Regulation of the immune response by soybean isoflavones

Contributions of nonhematopoietic cells and mediators to immune responses: implications for immunotoxicology

Immunotoxicology assessments have historically focused on the effects that xenobiotics exhibit directly on immune cells. These studies are invaluable as they identify immune cell targets and help characterize mechanisms and/or adverse outcome pathways of xenobiotics within the immune system. However, leukocytes can receive environmental cues by cell-cell contact or via released mediators from cells of organs outside of the immune system. These organs include, but are not limited to, the mucosal areas such as the lung and the gut, the liver, and the central nervous system. Homeostatic perturbation in these organs induced directly by toxicants can initiate and alter the outcome of local and systemic immunity. This review will highlight some of the identified nonimmune influences on immune homeostasis and provide summaries of how immunotoxic mechanisms of selected xenobiotics involve nonimmune cells or mediators. Thus, this review will identify data gaps and provide possible alternative mechanisms by which xenobiotics alter immune function that could be considered during immunotoxicology safety assessment.

Isoflavones in soy flour diet have different effects on whole-genome expression patterns than purified isoflavone mix in human MCF-7 breast tumors in ovariectomized athymic nude mice

SCOPE

Soy flour diet (MS) prevented isoflavones from stimulating MCF-7 tumor growth in athymic nude mice, indicating that other bioactive compounds in soy can negate the estrogenic properties of isoflavones. The underlying signal transduction pathways to explain the protective effects of soy flour consumption were studied here.

METHODS AND RESULTS

Ovariectomized athymic nude mice inoculated with MCF-7 human breast cancer cells were fed either Soy flour diet (MS) or purified isoflavone mix diet (MI), both with equivalent amounts of genistein. Positive controls received estradiol pellets and negative controls received sham pellets. GeneChip Human Genome U133 Plus 2.0 Array platform was used to evaluate gene expressions, and results were analyzed using bioinformatics approaches. Tumors in MS-fed mice exhibited higher expression of tumor growth suppressing genes ATP2A3 and BLNK and lower expression of oncogene MYC. Tumors in MI-fed mice expressed a higher level of oncogene MYB and a lower level of MHC-I and MHC-II, allowing tumor cells to escape immunosurveillance. MS-induced gene expression alterations were predictive of prolonged survival among estrogen-receptor-positive breast cancer patients, whilst MI-induced gene changes were predictive of shortened survival.

CONCLUSION

Our findings suggest that dietary soy flour affects gene expression differently than purified isoflavones, which may explain why soy foods prevent isoflavones-induced stimulation of MCF-7 tumor growth in athymic nude mice.

Dietary Elimination of Soybean Components Enhances Allergic Immune Response to Peanuts in BALB/c Mice

BACKGROUND

Food allergy research is hampered by a lack of animal models that consistently mimic human food allergic responses. Laboratory mice are generally fed grain-based chow made with large amounts of soybeans rich in immunomodulatory isoflavones. We tested the role of dietary soy components in the induction of food allergic responses in the BALB/c mouse strain, which is known to be resistant to anaphylaxis when orally challenged by food allergens.

METHODS

Mice were fed a soy-free diet for 2 generations. After weaning, mice were maintained on the same diet or fed a diet containing soy isoflavones, i.e. genistein and daidzein, followed by weekly oral sensitizations with crude peanut extract plus cholera toxin and finally challenged at week 7. The anaphylactic symptoms, body temperature, peanut-specific antibodies and mast cell degranulation were assessed.

RESULTS

Soy-free diet mice showed significantly higher anaphylactic symptom scores and mast cell degranulation after challenge and higher peanut-specific antibody levels than mice fed regular chow. Introduction of a regular soy diet or an isoflavone diet to soy-free diet mice significantly suppressed the allergic reactions compared to the soy-free diet.

CONCLUSION

Rodent diet is an important variable and needs to be taken into consideration when designing experiments involving animal models. Our results indicate that elimination of soy components from the diet enhances peanut sensitization in BALB/c mice. In addition to serving as a valuable tool to mimic human food allergy, the dietary influence on the immune response could have far-reaching consequences in research involving animal models.

Adult offspring of high-fat diet-fed dams can have normal glucose tolerance and body composition

Maternal high-fat diet consumption and obesity have been shown to program long-term obesity and lead to impaired glucose tolerance in offspring. Many rodent studies, however, use non-purified, cereal-based diets as the control for purified high-fat diets. In this study, primiparous ICR mice were fed purified control diet (10–11 kcal% from fat of lard or butter origin) and lard (45 or 60 kcal% fat) or butter (32 or 60 kcal% fat)-based high-fat diets for 4 weeks before mating, throughout pregnancy, and for 2 weeks of nursing. Before mating, female mice fed the 32 and 60% butter-based high-fat diets exhibited impaired glucose tolerance but those females fed the lard-based diets showed normal glucose disposal following a glucose challenge. High-fat diet consumption by female mice of all groups decreased lean to fat mass ratios during the 4th week of diet treatment compared with those mice consuming the 10–11% fat diets. All females were bred to male mice and pregnancy and offspring outcomes were monitored. The body weight of pups born to 45% lard-fed dams was significantly increased before weaning, but only female offspring born to 32% butter-fed dams exhibited long-term body weight increases. Offspring glucose tolerance and body composition were measured for at least 1 year. Minimal, if any, differences were observed in the offspring parameters. These results suggest that many variables should be considered when designing future high-fat diet feeding and maternal obesity studies in mice.

Genistein disrupts glucocorticoid receptor signaling in human uterine endometrial Ishikawa cells

BACKGROUND

The link between environmental estrogen exposure and defects in the female reproductive tract is well established. The phytoestrogen genistein is able to modulate uterine estrogen receptor (ER) activity, and dietary exposure is associated with uterine pathologies. Regulation of stress and immune functions by the glucocorticoid receptor (GR) is also an integral part of maintaining reproductive tract function; disruption of GR signaling by genistein may also have a role in the adverse effects of genistein.

OBJECTIVE

We evaluated the transcriptional response to genistein in Ishikawa cells and investigated the effects of genistein on GR-mediated target genes.

METHODS

We used Ishikawa cells as a model system to identify novel targets of genistein and the synthetic glucocorticoid dexamethasone through whole genome microarray analysis. Common gene targets were defined and response patterns verified by quantitative real-time reverse-transcription polymerase chain reaction. The mechanism of transcriptional antagonism was determined for select genes.

RESULTS

Genistein regulated numerous genes in Ishikawa cells independently of estradiol, and the response to coadministration of genistein and dexamethasone was unique compared with the response to either estradiol or dexamethasone alone. Furthermore, genistein altered glucocorticoid regulation of GR target genes. In a select set of genes, co-regulation by dexamethasone and genistein was found to require both GR and ERα signaling, respectively.

CONCLUSIONS

Using Ishikawa cells, we observed that exposure to genistein resulted in distinct changes in gene expression and unique differences in the GR transcriptome.

Developing therapies for peanut allergy

Peanut allergy is an IgE-mediated, persisting immune disorder that is of major concern worldwide. Currently, no routine immunotherapy is available to treat this often severe and sometimes fatal food allergy. Traditional subcutaneous allergen immunotherapy with crude peanut extracts has proven not feasible due to the high risk of severe systemic side effects. The allergen-specific approaches under preclinical and clinical investigation comprise subcutaneous, oral, sublingual and epicutaneous immunotherapy with whole-peanut extracts as well as applications of hypoallergenic peanut allergens or T cell epitope peptides. Allergen-nonspecific approaches include monoclonal anti-IgE antibodies, TCM herbal formulations and Toll-like receptor 9-based immunotherapy. The potential of genetically engineered plants with reduced allergen levels is being explored as well as the beneficial influence of lactic acid bacteria and soybean isoflavones on peanut allergen-induced symptoms. Although the underlying mechanisms still need to be elucidated, several of these strategies hold great promise. It can be estimated that individual strategies or a combination thereof will result in a successful immunotherapy regime for peanut-allergic individuals within the next decade.

Genistein inhibits osteoclastic differentiation of RAW 264.7 cells via regulation of ROS production and scavenging

Genistein, a phytoestrogen, has been demonstrated to have a bone-sparing and antiresorptive effect. Genistein can inhibit the osteoclast formation of receptor activator of nuclear factor-κB ligand (RANKL)-induced RAW 264.7 cells by preventing the translocation of nuclear factor-κB (NF-κB), a redox-sensitive factor, to the nucleus. Therefore, the suppressive effect of genistein on the reactive oxygen species (ROS) level during osteoclast differentiation and the mechanism associated with the control of ROS levels by genistein were investigated. The cellular antioxidant capacity and inhibitory effect of genistein were confirmed. The translation and activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 1 (Nox1), as well as the disruption of the mitochondrial electron transport chain system were obviously suppressed by genistein in a dose-dependent manner. The induction of phase II antioxidant enzymes, such as superoxide dismutase 1 (SOD1) and heme oxygenase-1 (HO-1), was enhanced by genistein. In addition, the translational induction of nuclear factor erythroid 2-related factor 2 (Nrf2) was notably increased by genistein. These results provide that the inhibitory effects of genistein on RANKL-stimulated osteoclast differentiation is likely to be attributed to the control of ROS generation through suppressing the translation and activation of Nox1 and the disruption of the mitochondrial electron transport chain system, as well as ROS scavenging through the Nrf2-mediated induction of phase II antioxidant enzymes, such as SOD1 and HO-1.

Nutritional abrogation of photoimmunosuppression: in vivo investigations

Skin cancer is a major public health concern, and the primary aetiological factor in the majority of skin cancers is ultraviolet radiation (UVR) exposure. UVR not only induces potentially mutagenic DNA damage but also suppresses cell-mediated immunity (CMI), allowing cancerous cells to escape destruction and progress to tumours. A considerable proportion of an individual's annual sun exposure is obtained outside the vacation period when topical and physical measures for photoprotection are irregularly used. Certain nutrients could provide an adjunctive protective role, and evidence is accruing from experimental studies to support their use in abrogation of photoimmunosuppression. Moreover, developments in clinical research methods to evaluate impact of solar-simulated radiation on cutaneous CMI allow the immune protective potential of nutritional agents to be examined in humans in vivo. This article summarises the mediation of CMI and its suppression by UVR, evaluates the methodology for quantitative assessment in vivo, reviews the human studies reported on nutritional abrogation of photoimmunosuppression including recent randomized controlled trials and discusses the mechanisms of photoprotection by the nutrients. This includes, in addition to antioxidants, novel studies of omega-3 polyunsaturated fatty acids and nicotinamide.

Androgen deprivation by flutamide modulates uPAR, MMP-9 expressions, lipid profile, and oxidative stress: amelioration by daidzein

The growth and development of prostate gland is governed by testosterone. Testosterone helps in maintaining the adipose tissue stores of the body. It is well documented that with advancing age there has been a gradual decline in testosterone levels. Our aim was to study the protective role of daidzein on flutamide-induced androgen deprivation on matrix degrading genes, lipid profile and oxidative stress in Wistar rats. Sub-chronic (60 days) flutamide (30 mg/kg b.wt) administration resulted in marked increase in expressions of matrix degrading genes [matrix metalloproteases 9 and urokinase plasminogen activation receptor]. Additionally, it increased the levels of low density lipoproteins, total cholesterol, triglycerides, and lowered the levels of high density lipoproteins and endogenous antioxidant levels. Oral administration of daidzein (20 and 60 mg/kg b.wt) restituted the levels to normal. Daidzein administration resulted in amelioration of the prostate atrophy, degeneracy and invasiveness induced by flutamide. Our findings suggest that the daidzein may be given as dietary supplement to patients who are on androgen deprivation therapy, to minimize the adverse effects related to it and also retarding susceptibility of patients to cardiovascular diseases.

Isoflavones, genistein and daidzein, regulate mucosal immune response by suppressing dendritic cell function

Lipopolysaccharide (LPS), a component of gram-negative bacterial cell walls, has been shown to have a strong adjuvant effect towards inhaled antigens contributing to airway inflammation. Isoflavones are anti-inflammatory molecules present in abundant quantities in soybeans. We investigated the effect of isoflavones on human dendritic cell (DC) activation via LPS stimulation and subsequent DC-mediated effector cell function both in vitro and in a mouse model of upper airway inflammation. Human monocyte-derived DCs (MDDC) were matured with LPS (or TNF-α) +/− isoflavones (genistein or daidzein). The surface expression levels of DC activation markers were analyzed by flow cytometry. Mature DCs +/− isoflavones were washed and cultured with freshly-isolated allogenic naïve CD4⁺ T cells for 5 days or with autologous natural killer (NK) cells for 2 hours. The percentages of proliferating IFN-γ⁺ CD4⁺ T cells and cytokine levels in culture supernatants were assessed. NK cell degranulation and DC cytotoxicity were measured by flow cytometry. Isoflavones significantly suppressed the activation-induced expression of DC maturation markers (CD83, CD80, CD86) and MHC class I but not MHC class II molecules in vitro. Isoflavone treatment inhibited the ability of LPS-DCs to induce IFN-γ in CD4⁺ T cells. NK cell degranulation and the percentage of dead DCs were significantly increased in isoflavone-treated DC-NK co-culture experiments. Dietary isoflavones suppressed the mucosal immune response to intra-nasal sensitization of mice to ovalbumin. Similar results were obtained when isoflavones were co-administered during sensitization. These results demonstrate that soybean isoflavones suppress immune sensitization by suppressing DC-maturation and its subsequent DC-mediated effector cell functions.