Potential value of a rice protein extract, containing proteinaceous inhibitors against cysteine proteinases from Porphyromonas gingivalis, for managing periodontal diseases.

Arg-specific gingipain (Rgp) is a major pathogenic determinant of Porphyromonas gingivalis which is a major pathogen in periodontal disease. We prepared protein extracts with Rgp-inhibitory activity from polished rice (Oryza sativa) and evaluated the effects of these extracts on the growth and pathogenicity of P. gingivalis. The extracts inhibited the proteolytic degradation of human proteins by P. gingivalis proteinases, and repressed the growth and homotypic biofilm formation of P. gingivalis. The disruption of adhesion of epithelial cells by P. gingivalis was also restricted by the rice protein extracts. Our results suggested that the rice protein extracts suppressed the pathogenicity and growth of P. gingivalis by inhibiting the bacterial proteinase activities, implying that the Rgp-inhibitory proteins prepared from rice may be potentially valuable as nutraceutical agents for preventing periodontal diseases.

Identification of proteinaceous inhibitors of a cysteine proteinase (an Arg-specific gingipain) from Porphyromonas gingivalis in rice grain, using targeted-proteomics approaches.

Porphyromonas gingivalis is known to be a major etiologic agent in the onset and progression of chronic periodontitis. Among various virulence factors that this bacterium produces, Arg- and Lys-specific cysteine proteinases (gingipains) are believed to be major determinants of the pathogenicity of P. gingivalis. Here, we report on our finding that there are inhibitors of these cysteine proteinases in a rice protein fraction. Comprehensive affinity chromatography and MS analyses resulted in the identification of 17 Arg-gingipain (Rgp)-interacting proteins in the rice endosperm. Of these, four proteins (i.e., a 26 kDa globulin, a plant lipid transfer/trypsin-alpha amylase inhibitor, the RA17 seed allergen, and an alpha amylase/trypsin inhibitor) were estimated to account for 90% of the Rgp inhibitory activity in the rice protein fraction, using a two-dimensional gel system of double-layer reverse zymography. In addition, a synthetic peptide derived from an Rgp-interacting protein, cyanate hydratase, could inhibit the growth of P. gingivalis and showed inhibitory activity against both the Arg- and Lys-gingipains. These results suggest that these rice proteins may be useful as nutraceutical ingredients for the prevention and management of periodontal diseases.