Differential effect of polysaccharide and nonpolysaccharide components in Sijunzi decoction on spleen deficiency syndrome and their mechanisms

Sijunzi decoction (SJZD), reported in "Tai Ping Hui Min He Ji Ju Fang" of the Song dynasty, is the basic prescription for the treatment of spleen deficiency syndrome (SDS) in traditional Chinese medicine (TCM). It is composed of Ginseng Radix et Rhizoma, Atractylodisa Macricephalae Rhizoma, Poria and Glycyrrhizae Radix et Rhizoma Praeparata Cum Melle.This study sought to explore the effects of different components in SJZD (including nonpolysaccharide NPS and active polysaccharide S-3) on SDS rats and their underlying mechanisms.First, SDS model rats were established by reserpine injection and then treated with SJZD, NPS and S-3. To clarify their effect on GI motility and immune function, the gastrointestinal (GI) hormone levels in rat serum and their related receptor expressions in rat intestine were detected by enzyme-linked immunosorbent assay (ELISA) and western blot, and the intestinal T lymphocyte expression were quantified by flow cytometry. The levels of SCFAs in feces and serum were measured by gas chromatography-mass spectrometry (GC-MS), and the gut microbiota composition was determined by 16S RNA sequencing. Furthermore, pseudo-germ-free (pGF) and gut microbiota dysbiosis (GMD) model rats were established to verify the key role of the gut microbiota in the treatment of SDS with SJZD, NPS and S-3.SJZD has a stronger therapeutic effect on intestinal immune and GI hormone secretion in SDS rats, while the efficacy of NPS and S-3 showed slight differences. NPS mainly regulated the secretion of GI hormones in SDS rats and directly improved intestinal immunity by increasing the expression of T lymphocyte cells, while S-3 mainly enhanced intestinal immune function by increasing the expression of T lymphocyte cells and repairing the intestinal barrier in both direct and indirect ways. Additionally, experiments in pGF and GMD rats have proven that the immune-enhancing effects of SJZD, NPS, and S-3 on SDS rats and the regulation of GI hormones of S-3 are related to modulation of the gut microbiota composition, while the regulation of GI hormones by SJZD and NPS is not completely dependent on this modulation. In particular, Lactobacillus, SMB53, Blautia, Dorea, Collinsella and Adlercreutzia were significantly modulated by SJZD, and 3 genera (including Lactobacillus, Dorea and SMB53) were also remarkably regulated by NPS. S-3 significantly increased the abundance of Butyricimonas and Collinsella, which were different from altered genera in the SJZD group.This study uncovered that NPS and S-3 are inseparable effective substances for SJZD in the treatment of SDS rats, in which NPS mainly improves intestinal motility dysfunction and S-3 mainly enhances intestinal immunity. The mediation effect of the gut microbiota is extremely important, but the regulating effect of NPS on gastrointestinal hormones has nothing to do with the gut microbiota.