Antithrombic and anti-atherogenic effects of partially defatted flaxseed meal using a laser-induced thrombosis test in apolipoprotein E and low-density lipoprotein receptor deficient mice

Hypocholesterolemic Efficacy of Secoisolariciresinol Diglucoside and Its Polymer in Rat

Hypercholesterolemia is a risk factor for cardiovascular disease. Conventional treatment methods include lifestyle changes and pharmaceutical interventions, but recently Health Canada approved a health claim for whole ground flaxseed as an alternative treatment for hypercholesterolemia. The literature suggests flaxseed lignans are responsible for the cholesterol-reducing effects of flaxseed. In this study, 96.1% secoisolariciresinol diglucoside (SDG) and a 50% SDG enriched polymer (SDG polymer) were investigated as treatments for hypercholesterolemia in rats. Wistar female rats were fed a 1% high-cholesterol diet for a one-week acclimatization prior to a 23-day intervention with enriched SDG or SDG polymer. A reduction in body weight normalized liver weight was observed in rats treated with enriched SDG when compared to the controls. Both enriched SDG (96.1%) and SDG polymer reduced serum triacylglycerol (19% and 15%, respectively) and increased high-density lipoprotein cholesterol (15% and 24%, respectively). Histopathologic analyses revealed lipid-lowering effects of either enriched SDG or SDG polymer along with lower steatosis scores and nonalcoholic fatty liver disease activity. Furthermore, the lack of statistical significance between SDG and SDG polymer treatment groups suggests that SDG polymer may be a potential alternative to enriched SDG for hypercholesterolemia with similar efficacy but lower cost.

Secoisolariciresinol Diglucoside of Flaxseed and Its Metabolites: Biosynthesis and Potential for Nutraceuticals

Secoisolariciresinol diglucoside (SDG), found mainly in flaxseed, is one of the essential lignans. SDG, as well as the beneficial fatty acid composition and high fiber content, has made flaxseed an important source of functional food or nutraceutical ingredients. Various studies have shown that SDG offers several health benefits, including protective effects against cardiovascular diseases, diabetes, cancer, and mental stress. These health benefits have been attributed to the antioxidant properties of SDG. Additionally, SDG metabolites, namely mammalian lignans, enterodiol and enterolactone, have shown promising effects against cancer. Therefore, understanding the biosynthetic pathway of SDG and its molecular mechanisms is a key to enable the production of new flaxseed cultivars rich in nutraceutical content. The present review highlights studies on the different health benefits of SDG, as well as lignan biosynthesis in flaxseed and genes involved in the biosynthetic pathway. Since SDG, the predominant lignan in flaxseed, is a glycosylated lignan, we also focus on studies investigating the genes involved in secoisolariciresinol glycosylation. These genes can be used to produce new cultivars with a novel level of glycosylation or lignan composition to maximize the yields of lignans with a therapeutic or protective potential.

Flaxseed: its bioactive components and their cardiovascular benefits

Cardiovascular disease remains the leading cause of mortality and morbidity worldwide. The inclusion of functional foods and natural health products in the diet are gaining increasing recognition as integral components of lifestyle changes in the fight against cardiovascular disease. Several preclinical and clinical studies have shown the beneficial cardiovascular effects of dietary supplementation with flaxseed. The cardiovascular effects of dietary flaxseed have included an antihypertensive action, antiatherogenic effects, a lowering of cholesterol, an anti-inflammatory action, and an inhibition of arrhythmias. Its enrichment in the ω-3 fatty acid α-linolenic acid and the antioxidant lignan secoisolariciresinol diglucoside as well as its high fiber content have been implicated primarily in these beneficial cardiovascular actions. Although not as well recognized, flaxseed is also composed of other potential bioactive compounds such as proteins, cyclolinopeptides, and cyanogenic glycosides, which may also produce biological actions. These compounds could also be responsible for the cardiovascular effects of flaxseed. This article will not only summarize the cardiovascular effects of dietary supplementation with flaxseed but also review its bioactive compounds in terms of their properties, biological effects, and proposed mechanisms of action. It will also discuss promising research directions for the future to identify additional health-related benefits of dietary flaxseed.

Effects of abomasal infusion of flaxseed (Linum usitatissimum) oil on microbial β-glucuronidase activity and concentration of the mammalian lignan enterolactone in ruminal fluid, plasma, urine and milk of dairy cows

Ruminal microbiota plays an important role in the conversion of plant lignans into mammalian lignans. The main mammalian lignan present in the milk of dairy cows fed flax products is enterolactone (EL). The objectives of the present study were to investigate the effects of abomasal infusion of flax oil on the metabolism of flax lignans and concentrations of EL in biological fluids of dairy cows. A total of six rumen-cannulated dairy cows were assigned within a 2 × 3 factorial arrangement of six treatments utilising flax hulls (0 and 15·9 % of DM) and abomasal infusion of flax oil (0, 250 and 500 g/d). There were six periods of 21 d each. Samples were collected during the last 7 d of each period and subjected to chemical analysis. Flax hull supplementation increased concentrations of EL in ruminal fluid, plasma, urine and milk, while flax oil infusion had no effect. Post-feeding, β-glucuronidase activity in the ruminal fluid of cows infused with 250 g flax oil was significantly lower for cows fed hulls than for those fed the control diet. The present study demonstrated that the presence of a rich source of n-3 fatty acids such as flax oil in the small intestine does not interfere with the absorption of the mammalian lignan EL and that lower ruminal β-glucuronidase activity had no effect on the conversion of flax lignans into EL in the rumen of dairy cows.

The α-linolenic acid content of flaxseed can prevent the atherogenic effects of dietary trans fat

Dietary intake of industrially hydrogenated trans fatty acids (TFA) has been associated with coronary heart disease. Dietary flaxseed can inhibit atherosclerosis induced by dietary cholesterol. The aim of this study was to determine whether supplementing the diet with flaxseed could protect against atherosclerosis induced by a diet enriched in TFA. Low-density lipoprotein receptor-deficient (LDLr−/−) mice were fed 1 of 14 experimental diets for 14 wk containing one of two fat sources [regular (pork/soy) or trans fat] at two concentrations (4 or 8%) and supplemented with or without dietary cholesterol (2%), whole ground flaxseed, or one of the components of flaxseed [α-linolenic acid (ALA), defatted fiber, or lignan]. Adding flaxseed to the diet partially mitigated the rise in circulating cholesterol levels induced by the cholesterol-enriched diet. Atherosclerosis was stimulated by TFA and/or cholesterol. Including milled flaxseed to an atherogenic diet significantly reduced atherosclerosis compared with the groups that consumed cholesterol and/or TFA. ALA was the only component within flaxseed that could inhibit the atherogenic action of cholesterol and/or TFA on its own. Dietary flaxseed protects against atherosclerotic development induced by TFA and cholesterol feeding through its content of ALA.

Release of angiotensin I-converting enzyme inhibitory peptides from flaxseed (Linum usitatissimum L.) protein under simulated gastrointestinal digestion

The scope of this study was to determine the ability of flaxseed (Linum usitatissimum L.) proteins to release angiotensin I-converting enzyme inhibitory (ACEI) peptides during simulated gastrointestinal (GI) digestion using a static (SM; no absorption in the intestinal phase) and a dynamic model (DM; simultaneous absorption of digested products in the intestinal phase via passive diffusion). Gastric and gastric + small intestinal digests of flaxseed proteins of both models possessed ACEI activity. The ACEI activity of the gastric + small intestinal digest in the DM (IC(50) unabsorbed, 0.05 mg N/mL; IC(50) absorbed, 0.04 mg N/mL) was significantly higher (p < 0.05) than that of the SM (IC(50), 0.39 mg N/mL). Two peptides, a pentapeptide (Trp-Asn-Ile/Leu-Asn-Ala) and a hexapeptide (Asn-Ile/Leu-Asp-Thr-Asp-Ile/Leu), were identified in the most active ACEI fraction (0.5-1 kDa) of the absorbable flaxseed protein digest by de novo sequencing.

Dietary lignans: physiology and potential for cardiovascular disease risk reduction

The present review of the literature on lignan physiology and lignan intervention and epidemiological studies was conducted to determine if lignans decrease the risks of cardiovascular disease in Western populations. Five intervention studies using flaxseed lignan supplements indicated beneficial associations with C-reactive protein, and a meta-analysis that included these studies also suggested lignans have a lowering effect on plasma total and low-density lipoprotein cholesterol. Three intervention studies using sesamin supplements indicated possible lipid- and blood pressure-lowering associations. Eleven human observational epidemiological studies examined dietary intakes of lignans in relation to cardiovascular disease risk. Five showed decreased risk with either increasing dietary intakes of lignans or increased levels of serum enterolactone (an enterolignan used as a biomarker of lignan intake), five studies were of borderline significance, and one was null. The associations between lignans and decreased risk of cardiovascular disease are promising, but they are yet not well established, perhaps due to low lignan intakes in habitual Western diets. At the higher doses used in intervention studies, associations were more evident.

Health effects with consumption of the flax lignan secoisolariciresinol diglucoside

Flaxseed is the richest source of the lignan secoisolariciresinol diglucoside (SDG). After ingestion, SDG is converted to secoisolariciresinol, which is further metabolised to the mammalian lignans enterodiol and enterolactone. A growing body of evidence suggests that SDG metabolites may provide health benefits due to their weak oestrogenic or anti-oestrogenic effects, antioxidant activity, ability to induce phase 2 proteins and/or inhibit the activity of certain enzymes, or by mechanisms yet unidentified. Human and animal studies identify the benefits of SDG consumption. SDG metabolites may protect against CVD and the metabolic syndrome by reducing lipid and glucose concentrations, lowering blood pressure, and decreasing oxidative stress and inflammation. Flax lignans may also reduce cancer risk by preventing pre-cancerous cellular changes and by reducing angiogenesis and metastasis. Thus, dietary SDG has the potential to decrease the incidence of several chronic diseases that result in significant morbidity and mortality in industrialised countries. The available literature, though, makes it difficult to clearly identify SDG health effects because of the wide variability in study methods. However, the current evidence suggests that a dose of at least 500 mg SDG/d for approximately 8 weeks is needed to observe positive effects on cardiovascular risk factors in human patients. Flaxseed and its lignan extracts appear to be safe for most adult populations, though animal studies suggest that pregnant women should limit their exposure. The present review discusses the potential health benefits of SDG in humans, with supporting evidence from animal studies, and offers suggestions for future research.

Experimental and clinical research findings on the cardiovascular benefits of consuming flaxseed

Functional foods and nutraceuticals are becoming popular alternatives to pharmacological treatments by providing health benefits and (or) reducing the risk of chronic diseases. Flaxseed is a rich source of 3 components with demonstrated cardioprotective effects: the omega-3 fatty acid α-linolenic acid (ALA), dietary fibre, and phytoestrogen lignans. Multiple clinical dietary intervention trials report that consuming flaxseed daily can modestly reduce circulating total cholesterol (TC) by 6%–11% and low-density lipoprotein (LDL) cholesterol by 9%–18% in normolipemic humans and by 5%–17% for TC and 4%–10% for LDL cholesterol in hypercholesterolemic patients, as well as lower various markers associated with atherosclerotic cardiovascular disease in humans. Evidence to date suggests that the dietary fibre and (or) lignan content of flaxseed provides the hypocholesterolemic action. The omega-3 ALA found in the flaxseed oil fraction also contributes to the antiatherogenic effects of flaxseed via anti-inflammatory and antiproliferative mechanisms. Dietary flaxseed may also protect against ischemic heart disease by improving vascular relaxation responses and by inhibiting the incidence of ventricular fibrillation.

Dietary flaxseed lignan extract lowers plasma cholesterol and glucose concentrations in hypercholesterolaemic subjects

Lignans, derived from flaxseed, are phyto-oestrogens being increasingly studied for their health benefits. An 8-week, randomised, double-blind, placebo-controlled study was conducted in fifty-five hypercholesterolaemic subjects, using treatments of 0 (placebo), 300 or 600 mg/d of dietary secoisolariciresinol diglucoside (SDG) from flaxseed extract to determine the effect on plasma lipids and fasting glucose levels. Significant treatment effects were achieved (P < 0.05 to < 0.001) for the decrease of total cholesterol (TC), LDL-cholesterol (LDL-C) and glucose concentrations, as well as their percentage decrease from baseline. At weeks 6 and 8 in the 600 mg SDG group, the decreases of TC and LDL-C concentrations were in the range from 22.0 to 24.38 % respectively (all P < 0.005 compared with placebo). For the 300 mg SDG group, only significant differences from baseline were observed for decreases of TC and LDL-C. A substantial effect on lowering concentrations of fasting plasma glucose was also noted in the 600 mg SDG group at weeks 6 and 8, especially in the subjects with baseline glucose concentrations > or = 5.83 mmol/l (lowered 25.56 and 24.96 %; P = 0.015 and P = 0.012 compared with placebo, respectively). Plasma concentrations of secoisolariciresinol (SECO), enterodiol (ED) and enterolactone were all significantly raised in the groups supplemented with flaxseed lignan. The observed cholesterol-lowering values were correlated with the concentrations of plasma SECO and ED (r 0.128-0.302; P < 0.05 to < 0.001). In conclusion, dietary flaxseed lignan extract decreased plasma cholesterol and glucose concentrations in a dose-dependent manner.

Mechanism of the Antithrombotic Effect of Dietary Diacylglycerol in Atherogenic Mice

INTRODUCTION

We have shown earlier that diacylglycerol (DAG) but not triacylglycerol (TAG) inhibited thrombus formation. The aim of the present study was to investigate the mechanism of this antithrombotic effect of DAG.

MATERIALS AND METHODS

Four different diets, the (1) Western-style high-fat diet (HFD) containing 20% lipid and 0.05% cholesterol (w/w), (2) TAG-rich and (3) DAG-rich HFDs containing 20% lipid and 0.05% cholesterol, but all lipid replaced by TAG or DAG oil with very similar fatty acid composition and the (4) Japanese-style low-fat diet (LFD) containing 7% oil but no cholesterol were given to apolipoprotein E and low-density lipoprotein (LDL) receptor double-deficient mice. Atherogenicity was assessed by morphology, mapping the whole aorta and measuring the total area of lipid-stained lesions. Endothelial function was measured by the flow-mediated vasodilation test. Platelet reactivity was assessed from native blood sample by a shear-induced platelet function test (hemostatometry). Serum lipoprotein profile was measured by HPLC.

RESULTS

Both the Western-style and the TAG-rich HFDs have accelerated atherosclerosis. In contrast, DAG-rich HFD inhibited the atherosclerotic process to an extent comparable with the Japanese-style LFD. There was no significant difference in platelet and coagulant activity between the studied diet groups. DAG-rich but not the TAG-rich HFD significantly suppressed serum LDL cholesterol level.

CONCLUSIONS

The present findings suggest that the mechanism of antithrombotic and anti-atherogenic effect of DAG may involve the protection of the vascular endothelium from injury and lowered serum LDL cholesterol.

Effects of dietary flaxseed on vascular contractile function and atherosclerosis during prolonged hypercholesterolemia in rabbits

Dietary flaxseed has significant anti-atherogenic effects. However, the limits of this action and its effects on vascular contractile function are not known. We evaluated the effects of flaxseed supplementation on atherosclerosis and vascular function under prolonged hypercholesterolemic conditions in New Zealand White rabbits assigned to one of four groups for 6, 8, or 16 wk of feeding: regular diet (RG), 10% flaxseed-supplemented diet (FX), 0.5% cholesterol-supplemented diet (CH), and 0.5% cholesterol- and 10% flaxseed-supplemented diet (CF). Cholesterol feeding resulted in elevated plasma cholesterol levels and the development of atherosclerosis. The CF group had significantly less atherosclerotic lesions in the aorta and carotid arteries after 6 and 8 wk than the CH animals. However, the anti-atherogenic effect of flaxseed supplementation was completely attenuated by 16 wk. Maximal tension induced in aortic rings either by KCl or norepinephrine was not impaired by dietary cholesterol until 16 wk. This functional impairment was not prevented by including flaxseed in the high-cholesterol diet. Aortic rings from the cholesterol-fed rabbits exhibited an impaired relaxation response to acetylcholine at all time points examined. Including flaxseed in the high-cholesterol diet completely normalized the relaxation response at 6 and 8 wk and partially restored it at 16 wk. No significant changes in the relaxation response induced by sodium nitroprusside were observed in any of the groups. In summary, dietary flaxseed is a valuable strategy to limit cholesterol-induced atherogenesis as well as abnormalities in endothelial-dependent vasorelaxation. However, these beneficial effects were attenuated during prolonged hypercholesterolemic conditions.

Effect of dietary vegetable and animal proteins on atherothrombosis in mice

OBJECTIVE

It is believed that vegetable and fish, but not animal, proteins prevent thrombosis. The present study compared the effect of long-term intake of purified vegetable and animal proteins (casein, pork, egg white, chicken, white and red fish, soybean, and potato) and powders from whole vegetable and animal meats (soybean, pork, chicken, and horse mackerel) on thrombotic tendency.

METHODS

Western-style high-fat diets with various proteins were given to mice deficient in apolipoprotein-E and low-density lipoprotein receptor for 8 or 12 wk. Thrombotic tendency was assessed by a laser-induced thrombosis test, severity of atherosclerosis was assessed by morphometric analysis of the aortic lesions, and reactivity of platelets was measured by a shear-induced platelet function test.

RESULTS

There was no difference in thrombotic tendency between the vegetable and animal protein diets with the exception of pork protein, which showed a prothrombotic effect. The latter was not observed in animals kept on a high-protein diet. Thrombotic tendency was not affected by preparation of dietary powders from whole pork, chicken, or horse mackerel meats and casein (control), all of which contained the same percentages of protein and lipid. In contrast, soybean powder showed an antithrombotic effect, which was mainly due to an inhibition of atherogenesis rather than to platelet inhibition.

CONCLUSION

Neither the purified animal nor the vegetable protein diet affected thrombotic tendency. Soybean powder inhibited atherothrombosis mainly by inhibiting the atherosclerotic process.

Endothelial dysfunction precedes atherosclerotic lesions and platelet activation in high fat diet-induced prothrombotic state

INTRODUCTION

Earlier we have demonstrated a prothrombotic state in spontaneously atherogenic rodents kept on Western-style high fat diet. The aim of the present study was to investigate the cellular mechanism of such prothrombotic state.

MATERIALS AND METHODS

Two kinds of diets, Western-style high fat diet containing 20% fat (w/w) and 0.05% cholesterol (w/w) and low fat diet containing 7% fat without cholesterol based on AIN93G, were added to diet-sensitive apolipoprotein E and low-density lipoprotein receptor double deficient male mice for 12 or 18 weeks from 6 weeks of age. Atherosclerosis was assessed by morphometry of the aortic wall or lipid-stained lesions. Endothelial function was measured by flow-mediated vasodilation (FMV) of the femoral artery. Platelet reactivity was measured ex vivo by a shear-induced platelet aggregation test.

RESULTS AND CONCLUSIONS

12 weeks feeding of mice with high fat diet significantly impaired FMV, as compared with mice fed with low fat diet (P<0.05). In contrast, there was no significant difference in the lipid-stained areas and in the reactivity of platelets between the two groups. 18 weeks feeding with high fat diet significantly impaired FMV (P<0.05) and enhanced both lipid-stained areas (P<0.05) and platelet reactivity (P<0.01). These findings show that in high fat diet-induced prothrombotic state, endothelial dysfunction precedes both the morphologically detectable lesions and the enhancement of platelet reactivity.

Dietary diacylglycerol extenuates arterial thrombosis in apoE and LDLR deficient mice

INTRODUCTION

Prevention of arterial thrombotic diseases has high priority in developed countries. An appropriate diet is thought to be the best way to prevent or reduce the risk of mortality from such diseases. The aim of the present study was to evaluate the effect of diacylglycerol (DAG)-rich diets on arterial thrombosis.

MATERIAL AND METHODS

Diet-sensitive congenital apolipoprotein E (ApoE) and LDL receptor (LDLR) double deficient mice were used. Thrombosis was assessed by the rate and extent of thrombus formation in the carotid artery of mice after laser irradiation. Plasma total cholesterol and triglyceride levels were measured by enzymatic assays. Four kinds of diets were used: high fat (Western-style) diet contained 20% fat (w/w) and 0.05% cholesterol (w/w); the TAG-rich and the DAG-rich high fat diet contained 20% TAG or DAG oil (w/w) with very similar fatty acid composition and 0.05% cholesterol ; Low fat (Japanese-style) diet contained 7% fat, without cholesterol. These diets were on the basis of AIN93G and were given to mice for 8 weeks from 6 weeks of age.

RESULTS

Western-style high fat and TAG-rich high fat diets significantly increased thrombogenicity compared with low fat diet. DAG-rich high fat diet showed the lowest value, and the extent of thrombogenicity was equivalent to the low fat diet group. Fasting plasma total cholesterol level of DAG-rich high fat and low fat diet groups were significantly lower than that of TAG-rich high fat and high fat diet groups. Fasting plasma triglyceride levels in DAG-rich high fat diet group were significantly lower than in the TAG-rich high fat diet group.

CONCLUSIONS

Dietary DAG but not TAG oil extenuates arterial thrombus formation. The mechanism of this effect is unclear and further investigated.

Adiponectin acts as an endogenous antithrombotic factor

OBJECTIVE

Obesity is a common risk factor in insulin resistance and cardiovascular diseases. Although hypoadiponectinemia is associated with obesity-related metabolic and vascular diseases, the role of adiponectin in thrombosis remains elusive.

METHODS AND RESULTS

We investigated platelet thrombus formation in adiponectin knockout (APN-KO) male mice (8 to 12 weeks old) fed on a normal diet. There was no significant difference in platelet counts or coagulation parameters between wild-type (WT) and APN-KO mice. However, APN-KO mice showed an accelerated thrombus formation on carotid arterial injury with a He-Ne laser (total thrombus volume: 13.36+/-4.25 x 10(7) arbitrary units for APN-KO and 6.74+/-2.87x10(7) arbitrary units for WT; n=10; P<0.01). Adenovirus-mediated supplementation of adiponectin attenuated the enhanced thrombus formation. In vitro thrombus formation on a type I collagen at a shear rate of 250 s(-1), as well as platelet aggregation induced by low concentrations of agonists, was enhanced in APN-KO mice, and recombinant adiponectin inhibited the enhanced platelet aggregation. In WT mice, adenovirus-mediated overexpression of adiponectin additionally attenuated thrombus formation.

CONCLUSIONS

Adiponectin deficiency leads to enhanced thrombus formation and platelet aggregation. The present study reveals a new role of adiponectin as an endogenous antithrombotic factor.