<i>In Vivo</i> Antidiarrhoeal Activity and Molecular Docking Studies of a Coumarin Isolated from the Root Extract of <i>Impatiens ethiopica</i> Grey-Wilson

Impatiens ethiopica Grey-Wilson has been traditionally used in the treatment of infectious diseases. This study aimed to evaluate the antidiarrhoeal potential of I. ethiopica root extract and its major constituent. The investigation employed in vivo models, including castor oil-induced diarrhoeal model, antienteropooling test, and charcoal meal test in mice. The 80% methanol extract of I. ethiopica significantly reduced the frequency of defecation, faecal weight, and diarrhoea onset at administered doses of 100, 200, and 400 mg/kg. The active root extract was sequentially separated into four fractions based on solubility using petroleum ether, chloroform, methanol, and water. Further fractionation of the methanol fraction via column chromatography yielded scopoletin (7-hydroxy-6- methoxycoumarin), confirmed through spectroscopic analysis. Scopoletin also exhibited significant antidiarrhoeal activity by reducing intestinal fluid accumulation and gastrointestinal (GI) motility at doses of 10, 20, and 40 mg/kg. Scopoletin is suggested to act on prostaglandin synthase (PGS, COX-2; PDB ID: 4COX), showing a promising docking score of −7.941 kcal/mol. It exhibits a strong binding affinity, forming hydrogen bonds with SER530 and engaging in - stacking interactions with TYR385 and TRP387 at specific COX-2 binding sites. These findings highlight that the antidiarrhoeal activity of I. ethiopica was attributed to the presence of scopoletin. Overall, these results uphold the traditional use of I. ethiopica roots in the treatment of diarrhoea and highlight the potential of scopoletin as antidiarrhoeal compound.