Exploring the interaction of phytochemicals from Hibiscus rosa-sinensis flowers with glucosidase and acetylcholinesterase: An integrated in vitro and in silico approach.

Targeting multiple factors such as oxidative stress, alpha glucosidase and acetylcholinesterase (AChE) are considered advantageous for the treatment of diabetes and diabetes associated-cognitive dysfunction. In the present study, Hibiscus rosa-sinensis flowers anthocyanin-rich extract (HRA) was prepared. Phytochemical analysis of HRA using LC-ESI/MS/MS revealed the presence of various phenolic acids, flavonoids and anthocyanins. HRA showed in vitro antioxidant activity at low concentrations. HRA inhibited all the activities of mammalian glucosidases and AChE activity. The IC50 value of HRA for the inhibition of maltase, sucrase, isomaltase, glucoamylase and AChE was found to be 308.02 ± 34.25 µg/ml, 287.8 ± 19.49 µg/ml, 424.58 ± 34.75 µg/ml, 408.94 ± 64.82 µg/ml and 264.13 ± 30.84 µg/ml, respectively. Kinetic analysis revealed mixed-type inhibition against all the activities except for glucoamylase (competitive) activity. In silico analysis confirmed the interaction of two active constituents cyanidin 3-sophoroside (CS) and quercetin 3-O-sophoroside (QS) with four subunits, n-terminal and c-terminal subunits of human maltase-glucoamylase and sucrase-isomaltase as well as with AChE. Molecular dynamics simulation, binding free energy calculation, DCCM, PCA, PCA-based free energy surface analysis ascertained the stable binding of CS and QS with target proteins studied. HRA could be used as complementary therapy for diabetes and cognitive improvement.

Inhibition of α-glucosidases by tea polyphenols in rat intestinal extract and Caco-2 cells grown on Transwell.

Inhibition of maltase, sucrase, isomaltase and glucoamylase activity by acarbose, epigallocatechin gallate, epicatechin gallate and four polyphenol-rich tea extract from white, green, oolong, black tea, were investigated by using rat intestinal enzymes and human Caco-2 cells. Regarding rat intestinal enzyme mixture, all four tea extracts were very effective in inhibiting maltase and glucoamylase activity, but only white tea extract inhibited sucrase and isomaltase activity and the inhibition was limited. Mixed-type inhibition on rat maltase activity was observed. Tea extracts in combination with acarbose, produced a synergistic inhibitory effect on rat maltase activity. Caco-2 cells experiments were conducted in Transwells. Green tea extract and epigallocatechin gallate show dose-dependent inhibition on human sucrase activity, but no inhibition on rat sucrase activity. The opposite was observed on maltase activity. The results highlighted the different response in the two investigated model systems and show that tea polyphenols are good inhibitors for α-glucosidase activity.

Inhibitory effects of mulberry leaf extract on postprandial hyperglycemia in normal rats.

We examined the inhibitory effects of aqueous ethanol extract from mulberry leaves (ME) on postprandial hyperglycemia in normal Wistar rats. ME dose-dependently suppressed the postprandial rise of blood glucose in rats, when ME (0.02-0.5 g/kg) was given 0.5 h before the administration of carbohydrates such as sucrose, maltose and starch. The ME dose showing 50% inhibition of the increment of blood glucose (ED50) was 0.11 g/kg for sucrose, 0.44 g/kg for maltose, and 0.38 g/kg for starch. ME and its basic fraction (MB) containing 1-deoxynojirimycin were assayed for their inhibitory effects (IC50) on disaccharidase derived from the small intestine of rats. The IC50 value of ME was 3.2 microg/mL for sucrase, 10 microg/mL for isomaltase, and 51 microg/mL for maltase. The IC50 value of MB was 0.36 microg/mL for sucrase, 1.1 microg/mL for isomaltase, and 6.2 microg/mL for maltase. The IC50 value of 1-deoxynojirimycin as the principle component in ME was 0.015 microg/mL for sucrase and 0.21 microg/mL for maltase, and this value was comparable to the IC50 of voglibose. The inhibitory activity of ME in a-amylase was weak. These results suggest that ME strongly suppresses postprandial hyperglycemia after carbohydrate loading by inhibiting the activity of disaccharidases in the small intestine of rats.

Evaluation of isofagomine and its derivatives as potent glycosidase inhibitors.

A pseudo-aza-monosaccharide and several pseudo-aza-disaccharide compounds were constructed based on replacement of the anomeric carbon with a nitrogen and the ring oxygen with a carbon. The inhibition constants of these compounds toward five different glycosidases, alpha-glucosidase, beta-glucosidase, isomaltase, alpha-mannosidase, and glucoamylase, were obtained. Isofagomine, the pseudo-aza-monosaccharide, shows a broad spectrum of strong inhibition against glycosidases. It is the most potent inhibitor of beta-glucosidase from sweet almonds reported to date and also a strong inhibitor of glucoamylase, isomaltase, and alpha-glucosidase. Isofagomine inhibits beta-glucosidase, glucoamylase, and isomaltase more strongly than 1-deoxynojirimycin where the ring oxygen has been replaced with a nitrogen. The alpha-1,6- linked pseudo-disaccharide showed very strong inhibition toward glucoamylase, being nearly as potent an inhibitor as acarbose. Pseudo-disaccharides in which the anomeric nitrogen was methylated to favor formation of either the alpha or beta substrate linkage generally had weakened inhibition for the glycosidases studied most likely due to steric interference with the various active sites. These results indicate that the presence of a basic group at the anomeric center is important for carbohydrase inhibition. The presence of a charged carboxylate group near the anomeric carbon which interacts with the basic nitrogen is suggested for these enzymes, particularly for beta-glucosidase. The presence of a second alpha-linked glucosyl residue is also critical for strong inhibition of glucoamylase.

Effect of an intestinal disaccharidase inhibitor (AO-128) on obesity and diabetes.

A new disaccharidase inhibitor, AO-128, showed 190-3900-fold more potent inhibition of purified rat small intestine sucrase-isomaltase (S-1) complex and 23-33-fold more potent inhibition of semipurified porcine small intestine disaccharidases than acarbose. AO-128 suppressed elevation of the blood glucose concentration after oral sucrose, maltose, and starch, but not after oral glucose, fructose, and lactose. The chronic addition of AO-128 to the diet produced antiobesity and antidiabetic actions in obese and/or diabetic animals. Undesirable side effects, such as diarrhea and soft feces, were observed only for the first 5-7 d and suppression of intestinal disaccharidase activities was observed even at the end of the experiment, suggesting that the suppressive or delaying effect of AO-128 on elevation of the postprandial blood glucose concentrations is involved in reduction in body weight gain and prevention and/or amelioration of the diabetic state. Thus, AO-128 is useful as an adjunct to the dietary management of obesity and diabetes.