Effects of simvastatin nanoparticles on septic-associated acute lung injury in mice by regulating inducible nitric oxide synthase / endothelial nitric oxide synthase system

Abstract

Objective To investigate effects of simvastatin nanoparticles on the balance of inducible nitric oxide synthase (iNOS)/endothelial nitric oxide synthase (eNOS) and the prognosis of septic mice with acute lung injury. Methods A total of 90 C57 / BL6 mice were divided into the sham operation group, sepsis group, gavage group, intravenous preparation group and nanoparticle group, with 18 mice in each group. The sepsis mouse model was established by cecal ligation and puncture (CLP). Mice in the gavage group received CLP operation after oral administration of simvastatin, and mice in intravenous preparation and nanoparticle groups were immediately injected preconfigured simvastatin intravenous preparations and simvastatin nanoparticles via tail vein respectively after CLP operation. Twelve mice in each group were used for 7-day survival assessment and the other 6 were collected specimen at 24 h time point. The survival of mice was observed every 24 hours, and the daily survival of each group was counted. In the meantime, the pathological changes were observed by hematoxylineosin (HE) staining, the pathological score of lung injury was calculated, and the expressions of iNOS and eNOS in lung tissues of 5 groups were detected by the immunohistochemical method. Results The Kaplan-Meier survival curve showed that the survival of mice in 5 groups on 7 days was significantly different (χ2 = 3.780, P < 0.001). Further comparison showed that the survival rate was significantly lower in sepsis and gavage groups than in the sham operation group (both P < 0.001), while it was significantly better in the nanoparticle group than in sepsis group (P = 0.001). HE staining results showed that no obvious pathological signs were found in lung tissues of mice in the sham operation group. Diffuse neutrophil infiltration, small alveolar space, thickened interalveolar septum, diffuse pulmonary interstitial edema, disordered cell arrangement and damaged integrity of some lung tissues were found in the sepsis group. The pathological findings in the gavage group were similar to those in sepsis group. Mice in intravenous preparation and nanoparticle groups revealed less neutrophil exudation, better alveolar integrity and lighter degree of injury than those in the sepsis group. The pathological scores of lung injury and expressions of iNOS and eNOS in the 5 groups were significantly different (F = 889.200, 9.633, 6.918; all P < 0.05). Further comparison showed that there were significant differences at pathological scores of lung injury and expressions of iNOS and eNOS between sepsis and sham operation groups (all P < 0.05). Compared with the sepsis group, pathological scores of lung injury and expressions of iNOS and eNOS in intravenous preparation and nanoparticles groups were significantly different (all P < 0.05), and the pathological score of lung injury in nanoparticle group was significantly lower than that in intravenous preparation group (P < 0.05). Conclusions Different simvastatin formulations have different effects, among which nanoparticle preparation has the most protective value for septic-related lung injury. Establishing the balance between eNOS and iNOS can be an important treatment site with protective effects. Key words: Simvastatin nanoparticles; Sepsis; Inducible nitric oxide synthase; Endothelial nitric oxide synthase; Mice