Screening, discovery, and characterization of angiotensin-I converting enzyme inhibitory peptides derived from proteolytic hydrolysate of bitter melon seed proteins.

UNLABELLED: In this study, new angiotensin-I converting enzyme (ACE) inhibitory peptides were comprehensively identified from a thermolysin digest of bitter melon (Momordica charantia) seed proteins. The hydrolysate was fractionated by reversed-phase high performance liquid chromatography (RP-HPLC), and the inhibitory activities of the resulting fractions were evaluated using ACE inhibitory assay. Two novel ACE inhibitory peptides (VY-7 and VG-8) were identified using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and database-assisted peptide sequencing. VY-7 and VG-8 were derived from momordin A and MAP30, respectively, and their IC50 values were as low as 8.64±0.60 and 13.30±0.62 μM, respectively. Lineweaver-Burk plots further indicated that VY-7, which showed the best IC50 value, acts as a competitive inhibitor. Notably, the content of VY-7 in crude thermolysin digest was determined to be as high as 14.89±0.88 μg/mg using LC-MS/MS quantification. In the spontaneously hypertensive rat (SHR) model, oral administration of VY-7 at 2mg/kg body weight significantly decreased the systolic blood pressure. The interaction between VY-7 and ACE was examined using molecular docking calculations and the results suggested that certain residues of VY-7 can fit perfectly into the S1, S1' and S2' regions of the binding pocket of ACE.

BIOLOGICAL SIGNIFICANCE: One of the most common supportive therapies for treating hypertension is the use of synthetic drugs to inhibit ACE activity. Synthetic ACE inhibitors possess good antihypertensive effects, but come with accompanying side effects. Therefore, food-derived ACE inhibitory peptides are regarded as safer alternatives and are attracting much attention for hypertension treatment. In this study, we comprehensively identified peptides derived from bitter melon (Momordica charantia) seed proteins (BMSPs) using a shotgun proteomics approach. Based on results from an in vitro ACE inhibitory assay, two peptides (VY-7 and VG-8) derived from momordin A and MAP30 proteins, respectively, showed good ACE inhibitory activities. For VY-7, which showed the best IC50 value (8.64±0.60 μM), the inhibition type was determined to be competitive inhibition, as found using a Lineweaver-Burk plot. The novel ACE inhibitory peptide VY-7 (at 2mg/kg body weight) as well as the crude hydrolysate of BMSPs (at 10 mg/kg body weight) showed significant and moderate antihypertensive effects, respectively, in an animal model of hypertension, spontaneously hypertensive rats (SHRs). The present work demonstrated the screening of ACE inhibitory peptides from BMSPs and, as far as we know, VY-7 is the first well-characterized antihypertensive peptide derived from bitter melon seeds.