Castanopsis is considered one of the largest genera in the family Fagaceae, and 24 species can be discovered in Indonesia. Regardless of the fact that there has been extensive research to demonstrate the anti-diabetic properties of different species of Castanopsis, out of all the Castanopsis species that are indigenous to Indonesia, Castanopsis argentea (Blume) A.DC. has not yet been thoroughly investigated in this field. 

One therapeutic approach to treat diabetes is to retard the absorption of glucose via the inhibition of enzymes, such as α-glucosidase, in the digestive organs. It is present in the small intestine and is responsible for decomposing disaccharides into monosaccharides. As the activeness of α-glucosidase increases, the chance of diabetic complications being caused due to hyperglycemic condition increases. Accordingly, it is vital to suppress the α-glucosidase enzyme to slow down the increase in blood sugar after meals through an antidiabetic drug, one of which is α-glucosidase inhibitors.

Leaves Extraction Procedure

1. Ethanol Extraction of Castanopsis Argentea

For the ethanol extract, C. argentea leaves were first ground into a powder using a blender. Following that, 1.26 L of 70% ethanol solvent was added to 252 g of powder, and 24 hours were set aside in an area shielded from sunlight. It was filtered using filter paper after being let to stand and the filtrate and dregs are separated. The dregs were obtained, then 1.26 mL of 70 % ethanol was mixed again, and macerated for 24 hours. The dregs were added with ethanol twice in succession. To create a dry extract, the filtrate was concentrated using a rotary evaporator at a temperature of 39°C.

2. Ethyl Acetate Extraction of Castanopsis Argentea

After obtaining 5-10 kg of C. argentea leaves, the leaves were wet-sorted to separate them from the stalks and other contaminants. The leaves were then chopped into little pieces, rinsed under running water, and dried. It was stored in a dry environment, away from light and pests, after passing through the drying process.

First, a blender was used to grind C. argentea into powder. 1.3 L of ethyl acetate was then mixed with 260g of the powder and let to stand for one day in a dark area away from direct sunlight. It was filtered with filter paper after being allowed to stand to separate the filtrate from the dregs. The collected dregs were combined with ethyl acetate and left to stand for a further 1 to 24 hours. The dregs were added with ethyl acetate again twice in a row until the filtrate obtained was concentrated with a rotary evaporator and water bath and then dried in an oven to obtain a dry extract.

a-glucosidase Inhibition Assay

This assay was done in several concentrations to triplicate to get IC50 value. The term IC50 stands for inhibitory concentrations, which quantifies the concentration of a certain drug required to be 50% inactive in the biological component in vitro. In this investigation, the IC50 method was utilized to see the relationship between α-glucosidase and certain inhibitors, including acarbose (sample) and the ethanol and ethyl acetate extracts.

Result

C. argentea has antidiabetic potential, both 70% ethanol extract and ethyl acetate extract. It is feasible to demonstrate that the ethyl acetate extract was more potent than the ethanol extract by comparing the obtained IC50 values. Even so, ethanol and ethyl acetate had higher IC50 values than the sample acarbose, suggesting that acarbose is the better α-glucosidase inhibitor. As a result, further research can be carried out by fractionating or isolating the active compound C. argentea to obtain better IC50 results.