Effects of Syzygium aromaticum-Derived Triterpenes on Postprandial Blood Glucose in Streptozotocin-Induced Diabetic Rats Following Carbohydrate Challenge

Abstract

PurposeRecent reports suggest that the hypoglycaemic effects of the triterpenes involve inhibition of glucose transport in the small intestine. Therefore, the effects of Syzygium spp-derived triterpenes oleanolic acid (OA) and maslinic acid (MA) were evaluated on carbohydrate hydrolyzing enzymes in STZ-induced diabetic rats and consequences on postprandial hyperglycaemia after carbohydrate loading. MethodsWe determined using Western blot analysis the expressions of α-amylase and α-glucosidase and glucose transporters SGLT1 and GLUT2 in the small intestine intestines isolated from diabetic rats treated with OA/MA for 5 weeks. In vitro assays were used to assess the inhibitory activities of OA and MA against α-amylase, α-glucosidase and sucrase. ResultsOA and MA ameliorated postprandial hyperglycemia in carbohydrate loaded diabetic rats as indicated by the significantly small glucose area under the curve (AUC) in treated diabetic animals compared with that in untreated diabetic rats. Western blotting showed that OA and MA treatment not only down-regulated the increase of SGLT1 and GLUT2 expressions in the small intestine of STZ-induced diabetic rats, but also inhibited small intestine α-amylase, sucrase and α-glucosidase activity. IC50 values of OA against α-amylase (3.60 ± 0.18 mmol/L), α-glucosidase (12.40 ± 0.11 mmol/L) and sucrase (11.50 ± 0.13 mmol/L) did not significantly differ from those of OA and acarbose. ConclusionsThe results of suggest that OA and MA may be used as potential supplements for treating postprandial hyperglycemia.Novelty of the WorkThe present observations indicate that besides improving glucose homeostasis in diabetes, OA and MA suppress postprandial hyperglycaemia mediated in part via inhibition of carbohydrate hydrolysis and reduction of glucose transporters in the gastrointestinal tract. Inhibition of α-glucosidase and α-amylase can significantly decrease the postprandial hyperglycaemia after a mixed carbohydrate diet and therefore can be an important strategy in the management of postprandial blood glucose levels in NIDDM patients.

The Effects of Syzygium Aromaticum-Derived Triterpenes on Gastrointestinal Ghrelin Expression in Streptozotocin-Induced Diabetic Rats

“…These results were in agreement with previous observations from studies conducted in our laboratory (Mapanga et However, both OA and MA had no significant effect on plasma insulin concentrations in the STZ-diabetic rats suggesting that the blood glucose lowering effects may be exerted via extra-pancreatic mechanisms. We have previously reported that OA and MA could prevent postprandial hyperglycaemia through the down-regulation of key intestinal carbohydrate hydrolyzing enzymes such as α-amylase and α-glucosidase as well as intestinal glucose transporters such as SGLT1 and GLUT2 (Khathi et al, 2013). The results of this study showed that the plasma ghrelin levels were significantly higher in the STZ-diabetic animals possibly as a result of the decreased plasma insulin levels (Buss et al, 2014).…”

“…Various medicinal plant extracts have been reported to significantly reduce food intake possibly through the reduction of plasma ghrelin levels (Bast et al, 2002;Fong, 2002). Studies conducted in our laboratory have shown that Syzygium aromaticum-derived oleanolic acid (OA) and maslinic acid (MA) reduce blood glucose concentrations in STZ-induced diabetic rats in sub-chronic studies through a variety of mechanisms (Khathi et al, 2013;Mkhwanazi et al, 2014;Musabayane et al, 2010;Ngubane et al, 2011). Furthermore, these triterpenes have previously been reported to reduce food intake through unknown mechanisms (Khathi et al, 2013;Mkhwanazi et al, 2014).…”

“…Studies conducted in our laboratory have shown that Syzygium aromaticum-derived oleanolic acid (OA) and maslinic acid (MA) reduce blood glucose concentrations in STZ-induced diabetic rats in sub-chronic studies through a variety of mechanisms (Khathi et al, 2013;Mkhwanazi et al, 2014;Musabayane et al, 2010;Ngubane et al, 2011). Furthermore, these triterpenes have previously been reported to reduce food intake through unknown mechanisms (Khathi et al, 2013;Mkhwanazi et al, 2014). This study was therefore designed to evaluate the effects of these triterpenes on plasma ghrelin concentrations as well as the gastrointestinal expression of this hormone.…”

Free radical scavenging and α-glucosidase inhibition, two potential mechanisms involved in the anti-diabetic activity of oleanolic acid

“…In addition to studies on the inhibition of amylase and glucosidase activities, in recent years new data have been reported showing that OA can also repress the expression of these proteins in the small intestine (Gabás-Rivera et al, 2013;Khathi et al, 2013), in addition to the glucose transporters SGLT1 and GLUT2, involved in the absorption of the saccharide from the lumen of the small intestine to the bloodstream.…”

Phytochemical and zootechnical studies of Physalis peruviana L. leaves exposured to streptozotocin-induced diabetic rats

“…Before induction, all rats were fasted 12 h (Ngueguim et al, 2016). Rats with serum glucose level above 300 mg/dl were Fokunang et al 125 considered as diabetic (Khathi et al, 2013).…”