Protective effect of senegenin on splenectomy-induced postoperative cognitive dysfunction in elderly rats

Postoperative cognitive dysfunction (POCD) is common in elderly patients. Senegenin, an active component of extracts from Polygala tenuifolia root, a traditional Chinese medicine, has neuroprotective and neuroregenerative effects. However, the mechanism underlying the effects of senegenin against postoperative cognitive impairment in elderly individuals has yet to be elucidated. The aim of this study was to investigate the protective effects of senegenin on the cognitive functions of elderly rats with splenectomy-induced POCD. Results from a Morris water maze test suggested that splenectomy induced a transient cognitive deficiency in the elderly rats; however, when the rats were treated with senegenin, the cognitive impairment was notably attenuated. Further experiments showed that senegenin significantly inhibited the mRNA and protein expression of several key pro-inflammatory cytokines, specifically, tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta), IL-6 and IL-8, in the hippocampal tissues of elderly rats following splenectomy. In order to investigate the molecular mechanism involved, the expression and activity of the Toll-like receptor 4 (TLR4) signaling pathway was assessed. On day 1 postoperatively, it was observed that senegenin markedly suppressed the mRNA and protein expression of TLR4, myeloid differentiation factor 88 (MyD88) and TIR domain-containing adaptor-inducing interferon-beta (TRIF). Furthermore, the phosphorylation levels of nuclear factor-kappa B (NF-kappa B) p65 and inhibitor of NF-kappa B (I kappa B alpha) were also decreased following senegenin treatment on the first day subsequent to surgery. These results suggest that senegenin suppressed splenectomy-induced transient cognitive impairment in elderly rats, possibly by downregulating two signaling pathways involved in inflammation, TLR4/MyD88/NF-kappa B and TLR4/TRIF/NF-kappa B, to further inhibit the expression of key pro-inflammatory cytokines, specifically, TNF-alpha, IL-1 beta, IL-6 and IL-8, and ultimately the neuroinflammation in the hippocampal tissues. In conclusion, the present study revealed that senegenin exhibited neuroprotective effects against splenectomy-induced transient cognitive impairment in elderly rats, which indicated that senegenin may be a promising agent for the treatment of POCD.