Study on the inhibitory effects of different polarity extracts of acorns on α – amylase and α – glucosidase
Type 2 diabetes (T2DM) is a chronic metabolic disease characterized by postprandial hyperglycemia. Its carbohydrate, protein and lipid metabolism are abnormal, leading to uncontrolled blood sugar levels. Clinical studies have found that alpha amylase and alpha glucosidase inhibitors can inhibit postprandial glucose peak, delay carbohydrate digestion, and reduce glucose level absorption. Alpha amylase inhibitors can act as carbohydrate blockers, limiting the digestion rate of the gastrointestinal diet and reducing carbohydrate intake and absorption. Alpha glucosidase inhibitors mainly reduce the degradation of polysaccharides and delay the absorption of carbohydrates in the intestine by reversibly occupying the binding sites between enzymes and substrates, ultimately achieving hypoglycemic effects. Therefore, alpha amylase and alpha glucosidase inhibitors are considered effective means of preventive treatment for hyperglycemia. However, currently clinical synthesis of alpha amylase and alpha glucosidase inhibitors is limited to acarbose, miglitol, and voglibose. Although these inhibitors can delay glucose absorption, they are usually accompanied by certain side effects during prevention and treatment, such as bloating, diarrhea, abdominal pain, etc. Seeking inhibitors with higher efficacy and fewer side effects has become a current research hotspot. Natural enzyme inhibitors from plants have attracted significant attention due to their low side effects and high activity functions.
Acorn is the fruit of Quercus acutissima and Quercus acutissima, widely distributed in Liaoning, Hebei, Shaanxi and other regions of China. It has attracted widespread attention due to its high content of tannins. With the deepening of research, it is found that acorn contains a variety of bioactive substances, such as protein, cellulose, flavonoids, polyphenols, etc., which have strong antioxidant, anti-inflammatory, bacteriostatic, anti-tumor and anti-aging effects, and can reduce the risk of cardiovascular disease, diabetes and microbial infection. This article uses wild acorns of Quercus acutissima as materials to study the inhibitory effects of different polar extracts on the activities of α – amylase and α – glucosidase. The active components are tracked by Folin phenol method, HPLC method, and molecular docking technology to infer the main active ingredients in the acorn active components, in order to lay a foundation for the study of acorn hypoglycemic function.

 

At present, research on the pharmacological activities of plant extracts mainly focuses on antibacterial, antioxidant, and anti-tumor aspects. Ayele et al. collected roots of croton plants from six different locations and found that their extracts have strong antioxidant activity. Their inhibitory effects on Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae are equivalent to positive antibiotics. Nakamura et al. used HPLC to identify methyl gallate, pentagalloyl glucose, and paeoniflorin in peony leaves, and found that they all have the ability to inhibit the proliferation, apoptosis, and cell cycle of oral squamous cancer cells, indicating that peony leaf extract has potential anti-tumor effects. In addition, plant extracts also have functions such as lowering blood sugar and lipids. Oak trees were first studied in Europe, and French acorn extract has been patented as a special medicine circulating in the market. But oak trees in our country rarely receive people’s attention. Previous studies have found that extracts from acorns in China have antibacterial, antioxidant, and anti-tumor activities, but there is limited research on their hypoglycemic effects, and the study of hypoglycemic mechanisms and components is not sufficiently in-depth. This study found that extracts of acorns with different polarities have inhibitory effects on alpha amylase and alpha glucosidase, and the inhibitory effect of ethyl acetate phase is much higher than that of the positive control acarbose group. Its IC50 values for alpha amylase and alpha glucosidase are 1.590 ± 0.073mg/g and 3.927 ± 0.019 (× 10-3mg/g), respectively. In addition, the total phenolic content obtained from the crude extract, ethyl acetate phase, petroleum ether phase, and residual water phase of acorns were 402.13 ± 11.79, 753.23 ± 32.18, 121.62 ± 3.20, and 252.44 ± 4.00mg/g, respectively, indicating that the enzyme inhibition rate of the ethyl acetate phase of acorns is proportional to the polyphenol content. This is consistent with the research findings of Pan et al.

On the basis of confirming that the polyphenol content in the ethyl acetate phase of acorns is the highest and its inhibitory effect on α – amylase and α – glucosidase is the best, this experiment further detected polyphenolic monomers in the ethyl acetate phase of acorns. HPLC analysis showed that the content of six polyphenolic compounds measured in the ethyl acetate phase was higher than other polar components, and the tannic acid content in the ethyl acetate phase was 500.75 ± 6.93mg/g, which was 10-50 times higher than other components, indicating that ethyl acetate has a good enrichment effect on tannic acid. The main active component in the ethyl acetate phase of acorns is still polyphenolic substances, suggesting that its enzyme activity inhibition is related to tannic acid. This is consistent with the research results of Ding et al. Finally, this experiment was the first to use molecular docking virtual screening and found that only tannic acid had good binding activity with alpha amylase and alpha glucosidase, further verifying that tannic acid has a strong inhibitory effect on alpha amylase and alpha glucosidase.

Tannic acid is a bioactive polyphenolic compound that exists in various plant groups. Structurally, tannic acid is a lactone of hexahydroxybenzoic acid and is considered a derivative of dimeric gallic acid. Mainly produced through hydrolysis of tannic acid, which is a widely distributed plant secondary metabolite. Tannic acid has attracted widespread attention due to its biological activities such as antioxidant, anti-inflammatory, antibacterial, anti-tumor, hypoglycemic, and lipid-lowering properties. At present, research has shown that tannic acid can be absorbed in the small intestine, and unabsorbed molecules are metabolized by large intestine microorganisms to form urolithin. Urolithin can be absorbed into the bloodstream and participate in systemic circulation, ultimately excreted with urine, or undergo biotransformation in intestinal and liver cells to form urolithin metabolites. Therefore, tannic acid has important research significance and development prospects in the field of medicine. In terms of lowering blood sugar, plant extracts have advantages over synthetic hypoglycemic drugs, such as high activity, low cost, fewer side effects, and energy conservation and environmental protection. As found in this study, the inhibitory effect of ethyl acetate on alpha amylase and alpha glucosidase is much greater than that of acarbose, which is consistent with the research of Alqahtani et al. But there are also people who hold the opposite view, such as Hbika, who have shown that the ethyl acetate extract of wormwood has no inhibitory activity on intestinal alpha glucosidase in rats. This may be related to the synergistic effects between different plant species and extracted components. There are unknown interactions between different active substances, which requires us to constantly study and explore. At present, reducing the side effects of synthetic drugs on the body without affecting the therapeutic effect is a challenge in treating various chronic diseases. Exploring alternative or co acting substances with acarbose is a new direction in the research of hypoglycemic drugs. Therefore, this study is expected to lay the foundation for finding alternatives or co crops for synthetic drugs.

In summary, the ethyl acetate extract phase of acorns has potential hypoglycemic effects. Its tannic acid content is abundant. As tannic acid content can indirectly quantify the presence of tannic tannins in plant-based foods, this study suggests that acorn materials can be the main source of tannic tannins. Additionally, it is speculated that its hypoglycemic effect is influenced by the content of tannic acid, which has the potential to serve as a substitute or co crop for acarbose.