Vasorelaxing and antihypertensive activities of synthesized peptides derived from computer-aided simulation of pepsin hydrolysis of yam dioscorin

Angiotensin-I-converting enzyme inhibitory peptides in milk fermented by indigenous lactic acid bacteria

Background and Aim:

Fermented milk can be used to produce antihypertensive peptides. Lactic acid bacteria (LAB) with its proteolytic system hydrolyze milk protein during fermentation to produce several peptides, which include antihypertensive bioactive peptides. This study aimed to investigate the ability of indigenous LAB for the production of angiotensin-I-converting enzyme inhibitory (ACE-I) peptides in fermented milk and to characterize the ACEI peptides.

Materials and Methods:

Reconstituted milk (11%) inoculated with ten LAB isolates, and then incubated at 37°C until it reaches pH 4.6. The evaluation was carried out for LAB count, lactic acid concentration, peptide content, and ACE-I activity. The low molecular weight (MW) peptides (<3 kDa) were identified using Nano LC Ultimate 3000 series system Tandem Q Exactive Plus Orbitrap high-resolution mass spectrometry.

Results:

The result showed that the ten LAB isolates were able to produce ACE-I in fermented milk with the activities in the range of 22.78±2.55-57.36±5.40%. The activity of ACE-I above 50% produced by Lactobacillus delbrueckii BD7, Lactococcus lactis ssp. lactis BD17, and Lactobacillus kefiri YK4 and JK17, with the highest activity of ACE-I produced by L. kefiri YK4 (IC₅₀ 0.261 mg/mL) and L. kefiri JK17 (IC₅₀ 0.308 mg/mL). Results of peptide identification showed that L. kefiri YK 4 could release as many as 1329, while L. kefiri JK 17 could release 174 peptides. The peptides produced were 95% derived from casein. The other peptides were from ά-lactalbumin, β-lactoglobulin, and serum amyloid A. The peptides produced consisted of 6-19 amino acid residues, with MWs of 634-2079 Dalton and detected at 317-1093 m/z. A total of 30 peptides have been recognized based on literature searches as ACE-I peptides (sequence similarity: 100%).

Conclusion:

L. kefiri YK4 and JK17 are the potential to be used as starter cultures to produce the bioactive peptide as ACE-I in fermented milk.

Purification of novel angiotensin converting enzyme inhibitory peptides from beef myofibrillar proteins and analysis of their effect in spontaneously hypertensive rat model

This study was conducted to purify the angiotensin converting enzyme (ACE) inhibitory peptides from beef myofibrillar proteins by using inexpensive enzymes alkaline-AK and papain. Different molecular weight peptides (<3 and <10 kDa) were obtained using ultrafiltration. The <3 kDa peptides obtained by alkaline-AK (AK3K) digestion showed the highest ACE inhibitory activity (74.29%) as compared to other alkaline-AK peptides, and a strong antihypertensive effect of AK3K was observed in the spontaneously hypertensive rat (SHR) model. The AK3K treatment groups (400 and 800 mg/kg body weight) exhibited a decrease in systolic blood pressure (SBP) by 28 and 35 mmHg, respectively in the SHR model. The study demonstrated that the ACE inhibitory peptide obtained from beef myofibrillar proteins had the sequence Leu-Ile-Val-Gly-Ile-Ile-Arg-Cys-Val, and could be possibly used for lowering the SBP.

135-Day Interventions of Yam Dioscorin and the Dipeptide Asn-Trp (NW) To Reduce Weight Gains and Improve Impaired Glucose Tolerances in High-Fat Diet-Induced C57BL/6 Mice

The C57BL/6J mice were fed a 135-day normal diet or a high-fat diet (HFD) without, or concurrent with, a single yam dioscorin (80 mg/kg) or dipeptide NW (40 mg/kg) intervention every day. The final body weights (g) of mice were 26.1 ± 1.4, 34.97 ± 2.1, 31.75 ± 2.6, and 31.66 ± 3.1, respectively, for normal diet-fed, HFD-fed, dioscorin-intervened, and NW-intervened group. The mice in both intervened groups showed similar less weight gains and had significant differences (P < 0.05) compared to those in the HFD group under the same cumulative HFD intakes. The blood biochemical index of mice with dioscorin interventions showed significantly lower contents in total cholesterol and low-density lipoprotein, and NW interventions showed significantly lower total triglyceride contents compared to those of the HFD group (P < 0.05). Both intervened mice exhibited similar reductions in total visceral lipid contents and have significant differences compared to those of the HFD group (P < 0.05). The dioscorin intervention was better than NW interventions in lowering blood glucose levels by oral glucose tolerance tests and both showed significant differences (P < 0.05) compared to those in the HFD group. Yam dioscorin or dipeptide NW will potentially be used for preventive functional foods of less body weight gains and impaired glucose tolerance controls, which require further clinical trial investigations.

Small Peptides Isolated from Enzymatic Hydrolyzate of Fermented Soybean Meal Promote Endothelium-Independent Vasorelaxation and ACE Inhibition

Fermentation of soybean is a process in which soy proteins are broken down into small peptides to exert various physiological functions beyond their nutritional value and to improve food source bioactive components responsible for health benefits. Enzymatic hydrolysis could speed up the degradation of proteins during fermentation of soybean, thus resulting in higher peptide production. In the present study, fermented soy meal (fermented with Bacillus subtilis from Douchi) was hydrolyzed by thermolysin, and the water extraction was then separated into four fractions using ultrafiltration membranes. Their vasorelaxation activities were screened, and the most potent fraction was further isolated and purified to obtain four peptides. Briefly, three peptides exerted a dose-dependent vasorelaxation (0.01-4.10 μM) in the phenylephrine preconstricted thoracic aorta ring of Sprague-Dawley rat (relaxation actions were all endothelium-independent), while one peptide induced vasoconstriction. Furthermore, an independent causal relationship between vasorelaxation and angiotensin converting enzyme (ACE) inhibition activities was found.

Synthesized Peptides from Yam Dioscorin Hydrolysis in Silico Exhibit Dipeptidyl Peptidase-IV Inhibitory Activities and Oral Glucose Tolerance Improvements in Normal Mice

RRDY, RL, and DPF were the top 3 of 21 peptides for inhibitions against dipeptidyl peptidase-IV (DPP-IV) from the pepsin hydrolysis of yam dioscorin in silico and were further investigated in a proof-of-concept study in normal ICR mice for regulating glucose metabolism by the oral glucose tolerance test (OGTT). The sample or sitagliptin (positive control) was orally administered by a feeding gauge; 30 min later, the glucose loads (2.5 g/kg) were performed. RRDY, yam dioscorin, or sitagliptin preload, but not DPF, lowered the area under the curve (AUC0-120) of blood glucose and DPP-IV activity and elevated the AUC0-120 of blood insulin, which showed significant differences compared to control (P < 0.05 or 0.001). These results suggested that RRDY and yam dioscorin might be beneficial in glycemic control in normal mice and need further investigations in diabetic animal models.

Effects of yam dioscorin interventions on improvements of the metabolic syndrome in high-fat diet-induced obese rats

BACKGROUND

The metabolic syndrome (MS) is termed a cluster of multiple metabolic risk criteria which is positively correlated with cardiovascular disease and type 2 diabetes mellitus (DM). Yam dioscorins have been reported to exhibit biological activities, however, little is known their preventive effects on the MS. Therefore, a high-fat (HF) diet was used to induce Wistar rat obesity and then yam dioscorin (50 mg/kg, dio50) was intervened daily concurrent HF diet (HF diet + dio50) for five weeks to check the changes of weights of body and tissues, blood pressures, and impaired glucose tolerances. The in vitro peptic hydrolysates of dioscorin with molecular mass between 3 kDa and 10 kDa and less than 3 kDa were used to determine dipeptidyl peptidase IV (DPP IV) inhibitory activities which DPP IV inhibitor has been reported to prevent and treat type 2 DM.

RESULTS

There were no significant difference in body weights, feed intakes, feed conversion, and weights of adipose tissues of obese rats in groups of HF and (HF diet + dio50). However, the systolic blood pressures in obese rats of 2-, 3- and 4-week dioscorin interventions were showed significantly lower (P < 0.05) compared to the HF group. The dioscorin intervention (HF+ dio50) was showed significantly different (P < 0.05) and improved the impaired glucose tolerances compared to HF group in obese rats by the oral glucose tolerance tests. It was also found that the fraction with different molecular mass of dioscorin peptic hydrolysates (5 mg/ml) showed inhibitory activities against DPP IV using sitagliptin phosphate as positive controls.

CONCLUSIONS

Yam dioscorins exhibit improved MS activities in obese rats which the related mechanisms may need further investigations.