Stimulatory effect of a pectic polysaccharide from a medicinal herb, the roots of Bupleurum falcatum L., on G-CSF secretion from intestinal epithelial cells.

The inner surface of the intestinal tract possesses a large area of mucosal membranes, and the intestinal epithelial cells exist at the interface between an antigen-rich lumen and a lymphocyte-rich lamina propria. The crosstalk that occurs between these compartments serves to maintain intestinal homeostasis, and the cytokine network plays an important role in the crosstalk. In this study, the effect of a pectic polysaccharide, bupleuran 2IIc from Bupleurum falcatum L., on cytokine secretion of intestinal epithelial cells was investigated in vitro. When murine normal colonic epithelial cell line MCE301 cells were stimulated with bupleuran 2IIc, the contents of granulocyte colony-stimulating factor (G-CSF) in the conditioned medium were significantly increased in dose- and time-dependent manners. The enhanced G-CSF gene transcription in MCE301 cells by the stimulation of bupleuran 2IIc was observed by RT-PCR. The enhanced G-CSF secretion by bupleuran 2IIc was also observed in C3H/HeJ mice derived primary cultured colonic epithelial cells. Bupleuran 2IIc was digested with endo-(1-->4)-alpha-D-polygalacturonase, and the resulting bupleuran 2IIc/PG-1 ("ramified" region) showed potent G-CSF secretion enhancing activity. The activity of bupleuran 2IIc/PG-1 disappeared after the removal of arabinosyl residues from bupleuran 2IIc/PG-1 by endo-(1-->5)-alpha-L-arabinanase digestion. These results suggest that the "ramified" region (bupleuran 2IIc/PG-1) is the active site for the G-CSF secretion enhancing activity of bupleuran 2IIc, and the arabinan moiety of bupleuran 2IIc/PG-1 plays an important role in expression of the activity.