Food Sci. Biotechnol. 20(1): 251-154 (2011) DOI 10.1007/s10068-011-0034-5
RESEARCH NOTE
Anti-diabetic Effect of Watermelon (Citrullus vulgaris Schrad) on Streptozotocin-induced Diabetic Mice Jiyun Ahn, Wonhee Choi, Suna Kim, and Taeyoul Ha
Received: 30 November 2008 / Revised: 8 February 2010 / Accepted: 20 October 2010 / Published Online: 28 February 2011 © KoSFoST and Springer 2011
Abstract The anti-diabetic potential of watermelon (Citrullus vulgaris Schrad) was evaluated in vivo. ICR mice were fed experimental diet containing none, 10% watermelon flesh powder (WM-P) or 1% watermelon rind ethanol extract (WM-E). At the end of 4 weeks, mice were administrated with streptozotocin (40 mg/kg, i.p.) for 5 consecutive days to induce diabetes. Supplementation with WM-E significantly decreased blood glucose level and increased serum insulin levels. Feeding of WM-P also induced moderate changes but those were not statistically significant. Immunohistochemical analysis showed watermelon effectively protected pancreatic cells death. These results suggest that watermelon has a beneficial effect on diabetes. Keywords: watermelon (Citrullus vulgaris Schrad), antidiabetic, streptozotocin, insulin
Introduction Diabetes mellitus is a metabolic disorder affecting the metabolism of carbohydrates, fat, and protein. It is a leading cause of human death and afflicts an estimated 6% of the adult population in industrialized nations. The worldwide incidence of diabetes mellitus is expected to continue to grow by 6% per annum, potentially reaching 200-300 million cases in 2010 (1). Streptozotocin (STZ), an antibiotic produced by Jiyun Ahn, Wonhee Choi, Taeyoul Ha ( ) Functional Food Technology Research Group, Research Division for Emerging Innovative Technology, Korea Food Research Institute, Seongnam, Gyeonggi 463-746, Korea Tel: +82-31-780-9054; Fax: +82-31-780-9225 E-mail:
[email protected] Suna Kim Deaprtment of Home Economics, College of Natural Science, Korea National Open University, Seoul 110-791, Korea
Streptomyces achromogenes, is the most commonly used agent in experimental diabetes (2). It was demonstrated that STZ induced damage to pancreatic cell membrane and evoked oxidative stress to islet cells (3, 4). In addition, STZ has been shown to induce DNA strand breaks and methylation in pancreatic islet cells (5). Watermelon (Citrullus vulgaris S.) is one of the few foods naturally rich in citrulline, with amounts varying from 0.7 to 3.6 mg/g of fresh weight (6). The citrulline is an amino acid that can be metabolized to arginine, a conditionally essential amino acid for humans by argininosuccinate synthase (ASS) and argininosuccinate lyase (7) in virtually all animal cells (8). Arginine is required for the formation of proteins and other molecules with enormous biological importance (8). Dietary arginine supplementation decreases serum glucose concentration in diabetic rats (9). And watermelon is a rich natural source of lycopene, a carotenoid of great interest because of its antioxidant capacity and potential health benefits (10). The mean lycopene concentration of watermelon is about 40% higher than the year-round mean for raw tomato (11). The watermelon has antioxidant (12), cardioprotective (13), and anti-inflammatory (14) activities. However little is known about the anti-diabetic effect. In this study, we examined the anti-diabetic activity of watermelon on STZ-induced diabetic mice.
Materials and Methods Materials Watermelon (WM) was supplied by Buyeo-gun, Chungnam, Korea. All chemicals used were of analytical grade. Preparation of WM flesh powder (WM-P) and WM rind ethanol extract (WM-E) For WM-P, red flesh
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from WM was freeze dried to a powder. In case of WME, 1 kg of freeze dried rind of WM were extracted with 80% ethanol (10 L) at room temperature for overnight and evaporated. The yield of extract was 28.9%. Animals Forty male ICR mice (Orient, Korea) averaging 4 weeks old were used. After 1 week acclimatization, the animals were randomly divided into 4 groups. Two of the groups were fed an experimental diet that was based on the AIN76 formula, and contained either 10% powder (WMP) or 1% extract (WM-E). The remaining 2 groups were fed the same diet but containing no WM. Induction of diabetes After 4 weeks of experimental diet feeding, STZ (40 mg/kg) dissolved in citrate buffer (pH 4.5) was injected intraperitoneally (i.p.) for 5 consecutive days. Mice in the control group were given vehicle alone. After 3 days, animals were sacrificed to collect blood and pancreas. Determination of blood glucose and serum insulin The blood samples were collected from tail vein after 6 hr fasting. The blood glucose was assayed by kit (R&D System, Minneapolis, MN, USA). Mouse insulin enzymelinked immunosorbent assay (ELISA) kit (R&D System) was used to measure serum insulin level. Immunohistochemical procedures After phlebotomized under anesthetizing with ethyl ether, pancreatic tissues were fixed in 10% neutral buffered formalin. The endogenous peroxidase activity was inhibited by incubating sections in 3% H2O2 in phosphate buffered saline (PBS) for 30 min. Nonspecific binding of antibodies was blocked by their incubation with a 1% horse serum (Gibco Invitrogen, Carlsbad, CA, USA) for 10 min. Sections were incubated with monoclonal rabbit antisera against mouse insulin protein (Sigma-Aldrich, St. Louis, MO, USA) for 1 hr at 4 o C. Binding of the antibody was visualized using a diaminobenzidin (DAB) solution and the slides were mounted and examined. Statistical analysis The results are presented as mean± standard error mean (SEM). Statistical analyses were performed using GraphPad Prism 4 software (San Diego, CA, USA). Data were considered significant at p
