Combination of dietary phytosterols plus niacin or fenofibrate: effects on lipid profile and atherosclerosis in apo E-KO mice

Hypolipidemic activity of phytochemical combinations: A mechanistic review of preclinical and clinical studies

Hyperlipidemia, a condition characterized by elevated levels of lipids in the blood, poses a significant risk factor for various health disorders, notably cardiovascular diseases. Phytochemical compounds are promising alternatives to the current lipid-lowering drugs, which cause many undesirable effects. Based on in vivo and clinical studies, combining phytochemicals with other phytochemicals, prebiotics, and probiotics and their encapsulation in nanoparticles is more safe and effective for managing hyperlipidemia than monotherapy. To this end, the results obtained and the mechanisms of action of these combinations were examined in detail in this review.

Maternal hypercholesterolemia enhances oxysterol concentration in mothers and newly weaned offspring but is attenuated by maternal phytosterol supplementation

In hypercholesterolemic pregnancies, the maternal environment is characterized by excessive levels of atherogenic lipids that may increase cardiovascular disease risk in mothers and their offspring. We examined the influence of maternal hypercholesterolemia and phytosterol (PS) intervention on the concentration and metabolism of oxysterols, bioactive oxygenated cholesterol derivatives that regulate arterial health and lesion progression, in mothers and their newly weaned offspring. Twenty-one female apoE^-/- mice were randomly assigned to three different diets throughout gestation and lactation: (1) chow, (2) high cholesterol (CH; 0.15%) and (3) CH with added PS (2%, CH/PS). At the end of the lactation period, mothers and pups were euthanized for serum and hepatic oxysterol analyses, hepatic transcriptional profiling of hepatic sterol regulatory targets and atherosclerosis. Hypercholesterolemic dams and their pups demonstrated increased (P˂.05) serum oxysterols [including 24 hydroxycholesterol (HC), 25HC, 27HC, 7αHC, 7βHC and 7 ketocholesterol)] compared with the chow group that were normalized by maternal PS supplementation. Hepatic oxysterol concentrations followed a similar pattern of response in mothers but were not altered in newly weaned pups. Hepatic mRNA expression suggested a pattern of enhanced abca1/g1 high-density-lipoprotein-mediated efflux but a reduction in biliary abcg5/g8 export in both dams and their pups. Although arterial lesions were not apparent in newly weaned pups, CH dams demonstrated enhanced atherosclerosis that was reduced upon PS intervention. These results demonstrate that offspring from hypercholesterolemic pregnancies have enhanced circulating oxysterol concentrations and highlight the potential utility of PS as a lipid-lowering option during hypercholesterolemic pregnancies for which there are currently limited options.

Nutraceutical therapies for atherosclerosis

Atherosclerosis is a chronic inflammatory disease affecting large and medium arteries and is considered to be a major underlying cause of cardiovascular disease (CVD). Although the development of pharmacotherapies to treat CVD has contributed to a decline in cardiac mortality in the past few decades, CVD is estimated to be the cause of one-third of deaths globally. Nutraceuticals are natural nutritional compounds that are beneficial for the prevention or treatment of disease and, therefore, are a possible therapeutic avenue for the treatment of atherosclerosis. The purpose of this Review is to highlight potential nutraceuticals for use as antiatherogenic therapies with evidence from in vitro and in vivo studies. Furthermore, the current evidence from observational and randomized clinical studies into the role of nutraceuticals in preventing atherosclerosis in humans will also be discussed.

Enzymatic synthesis of phytosteryl docosahexaneates and evaluation of their anti-atherogenic effects in apo-E deficient mice

Phytosterols have attracted much attention in recent years due to their health benefits, such as cholesterol lowering, anti-inflammatory, anti-atherogenicity, and anti-cancer potential. Docosahexaenoic acid (DHA) has been demonstrated to possess cardioprotective and immune-enhancing effects. Esterification of phytosterols with DHA may render improved physiochemical properties such as solubility, miscibility, oxidative stability and hence bioactivity and bioavailability. Thus, phytosteryl docosahexaneates (PS-DHA) may offer both the benefits of phytosterols and DHA, possibly in a synergistic manner. Here, we describe a method for enzymatic synthesis of phytosteryl docosahexaneates and evaluation of metabolic and cardiovascular benefits in apo-E deficient (apo E-KO) mice. The structures of phytosteryl docosahexaneates were confirmed by infrared (IR) and high performance liquid chromatography-mass spectrometry (HPLC-MS) using both normal and reverse phase chromatography. Apo E-KO mice were fed with an atherogenic diet containing 2% (w/w) PS-DHA for 7 weeks. Plasma lipid levels and the extent and complexity of atherosclerotic lesions were examined and compared with those in the control group. The PS-DHA-treated mice had significantly lower plasma cholesterol levels and three times smaller atherosclerotic lesions in the aortic roots. This pilot study suggests cardiovascular benefits for PS-DHA. Further experimental and clinical studies are needed to confirm such benefits of PS-DHA.

High dietary niacin may increase prostaglandin formation but does not increase tumor formation in ApcMin/+ mice

High doses of niacin (nicotinic acid) used to treat dyslipidemias cause flushing, due to high levels of prostaglandin D(2) (PGD(2)). GPR109A, a G-protein coupled receptor, triggers the flushing in the skin. In addition to boosting PGD(2), niacin binding to GPR109A activates the entire prostanoid cascade. We found that GPR109A occurs throughout the gastrointestinal tract. Mice that alternated between a 1% niacin diet and a control diet had higher urinary prostaglandin E(2) (PGE(2)) metabolite levels when on niacin (2.8-fold increase; 95% confidence interval, 1.8-3.9). PGE(2) promotes tumors in the intestines, whereas PGD(2) may have an opposite effect, on the basis of our report showing that transgenic hematopoietic prostaglandin D synthase suppresses intestinal adenomas in Apc(Min/+) mice. To determine if either tumor growth or tumor suppression prevails, we fed Apc(Min/+) mice a 1% niacin diet and assessed tumor development. A 1% niacin diet did not affect the number of tumors scored histologically in Apc(Min/+) mice at 14 wk (33 mice on niacin, 33 controls). Although niacin stimulates production of various prostaglandins, our results support an interpretation that very high intakes of niacin are safe in relation to intestinal tumors in this model.

Beyond cholesterol-lowering effects of plant sterols: clinical and experimental evidence of anti-inflammatory properties

Inflammation is a strong risk factor for cardiovascular disease. Dietary plant sterols are known to reduce plasma cholesterol levels and thereby reduce cardiovascular risk. Recent observations from animal and human studies have demonstrated anti-inflammatory effects of phytosterols. For example, several animal and human studies report reductions in the levels of proinflammatory cytokines, including C-reactive protein, after consumption of dietary plant sterols. Although the cholesterol-lowering effects of phytosterols in humans are well documented, studies on the effects of phytosterols on inflammatory markers have produced inconsistent results. This review summarizes and discusses findings from recent animal and human studies with regard to the potential anti-inflammatory effects of dietary phytosterols. Findings on the effects of plant sterols on inflammation remain limited and confounding. Future research using better-designed and well-controlled laboratory studies and clinical trials are needed to fully understand the mechanisms through which phytosterols influence inflammation. Additional well-designed placebo-controlled studies are needed to better understand how and to what extent dietary plant sterols may modify the immune system and the production of inflammatory markers.

Lack of evidence for antiatherogenic effects of wheat bran or corn bran in apolipoprotein E-knockout mice

Epidemiological studies have suggested that intake of whole grains is inversely associated with coronary artery disease. The mechanisms, however, are not completely clear. We tested the hypothesis that intake of wheat bran or corn bran would (1) increase the plasma concentration of phenolic antioxidants and (2) reduce atherosclerosis in apo E-knockout mice. Apo E-knockout (E-KO) mice were fed for 18 weeks with a 0.1% cholesterol-supplemented diet in the absence of grain brans or the presence of 1.7% yellow dent corn bran or 3.3% hard red spring wheat bran. The concentration of antioxidant ferulic acid in plasma and urine was measured by HPLC to monitor the bioavailability of grain phenolics. Plasma lipoprotein profiles were determined by a combination of HPLC and online enzymatic methods. Urinary 15-isoprostane F(2t), an in vivo LDL oxidation biomarker, and atherosclerotic lesions were analyzed by ELISA and histological methods, respectively. Dietary supplementation with corn or wheat bran resulted in a 4- and 24-fold increase, respectively, in urinary excretion of ferulic acid. The urinary recovery rate of ferulic acid from the two brans in apo E-KO mice was approximately 1.9-2.9%. Dietary corn bran but not wheat bran also significantly increased the concentration of total ferulic acid in plasma. Nevertheless, the supplementation with either bran product for 18 weeks did not significantly alter the urinary excretion of 15-isoprostane F(2t), change the lipoprotein profiles, nor reduce the atherosclerotic lesion development in this animal model. The results suggest that phenolic antioxidants from the two types of bran may not be sufficient to reduce atherosclerosis in this animal model.

Flaxseed oil and fish-oil capsule consumption alters human red blood cell n-3 fatty acid composition: a multiple-dosing trial comparing 2 sources of n-3 fatty acid

BACKGROUND

An increase in plasma n-3 fatty acid content, particularly eicosapentaenoic acid (20:5n-3; EPA) and docosahexaenoic acid (22:6n-3; DHA), is observed after consumption of fish oil-enriched supplements. Because alpha-linolenic acid (18:3n-3; ALA) is the direct precursor of EPA and DHA, ALA-enriched supplements such as flax may have a similar effect, although this hypothesis has been challenged because of reported low conversion of ALA into DHA.

OBJECTIVE

To address this question, we designed a clinical trial in which flax oil, fish-oil, and sunflower oil (placebo group) capsules were given to firefighters (n = 62), a group traditionally exposed to cardiovascular disease risk factors.

DESIGN

Firefighters were randomly divided into 6 experimental groups receiving 1.2, 2.4, or 3.6 g flax oil/d; 0.6 or 1.2 g fish oil/d; or 1 g sunflower oil/d for 12 wk. Blood was drawn every 2 wk, and the total phospholipid fatty acid composition of red blood cells was determined.

RESULTS

As expected, fish oil produced a rapid increase in erythrocyte DHA and total n-3 fatty acids. The consumption of either 2.4 or 3.6 g flax oil/d (in capsules) was sufficient to significantly increase erythrocyte total phospholipid ALA, EPA, and docosapentaenoic acid (22:5n-3) fatty acid content. There were no differences among groups in plasma inflammatory markers or lipid profile.

CONCLUSIONS

The consumption of ALA-enriched supplements for 12 wk was sufficient to elevate erythrocyte EPA and docosapentaenoic acid content, which shows the effectiveness of ALA conversion and accretion into erythrocytes. The amounts of ALA required to obtain these effects are amounts that are easily achieved in the general population by dietary modification.

Long-term phytosterol treatment alters gene expression in the liver of apo E-deficient mice

Dietary phytosterols significantly reduce plasma cholesterol concentrations and atherosclerosis in apolipoprotein E-knockout (apo E-KO) mice. We investigated the long-term effects of phytosterol treatment on gene expression in the liver of these mice. Male apo E-KO mice were fed an atherogenic diet supplemented with (n=6) or without (n=6) 2% (wt/wt) phytosterol mixtures for 14 weeks. Liver specimens were collected and stored in RNAlater immediately. mRNA was extracted and subjected to microarray analyses and real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR) assay for confirmation. Oligonuleotide microarray analysis of pooled samples (n=3) revealed that the expression of 132 genes/transcripts was significantly altered in treated animals, considering the false discovery rate (FDR) of 0.23. Real-time RT-PCR techniques confirmed these alterations in the expression of several of these genes, including Hmgcr (2.16-fold; P=.0002), Hmgcs1 (1.79-fold; P=.001), Hsd17b7 (2.11-fold; P=.028), Sqle (2.03-fold; P=.01), Cyp51 (1.8-fold; P=.001), Fads1 (1.55-fold; P=.031), Fads2 (2.17-fold; P=.047), Lpin1 (3.67-fold; P=.001), Ppargc1b (PGC-1beta; a coactivator of sterol-regulatory element-binding proteins; 1.66-fold; P=.007) and Cyp7B1 (1.81-fold; P=.025). In summary, our data suggest that long-term dietary phytosterols can alter the expression of a number of hepatic genes that regulate sterol metabolism in apo E-KO mice. It is possible that these changes are due to inhibition of cholesterol absorption, but are not a direct effect of plant sterols. Further multivariate correlation or association analysis is needed to establish the relations between changes in the expression of these genes and prevention of atherosclerosis by phytosterols.

Mouse models for atherosclerosis and pharmaceutical modifiers

Atherosclerosis is a multifactorial highly-complex disease with numerous etiologies that work synergistically to promote lesion development. The ability to develop preventive and ameliorative treatments will depend on animal models that mimic the human subject metabolically and pathophysiologically and will develop lesions comparable to those in humans. The mouse is the most useful, economic, and valid model for studying atherosclerosis and exploring effective therapeutic approaches. Among the most widely used mouse models for atherosclerosis are apolipoprotein E-deficient (ApoE-/-) and LDL receptor-deficient (LDLr-/-) mice. An up-and-coming model is the ApoE*3Leiden (E3L) transgenic mouse. Here, we review studies that have explored how and to what extent these mice respond to compounds directed at treatment of the risk factors hypercholesterolemia, hypertriglyceridemia, hypertension, and inflammation. An important outcome of this survey is that the different models used may differ markedly from one another in their response to a specific experimental manipulation. The choice of a model is therefore of critical importance and should take into account the risk factor to be studied and the working spectrum of the compounds tested.

Consumption of a novel dietary formula of plant sterol esters of canola oil fatty acids, in a canola oil matrix containing 1,3-diacylglycerol, reduces oxidative stress in atherosclerotic apolipoprotein E-deficient mice

The antiatherogenic properties of a novel dietary formula (PS-CO) of plant sterol esters of fatty acids, produced by enzymatic interesterification of plant sterols with canola oil (CO), in a CO matrix containing 1,3-diacylglycerol, were evaluated in apolipoprotein E-deficient mice. PS-CO consumption strongly tended to lower total plasma cholesterol levels by 21%, compared to the placebo group. Blood triglycerides were reduced by 38% and 36% compared to CO and placebo-fed mice, respectively. Serum lipid peroxide levels were lowered following PS-CO administration by 62% and 63%, compared to CO and placebo administration, respectively. Unlike CO supplementation, PS-CO consumption preserved serum paraoxonase (PON1) activity. Mouse peritoneal macrophages from PS-CO-fed mice exhibited reduced cellular uptake of oxidized-LDL compared to those from placebo-fed mice and demonstrated a tendency toward a decreased capability to release superoxide anions. These findings indicate that PS-CO supplementation is beneficial in reducing serum lipid levels, and serum and macrophage oxidative stress, thus contributing to the reduction in atherogenic risk factors.

Dietary phytosterols reduce probucol-induced atherogenesis in apo E-KO mice

We have previously shown strong pro-atherogenic effects of probucol in apolipoprotein E-knockout (apo E-KO) mice. The aims of the present study were to investigate whether (a) dietary phytosterols reduce probucol-induced atherogenesis and (b) beneficial interactions exist between these agents. Male apo E-KO mice fed with an atherogenic diet supplemented with phytosterols or probucol or their combination for 14 weeks. Single therapy with either phytosterols or probucol resulted in a 25% reduction in plasma total cholesterol (TC) concentrations as compared to the control group. The effects of the combination therapy were more profound (60% reduction). While phytosterols reduced atherogenesis by 60%, probucol caused an increase of 150% in atherogenesis. Addition of phytosterols to probucol substantially reduced pro-atherogenic effects of probucol. This was associated with improved high density lipoprotein (HDL) concentrations. The ratio of TC to HDL cholesterol was markedly reduced in the combination therapy group as compared to the probucol-treated group. A strong positive association between the ratio of TC to HDL cholesterol and the extent of atherosclerotic lesions was observed. The coronary arteries of the probucol-treated group showed various stages of atherogenesis from infiltration of monocytes into intima to complete occlusion of the vessel by atheromatous lesions. Such pathological findings were not observed in the combination therapy group. Approximately 40% of the mice in the probucol-treated group and 10% of the animals in the combination therapy group developed skin lesions. Further studies warrant the investigation of the underlying mechanisms of the observed beneficial interactions between dietary phytosterols and probucol.