In vitro and in-silico Anti-diabetic Evaluation of the Combination of Annona squamosa Linn., Leaf Extract and Oleanolic Acid

Diabetes mellitus (DM) is a metabolic disorder caused by insufficient insulin production from pancreatic β-cells or insulin resistance; its prevalence rapidly increases worldwide. Increasing reports indicate that most plant bioactive agents exhibited alternative and safe effects in managing DM. The study aims to evaluate the in vitro antioxidant and anti-diabetic efficacy of the combination of Annona squamosa Linn. (AS) leaf extract and Oleanolic acid (OA) using in vitro and in-silico approaches. The leaf of AS was extracted by soxhlet extraction using n-hexane and methanol. The methanol extract of AS (MEAS) was subjected to GC-MS analysis. Quantification of total phenolic and flavonoid content and OA were carried out by HPLC and HPTLC analysis, respectively. In vitro antioxidant (DPPH, NO, and H2O2) and anti-diabetic (α-amylase and α-glucosidase) potentials of MEAS, OA, and a combination of MEAS and OA (MEAS + OA) were studied at different concentrations using ascorbic acid and acarbose as standard, respectively. An in-silico study determined their binding interactions with α-amylase (PDB ID-1B2Y) and α-glucosidase (PDB ID-3W37). We found that the combination of MEAS + OA exhibited the highest in vitro antioxidant and anti-diabetic activities compared to MEAS and OA. It concluded that OA has a significant role in potentiating the anti-diabetic effect of A. squamosa. GC-MS analysis of MEAS revealed three major bioactives like bicyclo[7.2.0]undec-4- ene, 4,11,11-trimethyl-8-methylene-,[1R-(1R*,4Z,9S*)]-, germacrene D and undecane. The highest amount of phenolic (tannic acid and gallic acid) (150 μg/ml) and flavonoid (rutin and quercetin) (40 μg/ml) compounds were found in MEAS. OA was quantified as 356.74 ng/ml in MEAS by HPTLC. The significant inhibitory effects of MEAS, OA, and (MEAS + OA) on free radicals and α-amylase and α-glucosidase were observed concentration-dependent. However, MEAS + OA exhibited a greater percentage of inhibition than MEAS and OA alone. The in-silico analysis revealed highest docking-score of OA (-9.8 & -8.8), Germacrene D (-7.5 & -6.5) and Bicyclo[ 7.2.0]undec-4-ene, 4,11,11-trimethyl-8-methylene-,[1R-(1R*,4Z,9S*)]-, (-7.0 & -6.4) against IB2Y and 3W37 proteins, respectively.