Shuichi Kamo

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.

Comparison of bioavailability (I) between soyasaponins and soyasapogenols, and (II) between group A and B soyasaponins

OBJECTIVE The bioavailability and absorption of soyasaponins and soyasapogenols remain unclear; therefore, the aim of this study was to evaluate plasma soyasaponin and soyasapogenol concentrations and absorption characteristics. METHODS Sprague-Dawley rats were divided into three groups (n = 6), and each group was orally administered a single dose of each test sample. Blood was collected from the cervical vein and plasma soyasapogenol concentrations were measured. A Caco-2 cell monolayer absorption assay was performed in which both soyasapogenol A and B (10 μmol/L) were added to the apical side, and soyasapogenol concentrations on the apical and basolateral sides were determined. Permeability parameters also were calculated. RESULTS Absorption of soyasapogenol B was better than that of group B soyasaponins. The time needed to reach peak soyasapogenol B concentration in rats administered soyasapogenol B was 1 to 3 h, whereas that in rats administered group B soyasaponins was 8 h. The ratio of plasma soyasapogenol A to plasma soyasapogenol B was lower than the ratio in the test samples administered. The apical-to-basolateral absorption of soyasapogenol B in the Caco-2 human colon cancer monolayer cell model (apparent permeability coefficient [Papp], 5.5 × 10(-6) cm/sec) was higher than that of soyasapogenol A (Papp, 1.6 × 10(-6) cm/sec). CONCLUSION These results suggest that bioavailability of soyasapogenols is better than that of corresponding soyasaponins and that of group B soyasaponins is better than that of group A soyasaponins.

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.

Soyasapogenols reduce cellular triglyceride levels in 3T3-L1 mouse adipocyte cells by accelerating triglyceride lipolysis

Soyasapogenol is a soyasaponin aglycone, which has been suggested to exert a more potent function than the glycoside form. In this study, the effect of soyasapogenol A and B on cultured adipocyte cell function was investigated using mouse 3T3-L1 adipocyte cells. 3T3-L1 cells were treated with insulin, dexamethasone, and 3-isobutyl-1-methylxanthine for differentiation to adipocytes, and the cells were then cultured in the presence of soyasapogenol A or B (6.25 or 12.5 µM). The media were harvested and refreshed every 2 d. After a 10 d culture, the cells were harvested and the triglyceride content of the cells was determined. The triglyceride content of soyasapogenol B-treated cells was significantly lower than those of vehicle-treated cells. Glycerol and free fatty acid levels in the soyasapogenol-treated cell media were higher than those in vehicle cells. However, there was no difference in the level of adipose triglyceride lipase among soyasapogenol A-, soyasapogenol B-, and vehicle-treated cells. The secreted adiponectin and resistin levels of soyasapogenol-treated cell media were also different compared with those of vehicle-treated cells. Especially, the secreted resistin level in soyasapogenol B-treated cell media was obviously reduced compared with that of vehicle-treated cells. Taken together, these results suggest that soyasapogenol B exerted an anti-obesity and anti-diabetic effect on adipocytes by lowering the cellular triglyceride level by accelerating triglyceride lipolysis with reduced resistin secretion.