ANTI-FATIGUE AND ANTIOXIDATIVE ACTIVITIES OF PEPTIDES ISOLATED FROM MILK PROTEINS

Antioxidant peptides, the guardian of life from oxidative stress

Reactive oxygen species (ROS) are produced during oxidative metabolism in aerobic organisms. Under normal conditions, ROS production and elimination are in a relatively balanced state. However, under internal or external environmental stress, such as high glucose levels or UV radiation, ROS production can increase significantly, leading to oxidative stress. Excess ROS production not only damages biomolecules but is also closely associated with the pathogenesis of many diseases, such as skin photoaging, diabetes, and cancer. Antioxidant peptides (AOPs) are naturally occurring or artificially designed peptides that can reduce the levels of ROS and other pro-oxidants, thus showing great potential in the treatment of oxidative stress-related diseases. In this review, we discussed ROS production and its role in inducing oxidative stress-related diseases in humans. Additionally, we discussed the sources, mechanism of action, and evaluation methods of AOPs and provided directions for future studies on AOPs.

Effect of the protein hydrolysate of rice syrup meal on the endurance exercise performance of BALB/c mice

Rice is a staple food in Korea. The protein in rice reportedly contains higher levels of branched-chain amino acids (BCAAs) than proteins in other grains. Taking BCAAs during exercise can reduce muscle fatigue by reducing muscle glycogen depletion. However, there are limited studies reporting the anti-fatigue effect of rice protein. We investigate the muscular endurance and anti-fatigue effects of the protein hydrolysate of rice syrup meal in mouse models. BALB/C mice were divided into the following groups: control (CON), low and high dose rice syrup meal (RL: 1.5 g kg-1; RH: 3.0 g kg-1), and low and high dose protein hydrolysate of rice syrup meal (PL: 1.5 g kg-1; PH: 3.0 g kg-1). The total activity during a forced swimming test was analyzed by a behavioral assay. The mutual relationship between the anti-fatigue activity and energy metabolism was assessed by biochemical, enzyme activity, and gene expression analyses. The protein hydrolysate of rice syrup meal contained 32.18 mg g-1 BCAAs, such as leucine, isoleucine, and valine, and its BCAA ratio (2.5 : 1.0 : 1.4) was considered effective for endurance exercise. Furthermore, PH administration significantly increased the change in the maximum swimming duration by 4.2 min (3.77 ± 0.74 min) compared to that of the CON group (-0.42 ± 0.55 min, p < 0.01). The PH group showed significantly different changes in the blood glucose and lactate levels compared with the CON group; similarly, the aspartate amino transferase and alanine amino transferase levels were significantly lower in the protein hydrolysate of rice syrup meal group than the CON group (p < 0.001 and p < 0.01, respectively). The protein hydrolysate of rice syrup meal-mediated improvement of endurance performance was accompanied by an increased in adenosine triphosphate content in the muscle and decreased reactive oxygen species accumulation in the liver. In addition, mRNA and protein levels of phospho-AMP activated protein kinase (p-AMPK)/AMPK and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1-α), the major energy-related factors of protein hydrolysate of rice syrup meal, were significantly increased. The protein hydrolysate of rice syrup meal can be utilized as an efficacious natural resource for its muscular-endurance-enhancing and anti-fatigue effects.

Structural and functional properties of food protein-derived antioxidant peptides

The aim of this work is to provide a timely examination of the structure-activity relationship of antioxidative peptides. The main production approach involves enzymatic hydrolysis of animal and plant proteins to produce protein hydrolyzates, which can be further processed by membrane ultrafiltration into size-based peptide fractions. The hydrolyzates and peptide fractions can also be subjected to separation by column chromatography to obtain pure peptides. Although the structural basis for enhanced antioxidant activity varies, protein hydrolyzates and peptide fractions that contain largely low molecular weight peptides have generally been shown to be potent antioxidants. In addition to having hydrophobic amino acids such as Leu or Val in their N-terminal regions, protein hydrolyzates, and peptides containing the nucleophilic sulfur-containing amino acid residues (Cys and Met), aromatic amino acid residues (Phe, Trp, and Tyr) and/or the imidazole ring-containing His have been generally found to possess strong antioxidant properties. PRACTICAL APPLICATIONS: High levels of reactive oxygen species (ROS) in addition to the presence of metal cations can lead to oxidative stress, which promotes reactions that cause destruction of critical cellular biopolymers, such as proteins, lipids, and nucleic acids. Oxidative stress could be due to insufficient levels of natural cellular antioxidants, which enables accumulation of ROS to toxic levels. A proposed approach to ameliorating oxidative stress is the provision of exogenous peptides that can be consumed to complement cellular antioxidants. Food protein-derived peptides consist of amino acids joined by peptides bonds just like glutathione, a very powerful natural cellular antioxidant. Therefore, this review provides a timely summary of the in vitro and in vivo reactions impacted by antioxidant peptides and the postulated mechanisms of action, which could aid development of potent antioxidant agents. The review also serves as a resource material for identifying novel antioxidant peptide sources for the formulation of functional foods and nutraceuticals.

Production and transepithelial transportation of angiotensin-I-converting enzyme (ACE)-inhibitory peptides from whey protein hydrolyzed by immobilized Lactobacillus helveticus proteinase

Lactobacillus helveticus LB 10 proteinases immobilized with sodium alginate were used to hydrolyze whey protein to produce angiotensin-I-converting enzyme (ACE)-inhibitory peptides. The generated hydrolysates were tested for ACE-inhibitory activity and for their ability to be transported across Caco-2 cell monolayers. Using a response surface method, we determined that a proteinase concentration of 7.55 mg/mL, sodium alginate concentration of 2.03 g/100 mL, and glutaraldehyde concentration of 0.39% were found to be the optimal immobilization conditions. Compared with free proteinase, the immobilized proteinase had significantly higher pH, thermal and storage stability, and reusability. Whey protein hydrolysates were fractionated by gel filtration chromatography and ACE-inhibitory peptide mixtures were transported across Caco-2 cell monolayers in a human intestinal-absorption model. The di- and tripeptides KA, EN, DIS, EVD, LF, AIV, and VFK (half-maximal inhibitory concentrations (mean ± standard deviation) of 1.24 ± 0.01, 1.43 ± 0.04, 1.59 ± 0.27, 1.32 ± 0.05, 1.60 ± 0.39, 2.66 ± 0.02, and 1.76 ± 0.09 mmol/L, respectively) were detected on the basolateral side of the Caco-2 cell monolayer using ultra-performance liquid chromatography-tandem mass spectrometry. These results highlight that ACE-inhibitory peptides are present on the basolateral side of the Caco-2 cell model after transportation of whey protein hydrolysate across the Caco-2 cell membrane.

Antioxidant and anti-fatigue activities of egg white peptides prepared by pepsin digestion

BACKGROUND

Some hydrolyzed peptides derived from food proteins possess antioxidant and anti-fatigue activities. In this study, egg white protein powder (EWPP) was hydrolyzed with pepsin for various times, and four peptide fractions were separated from the hydrolysates by ultrafiltration. The antioxidant activity of the four peptide fractions was determined. The peptide fraction with the strongest antioxidant activity was used to evaluate its anti-fatigue effect and probable mechanisms.

RESULTS

The egg white peptides (EWPs) fraction with molecular weight 2-5 kDa (named EWPs2) showed stronger antioxidant activity than the other peptide fractions (P < 0.05). The swimming time to exhaustion of mice administered EWPs2 was longer (P < 0.05) than that of the control group. EWPs2 increased the levels of blood glucose (by 28.4-42.2%), muscle glycogen (by 6.4-10.6%) and liver glycogen (by 10.7-23.8%) and significantly decreased the levels of lactic acid in muscle and urea nitrogen in blood (P < 0.05).

CONCLUSION

Among the four peptide fractions, EWPs2 possessed the strongest antioxidant activity and exhibited an anti-fatigue effect. The experimental data could clarify partially the anti-fatigue mechanisms of EWPs and provide an important basis for developing EWPs as safe and natural antioxidants and anti-fatigue agents for wide use.