Antihypertensive properties of linoleic acid and fish oil omega-3 fatty acids independent of the prostaglandin system

Study on material basis and anti-hypertensive metabolomics of Zhengan-Xifeng-Tang(ZXT): A comparison between ZXT decoction and granules

High blood pressure is a serious human health problem and one of the leading risk factors for fatal complications in cardiovascular disease. The ZXT granules were prepared based on the Zhengan-Xifeng-Tang (ZXT) decoction. However, the therapeutic effects of ZXT granules on spontaneous hypertension and the metabolic pathways in which they may intervene are unclear. The aim of this study was to investigate the antihypertensive effect of ZXT granules on spontaneously hypertensive rats (SHR) and to analyze the metabolic pathway of intervention through chemical composition characterization, pharmacodynamics, and serum metabolomics analysis. After eight weeks of administration, serum and aortic arch samples were collected for biochemical, histopathology and serum metabolomics analysis to assess the effect of ZXT granules on SHR. The results showed that ZXT granules reduced aortic arch injury and blood pressure in SHR rats. Serum data from rats in each group was collected using LC-MS and 74 potential biomarkers were identified that showed significant differences between the model and control groups. Of these, 18 potential biomarkers were found to be deregulated after intervention with ZXT granules. These 18 potential differential metabolic markers are primarily involved in bile acid biosynthesis, arachidonic acid metabolism pathway, and fatty acid degradation. The results demonstrated that ZXT granules significantly affected blood lipids, aortic arch, and metabolic disorders in SHR rats. ZXT granules offer a new possibility for effective and convenient treatment of hypertensive patients.

Neuroinflammation in hypertension: the renin-angiotensin system versus pro-resolution pathways

Overstimulation of the pro-inflammatory pathways within brain areas responsible for sympathetic outflow is well evidenced as a primary contributing factor to the establishment and maintenance of neurogenic hypertension. However, the precise mechanisms and stimuli responsible for promoting a pro-inflammatory state are not fully elucidated. Recent work has unveiled novel compounds derived from omega-3 polyunsaturated fatty acids (ω-3 PUFAs), termed specialized pro-resolving mediators (SPMs), which actively regulate the resolution of inflammation. Failure or dysregulation of the resolution process has been linked to a variety of chronic inflammatory and neurodegenerative diseases. Given the pathologic role of neuroinflammation in the hypertensive state, SPMs and their associated pathways may provide a link between hypertension and the long-standing association of dietary ω-3 PUFAs with cardioprotection. Herein, we review recent progress in understanding the RAS-driven pathophysiology of neurogenic hypertension, particularly in regards to the chronic low-grade neuroinflammatory response. In addition, we examine the potential for an impaired resolution of inflammation process in the context of hypertension.

Lowering Effects of n-3 Fatty Acid Supplements on Blood Pressure by Reducing Plasma Angiotensin II in Inner Mongolia Hypertensive Patients: A Double-Blind Randomized Controlled Trial

Whether n-3 fatty acid (FA) has hypotensive actions among Chinese adults remains inconclusive. Hypertensive patients from Inner Mongolia, China ( n = 126) were recruited to a double-blind, randomized controlled trial. We investigated the effects of n-3 FA supplements on blood pressure (BP, mm Hg), plasma concentrations of angiotensin II (Ang II, pg/mL), and nitric oxygen (NO, μmol/L), using fish oil ( n = 41, 4 capsules/day, equivalent to 2 g of eicosapentaenoic acid plus docosahexaenoic acid) and flaxseed oil ( n = 42, 4 capsules/day, equivalent to 2.5 g of α-linolenic acid). Comparing to the control group (corn oil, n = 43), the mean systolic BP (-4.52 ± 9.28 vs -1.51 ± 9.23, P = 0.040) and the plasma Ang II levels (-12.68 ± 10.87 vs -4.93 ± 9.08, P = 0.023) were significantly lowered in the fish oil group, whereas diastolic BP ( P = 0.285) and plasma NO levels ( P = 0.220) were not. Such findings suggest that marine-based n-3 FA has a hypotensive efficacy in Chinese hypertensive patients possibly through inhibiting Ang II-dependent vasoconstrictions.

Omega-6 fats for the primary and secondary prevention of cardiovascular disease

BACKGROUND

Omega-6 fats are polyunsaturated fats vital for many physiological functions, but their effect on cardiovascular disease (CVD) risk is debated.

OBJECTIVES

To assess effects of increasing omega-6 fats (linoleic acid (LA), gamma-linolenic acid (GLA), dihomo-gamma-linolenic acid (DGLA) and arachidonic acid (AA)) on CVD and all-cause mortality.

SEARCH METHODS

We searched CENTRAL, MEDLINE and Embase to May 2017 and clinicaltrials.gov and the World Health Organization International Clinical Trials Registry Platform to September 2016, without language restrictions. We checked trials included in relevant systematic reviews.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) comparing higher versus lower omega-6 fat intake in adults with or without CVD, assessing effects over at least 12 months. We included full texts, abstracts, trials registry entries and unpublished studies. Outcomes were all-cause mortality, CVD mortality, CVD events, risk factors (blood lipids, adiposity, blood pressure), and potential adverse events. We excluded trials where we could not separate omega-6 fat effects from those of other dietary, lifestyle or medication interventions.

DATA COLLECTION AND ANALYSIS

Two authors independently screened titles/abstracts, assessed trials for inclusion, extracted data, and assessed risk of bias of included trials. We wrote to authors of included studies. Meta-analyses used random-effects analysis, while sensitivity analyses used fixed-effects and limited analyses to trials at low summary risk of bias. We assessed GRADE quality of evidence for 'Summary of findings' tables.

MAIN RESULTS

We included 19 RCTs in 6461 participants who were followed for one to eight years. Seven trials assessed the effects of supplemental GLA and 12 of LA, none DGLA or AA; the omega-6 fats usually displaced dietary saturated or monounsaturated fats. We assessed three RCTs as being at low summary risk of bias.Primary outcomes: we found low-quality evidence that increased intake of omega-6 fats may make little or no difference to all-cause mortality (risk ratio (RR) 1.00, 95% confidence interval (CI) 0.88 to 1.12, 740 deaths, 4506 randomised, 10 trials) or CVD events (RR 0.97, 95% CI 0.81 to 1.15, 1404 people experienced events of 4962 randomised, 7 trials). We are uncertain whether increasing omega-6 fats affects CVD mortality (RR 1.09, 95% CI 0.76 to 1.55, 472 deaths, 4019 randomised, 7 trials), coronary heart disease events (RR 0.88, 95% CI 0.66 to 1.17, 1059 people with events of 3997 randomised, 7 trials), major adverse cardiac and cerebrovascular events (RR 0.84, 95% CI 0.59 to 1.20, 817 events, 2879 participants, 2 trials) or stroke (RR 1.36, 95% CI 0.45 to 4.11, 54 events, 3730 participants, 4 trials), as we assessed the evidence as being of very low quality. We found no evidence of dose-response or duration effects for any primary outcome, but there was a suggestion of greater protection in participants with lower baseline omega-6 intake across outcomes.Additional key outcomes: we found increased intake of omega-6 fats may reduce myocardial infarction (MI) risk (RR 0.88, 95% CI 0.76 to 1.02, 609 events, 4606 participants, 7 trials, low-quality evidence). High-quality evidence suggests increasing omega-6 fats reduces total serum cholesterol a little in the long term (mean difference (MD) -0.33 mmol/L, 95% CI -0.50 to -0.16, I² = 81%; heterogeneity partially explained by dose, 4280 participants, 10 trials). Increasing omega-6 fats probably has little or no effect on adiposity (body mass index (BMI) MD -0.20 kg/m², 95% CI -0.56 to 0.16, 371 participants, 1 trial, moderate-quality evidence). It may make little or no difference to serum triglycerides (MD -0.01 mmol/L, 95% CI -0.23 to 0.21, 834 participants, 5 trials), HDL (MD -0.01 mmol/L, 95% CI -0.03 to 0.02, 1995 participants, 4 trials) or low-density lipoprotein (MD -0.04 mmol/L, 95% CI -0.21 to 0.14, 244 participants, 2 trials, low-quality evidence).

AUTHORS' CONCLUSIONS

This is the most extensive systematic assessment of effects of omega-6 fats on cardiovascular health, mortality, lipids and adiposity to date, using previously unpublished data. We found no evidence that increasing omega-6 fats reduces cardiovascular outcomes other than MI, where 53 people may need to increase omega-6 fat intake to prevent 1 person from experiencing MI. Although benefits of omega-6 fats remain to be proven, increasing omega-6 fats may be of benefit in people at high risk of MI. Increased omega-6 fats reduce serum total cholesterol but not other blood fat fractions or adiposity.

Omega-6 fats for the primary and secondary prevention of cardiovascular disease

BACKGROUND

Omega-6 fats are polyunsaturated fats vital for many physiological functions, but their effect on cardiovascular disease (CVD) risk is debated.

OBJECTIVES

To assess effects of increasing omega-6 fats (linoleic acid (LA), gamma-linolenic acid (GLA), dihomo-gamma-linolenic acid (DGLA) and arachidonic acid (AA)) on CVD and all-cause mortality.

SEARCH METHODS

We searched CENTRAL, MEDLINE and Embase to May 2017 and clinicaltrials.gov and the World Health Organization International Clinical Trials Registry Platform to September 2016, without language restrictions. We checked trials included in relevant systematic reviews.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) comparing higher versus lower omega-6 fat intake in adults with or without CVD, assessing effects over at least 12 months. We included full texts, abstracts, trials registry entries and unpublished studies. Outcomes were all-cause mortality, CVD mortality, CVD events, risk factors (blood lipids, adiposity, blood pressure), and potential adverse events. We excluded trials where we could not separate omega-6 fat effects from those of other dietary, lifestyle or medication interventions.

DATA COLLECTION AND ANALYSIS

Two authors independently screened titles/abstracts, assessed trials for inclusion, extracted data, and assessed risk of bias of included trials. We wrote to authors of included studies. Meta-analyses used random-effects analysis, while sensitivity analyses used fixed-effects and limited analyses to trials at low summary risk of bias. We assessed GRADE quality of evidence for 'Summary of findings' tables.

MAIN RESULTS

We included 19 RCTs in 6461 participants who were followed for one to eight years. Seven trials assessed the effects of supplemental GLA and 12 of LA, none DGLA or AA; the omega-6 fats usually displaced dietary saturated or monounsaturated fats. We assessed three RCTs as being at low summary risk of bias.Primary outcomes: we found low-quality evidence that increased intake of omega-6 fats may make little or no difference to all-cause mortality (risk ratio (RR) 1.00, 95% confidence interval (CI) 0.88 to 1.12, 740 deaths, 4506 randomised, 10 trials) or CVD events (RR 0.97, 95% CI 0.81 to 1.15, 1404 people experienced events of 4962 randomised, 7 trials). We are uncertain whether increasing omega-6 fats affects CVD mortality (RR 1.09, 95% CI 0.76 to 1.55, 472 deaths, 4019 randomised, 7 trials), coronary heart disease events (RR 0.88, 95% CI 0.66 to 1.17, 1059 people with events of 3997 randomised, 7 trials), major adverse cardiac and cerebrovascular events (RR 0.84, 95% CI 0.59 to 1.20, 817 events, 2879 participants, 2 trials) or stroke (RR 1.36, 95% CI 0.45 to 4.11, 54 events, 3730 participants, 4 trials), as we assessed the evidence as being of very low quality. We found no evidence of dose-response or duration effects for any primary outcome, but there was a suggestion of greater protection in participants with lower baseline omega-6 intake across outcomes.Additional key outcomes: we found increased intake of omega-6 fats may reduce myocardial infarction (MI) risk (RR 0.88, 95% CI 0.76 to 1.02, 609 events, 4606 participants, 7 trials, low-quality evidence). High-quality evidence suggests increasing omega-6 fats reduces total serum cholesterol a little in the long term (mean difference (MD) -0.33 mmol/L, 95% CI -0.50 to -0.16, I2 = 81%; heterogeneity partially explained by dose, 4280 participants, 10 trials). Increasing omega-6 fats probably has little or no effect on adiposity (body mass index (BMI) MD -0.20 kg/m2, 95% CI -0.56 to 0.16, 371 participants, 1 trial, moderate-quality evidence). It may make little or no difference to serum triglycerides (MD -0.01 mmol/L, 95% CI -0.23 to 0.21, 834 participants, 5 trials), HDL (MD -0.01 mmol/L, 95% CI -0.03 to 0.02, 1995 participants, 4 trials) or low-density lipoprotein (MD -0.04 mmol/L, 95% CI -0.21 to 0.14, 244 participants, 2 trials, low-quality evidence).

AUTHORS' CONCLUSIONS

This is the most extensive systematic assessment of effects of omega-6 fats on cardiovascular health, mortality, lipids and adiposity to date, using previously unpublished data. We found no evidence that increasing omega-6 fats reduces cardiovascular outcomes other than MI, where 53 people may need to increase omega-6 fat intake to prevent 1 person from experiencing MI. Although benefits of omega-6 fats remain to be proven, increasing omega-6 fats may be of benefit in people at high risk of MI. Increased omega-6 fats reduce serum total cholesterol but not other blood fat fractions or adiposity.

Omega 6 fatty acids for the primary prevention of cardiovascular disease

BACKGROUND

Omega 6 plays a vital role in many physiological functions but there is controversy concerning its effect on cardiovascular disease (CVD) risk. There is conflicting evidence whether increasing or decreasing omega 6 intake results in beneficial effects.

OBJECTIVES

The two primary objectives of this Cochrane review were to determine the effectiveness of:1. Increasing omega 6 (Linoleic acid (LA), Gamma-linolenic acid (GLA), Dihomo-gamma-linolenic acid (DGLA), Arachidonic acid (AA), or any combination) intake in place of saturated or monounsaturated fats or carbohydrates for the primary prevention of CVD.2. Decreasing omega 6 (LA, GLA, DGLA, AA, or any combination) intake in place of carbohydrates or protein (or both) for the primary prevention of CVD.

SEARCH METHODS

We searched the following electronic databases up to 23 September 2014: the Cochrane Central Register of Controlled Trials (CENTRAL) on the Cochrane Library (Issue 8 of 12, 2014); MEDLINE (Ovid) (1946 to September week 2, 2014); EMBASE Classic and EMBASE (Ovid) (1947 to September 2014); Web of Science Core Collection (Thomson Reuters) (1990 to September 2014); Database of Abstracts of Reviews of Effects (DARE) and Health Technology Assessment Database, and Health Economics Evaluations Database on the Cochrane Library (Issue 3 of 4, 2014). We searched trial registers and reference lists of reviews for further studies. We applied no language restrictions.

SELECTION CRITERIA

Randomised controlled trials (RCTs) of interventions stating an intention to increase or decrease omega 6 fatty acids, lasting at least six months, and including healthy adults or adults at high risk of CVD. The comparison group was given no advice, no supplementation, a placebo, a control diet, or continued with their usual diet. The outcomes of interest were CVD clinical events (all-cause mortality, cardiovascular mortality, non-fatal end points) and CVD risk factors (changes in blood pressure, changes in blood lipids, occurrence of type 2 diabetes). We excluded trials involving exercise or multifactorial interventions to avoid confounding.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials for inclusion, extracted the data, and assessed the risk of bias in the included trials.

MAIN RESULTS

We included four RCTs (five papers) that randomised 660 participants. No ongoing trials were identified. All included trials had at least one domain with an unclear risk of bias. There were no RCTs of omega 6 intake reporting CVD clinical events. Three trials investigated the effect of increased omega 6 intake on lipid levels (total cholesterol, low density lipoprotein (LDL-cholesterol), and high density lipoprotein (HDL-cholesterol)), two trials reported triglycerides, and two trials reported blood pressure (diastolic and systolic blood pressure). Two trials, one with two relevant intervention arms, investigated the effect of decreased omega 6 intake on blood pressure parameters and lipid levels (total cholesterol, LDL-cholesterol, and HDL-cholesterol) and one trial reported triglycerides. Our analyses found no statistically significant effects of either increased or decreased omega 6 intake on CVD risk factors.Two studies were supported by funding from the UK Food Standards Agency and Medical Research Council. One study was supported by Lipid Nutrition, a commercial company in the Netherlands and the Dutch Ministry of Economic Affairs. The final study was supported by grants from the Finnish Food Research Foundation, Finnish Heart Research Foundation, Aarne and Aili Turnen Foundation, and the Research Council for Health, Academy of Finland.

AUTHORS' CONCLUSIONS

We found no studies examining the effects of either increased or decreased omega 6 on our primary outcome CVD clinical endpoints and insufficient evidence to show an effect of increased or decreased omega 6 intake on CVD risk factors such as blood lipids and blood pressure. Very few trials were identified with a relatively small number of participants randomised. There is a need for larger well conducted RCTs assessing cardiovascular events as well as cardiovascular risk factors.

Selective and potent inhibitory effect of docosahexaenoic acid (DHA) on U46619-induced contraction in rat aorta

Inhibitory effects of docosahexaenoic acid (DHA) on blood vessel contractions induced by various constrictor stimulants were investigated in the rat thoracic aorta. The inhibitory effects of DHA were also compared with those of eicosapentaenoic acid (EPA) and linoleic acid (LA). DHA exhibited a strong inhibitory effect on the sustained contractions induced by U46619, a TXA(2) mimetic. This inhibitory effect of DHA was not affected by removal of the endothelium or by treatment with either indomethacin or N(ω)-nitro-l-arginine. DHA also significantly diminished PGF(2α)-induced contraction but did not show any appreciable inhibitory effects on the contractions to both phenylephrine (PE) and high-KCl. Similarly, EPA exhibited significant inhibitory effects against the contractions induced by both U46619 and PGF(2α) without substantially affecting either PE- or high-KCl-induced contractions. However, both DHA and EPA generated more potent inhibitions against contractions induced by U46619 than those by PGF(2α). In contrast, LA did not show significant inhibitory effects against any contractions, including those induced by U46619. The present findings suggest that DHA and EPA elicit more selective inhibition against blood vessel contractions that are mediated through stimulation of prostanoid receptors than those through α-adrenoceptor stimulation or membrane depolarization. Although DHA and EPA have similar inhibitory potencies against prostanoid receptor-mediated contractions, they had a more potent inhibition against TXA(2) receptor (TP receptor)-mediated contractions than against PGF(2α) receptor (FP receptor)-mediated responses. Selective inhibition by either DHA or EPA of prostanoid receptor-mediated blood vessel contractions may partly underlie the mechanisms by which these ω-3 polyunsaturated fatty acids exert their circulatory-protective effects.

Hypothalamic gene expression in ω-3 PUFA-deficient male rats before, and following, development of hypertension

Dietary deficiency of ω-3 fatty acids (ω-3 DEF) produces hypertension in later life. This study examined the effect of ω-3 DEF on blood pressure and hypothalamic gene expression in young rats, before the development of hypertension, and in older rats following the onset of hypertension. Animals were fed experimental diets that were deficient in ω-3 fatty acids, sufficient in short-chain ω-3 fatty acids or sufficient in short- and long-chain ω-3 fatty acids, from the prenatal period until 10 or 36 weeks-of-age. There was no difference in blood pressure between groups at 10 weeks-of-age; however, at 36 weeks-of-age ω-3 DEF animals were hypertensive in relation to sufficient groups. At 10 weeks, expression of angiotensin-II(1A) receptors and dopamine D(3) receptors were significantly increased in the hypothalamic tissue of ω-3 DEF animals. In contrast, at 36 weeks, α(2a) and β(1) adrenergic receptor expression was significantly reduced in the ω-3 DEF group. Brain docosahexaenoic acid was significantly lower in ω-3 DEF group compared with sufficient groups. This study demonstrates that dietary ω-3 DEF causes changes both in the expression of key genes involved in central blood pressure regulation and in blood pressure. The data may indicate that hypertension resulting from ω-3 DEF is mediated by the central adrenergic system.

Omega-3 fatty acids and metabolic syndrome: effects and emerging mechanisms of action

Epidemiological, human, animal, and cell culture studies show that n-3 fatty acids, especially α-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), reduce the risk factors of cardiovascular diseases. EPA and DHA, rather than ALA, have been the focus of research on the n-3 fatty acids, probably due to the relatively inefficient conversion of ALA to EPA and DHA in rodents and humans. This review will assess our current understanding of the effects and potential mechanisms of actions of individual n-3 fatty acids on multiple risk factors of metabolic syndrome. Evidence for pharmacological responses and the mechanism of action of each of the n-3 fatty acid trio will be discussed for the major risk factors of metabolic syndrome, especially adiposity, dyslipidemia, insulin resistance and diabetes, hypertension, oxidative stress, and inflammation. Metabolism of n-3 and n-6 fatty acids as well as the interactions of n-3 fatty acids with nutrients, gene expression, and disease states will be addressed to provide a rationale for the use of n-3 fatty acids to reduce the risk factors of metabolic syndrome.

Hypertension induced by omega-3 polyunsaturated fatty acid deficiency is alleviated by alpha-linolenic acid regardless of dietary source

Omega-3 polyunsaturated fatty acid deficiency, particularly during the prenatal period, can cause hypertension in later life. This study examined the effect of different sources of alpha-linolenic acid (canola oil or flaxseed oil) in the prevention of hypertension and other metabolic symptoms induced by an omega-3 fatty acid-deficient diet. Dams were provided one of three experimental diets from 1 week before mating. Diets were either deficient (10% safflower oil-DEF) or sufficient (7% safflower oil+3% flaxseed oil-SUF-F; or 10% canola oil-SUF-C) in omega-3 fatty acids. The male offspring were continued on the maternal diet from weaning for the duration of the study. Body weight, ingestive behaviors, blood pressure, body composition, metabolic rate, plasma leptin and brain fatty acids were all assessed. The DEF animals were hypertensive at 24 weeks of age compared with SUF-F or SUF-C animals; this was not evident at 12 weeks. These results suggest that different sources of ALA are effective in preventing hypertension related to omega-3 fatty acid deficiency. However, there were other marked differences between the DEF and, in particular, the SUF-C phenotype including lowered body weight, adiposity, leptin and food intake in SUF-C animals. SUF-F animals also had lower, but less marked reductions in adiposity and leptin compared with DEF animals. The differences observed between DEF, SUF-F and SUF-C phenotypes indicate that body fat and leptin may be involved in omega-3 fatty acid deficiency hypertension.

Dietary protein level interacts with omega-3 polyunsaturated fatty acid deficiency to induce hypertension

BACKGROUND

Dietary omega-3 fatty acid deficiency can lead to hypertension in later life; however, hypertension is affected by numerous other dietary factors. We examined the effect of altering the dietary protein level on blood pressure in animals deficient or sufficient in omega-3 fatty acids.

METHODS

Female rats were placed on one of four experimental diets 1 week prior to mating. Diets were either deficient (10% safflower oil; DEF) or sufficient (7% safflower oil, 3% flaxseed oil; SUF) in omega-3 fatty acids and contained 20 or 30% casein (DEF20, SUF20, DEF30, SUF30). Offspring were maintained on the maternal diet for the duration of the experiment. At 12, 18, 24, and 30 weeks, blood pressure was assessed by tail cuff plethysmography.

RESULTS

At both 12 and 18 weeks of age, no differences in blood pressure were observed based on diet, however, by 24 weeks hypertension was evident in DEF30 animals; there were no blood pressure differences between the other groups. This hypertension in DEF30 group was increased at 30 weeks, with systolic, diastolic, and mean arterial pressure all elevated.

CONCLUSIONS

These results indicate that the hypertension previously attributed to omega-3 fatty acid deficiency is dependent on additional dietary factors, including protein content. Furthermore, this study is the first to plot the establishment of omega-3 fatty acid deficiency hypertension over time.

Essential fatty acids and their metabolites could function as endogenous HMG-CoA reductase and ACE enzyme inhibitors, anti-arrhythmic, anti-hypertensive, anti-atherosclerotic, anti-inflammatory, cytoprotective, and cardioprotective molecules

Lowering plasma low density lipoprotein-cholesterol (LDL-C), blood pressure, homocysteine, and preventing platelet aggregation using a combination of a statin, three blood pressure lowering drugs such as a thiazide, a beta blocker, and an angiotensin converting enzyme (ACE) inhibitor each at half standard dose; folic acid; and aspirin-called as polypill- was estimated to reduce cardiovascular events by approximately 80%. Essential fatty acids (EFAs) and their long-chain metabolites: gamma-linolenic acid (GLA), dihomo-GLA (DGLA), arachidonic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) and other products such as prostaglandins E1 (PGE1), prostacyclin (PGI2), PGI3, lipoxins (LXs), resolvins, protectins including neuroprotectin D1 (NPD1) prevent platelet aggregation, lower blood pressure, have anti-arrhythmic action, reduce LDL-C, ameliorate the adverse actions of homocysteine, show anti-inflammatory actions, activate telomerase, and have cytoprotective properties. Thus, EFAs and their metabolites show all the classic actions expected of the "polypill". Unlike the proposed "polypill", EFAs are endogenous molecules present in almost all tissues, have no significant or few side effects, can be taken orally for long periods of time even by pregnant women, lactating mothers, and infants, children, and adults; and have been known to reduce the incidence cardiovascular diseases including stroke. In addition, various EFAs and their long-chain metabolites not only enhance nitric oxide generation but also react with nitric oxide to yield their respective nitroalkene derivatives that produce vascular relaxation, inhibit neutrophil degranulation and superoxide formation, inhibit platelet activation, and possess PPAR-gamma ligand activity and release NO, thus prevent platelet aggregation, thrombus formation, atherosclerosis, and cardiovascular diseases. Based on these evidences, I propose that a rational combination of omega-3 and omega-6 fatty acids and the co-factors that are necessary for their appropriate action/metabolism is as beneficial as that of the combined use of a statin, thiazide, a beta blocker, and an angiotensin converting enzyme (ACE) inhibitor, folic acid, and aspirin. Furthermore, appropriate combination of omega-3 and omega-6 fatty acids may even show additional benefits in the form of protection from depression, schizophrenia, Alzheimer's disease, and enhances cognitive function; and serve as endogenous anti-inflammatory molecules; and could be administered from childhood for life long.

Omega-3 polyunsaturated fatty acid supplementation reduces hypertension in TGR(mRen-2)27 rats

To establish the effect of dietary omega-3 PUFA on angiotensin II (ANG II)-mediated hypertension, male TGR (mRen-2)27 (Ren-2) rats (animals with high ANG II activity) were maintained on a diet either deficient or sufficient in omega-3 PUFA from conception. Half the animals on each diet were treated with the angiotensin-converting enzyme inhibitor, perindopril, from birth. Ren-2 rats fed the omega-3 PUFA deficient diet were significantly more hypertensive than those fed the omega-3 PUFA sufficient diet. Perindopril reduced the blood pressure of both omega-3 PUFA-deficient and omega-3 PUFA-sufficient diet-fed Ren-2 rats. Body weight, body fat and plasma leptin were reduced by perindopril treatment but not affected by omega-3 PUFA supply. Given that the elevated blood pressure of the Ren-2 rat is mediated by ANG II, the data suggest that omega-3 PUFA may reduce hypertension via the renin-angiotensin system.

Omega 3 fatty acids for prevention and treatment of cardiovascular disease

BACKGROUND

It has been suggested that omega 3 (W3, n-3 or omega-3) fats from oily fish and plants are beneficial to health.

OBJECTIVES

To assess whether dietary or supplemental omega 3 fatty acids alter total mortality, cardiovascular events or cancers using both RCT and cohort studies.

SEARCH STRATEGY

Five databases including CENTRAL, MEDLINE and EMBASE were searched to February 2002. No language restrictions were applied. Bibliographies were checked and authors contacted.

SELECTION CRITERIA

RCTs were included where omega 3 intake or advice was randomly allocated and unconfounded, and study duration was at least six months. Cohorts were included where a cohort was followed up for at least six months and omega 3 intake estimated.

DATA COLLECTION AND ANALYSIS

Studies were assessed for inclusion, data extracted and quality assessed independently in duplicate. Random effects meta-analysis was performed separately for RCT and cohort data.

MAIN RESULTS

Forty eight randomised controlled trials (36,913 participants) and 41 cohort analyses were included. Pooled trial results did not show a reduction in the risk of total mortality or combined cardiovascular events in those taking additional omega 3 fats (with significant statistical heterogeneity). Sensitivity analysis, retaining only studies at low risk of bias, reduced heterogeneity and again suggested no significant effect of omega 3 fats. Restricting analysis to trials increasing fish-based omega 3 fats, or those increasing short chain omega 3s, did not suggest significant effects on mortality or cardiovascular events in either group. Subgroup analysis by dietary advice or supplementation, baseline risk of CVD or omega 3 dose suggested no clear effects of these factors on primary outcomes. Neither RCTs nor cohorts suggested increased relative risk of cancers with higher omega 3 intake but estimates were imprecise so a clinically important effect could not be excluded.

REVIEWERS' CONCLUSIONS

It is not clear that dietary or supplemental omega 3 fats alter total mortality, combined cardiovascular events or cancers in people with, or at high risk of, cardiovascular disease or in the general population. There is no evidence we should advise people to stop taking rich sources of omega 3 fats, but further high quality trials are needed to confirm suggestions of a protective effect of omega 3 fats on cardiovascular health. There is no clear evidence that omega 3 fats differ in effectiveness according to fish or plant sources, dietary or supplemental sources, dose or presence of placebo.

Eicosapentaenoic acid inhibits vasopressin-activated Ca2+ influx and cell proliferation in rat aortic smooth muscle cell lines

The purpose of this study was to clarify how eicosapentaenoic acid (EPA), an omega-3 polyunsaturated fatty acid, modulates the vascular action of vasopressin in rat aortic smooth muscle cell lines. The effects of EPA on Ca2+ mobilization and DNA synthesis elicited by vasopressin were investigated and compared to those of Ca2+ channel blocking agents, by means of Ca2+ measurements and the incorporation of [3H]thymidine. Patch-clamp techniques were also employed. Vasopressin (100 nM) elicited an initial peak of intracellular Ca2+ ([Ca2+]i), followed by a sustained phase due to Ca2+ entry. Nifedipine or nicardipine (1 microM), a potent L-type Ca2+ channel blocker, partly inhibited the sustained phase, but La3+ completely abolished it. EPA (10 microM) also inhibited it even in the presence of nicardipine. Under voltage-clamp conditions with CsCl-internal solution, depolarizing pulses positive to -30 mV from a holding potential of -40 mV elicited a slow inward current. The inward current was blocked by La3+, nicardipine, and nifedipine (1 microM), suggesting that the inward current mainly consisted of the voltage-dependent L-type Ca2+ channel (ICa.L). EPA (1-30 microM) also inhibited ICa.L in a concentration-dependent manner. The inhibitory effect of EPA was observed at concentrations higher than 1 microM, and its half-maximal inhibitory concentration (IC50) was 7.6 microM. Vasopressin induced a long-lasting inward current at a holding potential of -40 mV. The vasopressin-induced current was considered as a non-selective cation current (Icat) with a reversal potential of approximately +0 mV. Both nifedipine and nicardipine (10 microM) failed to inhibit it significantly, but La3+ completely abolished Icat. EPA also inhibited vasopressin-induced Icat in a concentration-dependent manner; its IC50 value was 5.9 microM. Vasopressin (100 nM) stimulated [3H]thymidine incorporation. Exclusion of extracellular Ca2+ with EGTA or La3+ markedly inhibited it. EPA (3-30 microM) also inhibited the incorporation induced by vasopressin, while nifedipine and nicardipine (1 microM) only partly inhibited it. These results suggested that EPA, unlike nifedipine and nicardipine, inhibited vasopressin-induced Ca2+-entry and proliferation in rat vascular smooth muscle cells, where the inhibitory effects of EPA on Icat as well as ICa.L might be involved. Thus, EPA would exert hypotensive and antiatherosclerotic effects.

Influence of cellular incorporation of n-3 eicosapentaenoic acid on intracellular Ca2+ concentration and membrane potential in vascular smooth muscle cells

Long-term treatment with n-3 eicosapentaenoic acid (EPA) has been shown to exert hypotensive effects and have beneficial effects on atherosclerosis. To elucidate one of the underlying mechanisms of these effects, intracellular calcium concentration [Ca2+]i, and resting membrane potential were measured in rat vascular smooth muscle cells (A7r5 cell) treated with EPA, using Ca2+-sensitive dye fura-2 AM and the patch clamp technique. The alterations in fatty acid compositions of phospholipids and cell migration after treatment with EPA (30 microM) for 6 h-7 days were also examined. After treating cells with EPA, the EPA and DPA (docosapentaenoic acid) content of the phospholipid fraction (mol.%) increased in a time-dependent manner. Alternatively, arachidonic acid (AA) decreased, and then the ratio of EPA and AA (EPA/AA) increased significantly. The resting [Ca2+]i decreased from 170 +/- 46 nM (n = 16) in control cells to 123 +/- 29 nM (n = 16) in cells treated with EPA (30 microM) for 7 days. Vasopressin (100 nM), endothelin-1 (100 nM) and platelet-derived growth factor (PDGF 5 ng/ml) evoked an initial peak of [Ca2+]i, followed by a smaller sustained rise of [Ca2+]i in the presence of extracellular Ca2+. In EPA-treated cells, both the peak and the sustained rise of [Ca2+]i induced by these agonists decreased in comparison to the control cells. EPA treatment also decreased the transient [Ca2+]i rise evoked by these agonists in the absence of extracellular Ca2+. Under the current clamp condition, resting membrane potential was significantly higher in EPA-treated cells (-49.8 +/- 10.4 mV, n = 41) than in control cells (-44.6 +/- 7.4 mV, n = 41, P < 0.05), and the input resistance of the cell was lower in EPA-treated cells, while cell size and capacitance were not statistically different. In addition, long-term treatment with EPA for 7 days significantly inhibited PDGF-induced cell migration. These results suggest that cellular incorporation of n-3 eicosapentaenoic acid attenuates intracellular mechanisms related to changes of [Ca2+]i and affects membrane potential, thereby inhibiting migration of vascular smooth muscle cells. These actions of EPA may contribute to its vasorelaxant and antiatherosclerotic effects.

Inhibitory effects of omega-3 polyunsaturated fatty acids on receptor-mediated non-selective cation currents in rat A7r5 vascular smooth muscle cells

1. The effects of omega-3 polyunsaturated fatty acids on receptor-mediated non-selective cation current (Icat) and K+ current were investigated in aortic smooth muscle cells from foetal rat aorta (A7r5 cells). The whole-cell voltage clamp technique was employed. 2. With a K(+)-containing solution, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA, 30 microM) produced an outward current at a holding potential of -40 mV. This response was inhibited by tetraethylammonium (20 mM) or Cs+ in the patch pipette solution, and the reversal potential of the EPA-induced current followed the K+ equilibrium potential in a near Nernstian manner. 3. Under conditions with a Cs(+)-containing pipette solution, both vasopressin and endothelin-1 (100 nM) induced a long-lasting inward current at a holding potential of -60 mV. The reversal potential of these agonist-induced currents was about +0 mV, and was not significantly altered by the replacement of the extracellular or intracellular Cl+ concentration, suggesting that the induced current was a cation-selective current (Icat). 4. La3+ and Cd2+ (1 mM) completely abolished these agonist-induced Icat, but nifedipine (10 microM) failed to inhibit it significantly. 5. omega-3 polyunsaturated fatty acids (3-100 microM), EPA, DHA and docosapentaenoic acids (DPA), inhibited the agonist-induced Icat in a concentration-dependent manner. The potency of the inhibitory effect was EPA > DHA > DPA, and the half maximal inhibitory concentration (IC50) of EPA was about 7 microM. 6. Arachidonic and linoleic acids (10, 30 microM) showed a smaller inhibitory effect compared to omega-3 fatty acids. Also, oleic and stearic acids (30 microM) did not show a significant inhibitory effect on Icat. 7. A similar inhibitory action of EPA was observed when Icat was activated by intracellularly applied GTP gamma S in the absence of agonists, suggesting that the site of action of omega-3 fatty acids is not located on the receptor. 8. These results demonstrate that omega-3 polyunsaturated fatty acids can activate a K+ current and also effectively inhibit receptor-mediated non-selective cation currents in rat A7r5 vascular smooth muscle cells. Thus, the data suggest that omega-3 fatty acids may play an important role in the regulation of vascular tone.

Vascular relaxation to omega-3 fatty acids: comparison to sodium nitroprusside, nitroglycerin, papaverine, and D600

The vasorelaxant activity of the omega-3 fatty acids--docosahexaenoic (DHA) and eicosapentaenoic (EPA) acids--in comparison with other known vasodilators--sodium nitroprusside, nitroglycerin, papaverine, and D600--were studied in the isolated rat aorta. The relaxant responses of these vasodilators and fatty acids at concentrations of 1-100 microM were assessed in aortic rings contracted with norepinephrine (NE 10(-6) M) or with KCl (30 mM). Cyclic nucleotide enhancers (sodium nitroprusside, nitroglycerin, papaverine) were more effective in producing relaxation, regardless of the contractile mechanism, i.e., alpha-adrenoceptor stimulation or depolarization. In contrast, the omega-3 fatty acids produced augmented relaxation in NE-contracted vessels. Relaxations produced by DHA (15 +/- 2% to 45 +/- 10%) were similar to D600 (16 +/- 2% to 60 +/- 7%) in NE-contracted rings, but not in KCl contracted rings. The responses to D600 and DHA in KCl-contracted vessels were 79 +/- 2% to 104 +/- 3% and 5 +/- 1% to 21 +/- 3%, respectively. In another set of experiments, the effects of omega-3 fatty acids in the presence of albumin were examined; no significant differences in the induced relaxant responses were noted. These results suggest that the mechanisms of vascular relaxation, such as cyclic nucleotide elevation and calcium antagonism of potential-operated channels, are different from those induced by the omega-3 fatty acids.

Effect of omega-3 fatty acids on the vascular response to angiotensin in normotensive men

There is a widespread interest in fish oil as a dietary supplement and possible nonpharmacologic adjunct in the treatment of hypertension. The effect of dietary fish oil on blood pressure is controversial and the effect on systemic hemodynamics and regional vascular reactivity in humans is unknown. To address these questions, a double-blind, placebo-controlled, crossover study on the effect of dietary fish oil substitution was performed during a carefully controlled diet in 8 normotensive men. Systemic hemodynamics and the forearm vascular response to intrabrachial artery infusions of norepinephrine, phentolamine and angiotensin II were obtained. Compared with a safflower oil placebo, dietary fish oil had no effect on cardiac output (6.42 +/- 0.38 vs 6.87 +/- 0.28 liters/min, p = not significant) or 24-hour blood pressure (122/68 +/- 3/3 vs 122/68 +/- 3/2 mm Hg, p = not significant). The vascular response to norepinephrine and phentolamine was unchanged. Fish oil, however, significantly (p < 0.05) reduced forearm vascular resistance responses to angiotensin II. These changes were associated with a reduction in plasma triglycerides (64 +/- 9 vs 39 +/- 4 mg/dl, p = 0.02) and an increase in plasma eicosapentaenoic acid levels (0.51 +/- 0.25 vs 1.72 +/- 0.35 microM, p < 0.05). Substitution of a moderate dose of fish oil for fat in a "Western diet" selectively attenuates the vascular response to angiotensin independently of changes in alpha-adrenergic vasoconstriction or systemic hemodynamics.

The absorption of fish oils and concentrates

Both preventive and curative therapies have created a considerable demand for eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids. The most common sources for omega 3 fatty acids are fish oil. The concentrations of EPA and DHA in commercial oils, after modest enrichment, reach about 300 mg/g; alternative technologies can produce reasonably priced fish oils containing 400 or even 500 mg/g of omega 3 acids. When the acids are liberated from the glycerides, concentrates of ethyl esters or free acids with 65 to 70% total omega 3 fatty acids (at least 50% EPA + DHA) are readily prepared. Difficulties have arisen because most clinical trials have used fish oils of unspecified composition, and some trials are now based on either ethyl esters or free acids. There are at least three different, but not mutually exclusive, absorption routes in humans, namely the preduodenal route, the lymphatic route via chylomicrons, and the route via the portal vein to the liver. This makes it difficult to compare results. The difficulty in obtaining dose-related clinical data may in part be due to the form in which the omega 3 acids are offered and due in part to the natural presence of these fatty acids in the body. The nontriglyceride forms, especially the free acids, have been advocated for standardization of trials to facilitate interlaboratory comparisons.

Effects of omega-3, omega-6 and omega-9 fatty acids on vascular smooth muscle tone

The comparative effects of omega-3, omega-6 and omega-9 fatty acids on vascular smooth muscle tone were investigated. Docosahexaenoic acid (1-255 microM) and eicosapentaenoic acid (31-255 microM) inhibited phenylephrine-induced contractions, (8-63%) and (20-65%), respectively, which were not altered by indomethacin, NDGA, or by removal of the endothelium. Linoleic acid (18:2n6) and arachidonic acid (20:4n6) also induced significant relaxation. Therefore, fatty acid-induced relaxation of the rat aorta is specific to polyunsaturated fatty acids, 20:5n3, 22:6n3, 18:2n6 and 20:4n6.

The paradoxical effects of dietary fish oil on blood pressure

Dietary fish oil supplementation has received considerable interest as a non-pharmacological adjuvant in the treatment of several diseases, especially hypertension. However, epidemiological, clinical, and experimental evidence conflict. A hypothesis is proposed that fish oil, may have a variable effect on vascular reactivity and consequently, blood pressure. A mechanism is proposed and reasons for the variation in the literature suggested. On the basis of this analysis a potentially adverse effect of dietary fish oil on blood pressure in some individuals is suggested.

Resistance of the renal biosynthesis of prostaglandin E2 to the inhibitory effect of indomethacin in the rat in vivo

Our recent observation that the chronic administration of indomethacin (3.0 mg.kg-1.day) to hypertensive rats, while profoundly inhibiting the urinary excretion of 6-oxo-PGF1 alpha, dinor-6-oxo-PGF1 alpha and thromboxane B2, failed to reduce the urinary levels of PGE2, prompted us to study in more details the influence of indomethacin and of meclofenamate on the urinary excretion of prostaglandins in normal rats. A dose of 1.5 mg.kg-1 of indomethacin administered intraperitoneally was sufficient to cause a 70-75% reduction in the urinary excretion of dinor-6-oxo-PGF1 alpha and of 6-oxo-PGF1 alpha for a period of at least 12 hours. Doses of indomethacin lower than 2.5 mg.kg-1.12h beta 1 or a dose of meclofenamate equal to 5 mg.kg-1.12h beta 1 did not influence the urinary excretion of PGE2. Doses of indomethacin equal to or higher than 2.5 mg.kg-1 were needed to obtain a 50% reduction in the urinary levels of PGE2 for a period of 10-14 h. During these experiments, no circadian rhythm for the urinary excretion of 6-oxo-PGF1 alpha and of dinor-6-oxo-PGF1 alpha could be observed whereas the urine volume and the urinary excretion of PGE2 were found to be greater at night than during the day.(ABSTRACT TRUNCATED AT 250 WORDS)

Prostanoids and aldosterone-induced mild experimental hypertension in rats

The goal of this study was to determine the role of prostanoids in a new model of mineralocorticoid-dependent hypertension induced by the subcutaneous infusion of aldosterone (1 micrograms/hr) to normal male Sprague-Dawley rats. This regimen caused a mild and gradual increase in systolic pressure over a period of 4 weeks (113 +/- 1 vs. 137 +/- 3 mm Hg) and was associated with an increase in the in vivo formation of prostaglandins I2 and E2 and of thromboxane A2 in the kidney. High sodium intake induced a fall in the urinary levels of prostaglandin E2 and a rise in the arterial pressure of control rats (126 +/- 1 vs. 113 +/- 1 mm Hg) but did not influence aldosterone-induced hypertension. Indomethacin (3.0 mg/kg/day) caused a profound inhibition of the in vivo synthesis of prostaglandin I2 and thromboxane A2 without modifying the renal production of prostaglandin E2. Although indomethacin exerted no effect on aldosterone-induced hypertension in rats fed a normal diet, it caused a further rise in systolic pressure in aldosterone-treated rats fed a high sodium diet (157 +/- 6 vs. 140 +/- 4 mm Hg). The results of this study in a model of aldosterone-induced mild hypertension in the rat indicate that 1) aldosterone exerts a stimulatory effect on the renal synthesis of prostanoid, particularly prostaglandin E2; 2) thromboxane A2 and prostaglandin I2 do not seem to play a role in aldosterone-induced hypertension under conditions of normal dietary salt intake, whereas the role of prostaglandin E2 is unclear; 3) there is enough sodium in a normal diet to allow for the maximal expression of the hypertensive effect of aldosterone; 4) prostaglandin I2 seems to play a significant role in modulating the cardiovascular impact of a high sodium diet in aldosterone-treated rats; and 5) the renal biosynthesis of prostaglandin E2 is particularly resistant to the inhibitory effect of indomethacin in vivo.