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Title: Anti-diabetic effects of rice hull smoke extract in alloxan-induced diabetic mice

item YANG, JUN YOUNG - Ajou University Of Korea
item KANG, MI YOUNG - Kyungpook National University
item NAM, SEPK HYUN - Ajou University Of Korea
item Friedman, Mendel

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2011
Publication Date: 11/30/2012
Citation: Yang, J., Kang, M., Nam, S., Friedman, M. 2012. Anti-diabetic effects of rice hull smoke extract in alloxan-induced diabetic mice. Journal of Agricultural and Food Chemistry. 60:87-94. doi: 10.1021/jf2035077.

Interpretive Summary: Rice is a major source of nourishment for the world’s population, especially in Asia. 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 antioxidative, anti-allergic, anti-inflammatory, and antimicrobial activities against Salmonella in laboratory media and in infected mice. In the present study, we describe additional findings from antioxidative reactive oxygen, biomarker, cell viability, cytokine gene expression, enzyme, histology, and oral feeding experiments which suggest that the protective effect of rice hull smoke against diabetes in the mouse can be attributed to blockage of oxidative stress-induced damage of islet ß-cells of the pancreas and improved metabolism of glucose in the liver. The results imply that rice hull extract-supplemented functional foods may contribute to the prevention and management of diabetes. Because of multiple beneficial effects, it seems that rice hull smoke-treated foods may have advantages over the widely used wood smoke treatments designed to impart flavoring and preservative effects to food. Rice hulls produced worldwide provide a new source of bioactive compounds derived from an agricultural byproduct that merits further evaluation for their potential to impart antimicrobial and other health-promoting effects to food.

Technical Abstract: We investigated the protective effect of a liquid rice hull smoke extract (RHSE) against diabetes in alloxan-induced diabetic mice. Anti-diabetic effects of RHSE were evaluated in both the rat insulinoma-1 cell line (INS-1) and diabetic ICR mice induced by inraperitoneal (ip) injection of alloxan. Alloxan treatment (10 mM) increased cellular reactive oxygen species (ROS) levels in the INS-1 cells and inhibited the cells in a dose-dependent manner. Alloxan-induced ROS levels were inversely related to cell viabilities. Alloxan-induced nitric oxide (NO) generation was also inhibited by RHSE through inhibition of inducible nitric oxide synthase (iNOS) gene expression. RHSE also suppressed inflammatory reaction in INS-1 cells through inhibition of expression of pro-inflammatory genes, including tumor necrosis factor-a (TNF-a), interleukins-1ß (IL-1ß), and interleukin-6 (IL-6). Compared to control mice, dietary administration for two weeks of RHSE to alloxan-induced diabetic mice caused a decrease in blood glucose level and increases in both serum insulin and hepatic glycogen levels. Assay of hepatic glucose-regulating enzyme activities showed that RHSE induced decreases in glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK) levels and an increase in the glucokinase (GCK) level, thus restoring glucose-regulating enzyme levels to normal control values. Histopathology showed that ip injection of alloxan also induced damage of Langerhans islet cells of the pancreas and liver necrosis associated with diabetes. Oral administration of RHSE for two weeks restored the islet and liver tissues to normal levels. These results suggest that dietary rice hull liquid smoke-supplemented food could contribute to the prevention or therapy of diabetes by protecting insulin-producing pancreatic islet and the liver against damage triggered by oxidative stress and local inflammation.