Nobiletin ameliorates glucose tolerance by protecting against β-cell loss in type-2 diabetic db/db mice

Abstract

BackgroundNobiletin, a polymethoxy flavone contained in the peel of Citrus reticulata, has been known to have health benefits especially those related to improvement of type 2 diabetes. Our previous in vitro study demonstrated the insulinotropic and anti-apoptotic effects of nobiletin in pancreatic β-cells. These effects of nobiletin are postulated to be responsible for its anti-diabetic activity. PurposeWe evaluated the anti-diabetic effects of nobiletin on pancreatic β-cells of type 2 diabetic db/db mice. MethodsNobiletin was filled into an osmotic pump and implanted subcutaneously in the back of db/db mice for 2 weeks with continuous administration. The mice were then used for the experiments to elucidate the in vivo effects of nobiletin on glucose intolerance. ResultsThe continuous subcutaneous administration of nobiletin using osmotic pumps significantly reduced blood glucose levels in non-fasting state and during an oral glucose tolerance test. The nobiletin administration also ameliorated insulin sensitivity determined by insulin tolerance test, which was likely due to a reduction of white adipose tissue weight. In addition, β-cell mass was significantly larger in nobiletin-administered db/db mice compared to vehicle-administered db/db mice. These results suggest that continuous administration of nobiletin ameliorates glucose tolerance in type 2 diabetes, which is mediated by improving not only insulin resistance but also insulin secretion, the latter being due to protection against β-cell loss in diabetes. ConclusionNobiletin would have a valuable effect on the prevention of type 2 diabetes.