Phytochemical investigation of natural sweetener from stevia rebaudiana (Bartoni)
S. rebaudiana is an important plant because of the high concentration of steviol glycosides (SGs). Sugars and artificial sweeteners, which are used in general as well as in pharmaceutical field have shown multiple toxic effects. On the other hand SGs have shown sweetness profile many fold compared to sucrose along with many health benefits.The substitution of SGs as sweeteners seems to be a reasonable solution towards the safety issues. The antidiabetic activity of S. rebaudiana extract as well as SGs is well documented in literature. The association of diabetes with cancer is also well known factor. Taking in consideration the above mentioned factors we have investigated the anticancer potential of extracts of S. rebaudiana. Extracts was prepared using petrolieum ether, ethyl acetate, methanol, aqueous methanol and water. Three cell lines (A-549, H-460 and MCF-7) have been used to evaluate the anticancer potential using MTT assay. In case of A-549, MVE-5 showing IC50 value of 10 ?g/ml. Moreover, IC50 values of MVE-2 was also comparatively better and found to be less than 50 ?g/ml and MVE-4 had shown IC50 value of 90 ?g/ml. In case of H- 460 reasonably better IC50 have been observed for MVE-4 and MVE-5 which is 88 ?g/ml and 92 ?g/ml, respectively. In H-460 reasonably better IC50 have been observed for MVE-4 and MVE-5 which is 88 ?g/ml and 92 ?g/ml, respectively. But in case of MCF-7 breast cancer cell line MVE-1 and MVE-2 have shown IC50 value of 90 ?g/ml and 53 ?g/ml, respectively. Thus, various extracts have shown good antiproliferative activity and S. rebaudiana can be further investigated for its anticancer potential. Furthermore docking study on EGFR, v PI3K and mTOR receptor revealed that SGs have good binding affinity towards all the three mentioned receptors and can be suitably modified to explore its anticancer potential. Moreover unfavourable ADME profile can be overcome by structure modification. Thus on the basis of in-vitro and in-silico data we can conclude that S. rebaudiana extracts have promising anticancer potential. Further isolation of compounds have also been done successfully and total seven compounds have been isolated. Two compounds MVR-1 and MVR-5 have been successfully characterized and found to be quercetin and stevioside respectively which are already known compounds. Many reported SGs have shown poorer taste quality. Moreover taste quality of all SGs are different from one another. Thus docking studies were performed on SGs by constructing homology models of T1R2 and T1R3 subunits of human sweet taste receptors to explore the sweetness mechanism. Ramachandran plot, PROCHECK results and ERRAT overall quality factor indicated the acceptable quality of models. The binding pattern indicated that Asn 44, Ans 52, Ala 345, Pro 343, Ile 352, Gly 346, Gly 47, Ala 354, Ser 336, Thr 326 and Ser 329 are the main interacting amino acids residues of T1R2 and Arg 56, Glu105, Asp 215, Asp 216, Glu 148, Asp 258, Lys 255, Ser 104,Glu 217, Leu 51, Arg 52 of T1R3 respectively. Amino acids interact with SGs mainly by forming hydrogen bonds with hydroxyl group of glucose moieties. Maximum binding affinity has been obtained with SGs having total four glucose molecules attached with it and increase or decrease in glucose molecules reduced the binding afinityThere is significant variation in docked poses of all SGs. Taking in consideration the diverse binding patterns of various SGs as well as their structural features, we have proposed the mechanism of sweetness in the form of multiple point stimulation model. The present study will be helpful to know the proper mechanism of sweetness as well as binding patterns of SGs to sweet taste receptor. It will further helpful in understanding the difference in taste quality and will be used in improving the taste of SGs using semisynthetic approaches.