The Mechanisms of Alpha-Amylase Inhibition by Flavan-3-Ols and the Possible Impacts of Drinking Green Tea on Starch Digestion

Inhibitory Mechanism of Quercimeritrin as a Novel α-Glucosidase Selective Inhibitor

In this study, 12 flavonoid glycosides were selected based on virtual screening and the literature, and Quercimeritrin was selected as the best selective inhibitor of α-glucosidase through in vitro enzyme activity inhibition experiments. Its IC50 value for α-glucosidase was 79.88 µM, and its IC50 value for α-amylase >250 µM. As such, it could be used as a new selective inhibitor of α-glucosidase. The selective inhibition mechanism of Quercimeritrin on the two starch-digesting enzymes was further explored, and it was confirmed that Quercimeritrin had a strong binding affinity for α-glucosidase and occupied the binding pocket of α-glucosidase through non-covalent binding. Subsequently, animal experiments demonstrated that Quercimeritrin can effectively control postprandial blood glucose in vivo, with the same inhibitory effect as acarbose but without side effects. Our results, therefore, provide insights into how flavone aglycones can be used to effectively control the rate of digestion to improve postprandial blood glucose levels.

The inhibitory action of purple tea on in vivo starch digestion compared to other Camellia sinensis teas

In order to contribute to improve knowledge about the actions of Camellia sinensis extracts on starch digestion, several varieties were compared. The latter were green, oolong, white, black, and purple teas. The results are hoped to contribute to our understanding of the mode of action and potency of the various tea preparations as possible adjuvants in the control of post-prandial glycemia. The extracts were prepared in way similar to their form of consumption. All extracts decreased starch digestion, but the purple tea extract was the strongest inhibitor, their inhibitory tendency started at the dose of 50 mg/kg and was already maximal with 250 mg/kg. Maltose tolerance was not significantly affected by the extracts. Glucose tolerance was not affected by purple tea, but black tea clearly diminished it; green tea presented the same tendency. Purple tea was also the strongest inhibitor of pancreatic α-amylase, followed by black tea. The green tea, oolong tea, and white tea extracts tended to stimulate the pancreatic α-amylase at low concentrations, a phenomenon that could be counterbalancing its inhibitory effect on starch digestion. Based on chemical analyses and molecular docking simulations it was concluded that for both purple and black tea extracts the most abundant active component, epigallocatechin gallate, seems also to be the main responsible for the inhibition of the pancreatic α-amylase and starch digestion. In the case of purple tea, the inhibitory activity is likely to be complemented by its content in deoxyhexoside-hexoside-containing polyphenolics, especially the kaempferol and myricetin derivatives. Polysaccharides are also contributing to some extent. Cyanidins, the compounds giving to purple tea its characteristic color, seem not to be the main responsible for its effects on starch digestion. It can be concluded that in terms of postprandial anti-hyperglycemic action purple tea presents the best perspectives among all the tea varieties tested in the present study.

Effects of a Myrciaria jaboticaba peel extract on starch and triglyceride absorption and the role of cyanidin-3-O-glucoside

The purpose of this study was to perform a parallel and comparative investigation of the effects of a Myrciaria jaboticaba (common name jabuticaba) peel extract and of its constituent cyanidin-3-O-glucoside on the overall process of starch and triglyceride intestinal absorption. The peel extract inhibited both the porcine pancreactic α-amylase and the pancreatic lipase but was 13.6 times more potent on the latter (IC₅₀ values of 1963 and 143.9 μg mL^-1, respectively). Cyanidin-3-O-glucoside did not contribute significantly to these inhibitions. The jabuticaba peel extract inhibited starch absorption in mice at doses that were compatible with its inhibitory action on the α-amylase. No inhibition of starch absorption was found with cyanidin-3-O-glucoside doses compatible with its content in the extract. The extract also inhibited triglyceride absorption, but at doses that were considerably smaller than those predicted by its strength in inhibiting the pancreatic lipase (ID₅₀ = 3.65 mg kg^-1). In this case, cyanidin-3-O-glucoside was also strongly inhibitory, with 72% inhibition at the dose of 2 mg kg^-1. When oleate + glycerol were given to mice, both the peel extract and cyanidin-3-O-glucoside strongly inhibited the appearance of triglycerides in the plasma. The main mechanism seems, thus, not to be the lipase inhibition but rather the inhibition of one or more steps (e.g., transport) in the events that lead to the transformation of free fatty acids in the intestinal tract into triglycerides. Due to the low active doses, the jabuticaba peel extract presents many favourable perspectives as an inhibitor of fat absorption and cyanidin-3-O-glucoside seems to play a decisive role.

Three flavanols delay starch digestion by inhibiting α-amylase and binding with starch

The study aimed to reveal the different mechanisms of delaying starch digestion by ECG, EGCG and Procyanidin based on the perspective of α-amylase-flavanol interaction and starch-flavanol interaction. The interaction characteristics of flavanols with α-amylase were studied from five aspects: enzyme inhibition, kinetics, fluorescence quenching, circular dichroism (CD) and computer simulation. The IC50 of flavanols (ECG, EGCG and Procyanidin) against α-amylase were 172.21 ± 0.22, 732.15 ± 0.13 and 504.45 ± 0.19 μg/mL according to the results of α-amylase inhibition experiment, respectively. ECG and Procyanidin showed mixed inhibition against α-amylase, while EGCG showed non-competition against α-amylase. However, thermodynamic parameters，computer-based docking and dynamic simulation proved that ECG and EGCG-α-amylase complexs were mainly driven by van der Waals and hydrogen bonds, while Procyanidin-α-amylase complexs was driven by hydrophobic interaction. In addition, it was indicated, by means of starch‑iodine complex spectroscopy, that flavanols inhibited the digestion of starch not only through bind with α-amylase but also through bind with starch. Thus, flavanols as a starch-based food additive have the potential to be employed as adjuvant therapy for diabetes.

Flavonoids as potential agents in the management of type 2 diabetes through the modulation of α-amylase and α-glucosidase activity: a review

Type 2 diabetes (T2D) is one of the most prevalent metabolic diseases worldwide and is characterized by increased postprandial hyperglycemia (PPHG). α-Amylase and α-glucosidase inhibitors have been shown to slow the release of glucose from starch and oligosaccharides, resulting in a delay of glucose absorption and a reduction in postprandial blood glucose levels. Since current α-glucosidase inhibitors used in the management of T2D, such as acarbose, have been associated to strong gastrointestinal side effects, the search for novel and safer drugs is considered a hot topic of research. Flavonoids are phenolic compounds widely distributed in the Plant Kingdom and important components of the human diet. These compounds have shown promising antidiabetic activities, including the inhibition of α-amylase and α-glucosidase. The aim of this review is to provide an overview on the scientific literature concerning the structure-activity relationship of flavonoids in inhibiting α-amylase and α-glucosidase, including their type of inhibition and experimental procedures applied. For this purpose, a total of 500 compounds is covered in this review. Available data may be considered of high value for the design and development of novel flavonoid derivatives with effective and potent inhibitory activity against those carbohydrate-hydrolyzing enzymes, to be possibly used as safer alternatives for the regulation of PPHG in T2D.

Inhibition of starch digestion by flavonoids: Role of flavonoid-amylase binding kinetics

In this study, kinetics of binding between α-amylase and green tea flavonoids were investigated by fluorescence quenching (FQ). Their effect on α-amylase inhibition was evaluated. Whereas epicatechin (EC) and epigallocatechin (EGC) exhibited slow binding kinetics (in the order of minutes), epicatechin gallate (ECG) and epigallocatechin gallate (ECGC) exhibited very rapid binding (in the order of seconds) with Human Salivary α-amylase (HSA) and Porcine Pancreatic α-amylase (PPA). EGCG reached maximum inhibition of HSA and PPA with short incubation time whereas maximum inhibition of HSA and PPA by EC was reached only after 45 to 60 min of incubation. Similar results with ECG and EGC, but not in line with FQ kinetics, highlighted possible interferences of starch-flavonoid interaction in the binding and inhibition process. These results suggest that incubation times of enzymes and flavonoids shall be evaluated prior to enzyme inhibition testing in order to ensure consistent and reliable results.