Onion peel extracts ameliorate hyperglycemia and insulin resistance in high fat diet/streptozotocin-induced diabetic rats

Abstract

BackgroundQuercetin derivatives in onions have been regarded as the most important flavonoids to improve diabetic status in cells and animal models. The present study was aimed to examine the hypoglycemic and insulin-sensitizing capacity of onion peel extract (OPE) containing high quercetin in high fat diet/streptozotocin-induced diabetic rats and to elucidate the mechanism of its insulin-sensitizing effect.MethodsMale Sprague-Dawley rats were fed the AIN-93G diet modified to contain 41.2% fat and intraperitoneally injected with a single dose of streptozotocin (40 mg/kg body weight). One week after injection, the rats with fasting blood glucose levels above 126 mg/dL were randomly divided into 4 groups to treat with high fat diet containing 0 (diabetic control), 0.5, or 1% of OPE or 0.1% quercetin (quercetin equivalent to 1% of OPE) for 8 weeks. To investigate the mechanism for the effects of OPE, we examined biochemical parameters (insulin sensitivity and oxidative stresses) and protein and gene expressions (pro-inflammatory cytokines and receptors).ResultsCompared to the diabetic control, hypoglycemic and insulin-sensitizing capability of 1% OPE were demonstrated by significant improvement of glucose tolerance as expressed in incremental area under the curve (P = 0.0148). The insulin-sensitizing effect of OPE was further supported by increased glycogen levels in liver and skeletal muscle (P < 0.0001 and P = 0.0089, respectively). Quantitative RT-PCR analysis showed increased expression of insulin receptor (P = 0.0408) and GLUT4 (P = 0.0346) in muscle tissues. The oxidative stress, as assessed by superoxide dismutase activity and malondialdehyde formation, plasma free fatty acids, and hepatic protein expressions of IL-6 were significantly reduced by 1% OPE administration (P = 0.0393, 0.0237, 0.0148 and 0.0025, respectively).ConclusionOPE might improve glucose response and insulin resistance associated with type 2 diabetes by alleviating metabolic dysregulation of free fatty acids, suppressing oxidative stress, up-regulating glucose uptake at peripheral tissues, and/or down-regulating inflammatory gene expression in liver. Moreover, in most cases, OPE showed greater potency than pure quercetin equivalent. These findings provide a basis for the use of onion peel to improve insulin insensitivity in type 2 diabetes.

Quercetin can reduce insulin resistance without decreasing adipose tissue and skeletal muscle fat accumulation

“…The authors of those studies which found positive effects of quercetin on glycemic control proposed several mechanisms to explain the beneficial effect of this polyphenol: (a) the anti-oxidative protective action on the pancreatic islets (Coskun et al 2005;Babujanarthanam et al 2010;Jeong et al 2012), (b) the increase in adiponectin circulating concentration (Wein et al 2010), (c) the inhibition of small intestine glucosidase activity , (d) the reduction in the intestinal glucose absorption mediated by GLUT2 (Kwon et al 2007), (e) the increase in glucokinase activity (Vessal et al 2003) and (f) the increase in GLUT4 transporters in skeletal muscle (Jung et al 2011;Shen et al 2012;Anhê et al 2012).…”

Antioxidant activity of phenolic extracts from different cultivars of Italian onion (Allium cepa) and relative human immune cell proliferative induction

“…Recent literature is rich in both in vivo and in vitro studies reporting the antithrombotic (Lee et al, 2013), hypolipidemic (Lee et al, 2012b;Srinivasan, 2013), antidiabetic (Jung et al, 2011), antiobesity (Yoshinari et al, 2012), antioxidant (Alpsoy et al, 2013;Lee et al, 2012a), anti-inflammatory (Dorsch et al, 1990), cancer chemopreventive (Wang et al, 2012), and antiparasitic (Aboelhadid et al, 2013;Klimpel et al, 2011) properties of onion bulb extracts. Moreover, accumulated epidemiological studies suggest that a diet rich in onions may also have favorable effects on the risk of acute myocardial infarction (Galeone et al, 2009), and benign prostatic hyperplasia (Galeone et al, 2007).…”

Effects of Prosopis farcta fruit Hydroalcoholic Extract on Serum Concentrations of Glucose and Lipids in Insulin Resistance Model of Rats

“…It has been reported that quercetin has antidiabetic effect like metformin [27]. Quercetin, present in onion peel extracts, improved insulin sensitivity by up-regulating expressions of insulin receptor and glucose transporter as well as by promoting metabolism of glucose in peripheral tissues in diabetic rats [28]. This study can partly help to this claim that PFF due to have quercetin could lower glucose concentration.…”