Protective effect of soybean saponins and major antioxidants against aflatoxin B1-induced mutagenicity and DNA-adduct formation

Preparation of in vivo intermediate metabolites of soybean saponins with improved bioactivity by in vitro deacetylation and deglucosylation

Unlike natural soyasaponins and their aglycones formed by enzymatic hydrolysis in the human intestine, in vivo intermediate soyasaponin metabolites are difficult to prepare. Therefore, the pharmacological activities of in vivo intermediate soyasaponins remain uninvestigated. Herein, in vivo intermediate soyasaponins with purities of >90% were prepared by in vitro deacetylation (alkaline treatment) and deglucosylation (β-glucosidase treatment) of natural soyasaponins using preparative high-performance liquid chromatography. These compounds exhibited higher anti-inflammatory and antioxidant activities than natural soyasaponins in in vitro bioassays, suggesting that the intermediate soyasaponins can be used as improved bioactive food supplements. To the best of our knowledge, this is the first study reporting the in vitro preparation and bioassays of in vivo intermediate soyasaponin metabolites formed in the human intestine.

Research progress on the protection and detoxification of phytochemicals against aflatoxin B1-Induced liver toxicity

Aflatoxin B₁ (AFB₁) is a potent hepatotoxic toxin, which can cause hepatitis, cirrhosis, and liver immunological damage. It has been involved in the etiology of human hepatocellular carcinoma. AFB₁ can cause oxidative stress in the body's metabolism process, and then cause cytotoxicity, such as apoptosis and DNA damage. Scientific research has discovered that phytochemicals can induce the detoxification pathway of AFB₁ through its biotransformation, thereby reducing the damage of AFB₁ to the human body. In clinical treatment, certain phytochemicals have been effectively used in the treatment of liver injury due to the advantages of multiple targets, multiple pathways, low toxicity and side effects. Therefore, the article summarizes the toxic mechanism of AFB₁-induced hepatoxicity, and the related research progress of phytochemicals for preventing and treating its cytotoxicity and genotoxicity. We also look forward to the existing problems and application prospects of phytochemicals in the pharmaceutical industry, in order to provide theoretical reference for the prevention and treatment of AFB₁ poisoning in future research work.

Menopause-Associated Lipid Metabolic Disorders and Foods Beneficial for Postmenopausal Women

Menopause is clinically diagnosed as a condition when a woman has not menstruated for one year. During the menopausal transition period, there is an emergence of various lipid metabolic disorders due to hormonal changes, such as decreased levels of estrogens and increased levels of circulating androgens; these may lead to the development of metabolic syndromes including cardiovascular diseases and type 2 diabetes. Dysregulation of lipid metabolism affects the body fat mass, fat-free mass, fatty acid metabolism, and various aspects of energy metabolism, such as basal metabolic ratio, adiposity, and obesity. Moreover, menopause is also associated with alterations in the levels of various lipids circulating in the blood, such as lipoproteins, apolipoproteins, low-density lipoproteins (LDLs), high-density lipoproteins (HDL) and triacylglycerol (TG). Alterations in lipid metabolism and excessive adipose tissue play a key role in the synthesis of excess fatty acids, adipocytokines, proinflammatory cytokines, and reactive oxygen species, which cause lipid peroxidation and result in the development of insulin resistance, abdominal adiposity, and dyslipidemia. This review discusses dietary recommendations and beneficial compounds, such as vitamin D, omega-3 fatty acids, antioxidants, phytochemicals—and their food sources—to aid the management of abnormal lipid metabolism in postmenopausal women.

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.

Supplementation of Seaweeds Extracts Suppresses Azoxymethane-induced Aberrant DNA Methylation in Colon and Liver of ICR Mice

Background:

Seamustard and seatangle are commonly consumed seaweeds in Korea and rich sources of non-digestible polysaccharides which possess biological activities. However anti-mutagenic and anti-cancer activities of these seaweeds under physiological condition have not been clarified yet. The objective of this study was to investigate the effect of seaweeds consumption on azoxymethane (AOM) -induced DNA methylation at N⁷ and O⁶ position of guanine base, an indicator of DNA damage related to cancer initiation.

Methods:

Thirty ICR mice were divided into five groups and fed one of the following diets for two weeks: control diet, diet containing 10% water-soluble or water-insoluble fraction of seamustard or seatangle. After two weeks of experimental diet AOM was injected at 6 hours before sacrifice and N⁷-methylguanine (N⁷-meG) and O⁶-methylguanine (O⁶-meG) from the colon and liver DNA were quantified using a gas chromatography-mass spectroscopy.

Results:

Water-soluble fractions of both seamustard and seatangle significantly reduced AOM-induced production of N⁷-meG guanine in colon and liver. Also water-soluble fractions of these seaweeds suppressed the level of methylation at O⁶-guanine of colon and liver directly responsible for tumorigenesis. While water-insoluble fraction of seamustard suppressed the production of N⁷-meG in liver this seaweed fraction decreased O⁶-meG and the ratio of O⁶/N⁷-meG in liver. Water insoluble fraction of seatangle decreased both O⁶- and N⁷-meG in colon and liver. Supplementation of all seaweeds extracts increased fecal weight of animals and the increase of fecal weight by water-insoluble fraction of seaweeds were higher than that by water-soluble fraction.

Conclusion:

Seamustard and seatangle intake may effectively prevent colon and liver carcinogenesis by decreasing DNA damage and the mechanism of inhibiting carcinogenesis by seaweeds in a long term study are warranted.

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.

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.

Non-isoflavone phytochemicals in soy and their health effects

Epidemiological and clinical studies have linked consumption of soy foods with low incidences of a number of chronic diseases, such as cardiovascular diseases, cancer, and osteoporosis. Over the past decades, enormous research efforts have been made to identify bioactive components in soy. Isoflavones and soy protein have been suggested as the major bioactive components in soy and have received considerable attention. However, there are hundreds of phytochemical components in soybeans and soy-based foods. In recent years, accumulating evidence has suggested that the isoflavones or soy proteins stripped of phytochemicals only reflect certain aspects of health effects associated with soy consumption. Other phytochemicals, either alone or in combination with isoflavones or soy protein, may be involved in the health effects of soy. This review attempts to summarize major non-isoflavone phytochemicals in soy, as well as their bioavailability and health effects. In addition, a brief discussion of components formed during food processing is also included.

Gamma irradiation induced enhancement in isoflavones, total phenol, anthocyanin and antioxidant properties of varying seed coat colored soybean

Three Indian soybean genotypes, namely, Kalitur, Hara soya and NRC37 with black, green and yellow colored seed coat respectively were gamma irradiated at a dose of 0.5, 2.0, and 5.0 kGy. The total isoflavones and total phenol content (TPC) in all the genotypes increased significantly at a dose of 0.5 and 2 kGy respectively. The anthocyanin content was high in Kalitur, while other genotypes showed no detectable amounts of it. The hydroxyl radical scavenging activity (HRSA), DPPH free radical scavenging activity (FRSA) and total antioxidant power (TAP) were highest in Kalitur with black seed coat color. However, maximum enhancement in antioxidant properties was found in NRC37 with yellow followed by Hara soya with green seed coat color at a dose of 0.5 and 2.0 kGy. It was also observed that the 3 soybean genotypes showed an increase in antioxidant constituents and antioxidative properties at lower doses of 0.5 and 2.0 kGy while, the antioxidant effects of soy seeds were either decreased or remained constant at a higher dose of 5.0 kGy. It is suggested that mild gamma irradiation enhanced the antioxidant constituents and, hence, antioxidant potential of soybean seeds.

Morphological study on apoptosis Hela cells induced by soyasaponins

Soyasaponins are present in legumes and soybeans are the primary dietary source of saponins. SS-II, the second fraction of soyasaponins, was separated by column chromatographic method with D101A macroporous resin from soybean. In this paper, at the concentration range of 100-400 mg/L, SS-II had obvious cytotoxic effect on Hela cells by MTT assay. After Hela cells were treated with SS-II, typical apoptotic morphological changes, including nuclear fragmentation, cytoplasm shrinkage and decrease of cell volume, were observed by fluorescence microscope, transmission electron microscope (TEM) and confocal laser scanning microscope (CLSM), respectively. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay also confirmed that SS-II-treated Hela cells showed apoptotic features. The results suggested that soyasaponins were a potential antitumor compound and the apoptosis induced by soyasaponins was a key antitumor mechanism.

Antiproliferative crude soy saponin extract modulates the expression of IkappaBalpha, protein kinase C, and cyclooxygenase-2 in human colon cancer cells

Frequent consumption of soy and soy-based products is associated with reduced cancer incidence particularly for breast, colon, and prostate cancer. In this study, we examined the effect of crude soy saponin extract on PMA (phorbol 12-myristate 13-acetate)-induced inflammatory responses. Human adenocarcinoma cells (HT-29) were treated with various concentrations of saponin extract for 72 h. Cell growth was measured at 24, 48 and 72 h of incubation, and the PMA-induced expressions of cyclooxygenase-2 (COX-2), protein kinase C (PKC), and IkappaBalpha were determined. The results indicate that crude saponin extract decreased cell growth in a dose- and time-dependent manner. Crude soy saponin extract suppressed the degradation of IkappaBalpha in PMA-stimulated cells, while COX-2 and PKC expressions were significantly down-regulated. These findings support the hypothesis that the soy saponins reduce the risk of colon tumorigenesis possibly by suppressing inflammatory responses.

Use of human-derived liver cell lines for the detection of environmental and dietary genotoxicants; current state of knowledge

This article gives an overview of the results of genotoxicity tests, which have been conducted within the last 5 years with the human liver cell line HepG2. It is an update of an earlier review from 1998 (by Knasmüller et al.). In addition, a number of publications are discussed which are relevant for the use of human derived liver cell lines in genetic toxicology. They concern the establishment of new endpoints, the development of new cell lines and possible pitfalls and problems. HepG2 cells have been used to test a wide variety of compounds over the last years. The most interesting observations are that the cells are highly sensitive toward polycyclic aromatic hydrocarbons and that genotoxic effects are seen with a number of carcinogenic mycotoxins, that give negative results in other in vitro assays. Carcinogenic metals such as As and Cd caused positive results as well, whereas only marginal or negative results were seen with nitrosamines. The low sensitivity toward these latter carcinogens is probably due to a lack of cytochrome P4502E1 which catalyses their activation. Also, a number of structurally different synthetic pesticides as well as bioactive plant constituents ("natural pesticides") have been tested and with some of them genotoxic effects were found. In most experiments, the formation of micronuclei was used as an endpoint; however also the single cell gel electrophoresis assay is increasingly used. Several transfectant lines of HepG2 have been constructed which express increased levels of phase I enzymes (such as CYP1A1, CYP1A2, CYP2E1 etc.); furthermore, cell lines became available which express human glutathione-S-transferases. These new clones might be particularly useful for the investigation of specific classes of genotoxicants and also for mechanistic studies. Apart from HepG2 cells, a number of other human derived liver cell lines have been isolated, but so far no data from genotoxicity experiments are available, except for Hep3B cells, which were compared with HepG2 and found to be less sensitive in general. Studies with HepG2 clones of a different origin indicate that the cells differ in regard to their sensitivity toward genotoxicants; also medium effects and the cultivation time might affect the outcome of genotoxicity studies. Overall, the results support the assumption that HepG2 cells are a suitable tool for genotoxicity testing.

Soyasaponins: the relationship between chemical structure and colon anticarcinogenic activity

Soyasaponins are bioactive compounds found in many legumes. Although crude soyasaponins have been shown to have anti-colon carcinogenic activity, there have been no structure-activity studies. In this study, therefore, purified soyasaponins and soyasapogenins were tested for their ability to suppress the growth of HT-29 colon cancer cells, as determined by the WST-1 assay, over a concentration range of 0-50 ppm. Soyasaponin I and III, soyasapogenol B monoglucuronide, soyasapogenol B, soyasaponin A1, soyasaponin A2, and soyasapogenol A were evaluated. Also tested were mixtures comprising acetylated group A soyasaponins, deacetylated group A soyasaponins, and group B soyasaponins. The most potent compounds were the aglycones soyasapogenol A and B, which showed almost complete suppression of cell growth. The glycosidic soyasaponins by comparison were largely inactive. Soyasaponin A(1), A(2), and I, group B and deacetylated and acetylated group A fractions had no effect on cell growth. Soyasaponin III and soyasapogenol B monoglucuronide were marginally bioactive. These results suggested that the bioactivity of soyasaponins increased with increased lipophilicity. Results from in vitro fermentation suggested that colonic microflora readily hydrolyzed the soyasaponins to aglycones. These observations suggest that the soyasaponins may be an important dietary chemopreventive agent against colon cancer, after alteration by microflora.

Use of a human-derived liver cell line for the detection of cytoprotective, antigenotoxic and cogenotoxic agents

In this paper, we reviewed the data on the use of HepG2 cells to detect cytoprotective, antigenotoxic and cogenotoxic agents. Owing to their intact and inducible phase I and phase II enzymes, HepG2 cells are able to activate and detoxify xenobiotics and therefore reflect the metabolism of xenobiotics in the human body better than other metabolically incompetent cells used in conventional in vitro assays. Several dietary and non-dietary agents were found to be protective against different groups of cytotoxic and DNA-damaging xenobiotics in HepG2 cells and the mechanism of protection includes scavenging of electrophiles, reactive oxygen species and peroxides, inhibition of phase I activating enzymes, induction of phase II detoxifying enzymes and interactions with DNA-repair and/or replication processes. Additionally, certain non-mutagenic substances were found to enhance the effect of genotoxic agents in HepG2 cells by increasing the metabolic activation of the latter. In conclusion, HepG2 cells are of great relevance to detect cytotoxic and genotoxic substances and by extension cytoprotective, antigenotoxic and cogenotoxic agents.

Anticarcinogenic properties of a daidzein-rich fraction isolated from soybean

In a previous study, we demonstrated that the methanol extract of soybean powder contains an active component(s) that promotes the differentiation of HL-60 cells. Partial purification of the extract, using solvent fractionation and silica gel chromatography, produced an active fraction rich in daidzein. The daidzein-rich fraction (DRF) was evaluated for its cancer preventive potential by assessing its cytotoxic activity and effect on the expression of the transforming growth factor beta (TGF-beta) family of cytokines and their receptors. DRF appeared to exert cytotoxic activity via an apoptotic pathway as evaluated by a DNA fragmentation assay and caspase-3 induction. DRF also increased the expression of TGF-beta2, but had little effect on the expression of other members of the TGF-beta family of cytokines and their receptors, or on the expression of the vascular endothelial growth factor gene. In conclusion, the DRF isolated from the methanol extract of soybean may have the potential to prevent tumorigenesis and, therefore, deserves to undergo further evaluation of its active component(s) and in vivo evaluation for anticarcinogenic efficacy.