Identification of cationic peptides derived from low protein rice by-products and evaluation of their multifunctional activities.

Low protein rice (LPR) by-products were used as a source of novel multifunctional cationic peptides. The LPR by-products were separated by ampholyte-free isoelectric focusing (autofocusing) into 20 fractions containing peptides with different isoelectric points (pIs). Subsequently, the antimicrobial activity of each fraction was evaluated against four pathogenic microorganisms. In addition, the cationic peptides from fractions exhibiting antimicrobial activity were purified using reversed-phase high-performance liquid chromatography and identified using matrix-assisted laser/desorption ionization-time-of-flight mass spectroscopy. Of the 11 cationic peptides identified, five peptides with pI values greater than 9.31 and net charges greater than +2 were chemically synthesized for multiple functionalities, including antimicrobial, lipopolysaccharide (LPS)-neutralizing, and angiogenic activities. Among these five cationic peptides, only LPR-KRK, which had a net charge of +9, exhibited antimicrobial activity against three of the four pathogenic microorganisms tested. Chromogenic LPS-neutralizing assays using Limulus amebocyte lysate showed that the 50% effective concentrations of these five peptides were between 0.11 and 3.09 μM. Tube-formation assays using human umbilical vein endothelial cells showed that all five peptides exhibited significant angiogenic activity at 1 μM and 10 μM, while none exhibited hemolytic activity toward mammalian red blood cells at concentrations up to 500 μM. Our results demonstrate that these five cationic peptides exhibit multiple biological functionalities with little or no hemolytic activity. Thus, fractions containing cationic peptides obtained from LPR by-products have the potential to be used as dietary supplements and functional ingredients in food products.