Assessment of pharmacological activities of specialized metabolites of Withania somnifera (L.)

Abstract

Withania somnifera is a revered herb in the Indian medicinal system due to the presence of pharmacologically bioactive compounds. The roots and leaves of Ashwagandha contain various phytochemicals like phenols, flavonoids, quinones, steroids, etc. These phytochemicals are distributed among various tissues of this plant in varying concentrations. Since location and environmental factors (biotic and abiotic) play a key role in the biosynthesis of bioactive metabolites, the agro-climatic conditions are conducive to introducing and domesticating new exotic plant varieties with enhanced phytochemicals and withanolide contents. The present study focuses on the assessment of these bioactive compounds in different commercially available varieties for the cultivation of elite germplasm from the perspective of hill agriculture and sustainable development.In the study, total phenols were found to be highest in Jawahar-20 root, i.e., 82.714 mg/g (DW), followed by Poshita root, i.e., 64.02 mg/g (DW), while the least was found in Pratap leaf, i.e., 2.33 mg/g (DW). The concentration of total flavonoids varied significantly (p ≤ 0.05) from 1.98 ± 0.0.01 to 80.735 ± 4.33 mg QE/g (DW). Total flavonoids were found to be highest in Jawahar-20 root, i.e., 80.735 mg/g (DW), followed by Poshita leaf, i.e., 60.02 mg/g (DW), and least in Nimithli stem, i.e., 1.98 mg/g (DW). The total tannin content varied significantly (p ≤ 0.05) among the five varieties of Withania somnifera under the present study. The concentration of total tannin varied significantly (p ≤ 0.05) from 0.691 ± 0.51 to 36.09 ± 0.61 mg TAE/g (DW). Tannins were found to be highest in Jawahar-20 root, i.e., 36.09 mg/g (DW), followed by Poshita root, i.e., 29.287 mg/g (DW), while the least was found to be in Pratap seed, i.e., 0.682 mg/g (DW). Ortho-dihydroxy phenol was found to be highest in Jawahar-20 leaf, i.e., 40.081 mg/g (DW), followed by Jawahar-20 root, 19.31 mg/g (DW), and Poshita leaf, i.e., 19.02 mg/g (DW). Both recorded the same, and the least was found in Nimithli leaf, i.e., 0.95 mg/g (DW). Total antioxidant capacity was found to be highest in Jawahar-20 leaf, i.e., 16.70 mg/g (DW), followed by Jawahar-20 leaf, i.e., 11.51 mg/g (DW), and Poshita leaf, i.e., 11.31 mg/g (DW), both of which recorded the same almost least in Pratap leaf, i.e., 0.257 mg/g (DW). The DPPH activity was found to be highest in Poshita root, i.e., 92.39 at 1000 μg concentration, which was very near the ascorbic acid, i.e., 98.9 (a natural antioxidant), followed by Pratap leaf, i.e., 88.04, and least in Nimithli root, i.e., 58.36. The IC50 value of Pratap leaf was the least, i.e., 369.42, followed by Jawahar-20 stem, i.e., 370.32, and the highest IC50 value was found in Nimithli root, i.e., 877.22. The reducing power of five different varieties increased with increasing concentration. The varieties differed w.r.t. their total reducing power activity, i.e., the reducing power activity was highest in Poshita stem with an R2 value of 0.992, followed by Poshita root with an R2 value of 0.982, and least in Pratap seed with an R2 value of 0.565. Thus, Jawahar-20 and Poshita not only recorded higher phytochemicals but also withanolide A and withaferin A.