A mixture of apple pomace and rosemary extract improves fructose consumption-induced insulin resistance in rats: modulation of sarcolemmal CD36 and glucose transporter-4

摘要

Apple pomace is a by-product of the processing of apple for juice, cider or wine preparation. Rosemary is a herb commonly used as spice and flavoring agent in food processing. Evidence suggests that both apple pomace and rosemary have rich bioactive molecules with numerous metabolic effects. To provide more information for using apple pomace and rosemary as functional foods for management of metabolism-associated disorders, the present study investigated the insulin-sensitizing effect of a mixture of apple pomace and rosemary extract (AR). The results showed that treatment with AR (500 mg/kg, daily, by gavage) for 5 weeks attenuated chronic liquid fructose consumption-induced increases in fasting plasma insulin concentration, the homeostasis model assessment of insulin resistance index and the adipose tissue insulin resistance index in rats. Mechanistically, AR suppressed fructose-induced acceleration of the clearance of plasma non-esterified fatty acids during oral glucose tolerance test, and decreased excessive triglyceride accumulation and the increased Oil Red O staining area in the gastrocnemius. Furthermore, AR restored fructose-induced overexpression of sarcolemmal CD36 that is known to contribute to etiology of insulin resistance by facilitating fatty acid uptake, and downregulation of sarcolemmal glucose transporter (GLUT)-4 that is the insulin-responsive glucose transporter. Thus, these results demonstrate that AR improves fructose-induced insulin resistance in rats via modulation of sarcolemmal CD36 and GLUT-4.