Motohiro Maebuchi

Soybean β-Conglycinin Diet Suppresses Serum Triglyceride Levels in Normal and Genetically Obese Mice by Induction of β-Oxidation, Downregulation of Fatty Acid Synthase, and Inhibition of Triglyceride Absorption

The purpose of this study was to discover the effects of soybean β-conglycinin (7S-globulin) and glycinin (11S-globulin) on serum lipid levels and metabolism in the livers of normal and genetically obese mice. Male normal (ICR) and obese (KK-Ay) mice were fed ad libitum high fat diets for two weeks, followed by a 2-week restriction of diet (2 g diet/mouse/day) containing 20% casein, soybean β-conglycinin, or soybean glycinin, and then sacrificed immediately. Serum triglyceride (TG), glucose, and insulin levels of β-conglycinin-fed mice were lower than in casein- and glycinin-fed mice of both strains. In order to analyze the related events to these effects, enzyme activities and relative mRNA levels of lipid metabolism-related proteins were measured. The activities of two enzymes related to fatty acid β-oxidation were higher while that of fatty acid synthase was lower in livers of β-conglycinin-fed mice than of casein-fed both mice. Messenger RNA levels of acyl-CoA oxidase (fatty acid β-oxidation related enzyme) were significantly higher in livers of β-conglycinin-fed mice than of both casein-fed mice. On the contrary, mRNA levels of SREBP-1 and 2 tended to be lowered in livers of soy protein-fed mice than of both casein-fed mice. Fecal excretion of TG was higher in β-conglycinin-fed mice than in casein-fed mice. Our results demonstrated that the soy β-conglycinin diet reduced serum TG levels by acceleration of β-oxidation, suppression of fatty acid synthase and/or increased TG fecal excretion, and also diminished serum glucose and insulin levels. Some of these events might be caused at the transcriptional levels, judged from the result that relative messenger RNA levels of lipid metabolism-related proteins were altered. These results suggest that soy β-conglycinin could be a potentially useful dietary protein source for the prevention of hypertriglyceridemia, hyperinsulinemia, and hyperglycemia, which are recognized as risk factors for atherosclerosis.

Low resistin levels in adipose tissues and serum in high-fat fed mice and genetically obese mice: development of an ELISA system for quantification of resistin

Obesity is a major risk factor for insulin resistance. Resistin, an adipocyte-derived hormone-like molecule, is considered to serve as an important link between obesity and insulin resistance. However, the physiological role of resistin and the mechanism by which it neutralizes insulin action are still unclear. There are also conflicting reports that cast doubt on the cause of insulin resistance. In this study, we developed an enzyme-linked immunosorbent assay (ELISA) system for quantification of mouse resistin levels, analyzed in relation to insulin resistance. C57BL/6J mice fed high-fat diet compared with normal diet had low resistin levels (by 70%, P<0.01) in epididymal adipose tissues. Genetically obese mice, db/db and KK-A(y), had hyperinsulinemia and hyperglycemia but low resistin levels (decreases by 83 and 90%, both P<0.01) compared with C57/BL6J mice in epididymal adipose tissues. Serum resistin levels determined by Western blotting showed a similar pattern to those in adipose tissues. Resistin levels in adipose tissues correlated with serum adiponectin concentrations positively (r=0.49). Our results indicate that the novel ELISA system is suitable for measurement of resistin levels in adipose tissues. The results do not support a role for resistin in insulin resistance.

Changes in lipid metabolism by soy β-conglycinin-derived peptides in HepG2 cells.

In this study, HepG2 cells were treated with short peptides (7S-peptides) derived from highly purified soybean beta-conglycinin (7S), which was free from lipophilic protein, and the effect of the peptide treatment on lipid metabolism was determined. 7S-peptide treatment suppressed the secretion of apolipoprotein B-100 from HepG2 cells into the medium. The 7S-peptides also suppressed the incorporation of (3)H-glycerol and (14)C-acetate into triacylglyceride but not into major phospholipids, such as phosphatidylcholine and phosphatidylethanolamine. Additionally, the synthesis of cholesterol esters was dramatically decreased for 2 h after the addition of the 7S-peptides, whereas the synthesis of cholesterol remained unchanged by 4 h and increased by 8 h after the addition of the 7S-peptides. The cleaved nuclear form of SREBP-2 increased 8 h after the addition of the 7S peptides, suggesting a decrease in intracellular cholesterol levels. Analysis of changes in mRNA expression after 7S-peptide treatment suggested that the 7S-peptides lower the level of cholesterol in the endoplasmic reticulum, increase the mRNA of genes related to beta-oxidation of fatty acids, and increase the synthesis of cholesterol. From these results, it may be concluded that the peptides derived from 7S altered the lipid metabolism to decrease secretion of apolipoprotein B-100-containing lipoprotein from HepG2 cells.

Increased tyrosine in the brain and serum of mice by orally administering dipeptide SY

We examined the effect of orally administering L-Ser-L-Tyr (SY) dipeptide on the brain of a serine deficiency disease model mouse to attain the efficient delivery of L-Tyr and L-Ser into the mouse brain. Oral SY administration increased the L-Tyr level more efficiently than L-Tyr administration with the same intake dose, but did not significantly affect the L-Ser level when compared with L-Ser administration.

Quantitative mass spectrometric analysis of dipeptides in protein hydrolysate by a TNBS derivatization-aided standard addition method

The aim of this study was to establish, through a standard addition method, a convenient quantification assay for dipeptides (GY, YG, SY, YS, and IY) in soybean hydrolysate using 2,4,6-trinitrobenzene sulfonate (TNBS) derivatization-aided LC-TOF-MS. Soybean hydrolysate samples (25.0 mg mL(-1)) spiked with target standards were subjected to TNBS derivatization. Under the optimal LC-MS conditions, five target dipeptides derivatized with TNBS were successfully detected. Examination of the standard addition curves, with a correlation coefficient of r(2) > 0.979, provided a reliable quantification of the target dipeptides, GY, YG, SY, YS, and IY, in soybean hydrolysate to be 424 ± 20, 184 ± 9, 2188 ± 199, 327 ± 16, and 2211 ± 133 μg g(-1) of hydrolysate, respectively. The proposed LC-MS assay is a reliable and convenient assay method, with no interference from matrix effects in hydrolysate, and with no requirement for the use of an isotope labeled internal standard.