ABSTRACT
Objective:To investigate whether salidroside (SAL) improves lung tissue injury in rats with severe pneumonia (SP) through mediating toll-like receptor 4/nuclear transcription factor-κB/NOD-like receptor protein 3 (TLR4/NF-κB/NLRP3) signaling pathway.Methods:Seventy-five Wistar rats were used in this study. Fifteen of them were randomly selected as the sham operation group, and the others were induced by endotracheal infusion of Klebsiella pneumoniae ( Kp) suspension to construct a rat model of SP. After modeling, the rats were randomly divided into four groups with 15 rats in each group: model group, low-dose SAL group (30 mg/kg), high-dose SAL group (60 mg/kg) and dexamethasone (DXMS, 15 mg/kg) group. The sham operation group and the model group were given the same amount of normal saline for seven consecutive days. The wet-dry weight ratio (W/D) of lung tissues in each group was detected. HE and TUNEL staining methods were used to observe the morphology of lung tissues and cell apoptosis. The levels of TNF-α, IL-1β, IL-6, IL-18 and IL-10 in bronchoalveolar lavage fluid (BALF) were detected by ELISA. The expression of TLR4, myeloid differentiation factor (MyD88), NF-κBp65, phosphorylated NF-κBp65 (p-NF-κBp65) and NLRP3 at protein level in lung tissues was detected by Western blot. Results:The rat model of SP was successfully constructed by endotracheal infusion of Kp suspension. Compared with the sham operation group, the model group showed more severe edema of lung tissues, increased W/D value ( P<0.05), loose and incomplete alveolar structure, edema of alveolar wall and thickened alveolar wall, massive inflammatory cell infiltration, increased apoptosis rate as well as higher levels of TNF-α, IL-1β, IL-6 and IL-18 and lower lover of IL-10 in BALF. Moreover, the relative expression of TLR4, MyD88, NF-κBp65, p-NF-κBp65 and NLRP3 at protein level in lung tissues was increased in the model group ( P<0.05). Gradually improved pathological injury of lung tissues, decreased W/D value ( P<0.05), recovered alveolar structure, reduced alveolar wall edema and decreased cell apoptosis rate were observed in the low-dose and high-dose SAL groups as well as the DXMS group as compared with those of the model group. Besides, the three groups also showed decreased levels of TNF-α, IL-1β, IL-6 and IL-18 and increased level of IL-10 in BALF, and inhibited expression of TLR4, MyD88, NF-κBp65, p-NF-κBp65 and NLRP3 at protein level in lung tissues ( P<0.05). DXMS performed better in improving lung injury in rats with SP, followed by high and low doses of SAL ( P<0.05). Conclusions:SAL could reduce cell apoptosis and improve the Kp-induced lung injury in rats. The mechanism might be related to the blockage of TLR4/NF-κB/NLRP3 signaling pathway activation and inhibition of inflammatory factor expression.