A Novel Antihypertensive Peptide Identified in Thermolysin-Digested Rice Bran

Abstract

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.

Keywords: ACE-inhibitory activity; antihypertensive effects; novel peptides; rice bran.