The Impacts Of Regulating Toll-Like Receptor 4/Nuclear Factor-KB Signal Pathway On Rats With Ventilator-Induced Lung Injury

Objective:To study the impacts of regulating Toll-like receptor 4/nuclear factor-κB signal pathway on rats with ventilator-induced lung injury.Methods:Rats were tracheotomized and administered intratracheal injections of anti-TLR4 monoclonal antibody or saline, then ventilated for 4 h at a high tidal volume (HTV) of 40 ml/kg. Another group of control rats was administered intratracheal saline and allowed to ventilate for the same period at a normal tidal volume (NTV). Alveolar macrophages were isolated from the bronchoalveolar lavage fluid (BALF) from both groups of rats and stimulated for 16 h with TNF-a in the presence or absence of anti-TLR4 monoclonal antibody. Lung injury was assessed in rats after 4 h of ventilation by examining lung histopathology, wet/dry weight ratio, cell counts and cytokine levels in BALF, and cytokine levels in plasma. Levels of expression of TLR4, TLR9, MyD88 and NF-κB mRNA and protein were measured in cultured macrophages.Results:Compared to NTV rats, HTV rats showed higher pulmonary permeability, more severe inflammatory cell infiltration/lung edema, and higher levels of interleukin (IL)-1β,IL-6, and TNF-a in BALF and plasma. Alveolar macrophages from HTV rats expressed higher levels of TLR4, TLR9, MyD88 and NF-κB mRNA and protein than did macrophages from NTV rats. HTV rats pretreated with anti-TLR4 monoclonal antibody showed markedly attenuated signs of ventilation injury:less lung inflammation and pulmonary edema, fewer cells in BALF, and lower levels of ILs and TNF-a in BALF and plasma. Similarly, TNF-a-dependent increases in expression of TLR4, MyD88 and NF-κB mRNA and protein in alveolar macrophages were smaller when TNF-a was co-administered with anti-TLR4 antibody than when TNF-a was administered alone. Co-administering anti-TLR4 antibody also reduced TNF-a-dependent secretion of interleukins.Conclusions:TLR4 contributes significantly to ventilation-induced lung injury by activating the MyD88-NF-KB pathway, and pretreating rats with anti-TLR4 monoclonal antibody partially protects them against this injury by inhibiting MyD88-NF-κB signaling.