively promoting either relaxation or contraction of vascular smooth muscle via activation of either growth hormone receptors or prolactin receptors within the endothelium.

Eicosapentaenoic acid suppression of systemic inflammatory responses and inverse up-regulation of 15-deoxyΔ(12,14) prostaglandin J2 production

BACKGROUND AND PURPOSE

Eicosapentaenoic acid (EPA) has been shown to suppress immune cell responses, such as cytokine production and downstream PG production in vitro. Studies in vivo, however, have used EPA as a minor constituent of fish oil with variable results. We investigated the effects of EPA on systemic inflammatory responses as pure EPA has not been evaluated on immune/inflammatory responses in vivo.

EXPERIMENTAL APPROACH

Rabbits were administered polyinosinic: polycytidylic acid (poly I:C) i.v. before and after oral treatment with EPA for 42 days (given daily). The responses to IL-1β and TNF-α were also studied. Immediately following administration of poly I:C, body temperature was continuously monitored and blood samples were taken. Plasma levels of IL-1β, PGE2 (PGE2), and 15-deoxy-Δ(12,14)-PGJ2 (15d-PGJ2) were measured by enzyme immunoassay.

KEY RESULTS

Following EPA treatment, the fever response to poly I:C was markedly suppressed compared with pretreatment responses. This was accompanied by a parallel reduction in the poly I:C-stimulated elevation in plasma levels of IL-1β and PGE2. Paradoxically, the levels of 15d-PGJ2 were higher following EPA treatment. EPA treatment did not significantly alter the fever response or plasma levels of PGE2 in response to either IL-1β or TNF-α.

CONCLUSION AND IMPLICATIONS

Oral treatment with EPA can suppress immune/inflammatory responses in vivo via a suppression of upstream cytokine production resulting in a decreased fever response and indirectly reducing circulating levels of PGE2. EPA also enhances the production of the cytoprotective prostanoid 15d-PGJ2 indicating the therapeutic benefit of EPA.

The effects of dietary fish oil on exercising skeletal muscle vascular and metabolic control in chronic heart failure rats

Impaired vasomotor control in chronic heart failure (CHF) is due partly to decrements in nitric oxide synthase (NOS) mediated vasodilation. Exercising muscle blood flow (BF) is augmented with polyunsaturated fatty acid (PUFA) supplementation via fish oil (FO) in healthy rats. We hypothesized that FO would augment exercising muscle BF in CHF rats via increased NO-bioavailability. Myocardial infarction (coronary artery ligation) induced CHF in Sprague-Dawley rats which were subsequently randomized to dietary FO (20% docosahexaenoic acid, 30% eicosapentaenoic acid, n = 15) or safflower oil (SO, 5%, n = 10) for 6-8 weeks. Mean arterial pressure (MAP), blood [lactate], and hindlimb muscles BF (radiolabeled microspheres) were determined at rest, during treadmill exercise (20 m·min(-1), 5% incline) and exercise + N(G)-nitro-l-arginine-methyl-ester (l-NAME) (a nonspecific NOS inhibitor). FO did not change left ventricular end-diastolic pressure (SO: 14 ± 2; FO: 11 ± 1 mm Hg, p > 0.05). During exercise, MAP (SO: 128 ± 3; FO: 132 ± 3 mm Hg) and blood [lactate] (SO: 3.8 ± 0.4; FO: 4.6 ± 0.5 mmol·L(-1)) were not different (p > 0.05). Exercising hindlimb muscle BF was lower in FO than SO (SO: 120 ± 11; FO: 93 ± 4 mL·min(-1)·100 g(-1), p < 0.05) but was not differentially affected by l-NAME. Specifically, 17 of 28 individual muscle BF's were lower (p < 0.05) in FO demonstrating that PUFA supplementation with FO in CHF rats does not augment muscle BF during exercise but may lower metabolic cost.

Activity of Bradykinin B2 Receptor Is Regulated by Long-Chain Polyunsaturated Fatty Acids

The molecular and cellular mechanisms by which long-chain polyunsaturated fatty acids (LCPUFA) exert their beneficial effects on cardiovascular health remain obscure. While both LCPUFA and bradykinin (BK) signaling pathway play a role in the cardiovascular system, any direct link between the two is yet to be established. Using picosecond time-resolved fluorescence microscopy and a genetically engineered bradykinin B₂ receptor (B₂R) sensor (B2K-CC), we detected LCPUFA-induced conformational responses in the B₂R similar to those caused by its cognate ligand, BK. The selective B₂R antagonist (HOE-140) blocked the eicosapentaenoic acid (EPA, C20∶5, n-3) induced conformational response of the B2K-CC. Further analysis suggests that LCPUFA are capable of direct, B₂R-dependent activation of extracellular ligand-regulated kinases (ERK). From a wide range of fatty acids studied, varying in chain length, saturation, and position of double bonds, EPA, docosahexaenoic (DHA, C22∶6, n-3), docosadienoic (DDA, C22∶2, n-6), and dihomo-gamma linoleic (DGLA, C20∶3, n-6) fatty acids caused the highest ERK phosphorylation. EPA or DHA dependent ERK phosphorylation was inhibited by the selective B₂R antagonist. We show that LCPUFA stimulates downstream signaling by B₂R such as B₂R-dependent phosphorylation and expression regulation of endothelial nitric-oxide synthase (eNOS). Further analysis indicated that LCPUFA also alters levels of the eNOS transcription factor, kruppel-like factor 2 (KLF2). Moreover we show that EPA increases membrane fluidity on the same time scale as B₂R conformational response, suggesting that partitioning of LCPUFA into bilayer is a primary step required for receptor activation. In summary our data show that LCPUFA activate B₂R receptor at nanomolar concentrations suggesting a novel molecular mechanism by which fatty acids may affect the cardiovascular system.

Marine n-3 fatty acids alter the proteomic response to methylmercury in Atlantic salmon kidney (ASK) cells

Fish based diets have been linked to the amelioration of methylmercury (MeHg) induced symptoms in several epidemiological studies, particularly due to their contents of marine n-3 fatty acids. It has been suggested that n-3 fatty acids may mask the detrimental effects of MeHg due to their beneficial effect on the same biological functions which are negatively affected by MeHg. However, in vitro studies have implied that there may be direct interactions between the marine n-3 FAs and MeHg, which ameliorates MeHg toxicity through interactions at a biological level. To understand how marine n-3 FAs and MeHg interact in fish as a biological system, we wanted to investigate molecular interaction in a fish cell system. Atlantic salmon kidney (ASK) cells were pre-incubated with the marine n-3 FAs docosahexaenoic acid (22:6n-3, DHA) and eicosapentaenoic acid (20:5n-3, EPA) before exposing them to MeHg. Modulating effects of the marine FAs on MeHg toxicity were subsequently assessed using the exploratory technique of proteomics, in a factorial design. Thirty-four differentially regulated proteins were identified. From these; twenty-seven were shown to be differentially regulated by MeHg, twelve were regulated by the fatty acids, and another eight showed interaction effects between MeHg and the FAs. Several of the proteins were concomitantly affected by MeHg- and FA-main effects, as well as interaction effects. Functional annotations and pathway analysis of the proteins revealed that marine n-3 FAs and MeHg concurrently affected the abundance of protein markers relating to such molecular mechanisms as: cell signaling, calcium homeostasis, structural integrity, apoptosis, and energy metabolism. In conclusion, both marine n-3 FAs and MeHg can differentially affect the abundances of the same proteins, indicating modulating effects of EPA and DHA on MeHg metabolism, and possibly on its toxicity.

Evaluation of effects of eicosapentaenoic acid on Na⁺-K⁺-ATPase in sheep pulmonary artery

In the present study, we have evaluated the effects of eicosapentaenoic acid (EPA) on Na(+)-K(+)-ATPase in sheep pulmonary artery. Acute (30 min) and prolonged (24 h) exposure of arterial rings to EPA (30 μM) significantly decreased potassium chloride (KCl)-induced relaxation, an index of functional Na(+)-K(+)-ATPase activity. In acute exposure, the pD(2) and E (max) (the maximal response) values for KCl-induced relaxation were 3.21 ± 0.33 and 61.58 ± 11.30% (n = 5) versus control 3.58 ± 0.07 and 82.44 ± 2.36% (n = 24), respectively. The pD(2) and E (max) values for KCl-induced relaxation in arterial rings exposed to EPA for 24 h in organ culture were 2.52 ± 0.11 and 55.00 ± 5.72% versus control 3.04 ± 0.19 and 80.74 ± 11.96%, respectively; n = 4. Exposure of the arterial rings to EPA (30 μM) for 24 h in organ culture, significantly decreased (17.58 ± 2.15%) the protein expression of α(1) isoform of Na(+)-K(+)-ATPase. Acute exposure to EPA for 30 min significantly decreased (21.06 ± 5.89%) the Na(+)-K(+)-ATPase activity as measured by inorganic phosphate (Pi) release. EPA, up to 100 μM concentration, marginally (<10% of 80 mM KCl contraction) increased the basal tone of the pulmonary artery. Additionally, EPA (10-30 μM) had no effect on Mg(2+)-ATPase activity as well as on cyclic guanosine monophosphate (cGMP) production. All these results show that EPA has inhibitory effect on Na(+)-K(+)-ATPase in sheep pulmonary artery but prolonged exposure had no additional effect on sodium pump, and EPA-induced inhibition of Na(+)-K(+)-ATPase may be due to attenuation in protein expression of α(1) isoform of Na(+)-K(+)-ATPase independent of cGMP production.

Eicosapentaenoic acid-induced endothelium-dependent and -independent relaxation of sheep pulmonary artery

It is known that long chain polyunsaturated fatty acids, such as eicosapentaenoic acid (EPA), have beneficial effects on cardiovascular function including pulmonary hypertension. The purpose of the present study was to examine the mechanisms involved in EPA-induced relaxation of sheep isolated pulmonary artery by measuring isometric tension. Nitric oxide (NO) derived from constitutive nitric oxide synthase (cNOS) was measured by Greiss method in the presence of the inducible nitric oxide synthase (iNOS) selective inhibitor N-[[3-(aminomethyl) phenyl]methyl]-ethanimidamide, dihydrochloride (1400 W). EPA (10(-)(7)-10(-)(4)M) caused concentration-dependent relaxation of sheep pulmonary artery with a pD(2) of 5.56+/-0.09 and E(max) of 87.40+/-3.10% (n=9). N(G)-nitro-L-arginine methyl ester (L-NAME) 100 microM significantly attenuated (E(max) 41.95+/-6.70%; n=8) EPA-induced relaxation of endothelium intact arterial rings. Similarly, endothelium denudation markedly inhibited (E(max) 17.60+/-1.21%; n=4) EPA-induced relaxation. EPA (30 microM) significantly increased the cNOS-derived NO release (10.17+/-0.96; n=8 versus control 7.43+/-0.78 pmol/mg tissue wet wt./h; n=7) in endothelium intact vessels. However, EPA-stimulated NO release was markedly blunted by either 100 microM L-NAME (7.07+/-0.54 pmol/mg tissue wet wt./h; n=8) or endothelium removal (6.97+/-0.87 pmol/mg tissue wet wt./h; n=17). In endothelium-denuded K(+) (80 mM)-depolarized arterial rings, EPA (30 microM) significantly inhibited CaCl(2)-induced contractions (E(max) 42.77+/-5.90% versus control 94.78+/-9.82%; n=5). The fatty acid also inhibited nifedipine (1 microM)-insensitive 5-HT-induced contractions in this vessel (E(max) 70.57+/-4.88% versus control 161.50+/-17.46%; n=5). In conclusion, EPA relaxes sheep pulmonary artery primarily through endothelium-dependent NO release, and the residual endothelium-independent relaxation may result from inhibition of Ca(2+)-influx through L-type calcium channels, as well as 5-HT-stimulated intracellular Ca(2+) release.

DHA and EPA Down-regulate COX-2 Expression through Suppression of NF-kappaB Activity in LPS-treated Human Umbilical Vein Endothelial Cells

Inflammatory processes of vascular endothelial cells play a key role in the development ofatherosclerosis. We determined the anti-inflammatory effects and mechanisms of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on LPS-treated human umbilical vein endothelial cells (HUVECs) to evaluate their cardioprotective potential. Cells were pretreated with DHA, EPA, or troglitazone prior to activation with LPS. Expression of COX-2, prostaglandin E(2) (PGE(2)) and IL-6 production, and NF-kappaB activity were measured by Western blot, ELISA, and luciferase activity, respectively. Results showed that EPA, DHA, or troglitazone significantly reduced COX-2 expression, NF-kappaB luciferase activity, and PGE(2) and IL-6 production in a dose-dependent fashion. Interestingly, low doses (10 microM) of DHA and EPA, but not troglitozone, significantly increased the activity of NF-kappaB in resting HUVECs. Our study suggests that while DHA, EPA, and troglitazone may be protective on HUVECs under inflammatory conditions in a dose-dependent manner. However there may be some negative effects when the concentrations are abnormally low, even in normal endothelium.

Signaling pathways modulated by fish oil in salt-sensitive hypertension

Although many studies have indicated that fish oil (FO) improves cardiovascular risk factors and reduces histopathological manifestations of injury in experimental renal injury models, potential mechanisms underlying this protective effect have not been adequately defined. The objective of this study was to identify potential signaling pathways that confer protection in the Dahl rat model of salt-sensitive hypertension. Male Dahl salt-sensitive rats (n = 10/group) were provided with formulated diets containing 8% NaCl, 20% protein, and 25% FO or 25% corn oil (CO) for 28 days. FO reduced blood pressure (-11% at 4 wk; P < 0.05), urine protein excretion (-45% at 4 wk; P < 0.05), plasma cholesterol and triglyceride levels (-54%, P < 0.001; and -58%, P < 0.05), and histopathological manifestations of renal injury, including vascular hypertrophy, segmental and global glomerular sclerosis, interstitial fibrosis, and tubular atrophy. Interstitial inflammation was significantly reduced by FO (-32%; P < 0.001), as assessed by quantitative analysis of ED1-positive cells in sections of the renal cortex. FO reduced tubulointerstitial proliferative activity, as assessed by Western blot analysis of cortical homogenates for PCNA (-51%; P < 0.01) and quantitative analysis of Mib-1-stained sections of the renal cortex (-42%; P < 0.001). Decreased proliferative activity was associated with reduced phospho-ERK expression (-37%; P < 0.005) and NF-kappaB activation (-42%; P < 0.05). FO reduced cyclooxygenase (COX)-2 expression (-63%; P < 0.01) and membrane translocation of the NADPH oxidase subunits p47(phox) and p67(phox) (-26 and -34%; P < 0.05). We propose that FO ameliorates renal injury in Dahl salt-sensitive rats through the inhibition of ERK, decreased NF-kappaB activation, inhibition of COX-2 expression, and decreased NADPH oxidase activation.

A high-fat meal enriched with eicosapentaenoic acid reduces postprandial arterial stiffness measured by digital volume pulse analysis in healthy men

Diets rich in eicosapentaenoic acid [EPA; 20:5(n-3)] are associated with decreased arterial stiffness, but postprandial effects on vascular function are unknown. We investigated whether an EPA-enriched high-fat meal could improve postprandial vascular function. Seventeen healthy men ingested 2 test meals (51 g fat), 1 wk apart, in random order: 5 g EPA plus high-oleic sunflower oil (HOS) vs. HOS only. A second high-fat meal (44 g fat), the same on both study days, was provided 4 h later. Blood pressure and arterial function were measured using digital volume pulse (DVP) to derive a stiffness index (DVP-SI) and reflection index in fasting subjects at 3 and 6 h following the test meal. Blood samples were taken following the test meal for plasma 8-isoprostane F2alpha, nitric oxide (NO) metabolites (NOx), glucose, insulin, triacylglycerol, and fatty acid analysis. The plasma EPA concentration (mean +/- SD) reached a peak of 2.10 +/- 0.99 mmol/L following the EPA meal (5 h) and did not rise above 0.27 +/- 0.16 mmol/L 1 h following the placebo meal. DeltaDVP-SI did not differ between the 2 test meals at 3 h but was greater at 6 h following EPA (6 h -0.65 +/- 0.65 m/s) compared with placebo (6 h -0.33 +/- 1.26 m/s). Plasma 8-isoprostane F2alpha concentrations increased by 48% at 6 h compared with baseline following the EPA meal and plasma NOx decreased following both meals, with no differences between the meals in the changes. Changes in other variables measured also did not differ after subjects consumed the 2 meals. In conclusion, adding EPA to a high-fat meal results in acute changes in vascular tone, independent of changes in oxidative stress.

Characterization of the vasorelaxant mechanisms of the endocannabinoid anandamide in rat aorta

BACKGROUND AND PURPOSE

Studies in isolated preparations of vascular tissue (mainly resistance vessels) provide evidence that anandamide exerts vasorelaxation. The aim of the present work was to further characterize the mechanisms involved in the vascular response induced by anandamide in a conduit vessel, rat aorta.

EXPERIMENTAL APPROACH

Isometric tension changes in response to a cumulative concentration-response curve of anandamide (1 nM-100 micro M) were recorded in aortic rings from male Wistar rats. The involvement of a number of factors in this relaxation was investigated including endothelium-derived vasorelaxant products, cannabinoid and vanilloid receptors (transient potential vanilloid receptor-1 (TRPV1)), release of calcitonin gene-related peptide (CGRP), anandamide metabolism and the membrane transporter for anandamide.

KEY RESULTS

Anandamide caused a significant concentration-dependent vasorelaxation in rat aorta. This vasorelaxation was significantly inhibited by Pertussis toxin, by a non-CB1/non-CB2 cannabinoid receptor antagonist, by endothelial denudation, by inhibition of nitric oxide synthesis or inhibition of prostanoid synthesis via cyclooxygenase-2 (COX-2), by blockade of prostaglandin receptors EP4 and by a fatty acid amino hydrolase inhibitor. Antagonists for CB1, CB2, TRPV1 or CGRP receptors, an inhibitor of the release of endothelium-derived hyperpolarizing factor, and an inhibitor of anandamide transport did not modify the vascular response to anandamide.

CONCLUSIONS AND IMPLICATIONS

Our results demonstrate, for the first time, the involvement of the non-CB1/non-CB2 cannabinoid receptor and an anandamide-arachidonic acid-COX-2 derived metabolite (which acts on EP4 receptors) in the endothelial vasorelaxation caused by anandamide in rat aorta.

The vasodilator 17,18-epoxyeicosatetraenoic acid targets the pore-forming BK alpha channel subunit in rodents

17,18-Epoxyeicosatetraenoic acid (17,18-EETeTr) stimulates vascular large-conductance K(+) (BK) channels. BK channels are composed of the pore-forming BK alpha and auxiliary BK beta1 subunits that confer an increased sensitivity for changes in membrane potential and calcium to BK channels. Ryanodine-sensitive calcium-release channels (RyR3) in the sarcoplasmic reticulum (SR) control the process. To elucidate the mechanism of BK channel activation, we performed whole-cell and perforated-patch clamp experiments in freshly isolated cerebral and mesenteric artery vascular smooth muscle cells (VSMC) from Sprague-Dawley rats, BK beta1 gene-deficient (-/-), BK alpha (-/-), RyR3 (-/-) and wild-type mice. The 17,18-EETeTr (100 nm) increased tetraethylammonium (1 mm)-sensitive outward K(+) currents in VSMC from wild-type rats and wild-type mice. The effects were not inhibited by the epoxyeicosatrienoic acid (EET) antagonist 14,15-epoxyeicosa-5(Z)-enoic acid (10 mum). BK channel currents were increased 3.5-fold in VSMC from BK beta1 (-/-) mice, whereas a 2.9-fold stimulation was observed in VSMC from RyR3 (-/-) mice (at membrane voltage 60 mV). The effects were similar compared with those observed in cells from wild-type mice. The BK current increase was neither influenced by strong internal calcium buffering (Ca(2)(+), 100 nm), nor by external calcium influx. The 17,18-EETeTr did not induce outward currents in VSMC BK alpha (-/-) cells. We next tested the vasodilator effects of 17,18-EETeTr on isolated arteries of BK alpha-deficient mice. Vasodilatation was largely inhibited in cerebral and mesenteric arteries isolated from BK alpha (-/-) mice compared with that observed in wild-type and BK beta1 (-/-) arteries. We conclude that 17,18-EETeTr represents an endogenous BK channel agonist and vasodilator. Since 17,18-EETeTr is active in small arteries lacking BK beta1, the data further suggest that BK alpha represents the molecular target for the principal action of 17,18-EETeTr. Finally, the action of 17,18-EETeTr is not mediated by changes of the internal global calcium concentration or local SR calcium release events.

Longchain n-3 polyunsaturated fatty acids and microvascular reactivity: Observation in the hamster cheek pouch

Previous experiments in our laboratory, using the hamster cheek pouch microcirculation, have shown that precapillary vessels exhibit spontaneous rhythmic luminal variations, termed vasomotion, a myogenic activity sustained by a balance between membrane currents among which polarizing K(+) currents play an important role. In these microvessels, endothelium-derived relaxing factors (EDRFs) seem to regulate arteriolar diameter [via nitric oxide (NO) and cyclic GMP] and vasomotion [probably via endothelium-derived hyperpolarizing factor (EDHF)]. Fish or fish oil diet can decrease the risk of cardiovascular diseases, probably by modifying the conductance of selective ion channels, such as K(+) and/or Ca(++), and/or increasing the production of vasodilators, such as NO. To investigate its effect on microvascular reactivity, using the same preparation and an intravital microscope coupled to a closed circuit TV system, male hamsters were treated for 14 days, twice a day, with 0.4 mL/100 g body weight with fish or olive oil. An attempt was also undertaken to record in arterioles, in vivo, the membrane potential of smooth muscle cells during their vasomotor activity combining conventional microelectrode and intravital microscopy techniques. The effects of topical application of two vasodilators, acetylcholine [endothelium-dependent one, NO release and membrane hyperpolarization via Ca(++)-activated K(+) channels (K(Ca))] and sodium nitroprusside (endothelium-independent, NO donor and no change on membrane potential) and two vasoconstrictors which elicited membrane depolarization via Ca(++) channels, phenylephrine (alpha(1)-adrenergic receptor agonist) and serotonin (5-hydroxi-tryptamine) on mean internal diameter of arterioles and venules, arteriolar blood flows, spontaneous arteriolar vasomotion frequency and amplitude and functional capillary density (FCD, number of capillaries with flowing red blood cells per unit area of tissue) were determined. Anesthesia was induced by sodium pentobarbital (i.p.) and maintained with alpha-chloralose through the femoral vein. In the presence of vasomotion, the membrane potentials are slowly oscillating by about 20 mV around values of approximately -50 mV in perfect synchrony with vasomotor movements and depolarizing phases coincide with vasoconstrictions while polarizing ones with vasodilatations. Comparing all parameters, in control conditions, only the spontaneous vasomotion frequency was significantly higher (2.37 times higher) on the group treated with fish oil and persisted as such throughout all experiments. With topical application of the drugs mentioned above, the group treated with fish oil showed, for each drug concentration, a balance towards vasodilatation with consequent increase on arteriolar blood flow and on FCD, compared with the olive oil treated one. No significant changes on mean arterial pressure, spontaneous arteriolar vasomotion amplitude or venular diameter could be detected in the two groups. Our results support the concept that, in the hamster cheek pouch microcirculation, fish oil supplementation activates K(+) channels which act as the EDHF and might also increase the production of vasodilators, probably NO.

Omega-3 fatty acids: role in cardiovascular health and disease

Dietary omega-3 polyunsaturated fatty acids, eicosapentaenoic and docosahexaenoic acids, play an important role in cardiovascular health and disease. Clinical trials provide substantial evidence to support current dietary recommendations for omega-3 fatty acids in cardiovascular disease management. The cardioprotective benefits of omega-3 fatty acids may be attributed to multiple physiological effects on lipids, blood pressure, vascular function, cardiac rhythms, platelet function, and inflammatory responses. The metabolism of omega-3 fatty acids, physiological effects, and clinical considerations with current dietary recommendations and sources of omega-3 fatty acids are presented.

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.

Diacylglycerol-Containing Docosahexaenoic Acid in Acyl Chain Modulates Airway Smooth Muscle Tone

We synthesized and assessed the role of a diacylglycerol (DAG)-containing docosahexaenoic acid (DHA), that is, 1-stearoyl-2-docosahexaenoyl-sn-glycerol (SDHG), in the contraction of guinea pig airway smooth muscle (ASM). We compared its action with 1-stearoyl-2-arachidonoyl-sn-glycerol (SAG) and 1,2-dioctanoyl-sn-glycerol (1,2-DiC8), a stable DAG analog. The three DAGs (SAG, SDHG, and 1,2-DiC8) induced reversible concentration-dependent contraction of ASM. SDHG induced higher guinea pig ASM contraction than did SAG and 1,2-DiC8. The effects of SDHG were blocked, to different extents, by nifedipine (L-type Ca2+ channel blocker). By employing GF-109203X (protein kinase C [PKC] inhibitor) and lanthanum (La3+), a nonselective cation channel blocker, we observed that SDHG evoked ASM contractile response via PKC-dependent and PKC-independent (but Ca2+-dependent) pathways. Interestingly, SAG exerted its action only by increasing [Ca2+]i and did not require PKC activation. To probe the implication of calcium mobilization, we employed thapsigargin (TG), which also induced ASM contraction in a calcium-dependent manner. SDHG and 1,2-DiC8, in a PKC-dependent manner, induced the phosphorylation of CPI-17 (myosin light chain phosphatase inhibitor of 17 kD). Furthermore, SAG and TG failed to phosphorylate CPI-17 in ASM cells. Our results suggest that different DAG species, produced during a dietary supplementation with fatty acids, could modulate the reactivity of airway smooth muscles in a PKC-dependent and -independent manner, and hence, may play a critical role in health and disease.

Cardiovascular protective effects of n-3 polyunsaturated fatty acids with special emphasis on docosahexaenoic acid

It is widely accepted that n-3 polyunsaturated fatty acids (PUFAs) rich in fish oils protect against several types of cardiovascular diseases such as myocardial infarction, arrhythmia, atherosclerosis, or hypertension. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) may be the active biological components of these effects. Although the precise cellular and molecular mechanisms underlying the beneficial effects are still uncertain, the protective effects of n-3 PUFAs are attributable to their direct effects on vascular smooth muscle cell (VSMC) functions. These n-3 PUFAs activate K(+)(ATP) channels and inhibit certain types of Ca(2+) channels, probably via at least 2 distinct mechanisms. N-3 PUFAs favorably alter the eicosanoid profile and regulate cytokine-induced expression of inducible nitric oxide synthase and cyclooxygenase-2 via mechanisms involving modulation of signaling transduction events. N-3 PUFAs also modulate VSMC proliferation, migration, and apoptosis. These recent data suggest that modulation of these VSMC functions contribute to the beneficial effects of n-3 PUFAs on various cardiovascular disorders. Furthermore, recent studies strongly suggest that DHA has more potent and beneficial effects than EPA. However, many questions about the cellular and molecular mechanisms still remain to be answered.

Increased superoxide dismutase and Na+, K+-ATPase activities in aortic strips from potassium-adapted rats: implication for altered vascular reactivity

The contributions of superoxide dismutase (SOD) and Na(+), K(+)-ATPase to the altered vascular reactivity in potassium-adapted rats were investigated to test the hypothesis that smooth muscle hyperpolarisation may be involved. Isometric contractions to noradrenaline (NA), 5-hydroxytryptamine (5-HT), and relaxations to acetylcholine (ACh), levcromakalim (LEV) and sodium nitroprusside (SNP), were measured in aortic rings from potassium-adapted rats. Pieces of the aortae were also excised from the animals and assayed for SOD and Na(+), K(+)-ATPase. Maximum contractile responses were significantly attenuated (P<0.05) in aortic rings from the potassium-adapted rats to NA and 5-HT, while relaxations were also significantly augmented (P<0.05) in the same rings to LEV and SNP, but not to ACh. Both SOD and Na(+), K(+)-ATPase activities were significantly higher (P<0.05) in the aortae from the potassium-adapted rats compared to controls. It is concluded that the alteration in vascular smooth muscle reactivity may be due to hyperpolarisation caused by the activities of SOD and Na(+), K(+)-ATPase.

The novel serine protease PreR-Co promotes endothelium-independent vasorelaxation in rabbit aortic rings

The effect of a novel enzyme (PreR-Co) that activates renal prorenin was studied on rabbit aortas with and without endothelium. It was tested 1) in the basal tone of nonstimulated or ANG II-sensitized rings or rings precontracted with norepinephrine (NE), PGF(2alpha), high KCl concentration, and 2) in rings pretreated with enalaprilat, losartan, PD-123319, N(omega)-nitro-l-arginine methyl ester, HOE-140, indomethacin, or serine protease inhibitors (PMSF, aprotinin, or soybean trypsin inhibitor); kallilkrein and bradykinin were also tested in ANG II-sensitized rings. PreR-Co produced a vasorelaxant effect in the basal tone and in the precontracted rabbit aorta. The effect was endothelium independent, potentiated by endothelium removal or nitric oxide (NO) synthase inhibition, and abolished by boiling the enzyme. In addition, the effect improved when basal tone was increased in ANG II-sensitized aortic rings or in precontracted vessels. No activation of the ANG II, bradykinin, prostaglandin, or NO pathway mediating the PreR-Co response could be obtained, suggesting a direct action of the enzyme. This action seems to be dependent on esterasic activity because serine protease inhibitors like PMSF and aprotinin were able to block the vasorelaxant effect of PreR-Co.

Cytochrome P450-dependent eicosapentaenoic acid metabolites are novel BK channel activators

P450-dependent arachidonic acid (AA) metabolites regulate arterial tone by modulating calcium-activated (BK) potassium channels in vascular smooth muscle cells (VSMC). Because eicosapentaenoic acid (EPA) has been reported to improve vascular function, we tested the hypothesis that P450-dependent epoxygenation of EPA produces alternative vasoactive compounds. We synthesized the 5 regioisomeric epoxyeicosattrienoic acids (EETeTr) and examined them for effects on K(+) currents in rat cerebral artery VSMCs with the patch-clamp technique. 11(R),12(S)-epoxyeicosatrienoic acid (50 nmol/L) was used for comparison and stimulated K(+) currents 6-fold at +60 mV. However, 17(R),18(S)-EETeTr elicited a more than 14-fold increase. 17(S),18(R)-EET and the remaining four regioisomers were inactive. The effect of 17(R),18(S)-EETeTr was blocked by tetraethylammonium but not by 4-aminopyridine. VSMCs expressed P450s 4A1 and 4A3. Recombinant P450 4A1 hydroxylated EPA at C-19 and C-20 and epoxygenated the 17,18-double bond, yielding the R, S- and S, R-enantiomers in a ratio of 64:36. We conclude that 17(R),18(S)-EETeTr represents a novel, potent activator of BK potassium channels. Furthermore, this metabolite can be directly produced in VSMCs. We suggest that 17(R),18(S)-EETeTr may function as an important hyperpolarizing factor, particularly with EPA-rich diets.

Docosahexaenoic acid--induced vasorelaxation in hypertensive rats: mechanisms of action

The authors investigated the vasorelaxant properties of the omega-3 fatty acid, docosahexaenoic (DHA, 22:6n-3), and the possible involvement of endothelium-derived nitric oxide, prostanoids, opening of K+ channels, and/or modulation of calcium-mediated events. Isolated aorta from male spontaneously hypertensive rats (SHR) (age 16-17 weeks) were used to measure isometric tension. DHA-induced (1-100 mumol/l) relaxation was examined following contraction to norepinephrine (NE) (10(-6) mol/l) or high-K+ (80 mmol/l) solution in the presence and absence of various inhibitors and calcium-containing solution. DHA acid induced a significant vasorelaxant effect in both NE and high-K(+)-induced contracted SHR aortic rings, although DHA relaxations were greater in high-K(+)-induced contracted rings. In the absence of extracellular calcium, DHA (5-30 mumol/l) inhibited the initial phasic and sustained components of NE-induced contraction under different conditions. Inhibition of nitric oxide synthesis by N omega-nitro-L-arginine methyl ester hydrochloride (100 mumol/l) had no effect on DHA relaxations; however, indomethacin or nifedipine caused significant inhibition at > or = 30 mumol/l DHA. The K+ channel blocker, glibenclamide, but not tetraethyl-ammonium, also had an inhibitory effect on DHA-induced relaxation. These results indicate that DHA's vasorelaxant actions in SHR aorta are independent of endothelium-derived nitric oxide; however, at DHA concentrations > or = 30 mumol/l, vasodilatory prostanoids that activate ATP-sensitive K+ channels (KATP) may be involved. At lower concentrations, DHA-induced relaxation appears to be attributed to modulation of intracellular Ca2+ release and L-type Ca2+ channels in vascular smooth muscle cells. The vasorelaxant properties of DHA may contribute, in part, to the blood pressure-lowering effect of dietary fish oil in this hypertensive model.