Effects of soyasaponins on lipid peroxidation through the secretion of thyroid hormones

Immunomodulatory potential of dietary soybean-derived saponins

Soybeans are widely recognized as a valuable crop, often included as a high-quality protein source in production animal diets. In addition to contributing to the macronutrient composition of the diet, soybeans also contain many minor bioactive components which can influence the health and growth of animals. This review examined the immunomodulatory potential of soy saponins and their specific effects on the inflammatory response, oxidative stress, and intestinal barrier function. Saponins are amphiphilic molecules, a property imparted by their polar carbohydrate chains that attach to a nonpolar aglycone backbone. This structure also complicates their isolation, thus most research investigating soy saponins has been performed in models that only require small amounts of isolated material. Many experiments conducted in vitro or in rodents reported that saponins can reduce damage, particularly in conditions where a challenge was first introduced to stimulate inflammation or oxidative stress. It appears that saponins can exert their anti-inflammatory effects through modulation of the NF-κB pathway, reducing its activation and the release of pro-inflammatory molecules later in the cascade. Furthermore, soy saponins can influence levels of important anti-oxidative enzymes and reduce the generation of reactive oxygen species, thus attenuating levels of oxidative stress in the model. As these results were obtained from experiments done in vitro or in rodents, they neglect to provide a good representation of how soy saponins may affect some of the greatest consumers of soy-based products, with those being production animals. The work that has been done seems to indicate that soy saponins may exert similar anti-inflammatory and anti-oxidative effects in production animals as those observed in other research models along with immunostimulatory activity that may help boost host defense systems. Overall, there is a dearth of research regarding the effects of soy saponins on species that commonly consume soy products, which begins by developing more effective methods of saponin extraction.

Development of Extraction Method for Determination of Saponins in Soybean-Based Yoghurt Alternatives: Effect of Sample pH

The number of plant-based dairy alternative products on the market is growing rapidly. In the case of soybean-based yoghurt alternatives, it is important to trace the content of saponins, the phytomicronutrients with a disputable health effect, which are likely to be responsible for the bitter off-taste of the products. We present a new sample extraction method followed by hydrophilic interaction liquid chromatography with mass spectrometric detection (HILIC-MS) for identifying and quantifying soyasaponins in soybean-based yoghurt alternatives. Soyasaponin Bb, soyasaponin Ba, soyasaponin Aa, and soyasaponin Ab were quantified using commercially available standard compounds and with asperosaponin VI as the internal standard. As the recoveries of soyasaponins were unacceptable in yoghurt alternatives at their natural acidic pH, the adjustment of pH was performed as one of the first steps in the sample extraction procedure to achieve the optimum solubility of soyasaponins. The validation of the method included the assessment of linearity, precision, limit of detection and limit of quantification (LOQ), recovery, and matrix effect. The average concentrations of soyasaponin Bb, soyasaponin Ba, soyasaponin Ab, and soyasaponin Aa in several measured soybean-based yoghurt alternatives utilising the developed method were 12.6 ± 1.2, 3.2 ± 0.7, 6.0 ± 2.4 mg/100 g, and below the LOQ, respectively. This method provides an efficient and relatively simple procedure for extracting soyasaponins from yoghurt alternatives followed by rapid quantification using HILIC-MS and could find a rightful application in the development of healthier and better-tasting dairy alternatives.

Research progress of Traditional Chinese Medicine (TCM) in targeting inflammation and lipid metabolism disorder for arteriosclerosis intervention: A review

Atherosclerosis (AS) is a chronic disease caused by inflammation and lipid deposition. Immune cells are extensively activated in the lesions, producing excessive pro-inflammatory cytokines, which accompany the entire pathological process of AS. In addition, the accumulation of lipid-mediated lipoproteins under the arterial intima is a crucial event in the development of AS, leading to vascular inflammation. Improving lipid metabolism disorders and inhibiting inflammatory reactions are the primary treatment methods currently used in medical practice to delay AS progression. With the development of traditional Chinese medicine (TCM), more mechanisms of action of the monomer of TCM, Chinese patent medicine, and compound prescription have been studied and explored. Research has shown that some Chinese medicines can participate in treating AS by targeting and improving lipid metabolism disorders and inhibiting inflammatory reactions. This review explores the research on Chinese herbal monomers, compound Chinese medicines, and formulae that improve lipid metabolism disorders and inhibit inflammatory reactions to provide new supplements for treating AS.

Effect of Lactic Acid Fermentation on Legume Protein Properties, a Review

Legume proteins have a promising future in the food industry due to their nutritional, environmental, and economic benefits. However, their application is still limited due to the presence of antinutritional and allergenic compounds, their poor technological properties, and their unpleasant sensory characteristics. Fermentation has been traditionally applied to counteract these inconveniences. At present, lactic acid fermentation of legumes is attracting the attention of researchers and industry in relation to the development of healthier, tasty, and technologically adapted products. Hence, we aimed to review the literature to shed light on the effect of lactic acid fermentation on legume protein composition and on their nutritional, functional, technological, and sensorial properties. The antimicrobial activity of lactic acid bacteria during legume fermentation was also considered. The heterogenicity of raw material composition (flour, concentrate, and isolate), the diversity of lactic acid bacteria (nutriment requirements, metabolic pathways, and enzyme production), and the numerous possible fermenting conditions (temperature, time, oxygen, and additional nutrients) offer an impressive range of possibilities with regard to fermented legume products. Systematic studies are required in order to determine the specific roles of the different factors. The optimal selection of these criteria will allow one to obtain high-quality fermented legume products. Fermentation is an attractive technology for the development of legume-based products that are able to satisfy consumers’ expectations from a nutritional, functional, technological, and sensory point of view.

Microbial Fermentation and Its Role in Quality Improvement of Fermented Foods

Fermentation processes in foods often lead to changes in nutritional and biochemical quality relative to the starting ingredients. Fermented foods comprise very complex ecosystems consisting of enzymes from raw ingredients that interact with the fermenting microorganisms’ metabolic activities. Fermenting microorganisms provide a unique approach towards food stability via physical and biochemical changes in fermented foods. These fermented foods can benefit consumers compared to simple foods in terms of antioxidants, production of peptides, organoleptic and probiotic properties, and antimicrobial activity. It also helps in the levels of anti-nutrients and toxins level. The quality and quantity of microbial communities in fermented foods vary based on the manufacturing process and storage conditions/durability. This review contributes to current research on biochemical changes during the fermentation of foods. The focus will be on the changes in the biochemical compounds that determine the characteristics of final fermented food products from original food resources.

Dietary non-nutrients in the prevention of non-communicable diseases: Potentially related mechanisms

Among the 10 leading causes of death in developed countries are chronic non-communicable diseases (NCDs). The effect of these multifactorial diseases on public health has stimulated considerable research aimed at investigating their primary risk factors (genetic factors, stress, food intake, and amount of physical exercise). Thus, healthful foods (e.g., fruits, vegetables, oils, grains, and seeds) are sources of bioactive compounds that promote good health and disease prevention. Among their components are non-caloric substances identified as non-nutrients (polyphenols, phytosterols, saponins, and phytates), which have been found to have a role in modulating metabolic pathways, maintaining health, and preventing NCDs. The aim of this study is to demonstrate and review the performance of some non-nutrients, such as their antioxidant and anti-inflammatory action, modulation of the antiatherogenic lipid profile (higher high-density lipoprotein cholesterol, lower oxidized low-density lipoprotein, and triacylglycerols), reduction of glucose and fat intestinal absorption, increase in insulin sensitivity, and stimulation of nitic oxide synthesis.

Genetic and functional characterization of Sg-4 glycosyltransferase involved in the formation of sugar chain structure at the C-3 position of soybean saponins

Triterpenoid saponins are specialized metabolites, which are abundant in soybean seeds. They have a wide variety of effects on human health and physiology. The composition of sugar chain attached to the aglycone moiety of saponins can be controlled by genetic loci, such as Sg-1, 3, and 4. Among these, the homozygous recessive sg-4 impairs the accumulation of saponins that have an arabinose moiety at the second position of the C-3 sugar chain (i.e., saponins Ad and βa) in the hypocotyls. In this study, we found that sg-4 cultivars are disabled in Glyma.01G046300 expression in hypocotyls. This gene encodes a putative glycosyltransferase (UGT73P10) and is a homolog of GmSGT2 (UGT73P2) whose recombinant protein has been previously shown, in vitro, to conjugate the second galactose moiety at the C-3 position of soyasapogenol B monoglucuronide (SBMG). The sg-4 phenotype (absence of saponins Ad and βa in hypocotyls) was restored by introducing the Glyma.01G046300 genomic DNA fragment that was obtained from the Sg-4 cultivar 'Ibarakimame 7'. Although Glyma.01G046300 is expressed in the cotyledons even in the sg-4 cultivars such as 'Enrei', the induced premature stop codon mutation (W244*) resulted in impaired accumulation of saponin βa in this tissue also in the 'Enrei' genetic background. Furthermore, the recombinant Glyma.01G046300 protein was shown to conjugate the second Ara moiety at the C-3 position of SBMG using UDP-Ara as a sugar donor. These results demonstrate that Sg-4 is responsible for conjugation of the second Ara moiety at the C-3 position of soybean saponins.

Isolation and Characterization of the Soybean Sg-3 Gene that is Involved in Genetic Variation in Sugar Chain Composition at the C-3 Position in Soyasaponins

Soyasaponins are specialized metabolites present in soybean seeds that affect the taste and quality of soy-based foods. The composition of the sugar chains attached to the aglycone moiety of soyasaponins is regulated by genetic loci such as sg-1, sg-3 and sg-4. Here, we report the cloning and characterization of the Sg-3 gene, which is responsible for conjugating the terminal (third) glucose (Glc) at the C-3 sugar chain of soyasaponins. The gene Glyma.10G104700 is disabled in the sg-3 cultivar, 'Mikuriya-ao', due to the deletion of genomic DNA that results in the absence of a terminal Glc residue on the C-3 sugar chain. Sg-3 encodes a putative glycosyltransferase (UGT91H9), and its predicted protein sequence has a high homology with that of the product of GmSGT3 (Glyma.08G181000; UGT91H4), which conjugates rhamnose (Rha) to the third position of the C-3 sugar chain in vitro. A recombinant Glyma.10G104700 protein could utilize UDP-Glc as a substrate to conjugate the third Glc to the C-3 sugar chain, and introducing a functional Glyma.10G104700 transgene into the mutant complemented the sg-3 phenotype. Conversely, induction of a premature stop codon mutation in Glyma.10G104700 (W270*) resulted in the sg-3 phenotype, suggesting that Glyma.10G104700 was Sg-3. The gmsgt3 (R339H) mutant failed to accumulate soyasaponins with the third Rha at the C-3 sugar chain, and the third Glc and Rha conjugations were both disabled in the sg-3 gmsgt3 double mutant. These results demonstrated that Sg-3 and GmSGT3 are non-redundantly involved in conjugation of the third Glc and Rha at the C-3 sugar chain of soyasaponins, respectively.

Group B Soyasaponin Aglycone Suppresses Body Weight Gain and Fat Levels in High Fat-Fed Mice

Group B soyasaponins, found in soy, have various health-promoting properties, but it is unclear whether they have an anti-obesity effect. The aim of this study was to evaluate the anti-obesity effect of group B soyasaponin glycosides and aglycone in mice fed a high-fat diet. Six-week-old C57/BL6 mice were divided into three groups (each n=10) and orally administered a high-fat diet for 35 d; two of the groups also received group B soyasaponin glycosides or aglycone. Although there was no significant difference among the three groups in consumption, the weight of fat adipose tissue at autopsy was more than 30% lower in the group B soyasaponin aglycone group than in the control group, but X-ray computed tomography showed no significant difference in muscle weight between these two groups. The ratio of muscle to whole body weight was higher in the group B soyasaponin aglycone group than in the control group. These results suggest that group B soyasaponin aglycone has a stronger anti-obesity effect than group B soyasaponin glycosides, without a loss in muscle weight, and that it increases the ratio of muscle to whole body weight. To our knowledge, this is the first report showing the anti-obesity effect of soyasaponin aglycone in vivo using animal models.

New Triterpenoid Saponins from Green Vegetable Soya Beans and Their Anti-Inflammatory Activities

Ten compounds were isolated and identified from green vegetable soya beans, of which five are new triterpenoid saponins (1-5) and five are known compounds (6-10). The chemical structures of the five triterpenoid saponins (1-5) were elucidated to be 3β,24-dihydroxy-22β,30-epoxy-30-oxoolean-12-en 3-O-α-l-rhamnopyranosyl-(1 → 2)-β-d-xylopyranosyl-(1 → 2)-β-d-glucuronopyranoside, 1; 3β,24-dihydroxy-22β,30-epoxy-30-oxoolean-12-en 3-O-α-l-rhamnopyranosyl-(1 → 2)-β-d-(3″-O-formyl)-galactopyranosyl-(1 → 2)-β-d-glucuronopyranoside, 2; 22-keto-3β,24-dihydroxy oleanane-12-ene 3-O-α-l-rhamnopyranosyl-(1 → 2)-β-d-(3″-O-formyl)-galactopyranosyl-(1 → 2)-β-d-glucuronopyranoside, 3; 3β,22β,24-trihydroxy oxyolean-18(19)-ene-29-acid 3-O-α-l-rhamnopyranosyl-(1 → 2)-β-d-galactopyranosyl-(1 → 2)-β-d-glucuronopyranoside, 4; and punicanolic acid 3-O-α-l-rhamnopyranosyl-(1 → 2)-β-d-galactopyranosyl-(1 → 2)-β-d-glucuronopyranoside, 5 from the spectroscopic data (IR, GTC/FID, HR-ESI-MS, and 1D and 2D NMR). The nitric oxide release inhibitions of compounds 1-10 in LPS-stimulated RAW264.7 cells were evaluated, and the data suggested that compounds 1, 2, and 5 might possess moderate anti-inflammatory activities, with IC50 values of 18.8, 16.1, and 13.2 μM, respectively.

Hypoglycemic property of soy isoflavones from hypocotyl in Goto-Kakizaki diabetic rats

The present study was carried out to investigate the hypoglycemic effect of soy isoflavones from hypocotyl in GK diabetic rats. A single administration and long-term administration tests were conducted in GK diabetic rats to test the hypoglycemic effect of soy isoflavones. At the end of long-term administration trial, blood protein, cholesterol, triglyceride, glycosylated serum protein, C-reactive protein, insulin, aminotransferase, lipid peroxide, interleukin-6, tumor necrosis factor-α were estimated. Inhibition of soy isoflavones against α-amylase and α-glucosidase, as well as on glucose uptake into brush border membrane vesicles or Caco-2 cells were determined in vitro. In single administration experiment, soy isoflavones reduced postprandial blood glucose levels in GK rats. In long-term administration, hypoglycemic effect of soy isoflavones was first observed at week 12 and maintained till week 16. A significant reduction in fasting blood glucose, C-reactive protein, and lipid peroxide was noted at week 16. However, there was no significant treatment effect on blood insulin. Furthermore, soy isoflavone administration resulted in significant decreases in glycosylated serum protein, tumor necrosis factor-α, and interleukin-6. Other biochemical parameters, such as protein, cholesterol, triglyceride and aminotransferases were not modified, however. The results in vitro showed that soy isoflavones showed a potent inhibitory effect on intestinal α-glucosidase, but not on pancreatic α-amylase. Soy isoflavones also decreased glucose transport potency into brush border membrane vesicles or Caco-2 cells. It is concluded that soy isoflavones from hypocotyl, performs hypoglycemic function in GK rats with type 2 diabetes, maybe via suppression of carbohydrate digestion and glucose uptake in small intestine.

Comprehensive evaluation of the role of soy and isoflavone supplementation in humans and animals over the past two decades

Soy and soy-based foods are considered healthy, particularly in many Asia-Pacific countries, where soy products have long been consumed. Soy and soy-related products have been found to help prevent the occurrence of cardiovascular diseases and certain types of cancer, such as breast and prostate cancer. These products can also have antioxidative effects that alleviate hot flashes during menopause and bone loss. These biological and therapeutic functions are primarily due to the isoflavones derived from soy, whose structure is similar to the structure of 17-β-oestradiol. Despite the many health benefits for humans and animals, the application of isoflavones remains controversial because of their anti-oestrogenic properties. We focused on general information regarding isoflavones, as well as their structure, function, and application. We summarized evidence showing that dietary or supplemental isoflavones exert protective effects on the health of humans and animals. Based on the literature, we conclude that soy foods and isoflavones may be effective and safe; however, more high-quality trials are needed to fully substantiate their potential use.

Metabolic switching of astringent and beneficial triterpenoid saponins in soybean is achieved by a loss-of-function mutation in cytochrome P450 72A69

Triterpenoid saponins are major components of secondary metabolites in soybean seeds and are divided into two groups: group A saponins, and 2,3-dihydro-2,5-dihydroxy-6-methyl-4H-pyran-4-one (DDMP) saponins. The aglycone moiety of group A saponins consists of soyasapogenol A (SA), which is an oxidized β-amyrin product, and the aglycone moiety of the DDMP saponins consists of soyasapogenol B (SB). Group A saponins produce a bitter and astringent aftertaste in soy products, whereas DDMP saponins have known health benefits for humans. We completed map-based cloning and characterization of the gene Sg-5, which is responsible for SA biosynthesis. The naturally occurring sg-5 mutant lacks group A saponins and has a loss-of-function mutation (L164*) in Glyma15g39090, which encodes the cytochrome P450 enzyme, CYP72A69. An enzyme assay indicated the hydroxylase activity of recombinant CYP72A69 against SB, which also suggested the production of SA. Additionally, induced Glyma15g39090 mutants (R44* or S348P) lacked group A saponins similar to the sg-5 mutant, indicating that Glyma15g39090 corresponds to Sg-5. Endogenous levels of DDMP saponins were higher in the sg-5 mutant than in the wild-type lines due to the loss of the enzyme activity that converts SB to SA. Interestingly, the genomes of palaeopolyploid soybean and the closely related common bean carry multiple Sg-5 paralogs in a genomic region syntenic to the soybean Sg-5 region. However, SA did not accumulate in common bean samples, suggesting that Sg-5 activity evolved after gene duplication event(s). Our results demonstrate that metabolic switching of undesirable saponins with beneficial saponins can be achieved in soybean by disabling Sg-5.

Functional Properties of Microorganisms in Fermented Foods

Fermented foods have unique functional properties imparting some health benefits to consumers due to presence of functional microorganisms, which possess probiotics properties, antimicrobial, antioxidant, peptide production, etc. Health benefits of some global fermented foods are synthesis of nutrients, prevention of cardiovascular disease, prevention of cancer, gastrointestinal disorders, allergic reactions, diabetes, among others. The present paper is aimed to review the information on some functional properties of the microorganisms associated with fermented foods and beverages, and their health-promoting benefits to consumers.

Evaluation of cytotoxicity and immune modulatory activities of soyasaponin Ab: an in vitro and in vivo study

To improve the immune efficacy of protein subunit vaccines, novel adjuvants are needed to elicit a suitable protective immune response and to promote long term immunologic memory. In this work, soyasaponin Ab, a major constituent among group A soyasaponins in soybeans was purified and prepared from soy hypocotyls. The immunomodulatory effects of soyasaponin Ab both in vitro and in vivo were investigated, and its pro-immunomodulatory molecular mechanism was also studied. For in vitro assays, with mouse macrophage cell line RAW264.7 as the studying model, both cytotoxicity and immune stimulatory activity were investigated to evaluate the potential of soyasaponin Ab as the vaccine adjuvant. The results indicated that soyasaponin Ab could be significantly safer than Quillaja saponins (QS). Soyasaponin Ab showed no toxicities over the tested concentration ranges compared to QS. Soyasaponin Ab was proved able to promote releases of inflammatory cytokines like TNFα and IL-1β in a dose-dependent manner. Furthermore, NF-κB signalling was also activated by soyasaponin Ab effectively. In addition, with TLR4 gene expression of RAW264.7 cell inhibited by RNA interference, immune stimulatory effects by soyasaponin Ab dropped down significantly. On the other hand, the in vivo experiment results showed that anti-ovalbumin (OVA) IgG, IgG1, IgG2a, IgG2b were significantly enhanced by the soyasaponin Ab and QS groups (p<0.05 or p<0.01). The results suggested that compared to QS, soyasaponin Ab may represent a viable candidate for effective vaccine adjuvant. TLR4 receptor dependent pathway may be involved in immune stimulatory effects of soyasaponin Ab.

Soyasaponins can blunt inflammation by inhibiting the reactive oxygen species-mediated activation of PI3K/Akt/NF-kB pathway

We and others have recently shown that soyasaponins abundant in soybeans can decrease inflammation by suppressing the nuclear factor kappa B (NF-kB)-mediated inflammation. However, the exact molecular mechanisms by which soyasaponins inhibit the NF-kB pathway have not been established. In this study in macrophages, soyasaponins (A1, A2 and I) inhibited the lipopolysaccharide (LPS)-induced release of inflammatory marker prostaglandin E2 (PGE2) to a similar extent as the NF-kB inhibitor (BAY117082). Soyasaponins (A1, A2 and I) also suppressed the LPS-induced expression of cyclooxygenase 2 (COX-2), another inflammatory marker, in a dose-dependent manner by inhibiting NF-kB activation. In defining the associated mechanisms, we found that soyasaponins (A1, A2 and I) blunted the LPS-induced IKKα/β phosphorylation, IkB phosphorylation and degradation, and NF-kB p65 phosphorylation and nuclear translocation. In studying the upstream targets of soyasaponins on the NF-kB pathway, we found that soyasaponins (A1, A2 and I) suppressed the LPS-induced activation of PI3K/Akt similarly as the PI3K inhibitor LY294002, which alone blocked the LPS-induced activation of NF-kB. Additionally, soyasaponins (A1, A2 and I) reduced the LPS-induced production of reactive oxygen species (ROS) to the same extent as the anti-oxidant N-acetyl-L-cysteine, which alone inhibited the LPS-induced phosphorylation of Akt, IKKα/β, IkBα, and p65, transactivity of NF-kB, PGE2 production, and malondialdehyde production. Finally, our results show that soyasaponins (A1, A2 and I) elevated SOD activity and the GSH/GSSG ratio. Together, these results show that soyasaponins (A1, A2 and I) can blunt inflammation by inhibiting the ROS-mediated activation of the PI3K/Akt/NF-kB pathway.

Biological functionality of soyasaponins and soyasapogenols

Soyasaponins are a group of structurally complex oleanane triterpenoids primarily found in soybeans and have diverse biological properties. The recent investigations and findings (since 2000) regarding the biological functions of soyasaponins and their aglycones, including their anti-inflammatory, antimutagenic, anticarcinogenic, antimicrobial, and hepato- and cardiovascular-protective activities, are herein summarized. The primary conclusion is that the use of soyasaponins and soyasapogenols in functional foods should be considered.

The content of soyasaponin and soyasapogenol in soy foods and their estimated intake in the Japanese

Soyasaponins have been reported to promote various health functions. However, the total soyasaponin and soyasapogenol content in soy products and the daily intake remain to be fully elucidated. We developed a high-performance liquid chromatography coupled with tandem mass spectrometric (HPLC–MS/MS) method to evaluate the content of group A and B soyasaponins and soyasapogenols. The total soyasaponin content was measured after pretreatment converted soyasaponins to soyasapogenols. The total soyasaponin content in soy foods was 200–1800 nmol g⁻¹, although that of soy sauce was 2–7 nmol g⁻¹. The soyasapogenol to total soyasaponin ratio was 30–50% in long-term matured miso. The majority of the soyasapogenol detected was soyasapogenol B rather than soyasapogenol A, resulting in speculation that further steps are required to liberate aglycones from glycoside-conjugated soyasaponins in soyasapogenol A. We estimated the daily intake of total soyasaponins and soyasapogenols by the Japanese, which was 50.3 and 0.59 μmol, respectively. The soyasapogenol content and the soyasapogenol to total soyasaponin ratio was considerably low in most soy products, except for long-term maturated miso. The major source of the daily intake of soyasaponins and soyasapogenols were tofu and miso, respectively.

Genetic and chemical analysis of a key biosynthetic step for soyasapogenol A, an aglycone of group A saponins that influence soymilk flavor

Although certain saponins in soybean seeds have been reported to have health benefits, group A acetyl saponins cause undesirable bitter and astringent tastes in soy products. Therefore, reduction or elimination of group A saponins is an important target for soybean breeders. A wide survey of cultivated and wild soybean germplasm identified a mutant line that lacked group A saponins. The absence of soyasapogenol A, a group A saponin aglycone, is controlled by a single recessive allele, sg-5 that mapped genetically near the SSR marker, Satt117, on soybean chromosome 15 (linkage group E). The locus is epistatic to Sg-1, which controls the terminal sugar variation on the C-22 sugar chain of soyasapogenol A, and allelic differences at this locus lead to changes in the amount of DDMP saponins and their derivatives group B and E products. These findings provide a new insight into the biosynthetic pathway of soybean saponins, and identify a genetic approach that can be applied to improve the quality of foods produced from soybean.

Efficient protocol for isolation and purification of different soyasaponins from soy hypocotyls

Soyasaponins are naturally occurring triterpenoid glycosides associated with many biological activities. The aim of the present study was to develop an effective method for isolation and purification of differently glycosylated, acetylated, and 2,3-dihydro-2,5-dihydroxy-6-methyl-4H-pyran-4-one (DDMP)-conjugated soyasaponins from soy hypocotyls. Both gel filtration using Sephadex LH-20 chromatography (Amersham Pharmacia Biotech AB; elution phase: methanol, flow rate: 3.0 mL/min, sample loading: 60 mg) and high-speed countercurrent chromatography (stationary phase: n-butanol-acetic acid (5.0%, v/v), mobile phase: water flow rate: 3.0 mL/min, sample loading: 100 mg) could effectively fractionate isoflavones and soyasaponins from the crude extract with yield of soyasaponin complexes 20.5 mg and 22.3 mg, respectively. After fractionation, the soyasaponin complexes could be purified further using preparative HPLC to separate individuals. A total of nine soyasaponins, triacetyl soyasaponin Ab (yield 1.55%, HPLC purity >98%), Aa (2.68%, >99%), Ab (18.53%, >98%), Ae (0.85%, >98%), Ba (0.63%, >91%), Af (1.12%, >85%), Bb (3.45%, >98%) and Be (0.59%, >76.8%) were obtained. DDMP-conjugated groups, αg (2.06%, >85%), βg (7.59%, >85%), and γg (0.29%, >85%) that were very labile even in mild conditions, were also collected. The method described here can be used as an effective protocol to separate different soyasaponins occurring in the original sample.

Current knowledge and future direction of research on soy isoflavones as a therapeutic agents

Isoflavones, the most abundant phytoestrogens in Soy beans, are structurally similar to 17beta-estradiol. The antioxidant property of the soy isoflavones, namely, genistein and daidzein is well established in different experimental models and also in clinical studies. The compounds have been found effective in the management of diabetes by acting on peroxisome proliferator-activated receptors. It reduces the risk of coronary heart disease by reducing the level of low-density lipoprotein and triglycerides. Soy isoflavones have the potential in the treatment of osteoporosis to act on osteoclasts further to inhibit tyrosine kinase. Among the soy isoflavones, genistein is the potential compound found effective in the treatment of cancer by acting on androgen receptor further to inhibit tyrosine kinases. In this article, various aspects of the diverse biological activities of soy isoflavones and their potential clinical implications with mechanism of action, especially in the treatment and prevention of diabetes, cardiovascular diseases, cancer, osteoporosis, neuroprotection, and also future area of research on soy isoflavones are reviewed and discussed.

Genetic analysis of variations in the sugar chain composition at the C-3 position of soybean seed saponins

Saponins are sterols or triterpene glycosides that are widely distributed in plants. The biosynthesis of soybean saponins is thought to involve many kinds of glycosyltransferases, which is reflected in their structural diversity. Here, we performed linkage analyses of the Sg-3 and Sg-4 loci, which may control the sugar chain composition at the C-3 sugar moieties of the soybean saponin aglycones soyasapogenols A and B. The Sg-3 locus, which controls the production of group A saponin Af, was mapped to chromosome (Chr-) 10. The Sg-4 locus, which controls the production of DDMP saponin βa, was mapped to Chr-1. To elucidate the preference of sugar chain formation at the C-3 and C-22 positions, we analyzed the F(2) population derived from a cross between a mutant variety, Kinusayaka (sg-1(0)), for the sugar chain structure at C-22 position, and Mikuriya-ao (sg-3), with respect to the segregation of the composition of the group A saponins, and found that the formation of these sugar chains was independently regulated. Furthermore, a novel saponin, predicted to be A0-γg, 3-O-[β-d-galactopyranosyl (1→2)-β-d-glucuronopyranosyl]-22-O-α-l-arabinopyranosyl-soyasapogenol A, appeared in the hypocotyl of F(2) individuals with genotype sg-1(0)/sg-1(0)sg-3/sg-3.

Manipulation of saponin biosynthesis by RNA interference-mediated silencing of β-amyrin synthase gene expression in soybean

Soybean seeds contain substantial amount of diverse triterpenoid saponins that influence the seed quality, although little is known about the physiologic functions of saponins in plants. We now describe the modification of saponin biosynthesis by RNA interference (RNAi)-mediated gene silencing targeted to β-amyrin synthase, a key enzyme in the synthesis of a common aglycon of soybean saponins. We identified two putative β-amyrin synthase genes in soybean that manifested distinct expression patterns with regard to developmental stage and tissue specificity. Given that one of these genes, GmBAS1, was expressed at a much higher level than the other (GmBAS2) in various tissues including the developing seeds, we constructed two RNAi vectors that encode self-complementary hairpin RNAs corresponding to the distinct regions of GmBAS1 under the control of a seed-specific promoter derived from the soybean gene for the α' subunit of the seed storage protein β-conglycinin. These vectors were introduced independently into soybean. Six independent transgenic lines exhibited a stable reduction in seed saponin content, with the extent of saponin deficiency correlating with the β-amyrin synthase mRNA depletion. Although some transgenic lines produced seeds almost devoid of saponins, no abnormality in their growth was apparent and the antioxidant activity of their seeds was similar to that of control seeds. These results suggest that saponins are not required for seed development and survival, and that soybean seeds may therefore be amenable to the modification of triterpenoid saponin content and composition through molecular biologic approaches.

Effect of Soybean Hypocotyl Extract on Lipid Peroxidation in GK Rats

Vascular complications, as a consequence of atherosclerosis, are main causes of morbidity and mortality in patients with diabetes mellitus. There is increasing evidence that lipid peroxidation and oxidative modification of low density lipoprotein (LDL) is important in atherogenesis. In this study we investigated the effect of soybean hypocotyl extract (SHE), rich in isoflavones and saponins, on lipid peroxide (LPO) levels in liver, plasma and lipoproteins in GK diabetic rats, and its efficacy on the reduction of susceptibility of LDL and high density lipoprotein (HDL) to oxidation. The oxidative modification of LDL and HDL was determined with the lag time of copper ion-induced oxidation curve identified by the conjugated dienes. In SHE group which were fed diet containing 40 g/kg of SHE for 16 weeks, LPO levels in liver, plasma and HDL fraction were significantly decreased compared with the control group. The lag phage of LDL oxidation curve was prolonged noticeably by a mean of 27 min in SHE group as compared to the control group, indicating a reduced susceptibility to oxidation. The results suggest that intake of soybean hypocotyl extract might be useful for the prevention and treatment of diabetes mellitus and diabetes-associated diseases.