Alpha-glucosidase inhibitory activity and fractionation of bioactive compounds from bark extracts of sibucao (Caesalpinia sappan L.) In the Philippines

Abstract

Diabetes is a chronic disease that affects millions of people around the world. Although conventional medicine is available, it is usually accompanied by serious side effects such as gastrointestinal problem. Thus, the search for alternative medicine from natural sources is of primary importance. Context: The study is concerned with Caesalpinia sappan L. found in the vicinity of Baybay City, Leyte Philippines. Furthermore, it deals with ethanolic and aqueous extracts of the bark only. It was conducted to determine the alpha-glucosidase inhibitory activity of C. sappan to provide evidence to support its efficacy as a folkloric medicinal plant. Aims: This work aimed to evaluate the alpha-glucosidase inhibitory activity of aqueous and ethanolic bark extracts of Sibucao (Caesalpinia sappan L.) and to partially fractionate its bioactive compounds. Settings and Design: Extracts were prepared in increasing concentration to get IC50 values. Samples were analysed in triplicate both for extracts and fractions collected from chromatography. Methods and Material: Caesalpinia sappan L. bark samples were collected from the vicinity of Visayas State University. Plant materials were dried, weighed and stored. Aqueous and ethanolic bark extracts were prepared using water and 20% ethanol. The total phenolic content of the extracts were determined and the α-glucosidase inhibitory activity of crude bark and aqueous extracts were measured using the method of Kim et al., 2011. Partial fractionation of bioactive compounds was done successively using gradient elution. The α-glucosidase inhibitory activity of fractions were then determined and Rf values of active compounds were measured using thin layer chromatography (TLC). Results: Results revealed that aqueous extract (2000 ppm) and ethanolic extract (2000 ppm) show high α-glucosidase inhibitory activity of 100% and 59% respectively. IC50 values of aqueous and ethanolic extract were found to be 300.52 ± 1.467 ppm and 1560.81 ± 2.582 ppm, respectively. TLC of fractions show 7 peaks for aqueous extract and 6 peaks for ethanolic extract in which compound with Rf value 0.70 had the highest inhibitory activity of 65%. Conclusions: Taken together, the high α-glucosidase inhibitory activity of aqueous extracts support the effectiveness of C. sappan L. bark decoctions. In addition, results from bioassay-guided fractionation can be used as an effective tool for further isolation and characterization of α-glucosidase inhibitors from Caesalpinia sappan L. in the Philippines.