Alpha amylase inhibition and antioxidant activities of bicyclic diterpenoid lactones from Andrographis paniculata

Abstract

Andrographis paniculata is an important medicinal plant reported for its efficacy in the treatment and management of various medical conditions in different parts of the world. This study evaluates the α-amylase inhibitory and antioxidant activities of the crude extracts, solvent fractions and isolated compounds from aerial parts of A. paniculata. Chromatographic fractionation of the aqueous methanol fraction led to isolation of 14-deoxyandrographolide (1) and andrographolide (2). The isolated compounds were characterized by set of spectroscopic techniques such as nuclear magnetic resonance (NMR), infrared (IR) spectroscopy, mass spectrometry (MS) and their structures were confirmed by x-ray crystallography and by comparison of data with literature. The extract, fractions and isolated compounds were evaluated for anti-diabetic and antioxidant activities. Aqueous methanol fraction displayed the highest amount of total phenolic (TPC) and flavonoid content (TFC) of 9.42 ± 0.95 mg gallic acid equivalent/g (mg GAE/g) and 40.08 ± 17.93 mg quercetin equivalent/g (mg QUE/g) respectively amongst the extract and fractions. The aqueous methanol fraction, crude methanol extract and nhexane fraction exhibited better α-amylase inhibitory activity with an inhibitory concentration (IC50) of 0.057 ± 0.012, 0.0610 ± 0.035 and 0.080 ± 0.021 mg/mL respectively than acarbose, a standard reference drug with an IC50 value of 0.127 ± 0.013 mg/mL. Compound 1 and 2 exhibited a lower inhibitory activity with an (IC50) values of 0.637 ± 0.003 and 0.761 ± 0.013 mg/mL respectively. The results of these study on A. paniculata may justify its traditional use in the management of diabetes mellitus.