Citric Acid-Enriched Extract of Ripe (Siebold) Siebold & Zucc. Induces Laxative Effects by Regulating the Expression of Aquaporin 3 and Prostaglandin E in Rats with Loperamide-Induced Constipation.

Previously, we demonstrated that extracts of the ripe fruit (rPM) and unripe fruit (uPM) of (Siebold) Siebold & Zucc. and citric acid have a laxative effect, which is at least partially mediated by the increase in fecal parameters as seen in the low-fiber diet-induced constipation model rats. This study aims at investigating the laxative effects of citric acid-enriched aqueous extracts of rPM, uPM, and its active compounds, such as citric acid and malic acid, on loperamide-induced constipation rat models. Animal studies were conducted with loperamide-induced constipation animal models. The results showed that rPM and citric acid, the major organic acid compounds, significantly improved stool parameters (number, weight, and water content of the stools) generated in loperamide-induced constipation rats, without adverse effects of diarrhea. The gastrointestinal (GI) motility was activated fully in the rPM- and citric acid-treated rats than in rats treaded with loperamide alone. In addition, when rPM and citric acid were added to RAW264.7 cells and used to treat loperamide-induced constipation model rats, the secretion of prostaglandin E (PGE) increased significantly in cells and tissue. Furthermore, rPM and citric acid decreased the expression of the aquaporin 3 (AQP3) in the rat colons. Our results demonstrated that rPM and citric acid, the major organic acid compound in rPM, can effectively promote defecation frequency and regulate PGE secretion and AQP3 expression in the colon, providing scientific evidence to support the use of rPM as a therapeutic application.