Background: Acute lung injury (ALI), characterized by disruption of the lung alveolar-capillary membrane barrier and resultant pulmonary edema, and associated with a proteinaceous alveolar exudate, is a leading cause of morbidity and mortality. Currently, inflammation-oxidative stress interaction between TNF-α and NF-κB was identified as a key pathway of ALI. We hypothesized that a TNFR-Fc fusion protein would have beneficial effects in experimental ALI, and sought to test this idea in mice by blocking TNF-α.
Methods and results: Intratracheal instillation of lipopolysaccharide (LPS) into the lungs of ALI mice led to histiocyte apoptosis, and detection of serum and bronchoalveolar lavage fluid (BALF) cytokines, feedback between NF-κB and TNF-α, lung albumin leakage, lung damage, IκB kinase (IKK) and NF-κB activation, I-κB degradation, and oxidative injury. LPS administration raised pulmonary inflammation as reflected by increased inflammatory cytokines, alveoli protein concentration, and ALI scores. IKK is phosphorylated following LPS challenge, leading to I-κB degradation and NF-κB p65 phosphorylation. Furthermore, NF-κB is translocated into the nucleus and up-regulates TNF-α gene transcription. Infusion of TNFR-Fc 24h before LPS challenge significantly abrogated the increase of inflammatory cytokines, especially serum TNF-α concentration, as well as pulmonary alveoli protein levels, and diminished IKK and NF-κB activation and I-κB degradation. The nuclear translocation of NF-κB was inhibited, following by down-regulation of TNF-α gene transcription. In addition, LPS intratracheal instillation induced marked oxidative damage, such as a decrease in total anti-oxidation products and an increase in malondialdehyde (MDA), as well as up-regulation of oxidation enzymes. Histologic analysis and apoptosis scores revealed that the extent of tissue lesions was significantly reduced, but not abrogated, by TNF-α blockade.
Conclusion: Treatment with LPS alone increased inflammation and oxidative stress in ALI mice, while administration of TNFR-Fc 24h before LPS challenge broke the feedback between NF-κB and TNF-α, resulting in decreased pulmonary inflammation/oxidative damage and tissue destruction. These results suggest a potential role for TNF-α therapy to treat clinical ALI.