Objective: Vasoactive intestinal peptide (VIP) is a neuro-peptide that can modulate immunity. Previous studies indicated that VIP can attenuate the deleterious consequences of severe sepsis and septic shock by regulating production of inflammatory cytokines in immune activated cells. The signaling induced by bacterial components occurs primarily through Toll like receptors (TLRs). TLRs have been recognized to play a key role in pathogen recognition and innate immunity. It was convincingly demonstrated that lung is one of early suffered disaster organ and may trigger multiple organ dysfunction syndrome in sepsis. The present study was conducted to investigate the effects of VIP on TLR2/4 mRNA expressions on acute lung injury of endotoxic shock induced by lipopolysaccharide (LPS) in rat.
Method: Forty Sprague-Dawley rats were randomly divided into 3 groups, i.e., LPS shock group (n = 16), LPS + VIP group (n = 16), and control group (n = 8). LPS shock model was established by LPS (E. coli O(55)B(5) 10 mg/kg) with tail intravenous injection. The rats in LPS + VIP group were given a bolus of 5 nmol VIP intravenous injection follow by LPS. The rats in control group were given normal saline. The rats were sacrificed at 6 h, 24 h after being injected. The lung tissues were collected. The TLR2 mRNA and TLR4 mRNA expressions were detected by RT-PCR from the lung tissues. Pathological changes of the lungs were observed by light microscope and electron microscope 24 h after LPS injection.
Result: (1) Lung histopathology: the alveolar space was full with leukocyte, necrotic cells, segmental hemorrhage and protein effusion. Partial alveolar space was enlarged, lung interstitial edema were observed in LPS shock group. However, pathological changes of LPS + VIP group were milder than those in LPS shock group. (2) The expressions of TLR2 mRNA and TLR4 mRNA were significantly higher in LPS shock group compared with those of the control group (F = 16.638, P = 0.000; t = 5.876, P = 0.000), TLR2 mRNA and TLR4 mRNA expression on 24 h was down-regulated in LPS + VIP shock subgroup than those in LPS shock subgroup (F = 16.676, P = 0.000; t = 3.946, P < 0.001).
Conclusion: Expressions of TLR2 mRNA and TLR4 mRNA were up-regulated on LPS induced lung injury in rats. VIP mitigated lung injury induced by LPS, which may be related to TLR2 mRNA and TLR4 mRNA down-regulation of expression. The effect of VIP may suggest a protective mechanism in sepsis. VIP may play a potential protective role in severe infection.