Genistein stimulates duodenal HCO3− secretion through PI3K pathway in mice

Genistein has been proposed as a promising pharmacotherapeutic for cystic fibrosis. We recently found that genistein stimulates murine duodenal HCO3− secretion through cystic fibrosis transmembrane conductance regulator (CFTR). The aim of the present study was to determine the intracellular signal pathways involved in genistein-stimulated duodenal HCO3− secretion. Murine duodenal mucosal HCO3− secretion was examined in vitro in Ussing chambers by the pH-stat technique. The results showed that neither cAMP-dependent signal pathway inhibitors MDL-12330A and KT-5720, nor cGMP signal pathway inhibitors NS2028 and KT5823, nor calcium signal pathway inhibitors verapamil and W-13, altered genistein-stimulated duodenal HCO3− secretion. In calcium-free solution, genistein-stimulated duodenal HCO3− secretion was not altered either. Vanadate, an inhibitor of protein tyrosine phosphatase, only partially inhibited genistein-stimulated duodenal HCO3− secretion. However, both wortmannin and LY294002, two structurally and mechanistically distinct phosphatidylinositol 3-kinase (PI3K) inhibitors, markedly inhibited genistein-stimulated duodenal HCO3− secretion. Genistein increased duodenal mucosal PI3K activity and induced the phosphorylation of Akt, a signaling molecule downstream of PI3K, which was again inhibited by wortmannin. Estrogen receptor antagonist, ICI182,780, also markedly inhibited genistein-stimulated duodenal HCO3− secretion and genistein-induced PI3K activity increase in duodenal mucosa. These results demonstrate that genistein stimulates duodenal HCO3− secretion mainly through estrogen receptor and PI3K-dependent pathway. These findings contribute to the understanding of the molecular mechanism of genistein-induced anion secretion and further pharmacotherapeutic development and use of genistein or related substances in the treatment of diseases of epithelial tissues.