Anti-diabetic effects of rice hull smoke extract on glucose-regulating mechanism in type 2 diabetic mice

Authors: YANG, JUN, YOUNG - Ajou University Of Korea; MOON, EUPYO - Ajou University Of Korea; NAM, SEOK, HYUN - Ajou University Of Korea; Friedman, Mendel

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2012
Publication Date: 7/17/2012
Citation: Yang, J., Moon, E., Nam, S., Friedman, M. 2012. Anti-diabetic effects of rice hull smoke extract on glucose-regulating mechanism in type 2 diabetic mice. Journal of Agricultural and Food Chemistry. doi:10.1021/jf3017749.

Interpretive Summary: Rice is a major source of nourishment for the world’s population. World production of rice is estimated at around 680 million tons. About 20% of the harvested rice consists of hulls, which protect rice seeds during growth. A byproduct of the combustion of rice hulls is the smoke that is generated. In previous studies, we described the production and composition of a new rice hull liquid smoke with a smoky aroma and sugar-like odor prepared by pyrolysis of rice hulls followed by liquefaction of the resulting smoke. The liquid smoke contained 161 compounds, as characterized by GC/MS. The extract exhibited strong anti-inflammatory and in vivo antimicrobial activities against Salmonella bacteria in mice as well as anti-diabetic effects in alloxan-treated mice. In the present study, we describe additional findings on pro-inflammatory biomarkers, cytokine gene expression, glucose-metabolizing enzymes, histology, immunohistochemistry and plasma glucose, insulin, cholesterol, and triglyceride levels that indicate that the protective effect of the liquid smoke against type 2 diabetes in the mouse on a high-fat diet can be attributed to the blockage of oxidative stress-induced damage of Langerhans islet ß-cells of the pancreas and improved metabolism of glucose in the liver. The results suggest that human food and animal feed supplemented with rice hull smoke extract might contribute to the prevention and management of infections, diabetes, and other diseases.

Technical Abstract: The aim of this study is to determine the protective effect of a liquid rice hull smoke extract (RHSE) against type 2 diabetes induced by a high fat diet administered to mice. Dietary administration of 0.5% or 1% RHSE for 7 weeks results in significantly reduced blood glucose and triglyceride and total cholesterol concentrations, higher serum insulin levels and improved glucose tolerance, as assessed by an oral glucose tolerance assay, compared with the control group of mice fed high on a high-fat diet. Oral RHSE intake increased HDL (good)-cholesterol levels and decreased LDL (bad)-cholesterol levels. The hypoglycemic effect of RHSE was accompanied by changes in enzyme activities and cognate gene expression assessed using RT-PCR. Among the glucose metabolism regulating genes evaluated, hepatic glucokinase (GCK), the glucose transporters GLUT2 and GLUT4 and peroxisome proliferator activated receptor-' (PPAR-') were up-regulated, whereas glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK) were down-regulated in the liver of RHSE-administered mice. These changes resulted in restoring glucose-regulating molecule activities to normal control levels. Histopathology showed that a high-fat diet intake also induced liver necrosis and damage of the Langerhans islet in the pancreas, whereas RHSE administration restored necrotic damage to normal levels. Immunohistochemistry showed that the dietary administration of RHSE can restore the reduced insulin-producing ß-cell population in Langerhans islets associated with a high-fat diet intake to non-diabetic normal control levels in a dose-dependent manner. These results suggest that RHSE-supplemented food could protect insulin-producing islet cells against damage triggered by oxidative stress and local inflammation associated with diabetes. The dietary significance of the results is discussed.