Study On The Hypoglycemic Effect Of Red Rice Polyphenols

Red rice was so named because of its red bran. Among the rich rice resources, red rice resources ranked No.2. Many studies showed that polyphenols have antioxidant, fat lowering, and α-amylase activity inhibiting effect. However, studies on the physiological activity especially the hypoglycemic activity of polyphenols in red rice were rarely reported. This study investigated the extraction, purification and main ingredient of red rice polyphenols(RRP). The effect of RRP on digestion and adsorption of starch and the porcine pancreatic α-amylase(PPA) inhibitory mechanism of RRP was studied. Addionally, the effect of RRP on STZ-induced diabetic mice was evaluated. The study provided basic data and theoretical support for the applications in food and medicine of red rice.The red rice pigment was extracted by organic solvent. The macroporous resin and eluent during the purification of RRP were selected by comparing the macroporous resin adsorption and desorption properties and eluent elution performance. Results showed that the polyphenol purity of RRP was 90.87% after using macroporous resin HPD400 A and 70% ethanol to adsorb and desorb red rice pigment crude extract, and using Sephadex LH-20 and 70% acetone to adsorb and elute the previous product.The proanthocyanidins purity of RRP was 69.18%.The average degree of polymerization of procyanidins in RRP was measured by improved vanillin-hydrochloric acid method. The average degree of polymerization of procyanidins in RRP was 2.07. Addionally, the infrared spectrum of RRP was analyzed. Results showed that the main structural units of RRP was procyanidin.The effect of RRP on digestion of starch and adsorption of glucose were studied by in vitro enzemy activity assay and everted gut sac method. Results showed that during the starch digestion process, RRP can inhibit the activities of PPA, α-glucosidase, maltase and sucrose. Furthermore, the higher the concentration of polyphenols was, the stronger the inhibiting effect was. RRP can reduce rice starch digestibility. The starch digestibility of red rice was lower than that of white rice and peeled red rice. During the glucose absorption process, RRP can inhibit the uptake of glucose in intestine by inhibiting intestine Na+/K+-ATP enzemy activity.The mechanism of PPR pancreatic PPA inhibitory was studied by dynamic light scattering method, turbidity method, ANS method, fluorescence quenching method, circular dichroism, enzyme kinetics determination and molecular docking method. Results showed that RRP can aggregate with PPA. With the increasing of RRP concentration, the aggregation average particle size and turbidity increased and then became steady, aggregation derived count rate first increased and then decreased. RRP can reduce the surface hydrophobicity of PPA. RRP can make PPA occurs static quenching based, dynamic quenching supplemented fluorescence quenching. Meanwhile, PPR can make PPA fluorescence spectrum peak wavelength blue-shifted. After addition of PPR, the conformation of PPA changed. It showed that α-helix rate reduced, β-fold rate and β-angle rate increased. The PPA inhibition type of RRP was reversible noncompetitive and competitive mixed type. RRP can combine with ASP300, ASP197 and GLU233 which are active sites of it, and form hydrogen bond. At the same time, it can change the micro environment of PPA TRP58 and TRP59 resedue. Those may be the reason why RRP can inhibit the activity of PPA.The effect of RRP and red rice bran(RRB) on STZ-induced diabetic mice was studied by animal experiments. Results showed that in the aspect of short-term effect of RRP, the blood glucose changes of healthy mice was essentially similar after intaking different rice. At the same time, the blood glucose of STZ-induced diabetic mice after intaking white rice or peeled red rice was higher then that after intaking red or white rice+RRP. In the aspect of long-term effect of RRP and RRB on STZ-induced diabetic mice, the weight of the mice which long-term gavaged PPR or RRB increased or stabilized. Comparing with the negative group, the deterioration of polydipsia and polyuria symptom has been effectively controlled. After gavaging RRP or RRB, the blood glucose of mice decreased or slowly grew; glucose tolerance improved; liver antioxidant function and glucose metabolism was enhanced; insulin secretion increased; insulin sensitivity enhanced; islet cell apoptosis slowed, islet morphology was maintained; the islet cells were protected to some extent.