Submitted on January 8, 2007
Accepted on May 6, 2007
Lipid A Fraction of LPS Induces a Discrete MAPK Activation in Acute Lung Injury
Wen-Feng Fang1, Jae Hwa Cho1, Qianbin He1, Meng-Chih Lin2, Chao-Chien Wu2, Norbert F Voelkel3, and Ivor Samuel Douglas4*
1 Division of Pulmonary Sciences and Critical Care Medicine, University of Colorado at Denver and Health Sciences Center, 4200 E. 9th Ave, Denver, Colorado, 80220, United States
2 Division of Pulmonary and Critical Care Medicine, Chang Gung Memorial Hospital-Kaohsiung Medical Center, Chang Gung U. College of Medicine, Kaohsiung, Taiwan - Republic of China
3 Pulmonary Sciences and Critical Care Medicine, University of Colorado at Denver and Health Sciences Center, Denver, Colorado, United States; Division of Pulmonary Sciences and Critical Care Medicine, University of Colorado at Denver and Health Sciences Center, 4200 E. 9th Ave, Denver, Colorado, 80220, United States
4 Division of Pulmonary Sciences and Critical Care Medicine, Denver Health Medical Center, Denver, Colorado, United States; Division of Pulmonary Sciences and Critical Care Medicine, University of Colorado at Denver and Health Sciences Center, 4200 E. 9th Ave, Denver, Colorado, 80220, United States
* To whom correspondence should be addressed. E-mail: idouglas{at}dhha.org.
Background: Lipopolysaccharide (LPS) induces acute lung injury (ALI) via TLR4 mediated MAPK activation. The Lipid A fraction of LPS is considered to be the active moiety, but whether the Lipid A - TLR4 interaction accounts completely for ALI-associated MAPK activation in vivo has not been determined.
Hypothesis: The Lipid A fraction of LPS induces a discrete MAPK activation pattern in murine ALI.
Methods: Mice (C57BL/6J, C3H/HeJ) were treated with intratracheal instillations of purified Lipid A or LPS (10, 30 and 100µg/mouse) or vehicle. ALI was assessed by histology. Chromagenic myeloperoxidase (MPO) activity was measured in lung homogenates. MAPK expression was quantified by immunoblotting. In vitro ERK inhibitor studies using thioglycollate-elicited macrophages were also performed.
Results: MPO increased in a dose and time responsive fashion. Notably, MPO was 2.4-fold greater after Lipid A compared with LPS and vehicle at 6h after instillation (Lipid A 0.88 ±0.25; vs. LPS 0.37 ± 0.21 OD/min/mg; p<0.05). However ALI scores were comparable at 6 and 24 hrs between LPS and Lipid A. MPO was also comparable in vehicle treated or C3H/HeJ mice treated with LPS or Lipid A at 6 and 24 hours. Phospho-ERK activation was pronounced at 6 and 24h after Lipid A but not LPS treatment. In vitro studies confirmed the relationship between pERK activation and cytokine expression in macrophage stimulated with either LPS or Lipid A.
Conclusion: Compared with whole LPS, the Lipid A fraction is associated with amplified whole lung MPO and ERK activation 6h after intratracheal instillation in mice.
