Characterization of antioxidant fractions in curry leaf (Murraya koenigii L.) and molecular docking of selected bioactive compounds

Abstract

Curry leaf (Murraya koenigii L.) belonging to the family Rutaceae is one of the extensively used spices in traditional Indian medicine against variety of ailments. Curry leaf is reported to possess several pharmaceutical properties such as antioxidant, anticancerous, antidiabetic, anti-inflammatory, antidiarrheal, analgesic and hepatoprotective. The therapeutic potential of curry leaf is due to several chemical constituents such as carbazole alkaloids, phenols, flavonols, tannins, terpenes, and lipids. The overproduction of reactive oxygen species (ROS) serve as the initiation point for many diseases like cancer, diabetes, arthritis and Alzheimer’s. The ROS can be scavenged by antioxidants but side effects have been reported for synthetic antioxidants like butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT). Hence, natural antioxidants are gaining scientific attention now-a-days. Though, the pharmacological potential of curry leaf is well understood, very few reports are available on the role of bioactive phytocompounds for curing diseases by interacting with target proteins. The study entitled “Characterization of antioxidant fractions in curry leaf (Murraya koenigii L.) and molecular docking of selected bioactive compounds” was undertaken with the objective to characterize antioxidant fractions in curry leaf through in vitro assays and to identify the most potent bioactive compound through LC-MS/MS and molecular docking analyses. Oleoresin was extracted from curry leaf (var. Suvasini) and further subjected to in vitro antioxidant assay. Antioxidant fractions from curry leaf were separated by silica gel column chromatography using hexane: ethyl acetate solvent system in various proportions (100:0, 80:20, 60:40, 40:60, 20:80 and 0:100) and further subjected to antioxidant assay. Sub-fractionation of the fraction exhibiting the highest antioxidant activity was done at five minutes interval and sub-fractions were also subjected to antioxidant assay. Sub-fractions exhibiting maximum antioxidant activity were analyzed by LC-MS/MS. Compounds identified through LC-MS/MS analysis were docked against eight target proteins for cancer, seven for diabetes, four for arthritis and four for Alzheimer’s. Mature leaves of curry leaf recorded higher oleoresin recovery of 9.16 per cent and possessed high antioxidant activity with a DPPH inhibition of 85.19 per cent. Fraction eluted with hexane: ethyl acetate (60:40) recorded the highest yield of extract (707.4 mg) and showed the highest antioxidant activity with 88.68 per cent inhibition of

DPPH. Sub-fractionation of the fraction with the highest antioxidant activity has yielded 47 sub-fractions. Of the sub-fractions, 28th fraction showed the highest DPPH inhibition (91.51%) followed by 26th (91.08%), 34th (91.08), 38th (89.53%) and 40th (89.53%). The DPPH inhibition potential of sub-fractions 28th, 26th and 34th was similar to synthetic antioxidant BHA (91.89%). The LC-MS/MS analysis of these fractions revealed presence of 52 compounds in whole fraction (hexane: ethyl acetate 60:40), 62 in 26th sub-fraction, 51 in 28th and 34th sub-fraction, 49 in 38th sub-fraction and 45 in 40th sub-fraction. Seven compounds of curry leaf viz. alpha-aminodiphenylacetic acid, doxylamine, flucoxetine, histidinol, pheniramine, prometon and valylmethionine were found to interact with different targets for cancer. Maximum number of curry leaf phytocompounds interacted with targets for breast cancer, 17β hydroxysteroid dehydrogenase (17β HSD) and Polo-like kinase 1 (PLK1). valylmethionine inhibited 17β HSD and PLK1 with good binding energy of -66.7903 and -122.5233 kcal/mol respectively. Eight phytocompounds of curry leaf viz. alpha-aminodiphenylacetic acid, DL-2- aminooctanoic acid, doxylamine, flucoxetine, histidinol, pheniramine, prometon and valylmethionine interacted with seven different targets for diabetes. Maximum number of compounds interacted with the target fructose 1,6-bisphosphatase and valylmethionine inhibited the target with good docking score with a binding energy of -81.143 kcal/mol. Six compounds of curry leaf viz. alpha-aminodiphenylacetic acid, flucoxetine, norpropoxyphene, histidinol, pheniramine and valylmethionine interacted with four different targets of arthritis studied. Maximum number of compounds interacted with the target Nitric oxide synthase and it was inhibited by histidinol with good binding energy - 109.5131 kcal/mol. Five phytocompounds viz. alpha-aminodiphenylacetic acid, flucoxetine, norpropoxyphene, histidinol and valylmethionine interacted with four different targets for Alzheimer’s. Maximum number of compounds interacted with targets human beta- secretase 1, tau protein kinase and human butyrylcholinesterase. Good docking score was recorded for interaction of human beta-secretase 1 with histidinol. The study could bring about the potential of curry leaf as a natural antioxidant and could identify three safe phytocompounds viz. alpha-aminodiphenylacetic acid, DL-2- aminooctanoic acid and valylmethionine which could interact with targets for cancer, diabetes, arthritis and Alzheimer’s.