A Novel Antihypertensive Peptide Identified in Thermolysin‐Digested Rice Bran

Scope Hypertension is a risk factor for arteriosclerosis. In this study, we investigate the antihypertensive effect of protease‐digested rice bran in a spontaneously hypertension rat (SHR) model. We also purify a novel antihypertensive peptide from the digest. Methods and results Thermolysin‐digested rice bran (TRB) is administered to SHRs for 4 weeks, and systolic blood pressure (SBP) was measured weekly using the tail‐cuff method. TRB shows an antihypertensive effect in a dose‐dependent manner. TRB also reduces angiotensin I‐converting enzyme (ACE) activity in lung tissue and serum troponin I levels. TRB is fractionated by HPLC and ACE‐inhibitory activity in the HPLC fractions is measured. Peptides LRA and YY are identified from the two fractions with the strongest ACE‐inhibitory activity. Amino acid sequence of these peptides are found in a vicilin‐like seed storage protein, and identified in rice bran protein using the peptide mass fingerprint method. We confirm that LRA and YY are cleaved by thermolysin digestion of a model synthetic peptide. Orally administered LRA (0.25 mg kg−1) or YY (0.5 mg kg−1) lowers the SBP of SHRs at 4 h after administration. Conclusion We identify a novel, orally active antihypertensive peptide, LRA from the digest of rice bran protein. Thermolysin‐digested rice bran (TRB) decreases systolic blood pressure in spontaneously hypertensive rats (SHRs). TRB show a ACE inhibitory activity in vitro and in vivo, and reduced serum troponin I levels. A novel antihypertensive peptide, LRA from TRB, is also identified, and LRA is shown to be derived from At2g28490, the vicilin‐like seed storage protein. LRA (0.25 mg kg−1) decreases systolic blood pressure after oral administration.