Antihypertensive Effects, Molecular Docking Study, and Isothermal Titration Calorimetry Assay of Angiotensin I-Converting Enzyme Inhibitory Peptides from Chlorella vulgaris

Studies on the Interaction between Angiotensin-Converting Enzyme (ACE) and ACE Inhibitory Peptide from Saurida elongata

Angiotensin-converting enzyme (ACE) inhibitory peptides derived from food protein exhibited antihypertensive effects by inhibiting ACE activity. In this work, the interaction between ACE inhibitory peptide GMKCAF (GF-6) and ACE was studied by isothermal titration calorimetry (ITC), molecular docking, ultraviolet absorption spectroscopy, fluorescence spectroscopy, and circular dichroism spectroscopy. Experimental results revealed that the binding of GF-6 to ACE was a spontaneous exothermic process driven by both enthalpy and entropy. The interaction occurred via a static quenching mechanism and involved the alteration of the conformation of ACE. In addition, ITC and molecular docking results indicated binding of GF-6 to ACE via multiple binding sites on the protein surface. This study could be deemed helpful for the better understanding of the inhibitory mechanism of ACE inhibitory peptides.

In vitro effect of oxidized and reduced glutathione peptides on angiotensin converting enzyme purified from human plasma

Angiotensin converting enzyme (ACE, peptidyldipeptidase A, EC 3.4.15.1) plays an important role in the regulation of blood pressure. In this study, ACE was purified from human plasma by affinity chromatography in single step. The enzyme purified in 5367-fold from human plasma and specific activity was found to be 1208 EU/mg protein. The purity and molecular weight of ACE were determined by SDS-PAGE, which indicated two bands at around 60 kDa and 70 kDa on the gel. Effect of oxidized glutathione (GSSG) peptide and reduced glutathione (GSH) peptide on purified ACE activity were also investigated in which lisinopril was used as reference inhibitor. GSSG showed activation effect on ACE activity whereas GSH provided inhibition effect. In the lights of activity (%) versus activator graph for GSSG and activity (%) versus inhibitor graphs for GSH and lisinopril; IC₅₀ values for GSH and lisinopril were determined to be 16.2 μM and 0.781 nM, respectively. Type of inhibition for GSH and lisinopril from graph Lineweaver-Burk was found to be reversible non-competitive inhibition and K_i constants for GSH and lisinopril were calculated as 11.7 μM and 0.662 nM, respectively.

Purification and Identification of Angiotensin I-Converting Enzyme Inhibitory Peptides and the Antihypertensive Effect of Chlorella sorokiniana Protein Hydrolysates

Hot water was used to obtain Chlorella sorokiniana hot water extract (HWE). Subsequently, this byproduct was freeze-dried, hydrolysed at 50 °C using Protease N to obtain C. sorokiniana protein hydrolysates (PN-1), and then digested with a gastrointestinal enzyme (PN-1G). The inhibitory effects of the HWE and hydrolysates against angiotensin I-converting enzyme (ACE) were investigated. The soluble protein and peptide contents were 379.9 and 179.7 mg/g, respectively, for HWE and 574.8 and 332.8 mg/g, respectively, for PN-1. The IC₅₀ values of the HWE, PN-1, and PN-1G on ACE were 1.070, 0.035, and 0.044 mg/mL, respectively. PN-1G was separated into seven fractions through size exclusion chromatography. The sixth fraction of the hydrolysate had a molecular weight between 270 and 340 Da, and the lowest IC₅₀ value on ACE was 0.015 mg/mL. The amino acid sequences of the ACE-inhibitory peptides were Trp-Val, Val-Trp, Ile-Trp, and Leu-Trp, of which the IC₅₀ values were 307.61, 0.58, 0.50, and 1.11 µΜ, respectively. Systolic blood pressure and diastolic blood pressure were reduced 20 and 21 mm Hg, respectively, in spontaneously hypertensive rats after 6 h of oral administration with a dose of 171.4 mg PN-1 powder/kg body weight.

Critical Review and Perspectives on Food-Derived Antihypertensive Peptides

Food-derived peptides with antihypertensive properties have received great interest during the past 30 years. There is solid evidence of the effect of various peptide sequences in clinical trials, but their use in preventive or therapeutic treatments is not extensive. There are certain issues, such as the bioavailability or the mechanism of action, that would need to be clarified to establish a direct cause/effect relationship between the administered molecule and the observed effect. This perspective emphasizes the advances in the study of antihypertensive peptides and proposes future research topics that might encourage industry and health policy to exploit these food constituents.

Antihypertensive Effects of Two Novel Angiotensin I-Converting Enzyme (ACE) Inhibitory Peptides from Gracilariopsis lemaneiformis (Rhodophyta) in Spontaneously Hypertensive Rats (SHRs)

A variety of biologically active products have been isolated from Gracilariopsis lemaneiformis. In the present study, two novel angiotensin-converting enzyme (ACE) inhibitory peptides, FQIN [M(O)] CILR, and TGAPCR, were screened and identified from G. lemaneiformis protein hydrolysates by LC-MS/MS. The IC50 values of FQIN [M(O)] CILR and TGAPCR were 9.64 ± 0.36 μM and 23.94 ± 0.82 μM, respectively. In the stability study, both peptides showed stabilities of pH, temperature, simulated gastrointestinal digestion, and ACE hydrolysis. The Lineweaver–Burk plot showed that the two peptides were noncompetitive inhibitors of ACE. Molecular docking simulated the intermolecular interactions of two peptides and ACE, and the two peptides formed hydrogen bonds with the active pockets of ACE. However, FQIN [M(O)] CILR was more closely linked to the active pockets of ACE, thereby exerting better ACE inhibition. Spontaneously hypertensive rats (SHRs) were studied with an oral dose of 10 mg/kg body weight. Both peptides reduced systolic blood pressure (SBP) and diastolic blood pressure (DBP) in SHRs, of which FQIN [M(O)] CILR was able to reduce the systolic blood pressure by 34 mmHg (SBP) (p < 0.05). Therefore, FQIN [M(O)] CILR was an excellent ACE inhibitory peptide.

Isolation and Characterization of Angiotensin I-Converting Enzyme (ACE) Inhibitory Peptides from the Enzymatic Hydrolysate of Carapax Trionycis (the Shell of the Turtle Pelodiscus sinensis)

Carapax Trionycis (the shell of the turtle Pelodiscus sinensis) was hydrolyzed by six different commercial proteases. The hydrolysate prepared from papain showed stronger inhibitory activity against angiotensin I-converting enzyme (ACE) than other extracts. Two noncompetitive ACE inhibitory peptides were purified successively by ultrafiltration, gel filtration chromatography, ion exchange column chromatography, and high-performance liquid chromatography (HPLC). The amino acid sequences of them were identified as KRER and LHMFK, with IC₅₀ values of 324.1 and 75.6 μM, respectively, confirming that Carapax Trionycis is a potential source of active peptides possessing ACE inhibitory activities. Besides, both enzyme kinetics and isothermal titration calorimetry (ITC) assay showed that LHMFK could form more stable complex with ACE than KRER, which is in accordance with the better inhibitory activity of LHMFK.