PhD /Professor Dept. of Chemistry and Life Science, College of Bioresource Sciences, Nihon University FUJISAWA, Kanagawa, Japan
Diabetes mellitus is a serious disease because it often leads to serious complications such as retinopathy, nephropathy and neuropathy. Most of the patients suffering from diabetes mellitus are categorized into type 2 that shows the symptom of insulin resistance and/or deficiency. In order to prevent type 2 diabetes, it is important to suppress postprandial hyperglycemia by an appropriate daily food intake. We have already shown that rice albumin of 16 kDa (RA) effectively suppresses postprandial hyperglycemia even after glucose loading though it does not suppress mammalian α-amylase and only inhibits insect α-amylase. This study presents the mechanisms of action of RA on prevention of postprandial hyperglycemia. Intraperitoneal glucose tolerance test (IPGTT) showed that orally-administered RA did not suppress the increase in blood concentration of glucose that was intraperitoneally injected. This indicates that RA exerts its function not in the blood but in the gut. RA was hydrolyzed to a high-molecular peptide of 14 kDa (HMP) and low-molecular peptides (LMP) by digestive enzymes, and HMP and LMP fractions were orally administered to rats together with glucose to examine which peptide contributed to the function of RA. Beyond our expectation, both HMP and LMP suppressed the elevation in blood glucose level. HMP was shown to adsorb glucose and retard its diffusion rate like dietary fibers. On the other hand, LMP suppressed the expression of SGLT1 in STC-1 cells. Therefore, RA is hydrolyzed into HMP and LMP in the gut and effectively suppresses postprandial hyperglycemia by dual functions.