Evaluation of the in vitro release of isoflavones from soybean germ associated with kefir culture in the gastrointestinal tract and anxiolytic and antidepressant actions in zebrafish (Danio rerio)

Abstract

Abstract The gastrointestinal tract contains thousands of microorganisms present in the mucosa, derived from several different species, and these microorganisms have a direct relationship with immunity, homeostasis, and certain systemic diseases. The microorganisms present in kefir grains interact with the gastrointestinal and immune systems as well as with the intestinal microbiota. Isoflavones are the most commonly consumed phytoestrogens, with aglycone and glycoside forms. Therefore, in this study, the content of aglycone isoflavones released from kefir associated with soybean germ (KSG) was evaluated in a gastrointestinal digestion model in vitro, and the anxiolytic and antidepressant activity of KSG and the fermentation solution of kefir (FSK) were evaluated in models of anxiety and depression in zebrafish (Danio rerio). KSG was prepared as the 4-day fermentation product of 40 g/L brown sugar, 10 g/L soy germ, and 60 g/L kefir. Isoflavone content was evaluated during the gastric, intestinal, and colon phases in simulated gastrointestinal digestion and analyzed by high-performance liquid chromatography. KSG was administered orally to zebrafish for 30 days, at 200 mg/kg (group G1) and 400 mg/kg (G2), while G3 received 2 μL SFK. The scototaxis test (light–dark) was performed to assess anxiolytic activity, using caffeine (100 mg/kg) as an anxiolytic, buspirone (25 mg/kg) as a positive control, and distilled water as a negative control. To assess antidepressant activity, a new tank dive test was performed, using 1% ethanol as a depressant, fluoxetine (20 mg/kg) as a positive control, and distilled water as a negative control. An increase in the release of isoflavones in the gastric phase and a decrease in the intestinal and colon phases was demonstrated with KSG. Moreover, the behavioral patterns observed in the different experiments demonstrated that KSG and FSK produce anxiolytic and antidepressant effects.