Effects of high- and low-isoflavone (phytoestrogen) soy foods on inflammatory biomarkers and proinflammatory cytokines in middle-aged men and women

Phytoestrogens as cardioprotective agents

Epidemiologic studies have shown that women with a higher dietary intake of phytoestrogens, plant-derived compounds with partial estrogen agonist properties, have a lower incidence of cardiovascular disease and breast and uterine cancer than women with a lower dietary intake of these substances. The most-studied category of phytoestrogens is the isoflavones found in soybeans, chick peas, and other legumes. Genistein and daidzein are the 2 major forms of isoflavones and have demonstrated lipid-lowering properties, especially in hypercholesterolemic subjects. The mechanism for the hypocholesterolemic effects is unclear, but may involve altered hepatic metabolism, antioxidant properties, tyrosine kinase inhibition, and improved vascular reactivity. Other phytoestrogens, including coumestans and lignans, have shown unfavorable results with regard to their role in the prevention of coronary artery disease. Food and food supplements containing phytoestrogens are often advocated as an alternative to hormone replacement therapy (HRT) in women with contraindications to the use of conventional estrogen replacement or those wanting a natural alternative. In light of the recent trial results with HRT (estrogen plus progesterone), it would be prudent not to recommend phytoestrogens as cardioprotective substances until adequate safety and efficacy studies are completed.

Dietary protein type and cardiovascular disease risk factors

Observational studies suggested a negative association between vegetable protein and cardiovascular disease risk, whereas intervention studies have been less consistent. The majority of interventional studies that have evaluated the effects of soy protein compared to animal protein have used casein. Relative to casein, the effect of soy protein on lipids and lipoprotein appears to be variable and less dramatic than originally reported. When compared to animal proteins other than casein, relatively large intakes of soy protein (>/=25 g/d) appear to have a consistent, albeit small ( asymptotically equal to 5%), hypocholesterolemic effect. When assessed, no consistent additional benefit of soy protein on other cardiovascular disease risk factors; Lp(a), inflammatory markers, biomarkers of oxidative stress and endothelial function, has been reported. The data available on the effect of dietary protein on plasma lipids, lipoprotein levels, and cardiovascular disease risk factors is difficult to interpret and insufficient to account for the discrepancy between the observational and interventional studies.

The effect of diets high in protein or carbohydrate on inflammatory markers in overweight subjects

AIM

Increased levels of inflammatory markers have been associated with weight gain and cardiovascular disease. The aim of the present study was to investigate the effect of diets high in either carbohydrate or protein on the inflammatory markers C-reactive protein (CRP), haptoglobin and transferrin in plasma after weight loss.

METHODS

Fifty overweight subjects [age: 18-56 years, body mass index (BMI): 27-34] were randomly assigned to an ad libitum, fat-reduced diet (30% of energy, E%), either high in protein and low in carbohydrate (25 E and 45 E% respectively) or high in carbohydrate and low in protein (58 E and 12 E% respectively), during 6 months of strictly controlled dietary intervention with dietary counselling.

RESULTS

An average reduction of 25% in CRP and an average increase of 20% in haptoglobin and transferrin were seen in both groups, however, these changes were not significant. In cross-sectional analyses after the intervention CRP was associated with fat mass (r = 0.323, p = 0.03), and the changes in CRP were associated with various indices of body fatness (Deltabody weight r = 0.346, p = 0.02). Changes in body fatness were positively associated with Deltatransferrin (r = 0.344, p = 0.02) and nearly significantly associated with Deltahaptoglobin (r = 0.271, p = 0.07) after 6 months. Multiple regression analysis showed no associations between dietary protein and carbohydrate content and serum CRP, haptoglobin or transferrin concentrations, and this remained unaltered after adjustment for weight change.

CONCLUSION

Dietary carbohydrate/protein ratio has no effect on inflammatory markers, but the study confirmed that body fatness is positively associated with levels of serum CRP.

The effect of the phytoestrogen genistein and hormone replacement therapy on homocysteine and C-reactive protein level in postmenopausal women

BACKGROUND

The aim of the study was to evaluate the effect, in postmenopausal women, of the phytoestrogen genistein and hormone replacement therapy (HRT) on circulating two independent factors of cardiovascular risk: homocysteine and C-reactive protein (CRP).

METHODS

Ninety healthy postmenopausal women, from 50 to 60 years of age, were randomly assigned to receive genistein (n = 30; 54 mg/die) or continuous combined estrogen/progestin therapy (17-beta-estradiol 1 mg plus norethisterone acetate 0.5 mg) or placebo. Plasma homocysteine and serum CRP were measured at baseline and after 6 months of treatment.

RESULTS

In the genistein group, plasma homocysteine and serum CRP showed no statistically significant difference from baseline (homocysteine: 11.36 +/- 0.39 micromol/l; CRP: 1.73 +/- 0.31 mg/l) to 6 months treatment (homocysteine: 10.72 +/- 0.46 micromol/l; CRP: 2.13 +/- 0.45 mg/l), without any significant difference versus the placebo group (homocysteine: 11.25 +/- 0.43 micromol/l; CRP: 1.74 +/- 0.22 mg/l). In the HRT group there was a slight, but not significant reduction, of plasma homocysteine mean value from baseline (11.21 +/- 0.44 micromol/l) to 6 months treatment (10.45 +/- 0.38 micromol/l); whereas CRP mean value at the end of treatment (3.30 +/- 0.55 mg/l) was significantly higher from baseline (1.61 +/- 0.25 mg/l) (P < 0.01). However, after 6 months, no significant difference existed with the other two groups.

CONCLUSIONS

The phytoestrogen genistein, after 6 months treatment, does not modify the independent cardiovascular risk linked to circulating homocysteine or CRP level. Our experience confirms critical increase of CRP serum level after HRT treatment, but not plasma homocysteine significant variation.

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.

Bioavailability and bioefficacy of polyphenols in humans. II. Review of 93 intervention studies

For some classes of dietary polyphenols, there are now sufficient intervention studies to indicate the type and magnitude of effects among humans in vivo, on the basis of short-term changes in biomarkers. Isoflavones (genistein and daidzein, found in soy) have significant effects on bone health among postmenopausal women, together with some weak hormonal effects. Monomeric catechins (found at especially high concentrations in tea) have effects on plasma antioxidant biomarkers and energy metabolism. Procyanidins (oligomeric catechins found at high concentrations in red wine, grapes, cocoa, cranberries, apples, and some supplements such as Pycnogenol) have pronounced effects on the vascular system, including but not limited to plasma antioxidant activity. Quercetin (the main representative of the flavonol class, found at high concentrations in onions, apples, red wine, broccoli, tea, and Ginkgo biloba) influences some carcinogenesis markers and has small effects on plasma antioxidant biomarkers in vivo, although some studies failed to find this effect. Compared with the effects of polyphenols in vitro, the effects in vivo, although significant, are more limited. The reasons for this are 1) lack of validated in vivo biomarkers, especially in the area of carcinogenesis; 2) lack of long-term studies; and 3) lack of understanding or consideration of bioavailability in the in vitro studies, which are subsequently used for the design of in vivo experiments. It is time to rethink the design of in vitro and in vivo studies, so that these issues are carefully considered. The length of human intervention studies should be increased, to more closely reflect the long-term dietary consumption of polyphenols.

Immunomodulating Effects of CKBM on the Cytokine Production in Peripheral Blood Mononuclear Cells (PBMCs) from Healthy Volunteers

The current study investigated the immunomodulating effect of CKBM on cytokine induction in peripheral blood mononuclear cells (PBMCs) isolated from 20 healthy volunteers. Cytometric Bead Analysis (CBA) was used to study IL-2, IL-4, IL-6, IL-10, TNF-alpha and IFN-gamma. TNF-alpha and IL-6 were significantly increased in a CKBM dose- and time-dependent manner. Flow cytometry analysis showed an increased intracellular staining of IL-6 but not of TNF-alpha in CKBM treated PBMCs. In addition, MTT cell cytotoxicity assay showed that CKBM concentrations below 5% did not significantly affect the metabolic activities of PBMCs. The current study indicated that CKBM may modulate the immune response by inducing the secretions of TNF-alpha and IL-6, which are cytokine mediators of innate immunity and inflammation preparing or "priming" the body to combat diseases.

Soy isoflavone phyto-pharmaceuticals in interleukin-6 affections. Multi-purpose nutraceuticals at the crossroad of hormone replacement, anti-cancer and anti-inflammatory therapy

Interleukin-6 is a pleiotropic cytokine which plays a crucial role in immune physiology and is tightly controlled by hormonal feedback mechanisms. After menopause or andropause, loss of the normally inhibiting sex steroids (estrogen, testosterone) results in elevated IL6 levels that are further progressively increasing with age. Interestingly, excessive IL6 production promotes tumorigenesis (breast, prostate, lung, colon, ovarian), and accounts for several disease-associated pathologies and phenotypical changes of advanced age, such as osteoporosis, rheumatoid arthritis, multiple myeloma, neurodegenerative diseases and frailty. In this respect, pharmacological modulation of IL6 gene expression levels may have therapeutical benefit in preventing cancer progression, ageing discomforts and restoring immune homeostasis. Although "plant extracts" are used in folk medicine within living memory, it is only since the 20th century that numerous scientific investigations have been performed to discover potential health-protective food compounds or "nutraceuticals" which might prevent cancer and ageing diseases. About 2000 years ago, Hippocrates already highlighted "Let food be your medicine and medicine be your food". Various nutrients in the diet play a crucial role in maintaining an "optimal" immune response, such that deficient or excessive intakes can have negative consequences on the organism's immune status and susceptibility to a variety of pathologies. Over the last few decades, various immune-modulating nutrients have been identified, which interfere with IL6 gene expression. Currently, a broad range of phyto-pharmaceuticals with a claimed hormonal activity, called "phyto-estrogens", is recommended for prevention of various diseases related to a disturbed hormonal balance (i.e. menopausal ailments and/or prostate/breast cancer). In this respect, there is a renewed interest in soy isoflavones (genistein, daidzein, biochanin) as potential superior alternatives to the synthetic selective estrogen receptor modulators (SERMs), which are currently applied in hormone replacement therapy (HRT). As phyto-chemicals integrate hormonal ligand activities and interference with signaling cascades, therapeutic use may not be restricted to hormonal ailments only, but may have applications in cancer chemoprevention and/or NF-kappaB-related inflammatory disorders as well.

Soy isoflavone intake lowers serum LDL cholesterol: a meta-analysis of 8 randomized controlled trials in humans

Clinical trials have noted hypocholesterolemic effects of soy protein intake, but the components responsible are not known. This meta-analysis of 8 randomized controlled trials was conducted to more precisely evaluate the effects of isoflavones on blood LDL cholesterol concentration independently of soy protein level. PubMed was searched for English-language "randomized controlled trial" articles published from 1966 to 2003 that described the effects of soy protein isolate (SPI) intake with measured isoflavone levels on blood lipids in humans using the search terms "soy protein," "isoflavones," and "cholesterol." From 31 articles identified by the search, 8 articles (with 10 low vs. high isoflavone comparisons) were selected for the meta-analysis. Subjects in each comparison consumed similar dietary fat, cholesterol, and fiber; the reported body weight of subjects did not change significantly during treatment. Serum LDL cholesterol concentration in subjects who consumed SPI (mean 50 g/d) with high isoflavone content (mean intake 96 mg/d) decreased by 0.15 mmol/L (95% CI: 0.08 to 0.23 mmol/L; P < 0.0001) compared with those who consumed the same SPI level with low isoflavone content (mean intake 6 mg/d). Decreases in serum LDL cholesterol concentration in hypercholesterolemic and normocholesterolemic subjects were 0.18 mmol/L (95% CI: 0.01 to 0.35 mmol/L; P = 0.03) and 0.14 mmol/L (95% CI: 0.06, 0.23 mmol/L; P = 0.0008), respectively. With identical soy protein intake, high isoflavone intake led to significantly greater decreases in serum LDL cholesterol than low isoflavone intake, demonstrating that isoflavones have LDL cholesterol-lowering effects independent of soy protein.

Dietary fatty acids affect plasma markers of inflammation in healthy men fed controlled diets: a randomized crossover study

BACKGROUND

The effect of individual dietary fatty acids on emerging risk factors for cardiovascular disease that are associated with subclinical inflammation is unknown.

OBJECTIVE

The goal was to evaluate the role of dietary fat and specific fatty acids, especially trans fatty acids, in altering concentrations of markers of inflammation in humans fed controlled diets.

DESIGN

In a randomized crossover design, 50 men consumed controlled diets for 5 wk that provided 15% of energy from protein, 39% of energy from fat, and 46% of energy from carbohydrate. Eight percent of fat or fatty acids was replaced across diets with the following: cholesterol, oleic acid, trans fatty acids (TFAs), stearic acid (STE), TFA+STE (4% of energy each), and 12:0-16:0 saturated fatty acids (LMP).

RESULTS

Fibrinogen concentrations were higher after consumption of the diet enriched in stearic acid than after consumption of the carbohydrate diet. C-reactive protein concentrations were higher after consumption of the TFA diet than after consumption of the carbohydrate diet, but were not significantly different after consumption of the TFA and TFA+STE diets than after consumption of the LMP diet. Interleukin 6 concentrations were lower after consumption of the oleic acid diet than after consumption of the LMP, TFA, and STE diets. E-selectin concentrations were higher after consumption of the TFA diet than after consumption of the carbohydrate diet. Consumption of the TFA but not the TFA+STE diet resulted in higher E-selectin concentrations than did the LMP diet.

CONCLUSIONS

These data provide evidence that dietary fatty acids can modulate markers of inflammation. Although stearic acid minimally affects LDL cholesterol, it does appear to increase fibrinogen concentrations.

Dietary soy containing phytoestrogens does not have detectable estrogenic effects on hepatic protein synthesis in postmenopausal women

BACKGROUND

Dietary phytoestrogens are ligands for the estrogen receptor and may mimic estrogenic effects in vivo.

OBJECTIVE

To assess the biological activity of isoflavone phytoestrogens, we analyzed the effect of dietary soy isoflavone supplementation on in vivo bioassays of estrogenicity.

DESIGN

Fifty healthy postmenopausal women aged 50-75 y participated in a double-blind, placebo-controlled trial in which they received either soy protein isolate (40 g soy protein, 118 mg isoflavones) or casein placebo. Measurements were made at baseline and at 3 mo. Urinary isoflavone excretion was measured to reflect compliance. The bioassays of estrogenicity included measurement of hepatic proteins and gonadotropin concentrations.

RESULTS

Baseline characteristics were not significantly different between the soy and placebo groups. Urinary isoflavone excretion increased in the soy group and at the end of 3 mo was higher in the soy group than in the placebo group. In plasma samples from both groups, C-reactive protein increased significantly over the 3-mo treatment period, whereas sex hormone-binding globulin and thyroid-binding globulin decreased significantly. However, there were no significant differences between the groups in hepatic protein synthesis (change over 3 mo +/- SEM in the soy and placebo groups, respectively): C-reactive protein, 0.42 +/- 0.2 and 0.48 +/- 0.2 U/mL; sex hormone-binding globulin, -6.9 +/- 1.5 and -10.0 +/- 2.1 micro g/mL; thyroid-binding globulin, -16 +/- 8 and -26 +/- 7 nmol/L. Furthermore, gonadotropin and dehydroepiandrosterone sulfate concentrations did not change significantly in either group.

CONCLUSIONS

In healthy postmenopausal women, dietary soy isoflavones do not affect in vivo biological indicators of estrogenicity, including hepatic protein synthesis and gonadotropin concentrations. This suggests that soy isoflavones have little biologically relevant estrogenic effect in vivo in postmenopausal women.

Phytoestrogens

Collectively, plants contain several different families of natural products among which are compounds with weak estrogenic or antiestrogenic activity toward mammals. These compounds, termed phytoestrogens, include certain isoflavonoids, flavonoids, stilbenes, and lignans. The best-studied dietary phytoestrogens are the soy isoflavones and the flaxseed lignans. Their perceived health beneficial properties extend beyond hormone-dependent breast and prostate cancers and osteoporosis to include cognitive function, cardiovascular disease, immunity and inflammation, and reproduction and fertility. In the future, metabolic engineering of plants could generate novel and exquisitely controlled dietary sources with which to better assess the potential health beneficial effects of phytoestrogens.

The influence of dietary isoflavone on the uterotrophic response in juvenile rats

Current in vivo methods to identify and assess reproductive hazards of endocrine disrupting substances are often confounded by the presence of isoflavones (genistein, diadzein, glycitein), strongly hormonally-active substances, in the diet of laboratory rodents. However, studies that have attempted to study the influence of dietary isoflavone on qualitative and quantitative uterotrophic responses have been limited by the few doses of isoflavone tested, stress to the animals due to changing of the diet immediately prior to testing and/or comparing effects of diets of very different composition. The current study examined the effects of isoflavone on uterotrophic response by using immature female rats reared from conception on diets varying only in the amount of isoflavone concentrate (Novasoy) added to a virtually isoflavone-free soya-based diet. The effects of these diets, and a soya-free semipurified diet (AIN 93G) on uterotrophic responses to treatment with a strong (Ethinyl Estradiol, EE) or a weak (bisphenol A, BPA) estrogenic substance were examined. The pups were treated with subcutaneous injections of either EE (1 microg/kg/day), BPA (600 mg/kg/day) or corn oil (vehicle) control for 3 days starting at weaning on post natal day (PND) 21. On the morning of PND 24 pups were sacrificed and uterus weight, epithelium labeling index (Bromo deoxyuridine incorporation), uterine epithelium thickness, and peroxidase activity were determined. Diet did not influence unstimulated uterine weight, epithelial height or peroxidase activity except at the highest isoflavone diet where animals had significantly increases in all three endpoints. Uterine weight, epithelial thickness and peroxidase were all significantly increased by EE or BPA treatment. There was no evidence of diet-induced potentiation or inhibition of the stimulatory actions of either EE or BPA on either uterine weight or epithelial thickness while EE-induced increase in uterine peroxidase activity was increased synergistically by the highest dose of isoflavone. A similar response to the latter effect was seen in BPA treated animals although this response was not significantly different from that of BPA treated rats fed the isoflavone-free soy diet. The rate of endometrial epithelium labeling with BrdU was not altered by any treatment. These results indicate that dietary isoflavone content can directly influence uterine weight and other estrogen-dependent endpoints demonstrating the potential of these to reduce the active range of the uterotrophic assay. However, there is no indication that isoflavones impair or potentiate the stimulatory action of either strong (EE) or weaker (BPA) estrogen agonists on uterine weight or epithelial morphology although the data do suggest the potential for synergy between high isoflavone content and estrogen agonist in inducing uterine peroxidase.

Diet and C-reactive protein

C-reactive protein (CRP) is an independent predictor of cardiovascular events in healthy individuals and those with pre-existing disease. It also probably contributes to the disease process. CRP levels are higher in obese subjects and this link is almost certainly because of increased insulin resistance. Interventions that alter insulin resistance, such as weight loss, exercise, and conjugated linoleic acid, also alter CRP. Glycemic load is associated with CRP, but there have been no interventions with altered macronutrient composition. In the context of weight loss, macronutrient composition is probably not important. Alcohol lowers CRP, but the mechanism is unknown. The interaction between gender and obesity needs further work, but it appears that obesity has a greater effect on CRP levels in women.