The inhibitory effect of soy protein isolate on atherosclerosis in mice does not require the presence of LDL receptors or alteration of plasma lipoproteins

Rice Endosperm Protein Improves the Anti-Inflammatory Effects of High-Density Lipoprotein and Produces Lower Atherosclerotic Lesion Accelerated by the Renal Mass Reduction than Casein in a Mouse Model

Chronic kidney disease (CKD) impairs the anti-inflammatory effects of high-density lipoprotein (HDL) and increases cardiovascular mortality. Though the potential role of dietary interventions to manage HDL is well studied, the clinical trials aimed to increase HDL levels have failed to reduce cardiovascular risk, rendering HDL function to be explored as a more relevant clinical parameter. This study investigates the effects of rice endosperm protein (REP), a plant-based protein, on the anti-inflammatory properties of HDL and renal injury-driven atherosclerosis in comparison with casein, an animal protein.

Ten-week-old apolipoprotein E-deficient hyperlipidemic mice underwent uninephrectomy. The mice (n = 6 each) were pair-fed a normal casein-based diet or a REP-based diet (both with 20.0% protein content) for seven weeks. Atherosclerotic lesions were detected by en face Sudan IV staining of the aorta.

The number and sizes of the atherosclerotic lesions were significantly lower in the REP-based diet-fed group than the casein-based diet-fed group (p = 0.038). However, the REP-based diet neither elicited an ameliorative effect on kidney function or histology nor impacted the cholesterol profiles. Furthermore, HDL from the REP-based diet-fed mice significantly suppressed the inflammatory cytokine response of human umbilical vein endothelial cells than that from the casein-based diet-fed mice (MCP-1, p = 0.010; IL-6, p = 0.011; IL-1β, p = 0.028).

The REP-based diet has a higher potential to lessen the atherosclerotic lesions accelerated by renal mass reduction than a casein-based diet, which could be associated with the anti-inflammatory effects of HDL.

Dietary Avian Proteins Are Comparable to Soybean Proteins on the Atherosclerosis Development and Fatty Liver Disease in Apoe-Deficient Mice

Background and aim: The type and amount of dietary protein has become a topic of renewed interest in light of their involvement in metabolic diseases, atherosclerosis and thrombosis. However, little attention has been devoted to the effect of avian proteins despite their wide human consumption. The aim was to investigate the influence of chicken and turkey as sources of protein compared with that of soybean on atherosclerosis and fatty liver disease. Methods and results: To this purpose, male and female Apoe-deficient were fed purified Western diets differing in their protein sources for 12 weeks. After this period, blood, liver, aortic tree and heart base samples were taken for analyses of plasma lipids and atherosclerosis. Plasma triglycerides, non-esterified fatty acids, esterified cholesterol levels and radical oxygen species in lipoproteins changed depending on the diet and sex. Females consuming the turkey protein-containing diet showed decreased atherosclerotic foci, as evidenced by the en face atherosclerosis analyses. The presence of macrophages and smooth muscle cells in plaques were not modified, and no changes were observed in hepatic lipid droplets in the studied groups either. Paraoxonase activity was higher in the group consuming turkey protein without sex differences, but only in females, it was significantly associated with aortic lesion areas. Conclusions: Compared to soybean protein, the consumption of avian proteins depending on sex resulted in similar or lower atherosclerosis development and comparable hepatic steatosis.

Cholesterol-Lowering Nutraceuticals Affecting Vascular Function and Cardiovascular Disease Risk

PURPOSE OF REVIEW

The aim of this review is to provide an update on the effects of the dietary supplementation with cholesterol-lowering nutraceuticals and nutraceutical combinations affecting vascular function and CV risk in clinical interventional studies.

RECENT FINDINGS

Current evidence supports the mild-to-moderate cholesterol-lowering efficacy of red yeast rice, berberine, plant sterols, fibers, and some nutraceutical combinations whereas data on the individual cholesterol-lowering action of other nutraceuticals are either less striking or even inconclusive. There is also promising evidence on the vascular protective effects of some of the aforementioned nutraceuticals. However, except for red yeast rice, clinical interventional studies have not investigated their impact on CV outcomes. Evidence of both cholesterol-lowering and vascular protection is a prerogative of few single nutraceuticals and nutraceutical combinations, which may support their clinical use; however, caution on their uncontrolled adoption is necessary as they are freely available on the market and, therefore, subject to potential misuse.

A Novel Peptide from Soybean Protein Isolate Significantly Enhances Resistance of the Organism under Oxidative Stress

Recent studies have indicated that protein hydrolysates have broad biological effects. In the current study we describe a novel antioxidative peptide, FDPAL, from soybean protein isolate (SPI). The aim of this study was to purify and characterize an antioxidative peptide from SPI and determine its antioxidative mechanism. LC–MS/MS was used to isolate and identify the peptide from SPI. The sequence of the peptide was determined to be Phe-Asp-Pro-Ala-Leu (FDPAL, 561 Da). FDPAL can cause significant enhancement of resistance to oxidative stress both in cells as well as simple organisms. In Caenorhabditis elegans (C. elegans), FDPAL can up-regulate the expression of certain genes associated with resistance. The antioxidant activity of this peptide can be attributed to the presence of a specific amino acid sequence. Results from our work suggest that FDPAL can facilitate potential applications of proteins carrying this sequence in the nutraceutical, bioactive material and clinical medicine areas, as well as in cosmetics and health care products.

Bovine Peptic Casein Hydrolysate Ameliorates Cardiovascular Risk Factors in a Model of ApoE-deficient Mice but not Overweight, Mildly Hypercholesterolaemic Men

Associations have been shown between consumption of bovine dairy and decreased prevalence of metabolic related disorders. Milk peptides may promote both angiotensin-I- converting enzyme (ACE) inhibition for blood pressure (BP) lowering and insulin action for better glycaemic control. Less is known of other metabolic parameters. The aim of this study was to investigate effects of dairy peptic casein hydrolysate (CH) on markers of cardiovascular disease (CVD) risk in (1) an apolipoproteinE (ApoE) - deficient mouse model of high-fat fed hypercholesterolaem- ia, and, (2) a clinical study of moderate overweight and hypercholesterolaemia. In Trial 1, ApoE-deficient mice were supplemented with high dose CH (~1g/kg body weight) in a randomised, 9-wk, parallel design intervention, and blood and tissue samples harvested. In Trial 2, 24 mildly hypercholesterolaemic men were supplemented with lower dose CH (~0.1g/kg body weight, 10g/day, 3-wks) and matched whey protein control (WP, 10g/day, 3-wks) in a randomised, 9-wk, cross-over design intervention. Diets were separated by a 3-wk washout. Fasting blood and urine samples were collected, and blood pressure (BP) measured weekly. Clinical trial registration number, ACTRN 12611001013954. In ApoE-deficient mice, administration of CH significantly inhibited circulating total cholesterol concentrations by 37% (TC, P<0.01) and decreased aorta atherosclerotic lesion score by 25% (P<0.01). In the clinical study there were no significant differential effects of CH supplementation on CV markers, including serum lipids (TC, LDL-C, HDL-C, triglyceride), glucose and BP. Whilst high dose bovine peptic CH attenuated CVD risk in a murine ApoE deficient model of aggressive hypercholesterolaemia, no evidence of amelioration of risk by supplementation with a lower dose of CH in an overweight population of mildly hypercholesterolaemic men was found.

Dietary supplementation with soy isoflavones or replacement with soy proteins prevents hepatic lipid droplet accumulation and alters expression of genes involved in lipid metabolism in rats

Accumulation of hepatic lipid droplet (HLD) is the hallmark pathology of non-alcoholic fatty liver disease (NAFLD). This study examined the effects of soy isoflavones (ISF) and different amounts of soy proteins on the accumulation of HLD, lipid metabolism and related gene expression in rats. Weanling Sprague-Dawley rats were fed diets containing either 20 % casein protein without (D1) or with (D2) supplemental ISF (50 mg/kg diet) or substitution of casein with increasing amounts of alcohol-washed soy protein isolate (SPI, 5, 10, and 20 %; D3, D4, D5) for 90 days. Dietary casein (20 %) induced accumulation of HLD in female, but not in male rats. Both soy proteins and ISF remarkably prevented the formation of HLD. Soy proteins lowered hepatic total cholesterol and triglyceride in a dose-dependent manner. Interestingly, soy proteins but not ISF significantly increased free fatty acids in the liver of the female rats compared to D1. Proteomic analysis showed that at least 3 enzymes involved in lipogenesis were down-regulated and 7 proteins related to fatty acid β-oxidation or lipolysis were up-regulated by soy protein over D1. Additionally, 9 differentially expressed proteins identified were related to amino acid metabolism, 5 to glycolysis and 2 to cholesterol metabolism. Dietary ISF and SPI markedly reduced hepatic-peroxisome-proliferator-activated receptor γ2 (PPARγ2) and fat-specific protein 27 (FSP27) in female rats. Overall, this study has shown that partial or full replacement of dietary casein by soy protein or supplementation with soy ISF can effectively prevent the accumulation of HLD. The potential molecular mechanism(s) involved might be due to suppression of lipogenesis and stimulation of lipolysis and down-regulation of PPARγ2 and FSP27. This suggests that consumption of soy foods or supplements might be a useful strategy for the prevention or treatment of fatty liver diseases.

Soy protein inhibits inflammation-induced VCAM-1 and inflammatory cytokine induction by inhibiting the NF-κB and AKT signaling pathway in apolipoprotein E-deficient mice

PURPOSE

Inflammation is a hallmark of many diseases, such as atherosclerosis, autoimmune diseases, obesity, and cancer. Isoflavone-free soy protein diet (SPI(-)) has been shown to reduce atherosclerotic lesions in a hyperlipidemic mouse model compared to casein (CAS)-fed mice, despite unchanged serum lipid levels. However, possible mechanisms contributing to the athero-protective effect of soy protein remain unknown. Therefore, we investigated whether and how SPI(-) diet inhibits inflammatory responses associated with atherosclerosis.

METHODS

Apolipoprotein E knockout (apoE-/-) mice (5-week) were fed CAS or SPI(-) diet for 1 or 5 week to determine LPS- and hyperlipidemia-induced acute and chronic inflammatory responses, respectively. Expression of NF-κB-dependent inflammation mediators such as VCAM-1, TNF-α, and MCP-1 were determined in aorta and liver. NF-κB, MAP kinase, and AKT activation was determined to address mechanisms contributing to the anti-inflammatory properties of soy protein/peptides.

RESULTS

Isoflavone-free soy protein diet significantly reduced LPS-induced VCAM-1 mRNA and protein expression in aorta compared to CAS-fed mice. Reduced VCAM-1 expression in SPI(-)-fed mice also paralleled attenuated monocyte adhesion to vascular endothelium, a critical and primary processes during inflammation. Notably, VCAM-1 mRNA and protein expression in lesion-prone aortic arch was significantly reduced in apoE-/- mice fed SPI(-) for 5 weeks compared with CAS-fed mice. Moreover, dietary SPI(-) potently inhibited LPS-induced NF-κB activation and the subsequent upregulation of pro-inflammatory cytokines, including TNF-α, IL-6, IL-1β, and MCP-1. Interestingly, SPI(-) inhibited NF-κB-dependent inflammatory responses by targeting I-κB phosphorylation and AKT activation with no effect on MAP kinase pathway. Of the five putative soy peptides, four of the soy peptides inhibited LPS-induced VCAM-1, IL-6, IL-8, and MCP-1 protein expression in human vascular endothelial cells in vitro.

CONCLUSIONS

Collectively, our findings suggest that anti-inflammatory properties of component(s) of soy protein/peptides may be a possible mechanism for the prevention of chronic inflammatory diseases such as atherosclerosis.

Estrogens and atherosclerosis: insights from animal models and cell systems

Estrogens not only play a pivotal role in sexual development but are also involved in several physiological processes in various tissues including vasculature. While several epidemiological studies documented an inverse relationship between plasma estrogen levels and the incidence of cardiovascular disease and related it to the inhibition of atherosclerosis, an interventional trial showed an increase in cardiovascular events among postmenopausal women on estrogen treatment. The development of atherosclerotic lesions involves complex interplay between various pro- or anti-atherogenic processes that can be effectively studied only in vivo in appropriate animal models. With the advent of genetic engineering, transgenic mouse models of atherosclerosis have supplemented classical dietary cholesterol-induced disease models such as the cholesterol-fed rabbit. In the last two decades, these models were widely applied along with in vitro cell systems to specifically investigate the influence of estrogens on the development of early and advanced atherosclerotic lesions. The present review summarizes the results of these studies and assesses their contribution toward better understanding of molecular mechanisms underlying anti- and/or pro-atherogenic effects of estrogens in humans.

Soy protein diet and exercise training increase relative bone volume and enhance bone microarchitecture in a mouse model of uremia

Soy protein consumption and exercise training have been widely studied for their effects on the vasculature and bone in healthy populations, but little is known about the effectiveness of these interventions in chronic kidney disease (CKD). Cardiovascular disease and bone fracture risk are significantly elevated in CKD, and current pharmacological interventions have been unsuccessful in treating these conditions simultaneously. The purpose of this study was to compare the effects of a soy protein diet and endurance exercise training, alone or in combination, on cardiovascular and bone health in a mouse model of renal insufficiency. At 8 weeks of age, 60 female apolipoprotein E(-/-) mice underwent a two-step surgical procedure to induce uremia. These mice were then randomized at 12 weeks of age to one of four treatment groups for the 16-week intervention period: sedentary, control diet (n = 16); sedentary, soy protein diet (n = 18); exercise, control diet (n = 14); and exercise, soy protein diet (n = 12). There were no significant treatment effects on atherosclerotic lesion areas or aortic calcium deposits. We demonstrated a significant main effect of both diet and exercise on relative bone volume, trabecular number, trabecular separation, and trabecular connective density in the proximal femur as measured by microcomputed tomography. There were no treatment effects on trabecular thickness. We also showed a main effect of diet on plasma urea levels. These data suggest that soy protein intake and exercise training exert beneficial effects on properties of bone and plasma urea levels in mice with surgically induced renal impairment.

Isoflavone soy protein supplementation and atherosclerosis progression in healthy postmenopausal women: a randomized controlled trial

BACKGROUND AND PURPOSE

Although epidemiological and experimental studies suggest that dietary intake of soy may be cardioprotective, use of isoflavone soy protein (ISP) supplementation as a primary preventive therapy remains unexplored. We determined whether ISP reduces subclinical atherosclerosis assessed as carotid artery intima-media thickness progression.

METHODS

In a double-blind, placebo-controlled trial, 350 postmenopausal women 45 to 92 years of age without diabetes and cardiovascular disease were randomized to 2 evenly divided daily doses of 25 g soy protein containing 91 mg aglycon isoflavone equivalents or placebo for 2.7 years.

RESULTS

Overall, mean (95% CI) carotid artery intima-media thickness progression rate was 4.77 (3.39-6.16) μm/year in the ISP group and 5.68 (4.30-7.06) μm/year in the placebo group. Although carotid artery intima-media thickness progression was reduced on average by 16% in the ISP group relative to the placebo group, this treatment effect was not statistically significant (P=0.36). Among the subgroup of women who were randomized within 5 years of menopause, ISP participants had on average a 68% lower carotid artery intima-media thickness progression rate than placebo participants 2.16 (-1.10 to 5.43) versus 6.79 (3.56-10.01) μm/year (P=0.05). ISP supplementation had a null effect on women who were >5 years beyond menopause when randomized. There were no major adverse events from ISP supplementation.

CONCLUSIONS

ISP supplementation did not significantly reduce subclinical atherosclerosis progression in postmenopausal women. Subgroup analysis suggests that ISP supplementation may reduce subclinical atherosclerosis in healthy young (median age, 53 years) women at low-risk for cardiovascular disease who were <5 years postmenopausal. These first trial results of their kind warrant further investigation.

Biochemical evidence of atherosclerosis progression mediated by increased oxidative stress in apolipoprotein E-deficient spontaneously hyperlipidemic mice exposed to chronic cigarette smoke

Cigarette smoking is a major risk factor for cardiovascular disease. The induction of oxidative stress by smoking plays a key role in the progression of atherosclerosis. However, the underlying mechanisms are not fully understood. In the present study, we investigated whether long-term smoking can accelerate the progression of atherosclerosis and whether oxidative stress is implicated in its pathogenesis. Apolipoprotein E-deficient spontaneously hyperlipidemic mice, a model of atherosclerosis, were exposed to the gas-phase of smoke, from which tar and nicotine had been removed, for 15 min a day, 6 days a week, for 16 weeks. Exposure to cigarette smoke significantly increased the serum levels of oxidative stress markers such as thiobarbituric acid-reactive substances, oxidatively modified low-density lipoproteins, and 3-nitrotyrosine, but it did not affect serum cholesterol and triglyceride levels. Exposure to smoke also accelerated the accumulation of total cholesterol levels in the aorta that was accompanied by an increase in 3-nitrotyrosine levels of the atherosclerotic mice. These changes in the serum and aorta that progressed with exposure to smoke were prevented by vitamin E administration. Our data suggest that chronic cigarette smoking promotes and aggravates atherosclerosis and that the antioxidant vitamin E exerts an anti-atherogenic effect via reduction of oxidative stress.

Neither antioxidants nor genistein inhibit the progression of established atherosclerotic lesions in older apoE deficient mice

Supplements and diets enriched in antioxidants and soy isoflavones are purported to reduce cardiovascular disease risk. Many experimental studies have demonstrated inhibitory effects of antioxidants and soy isoflavones on the development of fatty streaks in animal models. However, it is still unknown whether antioxidants and isoflavones have comparable inhibitory effects on the progression of advanced stages of atherosclerosis. This is an important question because clinical trials in humans have not supported a cardio-protective role for antioxidants or isoflavones. Thus, we examined the effects of antioxidants and genistein on the progression and composition of established, advanced atherosclerotic lesions in the innominate arteries (IA) of older apolipoprotein E-deficient (apoE(-/-)) mice. Thirty-week-old male apoE(-/-) mice were fed chow with or without genistein (0.27%, w/w) for 6, 12 and 24 weeks. Twenty-week-old male apoE(-/-) mice were fed chow with or without a cocktail of antioxidants (vitamin E 0.2%, w/w; vitamin C 0.05%, w/w; and beta carotene 0.5%, w/w) for 10, 16, and 22 weeks. There were no significant differences in total plasma cholesterol, body weight, average lesion or medial area, or changes in lesion composition with either treatment in comparison to control mice.

Antiatherogenic effect of isoflavones in ovariectomized apolipoprotein e-deficient mice

The consumption of isoflavone-containing foods such as soybean and soybean products has been reported to have beneficial effects on the cardiovascular system in postmenopausal women. The present study was carried out to examine the mechanism underlying the beneficial effects of isoflavones in apolipoprotein (apo) E-deficient mice subjected to ovarian resection. Compared with sham-operated mice, ovariectomized mice had a larger arterial lesion area in the aortic root. Feeding the ovariectomized mice an isoflavone-containing diet (0.055 mg/kJ of total isoflavones/cal of diet) reduced the size of these lesions more than did feeding them with an isoflavone-free diet. Neither ovariectomy nor diet had a significant effect on the concentration of cholesterol in serum and urinary levels of isoprostanes, which are biomarkers for oxidative stress in vivo. The ovariectomized mice showed a greater increase in mRNA abundance for monocyte chemoattractant protein (MCP)-I in the aorta and in the level of nitric oxide (NO) secreted by peritoneal macrophages in culture than did the sham-operated mice. The isoflavone-containing diet lowered the MCP-I expression and the NO secretion more than did the isoflavone-free diet. These results suggest that dietary isoflavones confer an antiatherogenic effect by preventing the activation of macrophages due to the removal of ovaries.

Can stevioside in combination with a soy-based dietary supplement be a new useful treatment of type 2 diabetes? An in vivo study in the diabetic goto-kakizaki rat

The diterpene glycoside stevioside (SVS) and soy bean protein isolate have both been shown to have beneficial effects in diabetes treatment. As they each show different benefits we investigated whether the combination of both substances shows an improvement in the treatment of diabetes in Goto-Kakizaki (GK) rats. Over the course of 4 wk, the rats were fed with the following four test diets (n = 12 per group): 1. Standard carbohydrate-rich laboratory diet (chow), 2. chow + SVS (0.03 g/kg BW/day), 3. 80% SPI + 20% chow and 4. 80% SPI + 20 % chow + SVS (0.03 g/kg BW/day). At the end of the course conscious rats underwent an intra-arterial glucose tolerance test (IAGTT) (2.0 g glucose/kg BW). Compared to normal chow diet, stevioside in combination with SPI shows the following beneficial effects in GK rats with mild type 2 diabetes: 1. a 56% reduction in plasma glucose (p < 0.001), 2. a 118% increase in first-phase insulin (p < 0.005), 3. a 20% reduction in glucagons (p < 0.05), 4. a 28% reduction in total cholesterol (p < 0.001), 5. a 13% reduction in FFA (p < 0.01), 6. a 49% reduction in TG (p < 0.001) and 7. a 11% reduction in the systolic blood pressure (p < 0.001). In conclusion, the combination of stevioside and SPI has synergistic positive effects on the characteristic features of the metabolic syndrome, i.e. hyperglycemia, hypertension and dyslipidemia.

Soy protein containing isoflavones favorably influences macrophage lipoprotein metabolism but not the development of atherosclerosis in CETP transgenic mice

The possibility that soy protein containing isoflavones influences the development of experimental atherosclerosis has been investigated in ovariectomized mice heterozygous for the human CETP transgene and for the LDL-receptor null allele (LDLr(+/-) CETP(+/-)). After ovariectomy at 8 wk of age they were fed a fat/cholesterol-rich diet for 19 wk and divided into three experimental groups: dietary unmodified soy protein containing isoflavones (mg/g of diet), either at low-dose (Iso Low, 0.272, n = 25), or at high-dose (Iso High, 0.535, n = 28); and the atherogenic diet containing an isoflavone-depleted alcohol-washed soy protein as a control group (n = 28). Aortic root lipid-stained lesion area (mean microm2 x 10(3) +/- SD) did not differ among Iso Low (12.3 +/- 9.9), Iso High (7.4 +/- 6.4), and controls (10.7 +/- 12.8). Autoantibody titers against plasma oxidized LDL did not differ among the experimental groups. Using the control mice as the reference value (100%), in vitro mouse peritoneal macrophage uptake of labeled acetylated LDL-cholesterol was lower in the Iso High (68%) than in the Iso Low (85%) group. The in vitro percent removal by exogenous HDL of labeled unesterified cholesterol from macrophages previously enriched with human [4- 14C]-cholesteryl oleate acetylated LDL was enhanced in the Iso High group (50%). In spite of these in vitro potentially antiatherogenic actions, soy protein containing isoflavones did not modify the average size of lipid-stained area in the aortic root.

Effects of soy protein and genistein on blood glucose, antioxidant enzyme activities, and lipid profile in streptozotocin-induced diabetic rats

In the current study, the effect of soy protein and genistein, one of the main isoflavones in soybeans, on blood glucose, lipid profile, and antioxidant enzyme activities in streptozotocin (STZ)-induced diabetic rats was investigated. Male Sprague-Dawley rats were divided into nondiabetic control, STZ, STZ-genistein supplemented group (STZ-G; 600 mg/kg diet), and STZ-isolated soy protein supplemented group (STZ-ISP; 200 g/kg diet). Diabetes was induced by a single injection of STZ (50 mg/kg BW) freshly dissolved in 0.1 mol/L citrate buffer (pH 4.5) into the intraperitonium. Diabetes was confirmed by measuring the fasting blood glucose concentration 48-h post-injection. The rats with blood glucose level above 350 mg/dL were considered to be diabetic. Genistein and ISP were supplemented in the diet for 3 weeks. The supplementation of genistein and ISP increased the plasma insulin level but decreased the HbA(IC) level of the STZ-induced diabetic rats. The supplementation of genistein and ISP increased the glucokinase level of the STZ-induced diabetic rats. A significant reduction in glucose-6-phosphatase was observed in the groups treated with genistein and ISP in comparison with the diabetic control group. Hepatic superoxide dismutase, catalase, and glutathione peroxidase activities of the STZ-induced diabetic rats were significantly decreased in comparison with the control rats. Administering genistein and ISP to the STZ-induced diabetic rats significantly increased those enzyme activities. The concentration of thiobarbituric acid reactive substances in the STZ-induced diabetic rats was significantly elevated, while the genistein and ISP supplement decreased it to the control concentration. Genistein and ISP supplements seem to be beneficial for correcting the hyperglycemia and preventing diabetic complications.

Diet and murine atherosclerosis

Lipid-enriched diets are often used to induce or accelerate the rate of atherosclerotic lesion development in murine models of atherosclerosis. It appears that the induction of persistent hypercholesterolemia to levels > or approximately to 300 mg/dL is required for the development of experimental atherosclerosis in the mouse. A variety of different diets have been used that vary in the level of cholesterol, the level and type of fatty acid, and the absence or presence of cholate. Each of these components as well as the protein source has been shown to influence lipoprotein level and/or atherosclerosis, with dietary cholesterol being the major proatherogenic component. In some instances the effects of these components on the expression of hepatic genes relevant to lipid homeostasis has been observed. An appreciation of the effect of the differences in diet composition on these processes is important to compare results from different atherosclerosis studies, so the composition of the diets used should always be reported or referenced. Cholate should not be used unless its effects are being specifically investigated.

Soy protein containing isoflavones reduces the size of atherosclerotic plaques without affecting coronary artery reactivity in adult male monkeys

The cardiovascular effects of dietary soy on men or adult male experimental animals have received little attention. We determined the effects of long-term (31 mo) consumption of a commercially available soy protein concentrate containing experimentally varied concentrations of isoflavones on the development of atherosclerosis and vascular reactivity in adult male monkeys. The monkeys were fed atherogenic diets that differed only in the source of protein: Control (n = 30), casein and lactalbumin; low-isoflavone soy (n = 30), a mixture of unmodified soy protein isolate and isoflavone-depleted soy protein isolate containing 0.94 mg of isoflavones/g protein; and high-isoflavone soy (n = 31), unmodified soy protein isolate containing 1.88 mg of isoflavone/g protein. Plasma LDL cholesterol was reduced, whereas HDL cholesterol and apolipoprotein A-1 (P < 0.05) were increased in both groups that consumed soy protein. Atherosclerosis (mean plaque size in the coronary arteries) was reduced by approximately 34% (P < 0.05) in both groups fed soy protein. There were no effects of dietary soy on endothelium-dependent or -independent reactivity of coronary arteries. The results indicate that long-term consumption of soy protein containing a modest amount of isoflavones inhibits the early progression of coronary artery atherosclerosis without affecting endothelium-dependent or -independent arterial function.

Effects of soy isoflavones and conjugated equine estrogens on inflammatory markers in atherosclerotic, ovariectomized monkeys

The effects of dietary soy isoflavones (IF) and conjugated equine estrogens (CEE) on circulating inflammatory markers were determined at the end of a 3-yr study of ovariectomized monkeys consuming a moderately atherogenic diet. Treatments were: 1) control, receiving alcohol-extracted soy-protein-based diet with low IF content (comparable to approximately 5 mg/d); 2) CEE, added to the control diet at a dose comparable to 0.625 mg/d; and 3) IF, consumed as a part of unextracted soy protein isolate at a dose comparable to 129 mg/d. Serum soluble vascular cell adhesion molecule-1 (sVCAM-1) was reduced by both IF (P < 0.006) and CEE (P < 0.0001) relative to controls. Serum monocyte chemoattractant protein (MCP)-1 was reduced by CEE (P < 0.0001) but not by IF (P = 1.00). Treatments did not affect serum IL-6 (P = 0.40), soluble E-selectin (P = 0.17), or C-reactive protein (P = 0.15). Serum MCP-1 and, to a lesser extent, IL-6 significantly correlated with atherosclerosis (plaque area) in the iliac and carotid arteries (all P < 0.05). Serum MCP-1 was also strongly associated with coronary artery atherosclerosis and with indices of plaque inflammation and matrix remodeling (matrix metalloproteinase-9) in the coronary artery intima (all P < 0.01). We conclude that, in this well-established nonhuman primate model of atherosclerosis, this dose of soy IF provided an antiinflammatory effect specific for sVCAM-1, whereas the effects of CEE extended to both sVCAM-1 and MCP1. It is possible that the atheroprotective effects of IF and CEE are mediated, at least in part, by effects on VCAM-1. The sites of IF inhibitory effects on sVCAM-1 production are not known, but likely candidates include the liver and/or the cardiovascular system.

Soy, isoflavones and atherosclerosis

Consumption of soy protein is associated with a lower risk of cardiovascular disease in man, and reduced atherosclerosis in a variety of experimental animals. Although a portion of the cardiovascular protective effects appears to be due to reductions in plasma lipoprotein concentration, in most people the magnitude of this effect is relatively small. In many, but not all studies using animal models, the reduction in atherosclerosis is in part independent of changes in plasma lipids and lipoproteins. This implies that there may be a direct effect on the arterial wall of one or more of the components in soyprotein that reduces susceptibility to atherosclerosis. The most actively studied components of soy protein that may be responsible for these anti-atherogenic effects are the isoflavones and various protein factions. Extraction of isoflavones and other alcohol-soluble components from soy protein lowers, but does not eliminate its ability to reduce atherosclerosis. Surprisingly, in most studies, adding back the isoflavone-rich alcohol extract to the previously extracted soy protein, or to another protein, does not restore its lipoprotein lowering or anti-atherogenic properties. This implies that alcohol extraction either destroys an active component of soy, alters the structural integrity of the soy proteins, or disassociates a required isoflavone-soy protein complex. Understanding the mechanism of this effect is an important goal for future research. Likewise, the sites of action on the arterial wall, and the mechanisms by which various soy components act to reduce atherosclerosis are just now being studied. The recent demonstration that expression of estrogen receptor alpha is required for atheroprotection by soy protein provides important new mechanistic insight. Other properties of soy, including antioxidant, anti-inflammatory and potentially antithrombogenic properties need to be explored more mechanistically before the full potential of dietary soy protein for the protection from cardiovascular disease will be known.

Activation of nitric oxide synthesis in human endothelial cells by red clover extracts

OBJECTIVE

The unexpected findings of the Women's Health Initiative trial, where surrogate cardiovascular risk markers have failed to predict the cardiovascular performance of hormone therapy, showing no reduction of cardiovascular disease in postmenopausal women receiving hormonal preparations inducing a favorable lipid profile, raise the interest on how molecules with hormone-like activity used for the treatment of menopausal symptoms act on vascular cells. This is particularly important for estrogen-like compounds such as phytoestrogens, whose mechanisms of action may significantly differ from those of other estrogenic compounds.

DESIGN

Because endothelial-derived nitric oxide (NO) is a key regulator of vascular tone and atherogenesis as well as a well-characterized estrogen-regulated molecule, we studied the regulation of NO synthesis in cultured human endothelial cells by phytoestrogens contained in red clover extracts.

RESULTS

We show that red clover extracts activate NO synthesis in endothelial cells by recruiting transcriptional pathways but are not capable of inducing rapid NO synthesis through nongenomic mechanisms. During prolonged exposures, red clover extracts enhance the expression as well as the activity of endothelial nitric oxide synthase. These effects are mediated by a recruitment of estrogen receptor-beta. Moreover, we show that red clover-derived isoflavones synergize with 17beta-estradiol in increasing endothelial nitric oxide synthase activity and expression, therefore being devoid of antiestrogenic effects in human endothelial cells.

CONCLUSIONS

These results help to understand the mechanisms of action of phytoestrogens on the cardiovascular system and have relevant clinical implications.

Dietary raw peas (Pisum sativum L.) reduce plasma total and LDL cholesterol and hepatic esterified cholesterol in intact and ileorectal anastomosed pigs fed cholesterol-rich diets

Previous studies demonstrated the cholesterol-lowering effect of dietary legumes (mainly soybeans) in animals and humans, but the mechanisms by which they exert this effect are not completely understood. The contribution of the hindgut to this hypocholesterolemic effect is also not well documented. The present work was undertaken to investigate the effect of cholesterol-enriched (2.8 g/kg) casein (C) and raw pea seed (RP) diets on the cholesterol metabolism of intact (I) and ileorectal anastomosed (IRA) growing pigs. Four groups of 6 pigs were allocated to the treatments (C-I, C-IRA, RP-I, and RP-IRA pigs) for 3 wk. Plasma total cholesterol was lowered by the RP diet through a significant decrease in LDL cholesterol. The RP diet also decreased the hepatic concentration of esterified cholesterol and increased 3-hydroxy-3-methylglutaryl CoA reductase activity and LDL receptor synthesis. The biliary total cholesterol and bile acid concentrations were greater in RP- than in C-fed pigs. In addition, fecal bile acid output was higher in RP-fed pigs. The cecum-colon by-pass inhibited cholesterol and beta-sitosterol microbial transformation, lowered the bile acid output, and increased the primary to secondary bile acid output ratio, but its influence on cholesterolemia was negligible. These results suggest a hypocholesterolemic effect of the raw pea diet probably due to increased fecal bile acid output and an increased biliary bile acid concentration.

Endocrine and cognitive effects of short-time soybean consumption in women

BACKGROUND

Soy phytoestrogens are known to influence the hormonal status acting as partial estrogen agonists. Soy-derived food supplements are advised for hormone replacement therapy, prevention of atherosclerosis, age-related cognitive decline and even hormone-dependent cancer, although results from clinical studies are controversial. Whether increased soybean intake can affect the endocrine status and cognitive abilities is largely unknown.

AIM

To observe the effects of 1 week of increased soybean intake on sex hormone levels and spatial cognitive abilities in women.

SUBJECTS AND METHODS

16 young healthy female volunteers were asked to eat 900 g of soybeans within 1 week. Salivary testosterone (T), free and total plasma T, salivary and plasma estradiol (E) were measured by radioimmunoassay before and after the study period. Mental rotation (MR) and spatial visualization (SV) psychological tests were done at the days of sampling.

RESULTS

Soybean intake increased total plasma T levels (p < 0.02) while decreasing salivary T (p < 0.01) and not altering free plasma T levels. Salivary and plasma E levels were not changed. The results of MR and SV tests were improved after the study period.

CONCLUSION

Short-time increased soybean intake alters the level of total plasma and salivary T and improves spatial cognition in women. Whether this effect is mediated by modulation of estrogen receptors, changes in sex hormone-binding globulin production or changes in activity of steroid-competent enzymes needs further study.

Soy isoflavones affect sterol regulatory element binding proteins (SREBPs) and SREBP-regulated genes in HepG2 cells

Soy intake reduces cholesterol levels. However, both the identity of the soy component or components that contribute to this reduction and the cellular mechanism producing this reduction are unknown. Soy consists of protein, lipids, fiber, and phytochemicals including isoflavones. We propose that the isoflavone component of soy mediates this effect, at least in part, by affecting cellular sterol homeostasis. We investigated the effects of an isoflavone-containing soy extract and the individual isoflavones on the maturation of the sterol regulatory element binding proteins (SREBP) and the expression of SRE-regulated genes controlling lipid metabolism. We found a corresponding increase in the mature form of SREBP-2 in both soy extract- and isoflavone-treated HepG2 cells, whereas there was no significant change in the levels of SREBP-1. 3-Hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase protein and HMG CoA synthase mRNA levels also increased. When HepG2 cells were transiently transfected with HMG CoA synthase and LDL receptor reporter plasmids there was an increase in expression in response to soy extract or isoflavone treatment from both of these promoters, but this induction was blunted in the presence of sterols (P < 0.05). The mechanism responsible for this effect may be via a statin-like inhibition of HMG CoA reductase enzyme activity or by enhanced SREBP processing via the SREBP cleavage activating protein. We hypothesize that maturation of SREBP and induction of SRE-regulated genes produce an increase in surface LDL receptor expression that increases the clearance of plasma cholesterol, thus decreasing plasma cholesterol levels.

Dietary soy protein isolate and isoflavones modulate hepatic thyroid hormone receptors in rats

Thyroid hormone receptors (TRs) are regulators of many genes involved in cholesterol and lipid metabolism. The purpose of this study was to examine the effect of soy protein isolate (SPI) and isoflavones on hepatic TRs in rats. In Expt. 1, Sprague-Dawley rats were fed diets containing either casein or alcohol-washed SPI with or without isoflavone supplementation (5-1250 mg/kg diet) for 70, 190, and 310 d. The offspring (F1) were fed the same diets as their parents (F0). In Expt. 2, Sprague-Dawley rats were fed diets containing casein or casein plus isoflavones (50-400 mg/kg diet) for 120 d. The mRNA and protein contents of the hepatic TRs were measured by semiquantitative RT-PCR and Western blot, respectively. TRalpha1, TRalpha2, and TRbeta2 contents were not affected by SPI. However, the content of the 52-kDa TRbeta1 protein, the major isoform present in the liver, was markedly increased by dietary SPI in both sexes of F0 and F1 compared with casein. The supplemental isoflavones had no effect on TRbeta1, whereas the high doses of isoflavones (250 and 1250 mg/kg diet) reduced the hepatic TRalpha1 protein content in F1 male rats on d 28. SPI had no effect on total T3 and T4 levels. However, higher dose of supplemental isoflavones markedly increased T4 level in female rats. Overall, this study demonstrates for the first time that SPI upregulates hepatic TRbeta1 expression, and that isoflavones reduce the hepatic TRalpha1 level in young male rats. The SPI-induced TRbeta1 may play a role in mediating the hypocholesterolemic and lipid-lowering actions of soy protein.

Dietary soy beta-conglycinin (7S globulin) inhibits atherosclerosis in mice

Although beta-conglycinin (7S globulin), a major soy storage protein, stimulates the expression of LDL receptors and the degradation of LDL by hepatocytes in vitro, the in vivo effects of dietary beta-conglycinin on the cardiovascular system are unknown. We assessed the effects of dietary beta-conglycinin and other soy peptide fractions on the development of atherosclerosis in atherosclerosis-susceptible mice. At 6 wk of age, male and ovariectomized female apolipoprotein (apo) E-null mice and LDL receptor-null, apoB transgenic mice were assigned randomly to treatment groups that differed only in the source of dietary protein: 1) casein/lactalbumin, 2) isoflavone-containing soy protein isolate, 3) beta-conglycinin, 4) glycinin (11S globulin, another major soy storage protein), 5) beta-conglycinin-devoid soy protein, and 6) W008 (a peptide fraction produced by hydrolysis and precipitation of soy protein isolate). After 4 mo, aortic atherosclerosis (cholesteryl ester content) and plasma lipoprotein cholesterol concentrations were quantified using GLC. Relative to mice fed casein/lactalbumin-based diets, the extent of atherosclerosis was reduced in ovariectomized female mice fed all soy protein-containing diets. Relative to mice fed isoflavone-containing soy protein isolate, atherosclerosis was reduced only in mice fed the beta-conglycinin-containing diet. Mean reductions were 39 and 67% (all P <0.05) in male and ovariectomized female apoE null mice and 66% (P < 0.05) in male LDL receptor null mice. These effects were unrelated to variation in isoflavone content of the protein source and only minimally related to plasma lipoprotein cholesterol concentrations. We conclude that a diet rich in beta-conglycinin has atheroprotective effects that greatly exceed those of isoflavone-containing soy protein isolate and do not depend on LDL receptors or influences on plasma lipoproteins.

Estrogen decreases biglycan mRNA expression in resistance blood vessels

This study was designed to identify new gene targets of estrogen in the mesenteric arteries and to determine whether the soy phytoestrogens could mimic estrogen effects. Ovariectomized rats were treated with estradiol, genistein, or daidzein for 4 days. The mesenteric arteries were harvested, total RNA was extracted, mRNA was reverse transcribed in the presence of [33P]dCTP, and the labeled probes were hybridized with DNA microarrays. Analysis of the microarray data identified biglycan as a target of estrogenic regulation. Semiquantitative RT-PCR was used to confirm and quantitate the decrease in biglycan gene expression in response to estrogen (-37%), genistein (-15%), and daidzein (-10%). Treatment with the pure estrogen receptor antagonist ICI-182,780 reversed the inhibition of biglycan gene expression. The decrease in biglycan gene expression in response to estrogens was paralleled with a decrease in biglycan protein expression. Biglycan protein was localized to the media of the mesenteric arteries by immunohistochemistry. Collectively, these data suggest that biglycan is a vascular protein regulated at the genomic level by estrogens.

Soy isoflavones prevent ovariectomy-induced atherosclerotic lesions in Golden Syrian hamster model of postmenopausal hyperlipidemia

OBJECTIVE

Soy isoflavones, as dietary supplements, may reduce the formation of atherosclerotic lesions that increase in women after menopause. The objectives of this study were to determine whether (1) ovariectomized (ovx) hamsters will develop atherosclerotic lesions and (2) soy isoflavones can dose-dependently prevent the ovariectomy-induced rise in plasma cholesterol and atherosclerotic lesions in hamsters.

DESIGN

Seventy-two 6-month-old female Golden Syrian hamsters were randomly assigned to six groups: sham-operated; ovx control; ovx + 17beta-estradiol (E(2); 10 microg E(2) per kilogram of body weight); and ovx + 9.5 (low-dose), 19 (medium-dose), or 38 (high-dose) mg isoflavones per kilogram diet. Treatments were initiated immediately after surgery and continued for 120 days. Blood was drawn via abdominal aorta for assessment of circulating lipids, and tissues were collected, including the aortic arch for assessment of atherosclerotic lesions.

RESULTS

All three doses of isoflavones prevented the rise in plasma total cholesterol from ovx; and, as the isoflavone dose increases, the cholesterol-lowering effects of isoflavones become more pronounced (7.8%, 11.8%, and 19.6% reductions in total cholesterol for low-dose, medium-dose, and high-dose, respectively). Ovx hamsters developed atherosclerotic lesions without being on an atherogenic diet. Ninety-two percent of hamsters in the ovx control group had atherosclerotic lesions compared with only 8% in sham, 62% in the E(2) group, 29% in the low-dose group, 38% in the medium-dose group, and 58% in the high-dose group. The aortic fatty streak area was approximately 20 times higher in ovx hamsters compared with the sham animals. All doses of isoflavones were able to significantly reduce fatty streak area to that of the sham group.

CONCLUSIONS

Soy isoflavones, independent of the protein source, prevent hypercholesterolemia and the formation of atherosclerotic lesions induced by ovarian hormone deficiency in hamsters. The antiatherogenic mechanisms of isoflavones need further investigation.

Soy isoflavones exert antidiabetic and hypolipidemic effects through the PPAR pathways in obese Zucker rats and murine RAW 264.7 cells

The hypocholesterolemic and anti-atherosclerotic mechanism by which soy may exert a beneficial effect remains unclear. Peroxisome-proliferator activated receptors (PPAR) are promiscuous nuclear receptors that regulate the transcription of genes involved in lipid and glucose homeostasis and lipid metabolism within the cell. We hypothesize that the isoflavones improve lipid and glucose metabolism by acting as an antidiabetic PPAR agonist. Male and female obese Zucker rats (OZR) were used as a model of Type 2 diabetes, and OZR fed a high isoflavone soy protein diet displayed improvements in lipid metabolism consistent with results in humans treated with antidiabetic PPAR agonists such as the fibrates or glitazones. Liver triglyceride and cholesterol concentrations were lower in all OZR fed high-isoflavone soy protein diets than in rats fed low-isoflavone and casein diets (P < 0.05). Concurrently, PPAR-directed gene expression was evaluated in a cell culture model. An isoflavone-containing soy extract doubled PPAR-directed gene expression (P < 0.05) in RAW 264.7 cells containing either a PPARalpha or PPARgamma expression plasmid. A similar induction was observed when the soy isoflavones genistein or daidzein were used to treat cells. Both isoflavones doubled PPARalpha-directed gene expression (P < 0.05), whereas they increased PPARgamma-directed gene expression 200-400% (P < 0.05). This study suggests that soy isoflavones improve lipid metabolism, produce an antidiabetic effect, and activate PPAR receptors.

Dietary soy and soy isoflavones have gender-specific effects on plasma lipids and isoflavones in golden Syrian f(1)b hybrid hamsters

The specific components of soy responsible for its beneficial effects on plasma lipids are unknown. Golden Syrian F(1)B Hybrid hamsters (75 male, 74 female) were evaluated for the effect of dietary soy and soy isoflavones on plasma lipids. They were fed the following diets for 16 wk: casein/lactalbumin (C/L), soy protein with isoflavones [Soy(+)], soy protein with isoflavones removed [Soy(-)], Soy(-) plus isoflavone extract (IF), and C/L + IF. At necropsy, plasma total cholesterol, HDL cholesterol (HDLC), LDL + VLDL cholesterol (LDL + VLDLC), isoflavones, and uterine and accessory gland weights were measured. Male hamsters fed the three soy-containing diets had lower LDL + VLDLC concentrations than those fed the two C/L diets (P < 0.01), and those fed Soy(-) + IF did not differ from those fed Soy(+). In females, diet did not affect plasma LDL + VLDLC concentration. Females fed Soy(+) or Soy(-) had higher HDLC (P < 0.05) than those fed C/L. HDLC was not affected by diet in males. Due to higher equol production (P < 0.01), males had greater plasma isoflavone concentrations (P < 0.01) than females. There was a positive association between plasma total isoflavones and LDL + VLDLC (r = 0.65, P < 0.05) in females. These data suggest gender differences in plasma lipid and isoflavone responses to soy- based diets in Syrian F(1)B Hybrid hamsters, which offer an opportunity to explore effects of sex hormones on isoflavone metabolism and the effects of isoflavones on lipid metabolism.

The atheroprotective effect of dietary soy isoflavones in apolipoprotein E-/- mice requires the presence of estrogen receptor-alpha

OBJECTIVE

Although the mechanisms by which dietary soy inhibits atherosclerosis are unclear, one line of evidence implicates an important role for its phytoestrogenic isoflavones. We sought to determine whether soy isoflavones exert atheroprotective effects through estrogen receptor-dependent processes and, if so, which estrogen receptor subtype (ie, alpha or beta) is involved.

METHODS AND RESULTS

We compared the effects of diets rich in soy protein that were either isoflavone depleted (0.04 mg/g protein isolate) or isoflavone-replete, or Soy(+IF) (1.72 mg/g protein isolate) in apolipoprotein E-deficient (ee) mice that had been crossed with estrogen receptor-alpha- and -beta-deficient mice to produce double-knockout alphaalphaee and betabetaee mice and (estrogen receptor) wild-type controls (AAee and BBee). Both male and ovariectomized female mice were studied (n=10 to 17 per treatment group; total n=201). After 16 weeks, atherosclerosis was assessed by quantifying the aortic content of esterified cholesterol. Atherosclerosis was reduced 20% to 27% (P<0.05) by Soy(+IF) in betabetaee, BBee, and AAee mice but was unaffected in alphaalphaee mice. The inhibitory effect of Soy(+IF) was unrelated to sex, total plasma cholesterol, VLDL, LDL, and HDL cholesterol.

CONCLUSIONS

The results indicate a necessary role for estrogen receptor-alpha-dependent processes in mediating the atheroprotective effects of dietary soy isoflavones.

Hepatic cytochrome p450-2A and phosphoribosylpyrophosphate synthetase-associated protein mRNA are induced in gerbils after consumption of isoflavone-containing protein

Soy intake reduces cholesterol levels, but neither the exact component in soy causing this reduction nor the mechanism by which cholesterol is reduced is known with certainty. In this study, a genetic screen was performed to identify hepatic mRNA in gerbils regulated by soy or soy isoflavones. Gerbils were fed casein, an alcohol-washed soy-based diet (containing low levels of isoflavones), and the soy-based diet supplemented with an isoflavone-containing soy extract. After feeding for 28 d, gerbils were killed, hepatic RNA was isolated, and genes that were differentially expressed in any of the three dietary conditions were identified. Fifteen different mRNA were originally selected, including two mRNA that were studied further and shown to be highly regulated. Messenger RNA levels for both cytochrome P450-2A and phosphoribosylpyrophosphate synthetase-associated protein were up-regulated in a dose-dependent manner when soy replaced casein in the diet at 0, 33, 67 and 100% of original casein levels. A subsequent experiment used purified amino acid mixtures resembling the percentage amino acid composition of soy and casein to ensure that isoflavone-free protein sources could be tested. Using these mixtures, a 2 x 2 x 2 design tested: natural vs. synthetic protein sources, casein- vs. soy-based diets, and isoflavone extract-supplemented or supplement-free diets. This design demonstrated that these two mRNA were again significantly up-regulated more than twofold (P < 0.05) in gerbils fed all diets containing isoflavones. Induction of these two mRNA by soy may be due to the aryl hydrocarbon receptor element in the promoter region of both genes.