Submitted on September 18, 2007
Accepted on January 22, 2008
Protective Effects of Elevated Endogenous Surfactant Pools to Injurious Mechanical Ventilation
Cory Yamashita1, Amy Forbes2, Jenna M. Tessolini2, Li-Juan Yao1, James F. Lewis3, and Ruud A.W. Veldhuizen4*
1 Critical Illness Research, Lawson Health Research Institute, London, Canada
2 Critical Illness Research, Lawson Health Research Institute, London, Canada; Physiology and Pharmacology, The University of Western Ontario, London, Canada
3 Critical Illness Research, Lawson Health Research Institute, London, Canada; St. Joseph's Health Center, Division of Respirology , United States; Medicine, The University of Western Ontario, London, Canada; Physiology and Pharmacology, The University of Western Ontario, London, Canada
4 Critical Illness Research, Lawson Health Research Institute, London, Canada; Medicine, The University of Western Ontario, London, Canada; Physiology and Pharmacology, The University of Western Ontario, London, Canada
* To whom correspondence should be addressed. E-mail: rveldhui{at}uwo.ca.
Depletion of alveolar macrophages (AM) leads to an increase in endogenous surfactant which lasts several days beyond the repletion of AM. Furthermore, impairment to the endogenous pulmonary surfactant system contributes to ventilation induced lung injury. The objective of the current study was to determine whether increased endogenous surfactant pools induced via AM depletion was protective against ventilation induced lung injury. Adult rats were intratracheally instilled with either control or dichloromethylene diphosphonic acid (DMDP) containing liposomes to deplete AMs and thereby increase endogenous surfactant pools. Either 3 or 7 days following instillation, rats were exposed to 2 hours of injurious ventilation using either an ex vivo or in vivo ventilation protocol and were compared to non-ventilated controls. The measured outcomes were oxygenation, lung compliance, lavage protein and inflammatory cytokine concentrations. Compared to controls, the DMDP-treated animals had significantly reduced AM numbers and increased surfactant pools 3 days after instillation. Seven days after instillation AM numbers had returned to normal but surfactant pools were still elevated. DMDP treated animals at both time points exhibited protection against ventilation-induced lung injury, which included superior physiologic parameters, lower protein leakage, and lower inflammatory mediator release into the airspace, compared to animals not receiving DMDP. It is concluded that DMDP-liposome administration protects against ventilation induced lung injury. This effect appears to be due to the presence of elevated endogenous surfactant pools.
