Muscle Protein Signaling in C2C12 Cells Is Stimulated to Similar Degrees by Diverse Commercial Food Protein Sources and Experimental Soy Protein Hydrolysates.

Dietary protein stimulates muscle protein synthesis and is essential for muscle health. We developed a screening assay using C2C12 mouse muscle cells to assess the relative abilities of diverse commercial protein sources and experimental soy protein hydrolysates (ESH), after simulated gut digestion (SGD), to activate the mechanistic target of rapamycin complex I (mTORC1) muscle protein synthesis signaling pathway (p70S6K(Thr389) phosphorylation). Activation of mTORC1 was expressed as a percentage of a maximal insulin response. The bioactivities of proteins grouped by source including fish (81.3 ± 10.6%), soy (66.2 ± 4.7%), dairy (61.8 ± 4.3%), beef (53.7 ± 8.6%), egg (52.3 ± 10.6%), soy whey (43.4 ± 8.6%), and pea (31.4 ± 10.6%) were not significantly different from each other. Bioactivity for ESH ranged from 28.0 ± 7.5 to 98.2 ± 6.6%. The results indicate that both the protein source and processing conditions are key determinants for mTORC1 activation. Regression analyses demonstrated that neither leucine nor total branched-chain amino acid content of proteins is the sole predictor of mTORC1 activity and that additional factors are necessary.

Soy-based renoprotection.

Chronic kidney disease (CKD) is a significant public health problem as risk factors such as advanced age, obesity, hypertension and diabetes rise in the global population. Currently there are no effective pharmacologic treatments for this disease. The role of diet is important for slowing the progression of CKD and managing symptoms in later stages of renal insufficiency. While low protein diets are generally recommended, maintaining adequate levels of intake is critical for health. There is an increasing appreciation that the source of protein may also be important. Soybean protein has been the most extensively studied plant-based protein in subjects with kidney disease and has demonstrated renal protective properties in a number of clinical studies. Soy protein consumption has been shown to slow the decline in estimated glomerular filtration rate and significantly improve proteinuria in diabetic and non-diabetic patients with nephropathy. Soy's beneficial effects on renal function may also result from its impact on certain physiological risk factors for CKD such as dyslipidemia, hypertension and hyperglycemia. Soy intake is also associated with improvements in antioxidant status and systemic inflammation in early and late stage CKD patients. Studies conducted in animal models have helped to identify the underlying molecular mechanisms that may play a role in the positive effects of soy protein on renal parameters in polycystic kidney disease, metabolically-induced kidney dysfunction and age-associated progressive nephropathy. Despite the established relationship between soy and renoprotection, further studies are needed for a clear understanding of the role of the cellular and molecular target(s) of soy protein in maintaining renal function.

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.

Partially hydrolyzed soy protein shows enhanced transport of amino acids compared to nonhydrolyzed protein across an intestinal epithelial cell monolayer.

Consumption of protein hydrolysates has been proposed to stimulate muscle anabolism more than intact (nonhydrolyzed) proteins via accelerated delivery of amino acids for muscle protein synthesis (MPS). We evaluated whether the rate of amino acid uptake and transport across intestinal cells was enhanced for soy protein hydrolysates versus nonhydrolyzed soy protein. Intact and partially hydrolyzed proteins were subject to simulated gut digestion and applied to the apical surface of Caco-2 monolayers. Basolateral media was harvested after 3 h and quantitatively analyzed for free amino acids using ion-exchange chromatography and comparison to an included reference standard. Basolateral concentrations of all amino acids were higher (mean 32%) for hydrolyzed versus nonhydrolyzed protein with the greatest differences in histidine, lysine, and valine. Scale-up production of the soy protein hydrolysate did not diminish its enhanced absorption properties. These data support the hypothesis that hydrolyzed soy protein may provide dietary amino acids that are more rapidly transported across the intestinal epithelium versus intact soy protein. This would be important under conditions where rapid and increased levels of amino acids are needed such as in the stimulation of MPS.