Soy protein influences insulin sensitivity and cardiovascular risk in male lean SHHF rats

Maternal soy protein isolate diet during lactation programmes to higher metabolic risk in adult male offspring

Soy consumption and its components, including its protein, are related to the beneficial effects of the lipid profile, decreased insulin resistance and glycaemia. However, the safety of the consumption of products containing phytoestrogens in critical stages of development has been questioned, since they may be associated with endocrine-metabolic dysfunctions in adult life. The purpose is to evaluate the effects of maternal dietary soy protein isolate (SPI) during lactation on the breast milk composition, body composition, lipid and glycaemic profiles, and thyroid hormones of dams and offspring at weaning (21 days) and in adulthood (150 days). Lactating rats were divided into casein control (C) and SPI diet groups. At 150 days, the SPI offspring presented lower body protein mass and total mineral content, higher serum FT4, insulin, TC and TG. Maternal consumption of SPI during lactation programmes the progeny to higher metabolic risk profile.

Opposing effects of S-equol supplementation on metabolic and behavioral parameters in mice fed a high-fat diet

Phytoestrogens, such as daidzein and genistein, may be used to treat various hormone-dependent disorders. Daidzein can be metabolized by intestinal microbes to S-equol. However, not all individuals possess bacteria producing this metabolite, resulting in categorization of equol vs nonequol producers. Past human and rodent studies have suggested that supplementation of this compound might yield beneficial metabolic and behavioral effects. We hypothesized that administration of S-equol to diet-induced obese male and female mice would mitigate potential diet-induced metabolic and comorbid neurobehavioral disorders. To test this possibility, we placed 5-week-old C57 mice on a high-fat diet (HFD) to mimic the diet currently consumed by many Western adults. Animals were randomly assigned to S-equol supplementation (10 mg/kg body weight) or vehicle control group. After 4 weeks on HFD with or without S-equol supplementation, metabolic and behavioral phenotyping was performed. Although the initial hypothesis proposed that S-equol treatment would improve metabolic and neurobehavioral outcomes, this supplementation instead exacerbated aspects of HFD-induced metabolic disease, as indicated by suppressed physical activity in treated individuals, reduced energy expenditure in treated males, and serum chemistry changes (hyperglycemia in treated individuals; hyperinsulinemia and hypoleptinemia in treated males). Conversely, S-equol individuals exhibited less anxiety-like and depressive-like behaviors, as evidenced by increased exploratory time in the elevated plus maze by treated males and increased time spent mobile in the tail suspension test for treated individuals. In summary, S-equol may be beneficial in mitigating depression and anxiety disorders in individuals, but for indeterminate reasons, supplementation may worsen facets of metabolic disorders in obese individuals.

Protein source in a high-protein diet modulates reductions in insulin resistance and hepatic steatosis in fa/fa Zucker rats

OBJECTIVE

High-protein diets are being promoted to reduce insulin resistance and hepatic steatosis in metabolic syndrome. Therefore, the effect of protein source in high-protein diets on reducing insulin resistance and hepatic steatosis was examined.

METHODS

Fa/fa Zucker rats were provided normal-protein (15% of energy) casein, high-protein (35% of energy) casein, high-protein soy, or high-protein mixed diets with animal and plant proteins.

RESULTS

The high-protein mixed diet reduced area under the curve for insulin during glucose tolerance testing, fasting serum insulin and free fatty acid concentrations, homeostatic model assessment index, insulin to glucose ratio, and pancreatic islet cell area. The high-protein mixed and the high-protein soy diets reduced hepatic lipid concentrations, liver to body weight ratio, and hepatic steatosis rating. These improvements were observed despite no differences in body weight, feed intake, or adiposity among high-protein diet groups. The high-protein casein diet had minimal benefits.

CONCLUSIONS

A high-protein mixed diet was the most effective for modulating reductions in insulin resistance and hepatic steatosis independent of weight loss, indicating that the source of protein within a high-protein diet is critical for the management of these metabolic syndrome parameters.

Corn Gluten Hydrolysate Affects the Time-Course of Metabolic Changes Through Appetite Control in High-Fat Diet-Induced Obese Rats

This study first investigated the effects of corn gluten hydrolysate (CGH) (1.5 g/day) administration for 7 days on appetite-responsive genes in lean Sprague-Dawley (SD) rats. In a second set of experiments, the metabolic changes occurring at multiple time points over 8 weeks in response to CGH (35.33% wt/wt) were observed in high-fat (HF, 60% of energy as fat) diet-fed SD rats. In lean rats, the hypothalamus neuropeptide-Y and proopiomelanocortin mRNA levels of the CGH group were significantly changed in response to CGH administration. In the second part of the study, CGH treatment was found to reduce body weight and perirenal and epididymal fat weight. CGH also prevented an increase in food intake at 2 weeks and lowered plasma leptin and insulin levels in comparison with the HF group. This reduction in the plasma and hepatic lipid levels was followed by improved insulin resistance, and the beneficial metabolic effects of CGH were also partly related to increases in plasma adiponectin levels. The Homeostasis Model of Assessment - Insulin Resistance (HOMA-IR), an index of insulin resistance, was markedly improved in the HF-CGH group compared with the HF group at 6 weeks. According to the microarray results, adipose tissue mRNA expression related to G-protein coupled receptor protein signaling pathway and sensory perception was significantly improved after 8 weeks of CGH administration. In conclusion, the present findings suggest that dietary CGH may be effective for improving hyperglycemia, dyslipidemia and insulin resistance in diet-induced obese rats as well as appetite control in lean rats.

Synthetic and natural iron chelators: therapeutic potential and clinical use

Iron-chelation therapy has its origins in the treatment of iron-overload syndromes. For many years, the standard for this purpose has been deferoxamine. Recently, considerable progress has been made in identifying synthetic chelators with improved pharmacologic properties relative to deferoxamine. Most notable are deferasirox (Exjade(®)) and deferiprone (Ferriprox(®)), which are now available clinically. In addition to treatment of iron overload, there is an emerging role for iron chelators in the treatment of diseases characterized by oxidative stress, including cardiovascular disease, atherosclerosis, neurodegenerative diseases and cancer. While iron is not regarded as the underlying cause of these diseases, it does play an important role in disease progression, either through promotion of cellular growth and proliferation or through participation in redox reactions that catalyze the formation of reactive oxygen species and increase oxidative stress. Thus, iron chelators may be of therapeutic benefit in many of these conditions. Phytochemicals, many of which bind iron, may also owe some of their beneficial properties to iron chelation. This review will focus on the advances in iron-chelation therapy for the treatment of iron-overload disease and cancer, as well as neurodegenerative and chronic inflammatory diseases. Established and novel iron chelators will be discussed, as well as the emerging role of dietary plant polyphenols that effectively modulate iron biochemistry.

Genistein modulates NF-κB-associated renal inflammation, fibrosis and podocyte abnormalities in fructose-fed rats

The study determines the effect of genistein on inflammatory status and expression of nuclear factor-kappa B (NF-κB p65), transforming growth factor-β1 (TGF-β1) and receptor for advanced glycation end products (RAGE) in kidney of fructose-fed rats. Adult male Wistar rats were fed a diet containing either starch or fructose as the source of carbohydrate. Fifteen days later, after confirming the development of insulin resistance in fructose-fed rats, the rats in each dietary group were divided into two and treated with either genistein (1 mg/kg/day) in 30% dimethylsulfoxide (DMSO) or 30% DMSO alone for the next 45 days. The expression of NF-κB P(65), TGF-β1 and RAGE, histochemical localization of α-smooth muscle actin (α-SMA), levels of tumour necrosis factor-α (TNF-α) and interleukin-6(IL-6) and ultrastructural analysis were performed at the end of the experimental period. Fructose-fed rats displayed inflammatory changes in kidney. Increased expression of TGF-β1 and RAGE in cytosol and NF-κB p65 in nuclear fraction were observed. α-SMA expression was higher in fructose-fed rat kidney. Proliferation of connective tissue was evident from increased collagen deposition in perivascular and intraglomerular regions. Administration of genistein to fructose-fed rats reduced inflammation, fibrogenesis and NF-κB activation. Genistein also mitigated the structural changes such as basement membrane thickening, reduction in podocyte number and loss of glomerular filtration barrier integrity. These findings suggest that genistein prevents inflammation, fibrosis and early nephropathic changes in fructose-fed insulin resistant rats secondary to the attenuation of NF-κB activation.

Co-expression of alpha' and beta subunits of beta-conglycinin in rice seeds and its effect on the accumulation behavior of the expressed proteins

A transgenic rice that produces both the alpha' and beta subunits of beta-conglycinin has been developed through the crossing of two types of transgenic rice. Although the accumulation level of the alpha' subunit in the alpha'beta-transgenic rice was slightly lower than that in the transgenic rice producing only the alpha' subunit, the accumulation level of the beta subunit in the alpha'beta-transgenic rice was about 60% higher than that in the transgenic rice producing only the beta subunit. Results from sequential extraction and gel-filtration experiments indicated that part of the beta subunit formed heterotrimers with the alpha' subunit in a similar manner as in soybean seeds and that the heterotrimers interacted with glutelin via cysteine residues. These results imply that the accumulation level of the beta subunit in the alpha'beta-transgenic rice increases by an indirect interaction with glutelin. Immunoelectron microscopy revealed that the alpha' and beta subunits are localized in a low electron-dense region of protein body-II (PB-II) and that alpha' homotrimers in the alpha'beta-transgenic rice seeds seem to accumulate outside of this low electron-dense region.

A randomized controlled trial of the effects of flaxseed lignan complex on metabolic syndrome composite score and bone mineral in older adults

A randomized double-blind placebo controlled study design was used to assess the effects of flaxseed lignan complex supplementation during exercise training on a metabolic syndrome composite score and osteoporosis risk in older adults. A total of 100 subjects (>or=50 years) were randomized to receive flaxseed lignan (543 mg.day-1 in a 4050 mg complex) or placebo while completing a 6 month walking program (30-60 min.day-1, 5-6 days.week-1). Fasting serum glucose, triacylglycerol (TAG), high-density lipoprotein (HDL) cholesterol, low-density lipoprotein cholesterol, total cholesterol, interleukin-6, and tumor necrosis factor-alpha were measured every 2 months, while body composition, bone mineral density, and resting blood pressure were assessed at baseline and at 6 months. A composite Z score of 6 risk factors for metabolic syndrome (fasting glucose, HDL cholesterol, TAG, abdominal adiposity, blood pressure, and inflammatory cytokines) was calculated at baseline and at 6 months. Men taking placebo increased metabolic syndrome composite Z score (p < 0.05), but there were no changes in the other groups. A significant group x sex x time interaction was noted for TAG (p = 0.017) and diastolic blood pressure (p = 0.046), with men taking flaxseed lignan decreasing diastolic blood pressure relative to men taking placebo, and men taking placebo increasing TAG relative to men taking flax lignan. There were no differences between groups for change in bone measures, body composition, lipoproteins, or cytokines. Males taking the flaxseed lignan complex reduced metabolic syndrome score relative to men taking placebo, but a similar trend was not seen in females. Flaxseed lignan had no effect on bone mineral density or content, body composition, lipoproteins, glucose, or inflammation.

Dietary soy isoflavones increase insulin secretion and prevent the development of diabetic cataracts in streptozotocin-induced diabetic rats

Soy isoflavone-containing diets have been reported to be beneficial in diabetes. This present study investigated the hypoglycemic effects of isoflavones in streptozotocin (STZ)-induced diabetes. Diabetes was induced in male Sprague-Dawley rats by intraperitoneal injection of 100 mg/kg STZ. Diabetic rats were then randomly divided into 3 groups and received a special diet supplemented with casein (control), low-isoflavone soy (LIS) protein, and high-isoflavone soy protein (HIS) for 8 weeks. Compared with the control or LIS groups, those rats on the HIS diet had significantly increased body weight and serum insulin levels and reduced serum glucose and methylglyoxal levels. Serum glutathione levels were also increased in rats given the HIS diet compared with those in the control or LIS (P < .01). Serum high-density lipoprotein cholesterol level was significantly higher in HIS-fed rats than that of the control or LIS rats (P < .05). More importantly, the death rate and incidence of cataracts in the diabetic rats were markedly decreased in the HIS group. In conclusion, ingestion of high-isoflavone soy protein not only lowers glucose levels but also reduces the incidence of cataracts in diabetic rats. The beneficial effects of soy isoflavones are attributed to increased insulin secretion, a better glycemic control, and antioxidant protection.

Soya protein reverses dyslipidaemia and the altered capacity of insulin-stimulated glucose utilization in the skeletal muscle of sucrose-rich diet-fed rats

The present study investigates the benefits of dietary intake of soya protein upon dyslipidaemia and insulin resistance in rats chronically (8 months) fed a sucrose-rich (63 %) diet (SRD). For this purpose, we analysed the effectiveness of soya protein isolate in improving or reversing these metabolic abnormalities. Wistar rats were fed a SRD for 4 months. By the end of this period, stable dyslipidaemia and insulin resistance were present in the animals. From months 4 to 8, half the animals continued with the SRD and the other half were fed a SRD in which the source of protein casein was substituted by soya. The control group received a diet in which the source of carbohydrate was maize starch. The results showed that: (1) soya protein normalized plasma TAG, cholesterol and NEFA levels in the SRD-fed rats. Moreover, the addition of soya protein reversed the hepatic steatosis. (2) Glucose homeostasis was normalized without changes in circulating insulin levels. Whole-body peripheral insulin sensitivity substantially improved. Besides, soya protein moderately decreases body weight gain limiting the accretion of visceral fat. (3) By shifting the source of dietary protein from casein to soya during the last 4 months of the feeding period it was possible to reverse both the diminished insulin-stimulated glucose oxidation and disposal in the skeletal muscle of SRD-fed rats. This study provides new data showing the beneficial effect of soya protein upon lipid and glucose homeostasis in the experimental model of dyslipidaemia and insulin resistance.

Ginseng modifies the diabetic phenotype and genes associated with diabetes in the male ZDF rat

Asian ginseng (Panax ginseng) and its close relative North American ginseng (Panax quinquefolius) are perennial aromatic herbs that are widely used in Oriental medicine and have been acclaimed to have various health benefits including diabetes treatment. In this study, we compared the effects of a diet containing rosiglitazone to a diet containing ginseng (Panax quinquefolius) in male Zucker diabetic fatty (ZDF) rats. Animals were assigned to one of three diets: control, rosiglitazone (0.1 g/1 kg diet), or ginseng (10 g/1 kg diet). During the 11-week study, body weight, food intake, organ weight, blood glucose, plasma cholesterol, and plasma triglyceride levels were evaluated. Animals treated with rosiglitazone or ginseng exhibited increased body weight (p<0.05) and decreased kidney weight (p<0.05) compared to control animals. The rosiglitazone group demonstrated decreased food intake and plasma triglyceride levels versus the other groups (p<0.05). The ginseng group revealed decreased cholesterol levels relative to the control group (p<0.05). Furthermore, ginseng and rosiglitazone had marked effects on the expression of genes involved in PPAR actions and triglyceride metabolism compared to controls. In conclusion, ginseng modified the diabetic phenotype and genes associated with diabetes in the male ZDF rat. These data are encouraging, and warrant further research to determine the therapeutic value of this medicinal herb in treating human diabetes.

Soy protein and isoflavones influence adiposity and development of metabolic syndrome in the obese male ZDF rat

BACKGROUND/AIMS

Previously, we demonstrated that soy protein ameliorates the diabetic phenotype in several rodent models of obesity and metabolic syndrome (MS). This study was designed to further elucidate factors related to adiposity, glycemic control, and renal function in male Zucker Diabetic Fatty (ZDF/Lepr(fa)) rats.

METHODS

Animals were randomly assigned to one of four diets: control, casein (C); low isoflavone (LIS) soy protein; high isoflavone (HIS) soy protein, or casein + rosiglitazone (CR) for 11 weeks. At sacrifice, physiological, biochemical, and molecular parameters were determined.

RESULTS

Body weight and total adiposity were higher in LIS and CR diet groups despite lower food intake. Additionally, these animals exhibited differential regulation of adipose-specific proteins (PPAR-gamma and GLUT4) and enzyme activity (FAS and GPDH). HIS-fed animals had reduced total and liver adiposity. Glycemic control was prolonged in both soy-based and rosiglitazone (RGZ) groups. Renal dysfunction was significantly reduced in soy-fed and RGZ-treated rodents as demonstrated by lower levels of proteinuria and dilated tubules with proteinaceous casts.

CONCLUSION

Collectively, these data provide evidence that soy protein with low or high isoflavone content may have therapeutic significance in reducing severity of diabetes, MS, and renal disease as demonstrated in this preclinical model.

Role of dietary soy protein in obesity

Soy protein is an important component of soybeans and provides an abundant source of dietary protein. Among the dietary proteins, soy protein is considered a complete protein in that it contains ample amounts of all the essential amino acids plus several other macronutrients with a nutritional value roughly equivalent to that of animal protein of high biological value. Soy protein is unique among the plant-based proteins because it is associated with isoflavones, a group of compounds with a variety of biological properties that may potentially benefit human health. An increasing body of literature suggests that soy protein and its isoflavones may have a beneficial role in obesity. Several nutritional intervention studies in animals and humans indicate that consumption of soy protein reduces body weight and fat mass in addition to lowering plasma cholesterol and triglycerides. In animal models of obesity, soy protein ingestion limits or reduces body fat accumulation and improves insulin resistance, the hallmark of human obesity. In obese humans, dietary soy protein also reduces body weight and body fat mass in addition to reducing plasma lipids. Several potential mechanisms whereby soy protein may improve insulin resistance and lower body fat and blood lipids are discussed and include a wide spectrum of biochemical and molecular activities that favorably affect fatty acid metabolism and cholesterol homeostasis. The biologic actions of certain constituents of soy protein, particularly conglycinin, soyasaponins, phospholipids, and isoflavones, that relate to obesity are also discussed. In addition, the potential of soy protein in causing food allergy in humans is briefly discussed.