Antihypertensive effect of rice protein hydrolysate with in vitro angiotensin I-converting enzyme inhibitory activity in spontaneously hypertensive rats.

Angiotensin I-converting enzyme (ACE) plays a crucial role in the regulation of blood pressure as well as cardiovascular function. ACE catalyzes the conversion of angiotensin I to vasoconstrictor angiotensin II, and also inactivates the antihypertensive vasodilator bradykinin. Inhibition of ACE mainly results an overall antihypertensive effect. Food protein-derived peptides can have ACE-inhibiting properties and thus may be used as a novel functional food for preventing hypertension as well as for therapeutic purposes. In the present study, rice protein was hydrolyzed by protease Alcalase for 2 h and the resulted hydrolysate was determined for ACE inhibitory activity in vitro. The antihypertensive effect of rice protein hydrolysate was also investigated in spontaneously hypertensive rats (SHR). The Alcalase-generated hydrolysate showed strong in vitro ACE inhibitory activity with the IC50 value of 0.14 mg/ml. A significant decrease in systolic blood pressure in spontaneously hypertensive rats was observed following single oral administration of this hydrolysate at a dose of 600 mg/kg of body weight. A potent ACE inhibitory peptide with the amino acid sequence of Thr-Gln-Val-Tyr (IC50, 18.2 microM) was isolated and identified from the hydrolysate. Single oral administration of Thr-Gln-Val-Tyr at a dose of 30 mg/kg of body weight also significantly decreased blood pressure in SHR. These results suggest that in vitro ACE inhibitory activity and in vivo antihypertensive activity could be generated from rice protein by enzymatic hydrolysis. The rice protein hydrolysate prepared with Alcalase might be utilized to develop physiologically functional food with antihypertensive activity.