Bioactivity Guided Fractionation and Purification of Anti-Depressant Molecule from Ashwagandha (Withania somnifera)

Abstract

Background: Ashwagandha (Withania somnifera) is an important herb in the Indian traditional system of medicine for neurological disorders. However, the efforts for isolation and characterisation of a molecule with anti-depressant activity and development as a potent dosage form are limited. Objective: The objective of the present study was to characterize the Ashwagandha extract for its antidepressant fraction or constituent and to improve biological benefits at low doses. Methods: Aqueous methanol extract of Ashwagandha was prepared and fractionated into withanolides and flavonoids rich fractions. Withanolide rich fraction was subjected to phytochemical analysis to identify the active molecule/s. The compound was purified by using a semi-preparative HPLC system; identified using various spectroscopic techniques and anti-depressant activity was evaluated in rats. Enteric coating was performed on the extract and fractions after granulation and anti-depressant activity of coated samples were evaluated in rats. Results: Aqueous methanol extract of Ashwagandha and withanolide rich fraction showed prominent dose-dependent anti-depressant activity in forced swim test in rats. Phytochemical analysis of active fraction resulted in the isolation and characterization of a major withanolide glycoside present, namely withanoside X. Enteric coated aqueous methanol extract, withanolide rich fraction and withanoside X showed significant antidepressant activity at low doses as compared to the uncoated forms. Conclusion: The active fraction/isolated compound is sensitive to low pH of the stomach, thus enteric coating might be beneficial to protect the actives in the stomach, facilitating the sustainable release into the intestine and in turn reduce the dosage.