| ObjectiveAcute lung injury (ALI) is a critical clinical syndrome with high mortality. The pathological features mainly include inflammatory reaction and alveolar-capillary endothelial cell injury. The previous studies had indicated that ALI is a kind of inflammation, in which many inflammation mediators and cytokines play key roles in the pathological process. Although many clinic efforts were carried out for ALI, the therapy for ALI has not been improved. Recently, it was suggested that peroxisome proliferators activated receptors (PPARs) has the anti-inflammatory effect, so we propose that PPARs possibly is protective function to lung tissue in ALI. However, its mechanism of the potential anti-inflammatory properties of PPAR agonists on ALI has not been completely elucidated. Peroxisome proliferators activated receptors (PPARs) have three different subtypes: PPAR-α, PPAR-β/δ(also referred to as PPARδor NUC 1) and PPAR-γ. In this study, we detected the expressions of PPAR-αand PPAR-γin ALI lung induced by intravenous injection lipopolysaccharide, and observed the effects of PPAR-αagonist, PPAR-γagonist, antagon, agonist combining antagon, agonist combining agonist, respectively, on the expression of PPAR-αand PPAR-γin ALI rats lung during development of ALI. The study provided the strong evidence for the usage of PPAR-αand PPAR-γagonist in the treatment of ALI induced by lipopolysaccharide (LPS) in clinic.MethodsA rat model of ALI was established by intravenous injection of LPS at a dose of 5mg/kg. 216 male Wistar rats were randomly divided into nine goups: control group (normal saline with DMSO, ND group), LPS injured group (LPS with DMSO, LD group), wy14643 group (LW group), Troglitazone group (LT group), MK886 group (LM group), GW9662 group (LG group), wy14643+ MK886 group (LWM group), Troglitazone + GW9662 group (LTG group), wy14643+Troglitazone group (LWT group). Each group has four time spot: 1h, 2h, 4h, 8h; each time spot contained six Wistar rats. Method: ND group was injected with 2.5ml/kg normal saline after vein injection with 10% DMSO 3ml/kg for 30 min; LD group was injected with 5mg/kg LPS by vein after vein injection with 10%DMSO 3ml/kg for 30 min; The rest group was injected with 5mg/kg LPS after vein injection with MK886 3mg/kg (dissolved by 10%DMSO), Troglitazone 3mg/kg (dissolved by 10%DMSO), MK886 3mg/kg (dissolved by 10%DMSO), GW9662 1mg/kg (dissolved by 10%DMSO), respectively, for 30 min; For the LWM group, after the injection of wy14643 for 15 min, the MK886 was injected followed by infection of LPS after 30 min. For LTG group and LWT group, it was same as LWM group treatment. The rats were killed after the injection of LPS for 1h, 2h, 4h, 8h. The lung tissue was collected and the wet/dry weight ratio, lung histopathological change was observed, expression of PPAR-α, PPAR-γand TNF-αmRNA were detected. The immunohischemistry (IHC) was used to detect the protein expression of PPAR-αand PPAR-γin the lung tissues of all groups rats. ELISA was used to measure the concentration of TNF-αin the supernatants of lung and hematoplasma, respectively. Nuclear factor Kappa B (NF-κB) activation in lung homogenate of rats was measured by Western blotting (WB).Results1. In the control group, PPAR-αand PPAR-γwere expressed in the alveolar epithelial cells of lung tissues. The expression of PPAR-αand PPAR-γdeclined significantly in the lung tissues of injury rats by LPS than those in control group both at the mRNA and the protein level (P < 0.05).2. The expression of PPAR-αand PPAR-γin rat lung tissues at all time in group LW and group LT were significantly higher than those in group LD both at the mRNA and the protein level (P < 0.05), especially, at 2h and 4h group; The expression of PPAR-αand PPAR-γin rat lung tissues at all time in group LWM and group LTG were significantly decreased than control group (P < 0.05), but no significantly than group LD both at the mRNA and the protein level (P >0.05); Those at all time in group LM and group LG were much lower than group LWM and group LTG both at the mRNA and the protein level (P < 0.01).3. The expression of PPAR-αand PPAR-γin rat lung tissues at all time in group LWT were much higher than those in group LD both at the mRNA and the protein level (P< 0.05), However, there was no significant difference between group LW and group LWT (P> 0.05), So was between group LT and group LWT (P > 0.05).4. Wy14643 or Troglitazone inhibited remarkably the expression of TNF-αof ALI rat lung tissues at the mRNA level and of lung tissue and hematoplasma at the protein level than LD group (P <0.05); The expression of TNF-αin ALI rat lung tissues and hematoplasma in group LWM and group LTG both were decreased than control group (P <0.05), however, there was no significant difference than group LD (P>0.05). The expression of TNF-αin ALI rat lung tissues and hematoplasma in group LM and group LG enhance more remarkably than group LWM and group LTG (P <0.05).5. Compared with group LW and group LT, Wy14643 united with Troglitazone (group LWT) inhibited remarkably the expression of TNF-αin ALI rat lung tissues at the mRNA level and ALI rat hematoplasma at the protein level (P <0.05).6. LPS activated the NF-κB. The NF-κB activation of rats lung homogenate at all time in group LW and group LT decreased much more than those in group LD (P <0.05). The NF-κB activation of rats lung homogenate at all time in group LWM and group LTG has no significantly difference than those in group LD (P >0.05).7. Wy14643 united with Troglitazone (group LWT) could inhibit the activation of NF-κB in ALI lung tissues more than group LW and group LT (P <0.05).8. Wy14643 or Troglitazone increased PaO2, decreased W/D ratio and pathomorphological score of lung tissue, and inhibited the activity of MPO. However the function of antagon MK886,GW9662 was opposite to Wy14643 and Troglitazone. PaO2 , W/D ratio and pathomorphological score of lung tissue all were improved by united with Wy14643 and Troglitazone (P<0.05) than using Wy14643 or Troglitazone only and MPO activity was blocked much remarkably. Conclusion1. The expression of PPAR-αand PPAR-γof lung tissues are down-regulated both at the mRNA and protein level in ALI rats model by LPS, suggesting PPAR-αand PPAR-γis involved in the inflammation of ALI.2. Wy14643 up-regulates significantly the expression of PPAR-αin ALI lung tissues in rats both at the mRNA and the protein level. Troglitazone up-regulates remarkably the expression of PPAR-γboth at the mRNA and the protein level. Wy14643 combined with Troglitazone up-regulates the expression of PPAR-αand PPAR-γboth at the mRNA and the protein level, and no significant difference was found when using agonist alone (P>0.05).3. Both Wy14643 and Troglitazone can protect ALI lung tissues induced by LPS through inhibiting the activation of NF-κB, reducing the production of TNF-αand inhibiting the activation of MPO and improve PaO2, which could inhibit the inflammation of ALI lung. MK886 and GW9662 can block effects of Wy14643 or Troglitazone mentioned above. Wy14643 united with Troglitazone seems to be able to protect ALI lung tissues much better than used alone. Wy14643 or Troglitazone alone is able to protect lung tissue of ALI to some extent; The cooperation of Wy14643 and Troglitazone enhanced the protection.
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