Isolation, identification and in vivo antihypertensive effect of novel angiotensin I-converting enzyme (ACE) inhibitory peptides from Spirulina protein hydrolysate

The side effects of traditional antihypertensive drugs have driven people's interest in the discovery of novel angiotensin-I converting enzyme (ACE) inhibitory peptides with efficiency and safety. Spirulina possesses abundant proteins and is considered as a good source of bioactive peptides. To identify ACE inhibitory peptides, Spirulina protein was hydrolyzed by protease K, and the hydrolysate was separated by gel permeation chromatography and reverse phase HPLC. Thirty peptide sequences were identified from the ACE inhibitory fractions by LC-MS/MS, and 15 potential ACE inhibitory peptides were further selected by combined virtual screening and experimental investigation. Among the identified Spirulina peptides, TVLYEH (SpH-6, IC 50 = 2.88 μM) and LQAGGLF (SpH-7, IC 50 = 66.83 μM) were found to possess potent ACE inhibitory activity. The inhibition patterns of SpH-6 and SpH-7 were characterized as competitive inhibition. Molecular docking indicated that SpH-6 and SpH-7 could bind to the active pockets of ACE by forming hydrogen bonds, salt bridges and pi–pi stacking. Both SpH-6 and SpH-7 exhibited stable ACE inhibitory activity under different pH (2, 4, 6, 8, 10, 12) and temperature (0, 20, 40, 60, 80, 100 °C) conditions. The ACE inhibitory activity of SpH-6 decreased slightly after simulated gastrointestinal digestion, and SpH-7 was unstable against digestive enzymes. The in vivo antihypertensive effect demonstrated that oral administration of SpH-6 significantly reduced the systolic blood pressure and diastolic blood pressure of spontaneously hypertensive rats. The present study revealed the potential antihypertensive effects of SpH-6 and indicated that SpH-6 and Spirulina protein hydrolysate could be applied as nutritional supplements for blood pressure control.