In vitro and in vivo effects of hydrolysates from conglycinin on intestinal microbial community of mice after Escherichia coli infection

The Functional Interplay between Gut Microbiota, Protein Hydrolysates/Bioactive Peptides, and Obesity: A Critical Review on the Study Advances

Diet is an essential factor determining the ratio of pathogenic and beneficial gut microbiota. Hydrolysates and bioactive peptides have been described as crucial ingredients from food protein that potentially impact human health beyond their roles as nutrients. These compounds can exert benefits in the body, including modulation of the gut microbiota, and thus, they can reduce metabolic disorders. This review summarized studies on the interaction between hydrolysates/peptides, gut microbes, and obesity, focusing on how hydrolysates/peptides influence gut microbiota composition and function that improve body weight. Findings revealed that gut microbes could exert anti-obesity effects by controlling the host’s energy balance and food intake. They also exhibit activity against obesity-induced inflammation by changing the expression of inflammatory-related transcription factors. Protein hydrolysates/peptides can suppress the growth of pro-obesity gut bacteria but facilitate the proliferation of those with anti-obesity effects. The compounds provide growth factors to the beneficial gut bacteria and also improve their resistance against extreme pH. Hydrolysates/peptides are good candidates to target obesity and obesity-related complications. Thus, they can allow the development of novel strategies to fight incidences of obesity. Future studies are needed to understand absorption fate, utilization by gut microbes, and stability of hydrolysates/peptides in the gut under obesity.

Regulation of Intestinal Inflammation by Soybean and Soy-Derived Compounds

Environmental factors, particularly diet, are considered central to the pathogenesis of the inflammatory bowel diseases (IBD), Crohn’s disease and ulcerative colitis. In particular, the Westernization of diet, characterized by high intake of animal protein, saturated fat, and refined carbohydrates, has been shown to contribute to the development and progression of IBD. During the last decade, soybean, as well as soy-derived bioactive compounds (e.g., isoflavones, phytosterols, Bowman-Birk inhibitors) have been increasingly investigated because of their anti-inflammatory properties in animal models of IBD. Herein we provide a scoping review of the most studied disease mechanisms associated with disease induction and progression in IBD rodent models after feeding of either the whole food or a bioactive present in soybean.

Role of the Microbiome in Mediating Health Effects of Dietary Components

Numerous recent observation and intervention studies suggest that the microbiota in the gut and oral cavity play important roles in host physiology, including disease development and progression. Of the many environmental factors involved, dietary components play a pivotal role in shaping the microbiota community and function, thus eliciting beneficial or detrimental consequences on host health. The microbiota affect human physiology by altering the chemical structures of dietary components, thus creating new biological properties and modifying their lifetime and bioavailability. This review will describe the causal mechanisms between the microbiota and some specific bacterial species and diet components providing health benefits and how this knowledge could be incorporated in dietary strategies for improving human health.

Modulation of Gut Microbiota by Soybean 7S Globulin Peptide That Involved Lipopolysaccharide-Peptide Interaction

Soybean protein exhibits nutritional significance for the control of metabolic syndrome, and evidence suggests that gut microbiota are implicated in the control of metabolic disorders. This study aimed to investigate the modulation of pepsin-released peptides of soybean 7S globulin on gut microbiota and possible association between changes of gut microbiota composition and lipopolysaccharide (LPS)-peptide interaction. In vitro fermentation experiments showed that the extension region (ER) fragments of soybean 7S globulin selectively suppressed proinflammatory Gram-negative bacteria. ER peptides also promoted the highest production of short-chain fatty acids (SCFAs), which were associated with increase of the relative abundance of Lachnospiraceae and Lactobacillaceae. Isothermal titration calorimetry (ITC) and Langmuir monolayer studies demonstrated that ER peptides exhibited high affinity to LPS in the presence of Ca²⁺ and developed into β-sheet-rich aggregate structures, thus weakening the stability of LPS monolayers. This finding supplies a possible explanation for improvement of the effects of soybean 7S globulin on metabolic disease.

Soy compared with milk protein in a Western diet changes fecal microbiota and decreases hepatic steatosis in obese OLETF rats

Soy protein is effective at preventing hepatic steatosis; however, the mechanisms are poorly understood. We tested the hypothesis that soy vs. dairy protein-based diet would alter microbiota and attenuate hepatic steatosis in hyperphagic Otsuka Long-Evans Tokushima fatty (OLETF) rats. Male OLETF rats were randomized to "Western" diets containing milk protein isolate (MPI), soy protein isolate (SPI) or 50:50 MPI/SPI (MS) (n=9-10/group; 21% kcal protein) for 16 weeks. SPI attenuated (P<.05) fat mass and percent fat by ~10% compared with MS, but not compared with MPI. Serum thiobarbituric acid reactive substance and total and low-density lipoprotein cholesterol concentrations were lower (P<.05) with dietary SPI vs. MPI and MS. Histological hepatic steatosis was lower (P<.05) in SPI compared with MPI or MS. Lipidomic analyses revealed reductions (P<.05) in hepatic diacylglycerols but not triacylglycerols in SPI compared with MPI, which was associated with lower hepatic de novo lipogenesis (ACC, FAS and SCD-1 protein content, and hepatic 16:1 n-7 and 18:1 n-7 PUFA concentrations) (P<.05) compared with MPI and MS; however, MPI displayed elevated hepatic mitochondrial function compared with SPI and MS. Fecal bacterial 16S rRNA analysis revealed SPI-intake elicited increases (P<.05) in Lactobacillus and decreases (P<.05) in Blautia and Lachnospiraceae suggesting decreases in fecal secondary bile acids in SPI rats. SPI and MS exhibited greater (P<.05) hepatic Fxr, Fgfr4, Hnf4a, HmgCoA reductase and synthase mRNA expression compared with MPI. Overall, dietary SPI compared with MPI decreased hepatic steatosis and diacylglycerols, changed microbiota populations and altered bile acid signaling and cholesterol homeostasis in a rodent model of obesity.

Soy protein isolate inhibits hepatic tumor promotion in mice fed a high-fat liquid diet

Alcoholic and nonalcoholic fatty liver diseases are risk factors for development of hepatocellular carcinoma, but the underlying mechanisms are poorly understood. On the other hand, ingestion of soy-containing diets may oppose the development of certain cancers. We previously reported that replacing casein with a soy protein isolate reduced tumor promotion in the livers of mice with alcoholic liver disease after feeding a high fat ethanol liquid diet following initiation with diethylnitrosamine. Feeding soy protein isolate inhibited processes that may contribute to tumor promotion including inflammation, sphingolipid signaling, and Wnt/β-catenin signaling. We have extended these studies to characterize liver tumor promotion in a model of nonalcoholic fatty liver disease produced by chronic feeding of high-fat liquid diets in the absence of ethanol. Mice treated with diethylnitrosamine on postnatal day 14 were fed a high-fat liquid diet made with casein or SPI as the sole protein source for 16 weeks in adulthood. Relative to mice fed normal chow, a high fat/casein diet led to increased tumor promotion, hepatocyte proliferation, steatosis, and inflammation. Replacing casein with soy protein isolate counteracted these effects. The high fat diets also resulted in a general increase in transcripts for Wnt/β-catenin pathway components, which may be an important mechanism, whereby hepatic tumorigenesis is promoted. However, soy protein isolate did not block Wnt signaling in this nonalcoholic fatty liver disease model. We conclude that replacing casein with soy protein isolate blocks development of steatosis, inflammation, and tumor promotion in diethylnitrosamine-treated mice fed high fat diets. Impact statement The impact of dietary components on cancer is a topic of great interest for both the general public and the scientific community. Liver cancer is currently the second leading form of cancer deaths worldwide. Our study has addressed the effect of the protein source on hepatic tumor promotion in a mouse model reflecting aspects of non-alcoholic fatty liver disease (NAFLD). A high-fat liquid diet with casein as the protein source promotes hepatic injury and tumor promotion in diethylnitrosamine-treated mice. Replacing casein with a soy protein isolate led to a pronounced diminishment of tumor promotion and associated hepatic injury and inflammation. The study thus demonstrates that a dietary protein source can have beneficial, preventative effects on hepatic tumor promotion.

Soy Protein Compared with Milk Protein in a Western Diet Increases Gut Microbial Diversity and Reduces Serum Lipids in Golden Syrian Hamsters

BACKGROUND

Diet is a major factor influencing the composition and metabolic activity of the gut microbiota.

OBJECTIVE

This study investigated the effect of soy compared with dairy protein on the gut microbiota of hamsters to determine whether changes in microbiota could account for soy protein's lipid lowering properties.

METHODS

Thirty-two 6- to 8-wk-old, male Golden Syrian hamsters were fed a Western diet containing 22% (%wt) milk protein isolate (MPI) as the single protein source for 3 wk followed by 6 wk of one of 4 diets containing either [22% protein (%wt)]: MPI, soy protein concentrate (SPC), partially hydrolyzed soy protein isolate (SPI1), or intact soy protein isolate. Serum lipids, hepatic gene expression, and gut microbial populations were evaluated.

RESULTS

Serum total and LDL-cholesterol concentrations were lower in the SPC-fed group (183 ± 9.0 and 50 ± 4.2 mg/dL, respectively) than in the MPI group (238 ± 8.7 and 72 ± 3.9 mg/dL, respectively) (P< 0.05). Triglyceride (TG) concentrations were lower (P< 0.05) in the SPI1-fed group (140 ± 20.8 mg/dL) than in the MPI-fed group (223 ± 14.2 mg/dL). VLDL and non-HDL-cholesterol concentrations were lower (by 40-49% and 17-33%, respectively) in all soy-fed groups than in the MPI-fed group (P< 0.05). Sequencing of the 16S ribosomal RNA gene revealed greater microbial diversity in each soy-fed group than in the MPI-fed group (P< 0.05). The cholesterol- and TG-lowering effect of soy protein was associated with higher expression of 3-hydroxy-3-methylglutaryl-CoA reductase (Hmgcr), lanosterol synthase (Lss), and farnesyl-diphosphosphate farnesyl-transferase 1 (Fdft1) (1.6-2.5-fold higher), and lower steroyl-CoA desaturase-1 (Scd1) expression (37-46% lower) in all soy-fed groups (P< 0.05) compared with the MPI-fed group. Gut microbes that showed significant diet differences were significantly correlated (ρ = -0.68 to 0.65,P< 0.05) with plasma lipids and hepatic gene expression.

CONCLUSION

Dietary protein sources in male Golden Syrian hamsters fed a Western diet affect the gut microbiota, and soy protein may reduce lipogenesis through alterations of the gut microbial community.

Protective and reparative effects of peptides from soybean β-conglycinin on mice intestinal mucosa injury

Peptides derived from alcalase digestion of soybean β-conglycinin, containing 8.52% carbohydrate, exhibits an inhibition effect on pathogen adhesion or translocation to intestinal cells in vitro. In this study, the protective and reparative effects of β-conglycinin peptides on intestinal mucosa injury in vivo were studied using mice with dextran sulfate sodium (DSS)-induced intestinal mucosa injury. The results showed that β-conglycinin peptides contained approximately 21.77% glutamic acid (Glu), and significantly reduced the histological injury in mice both in the protective and reparative experiments. The myeloperoxidase activity of mice treated with β-conglycinin peptides decreased compared with those treated DSS in the positive control group. Immunohistochemical analysis also showed that β-conglycinin peptides inhibited the expression of inflammatory factor NF-κB/p65. These results suggested that peptides derived from soybean β-conglycinin exhibited protective and reparative effects on mice intestinal mucosa injury.

The positive effect of soybean protein hydrolysates-calcium complexes on bone mass of rapidly growing rats

It was previously found that soybean protein hydrolysates (SPHs) can bind with calcium to form soluble complexes and promote calcium uptake by Caco-2 cells. However, the role of SPHs-calcium complexes on bone mass still needs to be explored. Fast growing male and female rats (n = 72) were assigned to eight groups: Control, lactic acid calcium (LCa), SPHs-calcium complexes (SPHCa) and casein phosphopeptides calcium (CPPCa). After four weeks treatment, oral administration of SPHCa significantly increased femur BMD of rats compared with Control and LCa groups (P < 0.05), while there are no obvious difference on the BMD of femur and lumbar vertebrae between SPHCa and CPPCa groups. Also, SPHCa showed a tendency to improve the mechanical properties of vertebra lumber for female rats. These findings suggest that the SPHs-calcium complexes might have positive effects on bone accretion of fast growing animals. This study brings new insight for better understanding the role of soybean protein itself on bone mass.

Inhibitory action of soybean beta-conglycinin hydrolysates on Salmonella typhimurium translocation in Caco-2 epithelial cell monolayers

Soybean protein hydrolysates are widely used as functional foods as they have antioxidative properties able to enhance immune responses in humans. The alcalase enzymatic hydrolysates of beta-conglycinin were fractionated by ultrafiltration, and two main fractions, SP1 (<10 kDa) and SP2 (10-20 kDa), were obtained. The effects of these two fractions on the growth, development of epithelial cells, and formation of intercellular tight junctions were tested on an in vitro Caco-2 cell culture system. The inhibitory effects of SP1 and SP2 on the penetration of Salmonella typhimurium into Caco-2 epithelial cells were also examined. The results showed that the addition of >0.05 g/L of SP2 improved epithelial cell growth and that a concentration of 0.5 g/L of SP2 increased intercellular tight junction formation, which resulted in increased of transepithelial monolayer resistance (TER) values. Moreover, a lower S. typhimurium count compared to control was obtained when Caco-2 cells were grown in 0.05 and 0.5 g/L of SP2. These results show that beta-conglycinin hydrolysates play an important role in resisting S. typhimurium penetration into intestinal epithelial cells and that high molecular mass peptides (10-20 kDa) were more effective overall than low molecular mass peptides.