A4646 A novel endothelial NO-dependent vasorelaxing and anti-hypertensive peptide derived from rice bran

Abstract

Objectives: We recently identified a novel anti-hypertensive peptide Leu-Arg-Ala (LRA) from the enzymatic digestion of rice bran protein (Shobako et al., Mol. Nutr. Food res., 2018). Orally administered LRA at a dose of 0.25 mg/kg potently reduced the systolic blood pressure (SBP) in spontaneously hypertensive rats (SHRs), but had low ACE inhibitory activity (IC50 = 62 μM), explaining its potent hypotensive activity. In this study, we investigated vasorelaxing activity of LRA and the involvement of nitric oxide (NO) signaling. Methods: The vasorelaxing activity was determined by the mesenteric artery isolated from SHRs. Changes in SBP of SHRs were measured by tail-cuff method. Results: A novel rice bran-derived hypotensive peptide LRA exhibited vasorelaxing activity in the mesenteric artery of SHRs. Pretreatment with NG-Nitro-L-arginine methyl ester (L-NAME), an inhibitor of NO synthase (NOS), diminished the LRA-induced vasorelaxing activity. L-NAME also inhibited the anti-hypertensive effects of LRA. LRA also activated phosphorylation of endothelial NOS in human umbilical vein endothelial cells (HUVECs). Thus, these data suggest that LRA-induced vasorelaxing and anti-hypertensive activites were mediated by the activation of endothelial NO signaling. Next, we investigated mechanisms upstream of NO signaling. The LRA-induced vasorelaxant activity was not blocked by HOE 140 (bradykinin B2 antagonist), A779 (MAS antagonist) and wortomannin (PI3 kinase inhibitor), implying that NO-mediated vasorelaxing activity by LRA is independent of the bradykinin B2/MAS receptor-PI3 kinase activation. Conclusion: We found that LRA possibly exhibited vasorelaxing and hypotensive effects in a novel endothelial NO signaling-dependent manner. This is the first example of a NO-dependent vasorelaxing peptide identified from rice bran.