Introduction

Castanopsis Tungurrut is a plant harvested in Indonesia and Malaysia. The plant is often used for industrial needs, such as making furniture. As of now, there are no known medicinal properties of this plant yet. As a result, this study is to find potential antidiabetic activity of C. tungurrut (Blume) A. DC. leaf extract to inhibit alpha-glucosidase enzyme.

Diabetes has been a prevalent global health issue for centuries now, with about 422 million people globally suffering from it, and is typically characterized by the elevated blood glucose or sugar levels, in other words, hyperglycaemia. For people that are healthy, their pancreas, an organ located behind the liver and stomach, secretes digestive enzymes and the hormones insulin and glucagon into the bloodstream to control the amount of glucose in the body.

Regulation of blood glucose levels can be achieved indirectly through adjustments of the absorption of glucose in the blood. The function of α-glucosidase in the body is to catalyse the hydrolysis of starch to simple sugars. They essentially produce glucose for intestinal absorption, which would in turn increase the blood glucose levels. α-glucosidase inhibitors (AGIs) are widely seen in the treatments for type 2 diabetes. α-glucosidase is an enzyme that catalyses hydrolysis of starch into simpler sugars. They aid in the digestion of dietary carbohydrates and starches to synthesize glucose used for intestinal absorption, which would cause an increase in the blood glucose levels. Concluding to this, if the enzyme is being inhibited, the blood glucose levels would in theory decrease. Acarbose is an example of α-glucosidase that is used as an antidiabetic drug, which is used as a positive control in this investigation. The reason why acarbose is being used as a standard is due to the fact that it is presently a known drug for diabetes on the market. It is a complex oligosaccharide that acts as a competitive and reversible inhibitor of α-glucosidase. Its mechanism is to delay the digestion of carbohydrates, slowing down any absorption of glucose which results in a decrease of the blood glucose concentration. Thus, it has been approved for treating adults with type 2 diabetes mellitus.

Analysis

This assay was done according to Dewi et. al. with some modifications. The first step was to add 10μL of the Castanopsis Tunggurut sample into the microplate wells. 0.1M of phosphate buffer (pH 7.0) with a volume of 36μL is then added to the samples, and for each hole that the sample is not present, it would be replaced with buffer instead. Later, 17 μL of 5 mM P-nitrophenyl-α-D-glucopyranoside (PNPG) solution was mixed with 36 μL of 0.1M phosphate buffer (pH 7.0) The solution was mixed homogeneously and was incubated for 5 minutes at 37oC. After that, 17 μL α-glucosidase (0.062 unit) was added and the solution was incubated for 15 minutes at 37 oC. To stop the reaction, 1mL of 0.2 M Na2CO3 was added. The absorbance was measured using a UV spectrophotometer (Thermo Fischer Scientific Varioskan Flash) at λ = 400 nm. PNPG and phosphate buffer were used as control and quercetin as positive control. The blank was DMSO.

From the result, it can be concluded that the IC50 of acarbose is far lower than the IC50 of the Castanopsis Tunggurut sample in both ethanol and ethyl acetate. A lower IC50 would mean that it is a better inhibitor, and it is observed that acarbose has the lowest value, given that it is already a well-known α-glucosidase inhibitor. However, when comparing the two IC50 values of the sample in ethanol and ethyl acetate, the value of ethanol is lower than that of ethyl acetate. This means that when the sample is being put in ethanol, it would have a better performance in inhibition of α-glucosidase.

Conclusion

In conclusion, the plant Castanopsis Tunggurut has the potential for antidiabetic properties, given that it is able to inhibit the absorption of α-glucosidase at a high IC50 value. This is the case for being diluted in both the ethanol extract and the ethyl acetate extract. However, based on the results calculated and obtained, it can be concluded that being diluted in ethanol allowed for a lower IC50 value, indicating that it is more potent. However, both these dilutions deviate far from the IC50 value of acarbose, given that it is an already known drug in the market being used to treat this disease, and an overall better α-glucosidase inhibitor. For further investigations in the future, the plant can be isolated through fractionation to purification. This would allow a better, lower IC50 value.