Regulatory effects of saponins from Panax japonicus on colonic epithelial tight junctions in aging rats

BACKGROUND: Saponins from Panax japonicus (SPJ) are the most abundant and main active components of P. japonicus, which replaces ginseng roots in treatment for many kinds of diseases in the minority ethnic group in China. Our previous studies have demonstrated that SPJ has the effects of anti-inflammation through the mitogen-activated protein kinase (MAPK) and nuclear factor kappa B (NF-κB) signaling pathways. The present study was designed to investigate whether SPJ can modulate intestinal tight junction barrier in aging rats and further to explore the potential mechanism. METHODS: Aging rats had been treated with different doses (10 mg/kg, 30 mg/kg, and 60 mg/kg) of SPJ for 6 mo since they were 18 mo old. After the rats were euthanized, the colonic samples were harvested. Levels of tight junctions (claudin-1 and occludin) were determined by immunohistochemical staining. Levels of proinflammatory cytokines (interleukin-1β and tumor necrosis factor-α) were examined by Western blot. NF-κB and phosphorylation of MAPK signaling pathways were also determined by Western blot. RESULTS: We found that SPJ increased the expression of the tight junction proteins claudin-1 and occludin in the colon of aging rats. Treatment with SPJ decreased the levels of interleukin-1β and tumor necrosis factor-α, reduced the phosphorylation of three MAPK isoforms, and inhibited the expression of NF-κB in the colon of aging rats. CONCLUSION: The studies demonstrated that SPJ modulates the damage of intestinal epithelial tight junction in aging rats, inhibits inflammation, and downregulates the phosphorylation of the MAPK and NF-κB signaling pathways.