The effect of protein fractionation on the bioavailability of amino acids and peptides and insulin response and whether the protein source influences these effects in humans are poorly understood. This study compared the effects of different sources and degrees of hydrolysis of dietary protein, independent of carbohydrate, on plasma amino acid and dipeptide levels and insulin responses in humans. Ten subjects were enrolled in the study, with five subjects participating in trials on either soy or whey protein and their hydrolysates. Protein hydrolysates were absorbed more rapidly as plasma amino acids compared to nonhydrolyzed protein. Whey protein also caused more rapid increases in indispensable amino acid and branched-chain amino acid concentrations than soy protein. In addition, protein hydrolysates caused significant increases in Val-Leu and Ile-Leu concentrations compared to nonhydrolyzed protein. Whey protein hydrolysates also induced significantly greater stimulation of insulin release than the other proteins. Taken together, these results demonstrate whey protein hydrolysates cause significantly greater increases in the plasma concentrations of amino acids, dipeptides, and insulin.

Several hydroxyproline (Hyp)-containing food-derived collagen peptides were identified in human blood after oral ingestion of gelatin hydrolysates. However, these types of peptides were not quantified in human plasma. In this report, a sensitive LC-MS/MS method was introduced for simultaneous quantitative analysis of Hyp-containing peptides. All peptide concentrations were determined accurately, with all coefficients of determination (r(2)) >0.999. The method achieved detection and quantification limits of 0.01 pmol/ml and 12.5-1,000 pmol/ml in plasma, respectively. Concentrations were quantified for nine Hyp-containing peptides in human plasma by this method, identifying Pro-Hyp (C(max) = 60.65 +/- 5.74 nmol/ml) as the major constituent of food-derived collagen peptides, while the minor components were Ala-Hyp-Gly, Ser-Hyp-Gly, Ala-Hyp, Phe-Hyp, Leu-Hyp, Ile-Hyp, Gly-Pro-Hyp, and Pro-Hyp-Gly (C(max) from 23.84 to 0.67 nmol/ml). Thus a total of nine Hyp-containing peptides in human plasma were successfully quantified by this approach. The concentration of Hyp-containing peptides is substantially higher than that following oral administration of other peptides.

SummaryIn earlier studies we showed that dietary whey protein increased skeletal muscle and liver glycogen content in exercise-trained rats. However, little is known about whether ingredients of whey protein stimulate skeletal muscle glycogen accumulation. The aim of this study was to identify bioactive peptides in whey protein hydrolysates (WPH) which stimulated glucose uptake and glycogen synthesis rate in skeletal muscles. Branchedchain amino acid (BCAA)-containing dipeptides in WPH were identified using LC/MS/MS. L6 myotubes and isolated epitrochlearis muscles were used for the glucose uptake assays. The myotubes and muscles were incubated with or without 1 m M dipeptides, LY294002 a phosphoinositide 3-kinase (PI3-kinase) inhibitor, or GF102903X an atypical protein kinase C (aPKC) inhibitor, followed by measurement of 2-deoxyglucose uptake. Isolated muscles were incubated for 3 h with or without 1 m M Ile-Leu to determine glycogen synthesis rate. The BCAA-containing dipeptides, Ile-Val, Leu-Val, Val-Leu, Ile-Ile, Leu-Ile, Ile-Leu, and LeuLeu were detected in the WPH by LC/MS/MS. These dipeptides caused significant stimulation in glucose uptake rate in the L6 myotubes. Ile-Leu, the main component in WPH, also stimulated glucose uptake in isolated skeletal muscles. Stimulation of glucose uptake by IleLeu was completely inhibited by treatment with either LY294002, or GF109203X in both L6 cells and isolated muscles. Ile-Leu increased glycogen contents in isolated muscles. These results suggest that BCAA-containing bioactive dipeptides in WPH stimulate glucose uptake in skeletal muscles via the PI3-kinase and aPKC pathways, resulting in increased skeletal muscle glycogen contents.

No abstract

Recent studies showed that a combination of carbohydrate and protein was more effective than carbohydrate alone for replenishing muscle glycogen after exercise. However, it remains to be unclear whether the source or degree of hydrolysis of dietary protein influences post-exercise glycogen accumulation. The aim of this study was to compare the effect of dietary protein type on glycogen levels in the post-exercise phase, and to investigate the effects of post-exercise carbohydrate and protein supplementation on phosphorylated enzymes of Akt/PKB and atypical PKCs. Male Sprague-Dawley rats, trained for 3 days, swam with a 2% load of body weight for 4 h to deplete skeletal muscle glycogen. Immediately after the glycogen-depleting exercise, one group was killed, whereas the other groups were given either glucose or glucose plus protein (whey protein, whey protein hydrolysates (WPH), casein hydrolysates or branched-chain amino acid (BCAA) solutions. After 2 h, the rats were killed, and the triceps muscles quickly excised. WPH caused significant increases in skeletal muscle glycogen level (5.01 +/- 0.24 mg/g), compared with whey protein (4.23 +/- 0.24 mg/g), BCAA (3.92 +/- 0.18 mg/g) or casein hydrolysates (2.73 +/- 0.22 mg/g). Post-exercise ingestion of glucose plus WPH significantly increased both phosphorylated Akt/PKB (131%) and phosphorylated PKCzeta (154%) levels compared with glucose only. There was a significant positive correlation between skeletal muscle glycogen content and phosphorylated Akt/PKB (r = 0.674, P < 0.001) and PKCzeta (r = 0.481, P = 0.017). Post-exercise supplementation with carbohydrate and WPH increases skeletal muscle glycogen recovery by activating key enzymes such as Akt/PKB and atypical PKCs.

Collagen hydrolysate administration affects epidermal barrier function and dermal skin elasticity.

We investigated the effect of different types of dietary protein on glycogen content in liver and skeletal muscle of exercise-trained rats. Twenty-four male Sprague-Dawley rats (approximately 100 g; n 6 per group) were divided into sedentary or exercise-trained groups with each group being fed either casein or whey protein as the source of dietary protein. Rats in the exercised groups were trained during 2 weeks using swimming exercise for 120 min/d, 6 d/week. Exercise training resulted in an increase in the skeletal muscle glycogen content. Furthermore, the whey protein group significantly increased the skeletal muscle glycogen content compared with the casein group. The increase in glycogen content in liver was significantly greater in rats fed the whey protein diet compared with those fed the casein diet. We also found that the whey protein diet increased the activity of liver glucokinase, whereas it decreased the activities of 6-phosphofructokinase and pyruvate kinase compared with the casein diet. However, hepatic total glycogen synthase activity and mRNA expression were similar with the two diets. In the skeletal muscle, whey protein decreased only 6-phosphofructokinase activity compared with casein. Total glycogen synthase activity in the skeletal muscle in the whey protein group was significantly higher than that in the casein group. The present study is the first to demonstrate that a diet based on whey protein may increase glycogen content in liver and skeletal muscle of exercise-trained rats. We also observed that whey protein regulated glycogen metabolism in these two tissues by different mechanisms.

No abstract