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Effects of Onion (Allium cepa L.) Extract Administration on Intestinal α-Glucosidases Activities and Spikes in Postprandial Blood Glucose Levels in SD Rats Model
Department of Biomaterials Science and Technology, Yonsei University, Seoul 120-749, Korea
Department of Food and Nutrition, Hannam University, Daejeon 305-811, Korea
Department of Biotechnology, College of Life Science and Biotechnology, Yonsei University, Seoul 120-749, Korea
* Authors to whom correspondence should be addressed.
Received: 15 April 2011; in revised form: 19 May 2011 / Accepted: 31 May 2011 / Published: 8 June 2011
Abstract: Diets high in calories and sweetened foods with disaccharides frequently lead to exaggerated postprandial spikes in blood glucose. This state induces immediate oxidant stress and free radicals which trigger oxidative stress-linked diabetic complications. One of the therapeutic approaches for decreasing postprandial hyperglycemia is to retard absorption of glucose by the inhibition of carbohydrate hydrolyzing enzymes,α-amylase and α-glucosidases, in the digestive organs. Therefore, the inhibitory activity of Korean onion (Allium cepa L.) extract against rat intestinal α-glucosidases, such as sucrase, maltase, and porcine pancreatic α-amylase were investigated in vitro and in vivo. The content of quercetin in ethyl alcohol extract of onion skin (EOS) was 6.04 g/100 g dried weight of onion skin. The in vitro half-maximal inhibitory concentrations (IC50) of EOS and quercetin, a major phenolic in onion, on rat intestinal sucrase were 0.40 and 0.11 mg/mL, respectively. The postprandial blood glucose lowering effects of EOS and quercetin were compared to a known type 2 diabetes drug (Acarbose), a strong α-glucosidase inhibitor in the Sprague-Dawley (SD) rat model. In rats fed on sucrose, EOS significantly reduced the blood glucose spike after sucrose loading. The area under the blood glucose-time curve (AUClast) in EOS-treated SD rats (0.5 g-EOS/kg) was significantly lower than in untreated SD rats (259.6 ± 5.1 vs. 283.1 ± 19.2 h·mg/dL). The AUClast in quercetin-treated SD rats (0.5 g-quercetin/kg) was similar to in EOS-treated group (256.1 ± 3.2 vs. 259.6 ± 5.1 h·mg/dL). Results from this study indicates that although quercetin does have blood glucose lowering potential via α-glucosidase inhibition, there are other bioactive compounds present in onion skin. Furthermore, the effects of two weeks administration of EOS in a high carbohydrate-dietary mixture (Pico 5053) on sucrase and maltase activities in intestine were evaluated in SD rat model. Compared to the upper and middle parts of intestine, the activities of sucrase in the lower parts of intestine remained significantly higher after two weeks of EOS treatment. These results indicate that EOS may improve exaggerated postprandial spikes in blood glucose and glucose homeostasis since it inhibits intestinal sucrase and thus delays carbohydrate absorption, although clinical trials are needed.
Keywords: α-glucosidase; hyperglycemia; sucrase; postprandial spikes; Allium cepa
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Kim, S.-H.; Jo, S.-H.; Kwon, Y.-I.; Hwang, J.-K. Effects of Onion (Allium cepa L.) Extract Administration on Intestinal α-Glucosidases Activities and Spikes in Postprandial Blood Glucose Levels in SD Rats Model. Int. J. Mol. Sci. 2011, 12, 3757-3769.
Kim S-H, Jo S-H, Kwon Y-I, Hwang J-K. Effects of Onion (Allium cepa L.) Extract Administration on Intestinal α-Glucosidases Activities and Spikes in Postprandial Blood Glucose Levels in SD Rats Model. International Journal of Molecular Sciences. 2011; 12(6):3757-3769.
Kim, Sun-Ho; Jo, Sung-Hoon; Kwon, Young-In; Hwang, Jae-Kwan. 2011. "Effects of Onion (Allium cepa L.) Extract Administration on Intestinal α-Glucosidases Activities and Spikes in Postprandial Blood Glucose Levels in SD Rats Model." Int. J. Mol. Sci. 12, no. 6: 3757-3769.